epa superfund record of decision2-1 site location map for f. e. warren afb and zone c 2-2 zone c...

EPA/ROD/R08-01/5542002

EPA Superfund

Record of Decision:

F.E. WARREN AIR FORCE BASEEPA ID: WY5571924179OU(s) 11CHEYENNE, WY09/28/2001

TABLE OF CONTENTS

LIST OF TABLES iii LIST OF FIGURES iii LIST OF APPENDICES iii LIST OF ABBREVIATIONS AND ACRONYMS v

1.0 DECLARATION 1-1 1.1 SITE NAME AND LOCATION 1-1 1.2 STATEMENT OF BASIS AND PURPOSE 1-1 1.3 ASSESSMENT OF SITE 1-1 1.4 SELECTED REMEDY 1-1 1.5 STATUTORY DETERMINATIONS 1-3 1.6 DATA CERTIFICATION CHECKLIST 1-4 1.7 AUTHORIZING SIGNATURES 1-5

2.0 DECISION SUMMARY 2-1 2.1 SITE NAME, LOCATION AND BRIEF DESCRIPTION 2-1 2.2 SITE HISTORY AND ENFORCEMENT ACTIVITIES 2-2 2.3 COMMUNITY PARTICIPATION 2-5 2.4 SCOPE AND ROLE OF OPERABLE UNIT/RESPONSE ACTION 2-7 2.5 SITE CHARACTERISTICS 2-9 2.6 CURRENT AND POTENTIAL FUTURE LAND AND WATER USES 2-14

2.6.1 Land Uses 2-14 2.6.2 Groundwater and Surface Water Uses 2-15

2.7 SUMMARY OF SITE RISKS 2-16 2.7.1 Summary of Human Health Risk Assessment 2-16 2.7.2 Summary of Ecological Risk Assessment 2-18

2.8 REMEDIAL ACTION OBJECTIVES 2-20 2.9 DESCRIPTION OF ALTERNATIVES 2-21

2.9.1 Description of Remedy Alternatives 2-22 2.9.2 Distinguishing Features of Each Alternative 2-25

2.10 COMPARATIVE ANALYSIS OF ALTERNATIVES 2-25 2.11 PRINCIPAL THREAT WASTES 2-32 2.12 SELECTED REMEDY 2-33

2.12.1 Summary of Rationale for Selected Remedy 2-33 2.12.2 Description of the Selected Remedy 2-33 2.12.3 Summary of Estimated Remedy Costs 2-35 2.12.4 Expected Outcomes of Selected Remedy 2-35

2.13 STATUTORY DETERMINATION 2-36 2.13.1 Protection of Human Health and the Environment 2-36 2.13.2 Compliance with ARARs 2-37 2.13.3 Cost-Effectiveness 2-39 2.13.4 Utilization of Permanent Solutions and Alternative

Treatment Technologies 2-39 2.13.5 Preference for Treatment as a Principal Element 2-40 2.13.6 Five-Year Review Requirement 2-41

2.14 DOCUMENTATION OF SIGNIFICANT CHANGES FROM PREFERRED ALTERNATIVE OF PROPOSED PLAN 2-41

3.0 RESPONSIVENESS SUMMARY 3-1 3.1 STAKEHOLDER ISSUES AND LEAD AGENCY RESPONSES 3-1

4.0 REFERENCES 4-1

LIST OF TABLES

Table No. Title

2-1 Zone C Detailed Alternative Analysis 2-2 Zone C Comparative Analysis 2-3 Cost Summary for Selected Remedy2-4 Zone C Federal and Wyoming State Potential Applicable, or Relevant and Appropriate Requirements (ARARs)

LIST OF FIGURES

Figure No. Title

2-1 Site Location Map for F. E. Warren AFB and Zone C 2-2 Zone C Boundary and Historic Preservation Areas 2-3 TCE Isoconcentration and Water Table Contours 2-4 cis-l, 2-DCE Isoconcentration and Water Table Contours 2-5 Carlin Heights MFH Preliminary Concept Expansion Plan

LIST OF APPENDICES

Appendix Title

A Human Health and Ecological Risk Characterization SummaryB Supplemental Risk Assessment of SeepC Responses to Comments

Appendix Table Title

A-l Summary of Chemicals of Concern and Medium-Specific Exposure Point Concentrations A-2 Selection of Exposure Pathways for Zone C Human Health Risk Assessment A-3 Cancer Toxicity Data for COCs in Groundwater A-4 Noncarcinogenic Toxicity Data for COCs in GroundwaterA-5 RME and CTE Risk Characterization Summary for CarcinogensA-6 RME and CTE Risk Characterization Summary for NoncarcinogensA-7 Soil Screening Levels for Selection of COPECs A-8 Sediment Quality Values for Selection of COPECsA-9 Water Quality Values for Selection for COPECsA-10 Occurrence, Distribution, and Selection of Ecological Chemicals of Concern A-ll Assessment and Measurement Endpoints for the Ecological Risk Assessment B-l Permeability Constants for Chemicals of Concern in Happy Jack Road Seep Water B-2 Human Health Risk Assessment for Happy Jack Road Seep, Carcinogenic Risk and Noncarcinogenic Hazard Index for RME Highway Maintenance Workers Exposed to Analytes in Seep Water, Incidental Seep Water Ingestion B-3 Human Health Risk Assessment for Happy Jack Road Seep, Carcinogenic Risk and Noncarcinogenic Hazard Index for RME Highway Maintenance Workers Exposed to Analytes in Seep Water, Incidental Seep Water Inhalation of VOCs B-4 Human Health Risk Assessment for Happy Jack Road Seep, Carcinogenic Risk and Noncarcinogenic Hazard Index for RME Highway Maintenance Workers Exposed to Analytes in Seep Water, Dermal Contact with Seep Water

B-5 Human Health Risk Assessment for Happy Jack Road Seep, Carcinogenic Risk and Noncarcinogenic Hazard Index for CTE Highway Maintenance Workers Exposed to Analytes in Seep Water, Incidental Seep Water Ingestion B-6 Human Health Risk Assessment for Happy Jack Road Seep, Carcinogenic

Risk and Noncarcinogenic Hazard Index for CTE Highway Maintenance Workers Exposed to Analytes in Seep Water, Inhalation of VOCs

B-7 Human Health Risk Assessment for Happy Jack Road Seep, Carcinogenic Risk and Noncarcinogenic Hazard Index for CTE Highway Maintenance Workers Exposed to Analytes in Seep Water, Dermal Contact with Seep Water

B-8 Summary of Total Hazard Indices and Cancer Risks for Human Health Risk Assessment, Happy Jack Road Seep

B-9 Water Quality Values (WQVs) Used for Screening-Level Ecological Risk Assessment, Happy Jack Road Seep

B-10 Comparison of Chemical Concentrations to Water Quality Values, Ecological Evaluation of Seep Water at Happy Jack Road

Appendix Figure Title

A-l Human Health Conceptual Site Model A-2 Ecological Conceptual Site Model

LIST OF ABBREVIATIONS AND ACRONYMS

ug/l microgram per liter 4,4'-DDD 4,4'-dichloro-2,2-bis(p-chlorophenyl) ethylene 4,4'-DDT 4,4'-dichlorodiphenyltrichloroethane ARAR applicable or relevant and appropriate requirement ATC Air Training Command bgs below ground surface BOPU Board of Public Utilities CERCLA Comprehensive Environmental Response, Compensation, and Liability Act CFR Code of Federal Regulations COC chemical of concern COPC contaminant of potential concern COPEC chemical of potential ecological concern CRP community relations plan CTE central tendency exposure DCE dichloroethene or dichloroethylene EPA United States Environmental Protection Agency ES Engineering Science FEW F.E. Warren Air Force Base FFA Federal Facility Agreement FPTA Fire Protection Training Area FS feasibility study ft/day foot per day ft/year feet per year HI hazard index HQ hazard quotient IRP Installation Restoration Program LF-03 Landfill 3 LF-06 Landfill 6 MCL maximum contaminant level mg/L milligram per liter MNA monitored natural attenuation NA not analyzed or not applicable NCP National Oil and Hazardous Substances Pollution Contingency Plan

NPL National Priorities List NPV net present value O&M operation and maintenance OU operable unit PCB polychlorinated biphenyl PCE tetrachloroethene or perchloroethylene PES Parsons Engineering Science PRB permeable reactive barrier PRG preliminary remediation goal RA remedial action RAO remedial action objective RI remedial investigationRME reasonable maximum exposure ROD Record of Decision SARA Superfund Amendments and Reauthorization Act SDWA Safe Drinking Water Act SQV sediment quality value SVOC semivolatile organic compound TBC to be considered TCE trichloroethene or trichloroethylene TRV toxicity reference valueUSAF United States Air Force USC United States Code UV ultraviolet VOC volatile organic compound WDEQ Wyoming Department of Environmental QualityWQV water quality value

1.0 DECLARATION

1.1 SITE NAME AND LOCATION

The site name is F. E. Warren Air Force Base (FEW), and it is located in Cheyenne,Wyoming. This site was placed on the National Priorities List (NPL) in February 1990 andwas assigned the National Superfund Database identification number WY5571924179. ThisRecord of Decision (ROD) addresses remedial actions (RAs) at Zone C, Operable Unit (OU)11, Landfill 3 (LF-03). It primarily addresses the groundwater plume downgradient fromLF-03, but also incorporates prior response actions in Zone C.

1.2 STATEMENT OF BASIS AND PURPOSE

This ROD identifies the selected remedy for cleaning up the contaminated groundwaterwithin Zone C, OU 11, LF-03, FEW, Cheyenne, Wyoming. The selected remedy was chosen by theUnited States Air Force (USAF), the lead agency for the site, in accordance withComprehensive Environmental Response, Compensation, and Liability Act (CERCLA), as amendedby the Superfund Amendment and Reauthorization Act (SARA), and, to the extent practicable,the National Oil and Hazardous Substances Pollution Contingency Plan (NCP). This decisionis based on the Administrative Record file for this site. The U. S. EnvironmentalProtection Agency (EPA) and the State of Wyoming Department of Environmental Quality(WDEQ) concur with the selected remedy.

1.3 ASSESSMENT OF SITE

The response action selected in this ROD is necessary to protect public health or welfareor the environment from actual or threatened releases of pollutants or contaminants fromthis site, which may present an imminent and substantial endangerment to public health orwelfare.

1.4 SELECTED REMEDY

This ROD specifies the selected remedy for cleaning up the contaminated groundwater within Zone C, LF-03, OU11 at FEW. In addition, the ROD documents all interim and removal actions taken at this site to date and incorporates these actions, by reference, into this finalselected remedy for Zone C. The project management team, including the USAF, EPA, andWDEQ, identified and reviewed appropriate alternatives for addressing residual groundwater contamination. The USAF has selected extraction and aboveground treatment of contaminated groundwater, otherwise known as "pump and treat," as the remedy for this site. Thisdecision was based on the Feasibility Study (FS) conclusions (USAF 2000b) and otherdocuments in the Administrative Record.

The selected remedy for Zone C groundwater remediation, including previous activities incorporated into the selected remedy, contains the following general elements:

• A municipal water supply is being provided to the residents of Nob Hill through aninterim action taken at LF-03 in January 1997. This system has been turned over tothe Cheyenne Board of Public Utilities (BOPU), which will handle any and alloperation and maintenance (O&M) activities for the system.

• All waste and other source material was removed from LF-03, which was conducted inMarch and April 2000 as part of a non- time critical removal action. This completeremoval of the landfill waste and any impacted soils is expected to achieve cleanclosure for the landfill itself.

• Wells will be installed within the contaminated groundwater plume to capture waterwithin all on-site areas with concentrations of trichloroethene (TCE) above themaximum contaminant level (MCL) of 5 micrograms per liter (ug/L).

• Groundwater will be pumped from the wells into a treatment system designed tocollect and treat groundwater.

• Groundwater will be treated to remove volatile organic compounds (VOCs) by a proventechnology. The treatment technology will be selected during the remedial designphase of the process from among the four presumptive remedies for treatment ofgroundwater contaminated with VOCs. These are air stripping, carbon adsorption,chemical/ultraviolet (UV) oxidation, and aerobic biological reactors.

• Treated groundwater will be discharged to the surface, reinjected into the aquiferor discharged to a publicly owned treatment works. The effluent discharge optionwill be selected during the remedial design phase of the process.

• During implementation, institutional controls will protect human health and theenvironment by limiting exposure to contaminated groundwater. Institutionalcontrols, which will also ensure the integrity of the remedial systems by limitingaccess, include:

- Restrictive notices incorporated by the USAF into the FEW General Plan to prevent groundwater usage. The Installation Commander is responsible for

developing, maintaining and implementing the General Plan. The General Plan includes a map addressing Installation Restoration Program (IRP) sites and a section that highlights critical areas having limited or specialized development potential and factors these into the planning process for the Base,

- Issuing periodic Advisory Notices by the USAF, County Health Department, or another county agency to Nob Hill residents stating that the groundwater is not suitable for domestic use,

- Limiting access to the remedy equipment and monitoring network to authorized personnel only, and

- Annual review of the Base General Plan to ensure appropriate maintenance of the institutional controls.

• Periodic monitoring will be performed to demonstrate the effectiveness of theremedial action.

The principal threat for this site was the landfill waste, which has been removed fromLF-03. Residual contamination exists in the groundwater at present, providing a potentialrisk. Upon completion of the remedial action, there will be no contamination ingroundwater at concentrations above remedial action objectives (RAOs) either on- site oroff-site. Exposure to off-site Zone C groundwater will be limited by the provision of analternate water source for Nob Hill residents and by institutional controls during theremediation period. Therefore, the residual risk will be very low.

OU 11 is one of 13 operable units at FEW. The remaining OUs are at various stages in the investigation and cleanup process. Early response actions including interim remedialactions and removal actions have been conducted at OU2, OUS, OUS, and OU9, as well as atOU11. These actions will be consistent with the final actions selected. This is the fifthROD for a final remedy at FEW. Previous final RODs addressed OU1, OU4, OUS, and OUS. Theinvestigation and cleanup process for the remaining OUs at FEW is anticipated to continuefor the next several years, with the last OU ROD scheduled for 2009.

1.5 STATUTORY DETERMINATIONS

The selected remedy is protective of human health and the environment, complies withfederal and state requirements that are applicable or relevant and appropriate to theremedial action, is cost-effective, and utilizes permanent solutions to the maximum extentpracticable.

This remedy also satisfies the statutory preference for treatment as a principal elementof the remedy and permanently and significantly reduces the toxicity, mobility, and volumeof contamination.

Because this remedy will result in hazardous substances, pollutants, or contaminantsremaining on-site above levels that allow for unlimited use and unrestricted exposure, astatutory review will be conducted within 5 years of initiation of the remedial action toensure that the remedy is, or will be, protective of human health and the environment.

1.6 DATA CERTIFICATION CHECKLIST

The following information is included in the Decision Summary section (Section 2.0) ofthis ROD. Additional information can be found in the Administrative Record for this site. • Chemicals of concern (COCs) and their respective concentrations (Appendix A, Table

A- l),

• Baseline risk presented by the COCs (Appendix A, Sections 1.0 and 2.0),

• Cleanup levels for COCs and the basis for these levels (Section 2.8),

• How source materials constituting principal threats are addressed (Section 2.11),

• Current and future land use assumptions and current and future beneficial uses ofgroundwater used in the baseline risk assessment and ROD (Section 2.6.1),

• Potential land and groundwater use that will be available to the site as a result ofthe selected remedy (Section 2.12.4),

• Estimated capital, O&M, and total present worth costs, discount rate, and the numberof years over which the remedy cost estimates are projected (Table 2-1 and Table2-3), and

• Key factors leading to the selected remedy (Section 2.10).

1.7 AUTHORIZING SIGNATURES

a. The undersigned representative concurs with the Record of Decision for the Selected Remedy atZone C: Operable Unit 11, Landfill 3, F. E. Warren Air Force Base, Wyoming.

b. The undersigned representative concurs with the Record of Decision for the Selected Remedy atZone C: Operable Unit 11, Landfill 3, F. E. Warren Air Force Base, Wyoming.

c. The undersigned representative concurs with the Record of Decision for the Selected Remedy atZone C: Operable Unit 11, Landfill 3, F. E. Warren Air Force Base, Wyoming.

2.0 DECISION SUMMARY

2.1 SITE NAME, LOCATION AND BRIEF DESCRIPTION

The site name is F. E. Warren Air Force Base, and it is located in Cheyenne, Wyoming. TheBase is located on approximately 5,866 acres adjacent to the western city limits ofCheyenne, Wyoming. The base is bounded by Interstate 25 on the east, Old Happy Jack Roadto the south, Military Road on the southwest, Roundtop Road on the west, and open prairieon the north. Figure 2- 1 provides a site map of FEW and Zone C.

The IRP sites at FEW are divided into 13 OUs and a system of five investigative zones designated A, B, C, D, and E. The delineation of the zones is based on geographic features(e.g., surface water drainages) and distinguishing features (e. g., prominent featuressuch as LF-03). A zone may consist of one or several OUs. Zone C includes only OU11.

This ROD addresses remedy selection for Zone C, one of several administrative areas within FEW. Zone C is located in the southeastern corner of FEW and includes LF-03, a landfillwhose contents were excavated in March and April 2000 and relocated to the wasteco-location area, and the associated groundwater plume (OU11). Zone C is bounded on thenortheast by Crow Creek, on the east and south by the Base property line and on the westby Zone D. Happy Jack Road bisects Zone C from northeast to southwest.

Two housing areas are located near Zone C: Carlin Heights and Nob Hill. Carlin Heights is located partially in Zone C and to the west and northwest of the former landfill area.Zone C also includes acreage northwest and northeast of the triangular-shaped Nob Hillhousing subdivision, located just off-base between Happy Jack Road and Old Happy JackRoad. Nob Hill contains 16 residences.

The excavated landfill (LF-03) was located approximately 300 feet hydraulicallydowngradient from the Carlin Heights residential area and 1,100 feet upgradient of NobHill. Impacted groundwater associated with the former landfill (as defined by the TCE 5ug/L isocontour line) extending from the approximate center of the former landfill 2,200feet to the east-northeast, with a small portion of the plume extending under the Nob Hillarea.

An intermittent groundwater seep was identified in a drainage ditch along the north sideof Happy Jack Road, north of the Nob Hill subdivision. The flow rate of the seep is notknown. The seep was sampled and analyzed for VOCs in the second quarter of 2000 to assesswhether contaminants were present. Analytical results indicated that the seep wascontaminated with VOCs, and a supplemental human health risk assessment and environmentalevaluation were performed to assess potential risks associated with the seep. Rather thanusing the low levels identified in the seep water, which may be an artifact of thesampling methodology or aeration of the water as it emerges from the ground, analyticalresults from nearby well MW- 210 were used for the risk assessment. The human health andecological risk evaluation confirmed that the contaminants in groundwater with thepotential to discharge at the seep pose no unacceptable risk.

2.2 SITE HISTORY AND ENFORCEMENT ACTIVITIES

FEW has served a number of functions since its activation as a military base in the mid-1800s. United States Army outpost Fort D.A. Russell was established at this location in1867 to protect railroad workers. Largely due to the influence of Senator Francis E.Warren, Ft. Russell was selected in 1902 for expansion from a permanent post to theheadquarters for 12 companies of infantry and one battery of field artillery. To meet theneeds of the increased manpower, construction activity began in 1903. In 1905, Secretaryof War William Taft recommended enlargement of Ft. Russell to a brigade-size post; 150buildings were erected between 1905 and 1913. These facilities form a large part of thecurrent National Historic Landmark. An on-base cemetery contains the graves of soldiersfrom the earliest days of the fort to the present, including 20 of the famous "Buffalo

Soldiers" of the all-Black 9th and 10th Cavalry and 24th Infantry Regiments, who served atthe base during the "Indian Wars."

An airfield was located at Ft. Russell in 1919. O'Neil Airfield was the site oftranscontinental reliability test flights, and it was hoped that the post would become animportant stop for cross-country flights. By 1920, the Army had abandoned this notion andthe airfield was closed.

In honor of Senator Warren and his tremendous impact on the development of Ft. Russell,the post was renamed Fort Francis E. Warren in 1929. In 1930, the population of the postconsisted of 3,347 military personnel and 2,250 horses and mules. The post consisted of259 permanent buildings, 26 temporary buildings, and 10 permanent buildings underconstruction.

The next major construction episode in the history of the base occurred during World WarII. The area south of Crow Creek was chosen as the location of a Quartermaster Replacement Center. This facility trained 122,000 quartermaster specialists in a 2-year period. TheArmy constructed 387 new buildings between December 1940 and December 1941 to house and process 20,000 men at a time. All buildings were of temporary, wood frame construction seton concrete and brick piers or concrete slab foundations. In addition to the trainingfacility, a prisoner of war camp was established on the base in 1943.

In 1947, the property was transferred from the Army to the newly formed USAF and the base was assigned to the Air Training Command (ATC). In 1957, FEW was selected as the nation's first intercontinental ballistic missile complex. The complex consisted of two LaunchControl Centers, each having control of three missiles. In 1959, the first Atlas "D"missiles arrived at the Base, and the Base was transferred from the jurisdiction of ATC tothe Strategic Air Command. Fully active by the end of 1960, the 389th Strategic MissileWing was placed in readiness during the Cuban Missile Crisis in November 1962. A secondgeneration of missiles was developed between 1958 and 1962. Minuteman "B" missiles wereinstalled in 200 missile silos with 20 launch control sites spread over an area of 8,300square miles. In 1973, the Minuteman III replaced the Minuteman "B."

At present, the prime mission of FEW is to provide operational, maintenance, and security support for Peacekeeper and Minuteman III missiles. FEW was assigned to Air Combat Commandin June 1992, and then to Air Force Space Command in July 1993. In February 1998, theEnvironmental Restoration Section at FEW became Restoration Management. Regardless of thename change, all IRP efforts remain under the guidance of Space Command.

FEW was placed on the NPL in February 1990 and was assigned the National SuperfundDatabase identification number WY5571924179. FEW is a federal facility and the cleanup is funded by the Defense Environmental Restoration Act through the IRP, which presently FinalZone C Record of Decision F. E. Warren Air Force Base Cheyenne, Wyoming addresses 20contaminated locations at the Base. The locations are divided into 13 operable units, anda system of five investigation zones has now been developed for investigative purposes.Zone C, which includes LF-03, is one of these five zones. LF-03 was placed in the new OU11to streamline the environmental restoration process at FEW.

Figure 2-2 shows the location of LF-03 and delineates historic preservation areas withinZone C. The following designated historic preservation areas are identified on Figure 2-2:

Site # 48LA Field # Description Reports Type Comments NRHP EligibilitySHPO #

245 FEW-6 Lithic Scatter 6,9,33,38,83

P C 0899TPT036

272 FEW-45 Lithic Scatter 82 P NC 0899TPT036

273 FEW-46 Dump/LF 82 H NC 0899TPT036

505 FEW-157 Lithic Scatter 10, 13 P Partlydestroyedby HappyJack 1987

NC CRO

Notes:

Prehistoric Historic NRHP= National Register of Historic Places NC= not eligible C= eligible

LF-03 reportedly operated from the mid-1950s through the mid-1960s. All FEW refuse was disposed at LF-03 during its operation. Data collected during previous investigationssuggest that refuse burning occurred at LF-03 (Parsons Engineering Science [PES] 1999a).LF-03 was first identified as a site that might pose a hazard to human health or theenvironment in the mid-1980s (Engineering Science [ES] 1985). LF-03 and Landfill 6 (LF-06)were included in OUS under a federal facilities agreement (FFA) signed in September 1991.LF-03 was moved to OU 11 in 1999.

