casmalia site remediation project - california · dave roberson – exxon mobil jill tracy –...

Casmalia Office San Luis Obispo Office 3401 NTU Road 3575 Camino Purisima Casmalia, CA 93429 Arroyo Grande, CA 93420 (805) 801-1529

CASMALIA SITE REMEDIATION PROJECT

Corey Bertelsen Project Manager

February 15, 2016 To: Russell Mechem – EPA Mark Samolis – EPA Subject: Final Feasibility Study Report The Casmalia Resources Site Steering Committee (CSC) has prepared this Final Feasibility Study (FS) Report for EPA’s review. The Final FS Report incorporates all previous EPA comments and edits. As was the case with previous drafts of the FS Report that we have submitted, this Final FS Report was prepared as required by Section 11.6 of the Remedial Investigation/ Feasibility Study (RI/FS) Work Plan (CSC, 2004). The Final FS utilizes the information developed during the investigation and remedial activities undertaken for the Casmalia Resources Superfund Site (Site) and reported in the January, 2011 Final Remedial Investigation (RI) Report to evaluate and propose remediation alternatives for the Casmalia Superfund Site. The CSC is distributing copies of the Final FS Report to the distribution list that EPA provided us for the earlier submittal. The CSC is sending complete hard copies of the document to all of those you requested and the remainder of the distribution list is receiving a complete electronic copy (text, tables and figures). We look forward to your approval of the Final FS Report submittal. Regards,

Corey Bertelsen Casmalia Project Coordinator cc: Jim Dragna – Bingham McCutcheon Scott Mansholt – Chevron Dave Roberson – Exxon Mobil Jill Tracy – Sempra Chris Sherman – DSTC

Russell Mechem – EPA Mark Samolis – EPA of 2

Casmalia Office San Luis Obispo Office 3401 NTU Road 3575 Camino Purisima Casmalia, CA 93429 Arroyo Grande, CA 93420 (805) 801-1529

Mark Wuttig – CH2MHill Matthew Plate – EPA Gary Santolo – CH2MHill Patty Velez – DFG Christine Bucklin – DTSC Dan Niles – RWQCB Steve Henry – USFWS Artemis Antipas – CH2MHill Jaime Williams – CH2MHill

Casmalia Resources Superfund Site

Final

Feasibility Study

February 2016

Prepared for:

USEPA, Region 9 75 Hawthorne Street

San Francisco, CA 94105

Prepared by:

Casmalia Resources Site Steering Committee

Casmalia Resources Superfund Site Final Feasibility Study

CERTIFICATION STATEMENT This Final Feasibility Study (FS) for the Casmalia Resources Superfund Site, Santa Barbara County, California has been prepared in a manner consistent with the normal level of care and skill ordinarily exercised by professional engineers, geologists and environmental scientists. This report was prepared under the technical direction of the undersigned.

__________________________ Corey Bertelsen – Project Coordinator Principal, CB Consulting, Inc.

__________________________ Jude Francis, PhD, PE Principal Engineer, URS Corporation (an AECOM company)

__________________________ Gib Fates, PG Principal Geologist, URS Corporation (an AECOM company)

__________________________ Brian Bjorklund, PG, CHG Principal Geologist, Environmental Resources Management (ERM) – West, Inc

__________________________ Ted Cota, PG Technical Director, Environmental Resources Management (ERM) – West, Inc.

__________________________ Warren Chamberlain, PE, PG, CHG Principal, AMEC Environmental & Infrastructure, Inc.


__________________________ Mala Pattanayak Senior Scientist, Risk Assessor, Arcadis-US, Inc.

__________________________ Ruth Custance, Principal Scientist, Geosyntec Consultants


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TABLE OF CONTENTS EXECUTIVE SUMMARY ES-1 1.0 INTRODUCTION 1-1

1.1 Purpose and Scope 1-1 1.2 Feasibility Study Approach 1-1 1.3 FS Report Organization 1-5 1.4 References 1-5

2.0 SITE BACKGROUND 2-1

2.1 Site Description 2-1 2.2 Site History and Use 2-1

2.2.1 Site Operational Information 2-2 2.2.2 Site History Review 2-3 2.2.3 Facilities 2-4 2.2.4 NPDES Permits 2-17 2.2.5 Existing Surface Impoundments 2-18 2.2.6 Closure Activities and Response Actions, and Ongoing Monitoring 2-18 2.2.7 Groundwater and Surface Water Monitoring 2-22

2.3 References 2-24 3.0 SUMMARY OF PREVIOUS INVESTIGATIONS 3-1

3.1 Previous Site Investigations 3-1 3.1.1 Pre-EPA Assessment Activities 3-1 3.1.2 USEPA Response Activities 3-3 3.1.3 CSC Site Work Activities 3-3 3.1.4 RI/FS Activities 3-7

3.2 Previous Response Actions 3-10 3.3 References 3-10

4.0 PHYSICAL CHARACTERISTICS OF SITE AND STUDY AREAS 4-1

4.1 Surface Features 4-1 4.1.1 Site Boundaries 4-1 4.1.2 Physiography 4-1

4.2 Meteorology 4-2 4.3 Surface Water Hydrology 4-2

4.3.1 Surface Water Drainage Within Site Boundary 4-2 4.3.2 Site Storm Water Runoff Collection Ponds and Liquid Treatment Impoundments 4-3 4.3.3 Surface Water Drainages Outside Site Boundaries 4-4

4.4 Geologic Setting 4-4 4.4.1 Regional Geology 4-5 4.4.2 Local Geology 4-5 4.4.3 Regional Structure 4-7 4.4.4 Site Structural Features 4-7


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4.5 Hydrogeology 4-13 4.5.1 Regional and Site Hydrogeologic Setting 4-13 4.5.2 Site Hydrogeologic Physical Characteristics 4-14 4.5.3 Site Groundwater Flow Conditions 4-19

4.6 Demography and Land Use 4-30 4.6.1 Regional Land Use 4-30 4.6.2 Nearby Populations 4-30

4.7 Ecology 4-30 4.7.1 Site Habitats 4-30

4.8 B-Drainage Wetlands 4-31 4.8.1 Goals and Objectives 4-32 4.8.2 Hydrology, Function, and Operation 4-32

4.9 Site Conceptual Model 4-33 4.9.1 Site Features 4-34 4.9.2 Meteorology 4-34 4.9.3 Geology 4-34 4.9.4 Hydrogeology 4-35 4.9.5 Contamination 4-37 4.9.6 Exposure Pathways 4-42

4.10 References 4-43 5.0 NATURE AND EXTENT OF CONTAMINATION 5-1

5.1 Contaminant Sources 5-1 5.2 Affected Media 5-1 5.3 Summary of RI Results 5-2

5.3.1 Soils 5-2 5.3.2 Sediments 5-4 5.3.3 Soil Vapor 5-5 5.3.4 Surface Water 5-6 5.3.5 Groundwater and Nonaqueous Phase Liquids 5-8

5.4 References 5-12 6.0 CONTAMINANT FATE AND TRANSPORT 6-1

6.1 Surface Transport Pathways – COPC Fate and Transport 6-1 6.1.1 Surface Soil COPCs 6-1 6.1.2 Sediment COPCs 6-4 6.1.3 Surface Water COPCs 6-6

6.2 Subsurface Transport Pathways – COPC Fate and Transport 6-9 6.2.1 Subsurface Soil COPCs 6-9 6.2.2 Soil Vapor COPCs 6-12 6.2.3 Groundwater COPCs 6-15 6.2.4 NAPL COPCs 6-25

6.3 Summary and Conclusions 6-30 6.4 References 6-32


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7.0 SUMMARY OF RISK ASSESSMENT 7-1 7.1 Human Health Risks 7-1 7.2 Ecological Risks 7-13

7.2.1 Tier 1 ERA 7-22 7.2.2 Tier 2 ERA 7-24 7.2.3 Barium Toxicity 7-26

7.3 Land Ownership and Use 7-27 7.4 References 7-27

8.0 AREAS FOR FS EVALUATION, REMEDIAL ACTION OBJECTIVES,

GENERAL RESPONSE ACTIONS, ARARS, TI EVALUATION AND PRELIMINARY REMEDIATION GOALS 8-1

8.1 Summary of Study Areas for FS Evaluation 8-1 8.2 Remedial Action Objectives 8-2

8.2.1 Soil, Soil Vapor, and Sediments 8-3 8.2.2 Groundwater, NAPL, and Surface Water Media 8-3

8.3 General Response Actions 8-5 8.3.1 Soil and Sediment Media 8-5 8.3.2 Groundwater, NAPL, and Stormwater Media 8-6

8.4 Potential ARARs 8-7 8.4.1 Identification of Potential ARARs 8-8

8.5 Technical Impracticability Waiver 8-9 8.5.1 Spatial Extent of the TI Determination 8-10 8.5.2 Conceptual Site Model 8-10 8.5.3 Technical Impracticability Evaluation Process 8-12 8.5.4 Technical Impracticability Evaluation Conclusions 8-13

8.6 Preliminary Remediation Goals 8-15 8.6.1 Groundwater 8-15 8.6.2 Soil 8-16 8.6.3 Pond Surface Water and Sediment 8-18 8.6.4 Seep Surface Water 8-18 8.6.5 Treated Stormwater, Treated Pond Water, or Treated Groundwater for Surface Water Discharge 8-19 8.6.6 Summary of PRGs 8-19

8.7 Principal Threat Wastes 8-19 8.8 Basis for Action 8-20 8.9 References 8-23

9.0 IDENTIFICATION AND SCREENING OF TECHNOLOGIES 9-1

9.1 Initial Screening of Technologies 9-1 9.1.1 Soil/Sediment 9-1 9.1.2 Groundwater 9-2 9.1.3 Water Treatment 9-3 9.1.4 Vapor Treatment 9-4 9.1.5 Surface Water/Stormwater 9-4

9.2 Technology Screening for Soil and Sediment 9-4


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9.2.1 Soil 9-4 9.2.2 Sediments 9-6

9.3 Technology Screening for Groundwater, NAPL and Stormwater 9-7 9.3.1 Groundwater and NAPL 9-7 9.3.2 Stormwater 9-10

9.4 Extracted Water and Vapor Treatment 9-11 9.4.1 Extracted Water Treatment 9-11 9.4.2 Extracted Vapor Treatment 9-12

9.5 Summary of Retained Technologies 9-12 9.5.1 Soil/Sediment Technologies 9-12 9.5.2 Groundwater, NAPL and Stormwater Technologies 9-18

9.6 References 9-23 10.0 DEVELOPMENT AND SCREENING OF AREA-SPECIFIC REMEDIAL

ALTERNATIVES 10-1 10.1 Background Information for Technologies Considered 10-2

10.1.1 Capping and Pond Lining Technologies Considered in the Evaluation 10-2 10.1.2 Soil Management Considerations 10-12 10.1.3 Stormwater and Pond Water Management 10-14 10.1.4 Proposed Evaporation Pond in Remedial Alternatives 10-17 10.1.5 HELP and Groundwater Flow Modeling 10-21 10.1.6 Long Term Groundwater and Soil Vapor Monitoring 10-24 10.1.7 Monitored Natural Attenuation 10-24 10.1.8 Groundwater FS Area 5 North (TI Zone) Source Removal and Containment 10-25 10.1.9 Groundwater FS Area 5 South and West Remediation

and Containment 10-36 10.2 FS Area 1 – PCB Landfill, Burial Trench Area, Central

Drainage Area and Existing Capped Landfills Area 10-37 10.2.1 Nature and Extent of Contamination 10-37 10.2.2 Development of Remedial Alternatives 10-38 10.2.3 Screening of Remedial Alternatives 10-42

10.3 FS Area 2 – RCRA Canyon and West Canyon Spray Area 10-43 10.3.1 Nature and Extent of Contamination 10-43 10.3.2 Development of Remedial Alternatives 10-45 10.3.3 Screening of Remedial Alternatives 10-51

10.4 FS Area 3 – Former Ponds and Pads, Remaining Onsite Areas 10-52 10.4.1 Nature and Extent of Contamination 10-52 10.4.2 Development of Remedial Alternatives 10-55 10.4.3 Screening of Remedial Alternatives 10-59

10.5 FS Area 4 – Stormwater Ponds and Treated Liquid Impoundments 10-60 10.5.1 Nature and Extent of Contamination 10-60 10.5.2 Development of Remedial Alternatives 10-61 10.5.3 Screening of Remedial Alternatives 10-67

10.6 FS Area 5 – Groundwater 10-68 10.6.1 Nature and Extent of Contamination 10-68


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10.6.2 Existing Remedial Extraction Features 10-74 10.6.3 Development of Remedial Alternatives – Area 5 North 10-78 10.6.4 Development of Remedial Alternatives – Area 5 South 10-104 10.6.5 Development of Remedial Alternatives – Area 5 West 10-111 10.6.6 Screening of Remedial Alternatives – Area 5 North 10-115 10.6.7 Screening of Remedial Alternatives – Area 5 South 10-118 10.6.8 Screening of Remedial Alternatives – Area 5 West 10-119

10.7 References 10-121 11.0 DETAILED EVALUATION OF REMEDIAL ALTERNATIVES 11-1

11.1 Description of CERCLA RI/FS 9-Criteria 11-1 11.1.1 Cost Estimating Approach 11-4

11.2 Detailed Evaluation for FS Area 1 11-5 11.2.1 Description of Remedial Alternatives 11-5 11.2.2 Detailed and Comparative Analysis of Remedial Alternatives 11-15 11.2.3 Area 1 Evaluation Summary 11-17

11.3 Detailed Evaluation for FS Area 2 11-17 11.3.1 Description of Remedial Alternatives 11-18 11.3.2 Detailed and Comparative Analysis of Remedial Alternatives 11-34 11.3.3 Area 2 Evaluation Summary 11-37

11.4 Detailed Evaluation of FS Area 3 11-38 11.4.1 Description of Remedial Alternatives 11-38 11.4.2 Detailed and Comparative Analysis of Remedial Alternatives 11-49 11.4.3 Area 3 Evaluation Summary 11-51

11.5 Detailed Evaluation of FS Area 4 11-52 11.5.1 Description of Remedial Alternatives 11-52 11.5.2 Detailed and Comparative Analysis of Remedial Alternatives 11-70 11.5.3 Area 4 Evaluation Summary 11-72

11.6 Detailed Evaluation of FS Area 5 Groundwater 11-73 11.6.1 Description of Remedial Alternatives for Area 5 North 11-73 11.6.2 Detailed and Comparative Evaluation of Remedial Alternatives for

Area 5 North 11-95 11.6.3 Evaluation Summary for Area 5 North 11-99 11.6.4 Description of Remedial Alternatives for FS Area 5 South 11-100 11.6.5 Detailed and Comparative Evaluation of Remedial Alternatives for FS Area 5 South 11-105 11.6.6 Evaluation Summary for Area 5 South 11-109 11.6.7 Description of Remedial Alternatives for FS Area 5 West 11-109 11.6.8 Detailed and Comparative Evaluation of Remedial Alternatives for FS Area 5 West 11-114 11.6.9 Evaluation Summary for Area 5 West 11-117

11.7 Cost Estimate Uncertainty 11-118 11.8 Assumed Schedule for Cost Estimating Purposes 11-119 11.9 References 11-120


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12.0 DETAILED EVALUATION OF SITE-WIDE REMEDIAL ALTERNATIVES AND SUMMARY OF TOP RANKED REMEDY 12-1

12.1 Description of Site Wide Remedial Alternatives 12-1 12.1.1 SWR #1 – No Further Action 12-1 12.1.2 SWR #2 – Large Evaporation Pond 12-2 12.1.3 SWR #3 – Small Evaporation Pond 12-8 12.1.4 SWR #4 – No Evaporation Pond 12-9 12.1.5 SWR #5 – P/S Landfill Dewatering 12-11 12.1.6 SWR #6 – Aggressive Site Wide Groundwater Restoration 12-14

12.2 Detailed and Comparative Analysis of Site Wide Remedial Alternatives 12-16

12.2.1 Overall Protection of Human Health and Environment 12-16 12.2.2 Compliance with ARARs 12-18 12.2.3 Long Term Effectiveness 12-18 12.2.4 Reduction of Toxicity, Mobility, and Volume through Treatment 12-20 12.2.5 Short Term Effectiveness 12-21 12.2.6 Implementability 12-23 12.2.7 Cost 12-24 12.2.8 Green Impacts Assessment 12-26

12.3 Evaluation Summary and Top Ranked Remedy 12-27 12.3.1 CERCLA Detailed Evaluation Criteria Summary 12-27 12.3.2 Green Impacts Assessment Summary 12-29

12.4 Summary of Top Ranked Site-Wide Remedy – SWR #3 12-30 12.4.1 FS Area 1 – PCB Landfill, Burial Trench Area, Central Drainage Area 12-30 12.4.2 FS Area 2 – RCRA Canyon, WCSA 12-31 12.4.3 FS Area 3 – Former Ponds and Pads, Remaining Site Areas, Roadways, Maintenance Shed Area, Liquids Treatment Area,

Administration Building Area 12-32 12.4.4 FS Area 4 – Stormwater Ponds and Treated Liquid Impoundments 12-33 12.4.5 Groundwater, FS Area 5 12-35 12.4.6 Area 5 North 12-35 12.4.7 Area 5 South 12-36 12.4.8 Area 5 West 12-37

12.5 Storm Management Plan 12-37 12.5.1 Stormwater Management with Top-Ranked Remedy 12-37 12.5.2 New Evaporation Pond Sizing and Operation 12-38

12.6 Borrow Soil Source and Volumes for Top-Ranked Remedy 12-39 12.6.1 Soil (or Backfill) Requirements for the Top-Ranked Remedy 12-39 12.6.2 Borrow Soil Location 12-40

12.7 Green Remediation 12-41 12.7.1 Energy Use 12-41 12.7.2 Air Emissions 12-41 12.7.3 Impacts on Water 12-42 12.7.4 Impacts on Land and Ecosystems 12-42 12.7.5 Integrating Renewable Energy 12-42


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12.8 Top-Ranked Remedy Work Sequencing 12-43 12.9 References 12-44


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LIST OF TABLES Table 2-1 Waste Management Unit Chronology Table 2-2 General Pond Information Table 2-3 Pond Closure Information Table 2-4 Contaminated Liquids Extraction, Treatment, and Disposal Table 4-1 Meteorological Data Summary for Site – Temperature and

Wind Speed (2006–2007) Table 4-2 Meteorological Data Summary for Site – Evaporation and

Rainfall (1996–2007) Table 5-1 General RI/FS Data Needs Table 5-2 Summary of Chemicals Detected in Media – Remedial

Investigation Sampling Program Table 5-3 Summary of Risk-based Concentration Exceedances by

Media, Location, and Constituent Table 5-4 Range of Inorganic Constituents in Surface Water Drainage

Samples Table 5-5 Range of Detected Organic Constituents in Surface Water

Drainage Samples Table 5-6 Summary of Inorganic Analytical Results for Surface Water

Pond Samples Table 5-7 Summary of Detected Organic Analytical Results for Surface

Water Pond Samples Table 6-1 Estimated Physical and Chemical Properties of Detected

Constituents Table 6-2 Summary of Detected Chemicals by Chemical Analyte

Classes and Environmental Media Where Detected Table 6-3 Relative Mobility of Chemical Analytical Classes and

Representative Chemicals Table 6-4 Relative Degradation Potential of Detected Chemicals in

Various Chemical Analyte Classes Table 7-1 Chemicals of Concern in Surface Soil – Terrestrial Birds, Soil

Invertebrates, and Plants Table 7-2 Chemicals of Concern in Shallow Soil – Terrestrial Mammals,

Soil Invertebrates, and Plants Table 7-3 Chemicals of Concern in Sediment Based on Aquatic Wildlife

and Sediment Invertebrates Table 8-1 Summary of Areas for FS Evaluation Table 8-2 Technologies and Process Options for Soil, Soil Vapor,

and Sediment Table 8-3 Technologies and Process Treatment Options for Surface

Water, Groundwater, and NAPL Table 8-4 Remedial Action Objectives and General Response

Actions Summary by FS Area


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Table 8-5 The Proposed NPDES Standards for Offsite Discharge of Treated Stormwater, Pond Water or Treated Groundwater

Table 8-6A Ecological Chemicals of Concern and Risk-Based Concentrations in Soil

Table 8-6B Human Health Chemicals of Concern and Risk-Based Concentrations in Soil – Commercial/Industrial Worker

Table 8-6C Preliminary Remediation Goals for Chemicals of Concern in Soil

Table 9-1 Initial Screening of Remedial Technologies and Process Options

Table 9-2 Screening of Technologies – Soil, Soil Vapor and Sediment Table 9-3 Screening of Technologies – Groundwater, NAPL and

Stormwater Table 9-4 Screening of Technologies – Extracted Groundwater and

Vapor Treatment Table 10-1 List of Remedial Alternatives for Screening Analysis by FS

Area Table 10-2 Screening of Remedial Alternatives for FS Area 1 – PCB

Landfill, Burial Trench Area, Central Drainage Area Table 10-3 Screening of Remedial Alternatives for FS Area 2 – RCRA

Canyon and WCSA Table 10-4 Screening of Remedial Alternatives for FS Area 3 – Former

Ponds and Pads, Remaining On-site Areas, LTA, MSA Table 10-5 Screening of Remedial Alternatives for FS Area 4 –

Stormwater Ponds and Impoundments Table 10-6A Screening of Remedial Alternatives for Groundwater FS Area

5 North Table 10-6A-1 Risk Analysis for P/S Landfill Dewatering with Horizontal Wells Table 10-6B Screening of Remedial Alternatives for Groundwater FS Area

5 South Table 10-6C Screening of Remedial Alternatives for Groundwater FS Area

5 West Table 11-1 Selected Remedial Alternatives for Detailed 9-Criteria Analysis

by FS Area Table 11-2 Detailed Analysis of Alternatives for FS Area 1, PCB

Landfill, Central Drainage Area and Burial Trench Area Table 11-3 Detailed Analysis of Alternatives for Area 2, RCRA

Canyon and West Canyon Spray Area Table 11-4 Detailed Analysis of Alternatives for Area 3, Former

Pads and Ponds Subarea, Roadways and Remaining On-site Areas

Table 11-5 Detailed Analysis of Alternatives for Area 4, Stormwater Ponds and Treated Liquid Impoundments (RCF, A-Series, A-5, 13, 18 Ponds)

Table 11-6A Detailed Analysis of Alternatives for Area 5 North – Groundwater


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Table 11-6B Detailed Analysis of Alternatives for Area 5 South – Groundwater

Table 11-6C Detailed Analysis of Alternatives for Area 5 West – Groundwater

Table 12-1 Site-Wide Remedial Alternative Components Table 12-2 Detailed Analysis of Site-wide Alternatives Table 12-3 Summary of Area-specific Remedial Alternatives Evaluation Table 12-4 Cost Estimate for Site-wide Remedial Alternatives #2 to #6 Table 12-5 Summary of Site-wide Remedial Alternatives Evaluation Table 12-6 Cost Estimate Summary for Top-Ranked Sitewide Remedial

Alternative #3


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LIST OF FIGURES Figure 1-1 Site Location Map Figure 2-1 Current Site Layout Figure 2-2 Historical Site Layout Figure 2-3 Historical Time Line and Milestones Figure 2-4 Primary Pond/Pad Uses Figure 2-5 Closure Status of Former Surface Impoundments Figure 2-6 Selected Site Photographs (1970–2002) Figure 3-1 Conceptual Study Areas Figure 4-1 Pre-Development Site Drainage – 1959 Figure 4-2 Pond Levels, Volumes, and TDS Figure 4-3 Geologic Map of the Casmalia Quadrangle, Santa Barbara

County, California Figure 4-4 Regional Folds and Faults Figure 4-5 Regional Geologic Cross-Section Figure 4-6 Local Groundwater Basins Figure 4-7 Well Location Map – All Site Wells Figure 4-8 Areal Distribution of Historical Seeps Figure 4-9 Statistical Representation of Hydraulic Conductivity Results for

Upper/Lower HSUs Figure 4-10 Water Table Contour Map, December 2008 Figure 4-11 Site-wide Cross-section D-D’ Figure 4-12 Model Domain and Boundaries Figure 4-13 MODFLOW Model Domain and Layering Figure 4-14 Potentiometric Surface Contours/Particle Flow Map, Upper

HSU, 2004 (Dry) Figure 4-15 Potentiometric Surface Contours/Particle Flow Map, Upper

HSU, 2001 (Wet) Figure 4-16 Potentiometric Surface Contours/Particle Flow Map, Lower

HSU, 2004 (Dry) Figure 4-17 B-Drainage Habitat Pool Design – General Arrangement Plan Figure 4-18 B-Drainage Habitat Pool Design – Pool Centerline Profile Figure 4-19 Conceptual Site Model 1 – Transect through P/S Landfill,

Central Drainage Area, Former Ponds and Pads Area, and RCF Pond

Figure 4-20 Conceptual Site Model 2 – Transect through PCB Landfill, Burial Trench Area, Former Ponds and Pads Area, and RCF Pond

Figure 4-21 Conceptual Site Model 3 – Transect through RCRA Canyon, Pond A-5, A-Series Pond, and C-Drainage

Figure 4-22 Conceptual Site Model 4 – Transect through PSCT-1, Former Ponds and Pads Area, and B-Drainage

Figure 4-23 Conceptual Site Model Block Diagram Figure 4-24 Conceptual Site Model Block Diagram Detail


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Figure 5-1 Summary of Chemical Detections and Exceedances - All Media Figure 5-2 Metals in Soil and Sediment in Excess of RBCs (Cr, Cu, Zn) Figure 5-3 Organics in Soil and Sediment in Excess of RBCs (MCPP, Total

PCB Congeners, PCE, Total DDT, TCE, Dioxin TEQ - Mammalian)

Figure 5-4 Estimated Extent of Total Detected VOCs in Soil Vapor Figure 5-5 LNAPL, DNAPL, Total VOCs in Upper HSU Figure 5-6 LNAPL, DNAPL, Metals in Upper HSU Figure 5-7 LNAPL, DNAPL, Inorganics, Metals in Lower HSU Figure 5-8 DNAPL, Total VOC’s in Lower HSU Figure 5-9 Concentration Ranges for Chromium in Soil All On-Site Areas Figure 5-10 Concentration Ranges for Copper in Soil All On-Site Areas Figure 5-11 Concentration Ranges for Zinc in Soil All On-Site Areas Figure 5-12 Concentration Ranges for Total DDT in Soil All On-Site Areas Figure 5-13 Concentration Ranges for Dioxin TEQ (Mammalian) in Soil All

On-Site Areas Figure 5-14 Concentration Ranges for MCPP in Soil All On-Site Areas Figure 5-15 Concentration Ranges for Total PCBs as Congeners in Soil All

On-Site Areas Figure 5-16 Concentration Ranges for Tetrachloroethylene (PCE) in Soil All

On-Site Areas Figure 5-17 Concentration Ranges for Trichloroethylene (TCE) in Soil All

On-Site Areas Figure 5-18 Concentration Ranges for MCPP in Sediment All On-Site Areas Figure 5-19 Concentration Ranges of Acetone in Soil Vapor Figure 5-20 Concentration Ranges of Freon 113 in Soil Vapor Figure 5-21 Concentration Ranges of Methyl Ethyl Ketone in Soil Vapor Figure 5-22 Concentration Ranges of 1,3-Butadiene in Soil Vapor Figure 5-23 Concentration Ranges of Benzene in Soil Vapor Figure 5-24 Concentration Ranges of Tetrachloroethylene in Soil Vapor Figure 5-25 Concentration Ranges of Total Detected VOCs in Soil Vapor Figure 5-26 VOC-GW/Particle Flow Map, Upper HSU, 2004 (Dry) Figure 5-27 VOC-GW/Particle Flow Map, Upper HSU, 2001 (Wet) Figure 5-28 VOC-GW/Particle Flow Map, Lower HSU, 2004 (Dry) –

Between PCB Landfill and PSCT-4 Figure 5-29 VOC-GW/Particle Flow Map, Lower HSU, 2004 (Dry) – Near

RGPZ-6 and RGPZ-7 Figure 5-30 LNAPL in Upper HSU Observed or Inferred from Groundwater

Concentrations – Fall 2004 and Spring 2005 RI Sampling Figure 5-31 DNAPL in Upper HSU Observed or Inferred from Groundwater

Concentrations – Fall 2004 and Spring 2005 RI Sampling Figure 5-32 DNAPL in Lower HSU Observed or Inferred from Groundwater

Concentrations – Fall 2004 and Spring 2005 RI Sampling Figure 5-33a Arsenic Groundwater Concentrations Upper HSU Zone 1 Area,

North of PSCT – Remedial Investigation Sampling


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Figure 5-33b Arsenic Groundwater Concentrations Upper HSU Zone 1 Area, South of PSCT – Remedial Investigation Sampling

Figure 5-34 Arsenic Groundwater Concentrations Lower HSU Zone 1 Area – Remedial Investigation Sampling

Figure 5-35a Nickel Groundwater Concentrations Upper HSU Zone 1 Area – Remedial Investigation Sampling

Figure 5-35b Nickel Groundwater Concentrations Upper HSU Zone 1 Area, South of PSCT Trench – Remedial Investigation Sampling

Figure 5-36 Nickel Groundwater Concentrations Lower HSU Zone 1 Area – Remedial Investigation Sampling

Figure 5-37a Cadmium Groundwater Concentrations Upper HSU Zone 1 Area, North of PSCT – Remedial Investigation Sampling

Figure 5-37b Cadmium Groundwater Concentrations Upper HSU Zone 1 Area, South of PSCT Trench – Remedial Investigation Sampling

Figure 5-38 Cadmium Groundwater Concentrations Lower HSU Zone 1 Area – Remedial Investigation Sampling

Figure 5-39a Selenium Groundwater Concentrations Upper HSU Zone 1 Area – Remedial Investigation Sampling

Figure 5-39b Selenium Groundwater Concentrations Upper HSU Zone 1 Area, South of PSCT Trench – Remedial Investigation Sampling

Figure 5-40 Selenium Groundwater Concentrations Lower HSU Zone 1 Area – Remedial Investigation Sampling

Figure 6-1 VOC-GW/Particle Flow Map, Upper HSU, 2004 (Dry) Figure 6-2 VOC-GW/Particle Flow Map, Upper HSU, 2001 (Wet) Figure 6-3 VOC-GW/Particle Flow Map, Lower HSU, 2004 (Dry) Figure 7-1 Co-located Risks to Ecological Communities Figure 7-1A Co-located Risks to Ecological Communities Assuming Barium

is Not Toxic Figure 7-2 Co-located Risks to Wildlife Receptors Figure 7-2A Co-located Risks to Wildlife Receptors Assuming Barium is Not

Toxic Figure 7-3 Parcel Ownership in Site Vicinity Figure 8-1A FS Study Areas 1-4 Figure 8-1B FS Study Area 5 Figure 10-1A Caps Considered in FS Evaluation Figure 10-1B Area 5 North – P/S Landfill, Gallery Well + NAPL-Only Vertical

Extraction Wells Figure 10-1C Area 5 North – P/S Landfill, Gallery Well + Aggressive NAPL

Extraction Wells Figure 10-1D Area 5 North – P/S Landfill, Gallery Well + Horizontal Extraction

Wells Figure 10-1E Area 5 North – P/S Landfill, Bottom Elevation and Saturation

Thickness Contours


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Figure 10-2 Soil Borrow Areas Figure 10-3 Summary Analytical Results Exceedances for Soil – Area 1 Figure 10-4 Summary Analytical Results Exceedances for Soil – Area 2 Figure 10-5 Summary Analytical Results Exceedances for Soil – Area 3 Figure 10-5A Soil Sampling Locations – RISBON-59 Area Figure 10-5B Cross Section A-A’ Figure 10-5C Cross Section B-B’ Figure 10-6 Summary Analytical Results Exceedances for Soil – Area 4 Figure 11-1A FS Area 1 – Alternative 2 – RCRA – Equivalent Mono Soil Cap

5’ (BTA, CDA) + RCRA Prescriptive Cap (PCB Landfill) Figure 11-1B FS Area 1 – Alternative 2 – RCRA Cap (PCB Landfill), Soil

Cap (BTA) + Grading Plan Figure 11-1C FS Area 1 – Alternative 2 – Soil Cap (CDA) + Grading Plan Figure 11-2A FS Area 1 – Alternative 3 – Evapotranspirative Soil Cap 5’

(BTA, CDA) + RCRA Prescriptive Cap (PCB Landfill) Figure 11-2B FS Area 1 – Alternative 3 – Evapotranspirative Cap 5’ (BTA)

+ RCRA Cap (PCB Landfill) Grading Plan Figure 11-2C FS Area 1 – Alternative 3 – Evapotranspirative Cap (CDA) +

Grading Plan Figure 11-3A FS Area 1 – Alternative 4 – RCRA Cap (BTA, CDA, PCB

Landfill) Figure 11-3B FS Area 1 – Alternative 4 – RCRA Cap (PCB Landfill, BTA) +

Grading Plan Figure 11-3C FS Area 1 – Alternative 4 – RCRA Cap (CDA) + Grading Plan Figure 11-4A FS Area 1 – Alternative 5 – Excavate (Metals, Organics)

(BTA, 20’) (CDA, 5’) + RCRA – Equivalent Mono Soil Cap 5’ (BTA, CDA) +RCRA Cap (PCB Landfill)

Figure 11-4B FS Area 1 – Alternative 5 – RCRA Cap (PCB Landfill), Soil Cap (BTA) + Grading Plan

Figure 11-4C FS Area 1 – Alternative 5 – Soil Cap (CDA) + Grading Plan Figure 11-5A FS Area 2 – Alternative 2 – Eco-Cap (West Slope RCRA

Canyon, WCSA) + Grading/BMPs (Uncapped Areas) Figure 11-5B FS Area 2 – Alternative 2 – Stormwater Plan Figure 11-5C FS Area 2 – Alternative 2 – Eco Cap, and Grading Plan Figure 11-6A FS Area 2 – Alternative 3 – RCRA-Equivalent Mono Soil Cap

(West Slope RCRA Canyon) (5’) + Excavate (Portion of WCSA) (5’) + Grading/BMPs (Uncapped Areas)

Figure 11-6B FS Area 2 – Alternative 3 – Stormwater Plan Figure 11-6C FS Area 2 – Alternative 3 – RCRA Equivalent Mono Soil Cap,

Excavation, and Grading Plan Figure 11-7A FS Area 2 – Alternative 4 – RCRA-Equivalent Mono Soil Cap

(West Slope RCRA Canyon), Portion of WCSA) (5’) + Grading/BMPs (Uncapped Areas)

Figure 11-7B FS Area 2 – Alternative 4 – Stormwater Plan


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Figure 11-7C FS Area 2 – Alternative 4 – RCRA-Equivalent Mono Soil Cap and Grading Plan

Figure 11-8A FS Area 2 – Alternative 5 – RCRA-Equivalent Mono Soil Cap (West Slope RCRA Canyon) (5’) + Excavation (Portion of WCSA) (5’) + Clean Soil Cover (East Slope, WSCA) (2’)

Figure 11-8B FS Area 2 – Alternative 5 – Stormwater Plan Figure 11-8C FS Area 2 – Alternative 5 – RCRA-Equivalent Mono Soil Cap,

5’ Excavation, 2’ Soil Cover, and Grading Plan Figure 11-9A FS Area 2 – Alternative 6 – RCRA-Equivalent Hybrid Cap

(West Slope RCRA Canyon) (5’) + Excavation (Portion of WCSA) (5’) + Clean Soil Cover (East Slope, WSCA) (2’)

Figure 11-9B FS Area 2 – Alternative 6 – Stormwater Plan Figure 11-9C FS Area 2 – Alternative 6 – RCRA-Equivalent Hybrid Cap, 5’

Excavation, 2’ Soil Cover, and Grading Plan Figure 11-10A FS Area 2 – Alternative 7 – Evapotranspirative Cap (West

Slope RCRA Canyon) (5’) + Excavation (Portion of WCSA) (5’) + Clean Soil Cover (East Slope, WSCA) (2’)


Figure 11-10C FS Area 2 – Alternative 7 – Evapotranspirative Cap, 5’ Excavation, 2’ Soil Cover, and Grading Plan

Figure 11-11A FS Area 2 – Alternative 8 – RCRA-Equivalent Hybrid Cap (RCRA Canyon, WCSA)


Figure 11-11C FS Area 2 – Alternative 8 – RCRA-Equivalent Hybrid Cap, Entire Canyon

Figure 11-12A FS Area 2 – Alternative 9 – Evapotranspirative Cap (RCRA Canyon, WCSA)


Figure 11-12C FS Area 2 – Alternative 9 – Evapotranspirative Cap, Entire Canyon

Figure 11-13A FS Area 3 – Alternative 2 – RCRA Cap (Locations 2, 3, 4) + Excavate/Asphalt Cap (Location 1) (5’) + GW Monitoring (Location 10) + Grading/BMPs (Rest of Area 3)

Figure 11-13B FS Area 3 – Alternative 2 – RCRA Cap (Locations 2, 3, 4) + Grading Plan

Figure 11-13C FS Area 3 – Alternative 2 – Excavation (5') + Asphalt Cover (Location 1) + GW Monitoring (Location 10)

Figure 11-14A

FS Area 3 – Alternative 3 – RCRA Cap (Locations 2) + Excavate/Place in PCB Landfill (Location 3) (20'); (Location 4) (5') + Excavate/Asphalt Cap (Location 1) (5') + GW Monitoring (Location 10) + Grading/BMPs (Uncapped Areas)

Figure 11-14B FS Area 3 – Alternative 3 – RCRA Cap (Locations 2) + Excavate/Place in PCB Landfill (Location 3) (20'); (Location 4) (5') + Grading Plan

Figure 11-14C FS Area 3 – Alternative 3 – Excavation (5') + Asphalt Cover (Location 1) + GW Monitoring (Location 10)


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Figure 11-15A

FS Area 3 – Alternative 4 – RCRA Cap (Locations 2) + Excavate/Place in PCB Landfill (Location 3) (20'); (Location 4) (5'); (Location 10) (50') + Excavate/Asphalt Cap (Location 1) (5') + GW Monitoring (Location 10) + Grading/BMPs (Uncapped Areas)

Figure 11-15B FS Area 3 – Alternative 4 – RCRA Cap (Locations 2) + Excavate/Place in PCB Landfill (Location 3) (20'); (Location 4) (5') + Grading Plan

Figure 11-15C FS Area 3 – Alternative 4 – Excavation (5') + Asphalt Cover (Location 1) + Excavate/Place in PCB Landfill (Location 10) (50')

Figure 11-16A FS Area 3 – Alternative 5 – Excavate Locations 1, 2, and 4 (5'); Location 3 (20'); Location 10 (50') + Grading/BMPs (Uncapped Areas)

Figure 11-16B FS Area 3 – Alternative 5 – Excavation (Locations 2, 3, 4) + Grading Plan

Figure 11-16C FS Area 3 – Alternative 5 – Excavate Locations 1 (5') and Location 10 (50')

Figure 11-17A FS Area 4 – Alternative 2 – Eco-cap (RCF, A-Series Pond) + RCRA Cap (18) + Lined Retention Basin (A-5, 13) + New 11 Acre Evaporation Pond

Figure 11-17B FS Area 4 – Alternative 2 – Eco Cap (A-Series Pond, RCF Pond) Cross Sections

Figure 11-18A FS Area 4 – Alternative 3 – Eco Cap (RCF Pond) + RCRA Cap (18) + Lined Evaporation Pond (A-Series Pond) + Lined Retention Basin (A-5, 13)

Figure 11-18B FS Area 4 – Alternative 3 – Eco Cap (RCF Pond) + Grading Plan

Figure 11-18C FS Area 4 – Alternative 3 – Excavation + Lined Evaporation Pond (A-Series Pond) + Grading Plan

Figure 11-18D FS Area 4 – Alternative 3 – Lined Retention Basin (Pond A-5, Pond 13) + RCRA Cap (Pond 18) + Grading Plan

Figure 11-19A FS Area 4 – Alternative 4 – Eco Cap (RCF Pond) + RCRA Cap (18) + 11-Acre Evaporation Pond (A-Series Pond) + Lined Retention Basin (A-5, 13)


Figure 11-19C FS Area 4 – Alternative 4 – Excavation + Lined Evaporation Pond (A-Series Pond) + Grading Plan


Figure 11-20A

FS Area 4 – Alternative 5 – Eco Cap (RCF Pond, Portion of A-Series Pond) + RCRA Cap (18) + Six 1-Acre Evaporation Ponds (Portion of A-Series Pond) + Lined Retention Basin (A-5, 13)


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Figure 11-20C FS Area 4 – Alternative 5 – Six 1-Acre Lined Evaporation Ponds (A-Series Pond) + Grading Plan


Figure 11-21A FS Area 4 – Alternative 6 – Eco Cap (RCF Pond, A-Series Pond) + RCRA Cap (18) + Lined Retention Basin (A-5, 13)

Figure 11-21B FS Area 4 – Alternative 6 – Eco Cap (A-Series Pond, RCF Pond) Cross Sections

Figure 11-22A

FS Area 4 – Alternative 7 – ET Cap (RCF Pond, Portion of A-Series Pond) + RCRA Cap (18) + Six Lined 1-Acre Evaporation Ponds (Portion of A-Series Pond) + Lined Retention Basin (A-5, 13)

Figure 11-22B FS Area 4 – Alternative 7 – ET Cap (RCF Pond) + Six 1-Acre Evaporation Ponds (Portion of A-Series Pond) + Eco-Cap (Portion of A-Series Pond) Cross Sections

Figure 11-23A FS Area 4 – Alternative 8 – Excavate and Clean Backfill 5' (RCF, A-Series Pond) + RCRA Cap (18) + Lined Retention Basin (A-5, 13) + New 11 Acre Evaporation Pond

Figure 11-23B FS Area 4 – Alternative 8 – Excavate and Clean Backfill (A-Series Pond, RCF Pond) (5') + Grading Plan

Figure 11-24A FS Area 5 North Groundwater – Alternative 2 – Extraction (PSCT, Gallery Well) + Discharge Onsite

Figure 11-24B FS Area 5 North – Alternative 2 – Process Flow Diagram and Treatment System Layout

Figure 11-25A FS Area 5 North Groundwater – Alternative 3 – Extraction (PSCT, Gallery Well) + Extraction (NAPL Only, P/S Landfill) + Monitoring (12 New LHSU Wells) + Discharge Onsite

Figure 11-25B Area 5 North – Alternative 3 – Extraction (PSCT, Gallery Well) + Extraction (NAPL-Only, P/S Landfill)

Figure 11-25C Area 5 North – Alternative 3 – Process Flow Diagram and Treatment System Layout

Figure 11-26A Area 5 North Groundwater – Alternative 4 – Extraction (PSCT, Gallery Well) + Extraction (NAPL Only, P/S Landfill) + Monitoring (12 New LHSU Wells) + Discharge Offsite

Figure 11-26B Area 5 North – Alternative 4 – Extraction (PSCT, Gallery Well) + Extraction (NAPL-Only, P/S Landfill)

Figure 11-26C Area 5 North – Alternative 4 – Process Flow Diagram

Figure 11-27A

Area 5 North Groundwater – Alternative 5 – Extraction (PSCT, Gallery Well) + Aggressive NAPL Extraction + NAPL-Only Extraction (CDA) + Monitoring (12 New LHSU Wells) + Discharge Onsite

Figure 11-27B Area 5 North – Alternative 5 – Extraction (PSCT, Gallery Well) + Aggressive NAPL Extraction + Extraction (NAPL-Only, CDA)


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Figure 11-28A

Area 5 North Groundwater – Alternative 6 – Extraction (PSCT, Gallery Well) + Dewatering P/S Landfill + NAPL-Only Extraction (4 Existing Wells, CDA) + Monitoring (12 LHSU Wells) + Discharge Onsite

Figure 11-28B

Area 5 North – Alternative 6 – Extraction (PSCT, Gallery Well) + Dewatering P/S Landfill + Extraction (NAPL-Only in CDA, 4 Existing Wells) + Monitoring (12 New wells) + Treat and Discharge Onsite

Figure 11-28C Area 5 North – Alternative 6 – Process Flow Diagram and Treatment System Layout

Figure 11-29A

Area 5 North Groundwater – Alternative 7 – Extraction (PSCT, Gallery Well) + Dewatering P/S Landfill + NAPL-Only Extraction (12 New Wells, CDA) + Extraction (4 LHSU Wells) + Monitoring (8 LHSU Wells) + Discharge Offsite

Figure 11-29B

Area 5 North – Alternative 7 – Extraction (PSCT, Gallery Well) + Dewater P/S Landfill + Extraction (NAPL-Only in CDA, 12 New Wells) + Extraction (4 New LHSU Wells) + Monitoring (8 New LHSU Wells) + Treat and Discharge PSCT Groundwater Offsite


Figure 11-30A Area 5 South Groundwater – Alternative 2 – Extraction (PCT-A, PCT-B) + MNA

Figure 11-31A Area 5 South Groundwater – Alternative 3 – Extraction (PCT-A, PCT-B) + MNA

Figure 11-31B Area 5 South – Alternative 3 – Process Flow Diagram

Figure 11-32A Area 5 South Groundwater – Alternative 4 – Extraction (PCT-A) + In-Situ Reactive Wall (PCT-B) + MNA

Figure 11-33A Area 5 South Groundwater – Alternative 5 – Extraction (PCT-A, PCT-B) + Aggressive Extraction + MNA

Figure 11-33B Area 5 South – Alternative 5 – Process Flow Diagram

Figure 11-34A Area 5 West Groundwater – Alternative 2 – Extraction (PCT-C) + MNA

Figure 11-35A Area 5 West Groundwater – Alternative 3 – Extraction (PCT-C) + Treat and Discharge Offsite

Figure 11-35B Area 5 West – Alternative 3 – Process Flow Diagram

Figure 11-36A Area 5 West Groundwater – Alternative 4 – In-Situ Reactive Wall (PCT-C) + MNA

Figure 11-37A Area 5 West Groundwater – Alternative 5 – Aggressive Extraction (40 Wells) + Extraction (PCT-C) + MNA

Figure 11-37B Area 5 West – Alternative 5 – Process Flow Diagram Figure 12-1A Sitewide Remedial Alternative #2 – Larger Evaporation Pond Figure 12-1B Sitewide Remedial Alternative #2 – Process Flow Diagram Figure 12-2A Sitewide Remedial Alternative #3 – Smaller Evaporation Pond Figure 12-2B Sitewide Remedial Alternative #3 – Process Flow Diagram Figure 12-3A Sitewide Remedial Alternative #4 – No Evaporation Pond


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Figure 12-3B Sitewide Remedial Alternative #4 – Process Flow Diagram

Figure 12-4A Sitewide Remedial Alternative #5 – Evaporation Pond + P/S Landfill De-watering


Figure 12-5A Sitewide Remedial Alternative #6 – Aggressive Site-wide Extraction Groundwater Restoration


Figure 12-6A Cost Estimate Summary for Sitewide Remedial Alternatives, Millions (30-Year, 3%)

Figure 12-6B Cost Estimate Summary for Sitewide Remedial Alternatives, Millions (30-Year, 3%)

Figure 12-6C Cost Estimate Summary for Sitewide Remedial Alternatives by Area, Millions (30-Year, 3%)

Figure 12-7A Top Ranked Sitewide Remedy Map, SWR #3

Figure 12-7B Top Ranked Sitewide Remedy Map – Cap Section Details SWR #3

Figure 12-7C Stormwater Plan – SWR #3 Figure 12-7D RCF Pond, A-Series Pond, RCRA CYN Cross Sections-SWR

#3 Figure 12-8 Sitewide Earthwork Offsite and Onsite Borrow Areas Figure 12-9 Proposed Remedy Schedule


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LIST OF APPENDICES Appendix A Technical Impracticability Evaluation Appendix B Potential ARARs Appendix C Adjustment of Remedial Footprint – FS Areas 2 and 3 Appendix D Groundwater Flow Model Technical Memorandum Appendix E Cost Spreadsheets Appendix F Green Remedial Evaluation Appendix G Monitored Natural Attenuation Appendix H Stormwater Balance Model Appendix I Inorganic Compound Hydrographs Appendix J RBC Calculation Methodologies


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LIST OF ACRONYMS

°C temperature degree centigrade °F temperature degree Fahrenheit µCi micro-Curies µg/dl micrograms per deciliter µg/L micrograms per liter µg/m2-min micrograms per square meter per minute µm micron µmhos/cm microhms per centimeter µmol/g micromoles per gram µR/hr microrems per hour µV microvolts ΣSEM total SEM ΣSEM AVS total SEM minus AVS 0/00 per mil or parts per thousand 1×10-6 one in one million 2-D two-dimensional 3H tritium 3He helium-3 95 UCL 95 percent upper confidence limit ACAP Alternative Cover Assessment Project ADD Average Daily Dose AE assessment endpoint Ag silver Ag2S silver monosulfide Ah aryl hydrocarbon amsl above mean sea level APN Assessor’s Parcel Number ARAR Applicable or relevant and appropriate requirement ARCH air-rotary casing hammer Area area defined by the three-mile radius from the boundaries of

the Casmalia Site ASTM American Society for Testing and Materials ASTs Aboveground Storage Tanks ATL Air Toxics LTD atm atmosphere ATS Ameripure Treatment System ATV all-terrain vehicle AUF Area Use Factor AVS acid volatile sulfide AVS-SEM Acid Volatile Sulfide-Simultaneously-Extracted Metals BAF bioaccumulation factor Base Vandenberg Air Force Base BBL Blasland, Bouck, and Lee, Inc.


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BC Laboratory BC Analytical Laboratories BERA Baseline Ecological Risk Assessment bgs below ground surface BHHRA Baseline Human Health Risk Assessment Bio/PACT Biologically-activated/Powdered Activated Carbon

Treatment BKG background BMPs Best management practices BO Biological opinion BP before present BSHS Biological Species and Habitat Survey BTA Burial Trench Area BTAG Biological Technical Advisory Group BTEX benzene, toluene, ethylbenzene, and xylenes btoc below top of casing C/C Caustics/Cyanides C14 Carbon 14 age dating CA Caustic/Cyanide and Acid Landfill CaCO3 calcium carbonate Cal Prop 65 Safe Drinking Water and Toxic Enforcement Act of 1986 CalEPA California Environmental Protection Agency CAM California Assessment Method CAO Cleanup and Abatement Order CAS Chemical Abstract Service CASRN Chemical Abstract Services Registry Number CB Calibration Blank CBCI CB Consulting, Inc. CCB Continuing Calibration Blank CCR California Code of Regulations CCV Continuing Calibration Verifications Cd cadmium CD compact disk CDA Central Drainage Area CDD Chlorinated Dioxins CDF Chlorinated dibenzofurans CDFW California Department of Fish and Wildlife CdS Cadmium sulfide CERCLA Comprehensive Environmental Response, Compensation,

and Liability Act CESA California Endangered Species Act CFGC California Fish and Game Commission CFR Code of Federal Regulations CH Highly plastic clays (per Unified Soil Classification System) CHHSL California Human Health Screening Level Cis-1,2-DCE Cis-1,2-Dichloroethene


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CL Clay (per Unified Soil Classification System) cm centimeter cm/g centimeters per gram cm/sec centimeters per second cm2/sec square centimeters per second cm3/minute cubic centimeters per minute CNDDB California Natural Diversity Database CNPS California Native Plant Society CNS Casmalia Neutralization System COC chemical of concern COI chemical of interest COPC chemical of potential concern CPEC/COPEC chemical of potential ecological concern CPEO Center for Public Environmental Oversight cpm counts per minute CPT cone penetrometer test Cr Chromium CRLF California red-legged frog Cs-137 cesium-137 CSC Casmalia Resources Site Steering Committee CSF Cancer Slope Factor CSM Conceptual Site Model CSPE-R Chlorosulfonated polyethylene CTS California tiger salamander Cu copper CVOCs chlorinated volatile organic compounds CVRWQCB Central Valley Regional Water Quality Control Board CY Cubic Yard(s) DBCP 1,2 dibromo 3 chloropropane DBM Design Basis Memorandum DCA dichloroethane DCB dichlorobenzene DCE dichloroethylene/dichloroethene DDD dichlorodiphenyldichloroethane DDE dichlorodiphenyldichloroethylene DDT dichlorodiphenyltrichloroethane DEA diethylamine Dhc Dehalococcoides bacteria DHS Department of Health Services DIC Dissolved Inorganic Carbon DL Detection Limit DNAPL dense non aqueous-phase liquid DO dissolved oxygen DOC Dissolved Organic Carbon dpm disintegrations per minute


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DPT direct-push technology DQO data quality objective DTSC Department of Toxic Substances Control DUP duplicate DWR Department of Water Resources Dynes/cm dynes per centimeter EC electrical conductivity ECD electron capture detector Eco RBC Ecological risk-based concentration Eco SSL Ecological soil screening level EDB Ethylene dibromide EDD Electronic Data Deliverable EE/CA engineering evaluation/cost analysis Eh oxidation reduction potential EIA Ethylene interpolymer alloy EIR Environmental Impact Report ELAP California Environmental Laboratory Accreditation Program ENSO El Nino/La Nina – southern oscillation EPA Environmental Protection Agency EPC exposure point concentration EqP equilibrium partitioning EQS Environmental Quality Standard ERA Ecological Risk Assessment ERG Environmental Restoration Group ERH Electric Resistance Heating ERI Environmental Research, Inc. ERM Environmental Resources Management. Inc. ESA Endangered Species Act ESB Equilibrium Partitioning Sediment Benchmark ESL Ecological Screening Level ESRI Environmental Systems Research Technologies ET evapotranspiration Fe(II) ferrous iron Fe(III) ferric iron Fe0 zero-valent iron FeOOH mineral hydrous ferric oxide FeS iron monosulfide FID Flame Ionization detector Final Design Report

refers to the Revised Final Pesticides Solvent Landfill Cap Design Report

FML flexible membrane liner FMR field metabolic rate FOC fraction organic carbon FOD frequency of detection FPP Former Ponds and Pads


xxv

fps feet per second FS Feasibility Study FSP field sampling plan ft feet ft/ft feet per foot ft/min feet per minute ft/yr feet per year ftbtoc feet below top of casing g/cc grams per cubic centimeter g/cm3 grams per cubic centimeter GAC granular activated carbon GC gas chromatograph GCL geosynthetic clay liner GCW Historical name of Gallery Well GHG Greenhouse Gas GIS Geographic Information System gm gram gm/mol gram-mole or gmole gpm gallons per minute GPS global positioning system GRA General response action(s) Gregg Gregg In Situ, Inc. GS Golden State Aerial Surveys GSCA Geologic Siting Criteria Assessment GST gyro steering tool GW groundwater HAR Hydrogeologic Assessment Report Hc Henry’s Law constant HCSM Hydrogeologic Conceptual Site Model HDD Horizontal directional drilling HDPE High Density Polyethylene HEAST Health Effects Assessment Summary Tables HELP Hydrologic Evaluation of Landfill Performance (computer

model) HH Human health HH RBC human health risk-based concentration HHRA Human Health Risk Assessment HI Hazard Index HMW high molecular weight HNO3 nitric acid HQ hazard quotient HSA Hollow stem auger HSAA California Hazardous Substances Account Act HSCER Hydrogeologic Site Characterization and Evaluation Report HSIR Hydrogeologic Site Investigation Report


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HSR Hydrogeologic Summary Report HSU Hydrostratigraphic Unit HSWA Hazardous and Solid Waste Amendments HT hydrogen (tritium) gas HTO tritiated water vapor Hunt Hunt & Associates Biological Consultants HVAC heating, ventilation and air conditioning HVOCs halogenated volatile organic compounds Hz Hertz IC Initial Calibration ICB Initial Calibration Blank ICs Institutional Controls ICS Inference Check Samples ICV Initial Calibration Verifications ID inside diameter ILA Interim Liquids Agreement in/yr inches per year Intra Intrasearch IPR Interim Progress Report IRIS Integrated Risk Information System ISCO In-situ Chemical Oxidation ISCR in-situ chemical reduction ISTD In-situ Thermal Desorption J&E Johnson and Ettinger Vapor Intrusion Model JPEG Joint Photographic Experts Group K hydraulic conductivity Kd distribution coefficient Kdeg half-life kg kilogram(s) kg/L kilograms per liter kHz kilohertz Koc Organic carbon partition coefficient Kow octanol-water partition coefficient Kv kilovolt kW kilowatt kWh kilowatt-hours L liter(s) L/kg liters per kilogram LADD Lifetime Average Daily Dose lb pound LCRS leachate collection and recovery system LCS Laboratory Control Samples LDR Land Disposal Restrictions LF Landfill LLDPE linear-low density polyethylene


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LLTW low level threat waste LMW low molecular weight LNAPL light non aqueous-phase liquid LOAEL lowest observed adverse effect level LPGAC liquid-phase granular activated charcoal LRL Lower Explosive Limit LTA liquids treatment area LTE Long Term Effectiveness LTP liquids treatment plant LUC Land Use Controls M/S heavy metals/sludges m3 cubic meters m3/day cubic meters per day MACTEC MACTEC Engineering and Consulting, Inc. MBTA Migratory Bird Treaty Act MCL maximum contaminant level MCPA 2-methyl-4-chlorophenoxy-acetic acid MCPP 2-(4-Chloro-2-methylphenoxy) propionic acid MDL Method Detection Limit MEK Methyl ethyl ketone mg milligrams mg/kg milligrams per kilogram mg/kg bw day milligrams per kilogram of body weight per day mg/kg-day milligrams per kilogram of body weight per day mg/L milligrams per liter mg/m3 milligrams per cubic meter MH highly plastic silt (per Unified Soil Classification System) MIBK methyl isobutyl ketone MIP Membrane Interface Probe ML silt (per Unified Soil Classification System) ml milliliters ml/gm milliliter per gram ml/min milliliters per minute mm millimeters mm Hg millimeters of Mercury (pressure measurement unit) MMP Meteorological Monitoring Program Mn(II) manganese (II) Mn(IV) manganese (IV) MNA Monitored natural attenuation (the remedial alternative) MOEE Ontario Ministry of Environment and Energy Mol gram-mole MPC Maximum Permissible Concentration MPE Multi-Phase Extraction MPPE macro porous polymer extraction MS Matrix Spike


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mS/M milliSiemens per meter MSA Maintenance shed area MSD Matrix Spike Duplicate msl mean sea level MTBE Methyl tert butyl ether mV millivolts N/A, NA Not applicable NA Natural attenuation (the process) NaI sodium iodide NAPL Non-aqueous phase liquid NAWQC National Recommended Water Quality Criteria NCEA National Center for Environmental Assessment NCP National Contingency Plan ND Not Detected or Non-Detect NDMA n-nitrosodimethylamine NE non-equilibrium NFESC Naval Facilities Engineering Service Center NGVD National Geodetic Vertical Datum Ni nickel NIST National Institute of Standards and Technology NMD Normal Move Out NOAEL no observed adverse effect level NOI Notice of Intent NORCAL NORCAL Geophysical Consultants, Inc. NPDES National Pollution Discharge Elimination System NPV net present value NT Not Tested NTU Nephelometric Turbidity Unit O&M Operations and Maintenance OCDD octachlorodibenzo-p-dioxin OCDF octachlorodibenzofuran OD outside diameter OEHHA Office of Environmental Health Hazard Assessment OMM Operations and Maintenance Manual OM&M Operations Maintenance & Monitoring ORNL Oak Ridge National laboratory ORP oxidation-reduction potential (redox) OSHA Occupational Health and Safety Administration OSWER U.S. Office of Solid Waste and Emergency Response OVM organic vapor monitor P/S pesticide/solvent P/S Landfill, P/SLF

Pesticide/Solvent Landfill

PACT powder-activated carbon treatment PAHs polycyclic aromatic hydrocarbons


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Pb lead PCBs polychlorinated biphenyls pCBSA Parachlorbenzene sulfonic acid PCDD polychlorinated dibenzo p dioxin PCDF polychlorinated dibenzofuran PCE tetrachloroethylene/tetrachloroethene pcf pounds per cubic foot PCNB pentachloronitrobenzene PCT Perimeter Control Trench PE Performance Evaluation PEl Permissible Exposure Level PEST Parameter Estimation pg/g picograms per gram pg/L picograms per liter pH unit of measurement for acid/base properties PHGs Public Health Goals PID photoionization detector PLSS Public Land Survey System POC Point of Compliance PP Proposed Plan ppbv part(s) per billion by volume ppm parts per million ppmv part(s) per million by volume PPOs Poor Purging Organics ppt part(s) per trillion PRB Permeable Reactive Barriers PRG Preliminary Remediation Goal PSCT Perimeter Source Control Trench psf pounds per square foot psi pounds per square inch psig pounds per square inch gauge PTS Laboratories

Petroleum Testing Services Laboratories

PTW Principal threat wastes PUF plant uptake factor PVC polyvinyl chloride PW Pacific Western Aerial Surveys Pw pore water pressure QA/QC Quality Assurance/Quality Control QAPP Quality Assurance Project Plan QC Quality Control Qc Tip resistance QED QED Environmental Systems is a company specializing in

water quality remediation/sampling products R.G. Registered Geologist


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RA Risk Assessment RAGS Risk Assessment Guidance for Superfund RAO Remedial Action Objective RAP Remedial Action Plan RATL Reptile and Amphibian Toxicology Literature RBCs risk-based concentrations RCF Runoff Containment Facility RCRA Resource Conservation and Recovery Act RD Remedial design RDC Risk-Driving Chemical RDX nitroamine, an explosive, also known as cyclonite, hexogen,

T4, and cyclotrimethylenetrinitramine REI relative estimation interval RfC reference concentration RfD reference dose RFI Request For Information form RGMEW Routine Groundwater Monitoring Element of Work RI Remedial Investigation RI/FS Remedial Investigation/Feasibility Study RI/FS Work Plan Remedial Investigation/Feasibility Study Work Plan RICH RI Change Form RISBON Remedial Investigation soil boring onsite (soil boring

location designation – e.g., RISBON-59) RME Reasonable Maximum Exposure RO Reverse osmosis ROD Record Of Decision ROI Radius Of Influence ROS Remain On-Site ROST Rapid Optical Screen Tool RPD relative percent difference RPs Responsible Parties RRF Relative Response Factors RSD Relative Standard Deviation RTMV Reduction in Toxicity, Mobility, and Volume RWQCB California Regional Water Quality Control Board S Solubility SA semiannual SA Source Area SAP Sampling Analysis Plan SARA Superfund Amendments and Reauthorization Act SB Soil boring SBCAPCD Santa Barbara County Air Pollution Control District SC sandy clay (per Unified Soil Classification System) scfm standard cubic feet per minute SDG Sample Delivery Group


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SEM simultaneously extracted metals SF Square Feet SFRWQCB San Francisco Regional Water Quality Control Board SI Surface Impoundment (the) Site the Casmalia Resources Superfund Site SIC Silty Clay SL Screening Level SOP Standard Operating Procedure SOW Scope of Work SQG Sediment Quality Guideline SS Surface soil (0 to 6 inches bgs) STE Short Term Effectiveness SVE Soil Vapor Extraction SVL snout-vent length SVOC semi-volatile organic compound SWAT Solid Waste Assessment Test SWPPP Storm Water Pollution Prevention Plan SWRs Site-wide remedial alternatives T Temperature T&E Threatened and Endangered TBA tert-butyl alcohol TBC to be considered Tc-99 technetium-99 TCA trichloroethane TCDD tetrachlorodibenzo-p-dioxin TCE trichloroethylene/trichloroethene TCLP Toxicity Characteristic Leaching Procedure TCLs Target Cleanup Levels TD Total Depth TDS total dissolved solids TEF Toxicity Equivalency Factors TEQ toxicity equivalent TI technical impracticability TIC Tentatively Identified Compound TIE technical impracticability evaluation TIN triangulated irregular network TLVs Threshold Limit Values TM Technical Memorandum TMB trimethylbenzene TOC total organic carbon TOX Total Organic Halogens TPH total petroleum hydrocarbons TPHd total petroleum hydrocarbons (as diesel) TRS Township, Range, and Section TRM turf reinforcement mats


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TRV toxicity reference value TSCA Toxic Substances Control Act TSDF treatment, storage, and disposal facility tsf tons per square foot TU tritium unit UCL upper confidence limit UCSB MIB University of California, Santa Barbara, Map and Image

Library UF Uncertainty Factor UM University of Miami (Florida) URF Inhalation Unit Risk Factors URS URS Corporation USA Underground Service Alert System USACHHPM U.S. Army Center for Health Promotion and Preventive

Medicine USCS Unified Soil Classification System USEPA United States Environmental Protection Agency USFWS United States Fish and Wildlife Service USGS United States Geological Survey UST Underground Storage Tank UTL upper tolerance limit UU/UE Unrestricted Use/Unrestricted Exposure UVIF ultraviolet induced fluorescence UVOST ultra-violet optical screening tool Vb bulk volume VC vinyl chloride VESP vibratory shear enhanced processing VETS Vapor Extraction and Treatment System VOCs volatile organic compounds Vp. VP Vapor Pressure VPGAC Vapor Phase Granular Activated Carbon WAO wet air oxidation WCC Woodward-Clyde Consultants WCCB West Canyon Catch Basin WCSA West Canyon Spray Area WDC Water Development Corporation WDR Waste Discharge Requirement WHO World Health Organization WMU Waste Management Unit Work Plan June 2004 RI/FS Work Plan WST Western spade-foot toad ybp years before present Zn zinc ZVI zero-valent iron


ES-1

EXECUTIVE SUMMARY The Feasibility Study (FS) Report for the Casmalia Resources Superfund Site evaluates a range of remedial alternatives that address various soil, soil vapor, surface water, and groundwater contamination in accordance with the National Oil and Hazardous Substances Pollution Contingency Plan (NCP) and Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) guidance for conducting Remedial Investigation/Feasibility Study (RI/FS; EPA 1988). The FS relies on the site Remedial Investigations (RI) conducted from 2004 until 2009 and the risk assessments that are summarized in the Final RI Report (2011). Together, the Final RI Report and FS Report provide EPA with the key information necessary to issue the Proposed Plan and the Record of Decision (ROD) for the site. Site Background The Casmalia Resources Superfund Site is an inactive Class I hazardous waste management facility located in the northwestern corner of Santa Barbara County, California. The site, which was owned and operated by Casmalia Resources, began accepting wastes in the early 1970s. Site operations ceased in 1991. Former waste management operations at the site were conducted within an approximate 252-acre area which included landfills, storage and evaporation ponds, evaporation pads, oil field waste spreading areas, treatment units, and disposal wells and trenches. The site lies in a rural setting approximately 4 miles from the Pacific Ocean, approximately 10 miles southwest of the city of Santa Maria, and approximately 16 miles north-northwest of the city of Lompoc. The nearest population center is the unincorporated community of Casmalia, located approximately 1.2 miles south-southeast of the site. Land use surrounding the site includes agriculture, cattle grazing, and oil field development. There has been no indication that land use, particularly land use of the historical landfill, would be likely to change within the foreseeable future. In terms of regional setting, the site is located within the Casmalia Hills, which are characterized by easily erodible clay and silt soils and rolling grassy hills that are suitable for farming, ranching, and grazing. The site sits on a ridge that separates two distinct groundwater basins. The Santa Maria River Valley basin (Santa Maria) lies to the northeast, and San Antonio Creek Valley basin (San Antonio) lies to the south. Despite its geographic proximity, there is no evidence of direct groundwater flow from the site to the town of Casmalia. Groundwater beneath the site does not serve as a drinking water source either for the town of Casmalia or other communities. The town’s drinking water supply is obtained from the Santa Maria groundwater basin to the east, which is different from the groundwater underlying the site. The location of the waste disposal site was selected in large part because of its rural setting, its distance from densely populated areas, and its suitable, low permeability geological conditions that help provide containment. The waste management facility contained many closely-spaced former waste management units, disposal areas, and waste treatment and handling systems. The site has been stabilized and risks are being controlled. Figure ES-1 shows the current layout of the site, which includes the former waste management units (WMUs) operated by Casmalia Resources in the 1970s and 1980s, ponds for landfill liquids and systems for managing contaminated groundwater constructed in the 1980s, and the landfill caps and stormwater runoff control systems constructed in the late 1990s and early 2000s. The WMUs, historical and current response activities, and current site operations are summarized below.


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Casmalia Resources accepted a full range of listed and characteristic RCRA wastes as specified in Subparts C and D of 40 Code of Federal Regulations (CFR) 261 (A.T. Kearney/SAIC, 1987). These wastes are generally referred to as “RCRA wastes” because they are regulated under the federal Resource Conservation and Recovery Act (RCRA) as amended. The site accepted approximately 5.6 billion pounds of waste into 92 waste management or treatment facilities between 1973 and 1989. Wastes received at the site included: petroleum wastes, acids, bases, organic chemical solvents, petroleum solvents, paint sludge, pesticides, infectious wastes, septic tank pumpings, and sewage sludge.

Figure ES-1 – Current Site Layout Waste disposal units at the site included:

• 6 landfills; • 43 surface impoundments (or ponds); • 15 evaporation pads; • 2 non-hazardous waste spreading areas;

• 6 oil field waste spreading areas; • 11 shallow injection wells; • 7 disposal trenches; and • 1 drum burial unit.

The landfills include one former landfill (the RCRA Landfill) and five existing landfills (Pesticides/Solvents, [P/S], Metals, Caustics/Cyanide, and Acids). The site also had five waste treatment units: an acid/alkaline neutralization facility, a hydrogen peroxide treatment unit, oil recovery and treatment tanks, a wet air oxidation unit, and a temporary pilot-scale powder-activated carbon treatment (PACT) unit. Surface impoundments (used for evaporation and treatment of liquid wastes or for storing stormwater), and disposal pads (used to evaporate liquid wastes and site stormwater runoff) primarily occupied the southern and central portions of the site, whereas the landfill disposal areas were positioned along the northern and northeastern margins of the site.


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EPA has been involved with the site in a variety of contexts since the 1980s and has developed a thorough understanding of site conditions as well as the nature and extent of contamination. EPA has understood for many years that remediation would involve leaving waste in place, and managing residual wastes and liquids, as part of a combined containment and treatment remedy. Early response actions and site stabilization have included successful installation of engineering controls to contain waste (i.e. landfill caps), contain groundwater contamination (i.e. GW extraction trenches), extract site liquids for treatment (i.e. extraction wells and sumps), and manage extracted site liquids (i.e. liquid collection, treatment, and disposal systems). Specifically, Casmalia Resources performed some closure and cleanup activities in the late 1980s and early 1990s that included removing wastes from some of the six former the RCRA landfills and consolidating them into the P/S Landfill, removing the liquids from the ponds, removing contaminated soils beneath and in the vicinity of the ponds and pads, and constructing landfill leachate and groundwater extraction facilities. Five ponds that exist today were created during removal of the contaminated soils. The ponds (Runoff Control Facility [RCF], A-Series Pond, Pond A-5, Pond 13, and Pond 18) are now used for the control and evaporation of stormwater and treated and untreated liquids extracted from leachate and groundwater extraction facilities. Casmalia Resources did not close or clean up RCRA Canyon, which is located in the northwestern portion of the site and contained a RCRA landfill. Although the former landfill wastes were removed, RCRA Canyon still contains soils that have been contaminated from area-wide spraying of contaminated liquids. EPA performed emergency response actions from 1992 through 1996 to stabilize the site. These actions included interim operations of the groundwater control systems and other critical site maintenance. During this time EPA negotiated the Casmalia Consent Decree with the Casmalia Steering Committee (CSC) to continue site operations, perform the RI/FS, and implement the final remedy. The CSC began performing work under the Casmalia Consent Decree in 1997. This work has included extracting, treating, and disposing landfill leachate and contaminated groundwater, designing and constructing final landfill caps, performing groundwater monitoring activities, and performing the RI/FS. The CSC constructed landfill caps on four of the five landfills between 1998 and 2002 and a stormwater collection basin to convey clean stormwater from the four capped landfills to the B-Drainage and Casmalia Creek. From north to south, contaminated groundwater is currently extracted from the Gallery Well located at the toe of the P/S Landfill, Sump 9B and the Road Sump located south of the P/S Landfill, the 2,700 foot long Perimeter Source Control Trench (PSCT) located south of the five existing landfills, and three Perimeter Capture Trenches (PCTs) located at the southern perimeter of the site at the head of the A, B, and C Drainages. Liquids extracted from the Gallery Well are the most contaminated and contain both light and dense nonaqueous phase liquids (LNAPLs and DNAPLs). Liquids from the Gallery Well and Sump 9B are temporarily stored in tanks at the liquids treatment area and then disposed at a permitted disposal facility. Liquids from the PSCT are treated at the site using granular activated carbon (GAC) and then discharged to Pond 18 for evaporation. Liquids from the PCTs are the least contaminated and are discharged directly to the RCF and A-Series pond without treatment.


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Site stormwater from the RCRA Canyon located at the western part of the site is directed to the A-Series Pond. Stormwater from the central and eastern part of the site is directed to the RCF Pond. Ponds A-5, 13, and 18 receive only minor stormwater. The total dissolved solids (TDS) and metals concentrations in the ponds are very high, approaching or exceeding concentrations of seawater, because of high concentrations of salts and metals from the extracted groundwater and evaporation. Physical Characteristics Overall the site slopes from north-to-south and is bounded to the north by a ridge (North Ridge) and to the south by the A, B, and C Drainages. The B and C Drainages flow into the perennially flowing Casmalia Creek, located immediately west of the site. Casmalia Creek flows into Shuman Creek, which empties into the Pacific Ocean. The ephemeral North Drainage is topographically separated from the site by the ridge at the northern part of the site and also flows into Shuman Creek. The site does not overlie a groundwater basin that is used for potable use. It is underlain by low permeability weathered and unweathered claystone of the Sisquoc Formation which is underlain by the Monterey Formation at a depth of approximately 1,300 feet. In addition, localized fill occurs across the site and localized alluvium occurs along Casmalia Creek and remnants of the former drainages. The underlying Monterey Formation is composed of shale and other rocks that locally produce oil and gas. The upper weathered claystone is referred to as the Upper Hydrostratigraphic Unit (Upper HSU) and the underlying deeper unweathered claystone is referred to as the Lower Hydrostratigraphic Unit (Lower HSU). Groundwater flow is controlled primarily by weathering and fracturing since the host rock is low-permeability claystone. Most groundwater flow at the site occurs in fractures within the Upper HSU that occur at a density of several fractures per foot. A minor component of groundwater flow occurs within fractures of the Lower HSU which occur at a frequency of every several feet to every several tens of feet. The Upper HSU is more permeable than the Lower HSU. The permeability of both HSUs is quite low (i.e. K = 10-5 cm/sec and 10-6 cm/second, respectively). Groundwater flow is controlled by topography, the geologic structure of the contact between the two HSUs, and the liquids extraction facilities that are operated to control the migration of landfill leachate and contaminated groundwater. A natural groundwater flow divide occurs at the North Ridge. Groundwater north of North Ridge flows northward toward the North Drainage. Groundwater south of the ridge flows southward across the site. Contaminated aqueous-phase liquids, LNAPL, and DNAPL within the P/S Landfill are extracted by the Gallery Well at the southern perimeter of the landfill. The Gallery Well is located immediately upgradient of a clay barrier at the southern limit of the P/S landfill that provides additional containment of these liquids. Groundwater in the Upper HSU flows southward through the principal contaminant sources and is intercepted by Sump 9B and the PSCT. Groundwater south of the PSCT is influenced by surface water elevations in the ponds and intercepted by the PCTs. A significant amount of groundwater pumped from the PCTs is derived from surface water from the ponds. Groundwater in the Lower HSU flows southward underneath the principal containment sources and underneath the PSCT. Groundwater flow in the Lower HSU is much less significant than the flow in the Upper HSU because of the lower permeability and less extensive fracturing of the unweathered claystone.


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RI/FS Study Areas In the FS evaluation, 5 study areas were established and evaluated based on geographical proximity and/or similar impacted media. The 5 areas are listed below and shown in Figure ES-2:

FS Area 1 – PCB Landfill, Burial Trench Area, Central Drainage Area and Capped Landfills Area

FS Area 2 – RCRA Canyon, West Canyon Spray Area FS Area 3 – Former Ponds and Pads, Remaining Site Areas, Roadways, Liquids

Treatment Area and Maintenance Shed Area FS Area 4 – Stormwater Ponds and Treated Liquid Impoundments (A-Series, RCF, A-5,

18 and 13) FS Area 5 – Sitewide Groundwater and NAPL which is further divided into Groundwater

North; Groundwater South, and Groundwater West.

Figure ES-2 – FS Areas (left panel shows FS Areas 1 through 4; right panel shows FS Area 5) Nature and Extent of Contamination Contamination occurs pervasively throughout the entire site, including metals, VOCs, and SVOCs in soils, surface water, groundwater, and, to a very limited degree, in soil vapor. Principal contaminant sources include the existing landfill areas, the former waste disposal areas and facilities that have not previously undergone cleanup, and residual contamination from prior site cleanup activities. Soil Soil contamination occurs pervasively throughout Areas 1 and 2 and variably within Area 3. Contamination includes many different constituents of potential concern (COPCs), such as metals, VOCs, SVOCs, and other organic compounds.


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Area 1 is by far the most contaminated part of the site, encompassing the former landfills and many other former WMUs. Surface and subsurface soils in FS Area 1 north of the PSCT are primarily contaminated with metals and organic compounds. Many of these COPCs increase in concentration with depth and serve as sources for contamination of groundwater via infiltration. The preferred remedy for the five landfills in this area is capping, and capping four of the five former landfills has been completed as part of early action work at the site. In FS Area 2, COPCs were identified in the RCRA Canyon/WCSA and contain elevated levels of residual copper, chromium, and zinc that remain from the area-wide spraying of oil field and other wastes during disposal operations. The elevated concentrations of these metals occur in the top several feet of soil and diminish with depth. In FS Area 3, several discrete soil hotspot contamination areas contain high content ratios of metals, VOCs, and other organic compounds that serve as sources for groundwater contamination. These hotspot areas included shallow soil contamination in the Liquids Treatment Area (Hotspot 1), the former Maintenance Shed Area (Hotspot 2), deeper soil contamination from former Ponds A and B that were not sufficiently cleaned up by Casmalia Resources (Hotspot 3), shallow soil contamination south of PSCT-1 (Hotspot 4), and deeper soil contamination underneath RCF Road from a former waste pond that was not cleaned up by Casmalia Resources and which was discovered while drilling soil boring RISBON-59 (Hotspot 10). Pond Surface Water The surface water storage ponds play a critical, but temporary, role in collecting and storing stormwater and treated liquids in order to prevent uncontrolled discharges. The TDS and metals concentrations in the five ponds have been generally increasing over time due to high concentration of salts and metals from the extracted groundwater that is discharged to the ponds and evaporation. In addition, low levels of organic compounds are occasionally detected in some ponds. The TDS concentrations of the ponds were low after 32 inches of rain fell during the 1997/98 El Nino winter and fresh stormwater filled the ponds. Since that time, the TDS has steadily increased and now approaches, and in some areas exceeds, the salinity of seawater. The elevated TDS and metals exceed ecological risk screening levels, including those for the California Red Legged Frog, a special status species that formerly inhabited the ponds in the 1990s and early 2000s until the ponds became too salty. Underlying pond sediments also contain elevated levels of metals, VOCs, and other organic compounds and serve as potential sources for contamination of shallow groundwater via infiltration. Groundwater Contamination Groundwater contamination is pervasive throughout the entire site ( Area 5), including a highly diverse array of several hundred COPCs, comprising metals, VOCs, SVOCs, pesticides, PCBs, and other organics. Groundwater contamination is most prominent, however, throughout Groundwater North where most of the former waste management units and buried waste materials are located. Many years of monitoring data show that groundwater contamination has been contained within the historical site boundaries through a combination of constructed engineering controls and multiple natural attenuation processes.


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Groundwater North Groundwater North contains the most heavily contaminated groundwater within the site, primarily due to the presence of former waste management units, other waste burial areas, and high volumes of NAPL. These features provide ongoing sources of contamination for groundwater that flows from north to south through Groundwater North. Contamination is most highly concentrated in the weathered and fractured upper HSU claystone, but impacts the less permeable lower HSU as well. Contamination is contained within Area 1 by both (1) the existing perimeter source control trench (PSCT) and natural attenuation processes for the Upper HSU, and (2) natural attenuation alone for the Lower HSU, since the PSCT extends only to the base of the Upper HSU. Free-phase LNAPL and DNAPL occurs in the southern part of the P/S Landfill. The thickness of DNAPL measured at the bottom of the landfill exceeds 10 feet and the annual DNAPL extraction rate from the Gallery Well has ranged between 2,000 and 4,000 gallons. The volume of free phase DNAPL is estimated to be up to approximately 100,000 gallons. The actual DNAPL volume is uncertain. The thickness of LNAPL in the landfill also exceeds 10 feet. Extraction from the Gallery Well combined with the Clay Barrier limit the migration of LNAPL and aqueous phase liquids from the landfill toward the Central Drainage Area. However, these containment features are less effective for DNAPL because it is driven by density and can penetrate fractures in the unweathered claystone that underlies the waste in the P/S Landfill. Density-driven DNAPL migration from the landfill has likely occurred into the underlying fractures of the Lower HSU as indicated by free-phase DNAPL identified in core fractures and piezometers approximately 500 feet south of the P/S Landfill. The potential sources of that DNAPL include the free phase DNAPL present in the P/S Landfill and the former Pad 9A/B area in the Central Drainage Area. The depth and horizontal extent of DNAPL are uncertain. Ongoing DNAPL migration from the P/S Landfill may occur through fractures as long as the DNAPL pool in the landfill persists since it provides a source and driving force for continued migration. Very high concentrations of TDS (approaching that of seawater), metals, and organic compounds occur in the Upper HSU throughout the Burial Trench Area and Central Drainage Area with Total VOC concentrations exceeding 1,000,000 micrograms per liter (µg/L) or parts per billion (ppb). Limited amounts of free-phase LNAPL occur in the Central Drainage Area between the P/S Landfill and PSCT. The thickness of LNAPL measured in this area ranges from a sheen to slightly greater than one foot. The mobility of this LNAPL is considered to be low given the low-permeability of the Upper HSU. Residual NAPL is also likely in the Burial Trench Area based on high dissolved-phase groundwater concentrations. Dissolved-phase contaminants in the Upper HSU that move southward in groundwater are contained by the PSCT. VOCs occur in the Lower HSU beneath the Burial Trench Area, Central Drainage Area, and the North Ridge. Elevated metals occur beneath the North Ridge. VOCs beneath the Burial Trench Area occur as a result of strong downward hydraulic gradients carrying contaminants downward in this area. VOCs beneath the Central Drainage Area likely occur as a result of a combination of downward hydraulic gradients carrying contaminants downward and the free-phase DNAPL that occurs within fractures of the Lower HSU in this area. The migration of dissolved-phase contaminants in the Lower HSU moving southward through fractures is attenuated by naturally occurring mechanisms that include sorption, diffusion into the claystone matrix, and biodegradation. Although the rate of potential contaminant migration beneath the PSCT is


ES-8

uncertain, the overall mass is likely small because of the low rate of groundwater flow through the low permeability Lower HSU. A prominent surface seep periodically forms between the P/S Landfill and the PSCT due to a shallow water table that will intersect the ground surface in response to rainfall infiltrating over the area. This seep will not form if the water table is pumped down by Sump 9B. When it forms however, the seep is highly contaminated and has an LNAPL sheen. Groundwater modeling performed for the FS shows that the seep will no longer form under the remedial alternatives in which the area to the north of the PSCT is fully capped. Groundwater South Elevated concentrations of TDS, metals, and organic compounds occur in the Upper HSU south of the PSCT with total VOC concentrations ranging up to approximately 1,000 µg/L immediately south of the PSCT to less than 10 µg/L near the PCTs. Dissolved-phase contaminants in the Upper HSU moving southward in groundwater are contained by the A- and B-Drainage PCTs. Monitoring data demonstrate that contamination in the deeper, less permeable and less fractured Lower HSU is contained within the historical site boundaries through natural attenuation processes. Groundwater West Elevated concentrations of TDS and metals occur in the Upper HSU in the RCRA Canyon Area and to the south towards the C-Drainage PCT. Minor concentrations of organic compounds are also occasionally detected at low total VOC concentrations (generally less than 10 µg/L). Dissolved-phase contaminants in the Upper HSU moving southward in groundwater are contained by the C-Drainage PCT. Monitoring data show that minor contamination in the Lower HSU is effectively contained by natural attenuation processes. A prominent surface seep seasonally forms at the south end of RCRA Canyon in the winter. The seep forms in response to a shallow water table and upward groundwater gradients at the canyon bottom that are greater in the winter in response to rainfall infiltrating over the canyon. This seep is elevated in TDS and metals, which could result in risk to amphibians if the water is allowed to pond. The seep is also important in revealing the shallowness of groundwater in this area and pointing to a need to install low-permeability capping systems to contain and lower groundwater levels. Soil Vapor Soil vapor contamination occurs primarily in Areas 1 and Area 5 in association with the most extensive buried waste materials. Concentrations of VOCs in soil vapor occur in FS Area 1 and the northern part of Area 5 (Groundwater North). These VOCs result from contamination from the landfills and residual contamination in the Burial Trench Area and Central Drainage Area. Diffusion causes these VOCs to migrate outside of these areas, including south of the PSCT and north, outside the boundaries of the waste disposal site, into the North Drainage. The soil vapor concentrations in the North Drainage, however, are relatively low and are being monitored by a cluster of three soil gas probes along the North Ridge.


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The generation of landfill gas as methane is relatively insignificant because organic rich municipal solid waste was not disposed in the landfills. Gas flux testing of the interim soil caps, before the landfills were capped by the CSC between 1998 through 2002, did not indicate significant movement of methane and other VOCs through the soil caps. Summary of Site Risks A comprehensive risk assessment was conducted as part of the RI/FS process. The risk assessment is detailed in the RI report and summarized in the FS report. Consistent with EPA guidance and policy, the risk assessment includes (1) a human health risk assessment (HHRA), and (2) an ecological risk assessment. The HHRA includes a baseline risk assessment that evaluated cancer and non-cancer risks for existing site conditions and current land and water uses. The risk assessment then qualitatively evaluates risks for reasonably anticipated future land use scenarios. The ecological risk assessment quantitatively evaluates site risks to a wide range of plant & wildlife species, for current and future use scenarios, consistent with EPA policies and practices. Human Health Risk Assessment Baseline Risk Assessment: The baseline human health risk assessment (BHHRA) evaluates risks, for each site area, under current conditions. The BHHRA studies (1) sources of contamination in different media, (2) pathways of exposure, and (3) potentially impacted populations, called “receptors.” Sources of contamination include contaminated media, such as buried solid and liquid wastes, soil, groundwater, DNAPL, and soil vapor. The risk assessment also considers individual site features, such as former waste management units (e.g., landfills, pits, ponds, lagoons, disposal wells, and trenches). Consistent with EPA guidance Risk Assessment Guidance for Superfund (RAGS Part A) the BHHRA addresses major components, including (1) data review & evaluation, (2) exposure assessment, (3) toxicity assessment, (4) risk characterization, and (5) uncertainty analysis. The risk assessment then considered and developed appropriate quantitative risk calculations for exposure pathways, such as direct physical contact, ingestion, inhalation, and movement of contamination through air, soil, fractured rock, surface water, and groundwater. The HHRA evaluated groundwater, but did not calculate risks for groundwater due to the lack of complete exposure pathways and receptor populations. Instead, EPA is using MCLs as risk-based cleanup goals that are relevant and appropriate in decision making for groundwater response actions. Similarly, the BHHRA does not include detailed risk calculations for site features with incomplete exposure pathways, such as the landfills, which have already been capped. Current potential exposure activities currently include site workers, occasional trespassers, and local residents, such as local ranchers and neighbors. There are no completed exposure pathways to the Town of Casmalia. EPA has established a cumulative cancer range of 10-4 to 10-6 to manage cancer risks for Superfund cleanups. Non-cancer concerns are evaluated as a hazard quotient of less than or equal to one (HQ<1). Anticipated Future Use Scenarios: The risk assessment also evaluated risks associated with potential future land and water uses.


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The HHRA evaluated risks associated with site workers and trespassers. For future uses outside the historical site boundaries, the HHRA evaluated risks associated with ranchers, recreational users, and hypothetical future residents. The HHRA did not include quantitative risk calculations for residential exposure within the historical site boundaries to contaminated groundwater because EPA has no reasonable anticipation that the site will have future residential or commercial activities that would rely on groundwater beneath the historical landfill. However, EPA has taken the approach that MCLs are relevant and appropriate cleanup standards for groundwater. The HHRA assumes that groundwater is actionable and should be addressed in the cleanup strategy based on exceedances of MCLs, which are safe drinking water standards. The HHRA includes a detailed compilation of site risks. The RI provides risk calculation for cancer (10-4 to 10-6) and non-cancer risks (HQ>1) for all significant site areas and site features. As stated, the HHRA does not include calculations for groundwater, and EPA is using MCLs as risk-based cleanup goals, in its decision making for groundwater. Similarly, the HHRA does not include calculations for site features that either have already been closed (e.g., the capped landfills) or temporary facilities, such as the ponds, that will all have to be closed for a variety site management reasons. The results of the HHRA identified the following COCs for the site:

Soils:

o MCPP; o Tetrachloroethylene; and o Trichloroethylene.

Surface Water (Ponds):

o Arsenic

Site Groundwater [See FS Appendix A, Table A-3]: o COPCs that exceed, or may be reasonably expected to exceed MCLs.

Ecological Risk Assessment The ERA considered potential exposure pathways for the terrestrial uncapped areas and freshwater aquatic areas. The capped landfills and interstitial areas were not included in the ERA. Multiple exposure pathways were evaluated, including direct contact and uptake by plants and invertebrates as well as inhalation and ingestion by animals. The results of the Tier 1 and Tier 2 ERAs identified the following COCs for the site (barium was not included as a COC due to its expected low toxicity in the form of barium sulfate [i.e. drilling mud]):

Terrestrial Areas RCRA Canyon Area – Chromium, Copper, and Zinc

WCSA – Chromium, Copper, and Zinc

Roadway Area – Chromium and Copper


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Liquid Treatment Area – Cadmium, Chromium, Molybdenum, Selenium, Vanadium, Zinc,

MCPP, DDT, total DDT, and Hexachlorobenzene, and Mirex

Burial Trench Area – Chromium, Molybdenum, Selenium, Vanadium, Zinc, and TCE

Maintenance Shed Area – Cadmium, Chromium, Lead, Vanadium, Zinc, DDE, Total DDT, Dioxin TEQ, and Total TEQ

Central Drainage Area – Chromium, Molybdenum, Vanadium, Zinc, Dioxin TEQ, Total

TEQ, Bis(2-ethylhexyl)phthalate, and Endrin

Aquatic Areas

A-Series Pond – Arsenic, Cadmium, Chromium, Manganese, Mercury, Molybdenum, Selenium, Vanadium, and Zinc

RCF Pond – Chromium, Molybdenum, Selenium, Zinc, Avian PCB TEQ, Total TEQ, and

MCPP

Pond A-5 – Cadmium, Chromium, Molybdenum, Selenium, Zinc, and MCPP

Pond 13 – Cadmium, Selenium, and Zinc

Pond 18 – Cadmium and Chromium, Molybdenum, Selenium , Zinc, and MCPP

RCRA Canyon Runoff (if allowed to pond under future land use scenario) – Arsenic, barium, beryllium, cadmium, chromium, lead, manganese, mercury, molybdenum, nickel, selenium, silver, thallium, vanadium, zinc, benzo(b)fluoranthene, and ethylene glycol.

These COCs result in terrestrial risks to birds, mammals, and ecological communities (plants and soil invertebrates); and aquatic risks to birds, sediment dwelling invertebrates, aquatic life, aquatic plants, and amphibians.

The site also contains several listed threatened and endangered species, including the California Red Legged Frog (CRLF), the California Tiger Salamander, and the Western Spadefoot toad. EPA has been working with the U.S Fish and Wildlife Service (USFWS) and the California Department of Fish and Wildlife to address habitat mitigation and protection of these species. Basis for Action The FS has evaluated a variety of factors in developing alternative remedial actions for the site. The FS describes the basis for action for site areas and individual site features based on the nature and extent of contamination, evaluation of risks, and remediation technologies. Numerous factors extend beyond calculation of cancer health risk numbers. A large portion of the remedial alternatives address exceedances of ecological screening levels. Additional considerations include consistency with EPA and State of California policies, including California’s anti-degradation policies for groundwater, EPA’s preference for treatment and DNAPL source reduction, overall constructability, compatibility and integration with other site


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systems, and control of hydraulic gradients to prevent surface outflow and seeps. Principal Threat Wastes (PTWs) PTWs are by definition materials considered highly toxic or highly mobile that generally cannot be contained or present a significant risk to human health or the environment. According to the NCP and EPA guidance, EPA expects to use treatment to address principal threats posed at by a site wherever practicable and engineering controls, such as containment, for waste that poses a relative low long-term threat. The FS has identified several PTWs dprincipal threat wastes (PTWs) at the site based on site investigations, risk assessment work, and consideration of remedial technologies. Area 1 includes the bulk of PTWs, such as buried pesticides, solvents, caustics, cyanides, PCBs, metals, and acids contained within former landfills and other waste management units. NAPL (DNAPL & LNAPL) constitutes a PTW for Area 5 (GW-North). PTWs have been addressed at various stages throughout the history of the site. Where practicable, wastes, such as contaminated liquids, have been extracted for treatment at the site or at a permitted disposal facility. Where it is not technically practicable to treat PTWs, such as in landfills (Area 1) and groundwater (Area 5), the FS alternatives would continue to control the waste using source reduction, liquids treatment, and containment. Remedial Action Objectives (RAOs) and Applicable or Relevant and Appropriate Requirements (ARARs) The FS Report developed Remedial Action Objectives (RAOs) that describe in general terms what a remedial action should accomplish in order to be protective of human health and the environment. The RAOs were developed separately and then applied to individual FS Areas based on environmental media (surface soil, shallow soil, deep soil, soil vapor, surface water, and groundwater) and contaminant type (organics, inorganics). These RAOs are summarized below: Soil, Soil Vapor, and Sediments Prevent human exposure to risk-driving chemicals in soil, soil vapor and sediment such that

total carcinogenic risks are within the risk range of 10-4 to 10-6 (meaning one additional cancer in a population of between 10,000 and 1 million) and non-cancer hazard indices are less than 1 (HI<1) (meaning no non-cancer deaths). Potential human exposures include workers and trespassers at the site, and residents outside the site boundaries.

Prevent exposures to populations of ecological receptors for risk driving chemicals in soil, soil vapor and sediment such that risks are below the acceptable target levels: lowest-observed adverse effects level (LOAEL), and hazard quotients (HQ) less than 1.

Mitigate the potential for migration of contaminants in soil, soil vapor and sediment that could adversely affect groundwater quality.

Groundwater, NAPL, and Surface Water Media Prevent human exposures to risk-driving chemicals (primarily metals) in surface water such

that total carcinogenic risks are within the NCP risk range of 10-4 to 10-6 and non-cancer hazard indices are less than 1. Potential human exposures include workers and trespassers, and residents living outside the site.


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Prevent ecological exposures to risk-driving chemicals in surface water such that exposures are below acceptable levels (HQs less than 1 based on selected surface water benchmarks).

Restore groundwater quality to applicable standards, such as restore beneficial use, achieve MCLs where technically practicable.

Contain and/or control contamination sources within the site or subareas within the site, where groundwater restoration to applicable standards is not technically practicable.

Prevent or mitigate potential migration of contaminated groundwater via perimeter control. Remove DNAPL to the extent practicable and contain and/or control the migration of DNAPL

where removal is not technically practicable. Remove LNAPL to the extent practicable and contain and/or control the migration of LNAPL

where removal is not technically practicable. The FS also includes identifies the potential Applicable or Relevant and Appropriate Requirements (ARARs) for the potential remedies for the site. The complete ARARs analysis and selected list of potential ARARs are presented in Appendix B of the FS Report. Technical Impracticability Evaluation (TIE) for Area 5 North The site includes many technical complexities that warrant an evaluation of technical impracticability for groundwater restoration to MCLs for limited portions of the site. EPA guidance indicates that site conditions that may prevent GW restoration to MCLs should be evaluated in terms of (1) hydrogeologic factors, (2) contaminant-related factors, and (3) technology constraints on remediation system design and implementation. The FS Report includes a Technical Impracticability Evaluation (TIE) that discusses the technical impracticability of restoring contaminated groundwater for FS Area 5 North. As discussed in USEPA’s 1993 Guidance for Evaluating the Technical Impracticability of Ground-Water Restoration, there are a number of factors that can inhibit groundwater restoration which include hydrogeologic and contaminant-related factors, such as the presence of DNAPLs. This is particularly relevant to the Casmalia site, where NAPLs exist at the site as the result of the disposal of billions of pounds of liquid wastes within capped landfills. As described in the TIE, a TI determination is sought only for groundwater FS Area 5 North. This groundwater area includes the most highly contaminated parts of the site, including the Capped Landfills, the PCB Landfill, the Burial Trench Area, and the Central Drainage Area. LNAPLs and DNAPLs are found within this area. A TI determination is considered for both the Upper HSU and Lower HSU within this area for both organics and inorganics. The proposed “TI zone” is contained fully within the geographical boundaries of the site. At Groundwater North, there are many factors that preclude restoration of groundwater to drinking water standards, including the following:

Groundwater North contains high volumes of NAPL, including LNAPL and up to 100,000 gallons of pooled DNAPL that have accumulated at the base of the P/S landfill.

NAPLs have migrated into low permeability fractured bedrock and are nearly impossible to completely remove.

There are mixed wastes in groundwater (hydrocarbons, solvents, polychlorinated biphenyls [PCBs], metals, etc.) that are not treatable by a single technology.

Many of the contaminants are relatively immobile due to sorption and diffusion within the aquifer.


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The geology is complex; the overburden geology has extremely low permeability and the basement rock is highly fractured.

There are ongoing sources of contaminants that are encapsulated within capped landfills, such as pesticides and solvents within the Pesticide/Solvent (P/S) Landfill.

The most suitable remedial approach for Groundwater North is to implement source reduction, treatment, and containment to remove NAPLs in the source area, treat extracted liquids, contain and prevent further migration of the NAPLs and contaminated groundwater plume, and prevent exposure to contaminated groundwater. Groundwater modeling has shown that even very aggressive pump-and treat remediation would not restore groundwater in GW-North to MCLs over very long time frames on the order of several thousand years or more (essentially, in perpetuity). The FS also evaluated restoration time frames for areas GW-South and GW-West and has concluded that, although not strictly technically impracticable in the same sense as GW-North, it would take a very long time to restore groundwater in GW-South and GW-West to MCLs (several hundred years). GW-North differs from GW-South and GW-West in terms of (1) having more complex geology; (2) having a much greater volume of waste left in place; (3) having a much greater number and diversity of COCs; and (4) the having very large volumes of pooled and residual DNAPL. Based on EPA’s TI guidance, these are characteristics which are generally consistent with technical impracticability. In summary, delineation of the entire GW-North area as the TI zone is warranted for numerous reasons related to hydrogeologic considerations, contaminant characteristics, and technology constraints. Restoration to MCLs in GW-North is technically impracticable because (1) large volumes of pooled DNAPL have accumulated at the base of the P/S landfill within area GW-North; (2) residual waste will be capped in place; (3) even after DNAPL source reduction via extraction, residual DNAPL and waste materials will continue to be ongoing sources for localized groundwater contamination within GW-North; (4) contamination includes a mixture of hundreds of different COCs; (5) contamination occurs pervasively throughout GW-North, (6) hydrologic factors (i.e., fracturing, low permeability host rock and matrix diffusion) render remediation technologies ineffective within this area; and (7) GW contamination has been effectively contained within GW-North through a combination of engineering controls and natural attenuation. GW-North therefore is a reasonable choice for designating a small TI zone within the much larger site boundary. General Response Actions (GRAs) and Technology Screenings The FS includes an evaluation of General Response Actions (GRAs), based on environmental media (surface soil, shallow soil, indoor air, deep soil and groundwater) and contaminant type (organics, inorganics), to address the RAOs and potential ARARs. GRAs considered include institutional controls, containment, in-situ treatment, removal, ex-situ treatment, disposal, and reuse. Several cap types were also considered during the screening and detailed evaluation of remedial alternatives, described more fully below. The FS Report describes the process of evaluating a wide range of remedial technologies, with the goal of selecting a set of effective technologies for use as components in the remedial alternatives for the site. The technologies evaluated were related to the various media at the site including soil, sediment, stormwater, groundwater and NAPL. The technologies that were inappropriate were screened out in the initial screening.


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Area-specific Remedial Alternatives Screening and Detailed Evaluation The next step was to combine the technologies retained from the screening evaluation and the results of the TIE for groundwater FS Area 5 North and develop a range of appropriate remedial alternatives for each FS Area. The FS describes the process of performing a second screening evaluation of those remedial alternatives based on the three screening criteria from the CERCLA guidance (effectiveness, implementability, and cost). This screening evaluation used a 5-point rating scale for each criterion: poor, poor to moderate, moderate, moderate to good, and good. This evaluation screened out remedial alternatives that did not rate well on these criteria, resulting in recommending the appropriate remedial alternatives for the detailed 9-criteria evaluation. The next step was a detailed evaluation of the retained remedial alternatives for each FS Area using the criteria identified in the CERCLA guidance. Of the 9 criteria in the CERCLA guidance, the first seven criteria are addressed in the FS report. The two remaining criteria, state acceptance and community acceptance, will be addressed at a later date. Specifically, state acceptance will be addressed once the state has approved the FS report, and will be incorporated into the Proposed Plan. Community Acceptance will be addressed after EPA has received public comments on the Proposed Plan. The ROD will incorporate the final evaluation of these two criteria. The results of this evaluation were used to select a range of alternatives for each FS Area and assemble them into various site-wide remedial alternatives that would then be further evaluated in accordance with the CERCLA criteria. Finally, the FS Report also includes an evaluation of the “Green” aspects of the proposed remedial alternatives using EPA’s Principles of Greener Cleanups (EPA, 2009) and EPA’s Superfund Green Remediation Strategy (EPA 2010). The green remediation analysis was also performed and considered as an additional criterion for the screening level and detailed evaluations of the area-specific alternatives. Site Wide Remedial Alternatives Six (6) site wide remedial alternatives (SWRs) were developed for final evaluation based on the detailed evaluation of the area-specific alternatives summarized above. Each SWR is a combination of the remedial components from the area-specific detailed evaluation that range from “no action” to several aggressive restoration scenarios. Similar to the area-specific evaluation, the detailed evaluation of the SWRs was conducted in accordance with (1) the CERCLA criteria and (2) the “Green” aspects of remediation using EPA’s Principles of Greener Cleanups (EPA, 2009) and EPA’s Superfund Green Remediation Strategy (EPA 2010). The discussion of remedial alternatives ranges from least aggressive (e.g. No Further Action) to the most aggressive alternatives. The SWRs include some components that may be similar for several alternatives, or even all of the alternatives. Common components include engineered RCRA-equivalent capping systems, institutional controls (ICs), hot spot removal, liquids extraction, various programs for habitat mitigation, a limited TI determination, long-term operations and maintenance, and long term performance and compliance monitoring (OM&M). Other components, such as the size and type of evaporation ponds, different liquids treatment systems, inclusion of discharge, inclusion of aggressive pump & treat systems or horizontal directional drilling for landfill dewatering, clearly differentiate some of the components.


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All SWRs include institutional controls (ICs), primarily through land use covenants, that EPA anticipates would prohibit residential and commercial reuse. With the exception of the No Further Action SWR #1, each of the remedial alternatives addresses remediation of groundwater based on the presence of multiple COCs that exceed performance standards based on MCLs. The SWRs evaluated in the FS include components for long term groundwater monitoring for the purposes of monitoring system performance and compliance with performance standards. The compliance monitoring will include identification of groundwater monitoring networks, monitoring standards, and points of compliance (POCs) for compliance monitoring. At this point, EPA expects that two POCs will generally correspond to, or be located just outside of, (1) facility’s property boundaries to demonstrate no releases outside the historical site boundaries; and (2) the boundaries for Area GW-North in order to demonstrate compliance with a TI zone. Each of the six SWRs is described below, followed by a comparative analysis and a recommendation of which best meets the CERCLA criteria. Table ES-1 lists the remedies by FS Area that are assembled for each SWR. The titles of the various site wide remedy alternatives are not intended to completely describe the remedy and were chosen to distinguish each of the alternatives from the others.


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Table ES-1 – Summary of Site-Wide Remedial Alternatives Evaluation


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Site Wide Alternative #1 – No Further Action This alternative, which CERCLA requires to provide a basis of comparison with other remedial actions, provides no remediation, but takes into account the response actions that have either already been completed, such as the caps on the P/S Landfill and the EE/CA Area, or are ongoing (i.e. groundwater extraction and treatment/management from the existing Gallery Well, Sump 9B, PSCT, and PCTs features). Currently the Gallery Well and Sump 9B liquids are disposed at a permitted disposal facility. The PSCT liquids are treated at the site using GAC and discharged to Pond 18. PCT liquids are discharged to the RCF and A-Series Pond. Stormwater is retained in site ponds for evaporation, except for stormwater from the capped landfill area that is discharged to the B-Drainage and Casmalia Creek. This alternative is not protective of human health and the environment nor does it meet ARARs because of contaminants that are either not contained or result in unacceptable exposure. Site Wide Alternative #2 – Large Evaporation Pond SWR #2 would utilize a large evaporation pond (11 acres) for evaporation of treated extracted liquids and a portion of the stormwater runoff from RCRA Canyon. This alternative remediates the RCRA Canyon (FS Area 2) to meet all RAOs which do not by themselves require that all of the RCRA Canyon area be covered with some sort of cap. In doing so, this alternative assumes that some of the stormwater runoff from the RCRA Canyon would be directed to the new evaporation pond that would be constructed in the footprint of the existing A-Series Pond. Further remediation details for each FS Area are described below: FS Area 1 – PCB Landfill, Burial Trench Area, Central Drainage Area. FS Area 1 would

be covered with a cap that complies with the final cover requirements for hazardous waste landfills pursuant to federal law (a RCRA Cap). FS Area 1 includes the PCB Landfill, Burial Trench Area and the Central Drainage Area, covering a total area of approximately 28.8 acres. The proposed RCRA cap would be similar in design to the existing P/S Landfill Cap and the EE/CA Area Cap and tie into these caps. As described below for FS Area 3, the construction of the RCRA Cap would extend to cover the Maintenance Shed Area as well. Stormwater from FS Area 1 would be discharged to the B-Drainage and Casmalia Creek.

FS Area 2 - RCRA Canyon and West Canyon Spray Area (WCSA). FS Area 2 would be remediated by constructing an evapotranspiration (ET) cap that is approximately 5-feet thick over the western portion of the RCRA Canyon (8.4 acres) and excavating the relatively shallow contaminated soils of the WCSA and then backfilling with clean soil (5.5 acres). The western slope of the RCRA Canyon would be graded and stormwater Best Management Practices (BMPs) utilized to meet the substantive conditions of the General Permit for stormwater discharge. Stormwater from the western slope would be discharged down the B-Drainage and into Casmalia Creek. Stormwater BMPs would be utilized over the eastern slope of the RCRA Canyon (19.3 acres). Stormwater from this eastern area would not be discharged because of low-level (HQ<1) residual soil contamination. Instead, this stormwater would be directed into the new 11-acre lined evaporation pond that would be constructed in the footprint of the closed A-Series Pond.

The ET cap and excavation of the WCSA would reduce the residual ecological risks of this area to acceptable levels (i.e. HQ<1) by eliminating the exposure pathway for the ornate shrew and western meadowlark, which are the ecological receptors. In addition, the ET cap reduces surface water infiltration in this area of the site, thus lowering the level of the water table and likely eliminating the surface seep at the south end of the RCRA Canyon, which


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has elevated TDS and metals that could pose a risk to amphibians if the water were allowed to pond.

FS Area 3 – Former Ponds and Pads (FPP), Remaining (ROS) Areas. The RI Report

identified several localized areas of contaminated soil (i.e. hotspot locations) in FS Area 3 which had concentrations of contaminants that collectively create elevated ecological risks for soil invertebrates due to elevated organics or inorganics in the soil, but did not have any ecological risks to wildlife. Five of these hot spot locations would be remediated, which would reduce the residual ecological risks of the FPP and ROS areas to HQ<1. As is the case with FS Area 2, this is considered a conservative approach, considering that the exposed species is soil invertebrates and a higher HQ might have been justifiable. The contaminated soil hot spots in the former Ponds A/B, the area south of PSCT-1, and the Liquids Treatment Area would be excavated and placed under a cap; the contaminated soil hot spots in the Maintenance Shed Area would be covered with a RCRA Cap. Because there are not any concerns for human health or ecological risk for RISBON-59 (Hotspot 10), the proposed action for this location is long term monitoring of the groundwater with two additional downgradient monitoring wells to verify that there are no unacceptable impacts to groundwater. Stormwater from FS Area 3 would be discharged to the B-Drainage and Casmalia Creek under a General Permit.

FS Area 4 – Stormwater Ponds and Treated Liquid Impoundments. The stormwater and

treated liquids ponds that comprise FS Area 4 would be remediated as follows:

Pond 18 - removal of all liquids, placing clean soil within the pond footprint to re-grade it to match adjacent site topography, and a RCRA Cap to close the pond;

Pond A5 - removal of all liquids, placing excavated soil from the WCSA within the pond footprint to raise the bottom of the former pond approximately 10 to 15 feet. The pond footprint then would be capped with a double synthetic liner consisting of a high-density polyethylene layer and a geosynthetic clay layer (HDPE/GCL liner) and converted into a new retention basin that will be used as part of the RCRA Canyon stormwater management plan;

Pond 13 - removal of all liquids, placing a clean soil cover over the pond, and constructing a double HDPE/GCL liner over the clean soil that will serve as both a RCRA equivalent cap for the contaminated sediments in the pond and a liner so it may be converted to a lined retention basin; A-Series Pond - removal of all liquids, regrading the northeast corner of the pond to increase the pond size to approximately 11 acres, adding fill to raise the pond bottom above the water table, which is approximately 425 feet above mean sea level, and constructing a double-lined (e.g., dual HDPE liner) cap system over the former footprint of the pond to create the new evaporation pond that would be used as part of the liquids treatment and management system of the site. The double-lined system would include leak detection and a leachate collection and removal system:

RCF Pond - removal of all liquids, placing clean soil throughout the bottom of the pond to raise the pond bottom approximately 5 to 10 feet to prevent groundwater intrusion (~415 feet MSL), constructing a soil cap (or “eco-cap”) that is approximately 2-feet thick over the entire pond bottom area (thus covering all specific locations with elevated inorganics in the sediment), and construction of a new lined storm water channel through the middle of the former pond to the wetlands to convey the storm water runoff from the Central Drainage Area (CDA) and other capped portions of the site. For each of these existing ponds, any liquids remaining prior to remedial construction would be pumped to


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the new 11-acre evaporation pond in the footprint of the existing A-Series Pond. The new evaporation pond will also be required to handle future treated PSCT and PCT liquids.

FS Area 5 – Groundwater-North. Liquids extraction from multiple existing and new facilities would be performed to meet the RAO of controlling and containing contaminants and contaminant sources within the TI Zone. However, this area would not be remediated to meet MCLs. A Technical Impracticability (TI) waiver would be necessary for Groundwater-North because the presence of LNAPL, DNAPL, residual NAPL, and dissolved-phase organic and inorganic contamination in low-permeability fractured bedrock make it technically impracticable to remediate and meet the drinking water standards in this area. Within the P/S Landfill, extraction would continue from the existing Gallery Well and would also be performed by as many as 16 “NAPL-only” extraction wells that would be installed at the southern portion of the landfill to capture as much pooled LNAPL and DNAPL as possible. This extraction from the P/S Landfill would remove the “driving head” of the DNAPL that is likely causing DNAPL to spread into the Lower HSU beneath the P/S Landfill and Central Drainage Area. Within the Upper HSU, extraction would also continue from the PSCT to contain and prevent contaminated groundwater from migrating southward outside of the TI Zone. Extraction may also be performed from Sump 9B if the water table remains unacceptably high after capping in FS Area 1. Finally, approximately 12 new Lower HSU monitoring wells would be installed and monitored upgradient of PSCT-1 and PSCT-4 (three at each location with each location monitoring two depths) to verify that dissolved-phase contaminants and NAPLs are not migrating southward underneath the PSCT outside of the TI Zone. One or more of these new monitoring wells would be converted into extraction wells and liquids would be extracted if contaminants (VOCs or SVOCs) are detected at above MCLs. In addition, other contingency actions would be implemented as necessary that could include, if determined necessary by EPA: (1) immediate additional monitoring to characterize the release; and, (2) prompt implementation of corrective action, including installation of additional extraction wells. Groundwater extracted from the Lower HSU would be treated and discharged together with the PSCT liquids. The extracted volumes from the Lower HSU would be very small because of the low permeability of the Lower HSU. The liquids extracted from the Gallery Well and new NAPL-only wells in the P/S Landfill would be stored and shipped for treatment and disposal at an approved facility. The extracted liquids from PSCT would be treated at the site for organic removal using an upgraded liquids treatment system that is conceptually designed as an activated carbon treatment system, filtered for solids removal, and then transferred to the new 11-acre double-lined evaporation pond.

FS Area 5 – Groundwater-South. Within the Upper HSU, extraction would continue from

the PCT-A and PCT-B facilities to contain and prevent contaminated groundwater from migrating down the A- and B-Drainages. The current concentrations of dissolved-phase organic and inorganic (metals) contamination within the Upper HSU exceed MCLs (primarily arsenic, nickel, cadmium, and selenium). These concentrations will decrease over many decades due to naturally occurring conditions including dilution and flushing from infiltrating rainfall and natural degradation of organic compounds. The flushed contaminants would be extracted at the PCT-A and PCT-B facilities and extraction could be discontinued once


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contaminant levels achieve MCLs. This approach is referred to as Monitored Natural Attenuation (MNA) with perimeter containment. The Lower HSU of Groundwater South does not require remediation because the concentrations of organic and inorganic compounds in groundwater are below MCLs. The liquids extracted from the PCT-A and PCT-B facilities would be treated at the site for organic removal using an upgraded liquids treatment system that is conceptually designed as an activated carbon treatment system, filtered for solids removal, and then transferred to the new 11-acre lined evaporation pond.

FS Area 5 – Groundwater-West. Within the Upper HSU, extraction would continue from the PCT-C facility to contain and prevent contaminated groundwater from migrating down the RCRA Canyon and C-Drainage. Concentrations of the dissolved-phase inorganic (metals) contamination within the Upper HSU currently exceed MCLs (primarily arsenic, nickel, cadmium, and selenium). A significant source of this contamination is likely from the metals contamination in the overlying soils in the RCRA Canyon and WCSA and infiltration of surface water high in metals from Pond A-5 and the A-Series Pond. All of the SWRs (except SWR #1) would eliminate this contamination source from the ponds and reduce the source from the overlying soils. Once these sources are eliminated and reduced, the metals concentrations in Groundwater West will decrease over many decades due to naturally occurring conditions including dilution and flushing from infiltrating rainfall. The flushed contaminants would be extracted at the PCT-C facility, and extraction could be discontinued once contaminant levels achieve MCLs (i.e., MNA with perimeter containment). The Lower HSU of Groundwater West does not require remediation as the concentrations of organic and inorganic compounds in groundwater are below MCLs. The liquids extracted from PCT-C would be treated at the site for organic removal (using an upgraded liquids treatment system that is conceptually designed as an activated carbon treatment system), filtered for solids removal, and then transferred to the new 11 acre double-lined evaporation pond.

Site Wide Alternative #3 – Small Evaporation Pond SWR #3 is a variation of SWR #2 which would utilize a smaller (6 acre) evaporation pond instead of the larger (11 acre) pond. The primary difference in this alternative is additional capping in FS Area 2 to ensure that all stormwater runoff from the RCRA Canyon area can be discharged to the B-Drainage and Casmalia Creek rather than some having to be managed in the evaporation pond. Further details of the remediation for each FS Area are described below: FS Area 1 – PCB Landfill, Burial Trench Area, Central Drainage Area. FS Area 1 would

be remediated using the same remedy as SWR #2 above. FS Area 2 - RCRA Canyon and Western Canyon Spray Area. FS Area 2 would be

capped with either a RCRA equivalent ET cap or a RCRA equivalent hybrid cap that covers the western and eastern slopes of the RCRA Canyon and WCSA. The cap type for the different subareas would be selected during remedial design. With this particular capping, stormwater from the entire area will have acceptable ecological risks (i.e. HQ<1) and allow discharge to the drainage. In addition, the larger cap will significantly reduce surface water infiltration in this area, thus further lowering the level of the water table and assuring the


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elimination of the surface seep at the south end of the RCRA Canyon that has elevated TDS and metals.

FS Area 3 – Former Ponds and Pads, Remaining Site Areas. FS Area 3 would be

remediated using the same remedy as SWR #2 above.

FS Area 4 – Stormwater Ponds and Treated Liquid Impoundments. FS Area 4 would be remediated the same as for SWR #2, except that this alternative would utilize a smaller (6 acre) evaporation pond instead of the larger (11 acre) pond because no stormwater from RCRA Canyon would be discharged into it. The remainder of the A-Series Pond area would be capped with a soil cap (“eco-cap”).

FS Area 5 – Groundwater-North, Groundwater-South, and Groundwater-West. FS Area

5 would be remediated using the same remedy as SWR #2 above. Site Wide Alternative #4 – No Evaporation Pond SWR #4 is a variation of SWR #3 that would not include any evaporation pond. The pond is eliminated by adding a treatment plant at the site for PSCT and PCT liquids that treats both organics and inorganics to meet the substantive NPDES Permit requirements. The treated liquids are then discharged to Casmalia Creek, rather than managed in the evaporation pond. This alternative however, would require an “Exception” to the Basin Plan to address the requirement in the Basin Plan that prohibits waste discharge to surface waters within the Antonio Creek Sub-basin. The proposed remediation for each FS Area is described below: FS Area 1 – PCB Landfill, Burial Trench Area, Central Drainage Area. FS Area 1 would

be remediated using the same remedy as SWR #3 above. FS Area 2 - RCRA Canyon and Western Canyon Spray Area. FS Area 2 would be


FS Area 3 – Former Ponds and Pads, Remaining Site Areas. FS Area 3 would be remediated using the same remedy as SWR #3 above.

FS Area 4 – Stormwater Ponds and Treated Liquid Impoundments. FS Area 4 would be

remediated using the same remedy as for SWR #3, except that no evaporation pond would be constructed for management of stormwater or extracted liquids. All stormwater would be discharged to the B-Drainage and Casmalia Creek. Additional treatment would be added to treat PSCT and PCTs liquids to meet the substantive NPDES Permit requirements for both organics and inorganics and these treated liquids would then be discharged to the C Drainage west of the site rather than managed in an evaporation pond at the site. The bottom of the A-Series Pond would be partially filled to raise the pond bottom above anticipated groundwater levels and capped with a soil cap (eco-cap) similar to the cap proposed for the RCF Pond.

FS Area 5 – Groundwater-North, Groundwater-South, and Groundwater-West. FS Area

5 would be remediated similar to SWR #3 above except liquids extracted from the PSCT would be treated for organics and inorganics in accordance with the substantive requirements of a NPDES Permit, and then discharged to the C-Drainage west of the site rather than being managed in an evaporation pond at the site.


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Site Wide Alternative #5 – P/S Landfill Dewatering with Evaporation Pond SWR #5 is a variation of SWR #3 that would also include aggressive de-watering of the P/S Landfill using a number of horizontal extraction wells at the bottom of the landfill. As was the case with SWR #3, the treated PSCT and PCT liquids would be discharged in a new 6-acre evaporation pond that would be constructed in the footprint of the A-Series Pond, and all stormwater would be discharged to the B-Drainage and Casmalia Creek. The proposed remediation for each FS Area is described below: FS Area 1 – PCB Landfill, Burial Trench Area, Central Drainage Area. FS Area 1 would

be remediated using the same remedy as SWR #3 above.

FS Area 2 - RCRA Canyon and Western Canyon Spray Area. FS Area 2 would be remediated using the same remedy as SWR #3 above.


remediated using the same remedy as listed for SWR #3 above with one exception - the RISBON-59 hotspot (Hotspot #10) would be excavated and the contaminated soils moved to the PCB Landfill to be capped and covered as part of the closure of that landfill.

FS Area 4 – Stormwater Ponds and Treated Liquid Impoundments. FS Area 4 would be


FS Area 5 – Groundwater-North, Groundwater-South, and Groundwater-West. FS Area 5 would be remediated using the same remedy as for SWR #3 above for Groundwater South and Groundwater West. The Groundwater North remedy components are different, however. SWR #5 proposes aggressive de-watering of the P/S Landfill by constructing approximately five wells drilled horizontally underneath and into the landfill to de-water the bottom of the landfill. Under this alternative, the Gallery Well would remain in operation, but this alternative does not include the 16 “NAPL-only” wells in the P/S Landfill. The Gallery Well liquids, NAPLs, and other aqueous phase liquids drained from the P/S landfill would be sent to a permitted facility for disposal. SWR #5 also proposes that four existing monitoring wells located in the CDA would be converted to LNAPL skimming wells and the extracted LNAPL would be stored and shipped to a permitted facility for disposal. All of the other details of the remedy alternative remain the same.

Site Wide Alternative #6 – Aggressive Site wide Groundwater Extraction with No Evaporation Pond SWR #6 is a variation of SWR #5 that also includes construction and operation of approximately 80 new groundwater extraction wells located in Groundwater South and Groundwater West to decrease the time to achieve MCLs. In addition, SWR #6 proposes that extracted liquids would be treated sufficiently and discharged to the C Drainage west of the site in accordance with the substantive terms of a NPDES permit, such that no evaporation pond would be needed. This would require an “Exception” to the Basin Plan to address the requirement that restricts waste discharge to surface waters within the Antonio Creek sub-basin. The proposed remediation for each FS Area is described below: FS Area 1 – PCB Landfill, Burial Trench Area, Central Drainage Area. FS Area 1 would

be remediated using the same remedy as SWR #3 above.


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FS Area 2 - RCRA Canyon and Western Canyon Spray Area. FS Area 2 would be remediated using the same remedy as SWR #3 above.



FS Area 4 – Stormwater Ponds and Treated Liquid Impoundments. FS Area 4 will be remediated using the same remedy as for SWR #4 above.

FS Area 5 – Groundwater-North. FS Area 5, Groundwater North, would be remediated

using the same remedy as for SWR #5 above, with the following additions:

Approximately a dozen new LNAPL skimming wells would be installed in the CDA. The extracted LNAPL would be stored and shipped to a permitted facility for disposal.

Extraction would occur immediately from four of the twelve new monitoring wells that would be installed and monitored within the Lower HSU upgradient of PSCT-1 and PSCT-4 (three at each location with each location monitoring two depths) to assure that dissolved-phase contaminants and NAPLs are not migrating southward underneath the PSCT outside of the TI Zone. These liquids would be combined with the liquids extracted from the PSCT for treatment and disposal.

Liquids extracted from the PSCT would be treated for organics and inorganics in accordance with the substantive terms of a NPDES Permit and then discharged to the C Drainage west of the site rather than being managed in an evaporation pond at the site. The Gallery Well liquids, NAPLs, and other aqueous phase liquids drained from the P/S landfill would continue to be sent to a permitted facility for disposal.

FS Area 5 – Groundwater-South and Groundwater-West. FS Area 5, Groundwater South and Groundwater West, would be remediated using the same remedy as for SWR #5, except that approximately 80 new groundwater extraction wells would be located throughout the two areas and operated to decrease the timeframe that MCLs would be achieved. The liquids from the PCTs and the 80 new extraction wells would be treated for organics and inorganics in accordance with the substantive terms of a NPDES Permit and then discharged to the C Drainage west of the site rather than being managed in an evaporation pond at the site.

Cost Estimates for the Site Wide Remedy Alternatives The FS includes a detailed cost estimate for the sitewide remedial alternatives along with all the individual components. The cost estimates were prepared consistent with EPA guidance as well standard industry practice for engineering cost estimating. See Table ES-2. The cost estimates address capital construction and annual costs for operations, maintenance, environmental monitoring, and periodic replacement of system components. The estimates also include present value calculations, also prepared consistent with EPA and Office of Management and Budget (OMB) guidelines. For planning purposes, the FS calculates net present value (NPV) assuming remedy construction would occur between 2016 and 2020. Although subject to possible changes in schedule, the calculations use 2014 dollars and provide a useful basis of comparison for remedial alternatives. The estimates also incorporate long-term operation, maintenance, and


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monitoring, and provide calculations for durations of 30 years and 100 years, respectively, to address EPA guidance and provide reasonable estimates for long term operations in perpetuity. The cost estimates, particularly for the preferred alternative, will be reviewed again for the proposed plan and record of decision as part of the remedy selection process.

The FS presents cost estimates for discount rates of both 3% and 7%. The 7% discount rate is required by EPA guidance and the OMB, but the 3% discount rate may better reflect current and long-term future economic conditions. Although both estimates are useful for comparison of alternatives, the lower discount rates may generate more realistic estimates of actual costs for implementation. Table ES-2 – NPV Cost Estimates for Site Wide Remedy Alternatives (millions) (2014 $)

Site Wide Remedy Alternative 30 Year, 3% 30 Year, 7% 100 Year, 3% 100 Year, 7 %

Alternative 1 $53 $34 $86 $39

Alternative 2 $115 $85 $159 $92

Alternative 3 $120 $89 $164 $96

Alternative 4 $196 $138 $283 $152

Alternative 5 $147 $113 $192 $121

Alternative 6 $291 $210 $412 $229

Comparative Analysis and Recommended Alternative The FS closes with an evaluation of the SWRs based on the CERCLA criteria identified in the National Contingency Plan (NCP). The nine CERCLA criteria include the following: Threshold Overall Protection of Human Health and the Environment Compliance with ARARs Balancing Long Term Effectiveness (LTE) Reduction of Toxicity, Mobility, or Volume through Treatment Short Term Effectiveness (STE) Implementability Costs Modifying State Acceptance Community Acceptance Table ES-3 provides a summary of the SWRs based on the two threshold criteria and five balancing criteria. The table also assesses the alternatives in terms of green remediation. Although green remediation is not a formal ranking criterion under the NCP, it provides useful information regarding the incorporation of sustainability concepts and practices into Superfund


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remedies. The modifying criteria (i.e., state and community acceptance) will be addressed later in the Superfund process as part of the Proposed Plan and Record of Decision (ROD). The evaluation of the SWRs uses a 5-point rating scale ranging from poor, poor-to-moderate, moderate, moderate-to-good, and good for each criterion. Table ES-3 lists the SWRs along with their rankings for individual criteria. Table ES-3 – Summary of Site Wide Remedial Alternatives Evaluation

Note: Green Impacts Assessment is not a formal CERCLA ranking criterion, but is included as an additional consideration.

Threshold Criteria: Overall Protection of Human Health and the Environment: With the exception of the No Further Action Alternative, all sitewide alternatives (i.e., Alternative #2 through Alternative #6) achieve remedial action objectives (RAOs) and are protective. Compliance with ARARs: The FS includes a provisional ARARs analysis that identifies and evaluates a potential list of Applicable or Relevant and Appropriate Requirements. The list of potential ARARs contains chemical-specific, action-specific, and location-specific ARARs developed, in consultation with state and federal agencies consistent with EPA guidelines and practice. With exception of the No Further Action Alternative, all alternatives (Alternative #2 through Alternative #6) comply with the proposed ARARs, except SWR #3, which incorporates a TI ARARs waiver for a portion of the site delineated as FS Area 5 North (GW-North). Balancing Criteria: Long-Term Effectiveness: SWRs #3-6 are equivalent in terms of LTE. SWRs 3-6 are ranked above SWR #2 because they provide more widespread and effective capping systems. SWRs #3-6 also include more effective treatment systems with less reliance on evaporation ponds


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rather than relying on a single large evaporation pond (SWR #2). SWR #3 is rated better than SWR #2 with respect to LTE because it includes a cap (ET or Hybrid) that covers the entire RCRA Canyon/WCSA which will more effectively limit infiltration and provide greater certainty that all of the storm water runoff from the RCRA Canyon can be discharged safely under the substantive terms of the General Permit. It will also eliminate a seep at the southern part of the RCRA Canyon that contains elevated TDS and metals. SWR #3 uses a smaller evaporation pond than SWR #2, which would provide better protection of the ecological species compared to the larger 11-acre pond, thus increasing LTE. SWR #4 provides more aggressive liquids treatment to allow for discharge to Casmalia Creek and elimination of evaporation ponds, but is vulnerable to additional project risk and technical complexity. SWR #5 and SWR #6 provide even more aggressive extraction and treatment, through horizontal wells (SWR #5) and vertical wells (SWR #6), but are vulnerable to further project risk, technical complexity, and potential releases of hazardous materials as part of landfill dewatering (SWR #5) and long-term shipment of hazardous liquids for disposal. The project risks and complexities of SWRs #5 and #6 are discussed blow under “implementability.” Reduction of Toxicity, Mobility, or Volume through Treatment: Alternatives #2-4 are equivalent in terms of criterion #4, Reduction of Toxicity, Mobility or Volume through Treatment. This criterion focuses on EPA’s preference for treatment of contaminated liquids derived from principal threat wastes, where technically practicable, which for this site include NAPL and buried wastes in Areas 1 and Area 5. These three alternatives include DNAPL source reduction to extract pooled DNAPL from the P/S Landfill and liquids extraction from the PSCT and three PCTs for containment. Alternative #4 includes additional treatment of liquids to allow for discharge to Casmalia Creek instead of evaporation in ponds. Alternative #5 includes landfill dewatering through use of horizontal directional drilling to drain approximately 10 million gallons of contaminated groundwater from the P/S landfill. Although ranked higher in terms of volume reduction, dewatering contaminated liquids would require extensive treatment and would pose a number of technical challenges and considerable project risks, including the threat of uncontrolled releases, discussed below under “implementability.” Alternative #6, the most aggressive alternative, would include landfill dewatering and the installation of additional extraction wells for pumping and treatment of site liquids in GW South and GW West. The FS has determined, however, that Alternative #6 would not substantially increase protectiveness or reduce the time necessary to achieve performance standards, through restoration of GW to MCLs, in spite of the investment in additional cleanup technology. All alternatives, except for the No Further Action Alternative (i.e., Alternatives 2-6), are equivalent in terms of using containment to address principal threat wastes in Area 1, where the former landfills and burial areas are located. Short-Term Effectiveness: SWR #3 is top ranked with respect to short term effectiveness because it provides effectiveness in the short term with less vulnerability to project risk (complexity and uncertainty) associated with horizontal well drilling (SWR #5) or more aggressive pump and treat systems (SWR #6). SWR #3 is ranked higher than SWR #2 because the smaller evaporation ponds reduce adverse impacts to potential special status species. SWR #3 is ranked higher than SWR #4 because SWR #4 provides more aggressive liquids treatment to allow for discharge to Casmalia Creek and elimination of evaporation ponds, but is vulnerable to additional project risk and technical complexity. SWR #4 also requires a regulatory “exception” from the state RWQCB to the state Basin Plan to allow for discharge of treated liquids to Casmalia Creek. Implementability: Similar to short term effectiveness (STE) above, SWR #3 is top ranked with respect of implementability because it is readily implementable and would not face some of the


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technical challenges, or potential risks, associated with installation of more risky horizontal wells (SWR #5) or more aggressive pump and treat systems (SWR #6). SWR #5 is ranked low due to technical challenges inherent in horizontal directional drilling and potential risks of uncontrolled releases of large volumes of contaminated liquids. SWR #6 is ranked lowest for implementability due to technical complexity associated with aggressive pump and treat systems, such as installation, optimization, and monitoring of an 80-well extraction system, construction of additional liquids treatment systems, and long-term transport of large volumes of hazardous liquids. SWR #3 is ranked above SWR #2 due to reduced operations and maintenance for a smaller evaporation pond system. Costs: Costs generally increase from SWR #2 through SWR #6 as the SWRs become increasingly aggressive in terms of technically complexity. Significant cost drivers include costs for liquids treatment, horizontal drilling (SWR #5), collection, treatment and disposal of liquids, and installation of complex networks of extraction wells (SWR #6) associated with different alternatives. Although all responsive alternatives (SWR #2-6) meet RAOs, achieve protectiveness, and comply with ARARs or incorporate a TI waiver, SWR #2 and SWR #3 both are of significantly lower costs than the more aggressive SWR #4-6. SWR #3 is considered preferable, however, because it achieves lower costs, but provides a much higher level of protection for special status species than SWR #2 due to its smaller evaporation ponds. Evaluation of Combined Threshold and Balancing Criteria: The FS ranks SWR #3 as the top ranked alternative based on assessment of the CERCLA criteria. SWR #3 is fully protective, meets RAOs, and complies with ARARs. Overall, SWR #3 provides the most efficiency in terms of meeting project objectives while reducing project risks and reducing unnecessary technical challenges. SWR #3 also substantially reduces health and environmental risks associated with potential unintended releases. SWR #3 ranks higher than SWR #4 since SWR #4 has potential risk for unintended releases of hazardous chemicals to Casmalia Creek. SWR #5 and SWR #6 are vulnerable to potential releases from horizontal wells (SWR #5) and long-term shipments of hazardous liquids associated SWRs #5 and SWR #6. These higher levels of project risk and greater vulnerability to unintended releases are reflected in lower rankings for SWRs #4-6 for implementability, short term effectiveness, and cost. Green Remediation (Informal Criterion): Although not a formal CERCLA ranking criterion under the National Contingency Plan, the FS has acknowledged green remediation concepts in the development and consideration of remedial alternatives for the site. With respect to green impacts, SWR #3 is rated higher than SWRs #4 and #6 because they involve operation of a larger liquid treatment plant to treat inorganics over the long term for discharge. SWR #3 is rated higher than SWR #5 and SWR #6 because of the greater risks and potential impacts associated with the horizontal wells installation and the transportation and disposal of the dewatered liquids. SWR #3 is rated about the same as SWR #2 for green impacts assessment because the additional impacts of the ET cap construction across the entire RCRA Canyon/WCSA are balanced by the lower impacts with a smaller evaporation pond construction. Modifying Criteria: State Acceptance: California state regulatory agency representatives have been involved throughout the implementation of the RI/FS work. Evaluation of state acceptance will be addressed as part of the upcoming Proposed Plan and Record of Decision (ROD) for the site.


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Community Acceptance: Community representatives have played active roles throughout the implementation of the RI/FS work. Final evaluation of community acceptance will be addressed through the Proposed Plan and public comment period and Record of Decision (ROD). In conclusion, the preferred remedy, SWR #3 is a combined containment and treatment remedy that includes DNAPL source reduction, extraction and treatment of contaminated site liquids, and containment of waste materials in landfills, soils, and groundwater. The preferred remedy meets statutory requirements in terms of protecting human health and the environment; achieving ARARs; adopting permanent solutions; using treatment where technically practicable; and is cost-effective. Consistent with EPA’s approach for many legacy landfill-type sites, solid waste will be contained at the site. The preferred remedy will achieve containment through use of engineering controls, institutional controls, and natural attenuation. EPA also plans to implement treatment of liquids where technically practicable. The preferred remedy will include DNAPL source reduction and treatment through the installation of extraction wells to remove large volumes of DNAPL and thus reduce DNAPL sources that contribute to groundwater contamination. Extracted DNAPL will be transported to a permitted facility for further treatment and disposal. The preferred remedy also will expand the current use of extraction systems (containment trenches, extraction wells, and extraction sumps) to remove and provide for treatment of contaminated liquids. The remedy will make use of institutional controls, primarily through land use covenants, and will include rigorous long term operations, maintenance, and monitoring programs. Long term monitoring will include both performance and compliance monitoring. Because waste will remain at the site, EPA will conduct statutory five-year reviews to continue to evaluate and ensure the long term protectiveness of the remedy.


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1.0 INTRODUCTION The Casmalia Resources Site Steering Committee (CSC) has prepared this Final Feasibility Study (FS) report based on Section 11.6 in the Remedial Investigation/Feasibility Study (RI/FS) Workplan (2004). The FS was conducted in accordance with Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) and the National Contingency Plan (NCP, 40 CFR Part 300 et seq.). The FS is structured and was prepared in accordance with all appropriate U. S. Environmental Protection Agency (USEPA) FS guidance including the CERCLA RI/FS Guidance (USEPA 1988) and the FS cost estimating guidance (USEPA 2000). The site lies approximately 4 miles from the Pacific Ocean, approximately 10 miles southwest of the city of Santa Maria, and approximately 16 miles north-northwest of the city of Lompoc. The nearest population center is the unincorporated community of Casmalia, located approximately 1.2 miles south-southeast of the site. The site is accessed via NTU Road off of Black Road, approximately 1 mile north of the unincorporated community of Casmalia (Figure 1-1). Further information regarding site background, previous investigations, and physical characteristics is provided in the following sections.

1.1 Purpose and Scope The purpose of this FS is to evaluate a range of remedial alternatives that would address soil, soil vapor, surface water, and groundwater contamination in accordance with the NCP and CERCLA RI/FS guidance (USEPA 1988). The FS follows the overall evaluation approach described in the RI/FS workplan (2004), as approved by EPA. The FS relies on the results of the site remedial investigations conducted from 2004 through 2009, and the risk assessments that are documented in the Final RI Report (2011), as approved by EPA. Together, these documents will provide USEPA with key information necessary to issue the Proposed Plan for the Casmalia Resources Superfund Site. This CERCLA FS process involved the following:

Identifying remedial action objectives (RAOs) and general response actions (GRAs); Identifying potential Applicable or Relevant and Appropriate Requirements (ARARs); Screening available remedial technologies for impacted media; Developing appropriate remedial alternatives for the FS evaluation; Screening remedial alternatives to select the most promising alternatives; Conducting the detailed 9-criteria evaluation of the selected remedial alternatives; and, Performing a comparative analysis of the remedial alternatives.

1.2 Feasibility Study Approach As is described later in this document and as was provided by the RI/FS Workplan, the FS evaluation involves a staged approach by combining the individual RI study areas at the site into five FS areas (FS areas 1 to 5) and performing separate evaluations of multiple remedial alternatives for each FS area. This leads to a large number of potential cleanup alternatives. The FS then integrates the evaluations for each FS area and presents an evaluation of six (6) site-wide remedial alternatives using the results of the FS area evaluations. FS areas are described in Section 8 and depicted in Figures 8-1A and 8-1B.


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Stage I: Area-by-area evalutions Stage II: Evaluation of six (6) sitewide alternatives The FS presents a summary of the chemicals of concern (COCs) from each of the RI study areas and as appropriate combines some of the study areas to form the five new FS areas as presented in Section 8. COCs are those Chemicals of Potential Concern (COPCs)1 that were identified in the quantitative risk assessment as exceeding a risk threshold and therefore, warranted further evaluation in the FS. The soils, sediments, and surface water at the site are divided into four FS areas while groundwater is evaluated separately as FS Area 5. The evaluation of groundwater includes both the dissolved-phase groundwater plume and the nonaqueous phase liquid (NAPL) source areas. Both light nonaquous phase liquids (LNAPL) and dense nonaqueous phase liquids (DNAPL) occur in the source areas. For study areas where there is no significant ecological or human health risk, as provided in the RI/FS Workplan, the FS notes there is no need for further evaluation. This FS does not include a formal evaluation of the Capped Landfills Area, which includes the Pesticide/Solvent (P/S) Landfill and Engineering Evaluation/Cost Analyais (EE/CA) Area, other than including them as part of FS Area 1. The EE/CA Area consists of the Heavy Metals, Caustics/Cyanides, and Acids landfills. The CSC constructed Resource Conservation and Reconstruction Act (RCRA) caps, RCRA-equivalent caps, on these four landfills from 1999 through 2002, which were identified at the time of design and construction as presumptive remedies for these areas. The existing RCRA cap remedies remain the preferred and proposed remedy for these areas. Maintenance and monitoring of the existing RCRA cap and institutional controls (ICs) are recommended as part of the final site remedy. RAOs are presented initially as general statements in Section 8 by medium (soil, soil vapor and sediments media, and groundwater, NAPL, and surface water). Subsequently, the RAOs and Preliminary Remediation Goals (PRGs) are presented in more detail by study area and medium. PRGs as defined by USEPA, can be initial clean-up goals developed early in the remedy selection process based on readily available information, and are modified to reflect results of the baseline risk assessments. They also are used during analysis of remedial alternatives in the RI/FS. For the FS, PRGs have been identified as risk-based concentrations for soil and drinking water standards for groundwater. The human health-related RAOs for soil, soil vapor, and sediment were expressed in general terms consistent with the NCP, that is, in the risk range of 10-4 to 10-6. Similarly, the ecological risk goals for soil, soil vapor, and sediment are expressed as less than risk-based target levels (lowest-observed adverse effects level [LOAEL] or hazard quotients [HQ] less than 1). For groundwater and NAPL, the RAOs focused on: restoring groundwater to its beneficial use, meeting drinking water standards where practicable,; containing or controlling sources and mitigating potential migration outside the site boundaries where this is technically not practicable. The GRAs are presented as a range of options for these media, and form the basis for the development of remedial alternatives for each FS area. Section 8 includes a discussion of ARARs for the site and summarizes a Technical Impracticability Evaluation (TIE) for the northern groundwater area (FS Area 5 North) that is presented in Appendix A. A wide range of remedial technologies was identified and considered in the screening evaluation in Section 9, with the goal of selecting a set of relevant technologies for use as components of the remedial alternatives for the site. The screening was conducted as a two-

1 COPCs are defined as chemicals that are potentially site-related and were evaluated quantitatively in the risk assessment. See Section 7 for a summary of the process and results of activities to identify COCs from an initial list of COPCs.


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step process. The initial screening of technologies was conducted on a wide range of technologies relating to the various media at the site including soil, sediment, stormwater, groundwater, and NAPL. As provided for by the RI/FS Workplan, the technologies that were not applicable were eliminated in the initial screening. The second step is the formal technology screening and was conducted separately for each medium using the three screening criteria from CERCLA guidance: effectiveness; implementability; and, cost. The technology screening considered more site-specific factors, including site lithology and nature of contaminants, to retain the most promising technologies for use with remedial alternatives in each of the FS areas. The retained technologies from the screening evaluation were combined to develop a range of applicable remedial alternatives for each FS area in Section 10. As required by the RI/FS Workplan, the remedial alternatives specify the extent of the remedial action and other details specific to the FS areas to achieve the remedial action objectives. These remedial alternatives were then evaluated by a screening evaluation using the effectiveness, implementability, and cost criteria. Typically between five and ten remedial alternatives were evaluated in this screening evaluation for each FS area, including the No Action alternative required by CERCLA guidance. At this stage, the cost estimates provide an approximate range based on unit costs. The most promising alternatives from the screening evaluation were retained for the detailed 9-criteria analysis for each FS area in Section 11. The remedial alternatives selected for the detailed nine-criteria evaluation typically range between three and six remedial alternatives for each FS area, including the No Action alternative required by CERCLA guidance. Six site-wide remedial alternatives were assembled, ranging from lesser to more aggressive approaches to remediate the site, including the No Action alternative required by CERCLA guidance. To perform the analysis of several of the FS areas (specifically FS areas 2 and 3), a residual risk approach was used to define the areas to which the active remediation measures might be applied. When using a residual risk approach, the extent of impacted outdoor soil was nominally based on exceedance of ecological risk-based concentrations (RBCs) corresponding to a HQ < 1. Using a HQ < 1 is conservative, and as appropriate may have argued higher ecological risks. The areas of proposed remedial action (e.g., excavation or capping) are in some cases not precisely defined and approximate areas were assumed around samples showing exceedances for the FS evaluation. If some of these remedial alternatives are to be implemented, additional sampling may be needed during remedial design to define the areal extent of the remediation. In many cases, however, the extent of the remedy covered the entire footprint of the study area, in which case, the areal extent was well defined. In general, the remedial alternatives for each FS area address the contamination and remedial objective for the entire FS area. However, FS Area 3 is an exception; it has several hotspot locations with a wide range of contaminants dispersed over a large geographical area. In FS Area 3, each hotspot location is evaluated separately in the screening evaluation. These are then combined to Area-wide alternatives for the detailed evaluation. The No Action alternative typically refers to no remedial action or monitoring. However, it is worthy of note that some response actions have already been implemented at this site, such as the RCRA caps on the Capped Landfills Area (part of FS Area 1). As stated earlier, the presumptive remedy for the Capped Landfills Area is “maintenance and monitoring of the RCRA cap.” Hence, the No Action alternative for FS Area 1 assumes that no maintenance or


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monitoring of the existing RCRA cap is included. Similarly, for FS Area 5, there are existing response actions, including operations of the various site groundwater control features (e.g., liquids extraction from the perimeter source control trench [PSCT] and perimeter control trenches [PCTs]). For FS Area 5, the No Action alternative assumes that these groundwater control features would not be operated and no groundwater monitoring would be conducted. The FS area and site-wide remedial alternatives for detailed evaluation are evaluated by nine criteria as described in the CERCLA guidance (USEPA 1988). The nine criteria are divided into three categories: threshold criteria; balancing criteria; and, modifying criteria. The threshold criteria are evaluated by a Yes or No rating. The balancing criteria are rated using a five-point rating scheme ranging from poor, poor to moderate, moderate, moderate to good, and good, with poor being the worst and good being the best rating. For the cost criterion, a similar five-point rating scheme is used starting from low, low to moderate, moderate, moderate to high and high, with low having the lowest cost and high having the highest cost. The “green” aspects for the screening-level and detailed evaluations are evaluated using USEPA’s Principles of Greener Cleanups (USEPA, 2009) and USEPA’s Superfund Green Remediation Strategy (USEPA 2010). The green remediation analysis was considered as a modifying criterion for the screening level and detailed evaluations. The “green” criteria are rated using a five-point rating scheme defined by the “impact,” ranging from low, low to moderate, moderate, moderate to high, and high, with low being the best and high being the worst rating. To emphasize, a “high” rating does not mean that it is the most “green”, but that it has the highest “impact” and is the worst rating. Approximate cost estimates were developed for each remedial alternative based on the conceptual design of the remedial alternatives. Typically, cost estimates are based on vendor quotes or unit costs from remediation cost handbooks; some elements are based on specific experience at other sites. The cost estimates are comprehensive estimates of direct and indirect capital costs, and operation and maintenance (O&M) costs. The total contingency, including scope contingency and bid contingency, is assumed to be at the higher end of the typical range (35% to 50%) described in the USEPA cost guidance (USEPA 2000). The 35% contingency is used for capital costs for those technologies or remedial components that have been previously implemented at the site and have lower chance of unforeseen circumstances. For all other alternatives a 50% contingency is used for capital costs. For all alternatives a 50% contingency is used for the long-term O&M costs. The 50% contingency is considered particularly appropriate at this stage of conceptual design where there is still significant uncertainty about some of the details of design and operation. The previous USEPA cost estimates for the Casmalia Resources Superfund Site also used the same contingency. An exception to this involves the alternative to dewater the P/S Landfill using horizontal wells where, due to a very high uncertainty regarding the method and success of well installation and the volume of liquids that may be produced, a 75% contingency has been assumed for O&M. No contingency was assumed for the off-site disposal of liquids drained from the P/S Landfill through the horizontal wells. Present worth costs of remedial alternatives are estimated using two net discount rates and two timeframes. Discount rates of 3% and 7% were used over 30-year and 100-year timeframes. Present worth costs were estimated using (1) a net discount rate of 7% consistent with USEPA’s guidance (2000)and Office of Solid Waste and Emergency Response (OSWER) Directive 9355.3-20 as summarized in USEPA guidance (USEPA 2000), and (2) a net discount rate of 3% to assess sensitivity where the rate of return may be less than for the 7% scenario. Recent rates of inflation and returns on investment are consistent with that same range. Present worth costs were estimated using (1) a 30-year period of analysis as


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recommended in USEPA Guidance (1988), and (2) a 100-year period to assess sensitivity where the final remedy may be operated in perpetuity. The detailed cost spreadsheets for the remedial alternatives are presented in Appendix E. The cost estimates reflect several uncertainties such as the assumptions about the lateral extent of the COC-impacted area, the extraction flow rates or volumes of groundwater or DNAPL, etc. The cost estimates meet the accuracy requirements of the CERCLA guidance of +50% to -30%. The calculation of a 30-year discounted cost assumes the remedy will be constructed over approximately four summer seasons (beginning in 2016 and ending in 2020) and as such the capital costs are expended in that time frame. The FS approach used here follows the CERCLA FS guidance and the description laid out in the RI/FS workplan. The FS develops and compares remedial alternatives to assist USEPA in selecting the proposed remedy and preparing the Proposed Plan and the Record of Decision (ROD).

1.3 FS Report Organization A brief description of the various sections of the FS report is provided below:

Section 1.0 describes the scope, purpose and organization of the FS report. Section 2.0 presents a summary of site background and site history. Section 3.0 presents a summary of previous investigations. Section 4.0 describes physical characteristics of the site, including site geology and

hydrogeology. Section 5.0 describes the nature and extent of contamination by medium. Section 6.0 discusses contaminant fate and transport under site conditions. Section 7.0 presents a summary of human health and ecological risk assessments. Section 8.0 defines FS areas and presents RAOs and PRGs by medium, GRAs by

medium, potential ARARs, and a summary of the TIE and waiver request for groundwater ARARs.

Section 9.0 presents screening of remedial technologies by medium. Section 10.0 presents the remedial alternatives by FS area and the screening

evaluation. Section 11.0 presents the detailed evaluation (9-criteria evaluation) of remedial

alternatives by FS area. Section 12.0 presents the detailed evaluation (9-criteria evaluation) of site-wide remedial

alternatives and a summary of the top-ranked remedy. Additional details and supporting information are provided in technical appendices A through J.

1.4 References Final Remedial Investigation Report, January 2011. Remedial Investigation/Feasibility Study Work Plan, June 2004. USEPA, 2010. Superfund Green Remediation Strategy, September 2010.


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USEPA, 2000. A Guide to Developing and Documenting Cost Estimates during the Feasibility Study, USEPA and US Army Corps of Engineers, EPA 540-R-00-002 July 2000. USEPA, 2009. Principles for Greener Cleanups, Office of Solid Waste and Emergency Response (OSWER), August 2009. USEPA, 1988. Guidance for Conducting Remedial Investigations and Feasibility Studies Under CERCLA, USEPA 540/G-89/004, October 1988.


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2.0 SITE BACKGROUND This section presents a brief summary of the site development and land-use history, as well as the previous investigations and closure activities undertaken at the site. Information presented herein is summarized from Section 2 of the June 2004 RI/FS Work Plan (Work Plan) and Section 2 of the Final RI Report (RI Report) (CSC, 2004a, 2011, respectively). The reader is referred to these source documents for a more detailed treatment of these issues. The descriptions presented in this section have been updated with the most recent information available, including data developed during the Remedial Investigation.

2.1 Site Description The site is an inactive Class I hazardous waste management facility located in the northwestern corner of Santa Barbara County, California. For the purposes of this RI Report, the “site” refers to the approximate 252 acres encompassing the historical landfill footprint. The site, which was owned by Casmalia Resources and operated by Hunter Resources, Inc., began accepting wastes in the early 1970s. Site operations were ceased by 1991. Former waste management operations at the site were conducted within an area approximately 252 acres in size. Former waste management features included landfills, storage and evaporation ponds, evaporation pads, oil field waste spreading areas, treatment units, and disposal wells and trenches. The site lies approximately 4 miles from the Pacific Ocean, approximately 10 miles southwest of the city of Santa Maria, and approximately 16 miles north-northwest of the city of Lompoc. The nearest population center is the unincorporated community of Casmalia, located approximately 1.2 miles south-southeast of the site. The site is accessed via NTU Road off of Black Road, approximately 1 mile north of Casmalia (Figure 1-1). For purposes of this report, the term “Zone 1” encompasses the approximate 252 acres lying within the permitted boundary of the historical landfill site, and “Zone 2” encompasses those lands lying outside or beyond the site boundary. The physical features of the site, including site boundaries, topography, climate, hydrology, geology/hydrogeology, land use, demography, and wildlife habitats, are described in Section 4.0. Section 4.0 has also been updated with the most recent information available, including data developed during the Remedial Investigation.

2.2 Site History and Use The site is a former hazardous waste management facility opened in 1972 in accordance with California Regional Water Quality Control Board (RWQCB) Waste Discharge Permit No. 72-28. The original RWQCB waste discharge permit allowed a 61-acre hazardous waste disposal facility including 15 surface impoundments and one landfill area. The waste discharge permit was amended twice, once in 1976 to allow for a 118-acre expansion of the facility to the east and north (Permit No. 75-73), and again in 1980 (Permit No. 80-43) expanding the facility approximately 73 acres toward the west, bringing the facility to its present size of 252 acres (McClelland Consultants, 1989). The current and historical site layouts are shown on Figure 2-1 and Figure 2-2, respectively. Figure 2-3 presents a historical timeline of site development and related milestone events. The site ceased accepting liquid wastes in July 1987 and stopped accepting solid waste in November 1989. Casmalia Resources completed pond closure activities in the period from


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1989 to 1991 while they awaited approval to modify the site waste treatment and disposal methods and facilities. After being denied the necessary operating permits to continue waste disposal activities, Casmalia Resources suspended all site activities in 1991, with the exception of extracting liquids from the perimeter control trenches (PCTs). During the 1991 timeframe, Casmalia Resources also developed groundwater monitoring work plans and landfill closure and post-closure plans for the site. From 1992 through 1996, the USEPA maintained the site. The CSC took over site maintenance activities in 1996, and has been responsible for various site investigation and closure projects from that time through the present. Casmalia Resources accepted the full range of listed and characteristic RCRA wastes as specified in Subparts C and D of 40 Code of Federal Regulations (CFR) 261 (A.T. Kearney/SAIC, 1987). Wastes received at the site included (in part): petroleum wastes, acids, bases, organic chemical solvents, petroleum solvents, paint sludge, pesticides, infectious wastes, septic tank pumpings, and sewage sludge. Section 3.0 of the April 1988 RCRA Part B permit application (Woodward-Clyde Consultants, 1988b) includes a complete list of wastes accepted at the facility by landfill and treatment units. Waste disposal units at the site included:

6 landfills; 43 surface impoundments; 15 evaporation pads; 2 non-hazardous waste spreading areas; 6 oil field waste spreading areas; 11 shallow injection wells; 7 disposal trenches; and 1 drum burial unit.

Note that although contaminated liquids were eventually transferred to most site ponds, only a few of the site ponds directly received wastes. The site also had five waste treatment units: an acid/alkaline neutralization facility; a hydrogen peroxide treatment unit; oil recovery and treatment tanks; a wet air oxidation unit; and, a temporary pilot-scale powder-activated carbon treatment (PACT) unit. Surface impoundments (used for evaporation and treatment of liquid wastes or for storing stormwater), and disposal pads (used to evaporate liquid wastes and site stormwater runoff) primarily occupied the southern and central portions of the site, whereas the six landfill disposal areas were positioned along the northern and northeastern margins of the site. A few of the surface impoundments and evaporation pads were also present in some areas of the northern portion of the site between the major landfill cells (Figure 2-2). The variety of former and existing waste management units at the site are more fully described in the following sections. 2.2.1 Site Operational Information Numerous prior studies have been completed at the site and surrounding area since operations began, including those conducted in support of facility siting and design, regulatory permitting and compliance, waste characterization, and soil and groundwater investigations. The information presented in this section has been compiled and summarized primarily from technical reports previously prepared by others, and these reference documents are listed in Section 2.2 of the Work Plan. The reader is referred to these original source documents for a more detailed treatment of the topics summarized herein.


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Parties sending wastes to the site were required to prescreen or profile their wastes before shipping waste to the site. As part of their waste confirmation program, Casmalia Resources randomly tested approximately 10 to 20 percent of the incoming wastes. The waste pre-screening and confirmation testing programs employed at the site are more fully described in the Final Environmental Impact Report for the facility (McClelland, 1989). Casmalia Resources personnel directed haulers with drummed wastes to the drum handling facility south of the Pesticides/Solvents Landfill. Drummed wastes were placed on the loading dock where Casmalia Resources personnel compared the drum labels with the manifests and collected samples of any wastes that were visually inconsistent with the waste profile, then transported drummed wastes to the various landfills for final disposal. Haulers with bulk solid or liquid wastes were directed to a specific landfill, pond, or treatment system, depending on the waste characteristics. Casmalia Resources generally segregated incoming waste by primary type, and the wastes were handled in specific locations of the site based on whether they were acidic, caustic, oily, solvent-based, etc. Before leaving the site, empty trucks washed out their tanks and/or bins at the wash-out facilities located at ponds D and 16. 2.2.2 Site History Review In preparing the RI/FS Work Plan, the CSC reviewed available historical documents and aerial photographs, selected site topographic maps, and interviewed agency personnel. The CSC also met with former operations personnel who worked on the site from the mid and late 1970s through the present to collect additional historical and anecdotal information that may be relevant to remedial planning. Key historical documents reviewed in preparation of the Work Plan included the RCRA Facility Assessment (A.T. Kearney/SAIC, 1987), Environmental Impact Report (EIR) for the Casmalia Resources Class I Hazardous Waste Disposal Site Modernization Plan (McClelland Consultants, 1989), and the RCRA Part B Permit Application (Woodward-Clyde Consultants, 1988b). 2.2.2.1 Aerial Photograph Review In preparing the RI/FS Work Plan, the CSC conducted a review of available historical aerial photographs of the site for the time period 1956 through 2002. A complete listing of the photographs examined and the detailed findings of this review are presented in Appendix V of the RI Report; the salient findings of this review are summarized below. Select photographs depicting the sequential development and closure of the site are presented on Figure 2-6. The site was used for agricultural purposes prior to 1970. The initial site development was first apparent on the 1974 aerial photograph with several oil-field-related surface impoundments situated in the center of the site. Grading and continued surface impoundment expansion is noted in the 1979 and 1980 photographs. Some of the injection wells and disposal trenches were observed in the 1979 and 1980 photos. Waste disposal in the landfills was also noted in these photographs, as were the oil recovery tanks associated with the oil field waste ponds in the center of the site. By 1983, the A-series ponds had been developed and RCRA Canyon Area development was evident. Also by this time, the spreading and sludge-drying areas appeared to be active. A spray evaporation area in the southwestern portion of RCRA Canyon also was noted only in this photograph (and not in the 1982 or 1984 photographs). Some of the evaporation pads between


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the landfills also appeared to be active in the 1983 photograph. The building that was initially used for the Zimpro wet air oxidation system and the four associated tanks are shown on the 1983 photograph. In the 1985/1986 time period, spreading in the RCRA Canyon Area was notably active and a new pond was evident in the Burial Trench Area. Surface impoundment operations and waste disposal in the landfills continued. By 1988, the surface impoundments were observed to be empty and the site appeared drastically different as a result of the large amount of excavation and grading undertaken for pond closure. Filling in the landfills and using the pads between the landfills continued. The new administration building was observed in the 1988 photograph. In the 2002 photograph, the stormwater ponds and treated liquids impoundments are observed and the Pesticides/Solvents and Heavy Metals/Sludges landfills are capped; grading in the Caustics/Cyanides Landfill in preparation for capping is evident. By 2003, the Caustics/Cyanides and Acids landfills are capped. 2.2.2.2 Topographic Map Review In preparing the RI/FS Work Plan, the CSC collected selected historical topographic maps of the site for the pre-development through post-development time period to help define former surface drainage features, ponds and pads, liquids treatment facilities, site roads, and site support facilities. Maps from the time period 1956 through 1998 were reviewed, with those from the years 1956 (pre-development), 1982 and 1987 (operational period) providing the most relevant information for documenting historical site features. Relevant historical site features were identified and digitized onto base maps, and used to help plan the remedial investigation and sampling activities. Comparison of site topography between 1987 and 1998 demonstrates the nature and magnitude of cut and fill earthwork that was conducted across the site during earlier impoundment closure activities. The 1998 site topography is essentially the current topography, with the exception of grades in the capped landfill areas, a portion of the North Ridge area, and the B-Drainage wetlands area. A complete listing of the maps examined, scanned copies of the individual maps, and a discussion of the findings of this review are presented in Appendix W of the RI Report. 2.2.2.3 Agency Personnel Interviews In preparing the Work Plan, the CSC met with agency personnel who had involvement in prior site investigations, possessed personal knowledge of historical site operations and facilities, and/or were involved in emergency response actions during the 1992 to 1996 timeframe. Individuals interviewed included select staff from the RWQCB, Department of Toxic Substances Control (DTSC) and USEPA. These agency personnel interviews were used to gather additional relevant information regarding pond closure activities, and confirm information gleaned from the aerial photograph and topographic map reviews. Results of these interviews are documented in Appendix M of the Work Plan. 2.2.3 Facilities 2.2.3.1 Waste Management Units Casmalia Resources operated several waste management units at the site including:


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5 existing landfills, including the polychlorinated biphenyl (PCB), Pesticides/Solvents

(P/S), Heavy Metals, Caustics/Cyanides, and Acids landfills; Former RCRA Landfill; Former surface impoundments, including 43 liquid storage ponds and 15 evaporation

pads; 2 non-hazardous waste spreading areas known as Sludges 1 and 2; 6 oil-field waste spreading areas; Burial Cells Unit (or Burial Trench Area), including 11 shallow disposal wells and 7

disposal trenches; and Former drum burial unit.

The locations of the waste management units and treatment facilities are illustrated on Figure 2-2, Historical Site Layout. As part of the review of historical documents and photographs, the CSC prepared a summary table indicating the observed status of each waste management unit and treatment facility at the site. Table 2-1 chronicles the development status of each unit from 1973 through 2002, and indicates whether a particular area was being excavated (or developed), whether there was waste present in the disposal units during those years, and notes the years in which response actions or closure activities are evident. Also noted are areas where grading took place and whether a particular area appeared vegetated during that year’s photo. The information gleaned from the photo review was used to confirm some of the written records of site operations presented in the sections below. The nature of these various waste management units is generally described below. Note that although some closure activities were performed at the site, the sections below concentrate primarily on activities relevant to the operational years. The closure activities and response actions conducted at the site are summarized in Section 2.2.6. Existing Inactive Landfills Each landfill was constructed within individual natural canyons incised into native soils and claystone bedrock of the Todos Santos member of the Sisquoc Formation. The landfills were constructed prior to promulgation of the prescriptive regulatory requirements of Section 40 of the CFR, Part 264, regulations adopted pursuant to the Hazardous and Solid Waste Amendments (HSWA) to RCRA. Man-made liners and leachate collection systems were not installed beneath the landfills. As described below, the landfills were generally started at the south end of a canyon and native materials were excavated to bedrock (i.e., the unweathered claystone) to form the base of the landfills. Wastes were then placed at the base of the landfills and excavated native materials were placed over the wastes as cover. Existing inactive landfills at the site include the following:

PCB Landfill P/S Landfill Heavy Metals Landfill Caustic/Cyanide Landfill Acids landfill

Details regarding the construction, nature and volume of wastes waste disposed, and operational history of these landfills are presented below.


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In accordance with the closure plans prepared for the inactive landfills, Casmalia Resources constructed clay buttresses at the toes of the landfills, as necessary, to improve stability. Buttress soil materials were taken from the former Pond 11, former pads 10B, 10C, 10F, and 10G, and former Sludges 1 areas after those areas had been closed. With the exception of the PCB Landfill, Casmalia Resources also graded the landfills in accordance with the closure plans then prepared for each landfill. To achieve the desired grades, Casmalia Resources placed approximately 20 to 60 feet of stabilized soils excavated as part of the pond and pad closure activities. Wastes immediately below the surface of the Caustics/Cyanides Landfill were encountered while the CSC capped that landfill in 2001, indicating that wastes may have been placed in the stabilized soil layer during Casmalia Resources’ closure period. Casmalia Resources placed a minimal thickness of cover soil over the PCB Landfill because this landfill was never filled to capacity. The CSC improved the P/S Landfill buttress in 1998 and constructed a RCRA-equivalent cap over that landfill during the 1999 construction season. Corrective action activities for the P/S Landfill were completed by the CSC in 2001. The CSC constructed the portion of the EE/CA Area RCRA-equivalent cap over the Heavy Metals Landfill and the interstitial areas on either side of that landfill during the 2001 construction season. The CSC capped the remainder of the EE/CA Area (including the Caustics/Cyanides and Acids Landfills along with the interstitial areas) during the 2002 construction season. The CSC constructed a buttress for the Caustics/Cyanides Landfill as part of the EE/CA Area capping project. PCB Landfill The PCB Landfill is located in the northern area of the site between the Former RCRA Landfill and the Pesticides/Solvents Landfill. A portion of the area was first operated as a trench fill but Casmalia Resources changed filling techniques to an area fill method (A.T. Kearney / SAIC, 1987). The PCB Landfill was used for the disposal of non-liquid PCB-contaminated materials, such as drained electrical transformers, soil, rags, and other debris (Section 3.5.2.2, Page 3-22, McClelland Consultants, 1989). A total estimated 390,400 cubic yards of waste and soil cover at a ratio of 2.7:1 waste to soil cover were deposited in the PCB Landfill. The PCB Landfill operated under a Toxic Substances Control Act (TSCA) permit issued by USEPA in November 1978, and permits to expand this landfill were issued by USEPA in 1979 and again in 1980. The original size of PCB Landfill was 5.46 acres, but only 2.83 acres were useable due to terrain. An additional 14.08 acres was approved for use by USEPA in 1981, bringing the total permitted acreage of the landfill up to 20.54 acres; however, Casmalia Resources never used the additional fill area (A.T. Kearney / SAIC, 1987). Waste disposal operations at the PCB Landfill were discontinued in April 1986 (Section 3.5.2.2, Page 3-22, McClelland Consultants, 1989). As further discussed in Section 2.2.3.2, a compacted clay barrier was installed below the toe area of the PCB Landfill in 1980 to limit lateral subsurface fluid migration from the disposal cell. Soil cuttings generated during remedial investigation activities were placed into the PCB Landfill for disposal. Pesticides/Solvents Landfill The Pesticides/Solvents Landfill (also historically referred to as the Solvent/Pesticide Landfill) is located in the north-central portion of the site between the PCB Landfill and the Heavy Metals Landfill. The P/S Landfill began receiving waste during September 1979. Wastes were placed in an approximate 10.6-acre portion of the now capped 13.5-acre landfill area. The P/S Landfill was developed in an existing canyon and fill placement began at the toe of the landfill and wastes were placed to the north as filling operations continued. The landfill was developed by cut-and-fill methods, with excavations extending into the unweathered gray claystone. As


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additional lifts of waste were introduced, more excavation was performed at the head of the existing canyon, with removed native materials being used as daily and interim cover. Casmalia Resources also used oil field drilling muds as daily cover when available. Solid and liquid wastes placed into the P/S Landfill included organic solvents, paint, pesticides, asbestos, and infectious waste (Section 3.4.1.1, Page 3-6, McClelland Consultants, 1989). A full list of waste that was placed in the landfill (by USEPA waste code) is found in Table 3-5 (i) of the Part B permit application of 1988 (Woodward-Clyde Consultants, 1988b). By January of 1989, an estimated 899,000 cubic yards of waste, 527,990 cubic yards of daily soil cover, and 91,460 cubic yards of pond closure soils (a total of 1,518,450 cubic yards of waste and soil cover) were deposited in the landfill. The P/S Landfill also includes the oil field waste Spreading Area S-4. Based on a 1998 topographic map, an unknown volume of additional waste and soil was placed in the landfill after January of 1989 (Figure 3-2 of Foster Wheeler / GeoSyntec, 1999). Waste disposal activities in the currently capped P/S Landfill are believed to have ceased when former surface impoundment closure activities were discontinued in late 1990. As further discussed in Section 2.2.3.2, a compacted clay environmental barrier and fluid collection and extraction gallery were installed below the toe area of the P/S Landfill in 1980 to limit fluid migration from the disposal cell. Heavy Metals Landfill The Heavy Metals Landfill (also historically referred to as the Heavy Metals/Sludges Landfill) is located in the northeastern portion of the site between the P/S Landfill and the Caustics/Cyanides Landfill. Wastes were placed in an approximately 5.4-acre area of the currently capped 10.3-acre Heavy Metals Landfill. The Heavy Metals Landfill started receiving waste during November 1979. Construction of the Heavy Metals Landfill commenced with an approximate 20-foot-deep excavation just below the juncture of two small canyons. As lifts of waste were added, the working face was extended up the small canyons with some subexcavation preceding waste placement. The natural ridge between the two canyons was eventually removed during this process and utilized as interim cover material. Materials placed in the Heavy Metals Landfill included solidified bulk or containerized wastes containing heavy metals, sludges, empty plastic and metal drums, drilling fluids, and oil field wastes (Section 3.4.1.2, Page 3-6, McClelland Consultants, 1989). The Heavy Metals Landfill also included dried drilling mud and unspecified oil-field waste from Spreading Area S-3. A full list of waste that was placed in the landfill (by USEPA waste code) is found in Table 3-5 (h) of the Part B permit application of 1988 (Woodward-Clyde Consultants, 1988b). By January 1989, an estimated 230,090 cubic yards of waste, 135,130 cubic yards of daily soil cover, and 233,870 cubic yards of pond closure soils (a total 599,090 cubic yards of waste and soil cover) were deposited in the Heavy Metals Landfill. Comparison of cross-sectional maps of the landfill for March 1989 and January 1998 identify that an unknown volume of additional waste and soil was placed in the landfill after January of 1989 (Figures B3 and B4 of Foster Wheeler / GeoSyntec, 1999). Waste disposal activities in the landfill are believed to have ceased when former surface impoundment closure activities were discontinued in late 1990. In March 1988, liquids were encountered at the Heavy Metals Landfill toe during a landfill drilling program conducted to assess the presence of liquids in the landfills. Caustics/Cyanides Landfill The Caustics/Cyanides Landfill is located in the northeast corner of the site between the Heavy Metals Landfill and the Acids Landfill. Wastes were placed in an approximately 4.5-acre area of


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the currently capped 7-acre landfill. The landfill started receiving waste during July 1979. This landfill was initiated with only minimal excavation at the southwest end of a small canyon. As lifts were added, the working area was expanded up the canyon toward the northeast. The disposal unit was later expanded toward the east as the canyon side and a small ridge were excavated and used as interim cover. Waste materials placed into the Caustics/Cyanides Landfill included solidified bulk and containerized wastes containing caustics, cyanides, and sulfides. The Caustics/Cyanides Landfill also includes dried drilling mud and unspecified oil-field waste from Spreading Area S-2. A full list of waste that was placed in the landfill (by USEPA waste code) is found in Table 3-5 (g) of the Part B permit application of 1988 (Woodward-Clyde Consultants, 1988b). Dried drilling muds and oil-field wastes were also disposed of in this landfill (Section 3.4.1.3, Page 3-6, McClelland Consultants, 1989). By January 1989, an estimated 273,940 cubic yards of waste, 160,880 cubic yard of daily soil cover, and 318,850 cubic yards of pond closure soils (a total 753,670 cubic yards of waste and soil cover) had been deposited in the landfill. Comparison of cross-sectional maps of the landfill from March 1989 and January 1998 identify that an unknown volume of additional waste and soil was placed in the landfill after January of 1989 (Figure B5 of Foster Wheeler / GeoSyntec, 1999). Waste disposal activities in the landfill are believed to have ceased when former surface impoundment closure activities were discontinued in late 1990. In March 1988, liquids were encountered at the Caustics/Cyanides Landfill toe during a landfill drilling program conducted to assess the presence of liquids in the landfills. The Caustics/Cyanides Landfill includes a clay buttress constructed to stabilize waste and control fluid migration. Acids Landfill The 5.4-acre Acids Landfill is located along the eastern site boundary, south of the Caustics/Cyanides Landfill. The landfill started receiving waste during July 1979. The Acids Landfill was initiated at the west end of a small canyon as a narrow excavation less than 20 feet deep just east of the haul road. As lifts were added, more material was excavated from the base and sides of the small canyon. Waste materials placed into this landfill included solidified or bulk containerized acidic wastes. A full list of waste that was placed in the landfill (by USEPA waste code) is found in Table 3-5 (f) of the Part B permit application of 1988 (Woodward-Clyde Consultants, 1988b). By January 1989, an estimated 35,930 cubic yards of acid solid waste, 51,270 cubic yards of daily soil cover, and 138,570 cubic yards of pond closure soils (a total of 225,770 cubic yards of acid solid waste and soil cover) were deposited in the landfill. Comparison of cross-sectional maps of the landfill of March 1989 and January 1998 identify that an unknown volume of additional waste and soil was placed in the landfill after January of 1989 (Figure B6 of Foster Wheeler / GeoSyntec, 1999). Waste disposal activities in the currently capped landfill are believed to have ceased when former surface impoundment closure activities were discontinued in late 1990. In March 1988, no liquids were encountered at the landfill toe during a drilling program conducted to assess the presence of liquids in the landfills. Burial Trenches and Shallow Disposal Wells Waste disposal at the site began in the early 1970s with disposal in seven trenches directly south of the PCB Landfill and directly west of the P/S Landfill. Waste disposal in that area (referred to as the Burial Cells Unit, or Burial Trench Area) also included disposal in shallow wells in the mid to late 1970s and early 1980s. The disposal trenches were constructed by excavating a series of cells 15 to 40 feet square and approximately 15 feet deep. Cells were


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constructed in seven rows and assigned numerical designations, with the individual cells in a given row being assigned an alphabetical designation. Wastes deposited into the trenches consisted of a wide variety of bulk and containerized liquids and sludges, with the exception of Trench 6, which accepted only PCB wastes. Wastes disposed in the remaining trenches included acid and alkaline sludges, paint sludges, waste paints, waste solvents, oil, metal hydroxides, asbestos, empty pesticide containers, pesticides, iron sponge, diethylamine (DEA), plating sludges, naphtha, ink, and epoxide polymers and filter cake (A.T. Kearney / SAIC, 1987). Between December 1977 and September 1982, shallow disposal wells were drilled and operated in the area within the Burial Cells Unit. A total of 11 wells were drilled directly adjacent to the trenches within the Burial Cells Unit and were used for the purpose of liquid waste disposal. Available information indicates two of these wells (wells 10 and 11) lie between trenches 4 and 5, and the remaining nine wells lie between trenches 3 and 4. Wastes discharged into the wells included unspecified solvents, pesticides, acids, and miscellaneous waste materials (A.T. Kearney / SAIC, 1987). The shallow disposal wells consisted of approximate 4-foot-diameter borings extending to depths of between 30 and 40 feet. The wells were not cased, and Well 9 caved in during installation and was never placed in service. Each well head was equipped with a vent pipe, a quick disconnect coupling, an inspection hatch, and a visual float liquid level indicator to prevent overfilling. The wells were drilled adjacent to the disposal trenches with the intent that the trenches would absorb the liquid wastes. Although waste disposal in the wells was limited due to the low permeability of the strata, more than 1.3 million pounds of material were reported to have been discharged to these wells. Former RCRA Landfill and RCRA Canyon The Former RCRA Landfill is located in a natural canyon (currently referred to as RCRA Canyon, and historically sometimes as West Canyon) on the northwest side of the site. This area was at one time intended to be lined in preparation to receive RCRA-regulated waste from the McColl Superfund site; however, this never occurred. In late 1983 to early 1984, a small area within the uppermost portion of RCRA Canyon received an estimated 16,700 cubic yards of wastes removed from a portion of the Burial Cells Unit during development of Pond 23 (Woodward-Clyde Consultants, 1991). Wastes deposited into the Former RCRA Landfill at that time included, but were not limited to, solvents, pesticides, PCBs, oily wastes, and metals. When it became apparent that McColl wastes would not be delivered to the site, Casmalia Resources excavated the RCRA Canyon wastes. RCRA Canyon was also the location of the oil field waste spreading areas S-5 and S-6. The north and west slopes of RCRA Canyon received oil field wastes (primarily drilling mud), winery wastes, and spray irrigation of leachate and surface stormwater runoff collected from other portions of the site (Section 3.5.2.1, Page 3-22, McClelland Consultants, 1989). Trucks discharged loads of oil field wastes along the northern and western perimeter canyon road and the liquids wastes were allowed to flow down the sideslopes. Casmalia Resources constructed terraces in the canyon sidewalls so the wastes could dry and be turned by dozers working the benches. Dried wastes were reported to have been periodically removed and used as daily cover in the landfills. Some of the wastes on the sideslopes are still evident, and it is not clear how much of the wastes were moved for daily cover.


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Former Surface Impoundments Casmalia Resources utilized a total of 43 ponds and 15 evaporation pads to accommodate incoming wastes and to manage site stormwater and landfill leachates. General pond information, including the year built, construction notes, surface area and operational capacity is presented in Table 2-2, General Pond Information. The combined surface area of the ponds and pads is approximately 51 to 62 acres, and the operational capacity was in the 196 to 205 million gallon range. Note that two of the site’s 43 ponds identified were converted to pads and, as such, are “double counted.” Also presented in Table 2-2 are deposition notations, classes, and surface impoundment (SI) unit designations. The “deposition” notation was used to identify which ponds were direct deposit ponds as opposed to first through fourth generation transfer ponds. Note that only 12 of the site’s ponds directly received wastes (ponds 4, 15, 18, A-5, A, B, C, D, E, J, P, and T). The “class” designation originated as part of pond closure planning to indicate which ponds had hazardous, nonhazardous, and marginally hazardous sludges that had to be solidified prior to being placed in the site landfills. Finally, the “SI unit” designation was the numbering system used to refer to either a single pond, or to a group of ponds that were operated as a unit, accepting transfers from one another. There were 10 SI groupings; the remaining ponds were numbered with only their pond designation. Transfer of liquids to and from ponds in other SI units also occurred as part of site operations. Note that the original SI units as defined in the 1985 RCRA Part B permit application (Woodward-Clyde Consultants, 1985) did not specifically include pads. The former evaporation pads, however, are within the boundaries of the SI units as outlined in the 1985 RCRA Part B permit. As described in the 1985 Part B Permit Application (Woodward-Clyde Consultants, 1985), the remaining ponds were historically referred to as single pond surface impoundments, with the SI unit designation being the same as the pond name (these include: SI units / ponds 14, 16, 23, A, B, C, D, M, P, R, S, T, and V). The information presented in the historical 1985 RCRA permit application is used as an information source in Table 2-2 to illustrate differences in reported pond usage, size and operational capacity in the available documents. The 1988 RCRA permit application (Woodward-Clyde Consultants, 1988b) does not present the pond usage, size and operational capacity information. The limits of the SI units are indicated on Figure 2-4 along with colors indicating the ponds’ primary use. The notations for the primary pond usages varied among historical documents. The usage most fitting considering the ponds’ overall operational history is shown on Figure 2-4. Cross hatching is used to indicate ponds that were: direct discharge ponds; those that received wastewater from the Stringfellow site; and, those ponds that received treatment system effluent. The documented pond transfer information is for only the 1985 and 1986 time period; additional pond transfer activities likely occurred, although there is no single source documenting pond transfer activities. It is important to note that the SI unit designations did not govern pond transfer activities, and that hazardous liquids likely entered each of the ponds at some point during site operations. Surface impoundment construction began in 1972, and new impoundments were added or enlarged through 1985. These facilities were used for the receipt, treatment, storage, and evaporative disposal of acid and alkaline wastes, oil field wastes, industrial wastewater, and site stormwater runoff. In addition to the hazardous waste ponds and pads, two waste ponds (Sludges 1 and 2) were used for disposal of non-hazardous wastes such as sewage sludge.


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Historically, liquid wastes received at the facility were deposited directly into surface impoundments for treatment or evaporative disposal. Spray evaporation disposal techniques were also used to speed the rate of evaporation. The use of spray evaporation was discontinued in 1985 (Section 3.5.1, Page 3-9, McClelland Consultants, 1989). Liquids disposal to the ponds ceased by 1988, and surface impoundment closure activities were completed from 1988 to 1991. A summary of the pond closure information is presented in Table 2-3. Because of Casmalia Resources’ funding constraints during pond closure, closure reports were not prepared for all ponds and pads, although all ponds and pads underwent the same closure process under agency review. A general description of the former surface impoundments at the site is presented below. Detailed descriptions of the physical character, nature of contained wastes, and interrelations among the various surface impoundments are presented in the Hydrogeologic Assessment Report (Canonie Environmental, 1987), RCRA Facility Assessment (A.T. Kearney / SAIC, 1987), Final Environmental Impact Report (EIR) (Table 3.5-1, Page 3-13, McClelland Consultants, 1989), the Preliminary Pond and Pad Characterization document (Environmental Solutions, 1987) and the surface impoundment Closure Certification Reports (Canonie Environmental, 1989b; Brierley and Lyman, 1990a-g, 1991a-l). Former Ponds The surface impoundments that were used at the site can generally be separated into four categories based on their primary use. The general pond categories include:

Stormwater runoff control/evaporation ponds; Acid/alkaline ponds; Oil field waste ponds; and Washout ponds.

Details regarding the identity, construction, nature and volume of wastes disposed, and operational history of these former ponds are presented in Section 2 of both the Work Plan and the RI Report. Former Non-RCRA Sludge Areas Sludge areas 1 and 2 were located along the eastern side of the site and were used to spread dry, non-RCRA wastes such as sewage sludge and restaurant grease-trap sludges (Figure 2-4). Sludges were discharged from vacuum trucks, then periodically disked to promote aeration and drying. These areas were periodically cleaned out and the dried materials used for landfill cover material. Former Evaporation Pads A total of 15 evaporation pads were distributed through the site, including pads 1A, 4A, 7A, 8A, 8B, 8C, 9A, 9B, 10A, 10B, 10C, 10E, 10F, 10G, and 18 (Table 2-2 and Figure 2-4). Note that Pads 1A, 8B, and 8C were never permitted or used for waste management due to their proximity to the site boundaries. Nine of the remaining 12 pads were designated as being used for landfill runoff or leachate control; these pads are grouped with the “landfill runoff / leachate control” ponds on Figure 2-4. The relatively flat pads were designed to increase evaporation by spreading liquids or saturated solids at shallow depths across large surface areas. The pads


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were constructed of fill removed from other surface impoundments at the site and from fill in the vicinity of the pad. Although Table 2-2 indicates that the pads were all constructed in approximately 1985, there is evidence (based on the aerial photograph review) of activity on some of the pad locations prior to that time. Pads 10C, 10E, 10F, and 10G, and a portion of Pads 10A and 10B were covered by the EE/CA Area cap as part of earlier response actions for this area of the site. Oil Field Waste Spreading Areas Six areas at the site were used for the spreading and drying of oil field wastes and drilling mud. The initial spreading area (S-1) was located in the areas of pads 9A and 9B; disposal in this area likely began in 1981 (A.T. Kearney / SAIC, 1987). The other spreading areas (designated S-2 through S-6) were located primarily adjacent to access roads along the northern and western site boundaries, and varied from approximately 1.0 to 2.6 acres in area (Figure 2-2). The spreading areas were road embankments over which oil field wastes (and other wastes in the cases of S-5 and S-6) were sprayed from a truck driving along the road. The oil field and other wastes were allowed to dry, and the dried materials were subsequently excavated and used as cover materials for some of the landfills. Based on the cuts made during pond closure activities, the spreading area materials in pads 9A and 9B, and Pond 6 were likely excavated at that time. The spreading areas along the eastern and northern perimeter roads (S-2, S-3, and S-4) are currently under the capped landfills and associated perimeter roads. Residuals and erosion features associated with spreading areas 5 and 6 (located in RCRA Canyon) are currently visible. Former Drum Burial Unit According to Casmalia Resources personnel, disposal of drums occurred on an experimental basis in the area of former Pond 19 (Figure 2-2). Drums containing a small quantity of acidic waste were placed in this area between approximately December 1979 and June 1980, prior to construction and operation of the Acids Landfill. Drums in this area were subsequently covered during the construction of the base of Pond 19. These materials were reportedly removed during closure activities for Pond 19. 2.2.3.2 Subsurface Barriers and Extraction Facilities Subsurface compacted clay barrier walls were installed downgradient of the P/S and PCB landfills in 1980. The P/S barrier includes an extraction point called the Gallery Well. A subsurface barrier also was installed at the base of RCRA Canyon in 1984, and a barrier near Pond 20 was constructed in 1981/1982. As part of early site operations, subsurface clay barriers with extraction facilities also were installed in the B- and C-drainages in 1972/1973 and 1982, respectively (Penfield & Smith, 1973; Penfield & Smith, 1982; Woodward-Clyde Consultants, 1988a). A relatively shallow liquid extraction point, Sump 9B, was constructed in response to evidence of contamination observed during the closure of the former Pad 9B waste pad in 1988 (Harding ESE, 2001g). An additional shallow liquid extraction point, the Road Sump, was installed downgradient of Sump 9B in 1998 to intercept groundwater recharge potentially migrating downgradient from Sump 9B. Perimeter collection and extraction facilities, including three collection trenches and five extraction wells, were installed at the facility from February to April, 1989 in accordance with the


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site’s previous Remedial Action Plan (Canonie, 1988a; Brierley & Lyman, 1989c,1990h). These features, located along the A-, B-, and C-drainages, were originally called plume capture and control trenches but are commonly referred to today as the perimeter control trenches (PCTs). Also in accordance with the site's previous Remedial Action Plan (Canonie, 1988a), the extraction trench (or perimeter source control trench [PSCT]) was installed downgradient of the landfills in November 1990 (Brierly & Lyman, 1989a; Woodward-Clyde Consultants, 1991). Few details are available regarding the source(s) and physical characteristics of clay materials used in the construction of the various environmental barriers at the site. Available documentation for construction of the C-Drainage barrier indicates that clay materials were derived from three borrow sites reported to lie on Casmalia Resources property (Penfield & Smith, 1982). Site operations staff with historical knowledge of some clay barrier construction activities report clay borrow sites to include one location just west of the C-Drainage barrier in proximity to current RAP-1C, and another near the A-Drainage barrier in proximity to current RAP-1A (Larry Bailey, Sr., personal communication, 2011). This is supported by observations from historical aerial photographs from August and December 1981 which indicate apparent grading and soil excavation activities in these general areas (ERI, 2001). Laboratory permeability testing for samples of the clay material used in construction of the C-Drainage barrier reported permeabilities of these materials ranging from 1.2 EE-9 to 0.9 EE-8 centimeters per second (cm/sec), with a calculated average of 0.6 EE-8 cm/sec (Penfield & Smith, 1982). The permeability for materials comprising the P/S Landfill clay barrier was measured on a total of three samples collected from this feature during the RI, with reported permeabilities ranging from 2.57 EE-8 to 4.30 EE-8 cm/sec, and a calculated average of 2.32 EE-8 (CSC, 2011 – Appendix J). These various barriers and extraction facilities are further described in the following sections. PCB Landfill Clay Barrier An environmental barrier was constructed along the southwest corner of the PCB Landfill during December 1980 (Woodward-Clyde Consultants, 1988a). This barrier was constructed of compacted clay within a trench excavated to approximately 14 feet beneath the ground surface and installed a minimum of four feet into unweathered claystone bedrock (Pacific Materials Laboratory, 1980). The clay barrier was designed to be a minimum of 10 feet wide and reportedly includes a 6-mil polyethylene sheet lining on its downstream face. No leachate collection system was installed as part of this landfill barrier. P/S Landfill Clay Barrier and Gallery Well Casmalia Resources constructed a clay barrier and extraction point at the toe of the P/S Landfill in 1980. The clay barrier wall is reportedly approximately 200 feet long, 12 feet thick, and up to 50 feet deep (Woodward-Clyde Consultants, 1988a). It is believed that the barrier wall extends a minimum of 4 feet into the unweathered claystone formation (Pacific Materials Laboratory, 1981a). The location, alignment, top elevation, and physical properties of this feature were confirmed by an exploratory drilling and sampling program conducted as part of the Remedial Investigation. Details of the P/S Landfill clay barrier investigation are presented in Appendix J of the RI Report. The location of the P/S Landfill clay barrier, as confirmed during the RI, is also depicted on figures 2-1 and 2-2.


