vapor intrusion pathway feasibility study · connection with the property at 2010 east hennepin...

4300 MarketPointe Drive, Suite 200

Minneapolis, MN 55435

Phone: 952.832.2600

Fax: 952.832.2601

Vapor Intrusion Pathway Feasibility Study

East Hennepin Avenue Site

Minneapolis, Minnesota

Prepared for

General Mills, Inc.

April 2016

i

Vapor Intrusion Pathway Feasibility Study

April 2016

Contents

Executive Summary .............................................................................................................................................................................. 1

1.0 Introduction ........................................................................................................................................................................... 3

1.1 Scope of Feasibility Study ........................................................................................................................................... 4

2.0 Site Characterization........................................................................................................................................................... 6

2.1 Background ....................................................................................................................................................................... 6

2.1.1 Central Area Setting ................................................................................................................................................. 6

2.2 Previous Investigations and Response Action Activities ................................................................................. 6

2.3 Site Conceptual Model ................................................................................................................................................. 8

2.3.1 Vapor Sources ............................................................................................................................................................. 9

2.3.2 Geology and Hydrogeology .................................................................................................................................. 9

2.3.3 Spatial Distribution of Contaminants ................................................................................................................ 9

2.3.4 Potential Receptors.................................................................................................................................................10

2.3.5 Vapor Transport Mechanisms ............................................................................................................................10

2.3.6 Building Vapor Mitigation ....................................................................................................................................10

2.3.6.1 Central Area Building Mitigation Status ...............................................................................................11

2.4 Risk Assessment ............................................................................................................................................................11

3.0 Regulatory Considerations .............................................................................................................................................13

3.1 Remedial Action Objectives ......................................................................................................................................13

3.2 ARARs and TBCs ............................................................................................................................................................13

3.2.1 Classification of ARARs and TBCs .....................................................................................................................14

3.3 Preliminary Remediation Goals ...............................................................................................................................14

4.0 Technology Screening .....................................................................................................................................................16

4.1 Development of General Response Actions ......................................................................................................16

4.2 Evaluation and Screening of Technologies ........................................................................................................18

4.3 Retained Technologies ...............................................................................................................................................19

5.0 Development of Remedial Alternatives ....................................................................................................................21

5.1 Alternative 1 – No Further Action Beyond Previous Response Actions ..................................................21

5.2 Alternative 2 – Monitored Natural Attenuation ...............................................................................................21

5.3 Alternative 3 – Long Term O&M of SSD Systems ............................................................................................22

ii

5.4 Alternative 4 – Enhanced Bioremediation via Injection Events ..................................................................23

5.5 Alternative 5 – Enhanced Bioremediation via Recirculating System ........................................................24

6.0 Detailed Analysis of Alternatives .................................................................................................................................26

6.1 Detailed Analysis Overview .......................................................................................................................................26

6.1.1 Alternative Definition .............................................................................................................................................26

6.1.2 Evaluation Criteria ...................................................................................................................................................26

6.1.2.1 Threshold Criteria ..........................................................................................................................................26

6.1.2.2 Balancing Criteria...........................................................................................................................................27

6.1.2.3 Modifying Criteria .........................................................................................................................................28

6.1.2.4 Additional Considerations .........................................................................................................................28

6.1.3 Comparative Analysis of Alternatives ..............................................................................................................29

6.2 Detailed Analysis of Remedial Alternatives ........................................................................................................29

6.2.1 Alternative 1 – No Further Action Beyond Previous Response Actions .............................................29

6.2.1.1 Alternative 1 – Threshold Criteria ...........................................................................................................29

6.2.1.2 Alternative 1 – Balancing Criteria ............................................................................................................29

6.2.1.3 Alternative 1 – Additional Considerations ...........................................................................................30

6.2.1.4 Alternative 1 – Summary ............................................................................................................................30

6.2.2 Alternative 2 – Monitored Natural Attenuation ..........................................................................................30





6.2.3 Alternative 3 – Long-Term O&M of SSD Systems ......................................................................................32





6.2.4 Alternative 4 – Enhanced Bioremediation via Injection Events .............................................................34





6.2.5 Alternative 5 – Enhanced Bioremediation via Recirculation ...................................................................37


iii




6.3 Recommended Alternative .......................................................................................................................................39

7.0 Summary and Conclusions .............................................................................................................................................41

References .............................................................................................................................................................................................43

List of Tables

Table 1 Potential Action-Specific ARARs and TBCs

Table 2 Potential Location-Specific ARARs and TBC

Table 3 Potential Chemical-Specific ARARs and TBCs

Table 4 Remedial Technology and Process Option Screening

Table 5 Amendment Sensitivity Analysis

Table 6 Comparative Analysis Summary by Alternatives

Table 7 Alternative 2 Cost Estimate




List of Figures

Figure 1 Location Map

Figure 2 Study Area

Figure 3 Potential Off-Site TCE Sources

Figure 4 MPCA SA249 Groundwater and Soil Gas Sampling – TCE Results

Figure 5 Building Mitigation Status – April 2016

Figure 6 Glacial Drift Groundwater Monitoring Network

Figure 7 Alternative 4 – Enhanced Bioremediation via Injection Event(s)

Figure 8 Alternative 5 – Enhanced Bioremediation via Recirculation

List of Appendices

Appendix A Supporting Cost Details

Appendix B Sustainability Evaluation Summary

iv

Certifications

I hereby certify that this report was prepared by me or under my direct supervision and that I am a duly Licensed

Professional Engineer under the laws of the state of Minnesota.

April 6, 2016

Alec Danielson

PE #: 48763

Date

1

Executive Summary

This report describes the vapor intrusion (VI) pathway feasibility study completed by Barr Engineering Co.

(Barr) on behalf of General Mills, Inc. (General Mills) in Minneapolis, Minnesota. Feasibility study activities

were informed by the results of numerous soil, soil gas, and groundwater investigations conducted by

General Mills, the Minnesota Pollution Control Agency (MPCA), and others to assess volatile organic

compound (VOC) concentrations, primarily trichloroethylene (TCE) at and in the vicinity of the property at

2010 East Hennepin Avenue (Site), and a human health risk assessment (HHRA) prepared by Haley &

Aldrich, Inc. on behalf of General Mills (H&A, 2015). The Study Area, the larger area where investigations

have been conducted, is divided into four geographic regions, including the Site, Northeast Area, Central

Area, and Southwest Area. Feasibility study activities focus on the Central Area, only a portion of which

may be down-gradient of the Site.

Although off-Site sources are impacting shallow groundwater in the Central Area and the HHRA

concluded that exposure pathways in the Central Area currently are either incomplete or insignificant and

are not expected to be significant in the future, this feasibility study was prepared for the Central Area at

the direction of MPCA in its letter that provided comments to the Vapor Intrusion Pathway Investigation

Report (VIPI Report; Barr, 2015c, MPCA, 2015a). By preparing this study for the Central Area, General Mills

does not acknowledge or agree that TCE impacts in the Central Area or elsewhere in the Study Area are

associated with its former operations at the Site.

A great deal of remedial action work was completed at the Site and in the Study Area prior to beginning

this feasibility study. General Mills has completed sub-slab soil gas and/or indoor air sampling at 344

properties and installed sub-slab depressurization (SSD) systems for vapor mitigation at 189 properties in

the Study Area since November 2013. This work is documented in the Sub-Slab Sampling and Building

Mitigation Implementation Report (Implementation Report; Barr, 2015b). In addition to the numerous

investigations conducted by General Mills, this feasibility study follows 25 years of groundwater

remediation performed by General Mills.

The remedial action objective (RAO) developed for the Central Area as part of this feasibility study is to

maintain insignificant potential risk to human health from inhalation exposure to TCE in indoor air

resulting from TCE concentrations in soil gas and groundwater. As stated in the Remedial Action Plan

(RAP) Modification #1, dated March 11, 2014 (MPCA, 2014a) to the Response Order by Consent between

General Mills and the MPCA, dated October 23, 1984 (Consent Order; MPCA, 1984), General Mills is

responsible only for implementing response actions to address impacts that are due to its former

operations at the Site. By preparing this feasibility study and developing this RAO, General Mills does not

acknowledge or agree that TCE impacts in the Central Area or elsewhere in the Study Area are associated

with its former operations at the Site. The preliminary remediation goal (PRG) selected to evaluate the

remedial alternatives developed as part of the feasibility study is the MPCA intrusion screening values

(ISVs) for TCE in indoor air.

2

Various response action technologies were screened based on their ability to meet the RAO and PRG.

Appropriate technologies were then assembled into a range of remedial action alternatives that are

evaluated in the detailed analysis phase of the feasibility study. Response action technologies may target

the TCE-impacted soil vapor itself and/or the shallow groundwater that may act as a source of the TCE

impacts in soil vapor.

The response action technologies that were retained following the screening and used to develop

comprehensive remedial alternatives for further evaluation included:

Installation of additional SSD systems (at residential properties within the Central Area that

currently do not have active SSD systems);

Operations and maintenance (O&M) of SSD systems;

Institutional controls;

Monitored natural attenuation;

Expanded/modified groundwater extraction; and

In-situ groundwater bioremediation.

The five remedial alternatives developed as part of the feasibility study were:

Alternative 1 – No further action beyond previous response actions;

Alternative 2 – Monitored natural attenuation;

Alternative 3 – Long-term O&M of SSD systems;

Alternative 4 – Enhanced groundwater bioremediation via injection events; and

Alternative 5 – Enhanced groundwater bioremediation via recirculating system.

A detailed evaluation of each remedial alternative against criteria set forth in the Comprehensive

Environmental Response Compensation and Liability Act (CERCLA) was performed. The CERCLA

evaluation criteria include overall protection of human health and the environment, compliance with

applicable or relevant and appropriate requirements, long-term effectiveness and permanence, reduction

of toxicity, mobility or volume through treatment, short-term effectiveness, implementability, and cost.

Additional considerations with the potential to impact the community also were evaluated.

Alternative 3 – Long-term O&M of SSD systems presented the best balance of tradeoffs of the primary

balancing criteria and was selected as the recommended alternative based on the detailed analysis.

3

1.0 Introduction

This report describes the vapor intrusion (VI) pathway feasibility study activities completed by Barr

Engineering Co. (Barr), on behalf of General Mills, Inc. (General Mills). Feasibility study activities were

informed by the results of numerous soil, soil gas, and groundwater investigations completed in

connection with the property at 2010 East Hennepin Avenue (Site), including the VI pathway investigation

conducted in 2014 and 2015, and documented in the Vapor Intrusion Pathway Investigation Report (VIPI

Report; Barr, 2015c). The investigations assessed volatile organic compound (VOC) concentrations in soil,

soil gas, and groundwater at and in the vicinity of the Site, including impacts from off-Site sources where

elevated concentrations of trichloroethylene (TCE) are present in groundwater. The VI pathway

investigation work was conducted in accordance with the Remedial Action Plan (RAP) Modification #1,

dated March 11, 2014 (MPCA, 2014a) to the Response Order by Consent between General Mills and the

Minnesota Pollution Control Agency (MPCA), dated October 23, 1984 (Consent Order; MPCA, 1984). This

feasibility study is also informed by investigation work MPCA is conducting in the vicinity of the Site at a

recently established project area named the Southeast Hennepin Area Groundwater and Vapor Site

(SA249).

Since November 2013, sub-slab soil gas and/or indoor air sampling has been completed at 344 properties

and sub-slab depressurization (SSD) systems for vapor mitigation have been installed at 189 properties in

the Study Area. This work was completed in accordance with the RAP Modification #1 and is documented

in the Sub-Slab Sampling and Building Mitigation Implementation Report (Implementation Report; Barr,

2015b). In addition to the numerous investigations conducted by General Mills, this feasibility study

follows 25 years of groundwater remediation performed by General Mills pursuant to the Consent Order.

Thus a great deal of remedial action work was completed at the Site and in the Study Area prior to

beginning this feasibility study.

This feasibility study also is informed by the results of the human health risk assessment (HHRA) prepared

in 2015 by Haley & Aldrich, Inc. on behalf of General Mills. Although not required by the RAP

Modification #1, the HHRA was prepared to evaluate exposures to soil, groundwater, and indoor air

associated with residential and commercial property uses at and in the vicinity of the Site. The HHRA is

documented in the Human Health Risk Assessment Report (HHRA Report; H&A, 2015).

The Consent Order uses the term “Site” to refer to the former General Mills property at 2010 East

Hennepin Avenue (Figures 1 and 2). This terminology is retained in this report, and thus references to the

Site are intended to refer only to the property at 2010 East Hennepin Avenue. General Mills investigated

soil, groundwater, and soil gas at the Site and at locations northeast, south, and southwest of the Site as

part of the VI pathway investigation and other investigations. These areas are collectively referred to in

this report as the Study Area. The Study Area is divided into four geographical regions, including the Site,

the Northeast Area, the Central Area, and the Southwest Area (Figure 2). For the purpose of this feasibility

study, the southeast portion of the Site is included in the Central Area as shown on Figure 2.

4

This feasibility study was completed for the Central Area for the reasons described in Section 1.1. By

preparing this study for the Central Area, General Mills does not acknowledge or agree that TCE impacts

in the Central Area or elsewhere in the Study Area are associated with its former operations at the Site.

1.1 Scope of Feasibility Study

The RAP Modification #1 provides that a feasibility study be performed, as necessary, to mitigate the VI

pathway potential and reduce VOC concentrations in soil, soil gas, and groundwater due to General Mills’

former operations at the Site. Feasibility study activities are focused on the Central Area, only a portion of

which may be down-gradient of the Site. The feasibility study does not include the Northeast Area, which

is located hydraulically up-gradient of the Site and where off-Site sources have impacted shallow

groundwater with TCE, or the Southwest Area, where the evidence indicates that TCE impacts in

groundwater are not related to General Mills’ former operations at the Site. As noted above, by preparing

this study for the Central Area, General Mills does not acknowledge or agree that TCE impacts in the

Central Area or elsewhere in the Study Area are associated with its former operations at the Site.

This feasibility study was completed in general accordance with the United States Environmental

Protection Agency (EPA) guidance document for conducting remedial investigations and feasibility studies

under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). Based on

EPA guidance, a feasibility study should either be scaled down, as appropriate to the site and its potential

hazard, or eliminated altogether if a risk assessment indicates that a site poses little or no threat to human

health or the environment (EPA, 1988). The HHRA prepared for the Study Area concluded that the only

exposure pathway that may be potentially complete and of potential significance is vapor intrusion of

VOCs from shallow groundwater in the Northeast Area. The HHRA concluded that exposure pathways in

other areas, including the Central Area, were currently either incomplete or insignificant and not expected

to be significant in the future. Therefore, the scope of the feasibility study will be substantially informed

by CERCLA and associated EPA guidance and includes feasibility study components as appropriate for

conditions at the Central Area.

Although off-Site sources are impacting shallow groundwater in the Central Area and the HHRA

concluded that exposure pathways in the Central Area are currently either incomplete or insignificant and

not expected to be significant in the future, this feasibility study was prepared for the Central Area at the

direction of MPCA in its letter that provided comments to the VIPI Report (MPCA, 2015a).

TCE from one or more potential releases up-gradient of the Central Area are the predominant cause of

TCE concentrations in groundwater. Groundwater impacts up-gradient of the Central Area and the Site

are outside of the scope of this feasibility study. Until the extent and magnitude of the impacts associated

with the off-Site sources are defined and addressed, remedial action to address groundwater will not be

effective at reducing TCE concentrations in groundwater in the Central Area due to continuing re-

contamination from these up-gradient sources. It is assumed for the purposes of this feasibility study that

off-Site sources will be investigated and addressed by others.

5

The scope of work for the VI pathway feasibility study included the following tasks which are described in

the indicated report sections:

Summarizing site characterization information – Section 2.0;

Discussing regulatory considerations – Section 3.0;

Screening available remedial technologies – Section 4.0;

Developing remedial alternatives – Section 5.0;

Evaluating remedial alternatives – Section 6.0; and

Reporting results and summarizing conclusions – Section 7.0.

6

2.0 Site Characterization

This section summarizes the site characterization data collected to date. It provides background

information and summarizes investigation and response action work completed from the early 1980s to

the present. It presents the current understanding of the site conceptual model as it relates to the Central

Area and summarizes the HHRA.

2.1 Background

TCE, a widely used industrial and commercial solvent, is present in groundwater throughout the Study

Area with the highest concentrations measured up-gradient of the Site in the Northeast Area. The 700-

acre Mid-City Industrial neighborhood occupies the northeast portion of the Study Area. The Central Area

primarily includes residential properties intermixed with industrial and commercial properties.

A limited review of MPCA files in 2014 identified documented TCE releases to groundwater at several off-

Site properties and a review of various historic resources including city directories, fire insurance maps,

and regulatory database reports identified properties with potential solvent use and/or releases (Barr,

2015c). The approximate locations of these properties are shown on Figure 3.

Separately, in recognition that other sources of chlorinated solvents up-gradient and side-gradient of the

Site exist, MPCA is conducting soil, soil gas, and groundwater sampling in connection with SA249. In early

2015, MPCA completed a CERCLA pre-screening assessment for the purposes of listing SA249 on

Minnesota’s Permanent List of Priorities to conduct further investigations. Data collected to date by

MPCA at SA249 is summarized in Section 2.2 and the data was evaluated and incorporated into the site

conceptual model described in Section 2.3. The nature and extent of contamination from off-Site sources

in the Northeast Area have not yet been defined.

2.1.1 Central Area Setting

The Central Area is a primarily residential urban neighborhood covering approximately 40 acres. The

Central Area was first developed in the late 1800s with mature trees and tight road and alleyway spacing

consistent with development from this era. Within the Central Area there are 177 individual properties

(including the Site) with buildings covering approximately 8 acres and roads and alleyways covering

approximately 5 acres.

2.2 Previous Investigations and Response Action Activities

The VIPI Report provides an overview of the investigations and response actions completed by General

Mills (Barr, 2015c). Previous investigations and response actions conducted to date are summarized

chronologically below:

Multiple investigations have been conducted since the early 1980s to characterize soil and

groundwater conditions at and near the Site and the Central Area. The early investigations

detected VOCs, primarily benzene, toluene, ethyl benzene, and xylenes (BTEX) and, to a lesser

extent, chlorinated VOCs (cVOCs) including TCE, tetrachloroethylene (PCE), and 1,1,1-

7

trichloroethane (1,1,1-TCA) in soil and shallow groundwater in the southeastern corner of the Site

near a former disposal area. In contrast, TCE was the predominant constituent detected in

groundwater off-Site in the Central Area.

General Mills agreed to install and operate a groundwater extraction and treatment system

beginning in 1985 to limit the migration of TCE. The system was installed, operated, and

monitored as a groundwater remedial action under the Consent Order until 2010 when MPCA

suggested and then approved shutting down the system as the remedial objectives set forth in

the Consent Order had been met.

Once the remedial action objectives were met and the groundwater extraction and treatment

system was shut down, steps toward delisting the Site were initiated, including vapor intrusion,

potable water well, and surface water pathway evaluations. From 2011 into 2013, phased

investigations of shallow groundwater and soil gas were completed in accordance with MPCA-

approved work plans.

Sub-slab soil gas sampling and mitigation work began in November 2013 under MPCA oversight.

Sub-slab soil gas and/or indoor air sampling has been completed at 344 properties and SSD

systems have been installed at 189 properties since November 2013. The sub-slab soil gas

sampling results pointed to the likely existence of multiple TCE sources unrelated to the Site. This

work was completed in accordance with the RAP Modification #1 and is documented in the

Implementation Report (Barr, 2015b). The status of SSD systems in the Central Area is discussed

in Section 2.3.6.

In 2014, soil gas and groundwater investigation work was conducted under MPCA-approved work

plans at areas northeast, south, and southwest of the Site, and at the former disposal area on the

Site. TCE was detected in groundwater and soil gas at multiple locations northeast of the Site,

providing further evidence of the presence of off-Site TCE sources including sources up-gradient

of the Site (Barr, 2014b). No evidence of source material was found at the former disposal area at

the Site that could act as a continuing source of TCE to shallow groundwater (Barr, 2014c).

The VI pathway investigation was implemented in late 2014 and early 2015 under a work plan

approved by MPCA. The results of the investigation indicated that off-Site sources were

impacting TCE concentrations in groundwater and confirmed that the Site is not an ongoing

source of TCE to groundwater at concentrations that would contribute to the VI pathway in the

Study Area. The VIPI Report concluded that no current TCE source areas have been found on the

Site and that multiple sources in the Northeast Area, up-gradient of the Site, are the predominant

cause of TCE concentrations in groundwater in the Study Area (Barr, 2015c). Additionally, the VIPI

Report concluded that multiple potential sources of chlorinated solvents, unrelated to the Site,

exist throughout the Study Area. MPCA acknowledged multiple potential release sources of TCE

in the vicinity of the Site in its letter that provided comments to the VIPI Report and has started

investigating those potential sources (MPCA, 2015a).

8

A HHRA was prepared in 2015 to evaluate exposures to soil, groundwater, and indoor air

associated with residential and commercial property uses in the Study Area (H&A, 2015). The

HHRA is summarized in Section 2.4.

Sentinel vapor monitoring points and new groundwater monitoring wells were installed at the

Study Area in late 2014. Quarterly sampling of the sentinel monitoring network was completed in

December 2014, March 2015, June 2015, and September 2015. The results were documented in

the 2015 Sentinel Monitoring Network Report (2015 Sentinel Report; Barr, 2015d). The results

showed that the sentinel monitoring network locations are positioned appropriately to measure

changes in soil gas or groundwater concentrations at the perimeter of the soil gas monitoring

area developed for this project. The sentinel monitoring results collected to date indicate that

sources in the Northeast Area continue to impact the Central Area. The highest TCE

concentrations in soil gas and groundwater are detected at locations up-gradient and side-

gradient of the Site. The 2015 Sentinel Report recommended collecting an additional four

quarters of samples from the sentinel monitoring network beginning in the first quarter of 2016.

MPCA approved the 2015 Sentinel Report and concurred with the recommendation for another

four quarters of sampling in their letter, dated January 28, 2016 (MPCA, 2016).

In December 2015, Bay West LLC (Bay West), on behalf of MPCA, conducted an investigation

associated with SA249. Bay West installed 18 soil borings (SP-01 through SP-18) and six vapor

probes (VP-01 through VP-06) for the purposes of collecting soil, groundwater, and soil gas

samples for VOC analysis. The majority of the investigation locations were advanced in the

Northeast Area with several locations in the Central Area. Investigation results from SA249

indicate that sources in the Northeast Area continue to impact the Central Area and that multiple

sources may also be present in the Central Area. The highest TCE concentrations in soil gas and

groundwater were measured at locations up-gradient of the Site. TCE groundwater and soil gas

sampling results are shown on Figure 4.

Additionally, as described in the VIPI Report, several types of institutional controls (ICs) have been

implemented for protection of public health and the environment, limiting access to impacted soil and/or

groundwater at the Site and the Central Area to assure long-term protectiveness. The controls already in

place include a restrictive covenant that limits soil disturbance and groundwater use at the Site, and

required notification to the Minnesota Department of Health (MDH) of proposed groundwater well

construction, including water supply wells and wells or borings located in Special Well and Boring

Construction Areas, per Minnesota statutes and rules.

Sampling of the sentinel soil gas and groundwater monitoring network and glacial drift groundwater

monitoring network is planned for 2016 (Barr, 2015d; Barr, 2016).

2.3 Site Conceptual Model

The site conceptual model (SCM) for vapor intrusion in the Study Area presented in the VIPI Report has

been focused on the Central Area for purposes of this feasibility study and is further refined with data

collected from MPCA’s investigations associated with SA249 and sentinel monitoring conducted by Barr

9

on behalf of General Mills. The data collected to date indicates the presence of multiple TCE sources that

are impacting soil, groundwater, and soil gas in the Central Area. Information regarding documented

releases to groundwater and potential vapor sources, the physical characteristics of the area, the spatial

distribution of TCE, vapor transport mechanisms and migration pathways, potential receptors, and

mitigation measures installed as part of response actions completed by General Mills has been

incorporated into the discussion below.

2.3.1 Vapor Sources

As described previously, TCE was a commonly-used industrial and household solvent between the 1930s

and the 1990s and is still in use today. Documented releases of TCE to shallow groundwater are present

in the Northeast Area and potential users of TCE are present in the Central Area. The highest TCE

concentrations in groundwater in the glacial drift are present in the Northeast Area, which is hydraulically

up-gradient from the Central Area.

The extensive investigations conducted at the Site found no evidence of DNAPL or other source material

at or emanating from the Site. TCE is not detected in unsaturated soils at the Site, and only low

concentrations of TCE (less than 1 mg/kg) are reported in the soil below the water table near the former

disposal area based on recent investigations. These low concentrations are consistent with the dissolved

TCE measured in the shallow groundwater and do not indicate the presence of DNAPL or source material.

The Site is not an ongoing source of TCE to groundwater that would contribute to the potential vapor

intrusion pathway in the Central Area.

2.3.2 Geology and Hydrogeology

Glacial drift in the Central Area generally consists of heterogeneous fine- to medium-grained sand, with

lesser amounts of coarse sand and gravelly sand. In some locations, the sand and gravel deposits are

overlain by up to 20 feet of fill or peat. Glacial drift is underlain by discontinuous glacial till and/or shale

at the Central Area which together act as a confining unit. Groundwater within the glacial drift is present

at depths of 15 to 25 feet below ground surface (bgs). The shallow groundwater flow direction is and has

consistently been to the southwest, with little to no seasonal variation, since at least the early 1980s,

including the periods before and during the 25-year operating period of the legacy groundwater

extraction system. The groundwater flow direction and gradient are influenced locally by the saturated

thickness of the glacial drift above the glacial till and/or bedrock and other factors including: hydraulic

conductivity distribution, surface topography, and drainage features such as the Mississippi River.

Groundwater from the Northeast Area flows to the southwest into the Central Area.

2.3.3 Spatial Distribution of Contaminants

TCE is present in groundwater at various locations and varying concentrations within the Central Area.

The varying distribution, presence, and concentrations of TCE within the Central Area indicate multiple

sources. The TCE concentrations in groundwater in the Northeast Area are higher than concentrations in

the Central Area. The magnitude and extent of TCE in the groundwater in the Northeast Area are

undefined and the presence of DNAPL and other continuing sources of TCE to groundwater in the

10

Northeast Area are unknown. The down-gradient extent of TCE in groundwater is defined in the Central

Area.

2.3.4 Potential Receptors

The land use in the Central Area is primarily single- and multi-family residential development with some

interspersed commercial and industrial properties. Commercial and industrial buildings are the primary

land use at the Site and at several properties along Como Avenue SE. There are currently 14 buildings

present at the Site that are numbered Buildings 1 through 12, 14, and 15. Some buildings at the Site have

basements or crawlspaces, while others are slab-on-grade construction. Observed building slab

thicknesses at the Site ranged from 4 to 24 inches. The basement floor slabs of the residential properties

in the Central Area are typically 10 feet or more above the groundwater table.

Based on these land uses the following populations of receptors would be expected to reside or work

within the Central Area:

Long term residents, including young children, older children, adults and elderly adults;

Short term residents, including occupants of rental properties such as college students;

Commercial workers such as employees at commercial and industrial establishments; and

Visitors and patrons.

2.3.5 Vapor Transport Mechanisms

Based on the results of the various investigations conducted to date, the primary transport mechanism for

soil vapor within the Central Area is diffusion of vapors from groundwater into the shallow glacial drift.