Numerous investigations have been carried out since the mid-1980s to investigatecontamination associated with LF-03. These include:

• Installation Restoration Program, Phase I - Records Search (ES 1985), • Remedial Investigations for F. E. Warren Air Force Base (USAF 1991) • Focused Remedial Investigation for Landfill 3 (Ebasco 1995), • Final Treatability Study in Support of Monitored Natural Attenuation for Groundwater

at Landfill 3 (Site LF-03) (PES 1999b), • Final Remedial Investigation for Zone C (US AF 2000a) • Final Feasibility Study for Zone C (USAF 2000b).

Based on investigations prior to 1996, LF-03 is the only potential IRP site within Zone Cand therefore was the target of the 1999 Zone C Remedial Investigation (RI) investigation.During earlier investigations, tetrachloroethene (PCE) and TCE were detected ingroundwater off-base underlying the Nob Hill area. As a result, residents of the Nob Hillarea were placed on the public water system in January 1997. This action was carried outas an Interim Action by the USAF.

In accordance with the Action Memorandum prepared for the non-time-critical removal actiondated February 2000 (USAF 1996), all waste was removed from LF-03 during the summer of2000. Because all wastes have been excavated, LF-03 is expected to achieve clean closure.No further source response actions are expected. The action described in this RODincorporates the LF-03 closure and the Nob Hill water line construction into the finalZone C (OU11) remedy.

This ROD addresses RAs at Zone C, OU11, LF-03. It primarily addresses the groundwater plume downgradient from LF-03, but also incorporates prior response actions in Zone C. TheUSAF issues the ROD, with EPA and WDEQ concurrence on the content.

2.3 COMMUNITY PARTICIPATION

The USAF has prepared and implemented a community relations plan (CRP) in accordance with CERCLA requirements and the Federal Facility Agreement (FFA). The CRP describes community involvement activities that the USAF will undertake during remedial activitiesat FEW. The USAF has followed the requirements of the CRP, including holding publicmeetings and providing the opportunity for public comment throughout the cleanup process.

The RI/FS, other investigative reports and the Proposed Plan for the F. E. Warren AirForce Base in Cheyenne, Wyoming have been made available to the public throughout the site investigation. Most recently, the Proposed Plan was made available to the public on March12,2001. This and other documents associated with site investigation and remediation canbe found in the Administrative Record at the following locations:

Laramie County Library F. E. Warren Restoration 2800 Central Avenue Management Office Cheyenne, WY 82001 6203 15th Cavalry Avenue (307) 634-3561 F. E. Warren Air Force Base Hours of Operations: Cheyenne, WY 82005-2767 10 am to 9pm (Mon- Thur) (307) 773- 4355 10 am to 6 pm (Fri- Sat) Hours of Operations: 1 pm to 5 pm (Sun) 7:30 am - 4:00 pm (Mon - Fri)

The notice of availability of this document was published in the Wyoming Tribune Eagle on March 11, 2001. The fact sheet related to the Zone C ROD was mailed out to interestedparties and the Restoration Advisory Board on March 13, 2001. A public comment period forthe Proposed Plan was held from March 12, 2001, through April 11, 2001. In addition, apublic meeting was held on March 27, 2001, to present the Proposed Plan to a broadercommunity audience than those who had already been involved at the site. The meeting wasattended by four RAB members, two newspaper reporters, and two members of the CheyenneBoard of Public Utilities, in addition to representatives from the Air Force and itscontractors, EPA, and the WDEQ. At this meeting, representatives from FEW, EPA and theWDEQ answered questions about the site and the remedial alternatives. As described in theResponsiveness Summary (Section 3), which is part of this ROD, no written comments werereceived from the public and no comments were received verbally during the public meetingsthat would change the remedy selection process. Official transcripts of the publicmeetings were prepared and placed in the Administrative Record.

Comments on this ROD should be directed to the F. E. Warren Remedial Project Manager atthe following address:

Mr. John Wright Remedial Project Manager 90 SW/EM RPM 300 Vesle Drive, Suite 600 F. E. Warren AFB, WY 82005 Telephone: (307) 773-4147 john. wright@ warren.af.mil

2.4 SCOPE AND ROLE OF OPERABLE UNIT/RESPONSE ACTION

Operable Unit 11 is one of 13 OUs at FEW, which are at various stages in the investigationand cleanup process. Early response actions including interim RAs and removal actions havebeen conducted at OU2, OU3, OUS and OU9, as well as OU11. Early response actions at OU11 included construction of a municipal water line during 1996 and 1997 to supply water tothe residents of Nob Hill (Interim Action ROD OU3, USAF, February 1996 [this area hassince been changed to OU11]). During March and April 2000, all wastes from LF3 wereexcavated and placed in the waste consolidation area at LF5a. One 55 gallon drum of soilcontaminated with copper sulfate was manifested off-base using Clean Harbors, Inc. The

waste was disposed of at the Kimball, Nebraska facility (EPA ID No. NEB981723513), wherethe ultimate disposition was landfilling. In addition, a small amount of medical waste(less than 200 pounds) was collected and disposed with other base-generated medical wastethrough incineration. These early response actions will be consistent with final actionsselected.

The operable units identified at FEW are:

• OU1 Spill Sites 1 through 7 Soils • OU2 Spill Sites 1 through 7 Groundwater, Fire Protection Training Area (FPTA) 2

Groundwater, Plumes A through E Groundwater, Basewide Surface Water/Sediment • OU3 Landfill 6 (all media) • OU4 Acid Dry Wells (all media) • OUS FPTA 2 Soils • OU6 Open Burning/ Open Detonation Area (all media) • OU7 Firing Ranges (all media) • OU8 Landfill 5 (all media) • OU9 Landfill 2 (all media) • OU10 FTPA 1 and Landfill 7 (all media) • OU11 Landfill 3 (all media) (The subject of this ROD.) • OU12 Landfill 4 (all media) • OU13 Plumes A through E (Sources)

There have been four previously completed RODs for final remedies at FEW. The OU4 ROD was signed on December 30, 1992, and addressed the contamination associated with an aciddry well at the old transportation complex. Based on previously completed contaminatedsoil removal, the baseline risk assessment indicated no significant risk to human healthand the environment. Therefore, no further action was required at this site.

Operable Unit 5 addressed the FPTA 2 soils. The ROD for this OU was signed on November 4, 1994, and also indicated no further action was required based on the risk assessmentfindings of no significant risk to human health and the environment. As part of thisdecision, the groundwater beneath FPTA 2 was made part of OU2, basewide groundwater, whichis presently in the investigation phase of the cleanup process.

The OU1 ROD was signed on August 9, 1995, and addressed the contaminated soils at Spill Sites 1 through 7. The risk assessment conducted for this OU indicated that there was no significant risk to human health and the environment, therefore the ROD indicated that nofurther action was required for the soils at these sites. However, the groundwater beneaththese sites was not included, and it was also made part of OU2.

The OUS ROD was signed in September 2001, and addressed the Landfill 5, Zone B area. OUS will address the TCE-contaminated groundwater by extracting the groundwater and treatingit with the use of activated granular carbon. This ROD also included the excavation ofLF5b, which was completed in 2000 as a removal action, and an earthen cover that wasplaced on LF5a as an interim remedial action in 1999. The remedy for this OU is scheduledto begin operation in 2002.

The remaining OUs will be investigated and RODs completed in the following general orderand time frame:

OU11 - 2001, OU3 - 2001, OU6 - 2003, OU9 - 2004, OU12 - 2003, OU10 - 2004, OU13 - 2004, OU2 - 2005, OU7 - 2009.

Groundwater contamination from Zone C will be addressed under OU11. All of the investigations are being conducted in accordance with the FFA. The selected remedyaddressed in this ROD will not affect or interfere with other RAs currently planned atFEW, and it will be consistent with any future actions, to the maximum extent possible.

The response action described in this ROD will address the contamination within Zone C. In January 1997, a municipal water line was constructed to supply water to the residents ofNob Hill, in accordance with an interim ROD signed in February 1996. All waste withinLF-03 was excavated during 2000 to remove any sources that may have been present in thelandfill, in accordance with the Action Memorandum for the site. Together with theadditional measures to address groundwater contamination in Zone C described in this ROD,these actions make up the final action for Zone C and will result in permanent reductionof toxicity, mobility, and volume of the contamination at the site.

It is the goal of the USAF, EPA, and WDEQ to develop an overall approach to expedite the initiation of appropriate remedies at FEW, to ensure public participation in the process,and to ensure continuing protection of human health and the environment.

Presently, the OU11 remedial design is scheduled for completion in late 2001 withactivation of the extraction and treatment system to begin in 2002. This action, togetherwith the early responses previously completed, will be the final action for Zone C andwill result in permanent reduction of toxicity, mobility, and volume of the contaminationat the site.

2.5 SITE CHARACTERISTICS

FEW is located on approximately 5,866 acres adjacent to the western city limits ofCheyenne, Wyoming (Figure 2-1). FEW is bordered by agricultural land, ranches, andresidential areas of the city of Cheyenne and Laramie County. Most buildings, roads, andhuman activities are concentrated in the southern portion of the installation.

Zone C is located in the southeastern corner of FEW. The boundaries of Zone C are shown on Figure 2-2. LF-03, the primary feature in Zone C, occupies approximately 5 acres. Thislandfill was located 300 feet north of Happy Jack Road, 300 feet southeast of an FEWfamily housing area (Carlin Heights), and 1,100 feet northwest of the Nob Hill residentialarea. The Carlin Heights housing area is upwind and upgradient from LF-03 and the Zone Cgroundwater plume.

Nob Hill is located downwind and partially downgradient from LF-03 and the Zone C groundwater plume.

Based on previous investigations and groundwater plume maps, LF-03 is the apparent sourceof contaminants in Zone C. Reportedly operated from the mid-1950s to the mid-1960s, thelandfill received domestic solid waste, waste oils and solvents, battery acid, and otherwastes, although detailed records were not maintained. A review of air photos indicatesthat landfill operations continued until at least 1969.

Landfill material excavated during the RA consisted of more than 50 percent soil in mostcases, along with construction debris and domestic waste. The observed construction debrisincluded wire-reinforced concrete, asphalt, bricks, slate roofing tiles, glazed ceramictile, transite siding, dimensional lumber, rebar, asphalt shingles, drywall, sheet metal,pipe, and conduit. Sanitary waste material consisted of glass, soda bottles, paper, metalstraps, jars, tin cans, motor oil cans, wood, burned material, coal chunks, klinker, andcoal slag material. The maximum depth of the waste material was approximately 15 to 18feet below ground surface (bgs). Approximately 120,000 cubic yards of waste material andsoil were removed from LF-03.

The land in Zone C generally slopes to the east-northeast toward Crow Creek, a stream thatruns near the eastern boundary of the site. Zone C surface geology is composed ofunconsolidated alluvial deposits of interbedded clay, silt, sand, gravel, and cobbles. Thedeposits compose the upper part of the High Plains Aquifer at FEW, which is the principalsource of water for most of the water-supply wells in the area near FEW. At FEW, theQuaternary deposits and the upper part of the Ogallala Formation compose the upper part ofthe unconfined High Plains aquifer. The depth to groundwater in Zone C wells measured in

June 1999 ranged from 1.60 to 38.08 feet below the top of casing elevation. Thegroundwater flow direction at LF-03 is east-northeast, toward Crow Creek, which isconsistent with results from prior investigations.

Saturated soil conditions were not observed in any of the excavated trenches or test pits performed within LF-03, all of which extended beyond the bottom of the waste material. Thewater table measured in the four landfill piezometers exceeded 25 feet bgs. Therefore, anunsaturated zone approximately 10- 15 feet thick underlies the landfill.

As part of the Zone C RI investigation, aquifer testing was performed to determine thehorizontal hydraulic conductivity in the vicinity of LF-03. Hydraulic conductivities fromslug testing ranged from 0.06 foot per day (ft/day) at well ET-1M to 7.7 ft/day at well206, averaging approximately 1.8 ft/day, and had a geometric mean of 0.60 ft/day. Assumingan effective porosity of 0.20 and a hydraulic gradient of 0.02, the calculated groundwatervelocities range from 2 feet per year (ft/yr) at well ET-1M to 282 ft/yr at well MW206,and average 66 ft/yr or 22 ft/yr based on the geometric mean. A pumping test was conductedat well 64 in November 1999, following completion of a step test. The drawdown versus timeresults indicated a limited horizontal influence for the pumping well. This limitedinfluence may be due to a restricted horizontal extent of water-bearing materials, lateralheterogeneity or possibly alluvial/fluvial channeling. Similar response was noted in theobservation wells OB-1 and MW196A. The hydraulic conductivity (K) calculated from the pumptest data averaged 2.1 ft/day. This is similar to the average hydraulic conductivity of1.8 ft/day determined from slug tests.

Groundwater elevations at five well clusters were compared to assess the potential for avertical component of flow. The vertical gradient was downward at the upgradient wellcluster MW64/MW196A/MW196 and upward at well clusters MW199/MW199MI/MW199D andET-1S/ET-1M/ET-1D, which are located near the downgradient extent of the plume. Gradients were variable in the three intermediate well clusters. The vertical gradient between themiddle and deep screened intervals at the MW209 well cluster was upward during bothrounds, thereby limiting the downward migration of dissolved phase TCE in this area. Atthe downgradient MW199 and ET-1 well clusters, during both rounds of sampling the relativevertical gradients were upward in all screened intervals. These upward gradients shouldlimit the downward migration of dissolved phase VOCs in the vicinity of these wellclusters. There are no indications that non- aqueous phase contaminants are present inZone C. Based on the distribution of vertical gradients observed between the upgradientwell MW64/MW196A/MW196 cluster and the ET-1 well cluster, it appears that the upland areanear LF-03 is an area of groundwater recharge and the downgradient area near Crow Creek isan area of groundwater discharge.

Stream flow data from the RI indicate that a portion of Crow Creek is a losing streamwithin Zone C. During both high flow and low flow stream gauging events, the stream flowgauged at locations C7 and C8 was approximately 40 percent lower than the stream flowmeasured at the upstream (C6A) gauging location, indicating that this is a losing reach ofCrow Creek. During both measurement events, there was a slight gain in flow betweengauging locations C7 and C8, indicating that this is a gaining reach.

Within the footprint of the excavated area at LF-03, subsurface soils were contaminatedwith low concentrations of VOCs, polychlorinated biphenyls (PCBs), and semi-volatileorganic compounds (SVOCs) that can be attributed to past waste management activities atZone C. Surface and subsurface soils within the excavated area were also contaminated withlow concentrations of metals, organochlorine pesticides, and SVOCs. All waste material and contaminated soil beneath the waste was excavated and disposed at the on- site waste co-location area in 2000.

A plume of groundwater contaminated with chlorinated VOCs originates in the south- central portion of LF-03 and extends east- northeast approximately one-half mile toward CrowCreek. TCE, cis-l,2-dichloroethene (DCE), and trans-l,2-DCE were the most frequentlydetected organic compounds. The maximum concentrations of these constituents along withthe MCLs under the Safe Drinking Water Act (SDWA) for TCE, cis-l,2-DCE, and trans-1,2-DCE

are summarized below. Both TCE and cis-1,2-DCE were present at levels that exceeded thedrinking water standards. The contamination is relatively shallow, with a maximum depth ofcontamination approximately 40 feet bgs. The TCE and cis-1,2-DCE plumes are shown onFigures 2-3 and 2-4, respectively.

Constituent Maximum Level Detected (ug/L)

MCLs (ug/L)

TCE 95 5

cis-1,2-DCE 129 70

trans-1,2-DCE 7.1 100

Because the contaminated soil was removed from Zone C in 2000, the current routes of human and environmental exposure to contamination within Zone C are limited to exposure to groundwater, either through ingestion or direct contact.

To assess potential impacts to Crow Creek from groundwater contaminants, a MODFLOW model was used by PES (1999b) to evaluate three remedial alternatives: (1) monitorednatural attenuation (MNA) with institutional controls, (2) partial source removal and MNAfor the groundwater plume with institutional controls, and (3) complete source removal andMNA for the groundwater plume with institutional controls. Since the entire landfill wasremoved in the second quarter of 2000, it is believed that the third alternative mostaccurately defines the current situation. The model was calibrated to site data throughMay 1999.

The model was initially run to analyze the site for 50 years from the current time.Because the extent of the TCE plume was negligible after the 50-year simulation, the30-year simulation period was used. The model predicts maximum TCE concentrations of up to50 ug/L in shallow groundwater in the vicinity of wells 209 and PES-IS after 10 years andpredicts the 1 ug/L isopleth will extend to Crow Creek. After 30 years, plumeconcentrations continue to decline to maximum concentrations of approximately 10 ug/L,with the center of mass located downgradient between wells PES- 6S and 203. In nocircumstance does the 5 ug/L isopleth reach Crow Creek and, although groundwaterunderlying the site discharges to Crow Creek, the modeling indicates that the groundwatercontaminant plume will probably not impact Crow Creek in the future at levels abovecurrent or proposed surface water standards (2.7 ug/L for TCE).

Detailed discussions of model development and assumptions are included in the PES (1999b) report, in the Final Remedial Investigation Report for Zone C, F. E. Warren Air ForceBase, Cheyenne, Wyoming (USAF 2000a) and in the Final Feasibility Study for Zone C, F. E.Warren Air Force Base, Cheyenne, Wyoming (USAF 2000b).

The conceptual site model for this site is presented in Section 1.2 of Appendix A.

2.6 CURRENT AND POTENTIAL FUTURE LAND AND WATER USES

2.6.1 Land Uses

Currently Zone C supports residential and open space uses. Zone C is bisected by HappyJack road and includes the FEW Carlin Heights housing area. Crow Creek constitutes thenorthern and eastern boundaries of this zone. Base property to the south of Happy JackRoad is undeveloped open space. Much of the southeast portion of Zone C was used in 1994as a source of cover soil for covering Landfill 8, located on the west central portion ofthe Base.

Current adjacent land use includes the small county residential area of Nob Hill to thesouth, additional portions of Carlin Heights housing area to the west, and open spaceareas to the north. I-25 separates the installation from other mixed industrial/

residential areas to the east.

The FEW General Plan depicts the future land use in Zone C as open space and possibly residential. Portions of Zone C are shown as a potential expansion area for the CarlinHeights housing area as depicted on Figure 2-5. This potential expansion appears to besouthwest of and partially co-located with the previously excavated LF-03. The finaldecision on the location and schedule for this expansion has yet to be made. The potentialfor risk related to indoor air in residences was evaluated in the Zone C RI (USAF 2000a)assuming a slab- on- grade construction. Previous construction of base housing at FEW(Carlin Heights) has been above grade with a crawlspace, which would have less potentialindoor air exposure than the slab-on-grade construction evaluated in the RI. In addition,no COPCs were identified in surface and subsurface soil during the RI and no VOCs wereidentified as COPCs with modeled air concentrations that exceeded screening levels.

Although not included in the Base General Plan, the southeast corner of Zone C, locatedsouth of Happy Jack road, is proposed for lease to the Wyoming Game and fish Departmentfor construction of a new state headquarters facility. The timing for completion of thelease and the timing of construction are still to be determined.

2.6.2 Groundwater and Surface Water Uses

Zone C groundwater is not used as a drinking water source. The groundwater is being usedonly for irrigation and livestock in Nob Hill. An alternative drinking water supply wasprovided for Nob Hill residents in January 1997. At that time, the residents were informedthat their wells should not be used for drinking water and should only be used forlivestock and irrigation. Also at that time, all of the houses were disconnected fromtheir wells, such that the water could not be conveyed directly into the house fordomestic use. Because the groundwater in Zone C has the capacity to be used for drinkingwater, groundwater at the site is a potential drinking water source.

According to Mr. Herman Noyes, Cheyenne BOPU (Noyes 2001), the BOPU uses both surface water and groundwater resources and the municipal water supply is secure into theforeseeable future, based on present predictions of population growth.

The only significant surface water in or near Zone C is Crow Creek. Crow Creek ispresently classified as a Class 3 surface water (supporting or having the potential tosupport non-game fish only) under the Wyoming Water Quality Rules and Regulations (Wyoming1999). However, proposed changes to the Wyoming surface water regulations would add ormodify standards and reclassify some streams in the state, including Crow Creek.Therefore, Crow Creek may be reclassified as Class 2AB surface water (potential drinkingwater source and known to support game fish) and would be subject to additional standards.

Anticipated groundwater migration has the potential to impact Crow Creek. However, fateand transport modeling (assuming no remedy is in place) indicates that the groundwatercontaminant plume will not impact Crow Creek above the Class 2AB surface water standards(e.g., 2.7 ug/L for TCE).

A groundwater seep is located immediately north of Happy Jack Road. The seep is small and rarely has standing water.

2.7 SUMMARY OF SITE RISKS

As part of the Zone C RI (USAF 2000a), a baseline human health risk assessment andecological risk assessment were conducted for FEW in accordance with EPA Region VIII andWDEQ guidance (Wyoming 1999). A baseline risk assessment is a scientific procedure thatuses facts and assumptions to estimate the potential for adverse effects on humans,plants, or animals from exposure to chemicals, assuming no cleanup occurs. A riskassessment is used to determine if a site requires cleanup. The baseline risk assessmentidentified no quantifiable risk within Zone C. However, because two contaminants

attributable to site activities, TCE and cis-1,2-DCE, were detected in concentrationsexceeding MCLs, actions to restore the groundwater to drinking water standards arerequired. The response action selected in this ROD is necessary to protect the publichealth or welfare or the environment from actual or threatened releases of hazardoussubstances into the environment. The response action selected is based on the results ofthe Zone C risk assessment (USAF 2000a) and guidelines presented in A Guide to Preparing Superfund Proposed Plans, Records of Decision, and Other Remedy Selection DecisionDocuments (EPA 1999).

2.7.1 Summary of Human Health Risk Assessment

The purpose of the baseline human health risk assessment is to estimate potential currentand future risks to public health from site- related chemicals assuming no remedialactions will be conducted. Exposure to chemicals in surface soil, subsurface soil,sediment, surface water, and groundwater are addressed. The results of the baseline humanhealth risk assessment for Zone C are summarized in Appendix A.

In summary, hazard/risk was quantified for recreational visitors (child/adult) exposed to sediment and surface water, youth residents exposed to sediment and surface water, and child/ adult residents exposed to groundwater. Utility workers were not evaluated becauseno contaminants of potential concern (COPCs) with toxicity values were identified insurface and subsurface soil.