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Clay Barrier Construction The adobe clay barrier was constructed by excavating an east-west ditch along the southern edge of the P/S Landfill. This ditch was approximately 10 feet wide at the bottom to as much as 30 feet wide at the top of the ditch due to sloughing of the soils. The ditch was approximately 200 feet long running roughly east-west along the southern edge of the P/S Landfill and about 30 feet deep. The ditch was dug down approximately 5 feet beneath the blue-gray clay contact (i.e., keyed into the contact) using heavy equipment and was located to be as close to the waste face as possible. The clay barrier was eventually built up using locally-derived adobe clay material and other low-permeability soils to a height of approximately 50 feet; it is nominally 8 to 12 feet wide and 200 feet long. Gallery Well Construction Casmalia Resources also installed an extraction point directly upgradient of the clay barrier at that time to reduce the liquid levels in the P/S Landfill (Caldwell, et. al, 1982). The extraction point, now known as the Gallery Well, was historically known as SP-1 and GCW. The CSC continues to extract liquids from the Gallery Well. The Gallery Well reportedly extends 5 feet into the unweathered claystone. The base of the Gallery Well is seated in an approximate 4-foot-diameter collection basin filled with gravel. The Gallery Well consists of a 10-inch-diameter polyvinyl chloride (PVC) casing that extends approximately 84 feet from the existing ground surface. The lower 40 feet of casing is perforated to allow liquids to flow into the Gallery Well. RCRA Landfill Clay Barrier An environmental barrier was constructed downgradient of the RCRA Landfill during June to August 1984. This barrier was constructed at the southern end of Pond 43 (or West Canyon Catch Basin [WCCB]), which is located at the southern end of RCRA Canyon. The barrier was constructed of compacted clay within a trench excavated to approximately 30 feet beneath the ground surface, and was installed a minimum of four feet into unweathered claystone bedrock. The clay barrier is equipped with a leachate collection well, without sump pump, on the upgradient side of the barrier dam approximately at the mid-point (Attachment 21-1, Woodward-Clyde Consultants, 1988b). Former Pond 20 Clay Barrier Pond 20 served as a runoff control pond and was utilized in the evaporation system. It was constructed by Casmalia Resources in mid-to-late 1981 and contained a clay core barrier dam located at the pond’s southeast corner (Woodward-Clyde Consultants, 1988b). The clay core is reported to be 15 feet wide and was constructed of compacted material installed a minimum of 5 feet into the unweathered claystone (Pacific Materials Laboratory, 1981b, c). This barrier was sometimes referred to as the A-Drainage clay barrier, although it was located more specifically near the limits of former Pond 20. Sump 9B Sump 9B is a gravel-filled collection trench and associated extraction point installed directly downgradient of the P/S Landfill clay barrier and upgradient of the PSCT. Sump 9B is located approximately 200 feet downgradient (south) of the Gallery Well and was constructed during closure of former Pad 9B in response to the observation of contamination below the groundwater table in this location. This feature consists of a circular sump approximately 27


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feet deep and 12 feet wide. Extending approximately 100 to 150 feet westward from the sump is a shallow (estimated 8 to 12 feet deep) trench. The sump and trench are filled with gravel to approximately 6 feet below grade and covered with compacted fill material. The trench was not completed into the unweathered claystone. Drilling activities associated with the installation of the Sump 9B companion well in July 2001 confirmed that the sump was excavated and installed down to the unweathered claystone (Harding ESE, 2001e). An extraction point (Well 9B) was installed at the deepest portion of the sump (Harding ESE, 2001g). Perimeter Source Control Trench The PSCT is a continuous, approximately 2,650-foot-long and nominally 3-foot-wide gravel-filled collection trench covered with compacted fill material (Brierley & Lyman, 1989a). The PSCT was installed in 1990, on a roughly northwest-to-southeast alignment, across most of the central portion of the site, and is situated in a downgradient position relative to the five inactive landfill areas and the Burial Cells Unit (figures 2-1 and 2-2). The PSCT, while crossing most of the central portion of the site, does not extend west of the former Casmalia Neutralization System (CNS) and into the West Canyon Spray Area (WCSA)/RCRA Canyon Area. The PSCT extends to depths of between approximately 13 and 65 feet, depending on the depth at which unweathered claystone bedrock was encountered during construction. The PSCT is designed to intercept subsurface liquids migrating from north to south across the site. The major components of the PSCT include a filter fabric against the native alluvial or fill soils, a permeable gravel backfill, random backfill above the gravel, a low permeability cap to minimize water infiltration, and four collection sumps and associated extraction points. The gravel backfill extends approximately 10 feet above the highest level of groundwater seepage observed during excavation (Drawing D1046-007-2 through D1046-007-7, Brierley & Lyman, 1989a). The four collection sumps were constructed by excavating pits into unweathered claystone bedrock. Liquids collected in the PSCT flow along the bottom of the trench toward the center of each sump, away from engineered flow divides, which isolate the individual sumps. When liquid levels exceed the level of the flow divides, liquids flow along the base of the trench to the lowest point in the system located at extraction point PSCT-1. Currently, all four sumps have pumps installed, and liquids are extracted to maintain liquid action levels mandated by USEPA. Sumps PSCT-1 and PSCT-4 produce the most significant volumes. Liquids extracted from sumps are currently treated in the granular activated carbon (GAC) treatment system and discharged into Pond 18. A-Drainage Perimeter Control Trench A gravel-filled PCT and associated groundwater extraction points (PCT 1-A and extraction points RAP 1A, 2A, and 3A) were installed in 1989 to collect and pump groundwater at the southeast corner of the facility (Brierley & Lyman, 1990h). This PCT was constructed as an additional means for intercepting groundwater flow toward the A-Drainage area. Extracted liquids are discharged into the Runoff Containment Facility (RCF) Pond. B-Drainage Clay Barrier and Perimeter Control Trench A subsurface clay barrier was installed in 1973 directly downgradient from Pond 13 between the two low hills flanking the head of the B-Drainage (Penfield & Smith, 1973; Woodward-Clyde Consultants, 1988b). This clay barrier was constructed to restrict groundwater flow in the B-Drainage area. The barrier is reported to be 8 feet wide and approximately 50 feet deep, extending about 4 feet into unweathered claystone. The barrier is equipped with a 1-foot-wide


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gravel drainage gallery and associated extraction point (extraction point B-5) on its downgradient side to assist in groundwater collection and removal. A gravel-filled perimeter control trench and associated extraction point (PCT-B and extraction RAP-1B) was installed downgradient from the B-Drainage clay barrier in 1989 (Brierley & Lyman, 1990h). This PCT provides an additional means for intercepting groundwater flow in the B-Drainage area. Extracted liquids are discharged into the RCF Pond. C-Drainage Clay Barrier and Perimeter Control Trench A subsurface clay-core barrier was constructed between 1981 and 1982 at the southwest corner of the facility, directly down slope (south) of the five A-series ponds formerly located in this area (Loomis, 1982; Penfield & Smith, 1982; Woodward-Clyde Consultants, 1988b). This structure is over 1,000 feet long and was installed to intercept groundwater migrating southwesterly from the facility in the C-Drainage toward Casmalia Creek. The clay core is approximately eight feet thick and a maximum of 75 feet deep, extending a minimum of four feet into unweathered claystone bedrock. The clay barrier is equipped with an approximately one-foot-wide gravel drainage curtain on its upgradient face to assist in the collection of groundwater, which is removed by pumping at extraction point C-5. A gravel-filled PCT (PCT-C) was installed in 1989 as a northern extension to the pre-existing clay barrier (Brierley & Lyman, 1990h). This PCT provides additional control of groundwater that may otherwise migrate down the C-Drainage toward Casmalia Creek. Groundwater collected in PCT-C is removed from extraction point RAP-1C. Extracted liquids are discharged into the A-Series Pond. Road Sump The Road Sump is a subsurface collection and containment sump with an extraction pump designed to intercept and capture groundwater recharge potentially migrating downgradient from Sump 9B into an above ground concrete culvert adjacent to the Sump 9B Road. The Road Sump is approximately 10 feet in length and 3 feet wide and completely filled with gabion rock (ICF Kaiser, 1998c). The sump extends 1 foot down into the clay layer to a total depth of approximately 5.5 below ground surface. The Road Sump was constructed and installed with an 8-inch PVC well in November 1998. A well head and extraction pump was later installed in January 1999. Currently, groundwater level in the road sump is measured twice a day to maintain a compliance action level greater or equal to 6 feet below top of casing (ftbtoc). 2.2.3.3 Former Liquid Waste Treatment Systems Historical site treatment units and systems included the following:

CNS used to treat acidic and alkaline liquids; Hydrogen peroxide treatment system to control odors near Pond 3; Oil recovery and treatment system tanks operated north of Pond M; Zimpro wet air oxidation (WAO) unit used to oxidize organic liquids; and Zimpro PACT unit, which was a temporary pilot-scale treatment system.

Details regarding the nature and operational history of these former waste treatment systems are presented in Section 2 of both the Work Plan and the RI Report.


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2.2.4 NPDES Permits 2.2.4.1 NPDES Permit CA0049972 A National Pollutant Discharge Elimination System (NPDES) permit (CA 0049972) was issued to the CSC for the facility by the RWQCB in 1999. The permit was renewed by the RWQCB in 2004. This permit authorizes treated pond waters to be discharged in the event that site pond levels reach full capacity. The NPDES permit governs discharge of pond waters and extracted groundwater from the site to nearby Casmalia Creek. This NPDES permit has not been utilized to date (there have been no pond water or groundwater discharges). In 2012 the RWQCB notified the CSC that the Water Quality Control Plan for the Central Coast Basin (Basin Plan) contains a provision that prohibits waste discharges to certain inland waters, including all surface waters within the San Antonio Creek Subbasin (page V-8, Section IV.B Inland Waters, No. 2 in RWQCB 2011). This would include the discharge of treated pond water and treated groundwater because these treated waters would still be considered to be “waste” by the RWQCB. Casmalia Creek is within the San Antonio Creek Subbasin. Although the Basin Plan prohibits certain discharges, it also allows the RWQCB – subsequent to public hearing – to grant exceptions of any provision of the Basin Plan where the RWQCB determines (Basin Plan, Page V-11, Section IV.F, Exceptions to Basin Plan Requirements):

1. The exception will not compromise protection of waters for beneficial uses; and 2. The public interest will be served.

A report of waste discharge and application package would need to be prepared and submitted to the RWQCB in order to satisfy the substantive requirements for an exception to the Basin Plan prohibition for the discharge of treated pond water and treated groundwater to Casmalia Creek. As further discussed in Section 10.6, there is no current plan to request this exception. 2.2.4.2 NPDES General Stormwater Permit In 2003, the CSC issued a Notice of Intent (NOI) to Comply with the terms of the California NPDES General Stormwater Permit (General Permit WDID #342I018481) for discharge of stormwater collected from the capped landfills in efforts to minimize the amount of rain water runoff entering the ponds. The capped landfills comprise approximately 45-acres known as the P/S Landfill Cap and EE/CA Area Cap (completed in 2000 and 2002, respectively), and are designed and constructed to include a foundation layer, two separate layers of impermeable liner, a geocomposite drainage layer, and a vegetative cover that is a minimum of two feet of clean soil. Stormwater runoff from the capped landfills flows from to collection ditches that were built as part of constructing the landfill caps. The stormwater ditches are lined (either concrete or high-density polyethylene [HDPE]) and direct the runoff water to a retention basin built directly south of the capped landfills where the stormwater is collected pending discharge. Stormwater discharged from the retention basin enters six wetland pools designed and constructed (completed in 2009) along the southern boundary of the site within the B-Drainage area. Details of the retention basin, design capacity, and stormwater requirements are discussed in detail in a memorandum that accompanies the NOI to Comply with the Terms of the General Permit. Details of the B-Drainage Wetlands are discussed in detail in the Wetlands Final Design Report (Casmalia Resources Site Steering Committee, 2008). As of August 2011, nearly 12 million gallons of stormwater has been released under the terms of the


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General Permit. The area which is described in the General Permit is not included or covered by the NPDES Permit. 2.2.5 Existing Surface Impoundments Stormwater and treated liquids at the site are controlled and managed by a series of existing surface impoundments. Six unlined surface impoundments currently exist within the site boundary to store all surface runoff water and treated liquids. These facilities are briefly described in the following sections. 2.2.5.1 Stormwater Runoff Collection Ponds A total of four surface water runoff collection ponds are currently present at the site. Three of these ponds are located along the south-central and southwestern site boundary, and are identified as the RCF Pond, Pond 13, and the A-Series Pond (Figure 2-1). The RCF Pond lies in the area once occupied by portions of former ponds 3, 4, 9, 10, and 11. The A-Series pond lies in the area once occupied by portions of former ponds A-1, A-2, A-3, and A-4. Pond 13 is the most southerly (downgradient) of the original stormwater runoff containment ponds and is still utilized for its original purpose of runoff control. The remaining surface water runoff collection pond is a small unlined collection basin constructed during 2003 by the CSC in a portion of the Central Drainage Area (Figure 2-1). Clean stormwater runoff from the P/S Landfill cap and EE/CA cap is directed via drainage swales into this basin, and a pipeline from the basin allows impounded stormwater to be drained directly into the RCF Pond or the upper reaches of the B-Drainage for discharge outside the site boundary, bypassing uncapped areas of the site. This pipeline is equipped with valves and flow meters to control the location and rate of discharge. Discharges from this pond are permitted under the General NPDES permit. Test discharges from this basin were conducted during the 2005-2006 rain year. 2.2.5.2 Treated Liquids Impoundments Two treated liquid impoundments are currently present at the site. These ponds are located on the southwestern portion of the site, and are identified as Pond A-5 and Pond 18 (Figure 2-1). The locations of these two holding ponds largely correspond with those of former ponds of the same designation. Treated liquids extracted from Sump 9B and the Gallery Well were once discharged to Pond A-5, although Pond A-5 does not currently receive any liquids. Pond 18 currently receives treated effluent from the PSCT GAC-treatment system. 2.2.6 Closure Activities and Response Actions, and Ongoing Monitoring Previous closure activities/response actions completed by Casmalia Resources during site operations included closure of the former ponds and pads, and removal of two fuel tanks at the site. Additional response actions include CNS decommissioning completed by the CSC, and ongoing capture and treatment of liquids from the various active extraction points within the site, including PSCT-1, PSCT-2, and PSCT-4, the Gallery Well, Sump 9B, and the extraction points associated with the several clay barriers, collection galleries, and PCTs installed along the downgradient site margins. Liquids management activities at the site were initiated by Casmalia Resources and were continued by USEPA during the emergency response period until the CSC began work at the site. Finally, the CSC constructed RCRA-equivalent caps over four of the five existing site landfills.


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2.2.6.1 Surface Impoundment Closure Activities Closure of existing surface impoundments was implemented in accordance with Cleanup and Abatement Order (CAO) No. 89-60, issued by the RWQCB. The overall objective of closure operations was to remove hazardous constituents once present in the former surface impoundments to background or other cleanup levels approved by the RWQCB. The proposed removal activities and confirmatory sampling and analysis procedures associated with impoundment closure are described in the Existing Surface Impoundment Closure and Post-Closure Plan (Canonie Environmental, 1989b). Surface impoundment closure was undertaken in three stages: liquids removal, bottom sludge removal, and contaminated subgrade removal. Removed liquids were either evaporated or solidified for disposal into site landfill areas. Bottom sludges were similarly solidified and disposed of. Contaminated subgrade materials encountered during closure activities were relocated to site landfill areas for disposal. The excavation of subgrade materials continued until laboratory testing of confirmatory soil samples indicated that pre-approved analyte-specific background concentrations or Toxicity Characteristic Leaching Procedure-based (TCLP-based) Target Cleanup Levels (TCLs) had been achieved, or until further excavation became impracticable. After initial closure verification testing was completed to the satisfaction of investigators, all pond/pad excavations were examined by representatives of the RWQCB and the Department of Health Services, the predecessor agency to the Department of Toxic Substances Control. As described in the available closure certification reports, agency representatives required the collection of multiple additional verification samples for further analytical testing from each former impoundment area. In addition to sampling and testing former surface impoundment subgrade materials, approximately 84 samples were randomly collected for similar chemical testing from areas where impoundment fluid transfer pipelines and culverts had been removed. These samples were also compared to TCLs to confirm acceptable closure along former pipeline and culvert alignments. Agency-required verification sampling was performed in excavation sidewall areas, beneath entry and exit pipelines and culverts, as well as throughout the floor areas of impoundment excavation areas. It is estimated that in excess of 780 soil samples, or 11 to 12 samples per acre of impoundment area, were collected and chemically analyzed during the impoundment closure process to document closure conditions. Target cleanup levels were not met in all closure samples, and Casmalia Resources submitted closure reports for only 16 ponds and 3 pads. Casmalia Resources was negotiating with the agencies to secure the RCRA permits needed to keep the Site in operation during the pond closure period. When it became apparent that the site would not remain in operation, Casmalia Resources stopped preparing closure certification reports, although the closure work was completed (including removing and stabilizing sludges, excavating subgrade soils, and collecting confirmation and verification samples). According to the RWQCB, the data generated from many of the ponds was not transmitted to the agencies, even though the agencies participated in the pond closure walkthroughs at the site. None of the surface impoundment certification reports were formally approved by the RWQCB.


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Closure conditions and recommendations for the majority of former surface impoundments were presented to the RWQCB in a letter from the investigators overseeing the closure activities (Brierley & Lyman, 1990a). Closure conditions as described in this letter were based on analytical results for random confirmatory sampling, agency-required verification sampling, and the findings of field inspections by agency personnel. Closure conditions were also based on the assumption that the impoundment areas would be subsequently covered as part of a landfill closure or become the subsurface of a new, lined, RCRA Landfill. Based on available information, it appears that 40 out of the 58 former surface impoundments, or approximately 70% of the total number, were recommended for closure. Four entire impoundments (Pad 9A, Pad 9B, Pond R, and Pond 23) and limited portions of two others (the western one-third of Pond 6 and the southern berm area of Pond 19) were recommended for closure as landfills. Impoundments recommended for closure as landfills are restricted to the area lying north of the PSCT. They either overlie or are in close proximity to known existing contamination sources, including the Burial Cells Unit and the toe area of the P/S Landfill. The closure status of former surface impoundments as categorized above is shown on Figure 2-5. 2.2.6.2 Fuel Tank Removals Casmalia Resources removed two fuel tanks from the site. One was an underground diesel fuel tank associated with the Zimpro WAO system; it was located outside in the southeast corner of the current Operations Building (which formerly housed the WAO equipment). The approximately 500-gallon tank was reportedly removed when the WAO system was dismantled in the late 1980s. Casmalia Resources personnel reported that the tank removal was conducted under Santa Barbara County Fire Department regulations and oversight. Although Casmalia Resources submitted a closure report for this tank removal, the CSC has not been able to locate the associated documentation. The second tank Casmalia Resources removed from the site was an aboveground tank located in the transportation yard south of the A-Series Pond. The tank was on a concrete containment structure with curbing on the south side of NTU Road, and the pump and fuel dispenser were located north on the south side of NTU Road adjacent to Pond A-1. The tank was removed from the site in the late 1980s; no closure documentation was generated. 2.2.6.3 CNS Dismantling The CSC dismantled and decontaminated the tanks, process equipment, and piping associated with the CNS facility in November 1997. The CNS was originally installed by Casmalia Resources as a waste liquids treatment system for acidic, alkaline, and heavy metal contaminated liquid wastes. These activities included emptying residual sludges from the tanks, and draining other tanks, valves, and piping. After the tanks, equipment, and piping were removed, the CSC cleaned and pressure washed the remaining concrete containment structure, then collected wipe samples from the concrete. The results of the wipe samples indicated low concentrations of metals. Results of investigations conducted in support of this decommissioning and dismantling process are presented in the Final CNS Demolition Report (ICF Kaiser, 1998d). 2.2.6.4 Subsurface Site Liquids Management There are several extraction features at the site including the following: Gallery Well, Sump 9B, PSCT, the PCTs, and the Road Sump. Liquids have been extracted from these features since


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they were each installed, although the method for treating and/or disposing of these liquids has changed over time. Groundwater extraction has been ongoing since 1980, when Casmalia Resources constructed the Gallery Well and began operating it as a groundwater collection facility. Casmalia Resources subsequently constructed additional groundwater collection facilities consisting of PCT-A, PCT-B, and PCT-C in 1989, and the PSCT in 1990. USEPA intervened in 1992 and maintained critical site systems and performed maintenance on an interim basis until the CSC took over site maintenance. Responsibility for operation and maintenance of these facilities was transferred to the CSC in 1996 under an Administrative Order on Consent between the CSC and USEPA, under which the CSC conducts operation and maintenance under USEPA oversight. Table 2-4 summarizes the historical sequence of contaminated liquids control facility construction, extraction, treatment, and/or disposal. The CSC continues to operate and maintain these facilities under USEPA’s oversight under a 1997 Consent Decree. The groundwater collection facilities are operated to maintain water levels at or below specific criteria elevations. Criteria water level elevations are described by water level depths measured from a datum such as top of casing of the collection facility, and have been historically referred to as “action levels.” Daily liquid level measurements document compliance with the specific action levels established for each pertinent extraction point. Compliance with the established action levels is summarized in quarterly operations reports to the USEPA. 2.2.6.5 Landfill Closure Activities While the majority of landfill areas remain intact, wastes once deposited in the former RCRA Landfill and the former Drum Burial Area were removed and redeposited in one of the existing inactive landfill areas. With the exception of the PCB Landfill, the inactive site landfills have been capped. Landfill closure activities have included the following actions:

Removal of wastes from former RCRA Landfill sometime between April 1989 and early 1990;

Removal of wastes from the former Drum Burial Area between approximately December 1979 and 1980;

Capping of the P/S Landfill in 1999; and Capping of the Heavy Metals Landfill, Caustic/Cyanides Landfill, Acids Landfill, and

interstitials areas between these landfills (EE/CA Area Cap) during 2001-2002. 2.2.6.6 Site Spills and Seeps Since 1996, there have been some notable groundwater seeps and liquid spills resulting from extracted liquid pipeline breaks. These have included:

A contaminated seep known as the “9B Road Seep” that was located immediately west of the road traveling from PSCT1 to Sump 9B approximately 100 feet north of PSCT1. There have been no surface liquids in this seep location since 1999; however, when the seep did exist, elevated contaminant concentrations were noted;

A seep on the southern face of the Pond A-5 dike. That particular seep is greatly diminished since the water level in Pond A-5 has been lowered. That seep has been


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sampled a number of times over the years, and the water quality is similar to or better than the Pond A-5 liquids (which have all been below maximum contaminant levels [MCLs] for drinking water);

A seep in the southeastern dike of Pond 18. Although Pond 18 is on the western side of the road to the treatment area, the seep is on the eastern side of the road. That seep also has been periodically sampled over the years, and the results do not indicate significant contamination. The seep could be Pond 18 liquids or uncontaminated perched water;

An April 22, 2001, Gallery Well break; An October 14, 2001, PSCT pipeline break; and An April 11, 2005, approximate 85-gallon spill of RIPZ-8 purge water from mobile

polytank container. The locations of the more significant seeps are depicted on Figure 4-8. In addition to the more significant seeps and spills noted above, the CSC recorded a number of minor line leaks and subsequent liquid releases from 1996 to 2002 along the Sump 9B, Gallery Well, and PSCT conveyance pipeline corridors. These minor releases were generally in areas where the glued PVC pipe joints developed a drip and the cleanup was limited to removal of a small amount of soil. In these cases, the impacted soil was over-excavated and any observed areas of contaminated soil were removed and disposed at a permitted off-site facility. The PVC extracted-liquid pipelines for the Sump 9B, Gallery Well, and PSCT wells were replaced with welded HDPE pipe in 2000, 2001, and 2002 respectively. There have been no reported leaks or spills from any of the pipelines since the PVC pipe was replaced. The CSC performs daily pipeline inspections and notes any leaks or other conditions requiring maintenance on inspection forms. Leak repairs and non-routine activities (such as sampling seeps) are noted in the project log book maintained at the site. USEPA site personnel have access to the daily log book and inspection forms. 2.2.7 Groundwater and Surface Water Monitoring Site groundwater and surface water quality has been monitored since 1992; the monitoring consisted of measuring water levels and collecting water quality samples for laboratory analysis. The CSC initiated a routine monitoring program pursuant to the Consent Decree SOW in 1997. The monitoring is part of the Routine Groundwater Monitoring Element of Work (RGMEW). The RGMEW monitoring has been conducted on an approximately semiannual basis. The semiannual monitoring frequency was implemented to evaluate seasonal effects on water level and water quality data. Prior to 1992, the most comprehensive studies that included groundwater level and quality information were the Hydrogeologic Site Characterization and Evaluation Report, (Woodward-Clyde Consultants, 1988a) and the Hydrogeologic Site Investigation Report (Woodward-Clyde Consultants and Canonie Environmental, 1989). The location of current groundwater monitoring wells and piezometers is shown on Figure 4-7.


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2.2.7.1 Groundwater Level Monitoring Water level monitoring data have been collected and reported as part of water quality monitoring activities conducted at the site. Prior to 1992, the water quality monitoring activities included:

Hydrogeologic Assessment Report (HAR) (Canonie Environmental, 1987) Hydrogeologic Site Characterization and Evaluation Report (HSCER), (Woodward-Clyde

Consultants, 1988a) Groundwater Level Assessment Report, (Woodward-Clyde Consultants, 1988c) Hydrogeologic Site Investigation Report (HSIR), (Woodward-Clyde Consultants and

Canonie Environmental, 1989) Beginning in 1997, semiannual sampling events have been conducted and semiannual monitoring reports issued as part of the RGMEW. The semiannual monitoring and reporting activities include quarterly water level monitoring rounds, continuous water level monitoring from selected wells, and water level monitoring from liquid control features. 2.2.7.2 Groundwater Quality Monitoring Water quality monitoring data has been collected and reported as part of water quality monitoring activities conducted at the site. Prior to 1992, the water quality monitoring activities included, but were not limited to:

Casmalia Resources (groundwater monitoring during facility operational period) HSCER, 1988 HSIR, 1989

Beginning in 1992 and extending through 1996, the USEPA conducted several targeted sampling events encompassing the collection and analysis of samples from numerous monitoring points and environmental barrier systems at the site. Beginning in 1997, the CSC, as part of the RGMEW, has conducted 32 semiannual sampling events. Sampling occurred in accordance with RGMEW Field Sampling Plan (ICF Kaiser, 1997) or subsequent revised versions of the Field Sampling Plan (Harding Lawson Associates, 2000b and Harding ESE, 2001a). Samples were analyzed for COPC that include 206 compounds identified in the 40 CFR 264 Appendix IX – Groundwater Monitoring list and 23 additional unlisted compounds detected in samples collected from the site liquid control features. The compounds hydrazine, perchlorate, and n-nitrosodimethylamine (NDMA) were added to the analyte list for select wells starting in November 1999. In January 2009, the CSC requested a number of modifications to the RGMEW scope of work; as approved by EPA, these modifications have now been incorporated into the ongoing groundwater monitoring program at the site (MACTEC, 2009a). 2.2.7.3 Current Status of Site Monitoring Well Network Due to their age and damage or destruction as a result of closure activities performed by Casmalia Resources in the 1980s, many of the groundwater monitoring wells, piezometers, and other borings and casings drilled and installed by Casmalia Resources in the 1970s and 1980s


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were in poor condition or no longer in existence when the CSC began the RGMEW in 1997. Beginning in 1999, the CSC performed the following activities in response to an August 3, 1999 letter by USEPA:

Located and inspected all site wells Performed field investigation activities to locate, identify, and assess the condition of wells Repaired wells, as necessary, to meet minimum standards agreed to by USEPA and CSC Resurveyed the position and elevation of all wells

The CSC submitted a Final Well Inventory Report (MACTEC, 2006b) that was approved by USEPA. The Final Well Inventory Report is a stand-alone report that documents the condition and construction of the monitoring well network; it does not include the wells and piezometers installed as part of the RI. 2.2.7.4 Surface Water Quality Monitoring Surface-water quality monitoring data has been collected and reported as part of water quality monitoring activities conducted at the site. Prior to 1992, the surface water quality monitoring activities included:

HSCER, 1988 HSIR, 1989

Beginning in 1997, the CSC, as part of the RGMEW, has conducted and reported upon 32 semiannual sampling events. Sampling occurred in accordance with RGMEW Field Sampling Plan (ICF Kaiser, 1997) or subsequent revised versions of the Field Sampling Plan (Harding Lawson Associates, 2000b and Harding ESE, 2001a). Surface water samples collected from the existing stormwater runoff collection ponds and treated liquid impoundments were analyzed for COPCs that include 206 compounds identified in the 40 CFR 264 Appendix IX – Groundwater Monitoring list and 23 additional unlisted compounds detected in samples collected from the site liquid control features. Since 1997, the semiannual surface water quality monitoring activities were conducted in parallel with the groundwater level and groundwater quality monitoring events summarized above. 2.2.7.5 Surface Water Level Monitoring Surface water level monitoring data was collected and reported as part of site operation and maintenance activities. Beginning in October 1992, water level monitoring of the five ponds has been generally conducted on a daily basis as part of site maintenance and operation activities. Site operation and maintenance information, including pond water levels collected since September 26, 1996, when the CSC took over site responsibilities, have been reported in quarterly progress reports submitted to the USEPA.

2.3 REFERENCES A.T. Kearney/SAIC, 1987. RCRA Facility Assessment, Casmalia Resources Disposal Facility, Santa Barbara County, California, October 28. Boston Pacific, Inc., 2003. Construction As-Built Report. February


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Brierely & Lyman, 1991a. Pond 1 – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, February. Brierley & Lyman, 1991b. Pond 3 – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, April. Brierley & Lyman, 1991c. Pond 6 – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, February. Brierley & Lyman, 1991d. Pond 11 – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, February. Brierely & Lyman, 1991e. Pond 12 – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, February. Brierley & Lyman, 1991f. Pond 15 – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, February. Brierley & Lyman, 1991g. Pond 17 – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, February. Brierley & Lyman, 1991h. Pond 20 – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, February. Brierley & Lyman, 1991i. Pond A-1 – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, March. Brierley & Lyman, 1991j. Pond A-2 – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, March. Brierley & Lyman, 1991k. Pond A-3 – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, January. Brierley & Lyman, 1991l. Pond A-4 – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, March. Brierley & Lyman, 1990a. Summary of Results of a Closure Inspection on September 20, 1990. Letter to the RWQCB, November 9. Brierley & Lyman, 1990b. Pond 5 – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, December. Brierley & Lyman, 1990c. Pond 8 – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, October. Brierley & Lyman, 1990d. Pond 10 – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, December. Brierley & Lyman, 1990e. Pad 8A – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, November.


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Brierley & Lyman, 1990f. Pad 8B – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, November. Brierley & Lyman, 1990g. Pad 8C – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, December. Brierley & Lyman, 1990h. Performance Evaluation of the Effectiveness of the Plume Capture Collection Trenches, January. Brierley & Lyman, 1990i. West Canyon Closure Sampling Plan, Casmalia Resources Hazardous Waste Management Facility, August 9. Brierley & Lyman, 1989a. Final Construction Drawings, Perimeter Source Control Trench (PSCT), Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, May 31. Brierley & Lyman, 1989b. Final Construction Report for A, B, and C Plume Capture Collection Trenches, June. Brierley & Lyman, 1989c. Preliminary Performance Evaluation of the Effectiveness of the Plume Capture Collection Trenches, August. Caldwell, N.H., A. Loomis, and J.L. McBride, 1982. Casmalia Resources Internal Barriers – Design and Considerations. Prepared for California Department of Health Services – Hazardous and Toxic Substances Control Group. October. Canonie Environmental, 1989a. Existing Surface Impoundment Closure and Post-Closure Plan, Casmalia Resources Class I Hazardous Waste Management Facility. Canonie Environmental, 1989b. RCRA Solid Waste Landfill Closure and Post-Closure Plan, Casmalia Resources Class I Hazardous Waste Management Facility. Canonie Environmental, 1988a. Remedial Action Plan, Casmalia Resources, December. Canonie Environmental, 1988b. Pond 4 – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility. Canonie Environmental, 1987. Hydrogeologic Assessment Report (HAR). Casmalia Resources Class I Hazardous Waste Management Facility, Volume I-IV. November. Casmalia Resources, 1992. Revised Groundwater Monitoring Program, Casmalia Resources Hazardous Waste Management Facility. March. Casmalia Resources Site Steering Committee, 2008. Final Design Report – Former Casmalia Hazardous Waste Facility B-Drainage Alternate Habitat Area. June. Casmalia Steering Committee (CSC), 2011. Final Remedial Investigation Report. January Casmalia Steering Committee (CSC), 2009. [Tier 2 Ecological Risk Assessment] Sampling and Analysis Plan. March


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Casmalia Steering Committee (CSC), 2008. Draft Remedial Investigation Report. Casmalia Hazardous Waste Facility, Casmalia , California. Casmalia Steering Committee. April. Casmalia Steering Committee (CSC), 2007. Rev. Final Phase III RI Sampling Plan for Follow-up RISBON-59 Soil Sampling. March 27. Casmalia Steering Committee (CSC), 2006. Lower HSU DNAPL Evaluation/Draft NAPL Memorandum. March 31. Casmalia Steering Committee (CSC), 2005a. Casmalia Site Remediation RI/FS Interim Progress Report (IPR). Prepared for U.S. EPA Region 9. San Francisco, CA. Casmalia Steering Committee. February. Casmalia Steering Committee (CSC), 2005b. Revision 4 – Fall 2005 Phase II Sampling – Soil Vapor, Surface Drainage Water, and Background Soil. November 18. Casmalia Steering Committee (CSC), 2004a. RI/FS Work Plan. June. Casmalia Steering Committee (CSC), 2004b. Pond Water Management Plan – Revision 8. June 1. Casmalia Steering Committee (CSC), 2003a. Revised - Casmalia Pond Water Management Plan. January 31 Casmalia Steering Committee (CSC), 2003b. Pond Water Management – Update #7A. August 8. Casmalia Steering Committee (CSC), 2002. Casmalia Pond Water Management – Update #5. September 10. Casmalia Steering Committee (CSC), 2001. Casmalia Pond Water Management Plan. April 26. CH2MHill, 1997. Well Inventory Report, Casmalia, Resources Hazardous Waste Management Facility, Santa Barbara County, California. February. CH2MHill, 1996. Technical Memorandum, December 1994 Groundwater Sampling Results, Casmalia Hazardous Waste Management Facility, USEPA Contract No. 68-W9-0031/ WA No. 31-56-94H, January 22. Dames and Moore, 2000. Updated Sensitive Species Report, November. Environmental Research, Inc. (ERI), 2003a. Aerial Photographic Analysis of the Burial Trench Area. P/S Landfill Barrier, Pre-Site Drainages, Casmalia Disposal Site, May. Environmental Research, Inc. (ERI), 2003b. Supplemental Aerial Photographic Analysis, Casmalia Disposal Site. August. Environmental Research, Inc. (ERI), 2001. Aerial Photographic Analysis, Casmalia Disposal Site. April 27.


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Environmental Solutions, 1987. Preliminary Pond and Pad Characterization. Casmalia Hazardous Waste Management Facility. Ford Construction Company, Inc., 2003. Record of Documents, EE/CA Area Cap Construction, Casmalia Hazardous Waste Management Facility, Volume 1 of 3. January 31 Foster Wheeler, 2002. Construction Completion Report – P/S Landfill Cap Construction, Casmalia Hazardous Waste Management Facility, February. Foster Wheeler Environmental Corporation and GeoSyntec Consultants, Inc., 2001. Revised Final Report, EE/CA Area Cap Design. June 18. Foster Wheeler/GeoSyntec, 1999. Revised Final Pesticides Solvent Landfill Cap Design Report (Final Design Report), Casmalia Hazardous Waste Management Facility, July. Harding ESE, 2002. Semi-Annual Monitoring Report – October 2001, Casmalia Waste Management Facility, July. Harding ESE, 2001a. Revision 3 – Field Sampling Plan for Routine Groundwater Monitoring Element of Work. Casmalia Waste Management Facility. Harding ESE, 2001b. Interim Draft 2001 Fall Season Biological Species and Habitat Survey Report for the Casmalia Hazardous Waste Management Facility. Report to Casmalia Steering Committee. Harding ESE, 2001c. Pesticide Solvent Low Area Work Plan, Casmalia Hazardous Waste Management Facility, July. Harding ESE, 2001d. Gallery Well/Clay Barrier Investigation Work Plan, Casmalia Hazardous Waste Management Facility. Harding ESE, 2001e. Sump 9B Investigations Work Plan, Casmalia Hazardous Waste Management Facility. Harding ESE, 2001f. Report of Findings, Pesticide Solvent Landfill Low Area and Gallery Well/Clay Barrier Investigations, July 31. Harding ESE, 2001g. Sump 9B Summary Report, Casmalia Hazardous Waste Management Facility, October 4. Harding ESE, 2001h. Well and Piezometer As-Built Report, Summer 2000 Field Activities. Casmalia Waste Management Facility, May 21. Harding ESE 2001i. Semi-Annual Monitoring Report – July 2000, Casmalia Hazardous Waste Mgmt. Facility, Vol. 1 & 2, May 25. Harding ESE, 2001j. Semi-Annual Monitoring Report – May 2001, Casmalia Hazardous Waste Mgmt. Facility, December 24. Harding Lawson Associates (HLA), 2000a, Groundwater Data Summary Report, 1992 – 2000 Casmalia Waste Management Facility, October.


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Harding Lawson Associates (HLA), 2000b. Revision 2 – Field Sampling Plan for Routine Groundwater Monitoring Element of Work. Casmalia Waste Management Facility. Harding Lawson Associates (HLA), 1999. Semi-Annual Monitoring Report – April 1999, Routine Groundwater Monitoring Element of Work, December. Hunt & Associates, 2002. Results of Spring 2002 Aquatic Habitat Surveys for California Tiger Salamanders (Ambystoma californiense), Casmalia Landfill Facility, Santa Barbara County, California. Hunt & Associates, 2001. Draft Biological Species and Habitat Survey Report, Casmalia Hazardous Waste Management Facility, August. ICF Kaiser, 1999. Semi-Annual Monitoring Report – October 1998, Routine Groundwater Monitoring Element of Work, Casmalia Resources Hazardous Waste Management Facility, June. ICF Kaiser, 1998a. Final Technical Memorandum: Interim Collection/Treatment/Disposal of Contaminated Liquids Component of Work, Casmalia Resources Hazardous Waste Management Facility, May. ICF Kaiser, 1998b. Semi-Annual Monitoring Report – June 1998, Routine Groundwater Monitoring Element of Work, Casmalia Resources Hazardous Waste Management Facility, November. ICF Kaiser, 1998c. 9B Seep Containment Sump Design, Casmalia Site Liquids Management, Internal Project Memorandum to Sue Kraemer from Scott Elkind, dated September. ICF Kaiser, 1998d. Final CNS Demolition Report. January 8. ICF Kaiser, 1997. Routine Groundwater Monitoring Element of Work, Part I – Work Plan and Part II – Sampling and Analysis Plan. Revision 1, Casmalia Resources Hazardous Waste Management Facility. September. Loomis, A., 1982. Western Expansion Area. Consultant’s Report to Casmalia Resources Management. March 15. MACTEC, 2009a. Casmalia Groundwater Monitoring Program Technical Memorandum, Casmalia Superfund Site. January 12. MACTEC, 2009b. Combined Semiannual Monitoring Report, RGMEW 21st and 22nd SA Events - April 2008-March 2009, Casmalia Waste Management Facility, Casmalia California. June 30. MACTEC, 2008. Combined Semi-Annual Monitoring Report – RGMEW 19th and 20th SA Events, April 2007 – March 2008, Routine Groundwater Monitoring Element of Work. June 20. MACTEC, 2007. Combined Semi-Annual Monitoring Report – RGMEW 17th and 18th SA Events, April 2006 – March 2007, Routine Groundwater Monitoring Element of Work. September 20.


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MACTEC, 2006a. Combined Semi-Annual Monitoring Report – RGMEW 15th and 16th SA Events, April 2005 – March 2006, Routine Groundwater Monitoring Element of Work. December 12. MACTEC, 2006b. Final Well Inventory Report, Routine Groundwater Monitoring Element Of Work, Casmalia Site Remediation Project, Santa Barbara County, California. May 31. MACTEC, 2005. Combined Semi-Annual Monitoring Report – RGMEW 13th and 14th SA Events, April 2004 – March 2005, Routine Groundwater Monitoring Element of Work. July 13. MACTEC, 2004. Semi-Annual Monitoring Report – RGMEW 12th SA Event, October 2003 – March 2004, Routine Groundwater Monitoring Element of Work. September 8. MACTEC, 2003a. Semi-Annual Monitoring Report, April 2002, Casmalia Hazardous Waste Management Facility, Casmalia California, March 31. MACTEC, 2003b. Semi-Annual Monitoring Report – RGMEW 10th and 11th SA Events, October 2002 and May 2003, Routine Groundwater Monitoring Element of Work. October 31. MACTEC, 2002a. Interim 2002 Spring/Fall Biological Species and Habitat Survey Report, Casmalia Hazardous Waste Management Facility, Santa Barbara County, California. MACTEC, 2002b. Draft Well Inventory Report – 1999-2000 Survey, Routine Groundwater Monitoring Element Of Work, Casmalia Resources Hazardous Waste Management Facility, Santa Barbara County, California, December. McClelland Consultants, 1989. Final Environmental Impact Report, Casmalia Resources Class I Hazardous Waste Disposal Site Modernization Plan, September. Pacific Materials Laboratory, 1981a. Field Report to Steve Hunter, Casmalia Disposal. June. Pacific Materials Laboratory, 1981b. Technical Memorandum to Penfield & Smith Engineers, Inc. May 28. Pacific Materials Laboratory, 1981c. Field Report to Casmalia Disposal. October 31. Pacific Materials Laboratory, 1980. Soil Compaction tests, Interim Report for the PCB Pit Clay Core of Dike. Submitted to Ken Hunter c/o Penfield & Smith Engineers, Inc. December 31. Penfield & Smith Engineers, Inc. 1982. Final Engineer’s Report for Construction of Drainage Barriers for Casmalia Resources, Casmalia, California. July. Penfield & Smith Engineers, Inc. 1973. Grading Plan Drawing. May 23. Regional Water Quality Control Board, Central Coast Region (RWQCB), 2011. Water Quality Control Plan for the Central Coast Basin. June. URS, 2000. Draft Engineering Evaluation/Cost Analysis Report, Casmalia Hazardous Waste Management Facility, September 15.


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USEPA, 2006. Guidance on Systematic Planning Using the Data Quality Objectives Process (EPA QA/G-4). EPA/240/B-06/001. Office of Environmental Information Washington, DC 20460, February. USEPA, 2001. Comments on Groundwater Data Summary Report, letter dated August 8, 2001. USEPA, 1997. Consent Decree for Casmalia Hazardous Waste Management Facility, captioned U.S.A. v. ABB Vetco Gray Inc., et al., No. CV96-6518 CAS (RZx). June 27. USEPA, 1996a. Region IX Field Sampling Report, Casmalia Resources Groundwater Sampling, July 10 to 12, 1996, November 18. USEPA, 1996b. Final Report (on the USEPA 1995 Stormwater Discharge to Casmalia Creek), Casmalia Resources, Santa Maria, CA. July 1996. USEPA, 1995. National Enforcement Investigations Center (NEIC). Analysis Results from December 1994 Sampling; Casmalia Site, Santa Maria, California. NEIC Project M63, April 19. USEPA, 1993a. Guidance for Evaluating the Technical Impracticability of Groundwater Restoration (Interim Final). OSWER Directive 9234.2-25, September. USEPA, 1993b. Superfund's Standard Default Exposure Factors For The Central Tendency and Reasonable Maximum Exposure. Preliminary Review Draft, May 5. USEPA, 1993c. Wildlife Exposure Factors Handbook. Volumes I and II. Office of Research and Development. Washington D.C. U.S. Government Printing Office. USEPA/600/R-93/187 (a and b). Vector Engineering, Inc., 2003. Final Construction Quality Assurance Report for the EE/CA Area Cap at the Casmalia Resources Facility, Volume 1 of 3: Main Text - Appendixes A & B. February. Woodward-Clyde Consultants, 1991. Landfill Liquids Monitoring and Management Plan for Existing Landfill Closures, Casmalia Resources, May Woodward-Clyde Consultants, 1988a. Hydrogeologic Site Characterization and Evaluation Report (HSCER), Casmalia Resources Class I Hazardous Waste Management Facility, Volume I-IX, May 11. Woodward-Clyde Consultants, 1988b. RCRA Part B Permit Application, Casmalia Resources Hazardous Waste Management Facility (Volumes I through V), Casmalia, California, April 4. Woodward-Clyde Consultants, 1988c. Groundwater Level Assessment Report: Comparison of April 1988 to October 1987 Water levels, Casmalia Resources Hazardous Waste Management Facility. Woodward-Clyde Consultants, 1987. Existing Surface Impoundment: Design & Operations Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California. May 19.


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Woodward-Clyde Consultants, 1985. RCRA Part B Application, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California. April 26. Woodward-Clyde Consultants and Canonie Environmental, 1989. Hydrogeologic Site Investigation Report (HSIR) for Cleanup and Abatement Order (CAO) No. 80-61, Casmalia Resources Class I Hazardous Waste Management Facility, Volume I-VII. April 18. Woodward-Clyde Consultants and Canonie Environmental, 1988. Hydrogeologic Summary Report (HSR). Casmalia Resources Class I Hazardous Waste Management Facility.


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3.0 SUMMARY OF PREVIOUS INVESTIGATIONS This section provides an overview regarding the overall purpose, objectives, and scope of prior and ongoing investigations conducted at the site. Data from investigations completed at the site provide the basis for the current understanding of the extent of soil and groundwater contamination at the site. The scope of investigations proposed in the RI/FS Work Plan was based on the findings of investigations completed up to that point (i.e., 2004). Summary information for investigations completed since that time is briefly discussed below for completeness.

3.1 Previous Site Investigations and Activities Summarized in this section are the nature and scope of the principal investigations and activities conducted to date at the site. These investigations have been divided into four major categories, including pre-USEPA assessment activities, USEPA response activities, CSC site work activities, and RI/FS activities. The CSC Site Work Activities have been conducted pursuant to an Administrative Order on Consent (1996) or Consent Decree (1997), under USEPA oversight. Three primary historical characterization investigations have been conducted at the site:

Hydrogeologic Assessment Report (HAR) (Canonie Environmental, 1987); Hydrogeologic Site Characterization and Evaluation Report (HSCER) (Woodward-Clyde

Consultants, 1988); and Hydrogeologic Site Investigation Report (HSIR) (Woodward-Clyde Consultants and

Canonie Environmental, 1989). Each of these investigations was performed in response to agency requests for information about the site. Following is a brief description of each of these investigations. In addition, there have been several subsequent investigations and studies that were considered in developing the hydrogeologic conceptual site model. 3.1.1 Pre-USEPA Assessment Activities The following activities were conducted by Casmalia Resources in response to permitting and other regulatory requirements. 3.1.1.1 Hydrogeologic Assessment Report The HAR was the first comprehensive study to describe conditions at the site in relation to the waste disposal activities. The scope of the HAR focused on the southern portion of the site, where early waste disposal activities took place. The investigation was conducted in May 1987, and a report was submitted to the RWQCB in November 1987 (Canonie Environmental, 1987). The basic focus of the HAR was to assess the hydrogeology of the site in terms of the presence or potential for migration of wastes and/or waste constituents through the subsurface. The HAR


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also provided a comprehensive characterization of the wastes in each of the existing surface impoundments, identified the owners of the site, described the climatology of the site, described the nature of surface waters at the site, and described the relationship of the site to wells outside the site boundary and regional water resources. 3.1.1.2 Hydrogeologic Site Characterization and Evaluation Report The HSCER provided further characterization of the site and substantial additional information on the hydrogeological conditions and on the nature and extent of soil and groundwater contamination. Investigations for the HSCER were conducted by Woodward-Clyde Consultants over the period spanning May 1986 through November 1987. The work conducted helped to further delineate the nature and extent of soil contamination at and surrounding the site, and to further refine the site hydrogeologic model that was in development at the time. 3.1.1.3 Hydrogeologic Site Investigation Report The HSIR provided an update to the Hydrogeologic Summary Report (HSR) (Woodward-Clyde Consultants and Canonie Environmental, 1988). The HSIR primarily utilized and summarized information from all the previous investigations and work conducted at the site up to that point. However, the HSIR also included results of additional water and soil investigations conducted for CAO 88-145 (revised CAO 88-76). The HSIR represents the most comprehensive compilation of technical information available at that time regarding hydrogeologic conditions and the nature and extent of soil and groundwater contamination at the site. As part of the HSIR, background concentrations for selected organic chemicals and inorganic metals were developed. From the background sampling data, Threshold Limit Values (TLVs) were developed, and the background levels established were evaluated to determine appropriate concentrations for each chemical constituent for use in conjunction with closure of the surface impoundments, and for characterization of the lateral and vertical extent of contaminated soil at the site. These concentrations were/are referred to as Target Closure Levels (TCLs). 3.1.1.4 Brierley & Lyman Studies Casmalia Resources provided Final Construction Drawings for the PCTs and PSCT to the RWQCB in 1989 (Brierley & Lyman, 1989a and 1989b). The packages were provided to fulfill the requirements of the RWQCB CAO 88-61 Task i. The packages included drawings with specifications noted for required construction materials. In addition to the construction drawings, Casmalia Resources submitted a report titled “Preliminary Performance Evaluation of the Effectiveness of the Plume Capture Collection Trenches” (Brierley & Lyman, 1989c), and a follow-up report titled “Performance Evaluation of the Effectiveness of the Plume Capture Collection Trenches” (Brierley & Lyman, 1990h). The purpose of the reports was to describe the hydrogeologic impact of each of the collection systems from the time they were constructed through November 1989. The reports concluded that operation of the PCT-B and PCT-C collection systems was creating localized depressions in the groundwater table in the vicinity of the extraction sumps, and recommended continued operation with no operational changes.


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Casmalia Resources also submitted Closure Certification Reports for some of the former ponds and pads at the site (Brierley & Lyman, 1990b-g, 1991a-l). The agencies never formally approved these reports, although agency personnel were present for the various site inspections and walkthroughs associated with pond closure. Casmalia Resources also conducted sampling in the West Canyon (includes both the RCRA Canyon Area and West Canyon Spray Area) to evaluate the nature and extent of contamination due to waste disposal practices (Brierley & Lyman, 1990i). 3.1.2 USEPA Response Activities 3.1.2.1 Final USEPA Report on 1995 Stormwater Discharge The USEPA released stormwater from the site to Casmalia Creek in 1995 as an emergency measure to avoid pond overflow due to heavy rains. The USEPA (in conjunction with the United States Fish and Wildlife Service [USFWS] prepared a report detailing their analysis of environmental impacts associated with the stormwater discharge. The assessments included impacts on the environment, impacts to known special-status species, and impacts to the receiving surface water (i.e., Casmalia Creek). The final USEPA report on the 1995 stormwater discharge (USEPA, 1996) concluded that the 1995 stormwater discharge had no adverse impacts on either the special-status species or the creek habitat. 3.1.3 CSC Site Work Activities As noted above, all of the CSC Site Work Activities have been conducted pursuant to an Administrative Order on Consent (1996) or Consent Decree (1997), under USEPA oversight. 3.1.3.1 Part 1 EE/CA Work Plan Studies The CSC submitted a series of EE/CA Work Plans to the USEPA pursuant to a 1997 Consent Decree. The Part 1 EE/CA Work Plan (CSC 1998) included a conceptual site model for hydrogeology and for risk assessment at the site, a plan for evaluating existing data available for the site, a plan for performing additional site investigations as necessary to characterize the site for purposes of the baseline risk assessment, and a plan for performing an engineering evaluation and cost analysis of response actions for the EE/CA Area. The draft Part 1 EE/CA Work Plan was the basis for preparing an EE/CA Report (URS, 2000) that ultimately became the EE/CA Action Memorandum (USEPA 2001). The EE/CA Report proposed capping three landfills and the interstitial areas between these landfills. EE/CA Area cap construction was completed during 2001-2002. 3.1.3.2 Summer 2000 Field Activities Between May and September 2000, at the direction of the USEPA, the CSC installed and developed seven new chemical water quality wells and 25 new piezometers at the site. These


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monitoring points were installed to provide data in areas of the site where the USEPA had identified potential data gaps. The results of these activities were submitted to the USEPA in the report titled Well and Piezometer As-Built Report, Summer 2000 Field Activities (Harding ESE, 2001h). 3.1.3.3 Interim Liquids Investigations In 2001, the CSC conducted specific site investigations in response to USEPA requests, as first outlined in a March 24, 2000, letter from the USEPA to the CSC. The CSC and the USEPA agreed to a scope of work that addressed the USEPA’s March 24 demands in an October 2000 Interim Liquids Agreement (ILA) signed by both parties. Three separate work plans were prepared and investigations were completed to address the areas of concern noted below:

The potential “Low Area” within the P/S Landfill; The Gallery Well construction and status, including the location of the clay barrier; and The construction of Sump 9B and potential DNAPLs in the immediate vicinity.

The work plans described activities that were to be conducted to evaluate the specific concerns at the areas noted above (Harding ESE, 2001c, 2001d, and 2001e, respectively). The field work was completed in early 2001 and reports were submitted to the USEPA in July and October 2001. P/S Landfill Potential “Low Area” Investigation The objective of this investigation was to evaluate the presence of a potential “low area” in the excavated sub-grade of the P/S Landfill and the potential presence of DNAPLs that may be associated with that potential low area. Under the agreement reached with USEPA in the ILA, the CSC was to determine if a low area existed, and to identify whether DNAPL is present in the potential low area. The CSC proposed to accomplish this by conducting cone penetrometer testing (CPT) and installing piezometers using direct-push technology (DPT) in the P/S Landfill in the vicinity of the potential low area. The results of this investigation were submitted to the USEPA in the Report of Findings, Pesticide Solvent Landfill Low Area and Gallery Well/Clay Barrier Investigations, dated July 31, 2001 (Harding ESE, 2001f). Gallery Well and Clay Barrier Investigations The Gallery Well and clay barrier investigation work plan described five separate activities as listed under the “Gallery Well.” The work objectives and included activities are listed below:

Delineating the location and extent of the clay barrier that is located downgradient of the Gallery Well;

Confirming the depth and, as necessary, cleaning out any materials in the Gallery Well; Installing a dedicated pump to remove DNAPL from the Gallery Well; Installing additional piezometers along the upgradient side of the existing clay barrier; and Lowering the liquid action-level in the Gallery Well.

The results of these activities were included in the Report of Findings, Pesticide Solvent Landfill Low Area and Gallery Well/Clay Barrier Investigations dated July 31, 2001 (Harding ESE, 2001f).


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While the CSC completed the activities specified in the ILA work plans, the exact location, depth, and alignment of the P/S Landfill clay barrier were not adequately determined by this work. Additional work conducted as part of the RI field investigations confirmed the location, alignment, and character of the P/S clay barrier. The findings of this additional work are presented in Appendix J of the RI Report (CSC, 2011). Sump 9B Investigation The Sump 9B investigation included:

Lowering the liquid action-level in Sump 9B; Installing a companion well adjacent to Sump 9B; and Monitoring for the presence of DNAPL in the area immediately adjacent to Sump 9B.

The results of the Sump 9B investigation were submitted to the USEPA in the Sump 9B Summary Report, dated October 4, 2001 (Harding ESE, 2001g). 3.1.3.4 P/S Landfill Cap Design The Revised Final Pesticides Solvent Landfill Cap Design Report (Final Design Report) was prepared by the CSC to present the proposed design of the cap and modified buttress for the P/S Landfill at the site (Foster Wheeler/GeoSyntec, 1999). 3.1.3.5 P/S Landfill Cap Construction Completion Report The CSC submitted a draft Construction Completion Report - P/S Landfill Cap Construction (Foster Wheeler, 2002) to the USEPA to comply with the requirements of the Casmalia Consent Decree and Statement of Work (SOW). The Construction Completion Report provided USEPA certifications that the P/S Landfill cap was constructed in conformance with the approved specifications and provided USEPA as-built drawings for the completed construction work. The report also includes field and laboratory test data collected to document conformance with the plans and specifications. The USEPA provided comments on the draft P/S Landfill as-built report that were addressed by the CSC and incorporated in an addendum to the as-built report (Foster Wheeler, 2002) submitted to the USEPA. 3.1.3.6 EE/CA Area Landfill Cap Design The Revised Final EE/CA Area Cap Design Report (Final Design Report) was prepared by the CSC to present the proposed design of the caps and buttresses for the Heavy Metals/Sludges (M/S), Caustics/Cyanides (C/C) and Acids landfills and adjacent interstitial areas (collectively referred to as the EE/CA Area Cap) at the site (Foster Wheeler/GeoSyntec, 2001). This revised design report was submitted to address modifications to the original final design when waste was unexpectedly encountered at shallow depths on the C/C Landfill. The design for this landfill was modified as discussed in Design Change Request – DCR07 that was submitted to USEPA by the CSC in 2001 (Foster Wheeler/GeoSyntec, 2001).


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3.1.3.7 EE/CA Area Cap Construction Completion and As-Built Report In 2003, the CSC submitted the EE/CA Area cap construction completion and as-built report (Ford, 2003). This document includes an appendix entitled Construction Quality Assurance Report, EE/CA Area Closure (Vector, 2003), prepared to confirm that the EE/CA Area cap had been constructed and completed in general accordance with the plans and specifications. 3.1.3.8 Groundwater Data Summary Report The CSC prepared and submitted the Groundwater Data Summary Report (Harding Lawson Associates, 2000), pursuant to the requirements of the Consent Decree SOW. The report was prepared in response to USEPA concerns regarding the site groundwater monitoring program, including QA/QC, data presentation and data interpretation. The USEPA provided the CSC with comments on the Groundwater Data Summary Report in a letter dated August 8, 2001 (USEPA, 2001). The objective of this report was to provide a summary of groundwater quality and hydrogeologic data collected at the site by various parties since 1992. The data summarized in the report consisted of available groundwater chemical data, groundwater water-level data, and hydrologic data collected at the site between 1992 and 2000. The most recent chemical data considered in the report were collected in November/December 1999 as part of the 5th semiannual sampling event conducted under the RGMEW. 3.1.3.9 Landfill Cap Surface Water Runoff Collection Pond Design and Completion Report As described in Section 2.2.5.1, the CSC constructed a small unlined collection basin in a portion of the Central Drainage Area in 2003 to collect stormwater from the P/S Landfill and EE/CA Area caps (Figure 2-1) (Boston Pacific, 2003). 3.1.3.10 Pond Water Management The CSC implemented a pond water management program following the 1997/98 El Nino winter to reduce and maintain pond water volume in the five onsite ponds at safe levels so that they would not overtop their berms. The pond water management program is documented in a Pond Water Management Plan (CSC, 2001) and follow-up revisions, through Revision 8 (CSC, 2001, 2002, 2003a, 2003b, 2004a). The CSC removed water through a combination of spray irrigation, spray misting, and truck road dust control watering from 1998 through 2006. The CSC used additional RCF pond water for construction of the P/S Landfill cap in 1999 and construction of the EE/CA Area cap in 2001 and 2002. Clean stormwater was initially discharged from the P/S Landfill and EE/CA Area caps offsite to the B-Drainage in spring 2006 to test the small unlined collection basin in the Central Drainage Area that collects clean stormwater runoff (Figure 2-1). The CSC began routine offsite discharge of clean cap stormwater during the 2008/09 winter under the General NPDES permit. 3.1.3.11 Biological Species Surveys The USEPA requested that a biological species and habitat survey (BSHS) be conducted at the site in conjunction with work on the EE/CA Area cap design/construction.


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The findings of the surveys are summarized in the following reports:

Updated Sensitive Species Report (Dames and Moore, 2000) Draft Biological Species and Habitat Survey Report (Hunt & Associates, 2001) – Surveys were also conducted in 2002 for the tiger salamander (Hunt & Associates, 2002); and

Interim Draft 2001 Fall Season Biological Species and Habitat Survey Report (Harding ESE, 2001b) – Surveys were conducted in 2002 for plants and birds as well (MACTEC, 2002).

3.1.3.12 Ongoing Groundwater Monitoring and Reporting The CSC is currently performing ongoing groundwater monitoring and reporting in accordance with the RGMEW. Groundwater monitoring under the RGMEW began in 1997 in accordance with a Work Plan and Sampling and Analysis Plan (ICF Kaiser, 1997). Modifications have been made to the RGMEW in response to advances in the understanding of site conditions and changing or new data quality objectives. Monitoring is currently performed in accordance with Field Sampling Plan, Revision 5.0 (MACTEC, 2009). Currently, water levels are measured quarterly, samples are collected semiannually, and reports are prepared annually. A total of 32 semiannual sampling events have been completed to date, and results for the 2013 year represent the most recently submitted annual RGMEW report (AMEC, 2014). Expanded sampling events were performed during fall 2004 and spring 2005 (Events 14 and 15) to collect data needed for the RI. 3.1.3.13 Ongoing Soil Vapor Monitoring and Reporting The CSC is currently performing ongoing soil vapor monitoring and reporting in accordance with a Sampling and Analysis Plan (CSC, 2009a) prepared under the Consent Decree SOW. Soil vapor monitoring is being performed at three locations along the North and Northeast Ridge in response to VOC detections in soil gas sampling conducted during the RI field work from 2004 through 2007. Samples are collected semiannually and reports are prepared annually. A total of 5 years of monitoring have been completed for the most recent annual soil vapor monitoring report (GeoSyntec, 2014). 3.1.4 RI/FS Activities In compliance with the terms of the Consent Decree, the CSC prepared additional work plans and reports related directly to the RI/FS process. These documents include the following:

Remedial Investigation/Feasibility Study Work Plan (CSC, 2004b); Interim Progress Report (CSC, 2005a); NAPL Memorandum (CSC, 2006a); Phase II and III RI Sampling Plans (CSC, 2005b and 2007); and Tier 2 Ecological Risk Assessment Sampling and Analysis Plan (CSC, 2009b).

These documents are briefly described below.


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3.1.4.1 RI/FS Work Plan The final RI/FS Work Plan was developed during the period 2001 through 2004 through a series of iterative draft documents and related agency comments. The CSC prepared and submitted three draft versions of the Work Plan prior to submittal of the final document in June 2004. The final Work Plan document incorporates the issues identified in agency comments on prior draft versions, and presents the scope of work and investigative methods completed during performance of RI field investigations and the risk assessment process. In developing the RI/FS Work Plan, a series of historical aerial photograph reviews were conducted to assess how site activities and conditions evolved over time. These studies helped provide a better understanding of historical site features, activities, and conditions, and were used to help define the nature of work planned for the RI. A series of four aerial photograph studies were conducted between 2001 and 2003 by ERI, a USEPA contractor (ERI 2001, 2003a, 2003b). The RI/FS Work Plan identified areas of the site and surrounding area where historical information indicates prior settings, uses, operations, facilities, and/or waste management and disposal practices. These areas of common history are identified as “study areas” in the Work Plan, and the specific investigations conducted during RI field activities within each individual study area were developed based on an understanding of the historical uses of these areas. The identified study areas investigated during the RI are presented in Figure 3-1, and include the following: Soil and Sediment Study Areas

Capped Landfills; PCB Landfill; RCRA Canyon Area; West Canyon Spray Area; Burial Trench Area; Central Drainage Area; Liquids Treatment Area; Maintenance Shed Area; Administration Building Area; Roadways; Remaining On-Site Areas; Off-site Areas (areas outside the site boundary); Stormwater Ponds; and Treated Liquids Impoundments.

Surface Water and Groundwater Study Areas

Stormwater Ponds; Treated Liquids Impoundments; Northern Groundwater Area; Southern Groundwater Area; and Off-site Surface Water and Groundwater (surface water or groundwater outside the site

boundary).


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3.1.4.2 Interim Progress Report Upon completion of the majority of RI field sampling activities identified in the Work Plan, the CSC prepared an Interim Progress Report (IPR), which was submitted to the USEPA in February 2005 (CSC 2005a). A series of IPR addenda and follow-up errata were subsequently prepared and submitted to the USEPA in response to agency comments received on the initial IPR document, and subsequent addenda and errata submittals. These addenda and errata submittals primarily provided additional data summary and presentation formats to assist USEPA review of the Phase I investigation findings. Final comments on the IPR and addenda were specified in a letter from the USEPA dated March 6, 2006. The Final IPR, which incorporated responses to these final USEPA comments, was then prepared and submitted to the USEPA on April 14, 2006. The USEPA subsequently conditionally approved the IPR in a letter dated May 9, 2006. 3.1.4.3 NAPL Memorandum The CSC summarized the findings of the NAPL and other groundwater investigations in the IPR submitted to USEPA in February 2005 (CSC 2005a). In its September 26, 2005 comments on the IPR, the USEPA requested that the CSC synthesize the available data specifically regarding the presence of DNAPLs in the Lower Hydrostratigraphic Unit (Lower HSU), assess the potential for migration of site DNAPL, and document that information in a memorandum (CSC, 2006a). The NAPL memorandum was prepared to address USEPA’s comments and summarized all of the data collected at the site for both DNAPL and LNAPL. 3.1.4.4 Phase II and III RI Sampling Plans In response to USEPA comments on the IPR and related addenda, the CSC prepared and submitted two Phase II sampling plans, including the Final Fall 2005 Phase II RI Sampling Plan (CSC 2005b), dated November 18, 2005, and the Final Spring 2006 Phase II Sampling Plan (CSC 2006b), dated May 25, 2006. The Phase II Sampling Plans outlined additional field data collection activities designed to address agency comments. Planned Phase II field activities encompassed the collection of additional soil, soil vapor, and groundwater and surface water samples from specific areas of the site where Phase I findings indicated the need for further characterization. In response to the USEPA comments on requested interim data summary information resulting from Phase II investigations, the CSC prepared and submitted the Revised Final Phase III RI Sampling Plan (CSC 2007), dated March 27, 2007. The Phase III Sampling Plan outlined a limited subsurface investigation program to be completed in a specific portion of the site where Phase II investigations had not adequately delineated impacts initially encountered during Phase I investigations. 3.1.4.5 Tier 2 Ecological Risk Assessment Sampling and Analysis Plan After completing and reporting the Tier 1 Ecological Risk Assessment (ERA) in the draft RI Report (CSC, 2008), the CSC prepared the Next Steps for Ecological Risk Assessment memorandum (Next Steps Memo; ARCADIS, 2008) and accompanying Tier 2 ERA Sampling and Analysis Plan (CSC, 2009b). These documents outlined additional studies and methods to further evaluate pathways, receptors, and COCs driving risk at the site in order to refine risk estimates, and were designed to make the ecological risk assessment more site-specific and


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less generic. Details of the methods are provided in the Tier 2 ERA Sampling and Analysis Plan (CSC, 2009b). 3.1.4.6 Dehalococcoides Bacteria Sampling To verify that reductive dechlorination was the result of biologically-driven processes, the CSC analyzed groundwater samples collected from four site locations (Gallery Well, Sump 9B, LHSU well RGPZ-7C, and Upper Hydrostratigraphic Unit [Upper HSU] well B3B) for the presence of the Dehalococcoides bacteria (Dhc), which is a known degrader of chlorinated alkenes. The samples were collected on April 17 and 18, 2012. Testing for Dhc was not readily available at the time the RI/FS Workplan was prepared in 2004. Appendix G of this FS Report provides a summary of the sampling and analysis performed.

3.2 Previous Response Actions Previous response actions completed at the site include the cleanup, closure and/or removal of historical surface impoundments, waste spreading areas, disposal areas, and other related waste management facilities by Casmalia Resources. The CSC subsequently completed additional response actions, including capping of all existing landfills other than the PCB Landfill. These prior response actions are summarized above in Section 2.2.6, and Section 3.1.3 of this report.

3.3 References AMEC, 2014. RGMEW Report Events 31 and 32, April 2013 – March 2014, Casmalia Resources Superfund Site, Casmalia, California. May. ARCADIS, 2008. Memorandum: Next Steps for Ecological Risk Assessment (Revised). November. Boston Pacific, Inc., 2003. Construction As-Built Report. February Brierley & Lyman, 1991a. Pond 1 – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, February. Brierley & Lyman, 1991b. Pond 3 – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, April. Brierley & Lyman, 1991c. Pond 6 – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, February. Brierley & Lyman, 1991d. Pond 11 – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, February. Brierley & Lyman, 1991e. Pond 12 – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, February.


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Brierley & Lyman, 1991f. Pond 15 – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, February. Brierley & Lyman, 1991g. Pond 17 – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, February. Brierley & Lyman, 1991h. Pond 20 – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, February. Brierley & Lyman, 1991i. Pond A-1 – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, March. Brierley & Lyman, 1991j. Pond A-2 – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, March. Brierley & Lyman, 1991k. Pond A-3 – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, January. Brierley & Lyman, 1991l. Pond A-4 – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, March. Brierley & Lyman, 1990a. Summary of Results of a Closure Inspection on September 20, 1990. Letter to the RWQCB, November 9. Brierley & Lyman, 1990b. Pond 5 – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, December. Brierley & Lyman, 1990c. Pond 8 – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, October. Brierley & Lyman, 1990d. Pond 10 – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, December. Brierley & Lyman, 1990e. Pad 8A – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, November. Brierley & Lyman, 1990f. Pad 8B – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, November. Brierley & Lyman, 1990g. Pad 8C – Closure Certification Report, Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, December. Brierley & Lyman, 1990h. Performance Evaluation of the Effectiveness of the Plume Capture Collection Trenches, January. Brierley & Lyman, 1990i. West Canyon Closure Sampling Plan, Casmalia Resources Hazardous Waste Management Facility, August 9.


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Brierley & Lyman, 1989a. Final Construction Drawings, Perimeter Source Control Trench (PSCT), Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, May 31. Brierley & Lyman, 1989b. Final Construction Report for A, B, and C Plume Capture Collection Trenches, June. Brierley & Lyman, 1989c. Preliminary Performance Evaluation of the Effectiveness of the Plume Capture Collection Trenches, August. Canonie Environmental, 1987. Hydrogeologic Assessment Report (HAR). Casmalia Resources Class I Hazardous Waste Management Facility, Volume I-IV. November. Casmalia Steering Committee (CSC), 2011. Final Remedial Investigation Report. January Casmalia Steering Committee (CSC), 2009a. Casmalia Site Remediation Project. Sampling Plan for Soil Gas Monitoring (Surveys). April 6.

Casmalia Steering Committee (CSC), 2009b. [Tier 2 Ecological Risk Assessment] Sampling and Analysis Plan. March Casmalia Steering Committee (CSC), 2008. Draft Remedial Investigation Report. Casmalia Hazardous Waste Facility, Casmalia , California. Casmalia Steering Committee. April. Casmalia Steering Committee (CSC), 2007. Revised Final Phase III RI Sampling Plan for Follow-up RISBON-59 Soil Sampling. March 27. Casmalia Steering Committee (CSC), 2006. Lower HSU DNAPL Evaluation/Draft NAPL Memorandum. March 31. Casmalia Steering Committee (CSC), 2006b. Final Spring 2006 Phase II Sampling Plan. May 25. Casmalia Steering Committee (CSC), 2005a. Casmalia Site Remediation RI/FS Interim Progress Report (IPR). Prepared for U.S. EPA Region 9. San Francisco, CA. Casmalia Steering Committee. February. Casmalia Steering Committee (CSC), 2005b. Revision 4 – Fall 2005 Phase II Sampling – Soil Vapor, Surface Drainage Water, and Background Soil. November 18. Casmalia Steering Committee (CSC), 2004a. Pond Water Management Plan – Revision 8. June 1. Casmalia Steering Committee (CSC), 2004b. RI/FS Work Plan. June. Casmalia Steering Committee (CSC), 2003a. Revised - Casmalia Pond Water Management Plan. January 31


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Casmalia Steering Committee (CSC), 2003b. Pond Water Management – Update #7A. August 8. Casmalia Steering Committee (CSC), 2002. Casmalia Pond Water Management – Update #5. September 10. Casmalia Steering Committee (CSC), 2001. Casmalia Pond Water Management Plan. April 26. Casmalia Steering Committee (CSC), 1998. Part I Engineering Evaluation/Cost Analysis Work Plan, Response Action Element of Work, Casmalia Hazardous Waste Management Facility, Santa Barbara County, California. November 25. Dames and Moore, 2000. Updated Sensitive Species Report, November. Environmental Research, Inc. (ERI), 2003a. Aerial Photographic Analysis of the Burial Trench Area. P/S Landfill Barrier, Pre-Site Drainages, Casmalia Disposal Site, May. Environmental Research, Inc. (ERI), 2003b. Supplemental Aerial Photographic Analysis, Casmalia Disposal Site. August. Environmental Research, Inc. (ERI), 2001. Aerial Photographic Analysis, Casmalia Disposal Site. April 27. Ford Construction Company, Inc., 2003. Record of Documents, EE/CA Area Cap Construction, Casmalia Hazardous Waste Management Facility, Volume 1 of 3. January 31 Foster Wheeler, 2002. Construction Completion Report – P/S Landfill Cap Construction, Casmalia Hazardous Waste Management Facility, February. Foster Wheeler Environmental Corporation and GeoSyntec Consultants, Inc., 2001. Revised Final Report, EE/CA Area Cap Design. June 18. Foster Wheeler/GeoSyntec, 1999. Revised Final Pesticides Solvent Landfill Cap Design Report (Final Design Report), Casmalia Hazardous Waste Management Facility, July. Geosyntec, 2014. Soil Vapor Monitoring Report – 2014. Casmalia Site, 3401 NTU Road, Casmalia, California. May 12.

Harding ESE, 2001a. Revision 3 – Field Sampling Plan for Routine Groundwater Monitoring Element of Work. Casmalia Waste Management Facility. Harding ESE, 2001b. Interim Draft 2001 Fall Season Biological Species and Habitat Survey Report for the Casmalia Hazardous Waste Management Facility. Report to Casmalia Steering Committee. Harding ESE, 2001c. Pesticide Solvent Low Area Work Plan, Casmalia Hazardous Waste Management Facility, July.


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Harding ESE, 2001d. Gallery Well/Clay Barrier Investigation Work Plan, Casmalia Hazardous Waste Management Facility. Harding ESE, 2001e. Sump 9B Investigations Work Plan, Casmalia Hazardous Waste Management Facility. Harding ESE, 2001f. Report of Findings, Pesticide Solvent Landfill Low Area and Gallery Well/Clay Barrier Investigations, July 31. Harding ESE, 2001g. Sump 9B Summary Report, Casmalia Hazardous Waste Management Facility, October 4. Harding ESE, 2001h. Well and Piezometer As-Built Report, Summer 2000 Field Activities. Casmalia Waste Management Facility, May 21. Harding Lawson Associates (HLA), 2000, Groundwater Data Summary Report, 1992 – 2000 Casmalia Waste Management Facility, October. Hunt & Associates, 2002. Results of Spring 2002 Aquatic Habitat Surveys for California Tiger Salamanders (Ambystoma californiense), Casmalia Landfill Facility, Santa Barbara County, California. Hunt & Associates, 2001. Draft Biological Species and Habitat Survey Report, Casmalia Hazardous Waste Management Facility, August. ICF Kaiser, 1997. Routine Groundwater Monitoring Element of Work, Part I – Work Plan and Part II – Sampling and Analysis Plan. Revision 1, Casmalia Resources Hazardous Waste Management Facility. September. Loomis, A., 1982. Western Expansion Area. Consultant’s Report to Casmalia Resources Management. March 15. MACTEC 2009. Revision 5.0 of the Field Sampling Plan, Routine Groundwater Monitoring Element of Work. March 31. MACTEC, 2002. Interim 2002 Spring/Fall Biological Species and Habitat Survey Report, Casmalia Hazardous Waste Management Facility, Santa Barbara County, California. URS, 2000. Draft Final Report, Engineering Evaluation/Cost Analysis Report, Casmalia Hazardous Waste Management Facility, December 15. USEPA, 2001. Comments on Groundwater Data Summary Report, letter dated August 8, 2001. USEPA, 2001. EE/CA Action Memorandum. April 2001. USEPA, 1996. Final Report (on the USEPA 1995 Stormwater Discharge to Casmalia Creek), Casmalia Resources, Santa Maria, CA. July 1996.


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Vector Engineering, Inc., 2003. Final Construction Quality Assurance Report for the EE/CA Area Cap at the Casmalia Resources Facility, Volume 1 of 3: Main Text - Appendixes A & B. February. Woodward-Clyde Consultants and Canonie Environmental, 1989. Hydrogeologic Site Investigation Report (HSIR) for Cleanup and Abatement Order (CAO) No. 80-61, Casmalia Resources Class I Hazardous Waste Management Facility, Volume I-VII. April 18. Woodward-Clyde Consultants and Canonie Environmental, 1988. Hydrogeologic Summary Report (HSR). Casmalia Resources Class I Hazardous Waste Management Facility. Woodward-Clyde Consultants, 1988. Hydrogeologic Site Characterization and Evaluation Report (HSCER), Casmalia Resources Class I Hazardous Waste Management Facility, Volume I-IX, May 11.


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4.0 PHYSICAL CHARACTERISTICS OF SITE AND STUDY AREAS

This section presents an overview of physical site characteristics ascertained during site investigations and closure activities. Both surface and subsurface characteristics are presented. A summary discussion of site history, including the site development, former operations, facilities, waste management practices, closure activities, and prior site investigations, is provided in Section 2 of this report. The descriptions presented in this section have been updated with the most recent information available, including data developed during the Remedial Investigation. 4.1 Surface Features 4.1.1 Site Boundaries The former Casmalia Hazardous Waste Facility is located on the south-facing flank of the Casmalia Hills. Casmalia Canyon and Creek, and an unnamed surface drainage, flank the site on the west and north-northeast, respectively (Figure 1-1). Both drainages are relatively broad and eventually empty into Shuman Canyon and Creek. Casmalia Creek merges with Shuman Creek approximately 2 miles south of the site and approximately 1 mile west of the town of Casmalia. Shuman Creek empties into the Pacific Ocean, approximately 4 miles west of the confluence with Casmalia Creek. The unnamed drainage located to the north and northeast of the site has been referred to as the North Drainage in previous project documents. Three unnamed surface drainages exit the southern facility boundary, and have also been identified in previous documents, from east to west, as the A-Drainage (southeast corner), the B-Drainage (south-central boundary), and the C-Drainage (southwest corner). The B-Drainage and C-Drainage are tributaries to the larger Casmalia Canyon and Creek (Figure 1-1). The Consent Decree (USEPA, 1997) has separated the site and surrounding areas into two distinct parts: Zone 1 (the approximately 252-acre former waste disposal area) and Zone 2 (surrounding lands). Zone 1 is fenced, and encompasses all former operational areas of the S. Zone 2 extends outward from the limits of Zone 1 encompassing adjacent surrounding lands (Figure 1-1). The detailed description of these areas, as defined in the Consent Decree, is provided in Section 2.1 of this FS Report. 4.1.2 Physiography The site is located within the southern portion of the Coast Range geomorphic province of California. The site lies within the Santa Maria Basin, a triangular-shaped basin, bounded on the south by the Santa Ynez Mountains and on the east and northeast by the San Rafael Mountains, and extends offshore to the west. The site topography and surrounding area are characterized by rounded hills and slopes of gentle to moderate steepness. Valleys are typically broad with streams eroding uplifted hills composed mostly of Miocene claystones and depositing alluvial valley fill sediments. The site slopes generally toward the south and is situated along the south-facing slopes of the Casmalia Hills. Surface elevations within the site range from 835 feet above mean sea level (msl) at the crest of the North Ridge, which forms the northern facility boundary, to 375 feet msl at the southern boundary, which is located at the foot of two small hills that rise to the south of the site. Approximately 1.2 miles north and east of the facility, the Casmalia Hills gradually rise


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to heights of approximately 500 feet above the highest portion of the facility, located along the northern site boundary. The Casmalia Hills are one of a series of three ranges of low west-northwest-trending hills that form the southern border of the Santa Maria Valley. 4.2 Meteorology The site has a generally mild coastal climate characterized by morning fog and afternoon winds. Site meteorological data have been collected at three locations: the A-Drainage, the B-Drainage and the North Ridge. Data have been collected since mid-1999 through mid-2008. These data were collected from 1999 through 2003 for landfill cap construction air monitoring purposes, and after 2003 to be used for the RI and other Zone 1 perimeter air monitoring. Meteorological data collection was discontinued in 2008. Meteorological data collected at these locations includes wind speed, wind direction, and air temperature. Precipitation and evaporation data are also collected from instrumentation located just north of the administration building. Representative site data reflecting daytime hours from 2006 and 2007, including monthly temperature, wind speed, and wind direction, are summarized in Table 4-1. Monthly rainfall and evaporation data collected at the site are available for the period 1983 through the present. Monthly rainfall and evaporation measurements from 1996 through 2007 are summarized in Table 4-2. 4.3 Surface Water Hydrology This section summarizes the surface water and hydrologic features within the historical facility boundaries and nearby areas. Included are brief descriptions of historical and current surface water drainage within the site boundary, current surface water impoundments, and nearby drainages. 4.3.1 Surface Water Drainage Within Site Boundary The majority of site surface water is collected and stored in site ponds. Water on the western side of the site is directed ultimately to the A-Series pond. The majority of surface water runoff from the RCRA Canyon Area is directed around Pond A-5 via a bypass pipeline that discharges directly into the A-Series Pond. Ponds A-5 and 18 also collect surface water runoff draining from the lands adjacent to them. The RCF Pond receives most other site surface water runoff, with the exception of runoff from the P/S, Metals, Caustic/Cyanide, and Acids landfills. Historically, the Central Drainage Area was the outlet for the former canyons within which the P/S, Metals, Caustic/Cyanide, and Acids landfills were constructed. These landfills are now capped with impermeable membranes and surface water runoff is controlled and temporarily staged in the Central Drainage Area collection basin located at the toes of these landfills (Figure 2-1). Site drainage has evolved through time in response to the general progression of development from 1959 (pre-development conditions) through 1987. Pre-development site drainage is depicted in Figure 4-1. Changes in site surface water drainage patterns through this period, and their implication regarding the potential for discharge of site-related runoff outside the historical site boundary, are briefly discussed below. Further details regarding the evolution of site drainage characteristics through time are presented in Appendix W of the RI Report (CSC 2011).


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Pre-development conditions in the site vicinity reflect several relatively undisturbed, natural drainages descending in a generally southerly direction from a pronounced northwest-southeast trending drainage divide (Figure 4-1). This northerly divide coincides with the current northern site boundary, and served to separate the watershed for the North Drainage, located to its northeast, from the watersheds lying to its south and southwest. Natural drainage within the limits of the future site area flowed toward the south from this northern divide and into what are identified as the current B-Drainage and lower C-Drainage. Drainage from the western portion of the future site area, within what is now identified as RCRA Canyon, is separated from the upper reaches of the C-Drainage by a prominent north-northeast-to-south-southwest trending topographic divide. A more subtle topographic divide occurs in the southeastern corner of the future site area, which served to separate the site from the A-Drainage, which drains toward the east. These principal topographic divides have remained largely unchanged through the development history of the site, and serve to effectively isolate surface water runoff within the site area from that within the North-Drainage, the A-Drainage, and the upper C-Drainage. Earthwork associated with the progressive development of the site from the mid-1970s through the mid-to-late 1980s further modified drainage characteristics. The overall effect of these changes was to control surface water runoff within the site boundaries through the contouring of land surface to direct runoff into additional control structures and detention basins. Site topographic conditions extant in 1993, following the completion of early cleanup activities, are largely the same as they are today, and are such that all site surface water runoff is completely contained within the site boundaries (RI Report, Appendix W, CSC 2011 Attachment 1 – 1993 topographic map). 4.3.2 Site Storm Water Runoff Collection Ponds and Liquid Treatment Impoundments There are currently five ponds at the site (Figure 2-1). Of these ponds, three (RCF, A-Series and Pond 13) are exclusively utilized as collection and containment facilities for site stormwater runoff. Two ponds (Pond A-5 and Pond 18) are currently, or have historically been, utilized for collection and containment of treated extracted liquids from site treatment facilities. Beginning in October 1992, water level monitoring of the five ponds has been generally conducted on a daily basis as part of routine site maintenance activities. The CSC took over site maintenance responsibilities on September 26, 1996. Site maintenance information, including pond water levels collected since September 26, 1996, have been reported in Quarterly Progress Reports and submitted to the USEPA. Variations in pond levels, volumes and total dissolved solids (TDS) concentrations recorded in each of these ponds during the period 1998 through 2012 are presented in Figure 4-2. A small unlined collection (retaining) basin was constructed in 2003 within the Central Drainage Area to collect clean stormwater runoff from the P/S Landfill and EE/CA Area caps (Figure 2-1). Initial discharge of clean stormwater from the landfill caps to the B-Drainage began in spring 2006 to test the system, and routine discharge to the B-Drainage began during the 2008/09 winter under the substantive requirements of a General NPDES permit. The total pond water volume steadily decreased following the 2004/05 El Nino winter, in part due to this discharge to the B-Drainage (Figure 4-2). While heavy precipitation experienced during the 2010-2011 winter season resulted in a temporary increase in pond volumes, this increase was short-lived. Pond volumes have again begun to decrease in response to the combined effects of evaporation and overall drier weather since that time.


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The TDS of the five site ponds decreased during the 1997/98 El Nino winter through dilution of low TDS stormwater runoff. The TDS of the ponds has steadily increased since the 1997/98 winter through evaporation, until heavy precipitation experienced during the 2010-2011 winter season served to again decrease TDS concentrations through dilution by low TDS stormwater runoff (Figure 4-2). Due to lesser rainfall amounts experienced since 2010-2011 winter season, with the exception of Pond A-5, TDS concentrations in the onsite ponds have increased since October 2011. Annually, the TDS decreases in the winter and spring from stormwater runoff dilution and then increases in the summer and fall due to evaporation. As of October 2012, the TDS concentrations in Pond A-5, A-Series Pond, RCF, Pond 13, and Pond 18 were reported at 22,000, 28,000, 19,000, 25,000, and 23,000 milligrams per liter (mg/L), respectively. 4.3.3 Surface Water Drainages Outside Site Boundary Surface water runoff from those areas directly surrounding the site flows into one of four surface drainages identified as the North Drainage, the A-Drainage, the B-Drainage, and the C-Drainage (Figure 1-1). The A-Drainage area historically and presently flows toward the east-southeast from the southeast corner of the site, conveying surface runoff to an engineered drainage swale that supports flow only in response to rainfall events. Runoff through the A-Drainage ultimately flows into Shuman Creek and the Pacific Ocean. The B-Drainage is a shallow topographic depression trending to the south from Pond 13. The B-Drainage is an ephemeral feature that conveys runoff only in response to rainfall events. The drainage extends approximately one-half mile to the south of the site where it joins Casmalia Creek. The B-Drainage is bounded to the east and west by small hills that direct surface water and groundwater into it, and was the historical outlet for surface water flowing through the Central Drainage Area prior to the modifications made during site development activities. The C-Drainage consists of Casmalia Creek, a perennial stream that drains the watershed located west and northwest of the site. Casmalia Creek flows to the southeast and eventually joins Shuman Creek approximately 1.8 miles south of the site. Schuman Creek, in turn, flows westerly toward the Pacific Ocean. The C-Drainage bounds the southwest corner of the Site and historically, and presently, drains surface water that primarily falls outside the western site boundary. The North Drainage is located directly north and upgradient of the site boundary, and conveys surface runoff in a southeasterly direction from the watershed lying north of the site toward Shuman Creek, which ultimately drains into the Pacific Ocean. Based on observations made by site personnel, the North Drainage area is an ephemeral drainage that conveys surface runoff only in response to rainfall events. 4.4 Geologic Setting Casmalia Resources investigated the regional and local geology through numerous site-specific field investigations. Casmalia Resources drilled several hundred borings, installed several hundred groundwater monitoring wells and piezometers, and performed other investigation work to assess the site’s geology, hydrogeology, and nature and extent of contamination. The results of this work is documented in several reports, including the HSCER (Woodward-Clyde Consultants 1988a), Geologic Siting Criteria Assessment (GSCA – Woodward-Clyde Consultants 1988b), and HSIR (Woodward-Clyde Consultants and Canonie Environmental,


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1989). The geologic setting described below is summarized largely from information in these reports. The RI/FS Work Plan (CSC 2004) and the RI Report (CSC 2011) also contain descriptions of these earlier geologic investigations. Salient findings of these past investigations are briefly summarized below. The geologic setting of the facility is relatively homogeneous. The landfill sits atop an uplifted block of Neogene shallow marine sediments, the Todos Santos Member of the Sisquoc Formation. The Todos Santos Member of the Sisquoc Formation consists predominantly of fine grained silts and clays which have subsequently hardened to claystone. As such, the pristine (unweathered) claystone forms “basement” material. The site and surrounding hills served as a source of alluvium, which eroded into local canyons and lowlands, and fill material for landfill activity. In situ weathering (soil development) of the Todos Santos Member has resulted in the formation of a “weathering rind” that covers much of the site claystone. 4.4.1 Regional Geology The site is located on a topographic (structural) ridge within the Santa Maria Basin. The Santa Maria Basin is a triangular-shaped synclinal basin, bounded on the south by the Santa Ynez Mountains and on the east and northeast by the San Rafael Mountains. The shape of the landforms in the area has been governed by accretion of the California landmass and Neogene tectonic activities associated with the San Andreas transform fault system. The base of the Santa Maria Basin is formed by the upper Jurassic Franciscan Formation. Up to 27,000 feet of Tertiary-age marine and non-marine sediments are present in the Santa Maria Basin. Geologic formations present within the Santa Maria Basin, include the Knoxville, Lospe, Point Sal, Monterey, and Sisquoc. The surface expression of the regional geology is presented in Figure 4-3 (portion of regional geologic map, based on USGS Orcutt and Casmalia quadrangles – Dibblee 1989). The regional stratigraphy and structural relationships are depicted in Figures 4-4 and 4-5. The Monterey and Sisquoc formations comprise the upper 6,300 feet of sediments in the Santa Maria Basin. At the site, the upper Miocene Monterey Formation is present at approximately 1,300 feet beneath ground surface (Section 4.2, Page 4-2, Woodward-Clyde Consultants 1988a and 1988b). The Monterey Formation is approximately 5,000 feet thick and is composed of interbedded porcelaneous shale, chert, limestone, diatomaceous shale, and diatomite. Oil and gas are locally produced from fractured sections of the Monterey Formation including areas lying to the east and north of the site. Conformably overlying the Monterey Formation is the upper Miocene to middle Pliocene Sisquoc Formation. The Sisquoc is formally divided into two members: the lower Todos Santos Claystone Member, and the upper Tinaquaic Sandstone Member (Woodring and Bramlette 1950). Within the site boundary, the Todos Santos Claystone Member is present at the surface and extends to approximately 1,300 feet below ground surface (bgs). The Todos Santos Claystone Member is comprised of porcellaneous shale, platy shale, claystone, diatomite, and siltstone. The upper Tinaquaic Sandstone Member of the Sisquoc Formation is not present at the site. 4.4.2 Local Geology The following sections summarize the identified surface and near-surface geologic units present at the site. Site surface geologic conditions were documented as part of investigations completed for the HSCER (Figure 5-1-1; Woodward-Clyde Consultants 1988a) and are based


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on site conditions in the mid-to-late 1980s, before Casmalia Resources began pond closure activities. The site geologic map is presented in Figure 4-9 of the RI Report (CSC 2011). Although Casmalia Resources removed a large volume of former pond subgrade material and placed these materials into the current landfills in the late 1980s, the overall interpretation of the surface geologic conditions depicted in the site geologic map is applicable to current conditions. Geologic units recognized within the site boundary during prior investigations are briefly described below. 4.4.2.1 Alluvium, Colluvium, and Fill Typical of California hillside geology, the site’s hillside has undergone weathering and erosion to provide colluvium and alluvium sediment that was deposited within the hillside canyons and valley floors. Much of the original colluvium and alluvium once present at the site has subsequently been redistributed during development and operational activities. Colluvium is present as thin layers in undisturbed areas and has been documented on the hillsides surrounding the site, ranging in thickness from 5 to 10 feet, with some deposits up to 20 feet thick. Discontinuous, localized deposits of alluvium have been reported at the site. Engineered fill is present throughout the site as dikes, berms, environmental barriers, and solid waste disposal units. Fill material was also placed in association with landfill capping activities, and as buttresses at the toe of some landfills. Fill was generally derived from excavation of site soils and consists of silty clay and pebble-to-cobble size fragments of claystone and silty claystone (McClelland Consultants 1989). 4.4.2.2 Claystone Sediment of the Todos Santos Claystone Member of the Sisquoc Formation was originally deposited in a (Miocene to Late Pliocene) marine continental margin slope environment, as indicated by diatomaceous fossil types. At the site, the claystone has been informally divided into weathered and unweathered stratigraphic units. The differentiation between the two units is based on the presence or absence of weathering (i.e., difference in color, degree of fracturing and type of secondary mineralization). Within the facility, the weathered claystone is exposed across 90 percent of the site and ranges in thickness from 15 to 65 feet. The thicker sections of weathered claystone occur in areas of topographic highs, particularly in the northern portions of the site, and gradually thin to the south. The weathered claystone is yellowish-gray to pale olive to olive-gray, and ranges from massive to faintly bedded. Secondary mineralization appears most frequently as hematite staining on fracture and joint surfaces and commonly as well-developed gypsum infilling of fractures and joints (Woodward-Clyde Consultants 1988a). The weathered claystone is generally pervasively fractured. While much effort has been made to define fracture and jointing patterns within the weathered claystone, inherently the weathered claystone is predominantly the result of physical and diagenetic alteration of the surface exposure of the Todos Santos Claystone. As such, observed fracture patterns are surficial in nature (that is, to the depth of fresh unweathered claystone). Observed “structural trends” within the weathered claystone show wide variation; due to the processes that formed fractures within this unit, structural features within the unweathered claystone overprint the structural relationship developed due to regional tectonic influences. The unweathered claystone is exposed in less than 10 percent of site outcrop, and typically lies at depths of 15 to almost 100 feet bgs. The unweathered claystone is up to 1,300 feet thick and


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conformably overlies the Monterey Formation. The unweathered claystone is olive-black to gray olive-green (wet), and medium bluish-gray (dry) in color. The unweathered claystone is significantly less fractured than the overlying weathered claystone. 4.4.3 Regional Structure The site is located on a topographic high area in the Casmalia Hills within the transition zone between the Transverse Range geomorphic province to the south and the Coast Range geomorphic province to the north and northeast. The region is characterized Neogene faulting and folding. Major folds mapped in the vicinity of the site include the Purisima Anticline, the Santa Maria Syncline, the Pezzoni Anticline, and the Graciosa Anticline (Figure 4-4). The northeastern limb of the San Antonio Anticline has been mapped roughly parallel to the site’s southwestern boundary. The trend of the Casmalia Anticline has been mapped toward, but not through, the site. Most folds in the region generally trend to the northwest, and some are locally exploited for oil and gas production. Major faults mapped in the vicinity include the Lion’s Head Fault, the Pezzoni Fault, the Casmalia Fault, and the postulated Orcutt Frontal Fault (Figure 4-4). The site is located on a several-mile-wide crustal block between the Lion’s Head and Orcutt Frontal faults. Maximum credible earthquake calculations for the two faults closest to the site, the Lion’s Head and Orcutt Frontal faults, range from 6.6 to 7.1 (McClelland Consultants 1989). Minimum recurrence intervals for the Orcutt Frontal Fault range from 200 to 2,000 years based on slip rates, and from 2,000 to 100,000 years based on lack of evidence for ground surface fault rupture (Woodward-Clyde Consultants 1988b). Tectonic models of the area postulate that the crustal block bounded by the Lion’s Head and Orcutt Frontal faults has undergone structural deformation during the Cenozoic, but the crustal block is behaving in a rigid manner and undergoing little internal deformation (Woodward-Clyde Consultants 1988b). 4.4.4 Site Structural Features Geologic evaluations of the site by Casmalia Resources and the CSC have included mapping and analysis of local structural features including bedding, faults, lineaments, and fractures. Salient information from these investigations is summarized below. Casmalia Resources and the CSC obtained detailed information on subsurface bedding and fractures by drilling, coring, and logging of borings across the site. These subsurface investigations are briefly summarized below, followed by a summary of the subsurface structural features determined from these borings. This information is important to understand because structural features control groundwater flow and contaminant transport at the site. 4.4.4.1 Subsurface Investigations to Characterize Site Structural Features Casmalia Resources Casmalia Resources continuously cored and logged one vertical boring and three inclined borings in 1987, which were drilled up to a depth of approximately 225 feet bgs. The core was oriented. Logging of retrieved core included measuring fracture orientation, depths, attitude (strike and dip), widths, and infilling material type. Video logs and borehole geophysical logs were run, including natural gamma-ray and induction logs.


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Casmalia Resources performed a detailed geologic investigation of the facility and surrounding area as a part of the GSCA (Woodward-Clyde Consultants 1988b). This work included excavation, cleaning, geologic logging, and photo and videotape documentation of 6,800 feet of exploratory cuts and trenches on and adjacent (i.e., within 200 feet) to the facility to locate and characterize bedrock faults, shears, and fractures. The trenches included two north-south side-hill cuts at RCRA Canyon totaling 900 and 1,060 feet, respectively. Casmalia Steering Committee The CSC cored and logged boreholes for 16 piezometers (RGPZ series) in 2000 as part of the RGMEW. These borings were drilled up to approximately 250 feet bgs. The core was not oriented. Logging of retrieved core included measuring fracture depths, dip, and infilling material type. Downhole video logs and borehole geophysical logs were run that included gamma logs, e-logs, and acoustic logs (Harding ESE 2001). The CSC cored and logged boreholes RISB-1 and RISB-2, and RI monitoring wells and piezometers installed using air rotary drilling from 2004 through 2006. These borings were drilled up to approximately 250 feet bgs. The core was not oriented. Logging of retrieved core included measuring fracture depths, dip, and infilling material type. Downhole video logs were run for most borings. Borehole televiewer logs were run for select borings, and gamma logs were also run on deeper boreholes. The CSC also completed a geologic assessment of the RCRA Canyon side hill cuts originally excavated and logged by Casmalia Resources as part of the GSCA. The assessment was performed during September 2004 as part of the RI to confirm and field verify the previous data collected by Casmalia Resources, and integrate these data into the understanding of site structural features. 4.4.4.2 Bedding The Todos Santos Formation (unweathered claystone) is massive to faintly bedded, and is characterized by low-dipping (3 to 20 degrees) to essentially flat bedding planes with variable strike directions. In general, bedding inclinations are steepest in the southern and western areas (5 to 20 degrees) and decrease to the north (3 to 5 degrees). Regional geologic mapping depicts the San Antonio Syncline roughly paralleling the southwest boundary of the site, and the Casmalia Anticline trending northwest toward the site (Figure 4-4). Bedding plane attitudes do not support the presence of either structure in the near-surface beneath the site; however, the structures may be relatively deep, or located adjacent to the site. Stratigraphic correlations based on gamma ray signatures suggest that the site is underlain by broad undulations or low-amplitude flexures with a maximum dip of 3 degrees (Section 5.3.2, Page 5-28, Figure 5.1-1, Woodward-Clyde Consultants 1988a). Strike of the weathered and unweathered claystone low-angle beds is variable; the weathered claystone beddings exhibit a mean dip direction to the south-southwest, while the unweathered claystone bedding dips predominantly to the northeast at the dip angles noted above. By the very nature of the weathered claystone matrix, groundwater flow through “bedding planes” is likely to occur. However, groundwater flow through bedding planes in the unweathered claystone is not likely; within this unit, primary bedding is described as lamina, indicating primary bedding planes have not been buckled to create flowpaths. Further, downhole video logging of numerous boreholes drilled by the CSC and by Casmalia Resources


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show that where water enters the boreholes, it is generally associated with fracturing and not primary stratigraphic features. 4.4.4.3 Faults Faults and shear zones were characterized through a series of investigations including aerial reconnaissance of lineaments and field verification of identified lineaments, and excavation and logging of 6,800 feet of cuts and trenches. Based on these investigations, numerous minor, discontinuous faults and shear zones have been mapped in surface exposures and excavations at the site. Stratigraphic displacements ranging from 0.1 to 5 feet have been observed, although the faults are typically short and cannot be traced laterally for more than a few tens of feet. Evaluation of Quaternary deposits, surface geomorphic expressions, and comparison of the local fault orientations to the regional tectonic stress regime suggest that no faults within 200 feet of the site have been active in Holocene time (Section 5.3.3, Page 5-29, Woodward-Clyde Consultants 1988a). 4.4.4.4 Lineaments Lineament analyses identified four major and numerous minor lineaments within the vicinity of the site. Major lineaments include Casmalia Creek and the A-, B-, and C-Drainage areas. No offset strata were observed in Casmalia Creek; this lineament is interpreted to be the result of differential erosion. The A-, B-, and C-Drainage lineaments, and some of the numerous small discontinuous lineaments, are similar in orientation to the trends of faults and fractures mapped at the site. No major lineaments and no features exhibiting Holocene movement are located within a 200-foot radius of the site (Section 5.3.3, Page 5-32, Woodward-Clyde Consultants 1988a). 4.4.4.5 Fractures As summarized above, analysis of fractures and fracture patterns in the Todos Santos claystone at the site has been conducted as a part of the RI studies, as well as during several prior Casmalia Resources site investigations. Early investigations by Woodward-Clyde Consultants and Canonie Environmental included surface mapping of outcrops in RCRA Canyon and across the site, as well as the logging of fractures observed in core from both vertical and inclined borings (CB-4, CB-6I, CB-7I). The CSC obtained additional fracture data from core collected during borings and well installations and borehole geophysics performed as components of the RGMEW and the RI. Further, the CSC performed a literature and field review of the RCRA Canyon outcrop assessment performed by Woodward-Clyde Consultants, as a specific task of the RI, as is documented in Appendix H of the RI Report (CSC 2011). During the early studies, surface mapping was used to characterize fractures in the weathered claystone. Core from borings was used to characterize fractures in the unweathered claystone, as surface exposures of the unit were not available. Fracture apertures were measured in core samples using a feeler gauge. Disturbed core may have biased the measured apertures, and in-situ aperture sizes are likely smaller than those measured ex-situ due to the release of compressive stress and disturbance during drilling and measurement. Fracture orientations were plotted on stereographic projections and Rose diagrams (HSCER Figures 5.3-1 and 5.3-2 [weathered] and 5.3-3 and 5.3-4 [unweathered]) to evaluate trend frequencies and to compare trends in the weathered and unweathered claystone. The cumulative number of fractures versus depth for the inclined borings was also plotted and presented as HSCER Figure 5.3-8 (Woodward-Clyde Consultants 1988a). From that data it was concluded:


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The weathered claystone is more pervasively fractured than the unweathered claystone; The predominant fractures in the weathered claystone have high angle dips (greater

than 60 degrees), the strikes of which most frequently trend east-northeast and west-northwest;

Within the unweathered claystone, there is a wide range of fracture orientation and no discernible predominant orientation of fractures;

Some common fracture orientations occur in both the weathered and unweathered claystone, typically northeast- to east-northeast striking, near vertical fractures;

The density and degree of fracturing within the unweathered claystone vary between both distant and adjacent sampling locations;

The frequency of occurrence of fractures with apertures greater than 0.1 millimeters (mm) decreases at depths 100 feet below the weathered/unweathered claystone contact;

Clay constitutes the dominant mineral type of fracture infilling at depths 40 feet below the weathered/unweathered claystone contact; and

Video logging of boreholes show that where water enters the borehole, it is generally associated with fracturing and not stratigraphic features. Observations for boreholes drilled by the CSC are provided on geologic logs in Appendix E of the RI Report for the RI boreholes (CSC 2011), and in the Well Inventory Report (MACTEC, 2006) for earlier boreholes drilled by the CSC. Observations for boreholes drilled by Casmalia Resources are provided in the HSCER and HSIR (Woodward-Clyde Consultants 1988a, and Woodward-Clyde Consultants and Canonie Environmental 1989).

Observations of fracture density and size from these earlier studies were generally confirmed during coring activities completed in 2000 (Harding ESE 2001). Plots of the cumulative number of fractures against depth within borings completed during the 2000 drilling program were first presented in the RI/FS Work Plan and are republished in Appendix E of the RI Report as Figures E-23 through E-26 (CSC 2004 and 2011). The total depths investigated vary by boring, as do the explored depths within individual geologic units (i.e., weathered and unweathered claystone), which makes direct comparisons of fracture density versus depth difficult. However, the figures clearly illustrate that the degree and density of fracturing vary widely between locations. The figures also illustrate that while the frequency of fractures decreases with depth in some borings, other borings contain numerous fractures to the total depth explored (250 feet bgs maximum). During the Phase I and Phase II RI drilling investigations from 2004 to 2006, planar attitudes of bedding and fracture features noted in the core samples, geophysical logs, and optical televiewer images were analyzed to determine their orientations. Initial structural analyses of bedding and fractures were performed at eight locations using the geophysical logs and televiewer surveys. Fracture and bedding orientations were plotted on Schmidt lower hemisphere stereographic projections and Rose diagrams to evaluate trends. All fractures and dip orientations identified on the televiewer logs are summarized in Appendix E of the RI Report, as summarized above. After review of the initial analyses, additional Schmidt and Rose diagrams were created from the bedding and fracture data for the purpose of evaluating the orientations collectively, as well as by depth relative to the geologic unit. The bedding and structure data sets were also grouped by depth below the weathered and unweathered claystone contact. To evaluate fracture frequency, the cumulative numbers of fractures from the televiewer logs for each deep boring were plotted against depth for each borehole. The results


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of the RI structural analysis are in agreement with those of previous studies. The results show the following:

Significantly more fractures were observed in the weathered claystone than in the unweathered claystone. Plots of the cumulative number of fractures against depth within borings completed during the 2004 to 2006 RI drilling program are consistent with the findings of the 1987 (Casmalia Resources) and 2000 (CSC) drilling programs. The degree and density of fracturing vary widely between locations.

For the unweathered claystone, while the frequency of fractures decreased with depth in some borings, other borings contain fractures to the total depth explored (250 feet bgs maximum depth drilled).

The continuity between fractures may limit the extent of potential fluid pathways on a site-wide scale while the continuity on a local scale is sufficient to transmit groundwater, especially where higher groundwater gradients exist to drive groundwater through the generally lower permeability fractures in the unweathered claystone. These areas of higher gradients occur primarily in the upland areas, such between the North Ridge and the PSCT.

Review of the stereographic projections indicates fractures generally tend to be either subvertical or subhorizontal (though some or many of the features identified as subhorizontal fractures are likely bedding planes). Within the unweathered claystone, the subvertical fractures tend to strike northeast and dip to the northwest and southeast, but with some variability. The results of the additional structural analysis completed during RI borehole investigations are detailed in Figures E-53 through E-73 in Appendix E of the RI Report (CSC 2011). As noted above, the CSC conducted a review of geologic conditions in the RCRA Canyon Area as part of the RI field program. Areas of exposed bedrock were examined and geologic data collected as part of this effort. Observations and field data collected during this assessment indicate that the geologic units and nature and orientation of structural features exposed in the RCRA Canyon are consistent with those reported during prior studies completed at the site. The findings of RCRA Canyon Area geologic reconnaissance are detailed in Appendix H of the RI Report (CSC 2011). As noted above, the CSC performed optical televiewer video surveys to assess the dip and dip-direction of fractures and bedding planes at the site. Optical logging was performed in 8 boreholes (RGPZ-10B-2, RIPZ-10D, RG-11B2, RIPZ-15, RIPZ-16, RIPZ-17, RI-SB-1, and RI-SB-2); views of the weathered claystone were performed in boreholes RGPZ-10B-2, RIPZ-10D, RG-11B2, RIPZ-17, and RI-SB-1, the unweathered claystone was viewed in all boreholes. Detailed findings of the optical logging work are presented in the RI Report, including RI Report Table 4-3, RI Report Figures 4-12 and 4-13, and Appendix E, Table E-9 of the RI Report (CSC 2011). The salient results of these televiewer surveys are summarized below. Fractures within the weathered claystone display highly variable dip within boreholes, with the dip generally less than 30°(however, the dips observed within boreholes displayed higher angles as the borehole deepened, e.g., RG-11B2. The dip-direction of weathered claystone fractures is also highly variable. Within this unit, no “bedding planes” were observed, indicating that structural features observed within the weathered claystone are predominantly the result of weathering effects which have overprinted any pre-existing structural grain.


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Within the unweathered claystone, fractures are observed to display primarily relatively steep dips (predominantly between 50°and 90° with a significant population of fractures also displaying less steep dips (predominantly between 0°and 20°. Fracture dips between these two populations also occur (between 20°and 50°. Dip directions are also variable, but predominant dip-directions occur to the northwest, northeast, and southeast for the more steeply dipping fractures (greater than 20° and occur to the northeast and east for the less steeply dipping fractures (less than 20°. The dip direction of the more steeply dipping fractures is variable and not uniformly consistent with the regional strike, indicating that the steeper fractures observed at the site are secondary features. The dip direction of the less steep fractures observed in several boreholes is more consistent with the bedding dip directions. The shallow dip directions observed in borehole RI-SB-2 (at depth between ~60 to 150 ft bgs) are towards the east-south east and these shallower-dipping fractures may be indicative of a primary fracture, and was the interval in which DNAPL was observed within the borehole. As noted above, bedding planes were a predominantly observed feature within the unweathered claystone, with bedding planes generally observed at less than 20 which are consistent with surface observations. With regard to fractures acting as DNAPL pathways within the unweathered claystone, the fractures predominantly display steep dip angles (greater than 50° but also display a population of less steep angles (less than 20°. The greater frequency of more steeply dipping fractures would favor DNAPL flow to greater depth; however, the presence of the less steeply dipping fractures makes horizontal flow a potentially significant component of flow. On a site-wide basis, this general distribution of fracture orientations makes the likelihood relatively low that DNAPL will be transmitted to the surface because DNAPL will move downward into the more steeply dipping fractures as it migrates laterally along the more shallow dipping fractures. Given the thickness of the unweathered claystone (>1,000 feet), the generally small aperture of fractures, and the lack of interconnectivity between fractures on a site-wide scale, significant fluid movement of DNAPL to shallower intervals above the unweathered claystone at any appreciable rate is unlikely. Within the unweathered claystone, fractures are observed to decrease with depth in some boreholes while they are present throughout the depth of other boreholes. Therefore, the depth to which DNAPL migration occurs is not known. At depth, it is likely that fractures ultimately lead to dead-ends. As such, attempts to delineate DNAPL within such an environment would prove futile and could be counter-productive, as the installation of boreholes may lead to creation of additional flowpaths. Regional Data An independent study entitled Relationships Among In-Situ Stress, Fractures and Faults, and Fluid Flow: Monterey Formation, Santa Maria Basin, California, (Finkbeiner et al. 1997) reviewed the televiewer logs of four oil wells in the vicinity of the site. The study, though focused on the oil-rich Monterey Formation, included the Sisquoc Formation, of which the Todos Santos Sandstone is a member. “Well D” in the Orcutt field is of particular interest due to its proximity, east of the site. By analyzing stress-induced well-bore “breakout,” the ambient stress field at each well was determined in order to compare the mean horizontal stress direction against fracture orientation. It was noted that the apparent apertures of the fractures observed in the televiewer log had been amplified by spalling as a result of drilling; a caveat worth noting as regards the site-specific investigations. It is not known whether “spalling” effects affected the CSC’s data collection program.


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In contrast to relatively uniform horizontal stress directions, fracture orientation, dip, and frequency were determined to vary between locations and within each well. Fractures within the Sisquoc in Well D were characterized as dipping between 30 and 60 degrees in the southeasterly direction. Differential fracturing within a single well was determined to be lithology dependent, as soft beds such as mudstones (claystones) are characterized by widely spaced shear fractures, whereas harder, less ductile beds such as cherts and dolomites are characterized by an abundance of joints. The lack of evidence for the systematic development of stress-induced fracture sets within the relatively ductile claystone of the Monterey and Sisquoc formations in the region suggest that regional wide-scale interconnectivity of fractures (within the unweathered claystone) at the site may be unlikely, given the observed variation in site fracture orientation. Although regional data for the Sisquoc Formation suggest that regional wide-scale interconnectivity of fractures within the unweathered claystone at the site may be unlikely, the interconnectivity of fractures on a site-wide and more local scale is uncertain. The degree of fracture interconnectivity on a site-specific scale will govern to a large degree the transport of both dissolved-phase liquids and DNAPL away from contaminant source areas, as demonstrated by the nature and extent of contamination identified at the site. However, the movement of dissolved-phase liquids and DNAPL beyond the site boundaries now appears limited due to the operation of the groundwater control features. The primary transport mechanism into and through the unweathered claystone is fracture flow. A total of 408 boreholes have tested over 25,000 feet of unweathered claystone material; correlation of fractures between adjacent boreholes is difficult, indicating that there is uncertainty in assessing the interconnectivity of fractures throughout the site. Although the likelihood of an interconnected fracture system being present within the unweathered claystone on a site-wide scale is low, the interconnectivity of fractures on a local scale is more likely. One example occurs in the Central Drainage Area where DNAPL transport along fractures is indicated between either the P/S Landfill or Sump 9B southward to boreholes RGPZ-6C/6D and RGPZ-7C/7D. Within this portion of the site, both dissolved-phase and DNAPL groundwater contamination occurs more than 100-feet below the contact between the weathered claystone and unweathered claystone. Another example is the presence of dissolved-phase VOCs detected in RIPZ-16 in the Burial Trench Area. RIPZ-16 is screened approximately 100 feet below this contact. The primary transport mechanism for contaminants to reach these wells in the Central Drainage Area and Burial Trench Area is through interconnected fractures within the unweathered claystone. The depth to which fracture flow may occur is difficult to explore due to the high angle dip associated with fractures; the one example where fracture flow is noted (above), the fractures are measured to have relatively shallow dips at approximately 7 to 24 degrees. Even though site topography is steep, fractures containing NAPL have not been observed to daylight, and several historical surface seeps have stopped flowing since capping and groundwater flow control measures have been instituted at the site. 4.5 Hydrogeology 4.5.1 Regional and Site Hydrogeologic Setting The site is located in the Casmalia Hills, a topographic high separating two groundwater basins. The Santa Maria Valley groundwater basin occurs to the north and east, and the San Antonio Valley Creek groundwater basin lies to the south (Figure 4-6). The site lies between these two


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basins but drains to the Shuman Creek watershed, and is formally associated with the San Antonio hydrologic unit. The southern boundary of the Santa Maria Valley groundwater basin lies approximately 2.5 miles north of the Site. Consolidated non-water-bearing Tertiary rocks form the boundaries of the basin (Worts, 1951), which isolate the basin from the Casmalia Hills. Groundwater flow in the Santa Maria Valley basin follows the surface topography. At the southern boundary of the basin near the Casmalia Hills, groundwater flow is to the north away from the Site, and then westward to the Pacific Ocean. The northern boundary of the site is approximately 2.5 miles from the San Antonio Valley Creek groundwater basin. This groundwater basin also has consolidated non-water-bearing Tertiary rocks that form its boundaries; the groundwater flow follows surface topography. At the northern boundary of the basin, groundwater flows southward away from the Casmalia Hills, then westward to the Pacific Ocean. The Shuman Creek watershed drains the Casmalia Hills in the vicinity of the site and mostly is isolated by hill top ridges from the adjacent Santa Maria Valley and the San Antonio Valley Creek groundwater basins. The site is underlain by the Tertiary-age Todos Santos Member of the Sisquoc Formation. These Tertiary marine rocks are generally considered non-water-bearing compared to the unconsolidated sediments found within the nearby alluvial valleys and basins. Groundwater flow beneath the site generally follows topography; groundwater flows south offsite, then west via Shuman Creek towards the Pacific Ocean. 4.5.1.1 Water Classification The RWQCB has identified several beneficial uses for the surface waters (and therefore, associated groundwater) of the Shuman and Casmalia Creek watersheds in the San Antonio hydrologic unit. The beneficial uses include agricultural, municipal, and recreational use, as well as supporting various fresh, warm water wildlife habitats (RWQCB, 1994). 4.5.1.2 Inventory of Water Wells within a 3-mile Radius The most current well inventory study was conducted as part of the RI, and identified 38 water wells within a 3-mile radius of the site (RI Report, Appendix N, Figure N-1, CSC 2011). Based on well permits from 1926 to present, and contact with current property owners, the following data was derived for well status and usage. Agricultural and irrigation uses predominate (21 wells), followed by domestic (3 wells); the remaining 14 wells include two industrial wells, two test wells, and ten wells of unknown use and status. 4.5.2 Site Hydrogeologic Physical Characteristics Surface and subsurface site physical hydrogeologic characteristics influence groundwater flow. In addition to natural physical features, physical features constructed as part of historical waste disposal and cleanup activities conducted by Casmalia Resources, and more recent corrective actions performed by the CSC also influence groundwater flow. The hydrogeologic characteristics of both the natural and constructed conditions are summarized below within the geologic framework presented above. Casmalia Resources and the CSC investigated the site hydrogeologic conditions through numerous field investigations. Casmalia Resources drilled several hundred borings, installed


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several hundred groundwater monitoring wells and piezometers, and performed other investigation work to assess the site’s geology, hydrogeology, and nature and extent of contamination. The results of this work by Casmalia Resources are presented in many previous reports, including the HAR, HSCER and HSIR. The CSC supplemented this historical work with additional site-specific work performed as part of the RGMEW and RI. The CSC is currently performing semiannual, monthly, and continuous monitoring of selected wells as part of the RGMEW. Figure 4-7 illustrates the location of all current site wells and piezometers. The wells and piezometers shown on Figure 4-7 include those still in existence installed by Casmalia Resources in the 1970s and 1980s, those installed by the CSC from 1998 through 2006 as part of the RGMEW, and those installed by the CSC from 2004 through 2007 as part of the RI. The CSC’s Final Well Inventory Report (MACTEC 2006) is a stand-alone report that documents the condition and construction of the current monitoring well network, except the newer RI wells and piezometers. RI Report Appendix E provides as-built information and a table summarizing the construction details for the newer RI wells and piezometers installed after the 2006 Final Well Inventory Report (CSC 2011). 4.5.2.1 Vadose Zone The vadose zone in the vicinity of the site occurs in both the weathered and unweathered claystone, and includes local alluvium, colluvium, and fill deposits. The vadose zone is laterally extensive with maximum thickness of greater than 150 feet in the north and northeastern portions of the site. The thickness decreases to less than 30 feet in the south and in RCRA Canyon. Infiltration and flow characteristics of the vadose zone were investigated in the field at two locations at the site: one located in the weathered claystone, and the other located in the transition into the unweathered claystone (Woodward-Clyde Consultants and Canonie Environmental 1989). The study reported that water, when ponded, will saturate and flow along the fractures beneath the test plots within the vadose zone in the weathered claystone. The infiltration rate was 5.4x10-5 cm/sec, approximating the effective saturated hydraulic conductivity. The infiltration rate was approximated at 3.6x10-5 cm/sec for the transition to the unweathered zone. 4.5.2.2 Site Hydrostratigraphic Units The Todos Santos Member of the Sisquoc Formation (Todos Santos) is laterally and vertically extensive across the site. As described above, the near surface portion of the unit is extensively weathered. The near surface portion of this unit is observed to have a distinctly different hydrologic and chemical character (primarily from the differing types of materials found within fractures) as compared to the deeper unweathered unit. Based on the degree of weathering, two hydrostratigraphic units (HSUs), an Upper and Lower HSU, have been informally defined for the site. The Upper HSU consists of the weathered and transition zone claystone; the Lower HSU consists of the unweathered claystone. Overlying the weathered claystone are discontinuous surficial clayey soils, colluvium, alluvium, and fill. These materials are hydrogeologically distinct from the claystone and are not included in the Upper HSU as these surficial fill materials are discontinuous across the site.


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Previous reports suggested perched water may exist in the vadose zone. Perched water was identified in the northern portion of the site, generally along the northeast ridge top within the weathered bedrock zone. Perched water is associated with hydraulic conductivity differences at contacts between fill/Upper HSU, Upper HSU/Lower HSU, and geologic features such as fractures and bedding planes. Perched water was laterally discontinuous over distances of several feet to several tens of feet and was vertically discontinuous over distances of less than an inch to several feet In RCRA Canyon, local seeps occur. This moisture is associated with local geologic features that appear to be above the water table (Figure 4-8). During the wet season, however, the seeps appear to correspond with the water table, based on water-level measurements collected at Well SW-46. Surficial Material Surficial deposits at the site include clayey soils, colluvium, alluvium, and artificial fill ranging from a few feet to up to 50 feet thick. These near-surface deposits have been reworked over a majority of the site. The alluvium generally consists of silty clay, and is confined to drainages, where it has been observed on historical photographs. Fill consists of predominantly disturbed claystone with varying amounts of admixed alluvium. The thickest deposits are found in the central portion of the site where extensive excavation and backfilling occurred. The surficial deposits are in hydraulic communication with the underlying weathered claystone. Based on aquifer testing, these deposits are more permeable than the claystone, with surficial deposit hydraulic conductivities that range from 3.3 x 10-3 to 8.9 x 10-4 cm/sec (Section 7.2, Page 7-7, Woodward-Clyde Consultants 1988a). Because these deposits are generally unsaturated, they are of lesser importance to the site-wide groundwater flow. However, due to their higher conductivities, when saturated, they could provide important potential contaminant migration pathways. Upper Hydrostratigraphic Unit The Upper HSU consists of the weathered and highly fractured claystone. The thin, approximately 2- to 5-foot transition zone between the weathered and unweathered claystone is included in the Upper HSU. The Upper HSU is found beneath 90 percent of the site and ranges in thickness from approximately 30 to 60 feet. The Upper HSU is generally thicker in the higher topographic areas, although the unit is mostly to completely unsaturated in some of the topographically higher areas of the site. The Upper HSU is poorly transmissive and the HSIR cites a geometric mean hydraulic conductivity of 6.8 x 10-5 cm/sec. Lower Hydrostratigraphic Unit The Lower HSU consists of the unweathered claystone at the site. The top of the unit generally follows the surface topography. The unit is estimated to be approximately 900 to 1,300 feet thick and is underlain by Monterey shale. The Lower HSU has a much lower fracture density compared to that of the Upper HSU. Although groundwater flow occurs through fractures, most groundwater in this unit is in the matrix porosity. The Lower HSU is expected to approximate a porous medium on a large scale (hundreds of feet or more). This unit is less transmissive than the Upper HSU, and the HSIR cites a geometric mean hydraulic conductivity of 1.3 x 10-6 cm/sec. The geometric mean value of the matrix hydraulic conductivity from laboratory tests on samples of unfractured Lower HSU material (claystone matrix) was 8 x 10-8 cm/sec.


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Groundwater Control Features Several groundwater control features constructed by Casmalia Resources and the CSC, and currently being operated by the CSC, influence groundwater flow and contaminant transport at the site. These include subsurface clay barriers, extraction facilities, the current site ponds, and the landfills. These features are described in Section 2, and include the following: Subsurface Clay Barriers and Liquids Extraction Facilities

PCB Landfill clay barrier. P/S Landfill clay barrier and Gallery Well extraction well. Sump 9B extraction well Road Sump extraction sump PSCT extraction wells Former Pond 20 clay barrier RCRA Canyon clay barrier Clay barriers and associated extraction facilities at the B- and C-Drainages PCT extraction wells at the A-, B-, and C-Drainages

Site Ponds Stormwater Runoff Ponds

RCF Pond A-Series Pond Pond 13 Central Drainage Area collection basin

Treated Liquids Impoundments

Pond A-5 Pond 18

Landfills

P/S Landfill Metals Landfill Caustics/Cyanides Landfill Acids Landfill PCB Landfill

Site landfills include the four landfills capped by the CSC under the Consent Decree between 1999 and 2002 (P/S, Metals, Caustics/Cyanides, and Acids landfills) and a fifth landfill that currently has an interim soil cover (PCB Landfill). The former RCRA Landfill no longer exists. The P/S Landfill and EE/CA Area (Metals, Caustics/Cyanide, and Acids landfills) cap systems include (bottom to top): low permeability subgrade layer, 60 mil HDPE geomembrane barrier layer, geocomposite drainage layer, and a 2-foot thick vegetative soil layer. These caps have been effective at reducing rainfall infiltration, lowering liquid levels within and in the immediate vicinity of the landfills, and reducing liquids extraction rates from the P/S Landfill.


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4.5.2.3 Hydraulic Conductivity Testing Water Bearing Units Casmalia Resources conducted numerous historical field and laboratory tests to investigate the hydraulic properties of the water-bearing units at the site. The results are discussed in more detail in the RI/FS Work Plan, and RI report (CSC 2004 and 2011, respectively). The results of the field hydraulic conductivity investigations can be summarized as follows:

The hydraulic conductivity values are log-normally distributed; The highest hydraulic conductivity occurs in the fill and alluvial material, followed by the

weathered claystone and the unweathered claystone; and There are no site-wide or areal trends in hydraulic conductivity within the geologic units.

The apparent anisotropy observed in the laboratory data may be due to the limitations of laboratory methods for determining horizontal hydraulic conductivity using core samples.

Generally, the results of the investigations provided consistent estimates for the hydraulic conductivity of approximately 10-5 cm/sec in the Upper HSU and approximately 10-6 cm/sec in the Lower HSU. Evidence from various investigations indicates that fractures control hydraulic conductivity in the Upper and Lower HSUs. However, parameters such as fracture length, aperture, orientation, degree and nature of infilling, and interconnectivity are highly variable. This variability is enough to mask the expected general correlation of fracture density with higher hydraulic conductivity. Figure 4-9 presents a statistical summary of hydraulic conductivity results for both the Upper and Lower HSUs. Clay Barriers The clay barrier located at the toe of the P/S Landfill was constructed in 1981-1982 and is approximately 200-feet long, 13-feet thick and up to 50 feet deep, extending a minimum of 4feet into the underlying claystone. The measured hydraulic conductivity of three samples collected and tested by the CSC from the P/S Landfill clay barrier range from 2.57 x 10-8 to 4.3 x 10-8 cm/sec, which is consistent with an engineered compacted fill of low permeability (RI Report, Appendix J, CSC 2011). 4.5.2.4 Porosity The claystone units at the site are characterized by two types of porosities: the fracture porosity and the matrix (or bulk) porosity. The fracture porosity in the Upper HSU was estimated as ranging from 6 percent to 25 percent based on data from infiltration test results. However, this value appears to be too high to represent fracture porosity based on the observed fracture density. Comparison with the literature for fracture porosities in clay-rich sedimentary formations also indicates that the true fracture porosity may be less than 1 percent (Freeze and Cherry, 1979). Additionally, the fracture porosity estimated by the infiltration test is much higher than fracture porosities estimated using field hydraulic conductivity data. Mean total matrix porosities were 44 percent and 48 percent in the Lower and Upper HSUs, respectively. These values appear reasonable given the clayey nature of the HSUs.


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Comparable values established in the literature range from 30 to 70 percent for clayey deposits and 5 to 25 percent for sedimentary rocks (Freeze and Cherry 1979). 4.5.3 Site Groundwater Flow Conditions Groundwater flow at the site is influenced by rainfall infiltration and surface water recharge to the groundwater system, the physical characteristics of the subsurface materials through which groundwater flows, and groundwater discharge through evapotranspiration, groundwater extraction or direct discharge as seeps, streams, or ponds. Casmalia Resources and the CSC investigated site groundwater flow conditions through numerous field investigations and numerical groundwater flow modeling. Casmalia Resources installed several hundred groundwater monitoring wells and piezometers, and performed other investigation work to assess the site’s groundwater flow. Moreover, the CSC built on the historical work completed by Casmalia Resources with additional site-specific work performed as part of the RGMEW and RI. The CSC is currently performing semiannual, quarterly, and monthly water and NAPL level monitoring as part of the RGMEW. As part of the RI, the CSC installed additional piezometers and groundwater monitoring wells, collected additional water and NAPL level data, and conducted site-wide three-dimensional groundwater flow modeling. The modeling was performed to integrate the large amount of hydrogeologic data to further evaluate the site-wide and local flow conditions, and the hydraulic effectiveness of the current liquid extraction systems. The water table contour map in Figure 4-10 and hydrogeologic cross section in Figure 4-11 illustrate typical horizontal and vertical groundwater flow patterns and gradients at the site. These figures were constructed based on December 2008 groundwater monitoring data. 4.5.3.1 Groundwater Flow Model The CSC developed a three-dimensional, numerical groundwater flow model for the site to assist in the characterization of current groundwater flow conditions and to evaluate the potential effectiveness of alternative corrective measures as part of the Feasibility Study (Figure 4-12). As specified in the RI/FS Work Plan (CSC 2004), the United States Geologic Survey (USGS) finite-difference groundwater flow model code MODFLOW-2000 and the particle tracking code MODPATH were used to simulate three-dimensional groundwater flow at the site. The flow model was developed using site-specific geologic and hydrologic data, and calibrated to groundwater flow conditions at the site. Seven transmissive layers were used in the model to simulate the vertical and horizontal groundwater flow within and between the Upper and Lower HSUs (Figure 4-13). The model layer geometries were developed on the basis of the Upper/Lower HSU contact surface. Model layers 1 through 3 were used to simulate the Upper HSU, with the base of model layer 3 corresponding to the Upper/Lower HSU contact surface, and model layers 4 through 7 were used to simulate the Lower HSU. Detailed results of the groundwater flow model are presented in Appendix F of the RI Report (CSC 2011). Particle flow maps presenting simplified groundwater flow directions for the Upper and Lower HSUs are presented in Figures 4-14 through 4-16. Figures 4-14 and 4-15 present particle flow directions in the Upper HSU during dry conditions in 2004 and wet conditions in 2001, respectively, and Figure 4-16 presents particle flow directions in the Lower HSU during dry conditions in 2004.


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4.5.3.2 Groundwater and Surface Water Features and Flow Conditions Groundwater beneath the site occurs primarily as surficial underflow and has historically fed Casmalia and Shuman Creeks through the A-, B-, and C-Drainages. The natural groundwater flow system is largely governed by topography and the HSU contact surface, as illustrated by the groundwater elevation contours on the Water Table Contour Map (Figure 4-10), site-wide Cross-Section D-D’ (Figure 4-11), and groundwater particle flow maps (Figures 4-14 through 4-16). Shallow groundwater flow is now actively managed and contained by several engineered control features such as clay barriers, landfill caps, rainwater and treated liquid storage ponds, and multiple liquid extraction facilities as noted above. Liquid extraction facilities include the Gallery Well, Sump 9B, Road Sump, the PSCT (and extraction points PSCT-1, -2, -3, and -4), and PCTs (PCT-A, -B, and -C). Overall, the groundwater flow system has remained essentially constant between 1997 and 2009. Seasonally, except for the capped P/S Landfill and EE/CA Areas, groundwater elevations increase in response to winter rainfall and then decrease during the remaining summer dry season. Over the period of RGMEW monitoring, groundwater elevations have seen a net decrease; this is largely due to the effects of capping landfill cells and groundwater capture by the PSCTs. Although groundwater elevations change in response to climatic conditions, the overall site-wide lateral groundwater flow directions do not appear to be affected significantly by seasonal recharge. Natural groundwater storage is limited, though it has been augmented by the addition of refuse and fill material to landfill cells constructed within historical natural drainage features. Changes in groundwater storage over time are directly related to precipitation. There has been a net decrease in storage over time that is the result of a combination of recent dry years and decreased infiltration due to the capping of landfill cells and the management and collection of surface runoff between the capped areas (RI Report, Appendix F, CSC 2011). As described above, divergent flow from the North Ridge results from rainfall recharge and the three dimensional hydraulic conductivity distribution in the subsurface. The CSC constructed the groundwater flow model with a “no flow” boundary along the North Ridge to simulate this feature. Using this boundary condition, the model head solutions simulate divergent groundwater flow from the North Ridge northward to the North Drainage and southward through Zone 1. Using this boundary condition, the groundwater flow conditions in the Upper HSU and Lower HSU simulated by the model are consistent with the site-wide groundwater flow conditions described above. Site-wide Groundwater Flow Groundwater at the site exists primarily as surficial underflow and has been demonstrated to closely follow surface topography (RI Report, Section 4.5.3.1, CSC 2011). Groundwater flow is structurally controlled by the contact separating the more permeable Upper HSU from the less permeable Lower HSU. North Ridge The North Ridge is a natural recharge area and groundwater flow divide. Rainfall infiltrates into the subsurface along the North Ridge and moves vertically downward and laterally outward either northward toward the North Drainage or southward across the Zone 1 site area (Figures 4-10, 4-14, and 4-15). Groundwater also recharges the North Ridge area in the site vicinity from lateral groundwater recharge (inflow) from the west along the ridge. Although the hydraulic


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conductivity is relatively low, infiltrating groundwater moves downward in response to the strong downward vertical gradients in this area. The groundwater elevations have remained steady between 1997 and 2009, except for seasonal variations in response to rainfall patterns. Horizontally, the location of the divide is conceptually along the North Ridge, but its exact location has not been determined. Actual infiltration rates, HSU contact elevation, and subsurface hydraulic conductivity distribution influence the actual divide location. RCRA Canyon Area From the North Ridge above RCRA Canyon, groundwater moving southward will preferentially move through the more permeable Upper HSU and converge into RCRA Canyon (Figures 4-10, 4-14, and 4-15). Vertically downward gradients occur in upper RCRA Canyon, and vertically upward gradients locally occur in lower RCRA Canyon to the south. In response to these local upward gradients, some groundwater monitoring wells in RCRA Canyon are under artesian conditions (i.e., the water level in the well is above ground surface). Groundwater seeps have been historically observed in this area in response to seasonal rainfall and local upward gradients, including the RCRA Canyon Seep and the A-5/A-Series seep (Figure 4-8). Groundwater will flow southward along RCRA Canyon and discharge to Pond A-5. Groundwater elevations have remained steady between 1997 and 2009, except for variations in response to rainfall patterns. PCB Landfill and Burial Trench Area From the North Ridge above the PCB Landfill, groundwater moving southward will preferentially move through the more permeable Upper HSU, PCB Landfill materials, and Burial Trench Area towards the PSCT in the vicinity extraction well PSCT-4 (Figures 4-10, 4-14, and 4-15). Some groundwater from the PCB Landfill and eastern part of the Burial Trench Area may move towards the P/S Landfill. Strong vertically downward groundwater gradients occur throughout the PCB Landfill and Burial Trench Area. A clay barrier exists at the southern toe of the PCB Landfill. However, this barrier is not significant in affecting horizontal groundwater flow because it does not extend downward from ground surface to the HSU contact. From the Burial Trench Area, groundwater will flow southward toward the PSCT in the area of PSCT-4. Groundwater elevations in the PCB Landfill and Burial Trench Area have remained steady between 1997 and 2009, except for variations in response to rainfall patterns. P/S Landfill, Other Landfills, and Central Drainage Area From the North Ridge above the capped P/S Landfill and the other capped landfills, groundwater moving southward will preferentially move through the more permeable Upper HSU and landfill cells, which follow the original topography of the canyons in which the cells were constructed (Figure 4-10). Some groundwater from the PCB Landfill and eastern part of the Burial Trench Area may move towards the P/S Landfill. Vertically downward groundwater gradients occur at the northern parts of the four capped landfills as the downward gradients propagate southward from the North Ridge. Historically, groundwater level data have indicated that these downward gradients continued to the southern limits of the landfills. Capping of the P/S Landfill in 1999, capping of the EE/CA Area landfills (Metals, Caustic/Cyanide, and Acids) in 2001 and 2002, and subsequent maintenance of this approximately 40 acre contiguous impermeable cap has eliminated most rainfall infiltration. Eliminating infiltration has reduced the magnitude of the downward gradients at the landfills and


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led to an upward vertical gradient at the toe of at least two of the landfills (Metals and Caustic/Cyanide). Groundwater from the P/S Landfill Cap area and EE/CA Area Cap landfills will flow generally southward and converge toward the Central Drainage Area. The reduction in groundwater elevations from capping has reduced the volume of liquids migrating from these landfills relative to historical conditions before these landfills were capped. As an example, since 2002, the annual Gallery Well extraction rate has decreased by greater than 50 percent, and it no longer fluctuates significantly in response to rainfall since placement of the P/S Landfill cap. The vertical groundwater gradients at the P/S Landfill are shown in Cross Section D-D’ for December 2008 data (Figure 4-11). This cross section shows that the strong vertically downward gradients propagate from the North Ridge southward toward the southern half of the landfill. The vertical gradient direction and magnitude at the southern end of the landfill is not known because there are no well clusters screened at different depths to determine actual vertical gradients, as with the other landfills. The regional interpretation in Cross Section D-D’ is that the overall vertical gradient at the south part of the landfill is moderate and slightly downward. A localized upward gradient is shown at the Gallery Well, but this upward gradient is interpretative and not based on actual water level data from wells. Neutral to vertically upward groundwater gradients occur in the Central Drainage Area. Upward gradients within the larger Central Drainage Area are supported by local groundwater extraction at Sump 9B, the Road Sump, and the PSCT (i.e., the extraction from the shallow Upper HSU induces or supports upward gradients from the deeper Lower HSU). Historically, the shallow water table between the P/S Landfill and PSCT-1 would emerge as seeps during winter months when seasonal rainfall recharges and increases the water table elevation. Combined extraction from the PSCT, Sump 9B, and Road Sump facilities eliminates these seeps from forming between the P/S Landfill and PSCT-1. From the Central Drainage Area, groundwater will flow southward toward the PSCT in the area of PSCT-1. Groundwater elevations in the Central Drainage Area have remained steady between 1997 and 2009, except for variations in response to rainfall patterns. Southward flowing groundwater in the Upper HSU is intercepted by the PSCT. Southward flowing groundwater in the Lower HSU passes beneath the PSCT. The rate of groundwater flow underneath the PSCT is very small compared to the flow in the Upper HSU because of the significantly lower hydraulic conductivity of the Lower HSU compared to the Upper HSU. Former Ponds and Pads Area and Surface Water Ponds Groundwater moving southward from RCRA Canyon, southward from the PSCT, and locally derived from infiltrating precipitation will flow southward across the Former Ponds and Pads Area toward the surface water ponds. Under static conditions, the ponds may be a source of recharge to groundwater or act as a groundwater sink and receive base flow, depending on the water level within the ponds relative to the level of the adjacent water table. Surface water from Pond A-5 will seep to the A-Series Pond, while water from Pond 18 will seep into both the A-Series Pond and the RCF. Surface water from the RCF will seep into Pond 13. The A-Series Pond, RCF, and Pond 13 provide a source of recharge for much of the water withdrawn from the extraction wells at PCT-C, PCT-B, and certain parts of PCT-A. The mechanism for the majority of water loss from ponds is through the yearly evaporative cycle.


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Drainages Outside Historical Site Boundary Historically, groundwater naturally exited the site via one of three routes: the A-Drainage, the B-Drainage, and the C-Drainage (Figure 1-1). Today, groundwater extraction from the PCTs at the head of these drainages intercepts groundwater that would normally flow from Zone 1 (within historical site boundary) to Zone 2 (outside historical site boundary) and down these drainages. The natural groundwater flow divide at the northern perimeter of the site historically and currently prevents groundwater from moving from Zone 1 northward into Zone 2 and towards the North Drainage. The A-Drainage conveys water largely from east of the site boundary; however, groundwater flowing through the eastern portion of the site that might naturally travel through the drainage is presently captured by PCT-A. Surface water from the RCF and groundwater from the hill to the south (that separates the A- and B-drainages) likely recharge extraction wells in PCT-B and PCT-C. An upward groundwater gradient exists at the PCT-A area. Moderate vertically downward to upward gradients occur downgradient along the A-Drainage. The B-Drainage was likely the historical outlet for water flowing from the Central Drainage Area prior to modifications performed during past site operations. Currently, groundwater that would naturally flow though the B-Drainage is captured by the PCT-B. Surface water from Pond 13 and groundwater from the two hills to the south (that separate A-, B-, and C-drainages) likely recharge extraction at the PCT-B. An upward gradient exists at the PCT-B extraction well area, and mostly vertically upward gradients occur downgradient along the B-Drainage. The C-Drainage bounds the southwest corner of the site and historically, and presently, drains water that primarily falls outside the western site boundary. Groundwater flowing through the southwestern portion of the site that would naturally flow through the C-Drainage is pumped from the PCT-C. Surface water from the A-Series Pond and groundwater from the hill to the south (that separates the B- and C-Drainages) likely recharge the PCT-C. An upward groundwater gradient exists at the PCT-C extraction well area and mostly vertically upward gradients occur downgradient along the C-Drainage. The North Drainage drains water outside the historical site boundary. As described above, the groundwater flow divide is mapped conceptually along the North Ridge, but its exact location is unknown. Infiltration rates, HSU contact elevation, and subsurface hydraulic conductivity distribution will influence the actual divide location. Most, if not all, of the Zone 1 groundwater flows south from the divide across the Zone 1 area away from the North Drainage. North of the divide, however, groundwater moves northward toward the North Drainage (Figures 4-10, 4-14, and 4-15). Slight vertically upward gradients occur at the toe of the slope of the North Drainage perennial creek (unnamed drainage). Near the site, neutral to slight downward gradients exist beneath the North Drainage towards the east. Groundwater discharges to the North Drainage as seeps or weak springs in response to the horizontal and upward groundwater gradients. Groundwater flow within the North Drainage is east along the drainage direction. Groundwater elevations have remained steady between 1997 and 2009, except for variations in response to rainfall patterns. Landfill Caps Between 1999 and 2002, RCRA-equivalent caps or covers were constructed atop the P/S, Metals, Caustic/Cyanide, and Acids landfill cells across an approximately 40 acre contiguous area to prevent rainfall and surface water from infiltrating through the waste into the underlying HSUs. Rainwater falling onto the capped landfills now flows as overland surface flow to the


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Central Drainage Area retention basin at the toes of the landfill cells (Figure 2-1). Prior to landfill capping, rainfall infiltrated into the subsurface landfill waste materials or ran-off as surface water that was diverted and collected within the RCF Pond. Since capping was completed in 2002 and beginning with the 2008/2009 winter, stormwater captured in the retention basin is now routed to a wetland constructed within the B-Drainage area. As described above, since 2002 when the landfill caps were completed, the groundwater elevations measured in wells within and immediately surrounding the capped landfills decreased by approximately 10 to 25 feet, and stopped responding to seasonal rainfall. The lowering of groundwater elevations has reduced the volume of liquids migrating through these landfills relative to historical conditions. In turn, the volume of groundwater flowing into the Central Drainage Area has been reduced since the capping of the P/S, Metals, Caustic/Cyanide, and Acids landfills due to the reduced infiltration. Also, infiltration into the Central Drainage Area has been reduced by the diversion of rainwater from non-capped areas between the landfill cells via constructed drainage channels to the constructed wetland or ponds. Seeps Ephemeral seeps have been observed in several locations across the site (Figure 4-8); however, due in part to dry conditions in recent years, none have been observed since 2004, except for the seasonal seep at the south end of RCRA Canyon that forms each year, and the seep that recently formed in the vicinity of Sump 9B during the 2011/12 rainy season. Known seeps include:

A seep historically occurred at the base of the P/S Landfill in the vicinity of Sump 9B. Installation and extraction of liquids from Sump 9B has prevented the seep from emerging in this area, except for periods when the hydraulic efficiency of Sump 9B declines due to clogging (biofouling) of the well screen and gravel pack. When this occurs, extraction from Sump 9B no longer effectively depresses the shallow water table which then intersects ground surface, forming a seep. Sump 9B was redeveloped in 2003 and 2004 which prevented the seep from forming at that time, and was again redeveloped in 2012 which prevented the seep from recently forming during the 2011/12 rainy season;

A seep known as the “9B Road Seep” historically occurred seasonally during the rainy winter months south of Sump 9B immediately west of the road traveling from PSCT-1 to Sump 9B approximately 35 feet north of PSCT-1, which prompted the installation of the “Road Sump” extraction point. Liquids extraction from the Road Sump has prevented the seep from emerging in this area;

A seep on the southern face of the Pond A-5 dike historically occurred in response to water seeping through the dike from Pond A-5 to the A-Series Pond. This seep has been controlled by the lowering of the water level in Pond A-5;

A seep known as the Pond 18/RCF Pond Seep has been observed on the eastern side of the road to the treatment area, resulting from water seeping from Pond 18 to the RCF. This seep has not been observed since 2001; and,

At the bottom of RCRA Canyon, natural seeps occur seasonally during the winter rainy season from vertically upward groundwater gradients that are a result of the artesian hydrogeologic conditions described above for RCRA Canyon. These seeps are periodically active during the rainy season depending on rainfall. During a high rainfall year, the seeps can persist until the end of summer.


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Gallery Well As described above, groundwater from the North Ridge and potentially from the PCB Landfill and eastern part of the Burial Trench Area recharges the P/S Landfill. Groundwater and contaminated liquids move southward in the P/S Landfill until encountering the subsurface clay barrier at the toe of the landfill. The clay barrier and Gallery Well liquids extraction system are designed to control contaminated liquids from migrating outside of the landfill cell. The nature of these features is described in Section 2. Liquid extraction from the Gallery Well maintains the liquid levels along the Gallery Well bench below the upper limit of the clay barrier. As described above, since 2002, the annual Gallery Well extraction rate has decreased by greater than 50 percent, and the extraction rate no longer fluctuates significantly in response to rainfall due to the placement of the impermeable caps. Although the clay barrier is constructed of low-permeability material and inhibits liquids flow, model-simulated particle tracking results suggest that contaminated landfill liquids may bypass and escape into the Central Drainage Area around the east end the clay barrier. Sump 9B and Road Sump As described above, liquids extraction from Sump 9B and the Road Sump controls the seeps that seasonally occurred in the Central Drainage Area between the base of the P/S Landfill and PSCT-1. This liquid extraction also suppresses natural hydraulic gradients and reduces groundwater flow towards the PSCT. The flat topography near Sump 9B promotes infiltration of rainfall runoff and groundwater recharge, with groundwater encountered at only a few feet below ground surface. The increased groundwater recharge occurring in the Sump 9B vicinity counteracts the hydraulic impact of groundwater extraction. The local groundwater contours do not indicate the presence of a distinct capture zone associated with extraction at Sump 9B (RI Report, Appendix F, CSC 2011). During current pumping conditions, the water level in Sump 9B is usually maintained between 20 and 23 feet below top of casing (btoc), while the action level is set at 20 feet btoc. The shallow water table near Sump 9B is evidenced by a seep (the 9B Road Seep) that was observed south of Sump 9B in June 1998 (Figure 4-8). Consequently, in 1998 a collection sump was constructed near the seep, and is designated as the Road Sump. The Road Sump is operated on an as-needed basis and, therefore, does not have a persistent hydraulic impact. Also, as described above, extraction from Sump 9B is necessary to keep the naturally shallow water table depressed so that the seep that historically occurred at the base of the P/S Landfill near Sump 9B during the rainy season does not occur. Perimeter Source Control Trench As described in Section 2, Casmalia Resources constructed the PSCT, a continuous collection trench approximately 2,650 feet long and about 3 feet wide. The PSCT is designed to intercept subsurface liquids migrating from north to south across the site. These liquids originate from groundwater flow from the North Ridge, landfills, Burial Trench Area, and Central Drainage Area to the north.


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Currently, liquids are extracted from the PSCT-1, PSCT-2, and PSCT-4 sumps located within this barrier system. Action and operating water levels in these three sumps are currently below the Upper/Lower HSU contact. The current liquids extraction action levels are as low as the PSCTs can be practically pumped. Analysis of available groundwater elevation data indicates that the PSCT captures most groundwater migrating from north to south across the site within the Upper HSU. PSCT-1: December 2008 water levels demonstrate a northern horizontal gradient into PSCT-1 from the south indicating that the PSCT in this area captures southward groundwater flow within the Upper HSU. However, the 2004 (dry) model-simulated particle tracks pass through the trench in this area, indicating some uncertainty during drier conditions when a recharge mound from precipitation may not be present to the south of PSCT-1 (Figure 4-14). The bypass of the trench may be an artifact of the model (i.e., the model seeks a continuum, when in actuality the trench likely runs dry). Although an upward gradient exists, the model-simulated particle tracks indicate that groundwater within the Lower HSU may pass beneath the PSCT (Figure 4-16). Any groundwater flow under the PSCT would be relatively small due to the low hydraulic conductivity of the Lower HSU. PSCT-2: Sufficient piezometers do not exist to demonstrate hydraulic capture at PSCT-2. Although several piezometers exist (RIPZ-6, -7, -11, and -19), the rapid change in ground surface and HSU contact elevations in this area makes the capture zone assessment uncertain. Downward vertical groundwater gradients occur at PSCT-2 as indicated by December 2008 data. The model-simulated particle tracks indicate that groundwater within the Lower HSU may pass beneath the PSCT in this area (Figure 4-16). Any groundwater flow under the PSCT would be relatively small due to the low hydraulic conductivity of the Lower HSU. PSCT-3: Variable data for monitoring points in proximity to PSCT-3 indicates that the horizontal capture zone may be localized around PSCT-3. Slight downward vertical groundwater gradients occur at PSCT-3. The model-simulated particle tracks indicate that groundwater within the Lower HSU may pass beneath the PSCT in this area (Figure 4-16). Any groundwater flow under the PSCT would be relatively small due to the low hydraulic conductivity of the Lower HSU. PSCT-4: At PSCT-4, an inward gradient to the extraction well from the south was observed during December 2008. Downgradient well RG-2B (between PSCT-4 and well RG-4B) was dry during the December 2008 monitoring event. The total depth (TD) elevation of dry well RG-2B is above the well elevation RG-4B, as such, a dry reading from well RG-2B does not assist in demonstrating capture. While an inward gradient toward the extraction point was not indicated in downgradient well RIMW-5 during December 2008, the inferred capture by PSCT-4 is supported by the model-simulated particle tracks for the 2001 (wet) and 2004 (dry) conditions (Figures 4-14 and 4-15). As expected, the December 2008 water levels in piezometers RIPZ-9 and RIPZ-16, both upgradient of the PSCT, indicated an inward gradient to the extraction well consistent with the southward groundwater flow direction north of the trench. Slight upward groundwater gradients occur at PSCT-4 as demonstrated by the two closest piezometers pairs.


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The model-simulated particle tracks indicate that groundwater within the Lower HSU may pass beneath the PSCT in this area (Figure 4-16). Any groundwater flow under the PSCT would be relatively small due to the low hydraulic conductivity of the Lower HSU. Perimeter Control Trenches As described in Section 2, Casmalia Resources constructed the following PCTs at the head of the A-, B-, and C-Drainages to intercept groundwater at the site boundary and prevent migration of groundwater contaminants outside the historical site boundary. The current liquids extraction action levels are as lows as the PCT’s as can be practically pumped. PCT-A: Groundwater flow at the southeastern perimeter of the site is directed into the A-Drainage due to the presence of a prominent hill south of the Zone 1 boundary that separates the A-Drainage from the B-Drainage. Groundwater recharge through this hill causes a reversal of the flow gradient immediately south of the site boundary. This topographically induced groundwater barrier is complemented by the presence of PCT-A, which extends eastward across the head of the A-Drainage. Water levels in all three PCT-A extraction wells are generally maintained between 10 to 30 feet lower than the prevailing water levels immediately downgradient of the PCT. This generally demonstrates the reversal in groundwater gradients by the operation of PCT-A, and the effective prevention of groundwater movement from the site into the A-Drainage. The 2001 (wet) and 2004 (dry) model-simulated “reverse” particle tracks indicate that the source of groundwater to well RAP-1A is immediately to the north and east of the upgradient hillside (Figures 4-14 and 4-15). The modeling indicates that RCF surface water is not a source of recharge to well RAP-1A. Unlike well RAP-1A, much of the extracted groundwater at wells RAP-2A and RAP-3A likely originates from the nearby RCF Pond and the hill south of PCT-A. The 2001 (wet) and 2004 (dry) model-simulated “reverse” particle tracks show that RCF surface water is a source of recharge to well RAP-2A and RAP-3A. PCT-B: PCT-B contains an extraction well (RAP-1B), which is directly south of Pond 13 in the B-Drainage. Figure 4-10 shows the December 2008 water table surface in the vicinity of PCT-B. During December 2008, the groundwater elevation in well RAP-1B was 1.65 feet lower than the groundwater elevation in well B-5. Water level data at and nearby PCT-B does not indicate that the facility is effective in preventing groundwater flow beyond the site boundary. Maintaining a lower extraction level would induce stronger capture. However, a significant source of recharge to well RAP-1B has been surface water from Pond 13 and/or the RCF. As noted above for the B-Drainage, the water levels located near RAP-1B indicate upward vertical gradients. These upward gradients in the drainage bottom may in part be induced by rainfall recharge on the neighboring hillsides causing groundwater flow to converge at the drainage bottom. Although complete groundwater capture is not definitively demonstrated, the general chemistry concentrations in the B-Drainage downgradient wells do not show increases consistent with Pond 13 or RCF surface water concentration increases, supporting the conclusion that Pond 13 or RCF surface waters are not moving beyond the historical site boundary.


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Groundwater flow in the vicinity of PCT-B is further impeded by the reversal in groundwater gradients that occur immediately south of the site. The two prominent hills in Zone 2 on either side of the B-Drainage, where the topography rises to an elevation of more than 150 feet are above the topographic elevation of the southern perimeter of Zone 1. These topographic highs result in corresponding increases in groundwater elevation on either side of the B-Drainage. The net result is that groundwater gradients are oriented northward towards the Zone 1 site boundary, or directed into the B-Drainage. Thus, the head of the B-Drainage serves as a groundwater divide, preventing groundwater from flowing past PCT-B. The eastern and western edges of PCT-B terminate within these adjacent hills. There is no apparent seasonal trend to the observed variation in water levels within well RAP-1B, suggesting that the observed fluctuation may be related to pumping cycles in the well. PCT-C: Historical water levels in PCT-C and adjacent observation wells indicate that, under normal operations, a significant capture zone exists south of PCT-C, and horizontal gradients are reversed. However, the water level in well RIMW-9 may not support an interpretation of capture. The water levels in wells RAP-1C and C-5 are currently being maintained at historically low levels. A significant source of recharge to wells RAP-1C and C-5 has been surface water from the A-Series Pond, based on the similarity in general chemistry concentration trends between the wells and A-Series Pond surface water. As noted above for the C-Drainage, the water levels located near wells RAP-1C and C-5 indicate upward vertical gradients. These upward gradients in the drainage bottom may in part be induced by rainfall recharge on the neighboring hillsides causing groundwater flow to converge at the drainage bottom. Although complete groundwater capture is not definitively demonstrated, the general chemistry concentrations in the C-Drainage in downgradient wells do not show increases consistent with A-Series Pond surface water concentration increases, supporting the inference that A-Series Pond surface waters are not moving beyond the historical site boundary. At the southeastern end of the clay barrier, groundwater is impeded by a reversal in the groundwater gradient due to the hill between the B- and C-Drainages. Groundwater flow past the western end of the clay barrier is prevented by groundwater extraction from the PCT-C. Thus, PCT-C appears to be effectively preventing migration of groundwater beyond the site boundary in this vicinity. There is no apparent seasonal trend to the observed variation in water levels within wells RAP-1C and C-5, suggesting that the observed fluctuation may be related to pumping cycles in the wells. 4.5.3.3 Groundwater Flow Velocities Ranges of horizontal groundwater flow velocities have been calculated using representative hydraulic conductivities, hydraulic gradients, and porosities for the Upper and Lower HSUs (ICF Kaiser 1998). Flow velocities were estimated using Darcy's Law. The range of hydraulic conductivities used represents the highest and lowest Upper HSU values estimated from all permeameter, slug, pumping, and packer tests conducted. The mean value is the geometric mean of values from all tests conducted. Representative hydraulic gradients were calculated for the Upper HSU both north and south of the PSCT. Fracture porosities were estimated from site infiltration test results and literature.


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The following table summarizes representative groundwater velocities using combinations of the aquifer hydraulic parameters. The low velocities were estimated from low hydraulic conductivity and high fracture porosity values. The medium velocities were estimated from the medium hydraulic conductivity and fracture porosity values, and the high velocities were estimated from the high hydraulic conductivity and medium low fracture porosity values. In accordance with EPA’s June 18, 2003 comments, the high velocity estimates were recalculated using this combination of parameter values. However, because aquifer permeability appears to be a function of fracture intensity, it is unlikely that the highest velocities presented below are realistic, as it is unlikely that an aquifer zone would simultaneously exhibit both high hydraulic conductivity and low fracture porosity. HSU Hydraulic Hydraulic Fracture Fracture Flow Subarea Gradient

(cm/cm) Conductivity (cm/sec)

Porosity Rate (feet/year)

Upper HSU 0.2 Low 1.8 x 10-09 low 1 low 1.49 x 10-05 North of PSCT Mean 1.05 x 10-05 medium 5 medium 0.4 High 8.9 x 10-03 high 25 high 1,840 Upper HSU 0.08 Low 1.8 x 10-09 low 1 low 5.96 x 10-06 South of PSCT mean 1.05 x 10-05 medium 5 medium 0.2 High 8.9 x 10-03 high 25 high 735 Lower HSU 0.1 mean 1.03 x 10-06 estimated 1 mean 0.1

Note the high velocity estimates presented above likely are not representative of actual flow and transport rates, as it is unlikely that the highest hydraulic conductivity values used in the calculations are representative of the system as a whole or exist along any extended flow path through the system. Moreover, the actual groundwater flow rates through fractures occur along three-dimensional flow-paths, and are not equivalent to the two-dimensional velocity between two locations at the site. To determine the equivalent velocity between any two locations on a plan view map, the flow path tortuosity must be taken into account. As described in the HSCER (Section 9.3.3.1, Page 9-33, Woodward-Clyde Consultants 1988a), potential solute transport rates also were estimated based on Carbon-14 isotope age-dating of groundwater in the Lower HSU, as well as on observed contaminant migration in the Upper HSU. HSU Solute Transport Rate Upper HSU 10 ft/year Lower HSU 0.15 to 0.9 ft/year The comparability between the solute transport rate and the matrix groundwater flow rate in the Lower HSU indicates the importance of diffusion and adsorption in solute transport. The large hydraulic conductivity contrast between the Upper and Lower HSUs, and decreased fracture density suggest that the groundwater flux rate in the Lower HSU is less than 10 percent that of the Upper HSU, although there is a possibility that significant fluxes could occur between the HSUs. Order of magnitude estimates of groundwater velocity were calculated between well pairs in the Lower HSU using the Carbon-14 data (ICF Kaiser 1998a). The velocities between wells RP-1D


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and RP-4D, and between wells RP-4D and RP-6D, were 0.9 feet per year (ft/yr) and 0.2 ft/yr, respectively. 4.6 Demography and Land Use 4.6.1 Regional Land Use The area near the site is sparsely settled, and land use consists primarily of agriculture, cattle grazing, and oil field development. Oil fields in proximity to the site include the Casmalia Oil Field, the Orcutt Oil Field, the Guadalupe Oil Field, the Santa Maria Valley Oil Field, and the Jesus Maria Oil Field. Agricultural activities within the region consist primarily of dry land farming of wheat and beans, with minor areas devoted to production of grapes, tomatoes, strawberries, and other grain crops. 4.6.2 Nearby Populations Population centers in proximity to the site include the City of Santa Maria, located approximately 10 miles northeast of the site; the City of Guadalupe, located approximately 8 miles north of the site; and the City of Lompoc, located approximately 16 miles south-southeast of the site. Several small unincorporated towns are located closer to the site, including the towns of Casmalia (approximately 1.2 miles south of the site), Betteravia (approximately 4.75 miles to the north-northeast), and Orcutt (approximately 5.25 miles to the east). The large but sparsely developed Vandenberg Air Force Base lies approximately 1.25 miles west and 1.75 miles south of the site. The primary residential area for Vandenberg Air Force Base is approximately 8 miles south of the site. 4.7 Ecology 4.7.1 Site Habitats The CSC reviewed information from previous reports (Dames & Moore 1998) as well as from recent surveys to identify habitat types, sensitive species, and other flora and fauna that occur or potentially occur at the site. The findings of these studies are presented in the biological species and habitat survey (BSHS) for the site, which synthesized the results of the surveys conducted within and proximate to the site between fall 2000 and spring 2005 (RI Report, Appendix P, CSC 2011). Results of these surveys indicate that the site contains two general habitat types: upland (terrestrial) habitat and aquatic habitat. The terrestrial portions of the 252-acre site are predominantly disturbed, sparsely vegetated, and annually grazed non-native grassland. Upland habitat occurs primarily in the northern portion of the site (Hunt & Associates, 2001) and includes:

Non-native (ruderal) annual grassland; Disturbed coastal sage scrub; and Bare ground (primarily a result of construction activities at landfills).

The majority of aquatic habitat is located in the southern portion of the site and consists of large impoundments for the collection of surface-water runoff (Hunt & Associates 2001). These include the RCF Pond, the A-Series Pond, and Pond 13. Other ponds (A-5 and 18) are planned to be closed. Surface-water runoff is the primary source of water for the ponds. Riparian


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vegetation is not present along the edges of any of the five ponds on the site. This is likely due to the abrupt and steep topography change immediately adjacent to the water’s edge. Weedy grasses and forbs are present along the borders of the ponds; however, the pond borders also contain gravel, debris, and unvegetated soil. A few V-ditches, drainages, and catchment basins are located in the central portion of the site. Terrestrial habitat outside the site boundary is similar to that on the site, with the exception that it is utilized for cattle grazing, agricultural purposes, and oil field development, and thus of lower quality than that within the site boundary. Freshwater areas include riparian areas associated with Casmalia Creek and Shuman Creek. Casmalia Creek is located within 0.25 mile of the west boundary of the site and receives surface-water runoff from upland areas. Because of the proximity of the Casmalia Creek to the site and the potential for the creek habitat to support species that could also inhabit the site, biological surveys were conducted in the riparian habitat of the creek. Casmalia Creek merges with Shuman Creek approximately 2 miles south of the site and approximately 1 mile west of the town of Casmalia; Shuman Creek empties into the Pacific Ocean approximately 4 miles west of the confluence with Casmalia Creek. 4.8 B-Drainage Wetlands In 2006-2008 the CSC designed and constructed a series of six interconnected artificial wetland pools just south of Pond 13 in the upper reaches of the B-Drainage. This series of wetland pools is referred to as the B-Drainage wetlands, is bounded to the north approximately by the position of the existing B-Drainage clay barrier/extraction trench, and begins at an elevation of approximately 400 feet, or about 100 feet south of existing Pond 13 (Figure 1-1). The wetland pools are bounded to the south by the southern end of Parcel Number 113-260-002. The wetland pools’ eastern and western boundaries are dictated by the existing topography within the B-Drainage, and sit between the two hillsides that flank the drainage. The B-Drainage wetlands cover an area extending approximately 700 feet north to south, and ranging in width from approximately 80 to 110 feet. The general arrangement and centerline profile of the wetland pools are depicted in Figures 4-17 and 4-18, respectively. The design of the B-Drainage wetlands was conducted by the CSC under the Consent Decree. In June 2006 the CSC submitted a Design Basis Memorandum (Revision 2 DBM) to the USEPA (CSC 2006). The draft design presenting the design changes that were developed for the draft wetland habitat pools construction plans and specifications was submitted to USEPA on January 31, 2008. EPA presented its comments on the draft design and subsequent draft final design in letters to the CSC dated March 3, 2008, and May 20, 2008, respectively. The final approved design for the B-Drainage wetlands is presented in the Final Design Report – B-Drainage Alternate Habitat Area (CSC 2008a). The CSC is currently working with USEPA and the other resource agencies (United States Fish and Wildlife Service [USFWS], and California Department of Fish and– Wildlife [CDFW]) to develop improvements to the wetlands pools and neighboring hillside as a response to excessive sedimentation into the wetland pools that resulted from heavy rains during December 2010. The CSC submitted a draft Wetlands Erosion Control Improvement Work Plan (dated January 18, 2012; URS 2012) that USEPA conditionally approved in a letter dated May 30, 2012 (USEPA 2012). In accordance with the Work Plan, the CSC has been working with USEPA to develop conceptual designs to improve these wetlands.


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4.8.1 Goals and Objectives The B-Drainage wetlands are designed and constructed to serve as alternate habitat for target amphibian species (California Red-legged Frog, California Tiger Salamander, and Western Spadefoot Toad) which have been using the site ponds (RCF, A-Series, Pond 13, Pond 18, and Pond A-5). The intended biological function of the B-Drainage wetlands in regard to these target species is outlined in the USFWS Biological Opinion (USFWS 2007). The alternative habitat was established to provide a fresh water (low TDS) habitat at the site. The overall objective of the B-Drainage wetland pools is to provide a suitable and enhanced habitat for these target amphibian species that is an improvement to that found in the currently existing site ponds. Prior to construction of the B-Drainage wetlands, the RCF Pond collected stormwater runoff from the central portion of the site. The runoff from the capped landfills area was collected in an impoundment constructed within a portion of the central drainage area (Central Drainage Area collection basin – Figure 2-1). The CSC submitted a Notice of Intent to Comply with the terms of the General Permit to Discharge Storm Water Associated with Industrial Activity (General Permit) for the capped portion of the site in 2003, and received approval of the General Permit that year. The CSC did not immediately use the General Permit because of concerns that diverting stormwater runoff from the RCF Pond could aggravate what where already high salt concentrations (or TDS) in the RCF Pond and make the pond water unsuitable for the target species which had been observed in the pond earlier. USEPA completed a Section 7 consultation with USFWS focusing on this concern, as well as the future concern of closing the RCF and all other site ponds during future remedial actions. The USFWS issued a Biological Opinion for the site in 2008 which approved the construction of the B-Drainage wetlands as alternate habitat to mitigate any adverse impacts to target species from the closure of the site ponds. 4.8.2 Hydrology, Function, and Operation To determine the feasibility of creating the wetland pool habitat, as part of the Revision 2 DBM, the CSC completed a water balance analysis (CSC 2006) to determine if a sufficient volume of water is available in the B-Drainage watershed to maintain the water depths of the six proposed wetland pools. The objective of the wetlands is to create pools that hold water at least through the end of July each year (to accommodate the breeding cycles of the target amphibian species) but which also are dry for at least a month each year (to prevent the proliferation of either bullfrogs or fish in the pools, which would otherwise negatively impact the target species). To estimate the water budget, precipitation and surface-water inflow were considered as inflow of water, while surface-water outflow, surface infiltration, and evaporation represent the outflow of water. Using this methodology, a water balance was calculated for the wetlands pools. The primary source of water supply for the pools is the stormwater runoff collected in the upstream watershed (i.e., Zone 1 area – Figure 1-1). The Final Design Report provides the water balance calculations for each of the proposed pools based on a 1x10-6 cm/sec permeability and several different scenarios (CSC 2008a). The scenarios each considered the projected monthly water levels for each pool, the monthly runoff volume for each upstream watershed subarea, and the total runoff volume into the alternate habitat area. This analysis confirmed the wetland pools could typically maintain more than adequate water depths from November to June (CSC 2006). Since the design incorporated a Geosynthetic Clay Liner (GCL)


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liner under each wetland pool there is only minimal infiltration out of the bottom of the pools, thus water levels are managed by regulating the inflow to the wetland pools from the upstream watershed. In circumstances where dry conditions prevail during the breeding season of the target species and the required hydrological goal is not met by the primary water source (i.e., storm water and runoff collection), the water to the pools will be supplemented with additional water from the ranch well, an alternate high quality water source located on Casmalia Resources property within the C-Drainage controlled by USEPA. The ranch well is a non-potable water source with a production rate of approximately 20,000 gallons per day. Previous water quality analysis of this water source showed total suspended solids of approximately 1,000 mg/L. Since the pools essentially only lose water via evaporation, the application rate of ranch well water only has to equal that evaporation rate. In the spring and early summer months of the year, evaporation at the site is typically on the order of 5.8-inches per month, or 0.2-inches per day. The six wetland pools have approximately 1.5 acres of surface area, as such; expected evaporation rates are approximately 8,000 gallons/day. The pools were constructed, operated, and maintained in such a manner that adequate water depth is provided in the pools through the critical breeding period for the target species, and that water is absent for at least one month from August to October to prevent habitation by invasive predators which would otherwise negatively impact the target species. The pools are monitored to ensure water is present from November through July. Supplemental water sources are used in the event that natural rainfall and runoff is insufficient to maintain suitable water depth in the pools from November to July. Alternate water sources are of acceptable quality (low in TDS and salinity) are available to provide quality habitat for the target species. The pools are operated to allow complete release or evaporation of the water for at least one month to mitigate against the invasion of predatory species that may impede the survival of the target species. The CSC has operated the B-Drainage wetlands in accordance with the USEPA-approved Operations and Maintenance Manual (CSC 2008b) since construction. 4.9 Conceptual Site Model A conceptual site model (CSM) was developed based on the results of historical investigations and refined over time as new data were collected as part of the RGMEW, RI/FS Work Plan scoping activities, and performing the RI activities. The CSM is a summary of information included in the previous sections and elsewhere in this report, and presents the current understanding of physical and chemical conditions at the site. The CSM is graphically illustrated in the following figures that transects through key site areas, and summarized in the following text.

Figure 4-19 CSM 1 (P/S Landfill, Central Drainage Area, Former Ponds and Pads Area, and RCF Pond)

Figure 4-20, CSM 2 (PCB Landfill, Burial Trench Area, Former Ponds and Pads Area, and RCF Pond)

Figure 4-21, CSM 3 (RCRA Canyon Area, Pond A-5, A-Series Pond, and C-Drainage) Figure 4-22, CSM 4 (PSCT-1, Former Ponds and Pads Area, and B-Drainage)

These CSM transects were selected to illustrate the range of physical and chemical conditions at the site that are important with respect to characterizing the site’s physical characteristics, nature and extent of contamination, and fate and transport of contamination.


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The CSM is also graphically illustrated as block diagrams in Figures 4-23 and 4-24, which show site features, locations of groundwater and DNAPL contamination, the three groundwater areas, the conceptualized geology of the site, and the limits of the proposed technical impracticability (TI) zone. Figure 4-24 shows a more detailed view of the Zone 1 area. The details of these CSMs are further presented in Sections 4, 5, and 6. 4.9.1 Site Features The site is located on the south flank of Casmalia Hills located in the southern extent of the Coast Range geomorphic province. The topography of the site is relatively steep, dominated by a northwest-southeast trending ridge (the North Ridge) along the northern boundary. The site ranges in elevation from 835 feet msl along the North Ridge and slopes to 375 feet msl at the southern boundary. During historical operations, natural drainages on the southern flank of the North Ridge were excavated to unweathered bedrock and landfill cells were created within the enlarged canyons. These include the current P/S Landfill, PCB Landfill, Metals Landfill, Caustics/Cyanide Landfill, and Acids Landfill (Figures 2-1 and 2-2). Numerous liquid containment ponds and evaporation pads have existed in the lower elevations of the central and southern areas of the site, though most have been removed or capped. Five ponds currently occupy the southern site area within the footprint of former ponds and pads. These include the RCF Pond and Pond 13, the A-Series Pond and Pond A-5, and Pond 13 (Figure 2-1). South of the site border, prominent hills at the southwestern and southeastern corners define three drainages (A-, B-, and C-Drainages) through which surface water and groundwater naturally exit (Figure 1-1). 4.9.2 Meteorology The site is located in southern California, and subject to a Mediterranean climate typified by warm to hot summers and mild winters. Site water budget information gathered between June 1997 to March 2009 indicates a net loss in the water storage has occurred. The site’s average annual rainfall is approximately 17 inches, while average annual evaporation is approximately 50 inches. As such, the site has a net annual average evaporative loss rate of approximately 33 inches. Site rainfall patterns are influenced by the El Niño/La Niña-Southern Oscillation (ENSO). Annual rainfall can exceed 20 to 30 inches, or be less than 10 inches. The 1997/98 winter when 32.65 inches of rain fell at the site was a strong El Niño event. 4.9.3 Geology The geology of the site is dominated by massive to faintly bedded Todos Santos Claystone bedrock. The upper 30 to 60 feet of the claystone (informally referred to as the Upper HSU) has been eroded, physically weathered and diagenetically altered, resulting in the formation of a weathered rind of claystone with (pseudo-)fracture porosity. The weathered claystone has significantly greater fracture porosity than the underlying unweathered claystone (informally referred to as the Lower HSU). At the site, the Todos Santos claystone is approximately 1,300 feet thick and underlain by the oil-rich Monterey Formation. Alluvium locally occurs atop the claystone and within present and former drainages. Site operations have removed the weathered claystone from some areas (i.e., beneath the landfill cells) and emplaced refuse and other fill material in others (i.e., the landfill cells).


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4.9.4 Hydrogeology Two hydrostratigraphic units have been defined for the site, as indicated above. The distinction between the Upper and Lower HSUs is atypical, as the units are not separated by an aquitard or aquiclude, but rather, are defined by the degree of weathering of the claystone. The Upper HSU has moderate to low hydraulic conductivity (~10-5 cm/sec) while the Lower HSU has low hydraulic conductivity (~10-6 cm/sec). Site-wide groundwater flow and contaminant migration at the site is now controlled by a series of east-west oriented clay barriers and extraction trenches constructed within the Upper HSU and anchored within the Lower HSU and pumped sump-wells. Groundwater generally flows from the northern border of the site on the North Ridge to the lowlands in the south. The water table closely follows topography, and horizontal gradients are accordingly steep in the hilly northern portion of the site. Except under the North Ridge where the Upper HSU is unsaturated (dry), the water table typically occurs in the weathered claystone, where the fracture porosity is greater than the matrix and fracture porosities of the underlying unweathered claystone. Groundwater elevations between the North Ridge and the PSCT declined by over 10 to 20 feet after the RCRA caps were constructed on the four landfills from 1999 through 2002, as further described below. The North Ridge is a natural recharge area and groundwater flow divide. Rainfall infiltrates into the subsurface along the North Ridge and moves vertically downward and laterally outward either northward toward the North Drainage or southward across the Zone 1 site area. The location of the groundwater flow divide is conceptual along the North Ridge and its exact location is not quantified. Strong downward vertical groundwater gradients occur along the North Ridge. Although the hydraulic conductivity is relatively low, infiltrating groundwater moves downward in the Lower HSU in response to the strong downward vertical gradients in this area. From the North Ridge above RCRA Canyon, groundwater moving southward will preferentially move through the more permeable Upper HSU and converge into RCRA Canyon. Vertically downward gradients occur in upper RCRA Canyon and in lower RCRA Canyon to the south. Groundwater will flow southward along RCRA Canyon and discharge to Pond A-5 to the south. From the North Ridge above the PCB Landfill, groundwater moving southward will preferentially move through the more permeable Upper HSU, PCB Landfill materials, and Burial Trench Area towards the PSCT in the vicinity extraction well PSCT-4. Some groundwater from the PCB Landfill and eastern part of the Burial Trench Area may move towards the P/S Landfill. Strong vertically downward groundwater gradients occur throughout the PCB Landfill and Burial Trench Area. From the North Ridge, above the capped P/S Landfill and the other capped landfills (Metals, Caustic/Cyanide, and Acids), groundwater naturally flows through the enlarged drainages that define the landfill cells, toward the Central Drainage Area. Groundwater moving southward will preferentially move through the more permeable Upper HSU and landfill cells. Vertically downward groundwater gradients occur at the northern parts of the four capped landfills as the downward gradients propagate southward from the North Ridge. Historically, groundwater level data has indicated that these downward gradients continued to the southern limits of the landfills.


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Capping of the P/S Landfill in 1999, and the EE/CA Area landfills (Metals, Caustic/Cyanide, and Acids) in 2001-2002, and subsequent maintenance of the approximately 40 acre contiguous impermeable cap has eliminated most rainfall infiltration into the capped areas. Elimination of rainfall infiltration reduced the magnitude of the downward gradients of the landfills and has led to an upward vertical gradient at the toe of at least two of the landfills (Metals and Caustic/Cyanide). The vertical gradient at the toe of the P/S Landfill is not known because piezometers to determine the vertical gradient in this area do not exist. Groundwater from the EE/CA Area Cap landfills (Metals, Caustic/Cyanide, and Acids landfills) will flow southward and converge to the Central Drainage Area. The reduction in groundwater elevations from capping has reduced the volume of liquids migrating from these landfills relative to historical conditions. Contaminated liquids within the P/S Landfill are controlled by presence of a downgradient clay barrier and liquids extraction from the Gallery Well located on the upgradient side of the barrier. Capping of the P/S Landfill has led to a significant reduction in the volume of liquids extracted from the Gallery Well. Groundwater moving southward through the Central Drainage Area will preferentially move through the more permeable Upper HSU towards the PSCT in the vicinity extraction well PSCT-1. Neutral to vertically upward groundwater gradients occur in the Central Drainage Area between the P/S Landfill and PSCT-1. In the south, prior to site development, surface water and groundwater naturally exited through the A-, B- and C-Drainages at the southern perimeter of the site, which ultimately flows to the Pacific Ocean via Shuman Creek (Figures 1-1 and 4-1). The North Drainage to the north of the site also ultimately flows to the Pacific Ocean via Shuman Creek. Shallow groundwater flow is now managed by several constructed subsurface features including clay barriers, trenches, and extraction points where fluid levels are maintained at specified levels. Neutral to vertically upward groundwater gradients mostly occur in the A-, B-, C- and North Drainages near the site. The PSCT and related extraction points control migration of groundwater from the landfill cells, Burial Trench Area, and Central Drainage Area to the southern portion of the site (Figures 4-14 and 4-15). Control of leachate migration from the P/S Landfill into the Central Drainage Area is specifically addressed by impoundment behind a clay barrier and extraction via the Gallery Well. Groundwater entering the Central Drainage Area is further controlled by extraction via Sump 9B. Evaluation of groundwater flow and chemistry data indicate that the PSCT together with natural attenuation mechanisms is effective at controlling groundwater contaminant migration southward from the northern portion of the site. One potential exception to the effectiveness of these containment facilities, as further described below, is for DNAPLs that are known to occur in the Upper HSU and Lower HSU of the P/S Landfill and Central Drainage Areas. DNAPLs migrate through the subsurface in response to gravity driven-flow and may not be totally contained by the liquid collection systems. Fracture flow paths tend to be steep in angles, and as such, DNAPL flow to depth is likely limited, as fracture density decreases with depth. However, the DNAPL within deep fractures will reside in these zones as dead-end storage for an indefinite period of time; attempts to delineate fracture dead end storage zones would likely exacerbate DNAPL distribution, as DNAPL encountered while drilling is difficult to contain (e.g., RISB-02 where DNAPL flowed into and partially filled the borehole from fractures encountered at higher elevation). No DNAPL has been observed to daylight at any surface fracture or seep at the site. Five ponds are presently located in the southern portion of the site, which are sources of recharge to groundwater and also act as groundwater sinks that receive base flow, depending on the water level within the ponds relative to the level of the adjacent water table. As noted


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above, these include the RCF Pond, Pond 13, the A-Series Pond, Pond A-5, and Pond 18. Flow of groundwater through the A-, B-, and C-Drainages to areas outside the historical site boundary is controlled by extraction points within the PCTs located at the head of each drainage (PCT-A, PCT-B, and PCT-C, respectively). Evaluation of groundwater flow and chemistry data indicate that surface water from the site ponds is a significant source of recharge to each of the PCTs and that the PCTs are effective at controlling groundwater contaminant migration southward from the southern portion of the site for the B-Drainage. Groundwater seeps have been observed in several locations across the Site, however, due in part to dry conditions in recent years, none have been observed since 2004, except for the seasonal seep at the south end of RCRA Canyon that forms each year, and the seep that recently formed in the vicinity of Sump 9B during the 2011/12 rainy season. Two of the historical seeps no longer form because of lower water levels in the onsite ponds. The RCRA Canyon seep forms seasonally in response to winter precipitation that recharges groundwater and creates upward groundwater gradients at the base of the canyon. The Sump 9B seep forms seasonally in response to winter precipitation that recharges groundwater in this area and causes the shallow water table to intersect ground surface. Extraction from Sump 9B keeps the shallow water table depressed, preventing the seep from forming, except when the Sump 9B well screen and gravel pack become clogged (biofouled) reducing well performance. Sump 9B is periodically redeveloped when its performance declines; last performed after the 2011/12 rainy season. Based on seasonal changes in groundwater elevations (measured from 1997 to 2009), the estimated loss in site groundwater storage is approximately 9 acre-feet. The rate of loss in groundwater storage is noted to have increased in the periods following the capping of landfill cells, indicating the effectiveness of capping landfill cells to prevent surface water infiltration, however, changes in groundwater storage follow seasonal precipitation. 4.9.5 Contamination Soil and groundwater contamination at the site is the result of historical operation as a Class I hazardous waste management facility initially permitted by the RWQCB. Casmalia Resources began operating the in 1972 and ceased accepting waste in 1989. Waste disposal units included the following: 6 landfills, 43 surface impoundments, 15 evaporation pads, 2 non-hazardous waste spreading areas, 6 oil field waste spreading areas, 11 shallow injection wells, 6 disposal trenches, and 1 drum burial unit (Figure 2-2). The landfills, spreading areas, injection wells, and disposal trenches were located at the northern half of the site and most of the surface impoundments and evaporation pads were located at the southern half of the site. A few of the surface impoundments and evaporation pads were located in areas of the northern portion of the site between the major landfill cells. The site also had five waste treatment units: an acid/alkaline neutralization facility, a hydrogen peroxide treatment unit, oil recovery and treatment tanks, a wet air oxidation unit, and a temporary pilot-scale PACT unit. From 1988 through 1990, Casmalia Resources removed the small amount of landfill wastes that had been placed in RCRA Canyon. Casmalia Resources completed pond and pad closure activities in the period from 1989 to 1991. These closure activities included excavating contaminated subgrade soils for the ponds and pads at the southern half of the site, placing the excavated subgrade soils on the remaining 5 landfills, and constructing the PSCT and PCT extraction trenches. As a result of these activities, most of the current soil and groundwater contamination occurs at the northern half of the site, north of the PSCT extraction trench.


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Several site study areas were defined for the purposes of performing the RI/FS. Notable study areas that are used in the CSM include the following:

Capped Landfills – Includes the four existing landfills (Pesticides/Solvents, Metals, Caustic/Cyanide, and Acids) capped by the CSC from 1999 through 2002.

PCB Landfill – Includes the existing PCB Landfill that is not capped. RCRA Canyon Area and West Canyon Spray Area – Includes the former RCRA landfill

from which waste was previously removed, and the waste spreading and spraying areas not remediated.