Diffusion of vapors from groundwater occurs as a result of a concentration gradient between the

groundwater and the soil gas in the overlying glacial drift.

Vapor migration through preferential pathways may occur via natural and man-made pathways in the

subsurface (e.g., buried utilities) such that the feature creates a pathway from a source to a receptor.

Although utility plans indicate that sanitary sewers and other utilities are present, this potential pathway is

unlikely since the utility bedding materials are likely similar to the native sandy unsaturated zone soils. In

addition, no preferential pathways were identified based on the results of the extensive sub-slab soil gas

sampling performed throughout the Study Area.

2.3.6 Building Vapor Mitigation

Building mitigation systems, specifically active SSD systems, have been installed at 166 of the 177

properties in the Central Area (94 percent) as part of the sub-slab soil gas sampling and mitigation

project. The SSD systems are operating as designed and are considered by MPCA and EPA to be among

the most effective vapor intrusion mitigation strategies for existing or new buildings (MPCA, 2010; EPA,

2015). Additionally, post-mitigation indoor air sampling was performed at the 19 properties in the Central

Area with sub-slab soil gas TCE results greater than 2,000 g/m3 (Barr, 2015b). This sampling confirmed

11

that the SSD systems were operating effectively at properties with the highest TCE concentrations in sub-

slab soil gas. The current status of building mitigation in the Central Area and the larger Study Area is

shown on Figure 5. Information regarding the 11 properties in the Central Area that do not have SSD

systems is provided below.

2.3.6.1 Central Area Building Mitigation Status

Of the 11 properties in the Central Area that do not have active SSD systems, three properties (including

the Site) had indoor air sampling results below the applicable MPCA intrusion screening value (ISV), three

property owners declined SSD systems, and owners of five properties could not be reached or did not

provide access to participate in the sub-slab soil gas sampling and mitigation project.

Indoor air sampling was performed at five buildings (Buildings 8, 10, 11, 12, and 14) located at the Site

where at least one sub-slab soil gas sample had a reported TCE concentration greater than 60 g/m3 (10

times the industrial ISV). Reported TCE concentrations in indoor air were below the applicable ISV for all

samples collected (Barr, 2015a). Two residential properties in the Central Area had two rounds of indoor

air sampling with reported TCE concentrations in indoor air below the residential ISV (2.0 g/m3) for both

sampling events. Additionally, the owner of one of the two properties declined the installation of an

active SSD system due to the presence of an existing passive SSD system for radon mitigation and

because indoor air results were below the residential ISV.

Reported sub-slab soil gas TCE concentrations were below 20g/m3 (10 times the residential ISV),

indicating the VI pathway is insignificant, at two of the three properties where owners declined SSD

systems. Owners of these two properties were offered SSD systems because they were bounded by

properties with reported sub-slab soil gas TCE concentrations greater than 20 g/m3. TCE was greater

than 20 g/m3 in sub-slab soil gas at the other property where the owner declined a SSD system. A

minimum of three, good-faith attempts were made to obtain access to install SSD systems at the three

properties and the properties were referred to MPCA when access was not obtained.

Owners of five properties in the Central Area could not be reached or did not provide access after a

minimum of three good-faith attempts were made to obtain access and entry to each property to collect

samples as part of the sub-slab soil gas and mitigation project. These properties were referred to MPCA.

2.4 Risk Assessment

MPCA recommended preparation of a comprehensive risk assessment for all exposure pathways in its

most recent Five-Year Review for the Site (MPCA, 2014b). The HHRA prepared for the Study Area by

Haley & Aldrich, Inc. on behalf of General Mills considered all potential exposure pathways, including soil,

groundwater, and vapor intrusion (H&A, 2015). Direct exposure pathways to soil were either incomplete

or insignificant based on soil data collected from the Study Area. Similarly, direct exposure pathways to

groundwater were incomplete because groundwater in the Study Area is not used as a source of potable

water. The vapor intrusion pathway was evaluated further, and the HHRA concluded that the only

exposure pathway that may be potentially complete and of potential significance is vapor intrusion of

VOCs from shallow groundwater in the Northeast Area. The HHRA concluded that exposure pathways in

12

other areas, including the Central Area, were currently either incomplete or insignificant and not expected

to be significant in the future.

The MPCA provided comments on the HHRA in their letter dated November 3, 2015, and MDH provided

comments in a letter from MPCA dated November 12, 2015 (MPCA, 2015a; MPCA, 2015b). Responses to

MPCA and MDH/MPCA comments are in the letters from General Mills and Haley & Aldrich, Inc. to MPCA

dated April 6, 2016 (GMI, 2016; H&A, 2016).

13

3.0 Regulatory Considerations

This section presents remedial action objectives (RAOs), identifies potentially applicable or relevant and

appropriate requirements (ARARs) and to-be-considered criteria (TBCs), and presents preliminary

remediation goals (PRGs) for the vapor intrusion pathway at the Central Area that is the subject of this

feasibility study. The remedial action objectives, potential ARARs and TBCs, and PRGs are based on the

understanding of Central Area conditions developed during the various investigations and response

actions that have been completed and the results of the HHRA.

3.1 Remedial Action Objectives

In general, the RAOs provide the goals for protecting human health and the environment. The RAOs

address the contaminants of concern (COCs) and potential exposure routes and receptors, and provide an

acceptable contaminant level or range of levels for each exposure route that exceeds threshold criteria for

protection of human health, as defined by CERCLA and the National Contingency Plan (NCP), to human

health or the environment. The RAOs are to be as specific as possible without limiting the range of

remedial alternatives that can be developed for screening and detailed analysis.

The HHRA prepared for the Study Area considered all current and potential (future) exposure pathways,

and focused on the vapor intrusion pathway for further evaluation. The HHRA concluded that exposure

pathways in the Central Area were currently either incomplete or insignificant and not expected to be

significant in the future. The RAO developed for the Central Area focuses on maintaining protectiveness of

human health and the environment. TCE is the primary COC and drives potential human health risk in the

Central Area.

Accordingly, the remedial action objective (RAO) for the Central Area is to maintain insignificant potential

risk to human health from inhalation exposure to TCE in indoor air resulting from TCE concentrations in

soil gas and groundwater. As stated in the RAP Modification #1, General Mills is responsible only for

implementing response actions to address impacts that are due to its former operations at the Site. By

preparing this feasibility study and developing this RAO, General Mills does not acknowledge or agree

that TCE impacts in the Central Area or elsewhere in the Study Area are associated with its former

operations at the Site.

3.2 ARARs and TBCs

The NCP provides that remedial action alternatives be assessed to evaluate whether they attain applicable

or relevant and appropriate requirements (ARARs) under federal and state environmental laws or facility

siting laws, or provide grounds for obtaining a waiver. In addition to ARARs, the identification and

evaluation of remedial action alternatives may consider, as appropriate, other advisories, criteria, or

guidelines, collectively called to-be-considered criteria (TBCs). The final acceptable exposure levels should

be determined on the basis of the results of the risk assessment and the evaluation of the expected

exposures and associated risks for each alternative (EPA, 1988).

14

3.2.1 Classification of ARARs and TBCs

ARARs and TBCs are classified as action-specific, location-specific, or chemical-specific in the evaluation

process:

Action-specific ARARs and TBCs are technology- or activity-based requirements or limitations on

actions or conditions. They establish performance, design, or other similar specific controls or

regulations on actions. Action-specific ARARs and TBCs potentially applicable to the Central Area

are identified in Table 1.

Location-specific ARARs and TBCs are those requirements that relate to the geographical location

of a site and restrict actions or contaminant concentrations in certain environmentally sensitive

areas. Examples of areas regulated under such ARARs and TBCs include floodplains, wetlands,

and locations where endangered species or historically significant cultural resources are present.

Location-specific ARARs and TBCs potentially applicable to the Central Area are identified in

Table 2.

Chemical-specific ARARs and TBCs are usually health- or risk-based numerical values or

methodologies used to calculate acceptable chemical concentrations that may be found in or

discharged to the environment. Chemical-specific ARARs and TBCs include those that regulate

the release to the environment of specific substances having certain chemical or physical

characteristics or materials containing specific chemical compounds. Chemical-specific ARARs

and TBCs potentially applicable to the Central Area are identified in Table 3.

3.3 Preliminary Remediation Goals

PRGs are developed on the basis of chemical-specific ARARs, when available, other available information,

and site-specific risk-related factors (EPA, 1988). PRGs serve as goals for the remedial action alternatives

and typically consist of chemical concentrations that are considered protective of human health and the

environment (chemical-specific PRGs). There are two general sources of chemical-specific PRGs: (1)

concentrations based on ARARs and TBCs (ARAR/TBC-based PRGs); and (2) concentrations based on a risk

assessment (risk-based PRGs). Where chemical-specific ARARs exist for a COC, these ARARs are the basis

of the PRG. Where chemical-specific ARARs are not available, risk-based or TBC-based PRGs are applied.

There are no chemical-specific ARARs available for TCE that are applicable to the vapor intrusion pathway.

Vapor intrusion guidance documents prepared by both EPA and MPCA contain risk-based, generic

screening values for TCE concentrations in indoor air (EPA, 2015; MPCA, 2008). MPCA’s intrusion

screening values (ISVs), which were developed in conjunction with MDH and are based on an incremental

cancer risk threshold of one in 100,000 (1 x 10–5) and a non-cancer hazard quotient of 1, guided the sub-

slab soil gas sampling and mitigation project. The current TCE ISV for residential property use is 2 g/m3

and the current TCE ISV for commercial or industrial property use is 6 g/m3. MDH considers the

residential ISV a safe level that protects all people from health effects and the commercial/industrial ISV a

safe level for people who may have exposures in the work place over many years (MDH, 2016a). MPCA

ISVs for TCE were selected as PRGs for indoor air.

15

In general, there is a relationship between VOC-impacted groundwater concentrations and VOC

concentrations in overlying soil gas. Many factors can influence the relationship including chemical-

specific characteristics (e.g., Henry’s Law Constant) and site-specific conditions such as subsurface geology

(e.g., soil type and stratification) and the presence of preferential pathways. EPA and MPCA vapor

intrusion guidance provide generic screening values for groundwater that can be useful in initial

evaluation stages to help define the magnitude and extent of potential vapor intrusion impacts. However,

MPCA guidance states that their groundwater screening values (groundwater ISVs) “are designed to be

used as an additional line of evidence to help refine the SCM and to help determine the scope of further

investigation, and should not be applied alone to screen out vapor intrusion risk at a site or for remedial

action levels” (MPCA, 2010). EPA guidance states that vapor intrusion screening levels for groundwater

are not intended to be used as cleanup levels (EPA, 2015). Accordingly, a specific concentration-based

groundwater PRG was not developed for this feasibility study.

16

4.0 Technology Screening

The objective of developing and screening remedial action technologies is to compile an appropriate

range of technologies and processes for the media and location(s) where remedial action(s) may occur.

Appropriate technologies and process options are then assembled into a range of remedial action

alternatives that are evaluated in the detailed analysis phase of the feasibility study. Appropriate remedial

technology processes that meet the RAOs may involve the elimination or destruction of hazardous

substances, the reduction of hazardous substance concentrations to acceptable health-based levels,

prevention of exposure to hazardous substances via engineering or institutional controls, or a

combination of the above. Remedial alternatives are developed by assembling technology processes into

alternatives that address impacts for the identified media and locations of concern.

4.1 Development of General Response Actions

General response actions are medium-specific actions that satisfy RAOs (EPA, 1988). Response actions

may target the TCE-impacted soil vapor itself and/or the shallow groundwater that acts as a source of the

TCE impacts in soil vapor. General response actions for mitigating risks posed by soil vapor may be

applied individually or in combination.

Potential response actions and their ability to achieve the RAO and the PRG are summarized as follows

and in Table 4.

No Further Action: No further action is evaluated as a basis for comparison during the feasibility

study process, even though it typically does not achieve the RAOs and PRGs at sites where no

response actions have been implemented. However, as noted previously, General Mills has

already implemented significant response actions in the Central Area including operation of a

groundwater extraction system for 25 years and installation of SSD systems at 94 percent of the

properties. No further action beyond previous response actions is retained for consideration.

Vapor Mitigation: Vapor mitigation involves installing and operating building controls, such as

SSD systems or control of HVAC systems to maintain positive pressure, to disconnect the VI

pathway on a property-specific basis. Currently, buildings at 166 of the 177 properties (94

percent) within the Central Area have active SSD systems. Vapor mitigation is retained as a

general response action.

Institutional Controls: Institutional Controls (ICs) are legal and administrative tools used to

maintain protection of human health and the environment at sites where exposure to

contaminated materials could occur. EPA defines institutional controls as “non engineered

instruments that help minimize the potential for human exposure to contamination and protect the

integrity of the remedy” (EPA, 2012). ICs are generally consolidated into the following four

categories:

o Government controls (e.g., zoning, local ordinances)

17

o Proprietary controls (e.g., easements, restrictive covenants)

o Enforcement and permit tools (e.g., consent decrees, administrative orders)

o Informational tools (e.g., notices filed in the land records, advisories)

ICs restrict access to contaminated media by notifying property owners, perspective property

purchasers, and workers of contamination. ICs help ensure the effectiveness of remedial actions

by limiting activities that could degrade the effectiveness of the remedy, by providing access for

regulatory agencies to monitor the effectiveness of the remedy, and by requiring periodic

reporting. Institutional controls were retained as a general response action.

Containment: Containment technologies consist of physical or hydraulic containment to provide

a barrier between impacted groundwater and overlying structures to disconnect the VI pathway.

Possible containment remedial technologies include installing a buried horizontal grout cap over

impacted groundwater and horizontal hydraulic barriers. Containment was not retained as a

general response action for the Central Area due to lack of implementability and uncertain

effectiveness.

Physical Removal: Physical removal involves removing impacted soil, groundwater and/or soil

vapor. Remedial technologies for this general response action include soil excavation, soil vapor

extraction systems, in-situ thermal treatment, and groundwater extraction and treatment.

Physical removal has previously been implemented in the Central Area via operation of the legacy

groundwater extraction system and the reported excavation of the disposal area in 1981 (Barr,

2015c). Vapor extraction and in-situ thermal treatment were not retained due to the limited

radius of influence and access limitations. Soil excavation was not retained due to access

limitations and lack of source material. Expansion or modification of the groundwater extraction

system was retained as a general response action.

Biological: This general response action involves using biological processes, enhanced or natural,

to remediate impacted groundwater (bioremediation). Remedial technologies for biological

treatment vary, but may include monitored natural attenuation (MNA), phyto-remediation, and

various in-situ amendments to promote/support bioremediation. Several biological processes

have been effective for remediating TCE-impacted groundwater under appropriate conditions,

including: enhanced reductive dechlorination, aerobic co-metabolism, and biogeochemical

processes. Each of the biological processes occurs under different conditions, but the processes

can occur simultaneously within an impacted area or at different times with varying subsurface

conditions. Biological treatment was retained as a general response action.

Chemical: Chemical technologies involve adding chemicals to the subsurface that cause reactions

that destroy the chemical of concern. Chemical technologies are primarily composed of in-situ

chemical oxidation (ISCO), which uses a strong oxidant or in-situ chemical reduction (ISCR), which

uses a strong reducing agent. ISCO and ISCR have been used effectively at locations with high

TCE concentrations (e.g., source areas) but have not been used at locations with low-level

18

groundwater concentrations over a large area like the Central Area. Chemical treatment was not

retained as a general response action due to lack of implementability and unlikely effectiveness.

Electrical: Electrical technologies involve applying a voltage via an array (similar to a reactive

barrier) to electrically break down contaminants within the groundwater. This technology is still in

development and its effectiveness is unknown at locations similar in size to the Central Area.

Electrical treatment was not retained as a general response action due to unproven effectiveness

and lack of implementability.

4.2 Evaluation and Screening of Technologies

In this section, the general response actions that are retained in Section 4.1 for further evaluation are

subdivided into remedial technologies and are further screened. Descriptions of the retained remedial

technologies and associated process options are discussed in Section 4.3.

Remedial technologies are general categories of technologies within a general response action, and

process options are specific processes within a technology category. For example, in-situ bioremediation

and monitored natural attenuation are two remedial technology categories within the biological general

response action. Aerobic co-metabolism via injection wells and enhanced reductive dechlorination via

injection wells are two process options within the remedial technology category of in-situ bioremediation.

Potentially viable technologies and associated process options for each retained general response action

are summarized in Table 4. The potentially viable technologies and associated process options were then

screened based on effectiveness, implementability, and relative cost as required by the NCP. These

screening criteria are defined as follows:

Effectiveness: the ability of the remedial technology or process option to perform adequately to

achieve the RAO(s) alone or as part of an overall system. The evaluation considered whether the

remedial technology or process option has demonstrated effectiveness at other TCE-impacted

sites similar to the Central Area.

Implementability: the degree of difficulty expected in implementing a particular remedial

technology or process option under practical technical, regulatory, and access limitations and

schedule constraints. The evaluation considered whether the remedial technology or process

option has been implemented at other locations with similar technical, regulatory, and logistical

constraints.

Relative Cost: qualitative costs of each remedial technology or process option were developed

for comparative purposes and include construction and long-term O&M costs. The comparison

of relative cost is used to preclude further evaluation of technologies that are very costly where

other choices perform similar functions with comparable effectiveness at a lower cost. Relative

cost was assigned to each remedial technology for this evaluation; however, relative cost was not

used as a rationale to screen out a remedial technology or process option.

19

Screening was based on professional experience and judgment; published sources; knowledge of

chemical, geologic, and physical conditions in the Central Area; and experience with the previous

implementation of remedial actions in the Central Area.

4.3 Retained Technologies

Retained technologies were reviewed based upon effectiveness, implementability, and relative cost as

described within Section 4.2. Relative cost was not used to screen out remedial technologies during this

evaluation. A short description of each retained technology and its associated process options as applied

to the Central Area follows.

Install SSD Systems at Un-Mitigated Residences in the Central Area

This remedial technology involves installing mitigation systems at the remaining residences in the Central

Area without mitigation systems, provided receipt of property owner consent. Process options include

active SSD systems or positive pressure HVAC systems designed to provide a pressure barrier for sub-slab

vapors to enter the buildings. Active SSD systems are retained as the process option for this technology.

Operation and Maintenance (O&M) of SSD Systems

This remedial technology requires an O&M plan (process option) to be developed and implemented for

SSD systems within the Central Area. The objective of this plan will be to help ensure that the SSD

systems continue to disconnect the VI pathway by remaining functional over time. In addition, the SSD

systems will remain operational until they are no longer needed (e.g., sub-slab soil gas concentrations are

below risk-based levels). This process option is retained for further evaluation.

Institutional Controls Pertaining to SSD Systems

The process option for this remedial technology is area-wide institutional controls (ICs) pertaining to

active SSD systems. The ICs can be developed as a city-wide ordinance or other area-wide control, which

will require regulatory cooperation. ICs may be a component of an O&M plan. This process option is

retained for further evaluation.

Expanded/Modified Groundwater Extraction

This remedial technology has been implemented previously at the Central Area. Both process options for

this remedial technology involve removal of the contaminated groundwater via submersible pumps. The

removed groundwater will be treated and discharged to the storm sewer of via an existing, or separately

acquired, National Pollution Discharge Elimination System (NPDES) permit (process option 1) or the

contaminated groundwater will be treated and reinjected into the subsurface (process option 2). Both

process options are retained for further evaluation.

Monitored Natural Attenuation

The process option of this remedial technology is to allow the native microorganisms and natural

processes to reduce TCE concentrations and associated daughter products and to monitor the progress.

20

This process option can be achieved by developing and implementing a groundwater monitoring well

network and associated sampling plan. This process option is retained for further evaluation.

In Situ Bioremediation

Various in situ bioremediation process options exist. Process options using permeable reactive barriers

(PRBs) were not retained due to lack of implementability (limited access within the Central Area) and bio-

geochemical process options were not retained due to uncertain effectiveness (unlikely that the aquifer

matrix will support the chemical processes) and lack of implementability (engineered geochemical process

alternatives typically involve constructing PRBs). Aerobic co-metabolism via injection wells and enhanced

reductive dechlorination via injection wells are the process options retained for further evaluation. Both

process options require injection of a carbon substrate into the glacial drift groundwater. Aerobic co-

metabolism has an additional requirement of adding oxygen to the groundwater along with the carbon

substrate.

21

5.0 Development of Remedial Alternatives

Remedial technologies and associated process options that were retained for alternative development in

Section 4.0 are combined to form comprehensive remedial action alternatives. Assembly of alternatives

provides a method of identifying and screening the inter-relationships between remedial technologies

and process options applicable to the Central Area. Five alternatives are described in the following

sections.

Natural attenuation of TCE in groundwater will occur during all alternatives which leads to a reduction in

TCE concentrations over time. Additionally, the SSD systems previously installed in the Central Area will

continue to provide protection from vapor intrusion. These aspects will not be discussed in detail below.

5.1 Alternative 1 – No Further Action Beyond Previous Response

Actions

No further action includes no additional work beyond the past operation of the legacy groundwater

extraction system, previous installation of SSD systems, and existing institutional controls (ICs) already

implemented.

General Mills installed a groundwater extraction and treatment system in 1985 and operated the system

until 2010. The system was installed, operated, and monitored to limit the migration of TCE in

groundwater and reduce concentrations of TCE in groundwater as a remedial action under the Consent

Order. Approximately six billion gallons of groundwater were treated and an estimated 7,000 pounds of

TCE were removed from the glacial drift and deeper bedrock aquifers (Barr, 2015c). The system was shut

down in 2010 with approval from the MPCA.

As described in Section 2.3.6, active SSD systems have been installed at 166 of the 177 properties in the

Central Area. Additional detail regarding the sub-slab soil gas sampling and building mitigation work can

be found in the Implementation Report (Barr, 2015b).

Several types of ICs have been implemented for protection of public health and the environment, limiting

access to impacted soil and/or groundwater at the Site and the Study Area to assure long-term

protectiveness, as described in Section 2.2.

5.2 Alternative 2 – Monitored Natural Attenuation

Monitored natural attenuation (MNA) includes developing and implementing a groundwater monitoring

plan that will assess natural degradation of TCE. The groundwater monitoring plan will use the existing

groundwater monitoring well network (see Figure 6) and will include sampling for TCE, TCE daughter

compounds (e.g. dichloroethene, vinyl chloride, methane), electron acceptors (e.g., iron, manganese,

nitrate, sulfate, dissolved oxygen) and general chemistry parameters (e.g., total organic carbon, alkalinity,

hardness, pH). The suite of parameters was developed to be consistent with the parameters

recommended for evaluating MNA (EPA, 1998). It is assumed that VOC sampling (for TCE and daughter

compounds) will be conducted annually at 25 wells and that the full suite of MNA parameters will be

22

analyzed at samples collected from 10 wells within the monitoring well network. A report summarizing

the results of the monitoring will be provided to MPCA annually. The objective of this alternative is to

monitor natural processes within the glacial drift groundwater that act to decrease contaminants to levels

that would eliminate the need for SSD systems in the Central Area.

5.3 Alternative 3 – Long Term O&M of SSD Systems

Alternative 3 includes preparing a long-term O&M plan that would detail routine monitoring and

maintenance of the SSD systems in the Central Area. This alternative assumes that residences within the

Central Area have, or will have installed, a functioning SSD system (assuming cooperation from property

owners).

Initial Installation/Sampling

Alternative 3 includes installing active SSD systems at the 10 remaining residential properties within the

Central Area that do not currently have an active SSD system, provided property owner consent and

coordination. SSD system installation will include coordinating access, diagnostic testing, designing the

system for each property, installing the system, and evaluating initial performance, consistent with the

existing work plan (Barr, 2014a).

Alternative 3 also assumes that subsequent indoor air and sub-slab soil gas sampling will be conducted at

five commercial buildings (Buildings 8, 10, 11, 12, and 14) at the Site. Based on the indoor air results

collected to date, it is assumed that indoor air TCE results will be below the applicable ISV and that

installation of SSD systems at the five buildings will be unnecessary. However, if the applicable TCE ISV is

exceeded during the additional sampling, and assuming cooperation of the property owner, SSD systems

would be installed at one or more of the five buildings, as appropriate.

Operations and Monitoring

Alternative 3 includes preparing and implementing a long-term O&M plan for the SSD systems within the

Central Area. The developed O&M plan would include the methods and procedures to verify fan

operation, visually inspect the vent pipe, and visually inspect the manometer pressure gage. For the

purposes of this feasibility study, Alternative 3 assumes that the inspections would be completed by the

property owners with support provided by a technical resource on operation of SSD systems and support

provided for coordination and communication with contractors for routine maintenance. Due to the

demonstrated long-term reliability and simple operation of the SSD systems, it was assumed that visual

inspections completed by the property owners would be the least intrusive option to monitor the SSD

systems. On the rare occasion that maintenance is required, it was assumed that access would be

coordinated for an engineer and/or contractor to inspect and complete routine maintenance (e.g., fan

replacement). Additionally, a city ordinance could be developed to provide requirements for disclosure of

property-specific vapor data and existence of SSD systems in connection with property transactions.

23

5.4 Alternative 4 – Enhanced Bioremediation via Injection Events

Alternative 4 involves installing injection wells within the rights-of-way, delivering carbon substrate and

other amendments to promote enhanced biodegradation of TCE in the glacial drift groundwater, and

conducting performance monitoring. Access to rights-of-way is contingent upon negotiations with right-

of-way administrators (e.g. City of Minneapolis and the railroad). There is uncertainty associated with the

ability to gain access for the purposes of installing injection wells and delivering amendment. Subsurface

conditions, access limitations, and technology limitations provide significant uncertainty regarding the

effectiveness of Alternative 4. The appropriate substrate and amendment dosing would need to be

evaluated during the design phase, if selected.

Injection Well Construction and Initial Amendment Delivery

Alternative 4 includes construction of approximately 40 injection wells as tentatively shown on Figure 7.

The injection well locations were designed along transects perpendicular to groundwater flow along the

railroad tracks or road rights-of-way that provide the greatest access and space for injection well

installation. The injection well spacing was based on the anticipated radius of influence that could be

achieved with a fully penetrating well in the glacial drift, estimated hydraulic conductivity ranging from 20

meters per day (m/day) to 100 m/day, injection rates ranging from 25 gallons per minute (gpm) to 50

gpm, and limiting groundwater mounding adjacent to the injection wells below the depth of utilities and

basements. There is uncertainty regarding the radius of influence that could be achieved and injection

well spacing would be determined during the design phase. There is the potential that the radius of

influence varies significantly and delivery will not be successfully applied to significant portions of the

Central Area with limited access. It is assumed that reductive dechlorination would be the primary

biological process adjacent to the injection wells. The aerobic co-metabolic process would likely occur

near the periphery and other biogeochemical processes would occur as conditions are suitable.

Many factors influence the amount of carbon substrate required to create reducing conditions in the

aquifer supportive of anaerobic reductive dechlorination. Factors that significantly affect the estimated

quantity of substrate required include: natural demand from competing electron acceptors within the

aquifer (e.g., naturally occurring sulfate), the design period or treatment timeframe, and the design or

safety factor employed. The natural demand from the aquifer has been estimated based on site-specific

dissolved phase concentrations of major competing electron acceptors using a substrate estimating tool

(Parsons, 2010b). The design period and design factor can vary by amendment type and injection

program. A sensitivity analysis was performed using a range of recommended design periods and design

factor values (Parsons, 2010a). Results of the sensitivity analysis are presented in Table 5. Based on the

sensitivity analysis, it is estimated for the purposes of this feasibility study that approximately seven

million pounds of carbon substrate would be required for treatment of the Central Area. Emulsified

vegetable oil was selected as the carbon substrate based on its longevity in the subsurface for quantity

and cost estimating purposes; however, there is significant uncertainty regarding the carbon substrate

type and amendments that would perform most effectively.