All results for the recreational visitor and youth resident were below a hazard index (HI)of 1.0, the level below which effects are not expected to occur, and within or below EPA'starget cancer risk range of 1E-06 to 1E-04. It should be noted that the State of Wyoming'scriterion for acceptable lifetime excess cancer risk is 1E-06. The reasonable maximumexposure (RME) HI for the hypothetical resident (adult/child) was 3.0, and the estimatedpotential cancer risk was at 9E-05. The pathway contributing the highest potential riskwas the hypothetical ingestion of groundwater. TCE and arsenic were the biggest potentialrisk drivers, while a combination of the inorganics, particularly thallium, contributed toraising the HI above 1.0. The potential HI and risk to a residential receptor fromexposure to groundwater via the dermal and inhalation pathways is reduced to 4E-08 and2E-07. This assumes that drinking water would be obtained from a different source and thatgroundwater would only be used for bathing.

Site risks for carcinogens and noncarcinogens are presented in Tables A-3 and A-4, respectively.

A groundwater seep was identified in a drainage ditch along Happy Jack Road after the ZoneC RI (USAF 2000a) was submitted. This seep is located on the north side of Happy JackRoad, north of the Nob Hill subdivision. In the second quarter of 2000, a grab sample wascollected from the seep and analyzed for VOCs to assess whether contaminants were present.Because validated analytical results of sufficient quality were not available for theseep, contaminant concentrations in the seep were conservatively assumed to be identicalto those in an upgradient well, MW-210. This approach eliminated potential data qualityconcerns with the grab sample from the actual seep. The supplemental risk assessment andenvironmental evaluation presented in Appendix B indicate there are no significant humanhealth or ecological concerns from potential exposure to seep water in the Happy Jack Roadditch. The total RME cancer risk for a highway maintenance worker was estimated to be1E-08 and the total central tendency exposure (CTE) cancer risk was estimated to be 2E-09.The total RME and CTE non-carcinogenic HI, for all exposure pathways are 8E-04 and 3E-04,respectively.

2.7.2 Summary of Ecological Risk Assessment

The purpose of the baseline ecological risk assessment is to estimate potential risks tothe environment from site-related chemicals assuming no remedial actions will be taken.The results of the ecological risk assessment are used to identify chemicals and exposurepathways that need to be addressed by the remedial action. The results of the baseline

ecological risk assessment for Zone C are summarized in Appendix A.

In brief, based on hazard quotients (HQs) calculated for ecological receptors exposed tosurface soil, chromium and vanadium may present a risk to the terrestrial receptors inZone C. However, as a result of several compounding conservative assumptions used in theecological risk assessment, it appears that the small mammal and avian populations areunlikely to be at any appreciable risk from exposure to concentrations of site-relatedinorganic compounds.

Plants in Zone C exposed to concentrations of chromium and vanadium in surface soils may experience adverse effects. The HQs for chromium and vanadium slightly exceeded 1.0. However, the significance of these apparent risks to plants cannot be determined in viewof unknown soil pH values, which directly affect the bioavailability of chromium andvanadium to plants.

HQs were calculated for exposure of terrestrial plants to constituents in subsurface soilfrom the test pit/test trench samples. All HQs were below 1.0 for subsurface soil. Becausetoxicity reference values (TRVs) for terrestrial plants are not available for DDD, DDT,and benzoic acid, HQs were not calculated for these constituents. Therefore, additionaldata are required to assess the potential risk to plants from these constituents

In Crow Creek sediment, it is unknown whether four of the nine COPCs(1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, p-cymene, and cyanide) present anunacceptable risk to benthic macroinvertebrates. This uncertainty is based on the absenceof published sediment quality values (SQVs). However, it is unlikely that Zone C is thesource of these compounds found in Crow Creek sediment. Groundwater discharge to surfacewater is the expected principal pathway from LF-03 to Crow Creek. Of these compounds, only1,2,4-trimethylbenzene was detected in groundwater in two of the 65 samples analyzed. Inaddition, cyanide was detected in only four of the 65 groundwater samples analyzed.Concentrations of the six other COPCs (1,3-dichlorobenzene, 4,4'-dichloro-2,2-bis(p-cnlorophenyl) ethylene [4,4'-DDD], 4,4'-dichlorodiphenyltrichloroethane [4,4'-DDT], bis(2-ethylhexyl) phthalate, toluene, and arsenic) in sediment do not exceedavailable SQVs and are unlikely to present an unacceptable risk.

Based on the available sediment data, it is possible that the benthic macroinvertebratesare at some unquantifiable risk from the constituents for which there are no sedimentbenchmarks. However, because of the absence of SQVs for several sediment COPCs, theoverall health of the benthic community cannot be determined with the chemical datacurrently available. This issue will be evaluated further in the ongoing Basewide SurfaceWater Risk Assessment (OU 2).

In surface water, it is unknown whether seven of the eight COPCs (1,2,3-trichlorobenzene, 1,2,4-trimethylbenzene, n-butylbenzene, s-butylbenzene, t-butylbenzene, p-cymene, andnitrate) present an unacceptable risk to aquatic receptors. This uncertainty is based onthe absence of published water quality values (WQVs) for these compounds. However, ofthese organic compounds, only 1,2,3-trichlorobenzene and 1,2,4-trimethylbenzene weredetected in groundwater, the expected principal pathway from LF-03 to Crow Creek.1,2,3-Trichlorobenzene was detected in only one of 64 groundwater samples analyzed. Inaddition, 1,2,4-trimethylbenzene was detected in only two of the 65 groundwater samplesanalyzed. Although mercury may present risk to aquatic receptors, it should be noted thatthe HQ for mercury is estimated from one- half of an elevated reporting limit. The maximumdetected concentration of mercury is 0.00005 milligram per liter (mg/L), which produces anHQ of 4.2. This slight exceedance is not likely to present significant ecological risk toaquatic receptors.

Contaminated groundwater associated with the seep was evaluated and found to pose no unacceptable risk. Details can be found in Appendix B.

2.8 REMEDIAL ACTION OBJECTIVES

The remedial action objectives (RAOs) for this site are to:

• Remove all source material to eliminate direct exposure to hazardous material andpotential sources of further contamination,

• Restore the aquifer to drinking water standards,

• Eliminate potential exposure to groundwater contaminated with VOC concentrationsgreater than drinking water standards, and

• Limit contaminant migration to the surface water to levels that ensure thebeneficial use of this resource.

The NCP states the expectation that groundwater will be restored to beneficial use.

The preferred alternative will address the soil and groundwater contamination within ZoneC. All waste and associated soil within LF-03 was excavated during 2000 to remove anysources that may have been present in the landfill, in accordance with the ActionMemorandum for the site. By achieving clean closure of LF-03, the RAO of source removal toeliminate direct exposure to hazardous material and potential sources of furthercontamination will be achieved. The RAO of eliminating potential exposure to groundwatercontaminated with VOCs greater than drinking water standards is addressed by providing NobHill residents with municipal water supplies. At the completion of the preferredalternative, the aquifer will have been remediated to drinking water standards. Together,these actions will result in elimination of potential exposure to groundwater contaminatedwith VOC concentrations greater than drinking water standards.

The general RAO for groundwater is to restore it to beneficial use. An additional generalRAO for groundwater is to prevent contaminants from affecting Crow Creek above surfacewater quality rules. Based on these objectives, the preliminary remediation goals (PRGs)for this site are 5 ug/L for TCE, 70 ug/L for cis-1,2-DCE, 100 ug/L for trans-1,2-DCE, and2 ug/L for vinyl chloride. These are the drinking water MCLs for these contaminants andare protective of human health.

2.9 DESCRIPTION OF ALTERNATIVES

As described in the Zone C FS, the following groundwater remedial alternatives passed the preliminary screening and were evaluated in detail:

• Alternative 1 - No action, • Alternative 2 - Institutional controls, • Alternative 3 - MNA, • Alternative 4 - Hot spot extraction/treatment, • Alternative 5 - Entire plume extraction/treatment, • Alternative 6 - Permeable reactive barriers, and • Alternative 7 - Nob Hill extraction/treatment and main plume MNA.

The primary components of these alternatives are presented below. As source removalactivities and the provision of alternate water supplies have already been completed, thealternatives evaluated in the FS focused on addressing groundwater contamination. Thealternatives are numbered to correspond with the alternatives presented in the Zone Cgroundwater FS. The sections following the description of remedy alternatives provide theevaluation of each alternative relative to the criteria given in EPA's RI/FS guidance (EPA1988) and in the NCP [40 Code of Federal Regulations (CFR) 300.430(f)(5)(i)].

Certain elements are common to all remedial alternatives. Because each alternativereviewed will result in hazardous substances, pollutants, or contaminants remaining

on-site above levels that allow for unlimited use and unrestricted exposure, a statutoryreview will be conducted within 5 years after initiation of remedial action and every 5years until remedial goals are reached to ensure that the selected remedy is, or will be,protective of human health and the environment.

In addition, all of the alternatives except Alternative 1 - No Action would be subject to institutional controls and long- term monitoring. Institutional controls for the on- baseportion of the site would include restrictive notices incorporated by USAF into the FEWGeneral Plan to prevent groundwater usage. The Installation Commander is responsible fordeveloping, maintaining and implementing the General Plan. The General Plan includes a mapregarding IRP sites and a section that highlights critical areas having limited orspecialized development potential and factors these into the planning process for theBase. For the portion of the Zone C plume that extends into the Nob Hill subdivision,other institutional controls will be implemented

to restrict exposure to contaminated groundwater. These include the restrictions throughthe user Water Services Agreements signed by each Nob Hill property owner that wereimplemented by the Cheyenne BOPU concurrent with installation of the new water line tosupply Nob Hill residents with city water. Line item 7 of the agreement states, "Nodrilling of water wells will be allowed within said property so long as water service isfurnished by the BOPU or its successors."

In addition, Nob Hill residents will be notified periodically by the USAF, County Health Department or other county agency that the groundwater is unfit for human consumption. A component of long-term operation, maintenance, and monitoring of the final LF-03 remedywill be a certification by a Wyoming-registered professional engineer or geologist (PE orPG), that the institutional controls are still in place. None of the alternatives wouldresult in off-site water discharge. All of the remedial alternatives have been implementedat full scale elsewhere and represent proven technologies.

2.9.1 Description of Remedy Alternatives

Alternative 1 - No Action

• Baseline comparison alternative required by the NCP - no controls, monitoring orother components.

Alternative 2 - Institutional Controls

• Implementation and enforcement of administrative controls, including:

- Restrictive notices incorporated by USAF into the FEW General Plan to prevent groundwater usage. The Installation Commander is responsible for developing, maintaining and implementing the General Plan. The General Plan includes a map regarding IRP sites and a section that highlights critical areas having limited or specialized development potential and factors these into the planning process for the base, and

- Issuance of periodic Advisory Notices by USAF, County Health Department, or another county agency to Nob Hill residents stating that the groundwater is not suitable for domestic use.

Alternative 3 - Monitored Natural Attenuation (MNA)

• Periodic monitoring of wells within and outside the current plume area untilremedial goals are reached in approximately 49 years.

• Institutional controls implemented as described in Alternative 2.

Alternative 4 - Hot Spot Extraction/Treatment

• A series of groundwater extraction wells placed along the centerline of the plume.

• Extracted groundwater will be treated on- site to remove VOCs by a proventechnology. The treatment technology will be selected during the remedial designphase of the process from among the four presumptive remedies for treatment ofgroundwater contaminated with VOCs. These are air stripping, carbon adsorption,chemical/UV oxidation, and aerobic biological reactors. For costing purposes, airstripping was assumed to be part of the final remedy.

• Treated groundwater will be discharged to the surface downgradient of Nob Hill,reinjected into the aquifer, or discharged to a publicly owned treatment works. Theeffluent discharge option will be selected during the remedial design phase of theprocess. For costing purposes surface water discharge was assumed to be a part ofthe final remedy.


• System performance checks.

• Continuous performance monitoring until remedial goals are reached in approximately29 years.

Alternative 5 - Entire Plume Extraction/Treatment

• Groundwater extraction wells placed at locations selected to capture the entire areaof the contaminated groundwater plume.

• Extracted groundwater treated on- site to remove VOCs by a proven technology. Thetreatment technology will be selected during the remedial design phase of theprocess from among the four presumptive remedies for treatment of groundwatercontaminated with VOCs listed in Alternative 4. For costing purposes, air strippingwas assumed to be part of the final remedy.

• Treated groundwater will be discharged to the surface downgradient of Nob Hill,reinjected into the aquifer, or discharged to a publicly owned treatment works. Theeffluent discharge option will be selected during the remedial design phase of theprocess. For costing purposes, surface water discharge was assumed to be a part ofthe final remedy.




Alternative 6 - Permeable Reactive Barriers (PRB)

• Use of permeable walls containing a reactive medium (usually iron) to treat thecontaminants. The number, locations and construction methods will be determinedduring the remedial design phase. For evaluation purposes, it was assumed one PRBwould be located immediately upgradient of Nob Hill and another at the toe of plumenear Crow Creek.

• Barrier is installed in the saturated zone below the ground surface andperpendicular to the groundwater flow direction at a depth that will intercept allcontamination above MCLs.

• Contaminated groundwater flows through the barrier and into the treatment medium,and the contaminants are reduced to nontoxic byproducts.



Alternative 7 - MNA and Nob Hill Extraction/Treatment

• Groundwater extraction wells placed at locations selected to capture the portion ofthe contaminated groundwater plume moving off-site into the Nob Hill subdivision.

• Extracted groundwater treated on- site to remove VOCs by a proven technology. Thetreatment technology will be selected during the remedial design phase of theprocess from among the four presumptive remedies for treatment of groundwatercontaminated with VOCs listed in Alternative 4.

• Treated groundwater will be discharged to the surface downgradient of Nob Hill,reinjected into the aquifer, or discharged to a publicly owned treatment works. Theeffluent discharge option will be selected during the remedial design phase of theprocess.

• MNA as described in Alternative 3 for the "main plume" portion of the site.




2.9.2 Distinguishing Features of Each Alternative

The primary differences between alternatives are in their estimated costs and estimatedtime to achieve the RAOs or cleanup levels. These are summarized in Table 2-1. Thealternatives also vary in estimated time required for design and construction, withAlternatives 4 and 5 having longer lead times. The applicable or relevant and appropriaterequirements (ARARs) vary slightly by alternative. The extraction and treatment options(Alternatives 4, 5 and 7) will have to meet ARARs associated with bringing water andcontaminants to the surface (e.g., ARARs associated with air emissions and/or surfacewater discharges). The PRB and the extraction and treatment options will actively reducethe toxicity, mobility and volume of contaminants. Alternative 6 (PRB treatment) is theonly alternative that incorporates innovative technology.

Expected Outcome of Each Alternative All the alternatives will eventually provide groundwater that meets drinking waterstandards. The time frame to accomplish this varies considerably among the alternatives,as seen in Table 2-1. Upon the completion of each alternative, the land and groundwatercan be used without restriction. During the remedial action time period, land andgroundwater can be used only as provided for in the Base General Plan and otherinstitutional controls, which are common to all alternatives except Alternative 1 - NoAction. During the implementation phase, the areas of the former landfill that do notoverlie the contaminant plume may be used without restriction. Areas overlying the plumewill require restrictions on construction during implementation to prevent exposure tocontaminants. In addition, no groundwater can be extracted for human consumption from theplume area until the RA is complete. A potential benefit of all the alternatives is theability to expand the Carlin Heights residential area upon completion of the remedialaction. Another potential benefit of the extraction and treatment options (Alternatives

4, 5 and 7) is the potential to create a pond with treated discharge for the aestheticbenefit of a proposed Fish and Game facility in the southeast corner of the Base.

2.10 COMPARATIVE ANALYSIS OF ALTERNATIVES

The remedial alternatives were evaluated using criteria given in EPA guidance (EPA 1988)and in the NCP [40 CFR 300.430(f)(5)(i)] to determine which would be most protective ofhuman Final Zone C Record of Decision F. E. Warren Air Force Base Cheyenne, Wyoming health and the environment, cost effective, and easiest to implement. The cleanup methods evaluated for Zone C are described in Section 2.9. The clean-up method selection andscreening process are described in detail in the FS (USAF 2000b).

To comply with the NCP, the EPA criteria must be applied to all remedial alternatives.These criteria, as given in Guidance for Conducting RI/FSs Under CERCLA (EPA 1988) and theNCP [40CFR 300.430(f)(5)(i)] fall into three categories: threshold criteria, balancingcriteria and modifying criteria. The following table summarizes the nine criteria withinthese broad categories:

EVALUATION CRITERIA FOR SUPERFUND REMEDIAL ALTERNATIVES

Threshold Criteria - Criteria must be metbefore analternative can beconsidered as aremedy

Overall Protection of Human Health and the Environment determines whetheran alternative eliminates, reduces, or controls threats to public healthand the environment through institutional controls, engineering controls,or treatment.

Compliance with ARARs evaluates whether the alternative meets federal andstate environmental statutes, regulations, and other requirements thatpertain to the site, or whether a waiver is justified.

Balancing Criteria- Relative tradeoffsbetween differentcriteria areevaluated

Long-Term Effectiveness and Permanence considers the ability of analternative to maintain protection of human health and environment overtime.

Reduction of Toxicity, Mobility, or Volume of Contaminants ThroughTreatment evaluates an alternative's use of treatment to reduce theharmful effects of principal contaminants, their ability to move in theenvironment, and the amount of contamination present.

Short-term Effectiveness considers the length of time needed to implementan alternative and the risks the alternative poses to workers, residents,and the environment during implementation.

Implementability considers the technical and administrative feasibility ofimplementing the alternative, including factors such as the relativeavailability of goods and services.

Costs includes estimated capital and annual operations and maintenancecosts, as well as present worth cost. Present worth cost is the total costof an alternative over time in terms of today's dollar value. Costestimates are expected to be accurate within a range of +50 to -30percent.

Modifying Criteria - Evaluate whetherremedy is supportedby state andcommunity after thepublic comment period

State/Support Agency Acceptance considers whether the State agrees with oropposes the preferred alternative. WDEQ reviews and comments upon allimportant documents throughout the process.

Community Acceptance considers whether the local community agrees with oropposes the preferred alternative. Comments received on the Proposed Planare an important indicator of community acceptance.

The EPA criteria were applied to the evaluations of potential cleanup methods. For adetailed discussion of the comparative analysis of alternatives, please refer to the FSReport (USAF 2000b). The FS was made available to the public on December 21, 2000. TheProposed Plan provided the community a second opportunity to comment (between March 12through April 11, 2001) on the proposed clean-up methods.

The tables presented in this section list the alternatives considered feasible based ondata available at the time of the FS. Estimated costs and the preferred alternatives arepresented. The preferred alternatives provide the best balance of tradeoffs among thealternatives with respect to the evaluation criteria. The USAF expects the preferredalternatives will satisfy the statutory requirements in CERCLA Section 121(b) that theselected alternatives:

• Be protective of human health and the environment, • Comply with ARARs, • Be cost-effective, • Utilize permanent treatment alternatives, and • Satisfy the statutory preference for treatment.

The comparative analysis for selection of the preferred cleanup method for Zone C is summarized in the following sections and in Tables 2-1 and 2-2.

Overall Protection of Human Health and Environment

All alternatives, with exception of Alternatives 1 and 2, are protective of human healthand the environment. Alternative 1 will not adequately protect future potentialgroundwater users since no action will be taken to restrict exposure to contaminatedgroundwater. Alternative 2, Institutional Controls, eliminates the groundwater pathway onbase, but will not adequately protect future Nob Hill groundwater users, since nomonitoring program will be implemented. Alternative 3, MNA, eliminates the groundwaterpathway on base via institutional controls and will protect future Nob Hill groundwaterusers through a groundwater monitoring program that will confirm the continued lack ofexposure to contaminants. This conclusion is supported by groundwater modeling results.The alternatives that include active remedial systems for the plume (i.e., Alternatives4,5,6, and 7), are protective of human health and the environment since the activeremedial systems will remove contamination from groundwater before it reaches Crow Creek and/or migrates off-site. For these alternatives, on base exposure to groundwater contamination is mitigated by use of institutional controls. In all cases, there isminimal environmental risk.

Compliance with ARARs

The key ARARs relevant for all alternatives are compliance with state and federalgroundwater standards. All the alternatives, except Alternatives 1 and 2, will eventuallyprovide for groundwater that meets drinking water standards. Although Alternatives 1 and 2might eventually reach drinking water standards, there is no monitoring associated withthese alternatives so compliance with ARARs can not be verified. For the groundwaterextraction and treatment alternatives (Alternatives 4, 5 and 7), additional ARARs arefederal and state air quality standards and those which relate to surface discharge oftreated water if the treatment method results in air emissions or surface waterdischarges. The specific state ARARs for air quality that are relevant are Wyoming AirQuality Standards and Regulations, Chapters 5 and 6. Because of the low emissions of TCEand other VOCs potentially discharged by an air stripper, these rules will be met.Similarly, federal rules for the National Priority and Secondary Ambient Air QualityStandards (40 CFR 50), and National Emission Standards for Hazardous Air Pollutants (40CFR 60, 61 Part A) are identified as ARARs. The ARARs that govern injection of treatedgroundwater are primarily the Wyoming Water Quality Rules and Regulations, Chapters II andIII. The groundwater treatment system will be designed to ensure the system will meet thesubstantive requirements of these ARARs. The PRB alternative (Alternative 6) and all the

other alternatives that generate solid waste will also meet the substantive requirements of Wyoming Solid Waste Management Rules and Regulations, Chapters I and XV. None of the alternatives is anticipated to generate hazardous waste; however, if hazardous waste isgenerated, it will be managed such that the substantive requirements of the WyomingHazardous Waste Rules and Regulations, Chapters 1, 2, 8, 9, 11, and 13 are met. Thus, allalternatives meet the threshold criterion of meeting ARARs.

Long-Term Effectiveness and Permanence

Since each alternative will continue until groundwater within the plume meets the RAOs,all alternatives will have similar residual risks upon completion of the remedial actions.Therefore, the evaluation of this criterion hinges on the reliability and adequacy of thecontrols that are implemented. The reliability and adequacy of the first threealternatives are much lower than for the remaining four alternatives.

The No Action alternative is weakest in this regard because there will be neither further institutional controls nor active remediation that will ensure exposure to contaminated groundwater will be reduced or eliminated. Without further institutional controls oractive remediation, there is the possibility that site activities could result in exposureto groundwater above the RAOs. Thus, the reliability and adequacy of controls for the NoAction alternative are relatively poor. Alternative 2, Institutional Controls, includesmultiple mechanisms to ensure no further exposure to groundwater occurs, and therefore thereliability of the controls is judged to be fair. However, the alternative neitheractively remediates contamination nor demonstrates that contaminants are being attenuated.The reliability and adequacy of controls for Alternative 3, MNA, are better thaninstitutional controls alone because monitoring as part of MNA will conclusivelydemonstrate that contamination is being attenuated via natural processes.

The reliability of the four treatment alternatives in meeting restoration goals differsfrom their reliability in meeting treatment and containment goals. The pumpingalternatives (Alternatives 4, 5, and 7) rely on extraction of contaminated groundwater torestore the aquifer. Because of hydrogeologic uncertainties, it is possible thatadditional wells or alternate pumping strategies may be necessary to achieve restorationgoals. Alternative 6, PRBs, will reliably restore the aquifer provided site hydrogeologicand contaminant distribution are well defined. Significant changes in the understanding ofhydrogeology and/or contaminant distribution can impact the reliability of this technologyto meet restoration goals.