Burial Trench Area – Includes the 11 shallow injection wells and 6 disposal trenches. Central Drainage Area – Includes former ponds and pads, mostly not cleaned-up. Liquids Treatment Area – Includes several former waste treatment facilities and the

current extracted liquids treatment facilities. Former Pond and Pad Area – Includes former pond and pads mostly cleaned-up. Stormwater Pond and Treated Liquids Impoundments – Includes the five ponds at the

south part of the site (A-Series Pond, Pond A-5, RCF, Pond 18, and Pond 13). Additional study areas include the Maintenance Shed Area, Administration Building Area, Roadways, and the Remaining On-Site Area. 4.9.5.1 Surface Water and Groundwater Groundwater in the site vicinity is naturally of poor quality, due to low flow rates resulting in extended contact with the aquifer materials and a high rate of evaporation. The marine origin of the claystone and the slow migration rate of the groundwater result in a chemistry that includes significant concentrations of seawater constituents - metals and TDS. Groundwater is generally of the sodium-chloride type in the Upper HSU, and the sodium-chloride or sodium-sulfate type in the Lower HSU. Near the landfill cells and PSCT, groundwater is magnesium-sulfate dominated. One exception to the poor quality of groundwater is within the alluvium along Casmalia Creek. Groundwater in this alluvium is lower in TDS, likely due to percolation of fresh stormwater that flows down the drainage. TDS concentrations in the alluvium along Casmalia Creek are less than 2,000 mg/L. TDS in weathered and unweathered claystone outside the historical site boundary is variable and often exceeds 5,000 mg/L, and can exceed 10,000 mg/L. Contamination is predominantly located within the Zone 1 historical site boundary, though sporadic, low level contaminant concentrations have been detected within Zone 2 (outside the historical site boundary). VOCs are the most common, widespread, and mobile of the organic contaminants present, and are therefore used as proxy compounds to characterize organic contaminant movement as a whole. Arsenic is the most common and widespread of the inorganic contaminants present that exceed primary drinking water MCLs, and is therefore used as a proxy metal to characterize metals contaminant movement as a whole. Heavy metals, semi-volatile organic compounds (SVOCs), polycyclic aromatic hydrocarbons (PAHs), PCBs, herbicides, pesticides, and dioxins/furans are also present, as well as other chemical compounds. In the Upper HSU, VOC and inorganic contaminant zones are separated by the PSCT (Figures 4-19 and 4-20). The Zone 1 area north of the PSCT contains the majority of the metals, dissolved phased VOC contamination, and all of the known NAPL contamination. The VOC and metals plumes in the Upper HSU beneath the landfills converge and flow into the Central Drainage Area and into the PSCT in the PSCT-1 area. The VOC and arsenic plume in the


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Upper HSU and in the Burial Trench Area flows south into the PSCT in the PSCT-4 area. There is also an area of contamination located in the Burial Trench Area that extends to the southern portion of the PCB Landfill, which flows into the PSCT. The PSCT prevents contaminant movement to areas south of the trench, and contains the VOC and arsenic contamination in the northern areas. VOC and arsenic contamination south of the PSCT is likely the result of former liquid storage ponds in that area that have since been removed. VOCs are not present in the site ponds or the PCTs at the head of the A-, B-, and C- Drainages, except at very low levels when detected. Unlike the absence of these VOCs, TDS (salts) and metals are significantly elevated within surface water in the five site ponds, groundwater extracted at the PCTs, and other groundwater monitored at other wells in the vicinity of the ponds and PCTs. TDS and metals concentrations have steadily increased since the 1997/98 El Nino winter when a large amount of fresh stormwater runoff filled the ponds to near capacity and diluted TDS and metals concentrations. TDS concentrations in the ponds were below 10,000 mg/L in 1998 after dilution. TDS has steadily increased since then through evaporation and currently exceeds 20,000 mg/L in most ponds. Salts and metals increase over time because these are terminal ponds with no outflow. TDS concentrations increase year-to-year, with temporary dilution during winter stormwater runoff events. In the Lower HSU, dissolved VOCs in groundwater are present within four areas:

North Ridge Burial Trench Area; Central Drainage Area (including the southern edge of the Acids Landfill); Along the PSCT, including at extraction wells PSCT-1, PSCT-3, and PSCT-4.

The Central Drainage Area contains the highest levels of VOC contamination in the Lower HSU, which appears related to overlying Upper HSU VOC and NAPL contamination present between the P/S Landfill and the PSCT. Dissolved concentrations of arsenic and other metals in the Lower HSU are lower than in the Upper HSU; the highest dissolved metals concentrations in the Lower HSU are predominantly located along the North Ridge, on the border of Zone 1 and Zone 2. Higher concentrations of metals in the Lower HSU are also located within the Central Drainage Area, Burial Trench Area, and along the PSCT where there are elevated VOCs. Metals concentrations in the Lower HSU do not obviously appear to coincide with elevated concentrations in the overlying Upper HSU. It is not clear if the elevated metals in the Lower HSU under the North Ridge are from site-related impacts. Natural attenuation processes play an important role at the site, contributing both to containment and reduction of COC concentrations. Data compiled as part of the RI have shown the effectiveness of natural attenuation processes that include physical, chemical, or biological mechanisms. Natural attenuation naturally degrades COPCs, which limits the movement of contamination and gradually improves water quality. Natural attenuation is described in further detail later in this FS. 4.9.5.2 Nonaqueous Phase Liquids


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The P/S Landfill and Central Drainage Area are the only areas of the site where both free-phase (mobile) DNAPL and LNAPL were observed in the Upper HSU during drilling, are gauged in routine liquid level monitoring, and are inferred based on the concentrations of dissolved compounds (Figure 4-19). The Central Drainage Area is the only area of the site within the Lower HSU where DNAPL was gauged in routine liquid level sampling and inferred based on the concentrations of dissolved compounds. The Burial Trench Area was investigated for the presence of DNAPL and LNAPL, and although dissolved VOC concentrations are relatively high in this area, no wells or piezometers were observed to contain NAPL during liquids level monitoring (Figure 4-20). Significant volumes of free-phase LNAPL and DNAPL occur within the southern end of the P/S Landfill. Measured DNAPL thicknesses at the bottom of the P/S Landfill range from approximately 5 feet in piezometer RIPZ-27 (8 feet north of Gallery Well) and up to 14 feet in piezometer RIPZ-13 (150 feet north of Gallery Well). The liquids extraction pump maintains the DNAPL at a thickness of 2 feet at the Gallery Well. The Gallery Well has historically extracted approximately 3,000 to 4,000 gallons per year of DNAPL and minor volumes of LNAPL from the P/S Landfill. The rate of DNAPL extraction has been relatively stable for over 10 years, indicating that a significant volume of free phase DNAPL occurs in the landfill. There may be up to and over 100,000 gallons of free-phase DNAPL in the landfill based on: (1) extrapolating from the volume of continued extraction of DNAPL at a rate of several thousand gallons per year, and (2) volumetric calculations from the measured DNAPL thicknesses in the landfill and the dimensions of the base of the landfill potentially containing free-phase DNAPL. Several feet of DNAPL are currently present in two Lower HSU piezometers (Figure 4-22). These piezometers (RGPZ-7C and RGPZ-7D) are located approximately 500 feet south of the P/S Landfill and 150 feet north of PSCT-1. The deeper piezometer is screened from 138 to 148 feet bgs, more than 100 feet below the HSU contact. This DNAPL potentially migrated from one of two potential Upper HSU source areas through Lower HSU fractures to arrive at this location and depth. One potential DNAPL source is the large volume of known free-phase DNAPL within the P/S Landfill. Calculations indicate that historical and current DNAPL thicknesses in the P/S Landfill exceed the DNAPL pool height required to enter underlying fractures, given measured DNAPL properties and potential fracture widths. The other potential DNAPL source is the area of former Pads 9A and 9B located between the P/S landfill and PSCT-1. No potential low areas in the HSU clay contact were identified in this area that could potentially collect a pool of DNAPL, nor was any evidence found of free-phase DNAPL or visual observations of obvious mobile or residual-phase DNAPL. The vertical extent of free-phase DNAPL in the Lower HSU is not known with certainty. In addition, the localized horizontal extent of free phase DNAPL in the Lower HSU is uncertain in the area of the P/S Landfill and Central Drainage Area, although the horizontal extent of free phase DNAPL is not believed to extend beyond the site boundary. Once DNAPL has entered a fracture or fracture network, progressively smaller aperture fractures will be invaded if the DNAPL is allowed to extend itself vertically while remaining a continuous, interconnected phase. The DNAPL driving head is not only a function of the pool height in the overlying Upper HSU (or P/S Landfill) but also the height of DNAPL accumulated in the fractures beneath this pool. The large DNAPL volume in the P/S Landfill would provide an ongoing source to allow the DNAPL to extend itself. If the P/S Landfill is the source, the free-phase DNAPL in the landfill will provide a long-term source for DNAPL migration. However, as indicated above, DNAPL appears to be trapped in fracture zones that ultimately become dead-zones at depth. No DNAPL has been observed to daylight at surface fractures or groundwater seeps.


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As described above, neutral to vertically upward groundwater gradients occur in the Central Drainage Area between the P/S Landfill and PSCT-1. The vertical gradient at the toe of the P/S Landfill is not known because piezometers to determine the vertical gradient in this area do not exist. The direction and magnitude of the vertical gradients has changed over time in response to climatic conditions, landfill capping, and liquids extraction. Calculations performed with DNAPL densities and measured vertical gradients at the southern area of the Central Drainage Area and near PSCT-1 indicate that vertical gradients may currently be sufficient to stop downward DNAPL migration in this area. Data to assess vertical gradient conditions under the P/S Landfill are not available. LNAPL thicknesses up 1 to 2 feet occur in monitoring wells and piezometers within the Central Drainage Area between the P/S Landfill and PSCT-1 (Figure 4-19). Migration of LNAPL southward will be intercepted by either Sump 9B or the PSCT. 4.9.5.3 Soil, Sediment, and Soil Vapor Soil contamination attributable to former site operations is present at many of site study areas. Available data indicate a comparatively small list of inorganic and organic constituents are responsible for the soil impacts detected. With exceptions, inorganic exceedances in soil are restricted to surface or shallow-to-moderate depth soils (i.e., 0 to 10 feet bgs) in the areas south of the PSCT and west of the PCB Landfill and Burial Trench Area, and typically demonstrate diminishing concentrations with increased depth. These areas include the RCRA Canyon/West Canyon Spray Area and most of the Former Ponds and Pads Area. Not including the landfills, high concentrations of organic constituents, principally VOCs, PAHs, and/or PCBs, are locally present to the maximum depths explored at locations near former waste management facilities within the Central Drainage Area, select areas of the Former Pond and Pad Subarea, and the Burial Trench Area. Drilling and sampling for chemical analysis was not performed below the Upper/Lower HSU contact in many of these areas. Soil contaminants are interpreted to typically not persist appreciably below the contact between the upper weathered claystone and the underlying lower unweathered claystone due to the lower permeability of the underlying unweathered claystone. This assumption of the lack of contamination in the unweathered claystone may not be valid for areas north of the PSCT where the general contaminant levels are higher. Sediment, present in the stormwater ponds, treated liquids impoundments, and drainages outside the site historical boundary, is impacted by both inorganic (e.g., barium, cadmium, and selenium) and organic (e.g., 1,1-DCA, MCPP, and PCB toxic equivalent [TEQ]) constituents. Organic compounds are elevated in the stormwater and treated liquids ponds. Soil vapor contains elevated VOC concentrations at all sampled locations, including step-out locations outside the site historical boundary. Initial sampled locations were within the areas with expected elevated VOC concentrations (the interior of the capped landfills were not sampled). Additional step-out locations were then sampled to delineate the extent of VOCs in soil vapor. With only a few exceptions, those VOCs detected in step-out locations outside the site boundary were also reported to be present in site sampling locations. Maximum concentrations of VOCs that demonstrate the highest prevalence and reported concentrations are found along the eastern and northeastern limits of the capped landfills, south of the PSCT below the Maintenance Shed Area, the western limit of the Central Drainage Area and eastern margin of the Burial Trench Area, the southern and western Central Drainage Area, as well as


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west of the Burial Trench Area, the northwestern limit of the Capped Landfills Area, and two locations along the PSCT south of the Central Drainage Area and Burial Trench Area. Most of the elevated VOC concentrations likely originate in the primary source areas north of the PSCT, including the Burial Trench Area, Central Drainage Area, the P/S Landfill, and, to a lesser extent the other landfills. VOCs may also originate from residual contamination in other areas south of the PSCT, including the Liquids Treatment Area and former Ponds A and B. VOCs may migrate from higher concentration to lower concentration areas. Concentrations decrease outside of the capped landfills toward the east and toward the north, but are still detectable at the base of the North Drainage. Concentrations also decrease from the Burial Trench Area toward the west into the RCRA Canyon Area, and from the PSCT towards the south into the Former Ponds and Pads Area. During the RI phase, discrete, one-time soil vapor samples were collected from temporary (non permanent) probes located throughout the site. Since 2009, soil vapor samples have been collected semi-annually from three of those locations on the North Ridge of the site. As a part of the analysis and reporting for this sampling, temporal trends have been evaluated with respect to VOC concentration changes over time. No general concentration trend with respect to depth has been observed at the northern and eastern edges of the capped landfill area, the only locations where multi-depth soil vapor sampling was performed. Conceptually, elevated soil vapor concentrations occur near ground surface downward to the water table (Figures 4-19 and 4-20). 4.9.6 Exposure Pathways Potential contaminant exposure pathways at the site have been evaluated in relation to both human health and environmental receptors, and are discussed in detail in Section 7. Human health exposure pathways considered to be potentially complete include:

Incidental ingestion of soil, sediment, or surface water; Contact with soil, sediment, or surface water leading to dermal absorption; Inhalation of dust generated from soil or sediment; Inhalation of vapors emanating from soil, sediment, or surface waters into outdoor air; Inhalation of vapors emanating from soil vapor into outdoor air; and Ingestion of beef that has been exposed to site contamination.

Environmental receptor exposure pathways considered to be potentially complete and significant include:

Direct contact or uptake of soil by plants and soil invertebrates; Inhalation of burrow air by mammals; this also accounts for volatiles from groundwater; Incidental ingestion of soil by mammals and birds; Ingestion of contaminated prey tissue by mammals and birds; Direct contact or uptake of surface water by aquatic plants, aquatic invertebrates, and

amphibians; Direct contact of seep water by amphibians; Direct contact or uptake of sediment by aquatic plants, aquatic invertebrates, and

amphibians; Incidental ingestion of sediment by birds and mammals; Ingestion of surface water by birds and mammals; and


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Ingestion of contaminated prey tissue (aquatic invertebrates) by birds and mammals. 4.10 References Casmalia Steering Committee (CSC), 2011. Final Remedial Investigation Report. January. Casmalia Steering Committee (CSC), 2008a. Final Design Report, Former Casmalia Hazardous Waste Facility, B-Drainage Alternate Habitat Area. Casmalia, California. June, 2008. Casmalia Steering Committee (CSC), 2008b. Final B-Drainage Wetlands Operations and Maintenance (O&M) Manual, Casmalia Hazardous Waste Management Facility, Casmalia, California. October. Casmalia Steering Committee (CSC), 2006. Design Basis Memorandum, Revision. 2, Former Casmalia Hazardous Waste Facility B- Drainage Alternate Habitat Area. Casmalia, California. June, 2006. Casmalia Steering Committee (CSC), 2004. RI/FS Work Plan. June. Dames & Moore, 1998. Revised Application for NPDES Storm Water Discharge, Casmalia Hazardous Waste Management Facility, Casmalia, California, dated November 2. Dibblee, 1989. Geologic Map of the Casmalia and Orcutt Quadrangles, Santa Barbara County, California. Finkbeiner, T., Barton, C.A., and Zoback, M.D., 1997: Relationships Among In-situ Stress, Fractures and Faults, and Fluid Flow, Monterey Formation, Santa Maria Basin, California. AAPG. V81. pp.1975-1999. Freeze, Allen R. and Cherry, John A., 1979. Groundwater. Prentice Hall, Incorporated, New Jersey. 604 pages. Harding ESE, 2001. Well and Piezometer As-Built Report, Summer 2000 Field Activities. Casmalia Waste Management Facility, May 21. Hunt & Associates, 2001. Draft Biological Species and Habitat Survey Report, Casmalia Hazardous Waste Management Facility, August. ICF Kaiser, 1998. Semi-Annual Monitoring Report – September 1997, Routine Groundwater Monitoring Element of Work, Casmalia Resources Hazardous Waste Management Facility, January. ICF Kaiser, 1997. Routine Groundwater Monitoring Element of Work, Part I – Work Plan and Part II – Sampling and Analysis Plan. Revision 1, Casmalia Resources Hazardous Waste Management Facility, September. MACTEC, 2006. Final Well Inventory Report. May. McClelland Consultants, 1989. Final Environmental Impact Report, Casmalia Resources Class I Hazardous Waste Disposal Site Modernization Plan, September.


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Regional Water Quality Control Board (RWQCB), 1994. Water Quality Control Plan. RWQCB Central Coast Region, September. URS, 2012. Draft Wetlands Erosion Control Improvement Work Plan, B-Drainage Wetlands Habitat, Casmalia Resources Superfund Site, Casmalia, California. January 18. USEPA, 2012. Conditional Approval of Draft Wetlands Erosion Control Improvement Work Plan – B-Drainage Wetlands Habitat, Casmalia Resources Superfund Site. May 30. USEPA, 1997. Consent Decree for Casmalia Hazardous Waste Management Facility, captioned U.S.A. v. ABB Vetco Gray Inc., et al., No. CV96-6518 CAS (RZx). June 27. U.S. Fish & Wildlife Service (USFWS), 2007. Biological Opinion for the Site Stormwater Management, Stormwater Pond Closures, and Replacement Wetlands Construction, Casmalia Superfund Site, Casmalia, Santa Barbara County California (1-8-07-F-13). Woodring and Bramlette, 1950. Geology and Paleontology of the Santa Maria District, California. USGS Professional Paper 222. Woodward-Clyde Consultants, 1988a. Hydrogeologic Site Characterization and Evaluation Report (HSCER), Casmalia Resources Class I Hazardous Waste Management Facility, Volume I-IX, May. Woodward-Clyde Consultants, 1988b. Geologic Siting Criteria Assessment (GSCA), Casmalia Resources Hazardous Waste Management Facility, May 11. Woodward-Clyde Consultants and Canonie Environmental, 1989. Hydrogeologic Site Investigation Report (HSIR) for Cleanup and Abatement Order (CAO) No. 80-61, Casmalia Resources Class I Hazardous Waste Management Facility, Volume I-VII. April 18. Worts, 1951. Geology and Groundwater Resources of the Santa Maria Valley Area, California. USGS Water Supply Paper 1000.


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5.0 NATURE AND EXTENT OF CONTAMINATION Presented in this section is a summary of findings from the RI completed for the site. General RI/FS data needs are summarized in Table 5-1. Information regarding background conditions for soil, surface water and groundwater surrounding the site, and further details regarding the nature and extent of contamination detected at the site are presented in the Final RI Report (CSC, 2011).

5.1 Contaminant Sources The nature and distribution of contaminants within the various media at the site are directly related to operational and post-operational activities at the site, more specifically to the type and location of former waste management facilities and related features formerly or currently present. Such facilities and features constitute the sources of contamination detected in the environmental media assessed during the RI. Principal contaminant sources at the site include the following:

Existing landfill areas; Former disposal areas and site facilities that have not previously undergone cleanup;

and Residual contamination remaining from prior site cleanup efforts.

Of these, the existing landfill areas and untreated former disposal areas represent the most significant continuing sources of contamination at the site, with residual impacts from prior cleanup efforts being only locally significant. As further discussed below, the nature and distribution of the majority of chemical impacts to the various environmental media are readily attributable to one or more of these sources.

5.2 Affected Media Investigations completed as part of the RI have assessed the potential presence of chemical impacts to all pertinent environmental media at the site and within the surrounding areas, including the following:

Soil (surface and subsurface); Soil Vapor; Sediment; Surface Water; Groundwater; and NAPL.

Drawing on the findings of the various investigations completed, the nature and extent of chemical impacts to these various media are discussed below. The nature and extent of contamination, and human and ecological risks posed by this contamination, were defined during the RI field sampling and analytical testing activities, and are more fully detailed in the Final RI Report and its various attachments (CSC 2011). A summary of all detected chemicals identified during the RI sampling and analysis program by media is presented in Table 5-2, and the RBC exceedances by media, location, and constituent is presented in Table 5-3.


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5.3 Summary of RI Results The following discussions provide summaries of the detailed information presented in the Final RI Report and its various attachments. In addition to detailed compound-specific figures, these discussions are supported by a series of simplified figures which summarize the detailed RI findings of chemical analytical results for the various environmental media where a compound was detected, and/or found to exceed a site-specific risk level or regulatory contaminant level (e.g., MCL, or RBC). Note that some of the exceedances are likely related to naturally-elevated levels of the chemical of interest; this is particularly true for exceedance of metals in groundwater in the North Ridge area outside the site boundary. These summary figures include the following:

Detected compounds and/or exceedances in all media (anthropogenic and background) (Figure 5-1)

Compounds with exceedance of RBCs in soil and sediment (Figures 5-2 and 5-3); Total detected VOCs in soil vapor (Figure 5-4); and, Compounds with exceedance in groundwater and NAPL (anthropogenic and

background) (Figures 5-5 through 5-8) 5.3.1 Soils The sampling results from the various phases of RI soil sampling indicate that the majority of the site study areas have some level of soil contamination attributable to former site operations or facilities. The soil impacts are primarily associated with former disposal areas or previous site facilities. The soils impacts are typically inorganic and/or organic contaminants and have been documented in the following study areas:

Administration Building Area; Capped Landfills Area; RCRA Canyon Area; West Canyon Spray Area; Burial Trench Area; Central Drainage Area; Liquids Treatment Area; Maintenance Shed Area; Roadways Area; and Remaining On-site Area, including the Former Ponds and Pads Subarea.

The RI sampling program indicated there are no soil impacts of significance in soils outside the historical site boundary. Soil contamination was essentially contained within the former facility boundary. Soil impacts are evident within many portions of the former waste disposal facility. The nature and distribution of RBC exceedances detected in surface and subsurface soils at the site are illustrated in Figures 5-9 (Chromium in Soil), 5-10 (Copper in Soil), 5-11(Zinc in Soil), 5-12 (total DDT in Soil), 5-13 (Dioxin TEQ in Soil), 5-14 (MCPP in Soil), 5-15 (PCBs in Soil), 5-16 (tetrachloroethylene [PCE] in Soil), and 5-17 (trichloroethylene [TCE] in Soil). The locations where constituents were found to exceed site-specific human health and/or ecological risk-based concentrations in soil (HH RBCs and Eco RBCs, respectively) are much


5-3

more widely distributed across a larger number of study areas for inorganic constituents than for organic constituents. Inorganic constituents found to exceed Eco RBCs in surface and shallow soil at the site are limited to chromium, copper, and zinc. No inorganics were found to exceed their respective HH RBCs. Copper is widely present in excess of its Eco RBCs in surface, and to a lesser extent shallow subsurface, soils in both the RCRA Canyon Area and the West Canyon Spray Area. Exceedances for chromium and zinc are less frequent and widespread. Other study areas found to have one or more of these inorganic constituents in exceedance of their respective Eco RBCs include the Burial Trench Area, Liquids Treatment Area, Central Drainage Area, Maintenance Shed Area, Roadways Area, and Remaining On-site Area (including Former Ponds and Pads Sub Area). Significantly, however, in comparison to those in the RCRA Canyon Area and the West Canyon Spray Area, Eco RBC exceedances in these other study areas are typically more localized, occurring in only one to several discrete sampling locations, or clusters of sampling locations. The number and distribution of surface and/or shallow soil sampling locations with organic constituents in excess of site-specific RBCs is much more limited than that for inorganics. RBC exceedances for organics were limited to portions of six study areas, including the Burial Trench Area, Liquids Treatment Area, Central Drainage Area, Maintenance Shed Area, Roadways Area, and Remaining On-site Area (including Former Ponds and Pads Sub Area). In strong contrast to inorganics, no organic constituents were encountered in excess of their respective HH RBCs or Eco RBCs in either the RCRA Canyon Area or the West Canyon Spray Area. Organic constituents found to exceed RBCs in other study areas include total DDT, dioxin TEQ (Mammalian), MCPP, total PCB congeners, TCE, and PCE. Each of these organic constituents was found to exceed its respective Eco RBC in one or more locations within the above-listed study areas, whereas HH RBCs exceedances were limited to dioxin TEQ, MCPP, and PCE in only discrete single sample locations within the Central Drainage Area, Liquids Treatment Area, Maintenance Shed Area, and the Remaining On-site Area (including Former Ponds and Pads Sub-area). With the exception of total DDT which has a more broad and scattered distribution of exceedances, the majority of organics RBC exceedances occur within the central portion of the site in proximity to the toe of the P/S Landfill or former waste management units within the Central Drainage area and Former Ponds and Pads Subarea proximal to the PSCT. In general, organics RBC exceedances occur in isolated single or several clustered sampling locations. With a few noted exceptions described below, the depth and lateral extent of soil impacts in excess of RBCs has been adequately defined across the site. Elevated inorganic constituents are mostly restricted to surface or shallow to medium depth soils (i.e., 0 to 10 feet bgs), and typically demonstrate diminishing concentrations with increased depth. Exceptions to this general condition include localized occurrences of elevated inorganics at depths of at least 20 feet bgs in several borings completed in the Maintenance Shed Area and the Administration Building Area, and inorganics impacts in excess of 10 feet bgs in portions of the Central Drainage Area. Elevated concentrations of inorganic and organic constituents are also present in medium to deep soil in the vicinity of location RISBON-59, where soil impacts are locally found to extend to depths of at least 30 feet bgs (inorganics) and 55 feet bgs (organics). Elevated inorganic concentrations were also locally encountered at depths of at least 49 feet bgs along the southeastern margin of the site, along NTU Road south of the RCF Pond. High concentrations of organic constituents, principally VOCs, PAHs and/or PCBs, are locally present to the maximum depths explored in several borings completed in proximity to former waste management facilities within the Central Drainage Area, the Former Ponds and Pads Sub-area and the Burial Trench Area. High organic concentrations are present to depths of at least 20 feet bgs near former Ponds A and B just south of the PSCT, to depths of at least


5-4

5 feet bgs in a cluster of shallow borings completed north of the western end of the RCF Pond, to depths of at least 5 feet bgs in a cluster of several shallow soil borings just south of PSCT-1, and to depths of at least 48 feet bgs in the area between the toe of the P/S Landfill south to the PSCT. High VOC concentrations extending to depths of greater than 40 feet bgs in the Liquids Treatment Area are attributable to collection of these soil samples below the local water table, and likely reflect influences of contaminated groundwater present in the area. Maximum VOC concentrations were encountered in a boring completed within the approximate limits of former Pond B, followed by several deep borings completed in the Burial Trench Area. The maximum depth of soil impacts on site was encountered in the Burial Trench Area where former deep waste disposal operations have resulted in elevated inorganic concentrations in soil at depths of up to 44.75 feet bgs, and elevated organic concentrations at depths of up to 77.5 feet bgs. It should be noted that while there may be a few individual samples in a Study Area that exceed a RBC, the Study Area as a whole may not pose a significant risk due to the use of the 95-percent upper confidence limit (95 UCL) concentration in the ERA and HHRA. Moreover, it is important to note that elevated constituent concentrations encountered at depths in excess of 10 feet bgs are not pertinent to human health or ecological risks, as there are no complete exposure pathways to potential receptors. Soil sampling indicates that soil contamination has been contained within the historical facility boundary. The lateral extent of soil impacts in these above-listed areas is delineated by soil samples from surrounding borings that do not indicate significant contaminant concentrations. While the maximum depth of soil impacts has not been demonstrated in all these locations, with few exceptions, field observations and analytical results for the majority of borings completed across the site indicate that soil impacts typically diminish with increased depth beneath the surface. Moreover, in those locations where deep data are available, these data typically indicate that soil impacts do not persist appreciably below the contact between the upper weathered claystone and the underlying lower unweathered claystone. Soil conditions within the site and in areas outside the site boundary have been defined, and in conjunction with soil physical property data and the chemical data developed to date, allow evaluation of fate and transport of the contaminants present in soil, and provide data for evaluation of cleanup options within this Feasibility Study. 5.3.2 Sediments While inorganic constituents were present in sediment samples collected from the various site ponds and surrounding drainages, none were identified to be risk-driving chemicals, thus no RBCs were established for inorganic constituents in sediment. The distribution of organic constituents in sediment in excess of RBCs is illustrated in Figure 5-3. Only one organic constituent – MCPP – was detected in site sediments at concentrations in excess of its Eco RBC as illustrated in Figure 5-18 (MCPP in Sediment). No HH RBCs were exceeded for any sediment samples tested. MCPP is present above its Eco RBC in surface to shallow sediments (i.e., 0 to 5 feet bgs) in the following site ponds:

RCF Pond; Pond A-5; and Pond 18.


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Organic RBC exceedances for site sediments are limited to single, isolated sample locations in the above-listed ponds. No organic constituents were detected above their respective RBCs in the A-Series Pond, Pond 13, nor in sediment samples collected from within drainages outside the site boundary. While inorganic constituents, and to a lesser extent organic constituents, were locally detected in some sediment samples from drainages outside the site boundary, none were reported at levels in excess of established RBCs. Moreover, the locations of these sediment samples were situated either upstream or distal to the site, indicating these chemical detections are likely not site-related. The depths of chemical impacts and exceedances of site-specific RBCs have been defined in all sediment sampling locations. Sediment data collected during the RI characterize the nature and extent of impacts to this media. Sediment conditions within the site and in areas outside the site boundary have been defined, and in conjunction with sediment physical property data and the chemical data developed to date, allow evaluation of fate and transport of the contaminants present in sediment, and provide data for evaluation of cleanup options within this Feasibility Study. 5.3.3 Soil Vapor VOC concentrations above sample quantification limits were reported at all soil vapor sample locations, including both site and step-out locations outside the site boundary. A total of 43 individual VOCs were detected at the various sampling locations around the perimeter of the landfills, the Burial Trench Area, and Central Drainage Area, including chlorinated and aromatic hydrocarbons, acetone, methyl ethyl ketone and freon gases. The nature and distribution of VOCs detected in soil vapor at and in proximity to the site are illustrated in Figures 5-19 (Acetone), 5-20 (Methyl ethyl ketone [MEK]), 5-21 (Freon 113), 5-22 (1,3-Butadiene), 5-23 (Benzene), 5-24 (PCE), and 5-25 (Total VOCs). Chemicals detected in soil vapor that demonstrate some of the highest prevalence and reported concentrations, or that may contribute to human health or ecological risk, include acetone, methyl ethyl ketone, Freon 113, benzene, 1,3-butadiene, and PCE. Maximum concentrations of these chemicals were encountered along the eastern and northeastern limits of the Capped Landfills Area (acetone and 1,3-butadiene), south of the PSCT below the Maintenance Shed Area (1,3-butadiene and benzene), the western limit of the Central Drainage Area and eastern margin of the Burial Trench Area (Freon 113), the southern and western Central Drainage Area (PCE), as well as west of the Burial Trench Area, the northwestern limit of the Capped Landfills Area, and two locations along the PSCT south of the Central Drainage Area and Burial Trench Area (MEK). With only few exceptions, those VOCs detected in step-out locations outside the site boundary were also reported to be present in site sampling locations. The locations of the samples with elevated concentrations on the site are consistent with previously identified source areas at the site, including the existing capped landfills, Burial Trench Area, former Pond R where waste was not removed, and the PSCT which has historically contained free product. Although some chemicals have been detected in soil vapor outside the property boundary, these chemicals do not exceed risk-based screening levels. Moreover, exposure to soil vapor


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via vapor intrusion would be unlikely due to institutional controls for parcels around the site that would be included as part of all the remedial alternatives being considered. The soil vapor sampling conducted at several different times at the same locations outside the site boundary does not indicate any obvious temporal trends, and no general concentration trend with respect to depth was observed. Since 2009, the CSC has conducted a long-term soil vapor monitoring program at three perimeter locations to continue to track the slightly elevated chemical concentrations discussed above. That soil vapor sampling will continue to look for temporal trends and to confirm the concentrations do not pose an unacceptable risk. 5.3.4 Surface Water A total of 16 out of 27 inorganic constituents tested were reported in benchmark sampling locations in the North Drainage and upper C-Drainage at dissolved concentrations in excess of one or more screening levels. With few exceptions, for a given sampling period, reported values for these constituents in benchmark locations indicate concentrations in the North Drainage are typically elevated relative to those in upper C-Drainage. Noted differences in dissolved inorganic concentrations between these two benchmark locations are likely attributable to soil and hydrologic conditions unique to the North Drainage, and are affected by seasonal factors relating to rainfall and stormwater runoff. Detections of organic compounds in the benchmark locations were mainly limited to several SVOCs and dioxins reported at levels slightly in excess of screening levels. Concentration ranges of inorganic and organic constituents detected in surface water drainages are summarized in Tables 5-4 and 5-5, respectively. Available data generally indicate that surface water samples collected in the North Drainage contain a larger variety of constituents at overall higher concentrations than comparable samples collected from other drainages. The notable exceptions to this general condition include the presence of arsenic, molybdenum, nickel, selenium and N-Nitrosodipropylamine at maximum reported concentrations within surface water from the RCRA Canyon drainage, and the unique presence of acetone and acetonitrile in the RCRA canyon drainage relative to all other surface-water sampling locations. Surface water in the site ponds contains relatively low levels of organic compounds, though some VOCs, SVOCs, and PAHs are commonly detected at low concentrations. Concentrations of chlorinated VOCs are generally low to non-detect. Of the inorganic compounds, arsenic, nickel, chromium and selenium are commonly detected at elevated concentrations. Of the ponds sampled, Pond 13 has the highest concentrations of dissolved metals. TDS concentrations within the ponds have historically been higher than those observed in the drainages and RCRA Canyon, due to the increasing concentration of salts within the ponds as water evaporates. With few exceptions, inorganic constituents in the ponds are elevated relative to those present in drainages. Concentration ranges of inorganic and organic constituents detected in site ponds are summarized in Tables 5-6 and 5-7, respectively. TDS concentrations in site ponds are uniformly and consistently higher than corresponding concentrations reported for drainages both on the site and outside the site boundary. In general, concentrations of inorganic constituents in the site ponds have gradually increased over time since the 1997/1998 El Nino winter, with annual fluctuations corresponding to seasonal conditions. Available data for TDS concentration ranges through time are summarized below for each of the surface water drainages and ponds evaluated during the RI. Additionally,


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measured TDS concentration variations through time for each of the site ponds are depicted in Figure 4-2.

SURFACE WATER FEATURE

TDS RANGE (mg/liter)

TIME PERIOD

PONDS RCF 4,680 – 37,000 1995 – 2011 Pond 13 3,140 – 43,000 1995 – 2011 A-Series Pond 6,400 – 36,000 1995 – 2011 Pond A-5 7,580 – 43,000 1995 – 2011 Pond 18 7,200 – 40,000 1995 – 2011

SURFACE DRAINAGES

A-Drainage No Data -- B-Drainage No Data -- C-Drainage No Data -- RCRA Canyon 1,310 – 10,900 2001 – 2002 North Drainage 3,400 – 6,000 2006

A review of trend lines in Figure 4-2 indicates that TDS concentrations in each of the site ponds have overall increased on the order of three- to eight-fold during the period 1998 through 2010, with the maximum increase recorded for Pond A-5. TDS concentrations in all ponds decreased significantly in response to heavy rainfall and related stormwater runoff experienced during December 2010. Within the overall long-term trend of increasing TDS, concentrations recorded for the site ponds reflect seasonal fluctuations, with lower TDS concentrations recorded during the winter months (attributable to the introduction of fresh rainfall and surface runoff into the ponds), and higher TDS concentrations during the summer months (due to evaporation of pond water and resultant concentration of salts in the remaining water). TDS data for surface drainages are limited to only a few samples from the North Drainage and the RCRA Canyon Drainage (table above). Available TDS data for surface water drainages within and surrounding the site indicate concentrations lie below or at the low end of the range of such data for the site surface water ponds. Surface water flow within RCRA Canyon is ephemeral, and occurs only for periods of days to months in response to winter stormwater runoff and far lesser amounts from local seasonally-affected groundwater seepage. During heavy rainfall years, groundwater seepage persists into the summer months. Surface water in RCRA Canyon contains elevated concentrations of metals, most notably arsenic, nickel, and selenium, which are present at concentrations one to several orders-of-magnitude higher than reported for other surface water drainages (CSC, 2011 – Appendix D). Elevated metals concentrations detected in surface water samples collected from the lower RCRA Canyon drainage are likely attributable to a combination of sources, including runoff from surface soils along the flanks and bottom of the canyon containing elevated metals, and contribution from seasonal seepage of groundwater containing dissolved metals.


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5.3.5 Groundwater and Nonaqueous Phase Liquids The distribution of groundwater contamination is predominantly located within the Zone 1 boundary, with little to no contamination in Zone 2. Groundwater contamination consists of NAPLs and dissolved-phase organic and inorganic constituents. NAPLs at the site consist of both LNAPLs and DNAPLs. Both types are present within Zone 1 as a mobile (free) phase and immobile (residual) phase. LNAPLs are lighter than water and float on the water table, while DNAPLs are heavier than water and are found over 100 feet below the water table in the Central Drainage area. Constituents identified in LNAPL, DNAPL, and dissolved-phase contamination in groundwater include metals, VOCs, SVOCs, pesticides, herbicides, PCBs, and dioxins. The distribution of NAPL and dissolved-phase contaminants in groundwater is controlled by the physical characteristics of the groundwater flow system, contaminant source areas, contaminant properties, and ongoing liquids extraction from several extraction facilities. 5.3.5.1 Groundwater Flow Groundwater flow primarily occurs in the Upper HSU, a layer of weathered claystone that overlies the Lower HSU, a block of lower permeability unweathered claystone that occurs to a depth of more than 1,000 feet. Localized, moderately permeable alluvium occurs along current and former drainage bottoms, and is considered part of the Upper HSU when saturated. Flow in the Lower HSU occurs through interconnected fractures. While the interconnectivity of these fractures is uncertain on a site-wide scale, the presence of both dissolved-phase VOCs and DNAPL more than 100 feet below the top of the Lower HSU demonstrates that fractures are interconnected on a local scale. Detailed claystone core logging, borehole video logging, and borehole geophysics show that the unweathered claystone is variably fractured and that the degree and density of fracturing in both the upper and lower HSUs varies widely between locations. While the frequency of fractures decreases with depth in some borings, other borings contain numerous fractures to the total depth explored (250 feet bgs maximum), overall fracture density generally decreases with depth. However, the degree of Lower HSU fracture interconnectivity and the ability of the fracture network to transmit groundwater (and contaminants) cannot be definitively quantified because of the inherent variability in the fractures between boreholes. The overall tendency for decrease of fracture density with depth and apparent limited fracture connectivity suggest that the majority of fractures likely terminate at depth and act as areas of dead-zone storage. From the North Ridge, groundwater within the Upper HSU flows southward across the primary source areas (five landfills, burial trench area, and former waste ponds and pads) towards the PSCT where contaminated liquids (groundwater) are extracted, treated using GAC, and discharged to Pond 18. Contaminated liquids (groundwater, LNAPL, and DNAPL) are extracted from the Gallery Well at the southern toe of the P/S Landfill and from Sump 9B between the P/S Landfill and the PSCT. The Gallery Well and Sump 9B liquids are sent offsite for disposal. Groundwater within the Upper HSU in the RCRA Canyon and groundwater south of the PSCT flows southward toward the five ponds that occur at the south part of RCRA Canyon and between the PSCT and three PCTs. When the ponds are relatively full they may act as a source of groundwater recharge and when relatively low they may act as a point of groundwater discharge. The current pond water levels lie at historical lows. Groundwater extraction at the A-, B-, and C-Drainage PCTs controls groundwater from moving into these drainages. Surface water from the A-Series Pond and RCF are significant recharge sources to the PCTs. Extracted groundwater from the PCTs is discharged to the A-Series Pond and RCF for evaporation.


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Vertical downward hydraulic gradients and some groundwater flow occurs from the Upper HSU into the lower permeability Lower HSU in the upland areas. On the site, these downward gradients occur under the North Ridge and extend southward toward the PSCT. The vertical groundwater gradients are more neutral between the PSCT and PCTs. Localized upward hydraulic gradients occur along certain portions of the PSCT and PCTs in response to liquids extraction at these facilities. Localized upward gradients also occur in the Central Drainage Area between the Gallery Well and the PSCT. Neutral to upward gradients are present in the RCRA Canyon and drainages outside the site boundary. The upward gradients in combination with liquid extraction and containment features (PSCT and PCTs) act to restrict contamination to remain within the historical site boundary. 5.3.5.2 Groundwater Contamination In the Upper HSU, the levels of contamination are separated by the North Ridge groundwater flow divide between Zone 1 and Zone 2, liquids extraction at the PSCT within Zone 1 and by liquids extraction at the PCTs between Zone 1 and Zone 2. The Zone 1 area north of the PSCT contains the majority of the dissolved phased contamination and all of the known NAPL contamination. There is a potential for DNAPL to occur outside of this area due to DNAPL migration from the P/S Landfill or Central Drainage Area source(s) through Lower HSU fractures. However, potential fracture pathways likely have steep angles, and no DNAPL has been observed to daylight at surface fractures or seeps. Upper HSU – Dissolved-phase Organic Compounds Dissolved-phase contaminants that originate in the northern uphill portions of the site migrate southward with groundwater, primarily through the Upper HSU and toward the PSCT. Contaminants from the P/S Landfill, Metals Landfill, Caustics/Cyanide Landfill and Acids Landfill converge downhill towards the Central Drainage Area and into the PSCT in the PSCT-1 area. Contaminants from the PCB Landfill and Burial Trench Area flow south into the PSCT in the PSCT-4 area. In the perimeter areas, within Upper HSU groundwater, VOCs are sporadically detected at low concentrations along the North Ridge and slightly into the North Drainage and the A-, B- and C- drainage areas. Following operational closure of the facility, VOC movement within the Upper HSU is consistent with groundwater flow patterns. Groundwater contaminant distribution for total VOCs in relation to groundwater flow pathways within the Upper HSU and Lower HSU is depicted in several of iso-concentration maps, including Figures 5-26 (VOCs in Upper HSU, Dry) and 5-27 (VOCs in Upper HSU, Wet)) and Figures 5-28 (VOCs in Lower HSU, Between PCB and PSCT-4) and 5-29 (VOCs in Lower HSU, near RGPZ-6 and RGPZ-7). Upper HSU – Light and Dense Non Aqueous Phase Liquids The P/S Landfill and Central Drainage Area are the only areas of the site where both free-phase (mobile) DNAPL and LNAPL in the Upper HSU were observed during drilling, gauged in routine liquid level monitoring, and implied based on dissolved chemistry. The distribution of LNAPL and DNAPL within the Upper and Lower HSUs as observed in monitoring locations or interpreted from groundwater concentrations is depicted in Figures 5-30 (LNAPL in Upper HSU), 5-31 (DNAPL in Upper HSU), and 5-32 (DNAPL in Lower HSU). The distributions of LNAPL and DNAPL within the Upper and Lower HSUs are also presented on maps illustrating the total distribution of VOCs (Figures 5-5 and 5-8). The Central Drainage Area is the only area of the site within the Lower HSU where DNAPL was gauged in routine liquid level sampling and implied based on dissolved chemistry. There is also


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a significant area of contamination located in the Burial Trench Area that extends from its upgradient reach at the southern toe portion of the PCB Landfill, and flows downgradient into the PSCT. The Burial Trench Area was investigated for the presence of DNAPL and LNAPL, and although dissolved VOC concentrations are relatively high in this area, no wells or piezometers were observed to contain NAPL during liquids level monitoring. Significant volumes of free-phase LNAPL and DNAPL occur within the P/S Landfill. Approximately 3,000 to 4,000 gallons of DNAPL and minor volumes of LNAPL have historically been extracted and continue to be extracted from the Gallery Well within the P/S Landfill. The rate of DNAPL extraction has been relatively stable for over 10 years, indicating that a significant volume of free phase DNAPL occurs in the landfill. Where present, DNAPL thicknesses range from approximately 5 to 14 feet in piezometers within the southern end of the P/S Landfill. Based on DNAPL thickness measurements within the P/S Landfill, an estimated 100,000 gallons of free-phase DNAPL or more may exist in the landfill. Lower HSU – Dense Non Aqueous Phase Liquids Several feet of DNAPL are currently present in two Lower HSU piezometers located approximately 500 feet south of the P/S Landfill and 150 feet north of PSCT-1. The presence of DNAPL in this area of the site has been documented through the repeated gauging of these two Lower HSU wells (RGPZ-7C and RGPZ-7C), and further supported by direct observation of DNAPL flowing from unweathered claystone fractures into the RISB-02 borehole. This DNAPL potentially migrated from one of two potential Upper HSU source areas through Lower HSU fractures to arrive at these two Lower HSU well locations and depths. One potential DNAPL source is the large volume of known free phase DNAPL within the P/S Landfill. Based on operational records, such free phase DNAPL is suspected as being derived, at least in part, from containerized liquids disposed of into the P/S landfill which may have corroded or otherwise failed in some manner, potentially releasing liquids into the subsurface. The other potential DNAPL source is the area of former Pads 9A and 9B located between the P/S landfill and PSCT-1, although no free phase DNAPL is known to exist in this area. The vertical extent of free phase DNAPL in the Lower HSU is not known with certainty. Despite the installation of 408 boreholes that explored the Lower HSU, fracture connectivity between boreholes is difficult to demonstrate. The one exception that has allowed NAPL movement likely occurred in the Central Drainage area as evidenced by the orientation of the fractures to neighboring boreholes (as measured in borehole RISB-02) and presence of NAPL in the Sump 9B, RISB-02, and RGPZ-7C/D boreholes. The inferred lateral extent of Lower HSU DNAPL is that it may be limited to the area north of the PSCT in the vicinity of the P/S Landfill and Central Drainage Area. Despite the high level of investigative effort, sufficient borings and monitoring wells are not present in this area to definitively define the lateral and vertical extents or continuity of DNAPL in this portion of the site. However, taken together, site-wide groundwater concentration data coupled with direct observations during drilling and well installation activities in other portions of the site support the conclusion that DNAPL presence is limited to areas within the site boundary. Historical trends of VOCs at nearby wells indicate that the PSCT, in combination with natural attenuation mechanisms, appears to contain and capture the VOC contamination north of the PSCT; over time VOC trends in wells south of the PSCT appear to be declining. Upper HSU VOC contamination in groundwater south of the PSCT is the highest south of PSCT-1 and PSCT-4, and is typically one to two orders of magnitude lower in concentration


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than the concentrations observed in the Burial Trench Area and the Central Drainage Area. The VOC contamination may be residual contamination that existed in-place prior to the PSCT being installed. The VOC contamination sharply declines north of the current Ponds, and is generally not detected south of the five open ponds. Lower HSU – Dissolved-phase Organic Compounds and DNAPL The majority of the samples collected from the Lower HSU did not contain VOC concentrations in excess of the cleanup levels. However, areas of VOC presence in the Lower HSU primarily include: The Central Drainage Area; the Burial Trench Area; the southern edge of the Acids Landfill; along the PSCT; along the North Ridge; and northeast of the Caustic/Cyanide Landfill. The Central Drainage Area contains the greatest amount of VOC contamination in the Lower HSU, and this contamination appears directly related to overlying Upper HSU VOC contamination present between the P/S Landfill and PSCT. The greatest number of VOC cleanup level exceedances in the Central Drainage Area Lower HSU was detected in piezometer RGPZ-6D, which may be related to the Lower HSU DNAPL detected in nearby RGPZ-7C and RGPZ-7D. The Lower HSU location with the second greatest number of VOC exceedances is piezometer RIPZ-16, located in the Burial Trench Area. The remainder of Lower HSU wells with infrequent to few VOC exceedances occur along the PSCT, along the North Ridge, and northeast of the Caustic/Cyanide Landfill. Groundwater moving southward through the Lower HSU through the area containing VOCs beneath the Burial Trench Area and containing DNAPL and VOCs beneath the Central Drainage Area is not contained by the PSCT. The migration of dissolved-phase contaminants in the Lower HSU moving southward through fractures and potentially under the PSCT are attenuated by naturally occurring mechanisms that include sorption, diffusion into the claystone matrix, and biodegradation. Although the rate of potential contaminant migration beneath the PSCT is uncertain, the overall mass is likely small because of these natural attenuation mechanisms and the rate of groundwater flow is low through the low permeability Lower HSU. Upper HSU – Inorganic Constituents Dissolved concentrations of arsenic, nickel, cadmium, and selenium are prevalent in elevated concentrations throughout the Upper HSU in Zone 1.. These metals are generally not elevated in Zone 2, but when found in this area, they are believed to be naturally occurring. Similar to VOCs, the higher concentrations of metals in the Upper HSU are located north of the PSCT in the P/S Landfill and Central Drainage Area. However, elevated levels also occur south of the PSCT. Elevated metals present in groundwater in the RCRA Canyon area, including arsenic, nickel, and selenium, may emerge as groundwater seepage in this area of the site and potentially contribute to elevated metals concentrations in surface water runoff from the RCRA Canyon drainage during and following storm events. Unlike the general absence of VOCs in the ponds and PCTs, however, TDS (salts) and metals are significantly elevated within surface water in the five site ponds, groundwater extracted at the PCTs, and other groundwater monitored at other monitoring wells in the vicinity of the ponds and PCTs. Pond surface water is a recharge source to the PCTs. The concentrations of the salt and metals in the ponds that have been increasing due to evaporation since the 1997/98 El Nino winter are causing similar increases in metals and salts in the PCTs and surrounding area monitoring wells. The distributions of inorganic compounds and metals are presented in Figures 5-6 and 5-7.


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Lower HSU – Inorganic Constituents Metals concentrations in the Lower HSU are generally lower than in the Upper HSU. The highest dissolved metals concentrations in the Lower HSU are predominantly located along the North Ridge.The metal concentrations in the Lower HSU do not appear to coincide with the potentially elevated Upper HSU concentrations. The nature and distribution of select inorganic constituents detected in groundwater within the Upper HSU and Lower HSUs are depicted in a iso-concentration maps for arsenic (Figures 5-33a, 5-33b, and 5-34), nickel (Figures 5-35a, 5-35b, and 5-36), cadmium (Figures 5-37a, 5-37b, and 5-38), and selenium (Figures 5-39a, 5-39b, and 5-40).

5.4 References Casmalia Steering Committee (CSC), 2011. Final Remedial Investigation Report. January


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6.0 CONTAMINANT FATE AND TRANSPORT The following sections provide a summary of the media where chemical constituents are encountered at the site, and the physical, chemical, and biological processes that are potentially affecting the migration, persistence, and transformation of chemical classes in those media. Specific information regarding the physical and chemical properties of the detected constituents, the identity of chemicals detected within environmental media at the site, and the relative mobility and degradation of detected constituents are summarized in Tables 6-1 through 6-4. Using VOCs as indicator compounds, generalized groundwater chemical migration pathways through the Upper and Lower HSUs are presented in Figures 6-1 through 6-3. The following section discuss COPCs defined in the Baseline Ecological Risk Assessment. In some cases the list of COPCs has been revised based upon findings of the Tier 2 Ecological Risk Assessment.

6.1 Surface Transport Pathways – COPC Fate and Transport The migration of surface contaminants involves the fate and transport processes of chemicals associated with surface soil, sediment and surface water, and their impacts to potential receptors in the surrounding environmental setting. Surface soil chemicals and a discussion of surface soil contaminant migration are discussed in Section 6.1.1. Sediment chemicals and a discussion of sediment contaminant migration are discussed in Section 6.1.2. Surface water chemicals observed at the site and a discussion of surface water contaminant migration are discussed in Section 6.1.3. 6.1.1 Surface Soil COPCs Chemical constituents detected in surface soil in excess of screening levels, by COPC class, include:

VOCs – PCE, TCE; SVOCs – bis(2-ethylhexyl)phthalate; Pesticides and Herbicides – MCPP, 4,4’-DDE, 4,4’-DDT, and Hexachlorobenzene; Dioxins/Furans – Dioxin TEQ; PCBs – PCB Aroclor 1260, and PCBs (total); and Metals – barium, cadmium, chromium, copper, lead, and zinc.

6.1.1.1 Migration and Persistence of Surface Soil COPCs Although surface soil is a medium where many of the COPCs are detected, it is not a transport pathway itself; rather, surface soil serves as a medium that may contribute contaminants to other environmental pathways. Intermedia transport from surface soil to other environmental media is dependent upon a number of physical and chemical transport mechanisms. For example, soil erosion by rain or wind can entrain soil particles in water or into the atmosphere for redistribution and redeposition. Potential transport pathways for surface soils that may be carried and redeposited via surface water flow are discussed in Section 4.0, and historical drainage features are illustrated in Figure 4-1. Volatile chemicals that evaporate or de-sorb from surface soils would be emitted to the atmosphere. Leaching may occur when soil


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contaminants dissolve into soil pore water and migrate with water infiltration. Transport may also occur through entrainment in soil pore water of colloidal particles with adhered chemicals. The entrained particles follow the bulk fluid flow patterns in the soil. VOCs VOCs are organic compounds that exhibit relatively high vapor pressures, with typically limited solubility in water. Hence, a major transport process for VOCs from surface soil systems is volatilization. The most prevalent VOCs encountered in surface soil, TCE and PCE, are halogenated VOCs. Halogenated VOCs (HVOCs) are not expected to selectively concentrate on or be sorbed by soils. If HVOC vapors migrate and partition to the atmosphere, HVOCs will be degraded by photo-oxidation. Little biodegradation of HVOCs is expected to occur in surface soils, and processes other than volatilization do not appear to play a significant role in the removal of HVOCs from soil systems. SVOCs Semi-volatile organic compounds, such as bis(2-ethylhexyl)phthalate, are nonvolatile organic compounds that are relatively insoluble in water. Volatilization from either wet or dry soils is not expected to be an important fate process for this chemical class. Empirical data indicate that the degree of sorption of SVOCs is expected to increase as the natural organic carbon content of the soil matrix increases. The most important transport-controlling mechanism for SVOCs in surface soil appears to be adsorption to soil particles and potential redistribution by either wind or stormwater erosion. Sorption or bioaccumulation appears to be a significant environmental fate-governing mechanism for SVOCs. Biotic and abiotic biodegradation or transformation processes may act as removal mechanisms for SVOCs, but at relatively slow rates. Pesticides and Herbicides MCPP is a selective ‘broad-leaf’ post-emergence herbicide. Its distribution in the environment is initially dependent on its application as an aerosol during spray application and removal from air by gravitational settling. When released to soil, the herbicide MCPP will readily leach, and may dissolve into and be transported with runoff water. Based upon its molecular weight, MCPP is not expected to volatilize. In addition, MCPP is not expected to strongly adsorb to soil. MCPP’s bioaccumulation potential appears to be low. Biodegradation in soil may be faster if soil microbes are acclimated to the presence of MCPP. Dioxins and Furans Dioxins/furans are generally nonvolatile organic compounds that are insoluble in water. If released to soil, dioxins/furans are expected to be readily adsorbed to soil based on their insoluble nature and as indicated by their relatively high octanol-water partition coefficient (Kow). The degree of adsorption is expected to increase as the natural organic content in soil increases. The most important transport-controlling mechanism for dioxins/furans in surface soil appears to be adsorption to soil particles and redistribution by either wind or stormwater erosion.


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Sorption or bioaccumulation appears to be a significant environmental fate-governing mechanism for dioxins/furans. Biotic and abiotic biodegradation or transformation processes have not been demonstrated to be significant removal mechanisms for dioxins and furans. PCBs PCBs are generally nonvolatile organic compounds that are insoluble in water. PCBs are expected to strongly adsorb to soils and sediment, and not readily leach because of their insoluble nature, and as indicated by their relatively high Kow. The predominant environmental transport mechanism is believed to be via wind and rain erosion of soil particles. A secondary transport mechanism may be volatilization from impacted surface soils, and subsequent removal from the atmosphere via wet/dry deposition. In general, the lesser-chlorinated PCBs volatilize from soils more readily. In general, the persistence of PCBs increases with the degree of chlorination. Sorption or bioaccumulation appears to be the environmental fate-governing mechanism for PCBs. Limited data are available concerning the chemical degradation of PCBs in soil, but biotic and abiotic biodegradation or transformation processes have not been demonstrated to be significant removal mechanisms. Metals The measurement of anthropogenic metals contamination in environmental media is complicated by the presence of naturally-occurring metals. Dominant transport mechanisms for metals are surface water or wind erosion of surface soil and particulate transport. Significant downward transport of metals into soil is observed when the metal retention capacity of the soil is overloaded, or when metals are solubilized. The solubility of metals is often increased by low soil pH (acidic) conditions and decreased by high pH (alkaline) conditions. As soil concentrations of metals increase and the adsorptive capacity of the soil is exhausted, metals will migrate with infiltration water. Metals are generally persistent in the environment indefinitely because metals do not degrade. Unlike organic compounds that can be destroyed, metals can only be changed in the oxidation state, chemical species, and physical form. However, biotic and abiotic transformations have been identified that, in some instances, may reduce the toxicity of the metal, that is, transform from dissolved phase to solid phase due to a change in oxidation state. 6.1.1.2 Site-specific Examples of Constituent Transport from Contaminated Surface Soils Locations where elevated COPCs were detected in surface soil include:

RCRA Canyon Area – A variety of inorganic constituents, with barium being most prevalent, were detected in the majority of sampling locations in the RCRA Canyon Area. Metals, such as barium, cadmium, chromium, cobalt, lead, mercury, nickel, selenium, tin, and zinc were detected above screening levels.

West Canyon Spray Area – Metals, such as cadmium, chromium, cobalt, copper, iron, lead, nickel, tin, and zinc were detected above screening levels. Concentrations exceeded screening levels in locations primarily in the southern portion of the study area.


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Burial Trench Area – Exceedances above screening levels for inorganics in surface soils included lead, chromium, nickel and selenium, principally in the southern portion of the study area.

Metals, including barium, cadmium, chromium, copper, manganese, molybdenum, nickel, selenium, tin, and zinc detected in the site stormwater ponds, including the RCF Pond, the A-series pond, and Pond 13.

Inorganics, including barium, cadmium, copper, nickel, and selenium were detected at elevated levels in sediment samples from the treated liquids impoundments, including Pond A-5 and Pond 18.

Surface water runoff from other study areas likely transported these COPCs to the stormwater and treated liquids impoundments located on the site. Sediment data suggests COPCs transported to these locations either precipitated from solution into solid phases, or if transported on particulate surfaces, settled due to gravity. 6.1.1.3 Actions Taken to Disrupt Surface Soil Environmental Transport Pathways As discussed elsewhere in the FS Report, numerous actions have been taken that affect the fate and transport of chemicals at the site. Specific actions that have been taken to mitigate constituent transport in surface soil include:

Landfill Capping – Engineered landfill caps, such as the P/S Landfill cap and EE/CA cap, are designed to mitigate the erosive action of stormwater runoff and wind. Landfill cap design and construction prevent stormwater runoff contact with contaminated soils, and transport of contaminated soils. The vegetative cover prevents wind erosion of biotic cover soils.

Site stormwater runoff is captured and contained at the site to prevent transport of COPCs via surface water outside the site boundary. The RCF Pond, the A-series pond, and Pond 13 are designed to prevent transport of untreated surface water beyond the site boundary.

6.1.2 Sediment COPCs Chemical constituents detected in sediments in excess of screening levels, by COPC class, include:

VOCs – 1,1-dichloroethane (1,1-DCA); Pesticides and Herbicides – MCPP (2-(4-chloro-2-methylphenoxy)- Propanoic acid); PCBs – PCB Congeners; and Metals – barium, cadmium and selenium.

6.1.2.1 Migration and Persistence of Sediment COPCs Sediment is typically subjected to transport mechanisms similar to those that are active in surface soils. The primary process by which sediments are contaminated is the erosion of contaminated surface soil or rock, particulate transport, and deposition of particulates in stream channels and ponds. Potential transport pathways for sediments that may be carried and redeposited via surface water flow are discussed in Section 4.3, and historical drainage features are illustrated in Figure 4-1. Stormwater erosion and contamination of sediments is particularly


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important for low-solubility contaminants that are bound or sorbed to sediment particles, such as pesticides, herbicides, PCBs, and metals. VOCs VOCs are organic compounds that exhibit relatively high vapor pressures, with limited solubility in water. A major transport process for VOCs from surface sediment systems is volatilization. The most prevalent VOC encountered in sediment, 1,1-DCA, is a HVOC. HVOCs are not expected to selectively concentrate on or be sorbed by sediments. If a HVOC such as 1,1-DCA volatilizes from sediment and partitions to the atmosphere, it will be degraded by photo-oxidation. Little biodegradation of HVOCs is expected to occur in sediments, and processes other than volatilization do not appear to play a significant role in the removal of HVOCs from sediment systems. Pesticides / Herbicides MCPP is a selective ‘broad-leaf’ post-emergence herbicide. Its distribution in the environment is initially dependent on its application as an aerosol during spray application and removal from air by gravitational settling. When released to soil, the herbicide MCPP will readily leach, and may be dissolved into and transported with runoff water, thus explaining the potential accumulation in sediment. MCPP’s bioaccumulation potential appears to be low, and the compound can biodegrade in sediment. Biodegradation in sediment may be faster if microbes have acclimated to the presence of MCPP. PCBs PCB compounds are nonvolatile organic compounds that are insoluble in water. PCBs are expected to strongly adsorb to sediment, and not leach extensively because of their insoluble nature. The predominant environmental transport mechanism is through sediment particle transport via either wind- or rain-driven erosion. Therefore, accumulation of PCBs in sediment may be expected. Sorption or bioaccumulation appears to be the environmental fate-governing mechanism for PCBs. Limited data are available concerning the chemical degradation of PCBs in sediment, but biotic and abiotic biodegradation or transformation processes have not been demonstrated to be significant removal mechanisms. Metals The measurement of anthropogenic metals contamination in environmental media is complicated by the presence of naturally-occurring metals. Dominant transport mechanisms for metals are surface water or wind erosion of surface soil or rock and particulate transport. Therefore, accumulation of metals in sediment may be expected. Metals are generally persistent in the environment indefinitely because metals do not degrade. Unlike organic compounds that can be destroyed, metals can only be changed in the oxidation state, chemical species, and physical form.


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6.1.2.2 Site-specific Examples of Constituent Transport in or to Sediments Examples of elevated COPCs in sediments include:

Metals, including barium, cadmium, chromium, copper, manganese, molybdenum, nickel, selenium, tin, and zinc detected in the site stormwater ponds, including the RCF Pond, the A-series pond, and Pond 13.

Metals, including barium, cadmium, copper, nickel, and selenium detected at elevated levels in sediment samples from the treated liquids impoundments identified as Pond A-5 and Pond 18.

PCBs and pesticides (alpha chlordane, DDD, DDT, dieldrin, and/or endrin) detected above screening levels in sampling locations in the RCF Pond.

Surface water runoff from other site areas, such as the RCRA Canyon Area and the West Canyon Spray Area, likely transported dissolved or sediment-borne inorganic COPCs to the site stormwater and treated liquids impoundments. PCBs and pesticides (alpha chlordane, DDD, DDT, dieldrin, and/or endrin) detected in sediments within the RCF Pond may have been transported there prior to capping the P/S Landfill. 6.1.2.3 Actions Taken to Disrupt Environmental Transport Pathways to or via Sediment As discussed elsewhere in the FS Report, numerous actions have been taken that affect the fate and transport of chemicals at the site. Specific actions that have been taken to mitigate constituent transport to or via sediments include:

Surface water runoff is captured and contained within the site boundaries to prevent transport of COPCs via suspended particles or sediment. The RCF Pond, the A-series pond and Pond 13 are designed to prevent off-site transport of untreated surface water.

Surface Impoundment Closure Activities – Surface impoundments used during hazardous waste management operations have been closed. Closure activities removed contaminated liquids and bottom sludge, thus eliminated them as potential sources of contaminated sediment.

Landfill Capping – Engineered landfill caps, such as the P/S Landfill cap and EE/CA cap, are designed to mitigate the erosive action of surface water runoff. Landfill cap design and construction prevent stormwater runoff contact with contaminated soils, and transport of contaminated soils as suspended particles in stormwater. The landfill cap designs also mitigate the potential for wind erosion of contaminated soils, and subsequent redeposition as sediment in neighboring surface water bodies.

6.1.3 Surface WaterCOPCs Chemical constituents detected in surface water in excess of screening levels, by COPC class, include:

VOCs (acetone and acetonitrile); SVOCs (n-nitrosodipropylamine); PAHs; Dioxins / Furans; and Metals (arsenic, molybdenum, and selenium).


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6.1.3.1 Migration and Persistence of Surface Water COPCs Contaminant migration into surface waters at the site may occur through surface water runoff, groundwater seepage, and/or dust generation/redeposition. Upon reaching surface water, transport of chemicals can occur through advection and dispersion of solutes, suspended solids, and colloids. Intermedia transfer can occur if the surface water infiltrates into the subsurface, or through emission of volatile chemicals. Potential transport pathways for contaminated surface water are discussed in Section 4.0, and historical drainage features are illustrated in Figure 4-1. VOCs Volatile organic compounds tend to quickly volatilize into the atmosphere upon reaching surface water. Therefore, VOCs are rarely observed at detectable concentrations in surface water samples. However, those VOCs with relatively high solubilities or Henry’s Law constant may tend to remain dissolved in surface water and persist longer. SVOCs and PAHs Major transport processes for SVOCs and PAHs in surface water include migration as solutes in water, or sorbed to suspended particulate material. In natural water systems, solute transport is via surface water flow and/or groundwater seepage. Dioxins/Furans Dioxins/furans can enter surface water by a number of different mechanisms including surface water runoff, groundwater seepage, deposition of particulates from combustion sources, and deposition of particulates from wind erosion. Dioxins/furans are expected to adsorb to suspended particulate material in the water column and be transported to the sediment. In fact, binding to particulates and sediments is considered a primary removal process of dioxins/furans from surface water. Low water solubilities and high Kow coefficients indicate that dioxins/furans will strongly bind to organic matter. Dioxins/furans are also expected to bioconcentrate in aquatic organisms, if present. However, as a result of their binding to organic matter, the actual uptake and transfer to aquatic organisms may be less than predicted. Metals Metals can enter surface water by a number of different mechanisms including surface water runoff, groundwater seepage, and deposition of soil particulates from wind erosion. Once in surface water, major transport processes for metals are as solutes in surface water or sorbed to suspended particulate material, and subsequent dispersion via surface water flow. A variety of natural reactions in surface water may occur that will influence the speciation and mobility of metals in surface water, including water pH, precipitation/dissolution, oxidation/ reduction, sorption, or ion exchange. Precipitation, sorption, and ion exchange reactions would be expected to remove metals from the surface water column. 6.1.3.2 Site-specific Examples of Constituent Transport via Surface Water, or to Surface

Water Examples of elevated COPCs detected in surface water include:


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Metals, including barium, cadmium, chromium, copper, manganese, molybdenum, nickel, selenium, tin, and zinc detected in the site stormwater ponds, including the RCF Pond, the A-series ponds, and Pond 13. Of the surface water features sampled, Pond 13 has the highest concentrations of dissolved metals.

Metals, including arsenic, nickel, and selenium have been detected at elevated levels in water samples from the treated liquids impoundments identified as Pond A-5 and Pond 18.

Seasonal surface water runoff from RCRA Canyon stormwater and groundwater seepage (metals).

Groundwater seepage at the base of the dike embankments for Pond A-5 and Pond 18 from surface water in the ponds (metals).

Historical groundwater seepage between the P/S Landfill and PSCT-1 due to shallow water table (metals and organics). This seepage is controlled with liquids extraction from Sump 9B which depresses the naturally shallow water table, particularly during the winter rainy months. The seeps will reoccur if the well screen and gravel pack is allowed to become clogged and not periodically redeveloped. A seep last occurred in the Sump 9B area during the above normal 2011/12 rainy season.

Surface water runoff from other study areas, or in some cases seepage of contaminated groundwater to the ground surface, transported COPCs to the stormwater and treated liquids impoundments located at the site. Sediment data suggests COPCs transported to the ponds either precipitated from dissolved to solid phases, or if transported on particulate surfaces, were deposited in sediments due to gravitational settling. 6.1.3.3 Actions Taken to Disrupt Environmental Transport Pathways to Surface Water As discussed elsewhere in the FS Report, numerous actions have been taken that affect the fate and transport of chemicals at the site. Specific actions that have been taken to mitigate constituent transport to or via surface water include:

Site surface water runoff is captured and contained to prevent transport of COPCs via surface water outside the site boundaries. The RCF Pond, the A-series pond and Pond 13 are designed to prevent transport of untreated surface water beyond the site boundaries.

Surface Impoundment Closure Activities – surface impoundments used during hazardous waste management operations have been closed. Closure activities removed contaminated liquids, thus eliminating them as a source for further surface and subsurface soil contamination via leaching.

Landfill Capping – engineered landfill caps, such as the P/S Landfill cap and EE/CA cap, are designed to mitigate the erosive action of surface water runoff. Landfill cap design and construction prevent stormwater runoff contact with contaminated soils, and transport of contaminated soils.

Groundwater extraction from Sump 9B (which needs to be periodically redeveloped every several years to prevent clogging of the well screen and gravel pack) and the Road Sump prevents groundwater seepage from occurring between the P/S Landfill and PSCT-1.

Lowering of pond levels for Pond A-5 and Pond 18 decreases groundwater seepage at the base of the dike embankments of the ponds.


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6.2 Subsurface Transport Pathways – COPC Fate and Transport The migration of subsurface contaminants involves the fate and transport of chemicals associated with subsurface soil, soil vapor, groundwater, and NAPL, and their impacts to potential receptors in the surrounding environmental setting. Subsurface soil COPCs observed at the site are discussed in Section 6.2.1. Soil vapor chemical constituents, and contaminant transport processes are discussed in Section 6.2.2. Groundwater chemicals and a discussion of groundwater contaminant migration are discussed in Section 6.2.3. NAPL chemicals and a discussion of NAPL migration are discussed in Section 6.2.4. 6.2.1 Subsurface Soil COPCs Chemical constituents detected in subsurface soil in excess of screening levels, by COPC class, include:

VOCs – PCE, TCE SVOCs – bis(2-ethylhexyl)phthalate Pesticides and Herbicides – MCPP (2-(4-chloro-2-methylphenoxy)-Propanoic acid), 4,4’-

DDE, 4,4’-DDT, and Hexachlorobenzene Dioxins/Furans – Dioxin TEQ PCBs – PCB Aroclor 1260, and PCBs (total) Metals – barium, cadmium, chromium, copper, lead, and zinc.

6.2.1.1 Migration and Persistence of Subsurface Soil COPCs Subsurface soil is a medium that, by itself, is not a transport pathway; rather, COPCs adhered or absorbed to subsurface soil may partition and contribute to groundwater and soil vapor contamination. COPC transport from subsurface soil to other environmental media is dependent upon physical, chemical, and biological mechanisms, such as dissolution, and sorption/desorption processes. COPC transport is also influenced by the type of subsurface conduits (i.e., porous soil matrix or fractures) that govern the pathway for the redistribution. VOCs VOCs are organic compounds that exhibit relatively high vapor pressures, with limited solubility in water. A major transport process for VOCs from subsurface soil systems is volatilization and advective groundwater flow. The most prevalent VOCs encountered in subsurface soil are TCE and PCE. VOCs, particularly HVOCs like TCE and PCE, are not expected to selectively concentrate on or be sorbed by soils. If HVOC vapors migrate and partition to the atmosphere, HVOCs will be degraded by photo-oxidation. Recent identification of site microcosms (Appendix G) indicate that biodegradation of HVOCs is expected to occur in saturated subsurface soils where geochemical conditions are anaerobic. Volatilization and biodegradation appear to play a significant role in the removal of HVOC from soil systems. SVOCs A review of the physical, chemical, and biological data for SVOCs indicates that these compounds are generally nonvolatile organic compounds that are insoluble in water. SVOCs


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are expected to be readily adsorbed to subsurface soils because of their insoluble nature, and as indicated by their relatively high Kow. Compounds with Kow coefficients greater than 3 are considered to be relatively immobile in environmental media (Table 6-1). Sorption or bioaccumulation appears to be the primary environmental fate-governing mechanism for SVOCs. Volatilization of SVOCs is not expected to be a significant removal factor. Limited data are available concerning the chemical degradation of SVOC in soil, but abiotic degradation has not been demonstrated to be a significant removal mechanism. Therefore, physical and biological transformation (e.g., intermedia transfers and biodegradation) of SVOCs is expected to be minimal. Pesticides/Herbicides A review of the physical, chemical, and biological data for pesticides detected at the site indicates that most of these compounds are generally nonvolatile organic compounds that are insoluble in water. The detected pesticides are expected to be readily adsorbed to subsurface soils because of their insoluble nature, and as indicated by their relatively high Kow. Removal of pesticides from soil via biodegradation or abiotic processes is expected to be quite slow at the site. For example, pesticides such as endrin or DDT have observed half-lives in soil as great as 10 to 50 years. Sorption and/or bioaccumulation in plant and animal tissue appear to be the primary environmental fate-governing mechanism for most pesticides encountered at the site. The herbicides detected at the site are generally nonvolatile organic compounds that are relatively insoluble in water. Release of these compounds to the environment may have occurred either by commercial use of these chemicals as herbicides, or by disposal of spray rinsate from herbicide drums or spray equipment. Once released to soil, the herbicides detected at the site are expected to have a relatively high mobility based on lower Kow coefficients, compared to pesticides, such as DDT. However, the biodegradation potential of herbicides appears to be much greater than pesticides such as DDT. Lastly, the potential for bioaccumulation in plant and animal tissue also appears to be less for herbicides than for pesticides such as DDT. Dioxins/Furans Dioxin/furan compounds are generally nonvolatile organic compounds that are insoluble in water. Dioxins/furans are expected to be readily adsorbed to subsurface soil based on their insoluble nature, and as indicated by their relatively high Kow coefficients. Sorption or bioaccumulation appears to be a significant environmental fate-governing mechanism for dioxins/furans. Available field data on biotic and abiotic degradation or transformation processes are insufficient to confirm their importance in reducing dioxin/furan concentrations in the environment. PCBs PCB compounds are generally nonvolatile organic compounds that are insoluble in water. PCBs are expected to strongly adsorb to subsurface soils, and not leach extensively because of their insoluble nature, and as indicated by their relatively high Kow. In general, the persistence of PCBs increases with the degree of chlorination. Sorption or bioaccumulation appears to be the primary environmental fate-governing mechanism for PCBs.


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Limited data are available concerning the chemical degradation of PCBs in soil, but biotic and abiotic biodegradation or transformation processes have not been demonstrated to be significant removal mechanisms. Metals A review of the physical, chemical, and biological data for metals indicates that persistence and migration of these constituents are impacted by the metal’s chemical form, the matrix it is encountered in, soil type, and soil geochemistry. Unlike the organic COPCs, metals cannot be degraded. However, biotic and abiotic transformations have been identified that, in some instances, may reduce the toxicity of the metal. Significant downward transport of metals into soil is observed when the metal retention capacity of the soil is overloaded, or when metals are dissolved. The solubility of metals is often increased by reduced soil pH conditions. As soil concentrations of metals increase and the adsorptive capacity of the soil is exhausted, metals will migrate with infiltration water. Unlike organic compounds that can be destroyed, metals can only be changed in the oxidation state, chemical species, and physical form. 6.2.1.2 Site-specific Examples of Constituent Transport from Contaminated Subsurface Soils Locations where elevated COPCs were detected in both shallow and deepsoil include:

Landfills Area – The waste deposits of both the capped and uncapped landfills. RCRA Canyon Area – The residual waste deposits of the former RCRA Landfill area.

Drilling mud-like materials with staining are present at RITRRC-1. Burial Trench Area – Data indicate that shallow to deep soils, principally within the

central portion of the Burial Trench Area, have been significantly impacted by a variety of inorganic and organic constituents. Deep soil impacts by VOCs are also present along the southern margin of the area.

Central Drainage Area – Exceedances for organic constituents are limited almost exclusively to shallow to deep soils within the western portion of the study area, principally in proximity to the toe of the P/S Landfill, Sump 9B and locations situated down slope of these areas toward the PSCT.

Former Ponds & Pads Subarea – VOC concentrations in excess of screening levels (both TCE and PCE) are detected in medium depth soils in borings completed within the limits of former Pond A and Pond B, located in the north central portion of this area just south of the PSCT. Other borings completed within former Ponds A and B did not encounter similarly elevated organics, indicating that significant soil impacts related to these two former ponds are of limited lateral extent. Soil staining was present at the bottom of RITRON-1 and -2 that evaluated the former drainage feature between Pond C and Pond M. No indications of significant soil impacts were encountered in deep borings and membrane interface probe (MIP) investigations completed along historical drainage paths. Investigative findings indicate that prior soil cleanup activities conducted within the Former Ponds and Pads Subarea were very effective.

Remaining On-Site Area – The most prevalent inorganic exceedances encountered in subsurface soils included nickel and zinc. Organic exceedances of poor purging organics (PPOs) and PAHs were detected in deep soil in four separate locations along the southern site boundary. One location is associated with the former diesel fuel pump area south of former Pond A-1, and the others are in proximity to a former waste impoundment once located near the western end of the present RCF Pond that is visible on the 1974 and 1975 historical aerial photographs (RISBON-59 area – below).


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RISBON-59 Area – Available data, including analytical laboratory results, MIP measurements and field observations, indicate that the highest concentrations and greatest variety of contaminants within this area are present at depths of between approximately 27 to 36 feet bgs, and diminish both laterally and vertically away from this location. Contamination detected in the RISBON-59 area is coincident with the southern margin of former waste management Pond 2, as well as a preceding former waste impoundment visible on historical aerial photographs from 1974 and 1975.

At any of these locations, there is the potential that contaminated subsurface soils may be contributing to impacts observed in other environmental media, such as groundwater and soil vapor. While historical information indicates otherwise, it is theoretically possible that subsurface soil impacts at these locations may originate from other sources such as NAPL, and/or leaching of surface contaminants via infiltration of stormwater, surface water runoff, or impoundment liquids. 6.2.1.3 Actions Taken to Disrupt Subsurface Soil Environmental Transport Pathways As discussed elsewhere in the FS Report, numerous actions have been taken that affect the fate and transport of chemicals at the site. Specific actions that have been taken to mitigate constituent transport in subsurface soil include:

Surface Impoundment Closure Activities – Removal of liquids, bottom sludge and contaminated sub-grade material removed potential sources of inorganic and organic contaminants that could impact subsurface soils underlying the former ponds and pads. Impacted materials were stabilized and emplaced in the now-capped landfills.

Landfill Capping – Engineered landfill caps, such as the P/S Landfill cap and EE/CA cap, are designed and constructed to mitigate stormwater infiltration through waste materials, and subsequent leaching of waste materials into groundwater underlying the landfills.

6.2.2 Soil Vapor COPCs Typically, soil vapor has included VOCs exclusively. A total of 43 individual VOCs were detected at various soil vapor sampling locations around the perimeter of the landfills, the Burial Trench Area, and the Central Drainage Area, including chlorinated and aromatic hydrocarbons, acetone, methyl ethyl ketone, and freon gases. The most significant VOCs in terms of prevalence and highest concentrations include acetone, methyl ethyl ketone, Freon 113, benzene, 1,3-butadiene, and PCE. 6.2.2.1 Migration and Persistence of Soil Vapor COPCs VOCs VOCs encountered at the Site generally share similar volatility and water-solubility characteristics. When VOCs are released to soils, a significant fraction of the chemical rapidly partitions to the air by volatilization. VOCs are not expected to selectively concentrate on or be sorbed by soils or to be taken up and retained in biological tissues. However, VOCs with lower Kow coefficients, such as acetone and methyl ethyl ketone, are expected to have very high mobility through soil pores, as their migration by advection and diffusion is not retarded by sorption to soil surfaces. Biodegradation of VOCs borne in soil vapor as interphase transfer from soil gas to soil moisture in soil takes place, although the rate is controlled by the presence (or lack) of available oxygen, or a secondary carbon substrate. Therefore, degradation


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byproducts or daughter products of VOCs would be expected to be observed in the environment surrounding source areas. For example, elevated levels of PCE/TCE degradation daughter products 1,1-DCE, cis-1,2-dichloroethene (cis-1,2-DCE), and vinyl chloride (VC) were detected in soil vapor samples collected along the southern boundary of the Central Drainage Area, and the central portion of the Burial Trench Area. Elevated levels of PCE and TCE were detected in soil vapor samples collected from both these areas. The distribution of total VOCs in soil vapor is presented in Figure 5-4. 6.2.2.2 Site-specific Examples of Constituent Transport via Soil Vapor The primary source areas at the site where elevated soil vapor levels of VOCs were expected were areas where impacts to soil and groundwater are known to be significant. For example, primary source areas where elevated soil vapor concentrations have been detected include:

The Capped Landfills Area; The PCB Landfill; The Liquids Treatment Area; The Central Drainage Area; and The Burial Trench Area.

Subsurface migration of chemicals in soil vapor is due to advection and diffusion. Typically, diffusion is the dominant mechanism for vapor transport within the vadose zone. An exception to this rule is the case for landfills that have large amounts of readily biodegradable material which will decompose and produce large amounts of methane as a byproduct. Generation of large amounts of methane can lead to advective soil vapor transport away from the landfill source area. Large quantities of methane generation are usually associated with landfills that accept municipal and green waste. Testing of soil vapor at Casmalia Resources focused on organic hazardous wastes, and testing specifically for methane was limited. Methane sampling was conducted on a limited subset of wells as part of the MNA evaluation. Appendix O of the RI report (2011) describes detections of dissolved methane as being indicative of biological activity in groundwater. Soil vapors likely migrated beyond historical site boundaries away from these source areas northward into the North Drainage, eastward into the North Ridge, southward into the Former Ponds and Pads area, and westward towards the RCRA Canyon area. Prior to placement of the landfill caps, VOCs readily volatilized to the atmosphere, however since the placement of the landfill caps, VOCs are likely retarded from direct off-gassing and may become trapped beneath portions of the caps. These trapped VOCs will migrate laterally in response to diffusion gradients from the higher VOCs underneath the capped area to the lower concentrations outside of the capped areas. For example, the highest concentration of two of the lighter and more mobile VOCs, acetone and 1,3-butadiene, occurs along the north and eastern ridge area. These VOCs also extend northward into the North Drainage as described in Section 5. VOC off-gassing for the heavier DNAPL compounds is highest in and around the P/S landfill and along the PSCT. Typically the vapor density of such VOCs is greater than air, and VOC gas tends to reside in unsaturated pore spaces close to the water table. The rate of any organic vapor mass flux from soil will be a function of the soil properties as well as the chemical’s physical/chemical properties. Migrating soil vapors can cross contaminate groundwater that would otherwise not be contaminated solely due to groundwater contaminant


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transport. The soil vapor and potential groundwater impacts from migrating soil vapors are summarized below. Soil Vapor Impacts As shown in Figures 5-19 and 5-20, moderately elevated levels of acetone and methyl ethyl ketone were detected in soil vapor samples collected around the PCB landfill, Capped Landfills Area, Liquid Treatment Area, and within the Burial Trench Area. Moderately elevated concentrations of methyl ethyl ketone were also detected south of the Central Drainage Area. Low levels of 1,3-butadiene were also detected along the Capped Landfills Area northern boundary and step-out locations into the North Drainage, as well at the northwestern boundary of the PCB landfill (Figure 5-22). In general, acetone, methyl ethyl ketone, and 1,3-butadiene appear to exhibit greater mobility at the site than other organic compounds detected in soil vapor. The apparent increased mobility of these compounds can be traced to common physical characteristics these compounds share. For example, acetone and methyl ethyl ketone have Kow values that are less than 10 milliliters per gram (ml/gm), and both are very soluble in water. While 1,3-butadiene is not as soluble as acetone and methyl ethyl ketone, its vapor pressure properties indicate 1,3-butadiene will exist solely as a gas in the ambient atmosphere (Table 6-1). Groundwater Impacts The potential exists for soil vapor to impact groundwater via phase partitioning. Soil vapor in contact with groundwater (and soil moisture) will partition into the liquid phase in accordance with Henry’s Law and Raoults’ Law, where factors such as the partial pressure exerted on the liquid by the gas, the specific compound solubility, and the compound’s mole fraction in the mixture will determine the mass transfer rate. Areas where soil gas VOCs may impact groundwater occur where NAPL product is present or at the peripheral edges of the groundwater plumes or containment structures. 6.2.2.3 Actions Taken to Disrupt Soil Vapor as an Environmental Transport Pathway The P/S Landfill stopped receiving waste in 1986. The landfill was covered with stabilized materials from pond closure activities that were completed in the early 1990s. In the late 1990s, the CSC completed the design and construction of a landfill cap for the P/S Landfill. According to the P/S Landfill Revised Final Design Report (Foster Wheeler and GeoSyntec, 1999), a series of gas flux measurements were performed at the P/S Landfill to direct the development of the final landfill cap design. The objectives of these pre-capping soil vapor flux measurements on the cover of the P/S Landfill included:

Evaluating the potential for landfill gas emissions; Assessing whether a gas mitigation system would be needed to address VOC emission;

and; and Providing data for a gas collection system or layer design in the event a gas mitigation

system was deemed necessary. Field testing for soil vapor emissions from the P/S Landfill was conducted by measuring the flux of VOCs, fixed gases (nitrogen, oxygen, carbon dioxide, carbon monoxide, and methane), and organochlorine pesticides through the existing, undisturbed soil cap of the P/S Landfill. Surface gas flux emission sampling was performed in November 1997.


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Site investigations and historical records indicate that decomposable waste was not generally disposed within the P/S landfill. The landfill has not been expected to produce significant amounts of methane or other fixed gases that are commonly associated with breakdown of decomposable materials. In total, 10 VOCs were detected at concentrations at the method detection limit for the individual compounds. The highest flux of a VOC that was detected during the assessment was PCE (1.9 micrograms per square meter per minute [µg/m2-min]). Assuming the landfill capped areas cover 41 acres and PCE is being emitted equally from all landfill cells, then approximately 1-pound of PCE would be emitted by volatilization per day prior to landfill capping. The lack of significant methane or other fixed gases, such as would normally be associated with waste decomposition, was consistent with known site information that decomposable waste was not generally disposed in the P/S Landfill. These data demonstrated that landfill gas was not being produced at a significant rate prior to construction of the final P/S Landfill cap, and the rate of landfill gas production would not adversely impact a landfill cap. Based on these findings, it was concluded that the finalized landfill cap design constructed over the P/S Landfill would effectively eliminate the very low gas fluxes observed. The engineered capping system installed for the P/S Landfill and EE/CA Landfill areas altered the distribution and transport of soil vapor from these source areas. Installation of the caps increased the soil column thickness, and thus increased the distance between the primary contaminant sources (i.e., landfill wastes) and their potential emission point to the ambient atmosphere. The construction materials selected for the caps included fine-grained soils and low-permeability HDPE geomembranes to reduce advective and diffusive transport of soil vapor. 6.2.3 Groundwater COPCs As described in Section 5, VOCs were selected as indicators to help delineate the extent of organic compounds in groundwater. VOCs are generally more mobile in groundwater relative to the other classes of organic compounds (SVOCs, herbicides, pesticides, PCBs, and dioxins/furans) and the extent of the other classes of organic compounds is generally contained within the extent of VOCs. Therefore, VOCs are used to illustrate the transport of organic contamination. Also as described in Section 5, arsenic indicates the extent of metals because it is the most broadly elevated metal within the Upper HSU, it exceeds primary MCLs where elevated, and the extent of the other elevated metals is generally contained within the extent of elevated arsenic. Generally, VOCs that were detected in groundwater in the greatest number of wells and at relatively high concentrations (RI Report, Appendix G; Section 3.3.2; 2011) include:

PCE; TCE; cis-1,2-DCE; VC; and, Benzene.

Inorganic compounds that were detected in groundwater in the greatest number of wells and at relatively high concentrations included arsenic, nickel, cadmium, and selenium for metals that


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had primary MCL exceedances, and iron and manganese for metals that had secondary MCL exceedances. Organic COPCs. Figures 6-1 through 6-3 show the distribution of Total VOCs within Zone 1, in the Upper HSU and Lower HSU. There does not appear to be any significant VOC contamination in groundwater underlying areas outside the site boundary (Zone 2), in either the Upper HSU or Lower HSU. Within Zone 1, the lateral extent of VOC impacts within the Upper HSU is defined by the following features:

The area north of the PSCT contains the majority of the dissolved phase VOC contamination.

The northern extent of the Upper HSU contamination, from east to west, is limited to the western portion of the Caustic/Cyanide Landfill, the western half of the Acids Landfill, the southern portion of the Metals Landfill, the northern portion the P/S Landfill and at the Burial Trench Area south of the PCB Landfill.

The eastern extent of VOC contamination is delineated by several monitoring wells near the eastern extent of the PSCT and North Ridge wells.

The western extent of the VOC contamination is delineated by RI monitoring wells on the North Ridge and west of the PSCT.

The distribution of VOC contamination in the Upper HSU is consistent with groundwater flow directions.

There are also isolated locations of upper HSU groundwater impacts due to VOC contamination south of the PSCT. These impacts are highest south of PSCT-1 and PSCT-4. However, the contamination in these areas is typically one to two orders-of-magnitude lower than maximum concentrations observed north of the PSCT. The VOC contamination in this area may be associated with residual contamination extant before the PSCT was installed and related to the operation of the former waste disposal ponds. VOC impacts in groundwater were observed in four areas of the Lower HSU:

The North Ridge Area The Burial Trench Area; The Central Drainage Area; including the southern edge of the Acids Landfill; and Along the PSCT, including at extraction wells PSCT-1, PSCT-3, and PSCT-4.

The Central Drainage Area exhibits the greatest amount of VOC contamination in the Lower HSU, and is the only area in the Lower HSU where DNAPL is known to be present. The Lower HSU VOC contamination in the Central Drainage appears to be spatially related to overlying Upper HSU VOC groundwater contamination present between the P/S Landfill and PSCT. Inorganic COPCs. Figures 5-33a, 5-33b, and 5-34 show the distribution of arsenic within Zone 1, in the Upper HSU and Lower HSU. There appears to be no significant inorganic contamination in groundwater underlying Zone 2 in either the Upper HSU or Lower HSU. Within Zone 1, the general distribution of elevated metals is similar to the distribution of elevated VOCs in the Upper HSU, except for the ponds and PCTs. The higher concentrations of metals in the Upper HSU are generally located within the Central Drainage Area, similar to the higher concentrations of VOCs north of the PSCT. Elevated levels also occur south of the PSCT.


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Unlike the general absence of VOCs in the ponds and PCTs, however, TDS (salts) and metals are significantly elevated within surface water in the five site ponds, groundwater extracted at the PCTs, and other groundwater monitored at other monitoring wells in the vicinity of the ponds and PCTs. Pond surface water is a recharge source to the PCTs. The concentrations of the salt and metals in the ponds have been increasing due to evaporation since the 1997/98 El Nino winter, and similar increases in metals and salts in the PCTs and area monitoring wells are observed. The highest dissolved metals concentrations in the Lower HSU are predominantly located along the North Ridge on the border between Zone 1 and Zone 2., and do not appear to coincide with the elevated Upper HSU concentrations. Metals concentrations in the Lower HSU are generally lower than in the Upper HSU. 6.2.3.1 Migration and Persistence of Groundwater COPCs Natural attenuation processes play a critical role at the site, contributing both to containment and reduction of COC concentrations. Data compiled as part of the RI have shown the effectiveness of natural attenuation processes that include physical, chemical, or biological mechanisms. Natural attenuation naturally degrades COCs, which limits the movement of contamination and gradually improves water quality. The primary physical processes that result in the movement of dissolved-phase COPCs in groundwater are advection and dispersion. Advection is the movement of COPCs with the bulk movement of groundwater. Advection is generally the primary transport mechanism at the site with moderate to high groundwater flow rates. Mechanical dispersion is the mixing of COPCs with groundwater moving along the groundwater flow path. Dispersion will cause some COPC molecules to travel faster and some to travel slower than the average groundwater flow velocity. Dispersion will have the effect of spreading out (lowering) COPC concentrations as they advectively move with groundwater. Chemical diffusion will also contribute to the spreading of COPCs; chemical diffusion is driven by concentration gradients and independent of groundwater flow. In fine grained soil matrices (e.g., claystone), chemical diffusion is responsible for the dispersion of COPCs. Only highly “mobile” and “persistent” COPCs will move at the same or similar rate as groundwater flow. Most COPCs will move slower than groundwater due to retardation and natural attenuation mechanisms that include the following:

Biodegradation (organics). Biodegradation is the process where microbes degrade and destroy organic COPCs by transforming them into other byproducts. This will reduce the concentration of the organic COPCs along the groundwater flow path. Organics may degrade aerobically or anaerobically. Metals are not subject to biodegradation.

Sorption (organics and inorganics). Sorption is the process where organic and inorganic COPCs transfer from being dissolved in groundwater to the solid phase of the aquifer matrix. Sorption generally involves three primary mechanisms: adsorption onto the surface of the solid phase, precipitation onto the solid phase, and absorption (i.e., the diffusion into the solid phase).

Dilution (organics and inorganics). Dilution is the process where recharge from another source (e.g., rainfall infiltration) dilutes the organic and inorganic COPC concentrations. Dilution also results from dispersion (mechanical mixing).


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Hydraulic containment and chemical mass removal from groundwater also occurs via the groundwater extraction and treatment facilities at the site. This includes the current liquids extraction at the Gallery Well, Sump 9B, PSCT, and three PCTs, as described in Section 4. Hydraulic containment will act to change the direction of groundwater and contaminant flow paths. The migration and persistence of dissolved-phase COPCs based on their movement with groundwater movement, natural attenuation mechanisms, and hydraulic containment at the site are evaluated below. Figures 6-1 and 6-2 are a projection of the groundwater flow paths determined from MODFLOW modeling within the Upper HSU for the dry season (2004) and wet season (2001) model simulations, respectively. The release point for these tracking particles was along the North Ridge. Additional particle tracks were provided for “reverse particle tracking” from PSCT-4 and the three PCTs to more fully show groundwater flow paths and capture by the extraction facilities. The modeling indicates that groundwater (and contaminant) flow within the Upper HSU is downhill to the south and converges towards the Central Drainage Area. Figure 6-3 is a projection of the groundwater flow paths determined from MODFLOW modeling within the Lower HSU for the Dry (2004) model simulation. The release point for these tracking particles was north of the PSCT, to reflect contamination within the Lower HSU in this area. This includes the VOC’s detected north of PSCT-4 at RIPZ-16 and also the VOC and DNAPL detected north of PSCT-1 at piezometers RGPZ-7C and RGPZ-7D. The modeling indicates that groundwater (and contaminant) flow within the Lower HSU is south underneath the PSCT and continues southward toward the south part of the site. The particle tracks represent the direction of groundwater flow and where dissolved-phase COPCs will potentially migrate. However, the actual rate and distance that COPCs will migrate along these groundwater flow paths will be influenced by the natural attenuation mechanisms and active hydraulic containment. VOCs VOCs encountered at the site share similar volatility and water-solubility characteristics. When VOCs are released to soil or groundwater, a significant fraction of the chemical is expected to partition to soil vapor by volatilization. VOCs are not expected to selectively concentrate on or be sorbed by soils or to be taken up and retained in biological tissues. Biodegradation of VOCs will occur in groundwater and soils, although the rate is controlled by the presence (or lack) of available oxygen, other electron donors or acceptors, or secondary carbon substrates. Therefore, degradation byproducts or daughter products would be expected to be observed in the environment surrounding source areas. Solute migration with groundwater flow or volatilization and soil vapor migration are expected to play a significant role in the transport and removal of VOCs from the groundwater system. A variety of potential corrective action options may be considered to remediate the Upper and Lower HSUs at the site with respect to the mixture of chlorinated VOCs, their associated degradation products, and petroleum hydrocarbons. One potential option is utilization of natural attenuation processes. Natural attenuation is often defined as naturally occurring processes in soil and groundwater environments that act without human intervention to reduce the mass, toxicity, mobility, volume, and/or concentration of contaminants in those media. Consistent with standard practice and USEPA guidance, which encourage the use of multiple lines of evidence


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to assess MNA, three distinct lines of evidence were used to evaluate the effectiveness of natural attenuation processes:

Historical groundwater and/or soil chemistry data that demonstrate a clear trend of decreasing contaminant mass and/or concentration over time at appropriate monitoring or sampling points (the concept of a stable or shrinking plume).

Hydrogeologic and geochemical data that can be used to demonstrate indirectly that the appropriate natural attenuation processes are active at the site; and the rate at which such processes will reduce contaminant concentrations to required levels.

Data from field or laboratory microcosm studies. Identification of site-specific micro-organisms provided a line of evidence that confirms the presence of bacteria capable of degrading organic compounds or reducing metal compounds.

Each of these lines of evidence demonstrates the occurrence of natural attenuation processes at the site. As is often the case, biodegradation is the one of most important destructive attenuation mechanisms for organic compounds, and is the primary process that was evaluated for groundwater at the site (RI Report, Appendix O; 2011; and Appendix G, this report). An investigation was conducted to assess whether natural attenuation of both fuel hydrocarbon and chlorinated hydrocarbons is occurring at the site, particularly in locations proximal to the principal contaminant source areas, and in the vicinity of the PSCT. Findings of the natural attenuation (NA) assessment are summarized below for organic chemicals:

The destruction process of aerobic and anaerobic biological degradation of organic chemicals in the source and plume areas is occurring.

Non-destructive process are also occurring, including sorption and dilution from rainfall recharge and dispersion.

Organic chemical and geochemical analytical results support conclusion that a reductive dechlorination zone exists to the north of the PSCT. Reductive dechlorination may also be occurring south of the PSCT, but the evidence is less clear.

Electron donors and acceptors – The relative concentrations of sulfate, nitrate, and dissolved manganese at locations within, up- and down-gradient of the source and plume areas are consistent with biological degradation and the use of these electron donors and/or acceptors.

Presence of daughter or end-products – Dissolved methane, ethane, and chloride – were observed at elevated levels within the source and plume areas, indicating active biological degradation and complete dechlorination of chlorinated VOCs is occurring at the site.

General parameters – A decrease in oxidation-reduction potential (ORP =< -100 millivolts, or mV) and an increase in alkalinity (greater than 2-times background locations) were observed in the source and plume areas. Reduced or negative ORP levels provide an indirect indication of anaerobic conditions supportive of reductive dechlorination, and elevated alkalinity levels indicate complete biodegradation of organic compounds, due to the interaction between carbon dioxide and aquifer materials.

Identification of bacteria capable of degrading organic compounds. Identification of bacteria capable of reducing metals compounds.

The NA evaluation identified a number of key factors that lead to the conclusion that natural attenuation processes are active at the site, and these processes can play a significant role in a


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final remedy for groundwater at the site. Analysis of spatial and temporal trends in constituent concentrations demonstrates the effectiveness of natural attenuation processes. During the RI, investigators considered techniques to quantify rates of natural attenuation, but determined that such efforts would be ineffective due to the large number of constituents in groundwater and variable degradation rates. For example, the NA evaluation concluded that the use of tracer chemicals to normalize the effects of dispersion, dilution, sorption, etc. was not practical at the site. In additon, trimethylbenzene isomers were non-detect in a majority of the test or monitoring wells, and therefore, were not useful as tracers. Further, the use of chloride concentrations as an inorganic tracer was also inconclusive. Relatively high native levels of chloride in groundwater at the site appear to result from infiltration of water bearing elevated TDS levels or high inorganic solute concentrations below various ponds where continued evaporation took place. Nevertheless, bulk changes in chemical concentrations over time in individual wells and chemical concentration trends over distance clearly show the importance of ongoing natural attenuation processes at the site. Other Synthetic Organic Compounds (PAHs, PCBs, Herbicides, Pesticides, Dioxin/ Furans and Others) Synthetic organic compounds (excluding the VOCs), typically have less affinity for water (very low solubility) and a greater affinity to absorb to soil. Because of their higher molecular weight, these compounds tend to be viscous and less volatile than VOCs. Synthetic organic compounds will persist in the environment for long periods of time, but have been demonstrated to be biodegradable by specialized bacteria or fungi under favorable conditions; bacteria capable of degrading high carbon chain organic compounds have been identified within site groundwater (Appendix G). Higher molecular weight organic compounds, such as, PAHs, PCBs, herbicides, pesticides, and dioxin/furans, tend to be less mobile in groundwater, however, reduced and methanogenic groundwater conditions favor fermentation processes that support micro-organisms capable of breaking down these compounds. Metals The persistence and migration of metal constituents in groundwater are impacted by the metals’ chemical form and the geochemistry of the local groundwater system. Unlike the organic constituents of concern, metals cannot be degraded. However, biotic and abiotic transformations have been identified that, in some instances, may reduce the toxicity and/or mobility of the metal in a groundwater system. The solubility of metals is often increased by low (acidic) pH conditions in soil or groundwater. As soil concentrations of metals increase and the adsorptive capacity of saturated soil is exhausted, metals will migrate with groundwater. Unlike organic compounds that can be destroyed, metals can only be changed in the oxidation state, chemical species, and physical form. The potential for metal precipitation exists in areas of reduced groundwater conditions which exist mostly with the Central Drainage area. Metals mobility generally increases under acidic groundwater conditions; in general, much of the groundwater across the site has relatively high alkalinity, which tends to buffer acidic groundwater conditions. 6.2.3.2 Site-specific Factors Controlling Constituent Transport via Groundwater The following conclusions can be made regarding groundwater flow conditions at the site:


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The dominant large scale feature influencing groundwater flow at the site is a pervasive zone of weathering and enhanced secondary fracture conductivity in the Upper HSU.

The Upper HSU is poorly transmissive, the Lower HSU even less so. Borehole hydraulic tests reported by the USEPA (1986) yielded a maximum hydraulic conductivity of 31 ft/yr in the Upper HSU. The HSCER Report (Woodward-Clyde Consultants, 1988) cites a geometric mean hydraulic conductivity of 70.4 ft/yr in the Upper HSU, and 1.04 ft/yr in the Lower HSU.

The Upper/Lower HSU contact surface and associated permeability distribution influences flow conditions in the Upper HSU. Characterization of the contact surface includes borehole and geophysical data collected during summer and fall 2004 and 2006/2007 RI efforts.

A high degree of correlation exists between topographic elevation and water table elevation. This allows the topographic data to be used in guiding interpretation of water level data (Woodward-Clyde Consultants, 1988; ICF Kaiser, 1998).

Groundwater flow through Zone 1 is generally to the south. Groundwater at the southern perimeter of the Site is intercepted by the PCTs, extracted, and discharged to site surface impoundments.

Based on historical and recent groundwater elevation data from wells and piezometers, a groundwater flow divide that divides groundwater flow entering the site is present along the North Ridge, north of the landfills. The water table in this area receives recharge from precipitation and inflow from the higher ground west of the Zone 1 boundary. The flow divide occurs as a result of ground surface and Upper/Lower HSU contact topography, with lateral flow to the north and south away from the topographic divide. The flow divide exists in roughly the same location in both Upper and Lower HSUs, and occurs in roughly the same location throughout the year.

Comparison of the elevation of the Upper/Lower HSU contact with groundwater elevations in Upper and Lower HSU wells and piezometers during 2006 and 2007 indicates the Upper HSU beneath the North Ridge may be locally saturated after winter recharge events. The saturated thickness appears to vary in space and time with a maximum thickness of about 10 feet.

Based on historical and recent groundwater elevation data from nested wells and piezometers, vertical gradients vary across the site and change slightly during the water year. Downward vertical gradients are generally observed in the area between the North Ridge and the PSCT, and neutral or upward gradients are indicated near the PCTs. The vertical gradients change over time, with maximum downward gradients generally observed during the summer or fall.

Water budget analysis indicates the site as a whole exhibits a slight negative error, and more groundwater is being removed from the aquifer system than is recharging it.

Groundwater flow modeling confirms the overall conclusions regarding groundwater flow paths and the state of the site water balance. MODPATH results indicate curvilinear flow paths downward from the North Ridge recharge area, through the Upper and Lower HSUs, and upward flow and discharge at the extraction features and Ponds.

6.2.3.3 Actions Taken to Disrupt Contaminant Transport via or to Groundwater As discussed elsewhere in the FS Report, numerous actions have been taken that affect the fate and transport of chemicals at the site. Specific actions that have been taken to mitigate constituent transport in groundwater include:


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Surface Impoundment Closure Activities – Liquids removal from surface impoundments eliminated a water column and hydraulic head that may have led to subsequent leaching and dissolved-phase contaminant infiltration to groundwater underlying the site.

Landfill Capping – The installation of engineered landfill caps, such as the P/S Landfill cap and EE/CA cap, served to mitigate stormwater infiltration into waste materials, and subsequent leaching of waste chemicals into groundwater underlying the landfills.

Subsurface Site Liquids Management – Operation of the Gallery Well, Sump 9B, the PSCT, and the PCTs (PCT-A, PCT-B, and PCT-C) all affect groundwater flow and the migration of contaminants. The Gallery Well captures groundwater originating from the North Ridge area and P/S Landfill area. Sump 9B appears to capture groundwater originating from recharge within the Central Drainage Area north of sump 9B. Based on the distribution and concentrations north and south of the PSCT, the PSCT appears to contain VOC contamination in the northern areas, which helps limit the impact on areas south of the PSCT. The three PCTs were constructed to intercept groundwater at the downgradient site boundary and prevent off-site migration of groundwater contaminants.

6.2.3.4 Observed Response to Implemented Groundwater Control Measures The following provides a brief summary to the effectiveness of the site groundwater control features implemented above: Horizontal Groundwater Flow Analysis Historical representation of groundwater elevation contour maps (as illustrated in RI Report Appendix F, Figures F-3 through F-16; 2011) for groundwater elevations observed in three periods, i.e., March 2001, March 2004, and December 2008, indicate limited variability in the overall horizontal hydraulic gradient magnitudes and directions between the different periods. Further, groundwater flow patterns depicted on the groundwater contour maps for these three periods are consistent with those previously observed in the 1980’s, as documented by the USEPA (USEPA, 1986) and in the HSIR (Woodward Clyde Consultants and Canonie Environmental, 1989). Collectively, these data indicate that the current extraction system and landfill cap appear to have little impact on the lateral groundwater flow pattern in the site-wide scale; and thus the direction of groundwater flow across the site is largely governed by natural site features, such as surface topography and the HSU contact surface. In particular, the area between the topographic high of the North Ridge and the northern boundary of the landfills receives recharge from precipitation and inflow from the higher ground west of the Zone 1 boundary, and groundwater flows south through the landfills in the central area toward the low lying ponds, trenches, and creek boundaries (i.e., axes of A-, B-, C- drainages). The location of the groundwater flow divide along the North Ridge is conceptual, and its exact location is not quantified. As such, contaminant migration is generally unlikely for the groundwater originating from the major source area (as presented in RI Report Appendix G, Figure G-26; 2011) to flow northward to and/or across the North Ridge. The groundwater flow model incorporated this groundwater flow divide as a “no flow” boundary condition, predefining that any particle tracks started south of this no flow boundary would move south. This simulation is provided in the groundwater modeling results (RI Report Appendix F, Attachment F-3; 2011) and particle tracking analysis (RI Report Appendix F, Figure F-50; 2011), which show flow paths from just south of the North Ridge groundwater divide generally toward the south. By definition, these particles do not indicate flow from Zone 1 to the North Drainage.


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As described above, a projection of the groundwater flow paths determined from MODFLOW modeling within the Upper HSU for the Dry (2004) and Wet (2001) simulations are presented in Figures 6-1 and 6-2, respectively. The modeling indicates that the PSCT and PCT are effective in capturing liquids moving southward across the site within the Upper HSU. Notably the modeling indicates that for particles released on the North Ridge, groundwater flow will direct these particles to the site containment features. In regard to the Lower HSU, flow modeling indicates that groundwater flow in the shallow portion of the Lower HSU behaves similarly to that of the Upper HSU, and is effectively captured in the PSCT. However, modeling also suggests that some component of groundwater flow in the Lower HSU may pass beneath the PSCT. Any groundwater flow within the Lower PSCT that may pass beneath the PSCT would be relatively limited due to the low hydraulic conductivity of the Lower HSU. A detailed description of the methods and findings of groundwater modeling are presented in Appendix F of the Final RI Report (2011). Groundwater flow across the southern perimeter of the site between the A-, B-, and C- Drainages appears to be prevented by a reversal in groundwater flow direction immediately south of the Site, associated with the prominent hills that rise just south of the site boundary separating these three drainages. Groundwater in this southern area is channeled toward the head of each of the three drainages, where the PCT liquid control features are located. MODPATH result indicates that the PCTs capture groundwater from the following areas:

PCT-A captures groundwater originating from off-site areas to the north, site areas east and south of the PSCT, surface water from the RCF Pond, and the hills between the A- and B-Drainages.

PCT-B captures groundwater originating from areas south of the PSCT, surface water from Pond 13 and the RCF Pond, B-Drainage, and the hills between the A-, B-, and C-Drainages.

PCT-C captures groundwater originating from areas south of the PSCT and the A-Series Pond.

Although the site-wide groundwater horizontal flow pattern does not appear to be significantly affected by the implementation of current extraction system and landfill capping; observed data and model capture zone analyses (as presented in RI Report Appendix F; 2011) demonstrate the local influence of the existing facilities on the groundwater horizontal flow. Although modeling and manual analysis of water level data do not show complete capture with certainty, the analysis does show that the PSCT likely captures the majority of groundwater flowing southward through the Upper HSU. For example, inward horizontal gradients toward the extraction wells at PSCT 1 and PSCT 4 were first observed immediately after these two wells were installed in 1998. Particle tracking analysis with MODFLOW and MODPATH (RI Report Appendix F, Attachment F-3; 2011) indicates that PSCT-1 captures most groundwater originating from the North Ridge areas north and east of the Metals, Caustics/Cyanide, and Acids Landfills, as well as groundwater recharged within the Central Drainage north of PSCT-1. PSCT-2 captures most groundwater recharged in the area of the PCB Landfill and Burial Trench Area, and areas between the Burial Trench Area and PSCT northwest of PSCT-2. This is consistent with the observed water table contour maps (RI Report Appendix F, Figures F-8 and F-13; 2011) which show the alignment of the contour lines roughly perpendicular to the PSCT trenches, indicating that the potential for groundwater flow across the PSCT (along the non-pumping sections) is minimal. Groundwater horizontal gradients generally are steeper in the area north of the PSCT, and these steeper gradients coincide with the steeper topography.


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South of the PSCT, the groundwater horizontal gradients are more gradual, and further reduced by the presence of the site ponds. As described above, a projection of the groundwater flow paths determined from MODFLOW modeling within the Lower HSU for the Dry (2004) simulations are presented in Figure 6-3. The modeling indicates that groundwater (and contaminant) flow within the Lower HSU is south and that flow beneath the bottom of the PSCT and PCT may occur. Vertical Groundwater Flow Analysis Based on historical and recent groundwater elevation data from nested wells and piezometers, vertical gradients vary across the site and change slightly during the water year, with maximum downward gradients generally observed during the summer or fall. Comparative analyses on historical data of the vertical hydraulic gradients indicate the local influence of the existing extraction features and landfill capping on the groundwater flow and vertical transport. Site-wide downward vertical gradients (between Upper and Lower HSUs) are generally observed, with largest values in the area approximated by the North Ridge, which is consistent with a groundwater recharge area. However, neutral, slightly downward, or slightly upward gradients are indicated beneath the southern portions of the capped landfills and near the ponds, PSCT, and PCTs, most likely attributed to the implementation of extraction features and capped landfills. For example, an upward vertical hydraulic gradient at WP-8S/WP-8D (at the toe of the Metals Landfill) and RG-9B/RP-95 (at the toe of the Caustic/Cyanide Landfill) have been consistently observed since capping of these landfills occurred. Data do not exist to allow the determination of the vertical gradient at the toe of the P/S Landfill. The local groundwater vertical flow change due to the implementation of existing control facilities is further illustrated through comparative data analyses on the historical vertical hydraulic gradients before and after the year 2001 when capping remedies for the P/S landfill and Heavy Metal landfill were completed and the current groundwater extraction features were placed online. At the well pair RGPZ-7C/7D, located between Sump 9B and PSCT-1 (downgradient of the Gallery Well), the pre-2001 observed vertical hydraulic gradients (upward positive) had a range from -2.43 to 0.11 feet per foot (ft/ft) with a median value of -1.852 ft/ft, statistically less than the post-2001 observed gradients (with a median value of 0.051 ft/ft). Similar observations (i.e., the pre-2001 observed vertical hydraulic gradients are generally less than the post-2001 observed vertical hydraulic gradients) have been presented at the well pairs within 200-foot radii of PSCT-1 and include wells pairs RG-1B/1C, RGPZ-6B/6C and RGPZ-6C/6D. At the well pair of WP-8S and WP-8D, located at the toe of the Heavy Metals Landfill, the observed gradient is an example of an upward hydraulic gradient that develops without groundwater extraction but is significantly influenced by the recharge change associated with the 2001 capping over the Heavy Metal Landfill, as indicated by the fact that the pre-2001 observed vertical hydraulic gradients in a range of -0.182 and 0.165 ft/ft with a median value of 0.068 ft/ft, were statistically less than the post-2001 gradients ranging from 0.063 to 0.373 ft/ft with a median value of 0.230 ft/ft. The emplacement of groundwater control features (i.e., interception trenches and capping of landfill cells) has not significantly affected the overall groundwater flow direction across the site. However, changes to vertical gradients and a general decline in groundwater storage has been observed since control features were installed. The groundwater control features are fulfilling their design purpose in capturing and controlling the movement of contaminants within the site’s boundaries.


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6.2.4 NAPL COPCs Free phase LNAPL and/or DNAPL have both been detected in monitoring points in isolated locations north of the PSCT, including locations within the Central Drainage Area and the Capped Landfills Area (Section 5). Based on operational records, such free phase NAPL is suspected as being derived, at least in part, from containerized liquids disposed of into the P/S Landfill,which may have corroded or otherwise failed in some manner, potentially releasing LNAPL and/or DNAPL into the subsurface. As described in Section 5, free phase LNAPL is currently present within the P/S Landfill and south of the P/S Landfill in the Central Drainage Area from the Gallery Well at the toe of the P/S Landfill to just north of PSCT-1. Free phase DNAPL is present within the southern end of the P/S Landfill and in the Lower HSU in an area between the P/S Landfill and PSCT-1. To date, neither LNAPL nor DNAPL have been measured as a separate phase in any other area. NAPL has not been detected in the recently installed RI wells and piezometers in the Burial Trench Area (although observations during drilling may suggest NAPL in this area), or in other site wells and piezometers near and downgradient of the other landfills. The Upper HSU locations in the Central Drainage Area where LNAPL and DNAPL have been observed or inferred generally coincide with an historical site drainage that ran the length of the P/S Landfill and continued into the area that is now the RCF Pond. The findings of an ultraviolet induced fluorescence (UVIF)/MIP survey confirmed that NAPL presence was limited to the areas specified above. During the RI groundwater chemistry investigation activities (RI Report Appendix G – Groundwater Chemistry; 2011), LNAPL and DNAPL samples were collected and analyzed for chemical composition and physical properties from the following locations:

LNAPL – Gallery Well, GW-PZ-W, and Sump 9B-PB DNAPL – Gallery Well, RGPZ-7C, and RGPZ-7D.

For chemistry, the NAPL samples were analyzed for VOCs, SVOCs, PCBs, PAHs, herbicides, pesticides, metals and cyanide. For physical properties, the NAPL samples were analyzed for density, viscosity, NAPL-water interfacial tension, and flash point. Details regarding LNAPL and DNAPL physical properties and chemistry are provided in RI Report (CSC 2011). Laboratory analyses indicated that the composition of each LNAPL and DNAPL sample was a mixture of organic compounds including primarily VOCs with lesser concentrations of SVOCs, PAHs, herbicides, and metals. The predominant VOCs encountered in NAPL at the site include:

Total xylenes; PCE; Toluene; Methylene Chloride; Ethylbenzene; 1,1,1-Trichloroethane; Freon-113; and TCE.

The NAPL densities were as follows for the 2004 samples:


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LNAPL – 0.9905 grams per cubic centimeter (g/cm3) for the Gallery Well DNAPL – 1.0851 g/cm3 for the Gallery Well and 1.0184 g/cm3 for RGPZ-7C

The densities for both the LNAPL and DNAPL are relatively close to water, representing the mixture of both heavier and lighter components within each phase. The DNAPL densities are similar to 1994, 1998, and 2003 samples collected from the site. Interfacial tension plays a key role in assessing potential NAPL transport and dissolution into groundwater. The DNAPL-water interfacial tension (the surface tension between two liquids) was 2.8 dynes per centimeter (dynes/cm) as measured with groundwater, and 7.1 dynes/cm as measured with tap water for a 1998 DNAPL sample. This is a relatively low interfacial tension representing the solvent components in the DNAPL. 6.2.4.1 Migration and Persistence of NAPL COPCs The LNAPL and DNAPL at the site consist of a variety of organic and inorganic constituents. Organic compounds include VOCs, SVOCs, pesticides, herbicides, PCBs, and dioxins/furans. Metals include arsenic, nickel, cadmium, and selenium. The LNAP and DNAPL are a source of dissolved-phase organic and inorganic constituents to groundwater. VOCs are organic compounds that exhibit relatively high vapor pressures and will partition to the vadose zone as soil gas vapors. The fate and transport of dissolved phase organic and inorganic COPCs are described above. 6.2.4.2 Site-specific Factors Controlling Constituent Transport in NAPL The primary potential sources of NAPLs at the site lie north of the PSCT, and include the P/S Landfill and the former ponds and pads located south of the P/S Landfill but within the Central Drainage Area. An additional potential source area of NAPLs is the Burial Trench Area, but no free-phase LNAPL or DNAPL has been found there, as described in Section 5. It is reasonable to assume that the LNAPL and DNAPL in the Gallery Well represent a mixture of chemical liquids that were disposed of directly into the P/S Landfill. The drummed wastes placed in the P/S Landfill reportedly contained chemical mixtures in addition to single-compound spent solvents or other wastes. The P/S Landfill likely poses a continuing source of both LNAPLs and DNAPLs. LNAPL As described in Section 5, LNAPL has accumulated within the P/S Landfill behind the clay barrier in the vicinity of the Gallery Well. Due to its specific gravity of less than 1, LNAPL tends to float atop the water table, which is maintained at a level below the top of the clay barrier by liquids extraction from the Gallery Well. The distribution of LNAPL is known to occur from the north end of the P/S Landfill at RIPZ-14 southward to the area immediately surrounding the Gallery Well. Prior to installation of the P/S Landfill cap in 1999, no wells or piezometers existed to monitor for potential LNAPL accumulation. The first piezometers at the P/S Landfill (GW-PZ-E1 and GW-PZ-W) were installed in August 1999, about the same time that the P/S Landfill cap was constructed in fall 1999. After placement of the cap in 1999, and installation of two additional piezometers along the Gallery Well Bench (GW-PZ-E2 and –E3) and placement of CPT borings along Bench One of the P/S Landfill in 2001, LNAPL accumulation was observed to occur upgradient of the clay barrier.


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LNAPL accumulation was first noted in piezometer GW-P(E3), followed by GW-P(E2), GW-P(W), and then GW-P(E1). Additional piezometers were installed in 2004 for the RI on the top deck (RIPZ-14), on Bench 2 (RIPZ-39), on Bench 1 (RIPZ-13), and on the Gallery Well Road (RIPZ-38, RIPZ-23, RIPZ-24, and RIPZ-27). Since about 2004, the thickness of the LNAPL accumulation has been variable. The LNAPL thickness appeared to have largely declined through 2009. However, recent LNAPL thicknesses exceed 10 feet in some piezometers. Maximum thicknesses are 20.30 feet in RIPPZ-27 and 33.59 feet in RIPZ-38 according to June 18, 2010 liquid level measurements. While fluctuations in LNAPL thickness are observed in wells over time, the LNAPL is below the top of the clay barrier, and the Gallery Well appears to be capturing and removing LNAPL accumulating in this area. LNAPL occurs within the Central Drainage Area from the P/S Landfill southward toward the PSCT. Due to its specific gravity of less than 1, LNAPL tends to float atop the water table. Measureable LNAPL occurs in two of the three initial piezometers installed near Sump 9B in 1999 (SUMP-9B-PB, and -9B-PC) and additional wells and piezometers installed throughout the Central Drainage Area from 1998 through 2004. The thickness of LNAPL in all of the Central Drainage Area Wells has decreased through time from several feet to less than 1-foot. The LNAPL does not currently reach the PSCT. However, any southward LNAPL migration will be intercepted by the PSCT. Movement of LNAPL in the subsurface is controlled by several processes. LNAPL will move downward through the unsaturated zone where a fraction of the LNAPL will be retained by capillary forces as residual globules in soil pores. If sufficient LNAPL occurs, it will continue to move downward under the force of gravity until it reaches a physical barrier (e.g., low permeability strata) or is affected by buoyancy forces near the water table. Once the capillary fringe is reached, the LNAPL may move laterally as a continuous, free-phase layer along the upper boundary of the water-saturated zone and the water table. The principal migration direction will be in the direction of maximum decrease in water table elevation. The LNAPL mass may hydrostatically depress the capillary fringe and water table if a large enough mass of LNAPL is present. Infiltrating precipitation and passing groundwater in contact with residual or mobile LNAPL will dissolved soluble components and form an aqueous-phase contaminant plume. Removal of free-phase LNAPL from the subsurface can feasibly be performed by primary pumping methods. Removal of free-phase LNAPL will leave behind residual phase LNAPL in the unsaturated zone and capillary fringe that is trapped by capillary forces as residual globules in the soil pores. Removal of residual LNAPL is much more energy intensive than removal of free phase LNAPL because of these capillary forces holding residual LNAPL in place. DNAPL As described in Section 5, free phase DNAPL is known to exist at the following locations:

As a DNAPL pool overlying Lower HSU fractured claystone within the southern area of P/S Landfill. Free phase DNAPL occurs at the Gallery Well, RIPZ-27 immediately north of the Gallery Well, and RIPZ-13 approximately 150 feet north of the Gallery Well. The current measured DNAPL thicknesses are approximately 0.91 feet in RIPZ-27 and 14.38 feet in RIPZ-13. DNAPL at the Gallery Well is kept pumped-down to a thickness of approximately 2 feet. A DNAPL thickness of 9 feet at the Gallery Well was measured when initiating a DNAPL recovery test on July 9, 1997.

Within fractures of the Lower HSU claystone in the Central Drainage Area between the P/S Landfill and the PSCT. This free phase DNAPL occurs as a measurable thickness


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of several feet within Lower HSU piezometers RGPZ-7C and RGPZ-7D, approximately 500 feet south of the clay barrier and 150 feet north of the PSCT.

Pooled free phase DNAPL may also potentially be present, or historically have been present, overlying the Lower HSU of the Central Drainage Area in the area of former Pads 9A and 9B. However, pooled DNAPL was not identified in this area during RI activities. Free phase DNAPL has the potential to laterally migrate along the HSU contact in the P/S Landfill area. DNAPL also has the potential to migrate downward into and through the underlying fractured bedrock (i.e., Lower HSU) under certain conditions. Potential DNAPL penetration into the Lower HSU requires displacement of the water-saturated porous matrix or fractures. The driving force for DNAPL movement is the additional pressure buildup due to its higher density relative to water. Pore-scale capillary forces that retain water within pores or fractures counteract the additional pressure generated by the DNAPL pool. DNAPL is able to displace water only when the DNAPL pool height generates sufficient pressure to overcome the capillary pressures. As noted above, the densities of the DNAPLs found within the P/S Landfill and within the Lower HSU in the Central Drainage area are relatively low (i.e., between 1 and 1.1 gm/cm3). The low densities of these DNAPLs are due to the mixture of chemicals within them, which include many organic chemicals with individual densities less than water. The interfacial tension (i.e., the surface tension between two liquids) between the DNAPL and groundwater (at less than 10 dynes/cm) is also relatively low, apparently due to the presence of alcohols and/or inorganic surfactants that are present in the DNAPL. While the relatively low densities reduce the potential for DNAPL migration, the low interfacial tension produces the opposite effect, increasing the migration potential. Rl findings demonstrate that previous or current site conditions could have resulted in downward DNAPL migration based on reasonable assumptions for DNAPL properties (densities and interfacial tensions), DNAPL pooled heights, and fracture apertures (RI Report Appendix F, calculation in Attachment F-4; 2011). The observation of DNAPLs in piezometers RGPZ-7C and RGPZ-7D suggest that vertical migration of DNAPLs through the potentially interconnected fracture network in the Lower HSU has already occurred within the Central Drainage Area. The presence of DNAPL in the Lower HSU (at piezometers RGPZ-7C and RGPZ-7D) could be attributable to a number of past conditions at the site and associated factors including but not limited to those listed below:

DNAPL measured in piezometers RGPZ-7C and RGPZ-7D may have originated from the DNAPL in the P/S Landfill. Prior to 1996, liquid extraction from the Gallery Well was limited and the action level in the well was significantly higher, the DNAPL pool height behind the clay barrier was reported to be as high as 9 feet, which exceeds the theoretical thickness required to effect DNAPL entry into underlying fractures. The height of DNAPL in the P/S Landfill could be as high as 14 feet as measured in RIPZ-13.

DNAPL measured in RGPZ-7C and RGPZ-7D may have originated from Upper HSU sources in the area other than the P/S Landfill, including former Pads 9A and 9B or Pond R. The DNAPL may have migrated through a limited fracture network below these historical sources to the depths of the piezometers. Pooled DNAPL was not identified in the Upper HSU at any other areas outside the P/S Landfill during RI activities; however, the chemical and physical properties of the LNAPL identified in the Sump 9B area, with


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the exception of the 0.02 g/cm3 difference in density, is similar to the DNAPL identified in wells RGPZ-7C and RGPZ-7D.

The DNAPL noted in the Lower HSU may have entered the Lower HSU and migrated prior to the construction of the containment features of the P/S Landfill.

The potential for continued DNAPL migration into the Lower HSU is considered to be possible under current site conditions (i.e., with the current extraction systems operating in the P/S Landfill and the PSCT). Even though the extent of DNAPL in the Lower HSU is not known, and a DNAPL pool with greater than 100,000 gallons of free DNAPL resides behind the clay barrier, the barrier acts to restrain the pool while the Gallery Well extraction acts to relieve hydrostatic pressure exerted by the buildup of liquids. Calculations have demonstrated that the greater than 10-feet of DNAPL present in the vicinity of RIPZ-13 is sufficient to penetrate underlying fractures within the unweathered claystone. Extraction by the Gallery Well will have limited hydraulic effect to prevent downward DNAPL migration in the vicinity of RIPZ-13. The vertical extent of fractures underlying the DNAPL is also unknown. Investigation findings elsewhere at the Site suggest that fracture density decreases with depth at some locations, while fractures occur throughout the vertical depth drilled at other locations. Fracture interconnectivity is likely low on a site-wide scale but has been demonstrated to be interconnected on a local scale from dissolved-phase VOC contamination in the Lower HSU at the Burial Trench Area and free-phase DNAPL in the Lower HSU at the Central Drainage area. Based on DNAPL observed during borehole video logging and fracture and bedding plane orientations measured during borehole optical televiewer logging, DNAPL movement along fractures and bedding plane from either the P/S Landfill and/or the Sump 9B area to RGPZ-7C and RGPZ-7D appears to have occurred. The DNAPL movement appears to be complex because at intermediate locations RGPZ-6C and RGPZ-6D, only dissolved phase VOCs are present in these wells. It is possible the DNAPL migration bypassed the fractures screened in RGPZ-6C and RGPZ-6D in favor of surrounding wider fractures. As detailed, DNAPL density force analysis indicates the vertical hydraulic gradients in the southern Central Drainage Area are approximately equal to the gradients required to counteract DNAPL sinking (RI Report Appendix F, Attachment F-4). 6.2.4.3 Actions Taken to Disrupt Contaminant Transport as NAPL As discussed elsewhere in the FS Report, numerous actions have been taken that affect the fate and transport of chemicals at the site. Specific actions that have been taken to mitigate constituent transport in NAPL include the following: Subsurface Site Liquids Management - Note that presently LNAPL and DNAPL are both being recovered by liquid extraction conducted in the Gallery Well. The Gallery Well and associated clay barrier both serve to contain and collect DNAPL that may be migrating laterally along the contact with the Lower HSU under the P/S Landfill, as the containment feature is “keyed” approximately five feet into the underlying bedrock contact. The LNAPLs that exist in the P/S Landfill and Central Drainage Area are intercepted by a number of different physical containment features, including:

o The Gallery Well and clay barrier at the toe of the P/S Landfill o Sump 9B o The PSCT (collected by extraction well PSCT-1)

Although significant DNAPL is currently being removed by liquids extraction at the Gallery Well (at a rate of approximately 4,000 gallons per year), the time required to drain the DNAPL pool


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contained by the clay barrier is difficult to estimate as the configuration of the bottom of the P/S Landfill and the exact volume of the DNAPL pool are not known with certainty. As described in Section 5, once DNAPL has entered a fracture or fracture network, progressively smaller aperture fractures will be invaded if the pooled DNAPL source is allowed to extend itself vertically while remaining a continuous, interconnected phase. The DNAPL driving head is not only a function of the pool height in the overlying Upper HSU (or P/S Landfill) but also the height of DNAPL accumulated in the fractures beneath this pool. The potentially mobile DNAPL volume in the P/S Landfill does provide an ongoing source to allow the DNAPL to extend itself into fractures at depth. Diffusion of contaminant mass from DNAPL contained within claystone fractures into pore water of the claystone matrix between fractures affects the persistence of DNAPL in the fractures. This diffusion causes a redistribution of contaminant mass from fractures to the claystone matrix that can slow the advance of DNAPL migration. If the DNAPL source is controlled, this diffusion can ultimately cause DNAPL migration to cease and DNAPL to disappear from fractures by dissolution and diffusion into the porous matrix. A series of chloride diffusion tests was performed on core samples from the site (two alluvium samples, two weathered claystone, and two unweathered claystone samples); the diffusion rates into the unweathered claystone matrix ranged from 3 x 10-6 to 1 x 10-7 square centimeters per second (cm2/s), which is similar to results for the weathered claystone and about an order of magnitude greater than for the alluvium core. Given the relatively low hydraulic conductivity (~5X10-6 cm/s) of the unweathered claystone, chemical diffusion has the potential to attenuate both DNAPL and dissolved VOCs. Pumping can remove free-phase DNAPL from the P/S Landfill. Source reduction of free-phase DNAPL will leave behind residual phase DNAPL that is trapped by capillary forces as residual globules in the soil pores below the water table. Removal of residual DNAPL is much more energy intensive than removal of free phase DNAPL because of these capillary forces holding residual DNAPL in place, and may potentially be infeasible. Removal of free-phase DNAPL from Lower HSU fractures is likely not feasible because it is not possible to sufficiently characterize the site to identify all potential fractures that may contain DNAPL. Meeting this objective would require literally hundreds of deep borings and even then, the extent of mobile DNAPL in fractures would likely not be known. In addition, removing DANPL from select fractures that are found to contain mobile DNAPL would not be effective because of the very small storage capacity within fractures that would contain DNAPL. Any DNAPL removed from fractures would be replaced until the DNAPL source is removed. The most feasible method of controlling free-phase DNAPL migration in the Lower HSU is to remove the mobile DNAPL source (i.e., from the P/S Landfill if that is the source). This would result in stopping the mobile DNAPL in the fractures from being replenished, which would cause the DNAPL to stop advancing, and ultimately disappear through the process of matrix diffusion.

6.3 Summary and Conclusions This section provides the summary and conclusions of the contaminant fate and transport discussion and evaluation. Contaminants evaluated for fate and transport include those constituents identified in the nature and extent of contamination sections for each medium. Sufficient data has been collected to evaluate the presence, nature, and extent of chemical


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constituents in the various environmental media encountered at the site. The findings of the fate and transport evaluation can be summarized as follows:

The nature and distribution of chemicals present at the site with respect to the various environmental media is understood.

The physical and chemical factors affecting the fate and mobility of these chemicals in the environment, and the operative transport pathways for these chemicals in the various media are understood.

The location of principal contaminant sources at the site and how chemicals may migrate from these sources to other areas of the site within the various media is understood.

Many measures have already been undertaken to mitigate (historical) contaminant sources at the site and disrupt potential migration of these chemicals within the various media.

Sufficient information is available to identify those areas, chemicals, and media still requiring mitigation in order to reduce the mobility and potential unacceptable exposures at the site.

Surface water runoff from some study areas, such as the RCRA Canyon Area and the West Canyon Spray Area, has apparently transported surface soils containing elevated levels of COPCs, principally metals, into the stormwater and treated liquid impoundments, where they have accumulated in pond-bottom sediments.

Discrete areas of contaminated subsurface soils have locally manifested in impacts to other environmental media, including soil vapor and groundwater. Such examples include subsurface conditions in the Burial Trenches Area, the Central Drainage Area, the Capped Landfills Area, and to a limited extent the Former Pond and Pads Area just south of the PSCT.

Elevated soil vapor levels are locally present in association with some former disposal areas, most notably the Capped Landfill Area and the Burial Trenches Area. Available data indicate these disposal areas to be the principal contaminant source areas at the site, and that lateral soil vapor migration from these source areas occurs. Elevated VOCs occur away from these source areas outside the site boundary (to the north into the North Drainage and east into the North Ridge) and within the site (to the south across the PSCT into the former Ponds and Pads Area and to the west towards the RCRA Canyon area). Groundwater impacts are most pronounced in proximity to primary contaminant source areas, and impacts are generally greater north of the PSCT. Southerly migration of contaminated groundwater across the site is mitigated by continuing extraction from the PSCT, and potential migration into off-site areas is mitigated by the existing PCT groundwater collection systems, as well as by active and ongoing natural attenuation and biodegradation mechanisms.

Free phase LNAPL occurs within the P/S Landfill and Central Drainage Area between the landfill and PSCT-1. The Gallery Well and clay barrier appear to be effectively containing LNAPL within the P/S Landfill. LNAPL is not migrating to the south across the PSCT from primary source areas located north of this containment feature.

Free phase DNAPL occurs within the P/S Landfill and in the Lower HSU between the landfill and PSCT-1. The volume of pooled DNAPL in the landfill may exceed 100,000 gallons. The vertical extent of DNAPL in the Lower HSU is not known, however, investigation data suggest that fracture pathways (which are predominantly steep) diminish with depth. The horizontal extent of DNAPL within the Lower HSU in the vicinity of the P/S landfill and Central Drainage Area is also not known, although the potential for DNAPL to occur beyond the site boundary is considered to be low. Potential sources for the Lower HSU DNAPL could be the large DNAPL volume within


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the P/S Landfill or an unidentified potential DNAPL within the former Pad 9A/B area of the Central Drainage Area. Active DNAPL recovery and hydraulic containment occurs in proximity to these sources. The combination of extraction features and local upward vertical groundwater gradients acts to relieve pressure exerted by the DNAPL and inhibit further lateral and vertical DNAPL migration. Although extraction and locally upward vertical groundwater gradients occur, they may not be sufficient to prevent the continued potential for DNAPL migration.

6.4 References Final Remedial Investigation Report. January 2011 Foster Wheeler Environmental Corporation and GeoSyntec Consultants, Inc., 1999. Pesticides/Solvents (P/S) Landfill Cap, Revised Final Design Report. Casmalia Resources Hazardous Waste Management Facility. Casmalia, California. Prepared for Casmalia Steering Committee. January 15, 1999. ICF Kaiser, 1998. Technical Memorandum, Interim Collection/Treatment/Disposal of Contaminated Liquids Component of Work, Casmalia Hazardous Waste Management Facility. May 1998. United States Environmental Protection Agency (USEPA), 1986. Monitoring Evaluation Casmalia Resources Disposal Facility, Casmalia, California. July. Woodward-Clyde Consultants and Canonie Environmental, 1989. Hydrogeologic Site Investigation Report (HSIR) for Cleanup and Abatement Order (CAO) No. 80-61, Casmalia Resources Class I Hazardous Waste Management Facility, Volume I-VII. April 18. Woodward-Clyde Consultants, 1988. Hydrogeologic Site Characterization and Evaluation Report (HSCER), Casmalia Resources Class I Hazardous Waste Management Facility, Volume I-IX. May 11, 1988.


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7.0 SUMMARY OF RISK ASSESSMENT A comprehensive risk assessment was conducted as part of the RI/FS process. The risk assessment is detailed in the RI report and summarized in the FS report. Consistent with USEPA guidance and policy, the risk assessment includes (1) a human health risk assessment (HHRA), and (2) an ecological risk assessment (ERA). The HHRA includes a baseline risk assessment that evaluated cancer and non-cancer risks for existing site conditions and current land and water uses. The risk assessment then qualitatively evaluates risks for reasonably anticipated future land use scenarios. The ERA quantitatively evaluates site risks to a wide range of plant and wildlife species, for current and future use scenarios, consistent with USEPA policies and practices. Findings of the HHRA and ERA are presented in Section 8 and Appendix T (HHRA), and Section 9 and Appendix U (ERA) of the Final RI Report (2011). The findings of these studies are summarized in the following sections. 7.1 Human Health Risks The baseline human health risk assessment (BHHRA) evaluates risks, for each site area, under current conditions. The BHHRA studies (1) sources of contamination in different media, (2) pathways of exposure, and (3) potentially impacted populations, called “receptors”. Sources of contamination include contaminated materials and media, such as buried solid and liquid wastes, soil, groundwater, DNAPL, and soil vapor. The risk assessment also considers individual site features, such as former waste management units (e.g., landfills, pits, ponds, lagoons, disposal wells, and trenches). Consistent with USEPA Risk Assessment Guidance for Superfund (RAGS Part A), the BHHRA addresses five major components, including (1) data review & evaluation, (2) exposure assessment, (3) toxicity assessment, (4) risk characterization, and (5) uncertainty analysis. The BHHRA includes appropriate quantitative risk calculations for exposure pathways, addressing exposure to chemicals through direct physical contact, ingestion, and inhalation, from movement of contamination through air, soil, fractured rock, surface water, and groundwater. The BHHRA conducted for the site evaluated groundwater, but did not calculate risks for groundwater due to the lack of complete exposure pathways and receptor populations. Instead, USEPA is using MCLs as risk-based cleanup goals to be considered in decision making for groundwater response actions. Similarly, the BHHRA does not include detailed risk calculations for site features with incomplete exposure pathways, such as the landfills, which have already been capped. Current potential exposures may occur to onsite workers, occasional trespassers, and residents outside the site boundaries, such as local ranchers and potential neighbors. There are no completed exposure pathways to the town of Casmalia. USEPA has established a cumulative cancer range of 10-4 to 10-6 to manage cancer risks for Superfund cleanups. Non-cancer concerns are evaluated as a hazard quotient of less than or equal to one (HQ<1).

The objective of the baseline HHRA was to evaluate potential baseline health risks associated with chemicals detected at the site. The results of the HHRA in conjunction with the ERA findings can be used to identify chemicals and exposure media that may pose an unacceptable risk to current and/or future receptors at the site and to provide information for remedial planning. The risk


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assessment was prepared as part of the RI to evaluate potential exposures and “define risks to public health and the environment” related to soil, sediment, soil vapor, and surface water, and to subsequently provide information for the FS.

The overall approach used in the HHRA was based on United States Environmental Protection Agency (USEPA, 1989; 1991a,b; 1997a; 2002; 2004a,b) and California Environmental Protection Agency (CalEPA) guidance documents (1992; 2000; 2003; 2005; 2007a,b; 2009). The risk assessment consists of five major components organized in the following manner:

Data Review and Evaluation: A review of available data to characterize the site and

identify data gaps; to define the nature and extent of environmental contamination identified at the site; and to identify COPCs (defined as chemicals that are potentially site-related and were evaluated quantitatively in the HHRA).

Exposure Assessment: An assessment of the magnitude, frequency, duration, and routes of potential human exposure to site-related COPCs. The exposure assessment considers both current and likely future site uses and is based on complete exposure pathways to actual or probable human receptors (i.e., general groups that could come in contact with site-related COPCs). The exposure scenarios are summarized in the CSM, which includes the sources, affected media, release mechanisms, and exposure pathways for each identified receptor population.

Toxicity Assessment: A presentation of available information to identify the nature and degree of toxicity and to characterize the dose-response relationship (the relationship between magnitude of exposure and magnitude of potential adverse health effects on each receptor) for each COPC.

Risk Characterization: A synthesis of exposure and toxicity information to yield quantitative estimates of potential cancer risks and noncancer hazards to defined receptor populations. COCs, which are COPCs that were identified in the quantitative risk assessment as exceeding a risk threshold and warranting further evaluation in the FS are presented. In addition, it is anticipated that COCs will also include COPCs that occur in onsite groundwater in concentrations that exceed, or are reasonably expected to exceed MCLs (See FS Appendix A, Table A-3).

Uncertainty Analysis: A discussion of the uncertainties associated with each of the four previous steps to assist decision-makers in evaluating the risk assessment results in the context of the assumptions and variability in the data used.

For purposes of the HHRA, the site included both Zone 1 and Zone 2. Zone 1 (the site) includes the inactive Class I hazardous waste management facility and comprises approximately 252 acres. Zone 2 includes the area encompassing the extent of site-related contamination or potential contamination outside the Zone 1 boundary. Because potential human health effects from exposure to site-related chemicals are evaluated based on current and potential future land use scenarios, an important step in developing the risk assessment approach was to define baseline conditions. As discussed in the RI Report, the HHRA was developed assuming that certain remedies are already in place. In this way, any pathways of exposure considered incomplete, because of the existing or presumptive remedies, were not evaluated in the HHRA. The following areas of the site have been capped: (1) the P/S Landfill, and (2) the EE/CA Area, which includes the Heavy Metals, Caustics/Cyanides and the


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Acids Landfill and the areas between these landfills. As discussed in the RI Report, the PCB Landfill located adjacent to the P/S Landfill will also be capped. In addition, it is anticipated that the two treated liquids impoundments, Pond A-5 and Pond 18, will be drained as part of site remediation. As a result, potential exposures to treated liquid impoundment waters were not considered in the HHRA. However, impoundment sediments were evaluated as exposed surface soils, since the impoundments will be drained. As a part of this assumption, it is assumed that once drained, the treated liquid impoundment area will be graded as appropriate to minimize future collection of water.

Data Review and Evaluation

The data evaluation steps that were conducted to develop a risk assessment dataset, identify media-specific COPCs, and calculate exposure point concentrations (EPCs) for evaluation in the HHRA and ERA were previously discussed in detail in Section 7 of the RI Report. The data evaluation was conducted in addition to the procedures for field sampling, chain-of-custody, laboratory analysis, reporting and data validation that were conducted in accordance to the QAPP. The data evaluation was consistent with guidance provided by USEPA in Risk Assessment Guidance for Superfund (RAGS) (USEPA 1989), Guidance for Data Usability in Risk Assessments (USEPA 1992), Data Quality Assessment: Statistical Methods for Practitioners (USEPA 2006a) and guidance for calculating EPCs (USEPA 2007 a,b). All data determined to be of sufficient quality were carried forward into the COPC selection process. COPCs were selected for each environmental media (soil, sediment, surface water and soil vapor) for inclusion in the risk assessment. COPCs are defined as chemicals clearly associated with the site (e.g., chemicals that are prevalent) and present at concentrations higher than background levels. For the ecological risk assessment, COPCs are referred to as chemicals of potential ecological concern (COPECs). Prior to selecting the COPCs, the chemical dataset was filtered based on media and depth as appropriate. For soil and sediment, samples taken from depths less than or approximately equal to 5 feet below ground surface were selected. The filtered dataset included all Study Areas (including drainages extending beyond Zone 1), excluding background, historical West Canyon data, PCB landfills, and capped landfill areas. There was no division by depth for surface water and soil vapor. For groundwater, the samples collected from all onsite wells were reviewed to identify constituents exceeding drinking water standards. Study Areas included the following: Terrestrial Uncapped Areas:

RCRA Canyon; Liquid Treatment Area; West Canyon Spray Area; Burial Trench Area; Maintenance Shed Area; Central Drainage Area; Administration Building Area; Roadway Areas; Remaining Onsite Areas; and


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Former pond and pad areas south of the perimeter source control trench (PSCT). Ponds:

A-Series Pond RCF Ponds Pond A-5 Pond 13; and Pond 18

Drainages:

North Drainage A Drainage; B Drainage; Upper C Drainage; and Lower C Drainage

Groundwater:

Area 5 North (aka GW-North) Area 5 South (aka GW-South) Area 5 West (aka GW-West)

Additional areas such as seeps and RCRA Canyon runoff were also evaluated. However, as these areas were not identified as Study Areas in the RI/FS Work Plan (2004), they were subsequently evaluated separately and only for the ERA.

Exposure Assessment

The objectives of an exposure assessment are to identify receptors (populations) that may be exposed to chemicals in impacted media, the exposure pathways, and the route of potential intake. In addition, for pathways considered complete, the chemical concentrations to which the receptors are potentially exposed (EPCs) and the frequency, magnitude, and duration of these potential exposures (exposure parameters) must be estimated.

The following steps were considered in the exposure assessment:

Identification of potentially exposed receptor populations; Identification of complete exposure pathways; Estimation of exposure point concentrations for specific pathways; and Estimation of chemical intakes for receptor populations associated with each complete

exposure pathway.

The end product of the exposure assessment is a measure of chemical intake as an average daily dose (ADD) that integrates the exposure parameters for the receptors of concern (e.g., contact rates, exposure frequency, and duration) with the EPC for the media of concern. These ADDs are then used in conjunction with chemical-specific toxicity values (e.g., reference doses and cancer slope factors) to arrive at an estimate of potential health risks for the receptors of concern. This section describes the steps that were followed in the exposure assessment.


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Conceptual Site Model The CSM identifies potential chemical sources, release mechanisms, transport media, routes of chemical migration through the environment, exposure media, and potential receptors. Receptors that may be potentially exposed to site-related chemicals are identified and the likelihood of their potential exposures assessed through consideration of the current and the anticipated future use of the site. The CSM represents the understanding of the sources of chemicals of potential concern, the means by which they are released and transported within and among media, and the exposure pathways and routes by which both human and ecological receptors may contact them. For potential human health exposures, three specific CSMs were formulated for Zones 1 and 2 based on a review of previous and additional information that has been collected for the site (see Figures 6-1 through 6-3 of the RI/FS Workplan; 2004). The major components of the CSMs are discussed below and in more detail in Appendix T of the Final RI Report (2011). Exposure Pathways and Receptors Given the characteristics of the COPCs and conditions at the site and adjacent areas, several exposure pathways may be potentially complete. Exposure pathways and receptors were selected based on current and future use of the site.

Based on current, available information, the following exposure pathways were considered potentially complete for human receptors at the site:

Incidental ingestion of COPCs in soil, sediment, or surface water; Contact with soil, sediment, or surface water and absorption of COPCs through the skin; Inhalation of COPCs in windborne dust generated from soil or sediment; Inhalation of vapors emanating from soil, sediment, or surface water into outdoor air; Inhalation of vapors emanating from soil vapor into outdoor air; Inhalation of vapors emanating from onsite soil into indoor air; Inhalation of vapors emanating from soil vapor outside the site boundaries into indoor

air; and Ingestion of beef that has grazed near the site.

The current land-use of Zone 1 is a former hazardous waste management facility. As further described below in Section 7.3, land-use surrounding the site includes open-space, cattle grazing and oil-field development. The CSC acquired and controls much of the land around the site (Zone 2). In addition, there are other privately held land(s) on the southwest border of the site that are used for cattle-grazing. Parcels under ownership of Casmalia Resources Acquisition Property Company and Casmalia Resources have had deed restrictions that preclude them from being used as residential or certain other sensitive developments such as hospitals, day care, etc. These parcels will remain available only to grazing/ranching/oil and gas, or other industrial developments. Nevertheless, a hypothetical future residential exposure scenario for Zone 2 was included in the HHRA as the deed restriction process has not been completed. Residential exposure pathways were indicated as only potentially complete in the CSM due to the hypothetical nature of this pathway.


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There is no reasonable anticipation that groundwater below the site would be used as a potable water supply. Based on the well survey information, the groundwater beneath and in the immediate vicinity of the site is not currently being used for potable water. In addition, all the remedial alternatives being considered include ICs that would place restrictions on groundwater extraction and use.. Therefore, this exposure pathway was not considered complete and risk calculations were not developed in the HHRA. However, it is anticipated that groundwater constituents that exceed, or may be reasonably expected to exceed performance standards will be included as COCs. The following receptors may be potentially exposed to site-related chemicals within Zone 1:

Onsite workers maintaining the liquids treatment area, surface impoundments, and landfill covers and drainage structures;

Trespassers; and Ranchers using the NTU road to access their lands.

The following receptors were also evaluated in the HHRA since they are potentially exposed to site-related chemicals within Zone 2:

Ranchers working the fields along the southwest border of Zone 1; Consumers of beef raised in the fields near Zone 1; Recreational users of the drainage areas; and Hypothetical residents living near the site.

Middle school- and high school-aged children (11-17 year olds) were included as part of the evaluation for the recreational scenario. Recreational use of the surrounding area of the site, within Zone 2, is not expected. Access to this area is considered limited, no trails have been observed, and the area is used primarily for cattle grazing. Although the area surrounding the site does not appear to be used for recreational purposes, this scenario was evaluated in the HHRA as a conservative approach. Moreover, an assumption of once per month as the exposure frequency is considered conservative for this particular receptor given that person has a low potential for recreating within Zone 2. Exposure Point Concentrations EPCs are the concentrations of chemicals in environmental media to which receptors may be exposed through defined exposure pathways. EPCs were estimated for each of the environmental media associated with complete and potentially complete pathways identified in the CSM. These media and pathways include the following:

Surface (0 to 6 inches bgs) and shallow soil (0 to approximately 5 feet bgs; this also includes data from 5 – 5.5 feet bgs) considered for incidental ingestion, dermal contact, and inhalation of fugitive dust and vapor pathways, as well as ingestion of beef;

Surface (0 to 6 inches bgs) and shallow sediment (0 to approximately 5 feet bgs) considered for incidental ingestion, dermal contact, and inhalation of fugitive dust and vapor pathways;

Soil vapor considered for the vapor inhalation pathway; and


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Surface water considered for incidental ingestion, dermal contact and inhalation pathways.

Evaluating data collected from shallow soils (0 to approximately 5 feet bgs) accounts for potential future exposure to the subsurface soils if the site and adjacent areas become reconfigured and deeper soils are brought to the surface and made available for direct contact exposures (e.g., via incidental ingestion, dermal contact) and outdoor air inhalation of fugitive dust and vapors. While individuals are unlikely to have direct contact with impacted soil at depths greater than 5 feet bgs, the potential does exist for VOCs to migrate from beneath the subsurface. Therefore, soil vapor samples collected from the site and from outside the site boundaries at depths of greater than 5 feet bgs were used to evaluate the vapor pathways for a commercial/industrial worker (outdoor air) and a hypothetical resident (indoor air) living near the site, respectively. In addition, soil data from samples in close proximity to the Administration Building were used to evaluate the indoor air pathway for site commercial/industrial workers. Derivation of EPCs is discussed in more detail in Section 7 of the RI Report. EPCs were derived using the same statistical methodology for soil, sediment, and surface water. EPCs for the outdoor and indoor air exposure pathways in the HHRA were further developed using fate and transport modeling as described in detail in Appendix T of the Final RI Report (2011). Estimating Chemical Intake` The exposure assessment quantifies the magnitude, frequency, and duration of chemical intake (daily intake) by receptor populations. ADD or “Lifetime Average Daily Dose” (LADD) of COPCs for each exposure pathway was estimated. ADDs and LADDs were calculated using guidelines in the Risk Assessment Guidance for Superfund (USEPA 1989), site-specific information, and professional judgment, as appropriate. The ADD or LADD is estimated by multiplying an intake factor by the selected EPC (COPC concentration). The intake factor combines the site-specific and receptor-specific assumptions for a given exposure pathway and is expressed as the amount of media (e.g., soil) taken into the body per unit concentration of chemical in the media. Multiplying the intake factor by the selected EPC yields the ADD or LADD (mg/kg-day) for that receptor population and exposure pathway. The following is a generic equation used to estimate the daily dose:

FactorIntakeSummary x EPCSelected = day)-(mg/kg ADD/LADD

Separate intake factors are estimated for each exposure pathway. The values and assumptions used to estimate each intake factor are dependent on the exposure pathway and receptor population being evaluated. A more detailed description of the values used for the intake calculations are presented in Appendix T of the Final RI Report (2011).


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Toxicity Assessment

The toxicity assessment characterizes the relationship between the magnitude of exposure to a COPC and the nature and magnitude of adverse health effects that may result from such exposure. For purposes of calculating exposure criteria to be used in HHRAs, adverse health effects are classified into two broad categories: noncarcinogens and carcinogens. Toxicity criteria are generally developed based on the threshold approach for noncancer effects and the non-threshold approach for cancer effects.

Potential cancer effects resulting from human exposure to carcinogens are generally estimated quantitatively using oral cancer slope factors (CSFs) or inhalation unit risk factors (URFs). Oral CSFs are expressed in units of (mg/kg-day)-1. To characterize potential cancer risks from inhalation, URFs were converted when needed from units of (µg/m3)-1 to units of (mg/kg-day)-1 by assuming that an individual inhales at a rate of 20 cubic meters per day, and has an average body weight of 70 kg and this absorption is equivalent by either route (USEPA 1989).

Potential noncancer effects resulting from human exposure to noncarcinogens are estimated quantitatively using chronic reference doses (RfDs) for ingested chemicals and reference concentrations (RfCs) for inhaled chemicals. The RfD, expressed in units of milligrams of chemical intake per kilogram of body weight per day (mg/kg-day), is an estimate of the maximum human exposure level that can be present without an appreciable risk of deleterious effects during a designated time. The RfC is expressed in units of milligrams of chemical per cubic meter of air (mg/m3) and is an estimate of the maximum air concentration that can be present without an appreciable risk of deleterious effects. In addition, CalEPA (2000, 2003) has developed chronic Reference Exposure Levels for the Air Toxics Hot Spots program, which were used if they were more conservative than the RfCs.

As is the case for the CSFs, RfDs and RfCs are only available for oral and inhalation exposures. In the absence of criteria specific to the dermal exposure pathway, the oral RfDs were used to evaluate the dermal route of exposure.

In the HHRA, chronic toxicity criteria were selected (in order of preference) from the following sources: 1) CalEPA Office of Environmental Health Assessment (OEHHA) Toxicity Criteria Database, online (CalEPA 2007a); 2) USEPA’s (2007c) Integrated Risk Information System (IRIS) as referenced in USEPA Region IX Preliminary Remedial Goals (PRG) table (USEPA 2004b); 3) USEPA (1997b) Health Effects Assessment Summary Tables (HEAST), as referenced in the Region IX PRG table (USEPA 2004b); or 4) USEPA NCEA Superfund Health Risk Technical Support Center, as referenced in the USEPA PRG table (USEPA 2004b).

Risk Characterization

Risk characterization integrates the results of the toxicity assessment and the exposure assessment to estimate potential cancer risks and adverse noncancer health effects associated with exposure to chemicals detected at the site. This integration provides quantitative estimates of cancer risk and noncancer hazard that are then compared to acceptable standards. The risk characterization led to the identification of COCs. Chemicals of Concern are those COPCs that have been identified in the quantitative risk assessment as exceeding a risk threshold and therefore warranting further evaluation in the FS. For groundwater, COCs will include COPCs which exceed, or may be reasonably expected to exceed MCLs.

Risk assessment is an iterative process in which site, receptor, and chemical-specific data are


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used when available. When site-specific data are not available, conservative (i.e., health protective) assumptions are utilized. The use of repeated, conservative assumptions can lead to conservative estimations of risk but ensures protectiveness and provides an upper-bound estimate of the actual risk. Various demarcations of acceptable risk have been established by regulatory agencies. For example, the USEPA has established an acceptable risk range for Superfund sites. The National Contingency Plan (NCP; 40 CFR 300) indicates that lifetime incremental cancer risks posed by a site should not exceed a range of one in one million (1×10-6) to one hundred in one million (1×10-4) and noncarcinogenic chemicals should not be present at levels expected to cause adverse health effects (i.e., a hazard index [HI] greater than 1). Other relevant guidance (USEPA 1991b) additionally states that sites posing a cumulative cancer risk of less than 10-4 and hazard indices less than unity (1.0) for noncancer endpoints are generally not considered to pose a significant risk warranting remediation. The California Hazardous Substances Account Act (HSAA) incorporates the NCP by reference, and thus also incorporates the acceptable risk range set forth in the NCP. The RCRA Corrective Action program incorporates this same range of potential health risks as the “acceptable risk range” for determining whether corrective action is warranted at RCRA facilities and for closure purposes. Finally, The Safe Drinking Water and Toxic Enforcement Act of 1986 (California Proposition 65) regulates chemical exposures to the general population and is based on an acceptable risk level of 1 x 10-5. The maximum acceptable risk level for a site is between 10-4 and 10-6, and is selected on a case-by-case basis by USEPA. The risk range between 10-4 and 10-6 is commonly called the “discretionary risk range.” (USEPA 1991b).

For the purposes of the HHRA, a cumulative cancer risk of 1 x 10-5 and noncancer hazard index of 1 was used to compare commercial/industrial worker risk estimates. For all other potential exposures a cancer risk level of 1 x 10-6 and noncancer hazard index of 1 was used. These risk levels are used to provide context to the risk results and to support the following discussion which focuses on those pathways and chemicals that contribute the majority to the risk estimates. It is acknowledged that additional considerations such as technical feasibility, economic, social, political, and legal factors may be part of the final risk management decision. The results of the risk characterization are really the starting point for risk management considerations for a site (USEPA 1995).

Risk Characterization Results For potential exposures to site soils and sediments via direct contact (ingestion and dermal contact) and outdoor inhalation, only the Former Ponds and Pads (FPP) and Liquid Treatment Study Areas exhibited elevated risk for commercial/industrial worker exposures with a cumulative risk of 5 x 10-5 and a noncancer HI of 2, respectively. PCE in shallow soil was the primary risk driver for the FPP Study Area and MCPP was the primary risk driver for both surface and shallow soils at the Liquid Treatment Study Area. In addition, risk estimates for trespasser exposures to FPP soils were slightly elevated (2 x 10-6) due to the presence of PCE in subsurface soils. The sample locations that contributed the majority to these risk estimates were RISBON-37, RISBON-41 and RISBON-63 in the FPP Study Area just south of the PSCT and RISBLT-02 in the Liquid Treatment Study Area.

For soils/sediments outside the site boundary, cancer risk and noncancer hazard estimates for recreational and rancher exposures were below a cancer risk level of 1 x 10-6 and a noncancer hazard of 1.


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For site surface water, Ponds A-Series, 13 and RCF cancer risk estimates were elevated for commercial/industrial worker exposures (maximum cumulative risk of 8 x 10-5) and trespassers (maximum cumulative risk of 3 x 10-6) with arsenic being the primary risk driver. All noncancer HIs were below 1.

For the hypothetical resident assumed to be living adjacent to the site, the Burial Trench, Central Drainage, and FPP Study Areas exhibited elevated risk due to exposures from the transport of site vapors to locations adjacent to the site boundary, with a maximum cumulative risk estimate for the Burial Trench Study Area of 1 x 10-5. The primary risk drivers were tetrachloroethene and trichloroethene. The sample locations that contributed the majority to these risk estimates were RISBON-37, RISBON-41 and RISBON-63 in the FPP Study Area just south of the PSCT, RISBCD-07 in the Central Drainage Study Area and RISSBC-05 in the Burial Trench Study Area. It should be noted that the hypothetical resident evaluation is overly conservative in that the modeling assumes the resident is located adjacent to the Study Area being evaluated. In reality, the resident would be located some distance from the Study Area boundary thereby resulting in lower estimates of exposure. For the hypothetical residential exposures, only the vapor intrusion pathway resulted in a marginally elevated risk estimate with a cumulative risk estimate of 2 x 10-6. The primary risk driver for this pathway was 1,3-butadiene. When considering more recent soil vapor sampling, this risk estimate would be even lower and similar to the target risk level of 1 x 10-6. Uncertainty Analysis The methodology used in the HHRA is consistent with USEPA and CalEPA risk assessment guidance. However, the procedures used in any quantitative RA are conditional estimates given the many assumptions that must be made about exposure and toxicity. Major sources of uncertainty in risk assessment include (1) natural variability (e.g., differences in body weight or sensitivity in a group of people); (2) incomplete knowledge of basic physical, chemical and biological processes (e.g., the affinity of a chemical for soil, degradation rates); (3) model assumptions used to estimate key inputs (e.g., exposure, dose response models, fate and transport models); and (4) measurement error primarily with respect to sampling and laboratory analysis.

Site-specific factors, which this HHRA incorporated, decrease uncertainty, although uncertainty may persist in even the most site-specific RAs due to the inherent uncertainty in the process. However, because the assumptions used tend to be health-protective and conservative in nature, the estimated risks are likely to exceed the most probable risk posed to potential receptors at the site and actual risks would be much lower.

Some of the most significant elements affecting uncertainty for this HHRA include:

It was assumed that chemical concentrations remain constant over the duration of exposure. No abiotic or biotic degradation mechanisms, which reduce the concentrations of chemicals over time, are assumed to occur. This general assumption of steady-state conditions also applies to sources and chemical release mechanisms and may result in a conservative estimation of long-term exposure concentrations.

The exposure assumptions used for the reasonable maximum exposure (RME) approach are considered conservative and likely lead to overstating the most probable estimate of potential risk. For example, the RME exposure scenario assumes a


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hypothetical resident living adjacent to the site bounday will remain at the same location from birth through age 30 years for 350 days per year, or a commercial worker will work at the site for 25 years.

Intake parameters for the various exposure pathways (soil ingestion, dermal contact, inhalation) were conservatively assumed to be upper bound estimates (e.g., 3300 cm2 of exposed skin exposed every day–regardless of the weather conditions–or ingestion of 100 mg of soil each day over the exposure period for adults, etc.) for the RME approach.

For exposures via outdoor air inhalation, the outdoor air flux model assumes that the VOC is present at the surface and that the receptors will come into contact via outdoor air inhalation. When chemicals are present at depths below 6 inches, the flux would be lower resulting in lower estimates of potential risk.

Soil samples were collected as part of the Phase III RI where step-out borings were completed in the RISBON-59 area (located along NTU road, south west of the west end of RCF pond). However data from this round of sampling were not included in the risk evaluation. The Phase III data relevant for exposure from 0 to 5 feet bgs (samples collected at 0.5 feet bgs and 6 feet bgs) were compared to metals background upper tolerance limits (UTLs) and/or human health screening levels. This screening indicated marginal potential risks from the N-nitroso compounds in two samples. These samples represent a small potential exposure given that they represent a localized area of primarily subsurface impacts and site workers would not be in the area on a frequent basis. While there is some uncertainty in not including these samples, due to the localized nature of impact and infrequent exposure potential, the results and conclusions reached in this HHRA are not significantly impacted.

This HHRA assumed that the PCB Landfill has been capped as discussed in the conceptual site model earlier in the report. The PCB Landfill has an interim soil (claystone) cover of uncertain thickness placed in the 1980's with the northern part of the landfill currently used as a temporary storage area for investigation-derived waste. According to existing information (RCRA Part B Permit Application, Modernization Plan Final EIR), the interim cover soil generally came from the area in which the landfill was constructed and was placed at a minimum 1-foot thickness. The presence of a 1-foot minimum thickness of cover provides a barrier for human contact. In addition, due to the nature of the area being a landfill, worker exposure would not be expected due to intrusive activities beneath the cover. As a result potential human health risk to PCB Landfill contents is considered insignificant.

Consumption of beef by local ranchers did not appear to be a significant exposure pathway. Varying the assumption that ranchers consume from 10% to 100% of beef raised on their own lots still resulted in risk and hazard estimates that were much less than the target risk levels of 1 x 10-6 and 1, respectively. Therefore the results and conclusions reached in the HHRA for this pathway are not significantly impacted.

The risk assessment focused on soil from surface to approximately 5 feet bgs as this is considered the most likely depth interval that may be contacted. If significant concentrations were present at depths below that interval and the soil was brought to the surface then exposures may have been underestimated. To evaluate this issue, the data from greater than 5 feet to 10 feet bgs were reviewed. There was one area where deeper concentrations were significantly higher in RISBON-37. However, this location has already been identified in the risk assessment as posing a potential health risk and will likely be targeted for remediation.


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Default soil physical properties were used for the soil type, silty clay (SIC). Lack of site-specific values may introduce some uncertainty into the vapor modeling and may result in an over-prediction or under-prediction of vapor inhalation exposures from beneath the surface.

Hypothetical residents were evaluated as potential receptors for locations immediately adjacent to the historical waste facility boundary. Although included for risk assessment purposes, future residential land use is considered to be highly unlikely given (1) the site’s status as a former hazardous waste disposal facility and (2) the anticipated use of institutional controls, such as deed restriction to preclude residential land use.

For modeling of site impacts to locations outside the site boundaries via the windblown particulate and vapor pathways for soil, it was assumed that the hypothetical resident was located adjacent to the Study Area being evaluated. This is a conservative assumption as the actual location would likely be much farther from the site boundary resulting in decreased exposures.

Summary and Conclusions

The COPCs evaluated in the HHRA included inorganics, PCBs, dioxins, herbicides/pesticides, PAHs, SVOCs, and VOCs. The HHRA considered potential exposure scenarios that included inhalation of indoor air and outdoor air vapors, inhalation of particulates, dermal contact with surface water, and exposure via direct contact to soils and sediment. The results of the HHRA indicate that the following COPCs are primary risk drivers and are therefore, identified as COCs for the site:

Soils:

o MCPP; o Tetrachloroethylene; and o Trichloroethylene.

Surface Water (Ponds):

o Arsenic

Groundwater (See FS Appendix A, Table A-3): o COPCs that exceed, or may be reasonably expected to exceed MCLs.

For site soils, the FPP and Liquid Treatment Study Areas exhibited elevated risk estimates for commercial/industrial worker exposures. PCE in shallow soil was the primary risk driver for the FPP Study Area, and MCPP was the primary risk driver for both surface and shallow soils at the Liquids Treatment Study Area. Both of these chemicals are present at elevated concentrations in localized areas within these Study Areas. Tables 7-1 through 7-3 identify the COCs based on the HHRA (and ERA) by area. Table A-3 in the TI evaluation (Appendix A) identifies the constituents in groundwater that exceed MCLs. It is anticipated that COCs will include COPCs that exceed, or may be reasonably expected to exceed MCLs

In addition, the Burial Trench, Central Drainage, and FPP Study Areas exhibited elevated risk estimates for hypothetical residents assumed to be adjacent to the site boundary, exposures due to the transport of site soil contamination via windborne vapors. The primary risk drivers were


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tetrachloroethene and trichloroethene, which are both present at elevated concentrations in localized areas within the Study Areas. It should be noted that the hypothetical offsite resident evaluation is conservative in that the modeling assumes the resident is located adjacent to the Study Area being evaluated. For hypothetical residential exposures to soil, sediment and soil vapor outside the site boundary, only the vapor intrusion pathway results in a marginally elevated risk estimate. The primary risk driver for this pathway was 1,3-butadiene. When considering more recent soil vapor sampling, this risk estimate would be even lower and similar to the target risk level of 1 x 10-6 For soils/sediments outside the site boundaries, cancer risk and noncancer hazard estimates for recreational and rancher exposures were below a cancer risk level of 1 x 10-6 and a noncancer hazard of 1. Potential cumulative cancer risk and noncancer hazard estimates exceeded target health levels because of a few locations within a few Study Areas at the site. The sample locations that contributed the majority to the risk estimates were RISBON-37, RISBON-41 and RISBON-63 in the FPP Study Area just south of the PSCT, RISBLT-02 in the Liquids Treatment Study Area, RISBCD-07 in the Central Drainage Study Area and RISSBC-05 in the Burial Trench Study Area. Site cleanup, engineering controls and/or institutional controls should mitigate potential risks associated with these localized areas. Arsenic concentrations detected in several onsite surface-water impoundments, including the A-Series Pond, Pond 13 and the RCF, are estimated to pose a potentially unacceptable risk to onsite commercial /industrial workers. The potential exposure pathways for surface drainage waters, both within and outside the site boundaries, is considered incomplete, therefore no unacceptable risks are anticipated.

For soils/sediments outside the site boundary, cancer risk and noncancer hazard estimates for recreational and rancher exposures were below a cancer risk level of 1 x 10-6 and a noncancer hazard of 1.

7.2 Ecological Risks The objective of the ERA was to conduct a sitewide assessment using a tiered approach that would provide information for the RI/FS. To achieve this objective, the ERA assessed whether site-related chemicals in site media have adversely affected resident flora (plants) and migratory or resident fauna (animals).

Overview of Approach

The overall approach for the ERA followed all applicable guidance documents and regulations to identify those locations, receptors, and pathways that are drivers for risk management decisions. An ERA is the process of estimating and characterizing the likelihood that adverse ecological effects may be occurring or have occurred as a result of exposure to one or more chemical stressors (USEPA 1997c), and the process consists of the four main phases: (1) Problem Formulation, (2) Analysis, (3) Risk Characterization, and (4) Uncertainty Analysis. USEPA and CalEPA recommend that an ERA be conducted in an iterative or tiered manner, as described below. Although the same basic components are found within each tier of analysis, greater detail and refinement are characteristic of each successive tier. The components of the ERA are summarized in this section; details are presented in Appendix U of the Final RI Report


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(2011). The tiers evaluated are as follows:

In the Screening-Level ERA, components, such as use of maximum exposure estimates and conservative ecological benchmarks based on no-observed adverse effects levels (NOAELs), were incorporated and risks were estimated for all the chemicals of potential ecological concern (COPECs; defined as chemicals that are potentially site-related and were evaluated quantitatively in the ERA).

In the Tier 1 ERA, components, such as use of upper-bound exposure estimates and ecological benchmarks based on LOAELs, were incorporated and risks were estimated for all the COPECs. Two lists of chemicals were identified in the Tier 1 ERA: (1) in areas with no planned remedy (RCRA Canyon Area, WCSA, Administration Building Area, Roadway Area, Former Ponds and Pads Area, and Remaining Onsite Areas), those COPECs identified as exceeding a risk threshold were carried forward for further evaluation into the Tier 2 ERA; and, (2) in areas with anticipated remedies (Liquid Treatment Area, Burial Trench Area, Maintenance Shed Area, Central Drainage Area and all the Ponds), those COPECs that have been identified as exceeding a risk threshold were not carried forward to the Tier 2 ERA.

In the Tier 2 ERA, components, such as use of upper-bound exposure estimates, use of site-specific biota uptake values, and ecological benchmarks based on LOAELs, were incorporated and risks were estimated for all the risk driving COPECs carried forward to the Tier 2 ERA based on the results of the Tier 1 ERA. The purpose of the Tier 2 ERA was to identify COCs (i.e., those COPECs identified as exceeding a risk threshold) in areas with no anticipated presumptive remedy and therefore, warranting further evaluation in the FS.

Problem Formulation

Elements of Problem Formulation described in the ERA included discussion of: (1) environmental setting, (2) exposure areas, (3) CSM that included identification of exposure pathways and identification of ecological and indicator receptors, and (4) identification of assessment and measurement endpoints.

Environmental Setting The location and description of the site is discussed in Section 2.0 of the Final RI Report (2011), and detailed information on habitats and biota are provided in the BSHS Report (Appendix P of the Final RI Report [2011]). For the purposes of the ERA, the 252-acre site was divided into the following types of habitat: (1) terrestrial capped areas, (2) terrestrial uncapped areas, and (3) freshwater aquatic areas. A considerable area of the site is currently capped (approximately 47 acres) or anticipated to be capped (approximately 5 acres); exposures to ecological receptors from these areas of the site can be considered minimal to unlikely once all capping is complete and as long as the landfill caps are adequately maintained. Habitats and receptors present in the capped areas of the site are expected to be the same as those described as terrestrial uncapped areas. Terrestrial habitats and receptors in the areas outside the site boundaries are also expected to be similar to those at the site. The terrestrial uncapped areas of the site were generally characterized as disturbed, sparsely vegetated, annual grassland areas. Areas of undisturbed grassland and


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coastal sage scrub habitat containing native vegetation exist primarily in areas of the site that were not previously used in site operations. The freshwater aquatic areas include large impoundments for the collection of surface-water runoff at the site. These include the RCF Pond, the A-Series Pond, Pond 13, Pond 18, and Pond A-5. All ponds are anticipated to have presumptive remedies in place as part of the remedy to be selected by USEPA for the site. Weedy grasses, forbs, small areas of native vegetation, gravel, debris, and un-vegetated soil are present along the borders of the ponds. Although these ponds are generally degraded, use by birds, mammals, and aquatic life is likely and has been observed in previous surveys (Appendix P of the Final RI Report; 2011). These waters have been inhabited by aquatic invertebrates and amphibians (historically, but are not present under current conditions) and also may be used for foraging by mammals and birds. In addition, freshwater aquatic areas included RCRA Canyon runoff and drainages surrounding the site. Although the seeps at the site were not evaluated quantitatively, a qualitative description of risks was provided. Historically, the shallow water table between the P/S Landfill and PSCT-1 would emerge as seeps during winter months when seasonal rainfall recharges and increases the water-table elevation. The areas drained by these seeps represent the most contaminated areas of the site. Therefore, control of these seeps significantly reduces the risks from seeps associated with the site. Extraction at Sump 9B, the Road Sump, and PSCT eliminates these seeps from forming between the P/S Landfill and PSCT-1, even during times of high precipitation. Thus, risks from the seeps at the site are controlled by these facilities and are not expected to contribute to ecological risks. Conceptual Site Model The CSM relates the sources of site-related chemicals to the receptor populations by depicting the potential pathways for transport of the stressor and the routes of entry into the receptor. The CSM also facilitates development of exposure models and ecological benchmarks in the analysis phase of the assessment. The CSM identifies potentially complete exposure pathways and potential receptors by group (e.g., mammals, birds). The CSMs were developed on the basis of existing information regarding the nature and extent of chemical contamination, habitat types, and flora and fauna at the site. The exposure media evaluated included soils, sediment, surface water, and soil gas. The ecological receptors evaluated included terrestrial ecological communities (plants and soil invertebrates), freshwater ecological communities (sediment-dwelling invertebrates, aquatic life, and aquatic plants), terrestrial wildlife (reptiles, amphibians, mammals, birds, and deep burrowing mammals), and freshwater wildlife (amphibians, mammals, and birds). Identification of Exposure Pathways The following exposure pathways were identified as complete and significant and, therefore, were quantitatively evaluated in this ERA: Terrestrial Uncapped Areas:

• Direct contact or uptake of soil by plants and soil invertebrates.

• Inhalation of burrow air by mammals (this also accounts for volatiles from groundwater).


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• Incidental ingestion of soil by mammals and birds.

• Ingestion of surface water by mammals and birds from RCRA Canyon, WCSA, and A-Series Pond.

• Ingestion of contaminated prey tissue by mammals and birds. The incidental ingestion of soil, surface water, and prey tissue pathways are complete and significant for reptiles and amphibians in the terrestrial areas; however, due to limited toxicity data, potential risks to reptiles and amphibians in the terrestrial areas could not be estimated. Uncertainties associated with risks to reptiles and amphibians are discussed in Appendix U (ERA) of the Final RI Report (CSC 2011). Freshwater Aquatic Areas:

• Direct contact or uptake of surface water by aquatic plants, aquatic invertebrates, and amphibians.

• Direct contact or uptake of sediment by aquatic plants, aquatic invertebrates, and amphibians.

• Incidental ingestion of sediment by birds and mammals.

• Ingestion of surface water by birds and mammals.

• Ingestion of contaminated prey tissue (aquatic invertebrates) by birds and mammals. The incidental ingestion of sediment, ingestion of surface water, and ingestion of prey tissue pathways are complete and significant for amphibians. Due to limited toxicity data, potential risks to amphibians could not be estimated via these pathways. However, the direct contact pathway is considered to be the most significant pathway, and thus, protective of all exposure pathways for amphibians. Uncertainties associated with risks to amphibians are discussed in Appendix U (ERA) of the Final RI Report (2011). The following exposure pathway was identified as complete and potentially significant but was not quantitatively evaluated in the ERA:

Inhalation of volatiles in burrow air by amphibians, reptiles, and birds. Inhalation of volatiles by amphibians, birds, and reptiles is considered complete and significant; however, the tools to evaluate exposure and risk are lacking or highly limited and, therefore, were not quantitatively evaluated in the ERA. The following exposure pathways were identified as complete but not significant and, therefore, were qualitatively evaluated in the ERA:

Dermal contact with media (soil, sediment, surface water, and seeps) by reptiles, birds, and mammals.

Inhalation of particulates and volatiles in ambient air by reptiles, amphibians, birds, and mammals.

The following exposure pathways were identified as incomplete and, therefore, were not evaluated in the ERA:

Uptake or direct contact with groundwater by all receptors.


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Ingestion of groundwater by reptiles, amphibians, birds, and mammals. Inhalation of volatiles from groundwater by all receptors, except burrowing mammals.

Ingestion of surface water (i.e., seep water) by reptiles, amphibians, terrestrial mammals, and terrestrial birds was also considered incomplete, as the seeps no longer exist at the site; however, potential risks based on historical data are discussed qualitatively in Section 9.6 of Appendix U (ERA) of the Final RI Report (2011). Identification of Ecological Receptors and Indicator Species To characterize potential ecological risks associated with the site, general classes of ecological receptors, or functional groups that may be exposed to COPECs were identified to represent different trophic levels. Representative species were used to represent a wide range of receptors within each functional group. Terrestrial Habitats – the terrestrial portions of the site include the terrestrial uncapped areas at the site. Terrestrial Ecological Communities:

Terrestrial Plants: general category (not species-specific) Soil Invertebrates: general category (not species-specific)

Terrestrial Wildlife:

Amphibians: general category (not species-specific) Reptiles: western fence lizard (Sceloporus occidentalis) Mammals:

o Herbivorous small mammals: California vole (Microtus californicus) o Invertivorous small mammals: ornate shrew (Sorex ornatus) o Carnivorous mammals: striped skunk (Mephitis mephitis)

Birds: o Invertivorous ground-feeding birds: western meadowlark (Sturnella neglecta)

(breeding) o Herbivorous ground-feeding birds: western meadowlark (Sturnella neglecta)

(non-breeding) o Carnivorous birds (raptors): American kestrel (Falco sparverius)

Deep Burrowing Mammals: represented by the American badger (Taxidea taxus) Freshwater Aquatic Habitats – the aquatic portions of the site include the freshwater ponds, the surface-water runoff in RCRA Canyon, and the drainages surrounding the site. Freshwater Aquatic Ecological Communities:

Sediment-Dwelling Invertebrates: general (not species-specific) Aquatic Life: general (not species-specific) Aquatic Plants: general (not species-specific)

Freshwater Aquatic Wildlife:


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Amphibians: general (not species-specific) Mammals:

o Omnivorous/invertivorous small mammals: raccoon (Procyon lotor) Birds:

o Invertivorous wading birds: killdeer (Charadrius vociferus) o Invertivorous (breeding) diving birds (ducks): mallard duck (Anas platyrhynchos)

Selection of Chemicals of Potential Ecological Concern

In the Screening-Level and Tier 1 ERA, COPECs were selected following appropriate guidance (CalEPA 1996, USEPA 1997c), in a logical step-wise manner as summarized in the RI Work Plan (2004) and described in detail in Section 7.0 of the Final RI Report (2011). COPECs were selected for sitewide areas and for individual study areas as well. Data for each medium were used in the COPEC selection process. Briefly, the steps included:

Evaluation of frequency of detection (FOD); chemicals were selected as sitewide COPECs if the percentage of positive detections exceeded a 5% prevalence screen (i.e., the chemical was positively detected in 5% or more of the samples).

Identification of essential nutrients. Comparison of site data with background data (for metals in soil and sediment only)

where the maximum detected concentration of metals was compared to the 95% UTL; see Section 3.0 and Appendix A of the Final RI Report (2011).

Data Evaluation

The RI sampling approach was implemented to investigate the nature and extent of contamination at the site. The approach and methodologies employed during sampling activities are described in Section 3.0 of the Final RI Report (2011). Data evaluated for the ERA were based on the exposure pathways as described above. A complete description of the data analysis is presented in Section 7.0 of the Final RI Report (2011). For estimating exposures to ecological receptors at the site, the following site media data were evaluated:

Surface soil (0 to 6 inches below ground surface [bgs]); henceforth referred to as surface soil.

Surface and shallow soil (0 to 5 feet bgs; this also included data from 5 to 5.5 feet bgs); henceforth referred to as shallow soil.

Surface and deep soil (0 to 10 feet bgs; only for the deep burrowing receptor); henceforth referred to as deep soil.

Sediment (0 to 6 inches bgs). Surface water (from ponds and runoff). Soil gas.

The exposure depths were selected following guidance provided by CalEPA (1998). Exposures to terrestrial receptors are primarily via ingestion of prey items, although ingestion of soil, surface water, and inhalation of burrow air are also important pathways and were evaluated as appropriate. Burrow air was evaluated using soil vapor data collected at depths between 5 to 10


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feet bgs. Ingestion of prey items generally occurs at the surface, and prey items reside and take up chemicals from surface soils (and sediments), not from the bottom of the burrows. Therefore, surface soil (and sediments) was used to estimate uptake into prey items, except for plant tissue, where the greater EPC of the surface and shallow soil was used to model uptake. Soil (and sediment) ingestion generally is associated with foraging for prey items, although some soil ingestion may occur during grooming/preening that could include soils from deeper burrows. CalEPA guidance indicates that characterization of soil to 6 feet bgs is sufficient for the majority of ecological receptors (CalEPA 1998). For the burrowing receptors likely to be found at the site, a maximum depth of 5 feet bgs was considered sufficient to capture the range of burrow depths of the majority of small mammals present at the site (i.e., ranging from 6 inches for moles to 4 feet for squirrels, skunk, and fox). For mammals that can burrow deeper than 6 feet bgs (the badger), deep soil data were evaluated separately, as the list of COPECs could be different for surface and shallow soils. Groundwater data have been collected for the site, but are not considered relevant for the purposes of this ERA because no complete exposure pathway exists between site receptors and groundwater. The depth to groundwater is generally much deeper than 6 feet bgs, and plants are not expected to significantly uptake groundwater from the site. Please see the figure showing depth to groundwater in Attachment 8 of Appendix U (ERA) of the Final RI Report (2011). Additional sediment samples were collected to refine estimates of toxicity of specific metals in sediments to sediment-dwelling invertebrates at the site. An equilibrium partitioning (EqP) approach, commonly referred to as the Acid Volatile Sulfide – Simultaneously-Extracted Metals (AVS-SEM) method, promulgated by USEPA (2005a), was used. This method is summarized in Appendix U (ERA) of the Final RI Report (2011). Data evaluated for each exposure medium, the datasets generated, calculation of dioxin and PCB TEQs, and selection of COPECs for further risk evaluation are presented in Section 7.0 and Appendix X and are summarized in Appendix U (ERA) of the Final RI Report (2011). Exposure Assessment The methods that were used to estimate exposures for the ecological receptors for the ERA are described in Appendix U (ERA) of the Final RI Report (2011). Consistent with USEPA and CalEPA guidance, this assessment was conducted using upper-bound assumptions, thus providing a high level of protection for the receptors represented by the evaluated functional groups. Chemicals, receptors, and pathways showing unacceptable risks (i.e., where exposures exceed effects-based screening values) were further evaluated in Tier 2. Exposure Point Concentrations An EPC is the representative concentration of a constituent in an environmental medium that is potentially contacted by the receptor (USEPA 1997c). Following CalEPA guidance (CalEPA 1996), risks were estimated using both the maximum detected concentrations (Screening-Level) and the EPCs (i.e., 95% UCL) on the mean (Tier 1 and Tier 2) for each COPEC in each site medium. Data distributions and 95% UCLs for COPECs in site media were determined using USEPA’s ProUCL (V 4.0; USEPA 2007a,b). These EPCs were referred to as “non-spatial” EPCs. A complete description of statistical methods used is provided in Section 7.0 and Appendix X of the Final RI Report (2011).