24


For the purposes of this feasibility study, Alternative 4 assumes that the majority of the carbon substrate

and amendments will be delivered during initial injections and that the substrate will be distributed across

the treatment area via natural advective flow. However, there is significant uncertainty regarding

substrate distribution in the subsurface. Thus, the behavior of substrate distribution would need to be

evaluated as part of the design stage. Subsequent injections are assumed to occur periodically for three

years at the injection well network installed for the initial injection. Performance monitoring is included to

identify locations that would need subsequent injection.

After three years of injection at the initial injection wells, it is assumed that additional wells would be

needed to target specific locations within the Central Area where substrate delivery may have been

limited by natural advective flow. For the purposes of this feasibility study, Alternative 4 assumes that 20

new injection wells would be installed at locations to be identified during performance monitoring

conducted during the first three years. It is assumed that a higher initial dose would be used at the 20

additional wells, followed by subsequent injections for three additional years consistent with the initial

injection procedures.

5.5 Alternative 5 – Enhanced Bioremediation via Recirculating

System

Similar to Alternative 4, Alternative 5 involves installing injection wells within the rights-of-way for carbon

substrate delivery to the aquifer to promote biodegradation of TCE in the glacial drift groundwater. In

contrast to Alternative 4, Alternative 5 uses extraction wells within the Central Area and conveyance piping

to recirculate the amended groundwater within the Central Area. Alternative 5 also includes constructing

treatment control buildings where the extracted groundwater would be amended prior to reinjection and

assumes that access for treatment control buildings can be obtained within the Central Area. Given the

density of residential development in the Central Area, the treatment control buildings are assumed to

require two typical lots for construction of each treatment control building. There is significant

uncertainty regarding the ability to obtain access for the treatment control buildings. Access to rights-of-

way for injection well installation is contingent upon negotiations with right-of-way administrators (City of

Minneapolis and the railroad). There is uncertainty associated with the ability to gain access to install the

injection wells and piping. Subsurface conditions, access limitations, and technology limitations provide

significant uncertainty regarding the effectiveness of Alternative 5. The appropriate substrate and

amendment dosing that would be required would need to be evaluated during the design phase.

The recirculation system would have the flexibility to deliver high concentration solutions of carbon

substrate and other amendments at the beginning of operations while also having the ability to add

smaller quantities of amendments during recirculation. This functionality allows for amendment

distribution in the subsurface to be more precisely controlled than with Alternative 4; however, there is

significant uncertainty regarding the degree to which substrate distribution could be controlled. As with

Alternative 4, the behavior of substrate distribution would need to be evaluated during the design phase.

The recirculation system would have functionality to switch from promoting anaerobic conditions to

promoting aerobic conditions in the aquifer as necessary to promote the reductive dechlorination or the

25

aerobic co-metabolic process, respectively. Assumptions and costs for construction of appropriate

treatment facilities, maintenance to the system and wells, design phase considerations, performing

supplemental amendment delivery, and performance monitoring are all included within Alternative 5 as

discussed below.

Full Scale Recirculation System Construction and Initial Amendment Delivery

For purposes of this feasibility study, Alternative 5 assumes constructing 40 injection wells as conceptually

shown on Figure 8, constructing two new extraction wells and connecting to four existing extraction wells,

constructing conveyance piping, and constructing treatment control buildings that would contain pumps,

piping, valves, instrumentation, and controls. The treatment control buildings are assumed to be 3,500

square feet in size and constructed similar to a warehouse to provide sufficient capacity for tanks, pumps,

piping, and controls. Extraction well spacing is based on previous performance of the legacy groundwater

extraction system. The injection well locations were designed along transects perpendicular to

groundwater flow along the railroad tracks or road rights-of-way that provide the greatest access and

space for injection well installation. The injection well spacing is based on the anticipated radius of

influence that could be achieved with a fully penetrating well in the glacial drift unit, estimated hydraulic

conductivity ranging from 20 m/day to 100 m/day, injection rates ranging from 25 to 50 GPM, and

limiting groundwater mounding adjacent to the injection wells to depths below utilities and basements.

There is uncertainty regarding the achievable radius of influence; as such injection well spacing and

injection rate would need to be evaluated during the design phase.

Given the greater control and ability to adjust to conditions observed during implementation, it is

unknown what amendments would be added for Alternative 5. The recirculation system for Alternative 5

could be operated to promote either anaerobic reductive dechlorination or aerobic co-metabolic

processes. For preparing cost estimates, it was assumed that a carbon substrate of a similar dose to

Alternative 4 would initially be applied and that subsequent operations could be adjusted to maintain

reducing conditions or modified to promote aerobic co-metabolic degradation. Selection of the

dominant biological process and dosing requirements would be determined during the design phase.


For the purposes of this feasibility study, Alternative 5 assumes an initial injection of amendments

followed by operation of the recirculation system for up to 10 years. The first five years of operations will

include performance monitoring and system modifications based on conditions measured at the

treatment control buildings and at monitoring wells located within the Central Area. The recirculation

system would have the flexibility to adjust amendment type and dosing rates and would be operated by a

full-time operator to maximize the effectiveness of treatment.

Following five years of treatment, it is assumed that a sufficient amount of amendment would have been

delivered throughout the Central Area and the system would operate primarily for recirculation of

groundwater to promote uniform treatment across the Central Area.

26

6.0 Detailed Analysis of Alternatives

This section presents the detailed analysis of the remedial alternatives described in Section 5.0. The

purpose of the detailed analysis is to gather sufficient information to adequately compare the alternatives

and select a remedy.

6.1 Detailed Analysis Overview

The detailed analysis of the five alternatives consists of the following three components: 1) further

definition of each alternative with respect to volumes or areas of contaminated media to be addressed,

the technologies to be used, and the primary performance requirements associated with those

technologies; 2) an assessment and a summary of each alternative against the evaluation criteria; and 3) a

comparative analysis among the alternatives to assess the relative performance of each alternative with

respect to each evaluation criteria.

6.1.1 Alternative Definition

Each alternative was reviewed to determine if additional definition was required to apply the evaluation

criteria consistently and appropriately and to develop order-of-magnitude cost estimates. Information

considered to refine the alternatives consisted of preliminary design concepts and an evaluation of the

limitations, assumptions, and uncertainties associated with each alternative. An important factor in the

decisions was to provide a reasonable set of design assumptions for each alternative sufficient to provide

a reasonable detailed analysis.

6.1.2 Evaluation Criteria

EPA has established evaluation criteria to address the technical and policy considerations that have

proven to be important for selecting remedial alternatives. These criteria serve as the basis for conducting

the detailed analyses of the feasibility study and for subsequently selecting a remedial action. EPA

evaluation criteria are divided into the following three groups:

threshold criteria,

balancing criteria, and

modifying criteria.

In addition to the EPA evaluation criteria, this analysis evaluates additional considerations with the

potential to impact the community.

6.1.2.1 Threshold Criteria

Threshold criteria are defined as statutory requirements that each alternative must satisfy to be eligible for

selection.

Overall Protection of Human Health and the Environment – This criteria draws on assessments conducted

under other criteria, especially long-term effectiveness and permanence, short-term effectiveness,

27

compliance with ARARs and consideration of TBCs. It focuses on whether the alternative meets the RAO

and PRG and describes how risks are eliminated, reduced, or controlled.

As detailed in Section 2.4, a risk assessment was completed to evaluate potential risk to human health

(H&A, 2015). The risk assessment concluded that the exposure pathways in the Central Area were

currently either incomplete or insignificant and not expected to be significant in the future. Accordingly,

overall protection of human health and the environment is assessed by evaluating the additional

protection offered by each alternative compared to the no further action alternative (Alternative 1).

Radon is a naturally occurring radioactive gas that is present in shallow soils in Minnesota. While not

evaluated as part of this feasibility study, the SSD systems installed by General Mills also provides

protection to human health from radon. SSD systems are considered by MDH to be an effective

technology for mitigating radon and operate for many years with minimal maintenance requirements

(MDH, 2016b).

Compliance with ARARs – This evaluation criterion is used to evaluate whether the alternative complies

with federal, state, and local ARARs. It also addresses other information from advisories, criteria, and

guidance that is “to be considered” in the detailed analysis of an alternative.

6.1.2.2 Balancing Criteria

Balancing criteria are technical criteria upon which the detailed analysis is primarily based. The

assessment of the technical balancing criteria informs the assessment of the threshold criteria, modifying

criteria, and additional considerations.

Long-Term Effectiveness and Permanence – This assessment evaluates the long-term effectiveness and

permanence of the alternative in maintaining protection of human health and the environment after

response objectives have been met.

Reduction of Toxicity, Mobility, or Volume through Treatment – This assessment evaluates the anticipated

performance of the specific treatment technologies an alternative may employ.

Short-Term Effectiveness – This assessment evaluates the effectiveness of the alternative in protecting

human health and the environment during construction and implementation of a remedy until response

objectives have been met.

Implementability – This assessment evaluates the technical and administrative feasibility of the alternative

and the availability of required goods and services.

Cost – This assessment evaluates the capital and O&M costs of the alternative. The cost estimate is

prepared to an accuracy of plus 50 to minus 30 percent with the exception of those items noted to have

greater uncertainty. Anticipated accuracy range for FS cost estimates is consistent with EPA guidance

(EPA, 1988). This accuracy range is associated with the most likely cost of the project based on the level

of design that has been completed and the uncertainties in the project as scoped (e.g., quantity

uncertainties for wells and other capital cost items, pricing changes for amendments, variability in project

28

schedule/phasing, etc.). It does not include costs for future scope changes that are not part of the

planned project or risk contingency (e.g., additional media cleanup, change in technologies, new

contaminants of concern or expanded treatment areas, etc.). The present worth estimate is calculated

assuming a discount rate of 7 percent and a timeframe of 30 years. Supporting cost details for each

alternative are provided in Appendix A.

6.1.2.3 Modifying Criteria

Modifying criteria evaluate state and community acceptance of implemented remedial actions.

Assessments of the modifying criteria are not provided in this detailed analysis and will be completed

after the public comment period. The assessment of balancing criteria and additional considerations are

intended to inform the evaluation of state and community acceptance.

State Acceptance – This assessment reflects the state’s (or support agency’s) apparent preferences among

or concerns about alternatives.

Community Acceptance – This assessment reflects the community’s apparent preference among or

concerns about alternatives.

6.1.2.4 Additional Considerations

Additional considerations could be threshold or balancing criteria, but are evaluated separately in this

feasibility study to provide further details on distinct items with the potential to impact the community.

The assessment of threshold and balancing criteria incorporates the assessment of the additional

considerations.

Incremental Reduction in Vapor Intrusion Risk – This assessment provides a comparison of the reduction

in vapor intrusion risk associated with implementation of each remedial alternative relative to Alternative

1 (no further action beyond previous response actions).

Secondary Impacts – This assessment evaluates potential secondary impacts of implementing the

remedial alternative. In some cases, the risk of secondary impacts may be greater than the vapor

intrusion risk. Secondary impacts are considered during the evaluation of short-term effectiveness.

Sustainability – This assessment provides a comparison of sustainability impacts (e.g., greenhouse gas

impacts, energy footprint, and worker injury risk) associated with implementing each remedial alternative

relative to Alternative 1 (no further action beyond previous response actions). SiteWise™, a tool

developed for green and sustainable remediation, was the assessment method used to estimate

sustainability impacts. SiteWise™ estimates sustainability metrics by considering impacts associated with

the production of materials used in the remedy, transportation of personnel and equipment, equipment

use (e.g., pumps), and residual handling (e.g., waste disposal) throughout each phase of the remedial

action including construction, operation, and long-term monitoring. Further information regarding the

sustainability impacts evaluation is in Appendix B.

29

Construction Time – This assessment provides an estimate of the time required to implement the remedial

alternative.

6.1.3 Comparative Analysis of Alternatives

A comparative analysis of alternatives is conducted to evaluate the performance of each alternative

relative to the specific evaluation criteria and to identify the relative advantages and disadvantages of

each alternative. The comparative analysis of alternatives is summarized in Table 6.

6.2 Detailed Analysis of Remedial Alternatives

The alternatives described in Section 5.0 of this report are evaluated in detail using the evaluation criteria

presented in Section 6.1.2.

6.2.1 Alternative 1 – No Further Action Beyond Previous Response Actions

Alternative 1 includes no further action beyond the already-completed installation and operation of the

legacy groundwater extraction system, installation of the existing SSD systems, and existing institutional

controls already implemented. Natural attenuation of TCE in groundwater will occur as part of all

alternatives, including Alternative 1, which leads to a reduction in TCE concentrations over time.

6.2.1.1 Alternative 1 – Threshold Criteria

Overall Protection of Human Health and the Environment – Operation of the legacy groundwater

extraction system reduced TCE concentrations in groundwater in the Central Area. Installation of SSD

systems reduced potential exposure to TCE resulting from vapor intrusion. Significant effort has been

completed through installation and operation of these systems to protect human health and the

environment. The HHRA concluded that the exposure pathways in the Central Area were currently either

incomplete or insignificant and not expected to be significant in the future (H&A, 2015).

Compliance with ARARs – Alternative 1 would comply with chemical-, action-, and location-specific

ARARs.

6.2.1.2 Alternative 1 – Balancing Criteria

Long-Term Effectiveness and Permanence – SSD systems have a demonstrated track record of reliable

long-term performance. Alternative 1 does not include a systematic plan for O&M of the SSD systems to

verify and maintain long-term performance. Over the long term, natural attenuation processes will

eventually reduce TCE concentrations in groundwater.

Reduction of Toxicity, Mobility, or Volume through Treatment – The legacy groundwater extraction system

provided significant reduction in toxicity, mobility, and volume of TCE through the removal and treatment

of approximately six billion gallons of groundwater and removal of approximately 7,000 pounds of TCE.

The existing SSD systems significantly reduce the mobility of sub-slab soil gas to migrate into buildings.

Short-Term Effectiveness – Since Alternative 1 requires no further construction, there are no

implementation-related risks to workers, the community, or the environment from Alternative 1.

30

Implementability – Implementation has already been completed. Alternative 1 does not involve the

implementation of further actions.

Cost – No additional costs are associated with Alternative 1. General Mills has performed extensive

investigation and response action work in the Study Area since the early 1980s. General Mills spent over

$3.5 million on early investigation work and the installation and operation for 25 years of the legacy

groundwater extraction system. General Mills has spent over $11 million since late 2013 on vapor

intrusion investigation and installation of SSD systems.

6.2.1.3 Alternative 1 – Additional Considerations

Incremental Reduction in Vapor Intrusion Risk – Installation of existing SSD systems reduced potential

exposure to TCE resulting from vapor intrusion. Alternative 1 is the baseline for comparison.

Secondary Impacts – There are no secondary impacts resulting from implementation of Alternative 1.

Sustainability – Alternative 1 is used as the baseline for comparison for sustainability.

Construction Time – Alternative 1 does not require construction for further implementation.

6.2.1.4 Alternative 1 – Summary

The RAO has been substantially achieved through installing SSD systems at approximately 94 percent of

properties in the Central Area. Alternative 1 does not provide a systematic plan for O&M of the SSD

systems or address future VI risk as robustly as Alternative 3, but it has already been implemented and

poses no short-term risks due to construction activities or potential secondary impacts from remedial

activities like Alternatives 4 and 5.

6.2.2 Alternative 2 – Monitored Natural Attenuation

Alternative 2 relies on naturally occurring degradation of TCE in the groundwater and includes monitoring

of the natural attenuation process by collecting groundwater samples from the existing monitoring well

network and analyzing the samples for TCE, TCE daughter compounds, and common electron acceptors.

Additionally, the SSD systems previously installed in the Central Area will continue to provide protection,

although Alternative 2 does not provide a systematic plan for O&M of the SSD systems.


Overall Protection of Human Health and the Environment – The natural degradation rates observed in the

Central Area indicate that it will take a long time to reduce groundwater TCE concentrations to a level that

would eliminate the need for SSD systems. Alternative 2 evaluates groundwater conditions and assesses

the timeframe for natural treatment until it is not necessary to operate SSD systems to maintain

protection of human health and the environment.

Compliance with ARARs – Alternative 2 would comply with chemical-specific, action-specific, and location-

specific ARARs.

31


Long-Term Effectiveness and Permanence – Similar to Alternative 1, Alternative 2 does not include a

systematic plan for long-term O&M of the SSD systems. Over the long-term, natural attenuation

processes will eventually reduce groundwater concentrations.

Reduction of Toxicity, Mobility, or Volume through Treatment – Alternative 2 does not provide additional

treatment of soil gas or groundwater beyond naturally occurring degradation, which over time will reduce

groundwater concentrations. The existing SSD systems significantly reduce the mobility of sub-slab soil

gas to migrate into buildings.

Short-Term Effectiveness – Since Alternative 2 requires no further construction, there are minimal

implementation-related risks to workers, the community, or the environment. There would be a minimal

increased presence of workers in the neighborhood for completing groundwater monitoring events. The

groundwater monitoring events would involve an environmental professional driving to monitoring wells,

collecting groundwater samples, and transporting them to a laboratory for chemical analysis.

Implementability – Alternative 2 is readily implementable using the existing monitoring well network. The

services, materials, and technologies are available and implementation is technically and administratively

feasible.

Cost – The present worth cost to complete Alternative 2 is estimated to be $1.3 million with a range of

costs estimated between $0.9 million and $1.9 million. The cost estimate for Alternative 2 is summarized

in Table 7.


Incremental Reduction in Vapor Intrusion Risk – The incremental reduction in vapor intrusion risk is

negligible in the short-term when compared to Alternative 1. The additional monitoring of natural TCE-

degradation processes conducted for Alternative 2 does not directly address vapor intrusion risk.


Sustainability – The greenhouse gas emissions, energy footprint, and worker injury risk for Alternative 2

are similar to Alternative 1.

Construction Time – Alternative 2 could be implemented in less than a year. The existing monitoring well

network is considered sufficient for an effective monitored natural attenuation program.


Similar to Alternative 1, the RAO has been substantially achieved through installing SSD systems at

approximately 94 percent of properties in the Central Area. There is a long anticipated timeframe for

natural processes to degrade TCE to a level that would eliminate the need for SSD systems in the Central

Area. However, Alternative 2 provides a plan for monitoring of natural attenuation processes which is not

included in Alternative 1. Similar to Alternative 1, Alternative 2 does not provide a systematic plan for

32

O&M of the SSD systems or address future VI risk as robustly as Alternative 3, but it is easy to implement

and poses no short-term risks due to construction activities or potential secondary impacts from remedial

activities like Alternatives 4 and 5.

6.2.3 Alternative 3 – Long-Term O&M of SSD Systems

Alternative 3 includes preparing and implementing a long-term O&M plan that would provide measures

for routine monitoring and maintenance of the SSD systems. Elements of the O&M plan would include

verifying fan operation, visually inspecting the vent pipe, and visually inspecting the manometer pressure

gage. Alternative 3 assumes communication with and cooperation from property owners to conduct

visual inspections and coordinate routine maintenance needs.

Alternative 3 also includes installing active SSD systems at the remaining residential buildings within the

Central Area where active SSD systems have not been installed. This assumes cooperation from property

owners for access and installation of the SSD systems.

Additionally, natural attenuation of TCE in groundwater will occur as part of all alternatives, including

Alternative 3, which leads to a reduction in TCE concentrations over time. Monitoring of natural

attenuation processes is not included in Alternative 3.


Overall Protection of Human Health and the Environment – Long-term O&M provides added assurance

that the existing SSD systems will continue to operate safely and reliably. Alternative 3 provides

controllable protection of human health and the environment regardless of TCE concentrations in

groundwater and of the level of reduction in future TCE groundwater concentrations needed to eliminate

the vapor intrusion pathway. It provides confidence that the vapor intrusion pathway is disconnected, and

therefore, the SSD systems remain protective of human health and the environment.

Compliance with ARARs – Alternative 3 would comply with chemical-, action-, and location-specific

ARARs. Additionally, Alternative 3 most directly addresses the indoor air ISV as a TBC by providing

confidence that the VI pathway is disconnected.


Long-Term Effectiveness and Permanence – Alternative 3 provides a systematic plan for O&M of the SSD

systems to maintain long-term performance. Property owners can easily assess the operation of the SSD

systems through simple visual and auditory methods, as readily as they assess other home appliances. In

addition, an SSD systems are a simple technology that is regarded by MPCA and EPA as one of most

effective vapor intrusion mitigation strategies for existing or new buildings (MPCA, 2010; EPA, 2015). They

effectively disconnect the potential vapor pathway into a building, providing protection when uncertainty

exists regarding the level of reduction in future groundwater TCE concentrations needed to eliminate the

VI pathway.

Additionally, over the long term, natural attenuation processes will eventually reduce TCE concentrations

in groundwater.

33

Reduction of Toxicity, Mobility, or Volume through Treatment – The existing SSD systems significantly

reduce the mobility of sub-slab soil gas to migrate into buildings. A systematic approach for O&M of the

SSD systems provides a method to maintain the reduction in mobility of sub-slab soil gas into buildings

through verification and maintenance of the SSD systems. Alternative 3 does not provide additional

treatment of soil gas or groundwater beyond naturally occurring degradation, which over time will reduce

groundwater concentrations.

Short-Term Effectiveness – There would be negligible short-term exposure to TCE because there is no

handling of impacted groundwater or soil gas as part of Alternative 3. Because Alternative 3 directly

addresses the vapor intrusion pathway and can be implemented quickly, the risk of exposure while

implementing the remedy is significantly less than alternatives with a significant implementation stage

(e.g., Alternatives 4 and 5).

There would be disturbance to property owners and an increased presence in the neighborhood for

construction of up to 10 new SSD systems and maintenance of SSD systems. Maintenance events would

entail a contractor coordinating with a property owner for installing or repairing SSD system components

(e.g., fan, riser pipe, suction pit, manometer). Repair activities would be comparable to other appliances

or building maintenance activities performed by property owners. The short-term construction and

maintenance impacts for Alternative 3 are similar to Alternatives 1 and 2 and significantly less than

Alternatives 4 and 5.

Implementability – Alternative 3 is readily implementable using standard techniques for SSD installation

and O&M assuming cooperation from property owners for access during installation and routine O&M.

The services, materials, and technologies are available and proven, and implementation is technically and

administratively feasible.

Cost – The present worth cost to complete Alternative 3 is estimated to be $2 million with a range of costs

estimated between $1.4 million and $3.0 million. The cost estimate for Alternative 3 is summarized in

Table 8.


Incremental Reduction in Vapor Intrusion Risk – Alternative 3 provides the greatest incremental reduction

in current and future risk based on the reliability and effectiveness of the SSD systems in disconnecting

the potential VI pathway. Disconnecting the pathway helps assure the VI risk reduction since there is

uncertainty of the TCE groundwater concentration necessary to eliminate VI risk and long-term O&M

helps assure that the SSD systems continue to operate.


Sustainability – The greenhouse gas emissions, energy footprint, and worker injury risk for Alternative 3

are similar to Alternatives 1 and 2.

34

Construction Time – Alternative 3 could be implemented in less than a year assuming cooperation of

property owners.


Alternative 3 builds on the progress made by operating the legacy groundwater extraction system and

installing the existing SSD systems by installing additional systems and providing long-term O&M of the

SSD systems. SSD systems have been shown to be effective and reliable over the long term for mitigating

VI risk and directly disconnect the potential VI pathway. Long-term O&M with Alternative 3 is easy to

implement and will be only minimally intrusive for property owners in the Central Area. Alternative 3 has

minimal short-term risks due to construction activities and no secondary impacts from remedial activities

like Alternatives 4 and 5.

6.2.4 Alternative 4 – Enhanced Bioremediation via Injection Events

Alternative 4 involves installing injection wells within the rights-of-way and performing periodic injection

of carbon substrate and other amendments to support bioremediation of approximately 100 million

gallons of impacted groundwater over 40 acres in the Central Area. Within this area there are

approximately 177 individual property owners with buildings covering approximately eight acres. Road

and alleyway rights-of-way cover approximately five acres with significant infrastructure consisting of

water, stormwater, wastewater, electrical, and other underground utilities present beneath the rights-of-

way and throughout the Central Area. Due to the urban residential development, it is assumed for this

feasibility study that the injection wells would be installed primarily along two transects through the

Central Area. The carbon substrate and amendments would be injected using mobile tanker trucks.

The SSD systems previously installed in the Central Area will continue to provide protection, although

Alternative 4 does not provide a systematic plan for O&M of the SSD systems. Additionally, natural

attenuation of TCE in groundwater will occur as part of all alternatives, including Alternative 4. Monitoring

of natural attenuation processes is not included in Alternative 4, however, performance monitoring of the

remedy will be conducted.


Overall Protection of Human Health and the Environment – Although Alternative 4 would reduce TCE

concentrations in groundwater within the Central Area, the overall protection of human health and the

environment would not necessarily be improved through a reduction in TCE concentrations in

groundwater beyond the protection already offered by the existing SSD systems. It is unlikely that

Alternative 4 could achieve an effective and consistent reduction in groundwater concentrations

throughout the Central Area to a level that would eliminate the need for SSD systems.

Additionally, Alternative 4 has the potential to generate methane and vinyl chloride which may pose a

greater human health risk than the existing risk of TCE vapor intrusion as described in Section 6.2.4.3.

35

Compliance with ARARs – Alternative 4 would comply with chemical-, action-, and location-specific ARARs

with appropriate design and planning. It is unlikely that Alternative 4 can reduce the groundwater

concentrations sufficiently to meet the RAO.


Long-Term Effectiveness and Permanence – The effectiveness of Alternative 4 in reducing the

groundwater concentrations to a level that that would eliminate the need for SSD systems is highly

uncertain due to the size of the Central Area, limitations of advective flow distribution within a

heterogeneous aquifer with many preferential flowpaths, and access limitations due to the high density

residential development. If groundwater remediation is successfully implemented, the long-term

effectiveness of Alternative 4 may be somewhat better than Alternatives 1 and 2, similar to Alternative 5,

but less effective than Alternative 3. Similar to Alternatives 1 and 2, Alternative 4 does not provide a

systematic plan for long-term O&M of the SSD systems.

Reduction of Toxicity, Mobility, or Volume through Treatment – Alternative 4 would likely reduce the

volume of impacted-groundwater through treatment. There is a potential risk that complete degradation

would not be achieved by implementing Alternative 4 and that daughter-compounds with higher toxicity

(e.g., vinyl chloride) could be created. There is also a risk that complete degradation in an uncontrolled

manner would lead to generation of methane. Alternative 4 would provide greater reduction of volume

than Alternatives 1, 2, and 3, but less reduction in volume than Alternative 5. Alternative 4 does not

provide a reduction in mobility beyond the existing SSD systems that reduce the mobility of sub-slab soil

gas to migrate into buildings, and could potentially increase toxicity of the contaminants in groundwater.

Short-Term Effectiveness – Alternative 4 would expose workers to chemicals used as amendments in the

injection solution. It would also expose the neighborhood to increased construction traffic during

injection well installation and tanker traffic during injection delivery events.