The O&M requirements of the pumping alternatives (Alternatives 4, 5, and 7). are slightlyhigher than those for PRBs, but these systems can be easily adapted for minor changes inthe understanding of site hydrogeologic and contaminant distribution. Modifying PRBs afterinitial installation to correct for changes in the understanding of site conditionstypically requires more effort than incrementally modifying an extraction and treatmentsystem. In addition, the estimated life span of the reactive media is approximately 15years; the reactive media will need to be replaced at least once during the duration ofthe project.

Reduction of Toxicity, Mobility, or Volume Through Treatment

The alternative that best satisfies this criterion is Alternative 6, PRBs, because thistechnology destroys the chemical contaminants. Destruction efficiencies of thisalternative are expected to exceed 99 percent. Alternatives 1 and 2, No Action andInstitutional Controls, respectively, do not meet this criterion because the naturalprocesses that mitigate toxicity, mobility and volume will not be monitored or measured.Alternative 3, MNA, minimally meets this criterion since the natural processes thatattenuate the plume act very slowly on this site. Groundwater modeling results estimatethat MNA will eventually reduce the mass of contaminants by about 75 percent, but over avery long period (30 years or more).

The extraction and treatment alternatives are effective in reducing mobility and volumevia hydraulic capture and contaminant removal from groundwater. Based on modeling, it is expected that the contaminant mass within the plume will be reduced by greater than 95percent for all alternatives. Removal of contaminants from the extracted water is over99.9 percent for the treatment alternatives evaluated. Some of the technologies evaluated,however, primarily transfer contaminants from water to air. The VOCs that are emitted tothe atmosphere photolytically degrade, and thus there is an indirect reduction incontaminant toxicity.

Based on this analysis, Alternative 6 is most effective, followed by Alternatives 4, 5,and 7. Alternative 3, MNA, is the next most effective at meeting this criterion. MNAactively assesses the extent to which natural processes are reducing the toxicity,mobility and volume of the contamination. Alternatives 1 and 2 are least effective inmeeting this criterion because they rely solely on natural processes that work very slowlyon this site and do not attempt to monitor the mechanisms or rates of the reduction ofcontaminant toxicity, mobility and volume.

Short-Term Effectiveness

Alternatives 4, 5, 6, and 7 best meet the short-term effectiveness criterion. All thesealternatives will protect the community via treatment of groundwater moving off-site intothe Nob Hill area and will eliminate on-base exposure to contamination through acombination of institutional controls and active remediation. Alternative 2, InstitutionalControls, and Alternative 3, MNA, have the next highest short-term effectiveness,eliminating on-base and community exposures through institutional controls. The No Actionalternative has the least short-term effectiveness because it does not implement furtherrestrictions to Zone C activities that could lead to exposure to contamination. Workerswill be protected from exposure during implementation of all alternatives through the useof proper site controls and personal protective equipment.

The ecological impacts associated with this site are minimal for all alternatives. Thebaseline ecological risk assessment did not identify any ecological risks associated withTCE or cis-1,2-DCE. The construction activities associated with implementation of theactive remedial systems will be minimal. The greatest ecological impacts will be for theinstallation of the PRBs under Alternative 6. The next highest impacts will be for theinstallation of wells under Alternatives 4, 5, and 7. Alternative 3 has minimalenvironmental impacts associated with groundwater sampling.

The time for remediation for Alternatives 1, 2, 3, and 6 is 49 years, based on groundwater modeling. The reason for this consistency is that all these remedial alternatives rely onthe groundwater to either naturally degrade or migrate to the PRB. Alternative 5,extraction of the entire plume, has the shortest remediation time at 15 years. Alternative4 is the next shortest time at 29 years. Alternative 7, MNA with Nob Hill extraction, hasa total remediation time of 44 years.

Implementability

All of these alternatives can be implemented, and there are no exceedingly difficulttechnical challenges to overcome for any of these options. However, Alternatives 1 and 2,while technically implementable, fail to meet the threshold criteria of overall protectionof human health and the environment. Therefore, these may not be able to be implemented administratively. From a technical standpoint, Alternative 1 is the simplest to implement. Alternative 2 is the next easiest to implement and requires only administrative tasks. Alternative 3 is the next easiest to implement because it includes the implementation of institutional controls and groundwater sampling. Alternatives 4, 5, and 7 are judged to beharder to implement than Alternative 3 because they entail the installation of wells andthe construction of a treatment system. Alternative 6 is the most difficult to implementbecause of the challenges associated with installing PRBs in relatively deep trenches. Inaddition to being somewhat more technically challenging, the depth of the trenchingrequired will reduce the number of firms that can implement this option, although there

are still many contractors who have deep trenching capabilities.

Cost

The cost of alternatives was compared using four different cost perspectives for eachalternative: capital costs, O&M costs, periodic costs, and total net present value (NPV)costs, assuming a 5 percent discount rate. After Alternative 1, the No Action alternative,Alternative 2, Institutional Controls, is the lowest cost alternative followed byAlternative 3, MNA, for both capital and O&M costs. Alternatives 4, 5, 6 and 7 aresubstantially more expensive in terms of NPV, with the least expensive active remediation(Alternative 4, Hot Spot Extraction and Treatment) double that of MNA. The substantiallyhigher costs are the result of both higher capital costs and higher O&M costs. Of theactive alternatives, Alternatives 4 and 7 have the lowest NPVs, with estimates within 0.5percent of one another. Alternative 6, PRBs, has the highest O&M cost of any alternative,primarily due to the anticipated replacement of the entire reactive media after 9 years ofoperation. Table 2-1 includes cost comparisons of all alternatives across all four cost perspectives.

2.11 PRINCIPAL THREAT WASTES

The NCP establishes an expectation that treatment will be used to address the principalthreats (i.e., source material that is highly toxic and/or highly mobile) posed by a sitewherever practicable. No highly toxic or highly mobile source material was ever identifiedat LF-03 during site investigations. Therefore, no principal threat wastes were identifiedwithin Zone C. However, all landfill waste and the associated soil immediately below itwere removed in March and April 2000 and disposed on-site in the waste co-location area,thereby eliminating the waste as a primary risk as well. The continuing primary risk inZone C is groundwater, which Alternatives 3,4, 5, 6, and 7 address.

2.12 SELECTED REMEDY

2.12.1 Summary of Rationale for Selected Remedy

The USAF has selected groundwater extraction and treatment, Alternative 5, Entire Plume Extraction/Treatment, as the cleanup method for VOC-contaminated groundwater in Zone C atFEW. Based on the comparative analysis in Section 2.10, the preferred alternative wasselected over the other alternatives because it will provide the greatest overall benefitwhen evaluated against the nine criteria. It is the most cost-effective of thealternatives that actively remediate the main plume portion of the site and obtainsclean-up levels in the shortest amount of time. It is protective of human health and theenvironment and complies with all ARARs. It will achieve risk reduction through treatmentof contaminants in the groundwater and provides measures to prevent future exposure tocurrently contaminated groundwater.

Based on the information available at this time, the USAF, EPA and WDEQ believe the preferred alternative will be protective of human health and the environment, will complywith ARARs, will be cost-effective and will use permanent solutions to the maximum extentpossible. Because it will treat the contaminants constituting the primary risk at the site(groundwater), the remedy will also meet the statutory preference for the selection of aremedy that includes treatment as a principal element.

2.12.2 Description of the Selected Remedy

As stated above, the selected remedy is extraction and treatment of the entire groundwater plume. The primary features of this remedial alternative include:

• Installation of wells within the contaminated groundwater plume. These wells will beinstalled to depths that will intercept all on- site areas with contamination abovethe TCE MCL of 5ug/L.

• Treatment of groundwater to remove VOCs by a proven technology. The treatmenttechnology will be selected during the remedial design phase of the process.Technologies to be evaluated include air stripping, carbon adsorption, chemical/UVoxidation and aerobic biological reactors.

• Treated groundwater will be discharged to the surface, reinjected into the aquifer,or discharged to a publicly owned treatment works. The effluent discharge optionwill also be selected during the remedial design phase of the process.

• During implementation, institutional controls will protect human health and theenvironment by limiting exposure to contaminated groundwater. Institutional controlsfor this site include:

- Restrictive notices incorporated by the USAF into the FEW General Plan to prevent groundwater usage. The Installation Commander is responsible for

developing, maintaining and implementing the General Plan. The General Plan includes a map of IRP sites and a section that highlights critical areas having limited or specialized development potential and factors these into the planning process for the base, and

- Issuance of periodic Advisory Notices by USAF, County Health Department, or another county agency to Nob Hill residents stating that the water is not suitable for domestic use to limit exposure to contaminated groundwater.

- Limiting access to the remedy equipment and monitoring network to authorized personnel only, and

- Annual review of the Base General Plan to ensure appropriate maintenance of the institutional controls.

Additionally, the selected remedy includes the following actions that have already been completed:

• Addition of an alternate water supply for Nob Hill residents (an interim actioncompleted in January 1997), and

• Removal of all waste from LF-03 (a non-time-critical removal action completed in2000).

Periodic monitoring will be performed to demonstrate the effectiveness of the RA. A performance monitoring plan is a component of the groundwater extraction and treatment alternative. The performance monitoring plan will be developed in conjunction with the remedial design and will describe a groundwater monitoring program that is based oncurrently available site data and that extends over a 15-year period.

The groundwater extraction and treatment system will be expected to achieve theoperational goals in approximately 15 years. Therefore, the proposed performancemonitoring program sampling frequency is based on a 15-year monitoring period. Abovegroundtreatment system samples will be collected routinely during the 15-year operational lifeof the treatment system.

All sampled locations will be analyzed for an appropriate analytical suite, which will bedefined in the remedial design phase. Sampling and analysis will be performed to determinethe groundwater extraction and treatment system's effectiveness at achieving remediationgoals for the site. Water quality parameters will be measured from monitoring welllocations to verify that collected samples are taken from the same groundwater source. Theperformance program will be reviewed and may be changed accordingly as new data areobtained during the 15-year operating and monitoring period.

2.12.3 Summary of Estimated Remedy Costs

The costs associated with the selected remedy are summarized in Table 2-3. These costs are based on the best available information regarding the anticipated scope of the remedial alternative. Changes in the cost elements are likely to occur as a result of newinformation and data collected during engineering design of the remedial alternative.Major changes may be documented in the form of a memorandum in the Administrative Recordfile, an Explanation of Significant Differences, or a ROD amendment. This is an order- of-magnitude engineering cost estimate that is expected to be within -30 to +50 percent ofthe actual project cost.

2.12.4 Expected Outcomes of Selected Remedy

It is expected that once clean closure has been established for the LF-03 excavation,unrestricted use of the surface area for residential, industrial or recreationalactivities would be allowed. Clean closure certification is expected in late 2001. It isalso expected that the use of groundwater as a drinking water source may be allowed uponreaching the cleanup level of 5 ug/L of TCE. This cleanup level is expected to be reachedby the end of the fifteenth year of treatment. Finally, it is possible that during thetreatment process ponds or wetlands could be created at the discharge point for thetreated water. It is unknown whether these environmental enhancements will continue toexist once the treatment system is shut down. At this time FEW does not anticipate takingactions to augment the flow of water to these areas after project completion.

2.13 STATUTORY DETERMINATION

The USAF has selected groundwater extraction and treatment (Alternative 5, Entire Plume Extraction/Treatment) as the preferred alternative for cleaning VOC- contaminatedgroundwater in Zone C at FEW. The EPA and WDEQ concur with this selected remedy.

This ROD incorporates by reference the comparative analysis of the nine criteria set forthin Table 5-3 of the FS (USAF 2000b) as the basis for its remedy selection pursuant to theNCP, 40 CFR 300.430(e)(9)(iii) and 300.430(f)(4). According to the NCP preamble, the nineevaluation criteria give effect to the statutory mandates of Section 121 of CERCLA, and inparticular, the remedial action factors of Section 121(b)(l)(A)-(G); an analysis performedpursuant to the nine criteria concludes with selection of a remedy that meets thestatutory mandates.

Under CERCLA Section 121 and the NCP, the lead agency must select remedies that are protective of human health and the environment, comply with ARARs (unless a statutorywaiver is justified), are cost-effective, and utilize permanent solutions and alternativetreatment technologies or resource recovery technologies to the maximum extentpracticable. In addition, CERCLA includes a preference for remedies that employ treatmentthat permanently and significantly reduces the volume, toxicity, or mobility of hazardouswastes as a principal element and a bias against off-site disposal of untreated wastes.

2.13.1 Protection of Human Health and the Environment

Alternative 5 will protect human health and the environment by treating TCE-contaminated groundwater using groundwater extraction wells and a treatment system. The remedial action will reduce TCE concentrations in groundwater to MCLs as the extraction and treatmentinduces water flow through the aquifer, replacing contaminated water with "clean" water.In addition, the preferred alternative is a hydraulic containment system, usinggroundwater extraction from wells to prevent further migration of contamination beyond thepresent lateral extent. This hydraulic control/containment serves to curtail off-sitemigration of TCE or continued migration toward Crow Creek.

Currently, groundwater at Nob Hill is being used for irrigation and livestock. On-base groundwater at Zone C is not being used. There will be minimal risk to human health and

the environment during construction, operation, and maintenance of the selected remedy.Strict adherence to health and safety protocols and monitoring will minimize risk fromVOCs, dust, and noise.

2.13.2 Compliance with ARARs

The groundwater extraction and treatment system will comply with all ARARs. The ARARs are briefly described below and are presented in more detail in Table 2-4, which also listsother criteria, advisories, or guidance to be considered (TBC) for this remedial action.

Chemical-Specific ARARs

Chemical-specific federal ARARs include the following:

• Safe Drinking Water Act, 40 CFR, Subparts B, F, and G. Provides MCLs and MCL goalsfor select chemicals in drinking water. Primary drinking water regulations includehealth-based allowable concentrations of carcinogens and non-carcinogens in drinkingwater sources.

Chemical-specific Wyoming State ARARs include the following:

• Wyoming Environmental Quality Act/Wyoming Air Quality Standards and Regulations.Provide air emission standards for various chemicals and compounds, includingfugitive emissions which will be applicable only if air emissions are a result ofthe selected remedy.

• Wyoming Environmental Quality Act/Wyoming Water Quality Rules and Regulations.Provide standards for protection of surface water and groundwater.

• Wyoming Hazardous Waste Rules and Regulations. Identify and list hazardous wastes.

Action-Specific ARARs

Action-specific federal ARARs include the following:

• Clean Water Act, 33 U. S. Code (USC) 1251 et seq. Provides criteria and chemicalstandards for discharge of pollutants into waters of the United States. Setsrequirements for the control of stormwater runoff.

• Clean Air Act, 40 CFR Part 50. Establishes standards for ambient air quality toprotect public health and welfare, which will be applicable only if air emissionsare present.

The principal action-specific Wyoming State ARARs include the following:

• Wyoming Environmental Quality Act. Provides requirements for discharge into watersor emission of air contaminants, which will be applicable only if air emissions arepresent.

• Wyoming Water Quality Rules and Regulations. Provide regulations for discharges towaters of the state, including both surface and ground waters.

• Wyoming Air Quality Standards and Regulations. Provide standards for control ofemissions, including particulates and odors. Include requirements for construction,modification, and operation, which will be applicable only if air emissions arepresent.

• Wyoming Hazardous Waste Rules and Regulations. Provide standards for hazardous wastegenerators, transporters, and interim status standards for owners or operators ofhazardous waste treatment, storage, and disposal facilities that also apply toshort-term storage of hazardous waste.

• Wyoming Solid Waste Management Rules and Regulations. Prohibit dumping ofnon-hazardous solid waste (i.e., trash) on the site.

Location-Specific ARARs

Location-specific federal ARARs include the following:

• Clean Water Act - Dredge and Fill Regulations • Endangered Species Act • Fish and Wildlife Coordination Act • Migratory Bird Treaty Act • National Historic Preservation Act • Archaeological and Historical Data Preservation Act • Archaeological Resources Protection Act (1979)

The principal location-specific state ARARs include the following:

• Wyoming Water Quality Rules and Regulations. Provide water quality standards forgroundwater and surface waters based on the particular stream segment and providefor protection of wetlands.

In addition to the site-specific ARARs listed above, the USAF will comply with allapplicable laws related to transportation, treatment, and disposal activities related toFEW waste materials.

2.13.3 Cost-Effectiveness

In the lead agency's judgment, the selected remedy is cost-effective and represents areasonable value for the money to be spent. In making this determination, the followingdefinition was used: "A remedy shall be cost- effective if its costs are proportional toits overall effectiveness." (NCP §300.430(f)(l)(ii)(D)). This was accomplished byevaluating the "overall effectiveness" of those alternatives that satisfied the thresholdcriteria (i.e., were both protective of human health and the environment andARAR-compliant). Overall effectiveness was evaluated by assessing three of the fivebalancing criteria in combination (long-term effectiveness and permanence; reduction intoxicity, mobility, and volume through treatment; and short-term effectiveness). Overalleffectiveness was then compared to costs to determine cost-effectiveness. The relationshipof the overall effectiveness of this remedial alternative was determined to beproportional to its costs and hence this alternative represents a reasonable value for themoney to be spent.

The estimated present worth cost of the selected remedy is $2,209,000. The selectedremedy's cost provides a significant decrease in time to meet RAOs and protect humanhealth and the environment over other alternatives and is cost-effective. Table 2-1summarizes the cost-effectiveness comparison among alternatives and Table 2-3 presentscost details for the selected remedy. Minor differences exist between the two NPVs showndue to variability in estimating methods and numerical rounding.

2.13.4 Utilization of Permanent Solutions and Alternative Treatment Technologies

The USAF has determined that the selected remedy represents the maximum extent to which permanent solutions and treatment technologies can be utilized in a cost-effective manner.Of those alternatives that are protective of human health and the environment and complywith ARARs, the USAF has determined that the preferred alternative provides the bestbalance of tradeoffs in terms of long-term effectiveness and permanence; reduction in

toxicity, mobility or volume achieved through treatment; short-term effectiveness;implementability; and cost and also considers the statutory preference for treatment as aprincipal element and the preference of the State of Wyoming and the community.

Specifically, Alternative 5 was selected over the other alternatives because it providesthe best short-term effectiveness based on remediation time at a relatively smallincremental cost and implementability when compared to the other alternatives thatactively reduce the toxicity, mobility, and volume of contamination. Despite lower cost,Alternative 3, MNA, was assessed as being less effective at reducing the toxicity,mobility, and volume of contamination than Alternatives 5, 6, and 7, and was thereforeeliminated from further consideration based on the NCP preference for this criterion. Allthe alternatives that actively reduce toxicity, mobility, and volume are assessed assimilar relative to the other balancing criterion of long-term effectiveness andpermanence. Details of the analysis are presented in Section 2.10 and summarized in Table 2-1.

The selected remedy treats the primary risks associated with the groundwater and achieves significant reduction of VOC concentrations. The remedy can be implemented quickly and ina cost-effective manner.

The following elements of the preferred alternative are permanent solutions:

• Procurement of an alternative water supply for Nob Hill residents; • Excavation of all landfill waste and associated underlying soils; • Treatment of the groundwater TCE plume through removal of contaminants; • Treatment provided by the presumptive treatment technologies (air stripping and

carbon adsorption);

While alternative treatment technologies are not part of the preferred remedy, innovative technologies, such as monitored natural attenuation and permeable reactive barriers, were considered in the screening of technologies and were carried forward for detailed analysisin the feasibility study.

2.13.5 Preference for Treatment as a Principal Element

Contaminated groundwater that exceeds action levels established by EPA and WDEQ will be withdrawn from the ground, treated to remove VOCs from the water stream, then returned tothe aquifer. Therefore, the statutory preference for remedies that employ treatment as aprincipal element is satisfied.

2.13.6 Five-Year Review Requirement

Because the selected alternative will result in hazardous substances, pollutants, orcontaminants remaining on-site above levels that allow for unlimited use and unrestrictedexposure, a statutory review will be conducted within 5 years after initiation of remedialaction and every 5 years until remedial goals are reached to ensure that the selectedremedy is, or will be, protective of human health and the environment.

Five-year reviews are generally conducted as a site- wide review in which all remediesunder CERCLA are evaluated. Since the last review was finalized in fiscal year 1999, thenext review is expected no later than fiscal year 2004.

2.14 DOCUMENTATION OF SIGNIFICANT CHANGES FROM PREFERRED ALTERNATIVE OF PROPOSED PLAN

The Proposed Plan for the ROD was released for public comment on March 12, 2001. The preferred alternative identified in the Proposed Plan was a groundwater extraction andtreatment system, which was determined to be protective of human health and theenvironment. No written or verbal comments were received from the public during the

comment period that would change the remedy selection process. Because no communitycomments or new information was provided that alters any of the assumptions or conclusionsused in developing the preferred alternative, the preferred alternative is the selectedremedy without any changes.

3.0 RESPONSIVENESS SUMMARY

3.1 STAKEHOLDER ISSUES AND LEAD AGENCY RESPONSES

Community interest in CERCLA and IRP activities at FEW has fluctuated over the years since the initial record search and personnel interviews conducted for the USAF in September1985. There were no concerns expressed during the Zone C RI (USAF 2000a) or the FS Report(USAF 2000b) before the public comment period for the ROD.

At the time of the public comment period, the preferred alternative for the remedy at ZoneC had been identified by the USAF, with EPA and WDEQ concurrence. The preferredalternative, groundwater extraction and treatment, was presented in the Proposed Planthrough a fact sheet issued on March 13, 2001.

The public comment period on the Proposed Plan for the Zone C OU11 RA at FEW was held from March 12, 2001, to April 11, 2001, and a public meeting was held on March 27, 2001,to present the content of the ROD and the preferred alternative. No written or verbalcomments were received during the public comment period. Because no community comments ornew information was provided that alters any of the assumptions or conclusions used indeveloping the preferred alternative, the preferred alternative is the selected remedywithout any changes.

4.0 REFERENCES

Engineering Science. 1985. Installation Restoration Program, Phase I - Records Search, F. E. Warren AFB, Wyoming.

Ebasco. 1995. Focused Remedial Investigation For Operable Unit 3: Landfill 3 and Nob Hillat F. E. Warren Air Force Base, Wyoming.

Noyes, Herman. 2001. Personal communication with Bill DiGuiseppi, Earth Tech, Inc., June 21.

Parsons Engineering Science. 1999a. Draft Final Work Plan for a Treatability Study inSupport of Remediation by Natural Attenuation at Landfill 3 (Site LF-03), F. E. Warren AirForce Base, Cheyenne, Wyoming. March.

_____. 1999b. Final Treatability Study in Support of Monitored Natural Attenuation for Groundwater at Landfill 3 (Site LF-03), F. E. Warren Air Force Base, Cheyenne, Wyoming. December.

U. S. Air Force (USAF). 1991. Remedial Investigations for F. E. Warren Air Force Base, Wyoming: Cheyenne, Wyoming. Prepared by the United States Geologic Survey (USGS).