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For terrestrial receptors, a tiered approach was used to evaluate potential risks. As mentioned above, risks were estimated using both maximum detected concentrations (Screening-Level) and non-spatial EPCs (Tier 1 and Tier 2). The COPECs that indicate potential adverse risks (i.e., hazard quotients [HQs] greater than 1) identified in the risk estimates, based on non-spatial EPCs, were further evaluated using a spatial approach (also part of Tier 1). Soil EPCs were calculated on an area-weighted basis according to USEPA guidance (USEPA 2006b). These EPCs were referred to as “spatial” EPCs. A complete description of the methods used to calculate spatial EPCs is provided in Attachment 4 of Appendix U of the Final RI Report (2011). Soil gas exposures (maximum detected concentrations and non-spatial EPCs only) were calculated in milligrams per cubic meter (mg/m3) for burrowing mammals and presented in Attachment 3 of Appendix U of the Final RI Report (2011). Other evaluations included the RCRA Canyon runoff (maximum detected concentrations only). Exposure Scenarios The exposure scenarios evaluated for the ecological receptors are presented in the ERA and summarized below. As mentioned earlier, two other exposure areas not defined in the RI Work Plan (2004) were also evaluated. These included the RCRA Canyon runoff (quantitatively) and the seeps (qualitatively; A-Series Seep, Caustic/Cyanide and Acid Landfill [CA] Seep, Caustic Landfill [LF] Seep, and Seep 9B). Terrestrial Uncapped Areas The terrestrial uncapped areas evaluated included the following exposure units:

RCRA Canyon Liquid Treatment Area WCSA Burial Trench Area Maintenance Shed Area Central Drainage Area Administration Building Area Roadway Areas Remaining On-Site Areas Former Pond and Pad Areas A-Series Pond RCF Ponds Pond A-5 Pond 13 Pond 18

The treated liquid impoundments (Pond A-5 and Pond 18) have presumptive closure remedies, and the stormwater ponds (A-Series Pond, RCF Pond, and Pond 13) are anticipated to be closed as part of the remedy to be selected by USEPA for the site. Therefore, the treated liquid impoundments and the stormwater ponds were evaluated similarly to terrestrial areas. For terrestrial receptors, exposures were estimated for each of the units listed above and also


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for the two following sitewide scenarios:

Sitewide (i.e., all terrestrial uncapped units) with Pond A-5 and Pond 18 Sitewide without ponds (i.e., all terrestrial uncapped units only)

Freshwater Aquatic Areas The freshwater aquatic areas evaluated included the following exposure units: Site freshwater aquatic areas:

A-Series Pond RCF Ponds Pond A-5 Pond 13 Pond 18

Freshwater aquatic areas outside the site boundaries:

North Drainage A Drainage B Drainage Upper C Drainage Lower C Drainage

Runoff sample collected in RCRA Canyon Site freshwater seeps (qualitatively only):

A-Series Seep CA Seep Caustic LF Seep Seep 9B

For site freshwater aquatic receptors, exposures were estimated for each of the units listed above and also for the following two sitewide scenarios:

Pondwide (i.e., all site ponds) Stormwater Impoundments (A-Series pond, RCF Pond, and Pond 13)

Exposure Assumptions Ecological community exposures are expressed in terms of site media concentrations, whereas wildlife exposures are expressed in terms of a daily dose. For wildlife receptors, numerous exposure assumptions, such as food and water ingestion rates, body weights, and absorption factors, are defined in the ERA for estimation of the exposure doses for each wildlife receptor. These exposure parameters were obtained from literature sources and were used in all tiers of the ERA. In contrast, bioaccumulation factors (BAFs) for the Screening-Level and Tier 1 ERA were primarily obtained from guidance documents or other commonly used literature sources (described in detail in Attachment 1 of Appendix U of the Final RI Report; 2011), but were developed from site-specific uptake data for the Tier 2 ERA (see Appendix U of the Final RI


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Report; 2011). Effects Assessment The effects assessment includes the identification and development of toxicity values for ecological receptors. Following CalEPA guidance (CalEPA 1996), toxicity values were based on “no-effect” levels. The “no-effect” level is the concentration or dose at or below which no adverse effects on the test organism are observed. However, to evaluate a range of risk estimates for ecological receptors in all the tiers of the ERA, “lowest observable effects” data or other alternate “upper bound” toxicity values were also developed. For ecological communities and amphibians, effects are assessed using toxicity values referred to as “screening values.” Screening values are threshold concentrations expressed in milligrams per kilogram (mg/kg) or mg/L that are effect levels or benchmarks for organisms inhabiting/exposed to that matrix (soil, sediment, surface water). For terrestrial plants, soil invertebrate ecological communities and amphibians, single screening values were developed; for sediment-dwelling invertebrates and aquatic life, low and high screening values were developed; and for aquatic plant ecological communities and amphibians, single screening values were developed. For wildlife (mammals and birds), effects are assessed using toxicity values referred to as toxicity reference values (TRVs). A TRV is defined as a daily dose of a chemical expressed in milligrams of chemical per kilogram of body weight per day (mg/kg bw-day) and represents a dose associated with no-effect, lowest-effect, or mid-range-effects for ecologically relevant endpoints. For wildlife, a range of low and high TRVs were developed. Low TRVs were based on NOAELs and high TRVs were based on LOAELs or mid-range effect levels. TRVs could not be developed for reptiles due to limited toxicity data. Both NOAELs and LOAELs represent doses affecting receptors at the individual level. If risks (i.e., HQs over 1) are predicted at this level (i.e., when the estimated exposure dose exceeds the LOAEL), effects may be evident at the population level. Because there is a higher level of concern, NOAEL-based TRVs are considered when making risk management decisions for protected (threatened and endangered) species. 7.2.1 Tier 1 ERA Overall, the results of the Tier 1 ERA identified that risks to terrestrial birds at the site are driven mainly by:

Barium in the RCRA Canyon Area and the Former Ponds and Pads Area; Cadmium in the RCRA Canyon Area and WCSA; Chromium in the RCRA Canyon Area, Roadway Area, and WCSA; Copper in the RCRA Canyon Area, and WCSA; Lead in the RCRA Canyon Area, Roadway Area, and WCSA; Zinc in the RCRA Canyon Area and WCSA; Aroclor 1260 in the Roadway Area; and Total PCBs in the Former Ponds and Pads Areas.

Tables 7-1 through 7-3 identify the COCs based on the Tier 1 ERA for areas with a presumptive remedy in place , and Figures 7-1 and 7-2 provide an overall summary of co-located risks to ecological communities and wildlife receptors, respectively.


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Based on the results of the Tier 1 ERA, the invertivorous bird (based on the invertivorous meadowlark) was predicted to be the most sensitive terrestrial bird to potential adverse effects from exposure to these chemicals in soil 0 to 0.5 feet bgs, except for the herbivorous bird (based on the herbivorous meadowlark) from barium. Further evaluation was warranted for these risk-driving COPECs in the exposure areas listed above, for which no presumptive remedies are planned. Tier 1 risks to terrestrial mammals at the site are driven mainly by:

Barium in the RCRA Canyon Area; Cadmium in the RCRA Canyon Area and WCSA; Chromium in the RCRA Canyon Area, Roadway Areas, and WCSA; Copper in the RCRA Canyon Area, Roadway Areas, and WCSA; Zinc in the Roadway Area, RCRA Canyon Area and WCSA; Aroclor 1260 in the Roadway Areas; and Total PCBs in the Former Ponds and Pads Areas.

Based on the Tier 1 ERA, the invertivorous mammal (based on the shrew) was predicted to be the most sensitive terrestrial mammal to potential adverse effects from exposure to metals in soil 0 to 5 feet bgs. The carnivorous mammal (based on the skunk) was predicted to be the most sensitive terrestrial mammal to potential adverse effects from exposure to organics in soil 0 to 5 feet bgs. Potential adverse risk to deep burrowing mammals (0 to 10 feet bgs) via inhalation of burrow air or by ingestion of soil is expected to be unlikely from exposure to chemicals at the site. Further evaluation was warranted for these risk-driving COPECs in the exposure areas listed above, for which no presumptive remedies are planned. Tier 1 risks to terrestrial ecological communities (plants and soil invertebrates) at the site are driven mainly by:

Barium in the RCRA Canyon Area the Former Ponds and Pads Area; Chromium in the RCRA Canyon Area, Roadway Area, and WCSA; Copper in the RCRA Canyon Area, Roadway Area, and WCSA; and Zinc in the RCRA Canyon Area and WCSA.

Tier 1 risks to aquatic wildlife at the site are driven mainly by:

Chromium, manganese selenium, and vanadium in A-Series Pond; Barium and selenium in Pond A-5; Selenium in Pond 18; and Barium in RCF Pond.

Based on the Tier 1 ERA, the invertivorous bird (based on the killdeer) was predicted to be the most sensitive aquatic bird to potential adverse effects from exposure to these chemicals in surface sediment. However, all of these risk drivers are based on the maximum detected concentrations and may be overestimating potential risk to aquatic wildlife. Additionally, the diet for the aquatic wildlife was based on a mixture of sediment invertebrates and aquatic invertebrates, assuming 50% of each, and this general assumption could potentially introduce uncertainty to the risk estimates.


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Tier 1 risks to sediment-dwelling invertebrates at the site are mainly by:

Cadmium in the A-Series Pond, Pond 18, and Pond A-5; Nickel in A-Series Pond, Pond 13, Pond 18, and Pond A-5; Selenium in A-Series Pond, Pond 18, and Pond A-5; MCPP in RCF Pond, Pond 18, and Pond A-5; Acetone in RCF Pond; and 1,1-Dichloroethane in Pond A-5 and RCF Pond.

Based on the Tier 1 ERA, potential risk to aquatic life, aquatic plants, and amphibians are mainly from metals in the ponds. Risks to amphibians for the RCRA Canyon runoff were estimated based on a conservative scenario. This scenario evaluated the potential risk to aquatic receptors under the hypothetical scenario that water pools in RCRA Canyon, which based on site observations, does not occur under current site conditions. Additional evaluations of RCRA Canyon runoff and the potential for pooling once a remedy is in place for A-Series Pond will be evaluated in the FS. The seeps are currently dry and facilities (e.g., Sump 9B and Road Sump) are in place to control these seeps. Therefore, the seeps are not expected to be sources of exposure to amphibians, aquatic life, or aquatic plants. Risks to aquatic life in surface water from the RCRA Canyon runoff are from:

Arsenic, barium, cadmium, selenium, vanadium, benzo(b)fluoranthene, and ethylene glycol.

Risks to amphibians in surface water from the RCRA Canyon runoff are from:

Arsenic, barium, beryllium, cadmium, chromium, lead, manganese, mercury, molybdenum, nickel, selenium, silver, thallium, vanadium, and zinc.

Risks to aquatic plants in surface water from the RCRA Canyon runoff are from:

Arsenic, cadmium, nickel, and selenium. All of the existing ponds at the site are expected to be closed pursuant to the remedy to be selected by USEPA, and to be backfilled/graded to prevent accumulation of water; as such, they will be unavailable as a pathway for aquatic receptors, essentially eliminating the potential for adverse effects to aquatic receptors. Remedies for all ponds at the site are detailed as part of the FS process. Therefore, none of the chemicals in the ponds with HQs greater than 1 warrant further evaluation in the FS. 7.2.2 Tier 2 ERA As discussed in Appendix U of the Final RI Report, after completing and reporting the Tier 1 ERA in the draft RI Report, a Tier 2 ERA was completed to further evaluate pathways, receptors, and risk-driving COPECs identified in the Tier 1 ERA requiring further evaluation. The objectives of Tier 2 ERA were to provide valuable information for refining risks, reduce the overall uncertainty in the risk estimates by incorporating site-specific information into exposure estimates, to provide additional lines of evidence to provide a clearer understanding of the environmental benefit of reducing concentrations at the site, and ultimately to identify COCs for areas with no planned presumptive remedies for evaluation in FS. The Tier 2 ERA included


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additional studies and evaluations designed to make the ecological risk assessment more site-specific and less generic. The Tier 2 ERA included the following additional data collection and further evaluation efforts to further refine the ecological risks at the site:

Tissue sampling (plants, soil invertebrates, and/or small mammals); and Refinement of ecological benchmarks, including developing tissue TRVs to use as

additional weight-of-evidence in the risk characterization. The Tier 2 ERA was conducted by building on the results of the Tier 1 ERA and incorporating site-specific tissue and bioaccumulation data. The results of the Tier 2 ERA are discussed in detail in Section 9 and Appendix U of the RI Report (2011). The Tier 2 ERA focused on the risk driving-COPECs from the Tier 1 ERA, receptors, and exposure areas for which there is no presumptive remedy contemplated. The Tier 1 ERA predicted that invertivorous bird and mammal populations were the most sensitive terrestrial wildlife, and their risks were driven by exposure to chemicals in surface soil. The aquatic invertivorous bird (based on the killdeer) was generally predicted to be the most sensitive aquatic bird, exposed to chemicals in surface sediment. The risks to aquatic birds are similar to those for terrestrial birds when the Tier 1 ERA was conducted assuming the ponds would be drained. The pathway that generally contributed most to the risk estimate for all wildlife was food ingestion. As discussed above, it is anticipated that all the remedial alternatives being considered will include closure of all the ponds to close out known exposure pathways. The FS also includes critical area-specific remedial alternatives to prevent known exposures from surface impoundments as well as the Central Drainage Area, the Liquids Treatment Area, the Burial Trench, and Maintenance Shed Area. Therefore, the Tier 2 ERA focused on the remaining exposure areas and risk driving- COPECs from Tier 1 ERA, which included:

Administration Building Area; RCRA Canyon; West Canyon Spray Area; Roadway Areas; Remaining Site Areas; and Former pond and pad areas south of the PSCT.

Based on the results of the Tier 2 ERA, COCs were identified for further evaluation in the FS. Overall, the results of the Tier 2 ERA identified that risks to terrestrial birds at the site are driven mainly by the following COCs:

Barium, chromium, copper, and zinc in the RCRA Canyon Area; and Chromium, copper, and zinc in the WCSA.

The invertivorous bird (based on the invertivorous meadowlark) is predicted to be the most sensitive terrestrial bird to potential adverse effects from exposure to these chemicals in soil 0 to 0.5 feet bgs except for the herbivorous bird (based on the herbivorous meadowlark) for barium.


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For terrestrial mammals, a comparison of site-specific tissue data to tissue-based TRVs developed for kidney and liver tissue indicates that cadmium, chromium, copper, lead, and zinc are not expected to accumulate in target tissues at levels that would result in potential adverse risks. Tier 2 risks to terrestrial mammals at the site are driven mainly by the following COC:

Barium in the RCRA Canyon Area. The invertivorous mammal (based on the shrew) is predicted to be the most sensitive terrestrial mammal to potential adverse effects from exposure to metals in soil 0 to 5 feet bgs. The results of the spatial analysis indicate that for all receptors, potential risk from barium is the most wide-spread in the RCRA Canyon Area and sample-specific risks for the other receptors are co-located in RCRA Canyon and tend to be located on the west side of RCRA Canyon. In the WCSA, sample-specific risks are generally located in the central portion of WCSA and are co-located among receptors. Barium is the only COC in the Former Ponds and Pads Areas and the potential for cumulative risk to soil invertebrates beyond those identified for barium are likely minimal. 7.2.3 Barium Toxicity Historical activities indicate that drilling mud containing barium sulfate was spread in the WCSA and the RCRA Canyon. Barium sulfate, which is about four times more dense than water, is typically used by oil and gas industries as a weighing agent during drilling. High density barium sulfate is insoluble and therefore, provides stability for the drilling mud (Halliburton et al. 2007). Therefore, the risks to ecological receptors exposed to barium in soils in the WCSA and the RCRA Canyon were evaluated. Barium toxicity to ecological receptors (wildlife) is due to free barium ions which can be absorbed into lungs and intestines. Barium sulfate, being insoluble, does not cause significant toxicity as free barium ions are not released. However, soluble forms of barium (such as barium hydroxide) dissociate in water and release free barium anions which can readily be absorbed by lungs and intestines and cause adverse toxic effects (Halliburton et al. 2007). In 1993, USEPA exempted barium sulfate from the reporting requirements under Section 313 of the Emergency Planning and Community Right-to-Know Act of 1986 (USEPA 1993) and USEPA stated that:

“Human and animal data show that barium sulfate is essentially non-toxic to humans or other mammalian species. This is attributable to the very low solubility of the compound in water. Barium sulfate is not expected to be absorbed through the skin and is expected to be only minimally absorbed through the lung and gastrointestinal tract. Barium sulfate cannot reasonably be anticipated to cause acute or chronic toxicity in humans or adverse effects in the environment.”

The toxicity values used in the ERA as part of the RI for the site (2011) were all based on soluble forms of barium. The barium toxicity reference values (TRVs) for mammals and birds were based on toxic effects of barium chloride and barium hydroxide respectively, both highly soluble. Similarly, for plants and soil invertebrates, soluble forms of barium were used to develop screening levels. Menzie et al., (2008) compare the solubility and toxicity of barium sulfate to the soluble forms of barium used to develop screening levels in the USEPA Ecological


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Soil Screening Levels (EcoSSL) guidance (USEPA 2005b). Barium sulfate is considered nontoxic to invertebrates, plants, and wildlife (Menzie et al. 2008). Kuperman et al (2006) conducted range-finding tests for barium with four barium compounds to determine which compound was most suitable to produce a toxicity benchmark. Of the four compounds, only barium sulfate was insoluble and it did not affect adult survival of the three soil invertebrate species tested at concentrations as high as 10,000 mg/kg. Based on USEPA’s exemption of barium sulfate and the knowledge of historical activities at the WCSA and the RCRA Canyon, the calculated ecological risk from exposure to barium reported in the RI (2011) was overestimated. Considering that barium at the WCSA and the RCRA Canyon is barium sulfate and therefore, not toxic to ecological receptors, barium can be excluded as a COC. This impacts the remedial footprint proposed for the WCSA and the RCRA Canyon in the FS which was based on four COCs: barium, chromium, copper, and zinc. Figure 7-1a and 7-2a of this report provide an overall summary of co-located risks excluding barium to ecological communities and wildlife receptors, respectively. See Section 10.3 and Appendix C of this report for more details on adjustments to the remedial footprint for the WCSA and the RCRA Canyon.

7.3 Land Ownership and Use The site is located within a group of land parcels comprising approximately 4,500 acres that, during the time the site operated, were all owned by Kenneth Hunter or Casmalia Resources. As shown on Figure 7-3, the 252-acre area comprising Zone 1 (Figure 1-1) is located within portions of three parcels (parcels 113-260-02, 113-260-03, and 113-260-04), and is surrounded by numerous other parcels that are controlled as discussed below. Casmalia Resources continues to own parcels 113-260-002 and 113-260-003 which encompass most of Zone 1. A small area in the eastern portion of Zone 1 lies adjacent to parcel 113-260-004, which is currently under the ownership of Casmalia Resources Acquisition Property Company The acquisition company also owns three additional parcels lying to the north of Zone 1, including parcels 113-260-001, 113-220-012, and 113-220-010. A local rancher owns numerous parcels near the site vicinity (parcels 113-220-001, 113-260-011, 113-260-012, 113-260-013, 113-260-014, 113-260-015, 113-260-017, 113-260-019, 113-270-006, 113-270-015, and 113-270-016). The rancher’s land borders Zone 1 along a small portion of parcel 113-260-019 (Figure 7-3). Other major landholders in the vicinity include oil company property to the north (parcels 113-220-008 and 113-220-009), and another private property to the northeast of Zone 1 (parcel 113-230-006 and a portion of parcel 113-230-007). Current land use in the area is predominated by ranching and livestock/grazing, with some scattered oil and gas development. Parcels under ownership of Casmalia Resources Acquisition Property Company have already had deed restrictions placed upon them that precludes them from ever being used as residential or certain other sensitive developments such as hospitals, day care, etc. The Casmalia Resources Acquisition Property Company parcels will remain available only to grazing/ranching/oil and gas, or other industrial developments.

7.4 References CalEPA .1992. Supplemental Guidance for Human Health Multimedia Risk Assessments of

Hazardous Waste Sites and Permitted Facilities. California Environmental Protection


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Agency. Department of Toxic Substances Control. July. (Corrected and reprinted August 1996).

CalEPA. 1996. Guidance for Ecological Risk Assessment at Hazardous Waste Sites and

Permitted Facilities. Parts A and B. California Environmental Protection Agency. July 4. CalEPA. 1998. Depth of Soil Samples Used to Set Exposure Point Concentration for Burrowing

Mammals and Burrow-dwelling Birds in an Ecological Risk Assessment. HERD ERA Note Number 1. www.cwo.com/~herd1/ftp/econote1.pdf. California Environmental Protection Agency. May.

CalEPA 2000. Air Toxics Hot Spots Program Risk Assessment Guidelines Part IV. Technical

Support Document, Exposure Assessment and Stochastic Analysis. Office of Environmental Health Hazard Assessment. September.

CalEPA 2003. The Air Toxics Hot Spots Program Guidance Manual for Preparation of Health

Risk Assessments. Office of Environmental Health Hazard Assessment. CalEPA, 2005. Guidance for the Evaluation and Mitigation of Subsurface Vapor Intrusion to

Indoor Air - Interim Final. Department of Toxic Substances Control (DTSC). Revised February 7, 2005.

CalEPA, 2007a. Cancer Potency Factors - Toxicity Criteria Database. Office of Environmental

Health Hazard Assessment. Website address: http://www.oehha.ca.gov/risk/chemicalDB/ index.asp.

CalEPA, 2007b, Development of Health Criteria for Schools Site Risk Assessment Pursuant to

Health and Safety Code Section 901(g): Proposed Child-Specific Benchmark Change in Blood Lead Concentration for School Site Risk Assessment. available at: http://www.oehha.ca.gov/public_info/public/kids/index.html

CalEPA, 2009. Revised California Human Health Screening Levels for Lead. Integrated Risk

Assessment Branch. Office of Environmental Health Hazard Assessment. September. Casmalia Site Remediation RI/FS Work Plan. Prepared for U.S. EPA Region 9. San Francisco,

CA. Casmalia Steering Committee. June 2004. 439 pp. Final Remedial Investigation Report. Casmalia Resources Superfund Site. Casmalia Steering

Committee. January 2011. Halliburton, J.M., McHugh, T.E., and Higgins, E.A. 2007. Barium Sulfate: A Protocol for

Determining Higher Site-Specific Barium Cleanup Levels. Society of Petroleum Engineers. March.

Kuperman, R.G., Checkai, R.T., Simini, M., Phillips, C.T., Speicher, J.A., Barclift, D.J. 2006.

Toxicity benchmarks for antimony, barium, and beryllium determined using reproduction endpoints for Folsomia candida, Eisenia fetida and Enchytraeus crypticus. Environmental Toxicology and Chemistry 25:754-762.


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Menzie, C.A., Southworth, B., Stephenson, G. and Feisthauer, N. 2008. The importance of understanding the chemical form of a metal in the environment: The case of barium sulfate (barite). Human and Ecological Risk Assessment 14:974-991.

USEPA, 1989. Risk Assessment Guidance for Superfund Volume I, Human Health Evaluation -

Manual (Part A), USEPA 540/1-89-002, Office of Emergency and Remedial Response. Washington, DC.

USEPA, 1991a. Risk Assessment Guidance for Superfund, Volume 1, Human Health

Evaluation Manual, Supplemental Guidance Standard Default Exposure Factors, Draft Final, March 25, 1991, OSWER Directive 9285.6-03, Office of Solid Waste and Emergency Response, Washington, DC.

USEPA, 1991b. Role of Baseline Risk Assessment in Superfund Remedy Selection Decisions.

Office of Solid Waste and Emergency Response. PB91-921359. Washington, D.C. USEPA. 1992. Data Usability in Risk Assessment (Part A). U.S. Environmental Protection

Agency. Office of Emergency and Remedial Response. PB92-963356. April. USEPA. 1993. Barium Sulfate; Toxic Chemical Release Reporting Community Right-to-Know.

40 CFR Part 372, Federal Register. 58, No. 111, 32622-32628. United States Environmental Protection Agency. June 10.

USEPA, 1995. Guidance for Risk Characterization. USEPA Science Policy Council. Risk

Characterization Program. February. USEPA, 1997a. Exposure Factors Handbook. Volumes I-III. An Update to Exposure Factors

Handbook USEPA/600/8-89/043 March 1989. USEPA/600/P-95-002Fa, August. USEPA. 1997b. Health Effects Assessment Summary Tables. U.S. Environmental Protection

Agency. July.

USEPA. 1997c. Ecological Risk Assessment Guidance for Superfund: Process for Designing and Conducting Ecological Risk Assessments, Interim Final. EPA/540-R-97-006. U.S. Environmental Protection Agency, Office of Solid Waste and Emergency Response. June 5.

USEPA, 2002. Supplemental Guidance for Developing Soil Screening Levels for Superfund

Sites. Office of Solid Waste and Emergency Response. OSWER 9355.4-24. USEPA. 2004a. Risk Assessment Guidance for Superfund Volume I: Human Health Evaluation

Manual (Part E, Supplemental Guidance for Dermal Risk Assessment) Final. EPA/540/R-99/005. Office of Solid Waste and Emergency Response, Washington, DC. PB99-963312. OSWER 9285.7-02EP. July.

USEPA, 2004b. USEPA Region IX Preliminary Remediation Goals (PRG) Table. October. USEPA. 2005a. Procedures for the Derivation of Equilibrium Partitioning Sediment Benchmarks

(ESBs) for the Protection of Benthic Organisms: Metal Mixtures (Cadmium, Copper, Lead, Nickel, Silver and Zinc). EPA/600-R-02-011. U.S. Environmental Protection Agency, Office of Research and Development. January.


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USEPA. 2005b. Ecological Soil Screening Levels for Barium. United States Environmental

Protection Agency. Office of Solid Waste and Emergency Response. February. USEPA. 2006a. Data Quality Assessment: Statistical Methods for Practitioners. EPA QA/G-9S.

Office of Environmental Information. EPA/240/B-06/003. February. USEPA. 2006b. On the Computation of a 95% Upper Confidence Limit of the Unknown

Population Mean Based Upon Data Sets with Below Detection Limit Observations. EPA/600/R-06/022. U.S. Environmental Protection Agency. March. 146 pp.

USEPA, 2007a. ProUCL Version 4.0.01 Users Guide. Prepared by A. Singh, R.W. Maichele,

A.K. Singh, S.E. Lee and N. Armbya for USEPA ORD NERL, Las Vegas, NV. EPA/600/R-07/038. April.

USEPA. 2007b. ProUCL Version 4.0 Technical Guide. Office of Research and Development.

EPA/600/R-07/041. April USEPA, 2007c. Integrated Risk Information System (IRIS) Substance File Online Database.

Office of Research and Development, National Center for Environmental Assessment. Website address: http://www.epa.gov/iriswebp/iris/subst/index.html


8-1

8.0 AREAS FOR FS EVALUATION, REMEDIAL ACTION OBJECTIVES, GENERAL RESPONSE ACTIONS, ARARS, TI EVALUATION, and PRELIMINARY REMEDIATION GOALS

This section of the FS defines the areas that are carried forward into the FS for evaluation, and lists the RAOs and PRGs, GRAs and Potential ARARs for the Casmalia Resources Superfund Site. The RAOs, PRGs, and GRAs are presented by media, separately for soil and sediment, and groundwater, NAPL and stormwater. This section also presents a summary level discussion of the TI evaluation and request for a TI waiver including a summary of justification for a TI waiver with the detailed TIE presented in Appendix A. The TIE evaluates the practicability of returning groundwater to its beneficial use and provides a detailed rationale for the TI waiver of selected groundwater ARARs under NCP Section 300.430(f)(l)(ii)(C)(3) and the USEPA’s TI Waiver Guidance for groundwater restoration (USEPA 1993).

8.1 Summary of Study Areas for FS Evaluation Table 8-1 presents the list of Study Areas considered during the RI, HHRA and ERA, and provides an overall summary of the impacted media, primary COCs and risk considerations for each RI Study Area. Table 8-1 also identifies study areas that will be carried into the FS for formal evaluation. As noted on Table 8-1, the FS further groups the remaining RI Study Areas that have similar characteristics into FS Areas. Certain RI Study Areas such as the Administration Building Area, Offsite Groundwater and Offsite Drainages were determined to not require any additional FS evaluation based on the lack of significant human health or ecological risk. For the Capped Landfills Area, the FS reviews the capping previously completed under two interim removal actions. Tthe 1998 capping of the P/S Landfill as was required by the Consent Decree and the 2001 EE/CA Area capping completed under an EE/CA prepared by USEPA for the work. The FS evaluation concludes that the “Monitoring, Maintenance of Existing Cap, ICs, Groundwater monitoring” remedial alternative mitigates potential groundwater contaminant migration. For the RI Study Area labeled Offsite Groundwater, the RI sampling and previous RGMEW sampling of groundwater in this area noted only low levels of organics and inorganics which are not high enough to trigger any remediation requirements. Similarly, the VOCs measured in soil vapor in this RI Study Area (results of soil vapor sampling that focused on the north ridge of the site) do not exceed action levels and hence do not represent any unacceptable ecological or human health risk, and thus do not require any remediation at this time. While remedial technologies and alternatives are not formally evaluated in the FS for this study area, groundwater and soil vapor monitoring are anticipated to be included as components of the remedy to be selected by USEPA. Future exceedances of action levels could also trigger corrective action, such as active control measures, if determined necessary by USEPA. For the FS evaluation, the Study Areas that required further evaluation were grouped together to form five FS Areas based on geographical proximity or similar impacted media. The five FS Areas for evaluation are shown on Figures 8-1A and 8-1B and are listed below:


8-2

FS Area 1 – PCB Landfill, Burial Trench Area, Central Drainage Area and Capped Landfills Area

FS Area 2 – RCRA Canyon, West Canyon Spray Area FS Area 3 – Former Ponds and Pads, Remaining On-site Areas, Roadways, Liquids

Treatment Area and Maintenance Shed Area FS Area 4 – Stormwater Ponds and Treated Liquid Impoundments (A-Series, RCF, A-5,

18 and 13) FS Area 5 – Groundwater; Includes dissolved contaminants and NAPL in groundwater

and is divided into three areas:

o Area 5 North – Groundwater north of the PSCT o Area 5 South – Groundwater south of the PSCT o Area 5 West – Groundwater in and south of the RCRA Canyon

FS Areas 1 through 4 relate to surface media (e.g., soil and surface water), while FS Area 5 relates to groundwater. The groundwater evaluation includes dissolved phase contaminants in groundwater sitewide and, NAPL in groundwater that is focused on the NAPL source areas primarily in the vicinity of the P/S Landfill. The FS identifies stormwater as a separate study area (see Table 8-1) and subdivides stormwater into Capped Area stormwater, (b) RCRA Canyon stormwater, and (c) Uncapped Area stormwater (outside RCRA Canyon). Remedial objectives and response actions are also developed for this medium. Remedial components relating to appropriate storm water management are included in each of the soil FS Areas 1 through 4.

8.2 Remedial Action Objectives As discussed in the NCP, RAOs describe in general terms what a remedial action should accomplish in order to be protective of human health and the environment. RAOs are narrative statements that specify the COCs and environmental media of concern, the potential exposure pathways to be addressed by remedial actions, and the receptors to be protected. RAOs include both medium-specific and/or area-specific objectives for protecting human health and the environment. CERCLA requires that remedial actions:

Attain a degree of cleanup of hazardous substances, pollutants, and contaminants released into the environment and control of further release at a minimum which assures protection of human health and the environment” (Section 121(d)(1));

Comply with or attain the level of “any standard, requirement, criteria, or limitation under any Federal environmental law…or any promulgated standard, requirement, criteria, or limitation under a State environmental or facility siting law that is more stringent than any Federal standard, requirement, criteria, or limitation” that is found to be applicable or relevant and appropriate (Section 121(d)(2)(A)).

For the Casmalia Resources Superfund Site FS, the medium-specific objectives are proposed based on the results discussed in the RI Report, including the Human Health Risk Assessment, and the Tier 1 and 2 Ecological Risk Assessment. Here the RAOs are refined to specify the COCs and exposure pathways for applicable media in each study area. Because the site accepted a broad range of chemical wastes, the preliminary human health related RAOs for soil, soil vapor, and sediment were expressed in general terms consistent with the NCP (e.g., risk range of 10-4 to 10-6). Similarly, the ecological risk goals were expressed as generic screening values or risk targets.


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Tables 8-2 and 8-3 present the sitewide RAOs and GRAs ((see Section 8.3) by media and the applicable remedial technologies and process options. These tables were originally presented in the RI/FS Workplan and have been updated here in the FS. The table presents the media in two groups: 1) soil, soil vapor and sediment; and 2) groundwater, NAPL and stormwater. The FS presents a detailed evaluation of technologies and process options later in Section 9. Table 8-4 develops the RAOs and GRAs on an area-specific and media-specific basis as discussed below. 8.2.1 Soil, Soil Vapor, and Sediments Table 8-4 presents the RAOs for the soils separately for each FS Area based on environmental media (surface soil, shallow soil, soil vapor, deep soil and groundwater) and contaminant type (VOCs, non-VOCs). These RAOs are summarized below:

Prevent human exposures to COCs in soil, soil vapor and sediment such that total carcinogenic risks are within the NCP risk range of 10-4 to 10-6 and non-cancer hazard indices are less than 1 (HI<1). Potential human exposures include workers at the site, trespassers, and hypothetical offsite residents,

Prevent exposures to populations of ecological receptors for COCs in soil, soil vapor and sediment such that risks are below the acceptable target levels (lowest-observed adverse effects level or LOAEL hazard quotients less than 1).

Mitigate the potential for migration of contaminants in soil, soil vapor and sediment that could adversely affect groundwater quality.

8.2.2 Groundwater, NAPL, and Surface Water Media Table 8-4 also presents the primary RAOs for the NAPL/groundwater contamination source areas in deep soil or groundwater media and surface water. Table 8-4 presents the groundwater RAOs separately for each of the three groundwater areas (5 North, 5 South and 5 West). These RAOs are summarized for the sitewide groundwater and surface water media below:

Prevent human exposures to COCs in surface water such that that total carcinogenic risks are within the NCP risk range of 10-4 to 10-6 and non-cancer hazard indices are less than 1 (HI<1). Potential human exposures include site workers, trespassers, and hypothetical offsite residents,

Prevent ecological exposures to COCs in surface water such that exposures are below acceptable levels (HQs less than 1 based on selected surface water benchmarks, See Table 8-5).

Restore groundwater quality to applicable standards (e.g. restore beneficial use, achieve MCLs) where technically practicable.

Contain and/or control contamination within Zone 1 or subareas within Zone 1, where groundwater restoration to applicable standards is not technically practicable in those subareas.

Mitigate potential migration of groundwater contamination beyond the site boundaries via perimeter control.

Remove DNAPL to the extent practicable and contain and/or control the migration of DNAPL where removal is not technically practicable.

Remove LNAPL to the extent practicable and contain and/or control the migration of LNAPL where removal is not technically practicable.


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Table 8-5 presents the proposed standards for the offsite discharge of treated liquids (e.g., treated stormwater, pond water, or groundwater). The point of discharge would be to the C-Drainage west of the site. The proposed standards were selected based on the 1999 NPDES standards (revised 2004). The proposed standards are preliminary and subject to RWQCB review. Treated liquids would be discharged under the substantive terms of a site-specific NPDES Permit, which would require submittal of a report of waste discharge and application package to the RWQCB to request an exception to the Basin Plan prohibition for the discharge of treated liquids to Casmalia Creek (see Section 2.2.4 for a summary of the status of the NPDES Permit). Clean stormwater from areas that are remediated would be discharged offsite to the B Drainage and Casmalia Creek under the substantive requirements of the General Permit, which would include the preparation and adherence to the substantive requirements of a Storm Water Pollution Prevention Plan (SWPPP). The SWPPP identifies structural and non-structural controls that would be put in place to minimize negative impacts, caused by offsite storm water discharges, to the environment. The purpose of these controls is to minimize erosion and run-off of pollutants and sediment. The purpose of the General Permit is to confirm that stormwater discharges are properly monitored and that discharges and their potential impacts to the environment are controlled. The SWPPP establishes procedures for minimizing potential to be carried away in stormwater discharges through the use of Best Management Practices (BMPs). The ecological screening levels also presented in Table 8-5 for comparison purposes to the NPDES standards are concentrations that are protective of aquatic life based on the surface water screening levels presented in Table U-24 of the Final RI Report (CSC, 2011). Preference in selecting surface water screening levels was given to promulgated numeric water quality criteria for priority toxic pollutants and other water quality standards for the waters in the State of California. Chronic effects values were selected, where available, from the following hierarchy of sources (a value from the first source was used if available and, if not available, a value from subsequent sources was used in the order listed): USEPA Federal Register Title 40 CFR Part 131 Water Quality Standards Section 38-Established Numeric Criteria for Priority Toxic Pollutants for the State of California (USEPA 2006a); USEPA National Ambient Water Quality Criteria (USEPA 2006b); Oak Ridge National Laboratory: Toxicological Benchmarks for Screening Potential Contaminants of Concern for Effects on Aquatic Biota (Suter and Tsao 1996); USEPA Supplemental Guidance to Risk Assessment Guidance: Region 4 Bulletins, Ecological Risk Assessment (USEPA 2001); San Francisco Regional Water Quality Control Board (SFRWQCB) ESLs: Freshwater Aquatic Habitat Goals (SFRWQCB 2005); Central Valley Regional Water Quality Control Board (CVRWQCB) Recommended Numerical Limits to Translate Water Quality Objectives (CVRWQCB 2007); and Water Management Policies Guidelines Provincial Water Quality Objectives of the Ontario Ministry of Environment and Energy (MOEE,1999 revision).

The screening levels for amphibians are based on the lowest no-effect value (protective of sensitive species) of the empirical data cited in Ecotoxicology of Amphibians and Reptiles (Sparling et al. 2000); empirical data from the Database of Reptile and Amphibian Toxicology Literature (RATL) (Pauli et al. 2000); and empirical data from the ECOTOX database (USEPA 2007). Uncertainty factors were used to extrapolate to no-effect levels, when only effect-levels were available.


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8.3 General Response Actions GRAs are broadly-based descriptions of remedial actions that can potentially satisfy the RAOs discussed above. GRAs range from no further action to passive technologies focused on containment to active removal or destruction technologies. The GRAs developed for this FS include institutional controls, engineering controls, in-situ treatment, ex-situ treatment, or a combination of the above. Like RAOs, GRAs are medium-specific. GRAs were developed based on the findings of the RI Report (CSC, 2011). Tables 8-2 and 8-3 present the sitewide RAOs and GRAs by media and the applicable remedial technologies and process options. Ultimately, the retained technologies and process options for each GRA were combined to form remedial alternatives evaluated in this FS. The technology types are discussed in detail in the following section on screening of technologies (Section 9) and the remedial alternatives are developed and evaluated in Sections 10 and 11. 8.3.1 Soil and Sediment Media Table 8-4 presents the GRAs developed to address RAOs by environmental medium, contaminant type, exposure route and receptor. The typical GRAs for the soil/sediment are listed below by technology type:

No Action ICs

o Implement ICs to notify site workers of available information resources,

monitoring programs and any control measures relating to soil contamination that apply to portions or all of the site.

o Implement engineering controls (fencing, warning/information signs or notices, other) to restrict access to site or areas of contaminated soil.

Containment (Capping)

o Isolate contaminated soil with a physical barrier (soil cap, RCRA cap, hybrid cap,

evapotranspiration cap, or ecological cap).

In-situ Treatment

o In-situ treatment of soils and sediment by chemical, physical, biological, or thermal technologies to neutralize or stabilize contaminants without excavation

Ex-situ Treatment (Excavation)

o Remove contaminants or contaminated surface or shallow soil and treat by chemical, physical, biological or thermal technologies; replace with clean soil.

Disposal/Reuse

o Site landfill disposal, offsite landfill disposal, or site reuse as backfill soil

Monitoring


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o Monitor for remedy effectiveness/compliance. 8.3.2 Groundwater, NAPL, and Stormwater Media Table 8-4 presents the GRAs developed to address RAOs by environmental medium (groundwater, NAPL, storm water), contaminant type, exposure route and receptor. The typical GRAs considered for the groundwater, NAPL and storm water are listed below by technology type:

No Action ICs

o Implement ICs relating to restrictions on groundwater development.

Containment

o Implement source control including continued extraction of liquids from site

extraction features o Restrict infiltration by capping waste and routing stormwater under substantive

terms of the General NPDES permit or to evaporation ponds o Implement NAPL source removal with additional extraction using wells in the

source area or other technology to the extent practicable where significant reduction in risk will result.

o Monitor NAPL to ensure product does not migrate beyond existing containment features.

o Additional remedial actions as determined necessary by EPA.

In-situ treatment

o Where practicable and applicable, implement in-situ treatment with chemical, physical, biological, or thermal technologies to prevent contaminant migration

Ex-situ treatment (Extraction)

o Implement source control or source reduction including continued extraction of

liquids from extraction features, new vertical or horizontal wells, and aboveground chemical, physical, biological, or thermal treatment of groundwater

Disposal/Discharge

o Disposal or discharge to permitted treatment, storage and disposal (TSD) facility,

site ponds, or site reinjection

Monitoring

o Maintain groundwater and soil vapor monitoring program to verify the long-term effectiveness of the containment remedy, document natural attenuation of dissolved phase contaminants, and ensure compliance with performance standards.


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Using the technologies resulting from the technology screening process and the GRAs presented here, the FS process develops appropriate remedial alternatives for each FS Area. The remedial alternatives for each FS Area will go through a screening evaluation and the retained remedial alternatives will undergo detailed evaluation using the CERCLA criteria.

8.4 Potential ARARs The following section presents an overview of the ARARs evaluation process and generally identifies potential site ARARs. The complete ARARs analysis is presented in Appendix B. The CERCLA legislation as amended by the Superfund Amendments and Reauthorization Act of 1986 (SARA), promulgated the legal standards regarding ARARs (42 USC §§ 9610-9675, CERCLA §§ 101-405). CERCLA remedial actions must meet any fully “applicable” or “relevant and appropriate” federal standards, requirements, criteria, or limitations under federal environmental laws or state standards, requirements, criteria or limitations under a promulgated State environmental or facility siting laws that are more stringent than federal standards,. The terms “applicable” and “relevant and appropriate” are defined in 40CFR § 300.400(g)(1)- (2). Applicable requirements are those cleanup standards, standards of control, and other substantive environmental protection requirements, criteria, or limitations promulgated under federal or state law that specifically address the situation at a CERCLA site. The requirement is applicable if the jurisdictional prerequisites of the standard show a direct correspondence when objectively compared to the conditions at the site. If the requirement is not legally applicable, then the requirement is evaluated to determine whether it is relevant and appropriate. Relevant and appropriate requirements are those cleanup standards, standards of control, and other substantive environmental protection requirements, criteria, or limitations promulgated under federal or state law, that while not applicable, address problems or situations sufficiently similar to the circumstances of the proposed response action and are well suited to the conditions of the site. A requirement must be substantive in order to constitute an ARAR for activities conducted onsite. Procedural or administrative requirements such as permits and reporting requirements are not ARARs. The NCP provides that where ARARs do not exist, agency advisories, criteria, or guidances are "to-be-considered" (TBCs) useful "in helping to determine what is protective at a site or how to carry out certain actions or requirements" (55 Federal Register 8745). The NCP preamble states, however, that provisions in the TBC category "should not be required as cleanup standards because they are, by definition, generally neither promulgated nor enforceable, so they do not have the same status under CERCLA as do ARARs." 55 Fed. Reg. 8745. ARARs and TBC requirements are generally divided into three categories: chemical-specific, location-specific, and action-specific. Chemical-specific requirements set health or risk-based concentration limits or discharge limitations for specific chemicals. Location-specific requirements are restrictions placed on activities due to their particular location, for example, floodplains, earthquake faults, wetlands, etc. and may affect the type of remedial action selected for the site. Action-specific requirements are usually technology-based and include performance, design or similar criteria related to particular remedial actions. The action-specific


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requirements do not determine the selected remedial alternative, but indicate how or to what level a selected alternative must perform. 8.4.1 Identification of Potential ARARs The identification of potential ARARs and TBCs for the site was accomplished by reviewing federal, state and local laws, regulations and policies that relate to actions being considered for the site. A preliminary determination of potential ARARs and TBCs was made based upon the terms of these statutes, regulations and policies; consideration of USEPA guidance (USEPA 1988); and best professional judgment. Identification of potential ARARs was a site-specific determination involving a two-part analysis: first, a determination of whether a given requirement is applicable; and, if it is not directly applicable, whether it is relevant and appropriate. The remedial alternatives and process options were then evaluated in terms of their ability to comply with identified potential ARARs. Appendix B presents a list of potential ARARs based on type, action, media, and degree of applicability. Action-Specific ARARs: Action-specific ARARs include federal and/or state requirements for the identification and management of hazardous materials. Many requirements address design, construction, operation, and monitoring of the remedial alternatives. These standards address design of treatment, storage, containment, and monitoring systems at the site, such as caps, wells, trenches, tanks, drainage, and treatment systems. Many of the Action-Specific ARARs for the site include State of California requirements, such as the substantive requirements of some Title 22 and Title 23 regulations for the design, construction, post-closure care, and monitoring of systems that will be necessary for containment of waste materials in landfill-like closure systems. Such requirements address engineered capping systems (e.g., seismic design), surface water management, and development of monitoring systems. Additional requirements affect waste extraction and storage systems as well as management of surface water. Chemical-Specific ARARs: Chemical-specific ARARs are treatment standards and action levels for various media such as soil, groundwater, air emissions, and soil gas. Chemical-Specific ARARs for the site include a number of Santa Barbara County requirements for air emissions. They also include maximum contaminant levels (MCLs) which serve as relevant and appropriate performance standards for groundwater water quality. The preferred alternative includes a list of COCs for which MCLs would be waived for Area 5 North since even very aggressive cleanup technology would not be able to restore groundwater to MCLs within this area. Location-Specific ARARs: Location-Specific ARARs address requirements for specific geographic areas. Examples include California Basin Plans, waste discharge requirements for surface water, California groundwater classification and anti-degradation policies, and requirements to protect certain types of wildlife. The federal Endangered Species Act (ESA), for example, is an important location-specific ARAR that it sets requirements for threatened and endangered species within designated areas. In addition, certain regulations from the California Fish & Game Code establish protections or place restrictions on activities that could adversely impact plant and animal habitats.


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8.5 Technical Impracticability Waiver This section summarizes the TIE that evaluates the practicability of returning groundwater to its beneficial use, as established by ARARs, or by risk-based goals where no ARARs exist. The FS presents the detailed TIE as a stand-alone document in Appendix A. The TIE completes and replaces the preliminary TIE that was included in the Final RI Report (CSC January 2011). The TIE determined that consideration of a waiver of selected groundwater ARARs is warranted for portions of the site under NCP Section 300.430(f)(l)(ii)(C)(3) and the USEPA’s TI Guidance for groundwater restoration (USEPA 1993). Consistent with the SOW for the Consent Decree, the TIE presented in this FS Report includes the following six components, which constitute a full TI evaluation based on USEPA’s TI Guidance.

Component 1 – Identifying specific ARARs or media cleanup standards for which TI determinations are sought;

Component 2 – Evaluating the spatial area over which the TI decision may apply;

Component 3 – Developing a conceptual model that describes the geology, hydrogeology, groundwater contaminant sources, transport, and fate;

Component 4 – Evaluating the restoration potential of the site, including data and analyses that support any assertion that attainment of ARARs or media cleanup standards is technically impracticable from an engineering perspective;

Component 5 – Estimating the cost of the existing or proposed remedy options, including construction, operation, and maintenance costs; and,

Component 6 – Any additional information or analyses that the USEPA deems necessary for the TI evaluation based on comments provided on the TIE.

The USEPA TI Guidance identifies primary factors that may inhibit groundwater restoration:

Hydrogeologic limitations such as complex sedimentary deposits, aquifers of very low permeability, fractured bedrock aquifers, and other factors that make in situ treatment of contaminated groundwater extremely difficult; and,

Contaminant-related factors that may limit the success of an extraction or in situ treatment process (such as DNAPLs).

The FS assumes that MCLs are ARARs for groundwater at the site. The FS recognizes State anti-degradation policies, enacted under the Porter-Cologne Water Quality Act, that are designed to protect groundwater resources from degradation. The State has used its regional Basin Plans (e.g., Water Quality Control Plan for Central Coast Basin, CCRWQCB, June 2011) to designate most of the groundwater in California as suitable for potable reuse. In developing options for remediation, the FS considers MCLs to be relevant and appropriate for groundwater at the site. The remedial alternatives, particularly the preferred alternative, include components intended to contain contaminated groundwater on the site; reduce sources of contamination; extract contaminated liquids; and restore groundwater to MCLs where technically practicable.


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8.5.1 Spatial Extent of the TI Determination

As described in Section 4 of this FS Report, site groundwater has been divided into three primary remediation areas, which are referred to within the FS as Area 5 North, Area 5 West, and Area 5 South (see Figure 4-24, Conceptual Site Model block diagram detail). The proposed TI zone includes:

Area 5 North: This groundwater area includes the most highly contaminated parts of the site, including the Capped Landfills, the PCB Landfill, the Burial Trench Area, and the Central Drainage Area. LNAPLs and DNAPLs are found within this area. A TI determination is sought for both the Upper and Lower HSUs within this area for both organics and inorganics. This proposed “TI zone” is fully within the boundaries of the site. The base of the TI zone is proposed to be defined as 200 feet above mean sea level. This elevation is 100 feet below the deepest monitoring well in the P/S Landfill and Central Drainage Area, where DNAPLs are present (the deepest well, RP-94D, is screened between approximately 319 and 300 feet above mean sea level). Although the depth of all DNAPLs is uncertain in this area, the deepest observed DNAPLs were found at RGPZ-7D, which is screened between approximately 328 and 315 feet above mean sea level. The proposed base of the TI zone at 200 feet above mean sea level will fully encompass any known DNAPL impacts to groundwater within Area 5 North.

The following areas are not included in the proposed TI zone:

Area 5 South: This area includes the former Liquid Treatment Area and the former Ponds and Pads subarea, and is located immediately south (and downgradient) of the Area 5 North, described above.

Area 5 West: This area includes the RCRA Canyon and the West Canyon Spray Area, and is located west of Area 5 North and Area 5 South.

The Area 5 South and Area 5 West groundwater areas are evaluated within this FS. The FS and TIE examine the potential for restoration of groundwater to MCLs and conclude that it is technically impracticable to achieve full restoration to MCLs for all of Area 5 North. Delineation of the entire Area 5 North area is warranted for numerous reasons related to hydrogeologic considerations, contaminant characteristics, and technology constraints. Restoration to MCLs in Area 5 North is technically impracticable because (1) large volumes of pooled DNAPL have accumulated at the base of the P/S landfill within area Area 5 North; (2) residual waste will be capped in place; (3) even after DNAPL source reduction via extraction, residual DNAPL and waste materials will continue to be ongoing sources for localized groundwater contamination within Area 5 North; (4) contamination includes a mixture of a large number of different constituents (many of which exceed MCLs); (5) contamination occurs pervasively throughout Area 5 North, and (6) hydrologic factors (i.e., fracturing, low permeability host rock and matrix diffusion) render remediation technologies ineffective within this area..Area 5 North serves as a reasonable choice for designating a small TI zone within the much larger extent of site groundwater. The FS has considered the feasibility of numerous groundwater restoration technologies for Area 5 North, including pump-and-treat remediation, and concludes that such attempts to achieve restoration would prove ineffective. GW flow and transport modeling demonstrate that


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even after more than a thousand years, pump-and-treat remediation would not restore contaminated groundwater to MCLs. Buried waste would continue to provide ongoing sources for site groundwater contamination. Furthermore, substantial contamination is contained within the matrix of fine grained, very low permeability siltstone. Matrix diffusion would contribute to long term movement of contamination from the siltstone matrix into groundwater. Consequently, pump-and-treat actions could remove very large volumes of contaminated liquids from fractures, yet largely remain ineffective for contamination within the siltstone matrix which serves as the source for GW contamination. The FS considered the possibility of designating smaller portions of Area 5 North for active remediation via pump and treat or other active remediation technologies. However, this concept would be inefficient, and would provide negligible benefits compared to the substantial technical obstacles. Area Area 5 North contains multiple former waste management units (WMUs), including five former landfills as well as other waste burial areas. Waste materials and contamination are not confined within the mapped boundaries of the former WMUs, but vary substantially in terms of COC concentrations and are mixed and distributed pervasively throughout almost all of Area 5 North. The FS proposes to designate Area 5 North in its entirety because waste materials and contamination are not confined within a single waste management unit. All the remedial alternatives, except the No Further Action alternative, treat Area 5 North as a comprehensive unit and include expansion of the existing landfill caps to provide RCRA-equivalent capping for nearly all of area Area 5 North. 8.5.2 Conceptual Site Model

The TIE details a CSM for groundwater at the site. A three-dimensional diagram illustrating the CSM that shows site features and the potential TI zone is included as Figure 4-24 (Conceptual Site Model block diagram detail). This model is briefly summarized in the paragraphs that follow. The fundamental components of the CSM are briefly summarized below:

Two HSUs have been defined based on hydraulic conductivity. The distinction between the Upper and Lower HSUs is defined qualitatively based on geologic characteristics, such as hardness, color, fracture density, and degree of weathering of the claystone. The Upper HSU typically has moderate to low hydraulic conductivity (~10-5 cm/s) whereas the Lower HSU has low hydraulic conductivity (~10-6 cm/s). Groundwater does not migrate quickly or easily through these geologic materials; for perspective, this range of hydraulic conductivities of these native soils is the same as those required for low-permeability RCRA-equivalent landfill caps.

Site-wide groundwater flow and contaminant migration at the site is controlled by a series of east-west oriented clay barriers and extraction trenches constructed within the Upper HSU that are anchored within the Lower HSU and pumped using sump-wells. One extraction trench (the PSCT trench) is installed just south of the primary landfill and direct-disposal areas (roughly midway across the site), and a series of three different extraction trenches located along the southern property line (PCT Trenches A, B, and C) form a barrier to offsite groundwater migration.

Groundwater on and near the site is not used as a drinking water resource. Groundwater in the vicinity of the site ranges from brackish to highly brackish (i.e., brackish conditions are generally defined as TDS > 1,000 up to ~10,000 mg/L). TDS concentrations in groundwater for all Zone 1 and (Zone 2) wells are typically significantly


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greater than 1,000 mg/L and sometimes approach 20,000 mg/L. Groundwater flow beneath the site generally follows topography; groundwater flows south offsite, then west via Shuman Creek towards the Pacific Ocean. Shallow groundwater within the Shuman and Casmalia Creek watersheds is not used for drinking water because of poor yield and naturally high TDS levels.

Organic and inorganic contaminants have been detected in groundwater throughout the 252-acre site.

o The highest concentrations of organic and inorganic contaminants (including dissolved-phase constituents and separate-phase LNAPL and DNAPL) are found within Area 5 North, where significant amounts of waste materials are contained within the landfills and the Burial Trench Area. These impacts are found within the Upper HSU and Lower HSU, including fractured bedrock. Both organic and inorganic constituents exceed MCLs by several orders of magnitude. Total VOC concentrations exceed 1,000,000 µg/L in the Upper HSU and up to approximately 100,000 gallons of free-phase DNAPL occur in the P/S Landfill. Contamination in the Upper HSU is hydraulically contained by the PSCT trench from migrating to Area 5 South and natural attenuation mechanisms act to retard contaminants in the Lower HSU from migrating to Area 5 South.

o Organic and inorganic contaminants are found in high concentrations south of this area within Area 5 South at concentrations that exceed MCLs. However, the concentrations of dissolved-phase constituents are much lower than those within Area 5 North and NAPLs are not present. Total VOC concentrations ranging up to approximately 20,000 µg/L occur immediately south of the PSCT to approximately 10 µg/L near the PCTs. Although the former waste ponds and pads were largely excavated in this subarea, the organic compounds (e.g., dissolved solvents) and inorganic compounds (e.g., metals) present in groundwater might be due to residual contamination from either incomplete excavation of source soils or due to sorbed contaminants within the fractured claystone matrix that act as residual sources to groundwater impacts. Contamination is hydraulically contained by the PCT trenches from migrating offsite to the A and B Drainages.

o Inorganic contaminants are found in moderately elevated concentrations within Area 5 West at concentrations that exceed MCLs. Only infrequent detections of organic contaminants occur at concentrations below MCLs. Contamination is hydraulically contained by the PCT trench from migrating offsite to the C Drainage.

Offsite impacts outside of the 252-acre site are localized and low due to both natural hydrogeologic conditions (such as fine grained soils) as well as the long-term operation of both source and site perimeter hydraulic containment features. Low levels of some metals occur beneath the north ridge within the Lower HSU slightly to the north of Zone 1. It is not clear whether these are naturally occurring or from site impacts. Low levels of some organics are occasionally detected immediately south of the southern perimeter hydraulic containment features at concentrations below MCLs.

8.5.3 Technical Impracticability Evaluation Process

The TIE presents the extent of contamination and the geological considerations within the proposed TI zone. It also presents restoration alternatives that were developed to describe what actions would be necessary to restore groundwater to drinking water standards, and to


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understand the time frame to achieve those standards as well as the technical feasibility and costs of such actions. With that as a basis, the TIE evaluated the technical considerations and challenges of restoring groundwater in these areas to meet ARARs (MCLs). The restoration alternatives included detailed analyses of several different criteria (consistent with the criteria used in developing Feasibility Studies under CERCLA). The TIE concluded that even the most aggressive mass removal in soil and groundwater (i.e., aggressive excavation and long term groundwater extraction) would not be technically feasible, would not ultimately achieve the desired results, and would not significantly reduce the time frame to reach cleanup standards, regardless of cost. The TIE evaluated full restoration potential (i.e., the potential to restore groundwater to MCLs), and concluded that current remediation practices and available technology would not be able to restore groundwater to regulatory performance standards (MCLs). 8.5.4 Technical Impracticability Evaluation Conclusions

The primary justifications for a TI determination for Area 5 North are briefly summarized below:

There are large quantities (billions of pounds) of liquid and solid hazardous wastes that were disposed into landfills, ponds, evaporation pads, burial trenches, and injection wells at the site between 1979 and 1986. Much of that waste remains on site and it would not be safe or practical to consider removal. The previous disposal practices have resulted in releases of LNAPLs and DNAPLs into the hydrogeologically complex and heterogeneous environment of the site where low permeability and fractured overburden and bedrock exist. NAPL data, site hydrology, and fractures were evaluated and summarized in the RI process and is discussed again in the TIE and provides us sufficient information to evaluate site conditions.

The primary source of DNAPL product at the site is likely the P/S Landfill, where solid wastes and containerized liquid wastes are encapsulated beneath an engineered cap. Substantial thicknesses of DNAPL have been measured in piezometers installed within the P/S Landfill. Based on generalized volumetric calculations, estimates of the free-phase DNAPL volume range as high as 100,000 gallons. Moreover, the drums of liquid wastes may decay over time and leaks may occur, which would provide an ongoing source of DNAPL product to the base of the unlined landfill. These leaks would migrate to the base of the landfill where they could continue to migrate into fractures within the Lower HSU. The only way to ensure that no ongoing sources of DNAPL remain in this part of the site is to remove the entire contents of P/S Landfill. The TI evaluation includes a detailed analysis of this full restoration alternative, which determined that although the excavation and offsite disposal of the capped landfills is not theoretically impossible from an engineering perspective, the increased risks to human health and the environment from such a large-scale removal action would outweigh the potential benefits to water quality at the site. Although remediation costs are not a primary factor in a TI determination, the estimated cost for complete restoration of the capped landfills area (including landfill removal) is in the tens of billions of dollars.

Although hydraulic containment features (such as the PSCT) are currently in place, and working effectively, to limit horizontal migration of contaminants within the Upper HSU, the presence of contaminants in deep fractured bedrock in the Lower HSU demonstrates that there are pathways of aqueous phase chlorinated solvent contamination and DNAPL contamination between the P/S Landfill and potentially other source areas to the deeper bedrock (Lower HSU).


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The RI has identified chlorinated solvent contamination in the Central Drainage Area that is located several hundred feet from the P/S Landfill, and demonstrated widespread Upper and Lower HSU contamination in this area. Similarly, there are groundwater impacts from the Burial Trench Area that extend well south of the PSCT into the former ponds and pads subarea. This demonstrates that there is significant contamination outside of the areas where waste was disposed (landfill and Burial Trench Area) and reinforces the conclusion that contamination can move through irregularly fractured material (heterogeneous) of the Upper and Lower HSUs in a manner that poses severe challenges to full restoration.

The Upper HSU is a low-permeability, weathered claystone formation. LNAPLs and DNAPLs have been identified at several wells/piezometers within the Upper HSU, and it is likely that NAPLs may exist at other locations within the Upper HSU based on current groundwater chemistry data. DNAPL may be pooled in dead-end fractures or remain as residual in the fractures where diffusive losses to the porous matrix may dissipate DNAPL over time. These characteristics severely limit the hydraulic accessibility of DNAPL and, coupled with the low permeability of the Upper HSU, make removal of DNAPL and restoration of groundwater to background levels within any forseeable time frame (e.g., 1,000 years) impossible.

There are currently no available technologies that are known to be effective in restoring extensive DNAPL zones in complex, highly heterogeneous, highly weathered geologic environments to drinking water quality. Findings established in the scientific community suggest that over 99 percent of the DNAPL would likely have to be removed to achieve a meaningful decrease in groundwater concentrations. Geochemical modeling of diffusion from the fractured claystone, provided in the TI evaluation, shows that even if all DNAPL could be removed immediately, the slow diffusion of constituents out of the fractured claystone would keep groundwater concentrations above MCLs for a very long time (e.g., over 1,000 years). Research has shown that even at the few DNAPL sites that have achieved closure following full scale remediation (none of which involved DNAPLs in fractured bedrock like that observed at this site), groundwater concentrations could not be reduced to MCLs (USEPA, 2004; USEPA, 2009). Enhanced DNAPL restoration techniques, such as thermal, steam injection, flushing, etc, that have proven effective at some other DNAPL sites would not be effective in this heterogeneous and fractured claystone setting.

No in situ technology is capable of treating the diverse array of chemicals found in Area 5 North. In addition to NAPL, this area contains many different organics and inorganics (e.g., metals such as arsenic, nickel, cadmium, and selenium) that significantly exceed MCLs in both the Upper and Lower HSU by several orders of magnitude. Groundwater also contains elevated concentrations of TDS due to major ions that exceed secondary MCLs. Similar to the mechanism by which dissolved chemicals originating from a release of DNAPL diffuse into fractured media, high concentration dissolved metals would also be expected to diffuse into fractured media. Upon decreasing the concentrations of dissolved metals in groundwater (e.g., via groundwater extraction) reverse matrix diffusion would commence, and would result in slowly decreasing groundwater concentrations. Geochemical modeling provided in the TI evaluation demonstrates that even if groundwater extraction were capable of capturing all dissolved chemicals in groundwater, back diffusion of inorganic materials from the weathered bedrock formation would preclude groundwater restoration for hundreds of years.


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If a TI determination is established for Area 5 North, a monitoring network would be established that would demonstrate the containment of the groundwater impacts and help ensure compliance with overall performance standards. Details of these performance and compliance monitoring programs would be described in the Remedial Design phase of work. The site already has a significant water quality monitoring network in place. If EPA determines that additional interior “guard” wells or downgradient “compliance” monitoring wells are necessary, those will be described in the Remedial Design.

8.6 Preliminary Remediation Goals PRGs have been identified for the site based on the results of the ERA and HHRA. The results of the ERA and HHRA indicated that the primary media of concern was surface and shallow soil as described in Section 7. Although groundwater was not considered to be a risk to human health or to ecological receptors because there was not a complete pathway, concentrations of organic and inorganic constituents exceed drinking water standards as described in Section 5. COCs for soil media were identified from the COPCs and COPECs evaluated quantitatively in the HHRA and ERA, respectively, and are listed by FS Area in Table 8-4. RBCs were developed for the COCs to be used in conjunction with background concentrations to identify the PRGs for soil. As described in Section 4, the RWQCB has identified several beneficial uses for the surface waters (and therefore, associated groundwater) of the Shuman and Casmalia Creek watersheds in the San Antonio hydrologic unit. These include agricultural, municipal, and recreational use, as well as supporting various fresh, warm water wildlife habitats (RWQCB, 1994). Therefore, drinking water standards are used to identify the PRGs for groundwater at the site and the substantive portions of the 1999 NPDES Permit standards (revised 2004) are used to identify the PRGs for offsite discharge of treated stormwater, treated pond water or treated groundwater. Chemicals exceeding drinking water standards are also listed by FS Area in Table 8-4. 8.6.1 Groundwater

As discussed in the RI and supported by the well survey information presented in Appendix N of the RI, the groundwater beneath and in the immediate vicinity of the site is not currently being used for potable water. In addition, it is anticipated that groundwater extraction for purposes of potable water will not be allowed in the future because the final remedy is likely to include institutional controls that will preclude groundwater use. This groundwater exposure pathway was not considered complete and was not evaluated in the HHRA. However, it is anticipated that COCs will include COPCs that occur in site groundwater that exceed, or are reasonably expected to exceed MCLs. Drinking water standards are used to identify the PRGs for groundwater because the RWQCB considers groundwater to have a municipal beneficial use as noted above. If a TI determination is established for Area 5 North, it is assumed that underlying groundwater will be addressed via the TI waiver. Otherwise, MCLs would be considered the long-term cleanup goals for organics and inorganics. For Groundwater Area 5 South, it is assumed that MCLs are considered the long-term clean-up goal for organics (VOCs and SVOCs) identified as COCs. For inorganics (metals) identified as COCs in Area 5 South and Area 5 West, PRGs are assumed to be MCLs at present but background concentrations will be considered when evaluating performance of the remedial activities.


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8.6.2 Soil

In the RI, the results of the ERA and HHRA were used to identify COCs (constituents that contributed significantly to site risk) in surface (0 to 0.5 foot bgs) and surface and shallow soil (0 to 5.5 feet bgs). The COCs for consideration in the FS were selected from the ERA because potential risk at the site is driven primarily by effects to ecological receptors. The ERA (Tiers 1 and 2) was presented as Appendix U of the RI report (CSC 2011). The COCs listed as risk-driving chemicals are derived from the Tier 2 ERA for those study areas where the Tier 2 evaluation was performed whereas, in other study areas, the Tier 1 COCs are listed. While there are some human health risks, for the most part the acceptable soil concentrations are set by ecological concerns. The HHRA was presented as Appendix T of the RI report (CSC 2011). COCs were identified based on potential unacceptable risk to ecological and human receptors exposed to site media in study areas with no presumpedremedy in place, which include the RCRA Canyon, West Canyon Spray Area, Former Ponds and Pads South of the PSCT, Remaining On-site Areas and Stormwater Ponds. Tables 8-6a and 8-6b present the RBCs for the COCs identified for ecological and human receptors, respectively, using the methodologies presented in Appendix J of this report. The RBCs were then considered in the selection of PRGs to define remedial alternatives and specify impacted locations or areas for remedial evaluation. It should be noted that, while there may be a few individual samples in a study area that exceed an RBC, the study area as a whole may not pose a significant risk due to the use of the 95% UCL of the mean concentration in the ERA and HHRA. The 95% UCL statistical analysis was used to define a risk-based cleanup approach across a study area because it better represents the concentration to which a receptor may be exposed on a regular basis. Eco RBCs were developed for the ecological COCs as identified in the Tier 2 ERA in areas with no planned presumed remedy (CSC 2011) and include three metals (chromium, copper, and zinc) in soil. Risks were mainly driven by terrestrial wildlife (mammals and birds), and no unacceptable risks were identified for plants and soil invertebrates. No unacceptable risks were identified for special status, deep burrowing receptors (American badger) exposed to deep soil (5.5 to 10 feet bgs). Eco RBCs were not developed for:

organics in soil, because they were not identified as COCs in the Tier 2 ERA (CSC 2011).

constituents in sediment, because presumed remedies for all of the ponds will eliminate exposure pathways and, therefore, will eliminate unacceptable risk to aquatic receptors.

Tier 1 COCs in areas where a presumed remedy is in place (see Tables 7-1 through 7-3).

The approach and methods used to derive Eco RBCs for chromium, copper, and zinc are presented in Appendix J of this report, which includes a discussion of receptors, exposure parameters, and toxicity values used in the Eco RBC calculations. Typically, Eco RBCs can be calculated by rearranging the standard USEPA (1997) HQ equation to estimate soil concentrations based on a target HQ of 1 (i.e., back calculating for a concentration where exposure is equal to the target toxicity value). However, as quantitative forward risk calculations were already completed in the ERA, generating HQs for ecological receptors, a simplified


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method was used to calculate Eco RBCs incorporating exposure and effects data. An Eco RBC for each COC was calculated simply by dividing the exposure concentration of a COC for a study area by the HQ estimated for that study area and receptor to generate an Eco RBC for that COC that is protective of that specific receptor (i.e., each Eco RBC will correspond to an HQ of 1). For example, as shown in Table 8-6a, the copper HQ for the ornate shrew is 20 in the WCSA, and the surface and shallow soil (0 to 5.5 feet bgs) EPC for copper in the WCSA is 271 mg/kg. By dividing the EPC of 271 mg/kg by the HQ of 20 (unitless), an Eco RBC of 14 mg/kg for copper protective of the shrew and other terrestrial invertivorous mammals is generated. Equations and examples of the Eco RBC calculations are presented in Appendix J. As requested by USEPA, Eco RBCs for the ecological COCs identified in Tier 2 ERA were developed and presented for all of the terrestrial receptors in Table 8-6a (details in Appendix J). For the American badger, chromium, copper, and zinc were not identified as COPECs in the ERA (CSC 2011), because only those COPECs with maximum detected concentrations in the 0 to 10 feet bgs interval that were greater than maximum concentrations in the 0 to 5 feet bgs interval were selected as deep soil COPECs and evaluated further for deep burrowing receptors (the badger). and that are determined to be fully “applicable” or “relevant and appropriate” requirements. With one exception, chromium, copper, and zinc were only detected at concentrations below background in the 5.5 to 10 feet bgs interval. Chromium was detected within this depth interval in excess of background in one location in the Maintenance Shed area. However, as discussed in later sections, all corrective measures considered for this area involve capping or excavation of surface and shallow soils. Therefore, jointly, conditions for metals in soil indicate that Eco RBCs protective of the American badger are not needed. Table 8-6a presents the Eco RBCs for chromium, copper, and zinc for all the terrestrial receptors when these three COCs were identified in study areas with no presumed remedial action in place. Eco RBCs based on the most sensitive wildlife receptor (i.e., the receptor with the highest HQ) were selected to be protective of all of the ecological receptors at the site. Although Eco RBCs for chromium and zinc based on plants and invertebrates are less than the selected Eco RBCs based on wildlife, these lower Eco RBCs were not selected because the potential risk from chromium is highly uncertain due to high uncertainty associated with the plant and invertebrate benchmarks and the potential risk from zinc is not considered unacceptable for plants and invertebrates (i.e., more weight was given to risk results for birds and mammals that were determined using site-specific bioaccumulation information). Surface soil Eco RBCs are considered protective of soil invertebrates and terrestrial birds exposed to surface soil (0 to 0.5 foot bgs). Surface and shallow soil Eco RBCs are considered protective of plants and terrestrial mammals exposed to surface and shallow soil (0 to 5.5 feet bgs). HH RBCs were developed for the human health COCs based on the results of the HHRA (CSC 2011) and include three organics (MCPP, PCE, and TCE), and were based on exposures for the commercial/industrial worker. The approach and methods used to derive HH RBCs for MCPP, PCE, and TCE are presented in Appendix J, which includes discussion of receptors, exposure parameters, and toxicity values used in the HH RBC calculations. To develop the HH RBC, an assumption regarding the target lifetime incremental cancer risk and target noncancer hazard index is necessary. For the site constituents classified as carcinogens, a target risk of 1 x 10-5 was used to derive the HH RBC for the purposes of the FS data evaluation. This target risk level is the mid-point of the NCP discretionary risk range of 1 x


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10-6 to 1 x 10-4 used to evaluate risks at Superfund sites. For chemicals classified as noncarcinogens, an HQ of 1 was used. Table 8-6b presents the HH RBCs for MCPP, PCE, and TCE for the commercial/industrial worker based on carcinogenic and non-carcinogenic effects. The lowest (most conservative value) for each chemical is the selected HH RBC. The HH RBCs apply to surface and shallow soil (0 to 5.5 feet bgs) and are considered protective of the commercial/industrial worker. Soil PRGs for the site are presented in Table 8-6c and were based on the higher of the background concentration or RBC. Site-specific background concentrations based on the UTLs were developed for the site (CSC, 2011). For chromium, copper, and zinc, the surface and subsurface soil PRGs were based on the Eco RBCs as they were higher than background UTLs. For MCPP, PCE, and TCE, soil PRGs were based on the HH RBCs as there are no background UTLs for these chemicals. 8.6.3 Pond Surface Water and Sediment

Remedial approaches for the site have all presumed that all of the five existing ponds would be closed. Basis for closure of the ponds extends beyond human health risk and addresses other considerations such as ecological risks, implementability, and other site management factors. In addition, the ponds may serve as attractive nuisances under the federal Endangered Species Act (ESA) for threatened and endangered species including the California Red Legged Frog, the California Tiger Salamander, and the Western Spadefoot Toad. Although chemical concentrations of some constituents in pond surface water and sediment in the five site ponds were above background and exceeded concentrations that would result in HQs>1, RBCs were not developed because of the presumed remedy (i.e., closure of the ponds) that will eliminate unacceptable risk to ecological receptors. The constituents that exceeded a HQ of 1 primarily included select metals. In addition to elevated metals, the TDS of the ponds has become very high as described in Section 4.3.2 and shown in Figure 4-2. The presumed or anticipated remedy included in all remedial alternatives (except the No Action alternative), includes eliminating the existing surface water and then either excavating or capping the pond bottoms. Therefore, PRGs for pond surface water and sediment were not developed. 8.6.4 Seep Surface Water

Although chemical concentrations of some constituents in seep surface water were above background and exceeded concentrations that could result in a HQ of 1, RBCs were not developed because it is projected that these seeps will no longer occur once the final remedy is implemented. The constituents that could exceed HQ of 1 would primarily include the following:

Metals in the RCRA Canyon seep (which occurs seasonally in the winter and spring), Metals in the seeps between Pond 18 and the A-Series Pond and between Pond 18 and

the RCF (which currently do not occur because the pond levels are relatively low) Metals and organics in the seep near Sump 9B (which no longer occurs except

occasionally when extraction well Sump 9B becomes clogged). It is anticipated that the seeps in the RCRA Canyon and near Sump 9B will be eliminated with the capping remedies that are included in each of the remedial alternatives, except for the No Action alternative. The former seeps between Pond 18 and the A-Series Pond and between Pond 18 and the RCF Pond will no longer occur because of the presumed remedial action that eliminates the ponds, which are the source of the seeps (except for the No Action alternative). Therefore, PRGs for seep surface water were not developed.


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8.6.5 Treated Stormwater, Treated Pond Water, or Treated Groundwater for surface water discharge

The substantive provisions of the 1999 NPDES Permit standards (revised 2004) are used as PRGs (or treatment standards) for potential discharge of treated stormwater, treated pond water, or treated groundwater to the B-Drainage and Casmalia Creek. These standards are provided in Table 8-5. 8.6.6 Summary of PRGs

In summary, the media-specific PRGs are as follows:

Groundwater – Drinking water MCLs, except where a TI determination is approved for Area 5 North.

Soil – Concentrations summarized in Table 8-6c Pond Surface Water and Sediment – None, presumed remedial action will require the

elimination of existing pond surface water. Seep Surface Water – None, final remedy anticipated to eliminate seeps. Treated Stormwater, Treated Pond Water, or Treated Groundwater – Table 8-5

8.7 Principal Threat Wastes PTWs are those source materials considered to be highly toxic or highly mobile that generally cannot be reliably contained or would present a significant risk to human health or the environment if exposure were to occur. Several principal threat wastes (PTWs) have been identified at the site. According to the National Contingency Plan (NCP), EPA expects to: (1) use treatment to address principal threat wastes posed by a site wherever practicable; (2) use engineering controls, such as containment, for waste that poses a relative low long-term threat or where treatment is impracticable; (3) use a combination of methods, as appropriate, to achieve protection of human health and the environment; and (4) use institutional controls such as water use and deed restrictions to supplement engineering controls as appropriate for short- and long-term management to prevent or limit exposure to hazardous substances [see A Guide to Principal Threat Wastes and Low Level Threat Wastes, OSWER, 9380.3-06FS, November 1991].

Principal threats posed by the site have been addressed during various stages of response work. The owner/operator implemented some site cleanup actions (e.g. excavations, pond closures, and reconsolidation of pond bottoms and other materials into the existing five landfills) in the late 1980s while unsuccessfully seeking a RCRA permit for the site. Later, the CSC capped the Pesticides/Solvents Landfill in a removal action consistent with EPA’s presumptive remedy for landfills. The CSC also performed an EE/CA that evaluated options for managing principal threats associated with three of the landfills (Metals, Caustics/Cyanide, and Acids) and interstitial areas between these landfills in Zone 1 of the site, and capped these landfills in an ensuing removal action, again consistent with EPA’s presumptive remedy for landfills. Subsequently, the CSC has conducted an RI/FS for the entire site (Zone 1 and Zone 2) and a technical impracticability evaluation (TIE) for the most contaminated portion of the site that contains the five landfills (FS Area 5-North), incorporating the results of the previous EE/CA into the analysis. The FS and TIE contain evaluations of alternatives for addressing Principal Threat Wastes (PTWs) at the site.


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PTWs generally represent sources of contamination for one or more site media. PTWs at the Casmalia Resources Superfund Site are considered to occur pervasively throughout FS Area 1 and FS Area 5. Area 1 PTWs occur within a large number of former waste management units (WMUs), such as the five landfills, the Burial Trench Area, and the Central Drainage Area. Area 1 also includes significant mixed contamination in between the former waste management units. The deeper soils and hydrostratigraphic units underlying these areas are also heavily impacted. PTWs within FS Area 5 (aka Area 5 North) include pesticides, solvents, PCB, metals, caustics, and acids. Drummed waste and significant volumes of free-phase liquids are known to exist in the P/S Landfill. The P/S Landfill contains LNAPL and particularly large volumes of DNAPL, which represent sources for groundwater contamination. The FS evaluates strategies to reduce the volume of the NAPL source materials. LNAPL and DNAPL also occur within the Central Drainage Area. These PTWs contain numerous organic and inorganic chemicals at high concentrations across multiple chemical classes (e.g., VOCs, SVOCs, herbicides, pesticides, PCBs, dioxins/furans, metals, and cyanide).

Low level threat wastes (LLTWs) are considered to occur within contaminated soil for FS Areas 2, 3, and 4. LLTWs are those source materials that generally can be reliably contained and that would present only a low risk. They include source materials that exhibit low toxicity, low mobility in the environment, or are near health-based levels. PTWs are not anticipated to be present in these areas.

Identification of PTWs is intended to help streamline and focus the remedy selection process. The FS and TIE contain evaluations of a broad spectrum of alternatives for addressing principal threat wastes. Specifically, the FS screens and assesses a large universe of treatment and containment technologies and systems and ranks alternatives based on overall effectiveness. Consistent with EPA guidance, the FS includes multiple alternatives to address PTWs in Area1 and Area 5. The preferred alternative considers how PTWs and LLTWs can be managed in a manner that is protective of human health and the environment, complies with CERCLA, and is consistent with the NCP.

8.8 Basis for Action This section summarizes the basis for action for the remedial alternatives considered in Section 10. The basis for action considers the risk assessments for the site and RAOs in Section 8.2 as well as other site-specific conditions and characteristics. Multiple factors provide input to decision-making for response actions at the site. The former waste disposal site contains many different waste materials along with multiple impacted site media. Waste materials and impacted media include (1) surface and shallow waste materials and contaminated soil, (2) contaminated surface water, (3) extracted contaminated subsurface liquids, (4) contaminated pond sediments, (5) soil vapor, (6) large-volume sources of NAPL (DNAPL & LNAPL), and (7) contaminated groundwater with multiple commingled constituents many of which exceed MCLs. The FS screens technologies and evaluates remedial alternatives in order to address areas with unacceptable human health and ecological risk that exceed action levels and performance standards. The FS also considers other factors besides unacceptable risk and identifies and evaluates alternatives in order to create an integrated, technically feasible, readily implementable, reliable remedy that meets the statutory requirements of CERCLA, achieves ARARs, and seeks cost-effectiveness.


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The FS considers a variety of different factors in developing alternative response actions for the site. Numerous factors extend beyond calculation of cancer and non-cancer health risk numbers. A large portion of the remedial alternatives address portions of the site with exceedances of ecological risk screening levels. Additional considerations include consistency with EPA and State of California policies, including California’s anti-degradation policies for groundwater, CERCLA’s preference for treatment and DNAPL source reduction, overall constructability, compatibility and integration with other site systems, reduction of infiltration, control of hydraulic gradients to prevent surface outflow and seeps, and risk reduction in other areas for the site. The basis for action for different site media is summarized below. Surface and shallow waste materials and contaminated soil: The site contains large

volumes of surface and shallow waste materials and contaminated soils that pose risks to receptor populations through direct physical contact. These include ecological receptors, site workers, and trespassers. The risk assessment identified numerous locations, by site area and by specific systems and features, where potential exposure should be mitigated through installation of engineered capping systems or “hot spot” removal, i.e., excavation and reconsolidation in other sealed portions of the site. Decisions to cap portions of the site are consistent with EPA’s presumptive remedy guidance and evaluations of technical practicability. The FS evaluates various options for capping to contain pervasive contamination for all of Area 1 (former landfills and burial areas), Area 2 (RCRA Canyon), and parts of Area 3 (former ponds and pads area). Shallow waste and contaminated soils also serve as contamination sources for site groundwater. Capping or removal would be necessary – even if risk-based action levels were not exceeded – in order to prevent downward infiltration, which can further degrade groundwater. Capping also helps to gradually lower groundwater levels. Lowering of the water table reduces the driving force (hydraulic head) that can push groundwater contamination into fractured claystone rock under the site. Lowering of the water table also helps prevent surface seeps from forming in low spots where the water table can intersect the ground surface. Limiting infiltration would also reduce the volume of subsurface liquids that must be extracted in order to achieve hydraulic containment.

NAPL (LNAPL & DNAPL): The RI documented the presence of large volumes of NAPL, including LNAPL and DNAPL, in Area 5 North underlying Area 1. Monitoring has documented the presence of up to 100,000 gallons of pooled DNAPL that has accumulated at the base of the P/S Landfill. DNAPL has also been detected throughout fractured rock that underlies the site. This pooled DNAPL is a major source of contamination – and Principal Threat Waste (PTW) – which must be reduced as much as possible in order to meet regulatory requirements and prevent the spread of contamination. The FS evaluates multiple options for DNAPL source reduction, including use of vertical and horizontal extraction wells to pump out the DNAPL from the P/S Landfill.

Contaminated Groundwater: Like much of the groundwater in California, groundwater in the Central Coast (RWQCB Region 3), including the groundwater in the vicinity the site, is designated by the State as having a potential domestic and municipal beneficial use. Use of groundwater underlying the site would pose an unacceptable risk, if it were to be used, because it contains a large number of COCs that exceed action levels, namely MCLs. Although there is no reasonable anticipation that site groundwater would be used for domestic purposes, the FS considers MCLs to apply as ARARs for site groundwater. GW monitoring has demonstrated that site groundwater contains a mixture of several hundred different constituents. Although concentrations vary considerably, GW contamination is


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pervasive throughout the entire site. Groundwater in the site’s three groundwater areas contains many different constituents that exceed MCLs. Nevertheless, groundwater contamination has been effectively contained within the facility boundaries, due to (1) installation and operation of engineered containment features (containment trenches and extraction wells) and (2) natural attenuation processes.

Contaminated Surface Water: The site contains five ponds that were designed and constructed as temporary surface water storage facilities. These temporary ponds have become significant sources of contamination, and surface water management is a key challenge at the site. Stormwater runoff must be carefully managed to completely segregate clean stormwater run-off, derived from clean capped portions of the site, from contaminated run-off where rainwater comes into contact with surface waste materials or contaminated soil. Site run-off is stored in five stormwater ponds. In addition, clean run-off from the four capped landfills is discharged offsite, but can also be stored at the site if necessary. All five of the existing ponds contain very high levels of TDS which approach the concentration of seawater. Moreover, the contaminated liquids ponds contain constituents in concentrations that exceed action levels for surface water and require collection, treatment, and disposal. EPA, as well as state and community stakeholders have therefore expected that all of the ponds would be drained and closed.

The basis for action for closure of the five ponds extends beyond consideration of human health risks and includes other considerations, such as ecological risk, implementability, and site management factors. Closure of all the ponds is necessary due to combinations of various reasons, including (1) actionable human health risk levels in pond water (e.g., cancer risks between 10-4 to 10-6), (2) pond water exceedances of ecological risk screening levels (ESLs), (3) presence of underlying contaminated pond sediments; (4) the roles of pond water and contaminated pond sediments as sources of groundwater contamination via infiltration, (5) technical challenges and risks associated with the potential need to discharge surface water offsite, (6) challenges associated with collection, treatment, and disposal of site liquids; and (7) the roles of all five ponds as attractive nuisances under the federal Endangered Species Act (ESA) for threatened and endangered species at the site (the California Red Legged Frog, the California Tiger Salamander, and the Western Spadefoot Toad). Finally, the temporary need for the ponds will be eliminated during implementation of a comprehensive site remedy that includes other new stormwater and liquids management systems. In terms of ecological risk, all five ponds contain very high concentrations of TDS and metals that exceed ecological screening levels (HQ>1) for multiple COCs in both pond water and pond sediments. TDS concentrations in the ponds approach the levels found in seawater (20,000 – 40,000 ppm). The ecological risk assessment examined risks for the ponds, consistent with EPA guidance, for aquatic plants and amphibians. USEPA refers the reader to Section 9 of the RI and particularly to RI Appendix U for narrative, figures, and tables that present the results of the ecological risk analysis in toto. The unlined ponds also serve as sources for groundwater degradation via infiltration. Highly concentrated and contaminated pond water can infiltrate through contaminated pond sediments and infiltrate to groundwater. Closure of the ponds will also reduce infiltration and further reduce the volume of subsurface liquids that would need to be extracted in order to achieve hydraulic containment. Remediation of the ponds and pond sediments will require drainage of pond water, removal of pond sediments, and installation of engineered capping systems to prevent infiltration to groundwater.


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Finally, pond closure is necessary to address the Endangered Species Act. EPA and other resource agencies, particularly USFWS and CaDFW, determined that it is necessary to close the contaminated ponds to eliminate a current and future attractive nuisance for threatened and endangered species consistent with the ESA. The USFWS has issued a biological opinion (2008) that states the surface water ponds must be closed in order to eliminate attractive nuisances and mitigate adverse impacts to threatened and endangered species.

8.9 References CSC, 2011. Final Remedial Investigation Report, January 2011. CSC, 2004. Remedial Investigation/Feasibility Study Work Plan, June 2004. Cherry, 1996. “Concepts for the Remediation of Sites Contaminated with Dense Non Aqueous Phase Liquids (DNAPLs),” in Dense Chlorinated Solvents and other DNAPLs in Groundwater, J. F Pankow and J. A Cherry, eds., Waterloo Press, Portland, OR, pp. 475-506, 1996. Cherry, 1992. “Developing a Conceptual Framework and Rational Goals for Groundwater Remediation at DNAPL Sites,” Third International Conference on Ground Water Quality Research, Dallas, TX, June 21-24. 1992. Freeze, 1997. “A Framework for Assessing Risk Reduction Due to DNAPL Mass Removal from Low Permeability Soils,” Ground Water, Vol. 35, No. 1, pp. 111-123. Freeze, R. A., and D. A. McWhorter, 1997. USEPA, 1988. Guidance for Conducting Remedial Investigations and Feasibility Studies Under CERCLA, EPA 540/G-89/004, October 1988. USEPA, 1993. Guidance for Evaluating the Technical Impracticability of Groundwater Restoration, Office of Solid Waste Emergency Response (OSWER) Technical Directive 9234.2-25, US EPA, September 1993. USEPA, 1997. Ecological Risk Assessment Guidance for Superfund: Process for Designing and Conducting Ecological Risk Assessments, Interim Final. U.S. Environmental Protection Agency, Solid Waste and Emergency Response. OSWER 9285.7-25. June 1997. USEPA, 2000. A Guide to Developing and Documenting Cost Estimates during the Feasibility Study, US EPA and US Army Corps of Engineers, EPA 540-R-00-002 July 2000. USEPA, 2004. DNAPL Remediation: Selected Projects Approaching Regulatory Closure, EPA-R-04-016, U.S. Environmental Protection Agency, 2004. USEPA, 2009. DNAPL Remediation: Selected Projects Where Regulatory Closure Goals Have Been Achieved. OSWER Publication 524/R-09-008, August 2009. CVRWQCB. 2007. Recommended Numerical Limits to Translate Water Quality Objectives. Summary of: A Compilation of Water Quality Goals. Central Valley Regional Water Quality Control Board Cal EPA, August 2003. 186 pp. Available at: http://www.swrcb.ca.gov/rwqcb5/available_documents/index.html#WaterQualityGoals


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SFRWQCB. 2005. Screening for Environmental Concerns at Sites with Contaminated Soil and Groundwater. Appendix 1: Summary Of Selected Chronic Aquatic Habitat Goals. San Francisco Regional Water Quality Control Board, Oakland, CA. February. Interim Final Revision.

MOEE. 1999. Water Management Policies Guidelines Provincial Water Quality Objectives of the Ontario Ministry of Environment and Energy. July 1994, revised February 1999.

Pauli, B.D., J.A. Perrault and S.L. Money. 2000. RATL: A Database of Reptile and Amphibian Toxicology Literature. Technical Report Series No. 357.Canadian Wildlife Service, Headquarters, Hull, Québec, Canada.

Sparling, D.W., G. Linder, and C.A. Bishop, 2000.Ecotoxicology of Amphibians and Reptiles. SETAC Technical Publication Series.

Suter II, G. W. and C. L. Tsao, 1996.Toxicological Benchmarks for Screening Potential

Contaminants of Concern for Effects on Aquatic Biota: 1996 Revision. Oak Ridge National Laboratory, June.

USEPA, 1991: A Guide to Principal Threat and Low Level Threat Wastes (EPA, 1991) Office of Solid Waste Emergency Response (OSWER) Superfund Publication 9380.3-06FS, November.

USEPA. 2001. Supplemental Guidance to RAGS: Region 4 Bulletins, Ecological Risk Assessment. Originally published November 1995. U.S. Environmental Protection Agency Website version last updated November 30, 2001, available at: http://www.epa.gov/ region4/waste/ots/ecolbul.htm.

USEPA. 2006a. Water Quality Standards; Establishment of Numeric Criteria for Priority Pollutants for the State of California. 40 CFR Part 131 Section 38. pp. 1-39. April 2000; updated Dec 2006.

USEPA. 2007a. ECOTOX database. U.S. Environmental Protection Agency Website updated daily: http://cfpub.epa.gov/ecotox/

USEPA, 2006b.National Recommended Water Quality Criteria.U.S. Environmental Protection Agency Office of Water. Washington, D.C. 25 pp.

USEPA. 2007. ECOTOX database. U.S. Environmental Protection Agency Website updated daily: http://cfpub.epa.gov/ecotox/


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9.0 IDENTIFICATION AND SCREENING OF TECHNOLOGIES This section of the FS presents the screening evaluation of a very wide range of remedial technologies with the goal of selecting a set of relevant technologies for use as components in the remedial alternatives for the site. The screening was conducted as a two-step process. The initial screening of technologies was conducted on a wide range of technologies relating to the various media at the site including soil, sediment, storm water, groundwater and NAPL. The technologies that were not applicable were screened out in the initial screening. The second technology screening step was conducted separately for each media using the three screening criteria from CERCLA guidance namely, effectiveness, implementability and cost.

9.1 Initial Screening of Technologies As noted above, an initial screening of all identified technologies was conducted to screen out those technologies that were not applicable for this site. The technologies were reviewed based on general response actions, remedial alternatives and process options as shown in Table 9-1. The general response actions ranged from institutional controls, containment, excavation or extraction, ex-situ treatment and in-situ treatment depending on the media. For institutional controls, access restrictions such land use and groundwater use restrictions were retained as potentially applicable. Institutional controls have already been established for some properties located near the historic facility boundary. These include environmental covenants that run with the land. It is anticipated that all the remedial alternatives for the site will include some form of water use and land use restrictions (e.g., restrictions against residential use). The details of these ICs will be determined during remedial design. Monitoring will be included for all remedial alternatives. Long term monitoring, will include performance and compliance monitoring for most media, such as soil vapor, surface water, and groundwater.

9.1.1 Soil/Sediment

For containment response actions for soil, vapor barriers for building foundations, HVAC modification, and subslab venting were screened out because there is no development planned for the site and hence these technologies are not applicable. A wide range of capping systems from simple caps such as compacted soil covers to asphalt or concrete caps to complex multi-layer or engineered caps such as RCRA-prescriptive or RCRA-equivalent caps are retained as potentially applicable. Evapotranspiration (ET) caps, which minimize or prevent infiltration by removing moisture by evaporation and transpiration through vegetation and carefully engineered soil profiles and have been implemented at several California landfills, are retained. Erosion control measures such as geomats or turf reinforcement mats are retained to minimize erosion or sediment transport on sloped areas. For containment response actions related to future ponds or stormwater basins on site, two types of lining technologies were considered. These technologies are similar to capping technologies and are intended to prevent migration of stored liquids into the subsurface. For stormwater basins, a single composite HDPE liner (geotextile above with geomembrane below) over a compacted subgrade (foundation layer) is retained. For groundwater stored in


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evaporation ponds, a double liner system including a primary HDPE geomembrane with a drainage layer below, followed by a secondary HDPE geomembrane is retained. For soil excavation response actions, large diameter auger excavation was screened out because it is not considered applicable at this site for any deep excavations. Due to the cohesive nature of the claystone formation, steep sloped back conventional excavations are viable for locations where deep soil removal is necessary. For disposal/reuse options, landfill disposal at the PCB Landfill or reuse of excavated soil as backfill at other areas (e.g. as fill material for pond closure prior to capping) is retained. Disposal at a permitted landfill or TSDF is retained as well. For excavation/treatment, soil/solvent washing and chemical oxidation/reduction is screened out based on lack of effectiveness. Bioremediation, soil vapor extraction in soil piles, stabilization and thermal desorption are retained. For in-situ soil treatment response actions, in-situ bioventing, in-situ soil flushing, and in-situ steam injection were screened out because they are not applicable for site subsurface conditions. The technologies are well known to require a more permeable subsurface vadose zone to be effective. With these in-situ technologies, air flow (bioventing) or solvent flow (soil flushing) would be primarily in the fractures in the weathered claystone in the Upper HSU. This will not result in remediation of the contaminants in the matrix which actually has a higher porosity and likely a higher fraction of the contaminants. Steam injection was not retained for the same reason, with preferential flow of steam in the fractures. However, other thermal technologies including in-situ thermal desorption (ISTD) and ERH were retained for further evaluation because they are likely to fare better under these low permeability conditions. Soil vapor extraction is also retained as it is a very well developed technology for VOCs.

9.1.2 Groundwater

All remedial alternatives for groundwater were retained, except grout injection for containment. Grout injection was not retained because of its very limited effectiveness in this fractured bedrock formation. There are effective options such as clay barriers that have been successfully implemented for this purpose. Slurry walls and clay barriers are retained as physical containment measures for groundwater. Extraction and injection wells are retained as potentially applicable hydraulic containment measures. Horizontal barriers or soil caps are retained to prevent or minimize infiltration and thus indirectly considered a containment measure for groundwater. Phytoremediation is retained as a technology with potential applications in areas with shallow groundwater where evaporation and transpiration of groundwater can provide groundwater containment. For in-situ groundwater treatment, passive technology options such as monitored natural attenuation (MNA) and permeable reactive barriers (PRBs) or reactive walls are retained. For active in-situ treatment options, biosparging, steam injection, in-situ soil mixing, in-situ aerobic bioremediation, in-situ soil flushing and hydraulic fracturing were screened out due to the site’s fractured bedrock subsurface conditions. Section 4 of the RI report states that the geometric mean of the hydraulic conductivity of Upper HSU weathered claystone is approximately 1x10-5 cm/s while the Lower HSU mean is 1x10-6 cm/s and that fractures control hydraulic conductivity in both the Upper HSU and Lower HSU. Important points to note in


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evaluating in-situ technologies in this fractured bedrock site lithology include: 1) a fractured bedrock with a 1x10-5 cm/s conductivity is significantly worse with respect to in-situ remediation effectiveness from an unconsolidated formation with the same conductivity because with a fractured bedrock a majority of the flow (depending on in-situ remediation approach it could be vapor extraction flow or reagent injection flow, etc.) is going to be through the fractures while in an unconsolidated formation this will be more uniformly distributed; 2) a majority of the porosity in the Upper HSU is in the matrix (>40%) while the porosity of the fractures is <5% which implies that a majority of the contaminants would likely be in the matrix where the available porosity is. Hence, addressing the fracture porosity with the in-situ remediation approach will not address a significant portion of the contamination in the matrix. The clay stratigraphy of the Upper HSU and Lower HSU are discussed in more detail in the RI Report. Biosparging and in-situ aerobic bioremediation would not be applicable because of the challenges with injection in the fractured bedrock formation and because it would not be effective for a mix of chlorinated and petroleum VOCs that occur at this site. As discussed under soil technologies, in-situ flushing or in-situ steam injection would face the same challenges in the fractured bedrock formation with preferable flow in the fractures, and thus lead to poor effectiveness. Thermal technologies that can potentially fare better than steam injection such as in-situ thermal desorption and electric resistance heating (ERH) were retained for the Central Drainage Area south of the P/S Landfill for further evaluation. In-situ soil mixing with closely-spaced large diameter augers is intended to address deep soil contamination by mixing reagents such as oxidants, stabilizing agents, etc. Effectiveness of the mixing of these reagents in this weathered claystone formation is likely to be poor due to the anticipated clumpiness of the excavated soil. This technology cannot be implemented in the known DNAPL area within the footprint of the P/S Landfill due to challenges with drilling numerous large diameter auger holes and depth of source area within the landfill, and the health and safety concerns. In-situ chemical oxidation (ISCO), in-situ chemical reduction (ISCR) and in-situ anaerobic bioremediation are retained for further evaluation. For extraction/discharge, vertical and horizontal extraction wells are retained and extraction trenches that have already been used at the site are retained. For extraction/treatment options, all of the options including NAPL skimmers, hydraulic extraction, dual phase extraction and enhanced NAPL extraction are retained for further evaluation.

9.1.3 Water Treatment

For ex-situ water treatment, a wide range of technologies were retained including liquid phase activated carbon, powdered activated carbon, synthetic resin extraction, air stripper, advanced oxidation/UV oxidation, bioreactors, chemical reduction, chemical precipitation, ion exchange, reverse osmosis, membrane filtration, oil-water separator. None of the technologies were screened out. For discharge options, discharge of treated groundwater to sewers is not applicable. Discharge of treated groundwater to evaporation ponds, discharge of highly impacted groundwater to a permitted TSDF, and discharge to wetlands or streams under the substantive terms of site-specific NPDES permit are retained.


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9.1.4 Vapor Treatment

For ex-situ vapor treatment, all technologies were retained including thermal oxidation, adsorption, refrigeration/condensation, and scrubbers.

9.1.5 Surface Water/Stormwater

All options were retained for stormwater controls including stormwater BMPs, erosion controls, surface drains, and diversion channels. For stormwater treatment, constructed wetlands is retained for further evaluation. For discharge options, discharge to the sewer was not retained because it was not applicable. Other options such as discharge to ponds and discharge through wetlands under the substantive terms of the General Permit are retained.

9.2 Technology Screening for Soil and Sediment The FS conducts a second technology screening evaluation with those technologies that were retained from the initial screening. Table 9-2 presents the technology screening evaluations by contaminant scenario, media and the three screening criteria: effectiveness, implementability and cost. Effectiveness is the ability to achieve RAOs, which could include removal or destruction of contaminants, or mitigation of exposure, or contaminant containment. Implementability is the ability to implement the technology including reliability, vendor availability, administrative acceptance, etc. Cost includes Capital and O&M costs for the duration of remediation. The screening evaluation uses a rating scale ranging from poor, poor to moderate, moderate, moderate to good, and good for the Effectiveness and Implementability criteria. The screening evaluation also uses a rating scale ranging from low, low to moderate, moderate, moderate to high, and high for the Cost criterion.

9.2.1 Soil

9.2.1.1 Institutional Controls ICs are legal and administrative controls applied to properties to minimize the potential for human exposure to contamination and protect the integrity of the remedy. ICs control land or resource use and provide information that helps modify or guide human behavior at properties where the presence of contaminants prevents uncontrolled or unrestricted land uses. The primary retained ICs include deed restrictions or restrictive covenants that limit future development and restrict groundwater use. It is anticipated that ICs, in the form of land and water use restrictions, will be developed for all remedial alternatives.

9.2.1.2 Containment Containment technologies aim to control potential exposure to residual contaminants and include technologies such as soil capping and stormwater controls (e.g., BMPs, engineered


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stormwater diversion and erosion controls). For non-VOCs and VOCs in surface and shallow soil, asphalt or clay caps, RCRA-equivalent caps, ET caps, and RCRA prescriptive caps were retained as a protection from direct contact exposures. Also for soluble contaminants, these caps limit or prevent rainwater infiltration and soluble contaminant migration in groundwater. None of the process options under containment were screened out.

9.2.1.3 In-situ Treatment Several in-situ treatment technologies and process options (soil vapor extraction, ERH) have been screened out based on the low permeability and highly fractured nature of the bedrock. Section 4 of the RI states that the geometric mean of the hydraulic conductivity of Upper HSU weathered claystone is approximately 1x10-5 cm/s and that fractures control hydraulic conductivity in the Upper HSU. Important points to note in evaluating in-situ technologies in this fractured bedrock site lithology include: 1) a fractured bedrock with a 1x10-5 cm/s conductivity is significantly worse with respect to in-situ remediation effectiveness than an unconsolidated formation with the same conductivity because with a fractured bedrock a majority of the flow (depending on in-situ remediation approach it could be vapor extraction flow or reagent injection flow, etc.) is going to be through the fractures while in an unconsolidated formation this flow would be more uniformly distributed; b) a majority of the porosity in the Upper HSU is in the matrix (>40%) while the porosity of the fractures is <5% which implies that a majority of the contaminants are likely in the matrix where the available porosity is. Hence, addressing the fracture porosity with the in-situ remediation approach will not address a significant portion of the contamination in the matrix. For VOCs in shallow or deep soil, SVE is not retained primarily because of the limitations with the low permeability fractured or weathered bedrock formation as discussed earlier. The heterogeneous nature of the fractures makes the application and distribution of vacuum very uneven and hence ineffective. The SVE would remove VOCs from fractures but would be largely ineffective on the rock matrix. Thermally-enhanced SVE technologies such as in-situ thermal desorption and ERH are screened out based on the same limitations in effectiveness due to the fractured bedrock lithology. However, ISTD is retained for SVOCs and other organics as a representative thermal technology that could be applicable for the RISBON-59 (Area 3 Hotspot Location 10) even though it would face similar permeability challenges in the fractured bedrock formation. ERH is not retained because it is likely to be less effective than ISTD in these subsurface conditions. ISTD is retained as the only one of these in-situ thermal technologies that has potential effectiveness at this site.

9.2.1.4 Ex-situ Treatment Excavation and treatment or of impacted soils is discussed here. Excavation is generally retained for vadose zone soils but not for deep saturated zone soils. Thermal desorption for VOCs or SVOCs is not retained because landfill disposal at the site (e.g. at the PCB Landfill) or disposal to a permitted TSDF is a significantly more cost effective option and there is no significant need for to treat soils at the site. Thermal desorption costs are expected to be in the range of $200/ton, while transportation and disposal is expected to be in


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the range of $40 to 80/ton. Both of these options are less cost effective than PCB Landfill disposal but the PCB Landfill has limited capacity for waste storage estimated at approximately 140,000 cy. Vapor extraction in VOC-impacted soil piles is not retained due to poor effectiveness in the heterogeneous soils excavated from this weathered bedrock formation. The excavated soils are expected to be clumpy due to the low permeability claystone material and it would be difficult to uniformly apply a vacuum through this material. Disposal in the PCB Landfill or even disposal at a permitted TSDF would be more cost effective. Stabilization using cement, asphalt or other pozzolanic materials is retained for metals-impacted soils. Stabilized pond bottoms could be used as a leveling or foundation layer for constructing some of the anticipated caps at the site. Landfarming at the site is not retained because it is not effective for a majority of the site contaminants such as chlorinated solvents and metals. Landfarming is typically only used for soils impacted with petroleum hydrocarbons alone. Soils at this site have mixed contaminants that are not amenable to ex-situ biodegradation.

9.2.1.5 Disposal/Reuse Soil treatment/disposal at a permitted TSDF is retained because the PCB Landfill has limited capacity estimated at approximately 140,000 cy. Environmental impacts of transportation of large quantities of soil including greenhouse gas impacts would be significant compared to PCB Landfill disposal. Disposal at the PCB Landfill is retained because it is the most cost-effective option while there is capacity in the PCB landfill. However, PCB Landfill capacity to receive wastes is limited as discussed earlier.

9.2.2 Sediments

9.2.2.1 Stormwater controls Structural and nonstructural stormwater controls such as drains or swales, stormwater BMPs, detention basins are retained because the diversion of rainwater through drains/swales minimizes contact with impacted soils and contaminant transport via sediments.

9.2.2.2 Erosion controls Erosion controls such as geonets or geomats are retained because these controls are important to avoid erosion of impacted soils or soil caps especially those that are on moderate to steep slopes. Erosion of impacted soils can lead to transport of contaminated sediments.


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9.3 Technology Screening for Groundwater, NAPL and Stormwater This second, more detailed technology screening process evaluates those technologies that were retained in initial screening. Table 9-3 presents a description of the technology, the screening evaluation, and screening comments.

9.3.1 Groundwater and NAPL

9.3.1.1 Institutional Controls It is anticipated that ICs will be included for all remedial alternatives. ICs will include land use and water use restrictions that will run with the land. Groundwater use restriction is the primary institutional control that is retained for site or near-site groundwater. Other restrictions, such as land use covenants and well restrictions, can be potentially useful in the long term to control potential exposures. Long-term monitoring is retained for use in conjunction with other remedial components. This includes groundwater monitoring of wells at and outside of the site boundaries that has been conducted since 1997 under the RGMEW work plan that was last updated in 2009. Groundwater monitoring -- for performance and compliance purposes -- will be retained for all FS groundwater alternatives and carried into the final remedy. The details of the current program are outlined in RGMEW Workplan, dated March 2009 (CSC 2009a). The long term groundwater monitoring program will be revised as necessary, during remedial design (RD), remedial action, and long term O&M, as determined necessary by EPA.

9.3.1.2 Containment Slurry walls were retained due to their effectiveness in preventing groundwater migration in the Upper HSU. Slurry walls would be applicable for all three groundwater subareas: Area 5 North, 5 South and 5 West. This technology functions effectively for the P/S Landfill clay barrier and the PCT clay barrier. Slurry walls are long term physical containment technologies that will need to function throughout the entire course of the remedy. The FS retains hydraulic extraction in order to contain contamination within the Upper and Lower HSU. Extraction technologies include vertical wells, trench wells, or horizontal wells. Phytoremediation is retained for hydraulic containment in areas with low levels of organic and inorganic contamination (e.g. areas 5 South and 5 West) and a shallow water table. Phytoremediation for hydraulic control can be performed using phreatophytes, which are deep-rooted plants that obtain a significant portion of the water that they need from the phreatic zone (zone of saturation) or the capillary fringe above the phreatic zone. Uptake of groundwater from the capillary fringe can depress the water table leading to hydraulic containment or support of hydraulic containment. One challenge, however, is that TDS concentrations in groundwater are high which can be detrimental to plant growth and health.


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9.3.1.3 Passive In-situ Treatment For dissolved VOCs, MNA was retained. The detailed MNA evaluation in the Final RI (CSC 2011) documented strong evidence that biologically mediated degradation of petroleum and halogenated hydrocarbons is occurring, through aerobic, anaerobic and fermentative metabolic pathways. Historic monitoring of indicator parameters demonstrates effective biodegradation of organic chemicals in the plume areas in Area 5 South and supports evidence that a reductive dechlorination zone exists to the south of the PSCT trench. Permeable reactive barriers (PRBs) were retained to contain in-situ plumes and/or provide perimeter control. PRBs typically use reductant materials, such as zero valent iron (ZVI), to reduce dissolved chlorinated solvents in groundwater. PRBs installed by funnel-and-gate approaches were included due to the presence of clay barriers at the site that can be converted to a PRB.

9.3.1.4 Active In-situ Treatment Just as with the in-situ soil treatment technologies discussed earlier in Section 9.2.1.3, several active in-situ technologies were screened out due to the low permeability and fractured nature of the site’s lithology. Section 9.2.1.3 showed that most in-situ technologies are not retained primarily because of the low permeability coupled with the fact that these technologies can only address the fracture porosity, which is a small part of the total porosity that contains most of the contamination. Air sparging and biosparging were not retained for groundwater due to anticipated poor effectiveness and challenging implementability under the heterogeneous, low-conductivity subsurface conditions. Three in-situ soil heating technologies were evaluated for NAPL source area remediation including ISTD, ERH and steam injection. ISTD, a thermally-enhanced SVE, was retained because it is effective for VOC and SVOC contaminants and is implementable in a wide range of site lithologies. However, this technology would face some technical challenges in this weathered bedrock upper HSU formation as discussed earlier. ERH and steam injection were not retained for NAPL source area remediation in groundwater because they are expected to face greater challenges than ISTD in this weathered bedrock formation. Hence ISTD was retained as a representative in-situ thermal technology. ISCO with oxidants, like permanganate or persulfate, was evaluated and rejected because the oxidant injection approach would face significant challenges with injection in the weathered bedrock formation. The radius of influence of the oxidation would be very limited in this lithology. There would likely be preferential oxidant flow in fractures and highly heterogeneous distribution of oxidant. ISCO is rarely used with PRBs because oxidants are expended quickly during rapid reducing chemical reactions. Enhanced in-situ anaerobic bioremediation, which involves subsurface injection of microbes/substrates (bioaugmentation) or nutrients (biostimulation), was not retained as a standalone component. However, it is retained as a component to be used with ISCR. ISCR involves injection of microscale ZVI or placement of ZVI in PRBs as discussed earlier. ISCR is sometimes implemented with in-situ bioremediation (ISBR), using a carbon substrate, and this is retained. In-situ mechanical enhancements (pneumatic or hydraulic fracturing) were also


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retained as a supplement to enhance the ISCR technology. However, these technologies have significant uncertainties and will only be considered on a case-by-case basis when appropriate.

9.3.1.5 Extraction Wells Vertical wells, trench wells or horizontal wells can be used to extract impacted groundwater as part of hydraulic control or to intercept and extract NAPL as source control to limit contaminant migration. Based on this screening evaluation, vertical wells and trench wells are retained and these well types are a significant part of the existing remedy for source control near the NAPL source areas and perimeter plume control. Vertical wells that are placed within large diameter boreholes, placed in trenches or upgradient of clay barriers have proven to be effective at this site. Horizontal wells are retained primarily to evaluate their potential for extracting impacted groundwater under the site’s landfills (e.g., P/S Landfill) without having to drill through the landfill wastes. Horizontal directional drilling (HDD) is generally more expensive than trench wells. In unrestricted terrain, horizontal trench wells may be less effective in this site’s lithology because they will not be able to intercept and extract as much groundwater or NAPL liquids. However, horizontal wells are retained for the evaluation of dewatering the P/S Landfill, where drilling into landfill waste may be undesirable, to address source control and remove NAPL mass. With regard to NAPL extraction, all of these wells can be used to remove LNAPL and DNAPL mass from the subsurface, hydraulically control LNAPL migration, and partially control DNAPL migration. Hydraulic control of DNAPL is only partially effective because DNAPL migration is density driven and only partially influenced by hydraulic gradients. Removal of the mobile DNAPL source is necessary to control DNAPL migration.

9.3.1.6 Ex-situ Treatment Hydraulic extraction was retained for use with extraction from vertical wells, trenches or horizontal wells. Hydraulic extraction from trenches and wells is a significant part of the current response action for NAPL source control as well as perimeter control. For NAPL, mass reduction efficiency with hydraulic extraction is low, but VOC contaminant mass can be reduced in the dissolved phase. Cost depends on the density of wells and extraction flow rate, and is generally very high because of the need for long term operation. For dissolved plumes, this technology can serve as a control or containment feature and is used currently at the site. Dual phase extraction was not retained due to difficulty in extraction in this low permeability, fractured bedrock formation. Challenges faced by this technology have the same basis as the discussion relating to permeability and fracture flow for in-situ technologies discussed earlier (Section 9.3.1.4, Section 9.2.1.3). NAPL skimmers were retained because they can be effective for removal of DNAPL and LNAPL that comes into a well. Skimmers can be used for DNAPL-only skimming by optimizing the well construction for DNAPL entry into the well. Enhanced NAPL Recovery (also called Surfactant/Cosolvent Flushing) for NAPL is not retained because this technology works optimally in highly permeable alluvial (e.g. hydraulic conductivity of 10-3 cm/s) aquifers. The use of the water flood approach would involve extraction of


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groundwater overlying DNAPL and reinjection to enhance DNAPL recovery. The low permeability of the upper HSU would make reinjection difficult and would be further complicated by the high TDS and biofouling that would significantly impact and restrict the injection operations.

9.3.1.7 Disposal/Discharge/Reuse Discharge to evaporation ponds at the site is retained because evaporation ponds are a cost effective means of addressing high TDS and inorganics in treated groundwater. However, handling of treated water is limited by the available size of the evaporation pond. If groundwater extraction rates are too high to be handled by the evaporation pond, then more complex groundwater treatment should be considered to enable discharge of treated groundwater to the B Drainage or Casmalia Creek. Enhanced evaporation, such as that used in mines to reduce water volume, is retained because it is an effective way to reduce water volume, especially in those wet years when extracted groundwater and stormwater volumes peak. Discharge of treated groundwater to the B Drainage or Casmalia Creek is retained because it is the only option available if high groundwater extraction flow rates are considered that could not be handled in the evaporation ponds. This option would require treatment of all organic and inorganic contaminants in groundwater as well as the high TDS, which raises the complexity and cost of this approach. Discharge of extracted groundwater that is treated to remove contaminants such as VOCs, NAPL, metals and TDS with a complex treatment system (such as advanced oxidation, air stripping, LPGAC and reverse osmosis) to meet site-specific NPDES discharge limits is retained. The two discharge options discussed above would require a Basin Plan exception from the Regional Water Quality Control Board (RWQCB) for discharge of treated groundwater to the B-Drainage or Casmalia Creek. Disposal of liquids at a permitted TSDF is retained since it is the current approach used for the disposal of NAPL and the highly concentrated Gallery Well liquids. Also, disposal of the reject RO brine waste streams at a permitted TSDF is retained for those alternatives that involve discharge of groundwater treated for inorganics by reverse osmosis. Potential reuse of existing pond water during cap construction is retained as a green remediation and cost effective option.

9.3.2 Stormwater

9.3.2.1 Stormwater controls Stormwater controls such as drains, swales, BMPs, erosion controls and detention basins are retained because these controls are important to divert rainwater through drains/swales to minimize contact with impacted soils and to ensure the stormwater runoff from the site is clean. Where stormwater comes into contact with soils that can potentially impact stormwater quality, erosion control approaches are considered.


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9.3.2.2 Site discharge Discharge of stormwater from uncapped areas to evaporation ponds is retained because evaporation ponds are a cost effective means of addressing low levels of organics or inorganics. Evaporation rates at the site are high in the range of 44 to 48 inches per year. Evaporation pond sediments will accumulate inorganics deposited over a period of time and will need to be cleaned periodically.

9.3.2.3 Constructed Wetlands Constructed wetlands is retained as an approach to handle stormwater with low levels of contaminants. This technology can be effective at reducing contaminant levels. The wetlands in the B-Drainage are not an example of wetlands designed for treatment. These wetlands are designed to support amphibians in compliance with the Biological Opinion issued by USFWS.

9.3.2.4 Enhanced Evaporation Enhanced evaporation is retained because it is an effective technology that can reduce the volume of water in ponds at the site, especially in those wet years when extracted groundwater and stormwater volumes peak.

9.3.2.5 Discharge to the B Drainage or Casmalia Creek Discharge of clean stormwater from capped areas in accordance with the substantive terms of the General Permit is retained because it has already proved effective for discharge of clean stormwater from capped and unimpacted areas to the B Drainage or Casmalia Creek.

9.4 Extracted Water and Vapor Treatment Table 9-4 presents a summary of an evaluation of water and vapor treatment technologies for the respective extracted media. Generally, a larger set of treatment technologies was retained here with the goal of selecting the appropriate technology depending on the specific water or vapor streams during RD.

9.4.1 Extracted Water Treatment

Treatment of extracted groundwater is evaluated for hydraulic extraction alternatives. A wide range of water treatment technologies that are applicable to VOCs and metals contaminants are retained and potentially applicable. This includes liquid phase carbon adsorption, macroporous polymer adsorption, air stripper and advanced oxidation (UV Photo-oxidation) for VOCs treatment. Ion exchange and reverse osmosis are included for treatment of dissolved metals. Membrane filtration is retained for fine particle filtration and an oil-water separator is included for NAPL phase separation. Also for highly contaminated landfill leachates a combined biodegradation and carbon adsorption technology has been successfully used at other sites. This technology, called Bio-PACT, uses powdered activated carbon and is retained for potential


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use with the Gallery Well liquids. Other bioreactor technologies such as fluidized bed bioreactors are viable options though typically for lower VOC concentrations than found in the Gallery Well fluids. Only a subset of these technologies is included as a component in one or more of the remedial alternatives. The selection of these technologies in the future depends on the actual concentrations of contaminants in the extracted groundwater and the treated water disposal option selected.

9.4.2 Extracted Vapor Treatment

Though SVE is not a retained technology at this site, vapor treatment technologies are retained in this FS only as a secondary component that maybe required as part of the retained technologies that would need vapor treatment such as ISTD or air strippers or other technologies for groundwater leachate treatment. Thermal oxidizers, catalytic oxidizers and vapor phase granular activated carbon (VPGAC) adsorption were retained as examples of vapor treatment technologies. These technologies have been successfully applied at other sites with different influent vapor concentration ranges: thermal oxidizers at the highest (>1,000 ppmv), catalytic oxidizers in the midrange (200-1,000 ppmv) and carbon adsorption (<200 ppmv) at the lowest concentrations. Carbon adsorption can also be used at high influent concentrations but carbon regeneration at the site using steam or regeneration at a permitted facility will be required. Carbon regeneration with steam will create a VOC-containing wastewater stream that will need treatment or disposal. Polymeric resin adsorption has been used for high-influent waste stream concentrations but is not considered to be cost effective. For chlorinated VOCs, a chlorinated catalytic oxidizer can be used that is equipped with an alumina catalyst instead of the precious metal catalyst found in typical hydrocarbon catalytic oxidizers. However, the thermal treatment of chlorinated VOCs generates hydrochloric acid vapor that would need a scrubber that uses a neutralizing solution (e.g., a caustic soda solution). Acid scrubber is retained specifically if a thermal or catalytic oxidizer is used for chlorinated VOC vapor treatment to remove acid vapors (HCl) that are formed during oxidation. Wastewater would be generated by this process which would need to be treated/discharged in accordance with regulatory limits (e.g., NPDES requirements for storm drain discharge or discharge limits associated with the sanitary sewer system). Refrigeration/ condensation technology is not widely used in remediation applications, so it was not retained. However, if influent concentrations of chlorinated VOCs are very high and if there are regulatory constraints on the use of oxidizers, this is potentially a viable technology. For chlorinated VOC vapor concentrations that are low (<100 ppmv), vapor phase carbon is typically the most cost effective form of vapor treatment.

9.5 Summary of Retained Technologies This section describes in greater detail the remedial technologies retained for further evaluation in the FS. Tables 9-1 through 9-4 provided the rationale for retaining or screening out technologies.

9.5.1 Soil/Sediment Technologies

9.5.1.1 Institutional Controls Restrictive covenants are legal agreements between a property owner and a third party that place restrictions on the use of the property for environmental reasons. The covenant is


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recorded in the land records and “runs with the land,” binding future landowners to its terms. The intent of this IC is to control specified activities which may create risk or complete exposure pathways, and consequently to prevent or impose controls on specified activities by any property occupants and invitees. Examples of potential restrictive covenants include requiring agency review and/or sampling prior to any excavation, grading or drilling project; and requiring operation/maintenance of engineering controls. Restrictive covenants would include USEPA as a third party with rights to enforce their terms. Areas that have containment or engineering control remedies (e.g. RCRA caps) would require land use restrictions to ensure that the capped areas are monitored and protected for the long term.

9.5.1.2 Simple Caps (Soil, Clay or Asphalt Cap) Capping is an engineering control or containment technology and, for this FS, refers primarily to simple caps such as soil or asphalt capping of an impacted area of outdoor soil to limit potential direct contact exposures of ecological receptors or construction workers to contaminants. A simple soil or asphalt cap may reduce rainwater infiltration but is not intended to prevent infiltration or leachate migration to groundwater. A soil or clay cap is a low permeability soil cap that can be 1 foot to 5 feet thick that is appropriately compacted with a vegetative layer on top. Asphalt caps are considered for those areas with existing asphalt. Here the existing asphalt cap on the ___ Landfill will be evaluated for quality and adequacy based on performance standards acceptable to EPA and options such as seal coating would be implemented to improve integrity of the existing asphalt surface. It is anticipated that most of the existing asphalt material at the site will require replacement due to severe cracking. Capping an impacted area within an exposure area will typically require an IC to require protection, maintenance and monitoring of the cap for the future.

9.5.1.3 Ecological Cap Ecological Cap refers to a 2-foot thick soil cap that can be effective at addressing areas where the ecological exposure risk results from contaminants in shallow soil and for ecological exposure risk to burrowing animals in deeper soils. The 2-foot cover would be placed in 1-foot lifts with the first lift compacted to 90% relative compaction (ASTM D 1557) and the upper lift would be lightly compacted (85% compaction) and hydroseeded to allow vegetative growth. This soil cover surface would include a limited number of surface drains, and stormwater would largely sheet flow off the cap surface to the nearest concrete V-drains or stormwater channel. Erosion control measures would be incorporated to reduce erosion of the soil cover including, if needed, turf reinforcement mats on steep slopes.

9.5.1.4 RCRA Cap The RCRA cap is a multilayered landfill cap that is a baseline design and is prescribed for use in RCRA hazardous waste landfill applications (Subtitle C). These caps generally consist of an upper vegetative (topsoil) layer, a biotic barrier, a drainage layer, and a low permeability layer which consists of a synthetic liner over 2 feet of compacted clay. The compacted clay liners are effective if they retain a certain amount of moisture content but are susceptible to cracking if the clay material is desiccated. As a result alternate cap designs are usually considered for arid environments. The most critical components of a landfill cap are the barrier layer and the drainage layer. The barrier layer can be low-permeability soil (clay) and/or geosynthetic clay liners (GCLs). A flexible geomembrane liner is placed on top of the barrier layer.


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Geomembranes are usually supplied in large rolls and are available in several thickness (20 to 140 mil), widths (15 to 100 ft), and lengths (180 to 840 ft). The candidate list of polymers commonly used is lengthy, which includes polyvinyl chloride (PVC), polyethylenes of various densities, reinforced chlorosulfonated polyethylene (CSPE-R), polypropylene, ethylene interpolymer alloy (EIA), etc. Soils used as barrier materials generally are clays that are compacted to a hydraulic conductivity no greater than 1 x 10-6 cm/sec. Compacted soil barriers are generally installed in 6-inch minimum lifts to achieve a thickness of 2 feet or more. A composite barrier uses both soil and a geomembrane, taking advantage of the properties of each. The geomembrane is essentially impermeable, but, if it develops a leak, the soil component prevents significant leakage into the underlying waste. A biotic barrier is intended to prevent burrowing animals from damaging the geosynthetic liner. In this FS, a biotic barrier primarily refers to a 200 mil geonet synthetic material that has been used with other caps at the site, for example, at the EE/CA Area. Preliminary specifications on the conceptual design of these caps are presented in Section 10.1.

9.5.1.5 RCRA-equivalent Cap A RCRA-equivalent monosoil cap includes a 5-foot thick clay monocover that meets the performance standard of a compacted hydraulic conductivity of 1x10-6 cm/sec. This 5-foot monocover would meet all of the requirements of a RCRA prescriptive cap, including specifications for infiltration, and satisfies the RAOs established for stormwater management and groundwater. The clay soil for constructing this cap should meet preliminary specifications discussed in Section 10.1 and could be obtained from or borrow areas on or near the site or outside sources. However, clays have the potential to dry and fracture over the long term. This could result in water infiltration through the fractures compromising the intended matrix flow of low-permeability compacted clay. Dessication, as well as freezing, intrusion by plant roots, or burrowing animals can result in the development of preferential flow paths in clay barriers, thus compromising long term performance. A RCRA-equivalent hybrid cap as discussed in this FS refers to HDPE geomembrane with spikes on the bottom to reduce slip for use on steep slopes. The HDPE geomembrane would meet the hydraulic conductivity requirements of a RCRA equivalent cap. It would include a geocomposite drainage layer on top of the geomembrane and a biotic barrier and vegetative layer above that. The HDPE geomembrane would be placed on a foundation layer that is compacted and smoothed to ensure there is no damage to the membrane. A biotic barrier is intended to prevent burrowing animals from damaging the geosynthetic liner. As with the RCRA cap description earlier, a biotic barrier primarily refers to a 200 mil geonet synthetic material that has been used with other caps at the site. Preliminary specifications for this are discussed in Section 10.1. It is anticipated that final design specifications would be determined during the RD process subject to regulatory approval from EPA.

9.5.1.6 Evapotranspiration Cap ET caps are designed to prevent infiltration into wastes by storing precipitation in a soil layer until it is naturally evaporated or is transpired by the vegetative cover. They differ from more conventional cover designs that create physical barriers to limit infiltration, in that they rely on obtaining an appropriate water storage capacity in the soil rather than an as-built engineered low hydraulic conductivity. ET cap designs are based on using the hydrological processes (water balance components) at a site, which include the water storage capacity of the soil,


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precipitation, surface runoff, evapotranspiration, and infiltration. The greater the storage capacity and evapotranspirative properties are, the lower the potential for percolation through the cover system. A difference between an ET cap and the RCRA-equivalent clay cap is that the ET caps may adopt different soil specifications and only light compaction to ensure vegetation growth. ET cap designs typically include the following (USEPA 2011; USEPA 2003):

• Fine-grained soils, such as silts/clayey silts that have a high water storage capacity • Appropriate vegetation for long-term stability and evapotranspiration • Locally available soils to streamline construction and provide for cost savings

ET caps must be carefully designed and may be constructed as monocaps using a single moderate or fine-grained soil layer to retain water and support the vegetative community. An ET monocap design can be modified by adding a capillary break by placing a coarser grained material, usually a sand or gravel, under the monolithic fine-grained soil. The discontinuity in pore sizes between the coarser-grained and finer-grained layers forms a capillary break at the interface of the two layers. The break results in the wicking of water into unsaturated pore space in the finer grained soil, which allows the finer-grained layer to retain more water than a monolithic cover system of equal thickness. ET caps can be lower in cost compared to conventional clay caps especially in arid and semi-arid regions (e.g. areas with less than 10 inches and 20 inches respectively). In these environments, they may be less prone to deterioration from desiccation, cracking, and freezing/thawing cycles. ET caps also tend to exhibit better stability characteristics in sloped areas, because they do not contain geomembrane layers, which can cause slippage. In addition, site specific conditions, such as site location (e.g., appropriate soil) and landfill characteristics, may limit the use or effectiveness of ET caps. Local climatic conditions (amount, seasonal distribution, and form of precipitation) also can limit the effectiveness of an ET cover at a given site. As with other remedial alternatives, the FS includes representative conceptual designs for planning and cost estimation purposes. Final engineering designs and specifications would be determined during the FS process subject to EPA approval.

9.5.1.7 Stormwater Basin and Pond Liners There are two types of lining technologies for future ponds, depending on whether they are used for stormwater or used as an evaporation pond that holds groundwater. These technologies are similar to capping technologies; they are intended to prevent migration of stored liquids into the subsurface. For stormwater basins, a single composite HDPE liner (geotextile above with geomembrane below) would be installed above a compacted subgrade (a.k.a. foundation layer). For groundwater stored in evaporation ponds, a double liner system including a primary HDPE geomembrane with a drainage layer below, followed by a secondary HDPE geomembrane is proposed. The drainage layer drains by gravity any liquids leaking through the primary layer into a sump as part of a leachate collection and recovery system (LCRS). The secondary HDPE geomembrane is placed on a compacted foundation layer. A standard black HDPE geomembrane is proposed as the upper (primary) liner for increased heat retention to enhance evaporation potential. In addition, a leak detection system (such as lysimeters) to detect leaks in the vadose zone can be used below the secondary layer. Other options for leak detection include options such as using an electrically conductive geomembrane (thin conducting sheet


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adhered to the geomembrane) that can help identify leaks. More detail on these technologies including typical cross section details for these lining systems is discussed in Section 10.

9.5.1.8 Excavation Excavation would typically involve removal of shallow soil (typically depths of 5 feet bgs to protect ecological receptors) but in some cases deep soil (down to 20 feet bgs) across the assumed horizontal extent of impacted outdoor soil. This assumes the use of standard excavation equipment (excavator, backhoe etc.). The excavated soils are assumed to be placed within the site or transported to a permitted TSDF for treatment/disposal. The sides of the excavation would be sloped in accordance with geotechnical requirements (based on soil properties). The sloped sidewalls would provide clean overburden soils that will be used for backfill. Clean import fill would be borrowed from the northwest area of the site and compacted as required. The extent of the excavations discussed in the FS is preliminary and would be confirmed during RD. The excavation would typically extend in size (lateral extent and depth) until confirmatory soil sampling demonstrates that risk-based standards are achieved. Where the excavation abuts a building, the evaluation assumes the use of shoring such as sheet piles or soldier piles with lagging when the excavation is deeper than 5 feet bgs. For shallow excavations (≤5 feet bgs) that abut a building or structure, alternate means of excavation is assumed, such as slot-trenching, that avoids the cost of shoring. More detailed evaluation of excavation options would be considered in the design phase if any active excavation alternatives were to be implemented. The evaluation assumes that no excavations will occur beneath the footprint of buildings. Any smaller structures, subsurface pipelines, or wells in the vicinity of the excavation will be protected or replaced in kind during the excavation. Dust, VOC and odor emission control measures will be utilized to limit the nuisance to workers or community. Excavated soils will be tested with field instrumentation to ensure that VOC-impacted soils are handled appropriately and in compliance with SBCAPCD requirements. Ambient air monitoring will be conducted during the excavation to confirm there are no potential risks through air emissions. With regards to options for disposal of excavated impacted soil, the alternatives in the FS assume either placement in the PCB Landfill, placement under geosynthetic liner/cap or sent to a permitted facility. The PCB Landfill has a limited storage capacity. As discussed later under FS Area 1 (Section 10.2), the storage capacity in the PCB Landfill is estimated to be approximately 140,000 cy (Figure 11-1B). The total volume of potential soil excavations considered in this FS is significantly greater than the available storage capacity at the PCB Landfill. Hence some of the remedial alternatives with large excavation volumes were not considered for PCB Landfill disposal. The cost estimates for those alternatives assumed disposal of excavated soil at a permitted facility, which is significantly higher than disposal at the PCB Landfill. Another option for disposal of limited amounts of excavated soil is placement in ponds to raise the pond bottom before it is lined. Primarily low level impacted soils (e.g. low metals in shallow soils) were considered for placement under the HDPE liners in these former pond areas.

9.5.1.9 In-situ Thermal Desorption (also Thermal Conduction Heating) ISTD, also known as thermal conduction heating, is an in-situ thermal destruction system and enhanced SVE system that heats the soil up to 1,000oFahrenheit (oF) using resistive heating


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elements in thermal wells. The contaminants are either destroyed in-situ or volatilized and removed through vapor extraction. Soil is heated by thermal conduction, making this process very energy intensive. Unlike ERH, no current flows through soil. ISTD involves closely spaced wells (typically 8-20 feet apart) with the heating elements penetrating the entire thickness of the contaminated zone. Volatilized contaminants are treated in aboveground treatment units such as thermal oxidizers. This is considered a developing, innovative technology. It has been selected and implemented successfully for SVOCs (high PCB and pesticide source areas) and chlorinated solvents. Advantages of this technology are that it is an aggressive remediation approach that can remove a higher fraction of contaminant mass than conventional technologies and can complete remediation in a shorter timeframe. The conceptual design for ISTD at this site would involves vertical heater wells placed at 10-foot spacing across the extent of the impacted source area. Each heater well is a 3-inch steel casing with the heating element placed down the middle of the well and would span the treatment depth range. The power transformer would be connected to the nearest 13 kiloVolt (kV) power line and would be sized to deliver in the range of 1,000 to 2,000 kiloWatt (kW) of power depending on the size of the remediation area. SVE wells would be spaced 20 feet apart across the source area to capture the heated vapors for treatment in an aboveground treatment system as discussed above. Temperature monitoring points would be spaced about 50 feet apart across the impacted area with thermocouples placed at multiple depths at each point. An operation period of 1-2 years is typical for this remediation technology before reaching a point of diminishing returns.

9.5.1.10 Long-Term Monitoring Long-term monitoring is included as a technology component in the remedial alternatives evaluated in the FS. Monitoring programs would be planned and implemented in order to achieve a variety of objectives, including (A) performance monitoring, (B) detection monitoring, and (C) compliance monitoring. Monitoring includes activities such as monitoring of ICs, monitoring of an active remedial option during treatment, monitoring of a containment system such as a Cap remedy and long-term monitoring after treatment. Five-year reviews will be conducted by the US EPA and that will include monitoring the effectiveness of the various remedies at the site. Monitoring of various environmental media such as soil vapor or soil can also be conducted, as described below. The FS includes some general discussions of current and suggested enhancements to existing monitoring program. The details of each long term monitoring program, however, will be developed and revised progressively, subject to EPA approval, through RD, remedial action and the transition into long-term operations, maintenance, and monitoring (OM&M). Soil Vapor Monitoring A soil vapor monitoring program is also currently in place for the site that is expected to be continued as part of long term monitoring for the proposed remedy. The details of the current soil vapor monitoring plan are outlined in the “Sampling Plan for Soil Gas Monitoring”, dated April 2009 (CSC 2009b). Monitoring of Constructed Remedies

This includes the maintenance and monitoring of all site systems, including previously constructed structures and remedies proposed after the completion of this feasibility study. Monitoring would include a variety of system-specific monitoring strategies intended to address:


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(A) performance monitoring, (B) detection monitoring (e.g., early detection of possible releases), and (C) compliance monitoring to ensure compliance with performance standards. Monitoring may include sampling of site media (surface water, groundwater, soil, and soil vapor); instrumentation to monitor performance of individual site systems; and leak detection and notification instrumentation. The previously constructed structures would include a wide range of existing features such as the caps for the Capped Landfills Area. Periodic replacement or repair of caps is considered in the FS. Where controls such as a cap (RCRA cap, ecological cap or RCRA-equivalent mono soil cap) are implemented to control direct contact exposures or prevent infiltration, long-term monitoring and maintenance would be required to ensure that the engineering control continues to operate effectively and is not compromised. Periodic inspection and monitoring of the capped areas may identify the need for repairs due to subsidence or erosion. These long term repairs and maintenance of the cap are included as components in the remedial alternatives discussed later. As discussed earlier, restrictive covenants would be included that would require that the caps or other controls be protected for the long term.

9.5.2 Groundwater, NAPL and Stormwater Technologies

9.5.2.1 Natural Attenuation (Intrinsic Biodegradation) Intrinsic biodegradation is the naturally occurring process of biodegradation of petroleum hydrocarbons (especially lighter volatile hydrocarbons such as BTEX) by soil microbes. Intrinsic biodegradation occurs in the saturated zone at the fringes of the dissolved-phase plume and also in the vadose zone. Long-term monitoring includes annual groundwater monitoring of a set of wells located at or in the immediate vicinity of the source area to confirm that intrinsic biodegradation processes are continuing to be effective in preventing undesirable migration of hydrocarbons. Often there is an adequate number of existing wells in the vicinity of the source area; these wells would be considered for incorporation into an annual groundwater monitoring program for specific source areas.

9.5.2.2 In-situ Chemical Reduction/Bioaugmentation ISCR involves the direct injection of reductant chemicals through subsurface injection points or placement in a subsurface reactive barrier to reduce dissolved chlorinated hydrocarbon contaminants to relatively benign chemicals such as chloride ions and low concentrations of hydrogen and ethane dissolved in groundwater. Chemical reductants used for this type of application are typically ZVI (Fe0) which is supplied in granular form or in microscale or nanoscale particles that are injected in solution. Also, for chlorinated solvents remediation, ISCR is often combined anaerobic bioremediation by using a combination of ZVI and a carbon substrate to enhance bioremediation. A variety of carbon substrates are available such as emulsified vegetable oil for chlorinated solvent remediation. Edible oils are relatively low-cost, innocuous, food-grade substrates. These oils are preferably injected as emulsions for ease of implementation and better subsurface distribution. This technology would require that strongly reducing conditions are generated by addition of emulsified oil and that a microbial community capable of the reductive dechlorination is present. As with other in-situ technologies, this approach would face implementation difficulties due to the low permeability and heterogeneous character of soils at the site which would make it difficult to distribute the oil. The injection of emulsified oil can be implemented by direct-push probes or through injection wells. Typically, one round of injection can provide sufficient carbon to drive reductive dechlorination for as long


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as one year. This technology can be implemented to address source areas or as a permeable reactive barrier to address downgradient plumes. For chlorinated solvents, the various bioaugmentation options for groundwater include injection of electron donors (e.g., emulsified edible oil), methane (cometabolic enhancement) or microbes (e.g., KB-1) and nutrients. This ISCR/Bioaugmentation technology is retained for the screening evaluation of alternatives for use in a permeable reactive barrier or by injection for the source area.

9.5.2.3 Extraction Wells Vertical wells are installed by conventional hollow stem auger, mud rotary or other methods. This approach would require a series of closely-spaced wells to extract impacted groundwater as part of hydraulic control or extract NAPL as source control to limit contaminant migration. Vertical wells that are placed within large diameter boreholes, placed in trenches or upgradient of clay barriers are the most effective at this site. They can be used to remove LNAPL and DNAPL mass from the subsurface, hydraulically control LNAPL migration, and partially control DNAPL migration. Trench wells involve excavation of deep trenches that extend below water table to extract impacted groundwater as part of hydraulic control or source control to ensure DNAPL or dissolved contaminant migration is limited. They can be used to hydraulically control NAPL migration and as a perimeter plume control measure. Horizontal wells are installed by directional drilling methods that can extend several hundreds of feet long to access a greater portion of the saturated zone than vertical wells. They can be used to extract impacted groundwater as part of hydraulic control or extract NAPL as source control to ensure DNAPL or dissolved contaminant migration is limited. These wells have the potential to access contaminated groundwater under landfills without drilling through waste.

9.5.2.4 Hydraulic Extraction Hydraulic extraction involves the extraction of groundwater to increase the hydraulic gradient toward the extraction wells and remove any mobile NAPL contaminant as free product or in the dissolved phase. Hydraulic extraction (also called pump and treat) is well known to have limitations in addressing source area contamination because some or all of the NAPL/hydrocarbon contamination is adsorbed or tightly bound in the soil pore space and is removed only through dissolution into groundwater. Typically hydraulic extraction is performed using extraction pumps placed in groundwater wells typically 2 or 4 inches in diameter. In very tight formations such as bedrock conditions, hydraulic extraction would require larger diameter wells due to the low flow rates produced by the aquifer. For example, the Gallery Well at the site is placed adjacent to a clay barrier that dams the groundwater and uses an 8-inch casing with a long screen interval (40 feet) and placed in a large diameter borehole. Such extraction well enhancements are required to produce a reasonable extraction flow rate of 1 or 2 gpm in tight formations such as found at this site. Extracted groundwater from multiple wells are piped together and pumped to an aboveground groundwater treatment system discussed below. The hydraulic extraction alternative is assumed to operate for a 30-year timeframe for costing purposes.


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9.5.2.5 Water Treatment The primary contaminants in groundwater that may require treatment include VOCs, SVOCs, and inorganics (metals). The FS assumes that a treatment process train will utilize multiple processes including pre-treatment process such as liquid-liquid separator (also oil-water separator) and particulate filters. Liquid Phase Granular Activated Carbon (LPGAC) adsorption is likely the most viable option for VOCs in groundwater when concentrations are not very high. For high VOC and SVOC concentrations in groundwater such as would be found in the landfill leachate, multiple treatment processes in series would be required. One potential combination that is retained is advanced oxidation (hydrogen peroxide and ozone oxidation of dissolved phase hydrocarbons) and air stripping (parallel plate air stripper or packed tower stripper). Liquid-phase carbon adsorption is included in the treatment process train as a polishing or backup technology in the event either of the primary technologies fails. The FS also considers another combination for highly contaminated landfill leachate treatment which includes a combined biodegradation and carbon adsorption technology that has been successfully used at other sites. This technology, called Bio-PACT, uses powdered activated carbon and is retained for potential use with the Gallery Well liquids or other leachate extraction and treatment alternatives. The treated groundwater can be handled in one of three ways: discharged to storm drain, discharged to sewer or reinjected into subsurface. The discharge to storm drain alternative would likely require that the extracted groundwater is treated to MCLs to meet the substantive requirements of NPDES requirements. The site is not located in an area that currently has a storm sewer system so this alternative is not currently available. The FS assumes that any NAPL recovered from the liquid-liquid separator would be disposed at a facility that is permitted to receive such waste (likely Resource Conservation and Recovery Act [RCRA] hazardous waste). Other bioreactor designs such as fluidized bed bioreactors are also potentially viable options if the groundwater contaminant concentrations in the influent water are moderately high but not as high as the Gallery well liquids. Reverse Osmosis and membrane filtration (including ultrafiltration) are retained for possible use in water treatment. Vibratory Shear Enhanced Processing (VSEP) treatment is an example of such a technology that uses ultra- or nanofiltration membrane modules to treat the effluent in order to treat organics or metals and dissolved solids, generating a permeate stream that meets water discharge or reuse criteria. VSEP membrane systems can be utilized where traditional cross-flow membrane technologies faced substantial membrane fouling problems in the past. The VSEP is an attractive alternative to conventional filtration methods due to its vibrational, shear-enhancing design which reduces or eliminates fouling. Ion exchange technologies are not retained because ion exchange resins do not perform well with very high TDS levels found in groundwater at this site. Reverse Osmosis is better suited for groundwater conditions at this site. Resin based adsorption or extraction methods are also retained (e.g. Macro Porous Polymer Extraction, MPPE). MPPE technology is effective for removing dissolved hydrocarbons from water with high efficiencies of >99.9% down to ppb level by means of extraction in an MPP bed. MPP beads act as a carrier for an extraction medium that absorbs and extracts hydrocarbons from water. The MPP beads are regenerated and the hydrocarbon waste is recovered for disposal at a permitted facilityl.


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9.5.2.6 Vapor Treatment Some of the remediation technologies (e.g., thermal remediation technologies such as ISTD or air stripper) discussed here generate vapors that need treatment prior to discharge. The vapor treatment associated with an ISTD or air stripper is assumed to include a thermal/catalytic oxidizer initially until the concentrations decrease below certain thresholds. The oxidizers use fuel such as natural gas or propane to burn the contaminants. Thermal oxidizers use larger amounts of fuel and burn the contaminants at high temperatures (typically 1,400ºF). Catalytic oxidizers use less fuel and destroy the contaminants at lower temperatures (typically 700ºF) by contacting the vapors on a catalyst surface. For chlorinated solvent vapors (TCE, PCE), the retained vapor treatment option is a chlorinated catalytic oxidizer with an acid gas scrubber. After influent concentrations decrease, the vapor treatment approach is typically changed to vapor-phase granular carbon adsorption until cleanup is completed. There are some instances where oxidizers cannot be used; then, carbon adsorption is used even with high influent concentrations and the carbon is regenerated frequently using steam or an equivalent method. All vapor treatment systems will need to be operated to meet the substantive requirements of SBCAPCD, though no permits would be required.

9.5.2.7 Pond Water Enhanced Evaporation Treatment As discussed earlier, discharge of treated groundwater to evaporation ponds is retained as an option because evaporation ponds are an effective means of addressing high TDS and inorganics in groundwater treated for VOCs. Enhanced evaporation technologies such as those used in mines to reduce water volume are considered for use because they are effective technologies that can reduce the volume of pond water prior to remedy implementation and can reduce pond water volume in the future during wet years when extracted groundwater and stormwater volumes peak. Enhanced evaporation is a mechanical means of evaporation achieved by enhancing the contact between water and air using turbine blower technology that creates a fine mist of water droplets. The rate of evaporation will depend on climate factors at the site such as temperature, humidity and wind speed. In addition, the equipment can enhance evaporation by the production of very small droplets (<100 micron) that have a higher “hang time” and high speeds at which the droplets are ejected through nozzles by the blower. Enhanced evaporators are mechanical evaporation solutions, frequently used by industry, to meet zero discharge regulations with new or existing evaporation ponds. Some portable evaporators, or misters, can reduce the size of evaporation ponds required by enhancing the natural evaporation rate. These evaporators can pump up to 80 gpm of water and in ideal site conditions result in evaporation of greater than 10,000,000 gallons per year. This technology has been shown to handle high TDS in water and is relatively low in operating cost. Frequent changeouts of the nozzles can be anticipated when high dissolved solids are present in the pond water. Drift of the spray is a potential concern depending on wind speeds and direction and the exact location of the unit in regards to the site boundary. One of the options that has been used at some sites is netting (about 15 feet high) to capture spray drift. Another approach involves the use of wind speed sensors to automate shutdown and startup for the units if the wind exceeds specific parameters.


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9.5.2.8 Monitoring Monitoring is included as a technology component in the remedial alternatives evaluated in the FS. Monitoring includes activities such as monitoring of ICs, monitoring of an active remedial option during treatment, monitoring of a containment system and long-term monitoring after treatment. Five-year reviews will be conducted that will include monitoring the effectiveness of the various remedies at the site. Monitoring of various environmental media such as groundwater or stormwater can also be conducted, as described below. The FS includes some general discussions of current and suggested enhancements to existing monitoring program. The details of each long term monitoring program, however, will be developed and revised progressively, subject to EPA approval, through RD, remedial action and the transition into long-term OM&M. Groundwater Monitoring Long term Groundwater monitoring will indicate unanticipated/adverse changes in NAPL or dissolved-phase contaminant distributions at the site over time after any RAs. A point-of-compliance groundwater monitoring program will be developed in accordance with requirements for the Groundwater ROD and subsequent Groundwater Remedial Design Orders. Focused groundwater monitoring may be conducted during any active remedial system operation, to confirm remedy effectiveness in the vicinity of a source area. Groundwater monitoring of wells is currently being conducted annually and is included as part of all FS Area 5 remedial alternatives. The current details of the wells to be sampled and the analytes which are tested are outlined in RGMEW Workplan, dated March 2009 (CSC 2009a). It is anticipated that groundwater sampling may be revised, subject to EPA approval, throughout implementation of the remedial action. Stormwater/Sediment Monitoring Where engineering controls such as stormwater and erosion controls are implemented to prevent soil contaminants migration in stormwater runoff, long term maintenance and monitoring would be required to ensure effective operation. This includes periodic sampling of stormwater, monitoring of swales, drains, manholes, sediment removal, etc. This component also includes monitoring for erosion and repair of eroding slopes and vegetative layer monitoring and maintenance on capped surfaces, drainage channels, etc. Monitoring of Constructed Remedies This includes the maintenance and monitoring of all previously constructed remedies and remedies proposed after the completion of this feasibility study. Monitoring would include a variety of system-specific monitoring strategies intended to address: (A) performance monitoring, (B) detection monitoring (e.g., early detection of possible releases), and (C) compliance monitoring to ensure compliance with performance standards. Monitoring may include sampling of site media (surface water, groundwater, soil, and soil vapor); instrumentation to monitor performance of individual site systems; and leak detection and notification instrumentation. The previously constructed remedies would include a wide range of existing features such as the PSCT groundwater extraction and treatment system including the extraction wells, the Gallery Well and associated extraction system, the PCT groundwater


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extraction system, the extraction trenches and the clay barriers. Periodic replacement of existing features including the PSCT treatment system storage tanks are anticipated to occur about every 10 to 15 years. Periodic replacement of the PCT extraction trenches may be necessary as they are likely to get clogged with deposits with long term operation (e.g. 20 to 30 years). Long term repairs and maintenance are included as components in the remedial alternatives discussed later in this FS. As discussed earlier, it is anticipated that restrictive covenants would be implemented that would require that the caps or other controls be protected for the long term.

9.6 References CSC, 2011. Final Remedial Investigation Report, January 2011 CSC, 2009. Remedial Action Objectives Technical memorandum, August 2009 CSC, 2004. Remedial Investigation/Feasibility Study Work Plan, June 2004. FRTR, 2011. Federal Remediation Technologies Roundtable, http://www.frtr.gov and http://costperformance.org websites with technology and cost information. USEPA, 1988. Guidance for Conducting Remedial Investigations and Feasibility Studies Under CERCLA, EPA 540/G-89/004, October 1988 USEPA, 2000. A Guide to Developing and Documenting Cost Estimates during the Feasibility Study, US EPA and US Army Corps of Engineers, EPA 540-R-00-002 July 2000 CSC 2009a Routine Groundwater Monitoring Element of Work, Field Sampling Work Plan, MACTEC, March 31, 2009

CSC 2009b Sampling Plan for Soil Gas Monitoring, CSC April 6, 2009

USEPA, 2011 Fact Sheet on Evapotranspiration Cover Systems for Waste Containment EPA 542-F-11-001 February 2001

USEPA, 2003 Evapotranspiration Landfill Cover Systems Fact Sheet EPA 542-F-03-015 September 2003.

ITRC, 2003 Technical and Regulatory Guidance for Design, Installation, and Monitoring of Alternative Final Landfill Covers, ITRC, December 2003

USEPA, 2004 Draft Technical Guidance for RCRA/CERCLA Final Covers, US EPA, EPA 540-R-04-007, April 2004.


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10.0 DEVELOPMENT AND SCREENING OF AREA-SPECIFIC REMEDIAL ALTERNATIVES

Based on the technologies retained in the technology screening evaluation in Section 9, Section 10 develops a range of remedial alternatives for each FS Area and presents area-specific alternatives evaluation of those remedial alternatives. The remedial alternatives are based on applicable and retained remedial technologies from Section 9 with the goal of meeting the RAOs and PRGs defined earlier in Section 8. Table 10-1 lists and summarizes the area-specific remedial alternatives that are developed and evaluated in this section by FS Area. Tables 10-2 through 10-6 present the screening evaluation by FS Area in accordance with the three criteria identified in the CERCLA guidance (USEPA 1988). The screening evaluation will screen out any remedial alternatives that do not rate well on the three screening criteria (effectiveness, implementability, and cost), as required by the NCP, with the goal of selecting the appropriate area-specific remedial alternatives for the detailed CERCLA ranking criteria evaluation (also referred to as detailed evaluation) that is presented in Section 11, and ultimately the site-wide remedial alternatives that are developed and evaluated in Section 12. A green remediation assessment is also included for each alternative. Later in Section 12, Table 12-3 provides a road map to help track the area-specific alternatives that are developed and screened in this section, the area-specific alternatives that are retained for the detailed evaluation in Section 11, and the SWRs that are finally developed for detailed evaluation in Section 12. The circles shown for the area-specific screening evaluation and area-specific detailed evaluation are partially filled by quarters and correspond to the 5-point rating system used to evaluate the 3-criteria screening level and detailed evaluations. Filled circles are the most desirable and non-filled circles are the least desirable. Filled circles are then used to indicate which area-specific alternatives are assembled into the six site-wide remedial alternatives that are evaluated in Section 12. This section first presents a summary of the screening process and common background information that is useful in understanding the development and screening evaluation of the remedial alternatives for the various FS Areas that are described later in Section 10. The following paragraph describes the screening process. Section 10.1 provides the common background information for understanding the remedial alternatives. Sections 10.2 through 10.6 provide the development and evaluation for each of the FS Areas. The nature and extent of contamination of the Casmalia Resources Superfund Site was described from a site-wide perspective by contaminant type in Section 5. Here, for Sections 10.2 through 10.6 for each FS Area, the primary COCs, their extent of contamination and risk are described prior to development and evaluation of the remedial alternatives. The remedial alternatives are in turn based on applicable and retained remedial technologies from Section 9 with the goal of meeting the RAOs and PRGs defined earlier in Section 8. The screening evaluation in Sections 10.2 through 10.6 will compare the area-specific remedial alternatives based on the three screening criteria: effectiveness, implementability and cost (defined in Section 9). In addition, the screening process presents a green remediation assessment that evaluates the green and sustainability impacts (also called environmental footprint) including greenhouse gas (GHG) emissions (carbon footprint), resource usage such as fuels, water and landfills, other contaminant emissions, etc. The green remediation assessment, however, is not explicitly included in the detailed CERCLA ranking criteria evaluation. The screening evaluation uses a rating scale ranging from poor, poor to moderate, moderate, moderate to good, and good for effectiveness and implementability. For cost and


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green remediation assessment, the rating scale for the estimated costs and sustainability impacts (environmental footprint) ranges from low, low to moderate, moderate, moderate to high, high and very high. The screening evaluation is intended to screen out any remedial alternatives that do not rate well on these criteria with the goal of selecting the most appropriate remedial alternatives for the detailed evaluation that is presented in Section 11 of the FS. 10.1 Background Information for Technologies Considered This section provides background information regarding various common component technologies and factors that relate to multiple area-wide remedial alternatives being considered for the site. In lieu of repeating the descriptions of these technologies (e.g., capping) under each applicable remedial alternative discussed below, relevant background information is presented only once. Relevant background information is provided below for the following technologies/factors that bear on the remedial alternatives under consideration for the site:

Capping and Pond Lining Technologies Soil Management Considerations Stormwater and Pond Water Management Proposed Evaporation Pond HELP and Groundwater Flow Modeling Long-Term Monitoring Monitored Natural Attenuation Groundwater FS Area 5 North (TI Zone) Source Removal and Containment Groundwater FS Areas 5 South and West Remediation and Containment

10.1.1 Capping and Pond Lining Technologies Considered in the Evaluation Capping technologies represent common components that play significant roles in the evaluation for FS Areas 1 through 4 relating to soil contamination. In addition, pond lining technologies play a significant role in the evaluation for FS Area 4 relating to the temporary retention of stormwater (for stormwater management purposes) and the holding of partially treated groundwater (for disposal purposes). The capping technologies considered range from a simple asphalt cap to ecological-caps and more complex caps such as RCRA-equivalent caps and multi-layer RCRA-caps. The pond lining technologies range from simple single-layer pond liners for stormwater management purposes to complex liners such as multi-layer RCRA pond liners for partially treated groundwater disposal purposes. This section presents a brief description of these caps and pond liners prior to the actual remedial alternative descriptions in Sections 10 and 11. These are preliminary specifications, and detailed specifications and testing would be determined during remedial design to fully specify the cap designs for each FS Area. Figure 10-1A shows typical cross section details for six of these caps and two pond liners. The six capping technologies and two pond liner technologies considered in this FS include the following:


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Capping Technologies Pond Liner Technologies

Multi-layer RCRA cap RCRA-Equivalent cap Mono Soil cap Evapotranspiration (ET) cap RCRA-Equivalent Hybrid cap Ecological cap Asphalt cap

Single-Layer Pond Liner o (clean stormwater)

Multi-layer RCRA Pond Liner

o (evaporation pond)

Performance standards for each of these cap technologies are further discussed below. Note on terminology: Throughout this FS, the term “RCRA cap” is used synonymously with a RCRA-prescriptive cap, which is the multi-layered cap configuration presented in RCRA Subtitle C Regulations. In contrast, a “RCRA-equivalent” cap achieves RCRA performance standards (e.g., hydraulic conductivity), but retains flexibility in terms of materials and engineering design. As listed above, a range of cap technologies is evaluated for the landfill areas, ponds and other impacted soils at the site. As discussed in Section 9, some of the caps are intended to create a barrier to rainwater infiltration, some significantly reduce infiltration but do not prevent infiltration altogether, and other caps are intended primarily to prevent direct physical contact exposure to contaminants in soil but do not restrict infiltration into groundwater. In general, the approach to stormwater is to create sloped surfaces and include surface drains to direct clean stormwater from capped areas to the B-Drainage. The following briefly discusses the approach to capping and the general performance objectives of caps or pond lining technologies for FS Areas 1 through 4 at the site. Some of the landfill areas such as the PCB Landfill and the Burial Trench Area (BTA) have primary wastes where higher levels of contaminants will be left in place. Primary wastes are those wastes that were originally disposed in the Waste Management Units during the 1970s and 1980s. For the PCB Landfill, the FS assumes a RCRA cap as a presumptive remedy in order to prevent infiltration. The performance standard for RCRA cap permeability for this primary waste area is 10-6 cm/sec. In reality, the actual permeability of the HDPE liner (k<10-12 cm/sec) will substantially outperform the minimum performance standard. For other landfill areas such as the BTA, the FS evaluates RCRA or RCRA-equivalent caps including those with geosynthetics (RCRA cap, Hybrid cap) and some without geosynthetics (RCRA-equivalent mono soil cap or Evapotranspirative soil cap). For other areas such as the Central Drainage Area (CDA) that is directly downgradient of the primary waste landfill areas (e.g. P/S Landfill), and which have highly impacted groundwater and NAPL at depth and some shallow soil contamination, these areas are essentially treated similar to the primary waste landfill areas with RCRA or RCRA-equivalent caps. For the Maintenance Shed Area (MSA) (adjacent to the BTA and the P/S Landfill), a RCRA cap is considered as a primary option to match the existing Capped Landfills Area and the other RCRA or RCRA-equivalent caps considered for the CDA, BTA and PCB Landfill. A RCRA cap on the MSA will serve to prevent infiltration and thereby minimize contaminant migration in groundwater in Area 5 North. With this approach, the areas north of the PSCT are to be capped with essentially zero infiltration caps. This would result in one large (approximately 90-acre), contiguous zero infiltration cap for areas lying north of the PSCT, and also significantly lower the water table and the future extraction rates from the PSCT. For RCRA Canyon West Canyon Spray Area (WCSA), where drilling mud wastes were sprayed on the canyon slopes, the soils are impacted with metals that primarily pose a risk to ecological


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receptors. The choice of caps in this area is driven by the need to prevent direct soil contact by ecological receptors and the need to address cap stability concerns with the steep slopes of the canyon. In terms of geotechnical engineering, conventional geosynthetic lined caps could face serious slope stability problems. Slippage along boundaries between capping layers, for example, could pose a significant challenge and create instability. The choices of caps in this area include a RCRA-equivalent mono soil cap, ET cap and/or a Hybrid cap with a spiked geosynthetic liner for enhanced slope stability. For the area south of the PSCT, the impacted area at Ponds A/B and other shallow soils impacted with metals/organics are considered for either installation of a RCRA cap to prevent infiltration, or for soil excavation. For the other areas south of the PSCT, grading and BMPs will be implemented to reduce erosion and improve stormwater flow and quality out to Pond 13. At the Liquids Treatment Area where shallow impacted soils are present, an asphalt cap is considered, both with and without excavation. An asphalt cap is assumed for this area because it both protects against direct soil contact by ecological receptors and is an appropriate surface for the location of the current or future treatment system. For the existing ponds where the sediments are known to be impacted with metals that pose a potential ecological risk, a variety of cap options are considered, depending on the future use of the pond. Ponds A-5 and Pond 13 are considered important parts of the future stormwater plan for the

site where they would serve as stormwater retention basins. These retention basins would serve to temporarily impound and direct stormwater to the B-Drainage, and would be lined with a geosynthetic HDPE liner in order to minimize infiltration into groundwater. The construction of these retention basins would require raising the pond bottoms to prevent groundwater intrusion and so that stormwater flow through them would not require excessive pumping.

Pond 18 is not proposed to be used in the future, thus this pond will be backfilled to raise the

pond bottom and be topped with a RCRA cap to eliminate potential infiltration through the sediments, and the cap surface sloped to allow clean stormwater to run off.

The A-Series and RCF Ponds are primarily being evaluated for ecological caps that

eliminate potential direct contact exposures to ecological receptors. Prevention of infiltration is not the primary goal of the caps on the A-Series and RCF Ponds. However, many of the sitewide alternatives include the need for an evaporation pond for the disposal of partially treated groundwater. Stormwater from RCRA Canyon may also be diverted into an evaporation pond under one remedial alternative. The footprint of the A-Series Pond is the primary location being considered for a partially treated groundwater (and stormwater for one alternative) evaporation pond. This evaporation pond, or several smaller ponds, would contain extracted groundwater that is treated for organics but not for TDS and metals. As a result, the metals concentrations and salinity would become very high (i.e. brine). A significant portion of the metals and salinity in the extracted groundwater will originate from the primary waste materials north of the PSCT. Consequently, the evaporation pond will include a multi-layer RCRA liner to prevent infiltration of water containing high concentrations of metals and salinity. The multi-layer RCRA liner would be constructed with a double liner system that would include leak detection and a LCRS between the liners and a leak detection system beneath the liners. The construction of an evaporation pond would require raising the pond bottom to prevent groundwater intrusion and placing the liner


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system at the bottom which will serve as a cap over impacted sediments and prevent infiltration into groundwater.

Generally, the FS currently envisions that the RCF Pond would be closed. The RCF Pond

bottom would be raised by about 5 feet or more to prevent groundwater intrusion prior to construction of an overlying ecological cap on the RCF Pond. The surface of the ecological cap would be sloped and equipped with surface drains to collect and drain stormwater to Pond 13, which would also reduce infiltration compared to standing water in a pond.

The infiltration rates for various cap configurations used in FS Areas 1 through 4 were estimated using the HELP model as discussed below in Section 10.1.5. The following sections describe the design and construction considerations for the various types of caps and pond liners being considered. 10.1.1.1 RCRA Cap The conceptual RCRA cap design is similar to the existing RCRA cap that has been previously constructed on the EE/CA Area and is shown in Figure 10-1A. It includes the following layers from top down:

2-foot thick vegetative soil layer HDPE geonet biotic barrier geocomposite drainage layer 60-mil thick HDPE geomembrane GCL foundation layer

The vegetative layer is the upper-most layer of the cap that is intended to promote growth of vegetation, reduce wind and water erosion, and protect the underlying elements from damage. The vegetative top soil layer is 2 feet thick and lightly compacted (85 percent of maximum dry density, ASTM D 1557) to allow vegetation growth. The soils would be amended with biosolid and other amendments such as gypsum, fertilizer or mulch to enhance vegetation growth. A biotic barrier is included to limit burrowing of small animals through the geosynthetic layer. In this FS, a biotic barrier material primarily refers to synthetic materials such as a 200-mil HDPE geonet. This specific type of biotic barrier has been utilized at other sites and has also been utilized as a component in the engineered EE/CA Area cap previously constructed at this site. The drainage layer below intercepts water that enters the cap system and conveys it to surface water structures and thus reduces the potential of water infiltration into the low permeability layer. The geocomposite drainage layer is composed of a geotextile to protect the drainage layer from root impact, a geonet, and another geotextile sandwiched together to enhance drainage from the cap. The upper geotextile layer of the composite is intended to serve as a filter to reduce migration of fine particles that may clog the drainage layer. The low permeability layer of the cap system provides the primary control of water infiltration. The primary low permeability layer is a 60-mil, double-sided, textured, HDPE membrane. The HDPE membrane has an effective permeability <10-12 cm/sec per the manufacturer’s liner specification. Below this would be a low permeability GCL liner that is a needle-punched reinforced composite geosynthetic clay liner comprised of a uniform layer of granular sodium bentonite encapsulated between a woven and a nonwoven geotextile. This product is good for moderate to steep slopes and moderate to high load applications and a hydraulic conductivity of <10-9 cms/sec. The GCL


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is placed over a foundation layer composed of clayey soil compacted to attain a minimum of 90 percent compaction (ASTM D 1557). The construction of this type of cap starts with grading a leveling layer that would include cut and fill as needed to get the appropriate grade and slopes to construct the cap. The leveling process would reduce any areas of steep slopes to approximately 3:1 or less. At the top of the slope, the liner would be anchored typically in an anchor trench (typical 2 feet wide by 2 feet deep) and compacted soil placed over it. The design details of the required slope for any RCRA cap will be finalized during remedial design. A foundation layer of up to 2 feet thickness would be placed on top of the leveling layer. The borrow soil for the foundation layer and the vegetative layer are assumed to be from the borrow area discussed later in this section. The cut/fill soils for the leveling layer are primarily assumed to be from the same area that is being capped. A brief discussion of pre-processing and amendments required for the vegetative layer and the foundation layer during the prior construction of the P/S Landfill and the EE/CA Area Caps is presented in Section 10.1.2. Similar requirements for pre-processing and soil amendments are anticipated forthe NW borrow soils to achieve these performance criteria. The character and suitability of borrow soils would be further evaluated during remedial design. 10.1.1.2 RCRA-Equivalent Mono Soil Cap The conceptual RCRA-equivalent mono soil cap design is shown on Figure 10-1A and includes the following:

5-foot thick clay monocover Bottom 4 feet of compacted clay soils to 90 percent compaction Upper 1 foot of vegetative layer that is lightly compacted clayey soils to 85 percent

compaction (ASTM D 1557) The performance standard for this low permeability cap is to provide a compacted hydraulic conductivity of 1x10-6 cm/sec. This 5-foot monocover would meet all of the requirements of a RCRA cap, including specifications for infiltration, and satisfies the RAOs established for stormwater management and groundwater. As discussed later in Section 10.1.5, the proposed remedial alternatives which include a RCRA equivalent cap have been modeled using both the HELP infiltration model and the Groundwater Flow Model to demonstrate that the infiltration through a cap with a 1x10-6 cm/s hydraulic conductivity meets all RCRA cap requirements, and that there is an insignificant difference in infiltration for this monosoil cap as compared to a RCRA cap with lower conductivity. The monosoil cap, however, is potentially vulnerable to desiccation and cracking and therefore is not considered optimal for areas requiring the highest level of protection against infiltration. The construction of the RCRA-equivalent cap would start with grading a leveling layer that would include cut and fill as needed to get the appropriate grade and slopes to construct the cap. The 5-foot thick clay layer will be placed on top of the leveling layer in 6-inch lifts and compacted to attain a minimum of 90 percent compaction (ASTM D 1557) and meet the performance standard of 1x10-6 cm/sec for hydraulic conductivity. As with the other caps, the top vegetative layer soil will be treated with organic amendments and hydroseeded with a seed mix of native plant species to enable growth of the selected vegetation. When compacted to the above relative compaction standard, the following shear strength criteria should be met: internal angle of friction, ’ = 30o and cohesive strength, c’ = 100 psf (ASTM D4767). Additional shear strength criteria would be developed during remedial design for sloped areas and for any sloped


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areas using reinforcement (e.g., geogrids). Preliminary specification for the monocover soil is that it be classified by the Unified Soil Classification System as CL, SC or ML and have greater than 50 percent fines content. Detailed specifications would be developed during remedial design. Borrow soil or construction processes would be modified and/or augmented as necessary to meet specifications. The clay soil would be borrowed from a borrow area located outside the site historical boundaries, as discussed below in Section 10.1.2. The weathered claystone borrow material that is being considered to utilize in cap construction may need to be pre-processed to meet the hydraulic conductivity performance criterion. The top 1 foot layer will be the vegetative layer that is more lightly compacted (85 percent of maximum dry density) and would be amended with biosolid and other amendments to enhance vegetation growth. A brief discussion of pre-processing and amendments required for vegetative layer and foundation layer during the construction of the P/S Landfill and the EE/CA Area Caps is presented in Section 10.1.2. Similar requirements are anticipated with NW Borrow soils proposed for the caps evaluated in the FS to achieve these performance criteria. The character and suitability of borrow area soils would be further evaluated during remedial design. 10.1.1.3 Evapotranspiration Cap The conceptual evapotranspiration (ET) soil cap design is shown on Figure 10-1A and includes the following:

5-foot thick total soil cap Bottom 1 foot of compacted clay soils to 90 percent compaction Upper 4 feet of soil storage/vegetative layer that is lightly compacted clayey soils to 85

percent compaction (ASTM D 1557) Claystone material from borrow areas may require pre-processing to remove clods from

excavated material Vegetation from the area planted with roots extending into the upper 4-foot thick

vegetative layer ET caps are designed to utilize the hydrologic properties of soil and vegetation to prevent infiltration into wastes. ET caps store precipitation in a soil layer until it is naturally evaporated or is transpired by the vegetative cover. They differ from more conventional cover designs, which create physical barriers, in that they rely on having a sufficient water storage capacity in the soil rather than an as-built engineered low hydraulic conductivity. The greater the storage capacity and evapotranspirative properties are, the lower the potential for percolation through the cover system. The difference between an ET cap and the RCRA-equivalent clay cap is that the ET caps are only lightly compacted in the upper vegetative layer to ensure vegetation growth and hence a greater reliance on evapotranspiration to minimize infiltration. ET cap designs typically include the following (USEPA 2011a):

• Fine-grained soils, such as silts/clayey silts that have a high water storage capacity • Appropriate vegetation for long-term stability and evapotranspiration • Locally available soils to streamline construction and provide for cost savings

ET caps are constructed typically as monocaps using a single fine-grained (or graded) soil layer to retain water and support the vegetative community. ET caps can be lower in cost compared to conventional clay caps especially in arid and semi-arid regions (e.g., areas with less than 10 inches and 20 inches of rain per year, respectively). In these environments, they may be less


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prone to deterioration from desiccation, cracking, and freezing/thawing cycles. ET caps also tend to exhibit better stability characteristics in sloped areas, because they do not contain geomembrane layers, which may allow slippage. However, site specific conditions, such as site location (e.g., appropriate soil, landfill characteristics) and local climatic conditions (amount, seasonal distribution, and form of precipitation) can limit the effectiveness of an ET cover at a given site. Vegetation is selected to promote transpiration and minimize erosion by stabilizing the surface of the cover. Appropriate grasses, shrubs, and trees for the ET cover would be identified during design. A mixture of native plants would generally be planted, because they are usually more tolerant to regional conditions. A combination of warm- and cool-season species should provide water uptake throughout the entire growing season, which would enhance transpiration (Dwyer et al. 1999). This 5-foot ET cover would meet a similar infiltration performance standard to that of the 5-foot clay monocover discussed earlier, and satisfy the RAOs established for stormwater management and groundwater. As discussed later in Section 10.1.5, the proposed remedial alternatives have been modeled using both the HELP infiltration model and the Groundwater Flow Model to estimate infiltration rates through an ET cap and RCRA equivalent mono soil cap under simulated climatic conditions and demonstrate that there is an insignificant difference in infiltration as compared to a RCRA cap with lower conductivity. The construction of the ET cap would start with grading a leveling layer that would include cut and fill as necessary to get the appropriate grade and slopes to construct the cap. The 1 foot thick foundation clay layer will be placed on top of the leveling layer in 6-inch lifts and compacted to attain a minimum of 90 percent compaction (ASTM D 1557) and meet the performance standard of 1x10-6 cm/sec for hydraulic conductivity. The upper 4 feet of the vegetative layer will be placed in 12-inch lifts and lightly compacted to 85 percent relative compaction to allow vegetative growth. Shear strength criteria would be developed during remedial design for sloped areas and for any sloped areas using reinforcement (e.g., geogrids). Preliminary specification for the ET cap monocover soil is that it be classified by the Unified Soil Classification System as CL, SC or ML and have greater than 50 percent fines content. Detailed specifications would be developed during remedial design. Borrow soil or construction processes would be modified and/or augmented as necessary to meet specifications. The clay soil would be borrowed from the borrow area discussed below in Section 10.1.2. The weathered claystone borrow material preliminarily proposed to be utilized in cap construction may need to be pre-processed to meet the hydraulic conductivity performance criterion. Also, the vegetative layer would likely need biosolid amendments to enhance vegetation growth. These soils have been used previously during the P/S Landfill cap project to achieve the appropriate performance criteria. The borrow area soils would be further evaluated during remedial design. More discussion on the borrow areas is presented below in Section 10.1.2. Instrumentation to Monitor Performance of the ET Cap The criterion for judging the performance of an ET cap involves assessing the water balance for the system. The instrumentation proposed for monitoring the water balance would be one or more drainage lysimeter(s) similar in design to those used in the Alternative Cover Assessment Project (ACAP), where conventional covers (with resistive barriers) were compared with alternative covers (that rely on water storage principles) (Albright, W.H et al. 2010). The


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comparisons were carried out using instrumented drainage lysimeters that monitored various parameters of the water balance such as percolation, runoff and water storage (using moisture sensors) to enable estimation of evapotranspiration. The lysimeter(s) would be constructed adjacent to or within one section of the cap. Some general aspects of the construction design for an ACAP-type lysimeter are shown in Detail I on Figure 10-1A and include a sloped “bath tub” installation (e.g. 4:1 slope) with the base and sidewalls lined with a linear-low density polyethylene (LLDPE) geomembrane and a base geocomposite drainage layer to transmit water from the base of the cover to the collection and monitoring system. The cover soil layer would be lightly compacted and constructed similar to the cap. Determination of Appropriate ET Cover Thickness Typically, pilot testing would not be required to determine the appropriate soil thickness for the ET cover. Design computations can be performed to obtain a conservative estimate of the required thickness of the cover. The primary parameters addressed in the remedial design process will include: “required storage” – quantity of water that must be stored for the meteorological conditions at the site; and, “available storage” – quantity of water that can be stored in the proposed cover profile. The required storage equals the net infiltration during the wetter period of the year when precipitation exceeds evapotranspiration. Semi-empirical methods developed during the ACAP program will be used to estimate “required storage” and “cover thickness” during remedial design (Albright, W. et al., 2004). Optimal Soil Compaction, Soil Amendments and Vegetative Cover Soil bulk density can affect root penetration, water storage and water movement. Bulk density specifications during the construction of the ET cover soil should be established to prevent over-compaction. Excessive compaction by heavy equipment is a common problem during construction of ET covers. The dry unit weight of an undisturbed reference area is a good target to use for bulk density needs. Agronomic tests would be carried out to determine the soil amendments needed to optimize plant growth. The optimal vegetative cover would consist of native plants (well-adapted to the site) with deep roots that take up water from the entire thickness of the cover soils. 10.1.1.4 RCRA-Equivalent Hybrid Cap The conceptual RCRA-equivalent hybrid cap design is shown on Figure 10-1A and consists of the following layers:

2-foot thick vegetative layer HDPE geonet biotic barrier geocomposite drainage layer structured or embossed HDPE geosynthetic liner to reduce slip (e.g., spiked

geosynthetic liner) foundation layer

The construction of the cap would start with the leveling layer that would include cut and fill as necessary to get the appropriate grade and slopes to construct the cap. This liner is typically


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preferred in areas with steeper slopes, such as in the RCRA Canyon/WCSA (FS Area 2). The leveling process would reduce the areas of steep slopes to approximately 2:1 or less. A foundation layer of up to 2 feet thickness would be constructed with soils from the leveling process. A structured or embossed HDPE liner with spikes or equivalent would be placed on the foundation layer. The spikes on the underside of the liner are intended to reduce slip plane failures of the soil that is placed on top of the liner on steep slopes. These liners have been used as part of a capping system on 2:1 slopes at other sites. A geocomposite drainage layer would be placed on top of the HDPE liner, followed by a 2-foot vegetative layer that is hydroseeded. A biotic barrier is included above the drainage layer to limit burrowing animals from damaging the geosynthetic layer. Finally, the vegetative layer would be placed in 12” lifts and lightly compacted (85 percent of maximum dry density), and would be amended with biosolids and other amendments such as fertilizers or gypsum to enhance vegetation growth. Alternate options to replace the soil vegetative layer with synthetic products will be investigated if this alternative is selected. The soils for the foundation and vegetative layer would be obtained from the borrow area that is discussed later in this section. At the top of the slope, the liner would be anchored typically in an anchor trench (typical 2 feet wide by 2 feet deep) and compacted soil placed over it. Design details of the hybrid cap will be finalized during remedial design if this alternative is selected. 10.1.1.5 Ecological Cap The conceptual ecological cap (or ecological-cap) design is intended to prevent potential direct contact exposures to contaminants in shallow soil (0-5 feet bgs). The ecological cap is shown on Figure 10-1A and includes the following:

2-foot thick soil cover foundation layer

Ecological-caps are effective at addressing areas where the goal is to reduce the risk of ecological exposure which is the result of direct exposure to contaminants present in relatively shallow soil. Some cut/fill grading is assumed prior to capping as necessary to reduce the steepness of some of the sloped areas. A 2-foot soil cover is proposed rather than a 1-foot cover because it is considered better from a long term cap maintenance perspective. The 2-foot cover would use clayey soils obtained from borrow areas that are placed in 1-foot lifts. The first lift would be compacted to 90 percent relative compaction and the upper lift would be lightly compacted (85 percent compaction) and hydroseeded to allow vegetative growth. This soil cover surface would include a limited number of surface drains, and stormwater would largely sheet flow off the cap surface to the nearest concrete V-drains or stormwater channel. Erosion control measures would be incorporated to reduce erosion of the soil cover including, if needed, turf reinforcement mats on steep slopes. 10.1.1.6 Asphalt Cap The FS considers an asphalt cap at one area of the site (Liquids Treatment Area - LTA) with the objective of mitigating potential direct soil contact exposures to ecological species, and which would also serve as an asphalt surface for a road or storage area. The asphalt cap assumes a 4” thick asphalt surface with a 4” thick gravel base below it (Figure 10-1A). The asphalt cap in the LTA would also serve as a surface for placement of existing and future treatment equipment, storage tanks, etc.


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10.1.1.7 Pond Liner for Stormwater Retention Basins The FS evaluates and proposes liners for stormwater basins for several proposed pond features at the site. The proposed stormwater pond liner construction is shown on Figure 10-1A and includes the following layers:

1-foot soil cover Geocomposite HDPE liner 2-foot foundation layer

As with several other proposed cap options considered, an HDPE liner would be placed on top of a 2-foot thick foundation layer after leveling, if needed. The foundation layer should be compacted to 90 percent of maximum dry density per ASTM Standard D1557 and rolled with a smooth-drum compactor to ensure a smooth surface. The HDPE liner selected for this application is a geocomposite liner with a geotextile layer comprising bentonite on top adhered to a HDPE membrane below. On top of the liner, a 1-foot soil cover (typically sandy soil) would be placed. At the top of the slope, the liner would typically be anchored in an anchor trench (typical 2 feet wide by 2 feet deep) and compacted soil placed over it. Design details of the pond liner will be finalized during remedial design. Recommended pond depths with these liners are typically 15 feet. The stormwater retention basins would be designed to capture stormwater from the 100-year, 24-hour storm event. 10.1.1.8 Multi-Layer RCRA Pond Liner for Evaporation Ponds This section describes the liner system to be used for evaporation ponds, which would be constructed as follows, from top down:

A primary 60-mil thick HDPE geomembrane A 300-mil geonet drainage layer, as a lLCRS A secondary 60-mil thick HDPE geomembrane in lieu of a clay liner Vadose zone monitoring beneath the bottom HDPE geomembrane A 2-foot prepared subgrade or foundation layer

A double liner system is proposed including a primary 60-mil smooth HDPE geomembrane on the top with a drainage layer in the middle, followed by a secondary HDPE geomembrane below that is underlain by a 2-foot foundation layer. An HDPE liner was chosen for its long term performance due to its chemical resistance properties, resistance to ultraviolet radiation, high tensile strength, and high stress-crack resistance. The evaporation pond liner will be designed for long-term solar radiation exposure. A standard black HDPE geomembrane is proposed as the upper (primary) liner for increased heat retention to enhance evaporation potential. The drainage layer drains by gravity any liquids leaking through the primary layer into a sump as part of a LCRS. The secondary HDPE geomembrane is placed on a compacted foundation layer that is sloped at 1 percent or greater to allow gravity drainage towards an LCRS sump located within the footprint of the evaporation pond. The LCRS sump will be equipped with a liquids pump that is piped to an above ground storage tank. In addition, a leak detection system (such as lysimeters) to detect leaks in the vadose zone below the secondary layer will be evaluated during design. Other choices for leak detection include options such as using an


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electrically conductive geomembrane that has a thin conducting sheet adhered to the geomembrane that can help identify leaks. The LCRS would be designed per 40 CFR 264.221 (by reference from 10 CFR 40 and 6 CCR 1007-1, Part 18). If a leak occurs in the upper primary geomembrane, the LCRS is designed to minimize the hydraulic heads on the lower geomembrane liner by utilization of HDPE geonet. In addition, the geonet drainage material will have a transmissivity of 3x10-4 m2/sec or greater. The foundation layer shall be at least 2 feet thick and compacted to 90 percent relative compaction to yield a hydraulic conductivity of no more than 1x10-6 cm/sec. For leak detection, the geomembranes are typically tested after installation in accordance with ASTM D 7240, Geomembrane spark testing standards. The LCRS would be designed to handle the runoff from a 100-year, 24-hour storm event. 10.1.2 Soil Management Considerations Remedial alternatives being considered for the site involve both the use of borrow soil for cap construction purposes and the local excavation and disposal at the site of impacted soil from some specific identified areas. This section discusses the factors to consider in the evaluation and management of soil for the remedial technologies being considered in the FS. These factors include: location of soil borrow areas and available soil volumes; borrow soil quality and pre-processing requirements for cap construction based on prior cap construction experience at this site; and, available landfill storage space in the PCB Landfill for any excavations being considered in the remedial alternatives evaluation. 10.1.2.1 Soil Borrow Areas As discussed earlier in this Section, capping is a key component of a large number of the remedial alternatives evaluated in this FS. Each of the different types of caps requires significant volumes of clean soil which will be compacted to meet specifications of appropriate low permeability or vegetative covers. The clean soil required for cap construction for these remedial alternatives will come from locations adjacent to the northwest corner of the site, outside the historical site boundaries. Borrow soils for previous cap construction at the P/S Landfill and EE/CA Areas were taken from areas similar to the borrow soil areas currently proposed. As was the case during previous cap construction work at the site, the borrow soils are expected to be clean (i.e., contain no contaminants above previously established background concentrations), but this would be confirmed during remedial design. These borrow soils are part of the weathered claystone formation in the Upper HSU and have a high fines content. Figure 10-2 shows the preliminary location of the borrow areas labeled Borrow Areas A and B. Borrow Areas A and B are jointly referred to in the FS as the NW Borrow Area. Borrow Area A is in close proximity to the western property boundary and is estimated to produce approximately 10,000 cy per foot of cut. This area would be an ideal location for capping activities in the RCRA Canyon because of its proximity, especially to the west slope of the RCRA Canyon. Borrow Area B is further to the northwest and encompasses a larger area that can produce approximately 25,000 cy per foot of cut. The foundation layer and the vegetative layers would use clay soil from the NW Borrow area. The weathered claystone soils borrowed from these areas may need additional processing (e.g., for cap applications with more stringent criteria such as the RCRA-equivalent mono soil cap) to meet the hydraulic conductivity performance criteria of the compacted soils that make up


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the cap. If that is the case, the pre-processing may include screening and pulverization in a pug mill (or with a pulverizer). Site soils have been used previously during the P/S Landfill cap project and achieved stringent performance criteria with a minimum amount of additional processing that primarily involved size reduction. The character of borrow area soils would be evaluated during remedial design. In the event supplemental clay soils or bentonite are determined to be necessary, some imported materials will be supplemented as necessary to ensure the cap meets specifications. The vegetative layer may need addition of organic materials, biosolids, fertilizer, and/or nutrients to assist in vegetation growth. If a suitable amendment soil is not readily available at the site or from the NW Borrow Area, another local source of soil would be used, such as the nearby Laguna Sanitation District site. Borrow soil Properties – Prior Capping Efforts

The following is a summary of site borrow soil properties that were evaluated during the earlier design and construction of the P/S Landfill and EE/CA Area Caps. Similar properties are anticipated for the nearby NW Borrow Area soil, as is the anticipated level of processing and amendment that may be necessary prior to future soil placement and cap construction. The site borrow soil from the North Ridge was tested during previous cap construction activities and classified as MH and CH (high plasticity silt and clay) according to the Unified Soil Classification System (GeoSyntec 1999). The borrow soil was identified as a claystone material that required some crushing prior to or during placement and construction of the cap. The site borrow soil properties are described in the Design Change Request report (DCR-05, GeoSyntec 2001) as a sandy elastic silt that is a cohesive material having a density of 100 pcf, and under 2 feet of vegetative soil will have a normal stress of 200 psf or 1.4 psi. The vegetative layers had a compaction criterion of 85 percent of maximum dry density (ASTM D 1557). Some of the site borrow soils tested for use in the vegetative layer showed high levels of sodium. As a result a soil amendment including gypsum was added at a rate of 1 ton per acre to add calcium to the soils and enable vegetation growth. In addition, 2 percent biosolids (or 17 tons per acre) was mixed in the top 12 inches of the vegetative layer to enhance plant growth. Commercial fertilizer and mulch was added after the soil was placed as the vegetative layer was planted. The specifications also called for maximum ground pressure of 5 psi to be met with low ground pressure equipment. In the EE/CA Area Revised Final Design Report (GeoSyntec June 2001), GeoSyntec concluded that using site claystone compacted to a lower level of 85 percent of maximum dry density (per ASTM D1557) will provide the same or higher factors of safety as compared with imported silty sand compacted to 90 percent compaction. With regards to particle size for the vegetative layer, no more than 10 percent of particles by weight were allowed to be larger than 2-inches, with a maximum particle size of 6-inches. Soil on the side slopes and top deck were compacted to at least 90 percent of maximum dry density. For the foundation layer, material particle size requirements specified that no more than 10 percent of particles could be retained on a 1-inch sieve, a maximum particle size of 2-inches, and that soil did not contain concrete, rubble or other similar materials (DCR-04, GeoSyntec 1999). The site borrow soils were placed and compacted to achieve a hydraulic conductivity (based on ASTM D 5084) of at least 1x10-6 cm/s as verified during construction. The foundation material had undrained shear strength of 2000 psf as measured by the triaxial test (ASTM D2850). Each lift had a compacted thickness of 6”. Target compaction for the test cell was 95 percent of maximum dry density and moisture content was 4 percent above optimum (ASTM D 1557).