Implementability – Alternative 4 is implementable assuming rights-of-way work permits, railroad access,

and underground injection control program approvals can be obtained. Alternative 4 is implementable

using standard well drilling techniques and fluid injection using tanker trucks and temporary piping

connections. Installing the series of injection wells in close proximity to one another will be challenged by

the urban setting and the presence of underground utilities and mature trees. The services, materials, and

technologies are available and implementation is technically and administratively feasible, but potentially

difficult to implement given the numerous stakeholders and approvals required. Alternative 4 is more

difficult to implement than Alternatives 1, 2, and 3, but easier to implement than Alternative 5.

Cost – The present worth cost to complete Alternative 4 is estimated to be $26 million with a range of

costs estimated between $6 million to $90 million. There is significant uncertainty regarding the cost

estimate for Alternative 4 due to the influence of amendment quantity on total cost. Given the

approximate treatment volume of 100 million gallons, the estimated cost per volume of groundwater

targeted for treatment is approximately $0.26 per gallon. A review of TCE groundwater treatment projects

from the Remediation Technology Cost Compendium (EPA, 2001) and EPA’s database of Superfund

decision documents (EPA, 2016) indicates that groundwater treatment costs are typically between the

36

estimated cost and the high end of the estimated range calculated for Alternative 4. Groundwater

treatment completed at those sites was also not completed to a level that would eliminate the need for

SSD systems in the Central Area. The cost estimates are prepared to an accuracy of plus 50 to minus 30

percent, with the exception of items involving amendment quantity which have a larger range. The cost

estimate for Alternative 4 is summarized in Table 9.


Incremental Reduction in Vapor Intrusion Risk – It is uncertain whether Alternative 4 will be effective at

reducing TCE concentrations in groundwater throughout the Central Area sufficiently to eliminate the

need to operate the SSD systems.

Secondary Impacts – There are numerous potential secondary impacts associated with implementing

enhanced bioremediation. Providing a carbon substrate to the subsurface creates reducing conditions

that can lead to metals liberation in groundwater. The breakdown of TCE via the reductive dechlorination

process can generate daughter-compounds that may pose a higher risk to residents than TCE. Two

examples of this are the generation of vinyl chloride as a result of incomplete reductive dechlorination

and the generation of methane as a result of complete reductive dechlorination. While additional

controls of these compounds could be designed, such as an area-wide vapor extraction system, the access

limitations present in the Central Area and the limited radius of influence of vapor extraction systems

would not provide coverage for the entire Central Area. Vapor extraction systems were screened out as a

technology due to the lack of coverage as summarized in Table 4. The process of injecting carbon and

amendments can also lead to changes in color, turbidity, and odor of the groundwater. The risk of

secondary impacts for Alternative 4 may be greater than the existing risk of TCE vapor intrusion.

Sustainability – The greenhouse gas impacts are estimated at 3,800 metric tons CO2-equivalent and the

energy footprint is estimated at 66,000 million British Thermal Units (MMBTU) for implementation of

Alternative 4. The greenhouse gas impacts for Alternative 4 are equivalent to the impact of driving 800

passenger vehicles for one year or consuming 428,000 gallons of gasoline. The estimated worker injury

risk associated with implementing Alternative 4 is 1.0 accidents. Additional details regarding the

sustainability impact evaluation are provided in Appendix B.

Construction Time – Alternative 4 could be implemented in +/- five years assuming necessary permits can

be obtained. The timeframe for construction would be dependent on the results of final design,

performance monitoring, and the need for installation of additional wells.


It is unlikely that Alternative 4 would be effective at reducing groundwater concentrations to a level that

meets the RAO given the technical and logistical constraints in the Central Area. Alternative 4 is more

intrusive during implementation than Alternatives 1, 2, and 3 and it would have short-term risks due to

construction activities and secondary impacts from completing remedial activities. The potential benefit

of reducing groundwater concentrations provided by Alternative 4 may be less than the potential risks of

implementing this alternative.

37

6.2.5 Alternative 5 – Enhanced Bioremediation via Recirculation

Alternative 5 includes installing extraction and injection wells and conveyance piping within the rights-of-

way, and constructing two treatment control buildings for operating a groundwater recirculation system.

The recirculation system would inject carbon substrate and other amendments, extract groundwater, mix

amendments with the groundwater to maintain conditions suitable for bioremediation, and reinject the

amended groundwater. The treatment control buildings would be constructed to allow for adjustments to

the substrate and amendment solutions and to switch from anaerobic to aerobic conditions, as necessary

to promote reductive dechlorination or aerobic co-metabolic processes.

The SSD systems previously installed in the Central Area will continue to operate, although Alternative 5

does not provide a systematic plan for O&M of the SSD systems. Additionally, natural attenuation of TCE

in groundwater will occur as part of all alternatives, including Alternative 5. Monitoring of natural

attenuation processes is not included in Alternative 5, however, performance monitoring of the remedy

will be conducted.


Overall Protection of Human Health and the Environment – Although Alternative 5 would reduce TCE

concentrations in groundwater within the Central Area, the overall protection of human health and the

environment would not necessarily be improved through a reduction in TCE concentrations in

groundwater beyond the protection already offered by the existing SSD systems. There is also significant

uncertainty whether Alternative 5 could achieve an effective and consistent reduction in groundwater

concentrations throughout the Central Area to a level that would eliminate the need for SSD systems due

to the size of the Central Area, access limitations, and the heterogeneity of the glacial aquifer.

Additionally, Alternative 5 has the potential to generate methane and vinyl chloride which may pose a

greater human health risk than the existing risk of TCE vapor intrusion as described in Section 6.2.4.3.

Compliance with ARARs – Alternative 5 would comply with chemical-, action-, and location-specific ARARs

with appropriate design and planning.


Long-Term Effectiveness and Permanence – The effectiveness of Alternative 5 in reducing the

groundwater concentrations to a level that that would eliminate the need for SSD systems is highly

uncertain due to the size of the Central Area, limitations of advective flow distribution within a

heterogeneous aquifer with many preferential flowpaths, and access limitations due to the high-density

residential development. If groundwater remediation is successfully implemented, the long-term

effectiveness of Alternative 5 may be somewhat better than Alternatives 1 and 2, similar to Alternative 4,

but less effective than Alternative 3. Similar to Alternatives 1, 2, and 4, Alternative 5 does not provide a

systematic plan for long-term O&M of the SSD systems.

Reduction of Toxicity, Mobility, or Volume through Treatment – Alternative 5 provides for the greatest

potential for reduction of volume of groundwater impacts through treatment. There is a potential risk

38

that complete degradation would not be completed as part of implementing Alternative 5 and daughter-

compounds with higher toxicity (e.g. vinyl chloride) could be created. Alternative 5 does not provide a

reduction in mobility beyond the existing SSD systems that reduce the mobility of sub-slab soil gas to

migrate into buildings, and could potentially increase toxicity of contaminants in groundwater.

Short-Term Effectiveness – Alternative 5 would expose workers to chemicals used as amendments in the

treatment control buildings. Alternative 5 would also expose the neighborhood to heavy equipment

traffic during extraction and injection well installation, conveyance piping and treatment control building

installation, and maintenance of the control buildings, piping, and wells. Construction of the treatment

control buildings would require demolition of several buildings within the Central Area to provide

centralized locations for treatment process control. Construction of the conveyance piping would disturb

roads during installation and would require temporary road closures.

Implementability - Alternative 5 is implementable assuming access for the treatment control buildings,

rights-of-way work permits, railroad access, and underground injection control program approval can be

obtained. Alternative 5 is implementable using standard well drilling techniques, standard trenching and

conveyance piping installation techniques, water treatment and control plant installation processes, and

water treatment systems operations. Constructing the treatment control buildings will be challenged by

the need to acquire property or obtain access within the Central Area for the buildings. Installing the

series of injection wells, extraction wells, and conveyance piping will be challenged by the urban setting

and the presence of underground utilities and mature trees. The services, materials, and technologies are

available and implementation is technically and administratively feasible, but potentially difficult to

implement given the numerous stakeholders and approvals required. Alternative 5 is more difficult to

implement than Alternatives 1, 2, 3, and 4.

Cost – The present worth cost to complete Alternative 5 is estimated to be $42 million with a range of

costs estimated at $19 million to $100 million. There is significant uncertainty regarding the cost estimate

for Alternative 5 due to the influence of amendment quantity on total cost. Given the approximate

treatment volume of 100 million gallons, the estimated cost per volume of groundwater targeted for

treatment is approximately $0.42 per gallon. A review of TCE groundwater treatment projects from the

Remediation Technology Cost Compendium (EPA, 2001) and EPA’s database of Superfund decision

documents (EPA, 2016) indicates that groundwater treatment costs per volume are typically between the

estimated cost and the high end of the estimated range calculated for Alternative 5. Groundwater

treatment completed at those sites was also not completed to a level that would be protective of VI risk.

The cost estimates are prepared to an accuracy of plus 50 to minus 30 percent with the exception of items

involving amendment quantity which have a larger range. The cost estimate for Alternative 5 is

summarized in Table 10.


Incremental Reduction in Vapor Intrusion Risk – It is uncertain whether Alternative 5 will be effective at

reducing TCE concentrations in groundwater throughout the Central Area sufficiently to eliminate the

need to operate the SSD systems.

39

Secondary Impacts – There are numerous secondary impacts associated with implementing enhanced

bioremediation. Providing a carbon substrate to the subsurface creates reducing conditions that can lead

to metals liberation in groundwater. The breakdown of TCE via the reductive dechlorination process can

generate daughter-compounds that pose a higher risk to residents than TCE. Two examples of this

include the generation of vinyl chloride as a result of incomplete reductive dechlorination and generation

of methane as a result of complete reductive dechlorination. The process of injecting carbon and

amendments can also lead to a change in color, turbidity, and odor of the groundwater. Alternative 5

provides greater control over subsurface conditions than Alternative 4 by modifying the system

operations as appropriate to minimize secondary impacts. Alternative 5 provides relatively greater control

to promote complete dechlorination to reduce vinyl chloride generation, to promote aerobic conditions

for breakdown of methane, and/or to flush groundwater to promote stabilizing color, turbidity, and odor

alterations. The secondary impacts associated with Alternative 5 are less than the secondary impacts

associated with Alternative 4, but greater than the secondary impacts of Alternatives 1, 2, and 3.

Sustainability – The greenhouse gas emissions are estimated at 4,400 metric tons CO2-equivalent and the

energy footprint is estimated at 70,000 MMBTU for implementation of Alternative 5. The greenhouse gas

impacts for Alternative 5 are equivalent to the impact of 925 passenger vehicles driven for one year or

495,000 gallons of gasoline consumed. The greenhouse gas impacts and energy footprint estimated for

Alternative 5 are slightly higher than Alternative 4. The estimated worker injury risk associated with

implementing Alternative 5 is 4.0 accidents, approximately four times higher than Alternative 4.

Additional details regarding the sustainability impact evaluation are provided in Appendix B.

Construction Time – Alternative 5 could be implemented in +/- 10 years assuming treatment control

building locations can be identified and purchased, and the necessary approvals can be obtained. The

construction timeframe would be dependent on the results of final design and obtaining access for the

treatment control buildings.


There is significant uncertainty whether Alternative 5 would be effective at reducing groundwater

concentrations to a level that meets the RAO given the technical and logistical constraints in the Central

Area. Alternative 5 is the most intrusive of the remedial alternatives during implementation and would

have short-term risks due to construction activities and secondary impacts from completing remedial

activities. The potential benefit of potential VI risk reduction provided by Alternative 5 may be less than

the potential risks of implementing this alternative.

6.3 Recommended Alternative

The results of the detailed analysis were compiled to evaluate the performance of each alternative relative

to the specific criterion and to compare the advantages and disadvantages of each alternative. A

summary of the detailed analysis and the comparative evaluation is provided in Table 6.

Alternative 3 is the recommended alternative. This alternative provides the best balance of tradeoffs of

the five balancing criteria including cost effectiveness as required by CERCLA and the NCP. This

40

alternative provides the greatest protection to human health and the environment and complies with

ARARs.

41

7.0 Summary and Conclusions

This feasibility study was performed to evaluate alternatives to address the VI pathway in the Central Area

and included alternatives that directly mitigate vapor intrusion and alternatives that decrease the potential

for VI through a decrease in soil gas and groundwater concentrations. This feasibility study was

completed in general accordance with EPA guidance (EPA, 1988) and RAP Modification #1.

This feasibility study was performed for the Central Area, which has been impacted by up-gradient off-Site

sources in the Northeast Area, and only a portion of which is down-gradient of the Site. The HHRA

concluded that exposure pathways in the Central Area, including the VI pathway, are currently either

incomplete or insignificant and not expected to be significant in the future. Moreover, because multiple

sources of TCE exist in the Northeast Area that have yet to be characterized, remedial actions to address

groundwater will not be effective at reducing TCE concentrations in groundwater due to continuing re-

contamination from these up-gradient sources. Nevertheless, General Mills completed this feasibility

study at the request of MPCA. The remedial action objective for this feasibility study focuses on

maintaining insignificant potential VI risk.

A thorough screening of technology and process options was completed to evaluate technologies for

inclusion in remedial alternatives that could be implemented throughout the Central Area. The

technologies were screened based on demonstrated effectiveness at similar sites and on implementability

given the technical, logistical, and physical access constraints of the Central Area. The technologies that

were retained following the technology screening included:

Installation of additional SSD systems (at residential properties within the Central Area that

currently do not have active SSD systems),

O&M of SSD systems,

Institutional controls,

Monitored natural attenuation,

Expanded/modified groundwater extraction, and

In-situ bioremediation (considering both reductive dechlorination and aerobic co-metabolic

treatment and multiple process delivery options).

The five remedial alternatives assessed during detailed analysis were:

Alternative 1 – No Further Action Beyond Previous Response Actions,

Alternative 2 – Monitored Natural Attenuation,

Alternative 3 – Long-Term O&M of SSD Systems,

Alternative 4 – Enhanced Bioremediation via Injection Events, and

42

Alternative 5 – Enhanced Bioremediation via Recirculation.

Alternative 3 – Long-Term O&M of SSD Systems was selected as the recommended alternative. This

alternative provides the best balance of tradeoffs of the five balancing criteria. This alternative provides

protection to human health and the environment, complies with ARARs, and is cost effective as required

by CERCLA and the NCP.

43

References

Barr Engineering Co. (Barr), 2014a. Final Sub-Slab Sampling and Building Mitigation Work Plan, East

Hennepin Avenue Site. Prepared for General Mills, Inc. February 2014.

Barr Engineering Co. (Barr), 2014b. Summary of Phase 2G Vapor Intrusion Evaluation Results, East

Hennepin Avenue Site. Prepared for General Mills, Inc. May 11, 2014.

Barr Engineering Co. (Barr), 2014c. Disposal Area Investigation Results, 2010 East Hennepin Avenue Site.

Prepared for General Mills, Inc. May 23, 2014.

Barr Engineering Co. (Barr), 2015a. Indoor Air Sampling Report, 2010 E Hennepin Avenue, East Hennepin

Avenue Site. Prepared for General Mills, Inc. May 13, 2015.

Barr Engineering Co. (Barr), 2015b. Sub-Slab Sampling and Building Mitigation Implementation Report, East

Hennepin Avenue Site. Prepared for General Mills, Inc. June 2015.

Barr Engineering Co. (Barr), 2015c. Vapor Intrusion Pathway Investigation Report, East Hennepin Avenue

Site. Prepared for General Mills, Inc. July 2015.

Barr Engineering Co. (Barr), 2015d. 2015 Sentinel Monitoring Network Report, East Hennepin Avenue Site.

Prepared for General Mills, Inc. December 2015.

Barr Engineering Co. (Barr), 2016. 2016 Glacial Drift Network Groundwater Monitoring Plan, East Hennepin

Avenue Site. Prepared for General Mills, Inc. April 6, 2016.

General Mills, Inc. (GMI), 2016. Letter to Timothy Grape (MPCA) from Larry Deeney (General Mills)

regarding Vapor Intrusion Pathway Investigation – Response to MPCA Comments; East Hennepin

Avenue Site. April 6, 2016.

Haley & Aldrich, Inc. (H&A), 2015. Human Health Risk Assessment Report, East Hennepin Avenue Site.

Prepared for General Mills, Inc. July 31, 2015.

Haley & Aldrich, Inc. (H&A), 2016. Letter to Timothy J. Grape (MPCA) from Jay Peters (H&A) regarding

Response to the Human Health Risk Assessment Report for the General Mills/Henkel Corporation Site;

Minnesota Pollution Control Agency Site ID#: SR3. April 6, 2016.

Minnesota Department of Health (MDH), 2016a. Trichloroethylene (TCE) in Air, Site Assessment and

Consultation Unit, available at

http://www.health.state.mn.us/divs/eh/hazardous/topics/vapintrustce.pdf. January 26, 2016.

Minnesota Department of Health (MDH), 2016b. Vapor Intrusion, Site Assessment and Consultation Unit,

available at http://www.health.state.mn.us/divs/eh/hazardous/topics/vaporintrusion.pdf. February 2,

2016.

Minnesota Pollution Control Agency (MPCA), 1984. Response Order by Consent (Consent Order) between

General Mills and the Minnesota Pollution Control Agency (MPCA). October 1984.

Minnesota Pollution Control Agency (MPCA), 2008. Risk Based Guidance for the Vapor Intrusion Pathway,

Superfund, RCRA, and Voluntary Cleanup Section, MPCA Document Number c-s4-06. September

2008.

44

Minnesota Pollution Control Agency (MPCA), 2010. Vapor Intrusion Technical Support Document,

Remediation Division, MPCA Document Number c-rem3-01. August 2010.

Minnesota Pollution Control Agency (MPCA), 2014a. Remedial Action Plan Modification #1 (Exhibit B) to

the Response Order By Consent between General Mills and the Minnesota Pollution Control Agency

(MPCA), October 1984. March 11, 2014.

Minnesota Pollution Control Agency (MPCA), 2014b. Five-Year Review Report General Mills/Henkel Corp

Superfund Site, Minneapolis, Minnesota. Prepared by Minnesota Pollution Control Agency, December

2014.

Minnesota Pollution Control Agency (MPCA), 2015a. Letter to Larry Deeney (General Mills) from Timothy J.

Grape (MPCA) regarding Minnesota Pollution Control Agency Response to the Vapor Intrusion Pathway

Investigation Report for the General Mills/Henkel Corporation Site; Site ID#: SR3. November 3, 2015.

Minnesota Pollution Control Agency (MPCA), 2015b. Letter to Larry Deeney (General Mills) from Timothy J.

Grape (MPCA) regarding Response to the Human Health Risk Assessment Report for the General

Mills/Henkel Corporation Site; Minnesota Pollution Control Agency Site ID#: SR3. November 12, 2015.

Minnesota Pollution Control Agency (MPCA), 2016. Letter to Larry Deeney (General Mills) from Timothy

Grape (MPCA) regarding MPCA Response to the 2015 Sentinel Monitoring Network Report for the

General Mills/Henkel Corporation Site ; Site ID#: SR3. January 28, 2016.

Parsons Infrastructure & Technology Group, Inc. (Parsons), 2010a. Addendum to the Principles and

Practices Manual Loading Rates and Impacts of Substrate Delivery for Enhanced Anaerobic

Bioremediation. Prepared for Environmental Security Technology Certification Program (ESTCP)

Project ER-20067. January 2010.

Parsons Infrastructure & Technology Group, Inc. (Parsons), 2010b. Substrate Estimating Tool for Enhanced

Anaerobic Bioremediation of Chlorinated Solvents, Version 2.1. Prepared for Environmental Security

Technology Certification Program (ESTCP). November 2010.

United States Environmental Protection Agency (EPA), 1988. Guidance for Conducting Remedial

Investigations and Feasibility Studies under CERCLA. Office of Emergency and Remedial Response.

October 1988.

United States Environmental Protection Agency (EPA), 1998. Technical Protocol for Evaluating Natural

Attenuation of Chlorinated Solvents in Ground Water. Office of Research and Develop. September

1998.

United States Environmental Protection Agency (EPA), 2000. A Guide to Developing and Documenting Cost

Estimates During the Feasibility Study. Office of Emergency and Remedial Response. July 2000.

United States Environmental Protection Agency (EPA), 2001. Remediation Technology Cost Compendium.

Office of Solid Waste and Emergency Response, Technology Innovation Office. September 2001.

United States Environmental Protection Agency (EPA), 2012. Institutional Controls: A Guide to Planning,

Implementing, Maintaining, and Enforcing Institutional Controls at Contaminated Sites. Office of Solid

Waste and Emergency Response, Office of Enforcement and Compliance Assurance. December 2012.

45

United States Environmental Protection Agency (EPA), 2015. OSWER Technical Guidance for Assessing and

Mitigating the Vapor Intrusion Pathway from Subsurface Vapor to Sources to Indoor Air, Office of Solid

Waste and Emergency Response. June 2015.

United States Environmental Protection Agency (EPA), 2016. Search for Superfund Decision Documents,

available at http://www.epa.gov/superfund/search-superfund-decision-documents. Accessed March

2016.

Tables

Table 1

Potential Action-Specific ARARs and TBCs


Minneapolis, MN

Standard Requirement Citation

Potentially Applicable/

Relevant and Appropriate TBC1

Comments

RCRA Identification of Hazardous

Waste

Waste generator shall determine if the waste is

hazardous waste.40 CFR 261 No/No

Applicable for any remedial action where waste would be generated.

Generation of a hazardous waste is not anticipated.

RCRA Generators of Hazardous

Waste

Generation of contaminated media that is

characterized as a hazardous waste.40 CFR 262 No/No

Applicable where hazardous waste would be generated. Generation

of a hazardouse waste is not anticipated.

RCRA Transporters of Hazardous

Waste

Transportation of hazardous waste to off-site

facilities.40 CFR 263 No/No ARARs pertain only to activities conducted on-site.

RCRA Owners and Operators of

Hazardous Waste Treatment, Storage,

and Disposal Facilities

Management of hazardous waste. 40 CFR 264 No/No

Applicable for remedial action where hazardous waste would be

treated, stored or disposed of. Generation of a hazardouse waste is

not anticipated.

RCRA Management of Specific

Hazardous Waste and Specific Types

of Facilities

Management of specific hazardous wastes. 40 CFR 266 No/No These standards do not apply to remedial actions in the Central Area.

RCRA Land Disposal RestrictionsRestricts certain hazardous wastes from land

disposal.40 CFR 268 No/No

Applicable where hazardous wastes with land disposal restrictions

are generated. Generation of a hazardous waste is not anticipated.

Disposal of Solid Waste that is not a

Hazardous WasteGenerator of RCRA Subtitle D regulated waste. 40 CFR 257 Yes/-- Applicable if RCRA Subtitle D waste is generated (e.g., drill cuttings).

USDOT General Information,

Regulations and Definitions

Requirements for packaging, labeling, marking,

placarding, and motor vehicles used for

transportation of hazardous materials.

49 CFR 171 No/No ARARs pertain only to activities conducted on-site.

USDOT Hazardous Materials Table,

special provisions, communications,

emergency response, training and

security plans

Each person who offers hazardous material for

transportation or each carrier that transports it shall

mark each package, container, and vehicle in the

manner required.


USDOT Requirements for Shipments

and Packagings

Definitions of hazardous materials for

transportation purposes; requirements for

preparing hazardous materials for shipment.


OSHA Work on Contaminated Sites

Requirements for workers on uncontrolled

hazardous waste sites such as training, personal

protective equipment, recording and reporting work-

related fatalities/injuries/illnesses.

29 CFR 1904 - Recording and

Reporting Occupational

Injuries and Illnesses

29 CFR 1910 - Occupational

Safety and Health

29 CFR 1926 – Safety and

Health Regulations for

Construction

Yes/--Appropriate health and safey procedures would be implemented

during remedial actions.

Federal

Table 1

Page 1 of 5

Table 1



Minneapolis, MN




Comments

National Pollutant Discharge

Elimination System (NPDES) Program

Discharge limits, monitoring requirements, and best

management practices for surface water

discharges.

40 CFR 122-125 No/No

Substantive requirements may apply to extent that remedial action

includes discharge to surface waters. Surface water discharges are

not anticipated.

Clean Water ActImplements requirements for discharge of

pollutants to waters of the United States.33 USC 1251, et seq. Yes/--

Substantive requirements may apply to extent that remedial action

includes discharge to waters of the United States.

Clean Air ActRegulates air emissions from stationary and mobile

sources.42 USC 7401 et seq. No/No

Substantive requirements apply if identified pollutants are emitted in

excess of threshold amounts. This is not anticipated to occur.

EPA Effluent Guidelines

Treatment process must not allow waste to pass

through untreated or result in contaminated

sewage sludge.

40 CFR 403.5 No/NoApplicable to remedial actions that include discharge to a POTW.

Discharge to a POTW is not anticipated.

Injection Wells

Injection well must be designed for its intended use

and injection activity cannot allow fluids to migrate

into underground drinking water sources.

40 CFR 144 Yes/--Substantive requirements applicable to remedial actions that include

injection wells.

Onsite waste generationWaste generator shall determine if the waste is

hazardous waste.

Minnesota Rules Ch.

7045.0102 through 7045.0155No/No

Applicable where waste would be generated. Generation of a

hazardous waste is not anticipated.

Generators of Hazardous WasteGeneration of contaminated soils that are

characterized as hazardous wastes.

Minnesota Rules Ch.

7045.0205 through 7045.0325No/No

Applicable where hazardous waste would be generated. Generation

of a hazardouse waste is not anticipated.

Transporters of Hazardous WasteTransportation of hazardous waste to off-site

facilities.

Minnesota Rules Ch.

7045.0351 through 7045.0397No/No ARARs pertain to on-site activities only.

Owners and Operators of Hazardous

Waste Treatment, Storage, and

Disposal Facilities

Management of hazardous waste.Minnesota Rules Ch.

7045.0450 through 7045.0551 No/No

Applicable where hazardous waste would be treated, stored or

disposed of. Generation of a hazardouse waste is not anticipated.

Management of Specific Hazardous

Waste and Specific Types of FacilitiesManagement of specific hazardous wastes.

Minnesota Rules Ch.

7045.0652 through 7045.0686No/No

These standards do not apply to potential wastes generated by

remedial actions.

Hazardous Waste Regulations

State and Local

Table 1

Page 2 of 5

Table 1



Minneapolis, MN




Comments

County Regulation of Hazardous

Waste Management

Procedures for the MPCA’s overview of county

hazardous waste programs.

Minnesota Rules Ch.

7045.1000 through 7045.1030No/No

Hennepin County has an MPCA-approved county ordinance detailing

their hazardous waste programs. Generation of hazardouse waste is

not anticipated.

Land Disposal RestrictionsRestricts certain hazardous wastes from land

disposal.

Minnesota Rules Ch.

7045.1390No/No

Applicable where hazardous wastes with land disposal restrictions

are generated. Generation of a hazardous waste is not anticipated.

General requirements for management

of solid wasteRequirements and standards for solid waste.

Minnesota Rules Ch.

7035.0300 through 7035.0605No/No

Remedial action is not anticipated to include on-site disposal of solid

waste. Off-site disposal, if any, will be conducted in accordance with

RCRA Subtitle D requirements.

Individual Properties Responsibility for management of solid waste.Minnesota Rules Ch.

7035.0700 through 7035.0805Yes/--

Solid waste requirements would be applicable for storage, transport

and disposal of contaminated media generated during remedial

activities (e.g. drill cuttings).

Industrial Solid Waste Land Disposal

Facilities

Requirements for industrial solid waste land

disposal facilities.

Minnesota Rules Ch.

7035.1590 through 7035.2500No/No

Remedial actions do not involve an industrial solid waste land

disposal facility.