_____. 1996. Operable Unit 3 Interim Action Technical Memorandum. February.

_____. 1999a. Geochemical Background Concentrations of Selected Constituents in Soil, Shallow Groundwater, Surface Water, and Sediment, Operable Unit 2, Revised Draft, F. E. Warren Air Force Base, Cheyenne, Wyoming.

_____. 1999b. Draft Final Work Plan, Remedial Investigation/ Feasibility Study for Zone C, F. E. Warren Air Force Base, Cheyenne, Wyoming.

_____. 2000a. Final Remedial Investigation for Zone C, F. E. Warren Air Force Base, Cheyenne, Wyoming.

_____. 2000b. Final Feasibility Study for Zone C, F. E. Warren Air Force Base, Cheyenne, Wyoming.

U. S. Environmental Protection Agency. 1988. Guidance for Conducting RemedialInvestigations and Feasibility Studies under CERCLA. EPA 540-G-89-004, OSWER Directive9355.3- 01. October.

_____. 1996. Presumptive Response Strategy and Ex- Situ Treatment Technologies for Contaminated Groundwater at CERCLA Sites, Final Guidance. EPA 540-R-96-023, OSWER 9283.1-12. October.

_____. 1999. A Guide to Preparing Superfund Proposed Plans, Records of Decision, and Other Remedy Selection Decision Documents. EPA 540-R-98-031, OSWER 9200.1-23P. July.

_____. 2000. Baseline Risk Assessment Scoping Document, F. E. Warren Air Force Base, Cheyenne, Wyoming. February.

Wyoming, State of. 1999. Wyoming Surface Water Quality Standards, Second Draft. September.

Color Map(s)

The following pages containcolor that does not appear in

the scanned images.

To view the actual images, pleasecontact the Superfund Records Center

at (303) 312- 6473.

APPENDIX A

HUMAN HEALTH AND ECOLOGICAL RISKCHARACTERIZATION SUMMARY

TABLE OF CONTENTS

LIST OF TABLES A-ii

LIST OF FIGURES A-ii

LIST OF ACRONYMS A-iii

1.0 SUMMARY OF RISK HUMAN HEALTH RISK ASSESSMENT A-l-1 1.1 IDENTIFICATION OF CHEMICALS OF POTENTIAL CONCERN A-l-1 1.2 EXPOSURE ASSESSMENT A-l-4 1.3 TOXICITY ASSESSMENT A-l-7 1.4 RISK CHARACTERIZATION A-1-8 1.5 UNCERTAINTY A-l-10

2.0 SUMMARY OF ECOLOGICAL RISK ASSESSMENT A-2-1 2.1 ECOSYSTEMS POTENTIALLY EXPOSED A-2-1 2.2 CHEMICALS OF POTENTIAL ECOLOGICAL CONCERN A-2-1 2.3 EXPOSURE ASSESSMENT A-2-3 2.4 ECOLOGICAL EFFECTS ASSESSMENT A-2-6 2.5 ECOLOGICAL RISK CHARACTERIZATION A-2-6

3.0 REFERENCES A-3-1

LIST OF TABLES

Table No. Title

A-l Summary of Chemicals of Concern and Medium- Specific Exposure Point Concentrations A-2 Selection of Exposure Pathways for Zone C Human Health Risk Assessment A-3 Cancer Toxicity Data for COCs in Groundwater A-4 Noncarcinogenic Toxicity Data for COCs in Groundwater A-5 RME and CTE Risk Characterization Summary for Carcinogens A-6 RME and CTE Risk Characterization Summary for Noncarcinogens A-7 Soil Screening Levels for Selection of COPECs A-8 Sediment Quality Values for Selection of COPECs A-9 Water Quality Values for Selection for COPECs A-10 Occurrence, Distribution, and Selection of Ecological Chemicals of Concern A-ll Assessment and Measurement Endpoints for the Ecological Risk Assessment

LIST OF FIGURES

Figure No. Title

A-l Human Health Conceptual Site Model A-2 Ecological Conceptual Site Model

LIST OF ACRONYMS

4,4'-DDD 4,4'-dichloro- 2,2-bis(p-chlorophenyl) ethylene 4,4'-DDT 4,4'-dichlorodiphenyltrichloroethane ASTM American Society for Testing and Materials BW body weight GDI chronic daily intake COC chemical of concern COPC chemical of potential concern COPEC chemical of potential ecological concern CSF cancer slope factor CSM conceptual site model CTE central tendency exposure DCE dichloroethene or dichloroethylene EPA United States Environmental Protection Agency EPC exposure point concentration ERA ecological risk assessment FEW F. E. Warren Air Force Base HEAST Health Effects Assessment Summary Tables HHRA human health risk assessment HI hazard index HQ hazard quotient HSDB Hazardous Substances Data Base IRIS Integrated Risk Information System LF-03 Landfill 3 LOAEL lowest observed adverse effect level MCL maximum contaminant level mg/kg milligram per kilogram mg/kg-day milligram per kilogram-day mg/L milligram per liter NCEA National Center for Environmental Assessment RBC risk-based criterion RfD reference dose RI Remedial Investigation RME Reasonable Maximum Exposure ROD Record of Decision SHRTSC Superfund Health Risk Technical Support Center TCE trichloroethene or trichloroethylene UCL upper confidence limit USAF United States Air Force VOC volatile organic compound WDEQ Wyoming Department of Environmental Quality ug/L microgram per liter

1.0 SUMMARY OF RISK HUMAN HEALTH RISK ASSESSMENT

A human health risk assessment (HHRA) was conducted for Warren Air Force Base (FEW) Zone Cin accordance with United States Environmental Protection Agency (EPA) Region VIII andWyoming Department of Environmental Quality (WDEQ) guidance. This baseline risk assessmentproduced estimates of the potential current and future risks to public health fromchemicals of potential concern (COPCs) assuming there would be no remediation. Exposure to chemicals in surface soil, subsurface soil, sediment, surface water, and groundwater was addressed. The response action selected in this Record of Decision (ROD), is based on the results of the Zone C risk assessment (United States Air Force [USAF] 2000) and guidelines presented in A Guide to Preparing Superfund Proposed Plans, Records of Decision, and Other Remedy Selection Decision Documents (EPA 1999b). Ecological risks for Zone C were also evaluated in the Zone C baseline risk assessment and are discussed in Section 2.7.2 ofthis ROD.

1.1 IDENTIFICATION OF CHEMICALS OF POTENTIAL CONCERN

The organic COPCs evaluated in the FEW Zone C Remedial Investigation (RI) (USAF 2000) were selected based on the following criteria:

(1) Chemicals with concentrations below a series of screening thresholds (i.e., EPARegion III Risk-Based Concentrations [1999a]) were not retained as COPCs;

(2) Chemicals without toxicity data that are considered essential nutrients were notretained as COPCs; and

(3) Chemicals with a frequency of detection of 5 percent or less were not retained asCOPCs.

Inorganic COPCs were selected considering the above criteria as well as the results of a statistical background comparison. That is, inorganic COPCs with concentrations within naturally occurring (background) levels were not retained for the HHRA. COPCs in media not sampled (e. g., air) were identified from relevant sampled media using appropriate models. COPCs identified for quantitative or qualitative human health risk assessment in Zone C included:

• Surface soil: None

• Subsurface soil: None

• Crow Creek sediment: arsenic and p-cymene

• Crow Creek surface water: chloride, fluoride, bromide, 1,2,3-trichlorobenzene, andp-cymene

• Groundwater: aluminum, antimony, arsenic, chromium, fluoride, nitrate as Nitrogen,thallium, 1,4-dichlorobenzene, bromodichlorobenzene, chloroform, cis-1,2-DCE, TCE,and bromide

In the HHRA for Zone C, chemicals were selected as COPCs for further evaluation if concentrations exceeded risk-based levels developed based on a target risk of 10-6 .However, COPCs evaluated in the HHRA are not necessarily the chemicals of concern (COCs)that drive a remedial action (EPA 1999b). COCs rather than COPCs are analytes present atconcentrations that warrant a response action based on their contribution to the estimatedcumulative excess risk to human health. A response action is generally warranted if any ofthe following situations occur (EPA 1999b):

(1) The cumulative excess current or future carcinogenic risk based on the reasonable maximum exposure (RME) exceeds 10-4 ,

(2) The current or future noncarcinogenic hazard index (HI) based on the RME is greater than l,

(3) Site chemicals cause adverse environmental impacts, or

(4) Chemical-specific standards are exceeded and exposure to chemicals above theselevels is predicted for the RME.

Individual chemicals that contribute the greatest percentage of the cumulative excess riskor HI are selected as COCs and targeted for remediation. For FEW Zone C, no COCs werepresent in soil, sediment, surface water, or groundwater that contributed to a cumulativeexcess cancer risk above 10-4 or an HI above 1. However, trichloroethylene (TCE) andcis-l,2-dichloroethylene

(DCE) were selected as COCs in groundwater because they are likely attributable to former activities in Zone C and are present at concentrations that exceed federal maximumcontaminant levels (MCLs) (EPA 1999c). Recognizing that natural and man-made degradationof these chemicals may lead to the formation of regulated intermediate products, thepotential degradation products trans-1,2-DCE and vinyl chloride were also included asCOCs. Although modeling results have indicated that low TCE concentrations (less than 5micrograms per liter [Ug/L]) may reach Crow Creek from groundwater, it is anticipated thatimpacts to surface water, if any, will be at low concentrations and localized. Inaddition, a remedy that is protective of residential exposure to groundwater is protectiveof recreational receptors exposed to chemicals migrating from groundwater to surfacewater.

The COCs for FEW Zone C are presented in Table A-l. TCE, cis-1,2-DCE, and trans-1,2-DCEwere the most frequently detected volatile organic compounds (VOCs) with maximum concentrations of 95 ug/L, 129 ug/L, and 7.1 ug/L, respectively. TCE was the mostfrequently detected VOC in groundwater samples evaluated in the Zone C RI. TCE wasdetected above the federal MCL of 5 ug/L in 21 of the 95 groundwater samples evaluated inthe Zone C RI and at a maximum concentration of 113 ug/L at a test well southeast of theLandfill 3 (LF-03) boundary. Eleven Zone C wells (MW-203, MW-208, MW-209, MW-209M1,MW-210, MW-210M, PES-1S, PES-4D, PES-6S, PZ-1, and PZ-2) had detections of TCE above theMCL during both sampling rounds.

The areal distribution of cis-1,2-DCE in groundwater was similar to that of TCE with the maximum detection of 129 ug/L occurring in the test well located southeast of the LF-03 boundary, cis-1,2-DCE was detected above the MCL (70 ug/L) in two of the 99 samples evaluated in the Zone C RI (well MW-209 in Round 1 and well MW-208 in Round 2).

The maximum detection of trans-1,2-DCE corresponded with maximum detections of TCE and cis-1,2-DCE. trans-1,2-DCE was not detected above the federal MCL of 100 ug/L in any ofthe samples evaluated in the Zone C RI. However, recognizing that degradation of TCE maylead to the formation of regulated intermediate products such as 1,2-DCE, trans-1,2-DCEwas selected as a COC in groundwater. Vinyl chloride was detected at concentrationsranging from 0.3 ug/L to 51 ug/L between July and October 1993 and was not detected in anyof the groundwater samples from the 1999 Zone C RI. Vinyl chloride is believed to be anartifact of sampling and analysis, as described later in this section, but was alsoincluded as a COC because it is a degradation product of TCE.

In April 1994, groundwater samples were collected from the off-base Nob Hill area. TCE wasdetected in three of the 12 off-base groundwater samples at concentrations ranging from0.22 ug/L to 2.2 ug/L. cis-1,2-DCE, trans-1,2-DCE, and vinyl chloride were not detected inany of the monitoring wells sampled during the Nob Hill development.

TCE detections are presented on Figure 2-3, and cis-1,2-DCE detections are presented onFigure 2-4 of the main report. The receptors that were evaluated for groundwater exposureand resulting cumulative risks and His from the baseline risk assessment are discussed inthe following subsections.

1.2 EXPOSURE ASSESSMENT

Risk is evaluated by estimating the amount of a chemical in an environmental medium (soil, water, or air) that a person may ingest, inhale, or contact over a period of time (i.e.,exposure). A conceptual site model (CSM) is a schematic representation of potentialexposure that summarizes chemical source areas, chemical release mechanisms, environmentaltransport media, potential exposure routes, and potential receptors. The CSM used for theFEW Zone C baseline human health risk assessment is presented on Figure A- l.

Only complete exposure pathways were evaluated in the Zone C risk assessment. A complete exposure pathway includes all of the following elements:

• A source and mechanism of contaminant release, • A transport or contact medium (e.g., groundwater or soil), • An exposure point where humans can contact the contaminated medium, and • An exposure route (e.g., ingestion or inhalation).

The absence of any one of these elements results in an incomplete exposure pathway. Where there is no potential human exposure, there is no potential human health risk. The CSM for Zone C shows that human receptors could potentially contact chemicals detected in thefollowing media:

• Surface and subsurface soil, • Crow Creek surface water and sediment, • Groundwater, or • Air (i.e., dust or airborne VOCs).

In addition, human receptors who may contact chemicals detected in site media wereidentified as:

• Current/future on-site recreational visitors, • Current/future on-site occupational workers, or • Current/future on-site (hypothetical) residents.

The following exposure pathways were evaluated in the Zone C RI (USAF 2000):

• Ingestion, dermal, and inhalation exposure to groundwater in Zone C (young childrenand adult residents),

• Ingestion and dermal exposure to surface water in Crow Creek (youth residents andcurrent/future recreational receptors), and

• Ingestion and dermal exposure to sediments in Crow Creek (youth residents andcurrent/future recreational receptors).

Although potential exposure to surface and subsurface soils in Zone C would have typicallybeen addressed in the human health risk assessment, this exposure pathway was notevaluated because no COPCs were identified in surface or subsurface soils. Also, the fishingestion exposure pathway was not evaluated because the exposure pathway was consideredto be potentially complete but insignificant in contribution to the total risk estimate.Furthermore, VOCs in groundwater could potentially enter buildings in Zone C byinfiltration through a foundation. Therefore, screening equations from the AmericanSociety for Testing and Materials (ASTM) Standard Guide to Risk-Based Corrective ActionApplied at Petroleum Release Sites (1995) were used in the Zone C RI to assessvolatilization from groundwater to indoor air. The results of the modeling suggest thatreleases to indoor air would not pose an unacceptable threat to human health because noneof the EPA Region III ambient air risk-based criteria (RBCs) (1999b) were exceeded by thepredicted indoor air concentrations. Therefore, residential exposure to VOCs in indoor airwas not evaluated in the human health risk assessment for Zone C (USAF 2000). The exposure

pathways that were quantitatively evaluated in the risk assessment for Zone C aresummarized in Table A-2 in accordance with EPA recommendations in A Guide to PreparingSuperfund Proposed Plans, Records of Decision, and Other Remedy Selection DecisionDocuments (1999a).

Receptor intake estimates were calculated using chemical-specific exposure pointconcentrations (EPCs). The 95 percent upper confidence limit (UCL) on the arithmetic meanwas used to represent the EPC because it provides a conservative estimate of the averageconcentration (EPA 1994). In some cases, variability in measured concentrations and smallsample sizes produce a 95 percent UCL concentration that exceeds the maximum detectedconcentration. In these cases, that maximum detected concentration was used to representthe EPC. The 95 percent UCL was calculated in accordance with EPA guidance (1994) asfollows:

Normal Distribution:

95 UCL+x+t(s/sq. root of n)

where

UCL = upper confidence limit (milligram per kilogram [mg/kg] or milligram per liter [mg/L])

x = mean of the untransformed data (mg/kg or mg/L) s = standard deviation of the untransformed data (mg/kg or mg/L) t = Student t- statistic (e.g., from table published in Gilbert [1987], a = 0.05) n = number of samples

Lognormal Distribution:

95 UCL = e(x+0.5s2+sH/[sq. Root of n-1])

where

UCL = upper confidence limit (mg/kg or mg/L) e = constant (base of natural log, equal to 2.718) X = mean of the transformed data s = standard deviation of the transformed data H = H- statistic (e.g., from table published in Gilbert [1987]) n = number of samples

Sampling data from each exposure area were aggregated for the purpose of calculating the95 percent UCL. One-half the reporting limit was used as a proxy value for nondetects tocalculate summary statistics including the 95 percent UCL concentration. If the underlyingdistribution was unknown, lognormality was assumed (EPA 1992).

EPA intake models and default assumptions (USAF 2000) were also used to calculate receptor intakes. When EPA default assumptions were not available, site- specific information was compiled or professional judgment was used. The primary focus of the exposure assessmentfor this ROD is the groundwater exposure pathway.

1.3 TOXICITY ASSESSMENT

The estimated dose for a specific receptor was compared with toxicity values (i. e, cancerslope factors [CSFs] or reference doses [RfDs]) that are specific to the oral andinhalation pathways and obtained from the sources listed below in the following hierarchy:

• Integrated Risk Information System (IRIS) on- line database (EPA 1999d);

• Health Effects Assessment Summary Tables (HEAST) (EPA 1997a); and

• Provisional toxicity values obtained from EPA's National Center for Environmental Assessment (NCEA), as published in EPA Region III guidance (EPA 1999a).

CSFs represent the probability of cancer per unit intake of chemical (by oral, dermal, or inhalation routes) over a lifetime. RfDs are used to evaluate the threat of non-cancereffects. The RfD is a pathway-specific (i.e., oral, dermal, or inhalation) estimate of adaily chemical intake per unit body weight that is likely to be without deleteriouseffects (EPA 1989). The EPA has developed chronic RfDs to evaluate long-term exposures (7years to a lifetime), and subchronic RfDs to evaluate exposures of shorter duration (2weeks to 7 years). However, no subchronic RfDs were available for the COPCs at Zone C.Therefore, chronic RfDs were used for all receptors in the risk assessment. The CSFs andRfDs used to evaluate the COCs presented in this ROD are provided in Tables A-3 and A-4,respectively.

1.4 RISK CHARACTERIZATION

For carcinogens, risks are generally expressed as the incremental probability of anindividual developing excess cancer over a lifetime as a result of exposure to thecarcinogen. Excess lifetime cancer risk is calculated from the following equation:

Risk = GDI x CSF where

Risk = a unitless probability (e.g., 1 x 10-6) of an individual developing cancer

GDI = chronic daily intake averaged over 70 years (mg/kg-day) CSF = cancer slope factor, expressed as (mg/kg- day)-1

These risks are probabilities that usually are expressed in scientific notation. An excesslifetime cancer risk of 1 x 10-6 indicates that an individual experiencing the reasonablemaximum exposure estimate has a 1 in 1,000,000 chance of developing cancer as a result ofsite- related exposure. This is referred to as an "excess lifetime cancer risk" because itwould be in addition to the risks of cancer individuals face from other causes such assmoking or exposure to too much sun. The chance of an individual developing cancer fromall other causes has been estimated to be as high as one in three (EPA 1999b). EPA'sgenerally acceptable risk range for site- related exposures is 1 x 10-4 to 1 x 10-6.

The potential for noncarcinogenic effects is evaluated by comparing an exposure level overa specified time period with an RfD derived for a similar exposure period. An RfDrepresents a level that an individual may be exposed to that is not expected to cause anydeleterious effect. The ratio of exposure to toxicity is called a hazard quotient (HQ). AnHQ less than 1 indicates that a receptor's dose of a single contaminant is less than theRfD and that toxic noncarcinogenic effects from that chemical are unlikely. The HI isgenerated by adding the HQs for all COCs that affect the same target organ (e.g., liver)or that act through the same mechanism of action within a medium or across all media towhich a given individual may reasonably be exposed. An HI less than 1 indicates that,based on the sum of all HQs from different chemicals and exposure routes, toxic noncarcinogenic effects from all contaminants are unlikely. An HI greater than 1 indicatesthat site- related exposures may present a risk to human health.

The HQ is calculated as follows:

Noncancer HQ = GDI/RfD where

GDI = chronic daily intake (mg/kg-day) RfD = reference dose (mg/kg-day)

GDI and RfD are expressed in the same units and represent the same exposure period (i.e., chronic, subchronic, or short-term). As presented in Table A-5, the total excess RME carcinogenic risk from exposure to COCs in groundwater is 2 x 10-6 , which slightlyexceeds the State of Wyoming target risk of 1 x 10-6 but is below the risk level typicallyassociated with mandatory remediation requirements (1 x 10-4) (EPA 1990). In addition, thecumulative excess cancer risk estimated based on the central tendency exposure (CTE), oraverage exposure, is 2 x 10-7 , which is below the State of Wyoming target risk level.Furthermore, both the RME and CTE His of 0.085 and 0.037, respectively, for Zone C COCsare below the target HI of 1 (Table A-6). Although the cumulative lifetime cancer risksfor COCs in Zone C are below 1 x 10-4 (the risk level that is typically associated withmandatory remediation requirements [EPA 1990]) and none of the His exceeded 1, TCE andcis-1,2-DCE were selected as COCs in groundwater because they are likely attributable toactivities in Zone C and are present at concentrations that exceed federal MCLs (EPA1999c). Recognizing that natural and man-made degradation of these chemicals may lead tothe formation of regulated intermediate products, the potential degradation productstrans-1,2-DCE and vinyl chloride were also included as COCs. The cancer risks andnoncarcinogenic His presented in Tables A-5 and A-6, respectively, for TCE, cis-1,2-DCE,and trans-1,2-DCE were estimated in the Zone C RI for each relevant exposure pathway andenvironmental medium (e.g., groundwater).

1.5 UNCERTAINTY

The large number of assumptions made in this risk assessment introduces uncertainty in therisk assessment results. While this could potentially lead to an underestimation of risk,the use of numerous conservative (i.e., protective of human health) assumptions in thisrisk assessment probably resulted in a net overestimation of potential risk. The followingassumptions introduced uncertainty in the Zone C risk assessment results:

(1) Professional judgment was used to dismiss arsenic, aluminum and iron as COPCs insurface soil. These constituents are assumed to be naturally occurring even thoughstatistical background comparisons suggest they are present above background.Graphic presentations and comparisons with regional background data ranges were usedto conclude that these constituents are within background. This use of professionaljudgment in background comparisons could tend to underestimate the overall risk ifthese constituents are omitted from the risk assessment in error.

(2) At the request of EPA Region VIII, outliers were retained in the data sets whencalculating statistics (with the exception of an arsenic non-detect in sediment andin subsurface soil). This strategy could mask any hotspots that might exist, thuspotentially underestimating risk. It does, however, raise the 95 percent UCLconcentration, potentially overestimating risk.

(3) The EPA Region III RBCs for noncarcinogenic constituents were lowered by an order ofmagnitude for the COPC selection to assume a target HQ of 0.1 rather than the 1.0.This practice would tend to overestimate the hazardous health effects potentiallyposed by exposure to noncarcinogenic constituents. Reducing the target HQ to 0.1 isa simplified means of adjusting the RBC by the number of constituents affecting thesame target organs. Because there are rarely more than 10 constituents affecting thesame target organs, reducing the noncarcinogenic RBC by 0.1 would overestimate risk.