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10.1.2.2 Excavation Options and Site Landfill Storage Capacity All of the FS Areas that address impacted soil/sediment include alternatives that compare excavation options to capping options in the remedial evaluation. The excavation alternatives assume that the excavated impacted soil is either stored in the PCB Landfill or sent to a permitted facility. The PCB Landfill has a limited remaining storage capacity, and is proposed to be capped as part of a presumptive remedy for the landfill. As discussed later under FS Area 1 (Section 10.2), the storage capacity in the PCB Landfill is estimated to be approximately 140,000 cy prior to the construction of the presumptive RCRA cap remedy for this study area. The top elevation of waste storage in the PCB Landfill is assumed to be approximately 770 feet MSL (Figure 11-1B). The total volume of potential soil excavations considered in this FS is estimated to be significantly greater than the available storage capacity at the PCB Landfill. Hence, some of the remedial alternatives with large excavation volumes were not considered for PCB Landfill disposal (e.g., excavation of the trenches in the BTA). The cost estimates for those alternatives assumed disposal at a permitted facility of excavated soil, which is significantly higher in cost than disposal at the PCB Landfill. Another constraint is that any excavated wastes from other areas of the site that need to be placed in the PCB Landfill would need to be conducted prior to construction of the RCRA cap for the PCB Landfill. Other options for disposal of limited amounts of excavated soil include: 1) filling the bottom of ponds to raise the pond bottom (e.g., Pond A-5, Pond 13) that are proposed to be lined with a geosynthetic liner and converted to stormwater retention basins; and 2) filling the bottom of the A-Series Pond prior to conversion into a HDPE-lined evaporation pond. Primarily low level impacted soils (e.g., low concentration metals in shallow soils) were considered for placement under the HDPE liners in these former pond areas. Typically, most of the excavated areas are assumed to be backfilled with borrow soil from the NW Borrow Area. The location and physical properties of the borrow soil was discussed earlier. 10.1.3 Stormwater and Pond Water Management This section summarizes the approach to stormwater and pond water management at the site. Since many of the evaluated remedies involve dealing with stormwater runoff and closure of the existing site ponds, an integrated and site-wide approach to stormwater and pond water management is a central element to any corrective actions to be implemented at the site, and thus a critical step in the FS evaluation. 10.1.3.1 Stormwater Plan Stormwater management is an important element of any overall site remedy. Thus, the site-wide stormwater plan and related remedial objectives are discussed briefly in this section prior to the description and screening evaluation of the remedial alternatives for each FS Area. The stormwater plan is intended to meet the RAOs for stormwater management that read:

Prevent ecological exposures to COCs in surface water such that exposures are below acceptable levels (HQs less than 1 based on selected surface water benchmarks); and,

Prevent human exposures to COCs in surface water such that that total carcinogenic risks are within the NCP risk range of 10-4 to 10-6 and non-cancer hazard indices are


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less than 1. Potential human exposures include site workers, trespassers, and hypothetical local residents.

The concepts relating to the proposed site-wide stormwater plan are common to many of remedial alternatives being evaluated, and hence are presented here prior to the evaluation of alternatives. As discussed earlier, the remedies for each of the soil contamination areas (FS Areas 1 through 4) involves evaluation of a variety of different types of capping to achieve remedial objectives, and stormwater draining from each capped area requires appropriate management. In general, for areas of the site that are capped or covered with clean soil, the stormwater plan assumes discharging the clean stormwater runoff from these areas through drains or channels leading to the southern end of the site and running through a culvert under RCF Road to a proposed retention basin proposed to be constructed in the footprint of Pond 13 after it is closed. The water from this retention basin would flow through or around the existing wetlands pools and then to the B-Drainage under the substantive terms of the General Permit. The specifics of stormwater management are discussed in more detail below. Stormwater runoff from the capped portions of the site north of the PSCT but east of LTP Road (which include the PCB Landfill, the Burial Trench Area, the Maintenance Shed Area, the P/S Landfill, and the EE/CA Area) would flow to a culvert east of PSCT-1 and flow through a concrete drainage channel to the RCF Pond for discharge through or around the B-Drainage wetlands as discussed above. Stormwater runoff from the capped portions of the RCRA Canyon will sheet flow to a concrete drainage channel located in the centerline of the canyon, and will be directed into a lined retention basin which to be constructed in the footprint of Pond A-5 after it is closed. Stormwater from this area of the site will be held in this retention basin until the runoff from the east side of the site subsides, and then this stormwater would be released through the culvert under RCF Pond for discharge through or around the B-Drainage wetlands, as discussed earlier. Clean stormwater discharges from uncapped areas with BMPs that meet the substantive requirements of the site’s General Permit will also be discharged through or around the B-Drainage wetlands. If the stormwater runoff from the uncapped areas has come into contact with waste or contains site-related contamination, then this stormwater will be held and managed at the site. Further details regarding use of the General Permit and stormwater discharges from uncapped areas are discussed in Section 8.2 and under the remedial alternatives for each FS Area. 10.1.3.2 Current Pond Water Balance As of the start of the rainy season of 2012, there was a combined total of approximately 65,000,000 gallons of stormwater stored in the RCF Pond and A-Series Pond. Approximately 35,000,000 gallons were present in the RCF and approximately 30,000,000 gallons were present in the A-Series Pond. In order to remediate these ponds (which typically involves capping to close the ponds), the ponds must essentially be emptied before beginning the construction. This can be accomplished through appropriate water management practices during the years preceding remedy construction by implementing the provisions of the USEPA-approved Pond Water Management Plan and properly sequencing the remedy construction itself.


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The proposed pond water management approach includes the use of enhanced evaporation units (e.g., enhanced evaporation units, discussed in Section 9.5) within the footprint of the A-Series and RCF ponds. Mitigation measures to avoid spray drift outside of the footprint of the ponds include wind alarm systems or a control system with the ability of shut off evaporation system during excessive wind. Also, salt spray fences have been used at some sites to a avoid concerns with spray drift. The pond water management details will be finalized during remedial design and will include an evaluation of mitigation measures for the proposed enhanced evaporation. A “water balance” spreadsheet model (Appendix H) that is based on the varying site precipitation rates, includes the correlations for stormwater runoff coefficients and PSCT/PCT extraction rates, and a specific construction sequence. The proposed construction sequence is:

1. Operate the RCF and A-Series Pond enhanced evaporation system as necessary starting in 2013.

2. Transfer impounded stormwater from the A-Series Pond to the RCF Pond as necessary in order to empty the A-Series Pond first.

3. Complete the RCRA Canyon remedy (RCRA equivalent cap of the west slope and grading/BMPs of the east slope) during the first two summers of construction season (assumed in 2017). Use the stormwater of the RCF Pond as source of construction water as appropriate.

4. Complete the RCRA cap of the CDA, PCB Landfill, BTA, and Maintenance Area in the first two summers of construction (assumed in 2017 or 2018). Use the stormwater of the RCF Pond as source of construction water as appropriate. Begin to discharge stormwater runoff from the capped portions of the site north of the PSCT and east of the stormwater divide once the RCRA cap is completed.

5. Once the A-Series Pond is essentially empty complete the new evaporation pond in the footprint of the A-Series Pond.

6. Transfer treated PSCT/PCT liquids to the new evaporation pond after the third construction season and then plan to close Pond 18.

Pond water has previously been used for the foundation layer under a HDPE liner during the P/S Landfill and EE/CA Area cap construction and will likely be used in a similar fashion in the future for the CDA and other RCRA liner caps but the decision of where it can be used for an ET cap will be determined during the remedial design process. Assuming average total precipitation (i.e., 16” rain a year) over the next 6 to 7 years and use of the enhanced evaporation systems, the water balance spreadsheet projects both stormwater ponds can be emptied and the remedy construction completed. The water balance spreadsheet (Appendix H) has also been run with varying rainfall (which has a feature that allows randomly generated precipitation rates over a range of low end to high end precipitation) for the next 7 years, and project that the ponds can be emptied in time to complete the remedy construction. However, if atypically high precipitation is experienced over the next 7 years, there could be as much as 25 to 40 million gallons of stormwater that will need to be disposed of before remedy construction can be completed. In order to address that possibility, a contingency scenario has been included in the FS, wherein the remaining stormwater in the A-Series and RCF Ponds is treated using a granular activated charcoal and reverse osmosis (RO) system to remove organics and TDS in order to meet the substantive discharge requirements of an NPDES Permit. This sort of treatment will create up to approximately 8 million gallons of brine which will


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have to be managed at the site (i.e., evaporated), or will need to be removed to a permitted facility for disposal, thus adding costs to those currently summarized in the FS cost estimates. 10.1.4. Proposed Evaporation Pond in Remedial Alternatives Sections 10, 11, and 12 of the FS Report describe the remedial alternatives being evaluated in the FS, many of which include the use of a new evaporation pond for managing both partially treated extracted groundwater and any stormwater that cannot be discharged using the General Permit. The size of the proposed evaporation pond was selected to provide sufficient evaporation capacity to manage the projected rates for both of these volumes. The anticipated volumes of the extracted and treated liquids will depend on the groundwater remedy selected and these rates have some seasonal variations. In addition, the metals concentrations and salinity of the ponds will become very high (i.e., brine) due to long-term evaporation of the partially treated groundwater and potential stormwater that is discharged into the ponds for disposal. Extracted groundwater would be treated for organics but not for metals or salinity before it is pumped to the evaporation pond. The considerations 1) for evaporation pond sizing to assure that the ponds do not overtop, 2) for ecological protection to prevent wildlife from coming into contact with the ponds or 3) from being adversely impacted due to the attraction of the pond water, for the range of remedial alternatives considered in the FS, are presented below. 10.1.4.1 Evaporation Pond Sizing Many of the remedial alternatives considered for Area 4 include an evaporation pond at the site to handle treated PSCT and PCT groundwater. The size of the evaporation pond will depend on the following liquid volumes:

Treated liquids extracted from PSCT-1, PSCT-2, PSCT-3 and PSCT-4 Treated extracted liquids from the PCTs (RAP-1A, RAP-2A, RAP-3A, RAP-1B, RAP-

C5, and RAP-1C) The size of the pond would also depend on the extent of capping in FS Area 2 and FS Area 3 in the recommended remedial alternative. For example, if the recommended alternative does not include capping of the eastern or southern portion of the RCRA Canyon, the following stormwater runoff streams may need to be managed at the site in the evaporation pond in addition to the PSCT and PCT groundwater.

Stormwater runoff from the southern portion of the RCRA Canyon Stormwater runoff and rainfall from the area south of Pond A-5 and west of the road

to the LTP It should be noted that there are some remedial alternatives which were specifically identified to eliminate an evaporation pond at the site. In these cases the extracted groundwater and any stormwater runoff would be treated for organics and inorganics prior to discharge under the substantive requirements of an NPDES Permit. The projected volumes of these extracted groundwater and the stormwater runoff streams are discussed below.


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Treated liquids extracted from PSCT-1, 2, 3, 4 and from the PCTs (RAP-1A, RAP-2A, RAP-3A, RAP-1B, RAP-C5, and RAP-1C) - The volume of the treated liquids extracted from the PSCT and PCT wells will vary with total precipitation. Based on the Groundwater Flow Model and existing site data, approximately 8,000,000 gallons a year of treated liquids on average are expected, and the FS Report assumes a worst case (i.e., wet season) rate of 12,000,000 gallons a year.

Stormwater runoff from the east slope of the RCRA Canyon - The stormwater volume is a function of the uncapped area and varies with total precipitation. For those cases where the eastern slopes of the RCRA Canyon are not capped (an area of approximately 25 acres), the FS projects the stormwater runoff volume will average about 1,750,000 gallons a year (and be as low as 500,000 gallons a year during ,years of low total precipitation and as high as 5,000,000 gallons a year during years of high precipitation).

Stormwater runoff and rainfall from the area south of Pond A5 and west of the road to the LTP – As mentioned earlier, the stormwater volume is a function of the area and varies with total precipitation. Assuming the area is less than 20 acres, it is projected that the volume will average 1,000,000 gallons a year (and be as low as 350,000 gallons a year during years of low total precipitation and as high as 4,000,000 gallons a year during years of high precipitation).

The total average volume of the liquids expected to require management in the evaporation pond thus ranges from 7,750,000 gallons if the east slope of RCRA Canyon is also capped, to a maximum of 16,000,000 gallons a year if the RCRA Canyon is not capped. For those remedial cases where the evaporation pond must handle 7,750,000 gallons a year, the proposed evaporation pond will be approximately 6 acres. For those remedial cases where the evaporation pond must handle 16,000,000 gallons a year, the proposed evaporation pond will be approximately 13 acres. The required size of the evaporation pond is based on the historical evaporation rates of 44 inches/year, which provides an evaporation capacity of 1,200,000 gallons a year per acre. Both size evaporation ponds provide a safety factor of approximately 1.6 based on average total precipitation. And if the east-slope stormwater from the RCRA Canyon can be discharged directly into the B-Drainage, the safety factor increases to 2.0. Obviously in the case of high total precipitation, the capacity of the evaporation pond alone is not sufficient. Since this is the case, the FS includes a contingency and proposes installing “enhanced evaporation facilities” as part of the evaporation pond, which will add an ability to increase evaporation by as much as 6,000,000 gallons a year over and above the 7,000,000 to 14,000,000 gallons a year capacity from the 6-acre or 13-acre pond respectively. The enhanced evaporation system is used by the mining industry to maximize evaporation in ponds. It is anticipated that the enhanced evaporation system will only be operated when necessary. With the inclusion of the enhanced evaporation capacity, the safety factor of the system is approximately 2.3 based on average total precipitation and a safety factor of 1.25 based on maximum precipitation. 10.1.4.2 Ecological Protection for Evaporation Pond The metals concentrations and salinity of the surface water in the evaporation pond would become very high (i.e., brine) as the partially treated groundwater and stormwater evaporates over the long-term. The evaporation pond would also ultimately accumulate metals and other inorganic constituents in the top foot of soil covering the HDPE liner, and similarly, as time passes, sediment from stormwater runoff would build up in the bottom of the pond. Wildlife would be attracted to the evaporation pond because of the presence of water (regardless of its


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quality) and could come into contact with the water and sediments unless wildlife controls are implemented to prevent contact. Attraction to the evaporation pond, potential contact with the water and sediments, and implementation of controls to prevent contact could adversely affect wildlife. Wildlife species that could be attracted to the ponds include:

Reptiles and amphibians (including special status listed species CRLF, CTS, WST) Small and large mammals Resident and migratory birds and bats

Wildlife controls would be implemented to deter wildlife species from contacting the ponds. The types of wildlife controls that may be implemented are further described below. The types and design of the wildlife controls would be selected during remedial design (after the ROD) and after input and consultation with USFWS and California Department of Fish and Game (CDFG) on the potential impacts to wildlife species from the ponds. Input would be solicited from USFWS and CDFG on the types and effectiveness of the potential wildlife controls that would be considered. 10.1.4.2.1 Coordination with USFWS and CDFG The USFWSis responsible for administering the Endangered Species Act (ESA), which is designed to protect critically imperiled species from extinction. Such species are listed as endangered if in danger of extinction and threatened if likely to become endangered. The California Fish and Game Commission (CFGC) and CDFG are responsible for administering the California Endangered Species Act (CESA), which is designed to protect and preserve all native species and their endangered habitats, threatened with extinction and those experiencing a significant decline which, if not halted, would lead to a threatened or endangered designation. Based on criteria recommended by CDFG, the CFGC establishes a list of threatened and endangered species and assigns “species of special concern" designation to wildlife species that are at risk. The CRLF (Federally threatened) and CTS (Federally endangered and State threatened) are listed species and the WST is a State species of special concern at the Casmalia Resources Superfund Site. USFWS responsibilities also include administering the Migratory Bird Treaty Act (MBTA), which prohibits the taking, killing, possession, transportation and importation of migratory birds, their eggs, parts, and nests, except when authorized by the Department of Interior via permit. Most native songbirds, wading birds, waterfowl and birds of prey are protected under the MBTA. Many of these are found at the Casmalia Resources Superfund Site. If an evaporation pond were selected as part of the final remedy, USEPA, as the lead Agency, would coordinate with USFWS and CFGC to determine the substantive requirements for compliance with the ESA (and MBTA). If appropriate, USEPA would provide a description of the proposed action (construction and operation and maintenance of the evaporation pond), status of the special status species and habitat, the action area, status of the special status species in the action area, and the anticipated effects of the action on the special status species and habitat. USEPA would then classify the potential effects into one of the following categories:

No Effect – No consultation necessary May Affect – Either “Not Likely to Adversely Affect” or “Likely to Adversely Affect”


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If either a Not Likely to Adversely Affect or a Likely to Adversely Affect determination is made, USEPA would consult with USFWS and if a Likely to Adversely Affect determination is made, USEPA would coordinate with USFWS to determine appropriate measures to minimize or offset such adverse effects. As such measures were determined by USEPA, USEPA would incorporate such measures into the design, construction, and operation of the evaporation pond. USEPA also anticipates that CDFG would participate in its coordination with USFWS. 10.1.4.2.2 Potential Wildlife Controls As described above, controls would be implemented to deter wildlife contact with the evaporation ponds. The types of controls would be selected and designed during remedial design (after the ROD) and after input and consultation with USFWS and CDFG. The wildlife controls may include, but not be limited to, the following:

Perimeter fencing to reduce the chance of contact from amphibians and small and large mammals

Elimination of wildlife habitat within and around the perimeter fencing Hazing to deter contact from birds and bats Netting and/or screening mesh to reduce that chance of contact from birds Routine biological monitoring to verify effectiveness of the wildlife controls

10.1.4.3 Evaporation Pond Operations and Maintenance The evaporation pond would ultimately accumulate inorganics in the top foot of soil covering the HDPE liner, and as time passes sediment from the stormwater runoff and dissolved solids from the treated groundwater would build up in the bottom of the pond. The evaporation pond sediment would be sampled approximately every 5 years to gauge extent of impact with inorganics and other contaminants. The pond sediment would be sampled for metals (USEPA Method 6010), inorganic parameters (such as sodium, calcium, sulfur, phosphorous and nitrogen), and soil pH. The buildup of sediment in the pond would require periodic cleanout (dredging) of accumulated sediment to maintain evaporation pond capacity. The depth that triggers those removals would be defined in the future Operations and Maintenance Manual for the pond, but it likely would closely follow the procedures already defined for the lined B-Drainage Wetland pools. As these sediments would have elevated levels of inorganics, they would need to be disposed of at a permitted facility. The cost estimate for the evaporation pond in the FS includes these periodic O&M costs for dredging, assuming it occurs every 20 years. The pond water volume would need to be reduced during the pond cleanout events every 20 years. This would primarily occur by enhanced evaporation methods and preferably in late summer months when the water volume is expected to be lower. For the option with smaller individual ponds, this would be easier because the pond water can also be transferred from one small pond to another. The netting covering the ponds, if being used, would be elevated, allowing dredging/excavation equipment to perform soil removal under the netting. A drift fence (tin flashing) and netting also help prevent ecological species from contacting the water and sediments in the evaporation pond. A drift fence (tin flashing) and the netting (if used) are assumed to require replacement every 5 years and the hazing systems (if used) are replaced every 10 years. The evaporation pond liner and soil cover is also assumed to be replaced every 50 years for long term O&M costs.


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10.1.5 HELP and Groundwater Flow Modeling Computer modeling was conducted as part of the FS to estimate a number of important factors pertinent to the evaluation of FS alternatives, including cap infiltration rates, changes to groundwater flow and groundwater levels, and changes to anticipated extraction volumes from subsurface liquid control features. The nature and objectives of the modeling performed are further discussed below. 10.1.5.1 HELP Model The HELP model version 3.07 (Schroeder et al. 1994) was used to evaluate the performance of several landfill cover designs and to use infiltration estimates for the caps as a source term input for the Groundwater Flow Model discussed below. This section summarizes the HELP modeling approach and results. Details of the HELP modeling effort are presented in Attachment D1-1 (Appendix D). HELP modeling was performed to evaluate the following potential engineered cover options being considered in the FS that were discussed earlier in Section 10.1.1, and shown on Figure 10-1A (Details A through F, and H):

A RCRA cap A RCRA-equivalent cap consisting of a five-foot compacted clay cover A 5-foot thick evapotranspiration (ET) cap consisting of 4 feet of topsoil over a 1-foot

thick compacted clay foundation A RCRA hybrid cap consisting of 2 feet of topsoil, underlain by a geonet drainage layer,

flexible membrane liner (FML), and a 2-foot thick compacted clay foundation An Ecological cap consisting of a 2-foot thick compacted clay cover A Pond liner with HDPE membrane over compacted foundation

The above engineered covers were modeled using the default soil types available in the HELP model. The default soil types selected are similar to site soils available for construction of the covers. The borrow soil from the North Ridge was tested during previous cap construction activities and classified as MH and CH (high plasticity silts and clays) according to the Unified Soil Classification System (GeoSyntec 1999). Similar soils are anticipated for the nearby NW Borrow Area soil that will be used to construct future covers. The default soil types used in the HELP modeling of as-built covers ranged from silty loams to silty clays. These soil types have water-holding capacities (based on field capacity) that range from 3.41 to 4.93 inches per foot of soil. The HELP models were run for as-constructed permeabilities and permeabilities that reflect potential long-term aging of the as-built soils that may occur over time. The aged permeability was assumed to be approximately an order of magnitude larger than the as-constructed permeability based on the findings of Benson et al. (2011) and Melchior et al. (2010). The water-holding capacities of the aged soils ranged from 1.57 to 4.45 inches per foot of soil. Cover slopes were simulated at 2:1 and 3:1. A fair grass vegetative cover was used for all simulations. Evapotranspiration and weather data available in the HELP model for Santa Maria, California were used in the simulations. Precipitation was synthetically generated using the normal mean monthly precipitation for Santa Maria and coefficients for San Diego. The evaporative zone depth was varied between 12 and 36 inches depending on the thickness and type of soil cover. The evaporative zone depth is related to the rooting depths of the vegetation growing on the covers. The rooting depths for most types of grasses range from about 18 to 60 inches (Ali Harivandi et al 2009) depending on the grass species. Native purple needle grass, the state grass of California, has been reported to root as deep as 15 feet (Netstate 2009), but typically


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ranges from 2 to 6 feet (Tilley et al. 2009) compared to introduced annual grasses which are usually shallow rooted. A 36-inch evaporative zone depth appears reasonable if native grasses are used to seed the covers. The potential leakage from a geomembrane lined evaporation pond was evaluated using a semi-analytical equation developed by Giroud (1997) and is discussed in more detail in Attachment D1-1 (Appendix D-1). In principle, a geomembrane liner consists of an impermeable material that should preclude leakage. However, the occurrence of a limited number of manufacturing and/or installation defects is anticipated. The assumed number of liner defects used in the calculation is based on recommendations provided in Giroud and Bonaparte (1989a and 1989b) and Schroeder et al. (1994). The liner was assumed to have a good quality installation with 1 small-hole and 4 large-hole defects per acre. The liner was assumed to have good contact with the underlying compacted soil foundation. The compacted soil foundation was assumed to have an as-built permeability of 1 x 10-6 centimeters per second (cm/s). The HELP modeling results are presented in Attachment D1-1 (Appendix D-1). The percolation rates for the as-built covers range from essentially zero for the RCRA cap and RCRA hybrid cap, 0.49 to 3.60 inches per year (in/yr) for the RCRA equivalent covers, 0.49 to 1.28 in/yr for the ET covers, and 0.99 to 1.85 in/yr for the Ecological-cap covers. The varying percolation rates largely depend on the as-built soil permeabilities and the evaporative zone depth simulated in each design. The percolation rates for the aged covers range from near zero for the RCRA cap and RCRA hybrid covers, 0.79 to 3.89 in/yr for the RCRA equivalent covers, 1.27 to 3.34 in/yr for the ET covers, and 1.82 to 2.14 in/yr for the ECO-CAP covers. The varying percolation rates largely depend on the increased soil permeabilities as the covers age and the evaporative zone depth simulated in each design. HELP is known to over predict percolation through evapotranspiration covers in semi-arid and arid environments (Scanlon et al. 2002; Hauser and Gimon 2004; Hauser et al 2005; and Scanlon et al. 2005), so the predicted percolation rates are likely overestimates. The calculated leakage rates through the lined evaporation pond are summarized in Attachment D1-1 (Appendix D). The predicted leakage rates for the as-built pond ranged from 2.24 x 10-3 in/yr for a 1-foot pond water depth to 2.48 x 10-2 in/yr for a 10-foot pond water depth. The predicted leakage rates for an aged pond ranged from 1.23 x 10-2 in/yr for a 1-foot pond water depth to 1.36 x 10-1 in/yr for a 10-foot pond water depth. Leakage predictions using Giroud’s equation have been evaluated using numerical simulations (Foose et al. 2001). The results of Foose et al. (2001) suggest that Giroud’s (1997) equation generally overestimates leakage through a liner, particularly for composite liners (i.e., a geomembrane over a compacted soil foundation). Thus, the calculated leakage rates provided in Attachment D1-1 (Appendix D-1) are considered conservative as they are likely over predicted. The results of the HELP model were used as infiltration inputs for the Groundwater Flow Model discussed below. 10.1.5.2 Groundwater Flow Model Groundwater model simulations were performed to support the evaluation of the effectiveness of the proposed site-wide remedy for the FS. The site-wide groundwater flow models developed for the RI were used for this evaluation. The design, construction and calibration of the site-wide models are briefly described in Appendix D-1 and documented in more detail in Attachment F-3 to Appendix F of the Final Remedial Investigation Report (CSC 2011a).


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Minor modifications were made to the groundwater flow models developed for the RI to evaluate the effectiveness of the proposed site-wide remedy. In order to evaluate the potential impact of the proposed remedy on flows in the PSCT and PCTs, the trench extraction wells, which were represented in the original models as well nodes (point sinks) with fixed discharge rates, were converted to drain boundaries (head-dependent flow boundaries). The drain boundaries allow the flow rates of the trench extraction wells in revised models to vary with the changes in groundwater levels that result from the components of the proposed remedy. The drain boundary elevations were set at the pumping (action) levels of extraction wells, and the drain conductance values were adjusted so that drain boundaries approximately simulated the flow rates and heads at the well nodes in the calibrated 2004 (dry season) and 2001 (wet season) models. In addition, a hydraulic conductivity zone with a value of 5 feet/day in model layers 1-3 (Upper HSU) along the southwest margin of the A-Series Pond was extended northward under the A-5 Pond and a hydraulic conductivity zone with a value of 2.62 feet/day along the northern margin of the RCF Pond was extended southward under the pond. These modifications were made to reduce the model head solution elevations near the two ponds, which rose above the elevation of the ground surface after removal of the constant-head boundaries representing the existing ponds for the evaluation of the remedial alternatives. After the models were modified, the head and groundwater flow path solutions, and the volumetric mass balance from the modified groundwater models were compared to those from the original models to verify that the modifications did not significantly affect the calibration of the models. The modifications to the models and the results of the calibration verification are more fully described in Appendix D-1. The effectiveness of the proposed remedy in containing groundwater in the Upper and Lower HSUs was evaluated with the modified site-wide March 2004 (Dry Season) and March 2001 (Wet Season) flow models using particle tracking. Groundwater flow paths from the landfill areas to the trench withdrawal systems were calculated for the head solutions from the simulations of the proposed remedy. Horizontal and vertical groundwater capture by the PSCT and PCT containment systems were evaluated by placing particles along the ridgeline above the landfills in layer 3 (Upper HSU) and layer 4 (Lower HSU) of the models. Path lines were then calculated for steady-state flow conditions to fully delineate the ultimate flow paths of the particles within the model grids. The results of the particle tracking simulations of the proposed remedy for the Upper HSU are discussed and shown on figures in Appendix D-1. These figures show the major components of the site-wide remedial alternatives, the steady-state model head solutions and the calculated groundwater flow paths. The particle tracking simulations show that the remedial alternatives would be generally effective in containing impacted groundwater in the Upper and Lower HSU that flows southward from the landfill areas, except in the gap between the PCT-A and PCT-B trenches. In this area, the simulations suggest that some of the shallow groundwater flow that is currently discharged into the RCF Pond may bypass the western end of the PCT-A trench and eastern end of the PCT-B trench. As a result, the lateral extent of the PCTs will be evaluated during the design phase to determine if additional actions are warranted to ensure that there is no significant groundwater flow that bypasses the trenches. The results of the model simulations indicate that a significant reduction in the PSCT and PCT flows would occur due to the extended capping, the closure of the A-Series Pond, Pond A-5, Pond 13, the RCF Pond and Pond 18. These results are presented in Appendix D-1 and discussed in Section 10.6.2 under “Existing Site Remedial Features”. The model simulations also show that water table elevations would decrease significantly across most of the site due to the reduction in groundwater recharge from the expansion of the capping in Area 5 North and


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Area 5 West (Appendix D-1). In the RCRA Canyon, the water table elevations decrease between 20 to 50 feet (wet season model). In the A-Series Pond footprint, the water table elevations decrease 5 to 20 feet. In Pond A-5 and Pond 13, the water table elevations decrease about 20 feet and 10 feet respectively. In the vicinity of PSCT-4 and in the LTA, the water table elevations decrease more than 70 feet. These anticipated water table elevation changes are referenced in the remedial alternative evaluations for groundwater in Sections 10.6 and 11.6. 10.1.6 Long Term Groundwater and Soil Vapor Monitoring Groundwater monitoring of wells at the site and outside the site boundaries is currently being conducted annually and are included as part of all FS Area 5 remedial alternatives, as it is expected to be part of the proposed remedy. The details of the current groundwater monitoring program, including the wells which are sampled and the analytes which are tested, are outlined in the RGMEW Workplan dated March 2009 (CSC 2009a). A long term groundwater monitoring program would likely include additional periodic sampling of more wells for a broader range of analytes than is currently performed. A soil vapor monitoring program is also currently in place for the site that will be continued as part of long term monitoring for the proposed remedy. The details of the current soil vapor monitoring plan are outlined in the “Sampling Plan for Soil Gas Monitoring”, dated April 2009 (CSC 2009b). Similar to long term groundwater monitoring, a long term soil vapor monitoring program may include sampling of more probes than are currently monitored. Long term groundwater and soil vapor monitoring programs will likely be modified and expanded from the current programs. The ultimate long term monitoring programs will address both performance and compliance monitoring consistent with USEPA policies and guidelines. Monitoring would include a variety of system-specific monitoring strategies intended to address: (A) performance monitoring, (B) detection monitoring (e.g., early detection of possible releases), and (C) compliance monitoring to ensure compliance with performance standards. Detailed long term groundwater and soil vapor monitoring plans will be developed and revised progressively, subject to USEPA approval, through remedial design (RD), remedial action and the transition into long-term operations, maintenance, and monitoring (OM&M). The cost estimates in this FS assume a 25 percent higher annual cost than the current annual monitoring program costs. 10.1.7 Monitored Natural Attenuation The FS includes MNA as a component of several site-wide remedial alternatives. MNA is used by USEPA when referring to a particular approach to remediation. USEPA’s 1999 OSWER Directive 9200.4-17P clarifies USEPA’s policy regarding the use of MNA for cleanup of contaminated soil and groundwater in the Superfund, RCRA Corrective Action, and Underground Storage Tank programs. Directive 9200.4-17P defines MNA as “...the reliance on natural attenuation processes (within the context of a carefully controlled and monitored site cleanup approach) to achieve sites specific remediation objectives within a time frame that is reasonable compared to that offered by other more active methods. The ‘natural attenuation processes’ that are at work in such a remediation approach include a variety of physical, chemical, or biological processes that, under favorable conditions, act without human intervention to reduce the mass, toxicity, mobility, volume, or concentration of contaminants in soil or groundwater. These in-situ processes include biodegradation; dispersion; dilution; sorption; volatilization; radioactive decay; and chemical or biological stabilization, transformation, or destruction of contaminants” (USEPA, 1999, page 3).


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Extensive monitoring data demonstrate that natural attenuation processes (sorption, matrix diffusion, and biodegradation) can help provide effective containment of groundwater contamination within the boundaries of the landfill site and even within the site’s more narrowly defined subareas. MNA would be used in conjunction with source control as a component of the final remedy, particularly for Area 5 North. Area 5 North includes the most highly contaminated parts of the site, including the Capped Landfills, the PCB Landfill, the Burial Trench Area, and the Central Drainage Area. LNAPLs and DNAPLs are found within this area. A TI waiver may be invoked for this part of the site based on the TIE performed for this area, as documented in Appendix A. Control of contaminant sources is an important aspect of USEPA’s policy regarding the use of MNA. OSWER Directive 9200.4-17P further states that “Control of source materials is the most effective means of ensuring the timely attainment of remediation objectives” (USEPA, 1999, page 22). Appendix G summarizes the natural attenuation processes that are known to occur at the Casmalia Resources Superfund Site, based on the data collected during the RI and the known physical and chemical characteristics of the hydrogeologic system and contaminants at the site. MNA is a viable remedy to achieve site-specific remediation objectives when the time frame to reach these goals is considered reasonable compared to that offered by more active methods. While MNA is considered a “passive” remediation approach, it does not preclude the use of “active” remediation or the application of enhancers of biological activity (USEPA, 1999). Several active engineering control features exist at the site, including the existing trench containment systems, pump and treat systems, and naturally occurring biological activity. Due to the complex mix of contaminants found at the site, petroleum hydrocarbon compounds may act as electron accepting compounds for the reduction of chlorinated solvents and/or metal transformation. As presented in Appendix G, many of the bacteria identified at the site are capable of degrading organic compounds including petroleum and chlorinated VOCs and higher carbon chains organic compounds (e.g., PCB) and/or inorganic metal transformation. 10.1.8 Groundwater FS Area 5 North (TI Zone) Source Removal and Containment A TI waiver may be a component of the overall site-wide remedy for FS Area 5 North, if designated a TI Zone based on the TIE performed for this area as documented in Appendix A. A TI waiver may be used by USEPA where groundwater restoration is not attainable from an engineering perspective. USEPA’s 1993 OSWER Directive 9234.2-25 clarifies USEPA’s approach to evaluating the technical impracticability of attaining required groundwater cleanup levels and establishing alternative, protective remedial strategies where restoration is determined to be technically impracticable. The TIE for FS Area 5 North (Appendix A) was performed in accordance with OSWER Directive 9234.2-25. This directive describes that many factors can limit groundwater restoration that may be grouped under three general categories: hydrogeologic factors; contaminant-related factors; and, remediation system design inadequacies. The TIE concludes that each of these factors make attaining groundwater cleanup levels impracticable for FS Area 5 North, including the presence of free-phase LNAPL and DNAPL in the Upper HSU and free-phase DNAPL within claystone fractures of the Lower HSU. OSWER Directive 9234.2-25 identifies the following remediation objectives for a DNAPL zone: Remove the free-phase, residual and vapor phase DNAPL to the extent practicable and contain DNAPL sources that cannot be removed (USEPA, 1993, p. 3). The directive (p. 20) further states that:


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Sources should be located and treated or removed where feasible and where significant

risk reduction will result, regardless of whether USEPA has determined that groundwater restoration is technically impracticable

Source containment has several benefits. First, source containment will contribute to the

long-term management of contaminant migration by limiting the further contamination of groundwater and spread of potentially mobile sources, such as NAPLs. Second, effective source containment may permit restoration of that portion of the aqueous plume that lies outside of the containment area.

10.1.8.1 NAPL Source Contamination in TI Zone Monitoring data and generalized volumetric calculations indicate that up to 100,000 gallons of free-phase DNAPL and a similar volume of free-phase LNAPL may have accumulated at the southern portion of the P/S Landfill. A much smaller volume of free-phase LNAPL is present in the Central Drainage Area. The DNAPL volume estimate is calculated in the RI Report. Free-phase DNAPL also occurs in fractures of the Lower HSU in the Central Drainage Area and also likely beneath the southern portion of the P/S Landfill as a result of downward leakage of the DNAPL from the P/S Landfill into the underlying claystone fractures. The extent of free-phase LNAPL in the Upper HSU, free-phase DNAPL in the Upper HSU and Lower HSU, and inferred potential extent of LNAPL and DNAPL based on dissolved-phase concentrations of NAPL constituents are shown on Figures 5-30, 5-31, and 5-32. The extent of LNAPL and DNAPL is limited to FS Area 5, north of the PSCT as shown on these figures. The free-phase LNAPL is contained within the P/S Landfill by the clay barrier and extraction by the Gallery Well immediately north of the clay barrier. The more limited amount of free-phase LNAPL within the Central Drainage Area is relatively immobile and does not reach the PSCT, and would be contained by the PSCT if it were to migrate south. The free-phase DNAPL in the P/S Landfill is partially contained by the current remediation systems. The free-phase DNAPL in the landfill may potentially move downward and outward into the underlying fractures of the Lower HSU. The southern-most area where free-phase (mobile) DNAPL has been identified is at the RGPZ-7C/D well cluster located approximately 500 feet south of the landfill. A pathway between the free-phase DNAPL within the P/S Landfill and the downgradient CDA well has not been established, although it is plausible based on known information. 10.1.8.2 Dissolved-phase Contamination in Potential Future TI Zone Very high concentrations of TDS, metals, and dissolved-phase organic compounds occur in the Upper HSU in FS Area 5 North with Total VOC concentrations exceeding 1,000,000 g/L. Arsenic, nickel, cadmium, and selenium are the mostly widely occurring metals that exceed MCLs. Lower levels of VOCs occur in the Lower HSU beneath the Burial Trench Area, Central Drainage Area, and the North Ridge. Elevated metals occur beneath the North Ridge. VOCs beneath the Burial Trench Area occur as a result of strong downward hydraulic gradients carrying contaminants downward in this area. VOCs beneath the Central Drainage Area likely occur as a result of a combination of downward hydraulic gradients carrying contaminants downward and the free-phase DNAPL that occurs within fractures of the Lower HSU in this area. The extent of dissolved-phase organic contamination in groundwater is depicted by Total VOC concentrations (Figures 5-26 through 5-29) and the extent of metals contamination is depicted by arsenic, nickel, cadmium, and selenium concentrations (Figures 5-33a through 5-40).


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Groundwater underlying FS Area 5 moves south from the natural groundwater flow divide that occurs under the North Ridge. Dissolved-phase contaminants in the Upper HSU moving southward in groundwater are contained by the PSCT. Groundwater moving southward through the Lower HSU through the area containing VOCs beneath the Burial Trench Area and containing DNAPL and VOCs beneath the Central Drainage Area may not be completely contained by the PSCT. The migration of dissolved-phase contaminants in the Lower HSU moving southward through fractures and potentially under the PSCT are attenuated by naturally occurring mechanisms that include sorption, diffusion into the claystone matrix, and biodegradation. Although the rate of potential contaminant migration beneath the PSCT is uncertain, the overall mass is likely small because of these natural attenuation mechanisms and because the rate of groundwater flow is low through the low permeability Lower HSU. Very low levels of VOCs have been detected in the Lower HSU immediately south of the PSCT trench, south of the Central Drainage Area at PSCT-1 and south of the Burial Trench at PSCT-4. Chlorinated VOCs indicative of contaminant migration in the Lower HSU were detected during both of the expanded RGMEW events for the RI (Fall 2004 and Spring 2005) at less than 1 g/L south of PSCT-1 at RGPZ-8D (PCE and TCE) and at 3 to 4 g/L south of PSCT-3 at RGPZ-16D (vinyl chloride). Other VOCs were also detected, including those that may have been attributable to laboratory contamination (e.g., acetone and MEK). The limited density of the Lower HSU monitoring well network along the PSCT with respect to the preferential fracture transport pathways makes the distribution of potential VOCs moving southward under the PSCT uncertain. The travel time for groundwater to move through the Lower HSU from the Lower HSU DNAPL at RGPZ-7C/D to a point underneath PSCT-1 is calculated to be slightly less than 100 years using Darcy’s law and input parameters representative of the hydraulic conductivity, gradient, and fracture transport porosity in the area. The travel time is calculated to be 72 years and the average linear groundwater flow velocity is calculated to be 2.1 ft/yr assuming the following inputs into the Darcy’s law equation (V=Ki/Ne):

150 feet = Distance from RGPZ-7C/D wells containing Lower HSU DNAPL to PSCT-1. 1x10-6 cm/sec = K, Geometric mean from historical Lower HSU aquifer tests 0.1 ft/ft = 20’/200’ = i, gradient between 460’ and 440’ WLE contours in Lower HSU 0.05 = Ne, Fracture transport porosity

This calculated flow velocity and travel time is consistent with the 2-D model simulations presented in the TI Evaluation (Appendix A). There are several figures, one for each time step (time zero, 30, 100, and 500 years). The distance moved at a time of 100 years is consistent with the 72 years calculated above (Figure A2-4). Due to the viscous and immiscible nature of the DNAPL with respect to groundwater, the DNAPL travel time to traverse the same distance will be considerably longer. 10.1.8.3 Total Volume of Liquids in the P/S Landfill The P/S Landfill also contains a large volume of highly contaminated aqueous-phase liquids, in addition to the fee-phase LNAPL and DNAPL. The total volume of liquids has been estimated to be as high as approximately 10,000,000 gallons based on the volumetric calculations provided on Figure 10-1E. This calculated total liquid volume is based on the volumetric difference between the bottom elevation of the landfill (base of waste) and the water table, multiplied by an


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assumed porosity of 0.25 percent. Two scenarios are provided. One scenario assumes the bottom contours interpreted by Canonie (1988) and the other assumes the bottom contours updated with the findings from piezometers and CPTs pushed during the RI. 10.1.8.4 Removal of LNAPL, DNAPL, and Aqueous-phase Liquids from the P/S Landfill The liquids in the P/S Landfill result in a “driving force” (head) that facilitates: (1) downward migration of contaminated liquids through pooled DNAPL source areas and fractured bedrock; and, (2) horizontal migration into weathered and unweathered bedrock. This head contributes to the horizontal gradient that causes groundwater (and contaminants dissolved in groundwater) to move southward through the Lower HSU and underneath the PSCT. The area-specific alternatives evaluated in Sections 10 and 11 and the final site-wide remedial alternatives evaluated in Section 12 include a combination of (1) capping the remaining areas of FS Area 5 North that are not currently capped; and, (2) the extraction of liquids (LNAPL, DNAPL, and aqueous-phase) from the P/S Landfill. This combination will result in the lowering of the water table within the P/S Landfill which will reduce the head that facilitates: (1) downward migration of contaminated liquids through pooled DNAPL source areas and fractured bedrock; and, (2) horizontal migration into weathered and unweathered bedrock. Groundwater modeling performed to evaluate the site-wide remedial alternatives shows that the combination of capping and liquids extraction will actually cause the liquid level to fall below the bottom of waste (Appendix D). The primary difference in the remedial alternatives is the rate at which the water levels in the P/S Landfill will drop. The site-wide remedial alternatives assume that a RCRA cap (Detail A, Figure 10-1A) will be constructed on the remaining areas north of the PSCT that have not been capped (PCB Landfill, Burial Trench Area, Central Drainage Area). This will eliminate most recharge from precipitation to FS Area 5 North. The liquid level in the P/S Landfill will then drop as liquids naturally exit the landfill (due to downward and horizontally outward gradients) and are actively removed through one of the liquids extraction alternatives. Within the P/S Landfill, free-phase LNAPL and DNAPL are assumed to be removed using either vertical extraction wells or horizontal drainage wells in one of three potential approaches summarized below in the following sections, and are shown on Figures 10-1B, 10-1C and 10-1D.

Site‐wide Remedial Alternative Approach P/S Landfill Liquids Extraction Activities

Alternative 1 A Continued operation of the Gallery Well

Alternative 2, 3, and 4 B Continued operation of the Gallery Well and Additional Vertical NAPL extraction wells (includes extraction of LNAPL, DNAPL, and aqueous‐phase liquids)

Alternatives 5 and 6 C Continued Operation of the Gallery Well and Additional Horizontal Extraction Wells (will drain all liquids from landfill including LNAPL, DNAPL, and water)

10.1.8.5 Removal of Liquids from P/S Landfill using Approach A The existing Gallery Well is assumed to continue its current operation for all remedial alternatives (Approach A). The Gallery Well annually extracts approximately 2,000 to 4,000 gallons of DNAPL, 300,000 to 450,000 gallons of aqueous phase liquids, and minor amounts of LNAPL (the pump is currently located near the bottom of the well within DNAPL). A higher end


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estimate of approximately 100,000 gallons of free-phase DNAPL and a similar volume of LNAPL are thought to occur at the southern part of the P/S Landfill. A significant amount of this DNAPL would flow towards and be extracted by the Gallery Well, but a portion would likely be left behind which would continue to be a source of DNAPL migration into the underlying claystone fractures. DNAPL would likely be left behind because undulations in the bottom of the landfill and other low permeability areas within the landfill waste would act as barriers to DNAPL flow. The DNAPL extraction rate would decrease as the DNAPL pool directly connected to the Gallery Well becomes smaller and the total liquids extraction rate would decrease as the overall liquid level and volume in the P/S Landfill drops. LNAPL would enter the Gallery Wells as the liquids level drops and could then be extracted from the Gallery Well. It is estimated that the P/S Landfill would become desaturated in approximately 10 years (see Section 10.1.8.8 for discussion of dewatering timeframes). The NAPL and aqueous liquid volumes are assumed to decline over the dewatering timeframe at a rate of 5 percent to 10 percent a year. The declining NAPL and aqueous-phase liquid volumes are included in the cost estimates as follows:

Aqueous-Phase (Gallery Well) Extraction rates

Year Volume (gal)

1 450,000 2 427,500 3 406,125 4 385,820 5 366,530

6-10 250,000

NAPL (Gallery Well) Extraction Rates

Year Volume (gal)

1 3,000 2 2,850 3 2,700 4 2,570 5 2,440

6-10 1,000 10.1.8.6 Removal of Liquids from P/S Landfill using Approach B In addition to continued operation of the Gallery Well as described above for Approach A, additional vertical NAPL extraction wells would be installed at the southern part of the P/S Landfill to remove the DNAPL and LNAPL in this area. These wells would be installed with the goal of directly intercepting the DNAPL pool and overcoming the barriers to DNAPL flow that would likely leave DNAPL behind using only the Gallery Well. The additional vertical extraction wells would be installed at approximately 16 assumed new locations to be determined during remedial design. Various investigative approaches such as a CPT, MIP, and/or Ultra-Violet


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Optical Screening Tool (UVOST) direct push investigation program would be considered to map the bottom of the landfill and NAPL distribution so that the optimal well locations could be determined for the likely presence of recoverable DNAPL. The scope of these investigation activities will be determined during remedial design. Four wells could be placed on the bench road near RIPZ-13, four wells could be placed on a new bench road to the north, and eight wells could be placed on two new bench roads between RIPZ-13 and the Gallery Well (Figure 10-1B). The wells could be constructed and operated using one of two options, with the first option having two sub-options. Each method would screen the well 5-feet below the landfill into claystone bedrock.

Option 1a - One option would be to construct 4-inch diameter wells and use a single screen across the entire saturated zone (LNAPL, aqueous-phase, and DNAPL) (see detail on Figure 10-1B). Two extraction pumps would be placed into the well. The bottom pump would be placed at the top of the DNAPL zone and pumped slowly (pulsed pumping only several times per day) to recover the DNAPL that comes into the well by up coning. The top pump would be placed within the LNAPL and also pumped slowly to skim the LNAPL that comes into the well. Extraction of water would be minimized so that the LNAPL and DNAPL saturations and flow paths around each well are maintained at the maximum possible level which would maximize LNAPL and DNAPL recovery. Some water would be extracted, as appropriate, to slightly enhance the inward gradients towards the extraction wells.

Option 1b – A second option is similar to the first option, except that two screened

intervals would be constructed in the 4-inch diameter well, one across the LNAPL zone and one across the DNAPL zone (see detail on Figure 10-1B). LNAPL and DNAPL would be preferentially extracted. One limitation with this method is that DNAPL up coning cannot be tracked if it rises above the DNAPL screen (which is important to know to maximize DNAPL recovery) and the top LNAPL screen will become desaturated as the overall liquid levels drop in the landfill which would trap recoverable LNAPL against the blank casing.

Option 2 – A third option would be to construct larger 8-inch diameter wells, use a single

screen across the entire saturated zone (LNAPL, aqueous-phase, and DNAPL), place a single extraction pump in the well, and aggressively pump all liquids that enter the well. It is assumed that for a total of 16 vertical wells 5.25 million gallons per year (0.6 gpm/well) of aqueous-phase liquids will be extracted in addition to the LNAPL and DNAPL initially (see detail on Figure 10-1C). The dewatering timeframe for Option 2 is estimated to be smaller than Option 1 at 4 to 10 years (assume 5 years). Section 10.1.8.8 presents more details on the method to estimate the dewatering timeframes. In subsequent years, the extraction flow rates are assumed to decrease as the P/S Landfill is dewatered.

Options 1a and 1b are carried forward to the evaluation of site-wide remedial alternatives in Section 12, while Option 2 is screened-out in Section 11 before that step. For Options 1a and 1b, the DNAPL and LNAPL extraction rates would decrease as the DNAPL and LNAPL pools directly connected to the extraction wells become smaller and the total liquids extraction rate would decrease as the overall liquid level and volume in the P/S Landfill drops. It is estimated that the P/S Landfill would become desaturated in approximately 10 years. The declining NAPL, and aqueous-phase liquids volumes for Options 1a/1b are included in the cost estimates as follows:


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Option 1a/1b - Aqueous Phase (Gallery Well) Extraction rates

Year Volume (gal)

1 450,000 2 427,500 3 406,125 4 385,820 5 366,530

6-10 250,000

Option 1a/1b - NAPL Annual Recovery Volumes for NAPL Only + Gallery Well Extraction

Year Volume (gal)

1 13,000 2 10,400 3 8,320 4 6,700 5 5,300

6-10 1,500 For Option 2, the NAPL and aqueous-phase liquid flow rates and volumes are assumed to decline over a 5-year timeframe as follows:

Option 2 – Aggressive Aqueous Phase Extraction rates (16 vertical wells)

Year Flow Rate (gpm)

Volume (gal)

1 2 5,250,000 2 0.5 1,300,000 3 0.5 1,300,000 4 0.1 263,000 5 0.1 263,000

Option 2 - Aqueous Phase (Gallery Well) Extraction rates

Year Volume (gal)

1 450,000 2 112,500 3 112,500 4 56,000 5 56,000

Option 2 - NAPL Annual Recovery Volumes for NAPL Only + Gallery Well Extraction


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Year Volume (gal)

1 13,000 2 11,000 3 9,000 4 8,000 5 7,000

10.1.8.7 Removal of Liquids from P/S Landfill using Approach C In addition to continued operation of the Gallery Well, horizontal extraction wells, or drain lines, would be installed using horizontal directional drilling (HDD) in the P/S Landfill to expeditiously remove all liquids from the landfill, including the free-phase DNAPL and LNAPL from the southern part of the landfill. Conceptually, the primary advantages of this approach over Approach B are as follows:

The head that contributes to the horizontal gradient that causes groundwater (and any contaminants dissolved in groundwater) to move southward through the Lower HSU and underneath the PSCT would be reduced faster than for Approaches A and B.

The energy costs to operate the horizontal drains would be reduced because the liquids

would drain by gravity. Landfill dewatering could be achieved by installing a series of horizontal wells to act as horizontal gravity drains to remove liquids from the landfill and especially DNAPL trapped behind the P/S Landfill clay barrier. To dewater the P/S Landfill, five horizontal wells are assumed to be installed by directional drilling methods (Figure 10-1D). The horizontal wells would be constructed with 300 feet of screen in the southern part of the landfill. Two options for installation could be used. For either option, the wells would be “blind” (single entry) drilled from a starting point located in the vicinity of Sump 9B, approximately 300 feet south of the landfill.

Option 1 – One option would be to drill through the base of the P/S Landfill clay barrier and directly access the DNAPL pool at the bottom of the landfill. The well would be installed by advancing a pilot bore through the Upper HSU several feet into the base of the clay, installing conductor casing and pressure grouting it in place, advancing a borehole through the conductor casing approximately 300 feet into the landfill, and installing 4-inch diameter well materials (See detail on Figure 10-1D). This method has the advantage that the DNAPL pool can be accessed directly. A key disadvantage is that several feet of liquids, including DNAPL, may be left at the bottom of the landfill because the well casing cannot be placed directly on the bottom of the landfill.

Option 2 – A second option would be to drill underneath the P/S Landfill clay barrier and install the well within the claystone immediately beneath the DNAPL zone and then intercept the bottom of the landfill to the north. Using this method, the well would be installed by advancing the borehole down through the Upper HSU and into the Lower HSU, below the clay barrier, then angle back upward to intersect waste, following the slope of the Lower HSU contact along the base of the landfill (See detail on Figure 10-1D). The wells would be drilled starting in the vicinity of Sump 9B about 300 feet from the landfill (elev. ~ 480 ft MSL) and drilling down to below the P/S Landfill Clay Barrier


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(elev. ~ 470 ft MSL) and coming up and following the slope of the Lower HSU contact along the landfill bottom. Since the Lower HSU contact at the landfill bottom is sloped up, the borehole would be inclined upward toward the northwest at angles up to 20 percent slope. The wells would extend approximately 300 feet underneath the landfill, similar to the first option. This method has the advantage that drilling is not performed through the clay barrier. A key disadvantage is that the rates at which liquids drain through the claystone separating the bottom of the landfill and the underlying horizontal wells may be slow, limiting the rate at which the landfill is drained.

As discussed in Section 10.1.8.8, it is estimated that the P/S Landfill would become desaturated in approximately 4 to 10 years for Option 1 and Option 2 (assume 5 years). The declining DNAPL, LNAPL, and aqueous-phase liquids flow rates and volumes are included in the cost estimates as follows for each horizontal well:

Initially 2 gpm on average (5.25 million gallons/year for five wells) Decreasing in Years 2 and 3 to 0.5 gpm Decreasing in Years 4 and 5 to 0.1 gpm

P/S Landfill Dewatering Extraction rates (Horizontal Wells) and Volumes

Year Flow Rate

(gpm) Volume (gal)

1 2 5,250,000 2 0.5 1,300,000 3 0.5 1,300,000 4 0.1 263,000 5 0.1 263,000

NAPL (P/S LF Dewatering + Gallery Well) Extraction Volumes

Year Volume (gal)

1 13,000 2 11,000 3 9,000 4 8,000 5 7,000

The actual extraction rates may be higher, especially for Option 1, but would be throttled so that they could be managed with the site infrastructure. The initial extraction rates could exceed assumed extraction rates. The extracted liquids would be drained to an equalization tank and then to a NAPL-water separator. The NAPL and the water phase would be pumped and stored in stainless steel tanks for disposal to a permitted facility similar to the current Gallery Well liquids. Approximately ten 20,000-gallon stainless steel storage tanks would be included in the treatment compound to have adequate storage capacity at the site. While dewatering the P/S Landfill is being considered further in the FS for reasons outlined above, the technical challenges and risks associated with this option are significant, as outlined in the alternatives evaluation.


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10.1.8.8 Summary of Estimated Timeframes for P/S Landfill to become Desaturated Groundwater flow model simulations were performed to estimate the dewatering time frames for the southern portion of the P/S Landfill under the different site-wide remedial alternatives presented in Section 12. The site-wide groundwater flow models developed by the CSC for the Site Final Remedial Investigation were used for this evaluation. The design, construction and calibration of these models are briefly described in Section 2.0 of Appendix D-1 and documented in more detail in Attachment F-3 to Appendix F of the Final Remedial Investigation Report, Casmalia Resources Superfund Site (CSC 2011). Minor modifications were made to the site-wide groundwater flow models to simulate the remedial alternatives. These modifications are described in Section 3.0 of Appendix D-1. For this remedial time frame analysis, uncalibrated transient simulations were performed with the modified 2004 (Dry Season) model for SWRs 2 through 6. An estimated specific storage of 2 x 10-4/foot was used for model layers 1-3, which represent the Upper HSU, and a specific storage of 2 x 10-6/foot was used for model layers 4-7, which represent the Lower HSU. The estimated timeframes for the P/S Landfill to become desaturated are described in Appendix D-3 and summarized in a table below. The results of the model simulations indicate that the time frames for achieving dewatering of the southern portion of the P/S Landfill would be approximately 10 years for Approach A and Approach B, Options 1(a)/(b), which include continued operation of the Gallery Well and minimal groundwater extraction by the LNAPL/DNAPL extraction wells. For Approach B, Option 2 and Approach C, which include more aggressive extraction of LNAPL/DNAPL and groundwater extraction by vertical or horizontal extraction wells, the model simulation indicate that the time frames for achieving dewatering of the southern portion of the P/S Landfill would be approximately 4 to 10 years (assume 5 years for evaluation and costing purposes). These time frames to achieve dewatering are considered to be only rough approximations because of the uncertainty in the accuracy of the uncalibrated model simulations and the estimated values for the specific storage that were used for the Upper HSU and Lower HSU. However, they probably provide conservative estimates for the dewatering of the P/S Landfill since the actual time frames for the decline in measured water levels due to the installation of the existing caps on the P/S Landfill in 1999 and the EE/CA area in 2001 and 2002 were somewhat shorter, ranging between 1.5 and 4 years (Appendix D-3).

Approach Option

Estimated Time for P/S Landfill to

become Desaturated

P/S Landfill Liquids Extraction Activities

A - 10 Years Continued operation of the Gallery Well

B 1(a)/(b) 10 Years

Continued operation of the Gallery Well and Additional Vertical NAPL extraction wells (includes extraction

NAPL‐Only Vertical Extraction Wells


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Approach Option

Estimated Time for P/S Landfill to

become Desaturated

P/S Landfill Liquids Extraction Activities

2 5 Years

of LNAPL, DNAPL, and aqueous‐phase liquids)

Aggressive NAPL Vertical Extraction

Wells

C

1 5 Years Continued Operation of the Gallery Well and Additional Horizontal Extraction Wells (will drain all liquids from landfill including LNAPL,

DNAPL, and water)

Penetrate the Base of the Clay Barrier with Horizontal Wells

2 5 Years Drill Underneath the Clay Barrier with Horizontal Wells

10.1.8.9 Removal of LNAPL from Central Drainage Area Recovery of the free-phase LNAPL in the Central Drainage Area may be attempted although it is relatively thin, localized in aerial extent, and contained by the PSCT. LNAPL recovery would be performed using one of two approaches. Approach A would entail operating skimmer pumps from existing wells. Approach B would entail operating skimmer pumps from additional vertical LNAPL extraction wells. The new wells would be installed with the goal of directly intercepting the LNAPL pool and overcoming the barriers to LNAPL recovery with the existing wells that would likely leave LNAPL behind. These barriers include screens that are constructed below the LNAPL zone. The additional wells would be installed at approximately 12 assumed new locations to be determined during remedial design, which could include a CPT, MIP, and/or UVOST direct push investigation program to map the LNAPL distribution so that the optimal well locations and construction could be determined to maximize LNAPL recovery. 10.1.8.10 Containment of the TI Zone with Current Actions and Potential Future Remedy Containment of the TI Zone with the current actions in place and future remedy will be achieved by a combination of hydraulic containment and natural attenuation mechanisms. The PSCT hydraulically contains dissolved-phase contaminants and LNAPL from migrating southward from Area 5 North to Area 5 South. Monitoring data have demonstrated that natural attenuation mechanisms (sorption, matrix, diffusion, and biodegradation) are occurring across the Casmalia Resources Superfund Site, including Area 5 North. These natural attenuation mechanisms will retard contaminants in the Lower HSU from migrating to Area 5 South. Removal of DNAPL and other liquids from the P/S Landfill will remove the source of DNAPL migration from the P/S Landfill into the underlying Lower HSU fractures. Placing additional RCRA caps on the remaining areas of FS Area 5 that are currently not capped will cause the groundwater elevations in FS Area 5 to significantly drop, which will decrease the rate of groundwater flow and potential migration of dissolved-phase contaminants beneath the PSCT. Clearly documented natural attenuation of contaminants occurs and will limit potential migration of dissolved-phase contaminants. These remedial technologies are further evaluated as part of the remedial alternatives evaluations in Sections 10, 11, and 12.


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10.1.9 Groundwater FS Areas 5 South and West Remediation and Containment The FS does not include TI waivers as remedy components for FS Areas 5 South and West. The contaminant levels in these two areas are much lower than for FS Area 5 North and are summarized as follows:

FS Area 5 South – Elevated concentrations of TDS, metals, and organic compounds occur in the Upper HSU south of the PSCT with Total VOC concentrations ranging up to approximately 1,000 g/L immediately south of the PSCT to less than 10 g/L near the PCTs. Dissolved-phase contaminants in the Upper HSU moving southward in groundwater are contained by the A- and B-Drainage PCTs.

FS Area 5 West – Elevated concentrations of TDS and metals occur in the Upper HSU

in the RCRA Canyon Area and to the south towards the C-Drainage PCT. Minor concentrations of organic compounds are also occasionally detected at Total VOC concentrations generally less than 10 g/L. Dissolved-phase contaminants in the Upper HSU moving southward in groundwater are contained by the C-Drainage PCT. A prominent surface seep seasonally forms at the south end of RCRA Canyon in the winter. The seep forms in response to a shallow water table and upward groundwater gradients at the canyon bottom that are greater in the winter in response to rainfall infiltrating over the canyon. This seep is elevated in TDS and metals, which could result in risk to amphibians if allowed to pond.

The FS assumes groundwater can be contained using one of the following remedial approaches:

Site‐wide Remedial Alternative Approach Remediation and Containment Activities

Alternatives 1 through 5 A Continued operation of the PCTs and MNA

Alternative 6 B Continued operation of the PCTs, installation and operation of 100 Additional Vertical Groundwater Extraction Wells (60 in Area 5 South and 40 in Area 5 West), and MNA

For Approach A, perimeter containment would be provided by continued operation of the PCTs while contaminant concentrations would be reduced by either removing or capping source areas and allowing time for MNA mechanisms to reduce contaminant concentrations. One of the primary MNA mechanisms that will reduce contaminant concentrations will be precipitation recharge, dilution, and flushing of contaminants from FS Areas 5 South and West to the PCTs. Chemical transformation and biological process will act to reduce the concentrations of organic compounds (e.g., chlorinated solvents and petroleum hydrocarbons) but will be less effective for inorganics (e.g., metals). Reliance on chemical transformation and biological process to reduce the concentrations of organic and inorganic compounds is not critical because of the effective role that recharge, dilution, and flushing will play in reducing those concentrations. The estimated timeframes for groundwater to reach MCLs are calculated using the numerical model code FRACTRAN as documented in Appendix D-2. The model simulations for FS Area 5 West indicate that the time frames for achieving groundwater cleanup standards would range from 90 years (nickel) to 220 years (arsenic) and for FS Area 5 South would range from 80 years (nickel) to 260 years (arsenic). The simulated timeframes to achieve the MCLs are


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considered to be an order-of-magnitude, or more, approximation because of the spatial and temporal variability of the initial concentrations of metals in groundwater and the uncertainty in the accuracy of the other input parameters required by the model. For Approach B, perimeter containment would continue to be provided by operation of the PCTs and the MNA mechanisms that will reduce contaminant concentrations would be augmented by the installation of 60 vertical groundwater extraction wells at FS Area 5 South and 40 wells at FS Area 5 West. The timeframes for groundwater to reach MCLs using Approach B would be shorter than for Approach A, however, they would still be on the order of several decades or more. The uncertainty of the timeframes for groundwater to reach MCLs estimated using FRACTRAN for Approach A are likely greater than the reduction in timeframes from implementing Approach B. In addition, the use of in situ treatment walls to passively treat groundwater and provide perimeter containment in place of active groundwater extraction at the PCTs was also evaluated for the FS Area evaluations (Sections 10 and 11). The in situ treatment wall technology was not retained for the site-wide remedial alternatives evaluation (Section 12) because of the significant uncertainties about whether this technology would be effective at treating the elevated metals in FS Areas 5 South and West. 10.2 FS Area 1 – PCB Landfill, Burial Trench Area, Central Drainage Area and

Existing Capped Landfills Area This section presents the nature and extent of the COCs in FS Area 1, a brief description of the applicable remedial alternatives to address the contaminants, and the screening evaluation of these alternatives. 10.2.1 Nature and Extent of Contamination FS Area 1 is made up of the CDA, BTA, and PCB Landfill RI study areas of the site (Figure 10-3). Surface to shallow subsurface soils in the CDA and BTA are locally impacted by inorganic and/or organic constituents in excess of their respective Ecological RBCs. No soil data were collected for the PCB Landfill (sampling was not conducted in that study area during the RI because the area is planned to be capped as part of the site remedial measures). Ecological RBC exceedances were locally encountered within both the CDA and BTA for a variety of inorganic and organic constituents, including chromium, copper, zinc, total DDT, dioxin TEQ, MCPP, PCB congeners, PCE and TCE. No constituents were detected at concentrations which may pose an unacceptable risk to potential human receptors. With the exception of two locations, Ecological RBC and/or UTL exceedances detected within the BTA were all encountered at depths in excess of 5 feet bgs, and therefore do not pose a risk to potential ecological receptors. Exceptions include TCE and dioxin TEQ Ecological RBC exceedances in surface soil (RISSBC-05), and total DDT and dioxin TEQ, and copper and chromium at a depth of five feet bgs (RISSBC-05 and RISSBC-01, respectively). The depth of Ecological RBC exceedances for dioxin TEQ and total DDT is not defined below 5 feet bgs in location RISSBC-05, but inorganics Ecological RBC exceedances at RISSBC-01 are limited to a maximum depth of 5 feet bgs. PCB congeners were reported at concentrations far in excess of its Ecological RBC at a depth of 57.5 feet bgs in the single sample tested for this analyte at location RISBBC-04. Chromium and copper were reported at concentrations in excess of their UTLs as well as their Ecological RBCs in some samples collected from 10 to 37 feet bgs in


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some locations. Regardless of the depth encountered, with the limited exceptions, the vertical extent of all exceedances in this area is defined by the available data. Surface to shallow subsurface soil in the CDA is impacted by a variety of inorganic and organic constituents at levels in excess of their respective RBCs. Ecological RBC exceedances in this area are reported for eight locations within the CDA, all lying within the western portion of this area in proximity to the toe of the P/S Landfill or former surface impoundments. The majority of these exceedances are limited to surface soils, but some constituents are present at levels in excess of their UTL and/or Ecological RBCs at depths of up to 12 to 42 feet bgs in this area. Most notable among these are deep occurrences of PCE at RISBCD-06 and RISBCD-11A, and total DDT at RISBCD-07, RISBCD-08, RISBCD-11, and RISBCD-13. No Ecological RBC exceedances are reported for samples collected from the northern, central or eastern portion of the CDA. 10.2.2 Development of Remedial Alternatives Table 10-1 identifies the remedial alternatives and the remedial objectives for FS Area 1. Six remedial alternatives are listed here to undergo the screening analysis for FS Area 1, which is discussed in the next subsection. The objectives of the remedial alternatives for FS Area 1 are:

Prevent ecological receptors from potential exposures to contaminants in shallow soil (0-5 feet bgs) by options such as capping or excavation to meet soil PRGs for metals and VOCs;

Prevent or reduce rainwater infiltration and leaching of contaminants to groundwater at the PCB Landfill, BTA and CDA by capping or excavation;

Incorporate stormwater and erosion controls to minimize transport of contaminants in soil via stormwater sediments and allow discharge of stormwater from FS Area 1 via the site’s General Permit; and,

Allow the use of pond water for cap construction for the foundation layer below HDPE liner.

For the PCB Landfill, the RCRA presumptive remedy is a RCRA cap that covers an area of about 4.4 acres. All of the active remedial alternatives discussed in this FS assume a RCRA cap for the PCB Landfill. The PCB Landfill has an estimated capacity of approximately 140,000 cy of waste fill assuming the top elevation of the waste is approximately 770 feet MSL (Figure 11-1B). The top surface of the cap is sloped at 5 percent and the side slopes are assumed to be at 3:1 slope. Any excavated wastes from other areas of the site that need to be placed in the PCB Landfill would need to be conducted prior to construction of the RCRA cap for the PCB Landfill. For the BTA and CDA, various combinations of capping and excavation alternatives are evaluated. The Capped Landfills Area is included in FS Area,1 and the presumed remedy for this study area is the existing RCRA cap. Hence the Capped Landfills Area is not formally included in the evaluation. The necessity of a cap venting system for proposed caps and the caps constructed from 1999 to 2002 (P/S Landfill and EE/CA Area Caps) will be evaluated during remedial design for the selected remedy.


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Stormwater controls are common to all of the remedial alternatives and include surface V-drains along bench roads on the cap and perimeter ditches to minimize potential infiltration of surface water and provide clean stormwater runoff. Stormwater to the east of the stormwater divide along LTP Road would be directed to the southeast towards a culvert near PSCT-1 and then flow through a drainage channel to the southern portion of the site. The stormwater then goes through a culvert under RCF Road and into a proposed retention basin in the footprint of Pond 13 and through or around the wetlands under the site’s General permit. The six remedial alternatives for FS Area 1 are listed and briefly described below. 10.2.2.1 Alternative 1 No Action The No Action alternative is included as required by CERCLA guidance. 10.2.2.2 Alternative 2 RCRA-Equivalent Mono Soil Cap (BTA, CDA) (5’) + RCRA Cap (PCB

Landfill) + Stormwater Controls + ICs + Monitoring This alternative involves capping the BTA and the CDA (about 24.2 acres) with 5 feet of low permeability soil to meet the RCRA requirements for permeability of 1x10-6 cm/s and to prevent ecological receptors from potential exposures to shallow soil (0-5’ bgs) contaminants (Figure 11-1A). The low permeability soil cap would also minimize stormwater infiltration into soil and groundwater in order to reduce further VOC migration in soil and groundwater and provide a clean stormwater runoff. Typical conceptual cap designs for RCRA-equivalent mono soil cap was discussed in Section 10.1.1 and shown on Figure 10-1A. The total surface area for each of these capped areas will be 5.5 acres for BTA and 18.8 acres for CDA. The required import soil volumes to construct the caps for the BTA (49,000 cy) and the CDA (167,000 cy) would be obtained from the NW Borrow Area shown on Figure 10-2. A RCRA cap is included for the PCB Landfill as a presumptive remedy as discussed earlier. Typical conceptual cap design for the RCRA cap was discussed in Section 10.1.1 and shown on Figure 10-1A. The total surface area for the capped area is 4.4 acres for PCB Landfill. The required import soil volumes to construct the PCB Landfill cap (32,000 cy) would be obtained from the NW Borrow Area. Area 1 stormwater would be directed by surface drains towards a culvert near PSCT-1 and would then flow through a drainage channel to the southern portion of the site. The stormwater would flow through the culvert under RCF Road and then into the stormwater retention basin proposed in the footprint of Pond 13 and through or around the wetlands under the site’s General Stormwater permit. The low permeability soil cap and the adjacent RCRA cap areas would meet the RAO of minimizing infiltration into groundwater for groundwater protection and providing a clean stormwater runoff. The monitoring component of this alternative includes periodic inspection, maintenance and repair of the cap, and stormwater controls over the long term. 10.2.2.3 Alternative 3 Evapotranspirative (ET) Cap (BTA, CDA) (5’) + RCRA Cap (PCB Landfill)

+ Stormwater Controls + ICs + Monitoring This remedial alternative involves installing a RCRA cap on the PCB Landfill (4.4 acres) and installing a ET soil cap on the Burial Trench Area (5.5 acres) and the Central Drainage (18.8 acres) as shown on Figure 11-2A. The ET soil cap is 5 feet of engineered low permeability claylike soil with a compacted 1-foot foundation layer and a 4-foot vegetative layer that is lightly


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compacted to about 85 percent of maximum dry density. The soil cap is intended to store water, allow growth of vegetation and removal of soil moisture through transpiration and evaporation, thus minimizing infiltration. These caps would be tied into the adjacent Capped Landfills Area. The RCRA cap and the ET cap would meet the RAOs by preventing ecological receptors from potential exposures to shallow soil (0-5’ bgs) contaminants and significantly reducing rainwater infiltration into soil and groundwater. The ET cap for the BTA would require 10,000 cy of clay soil for the 1-foot thick foundation layer and 39,000 cy of soil for the 4-foot thick vegetative layer. And the ET cap for the CDA would require 33,000 cy of clay soil for the foundation layer and 133,000 cy of soil for the vegetative layer. The soils from the NW Borrow Area are claystone material that will require additional processing and will be compacted to 90 percent relative compaction to provide strength and low permeability characteristics to serve as the foundation layer. The vegetative layer requires less pre-processing of the borrow soil and will be lightly compacted at 85 percent relative compaction. A RCRA cap is included for the PCB Landfill as a presumptive remedy as discussed earlier. Typical conceptual cap design for the RCRA cap was discussed in Section 10.1.1 and shown on Figure 10-1A. The total surface area for the capped area is 4.4 acres for PCB Landfill. The required import soil volumes to construct the PCB Landfill cap (32,000 cy) would be obtained from the NW Borrow Area. Area 1 stormwater would be directed by surface drains towards a culvert near PSCT-1 and would then flow through a drainage channel to the southern portion of the site. The stormwater would flow through the culvert under RCF Road and then into the stormwater retention basin proposed in the footprint of Pond 13 and through or around the wetlands under the site’s General Stormwater permit. The low permeability soil cap and the adjacent RCRA cap areas would meet the RAO of minimizing infiltration into groundwater and providing a clean stormwater runoff. The monitoring component of this alternative includes periodic inspection, maintenance and repair of the soil cover, maintenance of the vegetation on the ET cap, and stormwater controls over the long term. 10.2.2.4 Alternative 4 RCRA Cap (PCB, BTA, CDA) + Stormwater Controls + ICs + Monitoring This alternative would involve placing a RCRA cap on the PCB Landfill, BTA and CDA as shown on Figure 11-3A. This cap would prevent direct contact with metals and organic contaminants in shallow soil and thus eliminate the risk to ecological receptors. Impacted soil excavated as part of remediation of other areas of the site would be placed in the PCB Landfill along with an appropriate thickness of soil cover. These capped areas are adjacent to the current Capped Landfills Area and would be tied into these existing adjacent caps. The total surface area for each of the proposed capped areas will be 4.4 acres for PCB Landfill, 5.5 acres for BTA, and 18.8 acres for CDA, for a total of 28.7 acres of cap. The required soil volumes to construct the caps for the BTA (36,000 cy), CDA (134,000 cy), and PCB Landfill (32,000 cy) would be obtained from the NW Borrow Area. The RCRA cap cross-section is as discussed in Section 10.1.1 and shown on Figure 10-1A. The surface of the RCRA caps will incorporate appropriate drainage controls including bench roads and V-drains. The stormwater would be directed towards a culvert near PSCT-1 and then flow through a drainage channel to the southern portion of the site and then onto Pond 13 and through or around the wetlands. Stormwater will be discharged under the substantive requirements of the General Stormwater Permit. The monitoring component of this alternative


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includes periodic inspection, maintenance and repair of the cap, and stormwater controls over the long term. 10.2.2.5 Alternative 5 Excavate (BTA, CDA remedial areas) (5’) + RCRA-Equivalent Mono Soil

Cap (BTA, CDA) (5’) + RCRA Cap (PCB Landfill) + Stormwater Controls + ICs + Monitoring

This alternative addresses the shallow soil that poses a potential ecological risk and involves excavation of shallow soil (0-5’) within portions of the BTA and CDA. The areas targeted for excavation are based on exceedances of the Ecological RBCs for metals and organics which were defined in the RI. Since the density of sampling points is limited, the area of cleanup goals exceedances is assumed to involve excavation of approximately 2.5 acres in the BTA (20,000 cy) and 5.5 acres in the CDA (44,000 cy). The excavated areas in the BTA and CDA would be backfilled with 5’ of clean soil from the NW Borrow Area (Figure 10-2). The entire BTA and CDA would be capped with a 5-foot low permeability soil cap. The import low permeability soil volumes for the BTA and CDA caps would be 49,000 cy and 167,000 cy, respectively. The PCB Landfill would be capped with a RCRA cap covering 4.4 acres and would require an import soil volume for cap construction of 32,000 cy from the NW Borrow Area (Figure 10-2). Typical RCRA cap design was presented earlier in Section 10.1.1 and is shown on Figure 10-1A. This alternative would also include the surface drains/swales required to minimize infiltration of rainwater across FS Area 1. The stormwater will be directed towards a culvert near PSCT-1 and then flow through a drainage channel to the southern portion of the site and then onto Pond 13 and through or around the wetlands. As with Alternative 3, periodic inspection, maintenance and repair of the cap, and stormwater controls are included. 10.2.2.6 Alternative 6 Excavate (Entire BTA) (20’) + Excavate (CDA remedial area) (5’) +

RCRA-Equivalent Mono Soil Cap (BTA, CDA) (5’) + RCRA Cap (PCB Landfill) + Stormwater Controls + ICs + Monitoring

This alternative involves excavation (20’) of soil across the entire footprint of the BTA (5.5 acres) to remove waste in trenches (approximately 180,000 cy) and the surrounding impacted shallow soils (metals, organics exceedances of Ecological RBCs) (5’) in the CDA covering 6.2 acres (approximately 50,000 CY) (Figure 11-4A). The objective of the excavation in the BTA is to remove all wastes deposited in the trenches, which is assumed to be at most 20 feet deep. If wastes in trenches are present at greater than 20 feet bgs, this alternative would include excavating deeper to remove trench wastes. For the BTA excavation, soils that are not considered to be part of trench wastes and are unimpacted can be reused as fill soil. The extent of the impacted shallow soil in the CDA is preliminary and is primarily assumed to be in the western portion of the CDA. This excavation would ensure that there is no potential risk for contact with COCs in shallow soil and would remove the waste material at the BTA as a potential source for deep soil and groundwater contamination. The excavated areas will be backfilled to grade and capped with a 5-foot thick low permeability soil cap to minimize infiltration. Typical cap design was presented earlier in Section 10.1.1. About 217,000 cy of low permeability soil would be imported from the NW Borrow Area for this RCRA-equivalent cap covering the CDA and BTA.


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The PCB Landfill would be capped with a 4.4-acre RCRA-equivalent cap. This would require importation of 32,000 cy of soil from the NW Borrow Area (Figure 10-2). Typical RCRA cap design was presented earlier in Section 10.1.1 and is shown on Figure 10-1A. The excavated soils are segregated, including use of confirmation sampling, to remove waste trench material from material that does not contain waste trench material. One-half of the waste trench material (35,000 cy) would be disposed in waste at the PCB Landfill and the other half would be sent for disposal as non-RCRA hazardous at Clean Harbors in Buttonwillow, California. Due to the limited storage capacity in the PCB Landfill and the large volume of soil with the excavation alternatives, disposal at a permitted facility of a portion of the waste materials is assumed. The VOC exceedances in deeper soil are not excavated but addressed by capping. Also, included in this alternative are the surface drains/swales that help minimize infiltration of surface water across all three parts of Area 1 (28.7 acres) and provide clean stormwater runoff. As with Alternative 3, periodic inspection, maintenance and repair of the cap, and stormwater controls are included. 10.2.3 Screening of Remedial Alternatives Table 10-2 shows the screening analysis of the six remedial alternatives described above. The screening of remedial alternatives is conducted using three primary screening criteria, namely, effectiveness, implementability, and costs. Each alternative is rated low, low to moderate, moderate, moderate to good, or good. For cost, each alternative is similarly rated with subjective ratings ranging from low to high, or very high. Also, included is a green impacts assessment that rates the alternatives with respect to green and sustainability impacts. The goal of this screening is to retain only those alternatives that are the most promising for detailed evaluation. With respect to effectiveness, Alternatives 2 through 6 are rated the same at moderate to good. All of these alternatives accomplish the objectives of eliminating potential exposures to ecological receptors, minimizing rainwater infiltration through the PCB Landfill, BTA and CDA, and clean stormwater from these capped areas can be discharged under the substantive requirements of the General Stormwater permit. Alternatives 2, 3 and 4 are similar capping alternatives with the only difference being the type of caps for the BTA and CDA. Alternatives 2 and 3 are marginally less effective in preventing infiltration compared to Alternative 4 that uses a RCRA cap. Alternative 5 incorporates shallow soil excavation (0-5 feet bgs) of impacted areas in the BTA and CDA while Alternative 6 excavates shallow soil and wastes placed in trenches in the BTA down to approximately 20 feet bgs. Alternative 6 accomplishes more by waste removal in trenches and provides greater groundwater protection but it is rated the same as Alternative 5 because of challenges and uncertainties with the deep excavation to remove hazardous wastes and potential exposure concerns for site workers. With respect to implementability, Alternatives 2, 3 and 4 are rated good while Alternative 5 is rated moderate to good and Alternative 6 is rated lower at moderate. Alternative 5 is rated a bit lower than Alternatives 2 and 3 because of minor challenges associated with the excavation in areas with slopes and a large number of monitoring wells, and the need for transportation and disposal of large quantities of soil to a permitted facility. Alternative 6 is rated lower because of technical challenges with removal of hazardous wastes from the deep excavation in the BTA. With respect to cost, Alternatives 2, 3 and 4 are estimated to be moderate to high while Alternatives 5 and 6 are high because they involve some or all of the excavated soil being disposed at a permitted facility. The cost for transportation and disposal is very high (e.g., for


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non-RCRA hazardous soil about $80/ton is assumed). Some amount of disposal at permitted facilities would be required because of the limitations in storage capacity at the PCB Landfill. With respect to the green impacts assessment, Alternatives 5 and 6 are rated worse than Alternatives 2, 3 and 4 because Alternatives 5 and 6 involve excavation and transportation and disposal of large quantities of impacted soil. 10.2.3.1 Summary of Screening Evaluation On the basis of this screening evaluation, Alternatives 5 and 6 generally rate lower than other alternatives but only Alternative 5 is screened out and Alternative 6 is retained as a representative of an aggressive source removal alternative. Though it would be higher in cost, Alternative 6 is retained because it involves removal of trench wastes in the BTA that would provide better groundwater protection than the other alternatives including Alternative 5. Hence a total of five alternatives including No Action are retained for detailed evaluation. 10.3 FS Area 2 – RCRA Canyon and West Canyon Spray Area This section presents a summary of the nature and extent of the COCs in FS Area 2, a brief description of the applicable remedial alternatives to address the contaminants present, and the screening evaluation of these alternatives. 10.3.1 Nature and Extent of Contamination FS Area 2 encompasses the RCRA Canyon and WCSA study areas of the site (Figure 10-4). Surface to shallow subsurface soils in these areas are locally impacted by inorganic constituents at concentrations in excess of their respective Ecological RBCs. Inorganics were not detected at concentrations exceeding their respective human health RBCs, and no organic constituents were detected in this area at concentrations which may pose an unacceptable risk to potential human or ecological receptors. Inorganics exceeding Ecological RBCs within FS Area 2 soil include chromium, copper and zinc. While elevated barium concentrations are widespread in the RCRA Canyon area, as discussed earlier in Section 7.2.3, based on the toxicity information available for barium sulfate, the form of barium likely to be present in these areas, barium was not considered toxic to ecological receptors and therefore, was excluded as a chemical of interest (COI) in soil in the WCSA and the RCRA Canyon (See Section 10.3.1.1 below). Chromium, copper and zinc comprise the only inorganics detected in excess of their Ecological RBCs within the limits of the WCSA. Available data indicate the occurrence of other inorganics in excess of their Ecological RBCs within the RCRA Canyon portion of FS Area 2 is always in conjunction with barium at concentrations one to several orders-of-magnitude greater. The predominance of barium within the RCRA Canyon area is consistent with the historical disposal of drilling muds in this portion of the site. Where sufficient data are available at depth, indications are that inorganic impacts in excess of Ecological RBCs for the majority of locations explored within FS Area 2 are generally limited to surface or shallow subsurface soils (i.e., up to approximately 5 feet bgs), and that concentrations typically diminish with increased depth beneath the surface. This observation is consistent with the source(s) of these impacts being deposition upon the land surface, either through direct deposit or through spray evaporation. In many locations within RCRA Canyon where the depth of exploration was limited to 5 feet bgs the depth of Ecological RBC and/or UTL


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exceedance has not been established. However, extrapolating from the data on the majority of locations explored, it is reasonable to assume that exceedances do not persist much below that depth. Inorganics Ecological RBC exceedances for the chromium, copper and zinc detected within the WCSA area are also generally limited to surface or, more rarely, shallow subsurface soils, with only one location not having the depth of Ecological RBC exceedance defined (RISSSA-09). Overall, the results of the Tier 2 ERA identified that risks to terrestrial birds at the site are driven mainly by:

Chromium, copper, and zinc in the RCRA Canyon Area; and, Chromium, copper, and zinc in the WCSA.

The invertivorous bird (based on the invertivorous meadowlark) is predicted to be the most sensitive terrestrial bird to potential adverse effects from exposure to these chemicals in soil 0 to 0.5 feet bgs. For terrestrial mammals, a comparison of site-specific tissue data to tissue-based TRVs developed for kidney and liver tissue indicates that cadmium, chromium, copper, lead, and zinc are not expected to accumulate in target tissues at levels that would result in potential adverse risks. The invertivorous mammal (based on the shrew) is predicted to be the most sensitive terrestrial mammal to potential adverse effects from exposure to metals in soil 0 to 5 feet bgs. The results of the spatial analysis indicate that sample-specific risks for the other receptors are co-located in RCRA Canyon and tend to be located on the west side of RCRA Canyon. In the WCSA, sample-specific risks are generally located in the central portion of WCSA and are co-located among receptors. 10.3.1.1 Risk-based Remedial Evaluation The primary chemicals of interest (COIs) in FS Area 2 were initially identified to include the metals, barium, chromium, copper and zinc in shallow soil, and the primary ecological receptors of concern were the ornate shrew and the western meadowlark. The remedial footprint proposed for FS Area 2 in the Revised Draft FS (CSC 2011b) was based on these four COIs. However, as discussed in Section 7.2.3 of this report, based on the toxicity information available for barium sulfate, the form of barium likely to be present in these areas, barium was not considered toxic to ecological receptors and therefore, has been excluded as a COI in soil in the WCSA and the RCRA Canyon. Locations where barium alone was a COI and other COIs at concentrations slightly above the ecological RBCs were identified, and the proposed remedial footprint in the WCSA and the RCRA Canyon were adjusted accordingly. Additionally, residual risks were estimated for ecological receptors that could potentially be exposed to soils outside the boundary of the adjusted remedial areas in the WCSA and the RCRA Canyon to assess if risks would be acceptable. The approach and methods used to adjust the remedial footprint is presented in Appendix C of this report. To summarize, the WCSA adjusted remedial footprint was increased from the proposed 5.2 acres by approximately 0.3 acres, making it a total of approximately 5.5 acres. The RCRA Canyon adjusted remedial footprint was reduced from the proposed 15 acres by approximately 6.6 acres, making it a total of approximately 8.4 acres. The residual risks calculated for the WCSA and the RCRA Canyon indicate that post-remedial risks to plant, soil invertebrate, mammal, and bird populations will be acceptable.


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In conclusion, excluding barium from the list of COIs and adjusting the proposed remedial footprint is expected to result in acceptable post-remedial risks to ecological receptor populations at the WCSA and the RCRA Canyon. 10.3.2 Development of Remedial Alternatives Table 10-1 identifies the remedial alternatives and the remedial objectives for FS Area 2. Ten remedial alternatives are listed here to undergo the screening analysis for FS Area 2 which will be discussed in the next subsection. The objectives of the remedial alternatives for FS Area 2 are:

Prevent ecological receptors from potential exposures to shallow soil (0-5 feet bgs) using options such as capping or excavation to meet soil PRGs for COCs (chromium, copper, zinc)

Eliminate groundwater seeps in the RCRA Canyon that can pose a risk to ecological receptors by reducing or minimizing rainwater infiltration into soil and groundwater in Area 2 to lower the groundwater level in the southern portion of the RCRA Canyon using various types or extent of capping

Enable discharge of combined stormwater flow from the RCRA Canyon and WCSA areas for discharge through or around the wetlands via the substantive requirements of the site’s General Permit; or, segregate uncapped area stormwater to a site evaporation pond

Incorporate stormwater and erosion controls (BMPs) to minimize transport of contaminants via stormwater sediments

Use of pond water during cap construction in Area 2 will be evaluated during remedial design

The ten remedial alternatives for FS Area 2 are briefly described below. 10.3.2.1 Alternative 1 No Action The No Action alternative is included as required by CERCLA guidance. 10.3.2.2 Alternative 2 Ecological-Cap (West Slope RCRA Canyon, WCSA remedial area) (2’) +

Grading/BMPs (Uncapped areas) + Stormwater Controls + ICs + Monitoring This alternative involves capping metals-impacted soils in the RCRA Canyon and the WCSA with an Ecological-cap. The remedial areas are identified based on the risk-based remedial evaluation presented in Section 7 and in Appendix C. The impacted remedial area to be addressed is the RCRA Canyon west slope (8.4 acres) and WCSA east slope (5.5 acres) (Figure 11-5A). The Ecological-cap would involve a 2-foot soil cover to control potential exposure to ecological receptors (ornate shrew and western meadowlark) as described earlier in Section 10.1.1. This Ecological-cap would require approximately 49,000 cy of borrow soil from the NW Borrow Area. Prior to cap construction, about 130,000 cy of cut/fill grading would be required for leveling and subgrade preparation to reduce slopes. The Ecological-cap surface would be designed to include surface drains to manage stormwater.


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The final surfaces of the Ecological-cap area will include surface drains to allow drainage of stormwater from the west slope of the RCRA canyon and the WCSA remedial area to a lined drainage channel that flows into a new retention basin that will be constructed in the footprint of the former Pond A-5. This stormwater will be sent by a gravity flow pipeline through or around the wetlands and then be discharged to the B-Drainage via the the substantive requirements of the General NPDES permit. The surface water runoff from the uncapped areas would be collected by an unlined drainage channel that leads to the proposed site evaporation pond which will be constructed in the footprint of the A-Series Pond where it would be managed. The stormwater runoff from the uncapped portions of FS Area 2 would be monitored for compliance with stormwater benchmarks and if considered clean would also be discharged under the substantive requirements of the General Permit. In the event that is not possible, the stormwater runoff from the uncapped portions of FS Area 2 will be directed to and managed in the proposed evaporation pond. This will result in a larger site evaporation pond size requirement. As with Alternative 2, periodic inspection, maintenance and repair of the cap, and stormwater controls are included. 10.3.2.3 Alternative 3 RCRA-Equivalent Mono Soil Cap (West slope RCRA Canyon) (5’) +

Excavate (WCSA remedial area) (5’) + Grading/BMPs (Uncapped Areas) + Stormwater Controls + ICs + Monitoring

This remedial alternative involves installing a RCRA-equivalent mono soil cap on the west slope of the RCRA Canyon which is approximately 8.4 acres (Figure 11-6A). The RCRA-equivalent mono cap comprises 5-feet of low permeability clay-like soil (see Section 10.1.1 for cap details) that will control potential exposures to ecological receptors (ornate shrew and western meadowlark) and will meet the RCRA permeability requirements and minimize surface water infiltration in the west slope area. Based upon modeling results, significant reduction in surface water infiltration is expected, over time, to lower the water table about 50 feet in the upper canyon and 20 feet at the southern end of the canyon and thus eliminate groundwater seeps and improve surface water quality in RCRA Canyon (Section 10.1.5 and Appendix D-1). Approximately 74,000 cy of borrow soil from the NW Borrow Area would be required to construct the west slope cap. Some grading and additional borrow soil would be required to reduce the steepness of some of the sloped areas in order to install the cap. The uncapped areas will be graded to reduce the steepness of some of the sloped areas and will incorporate BMPs to minimize erosion and potential entrainment of contaminants in stormwater runoff. A portion of the WCSA (5.5 acres) will be excavated to a depth of 5 feet bgs and the soil used as fill in Pond A-5 (discussed later for FS Area 4 – Section 10.5). The excavated portions of the WCSA will be backfilled to match grades. The extent and depth of the excavation is preliminary and would be confirmed during design to ensure that risk-based standards are met. The final surfaces of the west slope of the RCRA Canyon will include surface drains to allow drainage of stormwater from the west slope of the RCRA canyon to a lined drainage channel that flows into a new retention basin that will be constructed in the footprint of the former Pond A-5. This stormwater will be sent by a gravity flow pipeline through or around the wetlands and be discharged to the B-Drainage under the substantive requirements of the General Permit. The surface water runoff from the uncapped areas would be collected by an unlined drainage channel that leads to the proposed site evaporation pond which will be constructed in the footprint of the A-Series Pond where it would be managed. The stormwater runoff from the uncapped portions of FS Area 2 would be monitored for compliance with stormwater benchmarks and if considered clean would also be discharged under the substantive


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requirements of the General Permit. In the event that is not possible, the stormwater runoff from the uncapped portions of FS Area 2 will be directed to and managed in the proposed evaporation pond. As was the case with the above alternative, that would require more pond capacity. As with Alternative 2, periodic inspection, maintenance and repair of the cap, and stormwater controls are included. 10.3.2.4 Alternative 4 RCRA-Equivalent Mono Soil Cap (West slope RCRA Canyon, WCSA

remedial area) (5’) + Grading/BMPs (Uncapped Areas) + Stormwater Controls + ICs + Monitoring

This alternative involves placing a RCRA-equivalent mono soil cap on the west slope of the RCRA Canyon (8.4 acres) and a portion of the WCSA area (5.5 acres) to control potential exposures to ecological receptors (Figure 11-7A). The RCRA-equivalent mono cap is a 5-foot thick low permeability clay-like soil cap (see Section 10.1.1 for cap details) that will control potential exposures to ecological receptors (ornate shrew and western meadowlark) and will minimize surface water infiltration in the west slope and WCSA remedial areas. Based upon modeling results, significant reduction in surface water infiltration is expected to lower the water table about 50 feet in the upper canyon and 20 feet at the southern end and thus eliminate groundwater seeps and improve surface water quality in RCRA Canyon (Section 10.1.5 and Appendix D-1). Approximately 123,000 CY of borrow soil would be required to construct the soil caps for the two remedial areas, with borrow soil derived from the NW Borrow Area. The uncapped areas will be graded to reduce the steepness of some of the sloped areas and will incorporate BMPs to minimize erosion and potential contaminants in stormwater runoff. The stormwater runoff from the two capped areas will be collected by the lined drainage channel and drained to a proposed retention basin in the footprint of Pond A-5 and then by pipeline to Pond 13 and then through or around the wetlands and to the B-Drainage in accordance with the substantive requirements of the General Permit. The surface water runoff from the uncapped areas would be collected by an unlined drainage channel that leads to the proposed site evaporation pond which will be constructed in the footprint of the A-Series Pond where it would be managed. The stormwater runoff from the uncapped portions of FS Area 2 would be monitored for compliance with stormwater benchmarks and if considered clean would also be discharged under the substantive requirements of the General Permit. In the event that is not possible, the stormwater runoff from the uncapped portions of FS Area 2 will be directed to and managed in the proposed evaporation pond. Since the WCSA is not excavated in this alternative, Pond A-5 would require additional borrow soil as fill for constructing the retention basin. As with Alternative 2, periodic inspection, maintenance and repair of the cap and stormwater controls are included. 10.3.2.5 Alternative 5 RCRA-Equivalent Mono Soil Cap (West slope RCRA Canyon) (5’) +

Excavation (WCSA remedial area) (5’) + Soil Cover (Uncapped Areas) (2’) + Stormwater Controls + ICs + Monitoring

This alternative involves placing a RCRA-equivalent mono soil cap on the west slope of RCRA Canyon (8.4 acres) to control potential exposures to ecological receptors and minimize surface water infiltration on the west slope (Figure 11-8A). Based on modeling results, significant reduction in surface water infiltration is expected to lower the water table about 50 feet in the upper canyon and 20 feet at the southern end and improve surface water quality from the RCRA Canyon (Section 10.1.5 and Appendix D-1). This alternative is similar to Alternative 3, but includes in addition a clean soil cover 2 feet thick to improve stormwater runoff quality.


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A portion of the WCSA (5.5 acres) will be excavated to a depth of 5 feet bgs and the soil used as fill in Pond A-5 (discussed in FS Area 4). The excavated portions of the WCSA will be backfilled to match grades. The extent and depth of the excavation is preliminary and would be confirmed during design to ensure that risk-based standards are met. The uncapped portion of FS Area 2, including the WCSA excavated area, will be covered with a 2-foot clean soil cover (approximately 24.8 acres). Approximately 162,000 cy of borrow soil would be required to construct the west slope cap and the 2-foot clean soil cover. This remedial alternative includes a large amount of cut/fill grading estimated to be approximately 100,000 cy for the west slope of the RCRA Canyon and 30,000 cy for the WCSA to reduce slopes to about 2:1. For the steeper east slope of the canyon, the estimated cut/fill grading is about 270,000 cy to reduce slopes to about 2:1 or less prior to placement of the 2-foot clean soil cover. The capped west slope would include surface drains to collect stormwater and this would commingle with other stormwater from the soil cover areas. Since in this scenario the entire northern portion of the RCRA Canyon is capped with clean soil, all stormwater would be collected by a single stormwater drainage channel running down the middle of the canyon. The stormwater from the entire RCRA Canyon would flow through to the proposed retention basin in Pond A-5 and Pond 13, through or around the wetlands, and discharged to the B-Drainage in accordance with the substantive requirements of the General Permit. As with Alternative 2, periodic inspection, maintenance and repair of the cap, and stormwater controls are included. 10.3.2.6 Alternative 6 RCRA-equivalent Hybrid Cap (West slope RCRA Canyon) (5’) +

Excavation (WCSA remedial area) + Clean Soil Cover (Uncapped Areas) (2’) + Stormwater Controls + ICs + Monitoring

This remedial alternative involves installing a RCRA-equivalent hybrid cap on the west slope of the RCRA Canyon which is approximately 8.4 acres as shown on Figure 11-9A. The RCRA equivalent hybrid cap is a special 60-mil spiked HDPE liner with a 2-foot soil cover and biotic barrier. This alternative is similar to Alternative 5, but includes an HDPE liner instead of the RCRA-equivalent mono soil cap. The RCRA-equivalent cap will control potential exposures to ecological receptors and will prevent water infiltration through impacted soils. Based on modeling results, significant reduction in surface water infiltration is expected to lower the water table about 50 feet in the upper canyon and 20 feet at the southern end, eliminate seeps in this area, and improve surface water quality from the RCRA Canyon (Section 10.1.5 and Appendix D-1). A portion of the WCSA will be excavated and the soil used as fill in Pond A-5. The excavated portions of the WCSA will be backfilled to match grades and compacted to 85 percent relative compaction with a 6-inch vegetative layer on top. The uncapped remaining areas (19.3 acres) of the site will also be graded to reduce slopes (max 2:1 slope) and covered with 2 feet of clean soil. This remedial alternative includes a very large amount (estimated to be approximately 400,000 cy) of cut/fill grading to reduce slope angles in the steep areas to 2:1 or less in order to install the cap. The total cut/fill grading volume includes 100,000 cy for the west slope, 30,000 cy for the WCSA and 270,000 cy where the existing slopes are steepest (almost 1:1) along the east slopes of the canyon. The stormwater will be collected by surface drains to a concrete channel that allows drainage into a new retention basin that will be constructed in the footprint of the former Pond A-5. This


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stormwater will be sent by pipeline through or around the wetlands where it will be discharged to the B-Drainage under the substantive requirements of the General Permit. As with Alternative 2, periodic inspection, maintenance and repair of the cap, and stormwater controls are included. 10.3.2.7 Alternative 7 Evapotranspirative (ET) Cap (West slope RCRA Canyon)(5’) +

Excavation (WCSA remedial area) + Clean Soil Cover (Uncapped Areas)(2’) + Stormwater Controls + ICs + Monitoring

This remedial alternative involves installing a ET soil cap on the west slope of the RCRA Canyon which is approximately 8.4 acres as shown on Figure 11-10A. The ET soil cap is 5 feet of engineered low permeability claylike soil that includes a vegetative layer that is 4 feet thick and is lightly compacted to about 85 percent of maximum dry density, and a 1-foot thick compacted foundation layer. The soil cap is intended to store water, and allow growth of vegetation and removal of soil moisture through transpiration and evaporation. The ET cap will control potential exposures to ecological receptors and will reduce surface water infiltration. A portion of the WCSA will be excavated and the soil used as fill in Pond A-5. The excavated portions of the WCSA will be backfilled to match grades and compacted to 85 percent relative compaction with a 6-inch vegetative layer on top. This remedial alternative assumes some grading and additional borrow soil is required to reduce the steepness of some of the sloped areas (<2:1) in order to install the cap. This remedial alternative includes a large amount of cut/fill grading estimated to be approximately 100,000 cy for the west slope of the RCRA Canyon and 30,000 cy for the WCSA to reduce slopes to about 2:1. The uncapped remaining areas (19.3 acres) of the site will also be graded to reduce slopes (max 2:1 slope) covered with 2 feet of clean soil. For the steeper east slope of the canyon, grading of about 270,000 cy is estimated to reduce slopes to about 2:1 or less prior to placement of soil cover. The final surfaces of the capped west slope of the RCRA Canyon and the WCSA will be sloped and include surface drains to allow drainage of stormwater from the entire RCRA canyon to flow into a new retention basin that will be constructed in the footprint of the former Pond A-5. This stormwater will be sent by pipeline through or around the wetlands and discharged to the B-Drainage under the substantive requirements of the General Permit. As with Alternative 2, periodic inspection, maintenance and repair of the cap, and stormwater controls are included. 10.3.2.8 Alternative 8 RCRA Equivalent Hybrid Cap (Entire RCRA Canyon, WCSA) +

Stormwater Controls + ICs + Monitoring This remedial alternative involves installing a RCRA equivalent hybrid cap on the entire RCRA Canyon and WCSA, encompassing a total of 33 acres (Figure 11-11A). The RCRA equivalent hybrid cap uses a HDPE liner with spikes, a geocomposite drainage layer and a 2-foot vegetative soil cover with a biotic barrier as described earlier. The RCRA equivalent cap will control potential exposures to ecological receptors and will minimize rainwater infiltration across the entire RCRA Canyon and WCSA. Groundwater modeling indicates that minimizing infiltration through capping with a RCRA-equivalent hybrid cap will result in significantly lowering the water table in this area, thus eliminating groundwater seeps in RCRA Canyon, and that


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using the RCRA-equivalent hybrid cap indicates no significant difference in the expected lowering of groundwater levels compared to that for a RCRA cap (Appendix D-1). This remedial alternative includes a very large amount (estimated to be approximately 400,000 cy) of cut/fill grading to reduce slope angles in the steep areas to 2:1 or less in order to install the cap. The total cut/fill grading volume includes 100,000 cy for the west slope, 30,000 cy for the WCSA and 270,000 cy where the existing slopes are steepest (almost 1:1) along the east slopes of the canyon. Approximately 117,000 cy of borrow soil would be required to construct the soil caps. The final surfaces of the cap on the RCRA Canyon and WCSA will include approximately 16,000 linear feet of bench roads and surface drains to allow drainage of stormwater. The stormwater from the entire canyon would be collected by a concrete drainage channel running down the middle of the canyon into a proposed retention basin that will be constructed in the footprint of the former Pond A-5. This stormwater will be sent by pipeline through or around the wetlands where it will be discharged to the B-Drainage under the substantive requirements of the General Permit. As all runoff will be draining from clean, capped areas no stormwater would need to be sent to an evaporation pond. As with Alternative 2, periodic inspection, maintenance and repair of the cap and stormwater controls are included. 10.3.2.9 Alternative 9 Evapotranspirative (ET) Cap (entire RCRA Canyon, WCSA) +

Stormwater Controls + ICs + Monitoring This remedial alternative involves installing an ET cap on the entire RCRA Canyon and WCSA that is a total of 33 acres as shown on Figure 11-12A. The ET soil cap is 5 feet of engineered low permeability claylike soil that includes a vegetative layer that is 4 feet thick and is lightly compacted to about 85 percent, and a 1-foot thick compacted foundation layer. The soil cap is intended to store water, allow growth of vegetation and removal of soil moisture through transpiration and evaporation. This ET cap will control potential exposures to ecological receptors and will reduce surface water infiltration. As discussed above for Alternative 8, groundwater modeling indicates that minimizing infiltration through capping with an ET cap will result in significantly lowering the water table in this area, thus eliminating groundwater seeps in the RCRA Canyon, and that there is no significant difference in the expected lowering of groundwater levels between the ET cap and the RCRA or RCRA-equivalent cap (Appendix D-1). This remedial alternative includes a large amount of cut/fill grading estimated to be approximately 100,000 cy for the west slope of the RCRA Canyon and 30,000 cy for the WCSA to reduce slopes to about 2:1. For the steeper east slope of the canyon, due to the better stability characteristics of the ET soil cap, about 270,000 cy of grading is estimated to reduce slopes to about 2:1 or less in order to install the ET cap. The final surfaces of the western slope of the RCRA Canyon and WCSA will include surface drains to allow drainage of stormwater from the west slope of the RCRA canyon and WCSA to flow into a new retention basin that will be constructed in the footprint of the former Pond A-5. This stormwater will be sent by pipeline through or around the wetlands and discharged to the B-Drainage under the substantive requirements of the General Permit. The surface water runoff from the uncapped south end of the WCSA will be collected in a new site evaporation pond where it would be managed.


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10.3.2.10 Alternative 10 RCRA Cap (Entire RCRA Canyon, WCSA) + Stormwater Controls + ICs + Monitoring

This alternative involves constructing a RCRA cap over the entire RCRA Canyon and WCSA (36 acres) to address metals-impacted soils in the RCRA Canyon, control potential exposure to ecological receptors, minimize surface water infiltration and reduce the potential for seeps. The RCRA cap is similar to the EE/CA cap and will include the following layers (from bottom to top): low permeability soil foundation (2 feet), geomembrane and geocomposite drainage layer, vegetative layer (2 feet) including a biotic barrier. Modeling indicates that minimizing infiltration would lower the water table and eliminate groundwater seeps in the RCRA Canyon area. This remedial alternative includes a very large amount (estimated to be approximately 400,000 cy) of cut/fill grading to reduce slope angles in the steep areas to 3:1 or less in order to install the RCRA cap. The existing slopes are steepest (almost 1:1) along the east slopes of the canyon which is where the greatest amount of grading will be required. Approximately 257,000 cy of borrow soil would be required to construct the soil caps, including the vegetative and foundation layers. The final surfaces of the cap on the RCRA Canyon and WCSA will include bench roads and surface drains to allow drainage and conveyance of stormwater. The stormwater from the entire canyon would be collected by a concrete drainage channel running down the middle of the canyon into a proposed retention basin that will be constructed in the footprint of the former Pond A-5. This stormwater will be sent by pipeline through or around the wetlands and discharged to the B-Drainage under the substantive requirements of the General Permit. No stormwater would need to be sent to an evaporation pond. As with Alternative 2, periodic inspection, maintenance and repair of the cap and stormwater controls are included. 10.3.3 Screening of Remedial Alternatives Table 10-3 presents the screening evaluation of the ten remedial alternatives listed above for FS Area 2 using the CERCLA screening criteria. With respect to effectiveness, Alternative 2 is rated moderate, Alternatives 3, 4, 5, 6 and 7 are all rated moderate to good and Alternatives 8, 9 and 10 are rated good. All of the alternatives address the ecological-receptor exposures adequately. Alternative 2 is rated lower because the ecological-cap does not reduce infiltration significantly and thus potential for seeps and stormwater quality impacts remain. Alternatives 3, 4, 5, 6 and 7 would all reduce infiltration and result in the water table dropping in the Canyon and thus reducing potential for seeps and impacts to stormwater quality. Of these, Alternatives 5, 6 and 7 are considered better because they address the entire canyon and would likely result in cleaner stormwater discharges from the canyon. Alternatives 8, 9 and 10 are rated the highest for effectiveness though there are challenges with implementability that are discussed below especially with the geosynthetic-lined caps. With respect to implementability, Alternatives 3 and 4 are all rated moderate to good, Alternatives 2, 5, 6, 7, 8 and 9 are rated moderate and Alternative 10 is rated the lowest at poor to moderate. The primary issue with implementability of Alternative 8 and certainly Alternative 10 is the ability to construct a cap which includes liners on steep slopes. Portions of the east slopes of the canyon are currently at slopes of around 1:1. For cost estimating purposes, it is assumed that cut/fill grading would reduce the slopes on average to 2:1 or less. For Alternatives 8 and 10 that involve capping the entire RCRA Canyon and WCSA, the total cut/fill grading is estimated to be up to 400,000 cy to achieve a 2:1 or less steepness on the east slope.


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Alternative 10 was rated the lowest because even if the slopes are reduced to 2:1, the RCRA cap has the potential for slip failure at the HDPE geomembrane interface. With respect to cost, Alternatives 2, 3, 4, 5, 6 and 7 are estimated to be moderate to high, while Alternatives 8, 9 and 10 are high. Alternatives 2, 3, 4 and 6 include segregated drainage channels for uncapped area stormwater flows that would be directed to an evaporation pond, and hence this alternative would include the incremental increased cost of a larger evaporation pond. With respect to green impacts assessment, Alternatives 2, 3 and 4 are rated moderate, Alternatives 5, 6 and 7 are rated moderate to high, Alternatives 8, 9 and 10 are rated high for green and sustainability impacts or environmental footprint. 10.3.3.1 Summary of Screening Evaluation Based on the screening evaluation, only Alternative 10 is screened out and the other nine alternatives are retained for detailed evaluation in Section 11. Alternative 10 is rated worse than Alternatives 8 and 9 with respect to implementability and its cost and environmental footprint are high. Moreover, Alternative 10 with a HDPE liner raises reliability concerns with potential slip failure on steep slopes and hence is not included for detailed evaluation. 10.4 FS Area 3 – Former Ponds and Pads, Remaining On-site Areas This section presents a summary of the nature and extent of the COCs in FS Area 3, a brief description of the applicable remedial alternatives to address the contaminants, and the screening evaluation of these alternatives. 10.4.1 Nature and Extent of Contamination FS Area 3 encompasses the FPP, Remaining On-Site (ROS) Areas, LTA, and MSA study areas of the site (Figure 10-5). Surface to shallow subsurface soils within these areas are locally impacted by both inorganic and organic constituents at concentrations in excess of their respective Ecological RBCs. While such exceedances are typically limited to depths of less than approximately 10 feet bgs in these areas, isolated locations may have inorganics exceedances persisting to depths of up to 20 feet bgs. The majority of Ecological RBC and/or UTL exceedances reported in this area are for inorganic constituents in surface soil in numerous isolated locations distributed across the FPP/ROS area, including chromium, copper and zinc, with exceedances for copper being most prevalent. Organics exceedances in the FPP/ROS area include PCE, TCE, PCB congeners, and total DDT, with total DDT constituting the majority of these exceedances. Most exceedances are reported for surface soils; however, many of these locations did not include sampling beneath the surface, so there is no control on the depth to which these exceedances may extend. Findings in those locations where sampling was conducted to deeper levels often indicate that Ecological RBC and /or UTL exceedances are limited to depths of 5 to 10 feet bgs, with concentrations typically diminishing with increased depth. In some locations, however, maximum organics concentrations are reported for shallow to mid-depth soils (e.g., RISBON-37 and RISBON-64). Inorganics exceedances within this depth range are typically related to exceedance of their respective UTLs, as Ecological RCBs are not applicable to these depths.


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Surface and subsurface soil conditions for inorganics in the MSA and LTA are largely similar to those in the FPP/ROS area, with Ecological RBC and/or UTL exceedances locally reported for chromium, copper and/or zinc. While the majority of inorganics exceedances within these areas are limited to surface or shallow subsurface soil samples, exceedances for some inorganics are locally reported at depths of up to 9 feet bgs in the LTA (copper and zinc at RISBLT-07) and 20 feet bgs in portions of the MSA (chromium at RISBMS-04 and RISBMS-10). While elevated levels of organic constituents such as VOCs, PAHs, dioxin TEQ, pesticides and herbicides are locally present within portions of the MSA and LTA study areas, with the exception of isolated surface soil exceedances for dioxin TEQ and Total DDT in in the MSA study area (RISBMS-01 and RISSMS-03, respectively), such elevated organics are typically present at depths which do not pose risk to potential ecological or human receptors. Several soil borings completed along the southern margin of the FPP area in close proximity to the southern site boundary, including locations RISBON-59, and related step-out locations RISBON-83, RISBON-86B, RISBON-87B, RISBON-88B and RISBON-89, encountered elevated levels of organics in samples collected from depths ranging from 0.5 to 55 feet bgs. Collectively these borings constitute what is referred to as the “RISBON-59 area.” Elevated organics reported in these borings include principally PAHs, poor-purging compounds, and to a lesser extent PCBs. A detailed discussion of the nature and extent of contamination in the RISBON-59 area was presented in the Final RI, Appendix B (CSC 2011a). A graphical presentation of the extent of contamination is shown on Figures 10-5A, 10-5B and 10-5C that include East-West and North-South cross sections of the RISBON-59 area. While these constituents are not identified as COCs at the site, available data in this area indicate conditions may present a continuing threat to groundwater quality at the southern site boundary and thus merits evaluation in the FS. 10.4.1.1 Risk-based Remedial Evaluation For site soils, only the FPP and LTA had elevated risk estimates for commercial/industrial worker exposures. PCE in shallow soil was the primary risk driver for the FPP, and MCPP was the primary risk driver for both surface and shallow soils at the LTA. Both of these chemicals are present at elevated concentrations in localized areas within these Study Areas. Potential cumulative cancer risk and noncancer hazard estimates exceeded target health levels because of a few locations. The sample locations that contributed the majority to the risk estimates were RISBON-37, RISBON-41 and RISBON-63 in the FPP just south of the PSCT, and RISBLT-02 in the LTA. A summary of the various locations with risk exceedances for FS Area 3 is presented below. Figure 10-5 shows ten soil hotspot locations identified based on the Tier 1 risk evaluation in this FS Area. These hot spot locations are selected based on contaminant concentrations being significantly above the Ecological RBCs, or if the exceedances occur in a cluster of samples, or if there are multiple chemicals with exceedances of Ecological RBCs. These locations are listed in the table below along with their related Tier 1 ecological risk drivers. Please note that based on the Tier 2 ecological-risk evaluation, there are no significant risks to birds and mammals in this area. Other than the shallow soil impacts at Location 3, this is also the location of the former Ponds A/B down to a depth of about 20 feet bgs. Locations 6, 7, 8, and 9 have elevated levels of DDT, PCBs and metals (Cu and Cr), but they do not have significant ecological or human health risk based on Tier 2 analysis (Section 7). Locations 1 and 2 have impacted soil as shown in the table below, but no Tier 2 analysis was conducted due to presumed remedial actions planned for these areas. Location 10 (RISBON-59) is a deep soil impacted area with PAHs and


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low levels of PPCs and PCBs. Location 10 comprises an area impacted with SVOCs with potential for impacting groundwater, and does not pose a shallow soil risk to human or ecological receptors. A residual risk analysis for the FPP study area using the 95 percent UCL concentrations was conducted (Appendix C-2, Table C-2) for different remedial scenarios including Location 3, or Locations 3 and 4, or Locations 3, 4 and 5. This analysis showed that addressing Locations 3 and 4 with a cap would achieve the ecorisk objective of LOAEL HQ<1 for the FPP study area.

FS Area 3 "Hot Spot" Locations Ecological-Risk Evaluation Location Tier 1 Ecological/HH

Risk Driver Boring Locations Tier 2 Ecological/HH Risks

1 Ecological risk from Cu and Zn in surface soil, HH risk due to MCPP in surface soil

RISBON-75, RISBLT-11, RISBLT-02, RISSRS-11

Not carried into Tier 2 risk assessments because of "presumed remedial actions"

2 Ecological risk from Cadmium, Chromium, Lead, Vanadium, DDT in surface soil

RISBMS-04, RISSMS-01, RISSMS-02, RISBMS-11


3 HH risk from PCB, PCE in shallow soil and ecological risk from PCE, TCE, and DDT in shallow soils

RISBON-37, RISSON-09, RISSON-32, RISBON-63, RISSRS-21, RISBON-66


4 Ecological risk from Ba, DDT, PCB in surface soils

RISBON-64, RISSON-31, RISSON-35, RISSON-36

No ecological risk

5 Ecological risk from Ba, Cu, PCB in shallow soil

RISSON-20, RISBON-72, RISBON-30

No Ecological risk

6 Ecological risk from DDT, PCB in shallow soil

RISSON-39, RISSON-27, RISSON-40

No Ecological risk

7 Ecological risk from Cu, Cr in soil

RISBON-26 No Ecological risk

8 Slight Ecological risk from Cu in soil

RISBON-27 No Ecological risk

9 Ecological risk from DDT and PCB in soil

RISSON-1, RISSRS-13 No Ecological risk

10 PAHs, organics in deep soil

RISBON-59 No Ecological risk; Groundwater issue

Location 1 is part of the LTA and the presumed remedial action is either asphalt capping or a combination of excavation and asphalt capping Location 2 is the Maintenance Shed Area and the presumed remedial action is capping such as a RCRA cap.


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Location 3 is south of the PSCT and has impacted shallow soil as discussed earlier but is also the location of former Ponds A/B down to a depth of 20 feet bgs. The areal extent of this hotspot location is 2.2 acres and an assumed maximum depth of contamination of 20 feet bgs to address former Ponds A/B sediments with a total volume of soil of 71,000 cy. The presumed remedial action is either capping or excavation. Location 10 (RISBON-59) area is different from the other hotspot locations because the contaminants do not pose an ecorisk. Location 10 is impacted with organics such as PAHs and poorly purging compounds that are a potential concern for impacting groundwater. The contamination is currently primarily in soil, and approximately 175 feet by 175 feet and up to a maximum of 50 feet below RCF Road elevation. Figures 10-5A, B and C show two cross sections delineating the approximate extent of contamination along with observed contaminant concentrations. The bottom elevation of the depth of contamination is about 400 ft MSL with the water table around 415 feet MSL. The impacted soil volume is estimated to be 65,000 cy. 10.4.2 Development of Remedial Alternatives The alternatives for FS Area 3 focus on Locations 1 through 4 and Location 10. Locations 3 and 4 were included based on the risk-based evaluation discussed earlier. This section discusses the screening evaluation for each of these locations in FS Area 3 and Table 10-4 presents a summary of the screening evaluation. The objectives of the remedial alternatives for FS Area 3 are:

Prevent ecological receptors from potential exposures to shallow soil (0-5 feet bgs) at Locations 1, 2, 3 and 4 using options such as capping or excavation to meet soil PRGs for COCs

Prevent rainwater infiltration or minimize leaching of contaminants at Locations 2, 3, 4 and 10 to protect groundwater including capping, monitoring and source removal options

Incorporate stormwater drains for the capped areas to direct clean stormwater to the drainage channel near PSCT-1 for discharge through or around the wetlands under the substantive requirements of the General Permit.

Grading and BMPs in uncapped areas to minimize erosion and sediment transport and allow the stormwater that sheet flows from the uncapped areas to discharge through or around the wetlands under the substantive requirements of the General Permit.

The following combination of capping and excavation technologies was considered for Locations 1, 2, 3, 4 and 10 hot spot locations: Location 1 Asphalt cap or Excavation (0-5 feet bgs) of uncapped portion Location 2 Ecological-cap or RCRA cap Location 3 Ecological-cap, RCRA cap or Excavation (0-5 or 0-20 feet bgs) Location 4 Ecological-cap, RCRA cap or Excavation (0-5 feet bgs) Location 10 GW Monitoring, ISTD or Excavation (0-50 feet bgs) Using these options for each hot spot location, the most viable remedial alternatives were assembled as listed and described below, including the No Action alternative.


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10.4.2.1 Alternative 1 No Action The No Action alternative is included as required by CERCLA guidance. 10.4.2.2 Alternative 2 Ecological-cap (Locations 2, 3, 4) (2’) + New Asphalt Cap (Location 1) +

GW Monitoring (Location 10) + Grading/BMPs (Uncapped Areas) + Stormwater Controls + ICs + Monitoring

This alternative involves placing an ecological-cap with a 2-foot soil cover on Locations 2, 3, and 4, covering a total area of 6.5 acres. Details of the ecological-cap were described earlier in Section 10.1.1. An asphalt cap will be placed on the uncapped portion of Location 1 (1 acre) to form a contiguous asphalt/concrete pad. See Section 10.1.1 for cap details. Location 10 is primarily a groundwater concern. Groundwater will be monitored at Location 10 (RISBON-59) with two new monitoring wells to be installed downgradient of this potential groundwater contamination source. There are no significant groundwater impacts based on monitoring to date, but long term groundwater monitoring at this location is included as part of this alternative. The monitoring component of this alternative includes periodic inspection, maintenance and repair of the ecological-caps, and stormwater and erosion controls over the long term. This would include monitoring the asphalt cap at Location 1 and the proposed groundwater monitoring wells at Location 10 would be included in the long term monitoring program. Grading and BMPs are included for the rest of FS Area (about 40 acres) as part of stormwater and erosion controls. Various approaches to BMPs will be evaluated including grading rills/gullies, placing check dams with rip rap, silt fences, etc. The stormwater from the uncapped areas of Area 3 would sheet flow into the RCF Pond and then under the RCF Road via a new culvert, and then discharge through the Pond 13 retention basin through or around the wetlands and then to the B-drainage under the substantive requirements of the General Permit. 10.4.2.3 Alternative 3 RCRA Cap (Locations 2, 3, 4) + Excavate/New Asphalt cap (Location 1)

(5’) + GW Monitoring (Location 10) + Grading/BMPs (Uncapped Areas) + Stormwater Controls + ICs + Monitoring

This alternative involves extending the RCRA cap from the Capped Landfill Area over Locations 2, 3, and 4, covering a total area of 6.5 acres (Figure 11-13A). The details of the RCRA cap are as presented earlier in Section 10.1.1. The RCRA cap at these locations would be tied into the existing and proposed caps for FS Area 1. For Location 1, this alternative involves excavation of the top 5 feet of the uncapped soil area, encompassing an area of 1 acre, with a soil volume of 8,000 cy, and asphalt capping covering an area of 1 acre to get a contiguous asphalt/concrete pad. The excavated soils are disposed of at the PCB Landfill prior to capping. For Location 10 (RISBON-59), an SVOC-impacted source area that is considered a potential concern for groundwater, groundwater conditions will be monitored at two new wells to be installed downgradient of RISBON-59.


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The monitoring component of this alternative also includes periodic inspection, maintenance and repair of the RCRA and asphalt caps, and stormwater controls over the long term. Grading and BMPs are included for the rest of FS Area (about 40 acres) as part of stormwater and erosion controls as described in Alternative 2. 10.4.2.4 Alternative 4 RCRA Cap (Location 2) + Excavate ((Location 3) (20’); (Location 4) (5’)) +

Excavate/New Asphalt Cap (Location 1) (5’) + Groundwater Monitoring (Location 10) + Grading/BMPs (Uncapped Areas) + Stormwater Controls + ICs + Monitoring

This remedial alternative involves extending the RCRA cap over the Maintenance Shed Area (Location 2) and excavation of top 5 feet bgs and new asphalt cap for Location 1 as in Alternative 3. In addition, this alternative includes excavation of Hotspot Locations 3 and 4 south of the PSCT (Figure 11-14A). For Location 3, this alternative involves excavation of the top 20 feet with a soil volume of 71,000 cy. The Location 3 excavation in this alternative involves removal of the remaining impacted materials associated with the former Pond A/B sediments (down to 20 feet bgs) and the shallow soils (0-5 feet bgs) with Ecological RBC exceedances. The excavation sidewalls are assumed to be sloped 1:1. The excavation would extend in size until risk-based standards are achieved. The extent and depth of any proposed excavation of Pond A/B may be limited based on prior excavation experience in this area. For example, based on prior experience with excavation in the vicinity of Pond A/B, the depth of excavation may be limited by the location of the Lower HSU contact and to the north the close proximity of the PSCT trench that would pose a stability concern. The excavated soil from Location 3 is assumed to be disposed of at the PCB Landfill prior to capping of the PCB Landfill. For cost estimating purposes, it is assumed that about one-third of the excavated soil (24,000 cy) is segregated and reused as backfill while the remainder (47,000 cy) is disposed of in the PCB Landfill. To backfill the remainder of the excavation, clean fill is brought in from the NW Borrow Area (Figure 10-2). For Location 4, this alternative involves excavation of the top 5 feet with an estimated soil volume of 13,000 cy, The excavation sidewalls as assumed to be sloped 1:1. The extent of this excavation is preliminary and would be confirmed during remedial design. The excavation would extend in size until confirmatory sampling demonstrates that risk-based standards are achieved. For Hotspot Location 10 (RISBON-59), the remedial alternative proposes two additional Upper HSU downgradient groundwater monitoring wells to ensure that there is no impact in the future to groundwater from this deep soil impacted area. Grading and BMPs are included for the rest of FS Area (about 40 acres) as part of stormwater and erosion controls as described in Alternative 2. The stormwater in the drainage channel will flow under a culvert on RCF Road to Pond 13 and then through or around the wetlands to the B-Drainage under the substantive requirements of the General Permit. The monitoring component of this alternative also includes periodic inspection, maintenance and repair of the RCRA and asphalt caps, and stormwater controls over the long term. 10.4.2.5 Alternative 5 RCRA Cap (Location 2) + Excavate ((Location 3) (20’); (Location 4) (5’);

(Location 10) (50’))/Place in PCB Landfill/Backfill + Excavate/New Asphalt Cap


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(Location 1) (5’) + Grading/BMPs (Uncapped Areas) + Stormwater Controls + ICs + Monitoring

This remedial alternative involves extending the RCRA cap over the Maintenance Shed Area (Location 2) and excavation of Locations 1 and 3 as described in Alternative 4, but adds the excavation of Location 10 (Figure 11-15A). For Location 10, this excavation involves removal of the top 50 feet below the RCF Road. The Location 10 excavation extends about 175 feet by 175 feet and based on sloped sidewalls at 1:1, the total excavation soil volume is 65,000 cy. The excavation extends down to about 10 feet below the water table to a bottom elevation of around 400 feet MSL. This excavation would require dewatering prior to reaching the excavation bottom. As with Location 3, the excavated impacted soil from Location 10 is assumed to be disposed of at the PCB Landfill and clean backfill is brought in from the NW Borrow Area. Grading and BMPs are included for the rest of the FS Area (40 acres) as in the previous alternatives. The stormwater in the drainage channel will flow under a culvert on RCF Road to Pond 13 and then through or around the wetlands to the B-Drainage under the substantive requirements of the General Permit. 10.4.2.6 Alternative 6 Excavate (Locations 2, 4) (5’)/Place in PCB Landfill +Excavate Location 3

(20’)/Disposal at a Permitted Facility) + Excavate/New Asphalt Cap (Location 1) (5’) + In-Situ Thermal Desorption (Location 10) (0’-50’ bgs) + Grading/BMPs (Uncapped Areas) + Stormwater Controls + ICs + Monitoring

This alternative includes excavation of Locations 1, 2, 3, and 4 covering an area of 6.6 acres as discussed in Alternative 5 with a total soil volume of 115,000 cy. Excavated soil from Location 3 would be sent for disposal at a permitted facility due to limited capacity in the PCB Landfill. Other excavated soil would be placed in the PCB Landfill. The excavation sidewalls are assumed to be sloped 1:1. The extent of these excavations is preliminary and would be confirmed during remedial design. The excavation would extend in size until confirmatory sampling demonstrates that risk-based standards are achieved. To backfill the excavations, clean fill is brought in from the NW Borrow Area (Figure 10-2). For Location 10, this alternative includes ISTD covering an area about 175 feet by 175 feet down to 50 feet below the RCF Road. ISTD at Location 10 would involve installing closely-spaced SVE heater wells (10-foot spacing, 290 wells) to heat the 175’ x 175’ source area to about 300 to 400oF and simultaneously extract vapors using a conventional SVE blower system. The extracted vapors would be cooled and captured in a vapor-phase granular activated carbon system, or treated in a thermal oxidizer. The system is assumed to operate for up to 2 years. The electrical heating of the source area would require a large amount of electrical energy estimated to be approximately 13,000,000 kWh, based on assuming 200 kWhr per cubic yard. Grading and BMPs are included for the rest of FS Area 3 (about 40 acres) as part of stormwater and erosion controls as described in Alternative 2.


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10.4.2.7 Alternative 7 Excavate (Locations 1, 2, 4) (5’) + Excavate (Location 3) (20’) and (Location 10) (50’)/Disposal at a Permitted Facility + Excavate/New Asphalt Cap (Location 1) (5’) + Grading/BMPs (Uncapped Areas) + Stormwater Controls + ICs + Monitoring

This alternative involves excavation of the top 5 feet of Locations 1, 2, and 4 (8,000 cy, 21,000 cy and 9,000 cy, respectively) (Figure 11-16A). The excavation sidewalls are assumed to be sloped 1:1. The extent of these excavations is preliminary and would be confirmed during remedial design. The excavation would extend in size until confirmatory sampling demonstrates that risk-based standards are achieved. For Location 3, this alternative involves excavation of the top 20 feet with a soil volume of 71,000 cy. The Location 3 excavation in this alternative involves removal of the remaining impacted materials associated with the former Pond A/B sediments (down to 20 feet bgs) and the shallow soils (0-5 feet bgs) with Ecological RBC exceedances. The excavation sidewalls are assumed to be sloped 1:1. The excavation would extend in size until risk-based standards are achieved. The excavated soil from Location 3 is assumed to be disposed of at a Class I landfill with one-half non-RCRA hazardous and one-half non-hazardous. For cost estimating purposes, it is assumed that about one-third of the excavated soil (24,000 cy) is segregated and reused as backfill while the remainder (47,000 cy) is sent for disposal. To backfill the remainder of the excavation, clean fill is brought in from the NW Borrow Area (Figure 10-2). For Location 10, this excavation involves removal of the top 50 feet below the RCF Road with a soil volume of 65,000 cy. The Location 10 excavation extends about 175 feet by 175 feet and goes about 10 feet below the water table and hence would require dewatering prior to reaching the excavation bottom. As with Location 3, the excavated soil from Location 10 is assumed to be disposed of at a Class I landfill and clean backfill is brought in from the NW Borrow Area. Grading and BMPs are included for the rest of FS Area (about 40 acres) as part of stormwater and erosion controls as described in Alternative 2. 10.4.3 Screening of Remedial Alternatives Table 10-4 presents the screening evaluation of the seven remedial alternatives listed earlier for FS Area 3 using the CERCLA screening criteria. With respect to effectiveness, Alternatives 3, 4 and 5 are rated good, Alternative 7 is rated moderate to good and Alternatives 2 and 6 are rated lowest at moderate. Alternative 6 is rated lowest because of the limitations of in-situ technologies including ISTD in the low permeability claystone formation and the potential for emissions of contaminants during the drilling of 290 closely spaced wells and during treatment system operations, including potential system malfunctions. Alternatives 3, 4 and 5 are rated the highest because they are effective in addressing the RAOs for controlling ecological exposures, protecting groundwater and providing stormwater quality suitable for discharge. Alternative 2 is rated moderate because it would not provide adequate groundwater protection because the ecological-cap would allow infiltration and because of the uncertainty with stormwater quality. With respect to implementability, Alternatives 2, 6 and 7 are rated moderate while Alternatives 3, 4 and 5 are rated moderate to good. Alternative 2 is rated lower because of moderate concerns with respect to long term maintenance of ecological-caps, while Alternative 6 is rated


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lower due to challenges with ISTD implementation and reliability in this claystone formation, and Alternative 7 is rated lower because of challenges with the deep excavation (up to 50 feet below RCF Road) going below the water table. Alternatives 3, 4 and 5 are rated higher at moderate to good because there are no significant challenges with construction of the RCRA caps or the excavations. With respect to cost, Alternatives 2, 3, 4 and 5 are estimated moderate to high and Alternatives 6 and 7 are high. Alternative 2 is moderate to high (same as Alternative 3) in cost because it is expected to have higher O&M costs for maintenance and repair of the ecological-caps. Alternative 6 is high in cost because of the ISTD implementation at Location 10 to address 65,000 cy of the source area soils that would use a very large amount of electricity (estimated to be 13,000,000 KWhrs). Alternative 7 is high in cost because of the high cost of transportation and disposal at a permitted facility of the excavated source area soils. Some disposal at a permitted facility would be required because of the limited available space in the PCB Landfill. With respect to green impacts assessment, the impacts from Alternatives 2, 3, 4 and 5 are considered to be moderate while Alternatives 6 and 7 are high. The impacts from Alternatives 2 and 3 are considered to be the same because though Alternative 3 would have more impacts during construction, Alternative 2 would have more impacts over the long term due to greater amount of maintenance and repair. The impacts from Alternatives 4 and 5 are also considered to be moderate because they involve cap construction and excavations with disposal in the PCB Landfill. 10.4.3.1 Summary of Screening Evaluation Based on the screening evaluation, Alternatives 2 and 6 are not retained for the detailed evaluation. Alternative 3 is retained as a more viable option with higher effectiveness than Alternative 2. The RCRA caps in Alternative 3 provide greater groundwater protection and would tie into the other existing and proposed caps for FS Area 1. Alternative 6 is not retained because it is a very high cost option, with a high environmental footprint and uncertain effectiveness of the in-situ technology in the claystone formation. Alternative 7 is retained as a high mass removal alternative for the detailed evaluation and is considered better than Alternative 6. 10.5 FS Area 4 – Stormwater Ponds and Treated Liquid Impoundments This section presents a summary of the nature and extent of the COCs in FS Area 4, a brief description of the applicable remedial alternatives to address the contaminants, and the screening evaluation of these alternatives. 10.5.1 Nature and Extent of Contamination FS Area 4 encompasses the five existing ponds at the site, including the three stormwater ponds (the RCF, the A-Series Pond, and Pond 13) and the two treated liquids impoundments (Pond 18 and Pond A-5) (Figure 10-6). As discussed with USEPA, the FS anticipates that the liquids in these ponds will be removed as part of remediation at the site. Considering this, available data for sediment samples collected from these ponds during the RI have been evaluated relative to soil RBCs for the detected constituents. Inorganics exceedances of Ecological RBCs in this area are limited to copper in surface and shallow subsurface samples. Copper is found to locally exceed its Ecological RBC in multiple


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samples from four of the five ponds. The only organic constituent reported to exceed its Ecological RBC was PCB congeners in a single surface sample from the west end of the RCF Pond (RISESP-17). Available data indicate that inorganics concentrations typically diminish with increased depth beneath the surface, and that exceedances are limited to depths of less than 5 feet bgs. Arsenic concentrations detected in several site surface-water impoundments, including the A-Series Pond, Pond 13, and the RCF, are estimated to pose a potentially unacceptable risk to site commercial/industrial workers. As noted above, the FS assumes that all of the ponds will have the current water removed and that the footprint of the ponds will be backfilled/graded to prevent future accumulation of water; as such they will be unavailable as a pathway for aquatic receptors, essentially eliminating the potential for adverse effects to aquatic receptors. 10.5.2 Development of Remedial Alternatives Table 10-1 identifies the remedial alternatives and the remedial objectives for FS Area 4. Nine remedial alternatives are listed here to undergo the screening analysis for FS Area 4 which will be discussed in the next subsection. The remedial alternatives in FS Area 4 focus on the closing of the existing stormwater ponds (RCF Pond, A-Series Pond, 13) and the treated liquid impoundments (Pond A-5 and 18). The objectives of the remedial alternatives for FS Area 4 are:

Prevent ecological receptors from potential exposures to shallow soil or sediment (0-5 feet bgs) at the RCF Pond, A-Series Pond, Pond 18, Pond A-5, Pond 13 and any proposed evaporation pond at the site using various types of capping, pond lining or excavation approaches;

Prevent ecological exposures to COCs in surface water such that exposures are below acceptable levels through the use of netting, fencing and other deterrents to protect ecological species at the site;

Eliminate groundwater seepage into the footprint of the RCF, A-Series and other ponds at the site to protect ecological receptors;

Manage stormwater by eliminating pond water prior to and during FS construction and construct a new evaporation pond adequately sized to handle all water that cannot be discharged under the substantive requirements of the General Permit;

Incorporate stormwater drains for the capped areas to direct clean stormwater to the culvert under RCF Road for discharge through or around the wetlands under the substantive requirements of the General Permit; and,

Complement the remedial alternatives for FS Area 4 with the FS Area 5 groundwater remedial alternatives with regards to the need for an evaporation pond at the site.

The nine remedial alternatives for FS Area 4 are briefly described below. 10.5.2.1 Alternative 1 No Action The No Action alternative is included as required by CERCLA guidance.


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10.5.2.2 Alternative 2 Ecological Cap (RCF, A-Series Ponds) (2’) + Construct New 11-Acre Evaporation Pond + RCRA Cap (Pond 18) + Lined Retention Basins (Ponds A-5, 13) + Stormwater Controls + ICs + Monitoring

This remedial alternative involves managing existing stormwater in the A-Series Pond and RCF Pond as discussed in Section 10.1.3 to reduce or eliminate those volumes prior to remedy construction. The post remedy construction stormwater management plan for the site would utilize a new lined evaporation pond constructed north of the RCF Pond. The impacted bottom areas of the RCF Pond and A-Series Pond (total area of 22.4 acres) sediments would be raised to 415 feet and 425 feet elevation respectively and then capped with an ecological-cap (see Section 10.1.1 for cap details), which is comprised of a 2-foot soil cover (Figure 11-17A). A new, double-lined 11-acre evaporation pond with a LCRS and leak detection system would be constructed south of the PSCT and north of the RCF Pond. The construction of the evaporation pond (approximately 700 feet by 700 feet) would require excavation of 74,000 cy and using this material as fill in the areas of lower elevation and for the berm. The bottom of the pond will be set above anticipated future water table levels to avoid groundwater intrusion. The bottom would be lined with a geocomposite HDPE liner system to create the evaporation pond as described in Section 10.1.1.7. Environmental controls would be implemented to prevent wildlife contact with the evaporation pond as described in Section 10.1.4.2. The types of controls would be selected and designed during remedial design (after the ROD) and after input and consultation with U.S. FWS and CDFG. The wildlife controls may include, but not be limited to: perimeter fencing, elimination of wildlife habitat (vegetation), hazing, potential netting or screen mesh, and routine biological monitoring. A new lined retention basin would be constructed in the footprint of Pond A-5 (2.5 acres), which would be partially backfilled to ensure the pond bottom is above projected groundwater levels. Pond 13 (1.9 acres) would be partially backfilled using the Pond 13 dike and then lined with a HDPE material to convert it to another new lined retention basin. Pond 18 would be backfilled to match surface grades and ensure stormwater flows off that area of the site, and will be capped with a RCRA cap. The cap construction details for the ecological-cap, RCRA cap and the pond liner are discussed earlier in Section 10.1.1. The stormwater controls include drainage channels that would be constructed on a portion of the RCF and A-Series ponds to allow drainage from the Capped Landfills and the RCRA Canyon to flow through or around the existing wetlands and discharge to the B-Drainage under the substantive requirements of the General Permit. The monitoring component of this alternative includes periodic inspection, maintenance and repair of the caps, drainage channels, and stormwater controls over the long term. 10.5.2.3 Alternative 3 Ecological Cap (RCF Pond, Segregate East RCF) (2’) + Construct 11-

acre Lined Evaporation Pond (A-Series Pond) + RCRA Cap (Pond 18) + Lined Retention Basins (Pond A-5, Pond 13) + Stormwater Controls + ICs + Monitoring

This remedial alternative involves managing existing stormwater in the A-Series Pond and RCF Pond as discussed in Section 10.1.3 to reduce or eliminate those volumes prior to remedy


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construction. The post remedy construction stormwater management plan for the site would utilize a new lined evaporation pond constructed in the footprint of the A-Series Pond. The RCF Pond (11.4 acres) would be lined with an ecological-cap after it is drained and partially filled to raise the elevation of the West RCF bottom to a minimum of 415 feet MSL, while the east end of the RCF would be segregated with a 5-foot high berm (Figure 11-18A). Raising the bottom of the west end of the RCF Pond would ensure that there is no groundwater intrusion to this area of the former pond. Meanwhile, the east end of the RCF Pond will be segregated as a contingency measure that separates and evaporates any groundwater intrusion that may occur. The A-Series Pond (11 acres) would be converted to a new double-lined evaporation pond with a LCRS and leak detection system by first raising the bottom to 425 ft MSL with fill soil derived from excavation along the northeast shore line and if needed additional soil from the borrow area outside the site boundaries. The excavation of the northeast shoreline also serves to expand the size of the pond to 11 acres. The A-Series Pond bottom then would be lined with a dual HDPE liner system (Section 10.1.1.8) to convert it to the evaporation pond. Environmental controls would be implemented to prevent wildlife contact with the evaporation pond as described in Section 10.1.4.2. The types of controls would be selected and designed during remedial design (after the ROD) and after input and consultation with U.S. FWS and CDFG. The wildlife controls may include, but not be limited to: perimeter fencing, elimination of wildlife habitat (vegetation), hazing, potential netting or screen mesh, and routine biological monitoring. Pond 18 would be capped with a RCRA cap and graded to allow stormwater to sheet flow south to the A-Series Pond. Ponds A-5 and 13 would be backfilled with soil and lined to serve as retention basins for stormwater as described in Alternative 2. The cap construction details for the ecological-cap, RCRA cap and the pond liner are discussed in Section 10.1.1. The stormwater in the West RCF Pond would drain to the culvert under RCF Road by sheet flow and surface drains. The stormwater controls include drainage channels that would be constructed on a portion of the RCF Pond to allow drainage from the Capped Landfills in FS Area 1. All the stormwater from clean or capped areas would go through the retention basin in the footprint of Pond 13 to through or around the wetlands and B-drainage under the substantive requirements of the General Permit. The monitoring component of this alternative includes periodic inspection, maintenance and repair of the caps, drainage channels, and stormwater controls over the long term. 10.5.2.4 Alternative 4 Ecological Cap (RCF Pond) (2’) + Construct 11-acre Lined Evaporation

Pond (A-Series Pond) + RCRA Cap (Pond 18) + Lined Retention Basin (Pond A-5, Pond 13) + Stormwater Controls + ICs + Monitoring

This alternative involves managing liquids in the existing stormwater ponds as discussed in Section 10.1.3. The RCF Pond is lined with an ecological cap after it is drained and the pond bottom is raised to 415 feet MSL with borrow soil as in Alternative 2 (Figure 11-19A). Raising the bottom of the RCF Pond would ensure that there is no groundwater intrusion to the former pond. The A-Series Pond would be converted to an 11-acre lined evaporation pond as discussed in Alternative 3. Environmental controls would be implemented to prevent wildlife contact with the evaporation ponds as described in Section 10.1.4.2. The types of controls would be selected


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and designed during remedial design (after the ROD) and after input and consultation with U.S. FWS and CDFG. The wildlife controls may include, but not be limited to: perimeter fencing, elimination of wildlife habitat (vegetation), hazing, potential netting or screen mesh, and routine biological monitoring. Pond 18 is capped with a RCRA cap and Pond A-5 and Pond 13 are filled to raise the pond bottom and then lined to serve as stormwater retention basins as discussed in previous alternatives. The ecological cap on the RCF would be sloped and equipped with surface drains to direct stormwater towards the culvert under RCF Road as discussed for Alternative 3. All of the stormwater from the capped areas would drain through the retention basin in the footprint of Pond 13 and then through or around the wetlands to the B-Drainage under the substantive requirements of the General Permit as in the previous alternatives. The monitoring component of this alternative includes periodic inspection, maintenance and repair of the cap, drainage channels, and stormwater controls over the long term. 10.5.2.5 Alternative 5 Ecological Cap (RCF Pond, portion of A-Series Pond) + Construct 6-acre

Lined Evaporation Pond (A-Series Pond) + RCRA Cap (Pond 18) + Lined Retention Basin (Pond A-5, Pond 13) + Stormwater Controls + ICs + Monitoring

This alternative involves managing liquids in existing stormwater ponds as discussed in detail in in Section 10.1.3. The RCF Pond is lined with an ecological cap after it is drained and the bottom raised to 415 feet MSL across the entire pond as in Alternative 2 (Figure 11-20A). The A-Series Pond is converted to a 6-acre double-lined evaporation pond with a LCRS and leak detection system after the bottom is first raised to 425 feet MSL with fill soil from the northeast shore line. The bottom of the 6-acre evaporation pond is lined with a geocomposite HDPE liner system. The 6-acre pond will be split up into six 1-acre evaporation ponds located within the A-Series Pond footprint. The remaining area that is not included as part of the A-Series Pond footprint will be covered with an ecological cap and surface drains. Environmental controls would be implemented to prevent wildlife contact with the evaporation ponds as described in Section 10.1.4.2. The types of controls would be selected and designed during remedial design (after the ROD) and after input and consultation with U.S. FWS and CDFG. The wildlife controls may include, but not be limited to: perimeter fencing, elimination of wildlife habitat (vegetation), hazing, potential netting or screen mesh, and routine biological monitoring. Pond 18 is capped with a RCRA cap and Ponds A-5 and 13 are converted to retention basins as discussed in previous alternatives. The ecological cap on the RCF and portion of the A-Series Pond are sloped and equipped with drains to direct stormwater to the retention basin in the footprint of Pond 13. The stormwater from this retention basin flows through or around the wetlands to the B-Drainage under the substantive requirements of the General Permit. The monitoring component of this alternative includes periodic inspection, maintenance and repair of the cap, drainage channels, and stormwater controls over the long term. 10.5.2.6 Alternative 6 Ecological Cap (RCF Pond, A-Series Pond) (2’) + RCRA Cap (Pond 18)

+ Lined Retention Basin (Pond A-5, Pond 13) + Stormwater Controls + ICs + Monitoring

This alternative involves managing liquids in the existing stormwater ponds as discussed in Section 10.1.3. This alternative is the same as Alternative 2 except it does not include an evaporation pond. This alternative is intended to complement the remedial alternatives in Area 5


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groundwater (Section 10.6) where the groundwater is treated for both VOCs and inorganics and discharged under the substantive requirements of the General Permit and thus does not require an evaporation pond. The RCF Pond is lined with an ecological cap after it is drained and the pond bottom is raised to 415 feet MSL with borrow soil just as in previous alternatives (Figure 11-21A). The A-Series Pond bottom is raised to 425 feet MSL with fill soil from the northeast shore line and then covered with an ecological cap as in Alternative 2. Pond 18 is capped with a RCRA cap and Ponds A-5 and 13 are converted to retention basins as discussed in previous alternatives. The ecological caps on the RCF and the A-Series Pond are sloped and equipped with drains to direct stormwater to the retention basin in the footprint of Pond 13. The stormwater from this retention basin flows through or around the wetlands to the B-Drainage under the substantive requirements of the General Permit. The monitoring component of this alternative includes periodic inspection, maintenance and repair of the cap, drainage channels, and stormwater controls over the long term. 10.5.2.7 Alternative 7 ET Cap (RCF Pond, portion of A-Series Pond) + Construct 6-acre Lined

Evaporation Pond (A-Series Pond) + RCRA Cap (Pond 18) + Lined Retention Basin (Pond A-5, Pond 13) + Stormwater Controls + ICs + Monitoring

This alternative involves managing liquids in existing stormwater ponds as discussed in detail in Section 10.1.3. The RCF Pond is lined with an ET cap (see Cap Detail in Figure 10-1A) after it is drained and the bottom raised to 415 feet MSL (Figure 11-22A). The ET soil cap is 5 feet of engineered low permeability claylike soil that includes a vegetative layer that is 4 feet thick and is lightly compacted to about 85 percent and a 1-foot thick compacted foundation layer. The soil cap is intended to store water, allow growth of vegetation and removal of soil moisture through transpiration and evaporation. This ET cap will control potential exposures to ecological receptors and will reduce surface water infiltration. The A-Series Pond bottom is raised to 425 feet MSL with fill soil from the northeast shore line and a 6-acre double-lined evaporation pond is constructed within it including environmental controls as discussed in Alternative 5. The remaining portion of the A-Series Pond is covered with an ET cap. Pond 18 is capped with a RCRA cap and Ponds A-5 and 13 are converted to retention basins as discussed in previous alternatives. The ecological cap on the RCF and portion of the A-Series Pond are sloped and equipped with drains to direct stormwater to a retention basin in the footprint of Pond 13. The stormwater from this retention basin flows through or around the wetlands and then through the B-Drainage under the substantive requirements of the General Permit. The monitoring component of this alternative includes periodic inspection, maintenance and repair of the cap, drainage channels, and stormwater controls over the long term. 10.5.2.8 Alternative 8 Excavate/Clean Backfill (RCF Pond, A-Series Pond) + Construct New 11-

Acre Lined Evaporation Pond (North of RCF Pond) + RCRA Cap (Pond 18) + Lined Retention Basins (Pond A-5, Pond 13) + Stormwater Controls + ICs + Monitoring

This remedial alternative involves managing existing stormwater in the A-Series Pond and RCF Pond as discussed in Section 10.1.3 to reduce or eliminate those volumes prior to FS construction. The post remedy construction stormwater management plan would utilize a new lined evaporation pond constructed north of the RCF Pond.


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After emptying the two ponds, the RCF Pond and A-Series Pond (22.4 acres total) sediments would be excavated up to 5 feet below surface and backfilled/graded (Figure 11-23A). Additional fill would be used to raise the bottom of the RCF Pond to a minimum of 415 feet MSL. The east end of the RCF would be raised to a higher elevation to ensure the stormwater flows towards and through the culvert under the RCF Road. A new lined 11-acre evaporation pond would be constructed south of the PSCT and north of the RCF Pond including environmental controls as described in Alternative 2. The construction of the evaporation pond (approximately 700 feet by 700 feet) would require excavation of 74,000 cy and using this material as fill in the areas of lower elevation and for the berm. The bottom then would be lined with a geocomposite HDPE liner system to create the evaporation pond. Pond 18 would be capped with a RCRA cap and graded to allow stormwater to sheet flow south to the A-Series Pond. Ponds A-5 and 13 (total area of 4.1 acres) would be backfilled with soil and lined to serve as retention basins for stormwater as described in Alternative 2. The cap construction details for the RCRA cap and the pond liner are discussed in Section 10.1.1. All the stormwater from clean or capped areas would go through the retention basin in the footprint of Pond 13 through or around the wetlands to the B-drainage under the substantive requirements of the General Permit. The monitoring component of this alternative includes periodic inspection, maintenance and repair of the cap, drainage channels, and stormwater controls over the long term. 10.5.2.9 Alternative 9 RCRA Cap (RCF Pond, Pond 18) (5’) + Construct New 11-Acre Lined

Evaporation Pond (A-Series Pond) + Lined Retention Basins (Pond A-5, Pond 13) + Stormwater Controls + ICs + Monitoring

This remedial alternative involves managing existing stormwater in the A-Series Pond and RCF Pond as discussed in Section 10.1.3 to reduce or eliminate those volumes prior to FS construction. The post remedy construction stormwater management plan for the site would utilize a new lined evaporation pond constructed in the footprint of the A-Series Pond. The RCF Pond (11.4 acres) would be lined with a RCRA cap after it is drained, and the elevation of the pond bottom would be raised to a minimum of 415 feet MSL. Raising the bottom of this pond would minimize the potential for groundwater intrusion into the pond, and installing the RCRA cap would prevent infiltration into groundwater. The A-Series Pond (11 acres) bottom would be raised to 425 feet MSL with fill soil from the northeast shore line that would be excavated to expand the pond to cover 11 acres. The A-Series Pond then would be converted to an 11-acre double lined evaporation pond with a LCRS and leak detection system using a geocomposite HDPE liner system. Environmental controls would be implemented to prevent wildlife contact with the evaporation pond as described in Section 10.1.4.2. The types of controls would be selected and designed during remedial design (after the ROD) and after input and consultation with U.S. FWS and CDFG. The wildlife controls may include, but not be limited to: perimeter fencing, elimination of wildlife habitat (vegetation), hazing, potential netting or screen mesh, and routine biological monitoring. Pond 18 would be capped with a RCRA cap and graded to allow stormwater to sheet flow south to the A-Series Pond. Ponds A-5 and 13 (total area of 4.1 acres) would be backfilled with soil and lined to serve as retention basins for stormwater. The cap construction details for the RCRA cap and the pond liner are discussed in Section 10.1.1.


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All the stormwater from clean or capped areas would go through the retention basin in the footprint of Pond 13 through or around the wetlands to the B-drainage under the substantive requirements of the General Permit. The monitoring component of this alternative includes periodic inspection, maintenance and repair of the cap, drainage channels, and stormwater controls over the long term. 10.5.3 Screening of Remedial Alternatives Table 10-5 presents the screening evaluation of the nine remedial alternatives listed earlier for FS Area 4 using the CERCLA screening criteria. With respect to effectiveness, Alternative 2, 3, 4 and 8 are rated moderate, while Alternatives 5, 6, 7 and 9 are rated moderate to good. All alternatives address potential ecological exposure risks by capping or excavation and involve raising the pond bottoms for the RCF Pond and the A-Series Pond to minimize potential for groundwater intrusion. Alternatives 2, 3, 4 and 8 are rated lower at moderate because they have a larger 11-acre evaporation pond that is expected to not be as effective with respect to ecological species protection compared to a smaller or no evaporation pond. Alternative 8 in addition would have some concerns with emissions of contaminants as dust during excavation. Alternatives 5 and 7 have a smaller 6-acre evaporation pond that is constructed as six 1-acre ponds which enables construction of the netting and drift fences to protect ecological species and hence rated higher. Alternative 6 is rated higher because it does not have an evaporation pond and hence does not face the concern with ecological species. Alternative 9 is rated higher because the RCRA cap will prevent infiltration in the RCF Pond though the 11-acre evaporation pond would still face ecological concerns. With respect to implementability, Alternatives 2, 3, 4, 8 and 9 are all rated moderate due to the technical challenges with construction of the netting and drift fences to reliably protect ecological species. In addition, Alternative 8 is rated lower because of the moderate technical challenges with excavation/capping of the muddy pond bottoms and backfill compaction. Alternatives 5 and 7 are rated higher because the six 1-acre pond approach to evaporation pond construction faces less challenges and is considered more reliable with respect to species protection. Alternative 6 is rated higher because it doesn’t include construction of an evaporation pond. With respect to cost, Alternatives 5 and 6 are estimated to be moderate, Alternatives 3, 4 and 7 are moderate to high, and Alternatives 2, 8 and 9 are high. The estimated cost for Alternative 8 is high because of the high cost disposal at a permitted facility for excavated sediments and construction of a new 11-acre evaporation pond north of the RCF Pond, while Alternative 9 is high because it includes a RCRA cap across the RCF Pond. The estimated cost for Alternative 2 is high because it includes construction of a new 11-acre evaporation pond north of the RCF Pond. With respect to green impacts assessment (or environmental footprint), the impacts from Alternatives 5 and 6 are considered to be moderate, Alternatives 3, 4 and 7 are moderate to high, and Alternatives 2, 8 and 9 are high. Alternative 6 is considered to have the lowest impact because it doesn’t involve construction of an evaporation pond. Alternative 8 has the greatest impact because it involves excavation and disposal at a permitted facility of impacted sediments totaling about 140,000 tons (almost 10,000 truck trips) to Buttonwillow, California about 120 miles away. The impacts from Alternative 2 are also considered to be high due to the construction of a new 11-acre evaporation pond north of the RCF Pond that would involve a very large excavation. The impacts from Alternative 9 are considered high because it includes a


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RCRA cap for the RCF that involves a large amount of soil and HDPE liner material that is part of the cover system. 10.5.3.1 Summary of Screening Evaluation Based on the screening evaluation, Alternatives 2 through 8 are retained while Alternative 9 is not retained. Alternative 9 is similar to Alternatives 4 and 7 except it uses a RCRA cap instead of the Ecological cap or ET cap used in Alternatives 4 and 7 respectively. Alternative 9 is significantly higher in cost with the benefit of more effectively limiting infiltration than Alternatives 4 and 7. But the Ecological cap and ET cap also significantly limit infiltration as shown by the HELP model. Furthermore, Alternatives 2 through 8 meet the primary RAO of protecting ecological receptors from contaminants in sediments and preventing infiltration is not an RAO. 10.6 FS Area 5 – Groundwater This section presents the evaluation for groundwater remedial alternatives that includes the organics and inorganics dissolved plumes and the areas of NAPL at the site. VOCs are used to portray the extent of organics contamination because the other organic compounds (SVOCs, pesticides/PCBs, etc.) are contained within the VOC plume. The nature and extent of contamination and the development of remedial alternatives are discussed based on the individual groundwater subareas presented in Section 8. These groundwater subareas include: Area 5 North which is north of the PSCT and includes the PCB Landfill, BTA, CDA and the Capped Landfills; Area 5 South which is south of the PSCT; the FPP and existing RCF Pond and Pond 13, extending down to the southern site boundary; and, Area 5 West which includes the RCRA Canyon, WCSA and the existing ponds to the south, including Pond A-5 and the A-Series Pond. This section starts with the discussion of nature and extent of contamination in each of the three groundwater subareas, followed by a discussion of the existing remedial features in each of the groundwater subareas, and a subsection on development of remedial alternatives. The development of remedial alternatives subsection presents a preliminary evaluation of retained groundwater technologies from technology screening in Section 9, and provides a basis for the selection or inclusion of specific technology components in the selected remedial alternatives. This is followed by the description of the selected remedial alternatives. The remedial alternatives for groundwater include continued operation of some or all of existing extraction features as remedial components. The existing remedial features included in the remedial alternatives are the Gallery Well, and the PSCT in FS Area 5 North, the PCT-A and PCT-B in FS Area 5 South, and PCT-C in FS Area 5 West. In addition, Sump 9B and the Road Sump will be retained, as a contingency measure, if needed to control the potentially high future water table in this area. This section ends with the screening evaluation based on the screening criteria discussed earlier, leading to the selection of remedial alternatives for the detailed analysis in Section 11. 10.6.1 Nature and Extent of Contamination Presented below is a summary discussion of groundwater contamination in the three distinct groundwater areas which together comprise Zone 1 of the site, (i.e., Area 5 North, Area 5 South, and Area 5 West which are shown on Figure 8-1B). The nature and extent of dissolved phase contamination and NAPL in groundwater at the site is also described in Section 5.3.5.2 of this FS, and in greater detail in Section 5.4.5 and 5.4.6, and Appendix G of the Final RI Report (CSC 2011a).


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Groundwater contaminant distribution for total VOCs in relation to groundwater flow pathways within the Upper HSU and Lower HSU is depicted in several iso-concentration maps, including Figures 5-26 and 5-27 (Upper HSU) and Figures 5-28 and 5-29 (Lower HSU). The distribution of LNAPL and DNAPL within the Upper and Lower HSUs at the site as observed in monitoring locations or interpreted from groundwater concentrations is depicted in Figures 5-30, 5-31, and 5-32. The nature and distribution of inorganics in groundwater at the site are also depicted in several iso-concentration maps, including arsenic in the Upper HSU (Figures 5-33a and 5-33b) and Lower HSU (Figure 5-34), nickel in the Upper HSU (Figures 5-35a and 5-35b) and Lower HSU (Figure 5-36), cadmium in the Upper HSU (Figures 5-37a and 5-37b), and Lower HSU (Figure 5-38), and selenium in the Upper HSU (Figures 5-39a and 5-39b), and Lower HSU (Figure 5-40). In general, maximum concentrations of organic and inorganic constituents are encountered within Area 5 North, with lesser concentrations for these constituents present in Area 5 South. With only rare exception, groundwater contamination present in Area 5 West is restricted to inorganics. NAPL is present or suspected only within portions of Area 5 North within and in proximity to the P/S Landfill and in the adjoining Central Drainage Area. The nature and distribution of groundwater contaminants within each of the three FS Area 5 subdivisions is discussed in the following sections. 10.6.1.1 Area 5 North Area 5 North encompasses the groundwater zone lying between the North Ridge to the north, the PSCT to the south, and is bounded by the eastern limit of the West Canyon Spray Area to the west, and the site boundary to the east (Figure 8-1B). VOCs Area 5 North contains the primary source areas and the majority of the dissolved phase VOC contamination at the site. VOC concentrations in Area 5 North are much higher than those in other areas of the site, including Area 5 South, south of the PSCT. The areas with the highest concentrations of VOCs w i t h i n A rea 5 No r th are located within the P/S Landfill, the Central Drainage Area, the Burial Trench Area, and near the toe of the Metals, Caustic/Cyanide, and Acids Landfills. Reported concentrations for VOCs in the Upper HSU o f A r e a 5 N orth range from below laboratory reporting levels to in excess of 1,000,000 parts per billion (ppb). Time-concentration graphs indicate the following for Area 5 North:

Concentrations in the Burial Trench Area (SW-17, RIMW-6, IRMW-7, RIMW-8, SW-44), have been declining over the past several years, which .may be due to natural attenuation mechanisms (Final RI Report Section 6 and Appendix O – CSC 2011a). Concentrations in the PSCT-4 extraction well appear to be steady-to-declining, which may be related to the declining concentrations in the upgradient wells in the Burial Trench Area.

Concentrations in the Central Drainage Area and southern areas of the landfills have been relatively steady or increasing over the past several years. This may be because the overall mass of contamination is much greater in this area than the Burial Trench Area. As further described below, several of the wells are completed in areas that have residual or free-phase NAPLs present. Concentrations in the Gallery Well and Sump 9B extraction wells are relatively steady.


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The northern extent of the Upper HSU contamination in Area 5 North, from east to west, occurs in the Caustic/Cyanide Landfill and Acids Landfill westward through the Metals Landfill, P/S Landfill and to the Burial Trench Area south of the PCB Landfill. When saturated with groundwater, low levels of VOCs occur underneath the North Ridge along the northern limits of these landfills in the Upper HSU, but do not extend northward into the North Drainage. The eastern extent of VOC contamination in Area 5 North is delineated by several monitoring wells near the eastern extent of the PSCT, Caustic/Cyanide Landfill and North Ridge. The western extent of the VOC contamination is delineated by several monitoring wells on the North Ridge and west of the BTA and PSCT. Consistent with the groundwater flow direction moving south from the North Ridge groundwater flow divide, the VOC plumes in the Upper HSU beneath the landfills flow south and converge into the Central Drainage Area and into the PSCT in the PSCT-1 area. The VOC plume in the Upper HSU in the Burial Trench Area flows south into the PSCT in the PSCT-4 area. The distribution of VOC contamination in the Upper HSU within Area 5 North is consistent with overall site groundwater flow conditions. In the Lower HSU, the majority of the samples collected did not contain VOC concentrations in excess of MCLs/PRGs. However, low concentrations of VOCs occur within the Lower HSU at the following areas: The Central Drainage Area; the Burial Trench Area; the southern edge of the Acids Landfill; along the PSCT; along the North Ridge; and northeast of the Caustic/Cyanide Landfill. The elevated concentrations in the Burial Trench Area and along the North Ridge are in areas with strong downward hydraulic gradients. These gradients and resulting groundwater flow has carried VOCs from the higher concentration source areas downward into portions of the lower-permeability Lower HSU. The elevated concentrations along the PSCT are laterally downgradient of the higher dissolved-phase concentrations in the Burial Trench Area (RIPZ-16) and DNAPL present in the Central Drainage Area (RGPZ-7C/D). Inorganics Dissolved concentrations of arsenic, nickel, cadmium, and selenium are elevated throughout the site and are the most broadly elevated metals within the Upper HSU. These metals are elevated throughout most of the Zone 1 area, and generally exceed MCLs where elevated. Arsenic is the most broadly elevated metal within the Upper HSU, it exceeds primary MCLs where elevated, and the extent of the other elevated metals is generally contained within the extent of elevated arsenic. The distribution of elevated metals in Area 5 North is generally similar to that of elevated VOCs in the Upper HSU, with the highest concentrations generally occurring north of the PSCT in the P/S Landfill and Central Drainage Area. The higher concentrations of metals in the Upper HSU are generally located within the Central Drainage Area, similar to the higher concentrations of VOCs north of the PSCT. Metals concentrations in the Lower HSU are generally lower than in the Upper HSU. The elevated metals concentrations in the Lower HSU do not appear to coincide spatially with the elevated VOC concentrations in the Lower HSU to the degree that the distributions of elevated metals and elevated VOCs coincide for the Upper HSU. NAPL


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The P/S Landfill and Central Drainage Area are the only areas of the site where both free-phase (mobile) DNAPL and/or LNAPL were observed in the Upper HSU during drilling, gauged in routine liquid level monitoring, and/or implied based on dissolved constituent chemistry. The distribution of LNAPL and DNAPL within the Upper and Lower HSUs as observed in monitoring locations or interpreted from groundwater concentrations is depicted on Figures 5-30, 5-31, and 5-32. All of the known free-phase NAPL contamination that has been measured in monitoring wells, piezometers, or extraction wells is located in Area 5 North, north of the PSCT, although evidence of residual NAPL contamination has been observed during various investigations in other areas. Currently, LNAPL is present as a separate (free) phase in 12 Upper HSU wells and piezometers in an area from RIPZ-14 at the top of the P/S Landfill to just north of PSCT-1. In the Upper HSU, DNAPL is present as measurable amounts in P/S Landfill Piezometers RIPZ-13 and RIPZ-27, and the Gallery Well. In the Lower HSU, DNAPL is present in measurable amounts in piezometers RGPZ-7C and RGPZ-7D between the P/S Landfill and PSCT-1. Historically, small amounts (less than 0.2 foot) of LNAPL have been measured in RG-3B (in the former Pad 9A area), but LNAPL is no longer observed in this well. The Upper HSU locations in the Central Drainage Area where LNAPL and DNAPL have been observed or inferred generally coincide with an historical site drainage that ran the length of the P/S Landfill and continued into the area that is now the RCF Pond. To date, neither LNAPL nor DNAPL have been measured in any other site wells or piezometers. No free LNAPL or DNAPL have been directly measured in the Burial Trench Area, but residual NAPL may be present based on observations made during drilling and groundwater sampling, and the dissolved chemistry analyses. At RIMW-7, LNAPL was inferred during drilling and DNAPL could be present based on the dissolved-phase chemistry analysis. Only one DNAPL compound (Freon 113) was noted as a possible DNAPL indicator in the Upper HSU at RIMW-8. Because only one compound exceeded 10 percent of its solubility at that location, the likelihood of DNAPL there is low (if present, one would expect more chemicals suggesting the presence of DNAPL). Piezometers RIPZ-15 and RIPZ-16 were installed downgradient (south) of the Burial Trench Area and were screened to intercept potential DNAPL at the upper portions of the Lower HSU. To date, no free-phase LNAPL or DNAPL has been observed in Piezometers RIPZ-15 and RIPZ-16. NAPL has not been detected in the recently installed RI wells and piezometers in the Burial Trench Area (although observations during drilling may suggest NAPL in this area), or in other site wells and piezometers near and downgradient of the other site landfills. 10.6.1.2 Area 5 South Area 5 South encompasses the groundwater zone extending between the PSCT to the north and the site boundary to the south, bounded by the eastern limit of the West Canyon Spray Area and the site boundary to the west, and the site boundary to the east (Figure 8-1B). VOCs As groundwater extraction from the PSCT intercepts most, if not all, southward VOC contaminant migration north of the PSCT, VOC concentrations within Area 5 South are much lower than present in Area 5 North (Figures 5-26 and 5-27). This is demonstrated by the observed differences in distribution and concentrations of compounds detected to the north and south of the PSCT. Upper HSU VOC contamination in Area 5 South is the highest south of extraction points PSCT-1 and PSCT-4. The observed contamination in these two areas is typically one to two orders- of- magnitude lower in concentration than the concentrations


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observed in the Burial Trench Area and the Central Drainage Area, lying just across the PSCT to the north, within Area 5 North. The VOC contamination within Area 5 South sharply declines south of the existing site ponds and generally is not detected south of the five ponds, nor in areas to the south of the site. Maximum VOC concentrations within Area 5 South were detected at concentrations of approximately 25,000 and 10,000 ppb in wells located just south of PSCT-4 (Figure 5-26). The wells located just south of PSCT-1, PSCT-2, and PSCT-3 had VOC concentrations ranging from approximately 100 to 500 ppb, while the rest of the area south of the PSCT in the vicinity of the RCF Pond and Ponds 13 and 18 had VOC concentrations that ranged from below the laboratory detection limits, to approximately 50 ppb. VOCs were below 10 ppb for all other Area 5 South wells, with the exception of one well, located in RCRA Canyon, which had a VOC detection of 23 ppb (well SW-46). The time-concentration graphs for VOCs indicate the following for the areas south of the PSCT:

Concentrations immediately south of PSCT-4 (RG-2B, RG-4B) appear to have been relatively steady over the past several years.

Concentrations for many wells south of PSCT-1, -2, and -3 (RG-1B, RG-6B, RIMW-2, and WP-3S) have been declining over the past several years or have been relatively steady (RG-7B). This may due to the effectiveness of the PSCT at preventing southward contaminant migration from the northern primary source areas and natural attenuation mechanisms.

The low-level concentrations in the PCT extraction wells for the A-Drainage (RAP-3A), B-Drainage (RAP-1B), and C-Drainage (C-5) have been declining over the past several years. This may be due to natural attenuation mechanisms and also from dilution from pond water that recharges the PCTs. VOC levels in the ponds are very low to non-detect, and the flushing of this water through the Upper HSU has led to the decrease in PCT extraction well concentrations. The low-level concentrations immediately next to the C-Drainage PCT (RP-28B) have also been decreasing.

Area 5 South formerly contained ponds used for liquid impoundment, and site-related impacts from these former features are reported in previous documents (Woodward-Clyde Consultants and Canonie Engineering, 1989). Prior to construction of the PSCT, concentrations of organic compounds ranging up to thousands of micrograms per liter were detected in th i s a rea o f the s i te . These historical detections of organic compounds suggest that groundwater in Area 5 South was impacted by organic contaminants prior to construction of the PSCT. Although the data are limited, pond closure ac t i v i t i es and the construction of the PSCT appear to have resulted in stable or declining concentrations of organic compounds i n A r e a 5 S outh, as demonstrated by the time-concentration charts. Detections of organic compounds in Area 5 South are therefore largely attributed to pre-existing contamination rather than to ongoing southward plume migration across the PSCT since U S EPA begin extraction from the PSCT in 1992. Moreover, the progressive lowering of the action level e l e v a t i o n in the PSCT has increased the barrier’s effectiveness at preventing contaminant migration. Inorganics Similar to conditions in Area 5 North, elevated concentrations of arsenic, nickel and selenium are present across the majority of Area 5 South within the Upper HSU. Cadmium is present at elevated concentrations within the Upper HSU of Area 5 South, but is limited principally to a


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comparatively narrow zone directly south of the PSCT, and extending southerly below PSCT-1 toward the RCF Pond. Other isolated locations of elevated cadmium are locally present in proximity to the PCT trenches. With the exception of cadmium, elevated concentrations of these metals within the Upper HSU of Area 5 South typically extend from the PSCT on the north to, and in some cases slightly beyond, the southern site boundary. While the area of elevated metals occurrence in Area 5 South is largely contiguous with that of Area 5 North, there is a concentration break that typically corresponds with the PSCT, with higher concentrations lying to the north, and lower concentrations lying to the south of this feature. With the exception of isolated occurrences of arsenic and selenium in discrete locations directly south of the PSCT, no significantly elevated metals concentrations are present within the Lower HSU in Area 5 South. NAPL No areas of LNAPL or DNAPL occurrence have been documented through sampling and gauging activities or inferred based on dissolved contaminant concentrations in Area 5-South. 10.6.1.3 Area 5 West Area 5 West encompasses the groundwater zone underlying the West Canyon Spray Area and the RCRA Canyon Area. It extends from the North Ridge to the north, to the southern site boundary to the south, bounded by Area 5 South to the east, and the site boundary at the west ridge to the west (Figure 8-1B). VOCs VOCs were not detected at other than very low levels in groundwater in either the Upper or Lower HSUs within Area 5 West (Figures 5-26 through 5-29). The single well within Area 5 West reported to contain organic contaminants in excess of reporting limits is well SW-46 located in RCRA Canyon, which had a total VOCs concentration of 23 ppb. Inorganics Dissolved metals comprise the major groundwater contaminant within Area 5 West, and include arsenic, nickel, and selenium. Concentrations of these constituents within the Upper HSU in Area 5 West are largely comparable with those present within broad areas of the Upper HSU underlying both Area 5 North and Area 5 South; however, maximum groundwater concentrations for these metals are located in areas of the site lying outside Area 5 West (Figures 5-33a, b through 5-36, and 5-39a, b through 5-40). Maximum dissolved metals concentrations in Area 5 West are typically present in the lower (southern) portions of the RCRA Canyon drainage where surface water in the existing ponds, including the A-Series Pond and treated liquid impoundments Pond 18 and Pond A-5, is in contact with groundwater of the Upper HSU. Groundwater seeps present in the lower portion of RCRA Canyon are also reported to contain elevated concentrations of metals. No Lower HSU wells in Area 5 West are reported to contain elevated concentrations of dissolved metals. In contrast to the other two groundwater FS areas, with exception for one location in the southwestern corner of the site at PCT-C, no elevated concentrations of cadmium are reported for Area 5 West in either the Upper or Lower HSUs (Figures 5-37a, b and 5-38). NAPL


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No areas of LNAPL or DNAPL occurrence have been documented through sampling and gauging activities or inferred based on dissolved contaminant concentrations in Area 5 West. 10.6.2 Existing Remedial Extraction Features The existing site remedial features discussed below include the Gallery Well, Sump 9B, Road Sump and the PSCT in Area 5 North, the PCT-A and PCT-B in Area 5 South, and PCT-C in Area 5 West. This section presents a brief discussion of the current performance of these remedial features and their role as components in the remedial alternatives to provide control and containment of groundwater contaminants. The following discussion also provides a rationale for those features that are not included as components in the remedial alternatives discussed later. 10.6.2.1 Area 5 North The existing site extraction features in Area 5 North including the Gallery Well, Sump 9B, Road Sump and the PSCT are briefly discussed below. Detailed descriptions of these features were presented in Section 2.2.3 of the Final RI (CSC 2011a). Gallery Well The Gallery Well is located at the toe of the P/S Landfill and extracts highly concentrated leachate liquids from the landfill along with some DNAPL. The Gallery Well is a 10-inch well with a total depth of 78 feet btoc and a 40-foot screen interval. The extraction at the Gallery Well is proposed to continue in the same manner as current operations. The well would be equipped with a stainless steel Grundfos pump capable of pumping in the range of 2 to 5 gpm with a continuous flow action level of 63 feet btoc. Historically, the total annual extraction volume from the Gallery Well has ranged from 300,000 to 450,000 gallons. The extracted liquids are pumped to the treatment system in the Liquids Treatment Area. The liquids are separated into the NAPL phase and a groundwater. The NAPL liquid and impacted groundwater (leachate) are stored temporarily at the site and then trucked for disposal at a permitted facility. The FS assumes that total annual future extracted volumes of leachate liquids and DNAPL will be consistent with the current extraction rates at about 450,000 gallons of concentrated liquids and 3,000 gallons of DNAPL on average per year. Sump 9B Sump 9B is a shallow gravel-filled collection trench and associated extraction point installed directly downgradient of the P/S Landfill clay barrier and upgradient of the PSCT. Sump 9B is located approximately 200 feet downgradient (south) of the Gallery Well and was constructed during closure of former Pad 9B in response to the observation of contamination below the groundwater table in this location. This feature consists of a gravel-filled circular sump approximately 27 feet deep with an associated shallow (8 to 12 feet deep) trench. The trench was not completed into the unweathered claystone and was originally intended only to intercept previous site seeps from Pond/Pad 9A and 9B. An extraction point (Well 9B) was installed at the deepest portion of the sump. Currently, fluids removed from the sump are taken to a permitted facility for disposal. Extracted volumes have dropped significantly from the 1999/2000 time period of 620,000 gallons per year to 20,000 and 56,000 gallons in the 2008-2009 and 2009-2010 time periods, respectively. The decline in rate is most likely associated with the construction of a temporary “cap” on the slope immediately upgradient of the extraction feature


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(which is believed to have reduced surface recharge to the feature). Because Sump 9B is a relatively shallow extraction feature that does not adequately intercept any subsurface groundwater flow at appropriate depths, and because the groundwater flow modeling indicates that once a permanent cap is placed upgradient of the feature Sump 9B will completely dry up. Sump 9B is not considered necessary for hydraulic containment of the Upper HSU and continued liquids extraction for hydraulic containment is not assumed as a part of the final remedy. However, extraction from Sump 9B has been critical in eliminating the surface seep that has historically been present in this area without effective extraction. This seep forms when either Sump 9B is not extracted or if the efficiency of Sump 9B declines due to clogging of the well screen and filter pack. The performance of Sump 9B has been observed to decline over time. The surface seep forms during the winter months in response to rainfall recharging the shallow water table when the performance of Sump 9B becomes too degraded. The surface seep is highly contaminated and can have a LNAPL sheen. Periodic redevelopment of Sump 9B has been performed to effectively restore its performance so the seep does not occur. Although the groundwater flow modeling in Appendix D predicts that liquid levels will fall below Sump 9B after capping for the final remedy, the contingency operation of Sump 9B is retained in the event that the model is overly optimistic and the actual water level is shallower than predicted. Road Sump The Road Sump is a subsurface collection and containment sump with an extraction pump designed to intercept and capture groundwater recharge potentially migrating downgradient from Sump 9B into an above ground concrete culvert adjacent to the Sump 9B Road. The Road Sump is approximately 10 feet in length and 3 feet wide and completely filled with gabion rock. The sump extends 1 foot down into the clay layer to a total depth of approximately 5.5 feet below ground surface. The Road Sump was constructed and installed with an 8-inch PVC well in November 1998. A well head and extraction pump was later installed in January 1999. Currently, groundwater level in the road sump is measured twice a day to maintain a compliance action level greater or equal to 6 feet btoc. No liquids are currently being extracted at this feature and as a result, operation of the Road Sump is not included in the FS discussion of future remedial alternatives. Similar to Sump 9B, the Road Sump is retained in the event that the model is overly optimistic and the actual water level is shallower than predicted. PSCT The PSCT is a continuous, approximate 2,650-foot-long and nominally 3-foot-wide gravel-filled collection trench covered with compacted fill material (Brierley & Lyman, 1989a). There are four extraction points along the PSCT, PSCT-1 through PSCT-4. These are 8-inch PVC wells equipped with Grundfos pumps with levels controls. PSCT-1 provides majority of the flow and hence is equipped with a larger pump capable of 80 gpm while the other PSCT wells have pumps that can pump in the range of 10-40 gpm. The extraction pump in each well is activated based on a set of action levels to turn on and turn off the pump. The currently used action levels in feet btoc and total well depths are shown in table below.

Extraction Well Total Depth Action Levels

(Feet btoc) (Feet btoc)

PSCT-1 55 40

PSCT-2 62 56


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PSCT-3 66 54

PSCT-4 66 72

The extracted groundwater from the PSCT is treated at the Liquids Treatment Area in a groundwater treatment system using liquid phase carbon adsorption. The existing treatment system and the proposed upgrade are discussed below. The total annual volume of extracted liquids at the PSCT vary significantly based on annual precipitation, and ranges from 1.3 million gallons in 2008-2009 to greater than 6 million gallons in the 2010-2011 year. Future projected groundwater extraction rates are expected to be significantly lower based on the future capping remedies for the PCB Landfill, BTA and the CDA. Based on the results of groundwater modeling (Appendix D, site-wide remedial alternative (SWR) #3), the PSCT extraction rates would decrease from 2,838,000 gallons per year (average 2006-2011) to between 1,901,000 and 1,931,000 gallons per year based on dry season or wet season model results (see table below). The model predicts that PSCT-3 and -4 would dry-up over time, and all the flow will be at PSCT-1 and PSCT-2.

Extraction Well

Average Annual extraction

volume 2006-2011

GW Flow Model Annual

Extraction Estimate Dry to Wet season

(Gallons) (Gallons)

PSCT-1 through -4 2,838,000 1,901,000 to 1,931,000

10.6.2.2 Area 5 South The existing site extraction features in Area 5 South include PCT-A and PCT-B, and are briefly discussed below. Detailed descriptions of these features were presented in Section 2.2.3 of the Final RI (CSC 2011a). PCT-A and PCT-B The PCT-A is a gravel-filled trench at the southeastern perimeter of the site and has 3 extraction wells called RAP-1A, RAP-2A and RAP-3A. The PCT-B is a gravel-filled trench south of Pond 13 with one extraction well, RAP-1B. PCT-A and PCT-B are existing extraction features at the southern perimeter of the site that help meet the objective of mitigating potential migration of groundwater contaminants. The groundwater from these four wells is extracted with extraction pumps controlled by level controllers. The RAP well extraction is based on target levels rather than action levels. The currently used target levels and total depths for each extraction well are shown in the table below.

Extraction Well Total Depth Target Levels


RAP 1A 40 29

RAP 2A 56 45

RAP 3A 54 44

RAP 1B 72 61


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The extracted PCT-A and PCT-B groundwater is currently pumped back into the stormwater ponds (RCF Pond). The total volume of groundwater extracted from PCT-A and PCT-B per year is on average (2006-2011) 1.5 million gallons and 1 million gallons, respectively. Based on preliminary groundwater flow modeling results (Appendix D, SWR #3), the total extraction flow rate from PCT-A significantly decreases to between 2,323,000 and 3,619,000 gallons per year based on the future anticipated capping and pond closure remedy scenarios for the site (see table below). For the PCT-B, the model estimates the extraction rate increased slightly to between 3.3 and 4.2 million gallons. The FS considers conversion of the PCTs to in-situ reactive walls only for the PCT-B trench because the GW Flow Model projects a significant extraction flow rate for this trench. Since the projected flow rate for the PCT-A trench would be significantly reduced from current levels; the extraction approach would be relatively low in cost and is therefore preferred for the PCT-A trench. Please note that the cost of conversion of the PCT-A trench to a reactive wall would be greater than for the PCT-B because the PCT-A does not have a clay barrier and would require installation of a parallel soil-bentonite slurry wall for the conversion. The in-situ reactive wall option for the PCT-B is discussed further below under preliminary evaluation of groundwater technologies prior to the description of remedial alternatives.

Extraction Well

Average Annual Extraction

Volume 2006-2011


Extraction Estimate Dry to Wet Season

(Gallons) (Gallons)

PCT-A (RAP-1A through 3A) 1,527,000 2,323,000to 3,619,000

PCT-B (RAP-1B) 1,036,000 3,341,000to 4,220,000

10.6.2.3 Area 5 West The existing site extraction feature in Area 5 West is PCT-C, which is briefly discussed below. A detailed description of this feature was presented in Section 2.2.3 of the Final RI (CSC 2011a). PCT-C The PCT-C has a clay barrier along the southwest corner of the site with extraction well C-5 in a gravel curtain adjacent to the clay barrier and extraction well RAP-1C in a gravel-trench extension of the PCT-C. The groundwater from these two wells is removed with extraction pumps controlled by level controllers. The well extraction is based on target levels rather than action levels. The currently used target levels and total depths for each extraction well are shown in the table below.

Extraction Well Total Depth Target Levels


RAP 1C 68 55

C5 87 77

Based on the results of groundwater modeling (Appendix D, SWR #3) with the anticipated capping and pond closure remedies, the PCT-C extraction rates would increase from 2,405,000 gallons per year (average 2006-2011) to between 4,247,000 and 4,944,000 gallons per year


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based on dry season or wet season model results, respectively. The extracted groundwater from the PCT-C is pumped to the proposed evaporation pond in the footprint of the A-Series Pond and is not proposed to be treated because it would contain low levels of metals but no VOCs. Conversion of the PCT-C to an in-situ reactive wall is considered in the remedial alternatives because significant extraction flow rates are projected for these trenches. The in-situ reactive wall option for PCT-C is discussed further below under preliminary evaluation of groundwater technologies prior to the description of remedial alternatives.

Extraction Well

Average Annual Extraction

Volume 2006-2011


Extraction Estimate Dry to Wet

Season

(Gallons) (Gallons)

PCT-C (RAP-1C and C5) 2,405,000 4,247,000 to 4,944,000

10.6.3 Development of Remedial Alternatives – Area 5 North The introductory portion of this section provides a preliminary evaluation of select retained groundwater technologies and process options (from Section 9) prior to the discussion of groundwater alternatives to address various NAPL source locations and the dissolved contaminants (organics and inorganics) in Area 5 North. This preliminary evaluation provides a rationale for why certain retained technologies or specific source removals were not included in the subsequent discussion of groundwater remedial alternatives as components, and why and in what form others were included. The objectives of the remedial alternatives for FS Area 5 North are:

Contain and/or control contamination sources within the Area 5 North boundary, where groundwater restoration is not technically practicable, including dewatering the P/S Landfill by extracting liquids at the bottom of the landfill using vertical or horizontal wells;

Extraction at the perimeter of Area 5 North to provide containment for the potential TI Zone in the future in the Upper HSU;

Monitoring at the perimeter of Area 5 North to verify containment for the potential TI zone in the future in the Lower HSU, and implementation of extraction if necessary;

Remove DNAPL to the extent practicable and contain and/or control the migration of DNAPL where removal is not technically practicable;

Remove LNAPL to the extent practicable and contain and/or control the migration of LNAPL where removal is not technically practicable; and,

Allow discharge of treated groundwater either to the B Drainage or Casmalia Creek or, alternately, to an evaporation pond at the site.

This section first discusses evaluation of NAPL source reduction technologies applied to the identified NAPL source areas within Area 5 North, followed by technologies applicable to dissolved contaminants, leading to the description of remedial alternatives for Area 5 North in Section 10.6.3.7. As discussed earlier, the remedial alternatives for Area 5 North include continued operation of the existing Gallery Well and PSCT extraction as remedial components.