Solid Waste Management Facilities

Financial Requirements

Requirements for cost estimates and financial

assurances documentation.

Minnesota Rules Ch.

7035.2665 through 7035.2805No/No

Remedial actions would not involve construction of an industrial solid

waste storage facility.

Solid Waste Management Facility

Specific Technical Requirements

Requirements for facilities that dispose of mixed

municipal solid waste in or on the land.

Minnesota Rules Ch.

7035.2815 through 7035.2915No/No

Remedial actions would not involve management of a mixed

municipal waste landfill.

Abandonment of motor vehicles and

scrap metal

Requirement for disposal and reuse of abandoned

motor vehicles and other scrap metal.

Minnesota Rules Ch.

7035.3000 through 7035.3600No/No

Remedial activities would not involve disposal or reuse of abandoned

motor vehicles or scrap metal.

Solid Waste Programs and Projects

Requirements for application procedure for grants-

in-aid, state requirements, approval of applications,

and payments for programs or projects which will

encourage both the reduction of the amount of

material entering the solid waste stream and the

reuse and recycling of solid waste.

Minnesota Rules Ch.

7035.4000 through 7035.4600No/No

Remedial activities would not involve construction or management of

a solid waste management facility.

Infectious Waste

Requirements for owners and operators of

facilities, commercial transporters, and all

infectious waste.

Minnesota Rules Ch.

7035.9100 through 7035.9150No/No Remedial activities would not involve infectious waste.

Solid Waste

Table 1

Page 3 of 5

Table 1



Minneapolis, MN




Comments

Connection to public sewer State Plumbing Code (MDH). Minnesota Rules Ch. 4715 No/NoRemedial actions do not involve connecting to public sewer or water

systems.

Public Water Resource

Water appropriation permitting, standards and

criteria for alterations to structure of public water

(DNR).

Minnesota Rules Ch. 6115 Yes/--Applicable to remedial actions that involve appropriation of water

(e.g., groundwater extraction systems).

New well construction in contaminated

area

Allows for designation of special Well Construction

Area (MDH).

Minnesota Rules Ch.

4725.3650Yes/--

The Central Area is located within a Special Well Construction Area.

Substantive requirements may apply.

Monitoring well installation or

abandonment

Well and boring construction, use, maintenance,

and sealing information (MDH).Minnesota Rules Ch. 4725 Yes/--

Wells may be installed or abandoned as part of remedial activities.

Substantive requirements may apply.

Certification of Environmental

Laboratories

Laboratory accreditation requirements for the State

of Minnesota (MDH).

Minnesota Statute 144.97

through 144.98

Minnesota Rules Ch. 4740

Yes/--Laboratories that provide services for this project would be accredited

for the appropriate testing methods.

Water Pollution Control ActRegulates point source discharges to waters of the

state.Minnesota Statute 115 No/No

Substantive requirements apply to remedial actions that involve

discharge to storm sewers or surface water. Discharges to storm

sewers or surface water is not anticipated.

Water of the StateClassifies waters of the state and establishes

standards.Minnesota Rules Ch. 7050 No/No

Substantive requirements apply to remedial actions that involve

discharge to storm sewers or surface water. Discharges to storm

sewers or surface water is not anticipated.

Discharge to groundwater

Nondegradation goal, prohibition of discharge to

saturated zone, limitation on discharge to

unsaturated zone, remediation requirements.

Minnesota Rules Ch. 7060 Yes/--Applicable to remedial actions that involve discharge to groundwater

or unsaturated zone.

Groundwater use or contactEstablishes human health based groundwater

standards (MDH).

Minnesota Rules Ch.

4717.7500 and 4717.7801 to

4717.7900

No/NoThe geologic unit targeted for remedial actions is not used as a

drinking water source.

Air Quality

Air emissionsDuty to notify and abate excessive or abnormal

unpermitted air emissions.Minnesota Statute 116.061 No/No

Applicable to remedial actions that involve excessive or abnormal air

emissions. No such remedial actions are anticipated.

Air emissions Air quality rules.Minnesota Rules Chs. 7005,

7007, 7017No/No

Applicable to remedial actions that involve air emissions. No such

remedial actions are anticipated.

Air emissionsStandards of performance and emissions

inventory.Minnesota Rules Chs. 7019 No/No

These regulations would be applicable to remedial actions that

include emissions from stationary sources. No such remedial actions

are anticipated.

Air emissions Air emissions and waste management permits. Minnesota Statute 116.081 No/NoApplicable to remedial actions that involve air treatment and

emission. No such remedial actions are anticipated.

Groundwater Quality

Water Supply Regulations

Table 1

Page 4 of 5

Table 1



Minneapolis, MN




Comments

Sound generation Standards for noise generated during operations. Minnesota Rules Ch. 7030 Yes/--May need a waiver of this requirement if operation of construction

equipment exceeds noise standards.

Health and Safety

Worker protection Standards for worker health, safety and training. Minnesota Rules Ch. 5205 Yes/-- Requirements would be met for health and safety of workers.

1 "Yes/--": If a requirement is potentially applicable , determination of relevant and appropriate or TBC status is not made.

Noise Pollution Control

Table 1

Page 5 of 5

Table 2Potential Location-Specific ARARs and TBC

East Hennepin Avenue SiteMinneapolis, MN

Table 2Page 1 of 2

Standard Requirement CitationPotentially Applicable/ Relevant and Appropriate TBC1 Comments

National Archaeological and Historical Preservation Act

Construction on previously undisturbed land would require an archaeological survey of the area.

16 USC 469-469c Substantive requirements of 36 CFR 65, National Historic Landmarks Program.

No/No There are no known archaeological or historical sites located in the Central Area.

Federal National Historic Preservation Act, Section 106

Action to preserve historic properties; planning of action to minimize harm to properties listed on or eligible for listing on the National Register of Historic Places (NRHP).

Substantive Requirements of 36 CFR 800, Protection of Historic Properties16 USC 470, et seq.

No/No

There are five historic structures currently inventoried by the Minnesota State Historic Preservation Office located in the Central Area; none have been listed on the NRHP or are eligible for listing on the NRHP.

Endangered Species Act of 1973

Action to conserve endangered species or threatened species, including consultation with the Department of the Interior. Reasonable mitigation and enhancement measures must be taken, including live propagation, transplantation and/or habitat acquisition and improvement.

16 USC 1531, et seq. No/No There are no known records of endangered plant or animal species located in the Central Area.

Migratory Bird Treaty Act of 1972Protects almost all species of native birds in the U.S. from unregulated “take” which can include poisoning at contaminated sites.

16 USC 703, et seq. No/No There are no known records of the presence of migratory birds in the Central Area.

Wilderness ActArea must be administered in such a manner as will leave it unimpaired as wilderness and preserve its wilderness character.

16 USC 1131 et seq. No/No There are no Federally-owned wilderness areas located in the Central Area.

National Wildlife Refuge SystemOnly actions allowed under the provisions of 16 USC Section 688 dd(c) may be undertaken in areas that are part of the National Wildlife Refuge System.

50 CFR 35.1 et seq. No/No There are no National Wildlife Refuge areas located in the Central Area.

Fish and Wildlife Coordination Act, Fish and Wildlife Improvement Act of 1978, Fish and Wildlife Conservation Act of 1980

Provides protection for actions that would affect streams, wetlands, other water bodies or protected habitats. Any action taken should protect fish or wildlife.

16 USC 661-667e16 USC 742a-l16 USC 2901, et seq.

No/No There are no streams, wetlands, or other water bodies that could potentially be impacted by activities in the Central Area.

Clean Water Act, Section 404 Permitting requirements for dredge and fill materials to waters of the United States. 33 CFR 320-330 No/No No wetlands will be affected by remedial action.

Wild and Scenic Rivers ActAvoid taking or assisting in an action that will have direct adverse effect on a national, wild, or scenic recreational river.

16 USC 1271 et seq. 36 CFR 29740 CFR 6.302(e)

No/No There are no designated wild, scenic, or recreational areas in the Central Area.

Coastal Zone Management Act

Regulates activities affecting the coastal zone including lands thereunder and adjacent shoreline. Must conduct activities in a manner consistent with the approved State management programs.

16 USC 1451, et seq.15 CFR 93015 CFR 923

No/No The Central Area is not located within a designated coastal zone.

Coastal Barrier Resources Act, Section 3504

Prohibits any new federal expenditure within the Coastal Barrier Resource System. 16 USC 3501, et seq. No/No The Central Area is not located within a designated coastal zone.

Clean Water Act Establishes regulations pertaining to activities that affect the navigation of the waters of the United States.

33 CFR 320-32933 USC 1341, et seq. No/No There are no navigable waters in the Central Area. No discharge to

navigable waters is anticipated.

Federal

Table 2Potential Location-Specific ARARs and TBC


Table 2Page 2 of 2


Magnuson Fishery Conservation and Management Act

Provides for conservation and management of specified fisheries within specified fishery conservation zones (in federal waters).

16 USC 1801, et seq. No/No There are no fisheries located in the Central Area.

RCRA Standards for Identification of Hazardous Waste and Hazardous Waste Generator Requirements

Regulates generators of hazardous waste. 40 CFR 261, 262 No/No

Applicable for identification of hazardous wastes. Substantive requirements may be applicable if hazardous waste is generated as part of remedial action. Generation of hazardous waste is not anticipated.

RCRA Hazardous Waste Treatment, Storage, and Disposal Requirements

Regulates treatment, storage, and disposal of hazardous waste. 40 CFR 264 No/No Remedial action unlikely to include treatment, storage, or disposal

of hazardous waste.

EO 11988, Protection of Floodplains

Actions taken should avoid adverse effects, minimize potential harm, restore and preserve natural and beneficial values.

40 CFR 6, Appendix A; excluding Sections 6(a)(2), 6(a)(4), 6(a)(6); 40 CFR 6.302

No/No The Central Area is not located within a flood plain.

Rivers and Harbors Act of 1972 Permits are required for structures or work affecting navigable waters. 33 USC 403 No/No There are no navigable waters in the Central Area.

Endangered Species Protection of endangered species (DNR). Minnesota Rules Ch. 6134 No/No There are no known records of endangered plant or animal species in the Central Area.

Public Water Resources Classifies lakes and wetlands, appropriation permitting (DNR). Minnesota Rules Ch. 6115 No/No There are no streams, wetlands, or other water bodies impacted by

activities in the Central Area.

Shoreland and Floodplain Management Shoreland alterations or structures (DNR). Minnesota Rules Ch. 6120 No/No There is no shoreland in the Central Area.

Wetlands Conservation Act Protection of wetlands. Minnesota Statute 103G.221-2373 No/No There are no known wetlands in the Central Area.

Wetlands conservation Protection of wetlands, wetland functions for determining public values. Minnesota Rules 8420 No/No There are no known wetlands in the Central Area.

Ordinance for work in street right-of-way

Regulates obstructions and excavations in the city right-of-way through issuance of permits.

City of Minneapolis Code of Ordinances, Chapter 430 Yes/-- Substantive requirements applicable to on-site activities pertaining

to obstruction, excavation, and restoration.


State and Local

Table 3Potential Chemical-Specific ARARs and TBCs


Table 3Page 1 of 2


Safe Drinking Water ActNational Primary Drinking Water Standards setting maximum contaminant levels (MCLs).

40 CFR 14140 CFR 14240 CFR 143

No/No

Groundwater is not utilized as a drinking water source. Institutional controls at the Site and Central Area, including a Special Well and Boring Construction Area, require approval from MDH prior to new well construction.

Underground Injection Control Requirements Regulates subsurface injection of fluids. 40 CFR 144 Yes/-- Substantive UIC requirements may apply if remedial action

includes injection into groundwater.

Clean Water ActFederal Water Quality Standards (WQS)

Ambient Water Quality Criteria established to protect aquatic life and human consumers of water or aquatic life.

40 CFR 131 No/No Federal WQS are not ARARs.

Clean Water ActWetlands ProtectionSection 104

Protection of Wetlands 33 CFR 238 No/No No wetlands are anticipated to be affected by remedial action.

General Pre-Treatment Regulations for Existing and New Sources of POTWs

Effluent limitations and pre-treatment standards and guidelines for existing sources, new sources.

40 CFR 403 No/No Remedial action unlikely to involve discharge of wastewater.

National Pollution Discharge Elimination System (NPDES)

Regulates discharge of pollutant from point source into waters of the United States. 40 CFR 122 No/No

Substantive requirements may be applicable if discharge to surface water is part of a remedial action. Discharge to surface water is not anticipated.

National Ambient Air Quality Standards (NAAQS)

Establishes acceptable ambient air concentrations. 40 CFR 50 No/No NAAQS are not ARARs.

Clean Air ActNESHAP/NSPS/PSD

Establishes emission standards for hazardous air pollutants for which no ambient air quality standards exist.

40 CFR Part 53,60,61 No/NoSubstantive requirements applicable only if identified pollutants will be emitted in excess of threshold amounts. This is not anticipated to occur.

Vapor intrusion pathway

For evaluating the potential risks to human health caused by vapor intrusion (the migration of volatile compounds from contaminated soil or groundwater to the indoor air of occupied buildings).

OSWER Technical Guide for Assessing and Mitigating the Vapor Intrusion Pathway from Subsurface Vapor Sources to Indoor Air, OSWER Publication 9200.2-154, June 2015

TBC

EPA guidance document. The guidance contains vapor intrusion screening levels (VISLs) for indoor air, soil gas, and groundwater concentrations for use when evaluating the vapor intrusion pathway at contaminated sites. The guidance states that vapor intrusion screening levels for groundwater are not intended to be used as cleanup levels.

Federal

Table 3Potential Chemical-Specific ARARs and TBCs


Table 3Page 2 of 2


Health Risk Limits for groundwater

Establishes human health based groundwater standards (MDH) known as Health Risk Limits (HRLs).

Minnesota Rules Ch. 4717.7500 and 4717.7801 to 4717.7900 No/No


Groundwater Guidance Document

Framework for evaluating groundwater contamination and managing remediation decisions.

MPCA Groundwater Guidance Document, September 1998 TBC


Ambient Air Quality Standards Establishes acceptable air concentrations. Minnesota Rules Ch. 7009 No/No Remedial actions do not have emissions that will affect air quality.

Standards for Stationary Air Sources

Compliance with applicable state air pollution control rules for new and existing emission facilities.

Minnesota Rules Ch. 7011 No/No Substantive requirements applicable only if identified pollutants will be emitted in excess of threshold amounts.

Vapor intrusion pathway

For evaluating the potential risks to human health caused by vapor intrusion (the migration of volatile compounds from contaminated soil or groundwater to the indoor air of occupied buildings).

MPCA Risk-Based Guidance for the Vapor Intrusion Pathway, Superfund RCRA and Voluntary Cleanup Section, September 2008. MPCA Vapor Intrusion Technical Support Document, Remediation Division, August 2010.

TBC

MPCA guidance documents. The guidance contains intrusion screening values (ISVs) for indoor air, soil gas, and groundwater concentrations for use when evaluating the vapor intrusion pathway at contaminated sites. ISVs for trichloroethylene (TCE) were used to guide the sub-slab soil gas sampling and building mitigation project. The guidance states that groundwater ISVs should not be used for remedial action levels.


State and Local

Table 4Remedial Technology and Process Option Screening


Table 4Page 1 of 5

Remedial Technology 1,2,3 Process Option Description Effectiveness 3,4 Implementability 3,5 Relative Cost 6 Screening Comment

No Further Action None

No further action beyond completed operation of legacy groundwater extraction system, installation of vapor mitigation systems, and institutional controls already implemented.

Effective at addressing vapor risk to buildings with mitigation systems.

Legacy groundwater extraction system, vapor mitigation systems, and institutional controls already implemented.

Zero Retained for consideration.

Sub-slab depressurization (SSD) systems and floor sealing

Mitigate remaining buildings within the Central Area as appropriate based on sub-slab and/or indoor air sampling and where access is provided.

Very effective. Addresses risk to remaining residences within the Central Area.

Readily implementable as long as access is provided. Moderate Retained for consideration.

HVAC system to maintain positive pressure in building

Modify HVAC systems that maintain a positive pressure in the building basement to prevent soil gas migration to indoor air.

Effective. Addresses vapor intrusion risk where it can be implemented.

Not implementable due to the type, age, and variety of HVAC systems. Moderate Not retained for consideration due to lack of

implementability.

Operation and Maintenance of Mitigation Systems Operation and Maintenance (O&M) Plan

Develop and implement an O&M plan for vapor mitigation systems.

Very effective. Addresses long-term risk to buildings within the Central Area.

Readily implementable as long as access is provided. Low Retained for consideration.

ICs pertaining to mitigation systems City ordinance or other area-wide control

Ordinance or other area-wide control pertaining to mitigation systems.

Very effective for preventing potential exposure at locations with mitigation systems.

Requires city (or other regulatory agency) cooperation. Low Retained for consideration.

Physical Barrier Grout capPlace buried horizontal grout cap over groundwater impacts via grout injection (horizontal or vertical injection) to cut off the groundwater to indoor air exposure pathway.

Uncertain effectiveness as this technology has not been applied to mitigate vapor intrusion over a large area with access limitations.

Not implementable due to access limitations. HighNot retained for consideration due to lack of implementability and uncertain effectiveness.

Hydraulic Barrier Extraction wells with infiltration galleries

Promote a strong downward vertical gradient and clean shallow groundwater by extracting water from the bottom of the surficial aquifer and replenishing it at the top with treated water and/or stormwater via infiltration galleries.

Uncertain effectiveness in disconnecting the groundwater to soil gas pathway (unproven technology). Risk that residual soil gas may still be present for many years after implementation.

Readily implementable at select locations (within rights-of-way). Moderate Not retained for consideration due to

uncertain effectiveness.

Soil Excavation at Site Excavators, trucks Excavate source material at the Site. Recent investigations have not identified source material present at the Site.

Disposal area drums removed in 1981. Implementation on a small scale constrained by buildings, streets, and railroads.

Low Not retained since no source material has been identified at the Site.

Soil Excavation of Central Area Excavators, trucks Excavate soil impacted by groundwater beneath and throughout the Central Area.

This would require a very large volume of excavation to remove a small amount of TCE mass. Not effective as the residual groundwater impacts would not be removed by soil excavation. No source material from the Site has been found in the Central Area.

Not implementable due to access limitations. This alternative would require demolition and excavation of the entire Central Area.

Very high Not retained due to lack of implementability and effectiveness.

Restart Legacy Groundwater Extraction SystemExtraction wells with submersible pumps and treatment

Remove and/or contain contaminated groundwater for treatment and/or disposal.

Legacy groundwater system was effective at reducing groundwater concentrations 1-3 orders of magnitude. The groundwater extraction system was turned off after asymptotic recovery was measured. Not effective as a sole remedial technology because restarting the legacy groundwater extraction system would not significantly reduce groundwater concentrations in a reasonable timeframe.

Legacy Groundwater Extraction System removed approximately 7,000 lbs of TCE. Implementable if existing NPDES permit can be modified appropriately.

Low Not retained for consideration due to limited effectiveness.

No Action

Vapor Mitigation - Additional Installations

Install vapor mitigation systems at residences within the Central Area that do not currently have mitigation systems. There are 10 residences that do not currently have mitigation systems in the Central Area (5 owners did not provide access; 3 owners declined mitigation systems; and 2 properties with indoor air sampling TCE concentrations below applicable MPCA intrusion screening values or indoor air criteria).

Vapor Mitigation - O&M

Institutional Controls (ICs)

Containment

Physical Removal



Table 4Page 2 of 5


Extraction wells with submersible pumps, treatment, and discharge to storm sewer

Remove and/or contain contaminated groundwater for treatment and/or disposal.

Not effective as sole remedial technology because it does not remove risk of vapor intrusion until a distant timeframe as demonstrated by operation of the legacy groundwater extraction system. Groundwater extraction is effective at altering groundwater flow and providing containment/capture when used in combination with other remedial alternatives.

Readily implementable at select locations (within right-of-way) assuming existing NPDES permit can be modified appropriately.

Moderate Retained for consideration as part of a combined remedial approach.

Extraction with submersible wells and reinjection via injection wells

Remove and/or contain contaminated groundwater for treatment and/or injection.

Not effective as sole remedial technology because it does not remove risk of vapor intrusion until a distant timeframe as demonstrated by operation of the legacy groundwater extraction system. Groundwater extraction is effective at altering groundwater flow and providing containment/capture when used in combination with other remedial alternatives.

Readily implementable at select locations (within rights-of-way) assuming underground injection control program approval can be obtained.

Moderate Retained for consideration as part of a combined remedial approach.

Vertical injection and extraction wells

Use vertical wells to inject air into the groundwater and extract soil vapor from the vadose zone.

Moderate effectiveness within the sparge curtain where volatilization within air-flow channels is occurring. Likely not effective area-wide as right-of-way spacing (150-200 feet) is greater than radius of influence (10-20 feet) of sparge wells. Sparging may increase TCE vapor concentrations if SVE system does not adequately capture vapors.

Readily implementable at select locations (within rights-of-way). High Not retained for consideration due to limited

effectiveness.

Horizontal injection and extraction wells installed by directional drilling

Use horizontal wells to inject air into the groundwater and extract soil vapor from the vadose zone.

Moderate effectiveness within the sparge curtain where volatilization within air-flow channels is occurring. Likely not effective area-wide due to access limitations and width of influence (10-20 feet) of sparge wells. Sparging may increase TCE vapor concentrations if SVE system does not adequately capture vapors.

Not implementable throughout the Central Area due to presence of utilities and the offset distance required for directional drilling to reach target depth.

High Not retained for consideration due to lack of implementability and limited effectiveness.

Air Sparging with Soil Vapor Extraction (AS/SVE)

Expanded/Modified Groundwater Extraction



Table 4Page 3 of 5


Steam injection and vapor extraction via vertical wells

Steam injection via vertical wells to promote volatilization and destruction. Vapor extraction to collect generated vapors.

Very effective within the radius of influence of steam injection locations. Likely not effective as right-of-way spacing (150-200 feet) is greater than radius of influence (25-50 feet). Access limitations provide for similar total effectiveness as AS/SVE. Steam injection may increase TCE vapor concentrations if SVE system does not adequately capture vapors.

Readily implementable at select locations (within right-of-way). High Not retained for consideration due to limited

effectiveness.

Steam injection and vapor extraction via horizontal wells

Steam injection via horizontal wells to promote volatilization and destruction. Vapor extraction to collect generated vapors.

Very effective within the radius of influence of steam injection locations. Likely not effective area-wide as right-of-way spacing (150-200 feet) is greater than width of influence (25-50 feet). Access limitations provide for similar total effectiveness as AS/SVE. Steam injection may increase TCE vapor concentrations if SVE system does not adequately capture vapors.

Not implementable throughout the Central Area due to presence of utilities and the offset distance required for directional drilling to reach target depth.

High Not retained for consideration due to lack of implementability and limited effectiveness.

Electrical resistance heating and soil vapor extraction (SVE)

Installing electrode array to heat groundwater through electrical resistance. Vapor extraction to collect generated vapors.

Uncertain effectiveness for treatment of TCE in sandy aquifers (unproven technology for this application). Potential risk of increased TCE vapor concentrations in vadose zone if SVE system does not adequately capture vapors.

Not implementable as the necessary array spacing (10-20 feet) is less than what could be achieved within the right-of-way. Technology cannot be implemented at singular locations (array required).

High

Not retained for consideration due to the uncertain effectiveness and lack of implementability. Potential risk of increased TCE vapor concentrations in vadose zone if SVE system does not adequately capture vapors.

Radio frequency heating and soil vapor extraction (SVE)

Installing electrode array to heat groundwater through radio frequency. Vapor extraction to collect generated vapors.

Uncertain effectiveness for treatment of TCE in sandy aquifers (unproven technology for this application). Potential risk of increased TCE vapor concentrations in vadose zone if SVE system does not adequately capture vapors.

Not implementable as the necessary array spacing (10-20 feet) is less than what could be achieved within the right-of-way.

High

Not retained for consideration due to uncertain effectiveness and lack of implementability. Potential risk of increased TCE vapor concentrations in vadose zone if SVE system does not adequately capture vapors.

Thermal Conduction and Vapor Extraction

Heat aquifer matrix with thermal conductive wells and remove volatilized vapors with vapor extraction wells.

Very effective within the radius of influence of thermal conductive wells. Not effective area-wide as right-of-way spacing (150-200 feet) is greater than radius of influence (10-15 feet). Potential risk of increased TCE vapor concentrations in vadose zone if SVE system does not adequately capture vapors.

Not implementable due to the well spacing required (approximately 10-15 feet) within the right-of-way and the concern for adjacent utilities.

High

Not retained for consideration due to lack of implementability and limited effectiveness. Potential risk of increased TCE vapor concentrations in vadose zone if SVE system does not adequately capture vapors.

Ex Situ Thermal Treatment & Injection Contained recovery of oily wastes (CROW™) Process Heat extracted groundwater and reinject into the aquifer.

Uncertain effectiveness for treatment of dissolved phase TCE in sandy aquifers (unproven technology for this application).

Implementable at select locations (within right-of-way). High Not retained for consideration due to


Monitored Natural Attenuation (MNA)Allow native microorganisms to degrade contaminant and monitor progress

Establish a monitoring well network and sampling plan to monitor and evaluate groundwater quality over time.

Likely not effective to meet the remedial objectives within a reasonable timeframe. Groundwater monitoring data indicates that limited natural attenuation is occurring.

Readily Implementable Low Retained for consideration.

In Situ Thermal Treatment

Biological



Table 4Page 4 of 5


Aerobic co-metabolism via injection wells

Use injection wells to deliver carbon substrate and oxygen to the sub-surface to promote aerobic co-metabolism.

Moderate effectiveness demonstrated at sites with low-level impacts over large areas. Pilot testing necessary to confirm site-specific effectiveness. Potential risk of secondary groundwater impacts (e.g. metals liberation).

Readily implementable at select locations (within right-of-way). High

Retained for consideration as part of a combined remedial approach. Potential risk of secondary groundwater impacts.

Aerobic co-metabolism via permeable reactive barrier

Install trenches with reactive media to support aerobic co-metabolism.

Moderate effectiveness demonstrated at sites with low-level impacts over large areas. Pilot testing necessary to confirm site-specific effectiveness. Potential risk of secondary groundwater impacts (e.g. metals liberation).

Not implementable as there are not accessible locations for reactive barriers within the Central Area due to utilities and other interferences.

High Not retained for consideration due to lack of implementability.

Enhanced reductive dechlorination via injection wells

Use injection wells to deliver carbon substrate to the sub-surface to promote biodegradation of contaminants.

Moderate effectiveness demonstrated at sites with low-level impacts over large areas. Additional testing likely necessary to evaluate site-specific effectiveness. Potential risk of methane or low-chlorinated compound (e.g. vinyl chloride) accumulation. Potential risk of secondary groundwater impacts (e.g. metals liberation).


Retained for consideration. Potential risk of methane or low-chlorinated compound (e.g. vinyl chloride) accumulation. Potential risk of secondary groundwater impacts.

Enhanced reductive dechlorination via permeable reactive barrier or biowall

Install trench with reactive media to support enhanced reductive dechlorination.

Moderate effectiveness demonstrated at sites with low-level impacts over large areas. Additional testing likely necessary to evaluate site-specific effectiveness. Potential risk of methane or low-chlorinated compound (e.g. vinyl chloride) accumulation. Potential risk of secondary groundwater impacts (e.g. metals liberation).