(4) Ingestion, dermal, and inhalation exposure of utility workers to chemicals ingroundwater are potentially complete pathways that were not evaluated in the riskassessment because they are considered to be insignificant. Exposure to groundwaterin this scenario is likely insignificant (i.e., from incidental ingestion and dermalexposure to standing water in a trench and inhalation of VOCs in open air). Theutility worker is primarily exposed to surface and subsurface soil in and around a

trench. Therefore, exposure to surface soil is also likely low. In addition,concentrations of chemicals in groundwater and surface soil at the site arerelatively low. Therefore, overall chemical intake and risk are also likely low.

(5) Inhalation exposure to VOCs in indoor air is a potentially complete pathway notevaluated in the risk assessment because it is considered to be insignificant.Concentrations of VOCs in indoor air predicted by modeling were below conservativeRBCs for air.

(6) Ingestion of fish hi Crow Creek is potentially a complete pathway that was notevaluated in the risk assessment. It is not known whether a significant transportpathway exists from constituents at LF-03 to fish in Crow Creek. Therefore, the fishingestion pathway was considered to be potentially complete, although risk may below. Not evaluating fish in this risk assessment may have contributed to anunderestimation of hazard/ risk at the site.

(7) Exposure concentrations used in the risk assessment were the 95 percent UCL ormaximum detected value (whichever was lower). These concentrations likelyoverestimate actual average exposure to COPCs at the site.

(8) When available, standard EPA default values were used for exposure factor parametervalues. Most of these exposure factor values are reasonable high- end estimates ofexposure. However, when uncertainty was high regarding exposure factor parametervalues, conservative (health- protective) assumptions were used.

(9) EPA's methodology for toxicity assessment was specifically designed to ensure thatestimates of toxicity are protective of human health. Because uncertainties exist inthe toxicity assessment process, numerous conservative (health-protective)approaches are used, so as not to underestimate dose-response or hazard potential.

These include:

• Uncertainty factors of 10 to 10,000 in RfDs, • Assuming humans are more sensitive than the most sensitive laboratory species,• Assuming carcinogens do not have a threshold, and • Assuming that animal carcinogens also cause cancer in humans.

(10) EPA has used a conservative mathematical model, the linearized multistage model, forlow-dose extrapolation. EPA identifies the CSF and the upper 95th percentileconfidence limit on the slope of the resulting dose-response curve. The CSF isexpressed in units of risk per mg/kg-day, or (mg/kg-day)-1 , and is used to estimateexcess incremental lifetime cancer risk from the lifetime average daily intake of achemical. This represents an estimation of an upper-bound probability that anindividual will develop cancer as a result of exposure to the potential carcinogen.This model provides a conservative (protective) estimate of cancer risk at low dosesand is likely to overestimate the actual cancer risk. In the human health riskassessment, these assumptions probably contribute to an overestimate of toxicity ofCOPCs and of overall hazard/risk.

(11) Toxicity values for chronic exposure were used to evaluate all exposure scenarios,regardless of exposure duration. Therefore, hazard/risk may have been overestimatedfor scenarios of subchronic durations (e.g., child recreational visitor).

(12) The following COPCs did not have toxicity values: bromide, 1,2,3-trichlorobenzene,and p-cymene. The lack of toxicity values for these COPCs could contribute to anunderestimation of hazard/risk estimates, the magnitude of which depends on theconcentrations and (unknown) toxicity of the COPCs.

• Bromides are contained in some medications, with the most common side effect being conjunctivitis, and are not recommended for administration to pregnantor nursing patients. The only dose value provided in the Hazardous SubstancesData Base (HSBD) was a maternal intake of 5.4 grams per day, which producedrash, weakness and absence of crying in nursing infants. Compared to thisdose, the maximum detected concentrations in surface water and in groundwaterare very low and would unlikely to pose any threat to human health.

• 1,2,3- Trichlorobenzene was detected in surface water at a maximumconcentration of 0.57 ug/L. According to information in the HSDB, minimal eyeand throat irritation could occur with exposure to this chemical at 3 to 5parts per million in an industrial setting. The maximum concentration in thesurface water is considerably below this range. In addition, most of thesystemic effects noted for this chemical were via inhalation. Therefore, it isunlikely that the maximum detected concentrations in the surface water wouldpose any threat to human health.

• The maximum concentrations of p-cymene detected were 0.169 mg/ kg in sedimentand 0.46 ug/ L in surface water. According to the HSDB, p- cymene is a primaryskin irritant. Most systemic effects are noted in an industrial setting withexposure to vapors or direct contact with pure liquid cymene. It is unlikelythat exposure to this chemical through contact with surface water or sedimentin Crow Creek would pose any threat to human health.

(13) At the request of EPA Region VIII, the intake factors used in estimating thepotential His for noncarcinogenic constituents were age- adjusted for all media forthe recreational visitor (child/adult) and the residential receptor (child/adult).Although this practice tends to reduce overall risk to these receptors, particularlythe child, it also overestimates the risk for the adult receptor.

2.0 SUMMARY OF ECOLOGICAL RISK ASSESSMENT

The baseline ecological risk assessment (ERA) estimates potential risks to the environmentfrom site-related chemicals assuming no remedial actions will be taken. The results of theecological risk assessment are used to identify chemicals and exposure pathways that needto be addressed by the remedial action. This section summarizes the results of thebaseline ecological risk assessment for Zone C.

2.1 ECOSYSTEMS POTENTIALLY EXPOSED

The ecosystems and species at FEW are described in detail in Rosenlund (1992) and Elliott (1996). The landscape at FEW is characterized as rolling shortgrass prairie with scatteredrock outcrops. Situated among the extensive man-made facility infrastructure is adiversity of natural habitats, including shortgrass prairie, streams and riparian habitat,marshes, and wet meadows. A diversity of wildlife inhabits these habitats. The twoprincipal habitats of the ERA of Zone C are the shortgrass prairie and the stream (CrowCreek) that flows south adjacent to Zone C (USAF 1999a).

2.2 CHEMICALS OF POTENTIAL ECOLOGICAL CONCERN

The organic chemicals of potential ecological concern (COPECs) evaluated in the FEW Zone C RI (USAF 2000) were selected based on the following criteria:

(1) Biologically active chemicals (i.e., calcium, iron, magnesium, potassium, sodium)were not retained as COPECs;

(2) Chemicals detected at a frequency of 5 percent or less were not retained as COPECs,and

(3) Chemicals with concentrations below a series of screening thresholds (Tables A-7through A-9) were not retained as COPECs.

In addition, inorganic COPECs were selected considering the above criteria in addition tothe results of a statistical background comparison. That is, inorganic COPECs withconcentrations within naturally occurring (background) levels were not retained as COPECs.COPECs identified for a quantitative or qualitative ERA in Zone C included:

• Surface soil: chromium, lead, vanadium, zinc

• Subsurface soil: 4,4'-dichloro-2,2-bis(p-chlorophenyl) ethylene (4,4'-DDD),4,4'-dichloro-diphenyltrichloroethane (4,4'-DDT), benzoic acid

• Crow Creek sediment: 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene,1,3-dichlorobenzene, 4,4'-DDD, 4,4'-DDT, bis(2-ethylhexyl) phthalate, cyanide,p-cymene, and toluene

• Crow Creek surface water: 1,2,3-trichlorobenzene, 1,2,4-trimethylbenzene, mercury,nitrate as nitrogen, n-butylbenzene, p-cymene, sec-butylbenzene, andtert-butylbenzene

COPECs evaluated in the ERA (summarized in Table A-10) are not necessarily ecological COCsthat drive a remedial action (EPA 1999b). Ecological COCs, rather than COPECs, areanalytes present at concentrations that warrant a response action based on the magnitudeof the estimated risk of adverse effects to the environment. Numerical estimates ofecological risk are not the only descriptors that are considered during the evaluation ofremedial options (EPA 1997b). The following additional ecological risk descriptors listedbelow are considered (EPA 1997b):

(1) The location and areal extent of existing contamination above a threshold foradverse effects;

(2) The degree to which the threshold for contamination is exceeded or is likely to beexceeded in the future; and

(3) The expected half-life (qualitative or quantitative) of contaminants in theenvironment (e.g., sediments, food chain) and the potential for natural recoveryonce the sources of contamination are removed.

Individual chemicals that are present at concentrations likely to result in adverseecological impacts (based on analysis of the descriptors presented above) are selected asecological COCs and targeted for remediation. For FEW Zone C, no chemicals are present inZone C soil, sediment, or surface water that are likely to result in adverse ecologicaleffects (USAF 2000).


The purpose of the exposure characterization is to provide site-specific exposure data foruse in the risk characterization. Estimates of exposure to COPECs were developed for eachunique combination of three factors:

• COPEC and its concentration; • Exposure medium (soil, surface water, and sediment); and • Ecological receptor.

A CSM is a schematic representation of potential exposure that summarizes chemical source areas, chemical release mechanisms, environmental transport media, potential exposureroutes, and potential ecological receptors. The CSM used for the FEW Zone C baseline ERAis presented as Figure A-2.

Only complete exposure pathways were evaluated in the Zone C risk assessment. A complete exposure pathway includes all of the following elements:

• A source and mechanism of contaminant release, • A transport or contact medium (e.g., soil), • An exposure point where ecological receptors can contact the contaminated medium,

and • An exposure route (e.g., ingestion).

The absence of any one of these elements results in an incomplete exposure pathway. Where there is no potential exposure, there is no potential risk. The CSM for Zone C shows that ecological receptors could potentially contact chemicals detected in the following media:

• Surface and subsurface soil, • Crow Creek surface water and sediment, and • Air (i.e., dust or airborne VOCs).

Chemicals in groundwater were not evaluated in the ecological assessment becausegroundwater exposure is an incomplete pathway for ecological receptors. In addition,although exposure to air is a potentially complete exposure pathway, an assessment was notconducted because the risks are likely to be insignificant in comparison with theingestion exposure pathway. Furthermore, there is currently little ecological toxicityinformation available to address the inhalation exposure pathway.

The ecological CSM is shown on Figure A-2. Based on this information, quantitative evaluations of risk were performed for the following:

• Terrestrial plant exposure to constituents in surface and subsurface soil;

• Terrestrial invertebrate exposure to constituents in surface and subsurface soil;

• Terrestrial vertebrate exposure to constituents in food and surface soil (i.e.,birds and mammals);

• Aquatic plant exposure to constituents in surface water;

• Benthic macroinvertebrate exposure to constituents in sediment; and

• Fish exposure to constituents in surface water.

For terrestrial plants, soil invertebrates, benthic macroinvertebrates, and fish,exposures were expressed in terms of published concentrations (milligrams per kilogram ormicrograms per liter) in soil, sediment, or surface water, below which "toxicity is rarelyobserved" (Ingersoll et al. 1996). That is, published screening levels that are protectiveof ecological receptors in a given environmental medium were compared with chemicalconcentrations in Zone C soil, surface water and sediment. Sources of these publishedvalues include the following:

Surface Water:

• Efroymson, R. A., G. W. Suter II, B. E. Sample, and D. S. Jones. 1997. PreliminaryRemediation Goals for Ecological Endpoints. ES/ER/TM-162/R2. Prepared by the OakRidge National Laboratory for the U. S. Department of Energy. August.

• EPA 1986. Quality Criteria for Water. EPA 440/5-86-001. Office of Water Regulationsand Standards, Washington, DC.

• EPA 1999e. National Recommended Water Quality Criteria - Correction. EPA 822-Z-99-001. Office of Water, Washington, DC.

• State of Wyoming (1999). Quality Standards for Wyoming Surface Waters. Chapter 1.

Sediment:

• Canadian Council for Ministers of the Environment (CCME). 1999. "Canadian sedimentquality guidelines for the protection of aquatic life: Summary tables." In: CanadianEnvironmental Quality Guidelines. Winnepeg.

• Cubbage, J., D. Batts, and S. Breidenbach. 1997. Creation and Analysis of FreshwaterSediment Quality Values in Washington State. Washington State Department of Ecology,Sediment Management Unit. Publication 97- 323a. July.

• Efroymson, R. A., G. W. Suter II, B. E. Sample, and D. S. Jones. 1997. PreliminaryRemediation Goals for Ecological Endpoints. ES/ER/TM-162/R2. Prepared by the OakRidge National Laboratory for the U. S. Department of Energy. August.

• Ginn, T. C., and R. A. Pastorak. 1992 (as cited in Jones et al. 1997). "Assessmentand Management of Contaminated Sediments in Puget Sound." pp. 371-401 in SedimentToxicity Assessment, ed. G. A. Burton, Jr., Lewis Publishers, Boca Raton, Fla.

• Ingersoll, C. G., P. S. Haverland, E. L. Brunson, T. J. Canfield, F. J. Dwyer, C. E.Henke, N. E. Kemble, D. R. Mount, and R. G. Fox. 1996. "Calculation and Evaluationof Sediment Effect Concentrations for the Amphipod Hyalella azteca and the MidgeChironomus riparius." J. Great Lakes Res. 22( 3): 602- 623.

• Jones, D. S., G. W. Suter II, and R. N. Hull. 1997. Toxicological Benchmarks forScreening Contaminants of Potential Concern for Effects on Sediment-AssociatedBiota: 1997 Revision. ES/ER/TM-95/R4. Prepared by the Oak Ridge National Laboratoryfor the U. S Department of Energy. November.

• Persaud, D. R. Jaagumagi, and A. Hayton. 1993. Guidelines for the Protection andManagement of Aquatic Sediment Quality in Ontario. Ontario Ministry of theEnvironment, Water Resources Branch. ISBN 0-7729-9248-7.

Soil:

• Preliminary Remediation Goals for Ecological Endpoints (Efroymson et al. 1997).

For terrestrial vertebrate receptors (e.g., deer mouse, western meadow lark, and homedlark), exposure to concentrations of chemicals detected in Zone C surface soil wasexpressed in terms of doses received by the receptors. Doses are expressed as milligramsper kilogram body weight per day (mg/kg bw-day). The resulting doses were compared withtoxicity data from the literature (e.g., lowest-observed-adverse-effect levels [LOAELs])to develop an HQ.

2.4 ECOLOGICAL EFFECTS ASSESSMENT

The effects of chemicals in soil, surface water, and sediment were characterized for representative species expected to be sensitive to COPECs in Zone C (i.e., assessment endpoints). An assessment endpoint is defined by EPA (1997b) as "an explicit expression ofthe environmental value that is to be protected." In addition, a measurement endpoint is"a measurable ecological characteristic that is related to the valued characteristicchosen as the assessment endpoint" (EPA 1997b). The specific assessment and measurementendpoints for the ecological evaluation at FEW, Zone C are presented in Table A-l1.

2.5 ECOLOGICAL RISK CHARACTERIZATION

The basic method used to estimate risks to assessment endpoints from exposure to site-related COPECs involves the comparison of exposure concentrations of constituents orestimated doses to published threshold concentrations or LOAELs, respectively. This ratiois termed the HQ and is calculated as follows:

Hazard Quotient = COPC Exposure Concentration or Dose Threshold Level or LOAEL

HQs greater than 1.0 indicate that ecological exposures may exceed levels of expected toxicological tolerance in the receptors and suggest the need for further evaluation.However, several lines of evidence are considered when making risk management decisionsbased on the strengths and limitations of the ERA. For example, uncertainty in theexposure assumptions is evaluated to determine whether the risk estimates are likely to beoverestimates and consideration is given to whether the remedial actions themselves maycause greater adverse ecological impacts than the residual contamination.

The 95 percent UCL on the arithmetic mean was used to represent the exposure concentration because it provides a conservative estimate of the average concentration (EPA 1994). Insome cases, variability in measured concentrations and small sample sizes produce a 95percent UCL concentration that exceeds the maximum detected concentration. In these cases,that maximum detected concentration was used to represent the EPC. The 95 percent UCL wascalculated in accordance with EPA guidance (1994) as follows:

Normal Distribution:

95UCL=x+t(s/sq.rt. of n)

where

UCL = upper confidence limit (mg/kg or mg/L) x - mean of the untransformed data (mg/kg or mg/L) s = standard deviation of the untransformed data (mg/kg or mg/L) t - Student t-statistic (e.g., from table published in Gilbert [1987] a =0.05) n = number of samples

Lognormal Distribution:

(X+0.5s2+sH/sq.rt. of n-1)95UCL=e

where

UCL = upper confidence limit (mg/kg or mg/L) e = constant (base of natural log, equal to 2.718) x = mean of the transformed data s = standard deviation of the transformed data H = H- statistic (e.g., from table published in Gilbert [1987]) n = number of samples

Sampling data from each exposure area were aggregated for the purpose of calculating the95 percent UCL. One-half the reporting limit was used as a proxy value for nondetects tocalculate summary statistics including the 95 percent UCL concentration. If the underlyingdistribution was unknown, lognormality was assumed (EPA 1992).

Although individual HQ values can be summed into an HI in consideration of possible cumulative effects due to multiple contaminants (EPA 1997b), the HQs in the Zone C assessment were not added into a HI for two principal reasons:

• Uncertainty associated with interactions among COPCs (e. g., antagonism, synergy, oradditivity); and

• Uncertainty associated with the soil, surface water, and sediment benchmarks (e.g.,overlap of effect and no- effect concentrations and presence of co-occurringconstituents).

Numerical estimates of ecological risk (i.e., HQs) are not the only descriptors that areconsidered when making risk management decisions (EPA 1997b). Although the HQs for mercuryin surface water and HQs for chromium and vanadium in surface soil slightly exceeded thetarget HQ of 1 (Table A-10), it was concluded that chemicals present in Zone C soil,sediment, or surface water are unlikely to result in adverse ecological effects (USAF2000). This conclusion is based on the compounding conservative assumptions used in theERA for Zone C. As an example, assumptions such as 100 percent bioavailability were made,when in fact chromium, vanadium, and mercury are estimated to be 2 percent, 6 percent, and3 percent bioavailable, respectively (Hrudey et al. 1996, Agency for Toxic Substances andDisease Registry 1993, Conklin et al. 1982). Therefore, it appears that terrestrial plant,small mammal and avian populations are unlikely to be at any appreciable risk fromexposure to concentrations of site-related chemicals in soil. Although it is unknownwhether several COPCs in surface water and sediment present an unacceptable risk toaquatic receptors (based on the absence of published water quality values and soil qualityvalues), potential ecological risks from chemicals in surface water and sediment at FEWare currently being addressed in a separate evaluation of the entire aquatic ecosystem.

3.0 REFERENCES

ATSDR. 1993. Toxicological Profile for Chromium. Draft. U. S. Department of Health and Human Services.

Agency for Toxic Substances and Disease Registry (ATSDR). 1997. ATSDR's Toxicological Profiles on CD-ROM. New York: CRC Press.

American Society for Testing and Materials. 1995. Standard Guide to Risk-Based Corrective Action Applied at Petroleum Release Sites, El73 9-95.

Canadian Council for Ministers of the Environment (CCME). 1999. "Canadian sediment quality guidelines for the protection of aquatic life: Summary tables." In: Canadian Environmental Quality Guidelines. Winnepeg.

Conklin, A. W., C. S. Skinner, and T. L. Felton. 1982. "Clearance and Distribution of Intratracheally Instilled Vanadium - 48 Compounds in the Rat." Toxicol. Lett. 11:199-203. In: ATSDR 1997.

Cubbage, J., D. Batts, and S. Breidenbach. 1997. Creation and Analysis of Freshwater Sediment Quality Values in Washington State. Washington State Department of Ecology, Sediment Management Unit. Publication 97-323a. July.

Efroymson, R. A., G. W. Suter II, B. E. Sample, and D. S. Jones. 1997. PreliminaryRemediation Goals for Ecological Endpoints. ES/ER/TM-162/R2. Prepared by the OakRidge National Laboratory for the U. S. Department of Energy. August.

Elliott, A. G. 1996. Diversity and Factors Affecting Diversity of Small Mammals, Stream Macroinvertebrates, Reptiles, and Amphibians within F. E. Warren Air Force Base, Cheyenne, Wyoming. M. S. Thesis, Department of Zoology and Physiology University of Wyoming. Laramie, Wyoming.

Gilbert, R. O. 1987. Statistical Methods for Environmental Pollution Monitoring.VanNostrand Reinhold. New York.

Ginn, T. C., and R. A. Pastorak. 1992 (as cited in Jones et al. 1997). "Assessment and Management of Contaminated Sediments in Puget Sound." pp. 371-401 in Sediment Toxicity Assessment, ed. G. A. Burton, Jr., Lewis Publishers, Boca Raton, Fla.

Hrudley, S. E., W. Chen, and C. G. Rousseaux. 1996. Bioavailability in Environmental Risk Assessment. Lewis Publishers. New York.

Ingersoll, C., P. Haverland, E. Brunson, T. Canfield, F. Dwyer, C. Henke, N. Kemble, D.Mount and R. Fox. 1996. "Calculation and Evaluation of Sediment EffectConcentrations for the Amphipod Hyalella azteca and the Midge Chironomus riparius".Journal of Great Lakes Research 22(3): 602-623.

Jones, D. S., G. W. Suter II, and R. N. Hull. 1997. Toxicological Benchmarks for Screening Contaminants of Potential Concern for Effects on Sediment-Associated Biota: 1997 Revision. ES/ER/TM-95/R4. Risk Assessment Program, Health Sciences Research Division, Oak Ridge National Laboratory. Tennessee.

Persaud, D. R. Jaagumagi, and A. Hayton. 1993. Guidelines for the Protection andManagement of Aquatic Sediment Quality in Ontario. Ontario Ministry of theEnvironment, Water Resources Branch. ISBN 0-7729-9248-7.

Rosenlund, B. D. 1992. Interim F. E. Warren Air Force Base Fish and Wildlife Management Plan. U. S. Fish and Wildlife Service, Golden, Colorado.

Suter II, G. W. and C. Tsao. 1996. Toxicological Benchmarks for Screening Potential Contaminants of Concern for Effects on Aquatic Biota, 1996 Revision. Risk Assessment Program, Health Sciences Research Division, Oak Ridge National Laboratory. Tennessee.

United States Air Force. 1999. Draft Remedial Investigation for Zone A, F. E. Warren AirForce Base, Cheyenne, Wyoming.

_____ 2000. Final Remedial Investigation for Zone C, F. E. Warren Air Force Base, Cheyenne, Wyoming.

U. S. Environmental Protection Agency. 1986. Quality Criteria for Water. EPA 440/5-86-001.Office of Water Regulations and Standards, Washington, DC.

_____. 1989. Risk Assessment Guidance for Superfund, Volume 1: Human Health Evaluation Manual (Part A) Interim Final. EPA/540/1-89/002. Office of Emergency and Remedial Response.

_____. 1990. National Oil and Hazardous Substances Pollution Contingency Plan.

_____. 1991. Water Quality Criteria Summary. Table prepared by Ecological Risk Assessment Branch and Human Health Assessment Branch, Health and Ecological Criteria Office, Office of Science and Technology. Washington, DC.

_____. 1992. Water Quality Standards, Establishment of Numeric Criteria for Priority Pollutants; States' Compliance. Final Rule. Federal Register Vol. 57, No. 246.

_____. 1994. Region 8 Superfund Technical Guidance No. RA-03. Contaminants of Concern.Evaluating and Identifying Contaminants of Concern for Human Health. January.

_____. 1997a. Health Effects Assessment Summary Tables (HEAST) FY 1997 Update. Office ofResearch and Development, Washington, DC. July.