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Issues related to the following technologies process options, and remedial approaches are discussed below to provide context and perspective for the following discussion of groundwater remedial alternatives for Area 5 North:

Approach to NAPL source reduction in the southern portion of the P/S landfill (Section 10.6.3.1), including:

o NAPL-only extraction NAPL-only extraction well design Additional NAPL investigation and pilot testing NAPL-only extraction performance standards

o Aggressive NAPL extraction o P/S Landfill dewatering with horizontal wells

Approach to DNAPL source reduction in the CDA (Section 10.6.3.2), including: o DNAPL in the Upper HSU o DNAPL in the Lower HSU

Approach for LNAPL source reduction in the CDA (Section 10.6.3.3) Approach for residual NAPL source reduction in the BTA, (Section 10.6.3.4), including:

o NAPL in the Upper HSU o NAPL in the Lower HSU

Dissolved VOCs in Area 5 North (Section 10.6.3.5), including o Dissolved VOCs in the Upper HSU o Dissolved VOCs in the Lower HSU

Treatment of Gallery Well liquids at the site (Section 10.6.3.6) From the screening of technologies evaluation in Section 9 the primary retained technologies that are potentially applicable to active remediation of the NAPL areas are hydraulic extraction, NAPL skimmers, ISTD and ISCR. Various extraction well technologies such as vertical wells, trench wells and horizontal wells were retained as well. Vertical wells and trench wells are already operating effectively at the site. Horizontal wells were retained for consideration to evaluate the alternative of dewatering the P/S Landfill because the installation of these wells can technically avoid drilling through landfill wastes, as would be required with vertical wells. However, there are significant technical challenges with drilling horizontal wells such as borehole failures and casing breakage with blind drilling including the risk of potentially drilling into the wastes and potential for release of liquids or drilling muds during installation. These will be discussed later during the evaluation in Section 11. For NAPL source reduction technologies, the following sections discuss the approach for remedial alternatives for: (1) NAPL in the southern portion of the P/S Landfill; (2) DNAPL in the CDA in the Upper HSU and the Lower HSU; (3) LNAPL in the CDA, and, (4) Residual NAPL in the BTA. 10.6.3.1 Approach for NAPL Source Reduction in the Southern Portion of P/S Landfill Extraction with NAPL skimmer pumps and groundwater extraction pumps are considered for the southern P/S Landfill because it has a larger free phase NAPL area compared to NAPL in other areas. Specifically, there are three preferred remedial technology options for NAPL reduction in the P/S Landfill: (1) “NAPL-only” extraction with periodic skimmer pumps and a limited number of wells in the NAPL-impacted area; (2) “aggressive NAPL” extraction with continuous pumping of NAPL and groundwater with large diameter wells in the NAPL-impacted area; and (3)


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Dewatering P/S Landfill with horizontal wells. The extracted liquids would be treated in an aboveground treatment system or sent to a TSDF for disposal. Aggressive in-situ technologies (e.g., ISTD, ISCR) are not considered for implementation in the P/S Landfill because of the implementability challenges with installation of a large number of closely-spaced wells within the landfill footprint. NAPL-Only Extraction The NAPL-only extraction alternative discussed in this section refers to extraction from approximately 16 new 4-inch diameter NAPL-only wells in the Upper HSU. All of these wells would be located in the vicinity of RIPZ-13 near the toe of the P/S Landfill, and are assumed to include four wells placed on Bench Road 1 in the vicinity of RIPZ-13, four wells located on a new bench road to the north and eight located on two new bench roads between Bench Road 1 and Gallery Well Road. The design, number, and location of these “NAPL-only” wells will be finalized as part of the remedy design process, but the conceptual well design is discussed below and in Section 11.6 (see Figure 10-1B). NAPL-Only Extraction Well Design For the NAPL-only extraction alternatives, the wells could be constructed and operated using one of two options as summarized below. Prior to implementing any NAPL recovery through wells within the P/S Landfill, additional NAPL investigation and pilot testing would be performed to quantify potential NAPL recovery volumes and rates as discussed further below

Option 1 – LNAPL and DNAPL would be extracted from a single well screen (or gradient driven well), which would be constructed across the entire saturated zone (LNAPL, aqueous-phase, and DNAPL). A sump would be installed below the well screen to allow additional well casing for DNAPL storage. Two extraction pumps would be placed into the well. The bottom pump would be placed at the top of the DNAPL zone and pumped slowly (pulsed pumping only several times per day) to recover the DNAPL that comes into the well by up coning. The top pump would be placed within the LNAPL and also pumped slowly to skim the LNAPL that comes into the well. Extraction of water would be minimized so that the LNAPL and DNAPL saturations and flow paths around each well are maintained at the maximum possible level which would maximize LNAPL and DNAPL recovery. Some water would be extracted, as appropriate, to slightly enhance the inward gradients towards the extraction wells.

Option 2 – LNAPL and DNAPL would be extracted from a dual screen well (or gradient driven well), which would be constructed to isolate the water bearing zone with the goal of increasing NAPL recovery efficiency (Figure 11-25B). The well would be constructed by setting the lower screen for DNAPL recovery to bridge the contact between the weathered and unweathered claystone. In addition, a sump will be installed below the well screen to allow additional well casing for DNAPL storage. The upper screen interval would be placed across the water table to allow LNAPL to enter the well. These data would be compared to the NAPL production of the Gallery Well to see if any additional benefit would be gained from installing multiple wells through the landfill cap. One limitation with this method is that DNAPL up coning cannot be tracked if it rises above the DNAPL screen (which is important to know to maximize DNAPL recovery) and the top LNAPL screen will become desaturated as the overall liquid levels drop in the landfill which would trap recoverable LNAPL against the blank casing.


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Additional NAPL Investigation and Pilot Testing Prior to the installation of NAPL-only extraction wells, a minimally invasive exploratory program would be conducted using methods such as a CPT, MIP and /or Ultra-Violet Optical Screening Tool (UVOST) in situ screening tools. The purpose of this investigation would be to map the bottom of the P/S Landfill to determine where DNAPL may accumulate and obtain data on the potential presence of free-phase LNAPL and DNAPL that would be recoverable. The MIP and UVOST tools are sensitive to free phase DNAPL and LNAPL compounds. The details of the investigation scope and technologies will be developed during the remedial design phase. Upon completion of the exploratory program, select test locations showing thicker zones of NAPL would be selected for product recovery pilot testing. Product recovery testing would include the design and installation of one to three product recovery wells. The recovery well would be screened across the zone where NAPL is indicated on MIP or UVOST logs. Controlled pump testing and bail down tests would be performed to assess NAPL recovery rates. Controlled pump testing would be performed using established procedures, including those used for the previous RIPZ-13 pilot testing conducted in 2009. The bail down test would be performed using established procedures, including those outlined in USEPA document on effective product recovery at UST sites (USEPA 1996). The pump test and bail down test procedures would be modified, as appropriate, to incorporate experience from prior testing. NAPL-Only Extraction Performance Standards The feasibility of NAPL recovery would first be estimated based on the installation of test recovery wells and the performance of the hydraulics pilot testing. During the installation of the pilot test well, soil samples may be collected and analyses conducted to provide estimates of the NAPL saturation, relative NAPL and water permeabilities of the soil, and the physical properties of the recovered liquids (DNAPL, water, and LNAPL). The pilot test data would be compared to historical NAPL recovery data from the Gallery Well and RIPZ-13 in the P/S Landfill and to Sump 9B in the Central Drainage Area. The pilot test would involve pumping the wells at a very slow rate (e.g., less than 0.1 gpm) to maintain NAPL flow paths in the landfill waste materials. The objective would be to slowly remove LNAPL and DNAPL while minimizing water recovery. Excessive water recovery may cause water in the waste materials to interrupt the NAPL flow paths which could drastically reduce NAPL recovery efficiency. The extraction rates may be increased (e.g., 0.25, 0.5, and 1 gpm) to determine the ratio of NAPL to water recovery at each extraction rate. Following each pumping step, the test well would be allowed to recover to pre-pumping conditions and the changes in water and NAPL levels in the well would be monitored. Existing monitoring wells in the vicinity will be used as observation wells to obtain conductivity estimates, and determine if hydraulic communication between different levels within the landfill exist. NAPL recovered during testing would be analyzed for physical flow properties including NAPL density and viscosity (see Exhibit IV-13, USEPA 1996). Only upon obtaining and analyzing well hydraulics recovery data and the NAPL physical properties would estimates for full scale volumetric pumping rates and durations be established. The final performance standards for when to discontinue NAPL recovery will be determined after the NAPL extraction pilot testing and during remedial design of the NAPL extraction network. Examples of performance standards that could be implemented include the following:


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Recovery of large quantities of water (e.g., >80 percent) would be set as effectiveness limits, obtaining such a goal may lead to asymptotic levels and a reduction of NAPL thickness.

Once NAPL thickness has declined to below a certain thickness, the effectiveness of

further operating the extraction system would be evaluated. This thickness would likely be less than 1-foot and may be as low 0.1-foot or less.

The performance standards and need for additional NAPL extraction wells will also be evaluated while extracting NAPL from the NAPL extraction network. It is possible that additional NAPL extraction wells would be installed based on the performance of the initial NAPL extraction network. Aggressive NAPL Extraction The aggressive NAPL extraction alternative assumes continuous, aggressive total fluids (NAPL and groundwater) extraction from approximately 16 new large diameter (8-inch) vertical wells, installed in the Upper HSU in the same locations in the P/S Landfill as the NAPL-only wells described above. The typical well construction would involve a total depth of 80 feet bgs with a 40-foot screen interval (Figure 11-27B). The well would be equipped with a total fluids pneumatic pump. The aggressive extraction of total fluids from 16 wells is assumed to produce an average total flow rate of up to 10 gpm of landfill leachate that will be treated in a Liquids Treatment Plant (LTP). The total volume of leachate that would be treated at the site is estimated to be about 5.2 million gallons per year from the NAPL extraction wells under the aggressive NAPL extraction scenario. The design and location of these NAPL wells will be finalized as part of the FS remedy design process, but the conceptual well design is discussed in Section 11.6 and shown on Figure 11-27B. The conceptual design of the LTP is discussed below. The extracted liquids from P/S Landfill are expected to include DNAPL and LNAPL and a wide range of other organic and inorganic contaminants including VOCs, SVOCs, pesticides, dioxins, and metals. These liquids may be stored at the site and then disposed at an approved facility or treated at the site. If treated at the site for disposal to an evaporation pond, treatment would be performed to remove organic compounds. The LTP would utilize air stripping and carbon adsorption processes to treat organics for discharge to the site evaporation pond (Figure 11-27C). The site treatment train would include an equalization tank and NAPL-water separator with pre-treatment processes including particulate filtration, de-emulsification and acidification prior to treatment by the air stripper and LPGAC vessels. The pre-treatment processes are required for effective operation of the air stripper and other process units. The vapor stream generated from the air stripping towers would be treated by a dehumidifier and VPGAC vessels prior to discharge to the air. If treated at the site for disposal to the B-Drainage, robust treatment would be performed to remove both organic and inorganic compounds. Treatment of inorganics to discharge to the B Drainage or Casmalia Creek would include a RO unit and a VSEP unit. The RO unit will remove metals and dissolved anions while the VSEP will concentrate the reject brine waste from the RO unit. The waste brine will be very high in dissolved solids and is assumed to be approximately 15 percent of total water volume treated. The waste brine is assumed to be trucked to a permitted facility for disposal. The trucking option is a reasonable assumption for smaller


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disposal volumes such as 500,000 gallons per year (~2 trucks per week). However, this can highly problematic both logistically and from a cost perspective if the disposal volumes are high, say 2.5 million gallons per year, which could require almost 2 trucks per day. The separated NAPL phase will also be sent to a permitted facility for disposal similar to the Gallery Well liquids. The RO/VSEP membranes and the filter media will be sent to a permitted facility for disposal as hazardous waste. The activated carbon will be sent to a permitted facility for regeneration. The discharge of treated liquids to the B-Drainage would require a site-specific NPDES permit. This would require a report of waste discharge and NPDES application package to be developed and submitted to the RWQCB to request an exception to the Basin Plan prohibition for the discharge of treated liquids to the B-Drainage. Hence, if an alternative such as SWR #4 (discharge to the B Drainage or Casmalia Creek with no evaporation pond at the site) is selected; a lengthy process would be required to request this exception with no guarantee of success. P/S Landfill Dewatering with Horizontal Wells The concept and preliminary technical design of dewatering the P/S landfill using HDD was evaluated in this FS. This section of the FS describes the purpose and potential benefits of dewatering the P/S Landfill using horizontal wells, challenges and risks associated with HDD technology as applied to the P/S Landfill, and the conceptual design assumed for this alternative to support the remedial alternatives description presented later in Section 10.6.3.7. Table 10-6A-1 provides a risk analysis that describes the potential hazards or vulnerabilities, potential probabilities of occurrence, potential impacts, consequences of potential impacts, risk mitigation measures to reduce the probability of occurrence, and the probability of occurrence after risk mitigation. The vulnerabilities and risk mitigation are summarized in the text below. The purpose of aggressively dewatering the southern portion of the P/S landfill would be to lower the water table within the landfill and reduce the “driving force” (head) that facilitates: (1) downward migration of contaminated liquids through pooled DNAPL source areas and fractured bedrock; and, (2) horizontal migration into weathered and unweathered bedrock. As discussed in this FS, several other remedial alternatives considered in the FS lower the groundwater level below waste, but not as rapidly as this alternative. Landfill dewatering would be achieved by installing a series of horizontal wells (utilizing HDD methods) to act as horizontal gravity drains to remove liquids (especially DNAPL) trapped behind the P/S Landfill clay barrier. Conceptually, the primary technical benefits of this approach over the approach using NAPL-only or aggressive NAPL extraction wells would be:

The head that contributes to the horizontal gradient that causes groundwater (and any contaminants dissolved in groundwater) to move southward through the Lower HSU and underneath the PSCT would be reduced faster than if the vertical wells were used. This potential benefit would be greater with respect to the NAPL-only extraction wells rather than the aggressive NAPL extraction wells because the liquids removal rate from the aggressive NAPL extraction would be much higher than the NAPL-only extraction.

The energy costs to operate the horizontal drains would be reduced compared to the

use of vertical wells because the liquids would drain by gravity. Technically, there may be disadvantages with using horizontal wells to drain the landfill which include insufficient draining of the landfill if the horizontal wells are either (1) not able to be constructed along the bottom of the landfill, (2) constructed too far beneath the bottom of the


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landfill in the unweathered claystone, or (3) constructed at a spacing that is not dense enough (too few wells). The first issue would leave liquids (including free-phase DNAPLs) in waste below the horizontal wells. The second issue may result in insufficient liquids moving from the bottom of the landfill through the unweathered claystone due to the low permeability of the claystone and low frequency of fractures in the claystone. The third issue may result in a drainage rate that is too slow because the ideal well spacing and hydraulic effect (zone of influence) of individual wells is not known. To dewater the P/S Landfill, this alternative assumes five horizontal wells are installed by directional drilling methods (Figure 11-28A and 11-28B). Two options for installing the horizontal wells were considered: Option 1) drilling through the base of the P/S Landfill Clay Barrier, Option 2) drilling underneath the P/S Landfill Clay Barrier. For either option, the wells would be “blind” (single entry) drilled from a starting point located in the vicinity of Sump 9B, approximately 300 feet south of the landfill clay barrier. Both methods would include installing 300 feet of blank casing from this area to the clay barrier and then 300 feet of screen north of the clay barrier, either into or immediately beneath the landfill. The landfill bottom appears to rise more quickly after this distance towards the north and the advantages of using horizontal wells would diminish rapidly because the thickness of liquids becomes small. Also, the extent of the free-phase DNAPL zone does not appear to extend beyond this distance. Although HDD wells will require penetration of the P/S Landfill Clay Barrier, Option 1 facilitates direct access to the NAPL pool at the bottom of the landfill. Option 2 eliminates the need to penetrate the P/S Landfill barrier and the associated requirement for installation of a surface casing; however, it requires vertical hydraulic conductivity of the unweathered claystone in the Lower HSU to be sufficient to allow efficient drainage of landfill waste, with approximately five feet of vertical separation between the wells and the waste (needed to mitigate uncontrolled drainage of liquids during well installation). Option 2 also requires the driller to transition from weathered to unweathered materials, which in some cases may cause the drill bit to deflect off relatively hard materials, such as the unweathered claystone, instead of penetrating them, especially at shallow angles. For Option 1, a 14-inch pilot bore would be advanced through the Upper HSU (including alluvium. weathered claystone and the P/S Landfill buttress) and several feet into the base of the clay barrier, verified by drill head tracking methods (accurate to approximately 0.5 ft horizontally and 0.1 foot vertically). A 12-inch steel surface casing would then be installed and pressure grouted in place, including pressure grouting of the annular space around the casing. Finally, a 7 to 8 inch borehole would be advanced inside the surface casing, through the P/S Clay Barrier, and approximately 300 feet along the bottom of the landfill using oversize (5-inch ID) drill rods and a “knock-off” drill bit. The 3-inch or 4-inch well materials are subsequently inserted inside the drill rods (which prevents the landfill material from collapsing in around the well materials), using a blowout preventer installed on the surface casing as a precaution and a positive head of drilling fluid pressure to prevent backflow of landfill waste inside the drill rods and/or back through the surface casing. For Option 2, the borehole would be drilling down to below the P/S Landfill Clay Barrier, and then angle upward to intersect waste, following the slope of the Lower HSU contact along the base of the landfill. The wells are drilled starting in the vicinity of Sump 9B about 300 feet from the landfill (elev. ~ 480 ft MSL) and drilling down to below the P/S Landfill Clay Barrier (elev. ~ 470 ft MSL) and coming up and following the slope of the Lower HSU contact along the landfill bottom. Since the Lower HSU contact at the landfill bottom is sloped up, the borehole will be inclined upward toward the northwest at angles up to 20 percent slope. The wells are assumed


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to be a total of 600 feet long with 300 feet of screen interval inside the landfill footprint and 300 feet of blank casing. The horizontal wells are assumed to be 12” diameter boreholes that are installed as a blind hole in order to avoid drilling up through the landfill waste and into the liner and cap. The well casing is assumed to be 3-inch or 4-inch diameter stainless steel with a wire-wrapped screen. The initial drainage rates from the horizontal wells may be greater than 10 gpm per well based on experience at other landfills. Allowing the wells to freely drain would require an extremely large storage facility at the site and high rate of trucking and disposal at a permitted TSDF, which would not be feasible. It is assumed that the flow from the wells would be throttled so that the liquids could be effectively managed and disposed with a reasonable amount of infrastructure. Therefore, the conceptual design assumes that the extraction flow rate for each horizontal well is initially 2 gpm on average (5.25 million gallons/year for 5 wells) and decreasing in Years 2 and 3 to 0.5 gpm and Years 4 and 5 to 0.1 gpm and finally for Year 6 and onwards for a total flow rate of 200,000 gallons per year for all 5 wells. The extracted liquids will be drained to an equalization tank and then to a NAPL-water separator. The NAPL and the water phase are pumped and stored in stainless steel tanks for disposal to a permitted facility similar to the current Gallery Well liquids. Approximately ten 20,000-gallon stainless steel storage tanks are included in the treatment compound to have adequate storage capacity at the site. While dewatering the P/S Landfill is being considered further in the FS for reasons outlined above, the technical challenges and risks associated with this option are significant, as outlined below. The technical evaluation considers both industry experience in installing horizontal remedial wells and consultation with horizontal drilling vendors. This section of the FS describes the challenges and risks associated with HDD technology as applied to the P/S Landfill.

HDD and drain well challenges at the site are presented below under construction and O&M categories in terms of hazards/vulnerabilities and potential impacts. See Table 10-6A-1 for a description of these hazards and potential impacts along with potential probabilities of occurrence, consequences of potential impacts, risk mitigation measures to reduce the probability of occurrence, and the probability of occurrence after risk mitigation. Additional considerations are then provided for controlling the path of the borehole, terminating the borehole and well construction, health and safety issues related to HDD mud management, and HDD well efficiency. Construction Risk Factors

Insufficiently Draining the P/S Landfill (Options 1 and 2) o As mentioned above, the landfill may not be sufficiently drained if the horizontal wells

are either (1) not constructed along the bottom of the landfill, (2) constructed too far beneath the bottom of the landfill in the unweathered claystone, or (3) constructed at a spacing that is not dense enough (too few wells). The first issue will leave liquids in waste below the horizontal wells. The second issue may result in insufficient liquids moving from the bottom of the landfill through the unweathered claystone due to the low permeability of the claystone and low frequency of fractures in the claystone. The third issue may result in a drainage rate that is too slow because the ideal well spacing and hydraulic effect (zone of influence) of individual wells is not known

o Risk Mitigation: Robust field investigation would be performed prior to detailed design so that the configuration of the contact between the waste and top of


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unweathered claystone is understood at an appropriate level of detail. This investigation would include pushing numerous CPT borings into the landfill. However, even with a high density of CPT borings, uncertainty regarding the bottom configuration of the landfill will remain because the bottom of the landfill is likely benched and irregular resulting from original construction where the landfill was excavated to the weathered-unweathered claystone contact and then backfilled with waste material.

Uncontrolled release of Landfill Liquids (Options 1 and 2)

o Installing the horizontal wells will entail drilling from the Sump 9B area (south of the landfill) northward into (or immediately underneath) the landfill at an overall upward angle. Landfill liquids (DNAPL, LNAPL, aqueous phase liquids) may flow uncontrollably by gravity to the south along the borehole during drilling or the installed well.

o Risk Mitigation: The driller would utilize a pressure grouted surface casing (including a grouted annulus) keyed several feet into the clay barrier, combined with a blowout preventer at the surface to control flow back of liquids during well construction. Use of secondary containment to contain potential liquids that may be released is also assumed. In addition, the driller is assumed to utilize a special mud/fluids system for fluid management rather than an open pit method.

Losses of Borehole Circulation Fluids (Options 1 and 2)

o Encountering void spaces or fractures along the borehole path that results in loss of fluid circulation.

o Risk Mitigation: Typically fluid circulation loss can be overcome by thickening the drilling mud; however, it is not known if this method will be effective in an upward inclined borehole.

Penetrating the Clay Barrier (Option 1)

o Penetrating the clay barrier near the base would be required to adequately drain the south end of the landfill using horizontal wells. Drilling underneath the clay barrier may not facilitate proper drainage because of the low permeability of the claystone. Furthermore, drilling underneath the clay barrier may not allow placement of the horizontal wells at the optimum angle for proper drainage. The bore cannot be drilled upward at greater than approximately 20 degrees and would therefore bypass a portion of the NAPL pool at the bottom of the landfill, after the borehole passes underneath the clay barrier. The potential for borehole wash-out exists at the transition between different material, e.g., from clay barrier to waste material.

o Risk Mitigation: The driller would utilize a pressure grouted surface casing (including a grouted annulus) keyed several feet into the clay barrier, combined with a blowout preventer at the surface to control flow back of liquids during well construction.

Improperly Controlling the Path of the Borehole (Options 1 and 2)

o Installing the horizontal wells will require drilling through a variety of soil materials (alluvium, landfill waste, and claystone) and buried landfill debris at changing pitch angles. Interference associated with drums and other buried metal debris could interfere with conventional drill head tracking methods (walk over or wire line guidance system), which could compromise accurate placement of the well screen.


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o Risk Mitigation: The driller could utilize a higher power sonde or gyro steering tool (GST) system, which is not sensitive to magnetic disturbances and does not require access to the surface.

Borehole Collapse (Options 1 and 2)

o The landfill debris may partially collapse after the pilot bore is completed, which could preclude insertion of the well materials. Well materials are generally inserted into the bore in a single entry (blind end) application.

o Risk Mitigation: The driller would use oversized drill rod with a "knock-off"/expendable drill bit and insert the well materials inside the drill rods, effectively shielding them from borehole collapse.

Well Collapse (Options 1 and 2)

o Constructed wells may collapse if the crush strength of the selected material (HDPE, stainless steel) is not sufficient, or if the well material is not chemically compatible with the landfill liquids. If not chemically compatible, landfill liquids may degrade the well materials which would cause them to weaken.

o Risk Mitigation: The well materials will be selected so that they are chemically compatible and strong enough to avoid collapse

Chemical Compatibility (Options 1 and 2)

o Materials used in the process equipment (wellhead, pipes, tanks, valves, etc) may degrade and fail if not chemically compatible with the landfill liquids. This includes the "hard" components (pipes, tanks, etc.) and "soft" components (gaskets, O rings, etc).

o Risk Mitigation: The well materials will be selected so that they are chemically compatible with the landfill liquids. This would include bench-top studies where materials are exposed to landfill liquids to verify chemical compatibility before materials are used in the field.

Health and Safety During Construction (Options 1 and 2)

o Workers may become exposed to contaminated contents from the landfill during drilling and well installation. The exposure may be from drilling mud that contains contamination or from uncontrolled release of raw landfill liquids that may "drain" downslope back to the drilling location.

o Risk Mitigation: A detailed Health and Safety Plan will be developed and carefully followed during the work. Wear appropriate PPE (Level A/B/C) and perform air monitoring when the potential for exposure occurs. Stop work if ambient air concentrations exceed action levels. Stop work if drilling conditions indicate potential for uncontrolled release.

Operations and Maintenance Risk Factors (Options 1 and 2)

Well Efficiency and Clogging o The horizontal wells may clog over time due to scaling/fouling, fines intrusion, or

other factors o Risk Mitigation: Effectively develop wells during construction and, if necessary,

perform redevelopment during O&M. The well development procedure may require additional effort in an upward inclined well casing, than for a typical installation.


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Water Coning o Groundwater flow to the well is preferential to NAPL flow to the well. Water coning is

well known phenomena in oil well production and occurs due to water being the less viscous and the more mobile fluid in the presence of NAPL. Due to the long well screen and unknown fluid content (fluid ratios) along well screen water coning should be anticipated.

o Risk Mitigation: Due to the design of the HDD wells if water coning occurs there will be no way to recover well to NAPL production only. Effectively, the HDD well will result in high quantities of water production relative to NAPL recovery.

Uncontrolled Release During Site O&M

o Uncontrolled releases could occur from wells (at the wellhead), pipes, storage tanks, and other process equipment. This would include transferring liquids from site storage tanks to trucks for transport of the liquids to a disposal facility.

o Risk Mitigation: Develop O&M and preventative maintenance procedures which include contingency measures, install isolation features and employ secondary containment at all times.

Health and Safety During O&M

o Workers may become exposed to contaminated landfill liquids during operations and maintenance (while the landfill is draining). The exposure may occur during controlled O&M activities and accidental uncontrolled releases.

o Risk Mitigation: A detailed Health and Safety Plan would be followed at all times. Shut-off wells and discontinue routine operations if conditions indicate potential for uncontrolled release. Wear protective clothing and perform air monitoring during all operations. Upgrade to higher safety level (Level A/B/C) if release occurs.

Uncontrolled Release During Transport

o Uncontrolled releases could occur while transporting the liquids to the disposal facility.

o Risk Mitigation: Maintain O&M procedures and emergency response procedures in place.

Additional Considerations

Controlling the path of the borehole o The bottom of the P/S Landfill was constructed by excavation of canyon materials to

the weathered – unweathered claystone contact. This surface was later backfilled with waste material to create the landfill. The bottom of the P/S Landfill is both benched and irregular and gains over 220 feet of elevation over its approximately 1,400 foot length (i.e., up to 16 percent grade).

o The pathway of the HDD borehole would include, spudding the boreholes near Sump 9B area within the CDA and angling the borehole downwards 20 feet over a distance of approximately 150 feet to avoid penetration the base of the clay barrier. Leveling the borehole to allow for upward angle beneath the P/S landfill and then angling the borehole upwards at about a 20 percent rise for 300 to 500 feet to encounter and parallel the waste – unweathered bedrock contact. (Figure 11-28B).

o The borehole will not encounter the pool of DNAPL, unless purposely directed through the toe of the P/S Landfill clay barrier and buttress. Penetration of P/S


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Landfill clay barrier and buttress will compromise the integrity of the key containment feature.

o The proposed drains would be additionally angled at 1-2 percent grade into the landfill to intersect waste and facilitate drainage. The practical aspects of controlling the drill bit would be challenging.

o Controlling drill bit deflection when encountering materials of different mechanical properties (i.e., from weathered claystone to competent claystone and from claystone to waste materials of metallic drums containing liquids and landfill fill soil cover.

o Conventional drill bit tracking system work by electronically relating the drill string to the Earth’s magnetic field and inclination, the presence of large quantities of steel drums will interfere with tracking system and result in the installation of a blind borehole. As such, the position of the borehole (or well) with respect to target zones will never be known with any degree of accuracy.

Terminating the borehole and well construction o Since the horizontal drilling cannot be double-ended due to potentially damaging the

landfill cap and liner system, the borehole installation will utilize a single-ended or blind hole drilling method. It is well known that there is significantly greater number of borehole failures with blind hole drilling. This risk is discussed in an excerpt from the Center for Public Environmental Oversight (CPEO) technical report on “Horizontal Wells” -“As opposed to vertical wells, horizontal wells may have a greater potential to collapse. Borehole collapse is also more likely in single-ended drilling since the hole is left unprotected between drilling and reaming and between reaming and casing installation. Double-ended holes may be easier to install since reaming tools and well casing can be pulled backward from the opposite opening, and the hole does not have to be left open. “http://www.cpeo.org/techtree/ttdescript/horzwel.htm”. The waste over burden ranges from 100 to 150 feet in thickness of material behind the clay barrier.

o Blind hole drilling will also result in frequent casing breakage particularly while pushing the casing into the borehole that has numerous directional changes. Stainless steel casings will need to be used to provide adequate strength and chemical resistance for this application. However, stainless steel piping is less flexible than plastic piping and prone to breakage and/or blocking-off, when attempting to push them into boreholes with numerous twists and turns.

Health and Safety issues related to HDD mud management o The liquid head at the proposed target end points (300-500 feet behind the clay

barrier) will be at higher elevation than the starting point. As such to maintain borehole circulation an elaborate “blow-out prevention system“ will be required. It is not known if such a system exists for remedial HDD applications.

o Release of NAPL from puncturing drums. As shown on Figure 4-51 of the Final RI Report (CSC 2011a), the bottom of the P/S Landfill holds containerized liquid waste (stacked drums). Assuming that multiple horizontal wells will be required, the implementation of this remedy would likely result in the release of thousands of gallons of free NAPL into the formation if these drums were to be penetrated. The negative effects of this technology could far outweigh any potential benefit associated with attempting to reduce the groundwater levels in the landfill.

o HDD mud management concerns will be significant. The drilling mud will be considered hazardous; the borehole will be spudded in an area of known LNAPL


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contamination. Drilling mud from the HDD boreholes will be recirculated during the drilling process. However, it cannot be reused after the project is complete on other site due to high VOC/NAPL content.

o The high NAPL and VOC content of drilling mud and the landfill liquids will present a significant human health concern for drillers and other site workers during installation. Based on past drilling experience in the vicinity of the P/S Landfill level B personal protective equipment will be required, which incorporates, performing drilling activities with supplied air. Additional effort in the form of the development and placement of contingency plan items and equipment would need to be in-place to respond to a potential spill that might result utilizing the blind HDD method.

o The spent drilling mud (estimated at 100 tons for five 600-foot long boreholes) will be classified as hazardous waste, and waste material handling and disposal will require additional precautions and effort. Drilling mud will need to be disposed as RCRA hazardous waste and may need to be incinerated (estimated disposal cost at $1,400/ton).

HDD Well Efficiency o Preliminary estimates of horizontal well production are estimated at 0.26 to 2.6 gpm

assuming a hydraulic conductivity (K) of the waste of 10-6 to 10-5 cm/s, respectively. The actual hydraulic conductivity of the waste many be higher (e.g. 10-4 cm/s) based on experience at other landfills. The effective hydraulic conductivity of the landfill waste materials is not known because aquifer pump testing has not been performed. Experience at other landfills indicates that the initial drainage rates may exceed 10 gpm per well. The estimated time for the landfill to drain is uncertain. Using the 0.26 to 2.6 gpm estimated rates, the estimated time to dewater 10 million gallons of liquid from the five wells would take between 6 to 60 years at full efficiency. The actual time for the landfill to drain could be much shorter, however, based on flow rates that exceed 10 gpm. The well efficiency may be compromised (potentially 20-33 percent range) due to well construction defects (well development, well compression, screen clogging) and declining hydraulic head over time. Under this scenario, the operation time could be in the range of 20 to 200 years depending of formation hydraulic conductivity and well efficiency. This would be a conservative estimate if the well efficiency were higher.

o Even with a series of horizontal dewatering wells beneath the P/S landfill, it is possible that some groundwater flow will bypass the horizontal wells, and preferentially pass through the landfill waste material, and be captured by the existing Gallery Well. There is significant uncertainty with the total recoverable liquids volume and extraction flow rates that are possible with this approach.

Damage to the Gallery Well

o For the HDD wells scheme to be effective at least one of the HDD wells will need to run along the bottom axis of the landfill, and as such, likely encounter the Gallery Well, resulting either in the destruction of the well or significantly reducing its efficiency. It is a significant trade-off to risk damage to a proven site remedial feature that achieves containment and mass removal in the hope to potentially (and marginally) decrease the time needed to remove (an already depleting) reservoir of mobile DNAPL.


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The implementation of the remedy to dewater the P/S landfill by installing (inclined) horizontal gravity drain wells presents significant technological challenges. The benefit of installing horizontal drain wells while on the surface may appear more attractive than the installation of vertical wells, the risk of doing so is significantly higher for reasons outlined above. 10.6.3.2 Approach for DNAPL Source Reduction in the CDA The approach for DNAPL source reduction in the CDA is discussed below for the Upper HSU and Lower HSU. DNAPL in Upper HSU While there is no significant free DNAPL present in the CDA like there is in southern portion of the P/S Landfill, the remedial alternatives are assumed to address the residual saturation DNAPL extent defined by the >10 percent aqueous solubility contour (Figure 5-31). The FS considered two short-term, aggressive options for DNAPL remediation in the CDA, including ISTD and ISCR in the NAPL-impacted area in the Upper HSU. Long-term extraction options are not considered necessary to address this DNAPL area because the total NAPL volume and saturation in these areas is significantly less than in the southern portion of the P/S Landfill. Also, long-term extraction options are not considered necessary to address this NAPL area because the extraction system would primarily recover dissolved phase contaminants, which is already being implemented with the PSCT extraction just downgradient of the NAPL area in the CDA. However, a long-term extraction alternative is considered for the dissolved VOC plume across the entire Area 5 North (including the CDA), and is discussed later in this section. Brief evaluations for the ISTD and ISCR technologies for source reduction in the Upper HSU are presented below. In-situ Thermal Desorption (ISTD) ISTD is a thermal technology that heats the saturated zone soils in the Upper HSU source area with very closely spaced (10-foot spacing typical) wells. The areal extent of the DNAPL in the CDA Upper HSU is assumed to be approximately 400 feet by 100 feet based upon the 10 percent isoconcentration line on Figure 5-31. The electric heater wells would be constructed of steel that would be heated to temperatures of 1,000oF and connected to a vapor extraction piping network to extract heated vapors. It is assumed that each well has a total depth of 40 feet (drilled down 5 feet below the weathered-unweathered contact) and the well screen is between 5 feet and 35 feet bgs. Based on the assumed horizontal extent of 40,000 sf that is to be heated, approximately 400 electric heater wells would be required. The volume of soil to be heated is approximately 59,000 cy. Using an in-situ thermal remediation unit cost of $250/cy, the total cost of the remediation would be approximately $14.8M. With respect to effectiveness, this technology would face significant limitations due to the low permeability of the weathered bedrock in the Upper HSU, uneven heating in the heterogeneous formation and the preferential flow in the fractures that would not adequately remediate the matrix. From an implementability perspective, installation of 400 electric heater-SVE wells that are screened down to an average depth of 35 feet bgs within the CDA and the extraction and capture of these heated vapors would be a significant challenge in this weathered bedrock lithology. Given the significant effectiveness and implementability challenges with this process option, ISTD is not retained as a remedial component for DNAPL in the CDA for the detailed evaluation.


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In-situ Chemical Reduction (ISCR) ISCR is a chemical reduction technology for chlorinated solvents that would involve injection of microscale ZVI or a ZVI + carbon product (ISCR with bioaugmentation) in the Upper HSU by high pressure injection that involves hydraulic fracturing to increase the amount of injectate emplacement. The areal extent of the DNAPL in the CDA Upper HSU is assumed to be approximately 400 feet by 100 feet, as discussed above for ISTD. The injection points would need to be very closely spaced (assume 5 feet apart) and could require up to 1,600 direct push injections to average depths of around 40 feet bgs in the DNAPL-impacted area. This technology could be challenged from both implementability and effectiveness perspectives. High pressure injection may have the unintended effect of causing further DNAPL migration into deeper fractures into the Lower HSU. The effectiveness would be poorer than ISTD due to uneven distribution of the injectate in the heterogeneous, low permeability formation. Hence ISCR was also not retained as a technology for DNAPL in the remedial alternatives. DNAPL in Lower HSU The DNAPL observed in the lower HSU is relatively localized as discussed earlier in the Nature and Extent of Contamination discussion. The DNAPL in the Lower HSU has been directly observed in two piezometers (RGPZ-7C and -7D) and fractures from one additional borehole (RISB-02) in the CDA. The extent of DNAPL in the Lower HSU is interpreted to cover the area from the southern part of the P/S Landfill southward to the two piezometers in the CDA. Direct removal of DNAPL from fractures in the Lower HSU is not practicable. Instead, source removal of the DANPL in the P/S Landfill will be performed to remove the DNAPL source which will stop DNAPL migration in the Lower HSU. The dissolved-phase contaminants migrating southward from the DNAPL zone will be targeted by the remedial alternatives in this FS with groundwater monitoring (MNA) and, if demonstrated to be necessary by ongoing groundwater monitoring, limited hydraulic extraction. Natural attenuation of contaminants occurs and will limit the potential migration of dissolved-phase contaminants beneath the PSCT. Other technologies were not considered viable in the Lower HSU. Though the DNAPL extent is localized, it is considered in the evaluation because the Lower HSU groundwater is not captured by the PSCT. The objective of the remedial alternative here is to provide containment of the dissolved VOC plume in Area 5 North. As noted in the RI Report, identifying the location and extent of any DNAPL in the lower HSU, and its removal, is virtually impossible. Only limited hydraulic extraction was evaluated for active remedial alternatives for DNAPL or dissolved VOCs in the Lower HSU because of the physical limitations imposed due to contaminant depth in the lower HSU, the very low permeabilities and the uncertainties associated with designing an effective remedy when the precise mechanism for the deeper DNAPL contamination is unknown. Furthermore, with the relatively low levels of NAPL in the Lower HSU compared to the Upper HSU, hydraulic extraction in the Lower HSU could at best recover groundwater with relatively low VOC concentrations and not really recover any significant amount of NAPL or VOC contaminant mass. The limited monitoring or extraction of the Lower HSU is conducted through two wells in the CDA upgradient of the PSCT-1 (Figure 11-25A). Based on experience with purging other Lower HSU wells, the extraction at these wells is expected to yield at most 0.25 gpm, with most wells going dry and not recovering for extended periods. Relatively low volumes of groundwater are expected to be extracted with relatively low VOC concentrations, hence resulting in extremely low contaminant mass removals.


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10.6.3.3 Approach for LNAPL Source Reduction in the CDA Within the CDA, LNAPL migration is effectively contained by the PSCT. A pool of LNAPL exists within the CDA and has similar characteristics to the P/S Landfill pool, i.e., the LNAPL pool is composed of a mixture of compounds floating above the water table. In general the thickness of the LNAPL column measured in wells in the CDA is less than that of the P/S Landfill; principally due to the depth to water being less within the CDA. There is no evidence to suggest that LNAPL is spilling from the P/S Landfill to the CDA, indicating that the clay barrier located between these two areas is competent. Based on evaluation of LNAPL data, the thickness of LNAPL observed in some CDA monitoring wells is temporal and likely the result of well hydraulics rather than the actual thickness of LNAPL pool within the CDA area. A review of the time series plots of water level and NAPL thickness suggests that LNAPL build up in the wells most often occurs following a decline in the water elevation, and that once LNAPL enters the well casing, the LNAPL can persist for some time before dissipating from the well. Rapid changes in LNAPL thickness appear to occur in short time intervals, suggesting (i.e., giving the appearance) that LNAPL pool(s) exist that are moving through the CDA as a series of “slugs” of thickness in excess of 8 to 10 feet, as seen for wells 9B-PZ-C, RGPZ-5B, or RIMW-3, RIPZ-8. However, such a pattern of liquid movement is unlikely, particularly given that no upgradient NAPL source flow path exists between the P/S Landfill buttress and Sump 9B. The actual thickness of LNAPL in the CDA area is likely much less than indicated by the periodic LNAPL thickness spikes observed in well casings. In general, if the transient pulses observed in wells are attributed to well casing storage, then the thickness of LNAPL in the CDA is generally less than 1-foot in thickness. Dedicated LNAPL recovery (i.e., pumping) would be difficult using currently available technology due to the physical nature of the LNAPL. Due to the co-solvency of the constituent LNAPL compounds, the density of the LNAPL is 0.99 g/cm3 – closely approximating water. Currently available LNAPL pumps or skimmers rely on the density contrast between the LNAPL and water for operation (i.e., to set the level of the pump intake) therefore the ability to set control points for pump-on and pump-off liquid levels within an extraction well may require significant operational maintenance. The lack of density contrast between LNAPL and groundwater liquids would likely result in a significant portion of extracted liquids content being impacted groundwater, and separation of liquids post extraction would be required. The operation of dedicated LNAPL extraction well(s) likely offers no significant benefit in terms of LNAPL recovery efficiency. LNAPL is not considered a source of high risk to groundwater at this site and many of its constituents are more biodegradeable than DNAPL constituents. Furthermore, the dissolved petroleum VOCs from LNAPL can serve as electron donors for the reductive dechlorination of chlorinated solvents, a primary groundwater contaminant at the site. Since the benefit of LNAPL extraction is not expected to be significant, only two limited LNAPL extraction options are included in the remedial alternatives evaluation. One extraction option assumes that four existing monitoring wells (RGPZ-5B, RIPZ-8, RIMW-3 and RG-3B) in the CDA will be converted to LNAPL skimmer wells (Figures 11-25A, 11-25B). A solar skimmer is assumed that pumps LNAPL to a drum aboveground with a high level shutoff that is located adjacent to the well. Another more aggressive option, includes twelve new extraction wells in the LNAPL area that will be equipped with pneumatic LNAPL skimmers that are piped to a treatment compound (Figures 11-28A, 11-28B). The treatment compound would include a stainless steel NAPL storage tank that is periodically emptied for disposal at a permitted facility.


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10.6.3.4 Approach for Residual NAPL Source Reduction in the BTA The approach for NAPL source reduction in the Upper HSU and Lower HSU in the BTA is discussed below. NAPL in the Upper HSU ISTD was considered for the residual NAPL area as defined in the BTA by Figures 5-32 and 5-33 from the RI report. The NAPL area is assumed to be about 400 feet by 100 feet based on the 10 percent isoconcentration contour. It is assumed that each well has a total depth of 75 feet, is drilled down 5 feet below the weathered-unweathered contact, and has the well screen set between 15 feet and 70 feet bgs. Based on the assumed area of 40,000 sf that is to be heated, approximately 400 electric heater wells would be required, The volume of soil to be heated is approximately 81,000 cy and the electric energy usage would be approximately 16.2 million KWhrs. Using an in-situ heating unit cost of $250/cy, the total cost of the remediation would be approximately $20.2M. Similar to the challenges of applying ISTD in the CDA, this technology would face significant challenges with implementability and effectiveness in this weathered claystone. Also, the risk reduction as a result of this remediation is not significant since this area has relatively low NAPL saturations and there is a PSCT control feature downgradient that has been demonstrated to be effective in containing Upper HSU groundwater contamination and is expected to operate as part of the site remedy. Based on the above factors and the high cost, the ISTD source removal alternative for the residual NAPL in the BTA is not included in the detailed analysis. NAPL in the Lower HSU Though the likelihood of free DNAPL in the BTA is low, the Lower HSU in the BTA is targeted by the remedial alternatives in this FS with groundwater monitoring and limited hydraulic extraction (as in the CDA) with the primary objective of plume containment in Area 5 North. As noted in the RI Report, identifying the location and extent of any NAPL in the lower HSU and removal of that is virtually impossible. Only limited hydraulic extraction was evaluated for active remedial alternatives for NAPL or dissolved VOCs in the Lower HSU because of the physical limitations imposed due to contaminant depth in the lower HSU, the very low permeabilities and the uncertainties associated with designing an effective remedy when the precise mechanism for the deeper NAPL contamination is unknown. The limited monitoring or extraction of the Lower HSU is conducted through six wells upgradient of the PSCT-4 (Figure 11-25A). Based on experience with purging other Lower HSU wells, the extraction at these wells is expected to yield at most 0.25 gpm, with most wells going dry and not recovering for extended periods. Relatively low volumes of groundwater are expected to be extracted with relatively low VOC concentrations, hence resulting in extremely low contaminant mass removals. 10.6.3.5 Dissolved VOCs in Area 5 North The approach for remedial alternatives for dissolved VOCs for the Upper HSU and Lower HSU are discussed below. Dissolved VOCs in Upper HSU


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The FS proposes to address dissolved VOCs in Area 5 North by continuing operation of the PSCT extraction for VOC containment in the upper HSU. In addition, the FS conducts an evaluation of an aggressive hydraulic extraction alternative with wells across the most impacted areas of Area 5 North groundwater as a restoration alternative. The FS also evaluates an alternative to the PSCT extraction for VOC containment in the Upper HSU which involves conversion of the PSCT to an in-situ reactive wall. ZVI barriers are effective in degrading chlorinated VOCs and some dissolved metals. This technology is considered implementable and it would involve construction of a soil-bentonite slurry wall barrier a few feet downgradient of the existing PSCT trench along its entire length (2,650 feet). The ZVI would be placed into “gates” within this slurry wall barrier at about 400-foot spacing, with each gate about 12 feet wide and 25 feet long, for a total of about six gates along the length of the PSCT. However, there would be effectiveness challenges due to the complex mix of contaminants and due to very high TDS which could clog the ZVI barrier in shorter than typical timeframes. While the capital cost would be high, the operations and maintenance cost is a significant uncertainty. The O&M cost could be very high if the ZVI gates would need to be replaced frequently (e.g., every 10 years versus say, every 30 years). The in-situ reactive wall approach at the PSCT would also face some effectiveness and reliability challenges given that the groundwater at the PSCT has significantly higher VOC and metals concentrations than the PCTs. As a result, the in-situ reactive wall option for the PSCT is not carried through to the remedial alternatives. Addressing the dissolved VOCs in the Upper HSU primarily via PSCT extraction is considered adequate because the anticipated soil remedy for FS Area 1 is going to result in a cap that minimizes or eliminates infiltration over approximately 28 acres, including the CDA, thus making a contiguous capped area across almost 90 acres of FS Area 1. This elimination or minimization of infiltration would limit additional leaching of contaminants from the NAPL-impacted areas and additional downgradient contaminant migration. In addition, the capping would lower water tables significantly in the area, as shown by the groundwater modeling conducted (Appendix D), and thus decrease the extraction rates of groundwater from the PSCT (discussed earlier in Section 10.6.2). Hence the anticipated soil remedy for FS Area 1 would be a significant contributor to containment of VOC and metals contaminants in Area 5 North groundwater, and thus indirectly comprise an important component of the site groundwater remedy. Dissolved VOCs in Lower HSU For the Lower HSU, the remedial alternatives consider groundwater monitoring and limited hydraulic extraction as discussed earlier under NAPL in the Lower HSU for the CDA and BTA. In general, the PSCT provides hydraulic containment of the dissolved VOC plume in the Upper HSU. A review of the VOC analytical results for the Lower HSU monitoring wells downgradient of PSCT-1 and PSCT-4, show that the following:

Very low levels of VOCs have been detected in the Lower HSU immediately south of the PSCT trench, south of the Central Drainage Area at PSCT-1 and south of the Burial Trench at PSCT-3. Chlorinated VOCs indicative of contaminant migration in the Lower HSU were detected during both of the expanded RGMEW events for the RI (Fall 2004 and Spring 2005) at less than 1 g/L south of PSCT-1 at RGPZ-8D (PCE and TCE) and at 3 to 4 g/L south of PSCT-3 at RGPZ-16D (vinyl chloride). Dhc bacteria were recently detected in the Lower HSU well RGPZ-6C indicating the presence of dechlorinating bacteria in the Lower HSU groundwater.


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There are occasional recorded hits of organics at >10 g/L, but these are primarily acetone, MEK and chloroform, which have been characterized as likely laboratory contaminants. There are transient hits of tetrahydrofuran in two wells (DB-1 and RGPZ-8D) that are at >100 g/L, but these levels do not exceed MCLs. It is significant to note that the sample results from the monitoring well RGPZ-4C located south of PSCT-4 is non-detect for VOCs. Any groundwater extracted from Lower HSU wells downgradient of PSCT-1 and PSCT-4 would be considered essentially clean based on current sampling data.

The limited density of the Lower HSU monitoring well network along the PSCT with

respect to the preferential fracture transport pathways makes the distribution of potential VOCs moving southward under the PSCT uncertain.

A review of the purge and recovery data from Lower HSU monitoring wells shows that these wells cannot sustain production in excess of 0.25 gpm. Thus even if there was VOC contamination in the Lower HSU, the mass removal over the course of a year would be very small. The sustainable volume of groundwater that any Lower HSU well would be able to extract is very small. The ground water south of the PSCT in the Lower HSU is currently essentially clean (i.e., below MCLs) based on current monitoring results. The GW Flow Model projects that there is a potential flow path of dissolved-phase constituents through the Lower HSU beneath the PSCT. The travel time for groundwater from the Lower HSU DNAPL at RGPZ-7C/D to a point underneath PSCT-1 is calculated to be slightly less than 100 years using Darcy’s law and input parameters representative of the hydraulic conductivity, gradient, and fracture transport porosity in the area. The travel time is calculated to be 72 years and the average linear groundwater flow velocity is calculated to be 2.1 ft/yr assuming the following inputs into Darcy’s law equation (V=Ki/Ne):

150 feet = Distance from RGPZ-7C/D wells containing Lower HSU DNAPL to PSCT-1. 1x10-6 cm/sec = K, Geometric mean from historical Lower HSU aquifer tests 0.1 ft/ft = 20’/200’ = i, gradient between 460’ and 440’ WLE contours in Lower HSU 0.05 = Ne, Fracture transport porosity

This calculated flow velocity and travel time is consistent with the CSC’s 2-D model simulations presented in the TI Evaluation (Appendix A). There are several figures, one for each time step (time zero, 30, 100, and 500 years). The distance moved at a time of 100 years is consistent with the 72 years calculated above (Figure A2-4). The actual migration of VOCs are naturally attenuated by several mechanisms, including biodegradation, dilution from mixing with upwelling groundwater and absorption through interaction with the soil matrix. This will reduce the potential for VOC migration and the time that contaminant particles arrive at the PSCT. Based on current data, additional monitoring of VOCs in the Lower HSU may be adequate but limited extraction is evaluated as well. 10.6.3.6 Site Treatment of Gallery Well Liquids As discussed earlier, the FS proposes to continue operation of the Gallery Well and extraction of leachate as part of the remedial alternatives for Area 5 North. Currently, the Gallery Well liquids (highly concentrated leachate) are trucked to a permitted facility for disposal. A brief evaluation of a treatment option at the site for the Gallery Well liquids is presented here.


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The FS assumed the total liquids extraction rate from the GW would be the same as the current production of 450,000 gallons per year of highly concentrated leachate liquid. A batch type treatment system treating 10,000 gallon batches once a week was selected as the most appropriate process to treat a concentrated leachate liquid that is produced at these relatively low flow rates. As discussed in the technology screening, the Bio-PACT technology involves a combination of biodegradation and powder activated carbon technology that has been used successfully for leachate treatment at other landfill sites. This treatment system would primarily address the VOCs and organics but not the inorganics present at elevated concentrations. In order to address the inorganics, the treated leachate containing elevated inorganics would be pumped to the evaporation pond where the liquids would evaporate and leave the inorganics as a residual that would periodically be cleaned out and disposed of as a solid waste. This treatment system would require labor and would be high in operational cost. In comparison, the transportation and disposal cost is currently less than $1.50/gallon. Moreover, significant challenges can be expected in meeting VOC emissions requirements of the Santa Barbara County Air Pollution Control District for the Bio-PACT system. Also, this treatment process would involve handling, pumping, and transferring of these concentrated liquids, which increases the potential for releases or accidents. Overall, the disposal at a permitted facilityoption is a cost-effective option for handling the extracted liquids at current extraction rates, and has already been effectively implemented at the site. Hence, treatment of Gallery Wells liquids at the site is not retained. However, treatment of Gallery Well and other leachate liquids at the site is retained for those alternatives that involve aggressive extraction and require handling of large volumes of leachate liquids. 10.6.3.7 Description of Remedial Alternatives for Area 5 North In Appendix A and as summarized in Section 8.5, a groundwater ARAR waiver may be applied based on Technical Impracticability of restoring groundwater to drinking water standards for the potential TI Zone that includes the Upper and Lower HSU of Area 5 North for organic and inorganic contaminants. Where groundwater ARARs are waived at a Superfund site due to technical impracticability, the USEPA’s general guidance is that the site must consider source control and containment and source removal alternatives to the extent practicable to prevent further migration of the contaminated groundwater plume and prevent exposure to the contaminated groundwater. This section presents the development of remedial alternatives for Area 5 North. In light of the proposed TI waiver zone for Area 5 North, the remedial alternatives proposed in this section span the range of alternatives from low action to moderate action to the most aggressive action to satisfy the objectives of “control and contain” source contaminants and “source removal to the extent practicable”. All of the remedial alternatives include operation of the most effective existing remedial features in Area 5 North (e.g., PSCT, Gallery Well) as components, which provide control and containment of groundwater contaminants. The low action alternatives include only the operation of the PSCT and Gallery Well, while the more active remedial alternatives include removal of the NAPL source (NAPL-only and Aggressive NAPL extraction or P/S Landfill Dewatering), and the most aggressive alternative adds the extraction of impacted groundwater with 50 large diameter extraction wells, as further described below. In the evaluation of Area 5 North alternatives for groundwater, it should be noted that capping is anticipated as part of the soil remedy for FS Area 1 (including the Central Drainage Area, Burial Trench Area and the PCB Landfill) which will prevent or significantly minimize infiltration, reducing leaching VOCs and inorganics into groundwater. Thus the capping remedy for soils in


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FS Area 1 will be a significant source reduction measure for the groundwater remedy, though it is not formally listed as a remedy component in these alternatives below. Table 10-1 lists the eight remedial alternatives and remedial objectives for FS Area 5 North. The remedial alternatives for FS Area 5 North are briefly described below, followed by a screening analysis in Section 10.6.6. Alternative 1 No Action The No Action alternative is included as required by CERCLA guidance. No Action implies that the source control activities and monitoring that are ongoing currently would not be occurring. Alternative 2 Extraction (PSCT, Gallery Well) + Treat and Discharge PSCT Groundwater to Site Evaporation Pond + ICs + Monitoring This alternative includes continued extraction of liquids from the Gallery Well and PSCT for source control as it is currently being implemented. The PSCT liquids would be treated at the site for removal of organics (via an upgraded GAC system) and pumped to a new lined evaporation pond at the site (Figures 11-24A, 11-24B). Total annual extraction volumes of liquids from the PSCT are expected to drop significantly from current levels based on future proposed capping remedies for FS Area 1. Based on the results of groundwater modeling (Appendix D-1) that assume a proposed remedy scenario that prevents infiltration with caps at the PCB Landfill, BTA and CDA, the PSCT extraction rates decreased from 2,838,000 gallons per year (average 2006-2011) to between 1,901,000 and 1,931,000 gallons per year based on dry season or wet season model results as discussed earlier in Section 10.6.2. A base case evaporation pond size of 6 acres is assumed for this alternative. Extracted NAPL and liquids volume for the Gallery Well are assumed to be similar to current volumes at 450,000 gallons of liquids and 3,000 gallons of NAPL that are currently sent for disposal at a permitted facility. These extracted volumes are assumed to decrease with time as described earlier in Section 10.1.8.5. As described in Section 10.1.8.8, approximate estimates of the timeframe for dewatering the P/S Landfill were obtained using groundwater flow model simulations for various site-wide remedial alternatives. For the Gallery Well extraction scenario included in this alternative, an approximate estimate of 10 years for dewatering was developed. This alternative includes long term site-wide groundwater and soil vapor monitoring as discussed in Section 10.1.6. Alternative 3 Extraction (PSCT, Gallery Well) + Extraction (NAPL-only in P/S Landfill) +

Extraction (NAPL-only in CDA, 4 wells) + Monitoring (12 new Lower HSU wells) + Treat and Discharge PSCT Groundwater to Site Evaporation Pond + ICs + Monitoring

This alternative includes continued extraction of liquids and NAPL from the Gallery Well and PSCT as it is currently being implemented. In addition, this alternative adds NAPL-only extraction from new NAPL-only wells in the southern portion of the P/S Landfill (see Figures 11-25A, 11-25B).


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The NAPL-only extraction involves extraction from 16 new 4” NAPL-only wells in the Upper HSU in the vicinity of RIPZ-13 near the toe of the P/S Landfill. The objective of these NAPL-only wells and this alternative component is to extract to the extent possible, NAPL product only including DNAPL and LNAPL. The sixteen wells would include four wells placed on Bench Road 1 in the vicinity of RIPZ-13, four wells located on a new bench road to the north and eight located on two new bench roads between Bench Road 1 and Gallery Well Road. NAPL-only extraction implies the product is pumped periodically with NAPL skimmer pumps when sufficient NAPL has collected in the well. Total volume of NAPL extracted from the 16 wells with this alternative is assumed to be 10,000 gallons per year initially from the new NAPL-only wells along with 3,000 gallons from the Gallery Well. A total of 450,000 gallons of leachate liquids is assumed to be extracted from the Gallery Well. The Gallery Well liquids and the NAPL from the NAPL-only extraction wells are assumed to decrease with time over the dewatering timeframe, estimated to be approximately 10 years (see Section 10.1.8.8). The NAPL and liquids from the Gallery well and the NAPL-only extraction wells would be sent to a TSDF for disposal. Remedial design, construction, and initiation of extraction of NAPLs from the NAPL-only extraction wells would be performed expeditiously because the liquid levels in the P/S Landfill will decline rapidly within the first few years and ultimately to below the bottom of the landfill after the remaining area across FS Area 1 is capped as demonstrated with the groundwater flow model (Appendix D-3). Extraction of current free-phase NAPLs will not be practicable after the landfill becomes desaturated. Prompt initiation of field investigations for remedial design is critical to maximizing NAPL extraction. Four existing groundwater monitoring wells in the CDA would be converted to LNAPL extraction wells equipped with LNAPL skimmers to recover floating product. Twelve new Lower HSU groundwater monitoring wells are proposed, including three clusters of two wells each just upgradient of both PSCT-1 and PSCT-4, to monitor potential VOC migration under the PSCT in the Lower HSU. Contingency actions would be implemented as necessary if potential VOC migration occurred beneath the PSCT at concentrations of concern, as determined by USEPA. These contingency actions could include (1) immediate additional monitoring (for characterization of the release as determined necessary by USEPA) and (2) prompt implementation of corrective action, including conversion of monitoring wells to extraction wells and installation of additional extraction wells for hydraulic containment of the VOCs in the Lower HSU. Groundwater extracted from the Lower HSU would be treated and discharged together with the PSCT liquids. The extracted volumes from the Lower HSU would be very small because of the low permeability of the Lower HSU. The PSCT liquids would be treated at the site with an upgraded treatment system designed to remove organics, as in Alternative 2. The treated PSCT liquids will be pumped to a new lined evaporation pond at the site (assume base case of 6 acres). Based on the results of groundwater modeling (Appendix D) that assume a proposed remedy scenario that prevents infiltration with caps at the PCB Landfill, BTA and CDA, the PSCT extraction rates are anticipated to decrease as discussed in Alternative 2. This alternative includes long term site-wide groundwater and soil vapor monitoring as discussed in Section 10.1.6.


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Alternative 4 Extraction (PSCT, Gallery Well) + Extraction (NAPL-only in P/S Landfill) + Extraction (NAPL-only in CDA, 4 wells) + Monitoring (12 new Lower HSU wells) + Treat and Discharge PSCT Groundwater (No Evaporation Pond) + ICs + Monitoring

This alternative includes continued extraction of liquids and NAPL from the Gallery Well and PSCT trenches and NAPL-only extraction as discussed in Alternative 3. The difference from Alternative 3 is that in this alternative, the PSCT liquids would be treated at the site for removal of organics and inorganics using carbon adsorption and RO for discharge to the B-Drainage in accordance with the substantive requirements of an NPDES permit (Figures 11-26A, 11-26B and 11-26C). As discussed earlier, a Basin Plan exception from the RWQCB would be required to discharge to the B-Drainage. This alternative assumes that there is no evaporation pond at the site. The RO system that treats the inorganics will generate wastewater (brine) with high dissolved solids and metals. A reject concentrator is included to treat the wastewater to reduce the volume of brine waste. As discussed in previous alternatives, based on the modeling performed the PSCT extraction rates are expected to decrease with the anticipated capping remedies that will minimize or prevent infiltration (Appendix D-1). Also, as in Alternative 3, four existing groundwater monitoring wells in the CDA would be converted to LNAPL extraction wells equipped with LNAPL skimmers to recover floating product. Also similar to Alternative 3, twelve new Lower HSU groundwater monitoring wells are proposed, including three clusters of two wells each just upgradient of both PSCT-1 and PSCT-4 to monitor potential VOC migration under the PSCT in the Lower HSU. Contingency actions would be implemented as necessary if potential VOC migration occurred beneath the PSCT at concentrations of concern, as determined by USEPA. These contingency actions could include (1) immediate additional monitoring (for characterization of the release as determined necessary by USEPA) and (2) prompt implementation of corrective action, including conversion of monitoring wells to extraction wells and installation of additional extraction wells for hydraulic containment of the VOCs in the Lower HSU. Groundwater extracted from the Lower HSU would be treated and discharged together with the PSCT liquids. The extracted volumes from the Lower HSU would be very small because of the low permeability of the Lower HSU. The total volume of NAPL extracted from the 16 wells in the P/S Landfill with this alternative is assumed to be 10,000 gallons per year initially from the new NAPL-only wells along with 3,000 gallons from the Gallery Well. A total of 450,000 gallons of leachate liquids is assumed to be extracted initially from the Gallery Well. The Gallery Well liquids and the NAPL from the NAPL-only extraction wells are assumed to decrease with time over the dewatering timeframe, estimated to be approximately 10 years (see Section 10.1.8.8). Approximately, 285,000 gallons of brine per year is assumed to be generated from the RO system. The NAPL and liquids from the Gallery Well and the NAPL-only extraction wells, and the brine would be sent to a TSDF for disposal. This alternative includes long term site-wide groundwater and soil vapor monitoring as discussed in Section 10.1.6.


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Alternative 5 Extraction (PSCT, Gallery Well) + Extraction (Aggressive, 16 Large Diameter NAPL Wells) + Extraction (NAPL-only in CDA, 4 wells) + Monitoring (12 new Lower HSU wells) + Treat and Discharge to Evaporation Pond + ICs + Monitoring

This alternative includes continued extraction of liquids and NAPL from the Gallery Well and PSCT as in Alternative 3. This alternative changes the NAPL component to continuous aggressive total fluids extraction from new NAPL wells in the southern portion of the P/S Landfill (see Figure 11-27A and 11-27B for well details). The aggressive DNAPL extraction includes 16 new large diameter (8-inch) Upper HSU NAPL wells in the vicinity of RIPZ-13 in the P/S Landfill. The sixteen wells would include four wells placed on Bench Road 1 in the vicinity of RIPZ-13, four wells located on a new bench road to the north, and eight located on two new bench roads between Bench Road 1 and Gallery Well Road. The typical well construction would involve a total depth of 80 feet bgs with a 40-foot screen interval and 0.020” slot size. The well would be equipped with a total fluids pneumatic pump. The aggressive extraction of total fluids is assumed to produce an initial flow rate of up to 10 gpm of landfill leachate that will be treated in a Liquids Treatment Plant (LTP) to treat organics and discharged to an evaporation pond at the site. The extraction flow rate is expected to decrease over the duration of the timeframe for dewatering the P/S Landfill, which is estimated to be approximately 5 years for this alternative (see Section 10.1.8.8). The LTP will be a treatment process train including NAPL-separation, air stripping, and liquid phase carbon adsorption (Figure 11-27C). The NAPL-separator will remove DNAPL and LNAPL phases from the groundwater phase. The VOC-laden groundwater will be treated by air stripping that will remove a majority of VOCs into the vapor phase and the residual VOCs in groundwater will be treated by LPGAC. The vapor stream from the air stripper will be treated by VPGAC prior to discharge to atmosphere. Also, as in Alternative 3, four existing groundwater monitoring wells in the CDA would be converted to LNAPL extraction wells equipped with LNAPL skimmers to recover floating product. Also similar to Alternative 3, twelve new Lower HSU groundwater monitoring wells are proposed, including three clusters of two wells each just upgradient of both PSCT-1 and PSCT-4 to monitor potential VOC migration under the PSCT in the Lower HSU. Contingency actions would be implemented as necessary if potential VOC migration occurred beneath the PSCT at concentrations of concern, as determined by USEPA. These contingency actions could include (1) immediate additional monitoring (for characterization of the release as determined necessary by USEPA) and (2) prompt implementation of corrective action, including conversion of monitoring wells to extraction wells and installation of additional extraction wells for hydraulic containment of the VOCs in the Lower HSU. Groundwater extracted from the Lower HSU would be treated and discharged together with the PSCT liquids. The extracted volumes from the Lower HSU would be very small because of the low permeability of the Lower HSU. The total volume of leachate that would be treated at the site is estimated to be about 5.2 million gallons per year from the NAPL extraction wells and 1,900,000 gallons per year from the PSCT, with the 450,000 gallons per year from the Gallery Well being sent to a permitted facility for disposal. The total volume of NAPL extracted is assumed to be 10,000 gallons per year initially from the 16 new wells, and another 3,000 gallons per year from the Gallery Well, which would be sent to a TSDF for disposal. The NAPL liquids are assumed to decrease with time over the 5-year duration of dewatering the P/S Landfill as with previous alternatives.


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The treated leachate from the LTP along with the treated PSCT and PCT liquids will be discharged to a new larger (11-acre) evaporation pond north of the RCF Pond to handle the additional 5.6 million gallons of treated leachate and Gallery Well liquids compared to Alternative 2. This alternative includes long term site-wide groundwater and soil vapor monitoring as discussed in Section 10.1.6. Alternative 6 Extraction (PSCT, Gallery Well) + Dewater P/S Landfill (5 Horizontal Wells) +

Extraction (NAPL-only in CDA, 12 new wells) + Monitoring (12 new Lower HSU wells) + Treat and Discharge to Evaporation Pond + ICs + Monitoring

This alternative includes extraction from the PSCT and Gallery Well and adds 5 horizontal wells under the P/S Landfill to dewater it (Figure 11-28A). The horizontal well extraction of total fluids is expected to produce a total groundwater flow rate of up to 10 gpm of landfill leachate (initially) and decreasing in the subsequent 5 years, the estimated timeframe for dewatering the P/S Landfill (see Section 10.1.8.8). The PSCT groundwater would be treated in a new Liquids Treatment Plant (LTP) for VOCs and discharged to an evaporation pond at the site. Each horizontal well is a 4-inch diameter casing and approximately 600 feet in length and is assumed to produce a maximum of 2 gpm flow rate initially (Figure 11-28B). The 5 horizontal wells will be distributed horizontally to cover the area south of existing Bench Road 2 with goal of dewatering the P/S Landfill. The horizontal wells will need to be drilled through or under the clay barrier on the south end of the P/S Landfill and will terminate just north of Bench Road 2. Numerous vertical wells are along the alignment of the horizontal wells (including the Gallery Well) and some of these vertical wells will likely need to be abandoned and reinstalled after the horizontal drilling is completed. In this alternative, the dewatered landfill liquids are not treated at the site. They are transported for disposal at a permitted facility. Also, as in Alternative 3, four existing groundwater monitoring wells in the CDA would be converted to LNAPL extraction wells equipped with LNAPL skimmers to recover floating product. Also similar to Alternative 3, twelve new Lower HSU groundwater monitoring wells are proposed, including three clusters of two wells each just upgradient of both PSCT-1 and PSCT-4 to monitor potential VOC migration under the PSCT in the Lower HSU. Contingency actions would be implemented as necessary if potential VOC migration occurred beneath the PSCT at concentrations of concern, as determined by USEPA. These contingency actions could include (1) immediate additional monitoring (for characterization of the release as determined necessary by USEPA) and (2) prompt implementation of corrective action, including conversion of monitoring wells to extraction wells and installation of additional extraction wells for hydraulic containment of the VOCs in the Lower HSU. Groundwater extracted from the Lower HSU would be treated and discharged together with the PSCT liquids. The extracted volumes from the Lower HSU would be very small because of the low permeability of the Lower HSU. Total volume of NAPL recovered after the NAPL-liquid separation of the dewater P/S Landfill liquids (5.2 million gallons in Year 1 as discussed earlier) with this alternative is assumed to be 10,000 gallons per year initially along with 3,000 gallons from the Gallery Well. The NAPL liquids are assumed to decrease with time over the 5-year duration of dewatering the P/S


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Landfill. The NAPL and the Gallery Well and P/S Landfill dewater liquids would be sent to a TSDF for disposal. This alternative includes long term site-wide groundwater and soil vapor monitoring as discussed in Section 10.1.6. Alternative 7 Extraction (PSCT, Gallery Well) + Dewater P/S Landfill (5 Horizontal Wells) +

Extraction (NAPL-only in CDA, 12 new wells) + Extraction (4 new Lower HSU wells) + Monitoring (8 new lower HSU wells) + Treat and Discharge + ICs + Monitoring

This alternative includes extraction from the PSCT and Gallery Well and adds 5 horizontal wells under the P/S Landfill to dewater it, as in Alternative 6 (Figure 11-29A). The horizontal well extraction of total fluids is expected to produce a total groundwater flow rate of up to 10 gpm of landfill leachate (initially) and decreasing in the subsequent 5 years, the estimated timeframe for dewatering the P/S Landfill (see Section 10.1.8.8). The PSCT groundwater would be treated in a new Liquids Treatment Plant (LTP) for VOCs (Figure 11-29C) and inorganics and discharged to the B-Drainage in accordance with the substantive requirements of a NPDES permit. As discussed earlier, a Basin Plan exception from the RWQCB would be required to discharge to the B-Drainage. This alternative assumes that there is no evaporation pond at the site. The LTP will include LPGAC treatment to remove VOCs and RO to remove inorganics. The RO system that treats the inorganics will generate waste brine with high dissolved solids and metals. The horizontal wells will be distributed across the southern portion of the P/S Landfill and the construction details of the wells would be the same as in Alternative 6. As in Alternative 6, the dewatered landfill liquids are transported for disposal at a permitted facility. Also, as in Alternative 3, four existing monitoring wells in the CDA would be converted to LNAPL extraction wells equipped with skimmers to recover floating product. However, this alternative includes four new Lower HSU extraction wells just upgradient of PSCT-1 and PSCT-4 to extract groundwater in the Lower HSU and prevent potential VOC migration under the PSCT. In addition, eight new Lower HSU monitoring wells are proposed, including two clusters of two wells each just upgradient of PSCT-1 and PSCT-4. Contingency actions would be implemented as necessary if potential VOC migration still occurred beneath the PSCT at concentrations of concern, as determined by USEPA. These contingency actions could include (1) immediate additional monitoring (for characterization of the release as determined necessary by USEPA) and (2) prompt implementation of additional corrective action, including conversion of monitoring wells to extraction wells and installation of additional extraction wells for hydraulic containment of the VOCs in the Lower HSU. Groundwater extracted from the Lower HSU would be treated and discharged together with the PSCT liquids. The extracted volumes from the Lower HSU would be very small because of the low permeability of the Lower HSU. Total volume of NAPL recovered after the NAPL-liquid separation of the dewater P/S Landfill liquids (5.2 million gallons in Year 1 as discussed earlier) with this alternative is assumed to be 10,000 gallons per year initially along with 3,000 gallons from the Gallery Well. The NAPL liquids are assumed to decrease with time over the 5-year duration of dewatering the P/S Landfill. The NAPL and the Gallery Well and P/S Landfill dewater liquids would be sent to a TSDF for disposal. Approximately, 285,000 gallons of brine is assumed to be generated over a one year period from the RO system that would be sent to a TSDF for disposal.


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This alternative includes long term site-wide groundwater and soil vapor monitoring as discussed in Section 10.1.6. Alternative 8 Aggressive Extraction (50 Large Diameter Wells) + Extraction (Aggressive, 16

Large Diameter NAPL wells in P/S Landfill) + Extraction (PSCT, Gallery Well) + Treat and Discharge + ICs + Monitoring

This alternative adds an aggressive hydraulic extraction throughout the VOC plume extent with a high density of groundwater extraction wells as an attempt to achieve maximum source removal in groundwater at Area 5 North. The components of Alternative 5 including the aggressive NAPL extraction in P/S Landfill, the PSCT and Gallery Well extraction, and Lower HSU monitoring and potential extraction are assumed to continue operations. The alternative would be required if a Technical Impracticability waiver is not granted by USEPA. This aggressive hydraulic extraction involves installation of 50 new 8-inch diameter extraction wells with the screen intervals extending from the water table down to the weathered-unweathered contact. Extraction from these wells would be continuous and is assumed to initially produce about 0.2 gpm per well on average for a total of about 12 gpm with another 10 gpm from the aggressive extraction in the P/S Landfill. These flow rates are expected to decrease with time. This VOC- and metals-impacted groundwater would be treated aboveground in a dedicated treatment system designed to handle a 35 gpm flow rate. The total extraction flow rate is consistent with the maximum water budget estimated from the Groundwater Flow Model. These 50 wells would include 40 Upper HSU wells and 10 Lower HSU wells in Area 5 North. These wells are assumed to be placed at approximately 75-foot spacing within areas of greatest groundwater impacts. The extracted groundwater would be treated for NAPLs, VOCs, metals, SVOCs including PAHs and pesticides, and dissolved solids before discharge under a the substantive requirements of an NPDES permit. The treatment equipment is assumed to include a treatment train starting with an equalization tank, a liquid-liquid separator, filtration, acidification, air stripping, UV oxidation, neutralization, RO, membrane filtration and LPGAC as a polishing step. The vapor from the air stripper would be treated by VPGAC. Reverse osmosis treatment of water is assumed for dissolved metals and anions to allow discharge of treated water in accordance with the substantive requirements of an NPDES permit. This treatment would produce a reject brine stream that is assumed to be approximately 1.7 million gallons per year (about 15 percent of total flow) that would be sent to a permitted facility for disposal. The recovered NAPLs from the liquid-liquid separator would be sent to a permitted facility for incineration. This alternative includes long term site-wide groundwater and soil vapor monitoring as discussed in Section 10.1.6. 10.6.4 Development of Remedial Alternatives – Area 5 South This section provides a preliminary evaluation of select retained groundwater technologies and process options (from Section 9) prior to the assembly of groundwater alternatives to address dissolved VOCs and metals plumes in Area 5 South. This preliminary evaluation provides a rationale for why certain retained technologies were not included in the subsequent discussion of remedial alternatives as components and why and in what form others were included.


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This section first discusses evaluation of technologies applicable to dissolved contaminants, and the description of remedial alternatives for Area 5 South. The remedial alternatives for Area 5 South include continued operation of the existing PCT-A and PCT-B features as either extraction or containment features, as discussed below. 10.6.4.1 Evaluation of Technologies for Dissolved Contaminants in Area 5 South Based on the screening of technologies in Section 9, for dissolved contaminants in groundwater, hydraulic extraction, in-situ reactive walls, ISCR, and monitored natural attenuation were retained. Of these, hydraulic extraction, in-situ reactive walls, and monitored natural attenuation are included as components in the remedial alternatives. As summarized in Section 10.6.3.2, ISCR by injection of ZVI into the plume would be very difficult to implement given the very large size of the VOCs and inorganics plumes (tens of acres) and the fact that injection points would need to be spaced at a 5-foot spacing in this low permeability weathered claystone formation. The implementability of ISCR by injection is very poor given that it would need thousands of injection points, and hence not included in the remedial alternatives. However, in-situ chemical reduction by ZVI is included through the use of the in-situ reactive wall component in the remedial alternatives as discussed below. Area 5 South is addressed in the remedial alternatives with perimeter extraction at the PCT-A and PCT-B trenches, which are existing remedial features, or in-situ reactive walls at the perimeter that treat contaminants, thus ensuring capture of contaminants and no migration outside the historical site boundaries. As discussed earlier, in-situ reactive walls would use the funnel and gate concept and use ZVI as the reactive material. The reactive barrier would be constructed by cutting slots in the existing clay barrier and building a gate with ZVI that serves as the permeable reactive barrier while the clay barrier serves as the funnel. If there is an existing perimeter trench with no clay barrier, then a parallel soil-bentonite slurry wall would need to be constructed a few feet downgradient of the trench and the ZVI gates placed within it to form the reactive wall. Each gate would be about 8 feet wide placed in a slot in the clay barrier, and 12 feet long in the direction of groundwater flow, of which the ZVI material would be 3 feet (See Detail in Figure 11-32A and Design Calculations in Attachment E-1 in Appendix E). The groundwater would flow through a permeable pea gravel section before passing through the reactive ZVI. After passing through the ZVI, the groundwater would flow through another pea gravel zone before it enters back into the native formation. The top elevation of the ZVI would be placed below the lowest anticipated water table levels, and above the ZVI would be impervious fill. In groundwater Area 5 South, conversion of the PCT-B clay barrier to an in-situ reactive wall is included in the remedial alternatives because a significant extraction flow rate is projected for this trench. Meanwhile, the projected flow rate for the PCT-A trench is significantly reduced from current levels, and hence the extraction approach would be relatively low in cost and is preferred for the PCT-A trench. Also, the cost of conversion of the PCT-A trench to a reactive wall would be greater than for the PCT-B because the PCT-A does not have a clay barrier and would require a parallel 1,000-foot long soil-bentonite slurry wall for conversion to a reactive wall. Conversion of the PCT-B clay barrier to a reactive wall would involve cutting two relatively small slots along the 500-foot length of the barrier. The anticipated soil remedy for FS Area 3 including the Maintenance Shed Area, Pond A/B area and a metals impacted area south of the PSCT is capping to eliminate infiltration and minimize leaching of VOCs and inorganics. Hence, the soil remedy would provide further containment for


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contaminants (especially for VOCs) in Area 5 South groundwater, and thus be an important component of the groundwater Area 5 South remedy. 10.6.4.2 Monitored Natural Attenuation for Groundwater Natural Attenuation is the process whereby contaminant reduction occurs by one or more natural in-situ means through physical, chemical or biological interaction with the surrounding environment. MNA is a viable remedy to achieve site-specific remediation objectives when the time frame to reach these goals is considered reasonable compared to that offered by more active methods. The USEPA supports MNA as a viable remediation remedy when source control measures have been implemented and impacted groundwater has a low potential for contaminant migration, and prefers processes that degrade or destroy the contaminants (USEPA 1999). Source control measures at this site are provided by the landfill clay barriers, and contaminant migration is controlled by the PSCT and PCT features, and low hydraulic conductivity of the Lower HSU soils (unweathered claystone bedrock). The results of natural attenuation investigations were presented in the RI (CSC 2011a) that provided supportive evidence of the reductive dechlorination of chlorinated solvents at the site. An updated discussion and additional natural attenuation investigation data are presented in this report in Appendix G. The natural attenuation investigations during the RI provided evidence that reductive dechlorination was occurring in the P/S Landfill and areas within and immediately surrounding the CDA and BTA. Supportive evidence for natural attenuation includes:

the presence of hydrogen (the electron accepting compound for the reductive dechlorination process);

low dissolved oxygen levels (generally <1 mg/L, indicative of anaerobic conditions); the presence of carbon dioxide and methane off-gases, which indicates the presence of

ongoing biological activity, and; the presence of ethene and ethane, the final end products of PCE and TCE reductive

dechlorination chain. CSC recently analyzed liquid samples for the Dhc bacteria (the only known bacteria to facilitate the complete dechlorination of PCE to inert ethane/ethane) from three areas of the site where NAPL occurs (Gallery Well – within the P/S Landfill, Sump 9B - in the Central Drainage Area, and well RGPZ-7C – in the Lower HSU Fracture zone) and one downgradient location - Well B3B. The Dhc bacteria was detected in the Gallery Well, well RGPZ-7C, and the well B3B sample, and its presence provides evidence that in-situ mechanisms (involving Dhc bacteria) are capable of the destruction of the most highly toxic organic contaminants found at the site. On this basis, MNA is a proven remedial technology for site conditions, and Dhc is capable of acting at the micro-pore level. More discussion of the recent findings on the microbes present in groundwater is presented in Appendix G. While no direct testing was performed for petroleum hydrocarbon degradation, the presence carbon dioxide and methane, which are known end products of hydrocarbon degradation, suggest that these compounds are likely degrading via biological processes. The low dissolved oxygen values and absence of bionutrients (e.g., nitrate, sulfate) suggest that anaerobic degradation mechanisms are dominant where nitrate and sulfate are used as electron acceptors. Presence of methane is a strong indicator of anaerobic biodegradation.


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A discussion of the primary degradation mechanisms of organics and inorganics and their rates is presented in Appendix G, including biodegradation, volatilization, sorption, dilution. dispersion and diffusion. Analytical parameters collected historically indicate biodegradation of organic chemicals in the plume areas (Area 5 South) is occurring, and supports evidence that a reductive dechlorination zone exists to the south of the PSCT trench. With respect to inorganic compounds, no direct evidence was collected to indicate if biologically-mediated transformation of inorganic compounds is occurring. Natural attenuation for inorganics (arsenic, nickel, cadmium, selenium) is less certain at the site, but may occur under certain conditions that involve sorption, or redox conditions may possibly reduce dissolved metals concentrations or change the metal form to a less toxic metal in groundwater. The transformation of inorganic compounds (either precipitation or dissolution) will occur according to the variability of groundwater chemistry. As discussed in Appendix G, groundwater conditions favorable for the immobilization of arsenic are not identical to those favorable for the immobilization of selenium (USEPA, 2007). The most common mechanism anticipated for attenuation of inorganics is precipitation on soil particles in the formation. Some evidence supporting this mechanism is the staining of soils with inorganics along subsurface fractures. While the attenuation of inorganics is not conclusive, it is known that the anticipated remedy for the soil FS Areas would involve an extensive amount of capping that would minimize infiltration or contaminant migration in several locations including the PCB Landfill, Burial Trench Area and the Central Drainage Area (FS Area 1), Maintenance Shed Area, and portions of FS Area 3 south of the PSCT. The elimination of infiltration in the VOC and metals-impacted areas would minimize leaching of contaminants to groundwater, would lower water tables and reduce groundwater and contaminant transport rates in the Upper HSU. The natural attenuation of dissolved contaminants (especially VOCs) combined with the effect of capping large areas would enhance the long term attenuation of the VOCs, and possibly inorganics in groundwater. Hence, MNA is included as a component in the remedial alternatives discussed below. 10.6.4.3 Description of Remedial Alternatives for FS Area 5 South Area 5 South is primarily impacted with VOCs and inorganics at relatively low levels compared to Area 5 North. Unlike Area 5 North, a potential TI waiver will not be applicable to Area 5 South. In the presentation of Area 5 South alternatives for groundwater, it should be noted that capping or excavation is anticipated as part of the soil remedy for FS Area 3 (south of the PSCT) and the Maintenance Shed Area which will prevent or significantly minimize further leaching of VOCs and inorganics into groundwater. Thus the remedy for soils in FS Area 3 will be a significant source reduction measure for the groundwater remedy, though it is not formally listed as a remedy component in these alternatives below. Also, note that the PSCT would continue operation under all alternatives in Area 5 North, thus continuing in the long term to ensure that no contaminants migrate past the PSCT into Area 5 South. Table 10-1 lists the six remedial alternatives and remedial objectives for FS Area 5 South. The six remedial alternatives for FS Area 5 South are briefly described below, followed by a screening analysis in Section 10.6.7. The objectives of the remedial alternatives for FS Area 5 South are:


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Contain and/or control contamination sources within the site boundary, where groundwater restoration is not technically practicable;

Mitigate potential migration of groundwater contamination via perimeter control; Allow natural attenuation processes to slowly reduce contaminant concentrations (MNA)

with the long term objective of reaching MCLs for groundwater contaminants (organics and inorganics) though for inorganics background levels will be considered in the evaluation of future remedial activities;

Contain and/or control contamination sources by including aggressive groundwater extraction in the evaluation to supplement the natural attenuation processes that would otherwise slowly reduce contaminant concentrations; and,

Allow discharge of treated groundwater either to the B Drainage or Casmalia Creek to eliminate the need for an evaporation pond at the site or, alternately, to an evaporation pond at the stie.

Alternative 1 No Action The No Action alternative is included as required by CERCLA guidance. No Action implies that the source control activities and monitoring that are ongoing currently would not be occurring. Alternative 2 Extraction (PCT-A, PCT-B) + Treat and Discharge to Evaporation Pond + MNA +

ICs + Monitoring This alternative includes extraction from the PCT-A and PCT-B as it is currently being implemented. The extracted PCT-A and PCT-B liquids would be pumped to a new lined evaporation pond located in the footprint of the A-Series Pond (Figure 11-30A). These extracted liquids would be treated with LPGAC if VOCs are present before being discharged to the evaporation pond. Based on the results of groundwater modeling (Appendix D-1) that assume a proposed remedy scenario that prevents infiltration with caps at the PCB Landfill, BTA and CDA, the total annual extraction flow rates for the PCT-A and PCT-B are expected to increase moderately from 2.5 million gallons (average of 2006 to 2011) to a range of 5.6 million to 7.8 million gallons. As part of this alternative, the PCT-B gravel trench would be refurbished for more effective extraction operations. This alternative includes long term monitoring of groundwater site-wide to document natural attenuation via intrinsic biodegradation and other mechanisms across Area 5 South, and institutional controls, such as deed restrictions, to limit potential for exposures. As discussed earlier and in the Final RI report (CSC 2011a), the natural attenuation data provide strong evidence that biologically mediated degradation of petroleum and halogenated hydrocarbons is occurring, through aerobic, anaerobic, and fermentative metabolic pathways. This combined with anticipated remedies for sources south of the PSCT will help attenuate contaminant (especially VOCs) concentrations over the long term. As discussed earlier, the dispersion and dilution mechanisms in concert with the capping and pond closure remedies can restore the aquifer for VOCs and inorganics in reasonable timeframes (estimated 260 years for arsenic, Appendix D-2) This alternative includes long term site-wide groundwater and soil vapor monitoring as discussed in Section 10.1.6.


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Alternative 3 Extraction (PCT-A, PCT-B) + Treat and Discharge + MNA + ICs + Monitoring This alternative includes extraction from the PCT-A and PCT-B as in Alternative 2 but the extracted PCT-A and PCT-B liquids would be pumped to a LTP in the LTA to treat organics and inorganics in accordance with site-specific NPDES limits and then pumped to the B-Drainage for discharge (Figure 11-31A). The LTP is assumed to include a treatment train including an equalization tank, filtration, LPGAC and RO. The LTP includes a RO unit to treat inorganics and a reject concentrator to reduce the volume of waste brine produced. A total of 840,000 gallons of waste brine is sent to a permitted facility for disposal. As discussed in Alternative 2, based on the results of groundwater modeling (Appendix D-1) and the anticipated capping remedies at the PCB Landfill, BTA and CDA, the total annual extraction flow rates for the PCT-A and PCT-B are expected to increase from 2.5 million gallons (average of 2006 to 2011) to a range of 5.9 million to 7.8 million gallons. As part of this alternative, the PCT-B gravel trench would be refurbished for more effective extraction operations. This alternative includes long term monitoring of groundwater site-wide to document natural attenuation via intrinsic biodegradation and other mechanisms across Area 5 South, and institutional controls, such as deed restrictions, to limit potential for exposures. As discussed earlier and in the Final RI report (CSC 2011a), the natural attenuation data provide strong evidence that biologically mediated degradation of petroleum and halogenated hydrocarbons is occurring, through aerobic, anaerobic, and fermentative metabolic pathways. This combined with capping south of the PSCT will help attenuate contaminant (especially VOCs) concentrations over the long term. This alternative includes long term site-wide groundwater and soil vapor monitoring as discussed in Section 10.1.6. Alternative 4 Extraction (PCT-A) + In-Situ Reactive Wall (PCT-B) + MNA + ICs + Monitoring This alternative includes continued groundwater extraction for the PCT-A trench as part of mitigating potential migration. For the PCT-B trench, conversion to a passive, in-situ reactive wall treatment using ZVI is assumed instead of extraction (Figure 11-32A). The extracted PCT-A liquids will be sent to a new evaporation pond at the site. The in-situ reactive wall involves installing ZVI gates in the saturated zone by cutting slots into the clay barriers associated with these trenches and backfilling with ZVI powder. Two reactive wall slots (or gates) are assumed for the 500-foot long PCT-B clay barrier. The reactive walls proposed in the FS are intended to primarily treat low levels of dissolved metals (arsenic, nickel, cadmium and selenium) present in groundwater upgradient of the trenches and thus mitigate potential migration. As discussed earlier, the PCT-A is retained for extraction because the extraction flow rate is anticipated to decrease significantly based on assumed future capping remedies. PCT-B is converted to an in-situ reactive wall because the groundwater flow model predicts the extraction flow rates from this feature either stayed the same or increased. As discussed earlier, based on groundwater flow modeling and anticipated capping, the PCT-A extraction rates would increase from 1.5 million gallons to a range of 2.3 to 3.6 million gallons. A 6-acre evaporation pond is expected to be adequate to handle this PCT groundwater.


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As discussed in Alternative 2, the natural attenuation data provide strong evidence that biodegradation of chlorinated and petroleum hydrocarbons are occurring through multiple pathways in Area 5 South. This alternative includes long term site-wide groundwater and soil vapor monitoring as discussed in Section 10.1.6. In addition, reactive wall-specific monitoring is included in the vicinity of each gate at the PCT-B reactive wall to monitor performance over the long term. Alternative 5 Extraction (PSCT Westside Extension) + Extraction (PCT-A, PCT-B) + MNA +

ICs + Monitoring This alternative includes addition of a PSCT Westside extension with the objective of addressing contaminants south of the PSCT and the BTA to the components of Alternative 2. This would involve construction of an 800-foot extension of the PSCT trench westward from PSCT-3, traversing south of the Liquids Treatment Area. Two wells are assumed to be included within this Westside extension to capture the VOC groundwater plume south of PSCT-4 and the Burial Trench Area. The extraction from these wells would be processed using a system that treats the PSCT flows, discussed earlier under Area 5 North. Based on the groundwater flow modeling that assumes the anticipated future capping remedies, the water table is expected to drop more than 70 feet in the vicinity of the BTA and LTA to below the unweathered-weathered claystone contact. Since the PSCT trench extension is expected to be at maximum depth down to the unweathered claystone contact, it is likely that these two wells in the PSCT Westside extension are going to be dry or not produce any significant quantity of groundwater. This implies that the total PSCT groundwater extraction flow is not going to significantly change with this extension. This alternative includes extraction from the PCT-A and PCT-B as it is currently being implemented. The extracted PCT-A and PCT-B liquids would be pumped to a new lined evaporation pond located in the footprint of the A-Series Pond. Based on the results of groundwater modeling (Appendix D) that assume a proposed remedy scenario that prevents infiltration with caps at the PCB Landfill, BTA and CDA, the total annual extraction flow rates for the PCT-A and PCT-B are expected to increase as discussed in Alternative 2. As part of this alternative, the PCT-B gravel trench would be refurbished for more effective extraction operations. As discussed in Alternative 2, the natural attenuation data provide strong evidence that biodegradation of chlorinated and petroleum hydrocarbons are occurring through multiple pathways in Area 5 South. This alternative includes long term site-wide groundwater and soil vapor monitoring as discussed in Section 10.1.6. In addition, reactive wall-specific monitoring is included in the vicinity of each gate at the PCT-B reactive wall to monitor performance over the long term. Alternative 6 Aggressive Extraction (40 New Large Diameter Wells) + Extraction (PCT-A,

PCT-B) + Treat and Discharge + ICs + Monitoring This alternative is adds an aggressive hydraulic extraction scenario that would require a high density of groundwater extraction wells be installed as an attempt to achieve the maximum source removal in Area 5 South groundwater. This aggressive hydraulic extraction involves installation of 40 new 8-inch diameter extraction wells with the screen intervals extending from the water table down to the weathered-unweathered contact (Figure 11-33A). Extraction from these wells is continuous and is assumed to produce about 0.5 gpm per well on average, for a


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total of about 20 gpm, with VOC and metals-impacted groundwater being treated aboveground in a dedicated treatment system for discharge to a permitted facility. The total extraction flow rate is consistent with the maximum water budget estimated from the Groundwater Flow Model. Area 5 South would include 40 Upper HSU wells assumed to be placed at approximately 150-foot spacing in areas of greatest groundwater impacts. This alternative includes the operation of the PCT-A and PCT-B extraction wells as in Alternative 2 to ensure perimeter control. As part of this alternative the PCT-B trench will be refurbished to enhance effective extraction. The extracted groundwater would be treated for VOCs, metals, and dissolved solids discharge under a the substantive requirements of an NPDES permit. The treatment equipment is assumed to include a treatment train starting with an equalization tank, filtration, LPGAC RO and membrane filtration (Figure 11-33B). Reverse osmosis treatment of water is assumed for dissolved metals and anions to allow discharge of treated water in accordance with the substantive requirements of an NPDES permit. This treatment would produce a reject brine stream that is approximately 1.8 million gallons (about 15 percent of total flow) that is sent to a permitted facility for disposal. This alternative includes long term site-wide groundwater and soil vapor monitoring as discussed in Section 10.1.6. 10.6.5 Development of Remedial Alternatives – Area 5 West This section provides a preliminary evaluation of select retained groundwater technologies and process options (from Section 9) prior to the assembly of groundwater alternatives to address the dissolved metals plumes in Area 5 West. This preliminary evaluation provides a rationale for why certain retained technologies were not included in the subsequent discussion of remedial alternatives as components and why and in what form others were included. This section first discusses evaluation of technologies applicable to dissolved contaminants, and the description of remedial alternatives for Area 5 West. The remedial alternatives for Area 5 West involve continued operation of the existing PCT-C feature as either an extraction or containment feature, as discussed below. 10.6.5.1 Evaluation of Technologies for Dissolved Inorganics in Area 5 West Based on the screening of technologies in Section 9, for dissolved contaminants in groundwater, hydraulic extraction, in-situ reactive walls, ISCR and monitored natural attenuation were retained. As discussed earlier, Area 5 West groundwater is impacted with metals originating from RCRA Canyon and the WCSA (FS Area 2) and the A-5 and A-Series Ponds in FS Area 4. Area 5 West is addressed in the remedial alternatives with perimeter extraction at the PCT-C trench or an in-situ reactive wall at the perimeter, thus ensuring capture of contaminants and no migration beyond the site boundary. For Area 5 West, conversion of the PCT-C clay barrier to an in-situ reactive wall is included in the remedial alternatives because significant extraction flow rates are projected for this trench. This conversion would involve cutting four slots evenly spaced along the 1,500-foot long length of the clay barrier at the PCT-C. More details on the reactive barrier design are presented in Section 11. ISCR is retained for use only as part of the ZVI reactive wall technology and not as part of a direct push injection source reduction remedy because it would


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require thousands of direct push injection points at a close spacing, as discussed in Area 5 South. An essential component of source reduction for the groundwater remedy in Area 5 West is the anticipated capping remedy for the RCRA Canyon (FS Area 2) and the closure of the Ponds (A-5, A-Series) that would remove metals-impacted pond water and eliminate infiltration through metals-impacted soils/sediments that are the primary source of metals contamination to Area 5 West groundwater. 10.6.5.2 Effect of Capping on Aquifer Restoration Timeframes A separate fracture flow and solute transport model was also developed to estimate the remediation time frame for metals impacted groundwater in Area 5 West. The design of the Area 5 West model and the methods used to estimate the remediation time frame for the metals impacted groundwater are described in Appendix D-2. The remediation time frame for metals impacted groundwater in Area 5 West was estimated for the proposed capping remedy using a generalized fracture flow and transport model developed for this area. The remediation time frame was estimated for three representative metals, arsenic, nickel and selenium. The model simulations indicate that the time frames for achieving groundwater cleanup standards after source removal would range from 90 years (nickel) to 220 years (arsenic). As discussed in Appendix D-2, the simulated timeframes to achieve the MCLs are considered to be an order-of-magnitude approximation because of the spatial and temporal variability of the initial concentrations of metals in groundwater and the uncertainty in the accuracy of the other input parameters required by the model. The estimated remedial time frames for source area capping and complete source area removal (restoration) are expected to be similar in order of magnitude. 10.6.5.3 Monitored Natural Attenuation for Groundwater Natural Attenuation encompasses multiple processes that act to either destroy or dilute the concentration of COCs. A natural attenuation evaluation was presented in Appendix O in the Final RI (CSC 2011a). A follow up to the natural attenuation evaluation is presented in Appendix G of this document. Natural attenuation for inorganics can occur under certain conditions that involve sorption, or redox conditions can reduce dissolved metals concentrations or change the metal form to a less toxic metal in groundwater. Sorption reactions can include precipitation, adsorption on soil surface, absorption into matrix of soil minerals, or partition into soil organic matter. Sorption and redox reactions are the most dominant reactions that reduce mobility and toxicity of metal contaminants in groundwater. In addition, natural attenuation can occur through dissolution and dispersion mechanisms. As discussed earlier (Section 10.6.5.2), the timeframe for aquifer restoration for arsenic (highest concentration metal) with the capping and pond closure remedies is approximately 70 years, primarily through dispersion and dilution mechanisms. While detailed metal contaminant redox chemistry was not studied in the RI, the time-series data of these metals show that plumes are relatively stable. The evaluation of natural attenuation for inorganic compounds was not a primary focus of the RI, because the anticipated remedy for the soil FS Areas would involve an extensive amount of capping that would minimize or prevent infiltration in several areas, including RCRA Canyon/WCSA (FS Area 2) and the ponds (Pond A-5 and the A-Series Pond). The elimination of infiltration in the metals-impacted areas and pond closure would lower water tables, reduce groundwater flow rates and contaminant flux in the Upper HSU, and ensure capture in the PCT feature, as further discussed below.


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10.6.5.4 Description of Remedial Alternatives for FS Area 5 West Area 5 West is primarily impacted with inorganics that originate from stormwater percolation through a relatively highly metals contaminated lens of shallow soils in RCRA Canyon/WCSA (discussed in FS Area 2) and contact with pond water that contains high levels of inorganics from Ponds A-5 and the A-Series Pond (discussed in FS Area 4). Unlike Area 5 North, a TI waiver will not be applicable to Area 5 West. In the presentation of Area 5 West alternatives for groundwater below it should be noted that extensive capping proposed as part of the soil remedy for FS Area 2 (including RCRA Canyon and WCSA), and the pond water removal and pond closure proposed for Area 4 (Ponds A-5, A-Series Pond) will prevent or minimize infiltration, thereby significantly reducing leaching into groundwater. Thus the capping remedy for soils in FS Area 2 and pond closure remedies for FS Area 4 will be a significant and integral source removal component of the groundwater remedy, though it is not formally listed as a component in the alternatives below. Table 10-1 identifies the remedial alternatives and remedial objectives for FS Area 5 West groundwater. A total of six remedial alternatives for FS Area 5 West are briefly described below, followed by a screening analysis in Section 10.6.8. The objectives of the remedial alternatives for FS Area 5 West are:

Contain and/or control contamination sources within the site boundary, where groundwater restoration is not technically practicable;

Mitigate potential migration of groundwater contamination via perimeter control; Allow natural attenuation processes to slowly reduce contaminant concentrations (MNA)

with the long term objective of achieving MCLs for groundwater contaminants (inorganics) though background levels of inorganics will be considered in the evaluation of future remedial activities;

Contain and/or control contamination sources by including aggressive groundwater extraction in the evaluation to supplement the natural attenuation processes that would otherwise slowly reduce contaminant concentrations; and,

Allow discharge of treated groundwater either to the B Drainage or Casmalia Creek to eliminate the need for an evaporation pond at the site or, alternately, to an evaporation pond at the site.

Alternative 1 No Action The No Action alternative is included as required by CERCLA guidance. No Action implies that the source control activities and monitoring that are ongoing currently would not be occurring. Alternative 2 Monitored Natural Attenuation + ICs This alternative involves long term monitoring of groundwater to document natural attenuation and the institutional controls, such as deed restrictions, to limit potential for exposures. While detailed metal contaminant natural attenuation mechanisms (redox reactions, precipitation,


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dilution, dispersion) were not studied formally in the RI, the time-series data of these metals in Area 5 West show that plumes are relatively stable or declining for the inorganics of concern. As discussed earlier, the dispersion and dilution mechanisms in concert with the capping and pond closure remedies can restore the aquifer in reasonable timeframes (estimated 220 years for arsenic, Appendix D). For purposes of this FS evaluation, the groundwater monitoring and soil vapor monitoring will be the same scope as is currently implemented at the site. This alternative includes long term site-wide groundwater and soil vapor monitoring as discussed in Section 10.1.6. Extraction at the PCT-C would only be included as a contingency measure if contaminant migration and human health or ecological risks become a concern. Alternative 3 Extraction (PCT-C) + Treat and Discharge to Evaporation Pond + MNA + ICs +

Monitoring This alternative includes continued extraction of liquids from the PCT-C as it is currently being implemented (Figure 11-34A). Based on the results of groundwater modeling (Appendix D) that assume a proposed remedy scenario with capping in RCRA Canyon coupled with pond water removal and pond closure activities, the PCT-C extraction rates are expected to increase from 2.4 million gallons to a range of 5.6 to 7.8 million gallons. The extracted PCT-C groundwater would be discharged to an evaporation pond at the site. VOC contaminants are not anticipated in PCT-C liquids but if VOCs are observed they would be treated with LPGAC and discharged to the evaporation pond. The PCT-C gravel trench would be refurbished for more effective extraction operations. While natural attenuation for inorganics is not well documented at this site, as discussed in Alternative 2, the dispersion and dilution mechanisms in concert with the capping and pond closure remedies can restore the aquifer in a reasonable timeframe. This alternative includes long term site-wide groundwater and soil vapor monitoring as discussed in Section 10.1.6. Alternative 4 Extraction (PCT-C) + Treat and Discharge + MNA + ICs + Monitoring This alternative includes continued extraction of liquids from the PCT-C as in Alternative 3, but the inorganics in groundwater would be treated for discharge to the B-Drainage in accordance with a the substantive requirements of an NPDES permit (Figure 11-35A). The LTP is assumed to include a multi-stage treatment train including an equalization tank, filters, LPGAC and RO (Figure 11-35B). The LTP includes a RO unit to treat inorganics and a reject concentrator to reduce the volume of waste brine produced. A total of 630,000 gallons of spent brine is sent to a permitted facility for disposal. Based on the results of groundwater modeling (Appendix D-1) that assume a proposed remedy scenario with capping in RCRA Canyon coupled with pond water removal and pond closure activities, the PCT-C extraction rates are expected to increase from 2.4 million gallons to a range of 4.2 to 4.9 million gallons (Appendix D-1, SWR#3). The PCT-C gravel trench would be refurbished for more effective extraction operations. While natural attenuation for inorganics is not well documented at this site, as discussed in Alternative 2, the dispersion and dilution mechanisms in concert with the capping and pond closure remedies can restore the aquifer in a reasonable timeframe. This alternative includes long term site-wide groundwater and soil vapor monitoring as currently implemented at the site and discussed in Alternative 2. Alternative 5 In-Situ Reactive Wall (PCT-C) + MNA + ICs + Monitoring


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This alternative includes conversion of the PCT-C trench to a passive, in-situ reactive wall treatment feature using ZVI instead of extraction. The in-situ reactive wall involves installing gates in the saturated zone by cutting slots into the clay barrier associated with the trench and backfilling with ZVI powder (Figure 11-36A). Four reactive wall slots are assumed for the PCT-C clay barrier. The proposed reactive wall is intended to primarily treat low levels of dissolved metals (arsenic, nickel, cadmium and selenium) present in groundwater upgradient of the trench, and thus mitigate potential migration. Since there is no extraction in this alternative, the evaporation pond size required would be smaller. While MNA for inorganics is not well documented at this site, as discussed in Alternative 2, the dispersion and dilution mechanisms documented through the groundwater modeling effort (Appendix D) in concert with the capping and pond closure remedies can restore the aquifer in a reasonable timeframe. This alternative includes long term site-wide groundwater and soil vapor monitoring as discussed in Section 10.1.6. In addition, reactive wall-specific monitoring is included in the vicinity of each gate at the PCT-C reactive walls to monitor performance over the long term. Alternative 6 Aggressive Extraction (40 New Large Diameter Wells) + Extraction (PCT-C)

+Treat and Discharge + ICs + Monitoring This alternative is an aggressive hydraulic extraction that would require a high density of groundwater extraction wells be installed as an attempt to achieve maximum source reduction in groundwater in FS Area 5 West that is primarily impacted with metals. It involves installation of 40 new large diameter (8-inch) extraction wells (Figure 11-37A). Extraction from these wells would be continuous and is assumed to produce about 0.05 gpm per well for a total of about 2 gpm with metals-impacted groundwater being treated aboveground in a dedicated treatment system. The total extraction flow rate is consistent with the water budget estimated from the Groundwater Flow Model. These 40 wells are placed across the impacted groundwater zone in Area 5 West. These wells are assumed to be placed at approximately 75-foot spacing in areas of greatest groundwater impacts. The extracted groundwater would be treated for site contaminants, including dissolved solids, before being discharged under the substantive requirements of an NPDES permit. This alternative also includes groundwater extraction at the PCT-C to ensure no migration of contaminants outside the site boundaries, as in Alternative 3. Based on the results of groundwater modeling (Appendix D) that assume a proposed remedy scenario with capping in RCRA Canyon/WCSA (FS Area 2) coupled with pond closure remedies, the PCT-C extraction rates are assumed to be in the range of 4.2 to 4.9 million gallons. The treatment equipment is assumed to include a treatment train starting with an equalization tank, filtration, LPGAC, RO, and membrane filtration (Figure 11-37B). Reverse osmosis treatment of water is assumed for dissolved metals and anions to allow discharge of treated water in accordance with the substantive requirements of an NPDES permit. This treatment would produce a reject brine stream that is assumed to be approximately 800,000 gallons per year (15 percent of total flow) that is sent to a permitted facility for disposal. This alternative includes long term site-wide groundwater and soil vapor monitoring as discussed in Section 10.1.6. 10.6.6 Screening of Remedial Alternatives – Area 5 North


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Table 10-6A presents the screening evaluation of the eight remedial alternatives addressing dissolved phase groundwater and NAPL listed earlier for Area 5 North. With respect to effectiveness, Alternative 2 is rated poor to moderate while Alternatives 3, 4, 5, 6, 7 and 8 are all rated moderate to good. Alternative 2 is rated poor to moderate because it does not address removal of the NAPL source to the extent practicable though it does address the objective of source control. Alternatives 3, 4, 5, 6, 7 and 8 all address the objectives of source control and source removal in support of the potential TI waiver zone for Area 5 North. Alternatives 3 through 8 vary in their levels of aggressiveness in source removal starting with Alternatives 3 and 4 with NAPL-only removal in the southern P/S Landfill to Alternative 5 with aggressive NAPL extraction in the P/S Landfill, Alternatives 6 and 7 with dewatering the P/S Landfill, and Alternative 8 with aggressive hydraulic extraction across the entire VOC and inorganics plume in Area 5 North. Though Alternatives 5 through 8 are more aggressive in source reduction, the mass removal accomplished by these alternatives in the near term will be small fraction of the total contaminant mass in the subsurface and will not be significantly different from Alternative 3. Alternative 5 would face potential risks with drilling large diameter wells through the waste in the P/S Landfill. Alternatives 6 and 7 involve horizontal drilling below the clay barrier (a key containment feature), which would face a greater risk with potential release of highly contaminated liquids into the Upper HSU (see Table 10-6A-1 for risk analysis). Because of these higher risks, the effectiveness rating for Alternatives 5 through 7 are not rated higher than Alternatives 3 and 4. Alternative 8 is a very aggressive extraction alternative that would remove greater NAPL and dissolved contaminant mass from the subsurface but extracted concentrations will begin tailing off in the long term. Aquifer restoration will not be significantly different for Alternatives 5 through 8 compared to Alternatives 3 or 4. As explained in the TIE (Appendix A), with Alternative 8 even if the NAPL and dissolved organics are significantly reduced, organics will continue to diffuse out of the rock matrix over hundreds of years. Also, Alternative 8 would face greater short term effectiveness concerns related to treatment of highly concentrated leachate in a large, complex treatment train with potential for vapor or liquid contaminant releases during process upset conditions. Hence, Alternative 8 is rated similar to Alternatives 3 through 7 at moderate to good. With respect to implementability, Alternative 2 is rated good, Alternative 3 is rated moderate to good, Alternatives 4 and 5 is rated moderate, and Alternatives 6, 7 and 8 are rated poor to moderate. Alternative 2 is rated good because it is already implemented at the site. Alternative 3 with the installation of NAPL-only wells in the P/S Landfill is rated one step lower at moderate to good, while Alternative 4 is rated lower at moderate because of the challenges of reliable inorganics treatment to meet stringent NPDES discharge limits. Alternative 5 with installation of larger diameter wells in the P/S Landfill and operation of a 10 gpm leachate treatment system is rated moderate because of the technical challenges with drilling in the landfill and the operation of the complex treatment of highly contaminated leachate. Alternatives 6 and 7 are rated low at poor to moderate because of the technical challenges with installing horizontal wells below the clay barrier at the toe of the P/S Landfill (see Table 10-6A-1). Alternative 7 would in addition face challenges with inorganics treatment to meet stringent site-specific NPDES limits. Alternative 8 was also rated poor to moderate because of the technical challenges with installation and operation of a large pump and treat system with 50 extraction wells throughout Area 5 North and 16 NAPL extraction wells in the P/S Landfill extracting on average at a 35 gpm flow rate. The long term aggressive extraction would be an extreme challenge with clogging of wells due to high TDS and potential leaks from a very large and complex network of extraction piping. This alternative would also require a very large and complex treatment system that would increase the potential for emissions or releases of contaminants as groundwater or to the air. The stringent NPDES discharge limits would be a concern for the operational reliability of


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this system given the high TDS in groundwater. This alternative would also generate 1.8 million gallons or more of brine that would need to be handled in the evaporation pond; thus posing challenges for species protection and adding to the complexity of pond water management. Alternatively, the brine would need to be sent to a permitted facility for disposal. With respect to cost, Alternative 2 is moderate, Alternative 3 is moderate to high, Alternatives 4 through 8 are very high. Alternative 3 is moderate to high because it adds the installation and operation of the NAPL-only wells inside the P/S Landfill. Alternative 4 is high due to the RO treatment required to treat high inorganic concentrations for discharge in accordance with stringent NPDES limits. Alternative 5 is high because of the capital cost of leachate treatment plant, wells and piping network for a highly contaminated stream and the long term O&M costs for operation at up to 10 gpm. Alternatives 6 and 7 are high due to the high cost of disposal of liquids from the dewatering the P/S Landfill at a permitted facility. Alternative 8 is high because of the capital costs of the groundwater treatment plant, wells and piping network for the 35 gpm extraction system (50 wells) and the operational cost of the very complex treatment train to treat the groundwater for discharge in accordance with the substantive requirements of an NPDES permit. The treatment for the discharge would require RO type technologies to reduce total dissolved solids. The waste brine would require being sent to a permitted facility for disposal due to the significant challenges with ecological species protection from evaporation ponds. With respect to green impacts assessment (or environmental footprint), the impacts from Alternative 2 are low to moderate, Alternative 3 are moderate, Alternative 4 are moderate to high, Alternatives 5 through 8 are high. The impacts from Alternative 3 are one step higher than Alternative 2 because it includes NAPL-only extraction. The impacts from Alternative 4 are one step higher than Alternative 3 due to the impacts of electricity and waste disposal from the inorganics treatment by RO. The impacts from Alternatives 5, 6 and 7 with aggressive NAPL extraction or dewatering P/S Landfill are one step higher because of continuous operation of extraction pumps and the leachate treatment plant would increase the footprint. Finally, the impacts from Alternative 8 are considered to be the highest because it adds the extremely high energy requirements for the 35 gpm extraction and the complex treatment including air stripping blowers, carbon treatment and RO for discharge of groundwater. Alternative 8 would also include the emissions from transport of wastes generated by the treatment equipment including spent brine, spent carbon, NAPL, waste solids, filters, etc. to permitted facilities for the long term operations. 10.6.6.1 Summary of Screening Evaluation Based on the screening evaluation, Alternatives 2 through 7 are retained for the detailed evaluation in Section 11. Alternatives 2 through 7 address the objectives of control and contain sources and source removal to the extent practicable to support the proposed TI waiver zone in Area 5 North and have a moderate or higher rating for implementability. In addition, the anticipated capping remedies in FS Area 1 would be a significant source reduction component that supports the objectives of these groundwater alternatives. Alternative 8 is not retained because its implementability is rated poor to moderate with the implementation of this very large groundwater treatment system and the complexity of operations, the high cost and high green impacts. Also, its overall effectiveness is not rated higher than Alternatives 3 through 7, because the aquifer restoration timeframe will be similar – in the hundreds of years (see Appendix A), and due to concerns with risks from emissions and releases over the long term operations. In addition, its green impacts assessment and cost are the highest of the alternatives.


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10.6.7 Screening of Remedial Alternatives – Area 5 South Table 10-6B presents the screening evaluation of the six remedial alternatives addressing dissolved organics and inorganics in groundwater FS Area 5 South. With respect to effectiveness, Alternatives 2, 3, 5 and 6 are rated moderate, while Alternative 4 is rated poor to moderate. Alternatives 2, 3 and 4 include perimeter control at the PCT-A and PCT-B and monitored natural attenuation but Alternatives 2 and 3 are rated higher because of the greater certainty of effective perimeter control with extraction. Whereas, Alternative 4 faces concerns with the reactive wall effectiveness on a complex mix of metals and the impacts of high TDS in groundwater. Alternative 5 adds the PSCT Westside extension component but it is not likely to result in significant extraction with the new wells because the water table is expected to drop below the weathered-unweathered claystone contact. On a separate note, there is significant attenuation in the concentration of VOCs between wells RG-4B and downgradient wells RG-5B and WP-3S south of the PSCT indicative of a stable plume that is not migrating. Hence the risk reduction achievable with the PSCT Westside extraction is limited. Thus, Alternative 5 is rated the same as Alternatives 2 and 3. Alternative 6 adds a very aggressive extraction alternative with a 60 well groundwater extraction and treatment system, but extracted concentrations will begin tailing off in the long term. Aquifer restoration will not be significantly different from previous alternatives (at hundreds of years) because even if dissolved contaminant concentrations are reduced, organic and inorganic contaminants will continue to diffuse out of the rock matrix over hundreds of years. Also, Alternative 6 would have greater short term effectiveness concerns because it would involve operations of a very complex treatment train to enable discharge that would also increase the potential for leaks, equipment failures and releases of contaminants. Hence, Alternative 6 is rated similar to Alternatives 2, 3 and 5 at moderate. With respect to implementability, Alternative 2 is rated good, Alternative 3 is rated moderate, Alternative 4 is rated moderate to good, Alternative 5 is rated moderate, and Alternative 6 is rated poor to moderate. Alternative 2 is already implemented at the site and is rated good. Alternative 3 is rated lower at moderate because of the technical challenges associated with treating inorganics in groundwater to meet stringent NPDES discharge limits. Alternative 4 with the in-situ reactive wall is rated one step lower than Alternative 2 due to the lesser reliability with multiple metals with different redox chemistries and potential clogging of the ZVI reactive walls with the high TDS. Alternative 5 adds the PSCT Westside extension and is rated lower at moderate due to the challenges with recovering any significant groundwater due to the anticipated lowering of the water table below the weathered-unweathered contact. Alternative 6 was rated the lowest for implementability because of the complexity of the very large number of extraction wells and piping across Area 5 North, the challenge with clogging of wells due to high TDS, and concerns with leaks from a very complex network of extraction piping. This alternative would also require a very large and complex treatment system that would increase the potential for emissions or releases of contaminants as groundwater or to the air. The stringent NPDES discharge limits would be a concern for the operational reliability of this system. Alternative 6 would produce about 1.8 million gallons of brine that would need to be managed in the ponds at the site making the task of pond water management more complex. There could also be public concerns and close scrutiny with discharge of treated groundwater from the site into the local creek. With respect to cost, Alternative 2 is estimated to be low to moderate, Alternative 3 is high, Alternative 4 is moderate, Alternative 5 is rated moderate to high and Alternative 6 is rated very


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high. Alternative 2 is rated low to moderate because it only involves extraction and discharge of groundwater to the evaporation pond without treatment. Alternative 3 is rated high because it includes treatment of inorganics in groundwater to enable discharge in accordance with substantive NPDES permit limits. Alternative 4 is rated one step higher than Alternative 2 because it includes capital cost for construction of the reactive wall while Alternative 5 is rated moderate to high because it includes the capital cost of the PSCT Westside extension and the additional long term operating costs. Alternative 6 is rated very high because of the capital cost of leachate treatment plant and the long term O&M costs for continuous operation. It is rated very high because of the capital costs for the extraction and treatment equipment for the 30 gpm system (60 wells) and the operational cost of the very complex treatment train to treat the groundwater for organics and inorganics to enable discharge in accordance with the substantive requirements of an NPDES permit. With respect to green impacts assessment (or environmental footprint), the impacts from Alternative 2 are considered to be low to moderate, Alternative 3 are high, Alternative 4 are low, Alternative 5 are moderate to high, and Alternative 6 are high. The impacts from Alternative 4 are lower than Alternative 2 because Alternative 4 involves a passive in-situ reactive wall that does not involve use of fuel or electricity, while Alternative 2 involves active groundwater extraction for the long term. Alternative 5 adds the Westside PSCT installation and operation and consequently the impacts are one step higher than Alternative 2. The impacts from Alternative 6 are high because it adds the high energy requirements for constructing and operating a large network of groundwater extraction wells and a 30 gpm complex treatment system for a very long period of time. Alternative 6 would also include the emissions from transport of wastes generated by the treatment equipment including spent brine, spent carbon, waste solids, filters, etc. to permitted facilities for the long term operations. 10.6.7.1 Summary of Screening Evaluation Based on the screening evaluation, Alternatives 2, 3, 4 and 6 are retained for detailed evaluation in Section 11. The anticipated remedies in FS Area 3 south of the PSCT and the Maintenance Shed Area would be a significant source reduction component (minimizes leaching to groundwater) that supports the objectives of these groundwater alternatives. Alternative 6 is retained though there would be implementability challenges, very high cost and energy consumption, as a representative of an aggressive restoration alternative because there would not be a TI waiver for Area 5 South. Administrative challenges associated with discharge of treated groundwater into the B-Drainage can also be anticipated. Alternative 5 is not retained because the water table is expected to drop significantly with the anticipated site capping remedies in FS Area 1 and 3 and the amount of groundwater flow in the Upper HSU is expected to drop significantly. Hence, it is not likely that the PSCT Westside extension is going to capture a significant amount of groundwater though costs will be higher with the additional trench construction and pumping operations. Besides groundwater VOC concentrations do attenuate rapidly south of the PSCT and the BTA, so the PSCT Westside extension would not achieve a significant risk reduction. 10.6.8 Screening of Remedial Alternatives – Area 5 West Table 10-6C presents the screening evaluation of the six remedial alternatives addressing dissolved metals (primarily arsenic, nickel, selenium, cadmium) in Area 5 West.


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With respect to effectiveness, Alternative 2 is rated the lowest at poor, while Alternative 5 is rated poor to moderate and Alternatives 3, 5 and 6 are rated higher at moderate. Alternative 2 is a monitored natural attenuation alternative. For metal contaminants, natural attenuation can occur by redox reactions, sorption to the clay formation and dilution/dispersion. The rate of these attenuation processes is expected to be very slow. Control of sources by capping of metals-impacted soil areas in RCRA Canyon/WCSA and closure of ponds in FS Area 4 (Pond A-5 and A-Series Pond) will prevent further leaching to groundwater. However, Alternative 2 would not meet the RAO of mitigating potential for migration beyond the historical site boundaries by natural attenuation alone and is rated poor. Alternatives 3, 4, 5 and 6 would meet that RAO with perimeter extraction or in-situ treatment at PCT-C that ensures capture of contaminants. Alternative 6 in addition includes aggressive hydraulic extraction that attempts to treat impacted groundwater across Area 5 West. Based on calculations presented in Appendix A, the estimated timeframe for aquifer restoration in Alternatives 3 and 4 with capping is not significantly different from aquifer restoration timeframe for Alternative 6 (aggressive hydraulic extraction). With respect to implementability, Alternatives 2 and 3 are rated good while Alternative 4 is rated moderate, Alternative 5 is rated moderate to good and Alternative 6 is rated poor to moderate. Alternatives 2 and 3 are rated good because there are no technical challenges with implementation. Alternative 4 is rated lower than Alternative 3 at moderate because Alternative 4 includes inorganics treatment to enable discharge per substantive NPDES permit limits. Alternative 5 is rated lower at moderate to good because of technical challenges and reliability concerns with a ZVI reactive wall for a mix of metal contaminants with different redox chemistries and the potential impacts of high TDS on the reactive wall operations. Alternative 6 is rated the lowest at poor to moderate due to anticipated challenges with capturing groundwater from the extraction wells in this bedrock formation, the large number of wells and extensive piping network required, well clogging problems due to high TDS, and water treatment necessary to meet stringent NPDES discharge requirements due to the high TDS and metals. Also, there are potential public concerns with discharge of treated groundwater to local creek and need for larger evaporation pond to store reject brine solution that is very high in solids of about 788,000 gallons per year (assuming 15 percent reject). With respect to cost, Alternative 2 is low because it only includes groundwater sampling costs, Meanwhile, Alternative 3 is low to moderate, Alternative 4 is rated high, Alternative 5 is rated moderate and Alternative 6 is rated very high. Alternative 5 is rated higher than Alternative 3 because of the capital cost of the installation and replacement of the ZVI reactive walls. Alternative 6 is rated the highest because of the capital cost of leachate treatment plant and the long term O&M costs for continuous operation. Alternative 6 is rated very high because of the capital costs for the extraction wells, piping and treatment equipment for the 20 gpm system (40 wells) and the operational cost of the very complex treatment train to treat inorganics in the groundwater for discharge. With respect to green impacts assessment (or environmental footprint), Alternative 2 has the lowest impacts because it only involves sampling activities. The impacts from Alternative 5 are low, Alternative 3 are low to moderate, Alternative 4 are moderate to high and Alternative 6 are high. The impacts from Alternative 5 are lower than Alternative 3 at low to moderate because Alternative 5 involves a passive in-situ reactive wall while Alternatives 3 and 4 involves active groundwater extraction for perimeter control for a very long time. The impacts from Alternative 6 are high because it involves operating a large network of groundwater extraction wells and a complex 20 gpm treatment system with significant energy requirements for a very long period of time.


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10.6.8.1 Summary of Screening Evaluation Based on the screening evaluation, Alternative 2 is not retained because its effectiveness is poor because it does not include perimeter control and thus does not address the RAO of mitigating migration. Alternatives 3, 4 and 5 include perimeter control via PCT-C extraction or conversion of PCT-C to an in-situ reactive wall that prevents migration beyond the site boundaries, and hence are retained. Alternative 6 is retained because there is no TI waiver proposed for Area 5 West that is impacted primarily with low levels of dissolved metals. This aggressive alternative is included in the detailed evaluation to outline the challenges with implementability, high cost, high green impacts and long duration for aquifer restoration with this alternative. Hence a total of four active remedial alternatives (Alternatives 3, 4, 5 and 6) are retained for the detailed evaluation in Section 11. 10.7 References Albright, W.H., C.H Benson, and W.J. Waugh. 2010. Water Balance Covers for Waste Containment, Principles and Practice. ASCE Press

Albright, W. et al., 2004. J. Environ. Qual. 33:2317-2332.

Ali Harivandi, M., J. Baird, J. Martin, M. Henry, and D. Shaw. 2009. Managing Turf Grasses During Drought. University of California Division of Agriculture and Natural Resources Publication 8395. August. 9 pp.

Benson, C.H., W.H. Albright, D.O. Fratta, J.M. Tinjum, E. Kucukkirca, S.H. Lee, J. Scalia, P.D. Schlicht, and X. Wang. 2011. Engineered Covers for Waste Containment: Changes in Engineering Properties and Implications for Long-Term Performance Assessment. U. S. Nuclear Regulatory Commission NUREG/CR-7028, Volumes 1 and 2. December.

Bonaparte, R., B.A. Gross, D.E. Daniel, R.M. Koerner, and S. Dwyer. 2004. (Draft) Technical Guidance for RCRA/CERCLA Final Covers. U. S. Environmental Protection Agency, EPA 540-R-04-007. April. Brierley & Lyman, 1989a. Final Construction Drawings, Perimeter Source Control Trench (PSCT), Casmalia Resources Hazardous Waste Management Facility, Casmalia, California, May 31. CSC, 2011a. Final Remedial Investigation Report, January 2011. CSC 2011b Draft Feasibility Study. Casmalia Resources Superfund Site. Casmalia Steering

Committee. February 2011. CSC 2009a Routine Groundwater Monitoring Element of Work, Field Sampling Work Plan,

March 31, 2009. CSC 2009b Sampling Plan for Soil Gas Monitoring, April 6, 2009. CSC, 2004. Remedial Investigation/Feasibility Study Work Plan, June 2004.


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CSQA ,2003. California Stormwater BMPs Handbook, California Stormwater Quality Association, January 2003. Dwyer et al. 1999. Mixed Waste Landfill Design Report. Sandia National Laboratories. SAND99-2514. October 1999. ECHOS, 2000. Environmental Restoration Assemblies Cost Book, ECHOS Remediation Cost Handbook, 2000. Foose, G.J., C.H. Benson, and T.B. Edil. 2001. Predicting Leakage through Composite Landfill Liners. Journal of Geotechnical and Geoenvironmental Engineering, v. 127, no. 6, pp. 510-520.

FRTR, 2011. Federal Remediation Technologies Roundtable, http://www.frtr.gov and http://costperformance.org websites with technology and cost information. Geosyntec, 1999. P/S Landfill Final Design Report, GeoSyntec and Foster Wheeler, July 1999.

Geosyntec. 2001. Design Change Request Report, DCR-05, December 2001.

Giroud, J.P. 1997. Equations For Calculating The Rate Of Liquid Migration Through Composite Liners Due To Geomembrane Defects. Geosynthetics International, v. 4, nos. 3-4, pp. 335-348.

Giroud, J.P. and R. Bonaparte. 1989a. Leakage through Liners Constructed with Geomembranes, Part I – Geomembrane Liners. Geotextiles and Geomembranes, v. 8, pp. 27-67.

Giroud, J.P. and R. Bonaparte. 1989b. Leakage through Liners Constructed with Geomembranes, Part II – Composite Liners. Geotextiles and Geomembranes, v. 8, pp. 71-111.

Hauser, V.L. and D.M Gimon. 2004. Evaluating Evapotranspiration (ET) Landfill Cover Performance Using Hydrologic Models. Air Force Center for Environmental Excellence (AFCEE) Report AFD-071203-169, 58 pp and appendices.

Hauser, V.L., D.M. Gimon, J.V. Bonta, T.A. Howell, R.W. Malone, and J. R. Williams. 2005. Models for Hydrologic Design of Evapotranspiration Landfill Covers. Environmental Science & Technology, v. 39, pp. 7226-7233.

ITRC, 2003 Technical and Regulatory Guidance for Design, Installation, and Monitoring of Alternative Final Landfill Covers, December 2003.

Means 2005 Environmental Remediation Cost Handbook, Unit Costs. Means, 2003. Environmental Remediation Estimating Methods, 2nd Edition.


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Melchior, S., V. Sokollek, K. Berger, B. Vielhaber, and B. Steinert. 2010. Results From 18 Years Of In Situ Performance Testing Of Landfill Cover Systems In Germany. Journal of Environmental Engineering, v. 136, no. 8, pp. 815-823.

Netstate. 2009. http:// http://www.netstate.com/states/symb/grasses/ca_grass.htm Website accessed November 1, 2012.

Niles 2011 Telephone communication with Corey Bertelsen, dated July 7, 2011. Scanlon, B.R., M. Christman, R.C. Reedy, I. Porro, J. Simunek, and G.N Flerchinger. 2002. Intercode Comparisons For Simulating Water Balance Of Surficial Sediments In Semiarid Regions. Water Resources Research, v. 38, no. 12, 1323.

Scanlon, B.R., R.C. Reedy, K.E. Keese, and S.F. Dwyer. 2005. Evaluation of Evapotranspiration Covers for Waste Containment in the Arid and Semiarid Regions of the Southwestern USA. Vadose Zone Journal, v. 4, pp. 55-71.

Schroeder, P.R., N.M. Aziz, C.M. Lloyd, and P.A. Zappi and. 1994. The Hydrologic Evaluation of Landfill Performance (HELP) Model: User’s Guide for Version 3. U. S. Environmental Protection Agency Office of Research and Development, EPA/600/R-94/168a. September. 84 pp and Appendix.

Tilley, D., D. Dwyer, J. Anderson. 2009. Purple Needle Grass. U. S. Department of Agriculture Natural Resources Conservation Service Plant Guide. 5 pp.

USEPA, 1988. Guidance for Conducting Remedial Investigations and Feasibility Studies Under CERCLA, US EPA 540/G-89/004, October 1988. USEPA 1996 How To Effectively Recover Free Product At Leaking Underground Storage Tank Sites: A Guide For State Regulators, EPA 510-R-96-001, September 1996. USEPA, 1999: Use of Monitored Natural Attenuation at Superfund, RCRA Corrective Action and Underground Storage Tanks Sites. April. 1999 USEPA, 2000. A Guide to Developing and Documenting Cost Estimates during the Feasibility Study, US EPA and US Army Corps of Engineers, EPA 540-R-00-002 July 2000. USEPA, 2007 Monitored Natural Attenuation of Inorganic Contaminants in Groundwater Vol. 2, EPA/600/R-07/140, October 2007. USEPA 2009 Principles for Greener Cleanups, Office of Solid Waste and Emergency Response (OSWER), US EPA, August 2009 (http://www.cluin.org/greenremediation/). USEPA 2010 Superfund Green Remediation Strategy, September 2010. USEPA, 2011. Stormwater BMPs Presentation, http://www.ectc.org USEPA, 2011


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11.0 DETAILED EVALUATION OF AREA-SPECIFIC REMEDIAL ALTERNATIVES

Based on the area-specific remedial alternatives retained in Section 10, this section of the FS describes the retained remedial alternatives for each FS Area and presents the detailed evaluation for those remedial alternatives. Table 11-1 lists and summarizes the retained remedial alternatives for the FS Areas. Tables 11-2 through 11-6 present the detailed evaluation by FS Area in accordance with the first 7 of the 9 ranking criteria identified in the CERCLA guidance (USEPA 1988). The results of the detailed evaluation of alternatives in this section will be used to formulate site wide remedial alternatives (composed of various combinations of alternatives from each FS Area) in Section 12, where a separate detailed evaluation of site wide remedial alternatives will be performed. A green impacts assessment is included for each alternative in addition to the detailed evaluation. The CERCLA ranking criteria are described below before the presentation of the detailed evaluation by FS Area. As described earlier in Section 10, Table 12-3 provides a road map to help track the area-specific alternatives that are retained from the screening evaluation in Section 10 and the site-wide remedial alternatives that are finally developed for the detailed evaluation in Section 12. The circles shown for the area-specific screening evaluation and detailed evaluation are partially filled by quarters.Filled circles are the most desirable and non-filled circles are the least desirable. Filled circles are then used to indicate which area-specific alternatives were assembled into the six site-wide remedial alternatives evaluated in Section 12.

11.1 Description of CERCLA RI/FS 9-Criteria Nine federal criteria have been developed to evaluate the extent to which remedial alternatives meet the statutory requirements of the National Contingency Plan. The USEPA guidance describes these 9 criteria under three primary categories: threshold criteria, primary balancing criteria, and modifying criteria (USEPA 1988). The following is a brief description of the 9 criteria: Threshold Criteria are the criteria that must be met for an alternative to be considered or selected: Overall Protection of Human Health and the Environment assesses whether each

alternative provides adequate protection of human health and the environment. The overall assessment of protection draws on the analyses conducted for other evaluation criteria, especially long-term effectiveness (LTE) and permanence, short-term effectiveness (STE), and compliance with ARARs. The assessment describes how site risks posed through each pathway are eliminated, reduced or controlled through treatment, engineering, or institutional controls. The assessment also allows for consideration of whether an alternative poses any unacceptable short-term or cross-media impacts.

Compliance with ARARs addresses fulfillment of all applicable or relevant and appropriate requirements of federal or state law (as defined in CERCLA Section 121). The analysis


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summarizes which requirements are applicable or relevant and appropriate to an alternative and describes how the alternative meets these requirements. Compliance was evaluated for the three types of ARARs: chemical-specific ARARs, location-specific ARARs, and action-specific ARARs. The analysis also assesses whether waivers would be appropriate. Under certain circumstances, some ARARs may be waived. Only ARARs that apply to on-site remedial actions may be waived in accordance with statutory criteria; other statutory requirements, such as the requirement that remedies be protective of human health and the environment, cannot be waived. One of the specific waivers provided by CERCLA Section 121(d)(4) includes: Technical Impracticability - This waiver may be used where compliance with an ARAR is technically impracticable from an engineering perspective. Cost is a factor, although not generally the major factor in the evaluation of technical impracticability.

Primary Balancing Criteria are used to assess the relative advantages and disadvantages of each alternative in terms of its performance. These include: LTE and Permanence refers to the: (1) magnitude of residual risk remaining at the

conclusion of the remedial activities; and, (2) adequacy and reliability of controls that are necessary to manage treatment residuals and untreated waste. The residual risk of an alternative is related to the potential for persons or ecological receptors to be exposed to untreated waste, or treatment residuals, at the conclusion of remedial activities. Adequacy and reliability of controls addresses the uncertainties associated with long-term protection from residual contamination that may be left in place; the assessment of the potential need to replace technical components of the alternative, such as a cap, a slurry wall, or a treatment system; and the potential exposure pathways and risks posed should the remedial action need upgrading.

Reduction of Toxicity, Mobility, or Volume through Treatment (RTMV) addresses the use of treatment to reduce the harmful effects of principal contaminants, their ability to move in the environment and the amount of contamination present. This criterion addresses the statutory preference for selecting remedial actions that employ treatment technologies that permanently and significantly reduce toxicity, mobility and volume of the contaminants.

STE addresses the length of time and adverse impacts on human health and the environment posed during the construction and implementation period until remedial action objectives are met. It primarily addresses human health risks during remedial actions like excavation, transportation of hazardous materials, air-quality impacts or noise impacts from treatment operations. It also addresses protection of workers from hazards during remedial actions, effects to ecological receptors, the effectiveness and reliability of protective measures to be taken, and any environmental impacts during remedial operation.

Implementability addresses the technical and administrative feasibility of an alternative as well as the availability of required services and materials. Technical feasibility includes anticipated construction and operational difficulties and the reliability of the technology. Administrative feasibility includes coordination difficulties and difficulties in complying with agency requirements for permitting and obtaining construction rights-of-way. Administrative feasibility also includes consideration of property owner acceptance and conflicts between remedial alternatives and current land use. The third issue considered under implementability is the availability of services and materials for each alternative, including disposal services and storage capacity.

Costs include budgetary capital, O&M costs, and present worth costs. Capital costs consist of direct (construction) and indirect (non-construction and overhead) costs. Direct capital


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costs include equipment and installation costs. Indirect capital costs include engineering and design, permitting, startup and shakedown, and contingency costs. O&M costs include labor, materials, and energy costs once the remedy is constructed. A present worth analysis is used to evaluate costs that occur over the period of the remedial action by discounting future costs to a common base year. The present worth costs are estimated based on the number of years the remedy is operational. For purposes of this Feasibility Study, where engineering controls or institutional controls may last indefinitely into the future, 30-year and 100-year time periods are assumed. Cost estimates for the alternatives are developed to an accuracy of +50 percent to -30 percent. Further discussion of cost estimating methods and assumptions is presented below.

Modifying Criteria include State and community acceptance and are considered by USEPA in the selection of the remedy. These include: State Acceptance includes an assessment of the state’s position and key concerns

regarding the preferred alternative and other alternatives as well as any state comments on ARARs.

Community Acceptance describes acceptance of the alternative by the community, including an assessment of key positions, issues, or concerns expressed by interested community members.

Of these 9 criteria, the first seven criteria are addressed in this FS report. The two modifying criteria, State Acceptance and Community Acceptance, will be addressed later when that information becomes available. State Acceptance will be addressed once USEPA has received comments on the FS report, and will be incorporated to the extent possible into the Proposed Plan. State Acceptance will be further considered after receiving comments on the Proposed Plan. Community Acceptance will be addressed after USEPA has received public comments on the Proposed Plan. The ROD will incorporate the final evaluation of these two criteria. EPA seeks to incorporate green remediation practices into its remedial actions. As discussed earlier in Section 10, this FS considers green remediation but does not include it as a formal ranking criterion.This evaluation is presented as a qualitative rating (low, low to moderate, moderate, moderate to high and high) reflecting the extent of green and sustainability impacts (or environmental footprint) for each alternative after the discussion of the detailed evaluation for each FS Area. The higher the rating, the greater the environmental impacts or footprint, and hence the less green the alternative. The detailed evaluation in Sections 11.2 through 11.6 uses a rating scale as follows: Threshold Criteria are evaluated by assigning either a “yes” or “no” with respect to whether

each alternative (1) provides adequate protection of human health and the environment and (2) complies with ARARS.

Primary Balancing Criteria are evaluated using a rating scale ranging from poor, poor to

moderate, moderate, moderate to good, and good for the first four criteria (LTE and Permanence, RTMV, STE, and Implementability). Costs (the fifth criteria) are rated using a scale from low, low to moderate, moderate, moderate to high, and high.


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Green Assessment is conducted by assessing sustainability impacts (environmental footprint) and assigning impacts that range from low, low to moderate, moderate, moderate to high, and high.

The Modifying Criteria, i.e., state and community acceptance, are not covered in detail in the FS since they will be addressed later during the proposed plan process consistent with the NCP. 11.1.1 Cost Estimating Approach Approximate cost estimates were developed for each remedial alternative based on the conceptual design of the remedial alternatives. The conceptual design of specific remedial alternatives is presented in the FS. Costs were developed in a manner consistent with USEPA guidance (EPA 2000) unless otherwise documented below. Typically cost estimates are based on unit costs derived from remediation cost handbooks or on vendor cost estimates developed specifically for this site. Some elements of the cost estimates are based on judgment and on experience or cost data from the current operations at this site or other sites. The cost estimates are comprehensive estimates of direct and indirect capital costs and O&M costs and include sales tax and shipping costs, as appropriate. The cost estimate spreadsheet estimates present worth cost in 2014 dollars and the expected operating costs by year and the probable schedule for the capital expenditures so that a “then current” cost can be calculated. The cost spreadsheet used in this FS uses a template from the USEPA cost guidance (USEPA 2000). The total contingency including scope contingency and bid contingency is assumed to be at the higher end of the typical range (35 to 50 percent) described in the USEPA cost guidance (USEPA 2000). A 35 percent contingency is used for capital costs for those technologies or remedial components that have been previously implemented at this site and have a lower potential for unforeseen circumstances. For all other alternatives, a 50 percent contingency is used for capital costs. For all alternatives a 50 percent contingency for the long term O&M costs is used. The 50 percent contingency is considered particularly appropriate at this stage of conceptual design where there is still significant uncertainty about some of the details of design and operation. The previous USEPA cost estimates for the Casmalia Resources Superfund Site also used that same contingency. An exception to this involves the alternative to dewater the P/S Landfill, using horizontal wells where, due to very high uncertainty regarding the method and success of well installation and the volume of liquids that may be produced, a 75 percent contingency has been assumed for O&M and disposal of liquids at a permitted disposal facility. A summary of the contingency percentages used for each area-specific remedial alternative is included in Appendix E (Table E-9-0). No contingency was assumed for periodic costs that occur over the long term such as equipment replacement costs every 10 years or cap replacement costs every 50 years. Present worth costs of the remedial alternatives are estimated using two net discount rates of 3 percent and 7 percent, and two timeframes of 30 years and 100 years. These present worth cost estimates for varying discount rates are presented for comparison purposes. The most recent rates of inflation and returns on investment are consistent with that same range. The 100-year present worth cost is provided to estimate long term costs beyond the 30-year timeframe required by CERCLA guidance, and capture possible long term remedy replacement costs. Obviously, when calculating a total present worth with either of the two discount factors, it is assumed that there is not much increase in the present worth costs using this longer period. Additional details on the cost estimating procedures and assumptions and the detailed cost spreadsheets for the remedial alternatives are presented in Appendix E. The cost estimates reflect several uncertainties such as the assumptions about the lateral extent of the COC-


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impacted area, the extraction volumes of groundwater or NAPL, etc. The cost estimates meet the accuracy requirements of the CERCLA guidance of +50 percent to -30 percent. In the detailed evaluation in this section, the remedial alternative cost estimates are compared within each FS Area, while in Section 12, the cost estimates are presented for site-wide remedial alternatives. The present worth cost estimate for the site-wide remedial alternatives will include present worth of capital cost based on an assumed capital expenditure schedule and construction schedule (see Section 12.8) for a 3 percent and 7 percent discount rate The following sections present the results of first 7 of the 9-criteria analysis for each remedial alternative evaluated at each FS Area. The two threshold criteria are pass-fail type criteria, so the rating states “Yes” or “No” depending on whether the alternative satisfies the criterion or not. Each section includes a subsection for description of remedial alternatives retained from the screening evaluation, a subsection for detailed and comparative analysis of alternatives, and finally a summary of the evaluation. The subsection with the detailed and comparative analysis will present the 7-criteria evaluation and a qualitative evaluation for “green assessment” for the remedial alternatives. As mentioned earlier, results of these evaluations will be used to formulate site wide remedial alternatives in Section 12 for a final round of detailed evaluations. The following evaluation compares area-specific alternatives for the site. The alternatives include engineering controls (ECs), institutional controls (ICs), long term-monitoring, and long- term operations and maintenance (O&M). Although the details of engineering controls, monitoring, and long-term O&M are expected to vary among individual alternatives for each study area, ICs will remain similar or fairly consistent for most, if not all of the alternatives.

11.2 Detailed Evaluation for FS Area 1 This section presents the description of the active remedial alternatives, the detailed evaluation, the green impacts assessment evaluation, and the comparative analysis of alternatives for FS Area 1. Five remedial alternatives were selected in the screening evaluation in Section 10 for the detailed evaluation. Table 11-2 presents the detailed evaluation for the five selected alternatives. 11.2.1 Description of Remedial Alternatives The following is the description of the five remedial alternatives carried into the detailed analysis. 11.2.1.1 Alternative 1 No Action The No Action alternative is included as required by CERCLA FS guidance. 11.2.1.2 Alternative 2 RCRA-Equivalent Mono Soil Cap (5’) (BTA, CDA) + RCRA Cap (PCB

Landfill) + Stormwater Controls + ICs + Monitoring This alternative includes the following components for FS Area 1 (Figure 11-1A):

PCB Landfill covered with a RCRA cap over an area of 4.4 acres BTA covered with a 5-foot low permeability soil cap over an area of 5.5 acres


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CDA covered with a 5-foot low permeability soil cap over an area of 18.8 acres Stormwater controls including drainage and erosion controls for the capped areas and a

drainage channel to the proposed retention basin in the footprint of Pond 13 Place excavated wastes from other remedial actions in PCB Landfill prior to capping Allow use of pond water during cap construction for foundation or other layers below

HDPE liners Institutional controls, maintenance and monitoring to protect the capped areas

The objectives of this remedial alternative are:

Prevent ecological receptors from potential exposures to shallow soil (0-5 feet bgs) Prevent rainwater infiltration at the PCB Landfill and significantly reduce rainwater

infiltration into soil and groundwater at the BTA and CDA study areas that adjoin the landfills

Incorporate stormwater and erosion controls to minimize transport of contaminants via stormwater sediments and allow discharge of stormwater from FS Area 1 via the substantive provisions of the General Permit

The following provides a brief description of the conceptual design for the remedial alternative components: RCRA Cap for the PCB Landfill This alternative includes a RCRA cap for the PCB Landfill as shown on Figures 11-1A and 11-1B. The RCRA cap for the PCB Landfill is a presumptive remedy and is a common component in all the alternatives evaluated in FS Area 1. The conceptual design and preliminary performance standards for the RCRA cap were discussed earlier in Section 10.1.1.1. Detailed specifications would be developed during remedial design. The eastern side of the PCB Landfill cap would need to tie into the existing P/S Landfill cap. The borrow soils obtained from the NW Borrow Area for this cap may need to be screened and processed by pulverization before use. Hydroseeding would be used to spread a selected seed mix of native plant species on the top of the vegetative layer. The soil for the vegetative layer would also need the addition of organic materials and nutrients to assist vegetation growth. Specific processing requirements for the borrow soil and amendments used in prior capping activities (e.g., P/S Landfill, EE/CA Area) are discussed in Section 10.1.2. If adequate soil is not available from the site or the identified borrow areas, another local source of soil such as the nearby Laguna Sanitation District site would be used. Prior to construction of the PCB Landfill cap, any excavated waste soils from other areas of the site (e.g., Pond sediments) would be disposed of in the available space in the PCB Landfill. Also, use of pond water from the ponds is proposed for construction of caps specifically for soil layers below the HDPE liner (e.g. foundation layer). RCRA-Equivalent Mono Soil Cap for the CDA and BTA This alternative includes a RCRA-equivalent mono soil cap for the CDA and the BTA as shown on Figure 11-1A, 11-1B and 11-1C. The conceptual design of the RCRA-equivalent mono soil cap was discussed earlier in Section 10.1.1.2. Preliminary specification for the monocover soil is that it be classified by the Unified Soil Classification System as CL, SC or ML and have greater than 50 percent fines content. Detailed specifications would be developed during remedial design. Borrow soil or construction process would be augmented as necessary to meet specifications. The entire northern length of the CDA cap boundary would need to tie into the


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existing RCRA caps for the P/S Landfill and the EE/CA Area, and the eastern side of the BTA would need to tie into the planned P/S Landfill cap. The clay soil would be borrowed from the NW Borrow Area. The weathered claystone borrow material will likely need to be screened and pulverized/crushed in a pug mill (or with a pulverizer) prior to use to meet the hydraulic conductivity performance criterion. These soils have been used previously during the P/S Landfill Cap project to achieve these performance criteria. These borrow area soils would be evaluated during remedial design. In the event supplemental clay soils or bentonite are determined to be necessary during remedial design, some imported materials will be supplemented to ensure the cap meets specifications. Cut and Fill Soil Volumes for Leveling and Cap Construction For the PCB Landfill, the cut/fill volume for leveling is 20,000 cy (Figure 11-1B). The cut/fill volume refers to an approximate amount of a matched cut and fill for leveling that is required before the construction of the cap begins. If excavated impacted soils from other areas of the site are placed in the PCB Landfill, up to approximately 140,000 cy of space is available for use. See discussion of PCB Landfill storage capacity in Section 10.1.2, and Figure 11-1B for the PCB Landfill cross section showing the planned top elevation of the waste and the cap. The foundation layer will require a total of 16,000 cy of soil and the vegetative layer will require a total of 16,000 cy of soil that would be obtained from the NW Borrow Area. For the BTA, the cut/fill volume for leveling is 61,000 cy (Figure 11-1B). The clay monocover layer will require a total of 49,000 cy of soil primarily from the NW Borrow Area. For the CDA, the cut/fill volume for leveling is 120,000 cy (Figure 11-1C). The clay monocover layer will require a total of 167,000 cy of soil primarily from the NW Borrow Area. Stormwater Controls The top surface of the cap would be designed to collect and convey stormwater on the cap to the nearest collector drains along the perimeter roads. The slopes of the top of the landfill cap would vary between 3:1 (H:V) and 5:1 (H:V). The cap surface will include bench roads for access and V-drains to control and direct stormwater drainage. Preliminary locations of bench roads and drains are as shown on Figures 11-1A, 11-1B and 11-1C. Erosion control mats will be used in any small sections that have slopes steeper than 2:1 (H:V). Silt fences will be installed at the base of the construction areas to minimize potential contaminated soil transport as sediments in stormwater runoff. The bench roads will be constructed from 12-inch thick aggregate base. Rip-rap will be placed in the larger collector drains to slow the flow rate of stormwater and reduce erosion. The stormwater from the PCB Landfill and the BTA will be transported southeast along the perimeter drains towards the CDA. With this alternative, FS Area 1 would become one large capped area (about 90 acres), and the stormwater collected from all of FS Area 1 would go through the culvert and lined drainage channel near PSCT-1 to the RCF Pond. The stormwater would then flow under the RCF Road via a new culvert, and then discharge through or around the wetlands into the B-drainage (discharge governed by the existing General Permit). Existing Site Features


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All monitoring or extraction wells that are within the footprint of the PCB Landfill, BTA and CDA will be extended with new surface completions above the cap surface. About 30 wells are present in the CDA, 10 wells in the BTA and five wells in the PCB Landfill. The geomembrane will be attached via a collar to the well casings, as is typical for this type of technology, ensuring a watertight seal but still allowing for movement from settlement or displacement. Existing site roads and drains that are within the footprint of the proposed capped areas in this alternative would be reconstructed and likely relocated as perimeter roads and drains outside the capped areas. The detailed plans for the site roads and drains and how they would be connected to the drains in adjacent areas would be addressed during the remedial design phase. Sampling and Testing During remedial design, the slope stability will be evaluated as part of the cap design. During construction, the foundation layer will be tested for compaction and appropriate shear strength, and interface testing of the cap will be conducted. Air monitoring would be conducted during the grading and cap construction activities. Air monitoring would include field dust and VOC monitoring and one air and particulate sample collected for each field day that involves soil construction activities. Soil physical and geotechnical properties will be tested for the proposed borrow area at the northwest area of the site to ensure adequate quality and quantity of soils is available. The soil tests would include shear strength (ASTM D4767), moisture content (ASTM D2216), fines content (ASTM D1140), Atterberg limits (ASTM D4318), and hydraulic conductivity (ASTM D5084). Inspection, Monitoring, Maintenance and Institutional Controls The monitoring component of this alternative includes periodic inspection, maintenance and repair of the cap and stormwater controls over the long term. Periodic inspection and maintenance of the cap is assumed to include monitoring for subsidence or cap erosion. Inspection is also assumed to include stormwater facilities such as V-drains, collector drains and culverts. Institutional controls include land use restrictions and site monitoring, security and fencing to protect public access for the long term. The cap and stormwater controls system will be inspected after a significant seismic event and after major storm events. 11.2.1.3 Alternative 3 Evapotranspirative (ET) Cap (5’) (BTA, CDA) + RCRA Cap (PCB Landfill)

+ Stormwater Controls + ICs + Monitoring

This alternative includes the following components for FS Area 1 (Figure 11-2A): • PCB Landfill covered with a RCRA cap over an area of 4.4 acres • BTA covered with a 5-foot low permeability ET soil cap over an area of 5.5 acres • CDA covered with a 5-foot low permeability ET soil cap over an area of 18.8 acres • Stormwater controls including drainage and erosion controls for the capped areas and a

drainage channel to the proposed retention basin in the footprint of Pond 13 • Place excavated wastes from other remedial actions in PCB Landfill prior to capping • Allow use of pond water during cap construction for foundation layers or below HDPE

liners • Institutional controls, maintenance and monitoring to protect the capped areas



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• Prevent ecological receptors from potential exposures to shallow soil (0-5 feet bgs) • Prevent rainwater infiltration at the PCB Landfill and significantly reduce rainwater

infiltration into soil and groundwater at the BTA and CDA study areas that adjoin the landfills

• Incorporate stormwater and erosion controls to minimize transport of contaminants via stormwater sediments and allow discharge of stormwater from FS Area 1 via the substantive provisions of the General Permit

The following provides a brief description of the conceptual design for the remedial alternative components: RCRA Cap for the PCB Landfill This alternative includes a RCRA cap for the PCB Landfill as shown on Figures 11-2A and 11-2B. The conceptual design is the same as in Alternative 2 and preliminary performance standards for the RCRA cap were discussed earlier in Section 10.1.1.1. Detailed specifications would be developed during remedial design. ET Soil Cap for the CDA and BTA This alternative includes an ET soil cap for the CDA and the BTA, the design of which is based on hydrological processes at the site that include water storage capacity of soil, precipitation, surface runoff, evapotranspiration, and infiltration. The greater the storage capacity and evapotranspiration properties are, the lower the potential for percolation through the cap system. The ET cap would consist of a 1-foot thick foundation layer with clay soil compacted to 90 percent (ASTM D 1557) and 4 feet of claylike soil that is lightly compacted to about 85 percent for the vegetative layer. The ET cap would be placed in the CDA and the BTA as shown on Figure 11-2A, 11-2B and 11-2C. A more detailed description of the ET cap was presented in Section 10.1.1. The ET cap is intended to store water, thus allowing the growth of vegetation and the removal of soil moisture through evaporation and transpiration. Preliminary specification for the ET soil cap soil is that it be classified by the Unified Soil Classification System as CL, SC or ML and have greater than 50 percent fines content. Detailed specifications would be developed during remedial design. Borrow soil or construction process would be augmented as necessary to meet specifications. The entire northern length of the CDA cap boundary would need to tie into the RCRA caps for the P/S Landfill and the EE/CA Area and the eastern side of the BTA would need to tie into the P/S Landfill cap. The clay soil would be borrowed from the NW Borrow Area. The weathered claystone borrow material will likely need to be screened, pulverized/crushed in a pug mill (or with a pulverizer), and moisture conditioned prior to placement to meet the performance criterion for the ET cap (Section 10.1.1). These soils have been used previously for the P/S Landfill Cap project to achieve these performance criteria. The borrow area soils would be evaluated during remedial design. In the event supplemental clay soils or bentonite are determined to be necessary during remedial design, some imported materials will be supplemented to ensure the cap meets specifications. Cut and Fill Soil Volumes for Leveling and Cap Construction

For the PCB Landfill, the cut/fill volume for leveling is 20,000 cy (Figure 11-2B). If excavated impacted soils from other areas of the site are placed in the PCB Landfill, up to approximately 140,000 cy of space is available for use. See discussion of PCB


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Landfill storage capacity in Section 10.1.2 and Figure 11-2B for the PCB Landfill cross section showing the top elevation of the waste and the cap. The foundation layer will require a total of 16,000 cy of soil and the vegetative layer will require a total of 16,000 cy of soil that would be obtained from the NW Borrow Area.

For the BTA, the cut/fill volume for leveling is 61,000 cy (Figure 11-2B). The clay monocover layer will require a total of 49,000 cy of soil, derived primarily from the NW Borrow Area.

For the CDA, the cut/fill volume for leveling is 120,000 cy (Figure 11-2C). The clay monocover layer will require a total of 167,000 cy of soil, derived primarily from the NW Borrow Area.

Stormwater Controls The details of the V-drains, bench roads, slopes of the ET cap surface and erosion controls are as discussed for Alternative 2 earlier. Preliminary locations of bench roads and drains are shown on Figures 11-2A, 11-2B and 11-2C. The perimeter collector drains, direction of stormwater flow from these capped areas, the culvert and the drainage channel near PSCT-1, and discharge of stormwater to the B-Drainage is the same as in Alternative 2 (discharge governed by the existing General Permit). Existing Site Features All monitoring or extraction wells within FS Area 1 would be handled the same as in Alternative 2. Existing site roads and drains that are within the footprint of the capped areas would be reconstructed. Detailed plans for this would be addressed during remedial design, as discussed in Alternative 2. Sampling and Testing Details of testing during construction are the same as Alternative 2, and include compaction testing and air monitoring. During remedial design the slope stability will be evaluated. Other physical and geotechnical properties testing of the NW Borrow Area, as discussed earlier in Alternative 2 will be used in the evaluation. Inspection, Monitoring, Maintenance and Institutional Controls As with other alternatives, the monitoring component of this alternative includes periodic inspection, maintenance and repair of the cap and stormwater controls over the long term as in Alternative 2. Similarly, ICs are expected to include land use and water use restrictions.

11.2.1.4 Alternative 4 RCRA Cap (PCB Landfill, BTA, CDA) (5’) + Stormwater Controls + ICs + Monitoring

This alternative includes the following remedial components for each part of FS Area 1 (Figure 11-3A):

PCB Landfill covered with a RCRA cap over an area of 4.4 acres BTA covered with a RCRA cap over an area of 5.5 acres CDA covered with a RCRA cap over an area of 18.8 acres


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Stormwater controls including drainage and erosion controls for the capped areas Place excavated wastes from other remedial actions in PCB Landfill prior to capping Allow use of pond water during cap construction for foundation layers or below HDPE

liners Institutional controls, maintenance and monitoring to protect the capped areas


Prevent ecological receptors from potential exposures to contaminants in shallow soil (0-5 feet bgs)

Prevent rainwater infiltration at the PCB Landfill, BTA and CDA study areas Incorporate stormwater and erosion controls to minimize transport of contaminants via

stormwater sediments and allow discharge of stormwater from FS Area 1 via the substantive provisions of the General Permit

The following provides a brief description of the conceptual design for the remedial alternative components: RCRA Cap for the PCB Landfill, BTA and CDA This alternative includes a RCRA cap for the PCB Landfill, BTA and CDA as shown on Figures 11-3A, 11-3B and 11-3C. The conceptual design for the RCRA cap was discussed earlier in Section 10.1.1.1. The eastern side of the PCB Landfill and the BTA caps would need to tie into the P/S Landfill cap while the northern side of the CDA cap would need to tie into the P/S Landfill and the EE/CA Area caps. The borrow soils obtained from the NW Borrow Area for this cap may need to be screened and processed by pulverization before use. Hydroseeding would be used to spread a selected seed mix of native plant species on the top of the vegetative layer. The soil for the vegetative layer would also need the addition of organic materials and nutrients to assist vegetation growth. If adequate soil is not available, another local source of soil such as the nearby Laguna Sanitation District site would be used. Prior to construction of the PCB Landfill cap, any excavated waste soils from other areas of the site (e.g., Pond sediments) would be disposed of in the available space in the PCB Landfill. Cut and Fill Soil Volumes for Cap Construction For the PCB Landfill, the cut/fill volume for leveling is 20,000 cy (Figure 11-3B). If excavated impacted soils from other areas (e.g., Pond sediments) of the site are placed in the PCB Landfill, up to approximately 140,000 cy of space is available for use. See discussion of PCB Landfill storage capacity in Section 10.1.2 and Figure 11-3B for the PCB Landfill cross section showing the top elevation of the waste and the cap. The foundation layer will require a total of 16,000 cy and the vegetative layer will require a total of 16,000 cy of borrow soil. For the BTA, the cut/fill volume for leveling is 61,000 cy (Figure 11-3B). The foundation layer will require a total of 19,000 cy of soil and the vegetative layer will require a total of 19,000 cy of borrow soil. For the CDA, the cut/fill volume for leveling is 150,000 cy (Figure 11-3C). The foundation layer will require a total of 67,000 cy and the vegetative layer will require a total of 67,000 cy of borrow soil. Stormwater Controls


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The details of the V-drains, bench roads, slopes of the cap surface and erosion controls are as discussed for Alternative 2 earlier. Preliminary locations of bench roads and drains are shown on Figures 11-3A, 11-3B and 11-3C. The perimeter collector drains, direction of stormwater flow from these capped areas, the culvert and the drainage channel near PSCT-1, and discharge of stormwater to the B-Drainage is the same as in Alternative 2 (discharge governed by the existing General Permit). Existing Site Features All monitoring or extraction wells within FS Area 1 would be handled the same as in Alternative 2. Existing site roads and drains that are within the footprint of the capped areas would be reconstructed. Detailed plans for this would be addressed during remedial design, as discussed in Alternative 2. Sampling and Testing Details of testing during construction are the same as Alternative 2, and include compaction testing and air monitoring. During remedial design the slope stability will be evaluated. Other physical and geotechnical properties testing of the NW Borrow Area, as discussed earlier in Alternative 2, will be used in the evaluation. Inspection, Monitoring, Maintenance and Institutional Controls The monitoring component of this alternative includes periodic inspection, maintenance and repair of the cap and stormwater controls over the long term as in Alternative 2. 11.2.1.5 Alternative 5 Excavate (BTA) (20’) + Excavate (CDA remedial area) (5’) + RCRA-

Equivalent Mono Soil Cap (BTA, CDA) (5’) + RCRA Cap (PCB Landfill) + Dispose of Excavated Soil + Stormwater Controls + ICs + Monitoring

This alternative involves the following components for each part of FS Area 1 (Figure 11-4A):

PCB Landfill covered with a RCRA cap over an area of 4.4 acres BTA is excavated to remove source waste material (0-20’ bgs) over an area of 5.5 acres CDA is excavated to remove shallow (0-5’ bgs) soil over an area of 18.8 acres Stormwater controls including drainage and erosion controls for the capped areas Place excavated wastes from other remedial actions in PCB Landfill prior to capping Allow use of pond water during cap construction for foundation layers or below HDPE

liners Institutional controls, maintenance and monitoring to protect the capped areas


Prevent ecological receptors from potential exposures to shallow soil (0-5 feet bgs) Prevent rainwater infiltration at the PCB Landfill, BTA and CDA and remove the source

waste material in the BTA Incorporate stormwater and erosion controls to minimize transport of contaminants via

stormwater sediments and allow discharge of stormwater from FS Area 1 via the NPDES General Permit


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RCRA Cap for the PCB Landfill This alternative includes a RCRA cap for the PCB Landfill as shown on Figures 11-4A and 11-4B. The conceptual design for the RCRA cap is the same as in Alternative 2 and the performance criteria for RCRA caps was discussed earlier in Section 10.1.1.1. Detailed specifications would be developed during remedial design. Excavation of BTA down to 20 feet bgs This excavation is intended to remove the wastes deposited in trenches in the BTA that are impacting groundwater. The FS assumes excavation of the entire footprint of the BTA because there is significant uncertainty in the locations of the trenches. Figure 11-4B shows the proposed excavation for the BTA that covers an area of 5.5 acres down to 20 feet bgs. This will ensure removal of the trench materials but not wastes disposed through injection wells that are present at deeper levels, extending down to about 40 feet bgs. However, excavation to greater depths would be considered if significant amounts of trench wastes were found to extend below the 20-foot depth. The excavation sidewalls would be sloped 1:1. Any existing surface features (e.g., drains) within the footprint of the excavation would be diverted before commencing the excavation. The total excavated soil volume for the BTA is approximately 180,000 cy. The excavated waste in trenches and other impacted soil are assumed to be 50 percent of the total excavated soil (about 90,000 cy). The excavated wastes are expected to be segregated and staged separately for disposal. The excavated trench waste material is assumed to be a combination of RCRA hazardous and non-RCRA hazardous, and is proposed for disposal at a permitted disposal facility for cost estimating purposes. These wastes are not assumed to be disposed of in the PCB Landfill because of the limited total capacity available that will be used for disposal of materials from other remedial excavations. Import fill or borrow soil of approximately 77,000 cy from the NW area would be used as backfill to replace the waste material removed. The soil will be placed in 2-foot lifts and compacted. Shallow soils in the top 5 feet will be tested to achieve a relative compaction of 90 percent. The RCRA-equivalent mono soil cap would be constructed on top of the backfilled BTA to minimize infiltration, as discussed below. Excavation of the Shallow Impacted Soils in CDA (5 feet bgs) Figure 11-4C shows the western portion of the CDA being excavated down to 5 feet bgs in order to remove shallow soil contaminants, and backfilled with clean soil. The total volume of this excavation is approximately 39,000 cy and covers about 4.8 acres. The extent and depth of the excavation is preliminary and would be confirmed during remedial design to ensure that risk-based standards are met. The sidewalls would be sloped at 1:1. The excavated soils are assumed to be non-RCRA hazardous (metals) and sent for disposal to a permitted facility for cost estimating purposes. About 42,900 cy of clean backfill would be required to backfill the excavation, which would be derived from the NW Borrow Area or imported. The backfill soil will be placed in 12-inch lifts and compacted to 90 percent relative compaction. Since portions of the excavation are on slopes that are steeper than 2:1, additional backfill soil will be used to reduce the slopes and prepare it for placement of the RCRA-equivalent mono soil cap. RCRA-Equivalent Mono Soil Cap for the BTA and CDA This alternative includes a RCRA-equivalent mono soil cap for the CDA and the BTA, as included in Alternative 2 and shown on Figure 11-4A. The conceptual design and performance standard for the RCRA-equivalent mono soil cap was discussed earlier in Section 10.1.1.2. The


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eastern side of the BTA cap would need to be tied into the P/S Landfill cap while the northern side of the CDA cap would need to be tied into the P/S Landfill and EE/CA Area caps. Details about the borrow soil, potential need for pre-processing, and the vegetative layer are as discussed earlier in Alternative 2. Cut and Fill Soil Volumes for Cap Construction and Excavation For the PCB Landfill, the cut/fill volume for leveling is 20,000 cy (Figure 11-4B). If excavated impacted soils from other areas (e.g., Pond sediments) of the site are placed in the PCB Landfill, up to approximately 140,000 cy of landfill space is available. The foundation layer will require a total of 16,000 cy of soil and the vegetative layer will require a total of 16,000 cy of soil. For the BTA, the total excavation soil volume is 180,000 cy, the backfill import soil volume is 99,000 cy, and the clay monocover cap will require a total of 49,000 cy of soil, derived primarily from the NW Borrow Area. For the CDA, the cut/fill volume for leveling is 150,000 cy and the clay monocover layer will require a total of 167,000 cy of soil, derived primarily from the NW Borrow Area. Stormwater Controls The details of the V-drains, bench roads, slopes of the cap surface and erosion controls are as discussed in Alternative 2. Preliminary locations of bench roads and drains are shown on Figures 11-4A, 11-4B and 11-4C. The perimeter collector drains, direction of stormwater flow from these capped areas, the culvert and the drainage channel near PSCT-1, and discharge of stormwater through Pond 13 to the B-Drainage wetlands is the same as in Alternative 2 (discharge governed by the existing General Permit). Existing Site Features All monitoring or extraction wells within FS Area 1 would be handled the same as in Alternative 2, except the 10 wells in the BTA would need to be demolished and reinstalled, as appropriate, due to the deep excavation of the BTA. Existing site roads and drains that are within the footprint of the capped areas would be reconstructed. Detailed plans for this would be addressed during remedial design, as discussed in Alternative 2. Sampling and Testing Details of testing during construction are the same as Alternative 2 including compaction testing and air monitoring, except during excavation of the BTA the extent of air sampling would be significantly greater due to the very large excavation of hazardous wastes. Air sampling during BTA excavation would require a greater number of samples per day and greater number of upwind and downwind samples to ensure that no contaminants are emitted from the excavation. Confirmatory soil sampling of the excavation sidewalls and bottom will be conducted to document conditions following completion of the excavation. During remedial design the slope stability will be evaluated. Other physical and geotechnical properties testing of the NW Borrow Area, as discussed earlier in Alternative 2, will be used in the evaluation. Inspection, Monitoring, Maintenance and Institutional Controls


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The monitoring component of this alternative includes periodic inspection, maintenance and repair of the cap and stormwater controls over the long term, as in Alternative 2. However, this alternative includes an increased amount of air monitoring for personnel to ensure there are no significant emissions of contaminants that may impact workers or other receptors. 11.2.2 Detailed and Comparative Analysis of Remedial Alternatives Table 11-2 presents the detailed evaluation of the five remedial alternatives with respect to the seven Threshold and Primary Balancing CERCLA criteria. As discussed earlier in Section 11.1, the last two criteria, namely Public Acceptance and Community Acceptance, are not included here. In addition to the CERCLA 9 criteria, a column is added in Table 11-2 for “green impacts assessment”. The detailed analysis is followed by the comparative analysis where the CERCLA criteria for each alternative are compared. 11.2.2.1 Overall Protection of Human Health and Environment Alternatives 2 through 5 are rated as protective of human health and environment while Alternative 1 is not. Alternatives 2, 3, and 5 with a RCRA-equivalent soil cap or an ET cap, and Alternative 4 with a RCRA cap are all protective with respect to ecological and human health by preventing direct contact exposures to contaminants in soil. Alternatives 2, 4 and 5 are also protective of the environment because of the low permeability nature of the respective cap design. Furthermore, Alternative 3 (ET soil cap) is considered RCRA-equivalent, which provides an equivalent level of environmental protection as the RCRA caps. These alternatives are equally protective of the environment because they prevent or minimize infiltration and thus protect groundwater. These alternatives also include the same stormwater controls to ensure clean stormwater runoff from the capped areas may be discharged under the substantive terms of the General Permit. 11.2.2.2 Compliance with ARARs Alternatives 2 through 5 would be in compliance with ARARs including the state rule requiring a restrictive covenant when waste is left in place beyond unrestricted use levels. Alternatives 2 through 5 would be in compliance with the requirements for RCRA landfill closure requirements for the PCB Landfill. 11.2.2.3 Long Term Effectiveness Alternatives 2 through 4 are all rated moderate to good while Alternative 5 is rated moderate. Alternative 2 with a RCRA-equivalent mono soil cap, Alternative 3 with the ET cap, and Alternative 4 with a RCRA cap would control the potential for direct contact exposure to contaminants for ecological receptors and workers. Alternative 5 involves excavation of the BTA down to 20 feet bgs and excavation of the impacted soils at the CDA down to 5 feet bgs, followed by the placement of a RCRA-equivalent mono soil cap and disposal of excavated soils at a permitted disposal facility. The disposal of excavated BTA soils at a permitted disposal facility results in a lowered rating due to concerns with transferring contaminant risks to remote locations. Alternatives 2 through 5 would achieve the RAO relating to groundwater protection because these are all effective in controlling infiltration. ICs and maintenance and monitoring of the caps are included as part of Alternatives 2 through 5, which ensure long term effectiveness. Also, stormwater controls to minimize erosion and contaminant migration are included with Alternatives 2 through 5. In general, capping options will provide a clean surface water runoff


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that would allow stormwater discharge via the under the substantive terms of the General Permit. 11.2.2.4 Reduction of Toxicity, Mobility and Volume through Treatment Alternatives 2, 3, and 4 are rated poor because these alternatives do not involve removal or destruction of contaminants through treatment. There is no reduction in toxicity or volume but a minor reduction in mobility of contaminants due to the low permeability soil caps at the CDA and BTA. Alternative 5 is rated higher at poor to moderate because it involves excavation of impacted soils that reduces toxicity, mobility and volume. However, it is not rated higher than poor to moderate because this reduction is not through treatment, nor is the removal complete. The low permeability mono soil cap in Alternative 5 will minimize surface water infiltration similar to Alternatives 2, 3 and 4. 11.2.2.5 Short Term Effectiveness Alternatives 2, 3 and 4 are rated moderate to good while Alternative 5 is rated poor to moderate. Alternative 5 is rated lower because it involves excavation of impacted wastes in the BTA and CDA remedial areas. The BTA has the potential to cause some emissions of contaminants as dust or VOCs, and may pose a risk to workers. The maximum depth of the excavation of 20 feet in the BTA poses potential physical risks to construction workers as well. Alternatives 2, 3 and 4 only involve limited disturbance of shallow soils as part of the leveling layer for construction of the caps and hence do not pose any significant increase in contaminant exposure risk. 11.2.2.6 Implementability Alternatives 2, 3 and 4 are rated good, while Alternative 5 is rated moderate. Alternative 5 is rated lower because of significant technical challenges and uncertainties associated with the excavation extent and handling of impacted soils and wastes in the trenches in the BTA. The capping and excavation technologies are well developed and will not need pilot testing, though some geotechnical testing, slope stability evaluation and soil properties testing from the Borrow Areas would be included during remedial design. No significant challenges are expected with administrative acceptance, and several vendors are available for these alternatives. Extensive capping has already been implemented at the site previously. 11.2.2.7 Cost The total present worth cost is presented for Alternatives 2 through 5 in the table below for net discount rates of 3 percent and 7 percent and timeframes of 30 years and 100 years in 2014 dollars. The cost for Alternative 1 is $0 and is not shown. Alternatives 2, 3 and 4 are about the same for present worth cost, while Alternative 5 is the highest. A lower contingency of 35 percent for capital cost is used for Alternatives 2, 3 and 4 because similar cap remedies have been implemented previously at the site.

Alt No.

Capital Cost Annual

Cost

Total Present Worth

Time Frame

Discount rate 3 percent


2 $12,286,000 $ 318,000 30-yr $17,253,000 $13,422,000

100-yr $22,117,000 $14,176,000 3 $11,177,000 $ 318,000 30-yr $16,267,000 $12,572,000


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100-yr $21,036,000 $13,311,000

4 $14,018,000 $ 318,000 30-yr $18,793,000 $14,749,000

100-yr $23,806,000 $15,526,000

5 $31,785,000 $ 318,000 30-yr $34,592,000 $28,365,000

100-yr $39,456,000 $29,119,000 11.2.2.8 Green Impacts Assessment The range of green technologies and BMPs that can play a role in minimizing environmental impacts of the remedial alternatives and technology components are discussed in Section 12.7. Appendix F provides a qualitative comparison of the different alternatives with respect to the green impacts assessment criteria. Appendix F also assesses the environmental footprint for these alternatives based on green remediation criteria such as GHG emissions, energy usage, air emissions, collateral risk, community impacts, resources lost, and water usage. The Appendix F evaluation was used to determine an overall rating for the alternative in Table 11-2. In the summary rating in Table 11-2, Alternatives 2, 3 and 4 are rated similar at moderate with respect to green and sustainability impacts while Alternative 5 is rated high because of the significantly greater amount of earthwork involved and greater impacts. The larger amount of earthwork implies a greater amount of time for the earth moving equipment, higher fuel use, GHG and other air emissions, and resource use. 11.2.3 Area 1 Evaluation Summary The active remedial alternatives for Area 1, Alternatives 2, 3, 4 and 5, meet the threshold requirements of Overall Protection of Human Health and Environment and Compliance with ARARs, while Alternative 1 (No Action) does not meet the threshold criteria. As a result, Alternative 1 is not evaluated for the balancing criteria. Of the active remedial alternatives, Alternatives 2, 3 and 4 are rated higher than Alternative 5 for the short term effectiveness and implementability criteria due to the greater risks, potential for exposures and the technical challenges with the deep excavation of the trenches in the BTA. Alternative 5 is also rated lower for LTE compared to Alternatives 2, 3 and 4. Excavating the trench wastes would not likely substantially improve groundwater contamination, particularly since the BTA is located immediately upgradient of the PSCT trench which is planned to be operated as part of the site remedy. Alternatives 2, 3 and 4 are rated very similar to each other with respect to the nine criteria and the green assessment. The highest rated remedial alternative is Alternative 4 because, while it has essentially the same costs as Alternative 2, the long term viability and reduced O&M requirements of a RCRA cap provide additional benefits for this alternative. Please note that RCRA caps currently exist on the landfills adjacent to Area 1, and tying-in a RCRA cap to the existing adjoining RCRA cap will present less challenges.

11.3 Detailed Evaluation for FS Area 2 This section presents the description of the active remedial alternatives, the detailed evaluation, the green impacts assessment evaluation, and the comparative analysis for FS Area 2. Nine remedial alternatives were selected in the screening evaluation in Section 10 for the detailed evaluation. Table 11-3 presents the detailed evaluation for the nine selected alternatives.


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11.3.1 Description of Remedial Alternatives The following is the description of the nine remedial alternatives for the detailed analysis. 11.3.1.1 Alternative 1 No Action The No Action alternative is included as required by CERCLA FS guidance. 11.3.1.2 Alternative 2 Ecological-Cap (West Slope RCRA Canyon, WCSA Remedial Area)(2’) +

Grading/BMPs (Uncapped Areas) + Stormwater Controls + ICs + Monitoring This alternative includes the following components for FS Area 2 (Figure 11-5A):

West slope of RCRA Canyon (West slope) covered with a 2-foot ecological-cap over an area of 8.4 acres

WCSA remedial area covered with a 2-foot ecological-cap over an area of 5.5 acres Other uncapped areas in RCRA Canyon and WCSA over an area of 19.3 acres including

grading with BMPs Reduce rainwater infiltration through improved drainage Use of pond water for cap construction for foundation layers will be evaluated in

remedial design Institutional controls, maintenance and monitoring to protect the capped areas


Prevent ecological receptors from potential exposures to shallow soil (0-5 feet bgs) Reduce rainwater infiltration into soil and groundwater at RCRA Canyon/WCSA study

areas and lower the groundwater level in the southern end of the canyon to eliminate seeps

Incorporate stormwater and erosion controls to minimize transport of contaminants via stormwater sediments

Direct stormwater to a 20-acre evaporation pond Ecological-Cap for the West Slope and WCSA Remedial Area This alternative involves capping metals-impacted soils identified in Appendix C on the West slope of RCRA Canyon remedial area (8.4 acres) and the WCSA remedial area (5.5 acres) with a 2-foot clean soil cap and biotic barrier (i.e., the ecological-cap which was discussed earlier in Section 10 of the FS) to control potential exposure to ecological receptors (Figures 11-5A, 11-5B). The 2-foot soil cap is placed in 12-inch lifts and compacted to a relative compaction of 90 percent (ASTM D 1557), and the top 6-inches are mixed with organic amendments that are lightly compacted for vegetation growth. Some cut/fill grading is assumed prior to capping to reduce the steepness of some of the sloped areas. The cap surface would include bench roads along the length of the canyon. Cut/Fill Soil Volumes for Cap Construction

The total cut/fill grading for leveling prior to capping is estimated to be about 100,000 cy for the West slope remedial area and 30,000 cy for the WCSA remedial area.

Total borrow soil that would be needed for the ecological-cap in the West slope remedial area would be 30,000 cy and in the WCSA remedial area would be 19,000 cy. Clean soil would be derived from the NW Borrow Areas (Figure 10-2) for cap construction.


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Stormwater Controls The top surface of the cap would be designed to collect and convey stormwater on the cap to the nearest collector drains along the perimeter roads (Figure 11-5B, 11-5C). The slopes of the top of the landfill cap would vary between 2:1 (H:V) and 4:1 (H:V). The cap surface will include bench roads for access and V-drains for stormwater drainage. Erosion control mats will be used in any small sections that have slopes steeper than 2:1 (H:V). Silt fences will be installed at the base of the construction areas to minimize contaminated soil transport as sediments. The bench roads will be constructed from 12-inch thick aggregate base. Rip-rap will be placed in the larger collector drains to slow the flow rate of surface runoff and reduce erosion. Erosion control measures (e.g., jute mesh) are incorporated into the cap and the top surface is hydroseeded as a vegetative layer. Turf reinforcement mats (TRMs) will be used for any slopes steeper than 2:1, including the uncapped areas. The stormwater from the capped West slope and WCSA remedial areas will be drained to the proposed retention basin in the footprint of Pond A-5 and then conveyed by pipeline to Pond 13 and discharged through or around the wetlands and via the B-drainage (discharge governed by the the substantive terms of the General Permit). The discharge from the other uncapped areas in the east slope and WCSA will be collected and piped to the proposed lined evaporation pond at the location of the existing A-Series Pond. This will result in a larger evaporation pond size requirement. Monitoring of the stormwater quality from the uncapped areas that incorporated BMPs and grading would be evaluated for possible discharge, if this alternative is selected. Existing Site Features All monitoring or extraction wells that are within the footprint of RCRA Canyon and WCSA will be extended with new surface completion above the cap surface and resurveyed. Existing site features and drains that are within the footprint of the proposed capped areas in this alternative would be reconstructed and likely relocated as perimeter roads and drains outside the capped areas. The detailed plans for the site roads and drains and how they would be connected to the drains in adjacent areas would be addressed during the remedial design phase. Sampling and Testing During remedial design, the slope stability will be evaluated as part of the cap design. During construction, the ecological-cap soil layer will be tested for compaction and permeability. In addition, shear strength and interface testing of the cap will be conducted during remedy implementation. Air monitoring would be conducted during the grading and cap construction activities. Soil physical and geotechnical properties will be tested for the proposed borrow area to ensure that adequate quality and quantity of soils is available. Inspection, Monitoring, Maintenance and Institutional Controls The monitoring component of this alternative includes periodic inspection, maintenance and repair of the cap and stormwater controls over the long term. Periodic inspection and maintenance of the cap is assumed to include monitoring for subsidence or cap erosion. Inspection is also assumed to include stormwater facilities such as V-drains, collector drains and culverts. Institutional controls include land use restrictions and site monitoring, security and fencing to protect public access for the long term. The cap and stormwater controls system will be inspected after a significant seismic event and after major storm events.


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11.3.1.3 Alternative 3 RCRA-Equivalent Mono Soil Cap (West Slope RCRA Canyon) (5’) +

Excavation (WCSA Remedial Area)(5’) + Grading/BMPs (Uncapped Areas) + Stormwater Controls + ICs + Monitoring

This alternative includes the following components for FS Area 2 (Figure 11-6A):

West slope of RCRA Canyon covered with a 5-foot soil cap over an area of 8.4 acres WCSA remedial area excavated down to 5 feet bgs over an area of 5.5 acres Other uncapped areas in RCRA Canyon and WCSA over an area of 19.3 acres including

grading with BMPs as part of erosion controls Stormwater controls include separate drain systems for the capped and uncapped

areas, and erosion controls for the capped areas Use of pond water for cap construction for foundation layers will be evaluated in



Prevent ecological-receptors from potential exposures to shallow soil (0-5 feet bgs) Minimize rainwater infiltration into soil and groundwater at RCRA Canyon remedial area Separate stormwater flow from the capped areas to enable discharge via the substantive

terms of the General Permit Incorporate stormwater and erosion controls (BMPs) to minimize transport of

contaminants via stormwater sediments and direct stormwater from capped areas through or around the wetlands under the substantive terms of the General Permit

Direct stormwater from uncapped areas to a proposed lined evaporation pond The following provides a brief description of the conceptual design for the remedial alternative components: RCRA-Equivalent Mono Soil Cap – West Slope RCRA Canyon Remedial Area This alternative includes a RCRA-equivalent mono soil cap for the West slope RCRA Canyon remedial area (8.4 acres) as shown on Figures 11-6A, 11-6B and 11-6C. The conceptual design and preliminary specifications of the RCRA-equivalent mono soil cap were discussed earlier in Section 10.1.1.2. Detailed specifications would be developed during remedial design. Borrow soil or construction process would be augmented as necessary to meet specifications. The clay soil would be borrowed from the NW Borrow Areas. The weathered claystone borrow material may need to be pulverized/crushed prior to use to meet the hydraulic conductivity performance criterion. These soils have been used previously during the P/S Landfill Cap project to achieve these performance criteria. These borrow area soils would be evaluated during remedial design. In the event supplemental clay soils are determined to be necessary, some clay soils from a location outside the site boundaries will be supplemented to ensure the cap meets specifications. Also, as a contingency, if adequate soil is not available from the NW Borrow Areas, another local source of soil such as the nearby Laguna Sanitation District site will be used. Bench roads would be incorporated on the surface of the cap along the length of the canyon. Excavation of 5 Feet in West Canyon Spray Area


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The excavation of the top 5 feet of the WCSA remedial area (5.5 acres) is estimated to be a total in-place volume of 44,000 cy (Figure 11-6B and 11-6C). The extent and depth of the excavation is preliminary and would be confirmed during design to ensure that risk-based standards are met. The sidewalls of the excavation will be sloped 1:1. The excavated soil would be transported to backfill Pond A-5 as part of the pond closure prior to it being lined (further discussed under FS Area 4). The excavated area will be backfilled by excavating soil in the adjacent areas of the WCSA to match grades. The backfilled soils will be placed in 12-inch lifts and compacted adequately to ensure that the soil cover provides a barrier to surface water infiltration. The goal of the backfill will be to meet a hydraulic conductivity in the range of 1x10-6 cm/sec to 1x10-4 cm/s. The backfilled area will be sloped to allow stormwater to drain to concrete drains that are directed towards the proposed evaporation pond. Grading and BMPs for Other Areas (19.3 acres) The other areas of FS Area 2 include the northern part of the WCSA and the east slopes of RCRA Canyon (Figure 11-6A). This alternative of the FS assumes the steepest slopes greater than 2:1 will be graded to reduce steepness and appropriate Best Management Practice (BMP) erosion control measures will be implemented. The BMPs would include jute mesh or turf reinforcement mats along steep slopes to reduce erosion. Silt fences will be included at the bottom of slopes at the canyon bottom to serve as a filter and minimize sediment transport with stormwater. Approval of the final design for the grading and BMPs of this alternative with the RWQCB is expected to be required, if it was selected. Cut and Fill Soil Volumes for Cap Construction and Excavation

For the West slope RCRA Canyon remedial area, the cut/fill volume for leveling is 100,000 cy (Figure 11-6B). The clay monocover layer will require a total of 75,000 cy of borrow soil primarily from the NW Borrow Areas.

For the WCSA remedial area, the in-place excavation volume for a 5-foot deep

excavation is 44,000 cy (Figure 11-6C). The excavation will be backfilled to match grades by grading shallow soils adjacent to the excavation area in the WCSA.