Bio-geochemical via injection wells

Stimulate subsurface micro-organisms to convert naturally occurring minerals or added materials into reducing minerals that abiotically degrade contaminants.

Effectiveness is limited by aquifer mineralology. Effectiveness has not been demonstrated with injection wells at sites with low-level impacts over large areas.

Readily implementable at select locations (within right-of-way). High Not retained for consideration due to


Bio-geochemical via permeable reactive barrier

Install trench with reactive media to support abiotic bio-geochemical degradation of contaminants.

Moderate effectiveness demonstrated at sites with low-level impacts over large areas. Additional testing likely necessary to evaluate site-specific effectiveness.



Phyto-remediation Plant trees across the Central Area

Selected species of trees are planted across the Central Area to uptake, contain, degrade, or eliminate contaminants

Moderate effectiveness demonstrated at similar sites with no access limitations.

Not implementable (most of the treatment area is developed) Moderate Not retained for consideration due to lack of

implementability.

Inject chemical oxidants via temporary probes

Inject chemical oxidants with temporary injection points across the treatment area

Uncertain effectiveness as this technology has not been applied effectively to remediate low-level impacts over large areas. Likely not effective due to access limitations, radius of influence (5-10 feet), and one time application of oxidants. Potential risk of secondary groundwater impacts (e.g., metals liberation).


Not retained for consideration due to lack of effectiveness and risk of secondary groundwater quality impacts.

Inject chemical oxidants via injection wells

Inject chemical oxidants with permanent wells placed across the treatment area

Uncertain effectiveness as this technology has not been applied effectively with low-level impacts over large areas. Likely not effective due to access limitations and radius of influence (10-20 feet). Potential risk of secondary groundwater impacts (e.g., metals liberation).


Not retained for consideration due to uncertain effectiveness and risk of secondary groundwater quality impacts.

In Situ Bioremediation

In Situ Chemical Oxidation

Chemical



Table 4Page 5 of 5


Add chemical reductants to the subsurface via temporary probes

Add chemical reductants to the subsurface via temporary injection points across the treatment area

Uncertain effectiveness as this technology has not been applied effectively with low-level impacts over large areas. Likely not effective due to access limitations, radius of influence (5-10 feet), and one time application of reductants. Potential risk of secondary groundwater impacts (e.g., metals liberation).


Not retained for consideration due to lack of effectiveness and risk of secondary groundwater quality impacts.

Add chemical reductants to the subsurface via injection wells

Add chemical reductants to the subsurface via injection wells across the treatment area.

Uncertain effectiveness as this technology has not been applied effectively with low-level impacts over large areas. Likely not effective due to access limitations and radius of influence. Potential risk of secondary groundwater impacts (e.g., metals liberation).


Not retained for consideration due to uncertain effectiveness and risk of secondary groundwater quality impacts.

Add chemical reductants to the subsurface via permeable reactive barrier

Add chemical reductants to the subsurface by constructing a permeable reactive barrier.

Moderate effectiveness demonstrated at sites with low-level impacts over large areas. Pilot testing necessary to confirm site-specific effectiveness. Effectiveness is uncertain based on right-of-way spacing (150 - 200 feet), advective flow rate (800 feet per year) and ability to treat groundwater down-gradient of the barrier. Potential risk of secondary groundwater impacts (e.g., metals liberation).



Electrolytic Reactive BarrierVoltage is applied to electrodes within a permeable reactive barrier (PRB)

Electrical potential is applied to spaced electrodes within the PRB. Dissolved contaminants are subject to oxidation-reduction (or reduction-oxidation) dependent on the sequence of charges applied.

Uncertain effectiveness as this technology has not been demonstrated. The technology is effective at reducing flux, but the effectiveness for a larger area is dependent on advective transport to the barrier and diffusion from the aquifer matrix.

Implementable at select locations (within right-of-way). High Not retained for consideration due to


Notes:

Electrical

6 Relative cost is for comparative purposes only and is judged relative to the other processes and technologies that involve similar functions.

1 The remedial action objective is defined as the following: Maintain insignificant potential risk to human health from inhalation exposure to TCE in indoor air resulting from TCE concentrations in soil gas and groundwater. 2 The feasibility study area is defined as the Central Area.3 TCE from one or more potential releases up-gradient of the Central Area are the predominant cause of TCE concentrations in groundwater. Groundwater impacts up-gradient of the Central Area are outside of the scope of this feasibility study. Until the extent and magnitude of the impacts associated with the off-Site sources are defined and addressed, remedial action to address groundwater will not be effective at reducing TCE concentrations in groundwater in the Central Area due to continuing re-contamination from these up-gradient sources. 4 Effectiveness is defined as the ability to perform as part of an overall alternative that can meet the objectives within 30 years under conditions and limitations that exist onsite.5 Implementability is defined as the likelihood that the process could be implemented as part of the remedial action plan under the physical (work completed from public rights-of-way), regulatory, technical, and schedule constraints.

In Situ Chemical Reduction

Table 5Amendment Sensitivity Analysis


Table 5Page 1 of 1

Design Period (Years) 1 Design Factor 2 Quantity of Substrate Required (lb) 3

1 1 740,000 3 1 1,830,000 5 1 2,930,000 1 3 2,210,000 3 3 5,490,000 5 3 8,780,000 1 5 3,680,000 3 5 9,150,000 5 5 14,630,000 1 7 5,150,000 3 7 12,820,000 5 7 20,480,000

740,0007,320,00020,480,000

Notes1

2

3

4 The sensitivity analysis was performed by varying the design period and design factor in the ESTCP Substrate Estimating Tool (Parsons, 2010b).

Minimum Quantity of Substrate (lb) 4

Average Quantity of Substrate (lb) 4

Maximum Quantity of Substrate (lb) 4

Substrate is emulsified vegetable oil, 60% by weight

The design period is the number of years that active treatment is occuring. The amount of substrate required increases as the design period increases because the design tool accounts for flux of competing electron acceptors into the treatment zone. Design periods of 1, 3, and 5 years were evaluated. Active treatment and system operation may occur for 5-10 years for a recirculation approach, however a shorter design period (e.g.would be reasonable because recirculation would limit flux into the treatment zone from up-gradient).

The design factor is a safety factor to account for excess substrate demand. A design factor of 3-7 is recommended for slow release substrates like emulsified vegetable oil (Parsons, 2010a), however substrate delivery mechanisms should be considered when selecting a design factor as well. Lower design factors would be reasonable where it is relatively easy to add more substrate (e.g. recirculation systems), conversely higher design factors would be warranted for approaches that rely on one or two injection events. In addition, lower design factors should be used with more soluable substrate (e.g. lactate) to avoid spikes in substrate concentrations which can result in pH depression and excess methane production.

Table 6Comparative Analysis Summary by Alternatives


Table 6Page 1 of 2

Overall Protection of Human Health

and the Environment6

Compliance with ARARs7

Long-Term Effectiveness

and Permanence8

Reduction of Toxicity, Mobility,

or Volume through

Treatment9Short Term

Effectiveness10 Implementability11Estimated

Cost12Cost

Range13State

Acceptance14Local

Acceptance15

Incremental Reduction in

Vapor Intrusion Risk16

Adverse Secondary Impacts17

Adverse Sustainability

Impacts18Construction

Time19

Alternative 1 - No Further Action Beyond Previous Response Actions

◒ ◒ ◒ ○ ● ● $0 $0 Baseline None Baseline None

Alternative 2 - Monitored Natural Attenuation (MNA)

◒ ◒ ◒ ○ ● ● $1.3M $0.9M-$1.9M Minimal None Similar to baseline None

Alternative 3 - Long Term O&M of SSD Systems

● ● ● ○ ● ● $2.0M $1.4M-$3.0MAdded long-term benefit with O&M

None Similar to baseline < 1 year

Alternative 4 - Enhanced Bioremediation via Injection Event(s)

◒ ◒ ◒ ◒ ◒ ◒ $26M $6M-$90MSignificant Uncertainty20

Risk of methane generation, vinyl chloride generation, and metals liberation.

GHG impacts:3,800 metric tons CO2-eqEnergy footprint:66,000 MMBTUWorker injury risk:1.0 accidents

+/- 5 years

Alternative 5 - Enhanced Bioremediation via Recirculating System

◒ ◒ ◒ ● ◒ ◒ $42M $19M-$100MSignificant Uncertainty20

Risk of methane generation, vinyl chloride generation, and metals liberation.

GHG impacts:4,400 metric tons CO2-eqEnergy footprint:70,000 MMBTUWorker injury risk:4.0 accidents

+/- 10 years

Scale

○◒

Comments:

●

Remedial action objective:

Remedial Alternatives1

Additional Considerations5

Does not meet criteria

Potentially meets criteria

Meets criteria

Maintain insignificant potential risk to human health from inhalation exposure to TCE in indoor air resulting from TCE concentrations in soil gas and groundwater. As stated in the RAP Modification #1, General Mills is responsible only for implementing response actions to address impacts that are due to General Mills operations at the Site. The feasibility study area is defined as the Central Area. TCE from one or more potential releases up-gradient of the Central Area are the predominant cause of TCE concentrations in groundwater. Groundwater impacts up-gradient of the Central Area are outside of the scope of this feasibility study. Until the extent and magnitude of the impacts associated with the off-Site sources are defined and addressed, remedial action to address groundwater will not be effective at reducing TCE concentrations in groundwater in the Central Area due to continuing re-contamination from these up-gradient sources.

Modifying Criteria4Balancing Criteria3Threshold Criteria2

Table 6Comparative Analysis Summary by Alternatives


Table 6Page 2 of 2

Notes1

234567

89

10111213

1415161718

1920

General Mills has spent $14.5 million on extensive investigation and response action work in the project area since the early 1980s including operating the legacy groundwater extraction system for 25 years and installing SSD systems at 166 properties in the Central Area.

This assessment provides an estimate of the construction time required to implement the remedial alternative.

Statutory requirements that each alternative must satisfy to be eligible for selection.Technical criteria upon which the detailed analysis is primarily based.

This assessment evaluates potential adverse secondary impacts of implementing the remedial alternative. The risk of secondary impacts may be greater than the TCE vapor intrusion risk.This assessment provides an estimate of the adverse sustainability impacts (e.g., greenhouse gas impacts, energy footprint, worker injury-accident risk) associated with implementing the remedial alternative relative to Alternative 1 (No Further Action Beyond Previous Response Actions). Sustainability impacts were estimated using the SiteWise™ green and sustainable remediation tool. Additional details regarding the sustainability impact evaluation are in Appendix B.

This assessment reflects the state’s (or support agency’s) apparent preferences among or concerns about alternatives. This assessment will be completed after the public comment period.This assessment reflects the community’s apparent preferences among or concerns about alternatives. This assessment will be completed after the public comment period.This assessment provides a comparison of the reduction of vapor intrusion risk associated with implementation of each remedial alternative relative to Alternative 1 (No Further Action Beyond Previous Response Actions).

Cost range for alternatives represents the plus 50 minus 30 percent accuracy, except amendment related costs for Alternatives 4 and 5 which vary based on the range of amendment required as detailed in the sensitivity analysis (Table 5).The accuracy range is associated with the most likely cost of the project based on the level of design that has been completed and the uncertainties in the project as scoped.

There is significant uncertainty whether Alternatives 4 and 5 could achieve an effective and consistent reduction in TCE concentrations in groundwater throughout the Central Area to be protective of vapor intrusion risk.

The assessment against this criterion examines the effectiveness of alternatives in protecting human health and the environment during the construction and implementation of a remedy until response objectives have been met.This assessment evaluates the technical and administrative feasibility of alternatives and the availability of required goods and services.This assessment evaluates the capital and operation and maintenance (O&M) costs of each alternative.

Evaluation of state and community acceptance to implemented remedial actions.Additional considerations provide further details on the impact of remedial actions on the community. Additional considerations could be balancing or modifying criteria.The assessment against this criterion describes how the alternative, as a whole, achieves and maintains protection of human health and the environment.The assessment against this criterion describes how the alternative complies with ARARs, or if a waiver is required and how it is justified. The assessment also addresses other information from advisories, criteria, and guidance that the lead and support agencies have agreed is "to be considered".The assessment against this criterion evaluates the long-term effectiveness of alternatives in maintaining protection of human health and the environment after response objectives have been met.The assessment against this criterion evaluates the anticipated performance of the specific treatment technologies an alternative may employ.

Table 7Alternative 2 Cost EstimateEast Hennepin Avenue Site

Minneapolis, MN

Table 7Page1 of 1

Quantity Unit Unit Cost

Estimated Cost

Low Estimate

Cost

High Estimate

Cost

1.0 Contractor Preparation Subtotal 30,000$ 21,000$ 45,000$ 1.1 Monitored Natural Attenuation Work Plan 1 LS 30,000$ 30,000$ 21,000$ 45,000$

30,000$ 20,000$ 50,000$

2.0 Annual Groundwater Sampling Costs Subtotal 80,000$ 50,000$ 120,000$ 2.1 Well Sampling - VOCs 25 Well/Year 1,000$ 25,000$ 17,500$ 37,500$ 2.2 Well Sampling - MNA Parameters and VOCs 10 Well/Year 2,200$ 22,000$ 15,400$ 33,000$ 2.3 Project Management 1 Year 10,000$ 10,000$ 7,000$ 15,000$ 2.4 Annual Groundwater Report 1 Year 20,000$ 20,000$ 14,000$ 30,000$

77,000$ 53,900$ 115,500$ 960,000$ 670,000$ 1,430,000$

3.0 Contingency on Total Cost, 25% 250,000$ 170,000$ 370,000$ $1,300,000 $900,000 $1,900,000

1.12.1

2.22.32.4

3.0

Alternative 2 - Monitored Natural Attenuation

Capital Costs

Sampling Costs (Annual)

Contingency

Total Capital Cost

Annual O&M CostO&M Yrs 1-30 NPV

Contingency based on range of scope and bid contingency recommended in A Guide to Developing and Documenting Cost Estimates During the Feasibility Study (EPA, 2000).Discount rate taken from A Guide to Developing and Documenting Cost Estimates During the Feasibility Study (EPA, 2000).

Costs include labor, expenses, and laboratory costs for sampling and analyzing groundwater samples for VOCs.

AssumptionsCosts include preparation of a MNA work plan that details the methods, procedures, locations, and frequency of monitoring.

SubtotalTotal Cost (NPV, 30 years, 7% discount rate)

Costs include labor, expenses, and laboratory costs for sampling and analyzing groundwater samples for VOCs and MNA parameters. MNA parameter list includes 13 parameters recommended in Technical Protocol for Evaluating Natural Attenuation of Chlorinated Solvents in Groundwater(EPA, 1998).Project management is assumed to be 15 percent of total cost.Assumes preparation of an annual groundwater monitoring report that summarizes groundwater quality trends and natural degradation rates.


Minneapolis, MN

Table 8Page 1 of 1


Estimated Cost

Low Estimate

Cost

High Estimate

Cost

1.0 Preparation Subtotal 25,000$ 17,500$ 37,500$ 1.1 Mitigation System O&M Plan 1 LS 50,000$ 50,000$ 35,000$ 75,000$ 1.2 Access and Mitigation System Design Meetings 10 Properties 2,500$ 25,000$ 17,500$ 37,500$ 2.0 Engineering and Administration Subtotal 25,000$ 17,500$ 37,500$ 2.1 Mitigation System Design Follow-up 5 Properties 5,000$ 25,000$ 17,500$ 37,500$ 3.0 Install Residential SSD Systems Subtotal 200,000$ 140,000$ 300,000$ 3.1 Contractor and Support for Installations 10 Properties 20,000$ 200,000$ 140,000$ 300,000$ 4.0 Indoor Air Sampling at 2010 E Hennepin Subtotal 150,000$ 105,000$ 225,000$ 4.1 Paired Indoor Air Sampling and Sub-Slab Soil Gas Sampling 1 LS 150,000$ 150,000$ 105,000$ 225,000$ 5.0 Project Management Subtotal 60,000$ 42,000$ 90,000$ 5.1 Project Management, Capital Phase 1 Year 60,000$ 60,000$ 42,000$ 90,000$

Total Capital Cost 460,000$ 320,000$ 690,000$

6.0 Mitigation Systems Subtotal 91,800$ 64,000$ 138,000$ 6.1 Electrical Bill for Properties 176 Building/Year 60$ 10,600$ 7,000$ 16,000$ 6.2 Replacement Fan Cost 18 Fan/Year 2,000$ 36,000$ 25,000$ 54,000$ 6.3 O&M Management and Access Coordination 176 Building/Year 200$ 35,200$ 25,000$ 53,000$ 6.4 Project Management, O&M Phase 1 Year 10,000$ 10,000$ 7,000$ 15,000$

Annual O&M Cost 91,800$ 64,000$ 138,000$ O&M Yrs 1-30 NPV 1,140,000$ 790,000$ 1,710,000$

7.0 Contingency on Total Cost, 25% Subtotal 400,000$ 277,500$ 600,000$ $2,000,000 $1,400,000 $3,000,000

1.11.22.1

3.1

4.15.1

6.1

6.26.36.47.0

Discount rate taken from A Guide to Developing and Documenting Cost Estimates During the Feasibility Study (EPA, 2000).

Assumes coordination of access and design meetings for engineer and mitigation contractor. Does not include multiple design meetings to satisfy extraordinatry property owner requests.

Assumes replacement of fans every 10 years, replacement of an average of 1/10 of the fans during a given year, half of the fans are RadonAway Model RP145 and half are RadonAway model RP265, half a day of contractor time to install a replacement fan, cost includes property access efforts, and no engineer oversight time is required. Costs include contacting property owners annually regarding systems operating status.Project management is assumed to be 15 percent of O&M costs.Contingency based on range of scope and bid contingency recommended in A Guide to Developing and Documenting Cost Estimates During the Feasibility Study (EPA, 2000).

Assumes follow-up meetings at 50 percent of the houses without mitigation systems.

Assumes installation of a mitigation system including diagnostic testing, contractor management, finish carpentry, and preparation of a property summary report. Not included are sub-slab soil-gas testing, indoor air testing, basement floor replacement, or extensive wall or floor patching.

Assumes three sampling events, 13 sub-slab soil gas samples per event, 13 indoor air samples per event, data quality and management costs are equal to laboratory costs (based on costs associated with previous project work), sub-slab sampling is a two week effort per event for one person, indoor air sampling is a two week effort per event for two people (includes chemical inventory), and preparation of a Property Summary Report. Project management is assumed to be 15 percent of the total capital costs (Sections 1.0 through 4.0). Does not include meetings with MPCA regarding specific properties.

Assumes fans are operated 24 hours a day, 365 days a year, half of the fans are RadonAway Model RP145 and half are RadonAway model RP265, fans operated in accordance with manufacturers standards, energy rates based on November 1, 2015 Xcel Energy ratecard for Minnesota, and 176 houses with mitigation systems installed within the Central Area.

AssumptionsAssumes preparation of a mitigation system O&M plan that details the methods, procedures, locations, and frequency of routine mitigation system monitoring.

Alternative 3 - Long-Term O&M of SSD Systems

O&M Costs (Annual)

Capital Costs

Contingency

Total Cost (NPV, 30 years, 7% discount rate)


Minneapolis, MN

Table 9Page 1 of 1


Estimated Cost

Low Estimate

Cost

High Estimate

Cost Capital Costs

1.0 Engineering and Administration Subtotal 160,000$ -$ -$ 1.1 Project Management, Capital Phase 1 Year 60,000$ 60,000$ 50,000$ 90,000$ 1.2 Engineering and Design 1 LS 60,000$ 60,000$ 50,000$ 90,000$ 1.3 Construction Quality Assurance, Monitoring, & Reporting 1 LS 40,000$ 40,000$ 30,000$ 60,000$ 2.0 Planning and Preparation Subtotal 740,000$ 518,000$ 1,110,000$ 2.1 Access for Injection Well Installation 1 LS 100,000$ 100,000$ 70,000$ 150,000$ 2.2 Permitting 1 LS 100,000$ 100,000$ 70,000$ 150,000$ 2.3 Injection Design Phase Bench and Pilot Testing 1 LS 500,000$ 500,000$ 350,000$ 750,000$ 2.4 Monitoring Wells 10 Well 4,000$ 40,000$ 28,000$ 60,000$ 3.0 Injection Array Construction and Initial Amendment Delivery Subtotal 9,200,000$ 1,100,000$ 36,300,000$ 3.1 Injection Wells 40 Well 10,000$ 400,000$ 280,000$ 600,000$ 3.2 Initial Amendment Delivery 40 Well 220,000$ 8,800,000$ 756,000$ 35,700,000$

Total Capital Cost 10,100,000$ 1,700,000$ 37,500,000$

4.0 Supplemental Amendment Delivery Subtotal 900,000$ 100,000$ 3,600,000$ 4.1 Supplemental Amendment Delivery 1 Year 900,000$ 900,000$ 76,000$ 3,570,000$ 5.0 Monitoring Subtotal 1,290,000$ 904,000$ 1,930,000$ 5.1 Performance Monitoring Yrs 1-3 180 Samples/Year 6,000$ 1,080,000$ 756,000$ 1,620,000$ 5.2 Injection Well Maintenance 40 EA 500$ 20,000$ 14,000$ 30,000$ 5.3 Annual Groundwater Report 1 Year 20,000$ 20,000$ 14,000$ 30,000$ 5.4 Project Management, O&M Phase 1 Year 170,000$ 170,000$ 120,000$ 250,000$

2,190,000$ 1,010,000$ 5,530,000$ 3,600,000$ 1,100,000$ 11,300,000$

O&M Costs (Annual Years 4-6)6.0 Amendment Delivery Subtotal 4,600,000$ 518,000$ 18,150,000$ 6.1 Supplemental Injection Wells 20 Well 10,000$ 200,000$ 140,000$ 300,000$ 6.2 Initial Amendment Delivery at Supplemental Wells 20 Well 220,000$ 4,400,000$ 378,000$ 17,850,000$

4,600,000$ 520,000$ 18,150,000$ 7.0 Monitoring Subtotal 1,740,000$ 949,000$ 3,735,000$ 7.1 Supplemental Amendment Delivery at Supplemental Wells 1 Year 440,000$ 440,000$ 38,000$ 1,790,000$ 7.2 Performance Monitoring Yrs 4-6 180 Samples/Year 6,000$ 1,080,000$ 756,000$ 1,620,000$ 7.3 Injection Well Maintenance 60 EA 500$ 30,000$ 21,000$ 45,000$ 7.4 Annual Groundwater Report 1 Year 20,000$ 20,000$ 14,000$ 30,000$ 7.5 Project Management, O&M Phase 1 Year 170,000$ 170,000$ 120,000$ 250,000$

1,740,000$ 950,000$ 3,740,000$ 6,000,000$ 1,800,000$ 19,100,000$

O&M Costs (Annual Years 7-30)8.0 Monitoring Subtotal 124,000$ 82,800$ 176,000$ 8.1 Performance Monitoring Yrs 7-30 35 Samples/Year 2,400$ 84,000$ 58,800$ 126,000$ 8.2 Annual Groundwater Report 1 Year 20,000$ 20,000$ 14,000$ 30,000$ 8.3 Project Management, O&M Phase 1 Year 20,000$ 20,000$ 10,000$ 20,000$

124,000$ 83,000$ 176,000$ 1,000,000$ 700,000$ 1,400,000$

Contingency9.0 Contingency on Total Cost, 25% Subtotal 6,325,000$ 1,455,000$ 21,862,500$

$26,100,000

1.11.21.3

2.1

2.2

2.3

2.4

3.1

3.2

4.1

5.1

5.25.35.4

6.1

6.27.1

7.2

7.37.47.5

8.1

8.28.3

9.0

Annual O&M Cost Yrs 7-30O&M Yrs 7-30 NPV

Annual O&M Cost Yr 4

Alternative 4 - Enhanced Bioremediation via Injection

O&M Costs (Annual Years 1-3)

Annual O&M Cost Yrs 5-6


O&M Yrs 4-6 NPV

Project management is assumed to be 15 percent of O&M costs.It is assumed that 20 supplemental injection wells will be required to target areas of insufficient amendment delivery. This is assumed as a one time cost in year 4.

$6,100,000

Assumes installation of 2-inch stainless steel well screen with carbon steel riser.

Assumes well redevelopment by a licensed well driller using surging/pumping and biofouling treatment techniques.

It is assumed that supplemental amendment will be necessary to maintain conditions suitable for bioremediation. Supplemental amendments are assumed to be completed at the injection wells installed during initial construction. Supplemental amendment and delivery costs are assumed to be 10 percent of initial amendment and delivery costs per year. There is significant uncertainty regarding the quantity of amendments needed.

Costs include labor, expenses, and laboratory costs for quarterly sampling at 45 groundwater monitoring wells. Analysis inlcudes 25 parameters for monitoring anaerobic bioremediation processes and secondary water quality.

Assumes preparation of an annual groundwater monitoring report that summarizes groundwater quality trends and natural degradation rates.

Access includes costs associated with coordinating access to the public and railroad right-of-ways for injection well installation and amendment delivery operations.Permitting includes costs associated with applying for and securing permits for the work as required by local, State, and Federal regulations.

Injection pilot testing includes installation of one injection well and five monitoring wells for observation of in-situ conditions following injection. Assume 1 percent of amendment and delivery operations costs for full scale. Includes estimated labor and expenses for pilot and bench testing. It is assumed that methane mitigation measures will not be required during pilot testing.

Assumes installation of 2-inch stainless steel well screen with carbon steel riser, pitless adaptors, and traffic rated vaults.

Costs include amendment delivery to injection wells via tanker trucks assuming delivery of emulsified vegetable oil. Emulsified vegetable oil was selected based on in-situ longevity, advective flow rates, and delivery method. Given the uncertainty surrounding the quantity of amendments, a sensitivity analysis was completed using the Substrate Estimating Tool for Enhanced Anaerobic Bioremediation of Chlorinated Solvents, Version 1.2, November 2010, Parsons. The estimate cost assumes the average quantity developed during the sensitivity analysis. Costs were estimated using the range of amendment quantity developed during the sensitivity analysis.

$89,800,000Assumptions

Project management is assumed to be 15 percent of capital cost (excluding amendment expense).Engineering and design is assumed to be 15 percent of capital cost (excluding amendment expense).Construction quality assurance, monitoring, and reporting is assumed to be 10 percent of capital cost (excluding amendment expense).


Assumed as the same as initial amendment delivery costs on a per well basis. This is a one time cost in year 4.Costs assumed to be 10 percent of initial amendment delivery costs at the supplemental injection wells per year.Costs include quarterly sampling at 45 groundwater monitoring wells. Analysis inlcudes 25 parameters for monitoring anaerobic bioremediation processes and secondary water quality.

Assumes preparation of an annual groundwater monitoring report that summarizes groundwater quality trends and natural degradation rates.Project management is assumed to be 15 percent of O&M costs.

Assumes well redevelopment by a licensed well driller using surging/pumping and biofouling treatment techniques.

Costs include annual sampling at 35 groundwater monitoring wells. Analysis inlcudes 12 parameters for monitoring anaerobic bioremediation processes and secondary water quality.Assumes preparation of an annual groundwater monitoring report that summarizes groundwater quality trends and natural degradation rates.Project management is assumed to be 15 percent of O&M costs.

Contingency based on range of scope and bid contingency recommended in A Guide to Developing and Documenting Cost Estimates During the Feasibility Study (EPA, 2000).Discount rate taken from A Guide to Developing and Documenting Cost Estimates During the Feasibility Study (EPA, 2000).