_____. 1997b. Exposure Factors Handbook. EPA 600/P-95/002 Fa. August.

_____. 1999a. EPA Region III Risk-Based Concentration Table. April.

_____. 1999b. A Guide to Preparing Superfund Proposed Plans, Records of Decision, andOther Remedy Selection Decision Documents. EPA 540-R-98-031, OSWER 9200.1-23P. July.

____. 1999c. Integrated Risk Information System (IRIS). On-line database. September.

____. 1999d. Current Drinking Water Standards. On-line athttp://www.epa.gov/OGWDW/creg.html. November.

____. 1999e. National Recommended Water Quality Criteria - Correction. EPA 822-Z-99-001.Office of Water, Washington, DC.

Wyoming, State of. 1999. Wyoming Surface Water Quality Standards, Second Draft. September.

TABLES

FIGURES

APPENDIX B

SUPPLEMENTAL RISK ASSESSMENT OF SEEP

TABLE OF CONTENTS

LIST OF TABLES B-ii LIST OF ABBREVIATIONS AND ACRONYMS B-iii

1.0 HUMAN HEALTH RISK ASSESSMENT METHODOLOGY 1-1 1.1 IDENTIFICATION OF CHEMICALS OF CONCERN 1-2 1.2 EXPOSURE ASSESSMENT 1-3 1.3 TOXICITY ASSESSMENT 1-8 1.4 RISK CHARACTERIZATION 1-8

2.0 HUMAN HEALTH RISK ASSESSMENT RESULTS 2-1 3.0 SCREENING- LEVEL ECOLOGICAL RISK ASSESSMENT METHODOLOGY. 3-1

3.1 SCREENING- LEVEL PROBLEM FORMULATION 3-1 3.2 SCREENING- LEVEL EXPOSURE ESTIMATE 3-2 3.3 RESULTS OF THE SCREENING- LEVEL ECOLOGICAL RISK ASSESSMENT 3-3

4.0 REFERENCES 4-1

LIST OF TABLES

B-l Permeability Constants for Chemical of Concern in Happy Jack Road Seep Water B-2 Human Health Risk Assessment for Happy Jack Road Seep Carcinogenic Risk and

Noncarcinogenic Hazard Index for RME Highway Maintenance Workers Exposed to Analytesin Seep Water, Incidental Seep Water, Ingestion

B-3 Human Health Risk Assessment for Happy Jack Road Seep Carcinogenic Risk andNoncarcinogenic Hazard Index for RME Highway Maintenance Workers Exposed to Analytesin Seep Water, Incidental Seep Water, Inhalation of VOCs

B-4 Human Health Risk Assessment for Happy Jack Road Seep Carcinogenic Risk andNoncarcinogenic Hazard Index for RME Highway Maintenance Workers Exposed to Analytesin Seep Water, Incidental Seep Water, Dermal Contact with Seep Water

B-5 Human Health Risk Assessment for Happy Jack Road Seep Carcinogenic Risk and Noncarcinogenic Hazard Index for CTE Highway Maintenance Workers Exposed to Analytesin Seep Water, Incidental Seep Water, Incidental Seep Water Ingestion

B-6 Human Health Risk Assessment for Happy Jack Road Seep Carcinogenic Risk andNoncarcinogenic Hazard Index for CTE Highway Maintenance Workers Exposed to Analytesin Seep Water, Incidental Seep Water, Inhalation of VOCs

B-7 Human Health Risk Assessment for Happy Jack Road Seep Carcinogenic Risk andNoncarcinogenic Hazard Index for CTE Highway Maintenance Workers Exposed to Analytesin Seep Water, Incidental Seep Water, Dermal Contact with Seep Water

B-8 Summary of Total Hazard Indices and Cancer Risks for Human Health Risk AssessmentHappy Jack Road Seep, F. E. Warren AFB

B-9 Water Quality Values (WQVs) Used for Screening- Level Ecological Risk AssessmentHappy Jack Road Seep

B-l0 Comparison of Chemical Concentrations to Water Quality Values Ecological Evaluationof Seep Water at Happy Jack Road, F. E. Warren AFB.

LIST OF ACRONYMS

AT averaging time AWWARF American Water Works Association Research Foundation BW body weight GDI chronic daily intake CF conversion factor cm centimeters COC chemical of concern CSF cancer slope factor CTE central tendency exposure ED exposure duration EF exposure frequency EPA United States Environmental Protection Agency EPC exposure point concentration ERA ecological risk assessment ET exposure time FEW F. E. Warren Air Force Base HEAST Health Effects Assessment Summary Tables HHRA human health risk assessment HI hazard index HQ hazard quotient hr/day hours per day ICLR incremental lifetime cancer risk InhR inhalation rate IR ingestion rate IRIS Integrated Risk Information System kg kilogram L/m3 liter per cubic meter LOOT Louisiana Department of Transportation m3/m cubic meters per hour mg/kg-day milligram per kilogram-day mg/L milligram per liter NCEA National Center for Environmental Assessment NE not estimated PC permeability constant RAGS Risk Assessment Guidance for Superfund RBC risk-based concentration RfD reference dose RME reasonable maximum exposure SHRTSC Superfund Health Risk Technical Support Center ug/L micrograms per liter USAF United States Air Force VF volatilization factor WQV water quality value WYDOT Wyoming Department of Transportation

1.0 HUMAN HEALTH RISK ASSESSMENT METHODOLOGY

This section summarizes the human health risk assessment (HHRA) for groundwater that seeps into the Happy Jack Road ditch adjacent to Zone C at F. E. Warren Air Force Base (FEW). To conservatively evaluate risks from the groundwater seep, chemical data from the nearest upgradient monitoring well, MW-210, were used. Because chemical data are not currently available for the seep water, concentrations of all detected compounds in MW-210 were conservatively assumed to be present in the seep without adjustment for potential dilution through fate and transport mechanisms.

The primary objective of this HHRA for seep water at FEW is to evaluate risks to humanhealth resulting from potential exposure to chemicals that may be present in the seep nearthe facility boundary. To meet this objective, a limited quantitative HHRA was conductedfor a highway maintenance worker using projected site conditions and chemicalconcentrations. The HHRA was conducted in accordance with the following U. S.Environmental Protection Agency (EPA) guidance documents:

• Risk Assessment Guidance for Superfund, Volume I, Human Health Evaluation Manual,Part A (EPA 1989) and Part B (EPA 1991 a);

• Risk Assessment Guidance for Superfund, Volume I, Human Health Evaluation Manual,Supplemental Guidance: Dermal Risk Assessment Interim Guidance (EPA 1997b).

Detailed risk assessment methodology is provided in the Baseline Risk Assessment Scoping Document for F. E. Warren Air Force Base (United States Air Force [USAF] 1999). The HHRA has been organized into the following sections:

• Identification of chemicals of concern • Exposure assessment • Toxicity assessment • Risk characterization

The following sections briefly describe each of these steps for the seep water HHRA atFEW.

1.1 IDENTIFICATION OF CHEMICALS OF CONCERN

Because chemical data are not currently available for the seep water at Happy Jack Road,all detected chemicals from upgradient well MW-210 were conservatively assumed to bepresent in the seep without adjustment for potential dilution through fate and transportmechanisms. That is, chemical data were used in the HHRA without adjustment for physical,chemical, or biological transformations that may occur such as volatilization, hydrolysis,oxidation, reduction, or biodegradation. The following organic compounds were detected inMW- 210:

• Chloroform (0.45 microgram per liter [ug/L]) • cis-1,2-Dichloroethylene (17 ug/L) • Dichlorodifluoromethane (0.34 ug/L) • trans-1,2-Dichloroethylene (0.71 ug/L) • Trichloroethylene (37 ug/L)

Inorganic compounds (excluding the essential nutrients calcium, magnesium, potassium, and sodium) detected in MW-210 include:

• Aluminum (0.766 milligram per liter [mg/L]) • Barium (0.233 mg/L) • Bromide (0.4 mg/L) • Chloride (39.8 mg/L) • Chromium, total (0.0114 mg/L)

• Copper (0.00392 mg/L) • Fluoride (0.27 mg/L) • Iron (0.515 mg/L) • Manganese (0.0168 mg/L) • Nitrogen, nitrate as N (48.1 mg/L) • Sulfate as SO4 (56.7 mg/L)

Of the inorganic analytes detected, those that were determined to be above background concentrations in the Zone C Final Remedial Investigation Report (USAF 2000) include aluminum, bromide, chromium, fluoride, and nitrate as nitrogen (N). The concentrations ofthese compounds were compared with EPA Region III risk-based concentrations (RBCs) toselect inorganic chemicals of concern (COCs) for further evaluation. If inorganic analyte concentrations were above background conditions, as defined in the Zone C Final Remedial Investigation Report, and above the Region III RBCs, they were retained for furtherevaluation of the seep water. Based on these COC selection criteria, the only inorganiccompound retained for further evaluation is bromide. All detected organics were retainedas COCs.


An exposure pathway describes the course that a chemical takes from a source to an exposed individual. An exposure pathway is considered to be complete when the following factorsare present:

• A source of potentially toxic chemicals and mechanism of release, • A retention or transport medium, • A point of potential human contact with the contaminated medium, and • An exposure route for chemical intake by a receptor (e.g., ingestion, inhalation or

dermal contact) at the exposure point.

If one of these factors is missing, the exposure pathway is incomplete and does not pose ahealth hazard. The exposure scenario assessed in this HHRA is based on the most likelycurrent and future use of the ditch adjacent to Happy Jack Road. That is, a scenario hasbeen assumed in which highway maintenance workers could potentially be exposed tochemicals in seep water that has discharged into the ditch. Exposure pathways evaluated inthis assessment include incidental ingestion of seep water, inhalation of volatilecompounds, and dermal contact with seep water. Exposure via incidental seep wateringestion is assumed to be negligible based on the nature of the highway maintenanceactivities expected to occur in a ditch (e.g., mowing). However, this exposure pathway wasevaluated quantitatively as a conservative measure.

The highway maintenance worker was evaluated assuming reasonable maximum exposure (RME), which is defined in Risk Assessment Guidance for Superfund (RAGS) (EPA 1989) as the highest exposure that is reasonably expected to occur. Routinely, the RME is characterizedby using 90 th to 95 th percentile values for some exposure parameters (EPA 1993), whileaverage values are used for others (EPA 1989). A central- tendency exposure (CTE) scenariowas also evaluated. The CTE is defined by EPA as "either the arithmetic mean risk or themedian risk" which is derived using average or 50 th percentile values for all exposureparameters. It should be noted that it was necessary to make certain assumptions about theexposure conditions for some exposure parameters that are not available in the sources ofexposure factor information.

Exposure to chemicals in seep water is characterized in terms of chronic daily intake(GDI) and is expressed in units of milligrams per kilogram of body weight per day (mg/ kg-day). Intake is estimated using assumptions that characterize exposure to seep water suchas contact rate, exposure frequency, exposure duration, body weight, and averaging time.Whenever available, EPA default exposure parameters were used to provide consistency withEPA methods. The exposure parameters that define the highway worker exposed via seep wateringestion, inhalation of volatile compounds, and dermal contact with chemicals in seep

water are discussed below.

Seep Water Ingestion:

Chronic Daily Intake (mg/kg-day) = C x IR x ET x EF x ED x CF BW x AT

Parameter RME CTE

C = Chemical Concentration (mg/L) site-specific site-specific

IR = Ingestion Rate (mL/hour)(1) 10 5

5ET = Exposure Time (hours/day)(2) 1 1

EF = Exposure Frequency (days/year)(3) 5 2

ED = Exposure Duration (years)(4) 25 7

CF = Conversion Factor (L/mL) 0.001 0.001

BW = Body Weight (kg)(5) 70 70

AT = Averaging Time (days)(5)

Carcinogenic: 25,550 25,550

Noncarcinogenic: 9,125 2,555

Notes: (1) Although ingestion of seep water is considered negligible for highway maintenance workers, an RME intake rate of 10 milliliter (mL)/hour and CTE intake rate of 5 mL/hour were estimated using professional judgment. (2) Based on professional judgment - estimated time required to mow seep area. (3) Wyoming Department of Transportation (WYDOT) 2000. (4) EPA 1993 (5) EPA 1989

Ingestion Rate: Although ingestion of seep water is considered negligible for highway maintenance workers, an RME intake rate of 10 mL/hour and a CTE intake rate of 5 mL/hour were estimated using professional judgment.

Exposure Frequency. The exposure frequency is how often (i.e., how many days per year) the hypothetical receptor is potentially exposed to the medium of concern. Based oninformation from the Louisiana Department of Transportation (LOOT) (2000), the interstatesystem requires a minimum of five mowing cycles per year. This is an upper-bound estimateassuming conditions such as an extended growing season and high precipitation. Therefore,the RME exposure frequency is estimated to be 5 days per year. The Wyoming Department ofTransportation (WYDOT) was contacted regarding its frequency of highway maintenanceactivities. All roadsides are mowed one time per year during the fall. Roads near citiesare mowed one additional time during July (WYDOT 2000). In addition, the States ofMaryland and Missouri have published frequencies of twice per year (www.co.cal.md.us/ services/highway.htm and www.house.state.mo.us/bills97/bills97/HB463.htm, respectively). Therefore, the CTE exposure frequency is estimated as 2 days per year.

Exposure Duration. The exposure duration (ED) is the number of years that an individualcomes into contact with the environmental medium. The EPA standard default exposureduration for an occupational worker evaluated under the RME scenario is 25 years (EPA1993). The exposure duration for an occupational worker evaluated under the CTE scenariois 7 years (EPA 1993).

Exposure Time. The exposure time is defined as the number of hours per day (hr/ day) thata receptor is potentially exposed to the medium of concern. For highway maintenanceworkers, the exposure time is estimated as one hour per day based on professionaljudgment.

Body Weight. The body weight of adults is defined as 70 kilograms (kg). This value isbased on EPA guidance and is an average default value for adults (EPA 1989).

Averaging Time. Averaging time is expressed in days and is defined as the ED multiplied bythe number of days per year (ED x 365). The RME and CTE averaging time for carcinogenic constituents is defined as 25,550 days (70 years x 365 days per year) (EPA 1989). For the noncarcinogenic constituents, the RME averaging time is 9,125 days, and the CTE averagingtime is 2,555 days.

Inhalation of Volatile Organic Compounds:

Chronic Daily Intake (mg/kg-day) = C x InhR x ET x EF x ED x VF BW x AT

Parameter RME CTE


InhR - Inhalation Rate (m3/hour) (1) 1.45 1.45

ET = Exposure Time (hours/day) (2) 1 1

EF = Exposure Frequency (days/year) (3) 5 2

ED = Exposure Duration (years) (4) 25 7

VF = Volatilization Factor (L/m3) (5) 0.5 0.5

BW = Body Weight (kg) (6) 70 70

AT = Averaging Time (days) (6)


Noncarcinogenic : 9,125 2,555

Notes: (1) EPA 1997e (2) Based on professional judgment — estimated time required to mow seep area (3) WYDOT 2000. (4) EPA 1993 (5) EPA 1991a (6) EPA 1989

Inhalation Rate. To evaluate the potential inhalation of vapors, an inhalation rate of1.45 cubic meters per hour (m3/hr) was used (EPA 1997e). This value corresponds to anadult engaged in light activity (EPA 1997e). This inhalation rate was used for both theRME and CTE scenarios (EPA 1993).

Volatilization Factor. This parameter describes the relationship between chemicalconcentrations in seep water and the concentration of the volatilized constituents in air.EPA guidance (199la) recommends a default volatilization factor of 0.5 liter per cubicmeter (L/m3) for groundwater or surface water (EPA 199la).

Dermal Contact with Seep Water:

Chronic Daily Intake (mg/kg-day) = C x SA x PC x ET x EF x ED x CF BW x AT

Parameter RME CTE


SA = Surface Area (cm2) (1) 3,160 3,160

ET = Exposure Time (hours/ day)(2) 1 1

EF = Exposure Frequency (days/year) (3) 5 2

ED = Exposure Duration (years) (4) 25 7

PC = Permeability Constant (cm/hour) (5) chemical-specific chemical-specific

CF = Conversion Factor (L/cm3) 0.001 0.001

BW = Body Weight (kg) (6) 70 70

AT = Averaging Time (days) (6)


Noncarcinogenic: 9,125 2,555

Notes: (1) EPA 1997e (2) Based on professional judgment — estimated time required to mow seep area (3) WYDOT 2000. (4) EPA 1993 (5) EPA 1997b (6) EPA 1989

Body Surface Area. Based on EPA guidance, the average exposed skin surface area for anadult wearing long pants and short sleeves (Page 6-5 of Exposure Factors Handbook [EPA1997e]) is 3,160 square centimeters (cm2). This value is based on surface areas forindividual body parts published on Table 6-4, Page 6-8 of EPA Exposure Factors Handbook(EPA 1997e). This value was used for both the RME and CTE scenarios.

Permeability Constant

The permeability constant (PC) reflects "the movement of the chemical across the skin tothe stratum comeum and into the bloodstream" (EPA 1989). Chemical-specific values for thePC are available in EPA dermal risk assessment guidance (EPA 1997b) and presented in TableB-l for the COCs in the seep water.

1.3 TOXICITY ASSESSMENT

The purpose of the toxicity assessment is to provide a quantitative estimate of therelationship between the magnitude of highway maintenance worker exposure to chemicals inseep water and the likelihood or severity of adverse health effects. Toxicity values areused to provide a quantitative estimate of this relationship. Reference doses (RfDs) andcarcinogenic slope factors (CSFs) developed by EPA are the principal toxicity values usedto estimate risks to human health from exposure to noncarcinogens and carcinogens,respectively. Sources of RfDs and CSFs include:

• Integrated Risk Information System (IRIS) database (EPA 2000) • Health Effects Assessment Summary Tables (HEAST) (EPA 1997d) • EPA National Center for Environmental Assessment (NCEA) Superfund Health Risk

Technical Support Center (SHRTSC) memoranda

Toxicity values for COCs in seep water from MW-210 are summarized below.

Compound RfDo(mg/kg-day)

RfDi(mg/kg-day)

CSFo (mg/kg-day)-1

CSFi(mg/kg-day)-1

Bromide NA NA NA NA

Chloroform 1.0E-2 (a) 8.6E-5(c) 6.1E-3(a) 2.3E-8(a)

cis-1,2-Dichloroethylene 1.0E-2 (b) NA NA NA

Dichlorodifluoromethane 2.0E-l (a) 5.0E-2(b) NA NA

trans-1,2-Dichloroethylene 2.0E-2 (a) NA NA NA

Trichloroethylene 6.0E-3 (C) NA 1.1E-2(c) 1.9E-6 (c)

Notes: RfDo = Oral reference dose RfDi = Inhalation reference dose CSFo = Oral cancer slope factor CSFi = Inhalation cancer slope factor mg/kg-day = Milligrams per kilogram-day NA = Not available (a) IRIS, EPA 2000 (b) HEAST, EPA 1997d (c) NCEA,; CSFo, CSFi and RfDo values for trichloroethylene have been withdrawn.

1.4 RISK CHARACTERIZATION

The purpose of the risk characterization is to integrate the results of the exposure andtoxicity assessments to produce an estimate of potential carcinogenic risk andnoncarcinogenic health effects. Estimated GDIs are combined with the appropriate toxicityvalues to estimate the likelihood of adverse effects in an exposed population. Because offundamental differences in the methods used to estimate risk for noncarcinogenic andcarcinogenic health effects, the risks are characterized separately.

The potential for noncarcinogenic health effects was evaluated by comparing the GDI for individual compounds with the corresponding RfD. The resulting ratio is a hazard quotient (HQ), which is estimated using the following equation:

HQ = CDI/RfD where,

HQ = Hazard quotient (unitless) GDI = Chronic daily intake (mg/kg-day) RfD = Reference dose (mg/kg-day)

The resulting HQ is a ratio that is used to evaluate whether the estimated exposure maypresent a potential noncarcinogenic health threat (EPA 1989). When the GDI exceeds theRfD, (i.e., the HQ is greater than 1), there is a potential for adverse noncarcinogenichealth effects as a result of exposure to constituent concentrations.

Noncarcinogenic effects resulting from exposure to multiple compounds are estimatedthrough the calculation of a hazard index (HI). An HI is a summation of HQ values forindividual compounds and is used to evaluate whether an exposed individual is at risk ofdeveloping adverse health effects from simultaneous exposure to multiple chemicals through

all complete exposure pathways. Effects from exposure to multiple chemicals are assumed tobe additive. That is, potential synergistic or antagonistic interactions are notconsidered. The HI was estimated using the following equation (EPA 1989):

HI = CDIi/RfDi+CDI2/RfD2+ ...+ CDIi/RfDi

where, HI = Hazard index (unitless) CDIi = Chronic daily intake for chemical i (mg/kg-day) RfDi = Reference dose for chemical i (mg/kg-day)

An HI greater than 1 suggests that simultaneous exposure to all chemicals may present a potential noncarcinogenic health threat. The level of concern increases as the HIincreases.

Health risk associated with potential exposure to carcinogens was estimated as theincreased probability of an individual developing cancer during his or her lifetime as aresult of exposure to a carcinogenic compound. These incremental lifetime cancer risks(ICLRs) were computed using the estimated GDIs estimated in the exposure assessment andthe CSFs identified in the toxicity assessment. The ICLR was estimated by summing thecancer risks across all carcinogenic chemicals and all complete exposure pathways.

The following equation was used to estimate carcinogenic risk:

ICLR = GDI x CSF

where, ICLR = Incremental lifetime cancer risk (unitless) GDI = Chronic daily intake (mg/kg-day) CSF = Cancer slope factor (mg/kg-day)-1

The resulting ICLR represents the incremental probability of an individual developingcancer over a lifetime as a result of exposure to a potential carcinogen. Cancer riskswere summed across all chemicals and exposure pathways to produce total carcinogenic risksfor both the RME and CTE scenarios.

2.0 HUMAN HEALTH RISK ASSESSMENT RESULTS

The following subsections summarize the RME and CTE carcinogenic risks and noncarcinogenic His for highway maintenance workers exposed to components detected in seep water.Carcinogenic risks and noncarcinogenic His were estimated for each compound and exposurepathway. The individual risks were then summed across exposure pathways. RME risks and Hisare presented in Tables B-2 through B-4. CTE risks and His are presented in Tables B-5through B-7.

Reasonable Maximum Exposure:

Chemical-specific RME carcinogenic risks for the ingestion, inhalation, and dermalexposure pathways are provided in Tables B-2, B-3, and B-4, respectively. Carcinogenicrisks were summed across exposure pathways are presented below for each compound.

Chemical Carcinogenic Risk

Chloroform 2 x 10-9 Trichloroethylene 1 x 10-8

As presented in Table B-8, the total RME carcinogenic risk for a highway maintenanceworker exposed to compounds in seep water in the ditch adjacent to Happy Jack Road is 1 x10-8 , which is below EPA's target risk range of 1 x lO-4 to 1 x 10-6 (EPA 1991b).

Noncarcinogenic health effects were estimated by comparing the estimated GDIs to EPA-derived RfDs. The total chemical-specific HQs were summed across all exposure pathways andare presented below. Chemical-specific noncarcinogenic HQs and His are presented in TablesB-2, B-3, and B-4 for the ingestion, inhalation, and dermal exposure pathways,respectively.