Stormwater Controls The top surface of the cap will be sloped and will incorporate drains and bench roads and erosion controls as discussed in Alternative 2, and as shown on Figure 11-6B and 11-6C. Design details of the layout of drains and bench roads would be addressed during remedial design. The stormwater from the capped West slope will be drained to the proposed retention basin in the footprint of Pond A-5 and then conveyed by pipeline to Pond 13 and discharged through or around the wetlands to the B-drainage (discharge governed by the substantive terms of the General Permit). The discharge from the other uncapped areas in the east slope and WCSA will be collected and piped to the proposed lined evaporation pond at the location of the A-Series Pond. This will result in a larger evaporation pond size requirement. Monitoring of the stormwater quality from the uncapped areas that incorporated BMPs and grading would be evaluated for possible discharge, if this alternative is selected. Existing Site Features


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All monitoring or extraction wells within the West slope capped area would be handled the same as in Alternative 2. Wells in the WCSA excavated area will be protected during excavation and completed to accommodate the finished surface elevation. Existing site roads and drains that are within the footprint of the capped areas would be reconstructed and detailed plans for this would be addressed during remedial design. Sampling and Testing Details of testing during construction are the same as Alternative 2, including compaction testing and air monitoring. Soil sampling of the excavation sidewalls and bottom will be conducted to determine limits of excavation and as confirmation sampling for the excavation. During remedial design, the slope stability will be evaluated to determine the steepest acceptable slope and shear strength requirements for cap stability. Also, other physical and geotechnical properties testing of the NW Borrow Areas would be conducted as discussed earlier in Alternative 2. Inspection, Monitoring, Maintenance and Institutional Controls The monitoring component of this alternative includes periodic inspection, maintenance and repair of the cap and stormwater controls over the long term as in Alternative 2. 11.3.1.4 Alternative 4 RCRA-Equivalent Mono Soil Cap (West slope RCRA Canyon, WCSA

Remedial Area) (5’) + Grading/BMPs (Uncapped Areas) + Stormwater Controls + ICs + Monitoring


West slope of RCRA Canyon covered with a 5-foot soil cap over an area of 8.4 acres WCSA remedial area covered with a 5-foot soil cap over an area of 5.5 acres Other uncapped areas in RCRA Canyon and WCSA over an area of 19.3 acres including

grading with BMPs as part of erosion controls Stormwater controls including separate concrete stormwater channels for the capped

and uncapped areas Use of pond water for cap construction for foundation layers will be evaluated in



Prevent ecological receptors from potential exposures to shallow soil (0-5 feet bgs) Minimize rainwater infiltration into soil and groundwater at RCRA Canyon and WCSA

remedial areas Segregate stormwater flow from the capped areas to enable discharge via the

substantive terms of the General Permit Incorporate stormwater and erosion controls (BMPs) to minimize transport of

contaminants via stormwater sediments and allow discharge of clean stormwater from capped areas through or around the wetlands under the substantive terms of the General Permit

The following provides a brief description of the conceptual design for the remedial alternative components: RCRA-Equivalent Mono Soil Cap for the West Slope and WCSA Remedial Area


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This alternative includes a RCRA-equivalent mono soil cap for the West slope RCRA Canyon remedial area (8.4 acres) and the WCSA remedial area (5.5 acres) as shown on Figures 11-7A, 11-7B and 11-7C. The conceptual design and preliminary specifications of the RCRA-equivalent mono soil cap were discussed earlier in Section 10.1.1.2. Detailed specifications would be developed during remedial design. The construction of the cap would start with the leveling layer that would include cut and fill to get the appropriate grade and slopes to construct the cap. The leveling process would reduce the areas of steep slopes to approximately 2:1 or less. The clay soil would be borrowed from the NW Borrow Areas and may need to be pulverized/crushed prior to use to meet the hydraulic conductivity performance criterion as discussed earlier in Alternative 3. Borrow soil or construction process would be augmented as necessary to meet specifications. Bench roads would be incorporated on the surface of the cap along the length of the canyon. Grading and BMPs for other Uncapped Areas (19.3 acres) The other areas of FS Area 2 include the northern part of the WCSA and the east slopes of RCRA Canyon. The steepest slopes greater than 2:1 will be graded to reduce steepness and BMP erosion control measures will be implemented. The BMPs would include jute mesh, turf reinforcement mats and silt fences as discussed earlier in Alternative 3. Approval of the final design for the grading and BMPs of this alternative with the RWQCB is expected to be required, if it was selected. Cut and Fill Soil Volumes for Cap Construction and Excavation

For RCRA Canyon remedial area, the cut/fill volume for leveling is 100,000 cy (Figure 11-7B). The clay monocover layer will require a total of 75,000 cy of soil primarily from the NW Borrow Areas.

For the WCSA remedial area, the cut/fill volume for leveling is 30,000 cy (Figure 11-7B).

The clay monocover layer will require a total of 54,000 cy of soil primarily from the NW Borrow Areas.

Stormwater Controls The top surface of the cap will be sloped and will incorporate drains and bench roads and erosion controls as discussed in Alternative 2, and as shown on Figure 11-7B and 11-7C. Design details of the layout of drains and bench roads would be addressed during remedial design. The stormwater from the capped West slope and WCSA remedial area will be drained to the proposed retention basin in the footprint of Pond A-5 and then conveyed by pipeline to Pond 13 and discharged through or around the wetlands and to the B-drainage (discharge governed by the substantive terms of the General Permit). The discharge from the other uncapped areas in the east slope and WCSA will be collected and piped to the proposed lined evaporation pond at the location of the A-Series Pond. If the stormwater runoff meets the preliminary stormwater benchmarks of the General Permit (Table 8-5), it may be possible to discharge these volumes under the substantive terms of the General Permit. This option will be discussed with the RWQCB if sampling of the stormwater after remedy construction meets those criteria.


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Existing Site Features All monitoring or extraction wells within West slope and WCSA capped areas would be handled the same as in Alternative 2. Existing site roads and drains that are within the footprint of the capped areas would be reconstructed and detailed plans for this would be addressed during remedial design. Sampling and Testing Details of testing during construction are the same as Alternative 2 including compaction testing and air monitoring. During remedial design, the slope stability will be evaluated to determine the steepest acceptable slope and shear strength requirements for cap stability. Also, other physical and geotechnical properties testing of the NW Borrow Area would be conducted as discussed earlier in Alternative 2. Inspection, Monitoring, Maintenance and Institutional Controls The monitoring component of this alternative includes periodic inspection, maintenance and repair of the cap and stormwater controls over the long term as in Alternative 2. 11.3.1.5 Alternative 5 RCRA-Equivalent Mono Soil Cap (West slope RCRA Canyon) (5’) +

Excavation (WCSA Remedial Area)(5’) + Clean Soil Cover (Uncapped areas)(2’) + Stormwater Controls + ICs + Monitoring


West slope of RCRA Canyon covered with a 5-foot soil cap over an area of 8.4 acres WCSA remedial area excavated down to 5 feet bgs over an area of 5.5 acres Other uncapped areas in RCRA Canyon and WCSA over an area of 19.3 acres are

covered with 2-foot soil cover Stormwater controls include V-drains to collect stormwater on the cap and a concrete

drainage channel down the middle of the canyon for the West slope and WCSA areas Use of pond water for cap construction for foundation layers will be evaluated in



Prevent ecological receptors from potential exposures to shallow soil (0-5 feet bgs) Minimize rainwater infiltration into soil and groundwater at RCRA Canyon remedial area Incorporate stormwater and erosion controls (BMPs) to minimize transport of

contaminants via stormwater sediments One combined stormwater flow from the entire RCRA Canyon and WCSA areas to

enable discharge through the or around via the substantive terms of the General Permit This alternative is similar to Alternative 3 but adds a 2-foot soil cover to the other uncapped areas in FS Area 2. The following provides a brief description of the conceptual design for the remedial alternative components: RCRA-Equivalent Mono Soil Cap for the West Slope Remedial Area


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This alternative includes a RCRA-equivalent mono soil cap for the West slope RCRA Canyon remedial area (8.4 acres) as shown on Figures 11-8A, 11-8B and 11-8C. The conceptual design is as discussed for Alternative 3, and preliminary specifications of the RCRA-equivalent mono soil cap were discussed earlier in Section 10.1.1.2. Detailed specifications would be developed during remedial design. The clay soil would be borrowed from the NW Borrow Areas and may need to be pulverized/crushed prior to use to meet the hydraulic conductivity performance criterion as discussed earlier in Alternative 3. Borrow soil or construction process would be augmented as necessary to meet specifications. Bench roads would be incorporated on the surface of the cap along the length of the canyon. Excavation of 5 feet in WCSA Remedial Area The excavation of the top 5 feet of the WCSA remedial area (5.5 acres) is estimated to be a total in-place volume of 44,000 cy (Figure 11-8C). The extent and depth of the excavation is preliminary and would be confirmed during design to ensure that risk-based standards are met. The sidewalls of the excavation will be sloped 1:1. The excavated soil would be transported to backfill Pond A-5 as part of the pond closure prior to it being lined (further discussed under FS Area 4). The excavated area will be backfilled by excavating soil in the adjacent areas of the WCSA to match grades. The backfilled soils will be placed in 12-inch lifts and compacted adequately to ensure that the soil cover provides a barrier to surface water infiltration. The goal of the backfill will be to meet a hydraulic conductivity in the range of 1x10-6 cm/sec to 1x10-4 cm/s. The backfilled area will be sloped to allow stormwater to drain to concrete drains that are directed towards the proposed evaporation pond. 2-foot Clean Soil Cover for all Areas Outside the West Slope Cap (24.8 acres) The 2-foot clean soil cover will cover all uncapped areas outside of the West slope capped area including the 5.5 acres of the WCSA remedial area and 19.3 acres of other areas in FS Area 2 (Figure 11-8A). The 2-foot clean soil cover will be placed in 12-inch lifts and compacted to a relative compaction of 90 percent (ASTM D 1557) and the top 6-inches will be mixed organic amendments and will be lightly compacted for vegetation growth. The other areas include the northern part of the WCSA and the east slopes of RCRA Canyon. Some portions of the east slope are very steep (steeper than 2:1) and compacting the 2-foot soil cover may pose technical challenges. The steepest slopes will be graded to reduce steepness to a maximum of 2:1 slope and erosion protection measures will be implemented. These include jute mesh or turf reinforcement mats along steep slopes to reduce erosion. Silt fences will be included at the bottom of slopes at the canyon bottom to serve as a filter and minimize sediment transport with stormwater. Some areas that are very steep in the east slope may only use erosion control mats (e.g. turf reinforcement mats) if the 2-foot soil cover cannot be effectively placed and compacted due to steepness. Cut and Fill Soil Volumes for Leveling/Cap Construction and Excavation

For RCRA Canyon remedial area, the cut/fill volume for leveling is 100,000 cy (Figure 11-8B). The clay monocover layer will require a total of 75,000 cy of soil primarily from the NW Borrow Areas.

For the WCSA remedial area, the excavation volume for a 5-foot deep excavation is

44,000 cy (Figure 11-8C). The excavation will be backfilled to match grades by grading shallow soils adjacent to the excavation area in the WCSA.


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For the uncapped areas, the 2-foot clean soil cover would require a cut/fill volume of 300,000 cy and the soil cover will use a total of 88,000 cy from the NW Borrow Areas

Prior to placing the 2-foot soil cap, grubbing and grading of the uncapped areas is included as part of this alternative to prepare the surface for the 2-foot soil cover. A total of 88,000 cy of import soil from the NW Borrow Areas would be required for this. Stormwater Controls The top surface of the cap will be sloped and will incorporate drains and bench roads and erosion controls as discussed in Alternative 2 and as shown on Figure 11-8B and 11-8C. Design details of the layout of drains and bench roads would be addressed during remedial design. With this alternative, all of the stormwater from RCRA Canyon and WCSA will be drained through one combined concrete channel at the bottom of the canyon to the proposed retention basin in the footprint of Pond A-5. From there it will be conveyed by pipeline to Pond 13 and discharged through or around the wetlands and via the B-drainage (discharge governed by the substantive terms of the General Permit). This will reduce the size of the evaporation pond requirement compared to Alternative 3. There will be a small section in the south end of WCSA that will sheet flow directly into the proposed evaporation pond in the footprint of the A-Series Pond. Existing Site Features All monitoring or extraction wells within the West slope capped area would be handled the same as in Alternative 2. Wells in the WCSA excavated area will be protected during excavation. All wells in the WCSA backfilled area and other uncapped areas will be raised to the final cap surface elevation and resurveyed. Existing site roads and drains that are within the footprint of the capped areas would be reconstructed and detailed plans for this would be addressed during remedial design. Sampling and Testing Details of testing during construction are the same as Alternative 2 including compaction testing and air monitoring. During remedial design, the slope stability will be evaluated to determine the steepest acceptable slope and shear strength requirements for cap stability. Also, other physical and geotechnical properties testing of the NW Borrow Areas would be conducted as discussed earlier in Alternative 2. Inspection, Monitoring, Maintenance and Institutional Controls The monitoring component of this alternative includes periodic inspection, maintenance and repair of the cap and stormwater controls over the long term as discussed earlier in Alternative 2. 11.3.1.6 Alternative 6 RCRA-Equivalent Hybrid Cap (West slope RCRA Canyon)(5’) +

Excavation (WCSA remedial area) + Clean Soil Cover (Uncapped areas)(2’) + Stormwater Controls + ICs + Monitoring



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West slope of RCRA Canyon covered with a RCRA-Equivalent hybrid cap over an area of 8.4 acres

WCSA remedial area excavated down to 5 feet bgs over an area of 5.5 acres Other uncapped areas in RCRA Canyon and WCSA over an area of 19.3 acres are

covered with 2-foot soil cover Stormwater controls including separate concrete stormwater channels for the capped

and uncapped areas Use of pond water for cap construction for foundation layers will be evaluated in



Prevent ecological receptors from potential exposures to shallow soil (0-5 feet bgs) Minimize rainwater infiltration into soil and groundwater at RCRA Canyon remedial area Incorporate stormwater and erosion controls (BMPs) to minimize transport of


One combined stormwater flow from the entire RCRA Canyon and WCSA areas to enable discharge through or around the wetlands via the substantive terms of the General Permit

The following provides a brief description of the conceptual design for the remedial alternative components: RCRA-Equivalent Hybrid Cap for the West Slope RCRA Canyon This alternative includes a RCRA-equivalent hybrid cap for the West slope RCRA Canyon remedial area (8.4 acres) as shown on Figures 11-9A, 11-9B and 11-9C. This alternative is similar to Alternative 5 except it uses a RCRA-equivalent hybrid cap instead of a RCRA-equivalent mono soil cap. The conceptual design and preliminary specifications of the RCRA-equivalent hybrid cap were discussed earlier in Section 10.1.1.4. Detailed specifications would be developed during remedial design. The construction of the cap would start with the leveling layer that would include cut and fill to get the appropriate grade and slopes to construct the cap. The leveling process would reduce the areas of steep slopes to approximately 2:1 or less. A textured HDPE membrane with spikes would be placed on the foundation layer. The spikes on the underside of the membrane help to increase resistance to potential slippage on steep slopes (e.g. 2:1 or steeper). A geocomposite drainage layer would be placed on top of the membrane, overlain by a 2-foot vegetative layer that is hydroseeded as discussed in Section 10.1.1.4. The soils for the foundation and vegetative layer would be obtained from the NW Borrow Areas as discussed for other alternatives. Excavation of 5 feet in WCSA Remedial Area The excavation of the top 5 feet of WCSA is estimated to be a total volume of 44,000 cy (Figure 11-9C). The extent and depth of the excavation is preliminary and would be confirmed during design to ensure that risk-based standards are met. The details of the excavation, backfill and stormwater drains are the same as in Alternative 5. 2-foot Clean Soil Cover for all Areas Outside the West Slope Cap (24.8 acres)


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The 2-foot clean soil cover will cover all uncapped areas outside of the west slope capped area, including the 5.5 acres of the WCSA remedial area and 19.3 acres of other areas in FS Area 2 (Figure 11-9C). The details of the 2-foot clean soil cover including compaction and stormwater drains are the same as in Alternative 5. Cut and Fill Soil Volumes for Cap Construction and Excavation

For RCRA Canyon west slope remedial area, the cut/fill volume for leveling is 100,000 cy (Figure 11-9C). The vegetative layer will require a total of 30,000 cy of soil primarily from the NW Borrow Areas.

For the WCSA remedial area, the excavation volume for a 5-foot deep excavation is

44,000 cy (Figure 11-9C).

For the uncapped areas, the 2-foot clean soil cover would require a cut/fill volume of 300,000 cy and the soil cover would require 88,000 cy from the NW Borrow Areas

Stormwater Controls The top surface of the cap will be sloped and will incorporate drains and bench roads and erosion controls, as discussed in Alternative 2 and as shown on Figure 11-9B and 11-9C. Design details of the layout of drains and bench roads would be addressed during remedial design. With this alternative, all of the stormwater from RCRA Canyon and WCSA will converge into a single concrete channel at the bottom of the canyon that will be routed to the proposed retention basin in the footprint of Pond A-5. From there it will be conveyed by pipeline to Pond 13 and discharged through or around the wetlands and to the B-drainage wetlands (discharge governed by the substantive terms of the General Permit). This will reduce the size of the evaporation pond requirement compared to Alternative 3. There will be a small section in the south end of WCSA that will sheet flow directly into the proposed evaporation pond in the footprint of the A-Series Pond. Existing Site Features All monitoring or extraction wells within the West slope and WCSA capped areas would be handled the same as in Alternative 2. Wells in the WCSA excavated area will be protected during excavation. All wells in the WCSA backfilled area and other uncapped areas would be raised to the final cap surface elevation and resurveyed. Existing site roads and drains that are within the footprint of the capped areas would be reconstructed and detailed plans for this would be addressed during remedial design. Sampling and Testing Details of testing during construction are the same as Alternative 2, including compaction testing and air monitoring. Interface testing would also be conducted during construction to test suitability the spiked membrane interface. During remedial design, the slope stability will be evaluated to determine the steepest acceptable slope and shear strength requirements for cap


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stability. Also, other physical and geotechnical properties testing of the NW Borrow Areas would be conducted as discussed earlier in Alternative 2. Inspection, Monitoring, Maintenance and Institutional Controls The monitoring component of this alternative includes periodic inspection, maintenance and repair of the cap and stormwater controls over the long term as in Alternative 2. 11.3.1.7 Alternative 7 Evapotranspirative (ET) Cap (West slope RCRA Canyon) (5’) + Excavation (WCSA remedial area) + Clean Soil Cover (Uncapped areas)(2’) + Stormwater Controls + ICs + Monitoring This alternative includes the following components for FS Area 2 (Figure 11-10A):

• West slope of RCRA Canyon covered with a 5-foot low permeability evapotranspirative (ET) soil cap over an area of 8.4 acres

• WCSA remedial area excavated down to 5 feet bgs over an area of 5.5 acres • Other uncapped areas in RCRA Canyon and WCSA over an area of 19.3 acres covered

with 2-foot soil cover • Stormwater controls including separate concrete stormwater channels for the capped

and uncapped areas • Use of pond water for cap construction for foundation layers will be evaluated in

remedial design • Institutional controls, maintenance and monitoring to protect the capped areas


• Prevent ecological receptors from potential exposure to shallow soil (0-5 feet bgs) • Minimize rainwater infiltration into soil and groundwater at RCRA Canyon remedial area • Incorporate stormwater and erosion controls (BMPs) to minimize transport of


• One combined stormwater flow from the entire RCRA Canyon and WCSA areas to enable discharge through or around the wetlands via the substantive terms of the General Permit

The following provides a brief description of the conceptual design for the remedial alternative components: ET Soil Cap for the West slope RCRA Canyon This alternative includes an ET cap for the west slope of RCRA Canyon as shown on Figures 11-10A, 11-10B and 11-10C. The ET cap would consist of a 1-foot thick foundation layer with clay soil compacted to 90 percent (ASTM D 1557) and 4 feet of claylike soil that is lightly compacted to about 85 percent for the vegetative layer. A more detailed description of the ET cap and the cap performance criteria was presented in Section 10.1.1. The ET cap is intended to store water, thus allowing the growth of vegetation and the removal of soil moisture through evaporation and transpiration. Preliminary specification for the ET soil cap soil is that it be classified by the Unified Soil Classification System as CL, SC or ML and have greater than 50 percent fines content. Detailed specifications would be developed during remedial design. The clay soil would be borrowed from the NW Borrow Area. The weathered claystone borrow


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material may need to be screened, pulverized/crushed in a pug mill (or with a pulverizer), and moisture conditioned prior to placement to meet the performance criterion for the ET cap. A brief discussion of the pre-processing requirements and amendments required is presented in Section 10.1.2, based on experience from prior capping projects. Excavation of 5 feet in WCSA Remedial Area The excavation of the top 5 feet of WCSA is estimated to be a total volume of 44,000 cy (Figure 11-10C). The extent and depth of the excavation is preliminary and would be confirmed during design to ensure that risk-based standards are met. The details of the excavation, backfill and stormwater drains are the same as in Alternative 5. 2-foot Clean Soil Cover for all Areas Outside the West Slope Cap (24.8 acres) The 2-foot clean soil cover will cover all uncapped areas outside of the west slope capped area, including the 5.5 acres of the WCSA remedial area and 19.3 acres of other areas in FS Area 2 (Figure 11-10C). The details of the 2-foot clean soil cover including compaction and stormwater drains are the same as in Alternative 5. Cut and Fill Soil Volumes for Cap Construction and Excavation

For RCRA Canyon remedial area, the cut/fill volume for leveling is approximately 100,000 cy and the borrow soil volume for the cap construction is 75,000 cy (Figure 11-10C).

For the WCSA remedial area, the excavation volume for a 5-foot deep excavation is 44,000 cy (Figure 11-10C). The excavated soil would be transported and placed as fill to close Pond A-5.

For the uncapped areas, the 2-foot clean soil cover would require a cut/fill volume of 300,000 cy and the soil cover would require 88,000 cy from the NW Borrow Areas

Stormwater Controls The top surface of the cap will be sloped and will incorporate drains and bench roads and erosion controls as discussed in Alternative 2, and as shown on Figures 11-10A and 11-10B. Design details of the layout of drains and bench roads would be addressed during remedial design. The details of the stormwater drainage are the same as in Alternative 5. Existing Site Features All monitoring or extraction wells within the West slope and WCSA capped areas would be handled the same as in Alternative 2. Wells in the WCSA excavated area will be protected during excavation. All wells in the WCSA backfilled area and other uncapped areas will be raised to the final cap surface elevation and resurveyed. Existing site roads and drains that are within the footprint of the capped areas would be reconstructed and detailed plans for this would be addressed during remedial design. Sampling and Testing Details of testing during construction are the same as Alternative 2 including compaction testing and air monitoring. During remedial design, the slope stability will be evaluated to determine the


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steepest acceptable slope and shear strength requirements for cap stability. Also, other physical and geotechnical properties testing of the NW Borrow Areas would be conducted as discussed earlier in Alternative 2. Inspection, Monitoring, Maintenance and Institutional Controls The monitoring component of this alternative includes periodic inspection, maintenance and repair of the cap and stormwater controls over the long term as in Alternative 2. 11.3.1.8 Alternative 8 RCRA-Equivalent Hybrid Cap (entire RCRA Canyon, WCSA) +

Stormwater Controls + ICs + Monitoring This alternative includes the following components for FS Area 2 (Figure 11-11A):

Entire RCRA Canyon and WCSA covered with a RCRA-equivalent hybrid cap including West slope of RCRA Canyon, WCSA remedial area and other uncapped areas (33.2 acres)

Stormwater controls including a concrete stormwater channel for the entire capped RCRA Canyon and WCSA

Use of pond water for cap construction for foundation layers will be evaluated in remedial design

Institutional controls, maintenance and monitoring to protect the capped areas The objectives of this remedial alternative are:

Prevent ecological receptors from potential exposures to shallow soil (0-5 feet bgs) Minimize rainwater infiltration into soil and groundwater at RCRA Canyon and WCSA

remedial areas Segregate stormwater flow from the capped areas to enable discharge via the site’s

General Permit Incorporate stormwater and erosion controls (BMPs) to minimize transport of


The following provides a brief description of the conceptual design for the remedial alternative components: RCRA-Equivalent Hybrid Cap for the Entire RCRA Canyon and WCSA This alternative includes a RCRA-equivalent hybrid cap for the entire RCRA Canyon and the WCSA including the West slope (8.4 acres), WCSA remedial area (5.5 acres) and other areas (19.3 acres) as shown on Figures 11-11A, 11-11B and 11-11C. The conceptual design and preliminary specifications of the RCRA-equivalent hybrid cap were discussed earlier in Section 10.1.1.4. Detailed specifications would be developed during remedial design. The construction of the cap would start with the leveling layer that would include cut and fill to get the appropriate grade and slopes to construct the cap. The amount of cut/fill grading is expected to be very large (approximately 455,000 cy) because of the very steep slopes (almost 1:1) present in the east slopes outside the West slope and WCSA remedial areas. The leveling process would reduce the areas of steep slopes to approximately 2:1 or less. An HDPE membrane with spikes would be placed on the foundation layer. The spikes on the underside of the membrane help


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resist potential slippage of the membrane on steep slopes (e.g., 2:1 or steeper). The construction process for this cap would be identical to Alternative 6 discussed earlier. Cut and Fill Soil Volumes for Cap Construction and Excavation

For RCRA Canyon remedial area, the cut/fill volume for leveling is 100,000 cy (Figure 11-11C). The vegetative layer will require a total of 30,000 cy of soil primarily from the NW Borrow Areas.

For the WCSA remedial area, the cut/fill volume for leveling is 30,000 cy (Figure 11-11C). The vegetative layer will require a total of 19,000 cy of soil primarily from the NW Borrow Areas.

For the other areas (19.3 acres), the cut/fill volume for leveling is estimated to be approximately 300,000 cy (Figure 11-11B) to achieve a 2:1 slope. The vegetative layer will require a total of 68,000 cy of soil primarily from the NW Borrow Areas.

Stormwater Controls The top surface of the cap will be sloped and will incorporate drains and bench roads and erosion controls as discussed in Alternative 2 and as shown on Figure 11-11B and 11-11C. Design details of the layout of drains and bench roads would be addressed during remedial design. With this alternative, all of the stormwater from RCRA Canyon and WCSA will be drained through one combined concrete channel at the bottom of the canyon to the proposed retention basin in the footprint of Pond A-5. From there it will be conveyed by pipeline to Pond 13 and discharged via the B-drainage (discharge governed by the substantive terms of the General Permit). This will reduce the size of the evaporation pond requirement compared to Alternative 3. There will be a small section in the south end of WCSA that will sheet flow directly into the proposed evaporation pond in the footprint of the A-Series Pond. Existing Site Features All monitoring or extraction wells that lie within RCRA Canyon and WCSA remedial areas will be extended to the new surface completion of the capped surface and resurveyed. Existing site roads and drains that are within the footprint of the capped areas would be reconstructed and detailed plans for this would be addressed during remedial design. Sampling and Testing Details of testing during construction are the same as Alternative 2 including compaction testing and air monitoring. Interface testing would also be conducted during construction to test the spiked membrane interface. During remedial design, the slope stability will be evaluated to determine the steepest acceptable slope and shear strength requirements for cap stability. Also, other physical and geotechnical properties testing of the NW Borrow Area would be conducted as discussed earlier in Alternative 2. Inspection, Monitoring, Maintenance and Institutional Controls


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The monitoring component of this alternative includes periodic inspection, maintenance and repair of the cap and stormwater controls over the long term as discussed earlier in Alternative 2. 11.3.1.9 Alternative 9 ET Cap (entire RCRA Canyon, WCSA) + Stormwater Controls + ICs + Monitoring This alternative includes the following components for FS Area 2 (Figure 11-12A):

• Entire RCRA Canyon and the WCSA covered with a 5-foot low permeability ET soil cap over an area of 33.2 acres

• Stormwater controls including a concrete stormwater channel for the entire capped RCRA Canyon and WCSA

• Use of pond water for cap construction for foundation layers will be evaluated in remedial design

• Institutional controls, maintenance and monitoring to protect the capped areas The objectives of this remedial alternative are:

• Prevent ecological receptors from potential exposures to shallow soil (0-5 feet bgs) • Minimize rainwater infiltration into soil and groundwater at RCRA Canyon and WCSA

remedial areas • Incorporate stormwater and erosion controls (BMPs) to minimize transport of


• One combined stormwater flow from the entire RCRA Canyon and WCSA areas to enable discharge through or around the wetlands via the substantive terms of the General Permit

The following provides a brief description of the conceptual design for the remedial alternative components: ET Soil Cap for RCRA Canyon and WCSA This alternative includes an ET for the entire RCRA Canyon and the WCSA, for a total acreage of 33 acres, as shown on Figure 11-12A and 11-12C. The conceptual design of the ET cap is the same as in Alternative 7, and the cap performance criteria were presented earlier in Section 10.1.1. Cut and Fill Soil Volumes for Cap Construction For RCRA Canyon remedial area, the cut/fill volume for leveling is 280,000 cy (Figure 11-12C). The clay ET Cover will require a total of 295,000 cy of borrow soil primarily from the NW Borrow Area. Some grading and additional borrow soil may be required for this alternative to reduce the steepness of some of the sloped areas in order to install the cap. Stormwater Controls The final surface of the cap on RCRA Canyon and the WCSA will be sloped and will incorporate drains and bench roads and erosion controls as discussed in Alternative 2. The conceptual plan


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for the drains and bench roads are the same as Alternative 8 and are shown on Figures 11-12B and 11-12C. Design details of the layout of drains and bench roads would be addressed during remedial design. Existing Site Features All monitoring or extraction wells within RCRA Canyon and WCSA capped areas would be handled the same as in Alternative 2. Existing site roads and drains that are within the footprint of the capped areas would be reconstructed and detailed plans for this would be addressed during remedial design. Sampling and Testing Details of testing during construction are the same as Alternative 2 including compaction testing and air monitoring. During remedial design, the slope stability will be evaluated to determine the steepest acceptable slope and shear strength requirements for cap stability. Also, other physical and geotechnical properties testing of the NW Borrow Area would be conducted as discussed earlier in Alternative 2. Inspection, Monitoring, Maintenance and Institutional Controls The monitoring component of this alternative includes periodic inspection, maintenance and repair of the cap and stormwater controls over the long term as in Alternative 2. 11.3.2 Detailed and Comparative Analysis of Remedial Alternatives Table 11-3 presents the detailed evaluation of the nine remedial alternatives with respect to the seven Threshold and Primary Balancing CERCLA criteria. As discussed earlier in Section 11.1, the last two criteria namely, Public Acceptance and Community Acceptance are not included here. In addition to the CERCLA 9 criteria, a column is added in Table 11-3 for “green assessment”. The detailed analysis is followed by the comparative analysis where for each CERCLA criteria the ratings and performance of each alternative is compared. 11.3.2.1 Overall Protection of Human Health and Environment Alternatives 2 through 9 are considered protective of human health and the environment, with Alternatives 2, 4, 8 and 9 involving primarily capping that would ensure that the ecological receptors and workers are protected from contaminants in shallow soil in impacted soil areas. Alternative 3 would be protective because it involves a combination of capping for the West slope area and excavation for the WCSA remedial area. Alternatives 5 and 7 are similar to Alternative 3 but add a 2-foot clean soil cover to the uncapped areas in order to improve stormwater quality, and discharges all RCRA Canyon/WCSA stormwater under the site’s General Permit. Alternative 6 is similar to Alternative 3, but uses a RCRA-equivalent hybrid cap instead of a RCRA-equivalent mono soil cap. Alternative 8 would cap the entire canyon with a RCRA-equivalent hybrid geosynthetic cap and would allow stormwater to be discharged. Alternative 9 is similar to Alternative 8, but uses an ET cap over the entire canyon. Alternatives 2, 3, and 4 would split the capped and uncapped stormwater flows and direct uncapped stormwater to a proposed evaporation pond. ICs with each of these alternatives would ensure that future property owners and workers are aware of residual contamination under the cap and


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potential exposures, and the long term maintenance requirements of the caps and the stormwater controls. 11.3.2.2 Compliance with ARARs Alternatives 2 through 9 are rated yes while Alternative 1 is not considered compliant with ARARs. 11.3.2.3 Long Term Effectiveness In regard to LTE, Alternative 2 is rated poor to moderate while Alternatives 3 and 4 are rated higher at moderate and Alternatives 5 through 9 are rated moderate to good. Alternatives 2 through 9 would all control direct contact exposure to soil contaminants for ecological receptors and address ecological risk concerns. However, for Alternative 2 with the ecological-cap, the long term performance of the ecological-cap is uncertain. The ecological-cap may need more frequent cap repair and maintenance given the slopes of the canyon. With the ecological-cap, rainwater infiltration through impacted soils will not be significantly reduced. Alternatives 3 through 9 include RCRA-equivalent caps, hybrid caps or ET caps, which can significantly reduce rainwater infiltration, or excavation of contaminants – all of which are more protective of groundwater. Alternatives with a RCRA-equivalent mono soil cap (conductivity = 1x10-6 cm/s) or ET cap are not significantly different from a HDPE geomembrane cap (say 1x10-8 cm/sec) with respect to infiltration and water table lowering, as shown by the HELP model and Groundwater Flow Model (Appendix D). Alternatives 3 through 9 would all be effective in the short term in preventing direct contact and infiltration to protect groundwater. However, amongst these alternatives, Alternatives 3 and 4 primarily address only the remedial areas identified based on ecological risk. Alternatives 5, 6 and 7 that add a 2-foot soil cover over the uncapped areas and Alternatives 8 and 9 are more aggressive alternatives that cap the entire RCRA Canyon/WCSA remedial areas and would be expected to be better in LTE. However, with the steep east slopes of the canyon (2:1 slope after cut/fill grading), the 2-foot soil cover may have erosion concerns and need more maintenance in the long term. Also, the geosynthetic HDPE membrane has the potential for slip failure where the soil caps (e.g., RCRA-equivalent clay monocover or ET cap) would likely fare better. Alternatives 8 and 9 would be rated the highest with respect to LTE because it minimizes infiltration and is most reliably effective in meeting the RAOs in the long term. With the ecological-cap in Alternative 2 all stormwater from the canyon would need to be directed to the evaporation pond, which may pose challenges with pond water management during wet years. With Alternatives 3 and 4, the stormwater flows would be segregated and the capped area stormwater flow would be discharged to the B-Drainage under the substantive terms of the General Permit. With Alternatives 3 and 4, the uncapped areas include grading and BMPs to incorporate erosion and sediment control measures. However, in these cases it has been conservatively assumed the uncapped area stormwater would be directed to the evaporation pond for management. Alternative 5, 6 and 7 include a 2-foot soil cover over the uncapped areas and with this the stormwater from the entire RCRA Canyon and WCSA are combined and directed as clean stormwater to the B-Drainage, similar to Alternatives 8 and 9. ICs with each of these alternatives would ensure that future property owners and workers are aware of residual contamination under the cap and potential exposures.


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11.3.2.4 Reduction of Toxicity, Mobility and Volume through Treatment Alternatives 2 through 9 are rated poor because they primarily utilize capping or to a limited extent excavation and placement of impacted soils under a cap or membrane elsewhere at the site. Though it should be noted that Alternatives 5 through 9 could be marginally better because they more reliably control mobility and potential exposure to the contaminants in the long term and they allow all of RCRA Canyon stormwater to be discharged and thus not require an evaporation pond. 11.3.2.5 Short Term Effectiveness Alternatives 2 through 9 are all rated moderate to good because there are no significant risks, potential exposures to human or ecological receptors or impacts to the environment with these alternatives. Minor risks include potential exposures during cut/fill grading for leveling layer for cap construction and dust from excavation. All cap soils are clean soils from the NW Borrow Area and do not pose any concerns. 11.3.2.6 Implementability Alternatives 2, 3, and 4 are rated moderate to good while Alternatives 5, 6, 7, 8 and 9 are rated lower at moderate. The technical challenges with implementation are relatively small in the remedial areas where the slopes can be more easily reduced by cut/fill grading. Alternatives 5, 6, 7, 8 and 9 are rated lower at moderate because of the challenges with placing the membrane and compaction of the soil on steep east slopes (almost 1:1) of the canyon and the extensive cut/fill grading required to reduce slopes to 2:1. The challenge with the more aggressive alternatives that use a HDPE membrane or thick ET soil cap on the east slope relate to slope stability concerns over the long term. Excessive amounts of cut/fill grading on the order of 300,000 to 400,000 cy will be required to decrease the slopes to 2:1 or lower. Otherwise, several vendors are available for implementation of these alternatives. No significant administrative implementability concerns are anticipated. 11.3.2.7 Cost The total present worth cost is presented for Alternatives 2 through 9 in the table below for discount rates 3 percent and 7 percent and timeframes of 30 years and 100 years in 2014$. The cost for Alternative 1 is $0 and is not shown. Alternatives 2 through 4 are moderate in cost, while Alternatives 5, 6 and 7 are moderate to high and Alternatives 8 and 9 are high in cost. Alternative 3 was the lowest in present worth cost, followed by Alternatives 2, 4, 5, 7, 6, 9, and 8, in ascending order.

Alt No.

Capital Cost Annual

Cost

Total Present Worth

Time Frame



2 $ 8,269,000 $ 364,000 30-year $14,596,000 $10,923,000

100-year $20,385,000 $11,820,000

3 $ 9,105,000 $ 333,000 30-year $14,730,000 $11,177,000

100-year $19,508,000 $11,918,000

4 $ 10,565,000 $ 364,000 30-year $16,638,000 $12,682,000

100-year $21,915,000 $13,500,000


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5 $ 11,423,000 $ 395,000 30-year $18,011,000 $13,727,000

100-year $23,736,000 $14,614,000

6 $ 11,772,000 $411,000 30-year $18,627,000 $14,187,000

100-year $24,568,000 $15,108,000

7 $ 11,116,000 $395,000 30-year $17,738,000 $13,491,000

100-year $23,436,000 $14,374,000

8 $ 16,675,000 $ 489,000 30-year $24,513,000 $18,911,000

100-year $31,808,000 $20,042,000

9 $ 15,655,000 $473,000 30-year $23,301,000 $17,936,000

100-year $30,322,000 $19,024,000 11.3.2.8 Green Impacts Assessment The range of green technologies that can play a role in minimizing environmental impacts of the remedial alternatives and technology components are discussed in Section 12.7. Appendix F presents the qualitative assessment of the environmental footprint for these alternatives based on green remediation criteria such as GHG emissions, energy usage, air emissions, collateral risk, community impacts, resources lost, and water usage. The Appendix F evaluation was used to determine an overall rating for the alternative in Table 11-3. Alternative 2 is low to moderate while Alternatives 3 and 4 are moderate with respect to green and sustainability impacts. Alternative 2 has a lower amount of earthwork because it only includes a 2-foot ecological-cap while Alternatives 3 and 4 have larger excavation and capping activities. Alternatives 5 6 and 7 are moderate to high with respect to impacts due to extensive cut-fill grading soil volumes, larger soil capping activity, excavation, and the addition of a clean soil cover over 24 acres. Alternatives 8 and 9 have the largest capping activity with extensive cut-fill grading of up to 400,000 cy and are high with respect to impacts. The larger amount of earthwork implies a greater amount of operational time for the earth moving equipment, and higher fuel use, GHG and other air emissions and resource use. 11.3.3 Area 2 Evaluation Summary All of the active remedial alternatives for Area 2, Alternatives 2 through 9 meet the threshold requirements of Overall Protection of Human Health and Environment and Compliance with ARARs. Alternative 1 (No Action) is not evaluated for balancing criteria because it does not meet the threshold requirements. Alternative 2 is rated lower than other active remedial alternatives for LTE compared to other alternatives. Alternatives 3 and 4 are rated lower for LTE while Alternatives 5 through 7 are rated moderate to good and Alternatives 8 and 9 are rated good for LTE. Alternatives 3 and 4 also would likely require a larger evaporation pond because the stormwater discharge would likely not meet the substantive requirements of the General Permit. Alternatives 5, 6, 7, 8 and 9 are rated lower for Implementability than Alternatives 3 and 4 because of the challenges with the very steep east slope (1:1) which will require excessive cut/fill grading in the range of 300,000 to 400,000 cubic yards to reduce to a 2:1 slope. Alternatives 8 and 9 are also high in cost and have high green assessment impacts compared to Alternatives 5, 6 and 7. Based on this evaluation, Alternatives 8 and 9 that involve capping the entire RCRA Canyon/WCSA are the highest rated remedial alternatives because of higher LTE compared to


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Alternatives 5, 6 and 7, though the cost and green impacts are higher. With respect to implementability, there is no distinction between these alternatives as they are all rated the same as they would all need the significant grading activity to reduce the slopes to 2:1. Between the geosynthetic hybrid cap (Alternative 8) and the ET soil cap (Alternative 9), it is likely that the soil cap would perform better in the long term on the sloped surfaces.

11.4 Detailed Evaluation of FS Area 3 This section presents the description of the selected remedial alternatives, the detailed evaluation, the green impacts assessment evaluation, and the comparative analysis of alternatives for FS Area 3. Five remedial alternatives were selected after the screening evaluation in Section 10 was conducted on a location by location basis. Table 11-4 presents the detailed evaluation for the five selected alternatives. 11.4.1 Description of Remedial Alternatives The following is a description of the five selected remedial alternatives. 11.4.1.1 Alternative 1 No Action The No Action alternative is included as required by CERCLA guidance. 11.4.1.2 Alternative 2 RCRA Cap(Locations 2, 3, 4) + Excavate/New Asphalt Cap (Location

1)(5’) + GW Monitoring (Location 10) + Grading/BMPs (Other areas) + Stormwater Controls + ICs + Monitoring


RCRA cap for Locations 2, 3 and 4 over an area of 6.6 acres Excavate Location 1 down to 5 feet bgs over an area of 1 acre and install an asphalt cap Add 2 downgradient groundwater monitoring wells for Location 10 Stormwater controls with drainage and erosion controls for the capped areas including

drains that direct stormwater towards the drainage channel near PSCT-1 Grading and BMPs for uncapped areas over approximately 40 acres south of the PSCT

and east of LTP Road Evaluate the potential use of pond water for foundation layers during cap construction Institutional controls, maintenance and monitoring to protect the capped areas


Prevent ecological receptors from potential exposures to shallow soil (0-5 feet bgs) at Locations 1, 2, 3 and 4

Prevent rainwater infiltration at Locations 2, 3 and 4 to protect groundwater Monitor groundwater downgradient of Location 10 Incorporate stormwater drains for the capped areas to direct clean stormwater to the

drainage channel near PSCT-1 for discharge through or around the wetlands under the substantive terms of the General Permit.

Grading and BMPs in uncapped areas to minimize erosion and sediment transport and allow the stormwater that sheet flows from the uncapped areas to discharge through the or around wetlands via the substantive terms of the General Permit


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The following provides a brief description of the conceptual design for the remedial alternative components: RCRA Cap for Locations 2, 3 and 4 This alternative includes a RCRA cap for the Locations 2, 3 and 4 as shown on Figures 11-13A and 11-13B. The conceptual design and preliminary performance standards for the RCRA cap were discussed earlier in Section 10.1.1.2. Detailed specifications would be developed during remedial design. The northern and eastern sides of the Location 2 (MSA) cap would need to tie into the existing P/S Landfill cap and the proposed BTA cap, while the eastern side would need to tie into the anticipated cap for the CDA. The eastern side of Location 3 and the northern side of Location 4 caps would need to tie into the CDA cap as well. The borrow soils obtained from the NW Borrow Areas for this cap may need to be screened and processed by pulverization before use. Hydroseeding would be used to spread a selected seed mix of native plant species on the top of the vegetative layer. The soil for the vegetative layer would also need addition of organic materials and nutrients to assist vegetation growth. Cut and Fill Soil Volumes for Leveling/Cap Construction

For Location 2, the cut/fill volume for grading is 17,000 cy with a net import of 19,800 cy for the foundation layer and the vegetative layer.

For Location 3, the cut/fill volume for excavation is 13,000 cy with a net import of 15,600

cy for the foundation layer and the vegetative layer.

For Location 4, the cut/fill volume for excavation is 10,000 cy with a net import of 11,400 cy for the foundation layer and the vegetative layer.

Excavation and Asphalt Cap for Location 1 This alternative includes excavation of up to 5 feet of shallow soil to remove soils impacted primarily with metals that pose a risk to ecological receptors (Figure 11-13C).The excavation will be implemented in the uncapped area to the east that is not currently capped with asphalt or concrete. Some of the Location 1 area is covered with concrete or asphalt and contains process equipment and piping associated with the PSCT and Gallery Well liquids treatment system. The areas that are capped do not pose a current risk. The total area for excavation is approximately 1 acre with a maximum depth of 5 feet bgs. The total soil volume for excavation is approximately 8,000 cy. The extent and depth of the excavation is preliminary and would be confirmed during design to ensure that risk-based standards are met. The excavated soil will be disposed of in the PCB Landfill prior to construction of the PCB Landfill cap remedy. The sidewalls of the excavation will be sloped 1:1. Approximately 8,800 cy of clean borrow soil will be obtained from the NW Borrow Areas. The soil will be compacted to a 90 percent relative compaction (ASTM D1557). Any existing pipelines, electric conduits or other utilities associated with the Liquids Treatment Area would need to be protected or replaced. After backfill and compaction, the area would be covered with a 4-inch asphalt surface. The asphalt will be extended to adjacent gravel and soil areas to form a continuous concrete or asphalt capped surface in the Liquids Treatment Area that could potentially be useful for future site operations. Groundwater Wells and Monitoring for Location 10


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Location 10 encompasses impacted soils present under NTU Road down to a depth of 50 feet below road surface. This alternative includes the installation of two groundwater monitoring wells to serve as sentinel wells and monitor groundwater over the long term. Grading and BMPs for the Uncapped Portion of FS Area 3 Grading and BMPs are included for the uncapped portions (about 40 acres) of FS Area 3 as part of the stormwater and erosion controls for the area. Various approaches to BMPs to reduce erosion will be evaluated during remedial design, including grading rills/gullies, placing check dams with rip rap, silt fences, etc. The stormwater from the uncapped areas of Area 3 would sheet flow into the RCF Pond. The combined stormwater would then flow under the RCF Road via a new culvert, and then discharge through Pond 13 retention basin through or around the wetlands and to the B-drainage Stormwater Controls Preliminary locations of bench roads and drains are shown on Figures 11-13A and 11-13B. The stormwater from the capped areas of Locations 2, 3 and 4 will be directed to the southeast to the drainage channel near PSCT-1. The stormwater is transported through the drainage channel along with the Capped Landfills discharge via the B-Drainage wetlands same as in FS Area 1. Location 1 will be excavated and capped with asphalt and does not pose a concern for stormwater quality. Location 10 is not a known concern for stormwater because the contaminants are in deeper soils and not on surface soils. Existing Site Features All monitoring or extraction wells that are within the footprint of Locations 2, 3 and 4 will be extended with new surface completion above the cap surface and resurveyed. The monitoring wells or piezometers in Location 1 would be protected during the excavation. Existing site roads and drains that are within the footprint of the proposed capped areas in this alternative would be reconstructed. The detailed plans for the site roads and drains and how they would be connected to the drains in adjacent areas would be addressed during the remedial design phase. The existing building in the Maintenance Shed Area, including the foundation, will be demolished and disposed at a permitted disposal facility. In addition, two USTs (5,000 gallons and 2,000 gallons) will be excavated and disposed at a permitted disposal facility. Costs are included for the building demolition and USTs removal in the FS Area 3 cost estimates. Sampling and Testing During remedial design, the slope stability will be evaluated as part of the cap design. During construction, the foundation layer will be tested for compaction and appropriate shear strength, and interface testing of the cap will be conducted. Air monitoring would be conducted during the grading and cap construction activities. Air monitoring would include field dust and VOC monitoring and one air and particulate sample for each field day that involves soil construction activities. Soil physical and geotechnical properties will be tested for the proposed NW Borrow Area as discussed under FS Area 1.


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Inspection, Monitoring, Maintenance and Institutional Controls The monitoring component of this alternative includes periodic inspection, maintenance and repair of the cap and stormwater controls over the long term as discussed earlier in FS Area 1. The cap and stormwater controls system will be inspected after a significant seismic event and after major storm events. 11.4.1.3 Alternative 3 RCRA Cap (Location 2) + Excavate (Location 3 (20’), Location 4 (5’)) +

Excavate/New Asphalt Cap (Location 1)(5’) + Groundwater Monitoring (Location 10) + Grading /BMPs (Uncapped Areas) + Stormwater Controls + ICs + Monitoring


• RCRA cap for Location 2 over an area of 2.8 acres • Excavate Location 1 down to 5 feet bgs over an area of 1 acre and install an asphalt cap • Excavate Location 4 to 5 feet bgs over an area of 1.6 acres and Location 3 to 20 feet

bgs over an area of 2.2 acres, and backfill with clean fill • Add 2 downgradient groundwater monitoring wells for Location 10 • Grading and incorporation of BMPs in the uncapped sections (15 acres) of Area 3. • Stormwater controls with drainage and erosion controls for the capped areas including

drains that direct stormwater towards the drainage channel near PSCT-1 • Evaluate the potential use of pond water for foundation layers during cap construction • Institutional controls, maintenance and monitoring to protect the capped areas


• Prevent ecological receptors from potential exposures to shallow soil (0-5 feet bgs) at Locations 1, 2, 3 and 4

• Prevent rainwater infiltration at Location 2 to protect groundwater • Remove source areas in soil at Location 3 (former Ponds A/B) to protect groundwater • Monitor groundwater downgradient of Location 10 to assess potential impacts • Incorporate stormwater drains for the capped areas to direct clean stormwater to the


• Grading and BMPs in uncapped areas to minimize erosion and sediment transport and allow the stormwater that sheet flows from the uncapped areas to discharge through or around the wetlands via the substantive terms of the General Permit

RCRA Cap for Location 2 This alternative includes a RCRA cap for Location 2 as shown on Figures 11-14A and 11-14B. The conceptual design for the RCRA cap is the same as in Alternative 2, and preliminary performance standards for the RCRA cap were discussed earlier in Section 10.1.1.2. Detailed specifications would be developed during remedial design. The northern and eastern sides of the Location 2 (MSA) cap would need to tie into the existing P/S Landfill cap and the proposed BTA cap while the eastern side would need to tie into the anticipated cap for the CDA. The borrow soils obtained from the NW Borrow Areas for this cap may need to be screened and processed by pulverization before use. Hydroseeding would be used to spread a selected seed mix of native plant species on the top of the vegetative layer. The soil for the vegetative layer would also need addition of organic materials and nutrients to assist vegetation growth. Excavation and Asphalt Cap for Location 1


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This alternative includes excavation of up to 5 feet of shallow soil to remove soils impacted primarily with metals that pose a risk to ecological receptors (Figure 11-14C). The details of the excavation including soil volume, side wall slopes, backfill, and the asphalt cap are the same as in Alternative 2. Excavation of Shallow Soil (0-5 feet bgs) at Location 4 This excavation is intended to remove impacted shallow soils that can pose a risk to ecological receptors. Figure 11-14B shows the proposed excavation for Location 4 covering 1.6 acres. This area would be excavated down to 5 feet bgs, and the sidewalls sloped 1:1. The total impacted soil volume is approximately 13,000 cy. The extent and depth of the excavation is preliminary and would be confirmed during design to ensure that risk-based standards are met. The excavated soils are proposed for disposal at the PCB Landfill for cost estimating purposes. Clean soil for backfill will be obtained from the NW Borrow Areas and compacted in 1-foot lifts to a relative compaction of 90 percent (ASTM D 1557). The top surface will be sloped and drains incorporated on the surface to direct stormwater runoff into the drainage channel near PSCT-1. Excavation of Shallow Soil (0-20 feet bgs) at Location 3 (Former Pond A/B location) This excavation is intended to remove a soil source area where the former Ponds A/B were located that can potentially impact groundwater. Figure 11-14B shows the proposed excavation for Location 3. These areas would be excavated down to 20 feet bgs and the sidewalls sloped 1:1. The total impacted soil volume for Location 3 is approximately 71,000 cy. The extent and depth of the excavation is preliminary and would be confirmed during design to ensure that risk-based standards are met. For cost estimating purposes, the excavated soils are assumed to be transported for disposal at the PCB Landfill. Clean soil for backfill will be obtained from the NW Borrow Areas and compacted in 1-foot lifts to a relative compaction of 90 percent (ASTM D1557). The top surface will be sloped and drains incorporated on the surface to direct stormwater runoff into the drainage channel near PSCT-1. Soil sampling of the sidewalls and the bottom will be included to determine exact depths and extent of excavation. Groundwater Wells and Monitoring for Location 10 Location 10 encompasses impacted soils present under NTU Road down to a depth of 50 feet below road surface, and this alternative includes two groundwater monitoring wells to serve as sentinel wells and monitor groundwater over the long-term. Cut and Fill Soil Volumes for Leveling/Cap Construction and Excavation

For Location 1, the soil volume for excavation is 8,000 cy with a net import of 8,800 cy for the backfill.





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Grading and BMPs for the Uncapped Portion of FS Area 3 Grading and BMPs are included for the uncapped portions (about 15 acres) of FS Area 3 as part of the stormwater and erosion controls for the area. Various approaches to BMPs to reduce erosion will be evaluated during remedial design, including grading rills/gullies, placing check dams with rip rap, silt fences, etc. The stormwater from the uncapped areas of Area 3 would sheet flow into the RCF Pond. The combined stormwater would then flow under the RCF Road via a new culvert, and then discharge through the Pond 13 retention basin through or around the wetlands, and into the B-drainage (discharge governed by the substantive terms of the General Permit). Approval of the final design for the grading and BMPs of this alternative with the RWQCB is expected to be required if it was selected. Stormwater Controls Preliminary locations of bench roads and drains are shown on Figures 11-14A and 11-14B. The stormwater from the capped area of Location 2 will be directed to the southeast to the drainage channel near PSCT-1. The stormwater is transported through the drainage channel along with the Capped Landfills discharge via the B-Drainage wetlands, same as in FS Area 1. The top surface of the Location 3 and 4 excavations will be sloped and drains incorporated on the surface to direct stormwater runoff into the drainage channel near PSCT-1. Location 1 will be excavated and capped with asphalt and does not pose a concern for stormwater quality. Location 10 is not a known concern for stormwater because the contaminants are not present in surface soils. Existing Site Features All monitoring or extraction wells that are within the footprint of Location 2 will be extended with new surface completions above the cap surface and resurveyed. The monitoring wells or piezometers in Locations 1, 3 and 4 would be protected during the excavation. Existing site roads and drains that are within the footprint of the proposed capped areas in this alternative would be reconstructed. The detailed plans for the site roads and drains and how they would be connected to the drains in adjacent areas would be addressed during the remedial design phase. The existing building in the Maintenance Shed Area, including the foundation, will be demolished and disposed at a permitted disposal facility. In addition, two USTs (5,000 gallons and 2,000 gallons) will be excavated and disposed at a permitted disposal facility. Costs are included for the building demolition and USTs removal in the FS Area 3 cost estimates. Sampling and Testing During remedial design, the slope stability will be evaluated as part of the cap design. During construction, the foundation layer will be tested for compaction and appropriate shear strength, and interface testing of the cap will be conducted. Air monitoring would be conducted during the grading and cap construction activities. Air monitoring would include field dust and VOC monitoring. Soil sampling will be conducted during excavation of the sidewalls and bottom, which will help define the extent of excavation and will serve as confirmation sampling as well.


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Inspection, Monitoring, Maintenance and Institutional Controls The monitoring component of this alternative includes periodic inspection, maintenance and repair of the cap and stormwater controls over the long term as discussed earlier in Alternative 2. 11.4.1.4 Alternative 4 RCRA Cap (Location 2) + Excavate [Location 3 (20’); (Location 4)(5’);

Location 10)(50’)]/Place in PCB Landfill/Backfill + Excavate/New Asphalt Cap (Location 1)(5’) + Grading/BMPs (Uncapped Areas) + Stormwater Controls + ICs + Monitoring


• RCRA cap for Location 2 over an area of 2.8 acres • Excavate Location 4 to 5 feet bgs, Location 3 to 20 feet bgs, and Location 10 to 50 feet

bgs over an area of 4.4 acres and backfill with clean fill • Excavate Location 1 to 5 feet bgs and construct asphalt cap. • Grading and incorporation of BMPs in the uncapped sections (15 acres) of Area 3. • Stormwater controls with drainage and erosion controls for the capped areas, including

drains that direct stormwater towards the drainage channel near PSCT-1 • Evaluate the potential use of pond water for foundation layers during cap construction • Institutional controls, maintenance and monitoring to protect the capped areas


• Prevent ecological receptors from potential exposures to shallow soil (0-5 feet bgs) at Locations 1, 2, 3, 4, and 10.

• Remove source areas in soil at Location 3 (Ponds A/B) and Location 10 (RISBON-59) to protect groundwater

• Prevent rainwater infiltration at Location 2 to protect groundwater • Incorporate stormwater drains for the capped areas to direct clean stormwater to the


• Grading and BMPs in uncapped areas to minimize erosion and sediment transport and allow the stormwater that sheet flows from the uncapped areas to discharge through or around the wetlands via the substantive terms of the General Permit

RCRA Cap for Location 2 This alternative includes a RCRA cap for Location 2 as shown on Figures 11-15A and 11-15B. The conceptual design is the same as in Alternative 2, and preliminary performance standards for the RCRA cap were discussed earlier in Section 10.1.1.2. Detailed specifications would be developed during remedial design. Excavation and Asphalt Cap for Location 1 This alternative includes excavation of up to 5 feet of shallow soil to remove soils impacted primarily with metals that pose a risk to ecological receptors (Figure 11-15C). The details of the excavation including soil volume, side wall slopes, backfill and the asphalt cap are the same as in Alternative 2. Excavation of Shallow Soil (0-5 feet bgs) at Location 4


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This excavation is intended to remove impacted shallow soils that can pose a risk to ecological-receptors. Figure 11-15B shows the proposed excavation for Location 4 covering 1.6 acres. These areas would be excavated down to 5 feet bgs. The details of the excavation including soil volume, sidewall slopes, backfill, borrow soil source are the same as for Location 4 in Alternative 3. Excavation of Shallow Soil (0-20 feet bgs) at Location 3 (Former Pond A/B location) This excavation is intended to remove a soil source area where the former Ponds A/B where located that can potentially impact groundwater. Figure 11-15B shows the proposed excavation for Location 3. These areas would be excavated down to 20 feet bgs. The details of the excavation including the soil volume, sidewall slopes, backfill borrow soil source, and disposal at a permitted disposal facility are the same as for Location 3 in Alternative 3. Excavation of RISBON-59 Source Area (0-50 feet bgs) at Location 10 This excavation is intended to remove the source area soils that may impact groundwater. Figure 11-15C shows the proposed excavation from the top of the NTU Road surface (elev. 450 ft MSL) down to elevation of 400 ft MSL. The bottom of the excavation would be below the water table approximately at 415 ft MSL, but above the unweathered claystone contact. The horizontal extent of the impacted soil is about 175 feet by 175 feet. The excavation sidewalls would be sloped 1:1 on all four sides. The total impacted soil volume for excavation at this location is about 65,000 cy. The extent and depth of the excavation is preliminary and would be confirmed during design to ensure that risk-based standards are met. A portion of the excavated soil would be clean overburden from the side slope excavation. Additional soil sampling would be conducted to better define the excavation extent if this alternative is implemented. This excavation would require removal of a portion of RCF Road and thus affect access to portions of the site. It is assumed that a temporary access road would be required that provides a detour for RCF Road around the excavation. The RCF Road will be restored upon completion and backfilling of the remedial excavation in this area. Since a portion of the excavation is below the water table, dewatering is assumed to be required. A trench installed on the upgradient side of the excavation is assumed for the dewatering to support the excavation. An extraction rate of 10 gpm is assumed and the extracted water is treated with LPGAC to remove organics and to allow discharge to the RCF Pond. The excavated soil is assumed to be disposed at the PCB Landfill. Confirmation sampling would be conducted at the bottom and sidewalls of the excavation to confirm the source area at this location is removed. Clean fill is assumed to be brought in from an outside location, as the NW soil borrow area is likely to be limited for use in capping at other study areas at the site. Soil is backfilled and compacted to 90 percent relative compaction (ASTM D1557). Cut and Fill Soil Volumes for Leveling/Cap Construction and Excavation




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Grading and BMPs for the Uncapped Portion of FS Area 3 Grading and BMPs are included for the uncapped portions (about 15 acres) of FS Area 3 as part of the stormwater and erosion controls for the area. The approaches considered for grading and BMPs are the same as in Alternative 3. Stormwater Controls Preliminary locations of bench roads and drains are shown on Figures 11-15A and 11-15B. The stormwater from the capped area of Location 2 will be directed to the southeast to the drainage channel near PSCT-1. The stormwater is transported through the drainage channel along with the Capped Landfills discharge via the B-Drainage wetlands, same as in FS Area 1. Location 1 will be excavated and capped with asphalt and does not pose a concern for stormwater quality. Location 10 is not a known concern for stormwater because the contaminants are in deeper soils and not on surface soils. The top surface of the Location 3 and 4 excavations will be sloped and drains incorporated on the surface to direct stormwater runoff into the drainage channel near PSCT-1. Existing Site Features All monitoring or extraction wells that are within the footprint of Location 2 will be extended with new surface completion details above the cap surface and resurveyed, as required. The monitoring wells or piezometers in Locations 1, 3, 4, and 10 would be protected during the excavations. Existing site roads and drains that are within the footprint of the proposed capped areas in this alternative would be reconstructed. The detailed plans for the site roads and drains and how they would be connected to the drains in adjacent areas would be addressed during the remedial design phase. The existing building in the Maintenance Shed Area, including the foundation, will be demolished and disposed as discussed in Alternative 2. Sampling and Testing The sampling and testing conducted during the capping and excavation is the same as discussed under Alternative 3. Inspection, Monitoring, Maintenance and Institutional Controls


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The monitoring component of this alternative includes periodic inspection, maintenance and repair of the cap and stormwater controls over the long term as discussed in Alternative 2. 11.4.1.5 Alternative 5 Excavate (Locations 2, 4)(5’); (Location 3)(20’); (Location

10)(50’)//Disposal/Backfill + Excavate/New Asphalt Cap (Location 1)(5’) + Grading/BMPs (Uncapped Areas) + Stormwater Controls + ICs + Monitoring


Excavate shallow soil (0-5’ bgs) at Locations 1, 2, 4 over an area of 5.4 acres, and install an asphalt cap over backfilled area of Location 1

Excavate soil (0-20’ bgs) at Location 3 (former Ponds A/B) that covers 2.2 acres Excavate (0-50’ below NTU road surface) at Location 10 over an area of 30,625 square

feet Stormwater controls including drainage and erosion controls for residual contamination Evaluate the potential use of pond water for foundation layers during cap construction Institutional controls, maintenance and monitoring for stormwater controls


Prevent ecological receptors from potential exposures to shallow soil (0-5 feet bgs) at Locations 1, 2, 3 and 4

Remove source areas in soil at Location 3 (Ponds A/B) and Location 10 (RISBON-59) to protect groundwater

Prevent rainwater infiltration through impacted soils at Locations 1, 2, and 4 Incorporate stormwater and erosion controls to minimize sediment transport and allow

discharge of stormwater from FS Area 3 via the NPDES General Permit Excavation of Shallow Soil (0-5 feet bgs) at Locations 1, 2, and 4 This excavation is intended to remove impacted shallow soils that can pose a risk to ecological receptors. Figure 11-16B shows the proposed excavation for Locations 2 and 4, and Figure 11-16C shows the proposed excavation for Location 1, covering a total of 5.7 acres. These areas would be excavated down to 5 feet bgs. The sidewalls will be sloped 1:1. The total impacted soil volume for Locations 1, 2 and 4 is approximately 44,000 cy. The extent and depth of the excavation is preliminary and would be confirmed during design to ensure that risk-based standards are met. The excavated soils are proposed for disposal at the PCB Landfill for cost estimating purposes. Clean soil for backfill will be obtained from the NW Borrow Areas and compacted in 1-foot lifts to a relative compaction of 90 percent (ASTM D 1557).The top surface will be sloped and drains incorporated on the surface to direct stormwater runoff into the drainage channel near PSCT-1. Location 1 would be covered with a 4-inch asphalt cap after backfill and compaction, as discussed in Alternatives 2, 3 and 4. Excavation of Shallow Soil (0-20 feet bgs) at Location 3 (Former Pond A/B location) This excavation is intended to remove a soil source area where the former Ponds A/B were located that can potentially impact groundwater. Figure 11-16B shows the proposed excavation for Location 3. These areas would be excavated down to 20 feet bgs. The details of the excavation volumes, sidewall slopes and disposal are the same as in Alternative 3.


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Excavation of RISBON-59 Source Area (0-50 feet bgs) at Location 10 This excavation is intended to remove the impacted source area soils that are impacting groundwater. Figure 11-16C shows the proposed excavation from the top of the RCF Road surface (elev. 450 ft MSL) down to elevation of 400 ft MSL. The bottom of the excavation would be below the water table that is approximately at 415 ft MSL, but above the unweathered claystone contact. The horizontal extent of the impacted soil is about 175 feet by 175 feet. The excavation sidewalls would be sloped 1:1 on all four sides. The total impacted soil volume for excavation at this location is about 65,000 cy. The extent and depth of the excavation is preliminary and would be confirmed during design to ensure that risk-based standards are met. A portion of the excavated soil would be clean overburden from the side slope excavation. Additional soil sampling would be conducted to better define the excavation extent if this alternative is implemented. For cost estimating purposes, this soil is assumed to be one-half non-RCRA hazardous and one-half nonhazardous and sent to Waste Management at Kettleman Hills or Clean Harbors at Buttonwillow for disposal. The details of this component including dewatering for the excavation and backfill borrow soil are the same as in Alternative 4. Cut and Fill Soil Volumes for Leveling/Cap Construction and Excavation






Grading and BMPs for the Uncapped Portion of FS Area 3 Grading and BMPs are included for the uncapped portions (about 40 acres) of FS Area 3 as part of the stormwater and erosion controls for the area as discussed in Alternative 2. The stormwater from the uncapped areas of Area 3 would sheet flow into the RCF Pond. The combined stormwater would then flow under the RCF Road via a new culvert, and then discharge through Pond 13 retention basin through or around the wetlands and the B-drainage (discharge governed by the substantive provisions of the General Permit). Stormwater and Erosion Controls Preliminary locations of bench roads and drains are shown on Figures 11-16A and 11-16B.The stormwater and erosion control for these backfilled areas is the same as for Alternative 2. Existing Site Features


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All monitoring or extraction wells that are within the footprint of the excavations will be protected during excavation or replaced. Existing site roads and drains that are within the footprint of the proposed excavation areas in this alternative would be reconstructed. The detailed plans for the site roads and drains and how they would be connected to the drains in adjacent areas would be addressed during the remedial design phase. The existing building in the Maintenance Shed Area, including the foundation, will be demolished and disposed as discussed in Alternative 2. Sampling and Testing The sampling and testing conducted during the excavation including air monitoring and soil sampling is the same as discussed under the excavations in Alternative 3. Inspection, Monitoring, Maintenance and Institutional Controls The monitoring component of this alternative includes periodic inspection, maintenance and repair of the cap and stormwater controls over the long term as discussed earlier in Alternative 2. 11.4.2 Detailed and Comparative Analysis of Remedial Alternatives The detailed evaluation for the five remedial alternatives in addition to the No Action alternative is presented in Table 11-4. The following is the comparative analysis where the ratings and performance for each CERCLA criteria is compared for each alternative. 11.4.2.1 Overall Protection of Human Health and Environment Alternatives 2, 3, 4 and 5 are considered protective of human health and environment while Alternative 1 is not. Alternative 2 caps the primary ecological COCs at the Locations 2, 3 and 4 with a RCRA cap, and excavates Location 1. Groundwater is monitored in Alternative 2 with two sentry wells installed downgradient of Location 10. Alternatives 3 and 4 cap the primary ecological COCs at Location 2 and excavate Locations 1, 3, and 4. Groundwater monitoring sentry wells are added for Location 10 for Alternative 3 as well. Alternatives 4 and 5 include excavations at Locations 1, 3, and 4, as well as the Location 10 hot spot to a depth of 50 feet bgs, and backfilling the excavations with clean imported fill. The RCRA cap and the excavations ensure protection for ecological receptors while the monitoring wells at Location 10 monitor groundwater. Furthermore, the RCRA cap for Alternatives 2, 3, and 4 would prevent rainwater infiltration into underlying impacted soils. 11.4.2.2 Compliance with ARARs Alternatives 2, 3, 4 and 5 would be in compliance with ARARs relating to excavation of contaminated soils such as RCRA requirements if hazardous wastes are encountered, as well as requirements for a worker health and safety program.


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11.4.2.3 Long-Term Effectiveness Alternatives 2 through 4 are rated moderate to good while Alternative 5 is rated moderate for long-term effectiveness. Alternative 2 achieves the RAOs of eliminating exposure to contaminants in soil for ecological receptors by a RCRA cap over Locations 2, 3 and 4 and excavation of shallow soil at Location 1. In addition to the RCRA cap at Location 2, Alternative 3 includes excavations at Locations 1, 3, and 4, and Alternative 4 includes excavations at Locations 1, 3, 4, and 10 to achieve compliance with the RAOs. Alternative 5 achieves the RAOs by excavating at Locations 1, 2, 3, 4 and 10, but is rated one step lower due to concerns with long term exposure and risk with transfer of contaminants to an outside disposal facility. All of the alternatives are protective of groundwater by using either a RCRA cap or by excavation of contamination. Groundwater monitoring at Location 10 for Alternatives 2 and 3 would provide notification if this impacted soil poses a threat to groundwater. Alternatives 4 and 5 involve excavation of Location 10, but it is possible the excavated soil will be sent to a permitted disposal facility due to the limited storage capacity in the PCB Landfill, and the disposal raises concerns with potential risks or exposure during transport and/or disposal at remote locations. Alternative 5 with no capping will also allow greater infiltration and would not limit mobility or migration of deeper soil and groundwater contamination, as would those alternatives with a RCRA cap. 11.4.2.4 Reduction of Toxicity, Mobility and Volume through Treatment Alternative 2 is rated poor while Alternatives 3, 4, and 5 are rated poor to moderate. Alternative 2 is rated lowest because it does not remove contaminants and reduce RTMV through excavation or treatment. Alternative 3 does remove contaminant mass at Locations 3 and 4 in shallow soil by excavation, while Alternative 4 removes contaminant mass at Locations 3, 4 and 10. It should be noted that the contaminants are disposed in the PCB Landfill and capped, but not treated. Alternative 5 is also rated poor to moderate; though it involves the highest removal of contaminant mass, it is not rated higher because the contaminants are transferred to an outside facility and not treated. Also, Alternative 5 would allow a greater amount of surface water infiltration into groundwater and thus would not limit mobility or migration of deeper soil or groundwater contamination. 11.4.2.5 Short-Term Effectiveness Alternative 2 is rated good, Alternative 3 is rated moderate to good, and Alternatives 4 and 5 are rated moderate. Alternative 2 has no significant risks because it involves capping and no excavation of contaminated soils except for the limited cut/fill grading in the leveling process prior to capping. Alternative 3 is rated slightly lower because it involves shallow excavation with a moderate potential for emissions of COCs. Alternatives 4 and 5 both involve extensive excavations, including a 50-foot deep excavation at Location 10, and thus have a greater potential for emissions exposure and safety concerns. The safety concerns also include risks associated with transportation of large quantities of impacted soil , especially with Alternative 5. 11.4.2.6 Implementability Alternatives 2 and 3 are rated moderate to good while Alternatives 4 and 5 are rated lower at moderate. Alternative 2 does not face any significant challenges in implementation because it involves constructing a RCRA cap adjacent to other areas that have already been capped. At Location 2, the existing USTs and MSA building would be removed as part of site preparation. Alternative 3 would pose only minor challenges with the 20-foot excavation at Location 3.


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Alternatives 4 and 5 would face more challenges because of the deep excavation (50 feet below RCF Road) at Location 10, and the fact that this soil forms the roadbed for the RCF road and part of the berm for the RCF Pond. Also, some of the excavated soil from Location 10 would need to be sent to an outside facility due to the limited storage capacity in the PCB Landfill, which would require transportation of large quantities of soil to outside disposal facilities. 11.4.2.7 Cost The total present worth cost is presented for Alternatives 2, 3, 4 and 5 in the table below for discount rates 3 percent and 7 percent and timeframes of 30 years and 100 years in 2014$. The cost for Alternative 1 is $0 and is not shown. Alternatives 2, 3 and 4 are moderate in cost while Alternative 5 is high. Alternatives 2, 3, and 4 involving capping or limited excavations with disposal are significantly lower in total present worth cost than Alternative 5 which involves excavations including the removal of wastes in Ponds A/B and RISBON-59 and disposal of these wastes at a permitted disposal facility.

Alt No. Capital Cost

Annual Cost

Total Present Worth

Time frame



2 $ 5,909,000 $ 258,000 30-year $10,423,000 $7,801,000

100-year $14,030,000 $8,360,000

3 $6,681,000 $196,000 30-year $9,888,000 $7,619,000

100-year $12, 814,000 $8,072,000

4 $8,368,000 $196,000 30-year $11,389,000 $9, 912,000

100-year $14,460,000 $9,388,000

5 $ 25,564,000 $ 97,000 30-year $24,727,000 $20,854,000

100-year $25,885,000 $21,034,000 11.4.2.8 Green Impacts Assessment The range of green technologies and BMPs that can play a role in minimizing environmental impacts of the remedial alternatives and technology components are discussed in Section 12.7. Appendix F presents the qualitative assessment of the environmental footprint for these alternatives based on green remediation criteria such as GHG emissions, energy usage, air emissions, collateral risk, community impacts, resources lost, and water usage. The Appendix F evaluation was used to determine an overall rating for the alternative in Table 11-4. Alternatives 2 and 3 have moderate impacts; Alternative 4 has moderate to high: while Alternative 5 is rated high with respect to green and sustainability impacts. Alternative 2 has a lower amount of earthwork because it involves capping about 6.6 acres and excavating a shallow soil volume of 8,000 cy for disposal in the PCB Landfill. Alternative 5 is rated to have high impacts because it involves excavation of approximately 180,000 cy borrow soils and compaction of 166,900 cy and transportation and outside disposal of 157,500 tons. The larger amount of earthwork implies a greater amount of operational time for the earth moving equipment, and higher fuel use, GHG and other air emissions and resource use. 11.4.3 Area 3 Evaluation Summary All of the active remedial alternatives for Area 3, Alternatives 2 through 5 meet the threshold requirements of Overall Protection of Human Health and Environment and Compliance with


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ARARs. Alternative 1 (No Action) is not evaluated for balancing criteria because it does not meet the threshold requirements. Alternatives 2 and 3 are rated substantially better than Alternatives 4 and 5 with respect to STE and Implementability, while their ratings for LTE and RTMV are similar. Between Alternatives 2 and 3, Alternative 3 is rated higher for RTMV while Alternative 2 is rated higher for STE. Alternative 3 is slightly lower in total present worth cost, and their green impact assessments are the same. Based on this evaluation, Alternative 3 is the highest rated alternative.

11.5 Detailed Evaluation of FS Area 4 This section presents the description of the selected remedial alternatives, the detailed evaluation, the green impacts assessment evaluation, and the comparative analysis of alternatives for FS Area 4. Eight remedial alternatives were selected after the screening evaluation in Section 10. Table 11-5 presents the detailed evaluation for the eight selected alternatives. 11.5.1 Description of Remedial Alternatives 11.5.1.1 Alternative 1 No Action The No Action alternative is included as required by CERCLA guidance. 11.5.1.2 Alternative 2 Ecological-Cap (RCF, A-Series ponds) (2’) + Lined Retention Basin

(Pond A-5, Pond 13) + Construct 11-acre Evaporation Pond (North of RCF Pond) + RCRA Cap (Pond 18) + Stormwater Controls + ICs + Monitoring


Construct new 11-acre evaporation pond north of the RCF Pond and south of the PSCT Manage stormwater to eliminate pond water prior to and during FS construction as

discussed in the Stormwater Plan presented in Section 10.1.3 Raise the bottom of the RCF and A-Series Ponds above groundwater levels and

construct an ecological cap over the RCF and A-Series Ponds, covering a combined area of 19 acres

Line pond bottom for Ponds A-5 and Pond 13 to create stormwater retention basins over areas of 2.5 acres and 1.9 acres, respectively

RCRA cap for Pond 18 over an area of 2.8 acres Stormwater controls with drainage and erosion controls for the capped areas, including

drains that direct stormwater towards the culvert under RCF Road to the retention basin in the footprint of Pond 13

Institutional controls, maintenance and monitoring to protect the capped areas. The objectives of this remedial alternative are:

Prevent ecological receptors from potential exposures to shallow soil or sediment (0-5 feet bgs) at RCF and A-Series Ponds

Prevent ecological exposures to COCs in surface water such that exposures are below acceptable levels


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Manage stormwater by eliminating pond water prior to and during FS construction and constructing a new evaporation pond adequately sized to handle all water that cannot be discharged under substantive terms of the General Permit

Incorporate stormwater drains for the capped areas to direct clean stormwater to the culvert under RCF Road for discharge through or around the wetlands under the substantive terms of the General Permit.

The following provides a brief description of the conceptual design for the remedial alternative components: Ecological-cap for RCF Pond This alternative involves constructing an ecological-cap over the RCF Pond over an area of 11.4 acres which consists of a 2-foot thick layer of clean top soil to control potential exposure to ecological receptors after the pond has been emptied (Figure 11-17B). A 2-foot thick soil cover is proposed rather than a 1-foot thick cover because it is considered more resistant from a long term cap maintenance perspective. Ecological-caps are effective at mitigating areas where the ecological exposure risk is the result of contaminants in shallow soil and for ecological exposure risk to burrowing animals in deeper soils. Details on the ecological-cap design were presented in Section 10.1.1. Prior to constructing the ecological-cap, the pond will be filled to raise the bottom elevation to approximately 415 feet MSL. Approximately 95,000 cy of borrow soil would be required to raise the pond bottom elevation and is presumed to be borrowed from the NW Borrow Area. The fill soil will be lightly compacted to 85 percent maximum dry density (ASTM D1557) with a hydraulic conductivity of 10-4 to 10-5 cm/sec. The upper 2 feet of the fill soil will serve as the foundation layer for the cap and will be compacted to 90 percent and a hydraulic conductivity of 10-6 cm/sec. In addition, about 40,000 cy of borrow soil will be needed for the ecological-cap. The cap surface would be sloped and include bench roads and surface drains to direct stormwater through the culvert under RCF Road to Pond 13 retention basin and discharged under the substantive terms of the General Permit. Ecological-cap for A-Series Pond This alternative involves constructing an ecological-cap over the A-Series Pond over an area of 8 acres which consists of a 2-foot thick layer of clean top soil to control potential exposure to ecological receptors (Figure 11-17B). Prior to constructing the ecological-cap, the pond will be filled to raise the bottom to approximately 425 feet MSL. Approximately 85,000 cy of borrow soil would be required to raise the pond bottom elevation and is presumed to be borrowed from the NW Borrow Area. The fill soil will be lightly compacted to 85 percent maximum dry density (ASTM D1557) with a hydraulic conductivity of 10-4 to 10-5 cm/sec. The upper 2 feet of the fill soil will serve as the foundation layer for the cap and will be compacted to 90 percent and a hydraulic conductivity of 10-6 cm/sec. In addition, about 39,000 cy of borrow soil will be needed for the ecological-cap that is placed on top of the biotic barrier. The cap surface would include bench roads and surface drains. Construct 11-acre Evaporation Pond South of PSCT An 11-acre evaporation pond would be constructed north of the RCF Pond and south of the PSCT with a footprint of approximately 500 feet by 400 feet. About 74,000 cy of soil would need to be excavated in the north end of the pond and this soil would be used to form a berm on the south end and placed and compacted as the foundation layer for the pond bottom. A HDPE membrane double pond liner with a LCRS and leak detection system would be placed on the


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foundation layer and a 1-foot thick soil and gravel cover would be placed on top of the liner. The foundation layer would be up to 2-feet thick that is re-compacted excavated soil to a relative compaction of 90 percent (ASTM D1557). The double liner system would include a primary 60-mil smooth HDPE geomembrane on the top with a 200-mil geonet drainage layer in the middle, followed by a secondary HDPE geomembrane below that is underlain by the foundation layer. A standard black HDPE geomembrane is proposed as the upper (primary) liner for increased heat retention to enhance evaporation potential. The drainage layer drains by gravity any liquids leaking through the primary layer into a sump as part of a LCRS. The secondary HDPE geomembrane is placed on a compacted foundation layer that is sloped at 1 percent or greater to allow gravity drainage towards an LCRS sump located within the footprint of the evaporation pond. The LCRS sump will be equipped with a liquids pump that is piped to an above ground storage tank. In addition, a leak detection system (such as lysimeters) to detect leaks in the vadose zone below the secondary layer will be evaluated during design. More details on the multi-layer RCRA pond liner were presented in Section 10.1.1. The evaporation pond would need to be periodically (assumed every 5 years) sampled for sediments, and periodically (assumed every 20 years) dredged to remove any accumulation of sediment. Environmental controls would be implemented to prevent wildlife contact with the evaporation pond as described in Section 10.1.4.2. The types of controls would be selected and designed during remedial design (after the ROD) and after input and consultation with U.S. FWS and input from CDFG. The wildlife controls may include, but not be limited to: perimeter fencing, elimination of wildlife habitat (vegetation), hazing, potential netting or screen mesh, and routine biological monitoring. Enhanced Evaporation System An enhanced evaporation system is included in this alternative to increase evaporation rates as may be required during the wet years that produce slightly higher amounts of extracted groundwater for the PSCT and PCT extraction, and which have significantly higher volumes of stormwater runoff that must also be managed in the evaporation pond. The FS assumes the use of two enhanced evaporation systems capable of 80 gpm flow each for this system. RCRA Cap for Pond 18 This alternative includes a RCRA cap for Pond 18 (2.8 acres) as shown on Figure 11-18D. The conceptual design and preliminary performance standards for the RCRA cap was discussed earlier in Section 10.1.1. Detailed specifications would be developed during remedial design. The cut/fill grading for leveling would require about 8,000 cy and 10,000 cy for the foundation layer. The surface of the cap will be sloped to allow sheet flow of stormwater towards the A-Series Pond. The borrow soil for these layers would come from the adjacent berm. An additional 10,000 cy would be required for the vegetative layer and this would come from the NW Borrow area. Hydroseeding would be used to spread a selected seed mix of native plant species on the top of the vegetative layer. Lined Retention Basin in Footprint of Ponds A-5 and Pond 13 Both Ponds A-5 and Pond 13 are filled to raise the bottom above future anticipated groundwater levels and then lined to be used as stormwater retention basins followed by a foundation layer. A HDPE pond liner such as GCL would be placed on the foundation layer and a 1-foot thick soil


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and gravel cover would be placed on top of the liner. More details on the pond liner were provided in Section 10.1.1. Pond A-5 is filled with about 40,000 cy of soil followed by a foundation layer of 9,000 cy to raise the bottom elevation by about 20 feet to 460 feet MSL. The 1-foot thick cover soil would require approximately 4,400 cy of soil. Similarly Pond 13 is filled with about 13,000 cy of soil to raise the bottom about 15 feet to about 385 feet MSL. The 1-foot cover soil would require approximately 3,500 cy for Pond 13. Stormwater Controls The top surface of the Pond 18 cap would be sloped to allow sheet flow of stormwater from the Pond 18 footprint to the A-Series Pond. Erosion control mats will be used in any steeper sections of the RCF and A-Series Ponds near the perimeter. The lined retention basin in the footprint of Pond A-5 would collect stormwater from the capped areas in RCRA Canyon and the stormwater would drain to the RCF Pond. The RCF and A-Series Pond caps are sloped to drain stormwater through the culvert under RCF Road. The stormwater from the capped RCF and A-Series Ponds will be discharged through the Pond 13 retention basin and through or around the wetlands. If the capped stormwater flow cannot be discharged under the substantive terms of the General Stormwater Permit, then it would need to be pumped to the evaporation pond. In that event, a larger evaporation pond may be required. Sampling and Testing During construction, the foundation layer of the caps will be tested for compaction to meet a relative compaction of 90 percent (ASTM D1557). Air monitoring would be conducted during the grading and cap construction activities. Soil physical and geotechnical properties will be tested for the proposed NW Borrow Area to ensure adequate quality and quantity of soils is available. Evaporation pond sediments will be periodically (assumed every 5 years) sampled for metals and organics to determine when the sediments might need to be dredged (assumed every 20 years). Inspection, Monitoring, Maintenance and Institutional Controls The monitoring component of this alternative includes periodic inspection, maintenance and repair of the cap and stormwater controls over the long term as discussed earlier in other FS Areas. Contingency for Pond Water Treatment In the event the quantity of pond water that remains in the A-Series and RCF Ponds just prior to remedy construction cannot all be evaporated based on the stormwater management plan (Section 10.1.3), the FS includes a contingency plan to bring a mobile treatment system which utilizes GAC and Reverse Osmosis to treat organics, TDS and metals, and then discharge the remaining stormwater under the substantive terms of an NPDES permit. The RO treatment of the high TDS stormwater will produce a large proportion of brine (up to 30 percent) or reject that would either have to be recycled to the new evaporation pond and managed in that system or disposed at a permitted disposal facility.


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11.5.1.3 Alternative 3 Ecological-cap (RCF Pond, Segregate East RCF) (2’) + Construct 11-Acre Lined Evaporation Pond (A-Series Pond) + RCRA Cap (Pond 18) + Lined Retention Basin (Pond A-5, Pond 13) + Stormwater Controls + ICs + Monitoring


Construct new 11-acre evaporation pond in the footprint of the A-Series Pond Manage stormwater to eliminate pond water prior to and during FS construction as

discussed in the Stormwater Plan presented in Section 10.1.3 Raise the bottom elevation of the RCF and A-Series Ponds above groundwater levels

and construct an ecological-cap over the RCF Pond covering an area of 11.4 acres Line pond bottoms for Pond A-5 and Pond 13 to create stormwater retention basins over

areas of 2.5 acres and 1.9 acres, respectively RCRA cap for Pond 18 over an area of 2.8 acres Stormwater controls with drainage and erosion controls for the capped areas including





Manage stormwater by eliminating pond water prior to and during FS construction and constructing new evaporation pond adequately sized to handle all water that cannot be discharged under substantive terms of the General Permit


The following provides a brief description of the conceptual design for the remedial alternative components: Ecological-cap for RCF Pond and Segregate East RCF This alternative involves constructing an ecological-cap over the RCF Pond over an area of 11.4 acres which consists of a 2-foot thick layer of clean top soil to control potential exposure to ecological receptors after the pond has been emptied (Figure 11-18B). Details on the ecological-cap design were presented in Section 10.1.1.5. Prior to constructing the cap, the RCF Pond East (about 3 acres) will be segregated and the RCF Pond West will be filled to raise the bottom to approximately 415 feet MSL. Approximately 55,000 cy of borrow soil would be required to raise the RCF Pond West pond bottom elevation, and is presumed to be borrowed from the NW Borrow Area. The fill soil and foundation layer compaction requirements are as discussed in Alternative 2. The berm separating the east and west portions of the RCF Pond runs north-south about 750 feet and is about 25 feet wide at the base and about 5 to 8 feet in height. About 6,000 cy of soil would be required to construct the berm. In addition, about 37,000 cy of borrow soil will be needed for the ecological-cap. This soil would be borrowed from the NW Borrow Area. The cap surface would be sloped towards the southwest to direct stormwater through the culvert under RCF Road to Pond 13 retention basin and discharged under the substantive terms of the General Permit.


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Construct 11-acre Evaporation Pond in the Footprint of the A-Series Pond This alternative involves constructing a HDPE pond liner over the A-Series Pond after expanding it to cover an area of 11 acres (Figure 11-18C). The evaporation pond would receive treated PSCT and PCT groundwater and any stormwater that cannot be discharged from the site. Prior to placing the liner, the pond will be filled to raise the bottom to approximately 425 feet MSL. A HDPE double pond liner with a LCRS and leak detection system would be placed on a foundation layer and a 1-foot thick soil cover would be placed on top of the liner. Details of the evaporation pond liner are the same as in Alternative 2 and presented in more detail in Section 10.1.1 under the RCRA pond liner discussion. Approximately 37,000 cy of borrow soil would be required to raise the pond bottom elevation and another 36,000 cy as a foundation layer. A total of approximately 48,000 cy would be obtained by excavating the northeast shoreline of the A-Series Pond. Excavating the northeast shoreline will also expand the A-Series Pond to 11 acres from 8 acres. The fill soil and foundation layer compaction requirements are as discussed in Alternative 2. About 18,000 cy of borrow soil will be needed for the 1-foot thick soil cover on top of the pond liner. The soil cover would be a sandy material. The evaporation pond would need to be periodically (assumed every 5 years) sampled for sediments, and periodically (assumed every 20 years) dredged to remove any accumulation of sediment. Environmental controls would be implemented to prevent wildlife contact with the evaporation pond as described in Section 10.1.4.2. The types of controls would be selected and designed during remedial design (after the ROD) and after input and consultation with U.S. FWS and CDFG. The wildlife controls may include, but not be limited to: perimeter fencing, elimination of wildlife habitat (vegetation), hazing, potential netting or screen mesh, and routine biological monitoring. Enhanced Evaporation System An enhanced evaporation system is included in this alternative to enhance evaporation rates as may be required during the wet years, as discussed in Alternative 2. RCRA Cap for Pond 18 This alternative includes a RCRA cap for Pond 18 (2.8 acres) as shown on Figure 11-18D and discussed in Alternative 2. The conceptual design and preliminary performance standards for the RCRA cap was discussed earlier in Section 10.1.1. Detailed specifications would be developed during remedial design. Lined Retention Basin in Footprint of Ponds A-5 and Pond 13 Both Ponds A-5 and Pond 13 are filled to raise the bottom above future anticipated groundwater levels and then lined to be used as stormwater retention basins. The soil volumes to raise the pond bottoms, the foundation layer and soil cover are the same as Alternative 2. Stormwater Controls The top surface of the Pond 18 cap would be sloped to allow sheet flow of stormwater from the Pond 18 footprint to the A-Series Pond. Erosion control mats will be used in any steeper sections of the RCF and A-Series ponds near the perimeter. The lined retention basin in the footprint of Pond A-5 would collect stormwater from the capped areas in RCRA Canyon and the stormwater would drain to the western portion of the RCF Pond. The stormwater from the capped western portion of the RCF Pond will be discharged through the Pond 13 retention basin


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through or around the wetlands. The stormwater in the eastern portion of the RCF Pond will be retained for evaporation. A stormwater diversion ditch is included (Figure 11-13B) to the north and east of the RCF Pond to keep other stormwater out of the eastern portion of the RCF Pond. Sampling and Testing The monitoring during construction of the caps including compaction testing and air monitoring is similar to Alternative 2. Soil physical and geotechnical properties will be tested for the borrow soils during remedial design as discussed earlier. Evaporation pond sediments will be periodically (assumed every 5 years) sampled for metals and organics to determine when the sediments might need to be dredged (assumed every 20 years). Inspection, Monitoring, Maintenance and Institutional Controls The monitoring component of this alternative includes periodic inspection, maintenance and repair of the cap and stormwater controls over the long term as discussed earlier in other FS Areas. Contingency for Pond Water treatment In the event the quantity of pond water that remains in the A-Series and RCF Ponds just prior to remedy construction cannot all be evaporated based on the stormwater management plan (Section 10.1.3), the FS includes a contingency plan to bring a mobile treatment system to treat TDS and metals and then discharge the remaining stormwater under a new site-specific NPDES Permit, as discussed earlier in Alternative 2. 11.5.1.4 Alternative 4 Ecological-cap (RCF Pond) (2’) + Construct 11-acre Lined Evaporation

Pond (A-Series Pond) + RCRA Cap (Pond 18) + Lined Retention Basin (Pond A-5 and 13) + Stormwater Controls + ICs + Monitoring


Construct new 11-acre evaporation pond in the footprint of the A-Series Pond after raising the pond bottom above anticipated groundwater levels

Manage stormwater to eliminate pond water prior to and during FS construction as discussed in the Stormwater Plan presented in Section 10.1.3

Raise the bottom of the RCF Pond above anticipated groundwater levels and construct an ecological-cap over the RCF Pond covering an area of 11.4 acres

Line pond bottom for Ponds A-5 and Pond 13 to create stormwater retention basins over areas of 2.5 acres and 1.9 acres, respectively

RCRA cap for Pond 18 over an area of 2.8 acres Stormwater controls with drainage and erosion controls for the capped areas including





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The following provides a brief description of the conceptual design for the remedial alternative components: Ecological-cap for RCF Pond This alternative involves constructing an ecological-cap over the RCF Pond encompassing an area of 11.4 acres, which consists of a 2-foot thick clean top soil layer to control potential exposure to ecological receptors after the pond has been emptied (Figure 11-19B). Details on the ecological-cap design were presented in Section 10.1.1.5. Prior to constructing the cap, the pond will be filled to raise the bottom elevation to approximately 415 feet MSL. Approximately 95,000 cy of borrow soil would be required to raise the RCF Pond bottom elevation, and is presumed to be borrowed from the NW Borrow Area. The fill soil and foundation layer compaction requirements are as discussed in Alternative 2. In addition, about 40,000 cy of borrow soil will be needed for the ecological-cap. This soil would be borrowed from the NW Borrow Area. The cap surface would be sloped towards the southwest to direct stormwater through the culvert under RCF Road to the Pond 13 retention basin and discharged through or around the wetlands under the substantive terms of the General Permit. Construct 11-acre Evaporation Pond in the Footprint of the A-Series Pond This alternative involves constructing a HDPE double-pond liner with LCRS and leak detection system over the A-Series Pond after expanding it to cover an area of 11 acres (Figure 11-19C), as discussed in Alternative 3. Prior to placing the liner, the pond will be filled to raise the bottom to approximately 425 feet MSL. The borrow soil required for raising the bottom, the foundation layer, and soil cover is the same as in Alternative 3. The environmental controls that would be implemented to prevent wildlife contact with the evaporation pond are also the same as in Alternative 3. Enhanced Evaporation System An enhanced evaporation system is included to enhance evaporation rates especially during the wet years as described in Alternative 2. RCRA Cap for Pond 18 The RCRA cap design for Pond 18 covers 2.8 acres and is the same as that described for Alternative 2 (Figure 11-19D). Lined Retention Basin in Footprint of Pond A-5 and Pond 13


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Both Pond A-5 and Pond 13 are filled to raise the bottom above future anticipated groundwater levels and then lined to be used as stormwater retention basins as described earlier for Alternative 2. Stormwater Controls The top surface of the Pond 18 cap would be sloped to allow sheet flow of stormwater from the Pond 18 footprint to the A-Series Pond. Erosion control mats will be used in any steeper sections of the RCF and A-Series ponds near the perimeter. The lined retention basin in the footprint of Pond A-5 would collect stormwater from the capped areas in RCRA Canyon and the stormwater would drain to the RCF Pond. The RCF Pond cap will be sloped to drain stormwater through the culvert under RCF Road. The stormwater from the capped RCF Pond will be discharged through the Pond 13 retention basin through or around the wetlands. If the capped stormwater flow cannot be discharged under the General Permit, then it would need to be pumped to the evaporation pond. In that event, a larger evaporation pond may be required. Sampling and Testing The monitoring during construction of the caps including compaction testing and air monitoring is similar to Alternative 2. Soil physical and geotechnical properties will be tested for the borrow soils during remedial design as discussed earlier. Evaporation pond sediments will be periodically (assumed every 5 years) sampled for metals and organics to determine when the sediments might need to be dredged (assumed every 20 years). Inspection, Monitoring, Maintenance and Institutional Controls The monitoring component of this alternative includes periodic inspection, maintenance and repair of the cap and stormwater controls over the long term as discussed earlier in other FS Areas. Contingency for Pond Water Treatment A contingency plan to mobilize a mobile treatment system with GAC and Reverse Osmosis to treat organics, TDS and metals, and discharge the treated water under a new site-specific NPDES Permit is included as in Alternative 2. 11.5.1.5 Alternative 5 Ecological-cap (RCF Pond, Portion of A-Series Pond) (2’) + Construct 6-

acre Lined Evaporation Pond (A-Series Pond) + RCRA Cap (Pond 18) + Lined Retention Basin (Pond A-5 and Pond 13) + Stormwater Controls + ICs + Monitoring



Raise the bottom of the RCF Pond above groundwater levels and construct an ecological-cap over the RCF Pond covering an area of 11.4 acres

Raise the bottom of the A-Series Pond above groundwater levels with fill soil from the northeast shore line, and convert a portion of the A-series Pond to a 6-acre lined evaporation pond using a HDPE membrane liner. The remainder of the A-Series Pond (5-acre) will be covered with an ecological-cap similar to the RCF Pond.


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Line pond bottoms for Ponds A-5 and Pond 13 to create stormwater retention basins over areas of 2.5 acres and 1.9 acres, respectively




Prevent ecological receptors from potential exposures to shallow soil or sediment (0-5 feet bgs) at RCF and A-Series ponds


Manage stormwater by eliminating pond water prior to and during FS construction and constructing new evaporation pond adequately sized to handle all water that cannot be discharged under the substantive terms of the General Permit


The following provides a brief description of the conceptual design for the remedial alternative components: Ecological-cap for RCF Pond This alternative involves constructing an ecological-cap over the RCF Pond over an area of 11.4 acres, which consists of a 2-foot thick clean top soil layer to control potential exposure to ecological receptors after the pond has been emptied (Figure 11-20B). Details on the ecological-cap design were presented in Section 10.1.1.5. Prior to constructing the cap, the pond will be filled to raise the bottom elevation to approximately 415 feet MSL. Approximately 95,000 cy of borrow soil would be required to raise the RCF Pond bottom to this elevation, and is presumed to be borrowed from the NW Borrow Area. The fill soil and foundation layer compaction requirements are as discussed in Alternative 2. In addition, about 40,000 cy of borrow soil will be needed for the ecological-cap. This soil would be borrowed from the NW Borrow Area. The cap surface would be sloped towards the southwest to direct stormwater through the culvert under RCF Road to the Pond 13 retention basin and discharged through or around the wetlands under the substantive terms of the General Permit. Ecological-cap for portion of A-Series Pond This alternative involves constructing an ecological-cap over a 5-acre portion of the A-Series Pond, which consists of a 2-foot thick clean top soil layer to control potential exposure to ecological receptors (Figure 11-20C). Prior to constructing the ecological-cap, the pond will be filled to raise the bottom elevation to approximately 425 feet MSL. Approximately 48,000 cy of borrow soil would be required to raise the pond bottom to this elevation and is presumed to be borrowed from the NW Borrow Area. The fill soil and foundation layer compaction requirements are as discussed in Alternative 2. In addition, about 18,000 cy of borrow soil will be needed for the ecological-cap that is placed on top of the biotic barrier. The cap surface would include bench roads and surface drains.


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Construct 6-acre Evaporation Pond in the Footprint of the A-Series Pond This alternative involves constructing a HDPE double pond liner with LCRS and leak detection system over a 6-acre portion of the A-Series Pond (Figure 11-20C). The liner details are as discussed in Alternative 3 except the pond in this alternative is smaller at 6 acres. Prior to placing the liner, the pond will be filled using 48,000 cy of fill soil to raise the bottom elevation to approximately 425 feet MSL. The fill soil and foundation layer compaction requirements are as discussed in Alternative 2. In addition, 46,000 cy of fill soil will be needed to construct the six individual pond cells that are 1-acre each. The environmental controls that would be implemented to prevent wildlife contact with the evaporation pond are also the same as in Alternative 3. Enhanced Evaporation System An enhanced evaporation system is included to enhance evaporation rates, especially during wet years as described in Alternative 2. RCRA Cap for Pond 18 The RCRA cap design for Pond 18 covers 2.8 acres and is the same as that described for Alternative 2 (Figure 11-20D). Lined Retention Basin in Footprint of Pond A-5 and Pond 13 Both Pond A-5 and Pond 13 are filled to raise the bottom above future anticipated groundwater levels and then lined to be used as stormwater retention basins as described earlier for Alternative 2. Stormwater Controls The top surface of the Pond 18 cap would be sloped to allow sheet flow of stormwater from the Pond 18 footprint to the A-Series Pond. Erosion control mats will be used in any steeper sections of the RCF and A-Series Ponds near the perimeter. The lined retention basin in the footprint of Pond A-5 would collect stormwater from the capped areas in RCRA Canyon and the stormwater would drain to the RCF Pond. The RCF Pond cap will be sloped to drain stormwater through the culvert under RCF Road. The stormwater from the capped RCF Pond will be discharged through the Pond 13 retention basin through or around the wetlands. If the capped stormwater flow cannot be discharged under the substantive terms of the General Permit, then it would need to be pumped to the evaporation pond. In that event, a larger evaporation pond may be required. Sampling and Testing The monitoring during construction of the caps, including compaction testing and air monitoring, is similar to Alternative 2. Soil physical and geotechnical properties will be tested for the borrow soils during remedial design as discussed earlier. Evaporation pond sediments will be periodically (assumed every 5 years) sampled for metals and organics to determine when the sediments might need to be dredged (assumed every 20 years). Inspection, Monitoring, Maintenance and Institutional Controls


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The monitoring component of this alternative includes periodic inspection, maintenance and repair of the cap and stormwater controls over the long term as discussed earlier for other FS Areas. Contingency for Pond Water Treatment A contingency plan to use a mobile treatment system with GAC and Reverse Osmosis to treat organics, TDS and metals, and discharge the treated water under a new site-specific NPDES Permit is included, as in Alternative 2. 11.5.1.6 Alternative 6 Ecological-cap (RCF Pond, A-Series Pond) (2’) + RCRA Cap (Pond 18) +

Lined Retention Basin (Pond A-5 and Pond 13) + Stormwater Controls + ICs + Monitoring



Raise the bottom of the RCF Pond and A-Series Pond above groundwater levels and construct an ecological-cap over the RCF and A-Series Ponds

Line pond bottoms for Pond A-5 and Pond 13 to create stormwater retention basins over areas of 2.5 acres and 1.9 acres, respectively




Prevent ecological-receptors from potential exposures to shallow soil or sediment (0-5 feet bgs) at RCF and A-Series Ponds


Complement the remedial alternatives in Area 5 groundwater where the groundwater is treated for both VOCs and inorganics.

Manage stormwater by eliminating pond water prior to and during FS construction Incorporate stormwater drains for the capped areas to direct clean stormwater to the

culvert under RCF Road for discharge through or around the wetlands under the substantive terms of the General Permit.

The following provides a brief description of the conceptual design for the remedial alternative components: Ecological-cap for RCF Pond This alternative involves constructing an ecological-cap over the RCF Pond over an area of 11.4 acres, which consists of a 2-foot thick clean top soil layer to control potential exposure to ecological-receptors after the pond has been emptied (Figure 11-21B). Details on the ecological-cap design were presented in Section 10.1.1.5. Prior to constructing the cap, the pond will be filled to raise the bottom to approximately 415 feet MSL. Approximately 95,000 cy of borrow soil would be required to raise the RCF pond bottom and is presumed to be borrowed


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from the NW Borrow Area. In addition, about 40,000 cy of borrow soil will be needed for the ecological-cap. This soil would be borrowed from the NW Borrow Area. The fill soil and foundation layer compaction requirements are as discussed in Alternative 2. The cap surface would be sloped and include bench roads and surface drains to direct stormwater through the culvert under RCF Road to Pond 13 retention basin and discharged under the substantive terms of the General Permit. Ecological-cap for A-Series Pond This alternative involves constructing an ecological-cap over the A-Series Pond over an area of 11 acres which consists of a 2-foot thick layer of clean top soil to control potential exposure to ecological-receptors (Figure 11-21B). Prior to constructing the ecological-cap, the pond will be filled to raise the bottom to approximately 425 feet MSL. Approximately 85,000 cy of borrow soil would be required to raise the pond bottom and is presumed to be borrowed from the NW Borrow Area. The fill soil and foundation layer compaction requirements are as discussed in Alternative 2. In addition, about 39,000 cy of borrow soil will be needed for the ecological-cap that is placed on top of the biotic barrier. The cap surface would include bench roads and surface drains. RCRA Cap for Pond 18 The RCRA cap design for Pond 18 covers 2.8 acres and is the same as that described for Alternative 2 (Figure 11-18D). Lined Retention Basin in Footprint of Pond A-5 and Pond 13 Both Pond A-5 and Pond 13 are filled to raise the bottom above future anticipated water levels and then lined to be used as stormwater retention basins as described earlier for Alternative 2. Stormwater Controls With this alternative, all of the site’s stormwater would be sent to a permitted disposal facility. This alternative would require that the entire RCRA Canyon in FS Area 2 be capped. The stormwater from the ecological-cap on the A-Series Pond and Pond 18 cap will drain to the RCF Pond. The lined retention basin in the footprint of Pond A-5 would collect stormwater from the capped areas in RCRA Canyon and the stormwater would drain by gravity to the RCF Pond. The RCF Pond cap will be sloped to drain stormwater through the culvert under RCF Road. The stormwater from the capped RCF Pond will be discharged through the Pond 13 retention basin and through or around the wetlands. Sampling and Testing The monitoring during construction of the caps, including compaction testing and air monitoring, is similar to Alternative 2. Soil physical and geotechnical properties will be tested for the borrow soils during remedial design as discussed earlier. Inspection, Monitoring, Maintenance and Institutional Controls The monitoring component of this alternative includes periodic inspection, maintenance and repair of the cap and stormwater controls over the long term as discussed earlier in other FS Areas.


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Contingency for Pond Water Treatment A contingency plan to mobilize a mobile treatment system with GAC and Reverse Osmosis to treat organics, TDS and metals and discharge the treated water under a new site-specific NPDES Permit is included as in Alternative 2. 11.5.1.7 Alternative 7 ET cap (RCF Pond, Portion of A-Series Pond) + Construct 6-acre Lined

Evaporation Pond (A-Series Pond) + RCRA Cap (Pond 18) + Lined Retention Basin (Pond A-5 and 13) + Stormwater Controls + ICs + Monitoring



Raise the bottom elevation of the RCF Pond above anticipated groundwater levels and construct an ET cap over the RCF Pond covering an area of 11.4 acres

Raise the bottom elevation of the A-Series Pond above anticipated groundwater levels with fill soil from the northeast shore line, and convert a portion of the A-series Pond to a 6-acre lined evaporation pond using geo-composite HDPE liner. The remainder of the A-Series Pond (5-acre) will be covered with an ET cap similar to the RCF Pond.

Line Pond bottoms for Ponds A-5 and Pond 13 to create stormwater retention basins over areas of 2.5 acres and 1.9 acres, respectively




Prevent ecological-receptors from potential exposures to shallow soil or sediment (0-5 feet bgs) at RCF and A-Series Ponds




The following provides a brief description of the conceptual design for the remedial alternative components: ET cap for RCF Pond This alternative involves constructing an ET soil cap over the RCF Pond over an area of 11.4 acres. The ET cap would consist of a 1-foot thick foundation layer with clay soil compacted to 90 percent (ASTM D 1557) and 4 feet of claylike soil that is lightly compacted to about 85 percent for the vegetative layer. (Figure 11-22B). The ET cap is intended to store water, thus allowing the growth of vegetation and the removal of soil moisture through evaporation and transpiration.


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Preliminary specification for the ET soil cap soil is that it be classified by the Unified Soil Classification System as CL, SC or ML and have greater than 50 percent fines content. A more detailed description of the ET cap was presented in Section 10.1.1. Detailed specifications would be developed during remedial design. Prior to constructing the ET cap, the pond will be filled to raise the bottom elevation to approximately 415 feet MSL. Approximately 95,000 cy of borrow soil would be required to raise the RCF pond bottom and is presumed to be borrowed from the NW Borrow Area. The fill soil and foundation layer compaction requirements are as discussed in Alternative 2. In addition, about 101,000 cy of borrow soil will be needed for the ET cap. This soil would be borrowed from the NW Borrow Area, and augmented as necessary to meet design specifications. The weathered claystone borrow material may need to be screened, pulverized/crushed in a pug mill (or with a pulverizer), and moisture conditioned prior to placement to meet the performance criterion for the ET cap (Section 10.1.1). See discussion of processing and amendments used with claystone soils for previous site capping efforts in Section 10.1.2. The cap surface would be sloped towards the southwest to direct stormwater through the culvert under the RCF Road to Pond 13 retention basin and discharged under the substantive terms of the General Permit. ET cap for portion of A-Series Pond This alternative involves constructing an ET cap over a 5-acre portion of the A-Series Pond, which consists of 5 feet of engineered low permeability claylike soil that is lightly compacted to about 85 percent relative compaction (ASTM D 1557) (Figure 11-22B). Prior to constructing the ET cap, the pond will be filled to raise the bottom elevation to approximately 425 feet MSL. Approximately 48,000 cy of borrow soil would be required to raise the pond bottom and is presumed to be borrowed from the NW Borrow Area. In addition, about 44,000 cy of borrow soil will be needed for the ET cap. This soil would be borrowed from the NW Borrow Area, and augmented as necessary to meet design specifications. Construct 6-acre Evaporation Pond in the Footprint of the A-Series Pond This alternative involves constructing a HDPE double pond liner with LCRS and leak detection system over a 6-acre portion of the A-Series Pond (Figure 11-22B) as discussed in Alternative 3 except the size of the evaporation pond is smaller at 6 acres. Prior to placing the liner, the pond will be filled using 48,000 cy of fill soil to raise the bottom elevation to approximately 425 feet MSL. The fill soil and foundation layer compaction requirements are as discussed in Alternative 2. In addition, 46,000 cy of fill soil will be needed to construct the six individual pond cells that are 1-acre each. The environmental controls that would be implemented to prevent wildlife contact with the evaporation pond are also the same as in Alternative 3. Enhanced Evaporation System An enhanced evaporation system is included to enhance evaporation rates especially during wet years, as described in Alternative 2. RCRA Cap for Pond 18 The RCRA cap design for Pond 18 covers 2.8 acres and is the same as that described for Alternative 2 (Figure 11-18D). Lined Retention Basin in Footprint of Pond A-5 and Pond 13


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Both Pond A-5 and Pond 13 are filled to raise the bottom above future anticipated groundwater levels and then lined to be used as stormwater retention basins as described earlier for Alternative 2. Stormwater Controls The stormwater controls are the same as in Alternative 5, with the only difference being that in this alternative the RCF Pond has an ET cap instead of an Ecological-cap. Sampling and Testing The monitoring during construction of the caps, including compaction testing and air monitoring, is similar to Alternative 2. Soil physical and geotechnical properties will be tested for the borrow soils during remedial design as discussed earlier. Evaporation pond sediments will be periodically (assumed every 5 years) sampled for metals and organics to determine when the sediments might need to be dredged (assumed every 20 years). Inspection, Monitoring, Maintenance and Institutional Controls The monitoring component of this alternative includes periodic inspection, maintenance and repair of the cap and stormwater controls over the long term as discussed earlier for other FS Areas. Contingency for Pond Water Treatment A contingency plan to use a mobile treatment system with GAC and RO to treat TDS and metals and discharge the treated water under a new site-specific NPDES Permit is included, as in Alternative 2. 11.5.1.8 Alternative 8 Excavate (RCF Pond, A-Series Pond) (5’) + Construct New 11-acre

Lined Evaporation Pond (North of RCF Pond) + RCRA Cap (Pond 18) + Lined Retention Basin (Pond A-5, Pond 13)+ Stormwater Controls + ICs + Monitoring


Construct new 11-acre evaporation pond north of the RCF Pond and south of the PSCT Manage stormwater to eliminate pond water prior to and during FS construction as

discussed in the Stormwater Plan presented in Section 12 Excavate up to 5 feet of the sediments in the RCF and A-Series Ponds and backfill an

area of 19.4 acres Line pond bottom for Pond A-5 and Pond 13 to create stormwater retention basins over

areas of 2.5 acres and 1.9 acres, respectively RCRA cap for Pond 18 over an area of 2.8 acres Stormwater controls with drainage and erosion controls for the capped areas including




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The following provides a brief description of the conceptual design for the remedial alternative components: Excavation (2’-5’) for RCF Pond This alternative involves excavation of up to a maximum of 5 feet of shallow soil (sediments) across the RCF Pond that covers 11.4 acres after the pond water has been removed (Figure 11-23B). The depth of excavation at various locations across the RCF would be determined by a preliminary subsurface investigation to further delineate contamination. The sidewalls would be sloped back 1:1. For cost estimation purposes an average of 3 feet of excavation is assumed across the entire area. This would result in a total excavation of 55,000 cy. The excavated soils are assumed to be sent for disposal at Clean Harbors, Buttonwillow, California. A total of about 82,500 tons of soil are transported for disposal as a mix of non-RCRA hazardous and nonhazardous at a 50:50 ratio. At an estimated 800 tons per day of excavation and disposal, this excavation would last approximately 5 to 6 months and could be completed in one dry season. The excavation would be backfilled with clean borrow soil from the NW Borrow Area and compacted to a relative compaction of 90 percent (ASTM D 1557). The total borrow soil volume is estimated to be about 60,500 cy. In addition, raising the pond bottom elevation to 415 feet MSL to ensure being above the anticipated water table and incorporating a 1 percent top slope would require an additional 60,000 cy of fill from the borrow area. The backfilled surface would be sloped to the southwest to drain through the culvert under RCF Road to Pond 13 retention basin and discharged under the substantive terms of the General Permit. Excavation (2’-5’) for A-Series Pond This alternative involves excavation of up to a maximum of 5 feet of shallow soil (sediments) across the A-Series Pond that covers 8 acres after the pond water has been removed (Figure 11-23B). The depth of excavation at various locations across the A-Series Pond would be determined by a preliminary subsurface investigation to further delineate contamination. The sidewalls would be sloped back 1:1. For cost estimation purposes an average of 3 feet of excavation is assumed across the entire area. This would result in a total excavation of 39,000 cy. The excavated soils are assumed to be sent for disposal at Clean Harbors, Buttonwillow, California. A total of about 58,500 tons of soils are transported for disposal as non-RCRA hazardous and nonhazardous waste at a 50:50 ratio. At an estimated 800 tons per day of excavation and disposal, this excavation would last approximately 4 to 5 months. The excavation would be backfilled with clean borrow soil from the NW Borrow Area and compacted to a relative compaction of 90 percent (ASTM D 1557). The total borrow soil volume is estimated to be about 42,900 cy. In addition, raising the pond bottom elevation to 425 feet MSL to ensure being above the anticipated water table and to incorporate a top surface slope of 1


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percent, would require an additional 85,000 cy of fill from the NW Borrow Area. The backfilled surface would be sloped to the southeast and conveyed by pipeline to the culvert under RCF Road to Pond 13 retention basin and discharged under the substantive terms of the General Permit. Construct 11-acre Evaporation Pond North of RCF Pond A 11-acre double-lined evaporation pond with LCRS and leak detection system would be constructed north of the RCF Pond and south of the PSCT as discussed in Alternative 2. The environmental controls that would be implemented to prevent wildlife contact with the evaporation pond are also the same as in Alternative 2. Enhanced Evaporation System An enhanced evaporation system is included to enhance evaporation rates especially during wet years as described in Alternative 2. RCRA Cap for Pond 18 The RCRA cap design for Pond 18 covers 2.8 acres and is the same as that described for Alternative 2 (Figure 11-18D). Lined Retention Basin in Footprint of Ponds A-5 and Pond 13 Both Ponds A-5 and Pond 13 are filled to raise the bottom elevation above future anticipated groundwater levels and then lined to be used as stormwater retention basins as described earlier for Alternative 2. Stormwater Controls The top surface of the backfilled soil would incorporate a 1 percent slope and drains to collect and convey stormwater on the cap to the nearest collector drains. Erosion control mats will be used in any steeper sections of pond near the perimeter that have slopes steeper than 2.5:1 (H:V). The stormwater from the capped RCF and A-Series Ponds will be discharged through the Pond 13 retention basin through or around the wetlands. Sampling and Testing A greater amount of air monitoring and dust control would be required with this alternative during the excavation because it involves more extensive excavation of contaminated soils. Soil physical and geotechnical properties will be tested for the proposed NW Borrow Area to ensure adequate quality and quantity of soils is available for backfill. The backfilled soils will be tested for compaction. Evaporation pond sediments will be periodically (assumed every 5 years) sampled for metals and organics to determine when the sediments might need to be dredged (assumed every 20 years). Inspection, Monitoring, Maintenance and Institutional Controls The monitoring component of this alternative includes periodic inspection, maintenance and repair of the cap and stormwater controls over the long term as discussed earlier in other FS Areas.


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Contingency for Pond Water Treatment A contingency plan to use a mobile treatment system with GAC and Reverse Osmosis to treat TDS and metals and discharge the treated pond water under a new site-specific NPDES Permit is included as discussed under Alternative 2. 11.5.2 Detailed and Comparative Analysis of Remedial Alternatives The detailed evaluation for the eight remedial alternatives including the No Action alternative is presented in Table 11-5. The following is the comparative analysis where for each CERCLA criteria the ratings and performance of each alternative is compared. 11.5.2.1 Overall Protection of Human Health and Environment Alternatives 2 through 8 are considered protective because the pond water is pumped to the new evaporation pond and the direct contact exposures to sediment contaminants for ecological receptors are addressed by capping or excavation as part of pond closure requirements. Cap maintenance, monitoring and ICs for the capped or closed ponds would ensure that workers and ecological receptors are protected for the long term. Similarly the stormwater controls including erosion controls and stormwater drains and channel maintenance and monitoring would ensure that soil contaminants do not migrate through sediments. Alternatives 2 through 8 include a stormwater management plan that sends capped area stormwater discharge under the substantive terms of the General Permit and any uncapped area stormwater to an evaporation pond. Alternative 1 would not be protective because it does not include any remediation or ICs. 11.5.2.2 Compliance with ARARs Alternatives 2 through 8 would comply with ARARs; whereas Alternative 1 would not comply with ARARs or achieve RAOs. 11.5.2.3 Long Term Effectiveness Alternatives 2 and 8 are rated moderate while Alternatives 3, 4, 5, 6 and 7 are rated moderate to good. Alternatives 2 through 7 meet the RAOs by pumping out the pond water and capping the pond bottoms, while Alternative 8 meets the RAOs by excavating the impacted shallow soil up to a maximum of 5 feet bgs and placing clean backfill over it. This eliminates the potential direct contact exposures to workers and ecological receptors. Alternatives 2, 6 and 8 allow surface water infiltration in the RCF and A-Series Ponds and do not have a contingency if the groundwater rises unexpectedly in the future. Alternatives 3, 4, 5 and 7 will allow surface water infiltration at the RCF Pond but not at the A-Series Pond. Alternative 3 has a contingency plan with the berm segregating the East RCF that will allow evaporation of any groundwater infiltration. However, the concern of rising water table can be addressed by adequately raising the bottom of the ponds with fill prior to capping. 11.5.2.4 Reduction of Toxicity, Mobility and Volume through Treatment Alternatives 2, 3, 4, 5, 6 and 7 are rated poor while Alternative 8 is rated poor to moderate. None of the alternatives truly involve soil treatment to address contamination. Alternative 8 involves excavation to remove contaminants at that location but involves disposal at a Class I


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landfill. Though it does not involve treatment Alternative 8 is given one step higher rating of moderate. Alternatives 2 through 7 involve reduction of potential ecological exposures by capping and stormwater and erosion controls but because these do not involve any removal of contaminant mass and because there is not much difference between Alternatives 2 through 7 with respect to RTMV, they are all rated low and at the same rating of poor. 11.5.2.5 Short Term Effectiveness Alternatives 2, 3 and 4 are rated moderate, while Alternatives 5, 6 and 7 are rated moderate to good and Alternative 8 is rated poor to moderate. Alternatives 2, 3 and 4 include a larger 11-acre evaporation pond that has a higher potential for ecological exposures to pond water that is contains elevated inorganics and metals. This is because it is more difficult to provide effective ecological protection with the netting and drift fences with a larger pond. Alternatives 5 and 7 are rated higher because they include a smaller 6-acre evaporation pond that is constructed as six 1-acre pond cells, where the ecological protection measures can be more effectively implemented. Alternative 6 has no evaporation pond and hence does not require ecological mitigation measures. Alternatives 2 through 7 have no significant exposure risk because capping will mostly cover impacted sediments with only limited components of excavation such as cut/fill grading prior to capping and the northeast shoreline excavation for the A-Series Pond. However, Alternative 8 involves a significantly larger excavation (93,000 cy) of sediments up to 5 feet thick, which can cause potential contaminant emissions as dust and potentially pose a risk to workers. Routine dust control procedures with a water truck are included as part of all alternatives. In addition, Alternative 8 includes the risk of transporting 140,000 tons of impacted soil to an outside landfill (approximately 120 miles to Buttonwillow). Furthermore, Alternative 8 has a larger 11-acre evaporation pond that further lowers the rating for STE. 11.5.2.6 Implementability Alternatives 2, 3 and 4 are rated moderate, while Alternatives 5, 6 and 7 are rated higher at moderate to good, and Alternative 8 is rated moderate. As discussed with STE, Alternatives 2, 3 and 4 include a larger 11-acre evaporation pond that is considered more challenging to implement ecological protection measures and hence rated lower than Alternatives 5, 6 and 7. Alternatives 5 and 7 have a smaller 6-acre evaporation pond that is constructed as six 1-acre pond cells for which ecological protection is more easily provided. Alternative 6 has no evaporation pond and thus does not require such ecological protection. Alternatives 2 through 7 have minor challenges with capping the deepest portions of the ponds and difficulties with earthmoving equipment in muddy conditions. However, the challenges with Alternative 8 are considered somewhat greater because it involves excavation of the sediments that would likely be muddier and hence more challenging for excavation equipment. Several vendors are available with experience in landfill projects and, in general, excavation is not an implementability concern. 11.5.2.7 Cost The total present worth cost is presented for Alternatives 2 through 8 in the table below for discount rates 3 percent and 7 percent and timeframes of 30 years and 100 years in 2014$. The cost for Alternative 1 is $0 and is not shown. Alternatives 3 through 6 are moderate for cost while Alternative 7 is moderate to high and Alternatives 2 and 8 are high. Alternative 6 is the lowest in present worth cost because it does not include an evaporation pond, followed by Alternatives 5, 7, 3, 4, 2, and 8 in ascending order.


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Alt No.

Capital Cost Annual

Cost

Total Present Worth

Time frame



2 $18,272,000 $458,000 30-year $29,436,000 $22,217,000

100-year $41,378,000 $27,068,000

3 $13,739,000 $458,000 30-year $25, 447,000 $18,771,000

100-year $36,631,000 $20,505,000

4 $14,092,000 $458,000 30-year $25,761,000 $19,042,000

100-year $37,005,000 $20,785,000

5 $13,131,000 $386,000 30-year $21,621,000 $16,287,000

100-year $30,318,000 $17,636,000

6 $10,590,000 $255,000 30-year $14,524,000 $11,349,000

100-year $19,403,000 $12,105,000

7 $15,658,000 $386,000 30-year $23,869,000 $18,225,000

100-year $32,999,000 $19,640,000

8 $39,267,000 $396,000 30-year $48, 520,000 $38,878,000

100-year $58,495,000 $40,424,000 11.5.2.8 Green Impacts Assessment The range of green technologies that can play a role in minimizing environmental impacts of the remedial alternatives and technology components are discussed in Section 12.7. Appendix F presents the qualitative assessment of the environmental footprint for these alternatives based on green remediation criteria such as GHG emissions, energy usage, air emissions, collateral risk, community impacts, resources lost, and water usage. The Appendix F evaluation was used to determine an overall rating for the alternative in Table 11-5. Alternatives 3 through 6 are moderate while Alternative 2 and 7 are moderate to high and Alternative 8 is high with respect to green and sustainability impacts. Alternatives 2 and 7 have a larger amount of earthwork than the other alternatives and Alternative 8 has the highest including transportation. The larger amount of earthwork implies a greater amount of operational time for the earth moving equipment, and higher fuel use, GHG and other air emissions and resource use.

11.5.3 Area 4 Evaluation Summary

All of the active remedial alternatives for Area 4, Alternatives 2 through 8 meet the threshold requirements of Overall Protection of Human Health and Environment and Compliance with ARARs. Alternative 1 (No Action) is not evaluated for balancing criteria because it does not meet the threshold requirements. Alternatives 5, 6 and 7 are rated better with respect to STE and Implementability than Alternatives 2, 3 and 4. And with respect to LTE and RTMV, Alternatives 5, 6 and 7 are rated about the same as Alternatives 2, 3 and 4. Alternative 8 was clearly the lowest rated of the active remedial alternatives. Between Alternatives 5, 6 and 7, Alternative 7 is the highest in cost and in green impacts assessment rating. Between Alternatives 5 and 6, Alternative 6 is lower in cost but it requires that there be no evaporation pond, which means that all the extracted groundwater at the site be treated for inorganics by RO and discharged under the substantive terms of the General Permit. If the additional cost of inorganics treatment of groundwater is included, Alternative 6 would be very high in total


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present worth cost. Hence, Alternative 5 is considered the highest rated alternative in FS Area 4.

11.6 Detailed Evaluation of FS Area 5 Groundwater This section presents the description of the selected remedial alternatives, the detailed evaluation, the green impacts assessment evaluation, and the comparative analysis of the groundwater remedial alternatives for Area 5 North, 5 South and 5 West. As discussed earlier in Section 10.6, a groundwater ARAR waiver will be requested (as presented in Section 8.5 and Appendix A) based on Technical Impracticability of restoring groundwater to drinking water standards for the TI Zone that includes the Upper and Lower HSU of Area 5 North for organic and inorganic contaminants. Specifically, the TIE concluded that the groundwater restoration alternatives in the Area 5 North would not be able to restore the groundwater to MCL standards within a reasonable timeframe. Where groundwater ARARs are waived at a Superfund site due to technical impracticability, the USEPA’s general guidance is that the site must consider source control and containment and source removal alternatives to the extent practicable to prevent further migration of the contaminated groundwater plume and prevent exposure to the contaminated groundwater. The following subsection presents the combined alternative and the alternative descriptions. No ARAR waiver is requested for Area 5 South and Area 5 West and the remedial evaluations of the Upper HSU of Area 5 South and Area 5 West are addressed separately later in this Section 11.6.4 and Section 11.6.7 respectively. The groundwater in the Lower HSU of Areas 5 South and 5 West do not require any evaluation as they currently meet ARARs. 11.6.1 Description of Remedial Alternatives for Area 5 North Table 11-1 shows the list of seven retained remedial alternatives for Area 5 North resulting from the screening evaluation. This section presents a description of these remedial alternatives for Area 5 North, followed by the detailed analysis (Section 11.6.2), and evaluation summary (Section 11.6.3). In the presentation of Area 5 North alternatives for groundwater below, it should be noted that capping anticipated as part of the soil remedy for FS Area 1 (including the Central Drainage Area, Burial Trench Area and the PCB Landfill) will further prevent or minimize potential contaminant leaching into groundwater. Thus the capping remedy for soils in FS Area 1 will be a significant source reduction component of the groundwater remedy, though it is not formally listed as a remedy component in these alternatives below. Also, the existing remedial features such as the capping of the P/S Landfill and the EE/CA Area, and the PSCT extraction already provide containment or control of the source areas and are anticipated to continue to be in place as part of the future site remedy. 11.6.1.1 Alternative 1 No Action The No Action alternative is included as required by NCP. No Action implies that the source control activities and monitoring that are ongoing currently would not be occurring.


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11.6.1.2 Alternative 2 Extraction (PSCT, Gallery Well) + Treat and Discharge to Evaporation

Pond + MNA + ICs + Monitoring This alternative includes the following components for FS Area 5 North (Figure 11-24A):

Extraction of PSCT and Gallery Well as currently implemented for source control Treat and Discharge PSCT groundwater to evaporation pond MNA for dissolved organics plume in FS Area 5 North Sump 9B and Road Sump features are retained as a contingency measure Institutional controls, maintenance and monitoring to protect the groundwater


Contain and/or control contamination sources within the Area 5 North boundary, where groundwater restoration is not technically practicable.

Extraction at the perimeter of Area 5 North to provide containment for the TI Zone in the future in the Upper HSU

Monitoring at the perimeter of Area 5 North to verify containment for the TI zone in the future in the Lower HSU, and implementation of extraction if necessary.

The following provides a brief description of the conceptual design for the remedial alternative components. Extraction at PSCT The liquids from the PSCT would continue to be removed by extraction pumps in PSCT-1 through PSCT-4, as currently operated. Details of the PSCT wells, action levels for pumping and extraction flow rates were presented in Section 10.6.2 under the discussion of existing site features. These wells are 8-inch PVC casings equipped with pumps and level controls. The extraction pump in each well is activated based on a set of action levels to turn on and turn off the pump. The extracted groundwater from the PSCT is treated in a groundwater treatment system using liquid phase carbon adsorption located at the Liquids Treatment Area (Figure 11-24B). The treatment system and the proposed upgrade are discussed below. Future projected groundwater extraction rates are expected to be significantly lower than current extraction rates based on the future remedy including capping of extensive areas of the site that will greatly reduce surface water infiltration rates. Based on the results of groundwater modeling (Appendix D), the PSCT extraction rates would decrease from 2,838,000 gallons per year (average 2006-2011) to between 1.9 and 1.93 million gallons per year based on dry season or wet season model results as discussed in Section 10.6.2. Extraction at Gallery Well Details of the Gallery Well extraction were presented in Section 10.6.2. The extracted liquids are pumped to the treatment system area in the Liquids Treatment Area where they are separated into the NAPL phase and groundwater. The NAPL liquid and impacted groundwater (leachate) is trucked for disposal at a permitted facility. As described in Section 10.1.8, the liquid levels in the P/S Landfill will decline as liquids are extracted from the Gallery Well and recharge to Area 5 North is significantly reduced with construction of the RCRA caps over the remaining areas that have not yet been capped. The timeframe for dewatering was estimated based on groundwater flow simulations and for this scenario involving Gallery Well extraction it was estimated to be


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approximately 10 years as discussed in Section 10.1.8.8. The NAPL extraction rate would decrease because the NAPL directly connected to the Gallery Well becomes smaller and the total liquids extraction rate would decrease as the overall liquid level and volume in the P/S Landfill drops. Future extraction rates at the Gallery Well are assumed to be in the same range as that currently observed, starting at about 450,000 gallons of concentrated liquids and 3,000 gallons of NAPL per year. The extraction rates are assumed to decline at a rate of 5 percent to 10 percent per year over a 10-year timeframe over which it is estimated that the P/S Landfill will become dewatered. The Gallery Well extraction rate assumed in the cost estimate for this alternative for the 10-year timeframe was presented in Section 10.1.8.5. This remedial feature is assumed to continue operation in the remedial evaluation and would be a component in addressing the remedial objectives of source control and containing NAPL where removal of NAPL is not technically practicable. GWTS Upgrade The proposed groundwater treatment system is similar to the existing system except it is upgraded with new storage tanks, transfer pumps, extraction pumps, filters and instrumentation. The GWTS would separately treat the Gallery well liquids using NAPL-water separation for disposal at an outside facility and the PSCT groundwater with liquid phase carbon adsorption prior to discharge to the evaporation pond in the footprint of the A-Series Pond. The proposed GWTS would be located in the Liquids Treatment Area, similar to the current system (Figure 11-24B). The proposed GWTS includes two groundwater storage tanks for PSCT groundwater that are 16,000 gallon carbon steel tanks. Transfer pumps pump the groundwater through the sock filters that include a set of pre-filters and a polish filter, and then to LPGAC vessels. The six 2,000-lb LPGAC vessels are placed in a series-parallel configuration with two rows of 3 vessels in series. The treated water is discharged to the proposed evaporation pond in the footprint of the A-Series Pond. The GWTS would also receive the extracted liquids from the Gallery Well that are pumped first to a primary storage tank that is a 13,000 gallon stainless steel tank. There the liquids settle with the resulting separation of three phases: DNAPL phase at the bottom, LNAPL at the top, and the water phase in the middle. The water phase in the middle is transferred to the secondary tank that is also a 13,000 gallon stainless steel tank. Both of these liquids are transferred by trucks to a permitted location for treatment and disposal. The vapors from storage tanks are vented to six 200-lb vapor phase GAC drums to control VOC emissions. Evaporation Pond The evaporation pond would be sized based on the anticipated extraction rates from the PSCT and PCTs based on assumed capping remedies, and a stormwater management plan that is discussed in Section 10.1.3. The stormwater plan assumes that capping remedies anticipated for the FS Areas 1 through 4 would allow a significant amount of stormwater from capped areas to be discharged through the B-Drainage under the substantive terms of the General permit. Monitoring As discussed earlier in Section 10.1, long term groundwater and soil vapor monitoring programs will likely be modified and expanded from the current programs which are described in the RGMEW Workplan dated March 2009 (CSC 2009a) and in the “Sampling Plan for Soil Gas Monitoring”, April 2009 (CSC 2009b) respectively. The ultimate monitoring programs will


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address both performance and compliance monitoring consistent with USEPA policies and guidelines. A long term monitoring program would likely include additional periodic sampling of more groundwater monitoring wells for a broader range of analytes. 11.6.1.3 Alternative 3 Extraction (PSCT, Gallery Well) + Extraction (NAPL only, P/S Landfill) +

Treat and Discharge to Evaporation Pond + Monitoring (12 Lower HSU wells) + MNA + ICs + Monitoring

This alternative includes the following components for FS Area 5 North (Figure 11-25A):

Extraction of PSCT and Gallery Well as currently implemented for source control NAPL-Only Extraction (DNAPL and LNAPL) from the southern portion of the P/S Landfill Monitoring for LNAPL in the P/S Landfill and CDA Monitoring Lower HSU wells upgradient of PSCT-1 and PSCT-4 to ensure Lower HSU

plume containment MNA for dissolved organics plume in FS Area 5 North Sump 9B and Road Sump features are retained as a contingency measure Institutional controls, maintenance and monitoring to protect the groundwater







The following provides a brief description of the conceptual design for the remedial alternative components of Alternative 3. Some of the components are the same as Alternative 2 with the difference being the addition of NAPL-only extraction in the southern portion of the P/S Landfill, limited NAPL-only extraction in the CDA and monitoring of Lower HSU groundwater. Extraction at PSCT The liquids from the PSCT would continue to be removed by extraction pumps in PSCT-1 through PSCT-4, as currently operated and discussed in Alternative 2. The extracted groundwater from the PSCT is treated in a groundwater treatment system using liquid phase carbon adsorption located at the Liquids Treatment Area and discharged to the evaporation pond (Figure 11-25C). Extraction at Gallery Well Extraction at the Gallery Well is the same as in Alternative 2. GWTS Upgrade


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The proposed groundwater treatment system is similar to the existing system, and the details of the storage tanks and LPGAC vessels that would be replaced would be the same as in Alternative 2. The process flow diagram for the GWTS is shown on Figure 11-25C. NAPL-Only Well Installation in P/S Landfill The NAPL-only extraction alternative discussed in this section refers to extraction from approximately 16 new 4-inch diameter NAPL-only wells in the Upper HSU. All of these wells would be located in the vicinity of RIPZ-13 near the toe of the P/S Landfill, and are assumed to include four wells placed on Bench Road 1 in the vicinity of RIPZ-13, four wells located on a new bench road to the north and eight located on two new bench roads between Bench Road 1 and Gallery Well Road. The design, number, and location of these “NAPL-only” wells will be finalized as part of the remedy design process, but the conceptual well design is discussed below and in Section 11.6 (see Figure 11-18B). NAPL-Only Extraction Well Design For the NAPL-only extraction alternatives, the wells could be constructed and operated using one of two options as summarized below. Prior to implementing any NAPL recovery through wells within the P/S Landfill, additional NAPL investigation and pilot testing would be performed to quantify potential NAPL recovery volumes and rates as discussed in Section 10.6.3.1.

Option 1 – LNAPL and DNAPL would be extracted from a single well screen (or gradient driven well), which would be constructed across the entire saturated zone (LNAPL, aqueous-phase, and DNAPL) (Figure 11-25B). A sump would be installed below the well screen to allow additional well casing for DNAPL storage. Two extraction pumps would be placed into the well. The bottom pump would be placed at the top of the DNAPL zone and pumped slowly (pulsed pumping only several times per day) to recover the DNAPL that comes into the well by up coning. The top pump would be placed within the LNAPL and also pumped slowly to skim the LNAPL that comes into the well. Extraction of water would be minimized so that the LNAPL and DNAPL saturations and flow paths around each well are maintained at the maximum possible level which would maximize LNAPL and DNAPL recovery. Some water may be extracted, as appropriate, to slightly enhance the inward gradients towards the extraction wells.

Option 2 – LNAPL and DNAPL would be extracted from a dual screen well (or gradient driven well), which would be constructed to isolate the water bearing zone with the goal of increasing NAPL recovery efficiency (Figure 11-25B). The well would be constructed by setting the lower screen for DNAPL recovery to bridge the contact between the weathered and unweathered claystone. In addition, a sump will be installed below the well screen to allow additional well casing for DNAPL storage. The upper screen interval would be placed across the water table to allow LNAPL to enter the well. These data would be compared to the NAPL production of the Gallery Well to see if any additional benefit would be gained from installing multiple wells through the landfill cap. One limitation with this method is that DNAPL up coning cannot be tracked if it rises above the DNAPL screen (which is important to know to maximize DNAPL recovery) and the top LNAPL screen will become desaturated as the overall liquid levels drop in the landfill which would trap recoverable LNAPL against the blank casing.


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Prior to implementing any NAPL recovery through wells within the P/S Landfill, it is recommended that additional NAPL investigation and pilot testing be performed to quantify potential NAPL recovery volumes and rates as discussed earlier. These data would be compared to the NAPL production of the Gallery Well to see if any additional benefit would be gained from installing multiple wells through the landfill cap. Remedial design, construction, and initiation of extraction of NAPLs from the NAPL-only extraction wells would be performed expeditiously because the liquid levels in the P/S Landfill will decline rapidly within the first few years and ultimately to below the bottom of the landfill after the remaining area across FS Area 1 is capped as demonstrated with the groundwater flow model (Appendix D-3). Extraction of current free-phase NAPLs will not be practicable after the landfill becomes desaturated. NAPL-Only Extraction in P/S Landfill The NAPL-only wells (for either Options 1 or 2 discussed earlier) would be equipped with pneumatic DNAPL skimmer pumps placed in the well sump and LNAPL skimmer pumps around the water table depth. DNAPL and LNAPL would flow into the well and pumping rates would be controlled by level switches in the well and/or timers based on well recharge. The DNAPL and LNAPL from the skimmers in the extraction wells will be piped to the NAPL storage tanks in the LTA (Figure 11-25B). More discussion of the NAPL-only extraction including pilot testing requirements and performance standards for recovery was presented in Section 10.6.3.1. For example, recovery of large quantities of water (e.g., >80 percent) would be set as effectiveness limits, obtaining such a goal may lead to asymptotic levels and a reduction of NAPL thickness. Once NAPL thickness has declined to below 1-foot, the effectiveness of further operating the extraction system would be evaluated. A total of up to 10,000 gallons of NAPL is assumed to be extracted annually from these 16 wells by this NAPL-only approach which would decrease at a rate of 5 percent to 10 percent per year over the 10-year timeframe for dewatering the P/S Landfill. The declining NAPL-only extraction volumes used in the cost estimate for this alternative for the 10-year timeframe was presented in Section 10.1.8.5. These liquids would be sent to a permitted facility for treatment and disposal. Lower HSU Monitoring and Potential Hydraulic Containment This alternative includes monitoring of the Lower HSU zone to ensure there is containment in the Lower HSU near the perimeter of Area 5 North. This is achieved by installation of deep Lower HSU wells screened in the top 30 to 150 feet of the Lower HSU, with six wells near PSCT-1 and six wells near PSCT-4. The six wells are proposed as three clusters of two wells each, one screened in the upper portion of the Lower HSU and other screened in the lower portion of the Lower HSU. These wells will be included in the long term sitewide groundwater monitoring program. Contingency actions would be implemented as necessary if potential VOC or other contaminant migration still occurred beneath the PSCT at concentrations of concern, as determined by USEPA. These contingency actions could include (1) immediate additional monitoring (for characterization of the release as determined necessary by USEPA) and (2) prompt implementation of additional corrective action, including conversion of monitoring wells to extraction wells and installation of additional extraction wells for hydraulic containment of the VOCs in the Lower HSU. Groundwater extracted from the Lower HSU would be treated and discharged together with the PSCT liquids. The extracted volumes from the Lower HSU would be very small because of the low permeability of the Lower HSU.


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Monitoring For purposes of the evaluation, the groundwater monitoring and soil vapor monitoring will be as discussed in Alternative 2. In addition, NAPL would be monitored in the known NAPL areas to ensure there is no significant migration and to monitoring performance effectiveness of the NAPL remedial components. 11.6.1.4 Alternative 4 Extraction (PSCT, Gallery Well) + Extraction (NAPL only, P/S Landfill) +

Treat and Discharge + Monitoring (12 Lower HSU wells) + MNA + ICs + Monitoring This alternative includes the following components for FS Area 5 North (Figures 11-26A and 11-27B):

Extraction of PSCT and Gallery Well as currently implemented for source control Treatment of PSCT groundwater for organics and inorganics to allow discharge to under

the substantive terms of a site-specific NPDES permit, if required NAPL-Only Extraction (DNAPL and LNAPL) from the southern portion of the P/S Landfill Monitoring for LNAPL in the P/S Landfill and CDA Monitoring Lower HSU wells upgradient of PSCT-1 and PSCT-4 to ensure Lower HSU






Allow discharge of treated groundwater to eliminate the need for an evaporation pond Remove DNAPL to the extent practicable and contain and/or control the migration of

DNAPL where removal is not technically practicable. Remove LNAPL to the extent practicable and contain and/or control the migration of

LNAPL where removal is not technically practicable. The following provides a brief description of the conceptual design for the remedial alternative components of Alternative 4. This alternative is the same as Alternative 3 except in this alternative the extracted groundwater is treated for organics and inorganics for discharge. Extraction at PSCT The liquids from the PSCT would continue to be removed by extraction pumps in PSCT-1 through PSCT-4, as currently operated and discussed in Alternative 2. The extracted groundwater from the PSCT is treated for organics and inorganics at the Liquids Treatment Area (Figure 11-26C). Extraction at Gallery Well


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Extraction at the Gallery Well is the same as in Alternative 2. GWTS for Organics and Inorganics The PSCT groundwater treatment system for this alternative is assumed to treat metals, VOCs, and other dissolved solids sufficiently for discharge under the the substantive terms of the General or a site-specific permit. The process flow diagram for the GWTS is shown on Figure 11-26C. The treatment train would include pre-treatment steps such as an equalization tank and filtration to remove suspended solids. The process includes LPGAC treatment to treat organics prior to a RO unit to remove metals and dissolved anions. This would be followed by a VSEP unit to concentrate RO reject brine. The treated water would be discharged to the B-Drainage. The reject brine would be disposed at a licensed disposal facility, and is assumed to be about 15 percent by volume of the total treated liquid volume (about 285,000 gallons per year). NAPL-Only Well Installation Sixteen 4-inch vertical NAPL-only wells would be constructed in the southern portion of the P/S Landfill upgradient of the Gallery Well as discussed earlier in Alternative 3. NAPL-Only Extraction in P/S Landfill The NAPL-only wells would be equipped with pneumatic DNAPL skimmer pumps placed in the well sump and LNAPL skimmer pumps around the water table depth as discussed earlier with Alternative 3. Lower HSU Monitoring and Potential Hydraulic Containment This alternative includes monitoring of the Lower HSU zone by installation of Lower HSU wells screened in the top 30 to 150 feet of the Lower HSU, with six wells near PSCT-1 and six wells near PSCT-4 as discussed in Alternative 3. The six wells are proposed as three clusters of two wells each, one screened in the upper zone of the Lower HSU and other screened in the lower zone of the Lower HSU. Contingency actions would be implemented as necessary if potential VOC or other contaminant migration still occurred beneath the PSCT at concentrations of concern, as determined by USEPA. These contingency actions could include (1) immediate additional monitoring (for characterization of the release as determined necessary by USEPA) and (2) prompt implementation of additional corrective action, including conversion of monitoring wells to extraction wells and installation of additional extraction wells for hydraulic containment of the VOCs in the Lower HSU. Groundwater extracted from the Lower HSU would be treated and discharged together with the PSCT liquids. The extracted volumes from the Lower HSU would be very small because of the low permeability of the Lower HSU. Monitoring For purposes of the evaluation, the groundwater monitoring and soil vapor monitoring will be as discussed in Alternative 2. In addition, NAPL would be monitored in the known NAPL areas to ensure there is no significant migration and to evaluate the performance effectiveness of NAPL extraction components.


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11.6.1.5 Alternative 5 Extraction (PSCT, Gallery Well) + Extraction (Aggressive, 16 large

diameter NAPL wells) + Treat and Discharge to Evaporation Pond + Extraction (NAPL-only, 4 existing wells in CDA) + Monitoring (12 Lower HSU wells) MNA + ICs + Monitoring

This alternative includes the following components for FS Area 5 North (Figure 11-27A):

Extraction of PSCT and Gallery Well as currently implemented for source control Aggressive NAPL Extraction (DNAPL, LNAPL and groundwater) from the southern

portion of the P/S Landfill Aboveground Leachate Treatment Plant for liquids treatment and discharge to

evaporation pond Limited extraction for LNAPL in the CDA Monitoring Lower HSU wells upgradient of PSCT-1 and PSCT-4 to ensure Lower HSU

plume containment Monitoring for LNAPL in the P/S Landfill and the CDA MNA for dissolved organics plume in FS Area 5 North Sump 9B and Road Sump features are retained as a contingency measure Institutional controls, maintenance and monitoring to protect the groundwater







The following provides a brief description of the conceptual design for the remedial alternative components of Alternative 5. Most of the components are the same as in Alternative 3 with the replacement of NAPL-only extraction with aggressive extraction in DNAPL area in the southern portion of the P/S Landfill. Extraction at PSCT The liquids from the PSCT would continue to be extracted by extraction pumps in PSCT-1 through PSCT-4, as currently operated and discussed in Alternative 2. The extracted groundwater from the PSCT is treated in a groundwater treatment system along with the aggressive NAPL extraction liquids located at the Liquids Treatment Area (Figure 11-27B). Aggressive NAPL Well Installation in P/S Landfill Sixteen NAPL wells would be constructed in the southern portion of the P/S Landfill upgradient of the Gallery Well. The sixteen wells would include four wells placed on Bench Road 1 in the vicinity of RIPZ-13, four wells located on a new bench road to the north and eight located on two new bench roads between Bench Road 1 and Gallery Well Road. Well construction details for


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the NAPL wells are shown on Figure 11-27B. These aggressive NAPL wells are large diameter (8”) wells about 80 feet deep with a steel casing and a 40-foot screen just above the fill or unweathered contact and include a 5-foot deep sump that extends into unweathered claystone. This well is assumed to be installed by sonic drilling methods. Challenges can be anticipated with well drilling inside the landfill footprint due to potential obstructions and hazards that may be encountered while drilling into waste in the landfill. Installation of extraction wells should consider local soil texture in design of screen opening and filter pack material. Aggressive NAPL Extraction in P/S Landfill The objective of these wells and this alternative component is to extract total fluids at the maximum allowed rate from the formation with the goal of removing DNAPL and LNAPL mass. The sixteen aggressive NAPL wells would be equipped with a pneumatic total fluids extraction pump placed in the well sump. DNAPL and LNAPL would flow into the well and pumping rates would be controlled by level switches in the well and/or timers based on well recharge. The well would be operated by setting the well intake screen at the contact between the fill or weathered and unweathered claystone. The inward hydraulic gradients created by the aggressive extraction and overlying weight of the NAPL pool will drive NAPL into the well and to a height within the well casing to equilibrate with the surrounding hydrostatic pressure; possibly up to 10 feet within the well casing. In addition a sump will be installed below the well screen to allow additional well casing storage. . As described in Section 10.1.8, the liquid levels in the P/S Landfill will decline as liquids are extracted from the Gallery Well and the aggressive NAPL extraction wells and recharge to Area 5 North is significantly reduced with construction of the RCRA caps over the remaining areas that have not yet been capped. The extraction rates are assumed to decline with time over a 5-year timeframe that it is estimated for the P/S Landfill to become dewatered. The extraction rate of total fluids from the 16 wells is assumed to be approximately 10 gpm (5.2 million gallons) for Year 1 and decreasing as outlined in Section 10.1.8. A total of up to 10,000 gallons of NAPL per year is assumed to be extracted by this aggressive NAPL approach though a significant amount of hydrocarbon and solvent contaminants in the leachate would be treated in the dissolved phase. The NAPL recovery rates would decline with time over the dewatering timeframe for this alternative. These NAPL liquids will be sent to a permitted facility for disposal. Remedial design, construction, and initiation of extraction of NAPLs from the aggressive NAPL extraction wells would be performed expeditiously because the liquid levels in the P/S Landfill will decline rapidly within the first few years and ultimately to below the bottom of the landfill after the remaining area across FS Area 1 is capped as demonstrated with the groundwater flow model (Appendix D-3). Extraction of current free-phase NAPLs will not be practicable after the landfill becomes desaturated. Prompt initiation of field investigations for remedial design is critical to maximizing NAPL extraction. Leachate Treatment System The extracted liquids are expected to include DNAPL and LNAPL and a wide range of other organic and inorganic contaminants including VOCs, SVOCs, pesticides, dioxins, and metals. The treatment scheme will utilize air stripping and carbon adsorption to treat organics for discharge to the evaporation pond. The process flow diagram (Figure 11-27C) shows the treatment train starting with an equalization tank, NAPL-water separator, bag filters, air stripper and LPGAC vessels. Additional auxiliary process units such as de-emulsifiers, acidification, neutralization will be required for effective operation of the air stripper and other process units. The vapor stream generated from the air stripping towers would be treated by a VPGAC


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system. The separated NAPL phase will also be sent for disposal similar to the Gallery Well liquids. The activated carbon will be sent to an appropriate facility for regeneration. The treated water would still be high in dissolved solids is assumed to be sent to the proposed evaporation pond. In this case, due to the larger groundwater extraction volumes, a larger evaporation pond of 20 acres would be needed. Other technology combinations for leachate treatment would also be evaluated during remedial design (if such an alternative were selected) such as a treatment train involving Zimpro Bio-PACT technology and liquid phase carbon adsorption for polishing. LNAPL Extraction in CDA Despite the limitations with LNAPL extraction discussed earlier, this alternative includes conversion of four existing Upper HSU monitoring wells in the CDA that contain LNAPL into extraction wells. The four Upper HSU monitoring wells selected for LNAPL skimmer operations include RGPZ-5B, RIPZ-8, RIMW-3 and RG-3B. This will include placing solar power LNAPL skimmers at each well along with a drum at the well head to collect the recovered product. The drum will be equipped with a high level shutoff. No centralized collection system is included in this alternative. The product will be periodically pumped and transferred to the storage tanks that are part of the Gallery Well liquid tanks for disposal at a permitted facility. The FS report assumes that 500 gallons of LNAPL will be recovered per year from these wells with this extraction. Lower HSU Monitoring and Potential Hydraulic Containment This alternative includes monitoring of the Lower HSU zone by installation of Lower HSU wells screened in the top 30 to 150 feet of the Lower HSU, with six wells near PSCT-1 and six wells near PSCT-4 as discussed in Alternative 3. The six wells are proposed as three clusters of two wells each, one screened in the upper zone of the Lower HSU and other screened in the lower zone of the Lower HSU. Contingency actions would be implemented as necessary if potential VOC or other contaminant migration still occurred beneath the PSCT at concentrations of concern, as determined by USEPA. These contingency actions could include (1) immediate additional monitoring (for characterization of the release as determined necessary by USEPA) and (2) prompt implementation of additional corrective action, including conversion of monitoring wells to extraction wells and installation of additional extraction wells for hydraulic containment of the VOCs in the Lower HSU. Groundwater extracted from the Lower HSU would be treated and discharged together with the PSCT liquids. The extracted volumes from the Lower HSU would be very small because of the low permeability of the Lower HSU. Monitoring For purposes of the evaluation, the groundwater monitoring and soil vapor monitoring will be as discussed in Alternative 2. In addition, NAPL would be monitored in the known NAPL areas to ensure there is no significant migration and to evaluate the performance effectiveness of NAPL extraction components. 11.6.1.6 Alternative 6 Extraction (PSCT, Gallery Well) + Dewater P/S Landfill (5 Horizontal

wells) + Treat and Discharge to Evaporation Pond + Extraction (NAPL-only, 4 existing wells in CDA) + Monitoring (12 Lower HSU wells) MNA + ICs + Monitoring


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This alternative includes the following components for FS Area 5 North (Figure 11-28A): Extraction of PSCT and Gallery Well as currently implemented for source control Dewater P/S Landfill (Liquids including DNAPL, LNAPL and groundwater) from the

southern portion of the P/S Landfill Transportation and disposal of P/S Landfill liquids Limited LNAPL Extraction in the CDA Monitoring Lower HSU wells upgradient of PSCT-1 and PSCT-4 to ensure Lower HSU






Dewater P/S Landfill by extracting liquids at the bottom of the landfill Remove DNAPL to the extent practicable and contain and/or control the migration of


LNAPL where removal is not technically practicable. The following provides a brief description of the conceptual design for the remedial alternative components of this alternative. Most of the components are the same as in Alternative 3 with the replacement of NAPL-only extraction with Dewater P/S Landfill in the southern portion of the P/S Landfill. Dewater P/S Landfill / Horizontal Well Installation in P/S Landfill The concept of aggressive dewatering of the southern portion of the P/S Landfill is evaluated in the FS using horizontal wells as drains under the landfill, where the collected liquids are sent to a permitted facility for disposal. Section 10.6.3.1 discussed the challenges and risks with this technology and is mentioned below again as part of the remedial alternative description. The concept and preliminary technical design of dewatering the P/S landfill using HDD was evaluated in this FS. This section of the FS describes the purpose and potential benefits of dewatering the P/S Landfill using horizontal wells, challenges and risks associated with HDD technology as applied to the P/S Landfill, and the conceptual design assumed for this alternative to support the detailed evaluation of remedial alternatives presented later in Section 11.6.2. Table 10-6A-1 provides a risk analysis that describes the potential hazards or vulnerabilities, potential probabilities of occurrence, potential impacts, consequences of potential impacts, risk mitigation measures to reduce the probability of occurrence, and the probability of occurrence after risk mitigation. The vulnerabilities and risk mitigation are summarized in the text below. The purpose of aggressively dewatering the southern portion of the P/S landfill would be to lower the water table within the landfill and reduce the “driving force” (head) that facilitates: (1) downward migration of contaminated liquids through pooled DNAPL source areas and fractured


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bedrock; and, (2) horizontal migration into weathered and unweathered bedrock. As discussed in this FS, several other remedial alternatives considered lower the groundwater level below waste, but not as rapidly as would this alternative. In this alternative landfill dewatering would be achieved by installing a series of horizontal wells (utilizing HDD methods) to act as horizontal gravity drains for liquids (especially DNAPL) trapped behind the P/S Landfill clay barrier. Conceptually, the primary technical benefits of this approach over the approach using NAPL-only or aggressive NAPL extraction wells would be:

The head that contributes to the horizontal gradient that causes groundwater (and any contaminants dissolved in groundwater) to move southward through the Lower HSU and underneath the PSCT would be reduced faster than if the vertical wells were used. This potential benefit would be greater with respect to the NAPL-only extraction wells rather than the aggressive NAPL extraction wells because the liquids removal rate from the aggressive NAPL extraction would be much higher than the NAPL-only extraction.

The energy costs to operate the horizontal drains would be reduced compared to the

use of vertical wells because the liquids would drain by gravity. Technically, there may be disadvantages with using horizontal wells to drain the landfill which include insufficient draining of the landfill if the horizontal wells are either (1) not able to be constructed along the bottom of the landfill, (2) constructed too far beneath the bottom of the landfill in the unweathered claystone, or (3) constructed at a spacing that is not dense enough (too few wells). The first issue would leave liquids (including free-phase DNAPLs) in waste below the horizontal wells. The second issue may result in insufficient liquids moving from the bottom of the landfill through the unweathered claystone due to the low permeability of the claystone and low frequency of fractures in the claystone. The third issue may result in a drainage rate that is too slow because the ideal well spacing and hydraulic effect (zone of influence) of individual wells is not known. To dewater the P/S Landfill, this alternative assumes five horizontal wells are installed by directional drilling methods (Figure 11-28A and 11-28B). Two options for installing the horizontal wells were considered: Option 1) drilling through the base of the P/S Landfill Clay Barrier, Option 2) drilling underneath the P/S Landfill Clay Barrier. For either option, the wells would be “blind” (single entry) drilled from a starting point located in the vicinity of Sump 9B, approximately 300 feet south of the landfill clay barrier. Both methods would include installing 300 feet of blank casing from this area to the clay barrier and then 300 feet of screen north of the clay barrier, either into or immediately beneath the landfill. The landfill bottom appears to rise more quickly after this distance towards the north and the advantages of using horizontal wells would diminish rapidly because the thickness of liquids becomes small. Also, the extent of the free-phase DNAPL zone does not appear to extend beyond this distance. Although HDD wells will require penetration of the P/S Landfill Clay Barrier, Option 1 facilitates direct access to the NAPL pool at the bottom of the landfill. Option 2 eliminates the need to penetrate the P/S Landfill barrier and the associated requirement for installation of a surface casing; however, it requires vertical hydraulic conductivity of the unweathered claystone in the Lower HSU to be sufficient to allow efficient drainage of landfill waste, with approximately five feet of vertical separation between the wells and the waste (needed to mitigate uncontrolled drainage of liquids during well installation). Option 2 also requires the driller to transition from weathered to unweathered materials, which in some cases may cause the drill bit to deflect off


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relatively hard materials, such as the unweathered claystone, instead of penetrating them, especially at shallow angles. For Option 1, a 14-inch pilot bore would be advanced through the Upper HSU (including alluvium. weathered claystone and the P/S Landfill buttress) and several feet into the base of the clay barrier, verified by drill head tracking methods (accurate to approximately 0.5 ft horizontally and 0.1 foot vertically). A 12-inch steel surface casing would then be installed and pressure grouted in place, including pressure grouting of the annular space around the casing. Finally, a 7 to 8 inch borehole would be advanced inside the surface casing, through the P/S Clay Barrier, and approximately 300 feet along the bottom of the landfill using oversize (5-inch ID) drill rods and a “knock-off” drill bit. The 3-inch or 4-inch well materials are subsequently inserted inside the drill rods (which prevents the landfill material from collapsing in around the well materials), using a blowout preventer installed on the surface casing as a precaution and a positive head of drilling fluid pressure to prevent backflow of landfill waste inside the drill rods and/or back through the surface casing. For Option 2, the borehole would be drilling down to below the P/S Landfill Clay Barrier, and then angle upward to intersect waste, following the slope of the Lower HSU contact along the base of the landfill. The wells are drilled starting in the vicinity of Sump 9B about 300 feet from the landfill (elev. ~ 480 ft MSL) and advanced beneath the P/S Landfill Clay Barrier (elev. ~ 470 ft MSL), then angled upward to follow the slope of the Lower HSU contact along the landfill bottom. Since the Lower HSU contact at the landfill bottom is sloped up, the borehole will be inclined upward toward the northwest at angles up to a 20 percent slope. The wells are assumed to be a total of 600 feet long with on average 300 feet of screen interval inside the landfill footprint and 300 feet of blank casing. The horizontal wells are assumed to be 12” diameter boreholes that are installed as a blind hole in order to avoid drilling up through the landfill waste and into the liner and cap. The well casing is assumed to be 3-inch or 4-inch diameter stainless steel with a wire-wrapped screen. As described in Section 10.1.8, the liquid levels in the P/S Landfill will decline as liquids are extracted from the Gallery Well and horizontal wells and recharge to Area 5 North is significantly reduced with construction of the RCRA caps over the remaining areas that have not yet been capped. The extraction rates are assumed to decline with time over a 5-year timeframe that it is estimated for the P/S Landfill to become dewatered. The FS assumes with this conceptual design that extraction flow rate for each horizontal well is initially 2 gpm on average (5.25 million gallons/year for 5 wells) and decreasing in Years 2 and 3 to 0.5 gpm, Years 4 and 5 to 0.1 gpm, and finally for Year 6 and onwards for a total flow rate of 200,000 gallons per year for all 5 wells. The extracted liquids will be drained to an equalization tank and then to a NAPL-water separator. The NAPL and the water phase are pumped and stored in stainless steel tanks for disposal to a permitted facility, similar to the current Gallery Well liquids. Approximately ten 20,000-gallon stainless steel storage tanks are included in the treatment compound to have adequate storage capacity. While dewatering the P/S Landfill is being considered further in the FS for reasons outlined above, the technical challenges and risks associated with this option are significant, as outlined below. The technical evaluation considers both industry experience in installing horizontal remedial wells and consultation with horizontal drilling vendors. This section of the FS describes the challenges and risks associated with HDD technology as applied to the P/S Landfill.


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HDD and drain well challenges are presented below under construction and O&M categories in terms of hazards/vulnerabilities and potential impacts. The challenges presented below apply to both horizontal well options, Options 1 and 2, described in Section 10.6.3.1. See Table 10-6A-1 for a description of the hazards and potential impacts along with potential probabilities of occurrence, consequences of potential impacts, risk mitigation measures to reduce the probability of occurrence, and the probability of occurrence after risk mitigation. Additional considerations are then provided for controlling the path of the borehole, terminating the borehole and well construction, health and safety issues related to HDD mud management, and HDD well efficiency. Construction Risk Factors

Insufficiently Draining the P/S Landfill (Options 1 and 2) o As mentioned above, the landfill may not be sufficiently drained if the horizontal wells

are either (1) not constructed along the bottom of the landfill, (2) constructed too far beneath the bottom of the landfill in the unweathered claystone, or (3) constructed at a spacing that is not dense enough (too few wells). The first issue will leave liquids in waste below the horizontal wells. The second issue may result in insufficient liquids moving from the bottom of the landfill through the unweathered claystone due to the low permeability of the claystone and low frequency of fractures in the claystone. The third issue may result in a drainage rate that is too slow because the ideal well spacing and hydraulic effect (zone of influence) of individual wells is not known

o Risk Mitigation: Robust field investigation would be performed prior to detailed design so that the configuration of the contact between the waste and top of unweathered claystone is understood at an appropriate level of detail. This investigation would include pushing numerous CPT borings into the landfill. However, even with a high density of CPT borings, uncertainty regarding the bottom configuration of the landfill will remain because the bottom of the landfill is likely benched and irregular resulting from original construction where the landfill was excavated to the weathered-unweathered claystone contact and then backfilled with waste material.

Uncontrolled release of Landfill Liquids (Options 1 and 2)

o Installing the horizontal wells will entail drilling from the Sump 9B area (south of the landfill) northward into (or immediately underneath) the landfill at an overall upward angle. Landfill liquids (DNAPL, LNAPL, aqueous phase liquids) may flow uncontrollably by gravity to the south along the borehole during drilling or the installed well.

o Risk Mitigation: The driller would utilize a pressure grouted surface casing (including a grouted annulus) keyed several feet into the clay barrier, combined with a blowout preventer at the surface to control flow back of liquids during well construction. Use of secondary containment to contain potential liquids that may be released is also assumed. In addition, the driller is assumed to utilize a special mud/fluids system for fluid management rather than an open pit method.

Losses of Borehole Circulation Fluids (Options 1 and 2)

o Encountering void spaces or fractures along the borehole path that results in loss of fluid circulation.

o Risk Mitigation: Typically fluid circulation loss can be overcome in by thickening the drilling mud; however, it is not known if this method will be effective in an upward inclined borehole.


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Penetrating the Clay Barrier (Option 1)

o Penetrating the clay barrier near the base would be required to adequately drain the south end of the landfill using horizontal wells. Drilling underneath the clay barrier may not facilitate proper drainage because of the low permeability of the claystone. Furthermore, drilling underneath the clay barrier may not allow placement of the horizontal wells at the optimum angle for proper drainage. The bore cannot be drilled upward at greater than approximately 20 degrees and would therefore bypass a portion of the NAPL pool at the bottom of the landfill, after the borehole passes underneath the clay barrier. The potential for borehole wash-out exists at the transition between different material, e.g., from clay barrier to waste material.

o Risk Mitigation: The driller would utilize a pressure grouted surface casing (including a grouted annulus) keyed several feet into the clay barrier, combined with a blowout preventer at the surface to control flow back of liquids during well construction.

Improperly Controlling the Path of the Borehole (Options 1 and 2)

o Installing the horizontal wells will require drilling through a variety of soil materials (alluvium, landfill waste, and claystone) and buried landfill debris at changing pitch angles. Interference associated with drums and other buried metal debris could interfere with conventional drill head tracking methods (walk over or wire line guidance system), which could compromise accurate placement of the well screen.

o Risk Mitigation: The driller could utilize a higher power sonde or GST system, which is not sensitive to magnetic disturbances and does not require access to the surface.

Borehole Collapse (Options 1 and 2)

o The landfill debris may partially collapse after the pilot bore is completed, which could preclude insertion of the well materials. Well materials are generally inserted into the bore in a single entry (blind end) application.

o Risk Mitigation: The driller would use oversized drill rod with a "knock-off"/expendable drill bit and insert the well materials inside the drill rods, effectively shielding them from borehole collapse.

Well Collapse (Options 1 and 2)

o Constructed wells may collapse if the crush strength of the selected material (HDPE, stainless steel) is not sufficient, or if the well material is not chemically compatible with the landfill liquids. If not chemically compatible, landfill liquids may degrade the well materials which would cause them to weaken.

o Risk Mitigation: The well materials will be selected so that they are chemically compatible and strong enough to avoid collapse

Chemical Compatibility (Options 1 and 2)

o Materials used in the process equipment (wellhead, pipes, tanks, valves, etc) may degrade and fail if not chemically compatible with the landfill liquids. This includes the "hard" components (pipes, tanks, etc.) and "soft" components (gaskets, O rings, etc).

o Risk Mitigation: The well materials will be selected so that they are chemically compatible with the landfill liquids. This would include bench-top studies where materials are exposed to landfill liquids to verify chemical compatibility before materials are used in the field.


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Health and Safety During Construction (Options 1 and 2) o Workers may become exposed to contaminated contents from the landfill during

drilling and well installation. The exposure may be from drilling mud that contains contamination or from uncontrolled release of raw landfill liquids that may "drain" downslope back to the drilling location.

o Risk Mitigation: A detailed Health and Safety Plan will be developed and carefully followed during the work. Wear appropriate PPE (Level A/B/C) and perform air monitoring when the potential for exposure occurs. Stop work if ambient air concentrations exceed action levels. Stop work if drilling conditions indicate potential for uncontrolled release.

Operations and Maintenance Risk Factors (Options 1 and 2)

Well Efficiency and Clogging o The horizontal wells may clog over time due to scaling/fouling, fines intrusion, or

other factors o Risk Mitigation: Effectively develop wells during construction and, if necessary,

perform redevelopment during O&M. The well development procedure may require additional effort in an upward inclined well casing, than for a typical installation.

Water Coning o Groundwater flow to the well is preferential to NAPL flow to the well. Water coning is

well known phenomena in oil well production and occurs due to water being the less viscous and the more mobile fluid in the presence of NAPL. Due to the long well screen and unknown fluid content (fluid ratios) along well screen water coning should be anticipated.

o Risk Mitigation: Due to the design of the HDD wells if water coning occurs there will be no way to recover well to NAPL production only. Effectively HDD well will result in high quantities of water production relative to NAPL recovery.

Uncontrolled Release During O&M

o Uncontrolled releases could occur from wells (at the wellhead), pipes, storage tanks, and other process equipment. This would include transferring liquids from storage tanks to trucks for transport of the liquids to a permitted disposal facility.

o Risk Mitigation: Develop O&M and preventative maintenance procedures which include contingency measures, install isolation features and employ secondary containment at all times.

Health and Safety During O&M

o Workers may become exposed to contaminated landfill liquids during operations and maintenance (while the landfill is draining). The exposure may occur during controlled O&M activities and accidental uncontrolled releases.

o Risk Mitigation: A detailed Health and Safety Plan would be followed at all times. Shut-off wells and discontinue routine operations if conditions indicate potential for uncontrolled release. Wear protective clothing and perform air monitoring during all operations. Upgrade to higher safety level (Level A/B/C) if release occurs.

Uncontrolled Release During Transport

o Uncontrolled releases could occur while transporting the liquids to the permitted disposal facility.


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o Risk Mitigation: Maintain O&M procedures and emergency response procedures in place.

Additional Considerations

Controlling the path of the borehole o The bottom of the P/S Landfill was constructed by excavation of canyon materials to

the weathered – unweathered claystone contact. This surface was later backfilled with waste material to create the landfill. The bottom of the P/S Landfill is both benched and irregular and gains over 220 feet of elevation over its approximately 1,400 foot length (i.e., up to 16 percent grade).

o The pathway of the HDD borehole would include, spudding the boreholes near Sump 9B area within the CDA and angling the borehole downwards 20 feet over a distance of approximately 150 feet to avoid penetration of the base of the clay barrier. Leveling the borehole to allow for upward angle beneath the P/S landfill and then angling the borehole upwards at about a 20 percent rise for 300 to 500 feet to encounter and parallel the waste – unweathered bedrock contact. (Figure 11-28B).

o The borehole will not encounter the pool of DNAPL, unless purposely directed through the toe of the P/S Landfill clay barrier and buttress. Penetration of P/S Landfill clay barrier and buttress will compromise the integrity of the key containment feature.

o The proposed drains would be additionally angled at 1-2 percent grade into the landfill to intersect waste and facilitate drainage. The practical aspects of controlling the drill bit would be challenging.

o Controlling drill bit deflection when encountering materials of different mechanical properties (i.e., from weathered claystone to competent claystone and from claystone to waste materials of metallic drums containing liquids and landfill fill soil cover.

o Conventional drill bit tracking system work by electronically relating the drill string to the Earth’s magnetic field and inclination, the presence of large quantities of steel drums will interfere with tracking system and result in the installation of a blind borehole. As such, the position of the borehole (or well) with respect to target zones will never be known with any degree of accuracy.

Terminating the borehole and well construction o Since the horizontal drilling cannot be double-ended due to potentially damaging the

landfill cap and liner system, the borehole installation will utilize a single-ended or blind hole drilling method. It is well known that there is significantly greater number of borehole failures with blind hole drilling. This risk is discussed in the Center for Public Environmental Oversight (CPEO) technical report on “Horizontal Wells” -“As opposed to vertical wells, horizontal wells may have a greater potential to collapse. Borehole collapse is also more likely in single-ended drilling since the hole is left unprotected between drilling and reaming and between reaming and casing installation. Double-ended holes may be easier to install since reaming tools and well casing can be pulled backward from the opposite opening, and the hole does not have to be left open. “http://www.cpeo.org/techtree/ttdescript/horzwel.htm”. The waste over burden ranges from 100 to 150 feet in thickness of material behind the clay barrier.

o Blind hole drilling will also result in frequent casing breakage particularly while pushing the casing into the borehole that has numerous directional changes. Stainless steel casings will need to be used to provide adequate strength and


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chemical resistance for this application. However, stainless steel piping is less flexible than plastic piping and prone to breakage and/or blocking-off, when attempting to push them into boreholes with numerous twists and turns.

Health and Safety issues related to HDD mud management o The liquid head at the proposed target end points (300-500 feet behind the clay

barrier) will be at higher elevation than the starting point. As such to maintain borehole circulation an elaborate “blow-out prevention system“ will be required. It is not known if such a system exists for remedial HDD applications.

o Release of NAPL from puncturing drums. As shown on Figure 4-51 of the Final RI Report (CSC 2011), the bottom of the P/S Landfill holds containerized liquid waste (stacked drums). Assuming that multiple horizontal wells will be required, the implementation of this remedy would likely result in the release of thousands of gallons of free NAPL into the formation if these drums were to be penetrated. The negative effects of this technology could far outweigh any potential benefit associated with attempting to reduce the groundwater levels in the landfill.

o HDD mud management concerns will be significant. The drilling mud will be considered hazardous; the borehole will be spudded in an area of known LNAPL contamination. Drilling mud from the HDD boreholes will be recirculated during the drilling process. However, it cannot be reused after the project is complete on other site due to high VOC/NAPL content.

o The high NAPL and VOC content of drilling mud and the landfill liquids will present a significant human health concern for drillers and other workers during installation. Based on past drilling experience in the vicinity of the P/S Landfill level B personal protective equipment will be required, which incorporates, performing drilling activities with supplied air. Additional effort in the form of the development and placement of contingency plan items and equipment would need to be in-place to respond to a potential spill that might result utilizing the blind HDD method.

o The spent drilling mud (estimated at 100 tons for five 600-foot long boreholes) will be classified as hazardous waste, and waste material handling and disposal will require additional precautions and effort. Drilling mud will need to be disposed as RCRA hazardous waste and may need to be incinerated (estimated disposal cost at $1,400/ton).

HDD Well Efficiency o Preliminary estimates of horizontal well production are estimated at 0.26 to 2.6 gpm

assuming a hydraulic conductivity of the waste of 10-6 to 10-5 cm/s, respectively. The actual hydraulic conductivity of the waste many be higher (e.g. 10-4 cm/s) based on experience at other landfills. The effective hydraulic conductivity of the landfill waste materials is not known because aquifer pump testing has not been performed. Experience at other landfills indicates that the initial drainage rates may exceed 10 gpm per well. The estimated time for the landfill to drain is uncertain. Using the 0.26 to 2.6 gpm estimated rates, the estimated time to dewater 10 million gallons of liquid from the five wells would take between 6 to 60 years at full efficiency. The actual time for the landfill to drain could be much shorter, however, based on flow rates that exceed 10 gpm. The well efficiency may be compromised (potentially 20-33 percent range) due to well construction defects (well development, well compression, screen clogging) and declining hydraulic head over time. Under this scenario, the operation time could be in the range of 20 to 200 years depending of formation hydraulic


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conductivity and well efficiency. This would be a conservative estimate if the well efficiency were higher.

o Even with a series of horizontal dewatering wells beneath the P/S Landfill, it is possible that some groundwater flow will bypass the horizontal wells, and preferentially pass through the landfill waste material, and be captured by the existing Gallery Well. There is significant uncertainty with the total recoverable liquids volume and extraction flow rates that are possible with this approach.

Damage to the Gallery Well

o For the HDD wells scheme to be effective at least one of the HDD wells will need to run along the bottom axis of the landfill, and as such, likely encounter the Gallery Well, resulting either in the destruction of the well or significantly reducing its efficiency. It is a significant trade-off to risk damage to a proven site remedial feature that achieves containment and mass removal in the hope to potentially (and marginally) decrease the time needed to remove (an already depleting) reservoir of mobile DNAPL.

The implementation of the remedy to dewater the P/S landfill by installing (inclined) horizontal gravity drain wells presents significant technological challenges. The benefit of installing horizontal drain wells while on the surface may appear more attractive than the installation of vertical wells, the risk of doing so is significantly higher for reasons outlined above. Active LNAPL Extraction in CDA This alternative includes conversion of four existing Upper HSU monitoring wells in the CDA that contain LNAPL into extraction wells as discussed in Alternative 5. The FS report assumes that 500 gallons of LNAPL will be recovered per year from these wells with this extraction. Extraction at PSCT The liquids from the PSCT would continue to be extracted by extraction pumps in PSCT-1 through PSCT-4, as currently operated and discussed in Alternative 2. The extracted groundwater from the PSCT is treated in a groundwater treatment system using liquid phase carbon adsorption located at the Liquids Treatment Area (Figure 11-28C). Lower HSU Monitoring and Potential Hydraulic Containment This alternative includes monitoring of the Lower HSU zone by installation of Lower HSU wells screened in the top 30 to 150 feet of the Lower HSU with six wells near PSCT-1 and six wells near PSCT-4, as discussed in Alternative 3. The six wells are proposed as three clusters of two wells each, one screened in the upper zone of the Lower HSU and other screened in the lower zone of the Lower HSU. Contingency actions would be implemented as necessary if potential VOC or other contaminant migration still occurred beneath the PSCT at concentrations of concern, as determined by USEPA. These contingency actions could include (1) immediate additional monitoring (for characterization of the release as determined necessary by USEPA) and (2) prompt implementation of additional corrective action, including conversion of monitoring wells to extraction wells and installation of additional extraction wells for hydraulic containment of the VOCs in the Lower HSU. Groundwater extracted from the Lower HSU would be treated and


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discharged together with the PSCT liquids. The extracted volumes from the Lower HSU would be very small because of the low permeability of the Lower HSU. Monitoring For purposes of the evaluation, the groundwater monitoring and soil vapor monitoring will be as discussed in Alternative 2. In addition, NAPL would be monitored in the known NAPL areas to ensure there is no significant migration and to evaluate the performance effectiveness of NAPL extraction components. 11.6.1.7 Alternative 7 Extraction (PSCT, Gallery Well) + Dewater P/S Landfill (5 Horizontal

wells) + Treat and Discharge PSCT Groundwater + Extraction (NAPL-only, 12 new wells in CDA) + Extraction (4 Lower HSU wells) + Monitoring (8 Lower HSU wells) MNA + ICs + Monitoring

This alternative includes the following components for FS Area 5 North (Figures 11-29A and 11-29B):

Extraction of PSCT and Gallery Well as currently implemented for source control Treatment of PSCT groundwater for organics and inorganics to allow discharge under a

the substantive terms of a site-specific NPDES permit, if required Dewater P/S Landfill (liquids including DNAPL, LNAPL and groundwater) from the

southern portion of the P/S Landfill Transportation and disposal of P/S Landfill liquids at a permitted facility Active extraction for LNAPL in the CDA Limited Extraction at Lower HSU wells and Monitoring of Lower HSU wells upgradient of

PSCT-1 and PSCT-4 to ensure Lower HSU plume containment MNA for dissolved organics plume in FS Area 5 North Institutional controls, maintenance and monitoring to protect the groundwater





Dewater P/S Landfill by extracting liquids at the bottom of the landfill Remove DNAPL to the extent practicable and contain and/or control the migration of


LNAPL where removal is not technically practicable. The following provides a brief description of the conceptual design for the remedial alternative components of this alternative. This alternative is the same as Alternative 6 except the extracted PSCT groundwater is treated for organics and inorganics for discharge at a permitted facility. Dewater P/S Landfill Dewatering with Horizontal Wells in P/S Landfill


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The concept of aggressive dewatering of the southern portion of the P/S Landfill is evaluated in the FS using horizontal wells as drains under the landfill, where the collected liquids are sent to a permitted facility for disposal. Section 10.6.3.1 discussed the challenges and risks with this technology. The approach for P/S Landfill dewatering is as described earlier in Alternative 6. Active LNAPL Extraction in CDA This alternative attempts to remove LNAPL more aggressively in the CDA than in Alternatives 5 and 6. It includes installation of twelve new 4-inch extraction wells in the known LNAPL area within the CDA. Each well will be equipped with pneumatic LNAPL skimmers that are piped to a treatment compound located within the CDA. The treatment compound would include a stainless steel NAPL storage tank that is periodically emptied for disposal at a permitted facility. The FS report assumes that 1,000 gallons of LNAPL will be recovered per year from these wells with this extraction component. Extraction at PSCT The liquids from the PSCT would continue to be extracted by extraction pumps in PSCT-1 through PSCT-4, as currently operated and discussed in Alternative 2. The extracted groundwater from the PSCT is treated in a groundwater treatment system using a GWTS that treats for organics and inorganics and is located at the Liquids Treatment Area (Figure 11-29C). GWTS for Organics and Inorganics The PSCT groundwater treatment system for this alternative is assumed to treat metals, VOCs, and other dissolved solids for discharge under the substantive terms of a site-specific NPDES permit. The treatment approach assumed the same process train used in the groundwater restoration alternative in Appendix A TI Evaluation. The process flow diagram for the GWTS is shown on Figure 11-29C. The treatment train would include pre-treatment steps such as an equalization tank and filtration to remove suspended solids. The groundwater would be treated by LPGAC to remove organics prior to a RO unit to remove metals and dissolved anions. This would be followed by a VSEP unit to concentrate RO reject brine. The treated water would be discharged to the B-Drainage. The reject brine would be disposed at a EPA-approved, permitted disposal facility and is assumed to be about 15 percent by volume (285,000 gallons per year). Lower HSU Extraction and Monitoring This alternative includes extraction of groundwater from four Lower HSU wells to ensure containment of Lower HSU VOC plume within Area 5 North and continued monitoring of eight Lower HSU wells. This involves installation of twelve Lower HSU wells screened in the top 30 to 150 feet of the Lower HSU, with six wells near PSCT-1 and six wells near PSCT-4 as discussed in Alternative 3 (Figure 11-29A). The permeability of the Lower HSU formation is very low and groundwater yields are expected to be at most 0.25 gpm based on experience during purging and sampling activities for other Lower HSU wells in the vicinity. Based on experience, some of the Lower HSU wells may yield quite a bit less than 0.25 gpm. The Lower HSU wells have very low VOC concentrations and contaminant mass removals are expected to be very low. The liquids extracted from Lower HSU extraction wells would be combined with the PSCT liquids for treatment. Additional contingency actions would be implemented as necessary if potential VOC or other contaminant migration still occurred beneath the PSCT at concentrations of concern, as


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determined by USEPA. These contingency actions could include (1) immediate additional monitoring (for characterization of the release as determined necessary by USEPA) and (2) prompt implementation of additional corrective action, including conversion of monitoring wells to extraction wells and installation of additional extraction wells for hydraulic containment of the VOCs in the Lower HSU. Monitoring For purposes of the evaluation, the groundwater monitoring and soil vapor monitoring will be as discussed in Alternative 2. In addition, NAPL would be monitored in the known NAPL areas to ensure there is no significant migration and to evaluate the performance effectiveness of NAPL extraction components. 11.6.2 Detailed and Comparative Evaluation of Remedial Alternatives for Area 5 North The detailed evaluation for the seven remedial alternatives is presented in Table 11-6A. The following is the comparative analysis where for each CERCLA criteria the ratings and performance of each alternative is compared. 11.6.2.1 Overall Protection of Human Health and Environment All of the active remedial alternatives are rated “Yes” because they are protective of human health and the environment except for Alternative 1. These active remedial alternatives generally continue operations of the existing groundwater remedial features (e.g., P/S Landfill and EE/CA Area Cap, PSCT extraction) which will contain or control the source in support of the TI waiver for Area 5 North. Also, included as part of these alternatives is the anticipated capping of the PCB Landfill, CDA and BTA as part of the soil remedy and the resulting benefits from prevention of infiltration and potential chemical leaching to protect groundwater. All of these options are primarily containment and source reduction options, and aquifer restoration for FS Areas 5 South and 5 West will take hundreds of years. The TI evaluation presented in Appendix A demonstrated that restoration for Area 5 North is not practicable. Alternative 2 involves the continued operation of existing remedial features (e.g., PSCT extraction) involving source control, while Alternatives 3 and 4 include NAPL-only removal in the P/S Landfill. Alternatives 5, 6 and 7 are more aggressive alternatives, with Alternative 5 involving aggressive vertical well extraction (dewatering) in the P/S Landfill while Alternatives 6 and 7 involve dewatering the P/S Landfill using horizontal wells drilled through the base of the clay barrier or under the clay barrier and into landfill waste. While all active remedial alternatives are rated “Yes” for overall protection, it should be noted that there is significant potential human health risk to drillers and workers involved in the horizontal well installation and dewatering process. ICs including access restrictions and groundwater monitoring would be a component of all the remedial alternatives that would provide overall protection. 11.6.2.2 Compliance with ARARs For all remedial alternatives, assuming that the TI evaluation presented in Appendix A results in USEPA granting a TI waiver for the Area 5 North, then there are no chemical-specific groundwater ARARs for COCs within this area. All of the alternatives have components that involve treatment of PSCT groundwater or leachate that would be in compliance with action-specific and chemical-specific ARARs. Some challenges can be anticipated in meeting action-


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specific groundwater treatment ARARs and SBCAPCD requirements using the leachate treatment system with Alternative 5. Similarly, challenges can be anticipated with Alternatives 4 and 7 that involve treatment of groundwater to enable discharge in accordance with the substantive terms of a site-specific NPDES permit. Obtaining a site-specific NPDES permit or determining the substantive terms of such a permit from the RWQCB would require an exception to the Basin Plan prohibition of discharging treated groundwater and would face some uncertainty. All of the alternatives will be in compliance with ARARs requiring protection of sensitive ecological species from high TDS and inorganics in the proposed evaporation pond.

11.6.2.3 Long Term Effectiveness All of the active alternatives would address the RAO of containing or controlling VOC and inorganics sources with the existing remedial features in the Upper HSU (e.g., P/S Landfill and EE/CA Area Cap, PSCT extraction). MNA with a contingency for hydraulic containment would address the RAO of containing or controlling VOC sources in the Lower HSU. In addition, anticipated capping for BTA, CDA and PCB Landfill as part of the soil remedy would further contain contaminants in soil and reduce source contaminants in groundwater through minimizing infiltration, all of which support the control and containment requirement for the TI waiver for Area 5 North. Alternative 2 addresses the RAOs of containing or controlling sources and mitigating potential migration out of Area 5 North, but do not directly address NAPL under the P/S Landfill and the CDA. Alternative 2 is rated poor to moderate because it does not address the NAPL RAOs, while Alternatives 3 and 4 are rated higher at moderate because they address the NAPL RAO with NAPL-only extraction in the P/S Landfill. Alternative 4 is rated the same because it is identical to Alternative 3 but includes aboveground treatment of PSCT groundwater for inorganics to enable discharge and thus does not require an evaporation pond. Alternatives 5, 6 and 7 are more aggressive extraction alternatives focusing on the liquids within the P/S Landfill that will also remove large quantities of groundwater with NAPL. Alternatives 5, 6 and 7 are rated the same at moderate; however, although they would likely remove more contaminant mass, COC mass reduction would still be very small compared to total mass of contaminants in groundwater at the site. Alternatives 6 and 7 will likely lower the water table in the P/S Landfill, though they are not likely to entirely drain the landfill liquids. Other remedial actions such as the anticipated capping north of the PSCT will also in the long term result in lowering the water table. With all of these alternatives, COC mass reduction is modest, though natural attenuation, especially of the VOCs in Areas 5 North, is documented and will continue to contribute to mass reduction (Appendix G). Aquifer restoration with these alternatives would not be significantly different, and would take hundreds of years. As discussed in the TIE, even if an aggressive technology were able to remove significant amounts of contamination, due to the diffusion out of the claystone matrix, aquifer restoration would still take hundreds of years. Additional rationale for technical impracticability of remediating sitewide groundwater to applicable standards is presented in Appendix A. With ICs and monitoring included there is no potential for exposure to groundwater contaminants. 11.6.2.4 Reduction of Toxicity, Mobility and Volume through Treatment Alternative 2 is rated poor while Alternatives 3 and 4 are rated poor to moderate and Alternatives 5, 6 and 7 are rated moderate. All alternatives include contaminant reduction through the Gallery Well extraction and the PSCT extraction as part of source control. Alternatives 3 and 4 include in addition include NAPL-only extraction from the P/S Landfill.


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However, the reduction in contaminant mass would be relatively small fraction even with the assumed initial extraction rate of 10,000 gallons of NAPL per year by NAPL-only extraction. Alternative 5 uses a more aggressive NAPL extraction scheme that is rated one step higher at moderate because it will likely remove more contaminant mass. But the rate of NAPL recovery is expected to be the same as Alternatives 3 and 4 at 13,000 gallons of NAPL per year and would involve the burden of treating a large quantity of groundwater (5.2 million gallons per year) in the process. The total NAPL and dissolved contaminant removal with Alternative 5 would significantly tail off with time. Similarly, Alternatives 6 and 7 are aggressive schemes using horizontal wells to dewater the P/S Landfill. As with Alternative 5 it is rated moderate because it will recover large volumes initially (assumed 5.2 million gallons with 5 horizontal wells in Year 1) but decreasing significantly the following years and tailing off at 200,000 gallons per year after Year 5. Also, the total groundwater extraction rates and hence contaminant extraction rates from the PSCT and PCT are expected to decrease from current levels due to anticipated capping remedies at the site. For all of these alternatives, the COC mass reduction by extraction is modest compared to the total contaminant mass at the site. Though, natural attenuation especially of the VOCs in Areas 5 North is documented and will contribute to mass reduction in the long term. Overall, all of these alternatives are primarily containment type alternatives that would remove contaminants in groundwater at a slow rate and hence aquifer restoration is likely to take hundreds of years with any of them. 11.6.2.5 Short Term Effectiveness Alternative 2 is rated good and Alternative 3 is rated moderate to good while Alternative 4 is rated moderate and Alternatives 5, 6 and 7 are all rated poor to moderate. Alternative 2 has no significant risk to human health (workers or community) or environment as this system is currently operating effectively at the site. Alternative 3 is similar to Alternative 2, but some risks associated with drilling inside P/S Landfill can be expected. Alternative 4 is identical to Alternative 3 but is rated lower due to concerns with risk of failure of complex inorganics treatment process and potential release of groundwater with high inorganics to Casmalia Creek. Alternative 5 is rated lower because of the risks associated with installation of large diameter wells in the P/S Landfill and potential for VOC emissions or leaks from the LTP that will handle over 5 million gallons per year of highly concentrated leachate. Alternatives 6 and 7 are rated poor to moderate due to risks of potential leachate liquid or contaminated drilling mud releases during the well installation process especially because the well has to be drilled sloped upward following the Lower HSU contact with a blind hole drilling method. In addition, there is potential for exposures to VOCs and other subsurface contaminants for drillers and workers especially if the drill bit veers into the waste in the landfill. Another issue is the long term liability concerns with transportation and disposal of P/S Landfill liquids at permitted TSDFs. 11.6.2.6 Implementability Alternative 2 is rated good while Alternative 3 is rated moderate to good, Alternative 4 is rated moderate and Alternatives 5, 6 and 7 are rated poor to moderate. Alternative 2 is essentially already implemented and no challenges are anticipated. Alternative 3 is rated lower because it involves technical challenges with installation of vertical NAPL-only wells by drilling in the P/S Landfill while Alternative 4 is rated one step lower because of technical challenges and complexity of treating the high level of inorganics in groundwater to meet the site-specific NPDES limits. Alternative 5 is rated even lower because it involves technical challenges with drilling large diameter wells in the P/S Landfill, and leachate treatment plant operations to reliably meet regulatory water and vapor discharge requirements including RWQCB and SBCAPCD requirements. Alternative 5 would also require a larger evaporation pond (about 20


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acres) which would also pose a challenge with providing adequate protection to ecological species and administrative implementability concerns. Alternatives 6 and 7 are rated poor to moderate because of significant technical challenges with installation of horizontal wells going through the base of the clay barrier or under the clay barrier and precisely tracking the Lower HSU contact without drilling into the drum wastes in the landfills. With the blind hole drilling approach, the well casing will need to be pushed into the borehole which is potentially challenging and can lead to casing breakage. Other challenges with blind hole drilling is hole failure that requires re-drilling multiple holes. There are significant uncertainties with the anticipated groundwater volumes and flow rates from the horizontal wells. Alternative 7 faces an additional technical challenge with complex treatment of PSCT groundwater for inorganics and organics for discharge under the substantive terms of a site-specific NPDES permit. There would be a concern with potential violations of NPDES permit conditions with RO equipment failures. 11.6.2.7 Cost The total present worth (30-year) cost is presented for Alternatives 2 through 7 in the table below for a 3 percent and 7 percent discount rate in 2014$. The total present worth cost for Alternative 2 is the lowest and considered moderate, while Alternative 3 is moderate to high and Alternatives 4 through 7 are considered high. Alternative 4 is considered high in cost with GWTS treatment for inorganics followed by Alternative 5 that involves aggressive NAPL extraction and treatment. Finally, Alternatives 6 and 7 are also high and that includes the aggressive dewatering of P/S Landfill using horizontal wells. Of these alternatives, Alternative 7 is the highest in total present worth cost. Alternative 2 is also the lowest in capital cost and Alternative 7 is the highest in capital cost.

11.6.2.8 Green Impacts Assessment The range of green technologies and BMPs that can play a role in minimizing environmental impacts of the remedial alternatives and technology components are discussed in Section 12.7. Appendix F presents the qualitative assessment of the environmental footprint for these alternatives based on green remediation criteria such as GHG emissions, energy usage, air

Alt No. Capital Cost Annual Cost

Total Present Worth Time frame



2 $1,771,000 $1,834,000 30-year $23,833,000 $16,551,000

100-year $34,039,000 $18,134,000

3 $6,068,000 $2,128,000 30-year $31,445,000 $22,402,000

100-year $43,294,000 $24,240,000

4 $9,348,000 $3,118,000 30-year $53,750,000 $37,191,000

100-year $77,898,000 $40,935,000

5 $17,576,000 $3,021,000 30-year $44,037,000 $33,926,000

100-year $57,316,000 $35,985,000

6 $13,824,000 $6,527,000 30-year $56,755,000 $45,424,000

100-year $69,821,000 $47,450,000

7 $17,558,000 $7,536,000 30-year $79,820,000 $60,789,000

100-year $105,225,000 $64,727,000


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emissions, collateral risk, community impacts, resources lost, and water usage. The Appendix F evaluation was used to determine an overall rating for the alternative in Table 11-6A. Alternative 2 has the lowest impacts rated low to moderate because it involves continuation of current PSCT extraction and treatment operations. Alternative 3 would have higher impacts and is rated moderate, while Alternative 4 is rated moderate to high for impacts. Alternative 3 includes the NAPL-only extraction that would involve the energy usage of the air compressor that operates the pneumatic skimmer pumps while Alternative 4 would require an energy intensive system including RO to reduce inorganic concentrations in groundwater to enable discharge. All of the alternatives have the electricity and fuel usage and GHG emissions (carbon footprint) for the common PSCT and Gallery Well extraction components. Alternatives 5, 6 and 7 would have the highest impacts and are rated high. Alternative 5 would include the emissions, fuel use and materials consumptions from the aggressive continuous groundwater extraction wells and the operation of the leachate treatment system. Alternatives 6 and 7 would include the installation and operation of the horizontal drains and disposal of liquids at a permitted facility that would require transportation of liquids by truck daily (estimated 5 million gallons in Year 1). 11.6.3 Evaluation Summary for Area 5 North All of the active remedial alternatives for Area 5 North, Alternatives 2 through 7 meet the threshold requirements of Overall Protection of Human Health and Environment and Compliance with ARARs. Alternative 1 does not meet the threshold requirements and hence is not evaluated for the balancing criteria. Alternative 3 is rated better with respect to LTE and RTMV than Alternative 2 because it includes NAPL-only extraction in the P/S Landfill and limited LNAPL extraction in the CDA which Alternative 2 does not have. However, Alternative 3 is rated a bit lower with respect to STE and Implementability than Alternative 2. Alternative 4 is similar to Alternative 3 but is rated lower with respect to STE and Implementability because it involves a complex treatment system with RO that treats inorganics for discharge in compliance with stringent NPDES limits. Alternatives 5, 6 and 7 are aggressive extraction technologies that will remove more contaminant mass but because contaminant mass removal as a fraction of the total contaminant mass is not expected to be significantly different, they are rated the same for LTE as Alternative 3. However, with respect to RTMV, Alternatives 5, 6 and 7 are rated one step higher because a larger contaminant mass will be removed than Alternative 3. Aquifer restoration time frame would not be significantly different between Alternatives 3 and Alternatives 5, 6 or 7 and would take hundreds of years. Alternative 3 is rated significantly higher than Alternatives 5, 6 or 7 for STE and Implementability because there are greater implementability and STE (potential emissions) concerns with Alternative 5 (aggressive extraction) and with Alternatives 6 or 7 (horizontal wells dewatering) than with Alternative 3 (NAPL-only extraction). A detailed discussion of the risks and challenges with horizontal wells dewatering of the P/S Landfill was presented in Section 10.6.3.1 and Section 11.6.1.6. With respect to cost, Alternative 3 is significantly lower than Alternatives 5, 6 or 7 in present worth cost and capital cost. Also, Alternative 3 is rated better than Alternatives 5, 6 or 7 with respect to the green assessment criterion. Hence, Alternative 3 is considered the highest rated alternative. Alternative 3 which includes the current PSCT and Gallery Well extraction and adds the NAPL-only extraction in the southern portion of the P/S Landfill is the best rated alternative with respect to effectiveness and implementability and cost. The anticipated remedy of capping for the PCB Landfill, CDA and BTA would prevent infiltration and minimize leaching and thus provide significant groundwater protection. Other existing remedial features such as the P/S Landfill and EECA Area Caps also support the groundwater protection objective. MNA for the


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organics is documented in the Area 5 North and will continue to reduce contaminant mass over the long term. In summary, Alternative 3 would provide control and containment of the plume and source reduction required for the proposed TI waiver in the Area 5 North. 11.6.4 Description of Remedial Alternatives for FS Area 5 South Table 11-1 lists the five retained remedial alternatives for detailed analysis for Area 5 South. As discussed earlier, there is no ARAR waiver requested for groundwater in Area 5 South. This section presents a description of the remedial alternatives for Area 5 South, followed by the detailed analysis (Section 11.6.5), and evaluation summary (Section 11.6.6). In the presentation of Area 5 South alternatives for groundwater below, it should be noted that capping or excavation anticipated as part of the soil remedy for FS Area 3 (including the Ponds A/B, MSA and hotspot location near PSCT-1) and FS Area 4 (RCF Pond) will prevent or reduce infiltration through contaminated soils and significantly reduce the sources of organics and inorganics into this groundwater area. Thus the remedy for soils in FS Area 3 and the pond closure remedy for FS Area 4 will be a significant source removal component of the groundwater remedy though it is not formally listed as a remedy component in these alternatives. 11.6.4.1 Alternative 1 No Action The No Action alternative is included as required by NCP. No Action implies that the source control activities and monitoring that are ongoing currently would not be occurring. 11.6.4.2 Alternative 2 Extraction (PCT-A, PCT-B) + Treat and Discharge to Evaporation Pond +

MNA + ICs + Monitoring This alternative includes the following components for FS Area 5 South (Figure 11-30A):

Extraction of PCT-A and PCT-B as currently implemented to mitigate migration Institutional controls, maintenance and monitoring to protect the groundwater


Contain and/or control contamination sources within the site boundary Mitigate potential migration groundwater contamination via perimeter control. Allow natural attenuation processes to slowly reduce contaminant concentrations (MNA)

The following provides a brief description of the conceptual design for the remedial alternative components: Extraction at PCT-A, PCT-B The groundwater at the PCT-A and PCT-B would continue to be extracted through the RAP wells along the southern perimeter of the site as currently operated. Details of the PCT-A and PCT-B remedial features, the extraction wells (RAP-1A, 2A, 3A, RAP-1B and B-5), target levels for pumping, and extraction flow rates were presented in Section 10.6.2. Based on the results of groundwater modeling (Appendix D-1) with the anticipated capping at the site and pond closure remedy, the PCT-A extraction rates would decrease from 1.5 million gallons per year (average 2006-2011) to between 2.3 and 3.6 million gallons per year based on dry season or wet season model results (see Section 10.6.2.2). The PCT-B extraction rates are expected to be in the range of 3.3 to 4.2 million gallons per year. The total annual extraction flow rates for PCT-A and


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PCT-B combined are expected to increase moderately from 2.5 million gallons (average of 2006 to 2011) to a range of 5.6 million to 7.8 million gallons. The extracted groundwater from the PCT-A and PCT-B will be pumped to the proposed evaporation pond in the footprint of the A-Series Pond without treatment (as currently implemented). However, it will be treated with LPGAC if there are elevated VOCs in the PCT liquids in the future. Replace Trench PCT-B This alternative includes the replacement of the PCT-B trench to improve extraction efficiency. The PCT-B trench is 500 feet in length, 3 feet wide and on average 50 feet deep. This excavation will be completed with long reach hydraulic excavators and slurry wall construction techniques. This approach will not require sloping back the sidewalls and instead would use near vertical sidewalls that are held up with a biopolymer slurry. The existing gravel would be excavated and disposed at the PCB Landfill. Once the excavation has reached full depth to the unweathered claystone, the trench would be backfilled with gravel. One well will be constructed within the gravel trench replacing the existing RAP-1B well. Evaporation Pond The evaporation pond would be sized based on the anticipated extraction rates from the PSCT and PCTs and other extraction components with the remedial alternatives. These extraction rates are estimated based on the GW Flow Model and the assumed capping and pond closure remedies and a stormwater management plan that was discussed in Section 10.1.3. The stormwater plan assumes that capping remedies anticipated for the FS Areas 1 through 4 would allow a large portion of the stormwater to be discharged through the B-Drainage under the substantive terms of the General Permit. Monitoring Sitewide groundwater and soil vapor monitoring is included as described in Section 10.1.6. 11.6.4.3 Alternative 3 Extraction (PCT-A, PCT-B) + Treat and Discharge + MNA + ICs +

Monitoring This alternative includes the following components for FS Area 5 South (Figure 11-31A):

Extraction of PCT-A and PCT-B as currently implemented to mitigate migration Treatment of extracted groundwater for inorganics to enable discharge to the B-

Drainage under the substantive terms of a site-specific NPDES permit (no evaporation pond)

Institutional controls, maintenance and monitoring to protect the groundwater The objectives of this remedial alternative are:


The following provides a brief description of the conceptual design for the remedial alternative components:


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Extraction at PCT-A, PCT-B The groundwater at the PCT-A and PCT-B would continue to be extracted through the RAP wells along the southern perimeter of the site as discussed in Alternative 2. The extracted groundwater from the PCT-A and PCT-B will be pumped to an GWTS to treat inorganics. Groundwater Treatment The groundwater treatment system for this alternative is designed as a 10 gpm system assumed to treat metals, VOCs, and other dissolved solids for discharge to the B-Drainage under the site-specific NPDES permit. The treatment approach assumed the same process train used in the groundwater restoration alternative in Appendix A TI Evaluation (Figure 11-31B). The treatment train would include pre-treatment steps such as an equalization tank and filtration to remove suspended solids. The treatment processes would include LPGAC to treat organics (if any) and RO to treat inorganics in accordance with the site-specific NPDES permit. The reject stream from the RO unit would be treated by a VSEP unit to concentrate RO reject brine to reduce the volume of waste brine produced. The reject brine assumed to be about 15 percent by volume (840,000 gallons per year) would be sent to a permitted facility for disposal. Replace Trench PCT-B This alternative includes the replacement of the PCT-B trench to improve extraction efficiency. The PCT-B trench is 500 feet in length, 3 feet wide and on average 50 feet deep as discussed in Alternative 2. Evaporation Pond This alternative assumes that the PCT-A and PCT-B groundwater is treated and discharged. The inorganics treatment approach is used with the scenario where there is no evaporation pond at the site. Monitoring Sitewide groundwater and soil vapor monitoring is included as described in Section 10.1.6. 11.6.4.4 Alternative 4 Extraction (PCT-A) + In-situ Reactive Wall (PCT-B) + MNA + ICs +

Monitoring This alternative includes the following components for FS Area 5 South (Figure 11-32A):

In-situ reactive wall at PCT-B to mitigate migration and extraction at PCT-A Institutional controls, maintenance and monitoring to protect the groundwater


Contain and/or control contamination sources within the site boundary Mitigate potential migration of groundwater contamination via perimeter control. Allow natural attenuation processes to slowly reduce contaminant concentrations (MNA)

The following provides a brief description of the conceptual design for the remedial alternative components of Alternative 3.


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In-situ Reactive Wall at PCT-B The in-situ reactive wall for the PCT-B is the only component that is different from Alternative 2. The in-situ reactive wall for the PCT-B would use the funnel and gate concept by cutting slots in the clay barrier and building a gate that serves as the PRB while the clay barrier serves as the funnel (Figure 11-32A). PCT-B clay barrier is about 500 feet long and would have two gates. Each gate would be about 8 feet wide placed in a slot in the clay barrier and 12 feet long in the direction of groundwater flow. The reactive material would be ZVI that is approximately 3 feet thick. The thickness of the ZVI was estimated based on calculations and assumptions presented in Appendix E. The groundwater would flow through a permeable pea gravel section before passing through the reactive ZVI (see detail on Figure 11-32A). After passing through the ZVI, the groundwater would flow through another pea gravel zone before it enters back into the native formation. The top elevation of the ZVI would be placed below lowest anticipated water table levels and above the ZVI would be impervious fill. Challenges are anticipated with the PRB technology to address the complex chemistry of metals contaminants in groundwater including arsenic, nickel, cadmium, and selenium in the Upper HSU. ZVI based PRBs have most often been used for chlorinated solvents with only a limited number of applications addressing metals. A limited number of ZVI based PRBs have been implemented for metals such arsenic and chromium but this is typically a situation where one metal is a dominant contaminant being treated. However, when there are multiple metals being treated each with its own redox behavior the consistent long term performance of a PRB is uncertain. Sorption and precipitation of metals are sensitive to pH and redox conditions, especially for those metals with multiple valence states. In situ treatment technologies that change the pH or redox conditions in the subsurface to treat some contaminants can result in increased potential hazard from other contaminants. For example, arsenic is more mobile, soluble, and toxic in its reduced form (As[III]), whereas selenium and chromium are more mobile, soluble, and toxic in their oxidized forms (Se[VI] or Se[IV] and Cr[VI]). Arsenic has been shown to be removed in some PRBs (USEPA 2008) but the mechanism of removal is different from what is observed with Cr(VI) and chlorinated solvents. Arsenic on ZVI PRBs involved adsorption or precipitation on the iron surface while reductive precipitation for Cr(VI) and reductive dechlorination for chlorinated solvents. There have been failures of ZVI PRBs at some sites with multiple combinations of metals. For example, at a site with molybdenum and uranium a ZVI PRB (Morrison 2006) failed with complete bypass of the PRB and loss of hydraulic control due to clogging of the ZVI. Hence, there is significant uncertainty in the ability to assess the long term effectiveness of a ZVI PRB with respect to a treatment effectiveness and reliability of a mixture of metals and ensuring the discharge from the PRB does not exceed MCLs. A separate and known concern with ZVI PRBs at this site is the very high levels of TDS (in the order of10,000 mg/L) found in groundwater in close proximity to the proposed PRB location. This would be a significant concern because of the potential deposition of solids and clogging of the gates would reduce ZVI material life time and impact its cost effectiveness. Additional bench scale testing including column testing would be required to study the viability of this technology. Extensive hydrogeologic investigations would be required at each of PRB locations and computer modeling to determine the effectiveness of the gates to capture the respective plumes and to pass the discharge through the gates to the downgradient formation without excessive head loss. The models would be used to optimize the number and sizing of the gates and the necessity of upgradient collection system modification or downgradient


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distribution laterals. Additional monitoring wells would be required at a minimum two well clusters at each of the gates including upgradient, in-gate and downgradient in the Upper HSU. Extraction at PCT-A The groundwater at the PCT-A would continue to be extracted through the RAP wells (RAP-1A, RAP-2A, RAP-3A) along the southern perimeter of the site. The extraction flow rates for PCT-A is expected to decrease significantly with capping remedies as discussed earlier. The extracted groundwater from the PCT-A will be pumped to an evaporation pond. Evaporation Pond This evaporation pond will be sized to handle this PCT-A flow and other flows such as PSCT and any other extraction components in the remedial alternative. Monitoring Sitewide groundwater and soil vapor monitoring is included as described in Section 10.1.6. 11.6.4.5 Alternative 5 Aggressive Hydraulic Extraction (40 large diameter extraction wells, Area

5 South) + Extraction (PCT-A, PCT-B) + Treat and Discharge + ICs + Monitoring The following provides a brief description of the conceptual design for the remedial alternative components: This alternative includes the following components for FS Area 5 South (Figure 11-33A):

Aggressive Hydraulic Extraction across Area 5 South Extraction at perimeter PCT-A and PCT-B trench Groundwater aboveground inorganics treatment to enable discharge under substantive

terms of site-specific NPDES permit, if required Institutional controls, maintenance and monitoring to protect the groundwater


Contain and/or control contamination sources within the site boundary Mitigate potential migration of groundwater contamination via perimeter control. Increase the rate of contaminant reduction by aggressive groundwater extraction to

supplement the natural attenuation processes that would otherwise slowly reduce contaminant concentrations.

The following provides a brief description of the conceptual design for the remedial alternative components: Well Installation Forty (40) wells would be constructed in Area 5 South with extraction wells spaced about 100 to 150 feet apart for aggressive area-wide extraction. The wells would be placed in the area south of the PSCT and in and around the RCF Pond as shown on Figure 11-33A. The wells would be 8-inch diameter steel casings placed in a large diameter boring typically drilled with bucket auger drilling equipment. The wells will be screened down to the weathered-unweathered


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contact varying in total depth from 30 to 50 feet bgs. The objective of these wells and this alternative component is to extract groundwater at the maximum allowed rate from the formation with the goal of rapid contaminant mass removal. The forty (40) groundwater extraction wells would each be equipped with a pump that is capable of pumping at 1 gpm. The extraction wells will be connected by a network of below ground PVC piping that leads to the treatment compound in the Liquid Treatment Area. The total extraction flow rate is expected to be on average 20 gpm (assuming 0.5 gpm of sustained flow per well) combined with the PCT-A and B flow rates. The groundwater treatment system is designed to treat the combined flow and other extraction flows at the site. Groundwater Treatment The groundwater treatment system for this alternative is designed as a 30 gpm system assumed to treat VOCs and metals that are the primary contaminants for discharge to the B-Drainage. The treatment train would include pre-treatment steps such as an equalization tank, oil-water separator and filtration to remove suspended solids. The treatment system would include LPGAC to treat organics prior to a RO unit to remove metals and dissolved anions (Figure 11-33B). This would be followed by a VSEP unit to concentrate RO reject brine. The reject brine assumed to be about 15 percent by volume (2.4 million gallons per year) would be trucked to a permitted facility for disposal. Extraction at PCT-A, PCT-B The groundwater at the PCT-A and PCT-B would continue to be extracted through the RAP wells along the southern perimeter of the site as discussed in Alternative 2. The extracted groundwater from the PCT-A and PCT-B will be pumped to an GWTS to treat inorganics. Replace Trench PCT-B This alternative includes the replacement of the PCT-B trench to improve extraction efficiency. The PCT-B trench is 500 feet in length, 3 feet wide and on average 50 feet deep as discussed in Alternative 2. Evaporation Pond The treated groundwater stream from Area 5 South would be discharged to a creek and the reject brine stream (1.78 million gallons per year) would be trucked to a permitted facility for disposal. The inorganics treatment approach is used with the scenario where there is no evaporation pond at the site as in Alternative 3. Monitoring Sitewide groundwater and soil vapor monitoring is included as described in Section 10.1.6. 11.6.5 Detailed and Comparative Evaluation of Remedial Alternatives for FS Area 5 South The detailed evaluation for the five remedial alternatives including the No Action alternative is presented in Table 11-6B. The following is the comparative analysis where for each CERCLA criteria the ratings and performance of each alternative is compared.


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11.6.5.1 Overall Protection of Human Health and Environment All of the active remedial alternatives are rated “Yes” because they are protective of human health and the environment. These active remedial alternatives generally contain contaminants by capping soil contamination in upgradient areas, closing existing ponds and implementing perimeter capture to ensure contaminants do not migrate beyond the historical site boundaries. Alternative 1, where the existing remedial features are not operational is rated “No”. Alternative 1 does not meet the threshold criteria requirement and hence is not evaluated for the balancing criteria. Alternatives 2 and 3 are similar because they are both extraction alternatives but Alternative 3 attempts to treat and discharge the water in accordance with the substantive requirements of an NPDES permit in order to avoid having an evaporation pond at the site. Alternatives 2 and 4 are similar because they provide capture at the perimeter but the difference is that Alternative 4 uses a passive technology such as an in-situ reactive wall at the perimeter while Alternative 2 uses extraction as implemented currently. Alternative 5 is an aggressive hydraulic extraction approach that attempts to restore the aquifer by extracting and treating the groundwater for discharge under the substantive terms of a site-specific NPDES permit. Alternative 5 would still require the capping or excavation of impacted soils that are upgradient in FS Area 3 (Ponds A/B, Hotspot Location 4 near PSCT-1), closure of RCF Pond, and perimeter control to ensure capture of contaminants at the boundary. Based on groundwater modeling, the time frame for aquifer restoration under Alternative 5 is not significantly different from Alternatives 2, 3 and 4. ICs including access restrictions and groundwater monitoring would still be required as a component of all the remedial alternatives that would provide overall protection. Also, it should be noted that this impacted groundwater with low levels of organics and inorganics does not pose any present risk to humans or ecological species as there is no pathway for exposure. 11.6.5.2 Compliance with ARARs The remedial alternatives evaluated here include a restoration alternative (Alternative 5) because a TI waiver would not be applicable for Area 5 South. All of the active remedial alternatives would be in compliance with groundwater ARARs because these alternatives include extraction or in-situ treatment at the site downgradient boundary. Alternatives 2 and 4 involve no active treatment of groundwater while Alternatives 3 and 5 involve a complex treatment system to treat organics and inorganics and other contaminants to stringent levels in compliance with NPDES permit requirements. All alternatives are expected to be in compliance with action-specific ARARs, though moderate challenges can be anticipated in meeting action-specific groundwater treatment ARARs for Alternatives 3 and 5; specifically, ARARs related to RWQCB and SBCAPCD requirements for discharges from the groundwater treatment system. Chemical-specific ARARs will not be met for organics and inorganics in groundwater for a long time (decades to centuries) because of the timeframe to reach MCL levels with any of these alternatives. 11.6.5.3 Long Term Effectiveness Alternatives 2, 3, 4 and 5 address the RAO of containing or controlling sources and mitigating potential migration beyond historical site boundaries by perimeter capture either by extraction (Alternatives 2, 3 and 5) and in-situ reactive wall (Alternative 4). The sources of contaminants in groundwater include the impacted soil in FS Area 3 including the MSA, Ponds A/B and the pond water and sediments in the RCF Pond (FS Area 4) all of which are anticipated to be capped or


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closed as part of the site remedy. The soils remedy of capping would prevent infiltration and leaching to groundwater thus cutting off the flux of contaminants to groundwater, while pond closures would remove the pond water and cap the sediments with a HDPE liner. Natural attenuation of the organic contaminants is known to occur and would also slowly decrease concentrations over the long term. Groundwater modeling indicates that groundwater from the north would flush contaminants downgradient and be captured by the perimeter extraction wells. Alternatives 2, 3 and 5 are rated moderate while Alternative 4 is rated poor to moderate. Alternative 4 is rated lower because of long term effectiveness concerns with the reactive wall at PCT-B in capturing a mix of metal contaminants (As, Se, Cd, Ni) with different redox chemistries and high TDS that could clog the reactive barrier. With Alternative 5, contaminant concentrations would decrease at a slightly faster rate than with Alternatives 2 and 3. However, the actual removal rate of contaminants would be very slow because the average extracted groundwater concentrations of the organics and inorganics would be very low (<100 g/l). Also, the time frame for aquifer restoration with Alternative 5 is not expected to be significantly different from the restoration time for Alternatives 2 and 3, which were estimated to be approximately 260 years for arsenic (the predominant metal contaminant) with the assumed capping discussed earlier. Hence, Alternative 5 is rated the same as Alternative 2. 11.6.5.4 Reduction of Toxicity, Mobility and Volume through Treatment Alternatives 2, 3 and 4 are rated poor to moderate while Alternative 5 is rated one step higher at moderate. Even though Alternative 5 is an aggressive extraction technology, it is only rated slightly higher than the other alternatives because the actual mass removal rates are expected to be quite slow for each of the organic and inorganic contaminants. For example, assuming the average concentration of each organic and inorganic contaminant is <100 g/l in the extracted groundwater, the mass removal rate is estimated to be <15 lbs per year per contaminant. Significant reduction in contaminant concentrations and mass are expected to occur by the soil remedy of excavation or capping for the MSA and Ponds A/B and closing the RCF Pond which are the primary sources of contaminants in groundwater. Contaminant concentrations in groundwater are already relatively stable based on recent data prior to capping. Timeframe for restoration of the aquifer is not significantly different for these alternatives as discussed earlier. 11.6.5.5 Short Term Effectiveness Alternative 2 is rated good, Alternative 4 is rated moderate to good, Alternatives 3 and 5 are rated moderate. Alternative 2 is rated good because there is no significant risk to human health or the environment associated with the PCT-A and PCT-B extraction and discharge to the evaporation pond. The evaporation pond will include drift fences and nets to protect the ecological species such as the CRLF and the CTS from the high TDS pond water. Alternative 3 is rated lower because it involves a complex inorganics treatment system and there is potential for system failures to result in groundwater with very high inorganics being released into Casmalia Creek. Alternative 4 is rated lower than Alternative 2 but higher than Alternative 3 because it involves construction of the reactive barrier by cutting slots in the PCT-B clay barrier and filling with ZVI as the reactive material which has a small potential for exposures to construction workers during barrier construction. Alternative 5 is rated one step lower than Alternative 2 because of the potential for failures of the complex treatment system and resulting discharges of large volumes of high inorganics laden groundwater to surface water. Brine waste is assumed to be transported by truck for disposal at a permitted facility, which is a safety concern with the long term transportation of large volumes of brine. Also, large quantities of waste inorganic solids would be generated in removing high TDS levels estimated at more than


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100,000 lbs per year prior to NPDES compliant discharge while only a minimal <15 lbs per year of each contaminant is expected to be removed by the treatment system. 11.6.5.6 Implementability Alternative 2 is rated good while Alternatives 3 and 4 are rated lower at moderate and Alternative 5 is rated lowest at poor to moderate. Alternative 2 is rated good because it is already implemented and involves a relatively simple extraction process without treatment. Alternative 3 is rated lower because of the technical challenges with installation and operation of a complex inorganics treatment system to meet stringent NPDES limits. Alternative 4 is rated lower because of the moderate challenges with construction of the reactive barrier with the deep excavation and cutting slots in the clay barrier material to place ZVI. Alternative 5 is rated lower at poor to moderate because it involves construction of a large network of wells and a high flow rate complex treatment system with concerns affecting its reliability. Alternative 5 also assumed brine waste disposal by truck to a permitted facility which is a concern with respect to liability. If disposal at a permitted facility is not chosen, a larger evaporation pond to handle additional brine reject would be required. However, larger evaporation ponds (e.g. 11 acre or 20 acre) would face significant implementability challenges in meeting the ecological protection requirements. 11.6.5.7 Cost The total present worth (30-year) cost is presented for Alternatives 2 through 5 in the table below for a 3 percent and 7 percent discount rate in 2014$. The cost for Alternative 1 is $0 and is not shown. Alternative 2 is the lowest in present worth cost, followed by Alternative 4, then Alternative 3 and finally Alternative 5, the aggressive extraction alternative as the highest. It is noted that the annual O&M cost is high at $3.8 million and yet the system would only recover less than 10 lbs of each of the metal contaminant per year because of the very low concentration of metals anticipated in the influent to the treatment system.

11.6.5.8 Green Impacts Assessment The range of green technologies that can play a role in minimizing environmental impacts of the remedial alternatives and technology components are discussed in Section 12. Appendix F presents the qualitative assessment of the environmental footprint for these alternatives based on green remediation criteria such as GHG emissions, energy usage, air emissions, collateral


Total Present Worth

Time frame



2 $1,781,000 $305,000 30-year $7,677,000 $5,216,000

100-year $11,863,000 $5,867,000

3 $4,440,000 $1,693,000 30-year $37,233,000 $24,475,000

100-year $58,575,000 $27,784,000

4 $2,456,000 $220,000 30-year $7,407,000 $5,124,000

100-year $10,863,000 $5,660,000

5 $14,211,000 $4,030,000 30-year $91,720,000 $60,958,000

100-year $141,787,000 $68,720,000


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risk, community impacts, resources lost, and water usage. The Appendix F evaluation was used to determine an overall rating for the alternative in Table 11-6B. Alternative 4 is rated the lowest at low to moderate for impacts because it is a passive technology that does not involve extraction, and Alternative 2 has moderate impacts, Alternative 3 moderate to high impacts and Alternative 5 has the highest impacts due to the continuous extraction at 30 gpm and the high energy required for the RO treatment system. 11.6.6 Evaluation Summary for Area 5 South All of the active remedial alternatives for Area 5 South, Alternatives 2 through 5 meet the threshold requirements of Overall Protection of Human Health and Environment and Compliance with ARARs. Alternative 3 is rated lower than Alternative 2 for STE and Implementability due to the concerns with inorganics treatment for discharge of treated groundwater. Alternative 4 is rated lower than Alternative 2 for LTE, STE and Implementability. The primary concern with Alternative 4 is the effectiveness of the ZVI barrier with respect to treating multiple metals with different redox chemistries in a reliable manner as to ensure no migration beyond the historical site boundaries and the potential for clogging of the barrier with high TDS in groundwater. Besides, Alternative 3 is higher in present worth cost than Alternative 2. With regards to Alternative 5, the aggressive restoration alternative would reduce organic and inorganic contaminant concentrations at a slightly faster rate than Alternative 2. However, aquifer restoration with Alternative 5 would not be very different from that with Alternative 2, which was estimated to be 260 years (for arsenic, the dominant metal contaminant) with the assumed capping or excavation in FS Area 3 and pond closure in FS Area 4 discussed earlier. Since the groundwater treatment system influent concentrations are likely to be very low (<100 g/L), it is estimated that it is likely that less than 15 lbs per year of each organic or inorganic contaminant would be removed. In the process of removing these small quantities of contaminants every year, tens of thousands of pounds of other inorganics per year would be recovered through the filters and the RO membranes due to the very high dissolved solids concentration (as high as 10,000 mg/L). Furthermore, the high cost of Alternative 5, especially the O&M cost of $3.8 million per year to remove less than 15 lbs of each metal contaminant makes it very poor with respect to cost effectiveness. Hence, Alternative 2 is the highest-rated remedial alternative, which provides reliable capture at the perimeter with the PCT-A and PCT-B trench extraction. Also, the capping of the source area impacted soils in FS Area 3 and the closure of the ponds (RCF Pond) would prevent infiltration through contaminated soils and minimize leaching to groundwater. This will cut off the contaminant flux to groundwater and in the long term the flushing of groundwater from the north will transport residual contaminants towards the PCT-A and PCT-B where it would be captured. Also, it should be noted that this impacted groundwater in Area 5 South does not pose any present risk to humans or ecological receptors as there is no complete exposure pathway. 11.6.7 Description of Remedial Alternatives for FS Area 5 West Table 11-1 lists the five retained remedial alternatives for detailed analysis for Area 5 West. As discussed earlier, there is no ARAR waiver requested for groundwater in Area 5 West. This section presents a description of the remedial alternatives for Area 5 West, followed by the detailed analysis (Section 11.6.8), and evaluation summary (Section 11.6.9). In the presentation of Area 5 West alternatives for groundwater below, it should be noted that capping anticipated as part of the soil remedy for FS Area 2 (including RCRA Canyon and WCSA) and the pond closure remedy for FS Area 4 (Ponds A-5 and A-Series) will prevent or minimize infiltration and


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significantly reduce the sources of inorganics into groundwater of this area. Thus the capping remedy for soils in FS Area 2 and the pond closure remedy for FS Area 4 will be a significant source removal component of the groundwater remedy though it is not formally listed as a remedy component in these alternatives. 11.6.7.1 Alternative 1 No Action The No Action alternative is included as required by NCP. No Action implies that the source control activities and monitoring that are ongoing currently would not be occurring. 11.6.7.2 Alternative 2 Extraction (PCT-C) + Treat and Discharge to Evaporation Pond + MNA +

ICs + Monitoring This alternative includes the following components for FS Area 5 (Figure 11-34A):

Extraction of PCT-C as currently implemented to mitigate migration Institutional controls, maintenance and monitoring to protect the groundwater


Contain and/or control contamination sources within the site boundary, where groundwater restoration is not technically practicable.

Mitigate potential migration groundwater contamination via perimeter control. Allow natural attenuation processes to slowly reduce contaminant concentrations (MNA)

The following provides a brief description of the conceptual design for the remedial alternative components: Extraction at PCT-C The groundwater at the PCT-C would continue to be extracted through the RAP wells along the southern perimeter of the site as currently operated. Details of the PCT-C remedial feature, the extraction wells (RAP-1C and C5), target levels for pumping, and extraction flow rates were presented in Section 10.6.2. Based on the results of groundwater modeling (Appendix D, SWR #3) with the anticipated capping at the site and pond closure remedy, the PCT-C extraction rates would increase from 2,405,000 gallons per year (average 2006-2011) to between 4.2 million and 4.9 million gallons per year based on dry season or wet season model results. The extracted groundwater from the PCT-C is pumped to the proposed evaporation pond in the footprint of the A-Series Pond and is not proposed to be treated because it would contain low levels of metals but no VOCs. Replace Trench PCT-C This alternative includes the replacement of the PCT-C trench to improve extraction efficiency. The replacement PCT-C trench is assumed to be 1,500 feet in length, 3 feet wide and on average 50 feet deep. This excavation will be completed with long reach hydraulic excavators and slurry wall construction techniques. This approach will not require a sloping back of the excavation and would use near vertical sidewalls that are held up with a biopolymer slurry. The existing gravel would be excavated and disposed at the PCB Landfill. Once the excavation has reached full depth to the unweathered claystone, the trench would be backfilled with gravel. Two wells will be constructed within the gravel trench replacing the existing RAP-1C and C5 wells.


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The PCT-C excavation would face some challenges because of the limited amount of available space between the A-Series Pond and the clay barrier. Evaporation Pond The evaporation pond would be sized based on the anticipated extraction rates from the PSCT and PCTs and other remedial alternative components that include groundwater extraction. The extraction flow rates for pond sizing would be based on the GW Flow Model with assumed capping and pond closure remedies (see Section 10.1.4) and a stormwater management plan that was discussed in Section 10.1.3. The stormwater plan assumes that capping remedies anticipated for the FS Areas 1 through 4 would allow a significant amount of the ssite’s stormwater to be discharged through the B-Drainage under the substantive terms of the General permit. Monitoring Sitewide groundwater and soil vapor monitoring is included as described in Section 10.1.6. 11.6.7.3 Alternative 3 Extraction (PCT-C) + Treat and Discharge + MNA + ICs + Monitoring This alternative includes the following components for FS Area 5 (Figure 11-35A):

Extraction of PCT-C as currently implemented to mitigate migration Treat extracted groundwater for inorganics to discharge to Casmalia Creek in

accordance with the site-specific NPDES permit Institutional controls, maintenance and monitoring to protect the groundwater


Contain and/or control contamination sources within the site boundary, where groundwater restoration is not technically practicable.

Mitigate potential migration of groundwater contamination via perimeter control. Allow natural attenuation processes to slowly reduce contaminant concentrations (MNA)

The following provides a brief description of the conceptual design for the remedial alternative components: Extraction at PCT-C The groundwater at the PCT-C would continue to be extracted through the RAP wells along the southern perimeter of the site as currently operated but the extracted groundwater would be treated for inorganics as discussed below. Groundwater Treatment The groundwater treatment system for this alternative is designed as a 10 gpm system assumed to treat metals, VOCs, and other dissolved solids for discharge to Casmalia Creek under the site-specific NPDES permit. The treatment train would include pre-treatment steps such as an equalization tank, and filtration to remove suspended solids. The process includes LPGAC treatment to treat organics (if needed) prior to a RO unit to remove metals and dissolved anions (Figure 11-35B). This would be followed by a VSEP unit to concentrate RO


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reject brine. The reject brine assumed to be about 15 percent by volume (630,000 gallons per year) would be trucked to a permitted facility for disposal. Replace Trench PCT-C This alternative includes the replacement of the PCT-C trench to improve extraction efficiency. The replacement PCT-C trench is assumed to be 1,500 feet in length, 3 feet wide and on average 50 feet deep as discussed in Alternative 2. Evaporation Pond This alternative assumes that the PCT-C groundwater is treated for inorganics and discharged to the B-Drainage. The inorganics treatment approach and discharge is used with the scenario where there is no evaporation pond. Monitoring Sitewide groundwater and soil vapor monitoring is included as described in Section 10.1.6. 11.6.7.4 Alternative 4 In-situ Reactive Wall (PCT-C) + MNA + ICs + Monitoring This alternative includes the following components for FS Area 5 West (Figure 11-36A):

In-situ reactive wall at PCT-C to mitigate migration Institutional controls, maintenance and monitoring to protect the groundwater



The following provides a brief description of the conceptual design for the remedial alternative components of Alternative 3. In-situ Reactive Wall at PCT-C The in-situ reactive wall for the PCT-C would use the funnel and gate concept by cutting slots in the clay barrier and building a gate that serves as the permeable reactive barrier while the clay barrier serves as the funnel as discussed in Section 11.6.4 for the PCT-B reactive wall. Figure 11-36A shows a detail plan and cross section of the ZVI reactive wall. The PCT-C clay barrier is about 1,500 feet long and would have four gates. Each gate would be about 8 feet wide placed in a slot in the clay barrier and 12 feet long in the direction of groundwater flow. The reactive material would be ZVI that is approximately 3 feet thick. The thickness of the ZVI was estimated based on calculations and assumptions presented in Appendix E. Challenges anticipated with addressing the complex mix of metals in groundwater and the high TDS was discussed in Section 11.6.4 for the PCT-B reactive wall component in Alternative 4 of Area 5 South. Additional bench scale testing including column testing would be required to study the viability of this technology. Extensive hydrogeologic investigations would be required at each of PRB locations and computer modeling to determine the effectiveness of the gates to


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capture the respective plumes and to pass the discharge through the gates to the downgradient formation without excessive head loss. The models would be used to optimize the number and sizing of the gates and the necessity of upgradient collection system modification or downgradient distribution laterals. Additional monitoring wells would be required at a minimum two well clusters at each of the gates including upgradient, in-gate and downgradient in the Upper HSU. Evaporation Pond This alternative does not involve any extraction and the evaporation pond requirement for the site would be smaller. Monitoring Sitewide groundwater and soil vapor monitoring is included as described in Section 10.1.6. 11.6.7.5 Alternative 5 Aggressive Hydraulic Extraction (40 large diameter extraction wells, Area

5 West) + Extraction (PCT-C) + ICs + Monitoring This alternative includes the following components for FS Area 5 West (Figure 11-37A):

• Aggressive Hydraulic Extraction across Area 5 West • Extraction at perimeter PCT-C • Groundwater aboveground treatment for discharge under a site-specific NPDES permit • Institutional controls, maintenance and monitoring to protect the groundwater


Contain and/or control contamination sources within the site boundary Mitigate potential migration of groundwater contamination via perimeter control. Increase the rate of contaminant reduction by aggressive groundwater extraction to

supplement the natural attenuation processes that would otherwise slowly reduce contaminant concentrations.

The following provides a brief description of the conceptual design for the remedial alternative components: Well Installation Forty (40) wells would be constructed in Area 5 West with extraction wells spaced about 100 to 150 feet apart. The wells would be placed in area around the A-Series Pond, Pond A-5 and in the bottom of RCRA Canyon as shown on Figure 11-37A. The wells would be 8-inch diameter steel casings placed in a large diameter boring typically drilled with bucket auger drilling equipment. The wells will be screened down to the weathered-unweathered contact varying in total depth from 30 to 50 feet bgs. The objective of these wells and this alternative component is to extract groundwater at the maximum allowed rate from the formation with the goal of rapid contaminant mass removal. The forty (40) groundwater extraction wells would each be equipped with a pump that is capable of pumping at 1 gpm. The extraction wells will be connected by a network of below ground PVC piping that leads to the treatment compound in the Liquid Treatment Area. The total extraction flow rate is expected to be on average 2 gpm (assuming 0.05 gpm of sustained flow per well) from the aggressive extraction which is


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combined with the PCT-C extraction as in Alternative 2. The groundwater treatment system is designed to treat this combined flow and other extraction flows at the site. Groundwater Treatment The groundwater treatment system for this alternative is designed as a 20 gpm system assumed to treat metals and VOCs though metals are the primary contaminants. The treatment train would include pre-treatment steps such as an equalization tank and filtration to remove suspended solids. The process includes LPGAC treatment to treat organics (if needed) prior to a RO unit to remove metals and dissolved anions (Figure 11-37B). This would be followed by a VSEP unit to concentrate RO reject brine. The reject brine assumed to be about 15 percent by volume (788,000 gallons per year) would be trucked to a permitted facility for disposal. Extraction at PCT-C The groundwater at the PCT-C would continue to be extracted through the RAP wells along the southern perimeter of the site as discussed earlier in Alternative 2. Replace Trench PCT-C This alternative includes the replacement of the PCT-C trench to improve extraction efficiency. The replacement PCT-C trench is assumed to be 1,500 feet in length, 3 feet wide and on average 50 feet deep as discussed earlier in Alternative 2. Evaporation Pond The treated groundwater stream from Area 5 West would be discharged to the B-Drainage and but the reject brine stream (788,000 gallons per year) would be transported by truck and disposed at a permitted facility. The inorganics treatment approach and discharge is used with the scenario where there is no evaporation pond. Monitoring Sitewide groundwater and soil vapor monitoring is included as described in Section 10.1.6. 11.6.8 Detailed and Comparative Evaluation of Remedial Alternatives for FS Area 5 West The detailed evaluation for the five remedial alternatives including the No Action alternative is presented in Table 11-6C. The following is the comparative analysis where for each CERCLA criteria the ratings and performance of each alternative is compared. 11.6.8.1 Overall Protection of Human Health and Environment All of the active remedial alternatives are rated “Yes” because they are protective of human health and the environment except Alternative 1. These active remedial alternatives generally contain contaminants by capping soil contamination in upgradient areas, closing existing ponds and implementing perimeter capture to ensure contaminants do not migrate beyond historical site boundaries. Alternative 1, where the existing remedial features are not operational is rated “No”. Alternatives 2 and 3 are similar because they both provide capture at the perimeter but the


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difference is that Alternative 3 attempts to treat and discharge the water in accordance with the substantive terms of an NPDES permit in order to avoid having an evaporation pond at the site. Alternative 4 uses a passive technology such as an in-situ reactive wall at the perimeter while Alternative 2 uses extraction as implemented currently. Alternative 5 is an aggressive hydraulic extraction approach that attempts to restore the aquifer by extracting and treating the groundwater for discharge under the substantive terms of a site-specific NPDES permit. Alternative 5 would still require the capping or excavation of source area soils that are upgradient in RCRA Canyon/WCSA, closure of Pond A-5 and A-Series Pond, and perimeter control to ensure capture of contaminants at the boundary. Based on groundwater modeling, the time frame for aquifer restoration under Alternative 5 is not significantly different from Alternatives 2, 3 and 4. ICs including access restrictions and groundwater monitoring would still be required as a component of all the remedial alternatives that would provide overall protection. Also, it should be noted that this impacted groundwater with inorganics does not pose any present risk to humans or ecological species as there is no pathway for exposure. 11.6.8.2 Compliance with ARARs The remedial alternatives evaluated here include a restoration alternative (Alternative 5) because a TI waiver may not be applicable for Area 5 West as discussed in Appendix A. All of the active remedial alternatives would be in compliance with groundwater ARARs because these alternatives include extraction or in-situ treatment at the site downgradient boundary. Alternatives 2 and 4 involve no active treatment of groundwater while Alternatives 3 and 5 involve a complex treatment system to treat inorganics and other contaminants to stringent levels in compliance with NPDES permit requirements. All alternatives are expected to be in compliance with action-specific ARARs, though moderate challenges can be anticipated in meeting action-specific groundwater treatment ARARs for Alternatives 3 and 5; specifically ARARs related to RWQCB and SBCAPCD requirements using the groundwater treatment system. Chemical-specific ARARs for groundwater will not be met for inorganics for a long time (decades to centuries) because of the timeframe to reach MCL levels with any of these alternatives. 11.6.8.3 Long Term Effectiveness Alternatives 2, 3, 4 and 5 address the RAO of containing or controlling sources and mitigating potential migration by perimeter capture either by extraction (Alternatives 2, 3 and 5) and in-situ reactive wall (Alternative 4). The sources of metal contaminants in groundwater include the impacted soil in RCRA Canyon and WCSA (FS Area 2) and the pond water and sediments in Pond A-5 and A-Series Pond (FS Area 4) all of which are anticipated to be capped or closed as part of the site remedy. The soils remedy of capping would prevent infiltration and leaching to groundwater thus cutting off the flux of contaminants to groundwater, while pond closures would remove the pond water and cap the sediments with a HDPE liner. Some attenuation of the inorganic contaminants would occur slowly over the long term. Groundwater modeling indicates that new, clean groundwater from the north would flush contaminants in the saturated zone and would be captured by the perimeter. Alternatives 2, 3 and 5 are rated moderate while Alternative 4 is rated poor to moderate. Alternative 4 is rated lower because of long term effectiveness concerns with the reactive wall at PCT-C in capturing a mix of metal contaminants (As, Se, Cd, Ni) with different redox chemistries and high TDS that could clog the reactive barrier. With Alternative 5, contaminant concentrations would decrease at a slightly faster rate than with Alternative 2. However, the actual removal rate of contaminants would be very slow because


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the average extracted groundwater concentrations of the metals would be very low (~ 10s of g/l). Also, the time frame for aquifer restoration with Alternative 5 is not expected to be significantly different from the restoration time for Alternative 2, which was estimated to be approximately 220 years for arsenic (the predominant metal contaminant) with the assumed capping discussed earlier. Hence, Alternative 5 is rated the same as Alternative 2. 11.6.8.4 Reduction of Toxicity, Mobility and Volume through Treatment Alternatives 2, 3 and 4 are rated poor to moderate while Alternative 5 is rated moderate. Even though Alternative 5 is an aggressive extraction technology, it is only rated slightly higher than the other alternatives because the actual mass removal rates are expected to be quite slow for each of the metal contaminants. Assuming the average concentration of the inorganic contaminant is 40 g/l in the extracted groundwater, the mass removal rate is estimated to be <10 lbs per year. Significant reduction in contaminant concentrations and mass are expected to occur by the remedy of capping RCRA Canyon/WCSA and the Pond A-5 and A-Series Pond which are the primary sources of metals. Contaminant concentrations in groundwater are already relatively stable based on recent data prior to capping. Timeframe for restoration of the aquifer is not significantly different for these alternatives as discussed earlier. 11.6.8.5 Short Term Effectiveness Alternative 2 is rated good, Alternative 4 is rated moderate to good and Alternatives 3 and 5 are rated moderate. Alternative 2 is rated good because there is no significant risk to human health or the environment associated with the PCT-C extraction and discharge to the evaporation pond. The evaporation pond will include drift fences and nets to protect the ecological species such as the CRLF and the CTS from the high TDS pond water. Alternative 3 is rated lower because it involves a complex inorganics treatment system and there is potential for system failures to result in groundwater with very high inorganics being released into Casmalia Creek. Alternative 4 is rated lower than Alternative 2 because it involves construction of the reactive barrier by cutting slots in the PCT-C clay barrier and filling with ZVI as the reactive material which has a small potential for exposures to construction workers during barrier construction. Alternative 5 is rated one step lower than Alternative 2 because of the potential for failures of the complex treatment system and resulting discharges of large volumes of high inorganics laden groundwater to surface water. Brine waste is assumed to be transported by truck for disposal, which is a safety concern with the long term transportation of large volumes of brine. Also, large quantities of waste inorganic solids would be generated in removing high TDS levels estimated at more than 100,000 lbs per year prior to NPDES compliant discharge while only a minimal <10 lbs per year of each metal contaminant is expected to be removed. 11.6.8.6 Implementability Alternative 2 is rated good while Alternatives 3 and 4 are rated lower at moderate and Alternative 5 is rated lowest at poor to moderate. Alternative 2 is rated good because it is already implemented and involves a relatively simple extraction process without treatment. Alternative 3 is rated lower because of the technical challenges with installation and operation of a complex inorganics treatment system to meet stringent NPDES limits. Alternative 4 is rated lower because of the moderate challenges with construction of the reactive barrier with the deep excavation and cutting slots in the clay barrier material to place ZVI. Alternative 5 is rated lower at poor to moderate because it involves construction of a large network of wells and a complex treatment system with concerns affecting its reliability. Alternative 5 also assumed brine waste disposal by truck to a permitted facility. If disposal at a permitted facility is not chosen, a larger


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evaporation pond to handle additional brine reject would be required. However, larger evaporation ponds (e.g. 11 acre or 20 acre) would face significant implementability challenges in meeting the ecological protection requirements. 11.6.8.7 Cost The total present worth (30-year) cost is presented for Alternatives 2 through 5 in the table below for a 3 percent and 7 percent discount rate 2014$. The cost for Alternative 1 is $0 and is not shown. Alternative 2 is the lowest in present worth cost, while Alternative 4 is higher, Alternative 3 is next higher, and Alternative 5, the aggressive extraction alternative is high in present worth cost. It is noted that the annual O&M cost for Alternative 5 is very high at $2 million and yet the system would only recover less than 10 lbs of each of the metal contaminants per year because of the very low concentration of metals anticipated in the influent to the treatment system.

11.6.8.8 Green Impacts Assessment The range of green technologies that can play a role in minimizing environmental impacts of the remedial alternatives and technology components are briefly discussed in Section 12. Appendix F presents the qualitative assessment of the environmental footprint for these alternatives based on green remediation criteria such as GHG emissions, energy usage, air emissions, collateral risk, community impacts, resources lost, and water usage. The Appendix F evaluation was used to determine an overall rating for the alternative in Table 11-6C. Alternative 4 has the lowest impacts because it is a passive technology that does not involve extraction, and Alternative 2 has low to moderate impacts, Alternative 3 has moderate to high impacts, and Alternative 5 has high impacts due to the continuous extraction at 20 gpm and the high energy required for the RO treatment system. 11.6.9 Evaluation Summary for Area 5 West All of the active remedial alternatives for Area 5 West, Alternatives 2 through 5 meet the threshold requirements of Overall Protection of Human Health and Environment and Compliance with ARARs. Alternative 1 did not meet the threshold requirements and was not evaluated for the balancing criteria. Alternative 3 is rated lower than Alternative 2 for STE and Implementability due to the concerns with inorganics treatment for discharge of treated groundwater. Alternative 4 is rated lower than Alternative 2 for LTE, STE and Implementability.


Total Present Worth

Time frame



2 $2,633,000 $258,000 30-year $7,509,000 $5,290,000

100-year $11,144,000 $5,853,000

3 $5,005,000 $1,719,000 30-year $38,244,000 $25,231,000

100-year $59,843,000 $28,579,000

4 $4,450,000 $155,000 30-year $9,834,000 $6,912,000

100-year $13,256,000 $7,442,000

5 $12,844,000 $2,041,000 30-year $51,522,000 $35,231,000

100-year $77,471,000 $39,254,000


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The primary concern with Alternative 4 is the long term effectiveness of the ZVI barrier with respect to treating multiple metals with different redox chemistries in a reliable manner as to ensure no migration beyond historical site boundaries and the potential for clogging of the barrier with high TDS in groundwater. Besides, Alternative 3 is higher in present worth cost than Alternative 2. With regards to Alternative 5, the aggressive restoration alternative would reduce inorganic contaminant concentrations at a slightly faster rate than Alternative 2. However, aquifer restoration with Alternative 5 would not be very different from that with Alternative 2, which was estimated to be 220 years (for arsenic, the dominant metal contaminant) with the assumed capping in FS Area 2 and pond closure in FS Area 4 discussed earlier. Since the groundwater treatment system influent concentrations are likely to be very low (on the order of a few 10s of g/L), it is estimated that it is likely that less than 10 lbs per year of each metal contaminant (arsenic, cadmium, nickel, selenium) would be removed. In the process of removing these small quantities of metal contaminants every year, tens of thousands of pounds of other inorganics per year would be recovered through the filters and the RO membranes due to the very high dissolved solids concentration (as high as 10,000 mg/L). Furthermore, the very high cost of Alternative 5, especially the O&M cost of $2 million per year to remove less than 10 lbs of each metal contaminant makes it very poor with respect to cost effectiveness. Hence, Alternative 2 is the highest-rated remedial alternative, which provides reliable capture at the perimeter with the PCT-C trench extraction. Also, the capping of the source area impacted soils in RCRA Canyon/WCSA and the closure of the ponds (Pond A-5 and A-Series Pond) would prevent infiltration through contaminated soils and minimize leaching to groundwater. This will cut off the contaminant flux to groundwater and in the long term the flushing of clean groundwater from the north will transport residual metals contaminants towards the PCT-C where it would be captured. Also, it should be noted that this impacted groundwater in Area 5 West does not pose any present risk to humans or ecological receptors as there is no complete exposure pathway.

11.7 Cost Estimate Uncertainty Section 11 presents total net present value (NPV) cost estimates in 2014 dollars for each FS area for 30-year and 100-year time frames. The FS provides conceptual designs and cost estimates for the remedial alternatives. The cost estimates reflect an accuracy of +50 percent and -30 percent consistent with CERCLA FS guidance documents. The cost estimates are based on estimated capital and annual costs and include a contingency of 35 percent to 50 percent for both capital and O&M cost components. This contingency is in the upper end of the range of scope and bid contingencies referenced in the USEPA cost guidance (USEPA 2000). The 35 percent to 50 percent contingency is acceptable at this stage of conceptual design, and is consistent with other cost estimates used by USEPA for the site. The estimate for the dewatering of the P/S Landfill using horizontal wells represents a significant departure from 35 percent-50 percent contingency range. Due to a high level of uncertainty for well installation and liquids extraction, the FS adopts a 75 percent contingency for the P/S Landfill dewatering. A summary of the contingency percentages used for the various remedial alternatives in each FS Area are presented in Table E-9-0 in Appendix E. USEPA cost estimating guidance specifies using a net discount rate of 7 percent and acknowledges that there may be circumstances where an alternate discount rate may be appropriate. The FS uses discount rates of 3 percent and 7 percent. The cost estimating guidance relies on a discount rate analysis by OMB and the 7 percent discount rate is


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consistent with OMB Circular A-94. The 3 percent discount rate is consistent with recent rates of inflation and returns on investment. (see Section 12.8). The FS examines an assumed construction schedule that runs from 2018 through 2022 for planning and cost estimation purposes in Section 12, where site-wide remedial alternatives are evaluated. The cost assumptions and other details developed and used in the cost estimates are presented in the cost spreadsheets included in Appendix E. The cost estimates do not include line items for ICs since these costs would be nominal compared with other remedial components and would be included within the assumed range of accuracy of the estimate (+50 percent and -30 percent). Generally, the FS evaluated costs for remedial alternatives for capping or excavation for soils and extraction or in-situ treatment for groundwater. The assumed area and volume of impacted soil are significant factors in the quality of the cost estimates especially for excavation-related alternatives. The cost estimates seek to apply somewhat conservative values, but are realistic based on past site experience. Estimates of the areas and volumes of soil contamination are based on current site information. There are other factors that may contribute to the uncertainties in the FS cost estimates including:

1. Installation costs related to installation of large diameter NAPL wells or horizontal wells inside the P/S Landfill depending on the type of drilling methods used;

2. Technical challenges and safety concerns especially with horizontal wells under the P/S Landfill (discussed in Section 10.6.3.1) presents significant uncertainties;

3. Potential dewatering flow rates from horizontal wells and associated liquid disposal costs are a large uncertainty;

4. Uncertainty with the leachate treatment technology and its emission controls to meet local requirements;

5. Uncertainty with the ZVI reactive barrier performance at the PCT-B and PCT-C with a mixture of different metals and high dissolved solids and the frequency of its replacement;

6. Uncertainty with annual precipitation and the magnitude of stormwater or pond water volumes that would require handling during and after the remedy construction phase that could affect costs;

7. Uncertainty in O&M costs that are difficult to estimate but relatively small differences in annual O&M costs can change the present worth costs significantly with the 30-year and 100-year costs;

8. Uncertainty in estimating the amount of NAPL or aqueous phase liquids that would be recovered from the southern P/S Landfill by NAPL-only, or aggressive NAPL extraction or dewatering with horizontal wells.

If some of these technology components are selected, then bench scale, pilot testing or additional evaluation may be needed during remedial design to address these uncertainty issues that can affect cost.

11.8 Assumed Schedule for Cost Estimating Purposes The cost estimates for the various FS Areas assume the following site schedule:

Activity Year

USEPA Issues Record of Decision 2017


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Activity Year

Proposed Remedy Construction – Starts 2018

Proposed Remedy Construction – Completed 2022

Proposed Remedy Operations – Start 2022-2023

USEPA 1st Five-Year Review 2027

The calculation of 30-year and 100-year discounted costs assumes the remedy will be constructed over approximately five summer seasons (assumed to begin in 2018) and as such the capital costs are expended in that time frame as discussed in Section 12. During that time, the site O&M costs are expected to remain approximately the same as they currently are. The provisional schedule listed above represents an estimate for planning and cost estimation purposes. Revisions or modifications to the overall schedule, including various decision documents, the design process, or construction could lead to changes in the present value cost estimate (see Section 12.8).

11.9 References CSC, 2011. Final Remedial Investigation Report, January 2011 CSC, 2011a Draft Feasibility Study Report, February 2011 CSC 2011b B Drainage Wetlands Restoration and Erosion Control Improvement Plan, April 22, 2011 CSC 2009a Routine Groundwater Monitoring Element of Work, Field Sampling Work Plan, MACTEC, March 31, 2009 CSC 2009b Sampling Plan for Soil Gas Monitoring, April 6, 2009 CSC, 2004. Remedial Investigation/Feasibility Study Work Plan, June 2004. CSQA, 2003. California Stormwater BMPs Handbook, California Stormwater Quality Association, January 2003 ECHOS, 2000. Environmental Restoration Assemblies Cost Book, ECHOS Remediation Cost Handbook, 2000 FRTR, 2011. Federal Remediation Technologies Roundtable, http://www.frtr.gov and http://costperformance.org websites with technology and cost information. Landreth 1995 Waste Management Control Strategies for Landfills, Robert Landreth, July 1995 Means 2005 Environmental Remediation Cost Handbook, Unit Costs, RS Means 2005 Morrison 2006 Environmental Science and Technology, 40:2018-2024, 2006 Get-a-Quote.net 2011 National Construction Estimator, 2011 Niles 2011 Telephone communication with Corey Bertelsen, dated July 7, 2011


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USACE 2001 Checklist for Hazardous Waste Landfill Cover Design, US Army Corps of Engineers, ETL 1110-1-162, September 2001 USEPA, 2011. Stormwater BMPs Presentation, http://www.ectc.org USEPA, 2011 USEPA, 2000. A Guide to Developing and Documenting Cost Estimates during the Feasibility Study, USEPA and US Army Corps of Engineers, USEPA 540-R-00-002 July 2000 USEPA 1991 Design and Construction of RCRA/CERCLA Final Covers, USEPA, EPA 625/4-91/025, May 1991 USEPA 1988 Guide to Technical Resources for Design of Land Disposal Facilities, USEPA, EPA 625/6-88/ 018, June 1988 USEPA 1988a. Guidance for Conducting Remedial Investigations and Feasibility Studies Under CERCLA, USEPA 540/G-89/004, October 1988


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12.0 DETAILED EVALUATION OF SITE-WIDE REMEDIAL ALTERNATIVES AND SUMMARY OF TOP RANKED REMEDY

Based on the area-specific remedial alternatives retained in Section 11, Section 12 develops a range of SWRs and presents a detailed evaluation based on CERCLA ranking criteria. In addition, this section provides a summary of the evaluation, identifies a “top ranked” remedial alternative based on a comparative analysis of the alternatives and then provides additional information for the top ranked remedy. Table 12-1 lists and summarizes the site-wide remedial alternatives and their components by FS Area. Table 12-2 presents the detailed evaluation of 7 of the 9 CERCLA evaluation criteria in accordance with CERCLA FS guidance (USEPA 1988). A green impacts assessment is included for each alternative in addition to the 7-criteria evaluation. The CERCLA 9-criteria are described in Section 11. As described in Sections 10 and 11, Table 12-3 provides a road map to help track the area-specific alternatives that are retained from the screening evaluation in Section 10 and detailed evaluation in Section 11, and the site-wide remedial alternatives that are finally developed for the detailed evaluation in Section 12. The circles that are shown for the area-specific and site-wide remedial alternatives evaluations are partially filled by quarters and correspond to the 5-point rating system used for the CERCLA criteria detailed evaluation. Filled circles are the most desirable and non-filled circles are the least desirable. Filled circles are then used to indicate which area-specific alternatives were assembled into the six site-wide remedial alternatives evaluated in Section 12. Table 12-4 summarizes the costs for each of the site-wide remedial alternatives and Table 12-5 summarizes the detailed evaluation for the site-wide alternatives using the partially-filled circles. Table 12-6 presents the cost estimate summary of top ranked site-wide remedial alternative #3. The site-wide alternative cost estimates presented in Section 12 include present worth of capital cost based on an assumed construction schedule between 2018 and 2022. 12.1 Description of Site Wide Remedial Alternatives This section provides a description of the six site wide remedial alternatives developed for detailed evaluation. The six SWRs rely on the detailed evaluation process in Section 11 and each SWR is a logical combination of the remedial alternatives for individual FS Areas. Consistent with the NCP, the six SWRs cover the range of alternatives from “no action” to several “aggressive” remediation scenarios. The proposed SWRs and their components are discussed in the paragraphs below. The details of each of the alternative components are summarized in Table 12-1 and Figures 12-1A, B through 12-5A, B of the FS. The titles of the various SWRs are not intended to completely describe the remedy and were simply chosen to distinguish the alternatives. 12.1.1 SWR #1 - No Further Action This SWR (which is required for evaluation by CERCLA) assumes that there is no additional remediation other than remediation which has already been completed (i.e., the installation of RCRA caps on the P/S Landfill and the EE/CA Area) and that which is ongoing (i.e., groundwater extraction and treatment/management from the existing PSCT, PCTs, Sump 9B, and Gallery Well features).


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12.1.2 SWR #2 – Large Evaporation Pond This SWR addresses all of the site contamination and risk issues identified by the RI and respective risk assessments, and meets the previously identified RAOs presented in the FS report. SWR #2 meets the minimum requirements established for RCRA Canyon (FS Area 2), which do not by themselves require that all of RCRA Canyon area be covered with some sort of cap. This alternative assumes that only a portion of RCRA Canyon is capped and, as a result, some of the stormwater runoff from the Canyon is directed to a large (11 acre) evaporation pond that would be constructed in the footprint of the existing A-Series Pond to manage both that runoff and treated extracted liquids (Figure 12-1A). The remedial components of this SWR for each FS Area are briefly summarized below. A more detailed description of the individual FS Area remedial components of SWR #2 was provided earlier in Section 11 of this report. Table 12-3 shows which FS Area remedial components from Section 11 are combined for SWR #2. 12.1.2.1 FS Area 1 – PCB Landfill, Burial Trench Area, Central Drainage Area FS Area 1 would be capped with a RCRA cap that encompasses the PCB Landfill, Burial Trench Area, and the Central Drainage Area, covering a total area of approximately 28.8 acres. This remedial component of SWR #2 is Alternative 4 of FS Area 1, described in more detail in Section 11.2.1.4. The proposed RCRA cap will be similar in design to the existing P/S Landfill and EE/CA Area caps, and will tie into these caps. Use of pond water from the ponds is assumed during construction of the caps for soil layers below the HDPE liner such as the foundation layer. As described below for FS Area 3, the construction of this RCRA cap would be extended to cover the Maintenance Shed Area as well. 12.1.2.2 FS Area 2 - RCRA Canyon and West Canyon Spray Area FS Area 2 would be remediated by constructing an ET cap over the western slopes of RCRA Canyon and excavating and capping the relatively shallow contaminated soils of the WCSA. This remedial component of SWR #2 is similar to Alternative 3 of FS Area 2 (Section 11.3.1.3), except this site wide alternative includes an ET cap instead of a RCRA mono soil cap. The eastern slope of RCRA Canyon is graded and BMPs utilized to meet the substantive conditions of the General Permit for stormwater discharge. The ET cap and excavation of the WCSA reduces the residual risks of this area to acceptable levels (i.e., HQ<1) by eliminating the exposure pathway for the ornate shrew and western meadowlark (which, based on the Risk Assessment, are the two species with unacceptable ecological risks for this area). In addition, the ET cap serves to reduce surface water infiltration in this area of the site, thus lowering the level of the water table, reducing contaminant leaching into groundwater, and eliminating the surface seeps at the south end of RCRA Canyon. 12.1.2.3 FS Area 3 – Former Ponds and Pads, Remaining Site Areas The RI Report identified several localized areas of contaminated soil (i.e., hotspot locations) in FS Area 3 which had concentrations of contaminants that collectively create elevated risks. These locations have elevated ecological risks to soil invertebrates due to elevated organics or inorganics in the soil (but did not have any ecological risks to wildlife). Five of these hot spot locations would be addressed. By addressing these five locations, the residual ecological risks of the FPP and ROS areas are reduced to a HQ<1. As is the case with FS Area 2, this is considered a conservative approach considering that the exposed species are soil invertebrates, and a higher HQ might have been justifiable. The hot spots are either excavated


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and the contaminated soils placed under the PCB Landfill cap (Locations 1, 3 and 4 shown on Figure 12-1A), and covered with an asphalt cap (Location 1 in the LTA), or as is the case for Location 2, the Maintenance Shed Area, the location is covered with a RCRA cap. This remedial component of SWR #2 is Alternative 3 of FS Area 3 that is described in more detail in Section 11.4.1.3. For RISBON-59 (Location 10), because there are not any unacceptable human health or ecological risks, the proposed remedial component for this location is "long term monitoring" of the groundwater with two additional monitoring wells down gradient of RISBON-59. 12.1.2.4 FS Area 4 – Stormwater Ponds and Treated Liquid Impoundments FS Area 4 would be addressed with the following remedial actions as a component of SWR #2 for the various ponds at the site:

Pond A-5 - removal of all liquids, placing excavated soil from the WCSA within the pond footprint to raise the bottom of the former pond approximately 10 to 15 feet. The pond footprint is then capped with a double HDPE/GCL liner and converted into a new retention basin that will be used as part of RCRA Canyon stormwater management plan;

Pond 18 - removal of all liquids, placing clean soil within the pond footprint and regrade it to match adjacent site topography and facilitate stormwater runoff, and installation of a RCRA cap to "close" the pond;

Pond 13 - removal of all liquids, placing a clean soil cover over the pond, and constructing a double HDPE/GCL bottom liner in the pond so it may be converted to a lined retention basin. The double liner will also serve as a RCRA equivalent cap for the pond sediments;

A-Series Pond - removal of all liquids, regrading the northeast corner of the pond to increase the pond size to approximately 11 acres, placing clean soil throughout the bottom of the pond to raise the pond bottom to approximately 425 feet MSL above the future anticipated groundwater elevation, constructing a double-lined HDPE cap with LCRS and leak detection system over the former footprint of the pond to create a new 11-acre evaporation pond that will be used as part of the stormwater and liquids treatment and management system of the site;

RCF Pond - removal of all liquids, placing clean soil throughout the bottom of the pond to raise the pond bottom to approximately 415 feet MSL above the future anticipated groundwater elevation, constructing an ecological-cap over the entire pond bottom area (thus covering all specific locations with elevated inorganics in the sediment), and construction of a new lined stormwater channel through the middle of former pond and then through or around the wetlands to convey the stormwater runoff from the CDA and other capped portions of the site.

For each of these existing ponds, the liquids (total of approximately 65 million gallons at the start of the 2012 rainy season) would be removed by allowing them to continue to naturally evaporate and by enhanced evaporation equipment (e.g. enhanced evaporation equipment) within the footprints of the ponds. Some pond water will be used in the construction of the proposed caps in Area 1 and other areas below HDPE liners (for example, in foundation layers). Any liquids remaining in the ponds prior to remedial construction will be pumped to the new 11-acre evaporation pond that is proposed in the footprint of the existing A-Series Pond. The new evaporation pond will also be required to handle future treated PSCT and PCT liquids, as well as stormwater runoff from uncapped portions of RCRA Canyon Area. The new evaporation


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pond will be designed to mitigate impact on special status species that exist at the site. The mitigation for ecological protection, operations and maintenance of the evaporation pond are discussed in more detail in Section 10.1.4. This mitigation would potentially include the following elements to be determined during remedial design in consultation with USFWS and DFG:

Perimeter fencing to prevent contact from amphibians and small and large mammals Elimination of wildlife habitat within and around the perimeter fencing Hazing to deter contact from birds and bats Netting and/or screening mesh to prevent contact from birds Routine biological monitoring to verify effectiveness of the wildlife controls

This remedial component of SWR #2 is Alternative 4 of FS Area 4 and is described in more detail in Section 11.5.1.4. If the volume of liquids in the current ponds is too great to be effectively managed during remedial construction, a contingency measure would be implemented that entails treating the remaining pond liquids (that are high in TDS and metals) with GAC to remove any low level organics and RO to remove TDS and metals, and discharging the treated liquids to the B-Drainage under a future, new site-specific NPDES Permit. Obtaining a site-specific NPDES Permit would require the submittal of a report of waste discharge and application package to the RWQCB to request an exception to the Basin Plan prohibition for the discharge of treated liquids to the B-Drainage and Casmalia Creek (see Section 2.2.4 for a summary of the status of the current NPDES Permit and the process for obtaining a new one). 12.1.2.5 FS Area 5 – Groundwater - Area 5 North, Area 5 South, and Area 5 West As a part of the FS the site groundwater is separated into three sub areas, including Area 5 North (the Upper HSU and Lower HSU groundwater north of the PSCT and east of the road to the LTP), Area 5 South (the Upper HSU and Lower HSU groundwater south of the PSCT and east of the road to the LTP), and Area 5 West (the Upper HSU and Lower HSU groundwater in RCRA Canyon and areas west of the road to the LTP). Each of these groundwater areas was evaluated separately in the FS Report and in the TIE (Appendix A). FS Area 5 North A groundwater ARAR waiver would be implemented based on Technical Impracticability for the Upper and Lower HSU of Area 5 North, which is the TI Zone defined in Appendix A of this FS Report. While ARARs would be waived for Area 5 North, the RAO of source removal and controlling and containing contaminants within the TI Zone would be met. The FS proposes to continue to operate the existing Gallery Well to remove LNAPL, DNAPL and aqueous-phase liquids from the toe of the P/S Landfill and the PSCT to contain contaminated groundwater within the Upper HSU. Sump 9B would be operated, if necessary, to control the water table in the Central Drainage Area. This alternative also proposes to install approximately 16 “NAPL-only” extraction features within the southern part of the P/S Landfill to capture as much pooled LNAPL and DNAPL as possible in that area. The design and operation of the new NAPL-only wells is discussed in Section 11 of the FS Report.


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Finally, this alternative includes installation of 12 new Lower HSU monitoring wells upgradient of PSCT-1 and PSCT-4 which may be converted to extraction points to provide hydraulic containment if and when the sampling of these wells indicates the presence of VOCs or SVOCs above MCLs that may migrate beneath the PSCT in the Lower HSU. Six of the wells would be installed near PSCT-1 and six would be installed near PSCT-4. As discussed in Section 10.1.8, although groundwater moves very slowly underneath the PSCT in the Lower HSU, natural attenuation of contaminants limits the potential migration of dissolved-phase contaminants that have been detected at low levels in the immediate vicinity of the PSCT in the Lower HSU. The potential future TI Zone is currently contained with the exception of (1) DNAPL within the P/S Landfill and the Lower HSU fractures underlying the P/S Landfill and Central Drainage Area and (2) dissolved-phase contaminants in the Lower HSU that are potentially moving southward through fractures and under the PSCT. Removal of DNAPL and other liquids from the P/S Landfill will remove the source of DNAPL migration from the P/S Landfill into the underlying Lower HSU fractures. Placing additional RCRA caps on the remaining areas of FS Area 5 that are currently not capped will cause the groundwater elevations in FS Area 5 to significantly drop which will decrease the rate of groundwater flow and potential migration of dissolved-phase contaminants beneath the PSCT. Natural attenuation of contaminants occurs and will help to limit this potential migration of dissolved-phase contaminants. The liquids extracted from the Gallery Well will be stored and shipped for treatment and disposal at an approved facility. The extracted liquids from PSCT will be treated at the site for organic removal (using an upgraded liquids treatment system that is conceptually designed as an activated carbon treatment system), filtered for solids removal, then transferred to the new 11-acre lined evaporation pond which is proposed in the footprint of the closed A-Series Pond (Figure 12-1B). The treatment system will be determined during the remedial design. As noted above, in order to provide DNAPL and LNAPL source control in Area 5 North, the FS Report proposes to install approximately sixteen “NAPL-only” extraction wells which are 4-inch diameter wells that will be located in the vicinity of RIPZ-13 on or near Bench 1 in the P/S Landfill. These wells will be screened in the Upper HSU (i.e., in the landfill waste materials) to enable removal of both LNAPL and DNAPL that has the highest potential to migrate, and thus provide the most risk reduction. The NAPL extracted from these "NAPL" wells will be stored and trucked for disposal. Remedial design, construction, and initiation of extraction of NAPLs from the NAPL-only extraction wells would be performed expeditiously because the liquid levels in the P/S Landfill will decline rapidly within the first few years and ultimately to below the bottom of the landfill after the remaining area across FS Area 1 is capped as demonstrated with the groundwater flow model (Appendix D-3). Extraction of current free-phase NAPLs will not be practicable after the landfill becomes desaturated. Prompt initiation of field investigations for remedial design is critical to maximizing NAPL extraction. This remedial component of SWR #2 for Area 5 North is Alternative 3, described in more detail in Section 11.6.1.3. FS Areas 5 West and South Monitored Natural Attenuation will be relied on to remediate organics and inorganics for the Upper HSU of Area 5 South with perimeter containment provided by the PCT-A and PCT-B extraction features until groundwater meets remediation goals (MCLs). One of the primary


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natural attenuation mechanisms that will reduce contaminant concentrations will be precipitation recharge, dilution, and flushing of contaminants from across Area 5 South to the PCTs. Elimination of the current ponds that contain water with high TDS and elevated metals (RCF and Pond 13) and excavation of contaminated soils from Area 3 (described above) would eliminate contaminant sources to groundwater. The existing PCT-A and PCT-B extraction features will be operated and the liquids extracted will be treated at the site for organic removal (using an upgraded liquids treatment system that is conceptually designed as an activated carbon treatment system), filtered for solids removal, then transferred to the new 11-acre lined evaporation pond proposed in the footprint of the closed A-Series Pond. The treatment system will be determined during remedial design. Remediation of the Lower HSU in Area 5 South is not necessary based on data collected during the RI. This remedial component of SWR #2 for Area 5 South is Alternative 2, described in more detail in Section 11.6.4.2. Similar to Area 5 South, MNA will be relied on to remediate inorganics for the Upper HSU of Area 5 West with perimeter containment provided by the PCT-C extraction features until groundwater meets remediation goals (MCLs). Precipitation recharge, dilution, and flushing of contaminants from across Area 5 West to the PCT will reduce contaminant concentrations over time. Elimination of the current ponds with water with high TDS and elevated metals (Pond A-5, A-Series Pond, and Pond 18) would reduce contaminant sources to groundwater. Organics do not require remediation in the Upper HSU. The ET cap that is proposed to be placed on a portion of RCRA Canyon as described above will reduce infiltration and leaching of metals, thereby reducing the contaminant source to groundwater. The PCT-C extraction feature will continue to be operated, and the liquids extracted from the wells will be treated at the site for organic removal (using an upgraded liquids treatment system that is conceptually designed as an activated carbon treatment system), filtered for solids removal, then transferred to the new 11-acre lined evaporation pond which is proposed in the footprint of the closed A-Series Pond. Remediation of the Lower HSU in Area 5 West is not necessary. This remedial component of SWR #2 for Area 5 South is Alternative 2, described in more detail in Section 11.6.7.2. Finally, for SWR #2, the remedial component for Area 5 South and West includes a long term groundwater monitoring program designed to track organic and inorganic concentrations and confirm reduction to remediation goals (MCLs) over the long-term. 12.1.2.6 Groundwater Flow Model Results of SWR #2 The groundwater elevation changes and hydraulic effectiveness of SWR #2 were evaluated using the Groundwater Flow Model that was prepared as part of the RI Report (CSC 2011a). The modeling of site-wide remedial alternatives was performed using the numerical model code MODFLOW. The results are documented in Appendix D-1. The Groundwater Flow modeling indicates that with the proposed capping efforts the Gallery Well extraction rates will continue to decline and that the P/S Landfill will ultimately dry up (i.e., become desaturated) as the groundwater level beneath the P/S Landfill drops approximately 70 feet to below the bottom of the landfill. The modeling also indicates that the PSCT-1 extraction rates will be substantially lower than current rates, and that PSCT-2, PSCT-3, and PSCT-4 extraction points dry up. The Groundwater Flow modeling also indicates that with the proposed capping efforts the groundwater levels will fall below the bottom of Sump 9B, Sump 9B extraction rates will fall to zero, and the Road sump will remain dry. As such, neither of these existing extraction features will serve any purpose going forward, and the FS concludes that it is not appropriate or necessary to continue operation of Sump 9B or the Road Sump as part of the final remedy. However, they will be retained as a contingency measure in the event they are


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needed to control the water table elevation which is naturally shallow in the Central Drainage Area. The groundwater flow modeling predicts that the PSCT will continue to be effective in hydraulically containing groundwater within the Upper HSU of Area 5 North and that groundwater will pass beneath the PSCT in the Lower HSU. The known concentrations in the Lower HSU in the vicinity of the PSCT are very low based on the current well network. MNA will be relied on for the control of contaminants beneath the PSCT. However, as described above, the 12 new Lower HSU monitoring wells may be converted to extraction points to provide hydraulic containment if and when the sampling of these wells indicates the presence of VOCs or SVOCs above MCLs that may migrate beneath the PSCT. The P/S Landfill dewatering timeframes and rates with the Gallery Well extraction were discussed in Section 10.1.8 and Appendix D-3 with a summary presented in the table below:

Aqueous Phase (Gallery Well) Extraction Rates

Year Volume (gal)

1 450,000 2 427,500 3 406,125 4 385,820 5 366,530

6-10 250,000 As noted above, all of the existing PCTs extraction systems will continue to be operated. The Groundwater Flow Model predicts that the PCTs will continue to be effective in hydraulically containing groundwater within Areas 5 South and West. The Groundwater Flow Model predicts that the extraction rates of PCT-A, PCT-B and PCT-C will increase after closure of the ponds. The Groundwater Flow modeling indicates that the ponds (RCF, A-Series Pond, Pond A-5, Pond 18, and Pond 13) will be above the high groundwater elevation after backfilling them with soil. It is important that these ponds are above the high groundwater elevation to prevent salty groundwater with elevated metals from creating a seep that could result in elevated risk to ecological receptors. 12.1.2.7 Remediation Time Frame Evaluation Results of SWR #2 The remediation time frames for Areas 5 West and South were evaluated to estimate the remediation time frame for the concentration of metals to reach remediation goals (MCLs) after source areas were removed. The evaluation was performed with the numerical model code FRACTRAN. The results are documented in Appendix D-2. The model simulations for Area 5 West indicate that the time frames for achieving groundwater cleanup standards (MCLs) would range from 90 years (nickel) to 220 years (arsenic) after complete source removal. The model simulations for Area 5 South indicate that the time frames for achieving groundwater cleanup standards would range from 80 years (nickel) to 260 years (arsenic) after complete source removal. There is uncertainty in the actual time frames to


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achieve cleanup standards and the actual timeframe may range from several decades to centuries. 12.1.3 SWR #3 – Small Evaporation Pond SWR #3 is a variation of SWR #2 which includes a small (6 acre) evaporation pond rather than the larger pond. The primary difference in this alternative is additional capping in FS Area 2 (RCRA Canyon and WCSA) to ensure that all of the stormwater runoff from the area can be discharged via the substantive terms of the General Permit rather than managed in the evaporation pond (Figure 12-2A). The details of the remediation of each FS Area under SWR #3 are described in the paragraphs that follow. A more detailed description of the individual FS Area remedial components of SWR #3 was provided earlier in Section 11 of this report. Table 12-3 shows which FS Area remedial components from Section 11 are combined for SWR #3. 12.1.3.1 FS Area 1 – PCB Landfill, Burial Trench Area, Central Drainage Area FS Area 1 will be addressed using the same remedial components as listed for SWR #2 above. 12.1.3.2 FS Area 2 - RCRA Canyon and Western Canyon Spray Area FS Area 2 will be capped with an ET cap, RCRA Hybrid cap, or a combination of these two types of caps to cover the entire RCRA Canyon area (8.4 acre western area, 5.5 acre WCSA area, and remaining 19.3 acre area). As necessary, the slopes will be graded to achieve a 2:1 grade for stability of the slopes and caps. The cap will cover the areas with elevated metals that are a risk to ecological receptors and reduce or eliminate the recharge of rainfall to the cap which will lower the level of the water table and eliminate surface seeps. This will meet the substantive conditions of the General Permit and allow stormwater to be discharged from the entire RCRA Canyon to the B-Drainage. This component of SWR #3 is a combination of Alternative 8 of Area 2 (assumes RCRA Hybrid cap over entire area) and Alternative 9 of Area 2 (assumes ET cap over entire area). These cap alternatives are described in more detail in Sections 11.3.1.8 and 11.3.1.9. The actual types of caps that will be selected for different areas will be determined during detailed remedial design after the ROD. 12.1.3.3 FS Area 3 – Former Ponds and Pads, Remaining Site Areas FS Area 3 will be addressed using the same remedial components as listed for SWR #2 above. 12.1.3.4 FS Area 4 – Stormwater Ponds and Treated Liquid Impoundments FS Area 4 will be addressed with the same remedy as was proposed for SWR #2 above. In SWR #3, however, because of the additional capping in FS Area 2 (RCRA Canyon and WCSA), this alternative allows all of the stormwater from RCRA Canyon to be discharged to the B-Drainage. Hence the size of the evaporation pond that is required under this scenario is about half of that in SWR #2, and thus a 6-acre evaporation pond will be constructed in the footprint of the existing A-Series Pond, and the remainder of the existing pond bottom will be capped with an ecological-cap. The evaporation pond is actually a series of evaporation cells which altogether comprise 6 acres (Figure 11-20C). Each of the cells will be designed to mitigate impact on special status species that exist at the site. The mitigation for ecological protection, operations and maintenance of the evaporation pond are discussed in more detail in Section 10.1.4. This mitigation would potentially include the following elements to be determined during remedial design in consultation with USFWS and DFG:


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12.1.3.5 FS Area 5 – Groundwater Area 5 North, Area 5 South, and Area 5 West FS Area 5 will be remediated using the same remedial components as listed for SWR #2 above. The process flow diagram for the treatment of extracted groundwater, Gallery Well liquids and NAPL streams in this alternative is shown on Figure 12-2B. 12.1.3.6 Groundwater Flow Model Results of SWR #3 Again, the groundwater elevation changes and hydraulic effectiveness of this combination of remedial components were evaluated for the site using the Groundwater Flow Model that was prepared as part of the RI Report (CSC 2011a). The Groundwater Flow Modeling results for Area 5 North were similar to those from SWR #2 and indicate that the Gallery Well extraction rates will decline and that the P/S Landfill will ultimately dry up (i.e., become desaturated) as the groundwater level beneath the P/S Landfill drops approximately 70 feet (i.e., below the bottom of the landfill), that the PSCT-1 extraction rates will be substantially lower than current rates, and that PSCT-2, PSCT-3, and PSCT-4 extraction rates will go to zero as the sumps dry up. The modeling predicts that the PSCT will continue to be effective in hydraulically containing groundwater within the Upper HSU and that groundwater will continue to pass beneath the PSCT in the Lower HSU. The potential contaminant migration beneath the PSCT will be addressed by MNA and potentially converting the 12 new Lower HSU monitoring wells to extraction points, similar to SWR #2. The P/S Landfill dewatering rates with the Gallery Well extraction are the same as in SWR #2. The Groundwater Flow Model predicts that the extraction rates of PCT-A, PCT-B and PCT-C will increase after closure of the ponds. PCTs will continue to be effective in hydraulically containing groundwater within Areas 5 South and West. 12.1.3.7 Remediation Time Frame Evaluation Results of SWR #3 Again, the remediation time frames for Areas 5 West and South were evaluated to estimate the remediation time frame for the concentration of metals to reach remediation goals (MCLs) after source areas were removed. The estimated timeframes for Area 5 South to achieve groundwater cleanup standards would be the similar to those for SWR #2. The estimated timeframes for Area 5 West to achieve groundwater cleanup standards would be faster because a source of metals over the entire RCRA Canyon area would be capped under SWR #3 compared to a cap that only partially covers a part of RCRA Canyon under SWR #2. However, the predicted difference in time frames between SWR #2 and SWR #3 is likely within the range of the accuracy of the analysis performed and consequently is not quantified. 12.1.4 SWR #4 – No Evaporation Pond


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SWR #4 is a variation of SWR #3 but does not include an evaporation pond. The requirement for an evaporation pond is eliminated by adding a treatment plant at the site that would treat PSCT and PCT liquids for both organics and inorganics to meet the requirements of a future, new site-specific NPDES Permit (Figures 12-3A, B). The treated liquids are then discharged to the B-Drainage rather than managed in an evaporation pond. It should be noted that the process of requesting an exception to the Basin Plan prohibition would be a lengthy process with no guarantee of receiving an exception. With SWR #4, an evaporation pond is not constructed at the site. The details of the remediation of each FS Area are described in the paragraphs that follow. A more detailed description of the individual FS Area remedial components of SWR #4 was provided earlier in Section 11 of this report. Table 12-3 shows which FS Area remedial components from Section 11 are combined for SWR #4. 12.1.4.1 FS Area 1 – PCB Landfill, Burial Trench Area, Central Drainage Area FS Area 1 will be remediated using the same remedial component as listed for SWR #3 above. 12.1.4.2 FS Area 2 - RCRA Canyon and Western Canyon Spray Area Here the entire RCRA Canyon west slope (8.4 acres), WCSA (5.5 acres), and the other remaining 19.3 acres of FS Area 2 are all capped with an ET cap, Hybrid cap, or combination of the two cap types. Hence, similar to SWR #3 the stormwater discharge from RCRA Canyon will meet the substantive conditions of the General Permit and allow stormwater from the entire RCRA Canyon to be discharged under the substantive terms of the General Permit. This component of SWR #4 is a combination of Alternative 8 of Area 2 (assumes Hybrid cap over entire area) and Alternative 9 of Area 2 (assumes ET cap over entire area). These cap alternatives are described in more detail in Sections 11.3.1.8 and 11.3.1.9. The actual types of caps that will be selected for different areas and the detailed design of the contiguous cap will be determined during remedial design. 12.1.4.3 FS Area 3 – Former Ponds and Pads, Remaining Site Areas FS Area 3 will be remediated using the same remedial components as listed for SWR #3 above. 12.1.4.4 FS Area 4 – Stormwater Ponds and Treated Liquid Impoundments The FS Report proposes the same remedy for this FS Area as SWR #3, above, except that SWR #4 does not include an evaporation pond. In SWR #4, the liquids extracted from the PSCT and PCTs are treated to meet the substantive requirements of a future, new site-specific NPDES Permit for both organics and inorganics and discharged post-treatment to the B-Drainage rather than managed in an evaporation pond at the site. Determining the substantive terms of a site-specific NPDES Permit or of obtaining such a permit, if required, would involve the submittal of a report of waste discharge and application package to the RWQCB to request an exception to the Basin Plan prohibition for the discharge of treated liquids to the B-Drainage and Casmalia Creek (see Section 2.2.4 for a summary of the status of the current NPDES Permit and the process for obtaining a new one). As discussed earlier, the process of requesting an exception to the Basin Plan prohibition would be a lengthy process with no guarantee of receiving an exception. The bottom of the A-Series Pond is partially backfilled with soil to an elevation (approximately 425 feet MSL), above the future anticipated water table, and capped with an ecological-cap similar to the cap proposed for the RCF Pond. This component of SWR #4 is Alternative 6 of FS Area 4 and is described in more detail in Section 11.5.1.6.


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12.1.4.5 FS Area 5 – Groundwater Area 5 North, Area 5 South, and Area 5 West The FS Report proposes the same remedial components for this FS Area as for SWR #3 above, except that all of the extracted liquids from the PSCT, PCT-A, PCT-B, PCT-C are treated in a Liquids Treatment Plant designed to remove both organics and inorganics (Figure 12-3B). The inorganics treatment will include RO treatment to meet the requirements of a new NPDES Permit prior to discharge to the B-Drainage. The RO treatment will produce a brine stream that will be stored and disposed at an approved facility. This component of SWR #4 is Alternative 4 in Area 5 North, and is described in more detailed in Section 11.6.1.4. 12.1.4.6 Groundwater Flow Model Results of SWR #4 Again, the FS Report has evaluated the effectiveness of this combination of remedial components for the site using the Groundwater Flow Model that was prepared as part of the RI Report (CSC 2011a). The groundwater flow modeling results are the same as those for SWR #3 regarding the effectiveness of hydraulic containment of the PSCT and PCTs. The groundwater flow modeling indicates that with the proposed capping efforts the Gallery Well extraction rates will continue to decline and ultimately go to zero as the groundwater level beneath the P/S Landfill drops below the bottom of waste, that the PSCT-1 and PSCT-2 extraction rates will be substantially lower than current rates, and that PSCT-3, and PSCT-4 extraction rates will go to zero as the sumps dry up. As noted above, the FS proposes to continue to operate all of the existing PCT’s extraction systems. The Groundwater Flow Model predicts that the extraction rates of the PCT-A, PCT-B and PCT-C will increase compared to the average current extraction rates (Section 10.6.2). 12.1.4.7 Remediation Time Frame Evaluation Results of SWR #4 The estimated timeframes for Areas 5 South and 5 West to achieve groundwater cleanup standards would be similar to those for SWR #3. There is uncertainty in the actual time frames to achieve cleanup standards and the actual timeframe may range from several decades to centuries. 12.1.5 SWR #5 – P/S Landfill Dewatering SWR #5 is a variation of SWR #3 but also includes aggressive de-watering of the P/S Landfill using approximately five (5) extraction wells drilled horizontally and constructed with approximately 300 feet of screen north of the clay barrier (Figure 12-4A). The NAPL-only extraction wells assumed in SWRs #2, #3, and #4 are no longer necessary because the NAPLs would now be extracted with the horizontal wells. The details of the remediation of each FS Area are described in the paragraphs that follow. As was the case of SWR #3, the treated PSCT and PCT liquids are managed in a new 6-acre evaporation pond which is constructed in the footprint of the A-Series Pond. A more detailed description of the individual FS Area remedial components of SWR #5 was provided earlier in Section 11 of this report. Table 12-3 shows which FS Area remedial components from Section 11 are combined for SWR #5. 12.1.5.1 FS Area 1 – PCB Landfill, Burial Trench Area, Central Drainage Area FS Area 1 will be remediated using the same remedial component as listed for SWR #3 above.


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12.1.5.2 FS Area 2 - RCRA Canyon and Western Canyon Spray Area FS Area 2 will be remediated using the same remedial component as listed for SWR #3 above. 12.1.5.3 FS Area 3 – Former Ponds and Pads, Remaining Site Areas FS Area 3 will be remediated using the same remedial component as listed for SWR #3 above with one exception. The RISBON-59 hotspot will be excavated and the contaminated soils moved to the PCB Landfill to be capped and covered as part of the closure of that landfill. This component of SWR #5 is Alternative 4 in FS Area 3 and is described in more detail in Section 11.4.1.4. 12.1.5.4 FS Area 4 – Stormwater Ponds and Treated Liquid Impoundments FS Area 4 will be remediated using the same remedial component as listed for SWR #3 above. 12.1.5.5 FS Area 5 – Groundwater Area 5 North, Area 5 South, and Area 5 West FS Area 5 South and FS Area 5 West will be remediated using the same remedial components as listed for SWR #3 above. The Area 5 North remedial components are, however, different. SWR #5 continues to assume the following would be implemented as described for SWR #3:

Groundwater ARAR waiver for Area 5 North based on Technical Impracticability Operation of the Gallery Well and PSCT If necessary, operation of existing Sump 9B to control the water table Installation of 12 new Lower HSU monitoring wells upgradient of PSCT-1 and PSCT-4 If necessary, conversion of Lower HSU monitoring wells to extraction wells Operation of the PCTs for Areas 5 South and West

Instead of installing “NAPL-only” extraction features within the southern part of the P/S Landfill to capture pooled LNAPL and DNAPL, however, SWR #5 assumes aggressive de-watering of the P/S Landfill by constructing approximately five extraction wells drilled horizontally and constructed with approximately 300 feet of screen north of the clay barrier (Figure 12-4A). The horizontal extraction wells, or drain lines, would be installed in the P/S Landfill with the goal of expeditiously removing all liquids (aqueous phase liquids and free-phase DNAPL and LNAPL) from the landfill. These liquids would be temporarily stored and then shipped for disposal at an approved facility. Conceptually, the primary benefits of this approach over the approach for SWR #3 would be:

The hydraulic head that contributes to the horizontal gradient that causes groundwater (and any contaminants dissolved in groundwater) to move southward through the Lower HSU and underneath the PSCT would be reduced faster than for SWR #3.

The energy costs to operate the horizontal drains would be reduced because the liquids

would drain by gravity. Two options for installation could be used. For either option, the wells would be “blind” (single entry) drilled from a starting point located in the vicinity of Sump 9B, approximately 300 feet south of the landfill.


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Option 1 – One option would be to drill through the base of the P/S Landfill clay barrier and directly access the DNAPL pool at the bottom of the landfill. The well would be installed by advancing a pilot bore through the alluvium and Upper HSU several feet into the base of the clay, installing conductor casing and pressure grouting it in place, advancing a borehole through the conductor casing 300 feet into the landfill, and installing 4-inch diameter well materials. This method has the advantage that the DNAPL pool can be accessed directly. A key disadvantage is that several feet of liquids, including DNAPL, may be left at the bottom of the landfill because the well casing cannot be placed directly on the bottom of the landfill.

Option 2 – A second option would be to drill underneath the P/S Landfill clay barrier and

install the well within the claystone immediately beneath the DNAPL zone and then intercept the bottom of the landfill to the north. Using this method, the well would be installed by advancing the borehole down through the alluvium and Upper HSU and into the Lower HSU, below the clay barrier, then angle back upward to intersect waste, following the slope of the LHSU contact along the base of the landfill. This method has the advantage that drilling is not performed through the clay barrier. A key disadvantage is that the rates at which liquids drain through the claystone separating the bottom of the landfill and the underlying horizontal wells may be slow, limiting the rate at which the landfill is drained.

The conceptual design, technical viability and construction concerns of installing and operating these horizontal wells are discussed in detail in Section 10.6.3.1 and Section 11.6.1.6 of the FS Report. Those technical challenges and risks with the aggressive de-watering alternative include the following construction hazards and vulnerabilities as summarized in Table 10-6A-1:

Construction Risk Factors - Insufficiently Draining the P/S Landfill - Uncontrolled release of Landfill Liquids - Penetrating the Clay Barrier - Improperly Controlling the Path of the Borehole - Borehole Collapse - Well Collapse - Chemical Compatibility - Health and Safety during Construction

Operations and Maintenance Risk Factors

- Well Efficiency and Clogging during O&M - Uncontrolled Release during O&M - Health and Safety during O&M - Uncontrolled Release during Transport

SWR #5 also assumes that four existing monitoring wells located in the CDA will be converted to LNAPL skimming wells and the extracted LNAPL be stored and shipped for disposal. This component of SWR #5 is the same as Alternative 6 of Area 5 North described in detail in Section 11.6.1.6. The conceptual process flow diagram for the treatment of extracted groundwater, Gallery Well liquids and NAPL streams in this alternative is shown on Figure 12-4B. The treatment system will be determined during remedial design. All of the other details of SWR #5 remain the same as in SWR #4.


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12.1.5.6 Groundwater Flow Model Results of SWR #5 Again, the FS Report has evaluated the groundwater elevation changes and effectiveness of this combination of remedial components for the site using the Groundwater Flow Model that was prepared as part of the RI Report (CSC 2011a). The Groundwater Flow modeling indicates that with the proposed capping efforts the Gallery Well extraction rates will decline and ultimately go to zero, as was the case in SWR #3, as the groundwater level beneath the P/S Landfill drops below the bottom of the landfill, that the PSCT-1 extraction rates will be substantially lower than current rates, and that PSCT-2, PSCT-3, and PSCT-4 extraction rates will approach zero as the sumps dry up. The modeling predicts that the PSCT will continue to be effective in hydraulically containing groundwater within the Upper HSU and that groundwater will continue to pass beneath the PSCT in the Lower HSU. The potential contaminant migration beneath the PSCT will be addressed by MNA and potentially converting the 12 new Lower HSU monitoring wells to extraction points, similar to SWR #2. The P/S Landfill dewatering rates with horizontal wells were discussed in Section 10.1.8 and are presented in the table below:

P/S Landfill Dewatering Extraction (Horizontal Wells) Rates and Volumes

Year Flow Rate (gpm)

Volume (gal)

1 2 5,250,000 2 0.5 1,300,000 3 0.5 1,300,000 4 0.1 263,000 5 0.1 263,000

As noted above, the FS proposes to continue to operate all of the existing PCTs extraction systems. The Groundwater Flow Model predicts that the PCTs will continue to be effective in hydraulically containing groundwater within Areas 5 South and West. The Groundwater Flow Model predicts that the extraction rates of PCT-A, PCT-B and PCT-C will increase compared to the average current extraction rates (Section 10.6.2). 12.1.5.7 Remediation Time Frame Evaluation Results of SWR #5 The estimated timeframes for Areas 5 South and 5 West to achieve groundwater cleanup standards would be the similar to those for SWR #3. 12.1.6 SWR #6 – Aggressive Site wide Groundwater Restoration SWR #6 is a variation of SWR #5 which, in addition to including aggressive de-watering of the P/S Landfill using horizontal extraction wells, also includes the following (Figure 12-5A):

Construction and operation of approximately 12 LNAPL skimming wells in the CDA. Construction and operation of approximately 80 new groundwater extraction wells

located throughout Area 5 South and Area 5 West (Figure 12-5A).


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Similar to SWR #4, an evaporation pond is not needed because all contaminated liquids will be either treated for organics and inorganics (see Figure 12-5B) to meet the requirements of a future, new site-specific NPDES Permit for discharge to the B-Drainage (extracted liquids from the PSCT, PCT, and 80 new wells) or stored and shipped for treatment and disposal at an approved facility (extracted liquids from the Gallery Well and P/S Landfill horizontal wells). These other components of SWR #6 are the same as: Alternative 7 of Area 5 North (described in detail in Section 11.6.1.7) and Alternative 5 of Areas 5 South and West (described in detail in Sections 11.6.4.5 and 11.6.7.5). A more detailed description of the individual FS Area remedial components of SWR #6 was provided earlier in Section 11 of this report. Table 12-3 shows which FS Area remedial components from Section 11 are combined for SWR #6. The details of the remediation of each FS Area are described in the paragraphs that follow. 12.1.6.1 FS Area 1 – PCB Landfill, Burial Trench Area, Central Drainage Area FS Area 1 will be remediated using the same remedial component as listed for SWR #3 above. 12.1.6.2 FS Area 2 - RCRA Canyon and Western Canyon Spray Area FS Area 2 will be remediated using the same remedial component as listed for SWR #3 above. 12.1.6.3 FS Area 3 – Former Ponds and Pads, Remaining Site Areas FS Area 3 will be remediated using the same remedial component as listed for SWR #5 above. This includes excavating the RISBON-59 hotspot and placing the contaminated soils in the PCB Landfill to be capped and covered as part of the closure of that landfill. 12.1.6.4 FS Area 4 – Stormwater Ponds and Treated Liquid Impoundments FS Area 4 will be remediated using the same remedial component as listed for SWR #4 above. 12.1.6.5 FS Area 5 – Groundwater Area 5 North, Area 5 South, and Area 5 West In this site Wide Remedial Alternative, Area 5 North is remediated using the same remedial components as listed for SWR #5 above. The P/S Landfill dewatering rates with horizontal wells are the same as in SWR #5. The Area 5 South and Area 5 West remedy components include all of the groundwater extraction components as listed for SWR #5 but also include the construction and operation of approximately 80 new extraction wells located throughout Area 5 South and West. In SWR #6, because of the large volumes of extracted water (estimated 30 gpm), the liquids extracted from these 80 new wells will be treated along with the extracted liquids from the PSCT and PCTs to meet the substantive requirements of a future site-specific NPDES Permit for both organics and inorganics and discharged to the B-Drainage, rather than managed in an evaporation pond. An evaporation pond will not be constructed, similar to SWR #3. This component of SWR #6 is a combination of Alternative 5 of Area 5 South and Alternative 5 of Area 5 West that are described in more detail in Sections 11.6.4.5 and 11.6.7.5. SWR #6 also assumes that approximately a dozen new LNAPL skimming wells are constructed in the CDA and the extracted LNAPL stored and shipped for disposal. Finally, SWR #6 also assumes that four of the twelve new Lower HSU monitoring wells planned upgradient of PSCT-


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1 and PSCT-4 (discussed in SWR #2 above) are installed as extraction wells and operated immediately regardless of the sample results from those wells. 12.1.6.6 Groundwater Flow Model Results of SWR #6 Again, the FS Report has evaluated the groundwater elevation changes and effectiveness of this combination of proposed remedial components for the site using the Groundwater Flow Model that was prepared as part of the RI Report (CSC 2011a). The Groundwater Flow modeling indicates that with the proposed capping efforts the Gallery Well extraction rates will decline and ultimately go to zero, that the PSCT-1 extraction rates will be substantially lower than current rates, and that PSCT-2, PSCT-3, and PSCT-4 extraction rates will go to zero as the sumps dry up. The modeling predicts that the PSCT will continue to be effective in hydraulically containing groundwater within the Upper HSU. The modeling also predicts that the groundwater that formerly passed beneath the PSCT in the Lower HSU will now be hydraulically contained by the four new Lower HSU extraction wells. The P/S Landfill dewatering rates with horizontal wells are the same as in SWR #5 discussed earlier. As noted above, this SWR includes the continued operation of all of the existing PCT extraction systems. The Groundwater Flow Model predicts that the PCTs will continue to be effective in hydraulically containing groundwater within Areas 5 South and West. The Groundwater Flow Model predicts that the PCT-A, PCT-B, and PCT-C flow rates will increase moderately after the ponds are closed. 12.1.6.7 Remediation Time Frame Evaluation Results of SWR #6 The estimated timeframes for Areas 5 South and West to achieve groundwater cleanup standards would be the faster than those for SWR #3 because of the aggressive extraction from the 80 new wells. However, there is uncertainty in the actual time frames to achieve cleanup standards and the estimated time to achieve remediation goals is still expected to be several decades and potentially over a century.

12.2 DETAILED AND COMPARATIVE ANALYSIS OF SITE WIDE REMEDIAL

ALTERNATIVES This section evaluates and compares the six SWRs amongst themselves using the 7-criteria evaluation described in Section 11 of the FS Report. The 7-criteria evaluation results are summarized in Table 12-2 for each of the six SWR alternatives described earlier. As discussed in Section 11, the FS report addresses the first seven of the CERCLA criteria and the other two modifying criteria, State Acceptance and Community Acceptance, will be addressed later. Another factor considered in the FS evaluation that is not part of the 9-criteria analysis is “Green impacts assessment,” which was discussed earlier in Section 10. Table 12-4 summarizes the costs for each of the site-wide remedial alternatives and Table 12-5 summarizes the detailed evaluation for the site-wide alternatives using the partially-filled circles. 12.2.1 Overall Protection of Human Health and Environment


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The No Action alternative (SWR #1) does not meet the threshold criterion of protecting human health and the environment and is rated “No.” All of the active remedial alternatives (SWR #2 through SWR #6) are rated “Yes” because they are protective of human health and the environment. The active remedial alternatives (SWR #2 through #6) for FS Area 5 North generally continue operations of the existing groundwater remedial features (e.g., P/S Landfill and EE/CA Area caps; Gallery Well, and PSCT extraction) which will serve to contain or control the principal contaminant sources and mitigate potential contaminant migration outside of the potential future TI Zone. All of the alternatives include LNAPL and DNAPL source removal from within the P/S Landfill and two of the alternatives (SWR #5 and #6) include LNAPL source removal from the CDA. Also, included as part of these alternatives is the anticipated capping of the PCB Landfill, CDA, BTA, and MSA as part of the soil remedy, and the resulting benefits from prevention of infiltration and leaching to protect groundwater. All of these measures are primarily containment and source reduction options, and aquifer restoration for FS Area 5 North will not occur because the landfills will remain and removal of contaminants to remediation goals is technically impracticable as demonstrated in Appendix A. The active remedial alternatives (SWR #2 through #6) for FS Areas 5 South and West also generally continue operations of the existing groundwater remedial features (PCT extraction) which will serve to contain or control contaminant migration from Zone 1 to Zone 2. Capping, source removal, and MNA processes will act to reduce contaminant concentrations in these areas. The rate of restoration to achieve MCLs will take many decades or several centuries. . SWR #1 involves the continued operation of existing containment (caps) and groundwater remedial features involving source control and perimeter control. SWR #1 allows contaminated areas to remain unaddressed and continues use of the current evaporation ponds (which contain high levels of TDS and metals) which are a potential risk to ecological receptors. SWRs #2 and #3 add soil and landfill capping at the site and NAPL-only extraction in the P/S Landfill. SWR #4 is the same as SWR #3 but treats PSCT and PCT groundwater for inorganics and organics and discharges the treated water without the need for an evaporation pond. SWR #5 adds aggressive dewatering of the P/S Landfill with five horizontal wells and limited LNAPL extraction from four existing monitoring wells in the CDA. SWR #6 also adds aggressive extraction with 80 new wells in Area 5 South and 5 West and includes a more robust LNAPL extraction with 12 new extraction wells in the CDA. SWR #6 treats groundwater from the PSCT, PCTs, and 80 new wells for inorganics and organics and discharges the treated water without the need for an evaporation pond. ICs, including access restrictions and long term site monitoring, would be a component of all the remedial alternatives that would provide additional protection.


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12.2.2 Compliance with ARARs The No Action alternative (SWR #1) does not meet the threshold criterion of complying with ARARs and is rated “No.” Because the No Action Alternative fails both the CERCLA threshold criteria, it is not further evaluated below as to other CERCLA evaluation criteria. All of the active remedial alternatives (SWR #2 through SWR #6) are rates “Yes” because they meet compliance requirements, including for groundwater (assuming that the TI waiver for Area 5 North is granted). There would be chemical-specific ARARs for Areas 5 South and 5 West, and an aggressive extraction alternative is included in SWR #6 in an attempt to expeditiously reach these chemical specific ARARs (MCLs). The active remedial alternatives (SWR #2 through SWR #6) assume that FS Area 5 North would become a TI Zone and there would be a waiver from meeting ARARs. These alternatives include source reduction (free-phase NAPL removal) and liquids extraction for hydraulic containment of the Upper HSU for FS Area 5 North (the potential TI Zone). MNA would be employed to verify contaminant containment in the Lower HSU FS Area 5 North and groundwater extraction would be implemented if MNA demonstrated that this approach was no longer effective. For FS Areas 5 South and West, groundwater extraction would be performed at the site downgradient boundary for downgradient hydraulic containing while natural attenuation processes act to reduce contaminant levels to meet target cleanup levels (e.g., MCLs). All of the SWRs have components that involve treatment of liquids extracted from the PSCT and PCTs and some components include treatment of groundwater extracted from additional “aggressive” extraction wells. Groundwater or leachate that would be treated from these extraction facilities would be in compliance with action-specific and chemical-specific ARARs. All of the alternatives that require an evaporation pond will be in compliance with ARARs requiring protection of sensitive ecological species from high TDS and inorganics in the proposed evaporation pond. 12.2.3 Long Term Effectiveness With respect to LTE, SWR #1 is not rated because it does not meet the threshold criteria, SWR #2 is rated higher at moderate, SWR #3, #4, #5 and #6 are all rated moderate to good. The LTE of the SWRs is evaluated below by comparing the features that differ among the alternatives that cause them to have a different rating. SWR #5 and #6 with aggressive dewatering are rated the same as SWR #3 and #4 with NAPL-only extraction. Free-phase DNAPL and LNAPL would be effectively removed from P/S Landfill and the liquid levels in the P/S Landfill would drop below the bottom of the landfill under all four of these alternatives. Contaminant migration in the Upper HSU is effectively contained by extraction at the PSCT under all four alternatives. The primary conceptual benefit of installing the horizontal extraction wells, or drain lines, would be to expeditiously dewater the landfill which would enhance hydraulic containment because the reduction in groundwater migration (and any contaminants dissolved in groundwater) underneath the PSCT would be reduced faster than for SWR #3 and SWR #4. The landfill dewatering rates are estimated to be approximately 5 years for SWR #5 and #6 while for SWR #2 through #4 it is estimated to be approximately 10 years as discussed in Section 10.1.8 and Appendix D-3. The evaluation assumes extraction rates for SWR #5 and #6 of 2 gpm/well for the first year (5.2 million gallons per year) decreasing down to 0.1 gpm/well in the fifth year (263,000 gallons per year). For SWR #2 through #4, the evaluation assumes initial


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extraction rates of 450,000 gallons per year decreasing to 366,000 gallons per year for the fifth year and averaging 250,000 gallons per year between Year 6 and 10. Though SWR #5 and #6 would reduce liquid level elevations and remove contaminant mass at a faster rate than for SWR #3 and #4, it would likely not measurably change the rate of potential contaminant migration underneath the PSCT through the Lower HSU. As discussed in Section 10.1.8, although groundwater moves very slowly underneath the PSCT in the Lower HSU, natural attenuation of contaminants occurs and will limit this potential migration of the low-level of dissolved-phase contaminants that have been detected at low levels in the immediate vicinity of the PSCT in the Lower HSU. Under SWR #2 through SWR #5, twelve new Lower HSU monitoring wells would be installed upgradient of PSCT-1 and PSCT-4 which may be converted to extraction points to provide hydraulic containment if and when the sampling of these wells indicates the presence of VOCs or SVOCs above MCLs that may migrate beneath the PSCT in the Lower HSU. SWR #6 assumes that this extraction would occur upon installation. Either way, potential contaminant migration under the PSCT would be controlled, regardless of whether liquids from the P/S Landfill area extracted using NAPL-only vertical extraction wells or horizontal drain lines. SWR #3 is rated higher than SWR #2 because it includes an ET cap, RCRA Hybrid cap, or a combination of these two types of caps that cover the entire RCRA Canyon Area (8.4 acre western area, 5.5 acre WCSA area, and remaining 19.3 acre area) compared with partial capping under SWR #2. SWR #4 through SWR #6 include the same capping alternative as SWR #3. The more robust cap under SWR #3 through SWR #6 will more effectively reduce recharge to groundwater which will more reliably eliminate the surface seep at the south end of RCRA Canyon and allow all stormwater to be discharged to the B-Drainage. This would result in a smaller 6-acre evaporation pond (constructed as six 1-acre ponds in SWR #3) that is considered more effective for ecological protection in the long term than an 11-acre evaporation pond with SWR #2. SWR #3 provides greater certainty that all of the stormwater runoff from RCRA Canyon can be discharged under the substantive terms of the General Permit, thus reducing the required evaporation pond capacity. SWR #3 and SWR #4 are rated the same for LTE because the only difference is in the treatment and discharge of PSCT and PCT liquids, which does not affect the long term groundwater cleanup effectiveness. PSCT and PCT liquids would be treated for organics and inorganics for discharge to the B-Drainage eliminating the need for an evaporation pond under SWR #4, while the liquids would only be treated for organics and discharged to an evaporation pond under SWR #3. Both alternatives would be protective against potential impacts to wildlife. SWR #4 would be effective because there would be no evaporation pond and SWR #3 would be protective because of the mitigation for ecological protection that would be implemented. With regards to RISBON-59 in FS Area 3, SWRs #2, #3 and #4 involve groundwater monitoring to evaluate whether there are impacts to groundwater in the future while SWRs #5 and #6 involve excavation of the impacted soils. Since the groundwater monitoring to date downgradient of RISBON-59 has not shown significant contaminant leaching or migration, SWRs #2, #3 and #4 are not considered significantly different with regards to effectiveness compared to SWRs #5 and #6 with regards to the RISBON-59 impacted area. .


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In summary, the SWRs are ranked as follows for LTE, from best to worst rated:

SWR #3, #4, #5 and #6 are all rated moderate to good. o These alternatives all effectively contain contaminated liquids within Area 5 North

(the potential future TI Zone) and remove liquids from the P/S Landfill, including LNAPL and DNAPL. Placing a RCRA cap over the entire Area 5 North will cause the groundwater elevations to drop across the entire area and the P/S Landfill to dry up when combined with liquids extraction from the P/S Landfill. SWR #5 and SWR #6 will remove liquids from the P/S Landfill faster using horizontal wells than SWR #3 and SWR #4 that use vertical NAPL-only wells. However, the additional speed in removing P/S Landfill liquids is not judged to have a significant benefit with respect to containment.

o These alternatives all effectively contain contaminated groundwater within Areas 5 South and West. MNA processes (primarily precipitation recharge and flushing) will gradually reduce the concentrations of organic and inorganic contaminants to remediation goals (MCLs) over many decades to several centuries under SWR #3 through SWR #5. Installing 80 additional “aggressive liquids” extraction wells for SWR #6 will reduce the time to reach remediation goals, however it will still take many decades to over a century due to the lower permeability of the Upper HSU. The additional speed in achieving remediation goals is not judged to have a significant benefit given the uncertainty in the time that it may take to achieve remediation goals.

o These alternatives all effectively eliminate rainfall recharge across RCRA Canyon which will reduce or eliminate recharge to groundwater and the potential that the seep at the south end of RCRA Canyon persists. This seep (elevated in metals and TDS), could contaminate stormwater and require that it be retained causing an evaporation pond to be needed or causing it to become larger if already planned.

SWR #2 is rated moderate o This alternative is less effective than SWR #3 through #6 at eliminating rainfall

recharge across RCRA Canyon because it only partially caps the area, which would result in lower certainty that the seep at the south end of RCRA Canyon is eliminated. The area that is not capped would result in stormwater runoff that would need to be managed in an evaporation pond causing an evaporation pond to be needed or become larger if already planned for another use.

SWR #1 does not meet the threshold criteria requirements and hence the balancing criteria are not rated.

12.2.4 Reduction of Toxicity, Mobility, and Volume through Treatment With respect to RTMV through treatment, SWR #1 is not rated because it does not meet the threshold criteria, SWR #2, #3 and #4 are rated higher at poor to moderate, and the most aggressive alternatives SWR #5 and #6 are rated higher at moderate. The difference in the RTMV ratings is from the treatment of contaminated liquids and not the remediation of contaminated soils because the remediation of soils does not involve treatment. The remediation of contaminated soils involves simple excavation and disposal into either the PCB Landfill or at a permitted facility. All of the alternatives include the continued operation of the Gallery Well, PSCT, and PCT trenches which include the treatment of the extracted liquids either using active treatment systems, passive evaporation ponds, or treatment at permitted facilities.


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SWR #5 and #6, the most aggressive alternatives that include dewatering of the P/S Landfill using the Gallery Well and approximately five horizontal wells, are rated higher than SWR #2, #3 and #4 because they may potentially remove more contaminant mass for subsequent treatment. However, the contaminant mass removal will still be only a small fraction of the entire contaminant mass at the site. Moreover, aquifer restoration times will not change significantly even with this more aggressive extraction. Remediation of Area 5 North to cleanup goals (MCLs) is considered technically impracticable as demonstrated in the TIE in Appendix A. SWR #6 is considered more aggressive than SWR #5 because it includes aggressive extraction with 80 new wells in Area 5 South and 5 West, but it is not rated higher because the contaminant mass removed by this component (<50 lbs per year for COCs) is low due to low dissolved contaminant concentrations. SWR #2, SWR #3, and SWR #4 are all rated the same because they each include NAPL-only extraction from approximately 16 wells and Gallery Well extraction in the P/S Landfill, and there is no significant difference in contaminant mass removal with these alternatives. In summary, the SWRs are ranked as follows for RTMV, from best to worst rated:

SWR #5 and SWR #6 are rated moderate o These alternatives remove the most mass on a site-wide basis by dewatering the

P/S using horizontal drain lines (aqueous-phase liquids, DNAPL, and LNAPL) and operation of the Gallery Well. An incremental amount of additional mass is removed with SWR #6 with the additional LNAPL extraction wells in the CDA and the 80 aggressive extraction wells in Areas 5 South and West. However, this additional mass removed is not considered significant (<1 percent) compared to the mass removed using horizontal wells.

o A higher rating than moderate is not given because no soils are treated; they are either excavated and re-disposed or capped.

SWR #2, #3 and #4 are rated poor to moderate o Although these alternatives remove less mass than SWR #5 and SWR #6 in the near

term, the mass removed by the vertical NAPL-only wells and the Gallery Well from the P/S Landfill is still significant over the longer term as the P/S Landfill is dewatered.


12.2.5 Short Term Effectiveness With respect to STE, SWR #1 is not rated because it does not meet the threshold criteria, SWR #2 and SWR #4 are rated moderate and, SWR #3 is rated moderate to good, SWR #5 is rated poor to moderate, and SWR #6 is rated poor. SWR #5 and SWR #6 are rated significantly lower than the other alternatives primarily because of the concerns with potential exposure and environmental impacts faced with the dewatering the P/S Landfill component with horizontal wells. Concerns and challenges posed by this scenario were described in more detail in Section 10.6.3.1 and 12.1.5, and are listed briefly here:

Potential release of 1,000s of gallons of liquids in drums into formation Potential for puncturing clay barrier and release of liquids in CDA


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Potential for uncontrolled drilling muds and liquids release due to upward sloping well due to high pressure at well head.

Potential for VOC vapor exposure to drillers and workers. Potential for VOC vapor exposure to the community.

SWR #6 is rated lower than SWR #5 because, in addition to the horizontal wells into the P/S landfill, it includes aggressive hydraulic extraction from 80 wells across Area 5 South and 5 West, and a 30 gpm groundwater treatment system that treats organics and inorganics to allow discharge. While the groundwater treatment system treats relatively low contaminant concentrations, the reason STE is rated lower is because of the concern with meeting stringent NPDES Permit requirements, coupled with the potential for release of high inorganics laden groundwater due to treatment system malfunctions. SWR #4 is similarly rated lower than SWR #3 because of the complex inorganics treatment system required to meet stringent NPDES Permit requirements to allow discharge and the potential for malfunctions and release of high inorganics groundwater. The components of NAPL-only extraction in the P/S Landfill are the same for alternatives SWR #2, SWR #3, and SWR #4. The construction of these vertical extraction wells is safer than the installation of the horizontal wells for SWR #5 and #6, although there are still significant risks to worker safety and potentially the community while constructing and operating the wells from potential exposure to VOC vapors. The potential for an uncontrolled release of P/S Landfill liquids with vertical wells is much lower, however, then from the installation of the horizontal wells. In summary, the SWRs are ranked as follows for STE, from best to worst:

SWR #3 is rated moderate to good o SWR #3 is rated moderate to good because of concerns with health and safety

during drilling for well installation in the P/S Landfill and the concerns with ecological protection associated with the evaporation pond are relatively minor with the smaller 6-acre pond.

SWR #2 and SWR #4 are rated moderate o SWR #2 is rated lower at moderate because of concerns with health and safety

during drilling for well installation in the P/S Landfill and due to challenges with ecological protection for a larger 11-acre evaporation pond

o SWR #4 is rated lower at moderate because of concerns during drilling in P/S Landfill as in SWR #2 and because of potential impacts to the environment from release of high TDS groundwater in the B-Drainage resulting from malfunction of the complex RO system intended to treat very high TDS groundwater.

SWR #5 is rated poor to moderate o SWR #5 is rated lower at poor to moderate because of the concerns with drilling

horizontal wells under the P/S Landfill that raises concerns with potential impacts to the environment from release of landfill leachate resulting from puncturing the clay barrier and the potential for health risks from exposure to liquids during drilling and system operation.

SWR #6 is rated poor


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o SWR #6 is rated the lowest because it has all the risks with horizontal wells for SWR #5 and adds the concerns with treatment and discharge of an aggressive groundwater extraction and treatment approach that has the potential for release of high TDS groundwater to the B-Drainage.


12.2.6 Implementability With respect to Implementability, SWR #1 is not rated because it does not meet the threshold criteria, SWR #2 and SWR #4 are rated moderate, SWR #3 is rated moderate to good, SWR #5 is rated poor to moderate and SWR #6 is rated poor. SWR #5 and SWR #6 are rated significantly lower than the other alternatives primarily because of the challenges faced with the dewatering the P/S Landfill using horizontal wells that were discussed in more detail in Section 10.6.3.1 and 12.1.5 Concerns and challenges posed by this scenario are briefly listed here:

Challenges with drill bit veering due to borehole guidance system interference from metal drums in waste

Given the uneven bottom of the landfill, ensuring the borehole tracks the bottom of the landfill (Lower HSU contact) is very challenging and the best precision achievable may be within 5 or 10 feet of the bottom which will affect technical reliability of dewatering the landfill.

Challenges with blind hole drilling that more often result in borehole failure and casing breakage

SWR #6 is rated lower than SWR #5 because, in addition to the horizontal wells extraction, it includes aggressive hydraulic extraction from 80 wells across Area 5 South and 5 West and a 30 gpm groundwater treatment system that treats organics and inorganics to allow discharge. SWR #6 adds the technical challenges of treating a large groundwater flow rate with very high inorganic concentrations that need to be treated to meet stringent site-specific NPDES discharge limits. Also, challenges can be anticipated with meeting the substantive requirements of a site-specific NPDES permit for discharge to the B-Drainage because it would require a Basin Plan exception from the RWQCB. Though SWR #6 does not include an evaporation pond, and thus would not face the associated challenges, this benefit is considered less significant than the challenges of treating inorganics reliably. SWR #3 is rated better for implementability than SWR #2 because a smaller evaporation pond (6-acre) constructed as six 1-acre ponds can be better constructed for ecological protection and long term operations and maintenance of the pond than can SWR #2 with an 11-acre evaporation pond. SWR #4 is rated lower than SWR #3 because of the more significant technical challenges of operation of the groundwater treatment system for reliably treating inorganics to meet stringent NPDES Permit discharge limits. Though SWR #4 does not include an evaporation pond, and thus would not face the associated challenges, this benefit is considered less significant than the challenges of treating inorganics reliably. In summary, the SWRs are ranked as follows for Implementability, from best to worst:


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SWR #3 is rated moderate to good o This alternative is rated moderate to good because of the challenges with installation

of vertical wells in the P/S Landfill while it is rated higher than SWR #2 because the technical challenges with constructability of the ecological protection measures (e.g. netting, drift fences, etc.) are better with the smaller 6-acre evaporation pond. Also, the challenges with administrative acceptability would likely favor the smaller pond.

SWR #2 and SWR #4 are rated moderate o SWR #2 is rated lower than SWR #3 because of the larger 11-acre evaporation pond

and the technical challenges with constructability of ecological protection as discussed earlier. SWR #4 is rated lower because of the technical challenges with reliably treating high TDS groundwater to meet stringent NPDES limits and the administrative challenges with obtaining a site-specific NPDES permit that requires an exception to the Basin Plan.

SWR #5 is rated poor to moderate o SWR #5 is rated lower than the previous alternatives because of the technical

challenges with drilling horizontal wells due to drill bit veering, uneven landfill bottom and blind drilling borehole failure discussed earlier in Sections 10.6 and 11.6.

SWR #6 is rated poor o SWR #6 is rated the worst because of the technical challenges with horizontal wells

as in SWR #5 and the technical and administrative challenges of reliably treating high TDS groundwater as in SWR #4.


12.2.7 Cost The table below presents the Capital Cost, Annual Cost and Total Present Worth (30-year and 100-year) cost for a 3 percent and 7 percent discount rate for SWR #2 through #6 in 2014 dollars. Table 12-4 presents the costs with a description of the various area-specific components that comprise each of the SWRs. As mentioned earlier, the site-wide alternative cost estimates presented here include present worth of capital cost based on an assumed construction schedule. These cost estimates assume a 5-year construction schedule between 2018 and 2022 and a capital expenditure schedule that is equally distributed in each of the 5 years for a 3 percent and 7 percent discount rate. Figures 12-6 A, B, C illustrate the capital and O&M costs for each of the SWRs, by FS Area. The total height of each of the bars is the total present worth cost estimates using a 3 percent discount rate over a 30-year period. This figure is provided to simply portray the relative contribution of the different FS Areas to the total costs and is not intended to indicate that the combination of using the 3 percent discount rate over a 30-year period is a more or less valid scenario than using the 7 percent discount rate or the 100-year period. The estimated costs for SWR #1 are not rated because the alternative does not meet the threshold criteria, SWR #2 and #3 are moderate to high, and SWR #4, SWR #5, and SWR #6 are high. The costs for SWR #1 are the lowest in total present worth cost, which assumes a zero capital cost and continued current annual cost. Of the other site-wide remedial alternatives, SWR #2 is the lowest in total present worth cost while SWR #3 with a smaller evaporation pond and more capping is marginally higher. SWR #5 that includes the aggressive NAPL extraction by dewatering P/S Landfill is the next higher in total present worth cost followed by SWR #4 that includes long term inorganics treatment for discharge of treated groundwater. Finally, SWR #6


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that includes the aggressive NAPL extraction by dewatering and aggressive groundwater extraction with 80 new wells in Area 5 South and 5 West is the highest in cost.

SWR Alt No.

Capital Cost Annual O&M

Cost Time frame

Total Present Worth


Total Present Worth


2 $ 53,987,000 $ 3,997,400 30-year $115,445,000 $85,195,000

100-year $159,052,000 $91,956,000

3 $ 59,967,000 $ 4,065,400 30-year $120,224,000 $89,499,000

100-year $163,561,000 $96,218,000

4 $ 65,737,000 $ 7,772,400 30-year $195,733,000 $138,550,000

100-year $282,661,000 $152,025,000

5 $ 69,411,000 $ 8,464,000 30-year $147,035,000 $113,814,000

100-year $191,734,000 $120,744,000

6 $ 93,245,000 $ 14,849,000 30-year $291,069,000 $209,924,000

100-year $412,474,000 $228,744,000 In summary, the SWRs are ranked as follows for cost, from lowest (best) to highest (worst) based on Total Present Worth cost:

SWR #2 and SWR #3 (similar) o The costs for containment and source removal for Area 5 North represent 24 percent

of the total site-wide present worth (30-year, 3 percent) costs for SWR #3. These costs are primarily from the continued extraction of liquids from the Gallery Well and NAPL-only extraction wells, and disposal of these liquids at an approved facility. The continued extraction and treatment of liquids from the PSCT and disposal of these liquids to a new evaporation pond is a relatively small portion of the cost.

o The remaining 76 percent of the costs are relatively evenly distributed across the remaining FS Areas, including Area 5 South and West.

SWR #5


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o The higher costs for SWR #5 compared to SWR #2 and SWR #3 are due to the additional liquids extracted from the P/S Landfill using the horizontal drain lines and disposal of these liquids at an approved facility. This brings the percentage of the total costs for Area 5 North to 38 percent.

o The remaining 62 percent of the costs for SWR #5 are similar to those for SWR #2 and SWR #3.

SWR #4 o The higher costs for SWR #4 compared to SWR #2, SWR #3, and SWR #5 is

primarily due to the additional complex treatment needed to treat groundwater extracted from the PSCT and PCTs for inorganics using RO so the treated liquids can be discharged to the B-Drainage. The RO treatment to reduce the high-TDS groundwater to less than 1,000 mg/L is a labor and energy intensive process. In addition, RO treatment creates a brine waste stream that is disposed at a permitted facility. The costs for this treatment represent 37 percent of the total site-wide costs.

o The costs for containment and source removal for Area 5 North (the potential TI zone) represent 27 percent of the total cost

o The costs for the remaining areas represent 36 percent of the total cost. SWR #6 is highest (worst)

o Similar to SWR #4, the higher costs for SWR #6 compared to SWR #5 are primarily due to the additional complex treatment needed to treat groundwater extracted from the PSCT, PCTs, and 80 new extraction wells in Areas 5 South and West for inorganics using RO so the treated liquids can be discharged to the B-Drainage under an NDPES Permit. These costs also include brine waste stream disposal at a permitted facility. The costs for this treatment represent 48 percent of the total site-wide costs.

o The costs for containment and source removal for Area 5 North (the potential TI zone) represent 28 percent of the total cost

o The costs for the remaining areas represent 24 percent of the total cost SWR #1 does not meet the threshold criteria requirements and hence the balancing

criteria are not rated. 12.2.8 Green Impacts Assessment With respect to green impacts assessment, the impacts from SWR #3 are lower (meaning better or more “green”) than SWR #4 because SWR #4 involves operation of a larger LTP to treat inorganics with an energy-intensive RO process over the long term. The impacts from SWR #3 are lower compared to the impacts from SWR #5 and SWR #6 because of the greater risks and potential impacts with the horizontal wells installation and the transportation and disposal of the dewatered liquids. The impacts from SWR #6 are higher than for the impacts from SWR #5 because in addition to the dewatering of the P/S Landfill it also includes aggressive hydraulic extraction that operates over the long term. The impacts from SWR #3 are about the same as SWR #2 because the additional impacts of the ET cap construction across the entire RCRA Canyon/WCSA are balanced by the lower impacts with a smaller evaporation pond construction. In summary, the SWRs are ranked as follows for impacts, from lowest (best) to highest (worst):

SWR #2 and SWR #3 (similar) o SWR #2 and #3 are rated similar at moderate for impacts due to similar remedial

components with higher impacts from a larger cap in RCRA Canyon/WCSA in SWR #3 being balanced by a larger evaporation pond in SWR #2.

SWR #4


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o SWR #4 is rated poorer at moderate to high for impacts due to the large amount of energy that would be required for the long term treatment of inorganics for discharge in accordance with the substantive terms of a site-specific NPDES permits.

SWR #5 o SWR #5 is rated poorer at high for impacts due to the greater risks and potential

impacts with the horizontal wells installation and the transportation and disposal of the dewatered liquids.

SWR #6 is highest (worst) o SWR #6 is rated lowest at high for impacts as in SWR #5 and for impacts from high

energy consumption with an aggressive groundwater extraction and treatment of inorganics similar to SWR #4.

SWR #1 does not meet the threshold criteria requirements and hence is not evaluated here.

12.3 EVALUATION SUMMARY AND TOP RANKED REMEDY This section summarizes the evaluation of the site-wide remedial alternatives and identifies a top ranked remedial alternative based on the detailed evaluation criteria as a whole. As described above, a range of SWRs were developed and evaluated in detail in accordance with CERCLA guidance (USEPA 1988). A green impacts assessment was also performed. Table 12-5 provides a summary of the results of the detailed evaluation using circles that are partially filled by quarters and correspond to the 5-point rating system used for the CERCLA detailed evaluation criteria. Filled circles are the most desirable and non-filled circles are the least desirable. 12.3.1 CERCLA Detailed Evaluation Criteria Summary While SWRs #2 through #6 all adequately meet the RAOs and goals and objectives of the FS, SWR #3 is identified as the “top ranked” remedy for the Casmalia Resources Superfund Site. The basis for recommending SWR #3 is discussed in the paragraphs below where SWR #3 is compared with the other alternatives based on the results of the CERCLA detailed evaluation. The comparison focuses on the components of the alternatives that are variations from SWR #3 because as discussed above there are several common components that do not change between the alternatives. SWR #1 did not meet the requirements of the threshold criteria and hence was rejected from further consideration. SWR #3 is ranked better than SWR #2 because SWR #3 is rated better for LTE, STE and implementability, is similar for RTMV Through Treatment, and is approximately the same cost as SWR #2. SWR #3 is rated better with respect to LTE than SWR #2 because it includes an ET cap, Hybrid cap, or a combination of these two types of caps that cover the entire RCRA Canyon and that more effectively limit infiltration in the Canyon and provide greater certainty that the seep at the south end of the Canyon will cease and all of the stormwater runoff from RCRA Canyon can be discharged under the substantive terms of the General Permit. SWR #3 also uses a smaller evaporation pond than SWR #2 which would be better with respect to LTE based on protection of the ecological species compared to the larger 11-acre pond. A smaller evaporation pond is also rated better with respect to implementability and STE due to the challenges with operations and maintenance of a larger evaporation pond.


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SWR #3 is ranked better than SWR #4 because SWR #3 is similar with respect to LTE and RTMV but rated better with respect to implementability and STE and is significantly lower in present worth cost. With SWR #4, there are also potential technical implementability challenges that involve reliably treating groundwater using a complex treatment system for inorganics for discharge under stringent site-specific NPDES substantive permit limits (no evaporation pond). The total present worth cost of SWR #4 is significantly higher than SWR #3. SWR #3 is ranked better than SWR #5 because SWR #5 is similar with respect to LTE and rated slightly lower with respect to RTMV, but rated significantly lower with respect to implementability and STE. The low implementability and STE ratings reflect concerns and risks associated with dewatering of the P/S Landfill. The landfill draining utilizes multiple horizontal wells under the landfill that more quickly remove aqueous-phase liquids, LNAPLs, and DNAPLs from the landfill than the vertical wells assumed for SWR #2, SWR #3, and SWR #4. Despite this apparent benefit, this component does not offer significant technical benefits in terms of achieving the RAOs and consequently is not rated higher with respect to LTE. The concept of dewatering the landfill using horizontally drilled wells has a number of significant technical challenges which were discussed in more detail earlier in the report (Section 10.6.3.1). These challenges include grouting a conductor casing into the base of the clay barrier (if drilling through base of clay barrier), drilling angles required to install the wells under the clay barrier (if drilling under clay barrier), potential problems with accurately tracking the bottom of the landfill in the Lower HSU, drilling into the drummed liquid wastes in the landfill, possible release of significant volumes of contaminated liquids during construction and operations, and ultimately liquids recovery from these wells. SWR #5 is also rated lower with respect to STE due to risks of leachate liquid or contaminated drilling mud releases and VOC emissions during the horizontal well installation process, especially because the well has to be drilled in an upward-sloping profile following the LHSU contact with a blind hole drilling method. The cost estimate for SWR #5 is significantly higher, primarily driven by the disposal of the estimated 10 million gallons of liquids stored in the landfill to a permitted facility. There is the potential of having to re-drill boreholes multiple times but these costs are minor compared to the liquids disposal costs. The factors that could lead to having to re-drill could include hole failures with blind drilling, potential failures due to interference of borehole guidance systems, casing breakage due to multiple bends, and uncertainty with dewatering flow rates. The limited benefit in LTE of more rapidly lowering the groundwater levels in the landfill does not compensate or offset the implementability challenges this alternative would face. As discussed in the FS Report, Groundwater Flow Modeling demonstrates that the groundwater levels in the P/S Landfill will fall below the bottom of waste naturally over time without the dewatering proposed by this alternative. The use of horizontal wells would accelerate the dewatering process, but poses additional risks that could carry potentially severe consequences. Please note that while SWR #5 excavates RISBON-59 area (Location 10) and extracts a limited amount of LNAPL from existing CDA wells, this remedial action does not significantly enhance LTE over SWR #3. Hence, based on a lower rating of implementability and STE for SWR #5 and no significant LTE improvements and significantly higher costs, SWR #3 is ranked higher than SWR #5. SWR #3 is ranked better than SWR #6 because of the same implementability and STE challenges with horizontal wells for the P/S Landfill Dewatering as discussed with respect to SWR #5. Furthermore, SWR #6 would face additional implementability challenges with installation and operation of an aggressive 80 extraction well network (Areas 5 South and West) and the problems associated with reliably treating inorganics in a complex treatment system on a large scale for discharge under the substantive terms of an NPDES Permit, and the problems


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and reliability of handling and disposing of large volumes of waste brine that would result as waste residuals from the RO treatment process. The benefits of aggressively extracting liquids in Areas 5 South and North will not significantly increase LTE because the estimated time to reach remediation goals for these areas is still estimated to take several decades to more than a century. The costs associated with the complex treatment of the liquids for discharge are very high and result in significantly higher overall costs that are almost twice as high as the next highest cost alternative without a corresponding relative benefit. SWR #3 addresses EPA’s preference for reduction of toxicity, mobility, and volume through treatment. SWR #3 is a combined containment and treatment remedy that includes DNAPL source reduction, extraction and treatment of contaminated site liquids, and containment of waste materials. The site contains many former waste management units, including former landfills, waste burial areas, and burial trenches. Consistent with EPA’s approach for many landfill-type sites, solid waste will be contained at the site. SWR #3 will achieve containment through use of engineering controls, institutional controls, and natural attenuation. The FS also includes treatment of liquids where technically practicable. SWR #3 will include DNAPL source reduction and treatment through the installation of extraction wells to remove large volumes of DNAPL and thus reduce DNAPL sources that contribute to groundwater contamination. Extracted DNAPL will be transported offsite for disposal. SWR #3 also will expand the current use of extraction systems (containment trenches, extraction wells, and extraction sumps) to remove and provide treatment of contaminated liquids. Alternatives #2-4 are equivalent in terms of criterion #4, Reduction of Toxicity, Mobility or Volume through Treatment. This criterion focuses on EPA’s preference for treatment of contaminated liquids derived from principal threat wastes, where technically practicable, which for this site include NAPL and buried wastes in Areas 1 and Area 5. These three alternatives include DNAPL source reduction to extract pooled DNAPL from the P/S Landfill and liquids extraction from the PSCT and three PCTs for containment. Alternative #4 includes additional treatment of liquids to allow for discharge to Casmalia Creek instead of evaporation in ponds. Alternative #5 includes landfill dewatering through use of horizontal directional drilling to drain approximately 10 million gallons of contaminated groundwater from the P/S landfill. Although ranked higher in terms of volume reduction, dewatering contaminated liquids would require extensive treatment and would pose a number of technical challenges and considerable project risks, including the threat of uncontrolled releases, discussed below under “implementability.” Alternative #6, the most aggressive alternative, would include landfill dewatering and the installation of additional extraction wells for pumping and treatment of site liquids in GW South and GW West. The FS has determined, however, that Alternative #6 would not substantially increase protectiveness or reduce the time necessary to achieve performance standards, through restoration of GW to MCLs, in spite of the investment in additional cleanup technology. All alternatives, except for the No Further Action Alternative (i.e., Alternatives 2-6), are equivalent in terms of using containment to address principal threat wastes in Area 1, where the former landfills and burial areas are located. 12.3.2 Green Impacts Assessment Summary Although not a formal CERCLA criterion, green impacts were considered in the evaluation of alternatives. With respect to green impacts assessment, SWR #3 is rated as having lower impacts (i.e., better) than SWR #4 with respect to environmental impacts because SWR #4 involves operation of a larger GWTS to treat inorganics over the long term for discharge under the substantive terms of an NPDES Permit. SWR #3 is rated as having lower impacts with respect to SWR #5 and SWR #6 because of the greater risks and potential impacts with the horizontal wells installation and the transportation and disposal of the drilling wastes and


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dewatered liquids to a permitted disposal facility. SWR #6 is rated as having higher impacts (i.e., worse) than SWR #5 because, in addition to the dewatering of the P/S Landfill, it also includes aggressive hydraulic extraction and complex groundwater treatment that operates over the long term. SWR #3 is rated as being equivalent to SWR #2 for green impacts because the additional impacts of constructing the larger contiguous cap over RCRA Canyon area are balanced by the lower impacts with a smaller evaporation pond construction.

12.4 SUMMARY OF TOP RANKED SITE-WIDE REMEDY - SWR #3 This section presents a more detailed summary of the top ranked site remedy, i.e., SWR #3. Figures 12-7A through 12-7D presents a conceptual overview of the components of the top-ranked remedy. The paragraphs below discuss the remedy components by FS Area and provide additional information that is useful when considering the remediation (including additional information regarding stormwater management, a summary of soil borrow areas that are anticipated to be used for remedy construction, and a brief analysis of green remediation considered with the site remedy). This summary is followed by a discussion of the remedy schedule in Section 12.8. Table 12-6 presents the cost estimate summary for SWR #3. The cost estimate presented is a total present worth cost of the remedy based on 2014 dollars. Costs are presented for a 3 percent and 7 percent discount rate and over a 30-year and 100-year timeframe. As mentioned earlier, the site-wide alternative cost estimates presented here include present worth of capital cost based on the assumed 5-year construction schedule between 2018 and 2022 (See Section 12.8) for 3 percent and 7 percent discount rates. 12.4.1 FS Area 1 – PCB Landfill, Burial Trench Area, Central Drainage Area A RCRA cap would be constructed for FS Area 1 that includes the PCB Landfill, Burial Trench Area and the Central Drainage Area. The total surface area for each of these capped areas would be 4.4 acres for PCB Landfill, 5.5 acres for BTA, and 18.8 acres for CDA for a total of 28.7 acres of cap. This proposed RCRA cap would be similar in cross section (shown on Figure 12-7B) to the existing EE/CA Area cap and would tie into this and the P/S Landfill cap. The cap design is assumed to include a geocomposite drainage layer, a 60-mil HDPE geomembrane that is the primary barrier layer and a low permeability GCL overlying a foundation layer. Above the drainage layer, a HDPE biotic barrier and an overlying 2-foot vegetative layer that is hydroseeded is included. Extensive cut-fill grading is anticipated within the CDA to create a level subgrade that is of 3:1 slope or lower. The required soil volumes to construct the caps for the BTA (38,000 cy), CDA (134,000 cy), and PCB Landfill (32,000 cy) would be obtained from the NW Borrow Area. Further design details for the cap would be developed in the remedial design phase. As described below in FS Area 3, the RCRA cap would be extended to cover the Maintenance Shed Area. The clean soil for constructing the caps would be borrowed from the NW Borrow Area (Figure 10-2).The capped surfaces would be equipped with surface drains that are sloped to collect and drain stormwater out of this area. The drainages would include V-drains that run along the bench roads on the cap surface and perimeter drains. The stormwater from the PCB Landfill and the BTA would be transported in a southeasterly direction via the perimeter drains towards the CDA. The stormwater from the Capped Landfills would flow through a new lined drainage channel that flows south of PSCT-1 and then through the footprint of RCF Pond to a proposed lined retention basin in the footprint of Pond 13, and through or around the wetlands into the B-drainage.


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During remedial design the requirements (and necessity) of a venting system for the proposed caps and the existing caps would be evaluated. No specific design features for soil gas were required or have been found to be necessary for either the P/S Landfill cap or the EE/CA Area cap which were constructed from 1999 through 2003. This remedy also includes a monitoring component that involves periodic inspection and maintenance of these caps, surface drains, and erosion controls, and conducting repairs of the features as needed over the long term. In addition, the currently implemented soil vapor monitoring program (CSC 2009b) is expected to continue as part of the top-ranked remedy. For FS Area 1, the monitoring component also includes the inspection and maintenance of the existing Capped Landfills Area, which refer to the P/S Landfill and EE/CA Area caps. 12.4.2 FS Area 2 – RCRA Canyon, WCSA A contiguous large cap would be constructed for FS Area 2. This would consist of an ET cap, RCRA Hybrid cap, or a combination of these two types of caps over the entire RCRA Canyon that will include the 8.4 acre western area, 5.5 acre WCSA area, and remaining 19.3 acre area. The type of cap and construction of the cap will be determined during remedial design. The extent of the area covered by the ET and/or Hybrid cap and the excavation reduces the residual ecological risks of this area to acceptable levels (i.e., HQ<1). The cap is specifically designed to eliminate the exposure pathway for the ornate shrew and western meadowlark (which are the two species with unacceptable ecological risks for this area) and prevent or minimize infiltration through the impacted soils. The Groundwater Flow Model for the site was run using the components of SWR #3 and these results show significant reduction of infiltration, and as a result lowering of the water table in RCRA Canyon. This would eliminate the potential for seeps that can impact stormwater quality. The area with an ET cap would be comprised of a 1-foot thick compacted clay soil layer and an overlying 4-foot thick vegetative layer. The 1-foot thick clay layer will be placed on top of the leveling layer in 6” lifts and compacted to attain a minimum of 90 percent compaction (ASTM D 1557). The top 4-foot vegetative layer will be lightly compacted to 85 percent relative compaction. The vegetative layer would be treated with organic amendments and fertilizer, and hydroseeded with a seed mix of native plant species to enable growth of the selected vegetation. The 295,000 cy of clean soil for constructing the cap would be borrowed from the NW Borrow Area (Figure 10-2). Some soils from close proximity to the proposed borrow area have already been successfully used in P/S Landfill and EE/CA Area caps and have been shown to meet the 10-6 cm/sec hydraulic conductivity performance standard. The surfaces of the caps are equipped with surface drains that are sloped to collect and channel stormwater out of this area. The area with a Hybrid cap would be comprised of a spiked geosynthetic liner, a geocomposite drainage layer, an HDPE biotic barrier and an overlying 2-foot vegetative layer. The spiked geosynthetic liner would be placed on a compacted foundation layer (90 percent of maximum dry density). The vegetative layer would be placed in 12” lifts and lightly compacted (85 percent compaction), and would be amended with biosolids and other amendments such as fertilizers or gypsum to enhance vegetation growth. The 117,000 cy of clean soil for constructing the cap would be taken from the NW Borrow Area. As with the other caps, the surface would be equipped with drains that are sloped to discharge stormwater out of the area. The soil volume proposed for excavation in the WCSA remedial area is approximately 44,700 cy, which is proposed to be used as fill to raise the bottom of Pond A-5 before it is capped


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(discussed in FS Area 4). The extent and depth of the excavation is preliminary and would be confirmed during design to ensure that risk-based standards are met. Since extensive cut/fill grading will be required to reduce the slopes to 2:1 prior to constructing the cap especially in the east slope of the canyon, future design will evaluate whether this excavation would be required as a separate activity. For the FS evaluation, the excavated area is assumed to be backfilled by excavating soil in the adjacent areas of the WCSA to match grades. The backfilled soils will be placed in 1-foot lifts and compacted to lower permeability as much as practicable (in the range of 1x10-6 cm/sec to 1x10-4 cm/s) to ensure that the soil cover provides a reasonable barrier to surface water infiltration. The details of the soil cover performance standards and placement will be addressed further during remedial design. The backfilled area will be sloped to allow stormwater to sheet flow to concrete drains that are directed towards the proposed evaporation pond. The 5.5 acre WCSA area and remaining 19.3 acre area of FS Area 2 would be graded and then covered with an ET and/or Hybrid cap (approximately 24.8 acres). The stormwater from the capped west slope would commingle with the stormwater that sheet flows from the soil cover areas into one concrete drainage channel running down the middle of the canyon bottom. The capped stormwater flow from RCRA Canyon will flow through the proposed retention basin in the footprint of Pond A-5 that is lined with a HDPE pond liner (Figure 10-1). The capped area stormwater flow will be conveyed by gravity through a pipeline to the west RCF Pond. From there the water is conveyed through the culvert under RCF Road to a proposed retention basin in the footprint of Pond 13 and then through or around the wetlands and ultimately discharged into the B-drainage. As discussed earlier, the GW Flow Model projects that adding an ET cap on the entire RCRA Canyon would lower the groundwater level in the canyon by 50 plus feet in the northern portion of the canyon and 20 feet in the southern end. The projected groundwater level would be below the lined bottom of the new retention basin in the footprint of Pond A-5, eliminating any groundwater seeps which could otherwise impact the concentration of inorganics in stormwater. This remedy includes a monitoring component that involves periodic inspection and maintenance of these caps, surface drains, erosion controls, and conducting repairs of the features as needed over the long term. 12.4.3 FS Area 3 – Former Ponds and Pads, Remaining Site Areas, Roadways,

Maintenance Shed Area, Liquids Treatment Area, Administration Building Area The FS identified several localized areas of contaminated soil (i.e., hotspot locations) in FS Area 3 which had concentrations of contaminants that collectively create elevated risks. These locations have elevated ecological risks to soil invertebrates due to elevated organics or inorganics in the soil (but did not have any ecological risks to wildlife). Five of these hot spot locations would be addressed (Figure 11-13A). By addressing these five locations, the residual ecological risks of the FPP area would be reduced to a HQ<1. As is the case with FS Area 2, this is a conservative approach considering that the protected species is soil invertebrates and a higher HQ might have been justifiable. The primary remedy component here is covering Location 2 (Figure 12-2A) with a RCRA cap. For Location 2, the Maintenance Shed Area, the entire study area is proposed for the RCRA cap, as mentioned earlier under FS Area 1. For Location 3, excavation of the former Ponds A/B is proposed to a depth of 20 feet bgs, and for Location 4 (south of PSCT-1), excavation of shallow soils to a depth of 5 feet bgs is proposed. The demolition of the building in the MSA and the excavation and removal of two USTs is included as part of the remedy for this FS Area. As discussed earlier, the proposed RCRA cap for Area 1 and the MSA would create one large continuous RCRA cap across about 90 acres


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that would significantly reduce rainwater infiltration and protect groundwater. The surface of these RCRA caps would include surface V-drains along bench roads and perimeter drains that direct stormwater eastward to the concrete drainage channel near the PSCT-1 that flows to the lined retention basin in footprint of Pond 13 and to the B-Drainage (Figure 12-7C). For RISBON-59 (previously identified as Location 10), the hotspot does not represent any human health or ecological risks, but rather poses concern over potential impacts to groundwater. The proposed remedial component for this location is "long term monitoring" of the groundwater downgradient of RISBON-59 as there are no significant observed impacts currently in groundwater that may warrant excavation of these soils. Two additional groundwater monitoring wells are proposed downgradient of the impacted RISBON-59 area to be included in the site-wide monitoring program. For Location 1, up to 5 feet of shallow soil would be excavated to address metals-impacted soils that pose a risk to ecological receptors (Figure 11-10C). The total area for excavation is approximately 1 acre, with a maximum depth of 5 feet bgs and excavation soil volume of approximately 8,000 cy. The excavated soil would be disposed of in the PCB Landfill prior to construction of the PCB Landfill cap remedy. Approximately 8,800 cy of clean soil will be taken from the NW Borrow Area to backfill the excavation at Location 1. After backfill and compaction, the area would be covered with a new 4” asphalt surface. The asphalt will be extended to adjacent gravel and soil areas to form a continuous concrete or asphalt capped surface in the Liquids Treatment Area that could potentially be useful for future site operations. This remedy includes a monitoring component that involves periodic inspection and maintenance of these caps, surface drains, erosion controls and conducting repairs of the features as needed over the long term. 12.4.4 FS Area 4 – Stormwater Ponds and Treated Liquid Impoundments The following remediation would be performed for the various ponds at the site (See Figure 12-2A and Figures 11-20A through 11-20D for more details):

RCF Pond: Removal of all liquids, raising the pond bottom with fill to a minimum of 415 feet MSL to avoid groundwater intrusion, constructing an ecological-cap (2 feet soil cover), and construction of a new lined stormwater channel through the middle of former pond to the wetlands to convey the stormwater runoff from the CDA and other capped portions of the site;

A-Series Pond: Removal of all liquids, excavating the NE shoreline and using the excavated soil as fill to raise the pond bottom to a minimum elevation of 425 feet MSL to avoid groundwater intrusion, constructing a 6-acre evaporation pond comprising six individual 1-acre cells, each equipped with a geocomposite HDPE double pond liner with LCRS, underlying leak detection, and with a 1-foot soil cover (Figure 11-20C), for future treated PSCT and extracted PCT groundwater. The pond would be backfilled with soil to raise the bottom elevation above the future anticipated groundwater elevation. The remaining portion of the A-Series Pond would be covered with an ecological-cap;

Pond A-5: Removal of all liquids, placing clean soil from the WCSA excavation within the pond footprint to raise the pond bottom and place a geocomposite HDPE pond liner to convert it into a lined stormwater retention basin (Figure 11-20D);


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Pond 18: Removal of all liquids, placing clean soil within the pond footprint to regrade it to match adjacent site topography, and a RCRA cap to "close" the pond (Figure 11-20D);

Pond 13: Removal of all liquids, placing a clean soil cover over the pond, and placing a geocomposite HDPE pond liner to convert it into a lined stormwater retention basin to retain stormwater flows before discharging through or around the wetlands (Figure 11-20D).

For each of these existing ponds, the liquids (total of approximately 65 million gallons) would be removed by allowing them to continue to naturally evaporate and using enhanced evaporation (e.g. enhanced evaporation equipment) within the footprints of the ponds. Care would be taken to assure that any misting and irrigation is conducted within the footprints of the ponds to avoid concentrating metals and salts in Area 3 that have already been assessed during the RI. Any remaining liquids in the ponds prior to remedial construction would be transferred to the proposed new 6-acre evaporation pond (or six one-acre cells) in the footprint of the A-Series Pond that ultimately would be required to handle future treated PSCT and extracted PCT liquids. The evaporation pond is discussed further as part of FS Area 5 Groundwater and the Stormwater Plan below. In all cases, the pond would be graded to match the topography and the need to manage stormwater at the site is discussed later in this section. The evaporation pond would need to be periodically sampled to test the chemical concentrations in the sediment (the FS assumes this is required every 5 years) and periodically dredged to remove any contaminated sediment areas (the FS assumes every 20 years). The new evaporation pond would be designed to mitigate impact on special status species that exist at the site. The mitigation for ecological protection, operations and maintenance of the evaporation pond are discussed in more detail in Section 10.1.4. This mitigation would potentially include the following elements to be determined in consultation with USFWS and DFG:


In the event the quantity of pond water that remains in the A-Series and RCF Ponds just prior to remedy construction cannot all be managed in the new evaporation pond as discussed in the stormwater management plan (see Section 12.3), a contingency plan is included to bring a mobile treatment system to treat liquids containing TDS and metals and then discharge the remaining stormwater under a site-specific NPDES permit. Meeting the requirements of a site-specific NPDES Permit would require an exception to the Basin Plan prohibition for the discharge of treated liquids to the B-Drainage and Casmalia Creek. Also, to handle larger volumes of pond water during wet years, an enhanced evaporation system is included as part of this alternative for use on an as needed basis. As with the other FS Areas, this remedy includes a monitoring component that involves periodic inspection and maintenance of the caps, drains, erosion controls and repairs of the features as needed over the long term.


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12.4.5 Groundwater, FS Area 5 As discussed in the FS (Section 8.5 and Appendix A), a groundwater ARAR waiver would be requested for FS Area 5 North based on the Technical Impracticability of restoring groundwater to drinking water standards for the TI Zone that includes the Upper and Lower HSU for organic and inorganic contaminants. Where groundwater ARARs are waived at a Superfund site due to technical impracticability, the USEPA’s general guidance is that the site must consider source control and containment and source removal alternatives to the extent practicable to prevent further migration of the contaminated groundwater plume and prevent exposure to the contaminated groundwater. Such analysis was conducted as part of this FS. No ARAR waiver is requested for the Upper HSU Area 5 South or Area 5 West, both of which are impacted primarily with inorganics. The groundwater in the Lower HSU of Areas 5 South and 5 West does not require remediation as it currently meets ARARs. 12.4.6 Area 5 North The Gallery Well and extraction points of the PSCT would continue to operate for Area 5 North. As discussed in the FS, the purpose of the PSCT and Gallery Well is to address the RAOs that require "control and containment" and mitigate potential for migration to support the proposed TI Waiver Zone that includes Area 5 North groundwater. The FS Report has evaluated the top-ranked remedy for the site using the groundwater flow model that was prepared as part of the RI work. The groundwater flow model was discussed in detail in the Final RI Report (CSC 2011a). Appendix D of this FS includes a technical memorandum summarizing the Groundwater Flow Model results with the anticipated capping included in the FS Area remedies. That modeling indicates that the Gallery Well rates would continue to decline and ultimately go to zero as the groundwater level beneath the P/S Landfill drops below the bottom of the landfill, and that PSCT-1 rates will be substantially lower than current rates, and that PSCT-2, PSCT-3, and PSCT-4 will dry up. The modeling also indicates that Sump 9B will dry up. The FS concludes that it is not necessary to continue operation of Sump 9B. However, Sump 9B will be retained as a contingency measure in the event that water levels in the area are too shallow for the planned cap. The FS considered whether to continue to tank and truck the Gallery Well liquids for disposal versus treating these liquids at the site; and concludes that the outside disposal option is preferred. The PSCT liquids would be treated for organics removal (using an upgraded treatment system that will most likely be an activated carbon treatment system), filtered for solids removal, then transferred to a new 6-acre lined evaporation pond which would be located in the footprint of the A-Series Pond. “NAPL-only” extraction would be installed and operated at an assumed sixteen (16) locations. The new 4-inch NAPL-only wells would be located in the vicinity of RIPZ-13 in the southern portion of the P/S Landfill. The objective of these wells and this alternative component is to extract to the extent possible LNAPL and DNAPL product only. Additional extraction wells may be installed if determined necessary by USEPA in order to optimize extraction of DNAPL and LNAPL. The location and number of wells would be determined during design investigations that would include CPT, MIP, and/or UVIF direct push investigations at the south end of the landfill to delineate the bottom elevation of the landfill and extent of LNAPL and DNAPL. Preliminarily, it


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is assumed that the sixteen wells would include four wells placed on Bench Road 1 in the vicinity of RIPZ-13, four wells located on a new bench road to the north, and eight wells located on two new bench roads between Bench Road 1 and Gallery Well Road. Well location details for these NAPL-only wells screened in the Upper HSU (i.e., in the landfill waste) are shown on Figure 12-7B. These NAPL-only wells are 4–inch diameter wells about 80 feet deep with a steel casing. The screen will be constructed either with a single screen across the entire liquid column (LNAPL, aqueous-phase, and DNAPL) or a dual screen that would include a 1-foot screen just above the weathered-unweathered contact and a 10-foot screen in the vicinity of the water table for LNAPL, and include a 5-foot deep sump that extends into unweathered claystone to collect DNAPL. The final well construction and method of liquids extraction would be determined during pilot testing and remedial design. The NAPL-only wells would be operated to periodically extract DNAPL and LNAPL as it comes into the well using NAPL skimmer pumps. It is assumed that approximately up to 10,000 gallons of DNAPL and LNAPL per year could be removed in this manner from these wells. The NAPL extracted from these "NAPL-only" wells would be stored and trucked for disposal at a permitted facility. For the LNAPL that is present in the CDA, the FS showed that the LNAPL was effectively contained with the operation of the existing extraction and containment features. Limited LNAPL extraction with 4 or 12 wells in the CDA was evaluated but rated poorly for effectiveness due to very low recovery rates. Monitoring of LNAPL thickness is proposed in known impacted areas as part of the long term groundwater monitoring for the site with the goal of ensuring no LNAPL migration. In the Lower HSU, for planning and cost estimation purposes, the FS Report proposes to monitor twelve (12) Lower HSU monitoring wells, six wells each located upgradient of PSCT-1 and PSCT-4 to monitor VOCs to show containment within Area 5 North. These wells would be designed so that they can be converted to extraction points if in the future the concentrations of organics at that point warrant it. 12.4.7 Area 5 South Liquids extraction would continue from the PCT trenches (PCT-A and PCT-B) through the four RAP wells (RAP-1A, RAP-2A, RAP-3A, and RAP-1B) along the southern perimeter of Area 5 South. These extracted liquids would be commingled with the treated PSCT liquids and transferred to the new 6-acre evaporation pond in the footprint of the A-Series Pond. As is discussed in the FS, the purpose of the PCTs is to address the RAOs that require "control and containment" and mitigate potential for migration. Currently, the organics groundwater plume does not extend as far south as the PCTs, and the PCTs are currently addressing inorganics. The Groundwater Flow Model predicts that the PCT-A and PCT-B extraction rates increase following implementation of the top-ranked alternative compared to the current average extraction rates (Section 10.6.2). The PCT extraction would continue until groundwater achieves remediation goals. Source areas would be removed as described above for Area 3 (contaminated soil removal) and Area 4 (pond removal) which would remove sources of contamination to groundwater. Rainfall recharge and flushing of contaminants toward the PCTs and other MNA mechanisms will slowly reduce contaminant concentrations. Natural attenuation of VOCs in groundwater through biodegradation has been documented in this area and will help reduce organic contaminant mass in the long term. Metals remediation would occur primarily through flushing. This alternative includes long term groundwater monitoring to document the ongoing natural attenuation of organics and anticipated reductions in organic and inorganic concentrations over


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time. It is anticipated that remediation goals would not be achieved for several decades or a few centuries. The model simulations for Area 5 South indicate that the time frames for achieving groundwater cleanup standards would range from 80 years (nickel) to 260 years (arsenic) after source removal as described above. 12.4.8 Area 5 West Liquids extraction would continue from the PCT-C along the southern perimeter of Area 5 West. These extracted liquids would be commingled with the treated PSCT liquids and transferred to the new 6-acre evaporation pond in the footprint of the A-Series Pond. As is discussed in the FS, the purpose of the PCTs is to address the RAOs that require "control and containment" and mitigate potential for migration beyond the historical site boundaries. The groundwater in Area 5 West is impacted with elevated concentrations of inorganics. The PCT extraction would continue until groundwater achieves remediation goals. The flux of clean groundwater would disperse and reduce the inorganics by flushing them towards the PCTs. Capping the contaminated soils of RCRA Canyon (FS Area 2) and the closure of the A-Series Pond and Pond A-5 (FS Area 4) would remove the sources of metals. Similar to Area 5 South, it is anticipated that remediation goals would not be achieved for at least several decades and perhaps a few centuries. The model simulations for Area 5 West indicate that the time frames for achieving groundwater cleanup standards would range from 90 years (nickel) to 220 years (arsenic) after source removal as described above. As with the other groundwater areas, the component of the top-ranked remedy for Area 5 West includes long term groundwater monitoring designed to track the inorganics and confirm reduction to acceptable levels. 12.5 Stormwater Management Plan Although this is not a specific FS "area" for evaluation, the FS Report has evaluated how the SWR #3 would incorporate stormwater management for the site. The management of stormwater is a critical issue that must be considered as part of proposing the site remedy. The FS includes the following RAO for stormwater management that includes:

Prevent ecological exposures to COCs in surface water such that exposures are below acceptable levels (HQs less than 1 based on selected surface water benchmarks).

Prevent human exposures to COCs in surface water such that that total carcinogenic risks are within the NCP risk range of 10-4 to 10-6 and non-cancer hazard indices are less than 1. Potential human exposures include workers, trespassers, and hypothetical local residents.

The details of how stormwater will be managed with SWR #3 are summarized in the paragraphs that follow. Please note that a more detailed discussion of managing stormwater including plans for handling stormwater prior to construction is located in Section 10.1.3 of this report. 12.5.1 Stormwater Management with Top-Ranked Remedy As previously discussed, all of the site remedies anticipate that wherever possible stormwater runoff will be discharged under the substantive terms of the General Permit. As shown on


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Figures 12-7A and 12-7C, the FS Report proposes the following approach to manage stormwater with SWR #3:

1. Stormwater runoff from the capped portions of the site north of the PSCT but east of the stormwater divide (the PCB Landfill, the Burial Trench Area, the Maintenance Shed Area, the P/S Landfill, and the EE/CA Area) would sheet flow to a culvert east of PSCT-1 and flow through a concrete drainage channel to the southern end of the site. As currently proposed, the stormwater would flow under the existing RCF Road through a culvert into a lined retention basin constructed in the footprint of Pond 13. The water from this retention basin would flow through or around the wetlands to the B-Drainage.

2. Stormwater runoff from the uncapped portions of the site south of the PSCT but east of the stormwater divide (with the exception of the east end of the RCF Pond as discussed below) would sheet flow to the same culvert that runs under the RCF Road and would also flow into the lined retention basin constructed in the footprint of Pond 13. The stormwater would flow to the B-Drainage. The uncapped portions of the site south of the PSCT would be graded and stormwater BMPs would be included to ensure that the stormwater quality satisfies the substantive requirements of the General Permit. The stormwater in the RCF Pond that will be covered by an ecological-cap will also drain to Pond 13 and through or around the wetlands to the B-Drainage. The Groundwater Flow Model predicts that the capping that is proposed north of the RCF Pond would cause groundwater levels to drop below the current pond bottom. Thus groundwater is not expected to surface in this area. The bottom of the RCF Pond is raised to an elevation of approximately 415 feet MSL to provide assurance that stormwater is not impacted by groundwater.

3. Stormwater runoff from the entire RCRA Canyon (which in this SWR is completely capped) would sheet flow off the canyon walls into a concrete drainage channel and be directed into a lined retention basin that would be constructed in the footprint of Pond A-5. Stormwater would be held in this retention basin during rain events. As the runoff from the east side of the site subsides, the collected stormwater runoff would be released to gravity flow through a new pipeline under the LTP road to the lined retention basin constructed in the footprint of Pond 13. The elevation of the bottom of the new Pond A-5 area retention basin would be approximately 435 feet above MSL (approximately 25 feet higher than the elevation of the discharge point of that pipeline). The pipeline would run a total of about 1,000 feet in length. Preliminary calculations indicate the available elevation drop would exceed the pipe pressure, and stormwater would ultimately flow to the B-Drainage. The Groundwater Flow Model projects that adding an ET or Hybrid cap over RCRA Canyon would lower the groundwater level by more than 50 feet in the northern portion of the canyon and 20 feet in the south. The projected groundwater level would be below the bottom (and liner) of the new retention basin and thus seeps are not expected to occur (which could otherwise impact the stormwater’s chemical concentration of inorganics).

12.5.2 New Evaporation Pond Sizing and Operation The basis for the capacity and size of the proposed evaporation pond was discussed earlier in Section 10.1.4 of the FS. SWR #3 requires an evaporation pond which is approximately 6 acres in size. The evaporation pond will receive the PSCT and PCT groundwater that has been treated for organics. The evaporation pond will actually consist of a series of approximately six clustered 1-acre pond cells which will be designed and constructed to minimize any impact on


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special status species that may exist at the site. Implementation of this remedial alternative that relies upon use of evaporation ponds will include habitat mitigation measures to protect sensitive species subject to approval by USEPA in consultation with other appropriate agencies. 12.6 Borrow Soil Source and Volumes for Top-Ranked Remedy Construction of the top-ranked remedy would require volumes of borrow soil which would come both from excavation of specific features at the site and from outside of the site. The borrow soil would include foundation soil (which has minimum technical requirements for specific soil characteristics), ET cap soil (which has specific technical requirements that are discussed in the text below), and vegetative cover (which like the foundation soil has minimum technical requirements for specific soil characteristics). This section of the report summarizes the borrow source location (Figure 12-8) and the amount of borrow soil required for SWR #3. 12.6.1 Soil (or Backfill) Requirements for the Top-Ranked Remedy As shown on Figure 12-7A and discussed in the detailed summary of the top-ranked remedy alternatives of Section 10 and Section 11, SWR #3 includes the following:

1. ET cap would cover RCRA Canyon and the WCSA. The ET cap will cover the west slope, WCSA and the other areas covering an area of approximately 34 acres and require approximately 295,000 cubic yards of clean soil to create the 5 feet of cover and up to 400,000 cy of cut/fill grading to reduce slopes and form the foundation for that cap. The foundation does not require specific soil characteristics but the 5 feet of soil must meet the soil characteristics of an ET cap. These technical criteria are listed in Section 10.1.1 of the FS. As discussed below, based on the borrow soil testing that was completed as part of the P/S Landfill construction, the Upper HSU claystone soils available in the adjacent areas of the site will satisfy those soil characteristics. In addition, RCRA Canyon remedy includes the excavation of WCSA (5.5 acres). The excavation of WCSA will generate 44,700 cubic yards that will be used to backfill Pond A-5 discussed below. The WCSA excavation will be backfilled with NW Borrow Area soils.

2. Pond 18 would be backfilled to grade prior to constructing the RCRA cap. The backfill will serve as the foundation for the RCRA cap. Based on the current topography and measured elevation of the bottom of Pond 18, this portion of the top-ranked remedy would require a total of 18,000 cubic yards of backfill soil. Please note that it is planned to remove the existing Pond 18 dike and use that as the first or lower backfill volumes. Calculations indicate that the dike will provide 8,000 cubic yards of the backfill requirement, thus the borrow soil requirement will be 10,000 cubic yards. The RCRA cap will require an additional 10,000 cubic yards of vegetative cover.

3. Pond A-5 would be partially backfilled prior to placing the HDPE liner to create a clean stormwater retention basin. The backfill would serve as the foundation layer for the HDPE liner which would be used to construct the retention basin. At present the bottom of Pond A-5 is measured at its deepest point to be at elevation 425 feet MSL. The report assumes that Pond A-5 is backfilled to elevation 435 feet. As discussed elsewhere in this report, the FS proposes to excavate approximately 5 feet of soil from the 5.5 acres of the WCSA that requires remediation. The excavated soils will be moved to and placed in Pond A-5 and subsequently covered by the HDPE liner. Based on the current topography and measured elevation of the bottom of Pond A-5, the partial backfill will require a total of 49,000 cubic yards of soil obtained from the WCSA excavation. The


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lined retention basin will require a foot of vegetative cover over the liner, which is an additional 4,400 cubic yards of soil of clean soil to be derived from the NW Borrow Area.

4. Pond 13 would be partially backfilled prior to placing a HDPE geocomposite pond liner to construct a retention basin. The backfill would serve as the foundation layer for the HDPE liner used to construct the basin. The FS assumes backfilling Pond 13 to approximately elevation 385 feet MSL. Please note that the FS has assumed removing the existing Pond 13 dike and using that as the backfill volumes. Calculations indicate that the dike would provide all 13,000 cubic yards of the backfill requirement, thus there are no additional borrow soil requirements. The lined retention basin will require a foot of vegetative cover over the liner which is an additional 3,500 cubic yards of soil.

5. The RCF Pond would be backfilled to add approximately 5 to 10 feet to the current RCF Pond bottom elevation (minimum of 415 feet MSL) prior to constructing an ecological cap (described elsewhere in the FS) over the entire footprint of the pond. Based on the current topography and measured elevation of the bottom of the RCF Pond, this portion of the top-ranked remedy would require a total of 95,000 cy of soil to raise the RCF pond bottom. The ecological-cap would require 2 feet of vegetative cover, which is an additional 40,000 cubic yards of soil.

6. The A-Series Pond would be partially backfilled prior to placing a HDPE double liner system (with LCRS and leak detection system) to create a series of six 1-acre lined evaporation ponds. As discussed elsewhere in the FS, the remedy proposes to cut the NE corner of the pond (which is elevated approximately 20 feet above the current pond bottom) and use other borrow soil for a total of approximately 85,000 cy of soil to partially backfill the pond. The pond bottom would be raised to a minimum elevation of 425 feet MSL with this cut/fill and no other borrow soil will be required. The total volume of soil required to construct the six 1-acre cells with the berms and the 1-foot vegetative cover is 45,800 cubic yards that would be obtained from the NW Borrow Area. The remaining area of the A-Series Pond would be covered with an ecological-cap that will require 18,000 cubic yards of borrow soil.

7. The remedy would include constructing a RCRA cap over the CDA, BTA, PCB Landfill and the Maintenance Shed Area. The total area of that RCRA cap would be approximately 32 acres. In order to construct the cap, the area would be graded and a foundation layer created which would require a total of approximately 112,000 cubic yards of additional borrow soils. The RCRA cap would include 2 foot of vegetative cover over the HDPE liner, which is an additional 112,000 cubic yards of soil.

Thus the total borrow soil requirement for SWR #3 primarily from the NW Borrow Area is estimated at 818,000 cubic yards. Of this, 183,000 cubic yards is for backfill, 228,000 cubic yards is for ecological-caps or vegetative cover, 112,000 for foundation layers, and 295,000 cubic yards is for the ET cap. Due to the large volume of cut/fill grading activities to reduce slopes to 2:1 at RCRA Canyon/WCSA, a significant volume (up to 200,000 cy) of soil may be available for use as fill soil (e.g. for raising pond bottoms in Area 4). The details of the approach to cut/fill grading prior to capping and the amount of soil available for use as fill will be finalized during remedial design. 12.6.2 Borrow Soil Location The source locations of the required borrow soil for the top-ranked remedy are shown on Figure 12-8. The FS report anticipates getting the borrow soil (both foundation and vegetative cover and the ET cap soils) from the ridgeline located on the western boundary of the site. This area comprises parcels of land owned or controlled by the CSC. The location is ideal as it is located relatively close to the areas which will require borrow soil (so that transportation costs are


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minimized) and generally uphill (which assumes at least a large portion of the borrow soil can be pushed rather than trucked to its destination). The FS report has included a cross section for the cut that would be required to farm the borrow soil (Figure 12-8). As shown on the cross section, the borrow soil area will be graded to keep stormwater runoff from the area from flowing. While it is expected that borrow activities will need to meet the substantive General Requirements for Construction (which include grading, the substantive requirements of a SWPP, and using BMPs), as this area is contiguous to the CERCLA site and the work is being done as part of a CERCLA remediation, it will not be necessary to actually obtain a permit for the proposed grading activities. 12.7 Green Remediation As discussed in Sections 10 and 11, green remediation was consideredin the FS using a qualitative rating approach to compare alternatives and their environmental footprints. The top-ranked remedy was selected based on the CERCLA detailed rankingcriteria analysis with additional consideration of the green impacts assessment. A range of green remediation approaches will be considered during remedial design and are referred to as green remediation BMPs. Typical green remediation BMPs are listed here from USEPA fact sheets on green remediation (USEPA 2008, USEPA 2010, USEPA 2011) under the following categories: energy use, air emissions, impacts to water, impacts to land and ecosystems, and for incorporating renewable energy. Early use BMPs prior to project commencement include:

incorporation of green requirements into product and service procurements installation of modular renewable energy systems to meet low energy demands of field

equipment integrated schedules of various construction activities to allow resource sharing and

fewer days of field mobilization

12.7.1 Energy Use BMPs that can help reduce fuel consumption as well as waste generation during site investigations include:

using direct push technologies for drilling and sampling reusing wells and subsurface boreholes using field test kits instead of sampling (where appropriate)

Diesel fuel consumption by construction machinery and equipment can be conserved by:

selecting suitably sized and typed equipment instructing workers on avoiding idling engines employ auxiliary power units to power cab heating and air conditioning while stationary repowering engines with newer, more efficient engines

12.7.2 Air Emissions


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Field generation of contaminated or uncontaminated dust and mobilization of VOCs can be reduced by BMPs such as:

spraying water in vulnerable areas, in conjunction with water conservation and runoff management approaches

securing and covering material in open trucks hauling excavated material, and reusing the covers

revegetating excavated areas as quickly as possible limiting vehicle speeds at the site to 10 mph covering excavated areas with biodegradeable fabric that also can control erosion and

serve as a substrate for ecosystems or with synthetic material that can be reused Opportunities for reducing emissions of air pollutants from internal combustion engines used during remedy construction and implementation include:

Advanced diesel technologies including equipment with diesel particulate filters on exhaust

Alternative fuels and fuel additives including low sulfur diesel Fuel efficient and alternative vehicles Effective operations and maintenance to assure efficiency of vehicles and field

equipment 12.7.3 Impacts on Water Green remediation strategies to help reduce consumption of fresh water, reuse uncontaminated water, and/or minimize potential for contamination of water include:

cover soils with biodegradeable tarps and mats, rather than spraying with water, to suppress dust where applicable

explore options for reusing gray water, captured rainwater or pond water for cap construction, soil backfill and compaction, truck tire washing, etc.

use phosphate-free detergents to decontaminate equipment.

12.7.4 Impacts on Land and Ecosystems Green remediation strategies to help lessen the impacts to land and ecosystems include:

Installation of silt fences and basins to capture sediment runoff along sloped areas Quick-growth seeding and geotextile placements to stabilize sod in staging areas Planting native, noninvasive plants

12.7.5 Integrating Renewable Energy The concept of “greener cleanups” includes evaluating the potential for integrating renewable energy which typically involves:

Maximizing energy efficiency and monitoring energy demand for the remedy Exploring potential applications for production of energy at the site Conducting a preliminary renewable energy assessment Conducting a detailed economic and technical feasibility study for renewable power


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Consider purchasing clean renewable power Use of renewable energy provides a significant opportunity to reduce the environmental footprint of activities conducted during remediation construction and long term O&M activities. Substitution of energy from fossil fuels with energy from renewable resources is one of the five core elements of green remediation, Renewable sources of energy for production of electricity or direct power include:

Solar resources captured by photovoltaic (PV), solar thermal and/or concentrating solar power systems

Wind resources gathered through windmills to general mechanical power or turbines to generate electricity

Biomass such as untreated woody waste, agricultural waste, landfill gas These green remediation BMPs will be evaluated during remedial design and the appropriate ones selected for implementation. A brief evaluation of solar energy production is provided below based on assumed electricity requirements. 12.7.5.1 Evaluation of Solar Generation The site operations currently utilize on average about 16,000 kWh per month or 192,000 kWh per year. Assuming future site operations after the remedy are higher at approximately 300,000 kWh per year, then photovoltaic (PV) solar energy production is an option with a 30 kW to a 50 kW solar array at an approximate cost of $8 per watt to correspond to a capital cost in the range of $240,000 to $400,000. In addition to this being renewable power that reduces the environmental footprint of the long term remedy, this solar PV installation would reduce monthly electricity costs by 20 to 35 percent. Such a solar PV option and other renewable energy options such as wind energy would be evaluated during remedial design. 12.8 Top-Ranked Remedy Work Sequencing For planning and cost estimation purposes, the FS assumes the remedy would be constructed primarily during the spring/summer construction season (non-rainy season) over a period of about five years. The assumed construction sequence is summarized in the bullets below. The schedule assumes that the FS will progress on a schedule that follows USEPA signature of a Record of Decision (ROD) and would allow remedy construction to begin in about 2018 and end in 2022. Assumptions for work sequencing and preliminary schedule are suggested for planning purposes only. The actual schedule would be revised as necessary subject to USEPA approvals. A provisional draft construction schedule is shown on Figure 12-9 of the FS. Major components of a provisional schedule include the following assumptions: B-Drainage 1. After the ROD has been approved, expeditiously begin the remedial design field

investigations in the southern portion of the P/S Landfill to locate, design, construct, and begin extraction from the NAPL-only wells. Expeditious recovery of NAPL is important because it may drain into the underlying claystone fractures and become unrecoverable once the caps are constructed over the remaining Area 5 North area and the liquid levels in the landfill begin to decline and dry up.


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2. Complete the remedy for RCRA Canyon and WCSA (i.e., FS Area 2) which would include an ET cap and/or RCRA Hybrid cap over the entire area during the first summer construction season (in 2018). During that same timeframe the liquids from Pond A-5 would be transferred to the RCF Pond, the pond backfilled with the WCSA excavated soils, and the new lined retention basin in the footprint of the pond would be constructed. The proposed pipeline that conveys stormwater runoff from the capped western slope and soil capped eastern slope of RCRA Canyon would be built and put into service at this time. The stormwater runoff from the southern portion of RCRA Canyon would sheet flow to the A-Series Pond and be monitored during the first years to determine whether the stormwater meets the RWQCB’s General Permit substantive requirements and can be discharged.

3. Complete the recommended remedy for the CDA, PCB Landfill, BTA (i.e., FS Area 1), and

Maintenance Area and the FPP Area (i.e., FS Area 3) which is a RCRA cap during the second summer construction season (in 2019). The proposed concrete drainage channel that conveys the stormwater runoff from the northern part of the site through or around the wetlands would be built and put into service at this time. With the capping of FS Area 1 and FS Area 2 complete, the site can expect to see groundwater levels decline and extraction rates reduced as projected by the Groundwater Flow Model.

4. Complete the pond closures of the A-Series Pond, Pond 18, and Pond 13 (i.e., FS Area 4)

during the third summer construction season (in 2020). The A-Series Pond would be essentially emptied and the new evaporation pond will be constructed in the footprint of the A-Series Pond.

5. Complete the remedy for the RCF Pond (i.e., FS Area 4) which is adding an ecological-cap

to the raised pond bottoms and the area south of the PSCT (i.e., FS Area 3) which is grading and BMPs, during the fourth summer construction season (in 2021). Please note that the RCF Pond may require this construction occur in 2022 if the pond were unable to be emptied before that.

6. Complete the recommended groundwater remedy (i.e., all three subareas of FS Area 5)

during the fifth summer construction season (in 2022). By this time the extraction rates from the PSCT would have fallen as projected by the Groundwater Flow Model.

12.9 References CSC, 2011a. Final Remedial Investigation Report, January 2011. CSC 2011b Draft Feasibility Study, February 28, 2011 CSC, 2004. Remedial Investigation/Feasibility Study Work Plan, June 2004. Niles 2011 Telephone communication between Corey Bertelsen and Dan Niles of RWQCB

Central Coast, dated July 7, 2011 USEPA, 1988.Guidance for Conducting Remedial Investigations and Feasibility Studies Under

CERCLA, EPA 540/G-89/004, October 1988. USEPA, 2000.A Guide to Developing and Documenting Cost Estimates during the Feasibility

Study, US EPA and US Army Corps of Engineers, EPA 540-R-00-002 July 2000.


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USEPA 2008 Green Remediation: BMPs for Excavation and Surface Restoration, OSWER, US

EPA, December 2008 USEPA 2009 Principles for Greener Cleanups, Office of Solid Waste and Emergency

Response (OSWER), US EPA, August 2009 USEPA 2010 Superfund Green Remediation Strategy, US EPA, September 2010. USEPA 2010 Green Remediation BMPs: Clean Fuel and Emission Technologies for Site

Cleanup, OSWER, US EPA August 2010 USEPA 2011 Green Remediation BMPs: Integrating Renewable Energy Into Site Cleanup,

OSWER, US EPA April 2011