Minneapolis, MN

Table 10Page 1 of 1

Table 10 - Alternative 5 Cost EstimateEast Hennepin Avenue SiteMinneapolis, MN


Estimated Cost

Low Estimate

Cost

High Estimate

Cost Capital Costs

1.0 Engineering and Administration Subtotal 1,650,000$ -$ -$ 1.1 Project Management, Capital Phase 1 Year 620,000$ 620,000$ 430,000$ 920,000$ 1.2 Engineering and Design 1 LS 620,000$ 620,000$ 430,000$ 920,000$ 1.3 Construction Quality Assurance, Monitoring, & Reporting 1 LS 410,000$ 410,000$ 290,000$ 620,000$ 2.0 Planning and Preparation Subtotal 2,200,000$ 1,600,000$ 3,300,000$ 2.1 Access for Wells, Operations Building, and Conveyance Piping 1 LS 1,400,000$ 1,400,000$ 980,000$ 2,100,000$ 2.2 Permitting 1 LS 100,000$ 100,000$ 70,000$ 150,000$ 2.3 Recirculation Design Phase Bench and Pilot Testing 1 LS 700,000$ 700,000$ 490,000$ 1,050,000$ 2.4 Monitoring Wells 10 Well 4,000$ 40,000$ 28,000$ 60,000$ 3.0 Full Scale Recirculation System Construction and Initial Amendment Delivery Subtotal 12,700,000$ 3,700,000$ 41,900,000$ 3.1 Injection Wells 40 Well 10,000$ 400,000$ 280,000$ 600,000$ 3.2 Extraction Wells 2 EA 15,000$ 30,000$ 21,000$ 45,000$ 3.3 Conveyance Piping 5100 LF 70$ 360,000$ 252,000$ 540,000$ 3.4 Operations Building Construction 2 EA 700,000$ 1,400,000$ 980,000$ 2,100,000$ 3.5 Operations Equipment Procurement and Installation (Tanks, pumps, valves, etc.) 2 EA 820,000$ 1,640,000$ 1,148,000$ 2,460,000$ 3.6 System Startup 1 LS 250,000$ 250,000$ 175,000$ 375,000$ 3.7 Initial Amendment Delivery via Recirculation System 1 LS 8,600,000$ 8,600,000$ 770,000$ 35,700,000$

Total Capital Cost 16,600,000$ 5,300,000$ 45,200,000$

4.0 System Operation Subtotal 1,400,000$ 500,000$ 4,300,000$ 4.1 Supplemental Amendment Delivery 1 Year 860,000$ 860,000$ 77,000$ 3,570,000$ 4.2 Operations and Management Yrs 1-5 1 Year 400,000$ 400,000$ 280,000$ 600,000$ 4.3 Electricity 1 Year 30,000$ 30,000$ 21,000$ 45,000$ 4.4 Treatment Control Building Maintenance 1 Year 20,000$ 20,000$ 14,000$ 30,000$ 4.5 Injection Well Maintenance 40 EA 500$ 20,000$ 14,000$ 30,000$ 5.0 Monitoring Subtotal 1,270,000$ 889,000$ 1,905,000$ 5.1 Performance Monitoring Yrs 1-5 180 Samples/Year 6,000$ 1,080,000$ 756,000$ 1,620,000$ 5.2 Annual Groundwater Report 1 Year 20,000$ 20,000$ 14,000$ 30,000$ 5.3 Project Management, O&M Phase 1 Year 170,000$ 170,000$ 119,000$ 255,000$

2,700,000$ 1,400,000$ 6,300,000$ 11,100,000$ 5,800,000$ 25,900,000$

O&M Costs (Annual Years 6-10)6.0 System Operation Subtotal 170,000$ 120,000$ 260,000$ 6.1 Operations and Management Yrs 6-10 1 Year 100,000$ 100,000$ 70,000$ 150,000$ 6.2 Electricity 1 Year 30,000$ 30,000$ 21,000$ 45,000$ 6.3 Treatment Control Building Maintenance 1 Year 20,000$ 20,000$ 14,000$ 30,000$ 6.4 Injection Well Maintenance 40 EA 500$ 20,000$ 14,000$ 30,000$ 7.0 Monitoring Subtotal 1,270,000$ 889,000$ 1,905,000$ 7.1 Performance Monitoring Yrs 6-10 180 Samples/Year 6,000$ 1,080,000$ 756,000$ 1,620,000$ 7.2 Annual Groundwater Report 1 Year 20,000$ 20,000$ 14,000$ 30,000$ 7.3 Project Management, O&M Phase 1 Year 170,000$ 170,000$ 119,000$ 255,000$

1,440,000$ 1,010,000$ 2,170,000$ 4,300,000$ 3,000,000$ 6,400,000$

O&M Costs (Annual Years 11-30)8.0 Monitoring Subtotal 260,000$ 182,000$ 390,000$ 8.1 Performance Monitoring Yrs 11-30 35 Samples/Year 6,000$ 210,000$ 147,000$ 315,000$ 8.2 Annual Groundwater Report 1 Year 20,000$ 20,000$ 14,000$ 30,000$ 8.3 Project Management, O&M Phase 1 Year 30,000$ 30,000$ 21,000$ 45,000$

260,000$ 182,000$ 390,000$ 1,410,000$ 990,000$ 2,110,000$

Contingency9.0 Contingency on Total Cost, 25% Subtotal 8,352,500$ 3,772,500$ 19,902,500$

$41,800,000

1.11.21.3

2.1

2.2

2.3

2.43.13.2

3.3

3.4

3.5

3.6

3.7

4.1

4.24.34.44.5

5.1

5.25.36.16.26.36.47.17.27.3

8.1

8.28.39.0

Project management is assumed to be 15 percent of O&M costs.Operations and management for years 6-10 is assumed to be 25 percent of operations and management costs for years 1-5.

Assumes installation of 2-inch stainless steel well screen with carbon steel riser.

Assumes full-time operations engineer onsite for 8 hours a day for 365 days a year and technical support for treatment evaluation and system modifications.Assumes utility expense to operate the equipment and heat the treatment control buildings.Capital maintenance includes expenses for maintaining and replacing equipment.Assumes well redevelopment by a licensed well driller using surging/pumping and biofouling treatment techniques.Costs include labor, expenses, and laboratory costs for quarterly sampling at 45 groundwater monitoring wells. Analysis inlcudes 25 parameters for monitoring anaerobic bioremediation processes and secondary water quality.

Assumes construction of 3,500-square foot climate controlled building for each treatment control building.Assumes purchase and installation of equipment to collect, amend, and reinject groundwater. Equipment includes 58,000 gallons tankage, redundant injection pumps, mixing vessel, amendment metering and transfer pumps, electrical, instrumentation and controls, safety equipment, valves, piping, and appurtenances.Costs include oversight, troubleshooting, and system modification associated with system startup.Costs include amendment delivery to injection wells utilizing the treatment control building. Assumes emulsified vegetable oil based on in-situ longevity and delivery method. Given the uncertainty surrounding the quantity of amendments, a sensitivity analysis was completed using the Substrate Estimating Tool for Enhanced Anaerobic Bioremediation of Chlorinated Solvents, Version 1.2, November 2010, Parsons. The estimate cost assumes the average quantity developed during the sensitivity analysis. Costs were estimated using the range of amendment quantity developed during the sensitivity analysis.It is assumed that supplemental amendment will be necessary to maintain conditions suitable for bioremediation. Supplemental amendments are assumed to be completed at the injection wells installed during initial construction. Supplemental amendment and delivery costs are assumed to be 10 percent of initial amendment and delivery costs per year. There is significant uncertainty regarding the quantity of amendments needed.


Alternative 5 - Enhance Bioremediation via Recirculation System


Assumes preparation of an annual groundwater monitoring report that summarizes groundwater quality trends and natural degradation rates.

O&M Costs (Annual Years 1-5)

Annual O&M Cost Yrs 1-5


O&M Yrs 1-5 NPV

$18,900,000 $99,600,000Assumptions

Project management is assumed to be 15 percent of capital cost (excluding amendment expense).Engineering and design is assumed to be 15 percent of capital cost (excluding amendment expense).Construction quality assurance, monitoring, and reporting is assumed to be 10 percent of capital cost (excluding amendment expense).Access includes costs associated with coordinating access to property for installation or construction of infrastructure. This cost is assumed to include purchasing four properties, demolishing existing structures, and negotiating access to public and railroad rights-of-way. Permitting includes costs associated with applying for and securing permits for the work as required by local, State, and Federal regulations. Assumes labor and analytical expense to conduct laboratory bench testing, extraction well pumping test, and injection pilot testing. Bench testing assumes column testing using site groundwater and a variety of amendments. Pump testing includes completion of a pumping test at an extraction well with multiple observation monitoring wells to better develop the radius of influence of extraction and reinjection wells. Pilot testing includes injection of amendments and monitoring at multiple wells. It is assumed that methane mitigation measures will not be necessary during pilot testing.

Assumes installation of 2-inch stainless steel well screen with carbon steel riser, pitless adaptors, and traffic rated vaults.Assumes installation of 4-inch stainless steel well screen with carbon steel riser, pitless adapters, and traffic rated vaults.Assumes construction of 5,100 feet conveyance piping between the operations building and the extraction and injection wells. Costs include installing 4-inch HDPE pipe at a depth of 8 feet. Assumes trenching will occur in unpaved right-of-way space with the exception of pavement replacement at street crossings where existing pavements and curbs will be demolished and replaced at eight cross-streets.

Assumes utility expense to operate the equipment and heat the treatment control buildings.Capital maintenance includes expenses for maintaining and replacing equipment.Assumes well redevelopment by a licensed well driller using surging/pumping and biofouling treatment techniques.Costs include quarterly sampling at 45 groundwater monitoring wells. Analysis inlcudes 25 parameters for monitoring anaerobic bioremediation processes and secondary water quality.Assumes preparation of an annual groundwater monitoring report that summarizes groundwater quality trends and natural degradation rates.

Discount rate taken from A Guide to Developing and Documenting Cost Estimates During the Feasibility Study (EPA, 2000)

Project management is assumed to be 15 percent of O&M costs.Costs include labor, expenses, and laboratory costs for quarterly sampling at 45 groundwater monitoring wells. Analysis inlcudes 25 parameters for monitoring anaerobic bioremediation processes and secondary water quality.Assumes preparation of an annual groundwater monitoring report that summarizes groundwater quality trends and natural degradation rates.Project management is assumed to be 15 percent of O&M costs.Contingency based on range of scope and bid contingency recommended in A Guide to Developing and Documenting Cost Estimates During the Feasibility Study (EPA, 2000)

Figures

LOCATION MAPEast Hennepin Avenue Site


FIGURE 1

0 2,000 4,000

Feet

!;NService Layer Credits: Copyright:© 2013 National Geographic Society, i-cubedUSGS 7.5 Minute Quadrangle - Hennepin County

Note: Pink shaded areas in USGS map indicate residential areas.

2010 East Hennepin Ave

SOUTHWEST

NORTHEAST

CENTRAL

SITE§̈¦35W

456788

456730456752456727

456766

22nd

Ave S

E

Como Ave SE

Johnson St NE

30th

AveS

E

10th

AveS

E

18th

AveS

E

6th St SE

Como Ave

Winter St NE

Kennedy St NE

Traffic St NE

11th Av

e SE

Weeks Ave SE

Summer St NE

14th

Ave S

E

15th

AveS

E

7th St SE

Elm St SE

Cole Ave SE

Brook Ave SE

24th

AveS

E

Broadway St NE

Spring St NE

33rd

AveS

E

29th

AveS

E

Arth

urSt

NE

17th

AveS

E

16th

AveS

E

19th

A ve S

E

Garfi

eldSt

N E13

thAv

eSE

Delan

oStN

E

23rd

AveS

E

20th

AveS

E

21st

AveS

E

12th

AveS

E

Mckin

leySt

NE

Clev

el and

StNE

2 7th

AveS

E

25th

AveS

E

Taft

StNE

2 6th

AveS

E

Kasota Ave SE

Diagonal Rdwy

8th St SE

Wilso

nStN

E

Hard

ingSt

NE

Roos

evelt

StNE

Talmage Ave SE

Hoov

erSt

NE

Indus

trial

B lvd

G odw

ardS

tNE

E Hennepin Ave

STUDY AREAEast Hennepin Avenue Site


FIGURE 2

0 600 1,200

Feet

!;N

Maximum sub-slab soil gas TCE concentrationat each building shown.

Imagery: USGS NAIP (2015)

2010 East Hennepin AveOff-Site Property withDocumented TCE in GroundwaterBased on Review of MPCA FilesOff-Site Property with PotentialSolvent Use, ApproximateLocation of Current and/orHistoric BusinessCentral Area

Sub-slab Soil Gas TCE Concentrations< 20 ug/m3

20 - 60 ug/m3

60 - 100 ug/m3

100 - 500 ug/m3

500 - 2000 ug/m3

> 2000 ug/m3

Kozebar Co./ Cozy Baby

Carriage Co

Repair Shop

Cargill/International

Sugar

Stahl Mfg/ M&M WireClamp Co.

BowenProducts

GliddenPaint

MinneapolisCasket

Company

Amar's AutoService

Jewel Coal Company

Anne Gendein Trust Property/former Scott-Atwater Manufacturing

VP13270Lend Lease Trucking

LUST6600Shallow GW

TCE Conc.: 3,600 µg/L

2400 Traffic StreetVP22300VP23301VP23302

Shallow GWTCE Conc.: 41 µg/L

AmeriPride Services IncVP24750

LUST16906Shallow GW

TCE Conc.: 7.2 µg/L

Office/Warehouse - Traffic St.VP27480

Shallow GWTCE Conc.: 2.7 µg/L

Northwestern WarehouseVP13100VP13101


Como StudentCommunity

VP24930Shallow GW

TCE Conc.: 10.7 µg/L

Joe's Market

CNW EastMinneapolis Yard

Sears/former Scott-Atwater Manufacturing

LUST7905LUST7043


Franks Auto RepairLUST17726Shallow GW

TCE Conc.: 1,620 µg/L

East HennepinAuto Service Inc

LUST2477Shallow GW

TCE Conc.: 24 µg/L

Excel Metal Finishing Inc

Twin City Plating

Former Gas Station& Auto Repair

Pitcher MFGCo. / United

Chemical

WarnerMFG Co.

Gorshe AutoRepair

Shop &Storage

MN TankCo.

Postcard BuilderVP30090

15th Avenue HousingVP30330

Joe Baker'sAuto

§̈¦35W

456788

456730456752456727

456766

22n d

AveS

E

Como Ave SE

Johnson St NE

30th

AveS

E

10th

AveS

E

18th

AveS

E

6th St SE

Como Ave

Winter St NE

Traffic St NE

11th Av

e SE

Weeks Ave SE

Summer St NE

Kennedy St NE

14th

Ave S

E

7th St SE Elm St SE

Cole Ave SE

Brook Ave SE

24th

AveS

E

Broadway St NE

15th

Ave S

E

17th

Ave S

E

33rd

AveS

E

29th

AveS

E

Arth

urSt

NE

23rd

Ave S

E

16th

AveS

E

19th

A ve S

E

Garfi

eldSt

N E13

thAv

eSE

Delan

oStN

E

20th

AveS

E

21st

AveS

E

12th

AveS

E

Mckin

leySt

NE

Clev

el and

StNE

2 7th

AveS

E

25th

AveS

E

Taft

StNE

2 6th

AveS

E

Kasota Ave SE

Diagonal Rdwy

8th St SE

Hard

ingSt

NERoos

evelt

StNE

Talmage Ave SE

Hoov

erSt

NE

Indus

trial

BlvdG o

dwar

dStN

E

E Hennepin Ave

POTENTIAL OFF-SITE TCESOURCES

East Hennepin Avenue SiteMinneapolis, Minnesota

FIGURE 3

0 600 1,200

Feet

!;N

Maximum sub-slab soil gas TCE concentrationat each building shown.


2010 East Hennepin AveOff-Site Property withDocumented TCE in GroundwaterBased on Review of MPCA FilesOff-Site Property with PotentialSolvent Use, ApproximateLocation of Current and/orHistoric BusinessCentral Area

Sub-slab Soil Gas TCE Concentrations< 20 ug/m3

20 - 60 ug/m3

60 - 100 ug/m3

100 - 500 ug/m3

500 - 2000 ug/m3

> 2000 ug/m3

!(

!(

!(")

")

!(

!(

!(

!(

!(

!(

!(

!(!(")

")

!(

!(

!(

!(

")

")

S P-0321.4 ug/l (18-23')2.7 ug/l (50-54')

S P-0144.5 ug/l (15-20')13.6 ug/l (49-53')

S P-06742 ug/l (18-23')1080 ug/l (29-33')

S P-1779.1 ug/l (15-20')274 ug/l (38-42')

S P-16198 ug/l (15-20')316 ug/l (37-41')

S P-18253 ug/l (15-20')285 ug/l (36-40')

S P-05295 ug/l (12.5-17.5')685 ug/l (34-38')

S P-041.2 ug/l (15-20')75.4 ug/l (35-40')1260 ug/l (44-48')

S P-02<1.0 ug/l (15-20')1100 ug/l (35.5-39.5')

S P-077.1 ug/l (20-25')828 ug/l (39-43')

S P-08<1.0 ug/l (20-25')473 ug/l (35-40')584 ug/l (43-47')

S P-09<1.0 ug/l (20-25')1300 ug/l (41-45')

S P-12285 ug/l (25-30')

1810 ug/l (42.5-46.5')

S P-1335.8 ug/l (30-35')90.5 ug/l (45-50')

S P-14116 ug/l (37-41')78.9 ug/l (66-70')

S P-15132 ug/l (40-45')40.3 ug/l (53-57')

VP-05115 ug/m 3

VP-040.71 ug/m 3

VP-0244500 ug/m 3

VP-0318.8 ug/m 3

VP-01< 0.74 ug/m 3

VP-0662.7 ug/m 3

Com o Ave S E

S um m er S t NE

Johnson StNE

7th S t S E

EHennep in Ave

Weeks Ave S E

10t hAveSE

14th Ave S E

Winter S t NE

S E Elm S t

11th Ave S E

6th S t S E

8th S t S E

T a lm a d ge Ave S E

Hoover St NE

15th Ave SE

Hard ing S t NE

Fa irm ount Ave S E

K enned y S t NE

Tra ffic S tNE

Rollins Ave S E

Elm S t S E

Cole Ave S E

Brook Ave S E

18th Ave SE

25th Ave SE

26th Ave SE

29thAveSE

24thAveSE

27thAveSE

12th Ave SE

20th Ave SE

23rd Ave SE

13th Ave SE

19thAve SE

17th Ave SE 22nd Ave SE

21stA veSE

Garfield S t NE

Dela no St NE

Mckinley St NE

Clevela nd St NE

Stinson Blvd

Wilson St NE

Roosevelt St NE

Stin so nBl vd NE

Taft St NE

Dia gona l Rdwy

Industrial Blvd

16th Ave SE

Arthur St NE

K a sota Ave S E

456752

456727

§̈¦35W

MPCA S A249 GROU NDWATERAND S OIL GAS S AMPLING -

TCE RES U LT SEa st Hennep in Avenue S iteMinnea p olis, Minnesota

FIGU RE 4

0 500 1,000

Feet

!;N

Note: MPCA S A249 investiga tion d a ta fromNovem b er a nd Dec em b er 2015. S oil ga ssa m p ling d ep th of 8 ft b gs.

S a m p le IDTCE in Groundwa ter (Tem p Well S c reen

Dep th)

S a m p le IDTCE in S oil Ga s


2010 East Hennepin AveMPCA Investiga tion Loc a tion

!( S oil Prob e Loc a tion

") S oil-Ga s S a m p le Loc a tion

Centra l AreaOff-S ite Prop erty withDoc um ented TCE in Groundwa terBa sed on Review of MPCA FilesOff-S ite Prop erty with Potentia lS olvent U se, Ap p roxim a teLoc a tion of Current a nd/orHistoric BusinessProp erty Inc lud ed in MPCA’sS A249 S tud y a s of Ma y 28, 2015

! ! !

! ! !

! ! !

! ! !

! ! !

! ! !

! ! ! ! ! !

! ! ! ! ! !

! ! ! ! ! !

! ! ! ! ! !

! ! ! ! ! !

! ! ! ! ! !

! ! ! ! ! !

! ! ! ! ! !

! ! ! ! ! !

! ! ! ! ! !

! ! ! ! ! !! ! ! ! ! !

! ! ! ! ! !

! ! ! ! ! !

! ! ! ! !

! ! ! ! !

! ! ! ! !

! ! ! !

! ! ! !

! ! ! !

! ! ! !

! ! ! !

! ! ! !

! ! ! !

! ! ! !

! ! ! !

! ! ! !

! ! ! !

! ! ! !

! ! ! !

! ! ! ! ! ! ! !

! ! ! ! ! ! ! !

! ! ! ! ! ! ! !

! ! ! ! ! ! ! !

! ! ! ! ! ! ! ! ! !

! ! ! ! ! ! ! ! ! !

! ! ! ! ! ! ! ! ! !

! ! ! ! ! ! ! ! ! !

SOUTHWEST

NORTHEAST

CENTRAL

SITE456752

456752

456727

22nd

AveS

E

Como Ave SE

Cole Ave SE

Garfi

eldSt

NE

Hard

ingSt

NE

Taft

StNE

18th

AveS

E

Talmage Ave SE

Fairmount Ave SE

14th

Ave S

E

15th

AveS

E

Rollins Ave SE

17th Av eS E

7th St SE

8th St SE

Brook Ave SE

16th

AveS

E

19t h

Ave S

E

13th

AveS

E

23rd

AveS

E

20th

AveS

E

21st

AveS

E

12th

AveS

EE Hennepin Ave

Elm St SE BUILDING MITIGATIONSTATUS - APRIL 2016


FIGURE 5

0 300 600

Feet

!;N

2010 E Hennepin Ave

Central AreaBuilding Mitigation SystemInstalledBuilding Mitigation SystemNot Installed in Central Area

Central Area DetailMitigation Declined by PropertyOwner - Sub-Slab Soil Gas TCE<20 ug/m3

Mitigation Declined by PropertyOwner - Sub-Slab Soil Gas TCE>20 ug/m3

! ! ! ! ! ! ! ! !

! ! ! ! ! ! ! ! !

! ! ! ! ! ! ! ! !

! ! ! ! ! ! ! ! !

! ! ! ! ! ! ! ! !

Indoor Air TCE < ApplicableMPCA Intrusion ScreeningValue (ISV)Did Not Participate in Sub-SlabSoil Gas Sampling StudyProperty with Post-MitigationIndoor Air SamplingResidential Properties withoutMitigation Systems


*

*

*

**

!A

!A

!A

!A!A

!A

!A

!A

!A

!A

!A

!A

!A

!A

!A

!A

!A

!A

!A

!A

!A

!A

!A!A

!A!A

!A!A

!A!A

!A!A

!A!A

!A!A

!A!A

!A

!A!A

!A

!A!A

!A!A

456752

Weeks Ave SE

22nd

AveS

E

Como Ave SE

Winter St NE

7th St SE

Talmage Ave SE

24th

AveS

E

Fairmount Ave SE

8th St SE

15th

AveS

EKasota Ave SE

Cole Ave SE

17th

AveS

E

16th

AveS

E

1 9th

AveS

E

Garfi

eldSt

NE13

thAv

eSE

23rd

AveS

E

14th

AveS

E

20th

AveS

E

2 7th

A veS

E

25th

AveS

E

2 6th

AveS

E

Wils

onSt

NE

Taft

StNE

Traffic St NE

Elm St SE

E Hennepin Ave

21st

AveS

E

311GS

312GS

313GD

315GS

301GS

314GS

2

109

110

111

112 113

B

V

W

SMW1

311GD

SMW25

309GS

312GD

313GS

318GS

SMW3

SMW6

306GD306GS

315GD

301GD

SMW10

SMW19

SMW22

314GD

SMW16

308GS

305GD

Q

ST

X

308GD

307GD307GS

310GS

309GD

317GS

316GD

303GS

316GS

302GS

305GS

304GS

GLACIAL DRIFT GROUNDWATERMONITORING NETWORK


FIGURE 6

0 400 800

Feet


Central AreaMonitoring Well Locations

!A Glacial Drift Monitoring Well

!AGlacial Drift NestedMonitoring Well

* Glacial Drift Pump-Out Well

!;N


!(

!(

!(

!(

!(

!(

!(

!(

!(

!(!(!(!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(!(!(!(!(

!(

!(

!(

!(

!(!(

Como Ave SE

E Hennepin Ave

Talmadge Ave SE

Weeks Ave SE

15th

Ave S

E

8th St SE

Cole Ave SE

SE Elm St

Hoov

er St

NE

Hardi

ng St

NE

Taft

St NE

Elm St SE

Fairmount Ave SE

Rollins Ave SE

Brook Ave SE

18th

Ave S

E

25th

Ave S

E

24th

AveS

E

20th

Ave S

E

23rd

Ave S

E

19th

AveS

E

17th

Ave S

E

22nd

Ave S

E

2 1s t

AveS

E

Diago

nal R

dwy

Stins

onBl v

d NE

16th

Ave S

E

14th

Ave S

E

456727

456752

ALTERNATIVE 4 - ENHANCEDBIOREMEDIATION VIA INJECTION

EVENT(S)East Hennepin Avenue Site

Minneapolis, MinnesotaFIGURE 7

0 300 600

Feet


Central Area

!( Proposed Injection Well

Railroad Property Parcels

!;N


!?

!(

!(

!?

!?!?

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(!(!(!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(!(!(!(!(

!(

!(

!(

!(

!(!(

Como Ave SE

E Hennepin Ave

Talmadge Ave SE

Weeks Ave SE

15th

Ave S

E

8th St SE

Cole Ave SE

SE Elm St

Hoov

er St

NE

Hardi

ng St

NE

Taft

St NE

Elm St SE

Fairmount Ave SE

Rollins Ave SE

Brook Ave SE

18th

Ave S

E

25th

Ave S

E

24th

AveS

E

20th

Ave S

E

23rd

Ave S

E

19th

AveS

E

17th

Ave S

E

22nd

Ave S

E

2 1s t

AveS

E

Diago

nal R

dwy

Stins

onBl v

d NE

16th

Ave S

E

14th

Ave S

E

456727

456752

ALTERNATIVE 5 - ENHANCEDBIOREMEDIATION VIA

RECIRCULATIONEast Hennepin Avenue Site

Minneapolis, MinnesotaFIGURE 8

0 300 600

Feet


Central Area

!?Proposed Extraction Well(Existing Location)

!( Proposed Extraction Well

!( Proposed Injection Well

ForcemainTreatment System ControlBuilding (Typical / LocationNot Specified)Railroad Property Parcels

!;N


Appendix A

Supporting Cost Details

Table A-1Unit Cost Details


Table A-1Page 1 of 3

Alternative Cost Item Item Unit Unit Cost Reference Supporting Details

2 1.1 Monitored Natural Attenuation Work Plan LS 30,000$ Engineer Estimate Based on knowledge of site conditions and professional judgement. 1

2 2.1 Well Sampling - VOCs Well/Year 1,000$ Engineer Estimate and Vendor Quotes Assumes $900 for labor and expenses to collect samples and review and manage analytical data. Assumes VOC analysis at $100/sample.

2 2.2 Well Sampling - MNA Parameters and VOCs Well/Year 2,200$ Engineer Estimate and Vendor Quotes

Assumes $1,800 for labor and expenses to collect samples and review and manage analytical data. Assumes MNA parameter list analysis at $400/sample. MNA parameter list includes 13 parameters recommended in Technical Protocol for Evaluating Natural Attenuation of Chlorinated Solvents in Groundwater, EPA, 1998.

2 2.3 Project Management Year Calc in Summary Engineer Estimate Based on knowledge of site conditions and professional judgement. 1

2 2.4 Annual Groundwater Report Year 20,000$ Engineer Estimate Assumes preparation of an annual groundwater monitoring report that summarizes groundwater quality trends and natural degradation rates.

3 1.1 Mitigation System O&M Plan LS $ 50,000 Engineer Estimate Based on knowledge of site conditions and professional judgement. 1

3 1.2 Access and Mitigation System Design Meetings Properties $ 2,500 Engineer Estimate Cost assumes 10 hours for access, four hours for design meetings, and contractor costs. Does not include multiple design meetings to satisfy extraordinatry property owner requests.

3 2.1 Mitigation System Design Follow-up Properties $ 5,000 Engineer Estimate Based on knowledge of site conditions and professional judgement. 1

3 3.1 Contractor and Support for Installations Properties $ 20,000 Engineer Estimate Assumes installation of a mitigation system including diagnostic testing, contractor management, finish carpentry, and preparation of a property summary report. Not included are sub-slab soil-gas testing, indoor air testing, basement floor replacement, or extensive wall or floor patching.

3 4.1 Paired Indoor Air Sampling and Sub-Slab Soil Gas Sampling LS $ 150,000 Engineer Estimate and Vendor Quotes

Assumes three sampling events, 13 sub-slab soil gas samples per event, 13 indoor air samples per event, data quality and management costs are equal to laboratory costs (based on costs associated with previous project work), sub-slab sampling is a two week effort per event for one person, indoor air sampling is a two week effort per event for two people (includes chemical inventory), and preparation of a Property Summary Report.

3 5.1 Project Management, Capital Phase Year Calc in Summary Engineer Estimate Based on knowledge of site conditions and professional judgement. 1

3 6.1 Electrical Bill for Properties Building/Year $ 60.00 Engineer Estimate and

Published Electrical Utility Rates

Assumptions: 1) Fans are operated 24 hours a day, 365 days a year, 2) Half of the fans are RadonAway Model RP145 and half are RadonAway model RP265, 3) Fans are operated in accordance with manufacturers standards, 4) Energy rates based on November 1, 2015 Xcel Energy ratecard for Minnesota, 5) 176 houses with mitigation systems installed within the Central Area.

3 6.2 Replacement Fan Cost Fan/Year $ 2,000 Engineer Estimate and Vendor Quotes

Assumptions: 1) Replacement of fans every 10 years, 2) Replacement of an average of 1/10 of the fans during a given year, 3) Half of the fans are RadonAway Model RP145 and half are RadonAway model RP265, 4) Half a day of contractor time to install a replacement fan, 5) Cost includes property access efforts, 6) No engineer oversight time is included within this cost.

3 6.3 O&M Management and Access Coordination Building/Year $ 200 Engineer Estimate Based on knowledge of site conditions and professional judgement. 1

3 6.4 Project Management, O&M Phase Year Calc in Summary Engineer Estimate Based on knowledge of site conditions and professional judgement. 1

4 2.1 Access for Injection Well Installation LS Calc in Summary Engineer Estimate Access includes costs associated with coordinating access to the public and railroad right-of-ways for injection well installation and amendment delivery operations.

4 2.3 Injection Design Phase Bench and Pilot Testing LS 440,000$ Engineer EstimateBench and Pilot testing include 500 hours of labor at $115/hour, $20,000 expenses, installation of one injection well at $10,000 per well, installation of five monitoring wells at $4,000 per well, performance monitoring at five monitoring wells quarterly for one year at $2,000 per sampling event, $30,000 for PM and work plan development, $10,000 for permitting, and amendment costs assuming average amendment quantity.

4 3.2 Initial Amendment Delivery Well 220,000$ Engineer Estimates and Vendor Quotes

Amendment costs assume $1.15/pound of emulsified vegtable oil. The quantity of amendments needed is based on theoretical demand and groundwater monitoring data. Bench and pilot testing is necessary to determine amendment dosing. Even with rigorous pilot testing, total demand may vary based on aquifer heterogeneity. Given the uncertainty surrounding the quantity of amendments, a sensitivity analysis was completed using the Substrate Estimating Tool for Enhanced Anaerobic Bioremediation of Chlorinated Solvents, Version 1.2, November 2010, Parsons. This cost assumes the average quantity developed during the sensitivity analysis. The total quantity of amendments ranges from approximately 0.1X to 3X the average.

5 2.1 Access for Wells, Operations Building, and Conveyance Piping LS 1,350,000$ Engineer EstimateAccess includes costs associated with coordinating access to property for installation or construction of infrastructure. This cost is assumed to include purchasing four properties, demolishing existing structures, and negotiating access to public and railroad rights-of-way. Property purchase: four residential lots - $300k each. Existing Structure Demolition: four houses - $25,000 each. Negotiating railroad ROW access: $50,000.

Alternative 2 Costs

Alternative 3 Capital Costs

Alternative 3, O&M Costs

Alternatives 4 and 5 Engineering, Administrative, Planning, Preparation, and Construction Costs




Alternative Cost Item Item Unit Unit Cost Reference Supporting Details

5 2.3 Recirculation Design Phase Bench and Pilot Testing LS 670,000$ Engineer EstimateBench and Pilot testing include 750 hours of labor at $115/hour, $30,000 pumping test, $20,000 expenses, installation of one injection well at $10,000 per well, installation of five monitoring wells at $4,000 per well, performance monitoring at five monitoring wells quarterly for one year at $2,000 per sampling event, $30,000 for PM and work plan development, $10,000 for permitting, and amendment costs assuming average amendment quantity.

5 3.2 Extraction Wells EA 15,000$ Bid from Contractor with Additional Items and Scaling Assumes installation of 4-inch stainless steel well screen with carbon steel riser, pitless adapters, and traffic rated vaults.

5 3.3 Conveyance Piping LF 65$ Engineer Estimates and RS Means Unit Rates

Assumes construction of 5,100 feet conveyance piping between the operations building and the extraction and injection wells. Costs include installing 4-inch HDPE pipe at a depth of 8 feet. Assumes trenching will occur in unpaved right-of-way space with the exception of pavement replacement at street crossings where existing pavements and curbs will be demolished and replaced at eight cross-streets.

5 3.4 Operations Building Construction EA 660,000$ Engineer Estimate RS Means Unit Rates See the supporting details in Table A-2

5 3.5 Operations Equipment Procurement and Installation (Tanks, pumps, valves, etc.) LS 820,000$ Engineer Estimate and Vendor

Quotes See the supporting details in Table A-2

5 3.6 System Startup LS 250,000$ Engineer Estimate Based on knowledge of site conditions and professional judgement. 1

5 3.7 Initial Amendment Delivery via Recirculation System LS 8,600,000$ Engineer Estimate and Vendor Quote

Costs include amendment delivery to injection wells utilizing the treatment control building. Amendment costs assume $1.15/pound of emulsified vegtable oil. The quantity of amendments needed is based on theoretical demand and groundwater monitoring data. Bench and pilot testing is necessary to determine amendment dosing. Even with rigorous pilot testing, total demand may vary based on aquifer heterogeneity. Given the uncertainty surrounding the quantity of amendments, a sensitivity analysis was completed using the Substrate Estimating Tool for Enhanced Anaerobic Bioremediation of Chlorinated Solvents, Version 1.2, November 2010, Parsons. The average amendment quantity was estimated as 7,320,000 pounds. Assumes 2,000 liters of KB1 bioaugmentation culture.

5 3.7 Initial Amendment Delivery via Recirculation System - Low LS 1,100,000$ Vendor Quote and Engineer Estimate

Costs include amendment delivery to injection wells utilizing the treatment control building. Amendment costs assume $1.15/pound of emulsified vegtable oil (EVO). The quantity of amendments needed is based on theoretical demand and groundwater monitoring data. Bench and pilot testing is necessary to determine amendment dosing. Even with rigorous pilot testing, total demand may vary based on aquifer heterogeneity. Given the uncertainty surrounding the quantity of amendments, a sensitivity analysis was completed using the Substrate Estimating Tool for Enhanced Anaerobic Bioremediation of Chlorinated Solvents, Version 1.2, November 2010, Parsons. The low range of EVO quantity was estimated at 740,000 pounds. Assumes 2,000 liters of KB1 bioaugmentation culture.

5 3.7 Initial Amendment Delivery via Recirculation System - High LS 23,800,000$ Vendor Quote and Engineer Estimate

Costs include amendment delivery to injection wells utilizing the treatment control building. Amendment costs assume $1.15/pound of emulsified vegtable oil (EVO). The quantity of amendments needed is based on theoretical demand and groundwater monitoring data. Bench and pilot testing is necessary to determine amendment dosing. Even with rigorous pilot testing, total demand may vary based on aquifer heterogeneity. Given the uncertainty surrounding the quantity of amendments, a sensitivity analysis was completed using the Substrate Estimating Tool for Enhanced Anaerobic Bioremediation of Chlorinated Solvents, Version 1.2, November 2010, Parsons. The low range of EVO quantity was estimated as 20,480,000 pounds. Assumes 2,000 liters of KB1 bioaugmentation culture.

4, 5 1.1 Project Management, Capital Phase LS Calc in Summary Engineer Estimate Based on knowledge of site conditions and professional judgement. 1

4, 5 1.2 Engineering and Design LS Calc in Summary Engineer Estimate Based on knowledge of site conditions and professional judgement. 1

4, 5 1.3 Construction Quality Assurance, Monitoring, & Reporting LS Calc in Summary Engineer Estimate Based on knowledge of site conditions and professional judgement. 1

4, 5 2.2 Permitting LS 100,000$ Engineer Estimate Based on knowledge of site conditions and professional judgement. 1

4, 5 2.4 Monitoring Wells Well 4,000$ Bid from Contractor Assumes installation of 2-inch stainless steel well screen with carbon steel riser.

4, 5 3.1 Injection Wells Well 10,000$ Bid from Contractor with Additional Items Assumes installation of 2-inch stainless steel well screen with carbon steel riser, pitless adaptors, and traffic rated vaults.

4 5.1 Performance Monitoring Yrs 1-3 Samples/Year 6,000$ Engineer Estimate and Vendor Quotes

Assumes quarterly sampling at 45 groundwater monitoring wells, $4,500 for labor and expenses to collect samples and review and manage analytical data, parameter list analysis at $1,500 per sample. Analysis inlcudes 25 parameters for monitoring anaerobic bioremediation processes and secondary water quality.

4 6.1 Supplemental Injection Wells Well 9,674$ Bid from Contractor with Additional Items

It is assumed that 20 supplemental injection wells will be required to target areas of insufficient amendment delivery. This is assumed as a one time cost in year 4.

4 6.2 Initial Amendment Delivery at Supplemental Wells Well 219,412$ Engineer Estimate Assumed as the same as initial amendment delivery costs on a per well basis. This is a one time cost in year 4.4 7.1 Supplemental Amendment Delivery at Supplemental Wells Year Calc in Summary Engineer Estimate Costs assumed to be 10 percent of initial amendment delivery costs at the supplemental injection wells per year.

4 7.2 Performance Monitoring Yrs 4-6 Samples/Year $ 6,000 Engineer Estimate and Vendor Quotes

Assumes quarterly sampling at 45 groundwater monitoring wells, $4,500 for labor and expenses to collect samples and review and manage analytical data, parameter list analysis at $1,500/sample. Analysis inlcudes 25 parameters for monitoring anaerobic bioremediation processes and secondary water quality.


Assumes annual sampling at 35 groundwater monitoring wells, $2,000 for labor and expenses to collect samples and review and manage analytical data, parameter list analysis at $400/sample. Analysis inlcudes 12 parameters for monitoring anaerobic bioremediation processes and secondary water quality.

5 4.2 Operations and Management Yrs 1-5 Year 400,000$ Engineer Estimate Assumes full-time operations engineer onsite for 8 hours a day for 365 days a year and technical support for treatment evaluation and system modifications.

Alternatives 4 and 5, O&M Costs




Alternative Cost Item Item Unit Unit Cost Reference Supporting Details 5 4.3, 6.2 Electricity Year 25,000$ Engineer Estimate Assumes utility expense to operate the equipment and heat the treatment control buildings.

5 4.4, 6.3 Treatment Control Building Maintenance Year Calc in Summary Engineer Estimate Capital maintenance includes expenses for maintaining and replacing equipment.

5 5.1 Performance Monitoring Yrs 1-5 Samples/Year 6,000$ Engineer Estimate and Vendor Quotes

Costs include labor, expenses, and laboratory costs for quarterly sampling at 45 groundwater monitoring wells. Analysis inlcudes 25 parameters for monitoring anaerobic bioremediation processes and secondary water quality.

5 6.1 Operations and Management Yrs 6-10 Year Calc in Summary Engineer Estimate Operations and management for years 6-10 is assumed to be 25 percent of operations and management costs for years 1-5.


Costs include labor, expenses, and laboratory costs for annual sampling at 35 groundwater monitoring wells. Analysis inlcudes 12 parameters for monitoring anaerobic bioremediation processes and secondary water quality.


Costs include labor, expenses, and laboratory costs for annual sampling at 35 groundwater monitoring wells. Analysis inlcudes 12 parameters for monitoring anaerobic bioremediation processes and secondary water quality.

4, 5 Multiple Injection Well Maintenance EA 500$ Vendor Quotes Assumes $350/hour for drilling crew and one hour at each well, plus $150 for biofouling treatment.

4, 5 Multiple Annual Groundwater Report Year 20,000$ Engineer Estimate Based on project specific costs for previous annual groundwater monitoring reports.4, 5 Multiple Project Management, O&M Phase Year Calc in Summary Engineer Estimate Based on project specific costs for previous annual groundwater monitoring reports.

4, 5 4.1 Supplemental Amendment Delivery Year Calc in Summary Engineer Estimate Assumed to be 10 percent of initial amendment and delivery costs per year. There is significant uncertainty regarding the quantity of amendments needed.

Notes1 The opinion of probable remedial action cost provided in this table is made on the basis of Barr’s experience and qualifications and represents our best judgment as experienced and qualified professionals familiar with the project.

Appendix B

Sustainability Evaluation Summary

B-1

B. Sustainability Evaluation Summary

Five potential remedial alternatives are evaluated in the vapor intrusion (VI) pathway feasibility study

completed by Barr Engineering Co. (Barr) on behalf of General Mills, Inc. (General Mills). The five remedial

alternatives are described in depth in the main text of the feasibility study. Of the five alternatives, the

costs and benefits of Alternative 4 (enhanced groundwater bioremediation via injection events) and

Alternative 5 (enhanced groundwater bioremediation via recirculation) were considered using a screening

level life cycle assessment (LCA) of the greenhouse gas (GHG) and total energy impacts. SiteWise™, a tool

developed for green and sustainable remediation, was the LCA method used. The impacts considered in

this LCA were the impacts above the baseline level of impacts associated with Alternative 1 (no further

action beyond previous response actions). Impacts associated with Alternative 2 (monitored natural

attenuation) and Alternative 3 (long-term operation and maintenance of SSD systems) were assumed to

be similar to the baseline. Impacts from activities and materials included in the LCA of Alternatives 4 and

5 include those with information readily available from data used in the feasibility study cost analysis.

Exclusions from the LCA are described in the details below.

B.1 Remedial Alternatives Evaluated

Alternative 4 involves installation of injection wells within public and railroad rights-of-way and periodic

injection of carbon substrate and other amendments to support bioremediation of impacted shallow

groundwater. The carbon substrate and amendments would be injected from mobile tanker trucks.

Alternative 5 involves installation of extraction and injection wells within public and railroad rights-of-way,

installation of conveyance piping within rights-of-way, and construction of two treatment control

buildings for operation of a groundwater recirculation system to support bioremediation of impacted

shallow groundwater.

Estimated quantities, equipment use, and fuel consumption were prepared for Alternatives 4 and 5 as part

of the feasibility study cost analysis.

B.2 LCA Type

The LCA presented in this report is a screening-level comparative analysis loosely based on the ISO 14040

framework (ISO, 2006). Although not fully ISO-compliant, the analysis provides useful insights about

tradeoffs. The findings are intended to be used to provide a comparative assessment between

Alternatives 4 and 5 and the baseline. The LCA framework used for this assessment is described in

Table B1.

B-2

Table B1. LCA Framework and Assumptions for Goal and Scope Definition

Goal of the Study:

To characterize potential life cycle impacts for consideration as an assessment comparing remediation alternatives.

To characterize the order of magnitude scale of the potential life cycle impacts for the design life of one or more alternatives.

The intended use of these estimates is for screening-level comparison of conceptual alternatives, similar to how feasibility cost estimates are used.

Functional Unit: Construction, 10 years of system operation, and an additional 20 years of groundwater monitoring.

System Boundary:

Activities related to bioremediation of shallow groundwater.

Operation of the sub-slab depressurization (SSD) systems at individual properties is excluded from the analysis. These impacts are considered to be "baseline" impacts.

Impacts related to bioremediation are considered to be in addition to the baseline impacts common to all alternatives.

Assumptions and

Limitations:

Impacts from certain activities or materials are excluded if reliable information is not available. These include: potential demolition of existing property on potential treatment plant sites, building materials for exterior of treatment buildings, equipment in treatment buildings (proprietary).

All excavated soil is assumed to be reused at the project (refilling trenches and soil cuttings from well installation) or beneficially used in the local area. It is assumed no soil will be landfilled.

End of life impacts are not included in this analysis.

The potential life cycle impact quantifications may not conform to specific global or national reporting methodology(s).

Impact Categories and

Assessment Method:

Assessment method is U.S. Army Corps of Engineers SiteWise™ and includes total energy and GHG impacts.

Normalization and Weighting:

Weighting is not included in this assessment. Normalization is only included in SiteWise™ in the global warming potential assessment as carbon dioxide equivalents for all GHG emissions.

B.3 Life Cycle Inventory (LCI)

B.3.1 Definition

A Life Cycle Inventory (LCI) is defined in ISO 14040 as “the phase of the life cycle assessment involving the

compilation and quantification of inputs and outputs for a product throughout its life cycle.”

The LCI is essentially a process analysis for the assumed functional unit and system boundaries. Data for

each material and process within the system boundary are quantified and generally allocated as energy

inputs, material inputs, outputs, waste, and emissions to air, water, or soil. The LCI input-output analysis

was performed using the SiteWise™ tool.

Per ISO 14040, the LCI results provide the starting point for the life cycle impact assessment.

B.3.2 Inventory Summary

This inventory is the functional unit and system boundary as defined at this time. Material and process

quantities are based on available feasibility designs and cost estimates. A summary of quantities used for

developing the LCI is shown in Table B2.

B-3

Table B2. Life Cycle Inventory for Alternatives 4 and 5

Work Item

Alternative 4 – Enhanced Groundwater Bioremediation via Injection Events

Alternative 5 – Enhanced Groundwater Bioremediation via Recirculating System

Well Construction Materials

Quantity 60 injection wells; 10 monitoring wells

40 injection wells; 10 monitoring wells; 2 extraction wells

Labor Construction (installation, earthwork) Construction (installation, earthwork)

Materials Sand, gravel, bentonite, cement, concrete, steel, stainless steel

Sand, gravel, bentonite, cement, concrete, steel, stainless steel

Transportation Truck trailer – local sourcing; approx. 20 miles

Truck trailer – local sourcing; approx. 20 miles

Well Drilling

Labor Construction (Drilling) Construction (Drilling)

Equipment Hollow stem auger drill rig Hollow stem auger drill rig

Other Local beneficial use of soil cuttings from drilling – no landfilling

Assume local beneficial use of soil cuttings from drilling – no landfilling

Piping

Quantity 5,100 linear feet + 10% for treatment building interior

Labor Construction (Trenching)

Equipment Excavator and roller

Transportation Truck trailer – local sourcing; approx. 20 miles

Materials HDPE

Other Assume excavated soil used to refill trenches – no landfilling

Amendment

Materials 60% vegetable oil, 40% water emulsion

60% vegetable oil, 40% water emulsion

Quantity1 12,100,000 pounds 8,050,000 pounds

Transportation Tanker truck – out of state sourcing; approx. 800 miles

Tanker truck – out of state sourcing; approx. 800 miles

Labor Technical (well monitoring) Technical (well monitoring)

Other 155,000 gallons chase water

Treatment Building

Quantity 2 buildings; 3,500 sq. ft. pad each

Labor Construction (installation, earthwork)

Equipment Excavator, roller

Transportation

Truck trailer – local sourcing; approx. 20 miles

B-4

Work Item



Treatment Building, continued

Materials

Concrete and gravel – only pad materials included

Other

Assume local beneficial use of excavated soil – no landfilling

Recirculation/Treatment

Duration 10 years

Labor Operating engineer

Equipment Electric pumps, mixers, blowers 1 Initial amendment quantity (7,320,000 pounds) for both Alternatives estimated based on a sensitivity analysis as

described in Sections 5.4 and 5.5 of the feasibility study. Subsequent amendment delivery (732,000 pounds) to maintain amendment levels assumed for both Alternatives. Supplemental injection wells and amendment (4,030,000 pounds) assumed for Alternative 4 to target specific locations where substrate delivery may have been limited by advective flow.

B.4 Life Cycle Impact Assessment (LCIA)

B.4.1 Definition

Life Cycle Impact Assessment (LCIA) is defined in ISO 14040 as “the phase of the life cycle assessment

aimed at understanding and evaluating the magnitude and significance of the potential environmental

impacts for a product system throughout the life cycle of the product. LCIA assigns LCI results to impact

categories.”

The assessment serves to allocate the inventory items to predetermined environmental impact categories,

which are then characterized based on the methodology implemented. There was no regionalization of

impacts for this assessment.

B.4.2 Impact Assessment Summary

This study implements methodology set forth in the SiteWise™ Version 3 model. This impact assessment

is for the functional unit and system boundary as defined at this time. SiteWise™ results for project

impacts in categories of global warming potential, energy footprint, accident risk, and water and

electricity consumption are summarized in Table B3. The global warming potential includes the carbon

dioxide equivalent emissions associated with the production of materials used, fuels consumed, and

electricity used. Energy footprint includes the embodied energy of materials used, fuels consumed, and

electricity used. Accident risk is an estimate of potential injuries based on data from the U.S. Department

of Transportation and Bureau of Labor Statistics. Water consumption includes direct water use during

injection and cooling water consumed during the production of electricity used. Electricity used includes

the MWh of electrical usage. Findings for GHG emissions and total energy used (footprint) are also

illustrated on Figure B1 and Figure B2.

B-5

Table B3. Environmental Impact Assessment Summary

Impact Category Characterization Factor



Global Warming Potential (GWP), Air

Metric tons CO2-eq

3,800 4,400

Energy Footprint MMBTU 66,000 70,000

Water Consumption Gallons 155,000 1,170,000

Electricity Consumption MWH 0 2,300

Accident Risk, Injury Potential accidents 1.0 4.0

Figure B1. Greenhouse Gas Footprint Comparison of Alternatives 4 and 5

0.00

500.00

1000.00

1500.00

2000.00

2500.00

3000.00

3500.00

4000.00

Alternative 4 Alternative 5

Me

tric

To

ns

GHG Emissions

Injection and recirculation

Construction Equipment

Transportation

Amendment

Construction Materials

Well Materials

0.00

500.00

1000.00

1500.00

2000.00

2500.00

3000.00

3500.00

4000.00

4500.00

5000.00


Met

ric

Ton

s

GHG Emissions



Transportation

Amendment


Well Materials

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000


Met

ric

Ton

s

GHG Emissions



Transportation

Amendment


Well Materials

B-6

Figure B2. Total Energy Footprint Comparison of Alternatives 4 and 5

Overall, GHG and total energy impacts from Alternatives 4 and 5 are similar. The details regarding which

activities contribute to overall impacts, however, is slightly different. Amendment use is a major driver to

GHG and total energy impacts for both Alternatives 4 and 5, although impacts from amendment use are

about 50% higher for Alternative 4 compared to Alternative 5. The lower impacts from amendment use in

Alternative 5, however, are more than offset by the GHG and total energy impacts from electrical use

associated with groundwater recirculation.

Impacts from transportation of materials are also sizable contributors to both alternatives and are

primarily associated with the transport of amendment. Impacts from transportation are approximately

50% higher for Alternative 4 compared to Alternative 5. Incremental impacts associated with well

construction are relatively small and similar for Alternatives 4 and 5. Impacts from construction materials

and equipment are also relatively small, but approximately two and a half times higher for Alternative 5

compared to Alternative 4.

The GHG impacts associated with each alternative are compared to equivalencies determined by the EPA

to provide an estimate of the order of magnitude of the impacts. The GHG impacts from Alternative 4 are

equivalent to the combined impact of 800 passenger vehicles driven for one year or 428,000 gallons of

gasoline consumed above the baseline. The GHG impacts from Alternative 5 are equivalent to the

combined impact of 925 passenger vehicles driven for one year or 495,000 gallons of gasoline consumed

above the baseline.

0.00E+00

1.00E+04

2.00E+04

3.00E+04

4.00E+04

5.00E+04

6.00E+04

7.00E+04


MM

BTU

Total Energy Used



Transportation

Amendment


Well Materials

0.00E+00

1.00E+04

2.00E+04

3.00E+04

4.00E+04

5.00E+04

6.00E+04

7.00E+04

8.00E+04


MM

BTU

Total Energy Used



Transportation

Amendment


Well Materials

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000


MM

BTU

Total Energy Used



Transportation

Amendment


Well Materials

B-7

B.5 Limitations

The following limitations should be recognized for this LCA study:

The impact assessment should be used for evaluating the factors identified in the goal and scope.

The impact assessment is comparative and should be used for evaluating the scenarios as defined

herein.

The findings should not be used as an absolute, stand-alone footprinting assertion for any single

scenario assessed. Rather, the findings are intended to be used for comparative purposes for the

scenarios presented.

The methodology may not conform to the requirements of third-party reporting entities, such as

Climate Registry or other formalized reporting protocols.

The LCA does not provide estimates of actual risk and is simply a screening tool to allow

consideration and quantification of the potential for impacts.

This analysis focuses on normal operations and is not intended for assessment of accidental

situations (e.g. accidental amendment spills).

The findings are intended to be used to inform decision making and assist in scoping potential

detailed analyses in the future.

B.6 Conclusions

The boundaries of this LCA include impacts above the baseline level of Alternative 1. This assessment

indicates that both Alternative 4 and Alternative 5 have probable life cycle impacts significantly greater

than the baseline impacts associated with all five alternatives. The probable impacts associated with

Alternative 5 are higher than those associated with Alternative 4.

B.7 References

International Standards Organization (ISO), 2006. ISO 14040:2006, Environmental Management – Life Cycle

Assessment – Principles and Framework. 2006.

U.S. Environmental Protection Agency (EPA), 2016. Greenhouse Gas Equivalencies Calculator, available at

https://www.epa.gov/energy/greenhouse-gas-equivalencies-calculator. Accessed April 2016.

U.S. Environmental Protection Agency (EPA), 1993. Life-Cycle Assessment: Inventory Guidelines and

Principles, Office of Research and Development. February 1993.

U.S. Navy, U.S. Army Corps of Engineers, Battelle. SiteWise™ Version 3 Tool for Green and Sustainable

Remediation. 2013.

https://www.epa.gov/energy/greenhouse-gas-equivalencies-calculator