Chemical Noncarcinogenic Hqs

Bromide NE Chloroform 7 x 10-4 cis-1,2-Dichloroethylene 1 x 10-5 Dichlorodifluoromethane 1 x 10-6 trans-1,2-Dichloroethylene 2 x 10-7 Trichloroethylene 6 x lO-5

If RfDs were unavailable, noncarcinogenic HQs could not be estimated (NE). As shown inTable B-8, the total noncarcinogenic HI for all exposure pathways and compounds is 0.0008which is below the target HI of 1.0 (EPA 1991b).

Central Tendency Exposure: Chemical-specific CTE carcinogenic risks for the ingestion, inhalation, and dermalexposure pathways are provided in Tables B-5, B-6, and B-7, respectively. Carcinogenicrisks were summed across exposure pathways are presented below for each compound.

Chemical Carcinogenic Risk

Chloroform 2 x lO-10 Trichloroethylene 1 x 10-9

As presented in Table B-8, the total CTE carcinogenic risk for a highway maintenanceworker exposed to compounds in seep water in the ditch adjacent to Happy Jack Road is 2 x10-9 , which is below EPA's target risk range of 1 x 10-4 to 1 x 10-6 (EPA 1991b).

Noncarcinogenic health effects were estimated by comparing the estimated GDIs toEPA-derived RfDs (EPA 2000), (EPA 1997d). As presented in Table B-8, the totalchemical-specific HQs were summed across all exposure pathways and are presented below.Chemical-specific noncarcinogenic HQs and His are presented in Tables B-5, B-6, and B-7for the ingestion, inhalation, and dermal exposure pathways, respectively.

Chemical Noncarcinogenic Hqs

Bromide NE Chloroform 3 x 10-4 cis-1,2-Dichloroethylene 4 x lO-6 Dichlorodifluoromethane 4 x 10-7 trans-1,2-Dichloroethylene 8 x 10-8 Trichloroethylene 2 x lO-5

If RfDs were unavailable, noncarcinogenic hazard quotients could not be estimated (NE).The total noncarcinogenic HI for all CTE exposure pathways and compounds is 0.0003, whichis below the target ffl of 1.0 (EPA 1991b).

3.0 SCREENING-LEVEL ECOLOGICAL RISK ASSESSMENT METHODOLOGY

This section summarizes the screening- level ecological risk assessment (ERA) forgroundwater that seeps into the Happy Jack Road ditch adjacent to Zone C at F. E. WarrenAir Force Base (FEW). As described in Appendix A for the HRHA, chemical data from thenearest upgradient monitoring well (MW), MW-210, were used for the evaluation (see FigureA.1 of Appendix A). Because chemical data are not currently available for the seep water,concentrations of all detected compounds in MW-210 were conservatively assumed to bepresent in the seep without adjustment for potential dilution through fate and transportmechanisms.

The primary objective of the ERA for seep water at FEW is to evaluate risks to ecological receptors resulting from potential exposure to chemicals that may be present in the seepnear the facility boundary. Steps 1 (screening-level problem formulation) and 2(screening-level exposure estimate) of the eight-step ecological risk assessment processdescribed in Framework for Ecological Risk Assessment (EPA 1992) were conducted toevaluate potential ecological effects from exposure to seep water at Happy Jack Road.Although ecological exposure to seep water at Happy Jack Road is likely to be extremelylimited, a screening-level evaluation of chemical concentrations in upgradient groundwaterMW-210 was conducted as a conservative measure, and the potential for adverse effects ofcompounds in seep water on aquatic organisms was quantified. Steps 1 and 2 of thescreening-level ERA process are described below. Details of the ecological risk assessmentprocess for FEW are presented in the Baseline Risk Assessment Scoping Document (USAF1999).

3.1 SCREENING-LEVEL PROBLEM FORMULATION

As described in Appendix A for the human health evaluation, chemical data were used in the ERA without adjustment for physical, chemical, or biological transformations that mayoccur such as volatilization, hydrolysis, oxidation, reduction, or biodegradation. Thefollowing organic compounds were detected in MW-210:

• Chloroform (0.45 ug/L) • cis-1,2-Dichloroethylene (17 ug/L) • Dichlorodifluoromethane (0.34 ug/L) • trans-1,2-Dichloroethylene (0.71 ug/L) • Trichloroethylene (37 ug/L)

Inorganic compounds (excluding the essential nutrients calcium, magnesium, potassium, and sodium) detected in MW-210 include:

• Aluminum (0.766 mg/L) • Barium (0.233 mg/L) • Bromide (0.4 mg/L) • Chloride (39.8 mg/L) • Chromium, total (0.0114 mg/L) • Copper (0.00392 mg/L) • Fluoride (0.27 mg/L) • Iron (0.515 mg/L) • Manganese (0.0168 mg/L) • Nitrogen, nitrate as N (48.1 mg/L) • Sulfate as S04 (56.7 mg/L)

Of the inorganic analytes detected, those that were determined to be above background concentrations in the Zone C Final Remedial Investigation Report (USAF 2000) were retainedas COCs and include aluminum, bromide, chromium, fluoride, and nitrate as N.

3.2 SCREENING-LEVEL EXPOSURE ESTIMATE

Quantification of potential adverse effects was accomplished through the calculation of screening- level ecological HQs. The concentrations of all organic compounds detected in upgradient groundwater MW-210 were compared to conservative water quality values (WQVs) presented in Table B-9. All inorganic compounds detected in MW-210 that were determined tobe above background in the Zone C Remedial Investigation Report (USAF 2000) were also evaluated as COCs.

WQVs used in the screening-level assessment were developed for screening purposes and are values below which there is no concern regarding adverse ecological effects. WQVs were compared with COC concentrations in upgradient groundwater MW-210 to developscreening-level HQs. WQVs were selected primarily from the State of Wyoming surface waterquality standards (WYDOT 1999) and EPA databases according the following hierarchy:

1. Chronic Quality Standards for Wyoming Surface Waters (1999) 2. National Recommended Chronic Water Quality Criteria (EPA 1999) 3. Water Quality Criteria Summary (EPA 1986) 4. Preliminary Remediation Goals (PRGs) for Ecological Endpoints (Efroymson et al. 1997) 5. Adjusted Acute Quality Standards for Wyoming Surface Waters (1999) 6. Adjusted Acute National Recommended Water Quality Criteria (EPA 1999) 7. Adjusted Acute Quality Criteria for Water (EPA 1986)

These screening benchmarks for surface water are presented in Table B-9. Theconcentrations have been adjusted, when necessary, to site-specific hardness (average—275mg/L as calcium carbonate [CaCOs]) and pH (average = 7.4). Also, if acute standards wereapplicable, they were adjusted to chronic criteria using an uncertainty factor of 0.1 (EPA1997a). The HQs were expressed as the ratio of COC concentrations to WQVs. The HQs wereestimated as follows:

HQi = EPCi/WQVi

where,

HQ = hazard quotient for constituent i (unitless) EPQ = exposure point concentration for constituent i (mg/L) WQVi = water quality value for constituent i (mg/L)

The resulting HQ is a ratio that can be used to evaluate whether the constituent ispresent at a level that will likely result in adverse ecological effects (EPA 1997c). Thatis, when the EPC exceeds the WQV (i.e., the HQ is greater than 1), there is a potentialfor adverse ecological affects.

3.3 RESULTS OF THE SCREENING-LEVEL ECOLOGICAL RISK ASSESSMENT

The results of the screening-level ecological assessment are presented in Table B-10. TheHQs for all COCs were below 1.0 with the exception of aluminum (HQ = 8.8). Aluminum is not expected to pose ecological concern based on the extremely limited potential forecological exposure within the seep. In addition, the concentration of aluminum used asthe EPC is the total concentration of aluminum measured at MW-210 and likely includes alarge fraction of aluminum in forms that are not biologically reactive (i.e., organicallycomplexed or sorbed by particulates). As a result, the toxicity of aluminum is likelyoverestimated (British Columbia Ministry of Environment, Lands, & Parks 1988).

Bromide, dichlorodifluoromethane, fluoride, and nitrate as N could not be evaluatedbecause of a paucity of toxicity data. It is unlikely that these compounds are present atconcentrations that pose ecological risk, particularly considering the limited ecologicalexposure expected to occur in the seep.

According to the British Columbia Ministry of Environment, Lands, & Parks (1981a), total fluoride in fresh water should not exceed 0.3 mg/L when water hardness is greater than 50mg/L as CaCOs. The average surface water concentration of CaCOa at FEW is 275 mg/L. The concentration of fluoride in MW-210 is 0.27 mg/L, which is below the fresh water standardset in British Columbia, Canada.

The fresh water quality standard for nitrate set by the British Columbia Ministry ofEnvironment, Lands, & Parks (1981b) is 200 mg/L. The concentration of nitrate detected inMW-210 is 48.1 mg/L which is well below the standard set in British Columbia, Canada.

Dichlorodifluoromethane (CFC-12) is a volatile refrigerant that will not likely bepersistent in a seep environment, particularly at a groundwater concentration of 0.34ug/L. Bromide is a drinking water disinfection by-product and is ubiquitous throughout theUnited States (Amy et al. 1995). Although no ecological water quality standards wereidentified for this compound, a groundwater quality standard of 10 mg/L has been proposedby the American Water Works Association Research Foundation (Amy et al. 1995). Theconcentration of bromide in MW-210 is 0.4 mg/L, which is well below the proposed 10 mg/Lstandard.

In summary, concentrations of COCs evaluated in MW-210 are unlikely to pose ecologicalrisk based on the following:

1. Concentrations of COCs in MW-210 are well below published water quality values foraquatic receptors.

2. Concentrations of COCs in MW-210 were conservatively assumed to be present in theseep without adjustment for potential dilution through fate and transportmechanisms. That is, chemical data were used in the screening-level ERA withoutadjustment for physical, chemical, or biological transformations such asvolatilization, hydrolysis, oxidation, reduction, or biodegradation that may occur.

3. Ecological exposure is likely to be extremely limited in Happy Jack Road ditch.

4.0 REFERENCES

Amy, Gary, Mohamed Siddiqui, Wenyi Zhai, Jean DeBroux, and Wilbert Odem. 1995. Survey ofBromide in Drinking Water and Impacts on DBF Formation. American Water WorksAssociation Research Foundation (AWWARF), University of Colorado at Boulder,Boulder, Colorado. March.

British Columbia Ministry of Environment, Lands, & Parks. 198 la. Water Quality Criteriafor Fluoride. Overview Report. Resource Quality Section Water Management Branch.

____. 1981b. Water Quality Criteria for Nitrogen (Nitrate, Nitrite, and Ammonia). Overview Report. Resource Quality Section Water Management Branch.

____. 1988. Water Quality Criteria for Aluminum. Overview Report. Resource Quality SectionWater Management Branch. March.

Efroymson, R. A., G. W. Suter, II, B. E. Sample and D. S. Jones. 1997. PreliminaryRemediation Goals for Ecological Endpoints. Oak Ridge National Laboratory.ES/ER/TM-162/R2. August.

Louisiana Department of Transportation (LOOT). 2000. Downloaded from http://www.dotd.state.la.us/press/archives/wildflower.html.

OSWER Directive 9285.7-01B. Office of Solid Waste and Emergency Response, Washington DC. December.

United States Air Force (USAF) 1999. Baseline Risk Assessment Scoping Document for F. E. Warren AFB, Cheyenne, Wyoming. February.

____. 2000. Final Remedial Investigation for Zone C. F. E. Warren AFB, Cheyenne, Wyoming.

United States Environmental Protection Agency (EPA). 1986. Water Quality Criteria Summary. Table prepared by Ecological Risk Assessment Branch and Human Health Risk Assessment Branch. Heath and Ecological Criteria Division, Office of Science and Technology. Washington

____. 1989. Risk Assessment Guidance for Superfund, Human Health Evaluation Manual, PartA-Volume I. Interim Final. EPA/540/1-89/002. Office of Emergency and Remedial Response,Washington DC. December.

____. 1991a. Risk Assessment Guidance for Superfund, Human Health Evaluation Manual, Part B - Volume I. "Development of Risk-based Preliminary Remediation Goals."

____. 1991b. "Role of the Baseline Risk Assessment in Superfund Remedy SelectionDecisions." Memorandum from Don R. Clay, U. S. Environmental Protection Agency toDirectors of Waste Management Division (Regions I, IV, V, VII, VIII), Emergency andRemedial Response Division (Region II), Hazardous Waste Management Division (RegionsHI, VI, DC), and Hazardous Waste Division (Region X). Office of Solid Waste andEmergency Response Directive 9355.0- 30. April.

____. 1992. Framework for Ecological Risk Assessment. Risk Assessment Forum, Washington,D.C. EPA/630/R-92/001.

____. 1993. Superfund's Standard Default Exposure Factors for the Central Tendency and Reasonable Maximum Exposure. Draft. November.

____. 1997b. Risk Assessment Guidance for Superfund, Volume I: Human Health Evaluation Manual Supplemental Guidance, Dermal Risk Assessment Interim Guidance. Office ofEmergency and Remedial Response, Washington DC. May.

____. 1997e. Exposure Factors Handbook. EPA/600/P-95/002Fc. Office of Research and Development, Washington DC. August.

____. 1997d. Health Effects Assessment Summary Tables (HEAST). FY1997 Update. EPA 540/R-97-036. Office of Research and Development, Office of Emergency and Remedial Response, Washington, D. C. July.

____. 1997a. Uncertainty Factor Protocol for Ecological Risk Assessment: Toxicological Extrapolations to Wildlife Receptors. EPA Region VIII, Ecosystems Protection and Remediation Division, Denver, Colorado. February.

____. 1997c. Interim Final for Ecological Risk Assessment Guidance for Superfund: Process for Designing and Conducting Ecological Risk Assessments. Office of Solid Waste and Emergency Response, Washington, D.C. EPA 540-R-97-006. June.

____. 1999. National Recommended Water Quality Criteria - Correction. EPA 822-Z-99-001. Office of Water. April.

____. 2000. Integrated Risk Information System (IRIS) chemical files.

Wyoming Department of Transportation (WYDOT). 1999. Wyoming Surface Water QualityStandards, Second Draft, May 1999. (September). Printed from: http://deq.state.wy.us/wqd/chldrf2.htm.

____. 2000. Personal communication between Jennifer Sanders of Earth Tech and Mr. Tony Abila of the Highway Maintenance Division.

Wyoming, State of. 1999. Wyoming Surface Water Quality Standards, Second Draft, May.On-line at http://deq.state.wy.us/wqd/ch1drf2.htm.

TABLES

APPENDIX C

RESPONSE TO COMMENTS

Responses to Comments on the Draft Final Record of Decision for

Zone C, Operable Unit 11, Landfill 3 F. E. Warren Air Force Base

July 2001

WDEO August 10, 2001 Comments:

"The Wyoming Department of Environmental Quality has reviewed the above referenced document. All of our comments have been addressed. We have also reviewed and concur with the Environmental Protection Agency's comments."

EPA August 14, 2001 Comments:

Comments are keyed to the document by Page, Section (Sec.), Column (Col.), paragraph, sentence, figure, table, or line as indicated. The general outline structure of the RODwas followed to identify specific comments. Most of the following pertain to how EPAcomments on the draft ROD were addressed.

General Comments

1. Comment: None offered.

Response: None Required.

Specific Comments

2. Comment: Sec. 1.4, Page 1-2, first bulletin describing the selected remedy. EPArecommends rephrasing "An alternate water supply" to "A municipal water supply." Thiswould make it clearer that the alternate supply is a permanent pipeline hookup as opposedto something like bottled water.

Response: The first bulletin has been rephrased as suggested. It now reads, in part: "A municipal water supply is being provided to the residents of Nob Hill through an interim action taken at LF-03 in January 1997."

3. Comment: Sec. 1.4, Page 2-1, last two paragraphs. These two paragraphs may beoptionally deleted. While the discussion does add to flow, these particular elements are discussed elsewhere in this ROD and are not specifically required in the Declaration section by guidance.

Response: We understand the comment to refer to Section 1.4 Page 1-3, last two paragraphs.The comment is noted, and the Air Force chooses to retain these paragraphs for clarity,even though this discussion is not specifically required by the guidance.

4. Comment: Sec. 2.2, Site History and Enforcement Activities, last paragraph, last sentence. Change "issued" to "issues".

Response: The sentence has been modified as suggested. It now reads: "The USAP issues theROD, with EPA and WDEQ concurrence on the content."

5. Comment: Sec. 2.3, Community Participation. Briefly describe the attendance at the public meeting (i.e., who was there who was not Air Force, Air Force contractor, EPA, or WDEQ?)

Response: Attendance at the public meeting is described as suggested. The modified paragraph now reads:

"The notice of availability of this document was published in the Wyoming TribuneEagle and the Casper Star- Tribune on March 11, 2001. The fact sheet related to theZone C ROD was mailed out to interested parties and the Restoration Advisory Boardon March 13, 2001. A public comment period for the Proposed Plan was held from March12, 2001, through April 11, 2001. In addition, a public meeting was held on March27, 2001, to present the Proposed Plan to a broader community audience than thosewho had already been involved at the site. The meeting was attended by four RABmembers, two newspaper reporters, and two members of the Cheyenne Board of PublicUtilities, in addition to representatives from the Air Force and its contractors,EPA, and WDEQ. At this meeting, representatives from FEW, EPA and the WDEQ answeredquestions about the site and the remedial alternatives. As described in theResponsiveness Summary (Section 3), which is part of this ROD, no written commentswere received from the public and no comments were received verbally during the public meetings that would change the remedy selection process. Official transcriptsof the public meetings were prepared and placed in the Administrative Record."

6. Comment: Sec. 2.4, Scope and Role of Operable Unit/Response Action, first paragraph.The second to last sentence states "all hazardous wastes excavated were taken off-site to a licensed hazardous waste treatment and storage facility..." Describe the amount ofwaste, how it was hazardous (e.g., characteristically hazardous based on lead), and thename and EPA identification number of the receiving facility. This is necessary to be ableto demonstrate and track compliance with the "Off-site Rule". If this statement abouthazardous waste is not accurate, then clearly identify none of the wastes were hazardousunder the definitions of RCRA.

Response: The text in the first paragraph of Section 2.4 was revised to read:

"During March and April 1999, all wastes from LF3 were excavated and placed in thewaste consolidation area at LF5a. One 55 gallon drum of soil contaminated withcopper sulfate was manifested off-base using Clean Harbors, Inc. The waste wasdisposed of at the Kimball, Nebraska facility (EPA ID No. NEB981723513), where theultimate disposition was landfilling. In addition, a small amount of medical waste(less than 200 pounds) was collected and disposed with other base-generated medicalwaste through incineration. These early response actions will be consistent withfinal actions selected."

7. Comment: Sec. 2.5, Site Characteristics, Page 2-11, first (partial) paragraph. There isa statement that the draw down versus time results indicated the horizontal extent ofwater-bearing materials is likely limited. This needs some clarification. Could theresults not also mean a limited horizontal extent to the influence of pumping? Is there adefinable perched aquifer? Is the intent to imply a saturated and mobile "channel" withinotherwise unsaturated and relatively immobile fines?

Response: The results indicate that the pumping had a limited horizontal influence. There may be several causes of that limited influence, among them the limited horizontal extent of water-bearing materials, which may be due to buried alluvial/ fluvial channelsor general heterogeneity of soil types. The evidence does not appear to support thepresence of a perched aquifer, since the local water table is relatively consistent acrossthe site. The text will be revised to allow for these alternate interpretations, asfollows:

"A pumping test was conducted at well 64 in November 1999, following completion of astep test. The drawdown versus time results indicated a limited horizontal influencefor the pumping well. This limited influence may be due to a restricted horizontalextent of water- bearing materials, lateral heterogeneity or possibly alluvial/fluvial channeling. Similar response was noted in the observation wells OB-1 andMW196A. The hydraulic conductivity (K) calculated from the pump test data averaged2.1 ft/ day. This is similar to the average hydraulic conductivity of 1.8 ft/daydetermined from slug tests."

8. Comment: Sec. 2.6.2, Groundwater and Surface Water Uses. The seep should also be described here. It would be helpful to describe the (small) size and that standing wateris rare. When standing water exists, it would be used only by wildlife.

Response: The following paragraph has been added to the end of Section 2.6.2.

"A small groundwater seep is located immediately north of Happy Jack Road. This seepis small and rarely has standing water. When standing water does exist, it wouldonly be used by wildlife."

9. Comment: Sec. 2.10, Comparative Analysis of Alternatives, Page 2-27, following the bulletins. The discussion for "Overall Protection of Human Health and the Environment" is treated as if it were a modifying, rather than threshold criteria both on Page 2-27 and Table 2-2. Rephrase the discussion such that the alternative meets the criterion or not.If not, explain why not. If protective, then explain how the alternative is protective. Identify Table 2-2 as a summary of the key points for the threshold and balancingcriteria. Table 2-2 does a good job of ranking the alternatives relative to theirperformance with the modifying criteria to help describe the trade-offs among thebalancing criteria. However, the Overall Protection of Human Health and the Environmentand Compliance with ARARs are relatively ranked, and cannot be so as threshold criteria.The simplest "fix" may be to just remove these two criteria from Table 2-2. Otherwise, thetable will need to be restructured for the threshold criteria (meets criterion or does notmeet criterion as headers).

Response: Table 2-2 has been modified to eliminate the rows for "Overall Protection of Human Health and the Environment" and "Compliance with ARARs." The discussion for "Overall Protection of Human Health and the Environment" has been reworded as follows:

"All alternatives, with exception of Alternatives 1 and 2, are protective of human health and the environment. Alternative 1 will not adequately protect futurepotential groundwater users since no action will be taken to restrict exposure tocontaminated groundwater. Alternative 2, Institutional Controls, eliminates thegroundwater pathway on base, but will not adequately protect future Nob Hillgroundwater users, since no monitoring program will be implemented. Alternative 3,MNA, eliminates the groundwater pathway on base via institutional controls and willprotect future Nob Hill groundwater users through a groundwater monitoring programthat will confirm the continued lack of exposure to contaminants. This conclusion issupported by groundwater modeling results. The alternatives that include activeremedial systems for the plume (i.e., Alternatives 4, 5, 6, and 7), are protectiveof human health and the environment since the active remedial systems will removecontamination from groundwater before it reaches Crow Creek and/or migrates off-site. For these alternatives, on base exposure to groundwater contamination ismitigated by use of institutional controls. In all cases, there is minimalenvironmental risk."

10. Comment: Figure 2-5, Carlin Heights MFH Preliminary Concept Expansion Plan. Theexpansion may overlay both Plume E being addressed in OU2 and the LF3 associated plume. Isthe modeling done in the risk assessment for indoor air sufficient to state no significantrisk if houses are built as planned? If the modeling is acceptable (i.e., the assumptionscorrespond and the results indicate risk is not significant), then state it here. If not,identify what controls are needed in the BGP. Is the construction to be slab, crawlspace,or basement (if not known, can a control in the BGP specify prohibitions to crawlspace orbasement)? These are issues which should be addressed in Sec. 2.6.1 (at least to the levelof detail the performance standard is clear). The possibilities include: