USACE_2004_Final_Record_of_Decision_AOC_50_Devens.pdf

SDMS DocID 000201577

FINAL

RECORD OF DECISION

AOC 50, Devens, Massachusetts January 22, 2004

Table of Contents

PART 1 : THE DECLARATION................................................................................................................. i ...............................................................................................................SITE NAME AND LOCATION i

.............................................................................................STATEMENT OF PURPOSE AND BASIS i STATE CONCURRENCE .................................................................................................................. i ASSESSMENT OF SITE ......................................................................................................................... i

...................................................................................DESCRIPTION OF THE SELECTED REMEDY i

STATUTORY DETERMINATIONS

................................................................................................DATA CERTIFICATION CHECKLIST iv ..............................................................................................................AUTHORIZING SIGNATURES v

......................................................................................................PART 2: THE DECISION SUMMARY 1 ............................................................1.0 SITE NAME, LOCATION, AND DESCRIPTION 1

....................................................2.0 SITE HISTORY AND ENFORCEMENT ACTIVITIES 1

2.1 LAND USE AND RESPONSE HISTORY

2.1.1 Fueling Systems

2.1.2 Drywell, Tetrachloroethene Drum Storage Area, and Cesspool

.............................................................................................................................2.1.2.1 Drywell 3 .............................................................................2.1.2.2 Tetrachloroethene Drum Storage Area 3

2.1.2.3 Cesspool

..............................................................................................2.2 ENFORCEMENT HISTORY 4

.....................................................................................3.0 COMMUNITY PARTICIPATION 5

4.0 SCOPE AND ROLE OF THE RESPONSE ACTION

5.0 SUMMARY OF SITE CHARACTERISTICS

5.1 AOC 50 CONTAMINANT CHARACTERIZATION

............................................................................................................5.1.1 Soil Characterization 7

.................................................................................................5.1.1.1 Fuel-Related Compounds 7

5.1.1.2 PCE and Related Compounds

..............................................................................................Groundwater Characterization 8 ...........................................................................................CONCEPTUAL SITE MODEL 9

..................CURRENT AND POTENTIAL FUTURE LAND AND RESOURCE USES 10

SUMMARY OF SITE RISKS

HUMAN-HEALTH RISK ASSESSMENT

...................SCREENING-LEVEL ECOLOGICAL RISK ASSESSMENT SUMMARY 16

BASIS FOR RESPONSE ACTION

PRINCIPAL THREAT WASTES

GENERAL STATUTORY REQUIREMENTS AND REMEDIAL ACTION

OBJECTIVES

APPLICABLE OR RELEVANT AND APPROPRIATE REQUIREMENTS

Chemical-Specific ARARs Location-Specific ARARs Action-Specific ARARs

........................................................................................Massachusetts Contingency Plan 22 .........................................................................................................CLEANUP LEVELS 23

................................................................................Interim Groundwater Cleanup Levels 23 .................................................................................................Porewater Cleanup Levels 24

.............................................................................DESCRIPTION OF ALTERNATIVES 25

DESCRIPTION OF ALTERNATIVES FOR AOC 50

....................................................................................................Alternative 1: No Action 25

Alternative 2: Soil Vapor Extraction. Monitored Natural Attenuation. Institutional Controls

Alternative 3: Soil Vapor Extraction. Groundwater Extraction. Ex-Situ Treatment by Air Stripping and Carbon Adsorption. Surface Water Discharge. Monitoring. Institutional Controls Alternative 4: Soil Vapor Extraction. In-Well Stripping. Monitoring. Institutional Controls

Alternative 5: Soil Vapor Extraction. Enhanced Reductive Dechlorination. Monitoring.

Institutional Controls Alternative 6: Soil Vapor Extraction. Enhanced Reductive Dechlorination. In-Well Stripping/Aerobic Bioremediation. Monitoring. Institutional Controls Alternative 7: Soil Vapor Extraction. Enhanced Reductive Dechlorination. Zero-Valent Iron. In-Well StrippingIAerobic Bioremediation. Monitoring. Institutional Controls Alternative 8: Soil Vapor Extraction. Chemical Oxidation. In-Well Stripping. Monitoring.

Institutional Controls Alternative 9: Soil Vapor Extraction. Enhanced Reductive Dechlorination. Groundwater Extraction. Ex-Situ Treatment by Air Stripping and Carbon Adsorption. Surface Water Discharge. Monitoring. Institutional Controls

SUMMARY OF THE COMPARATIVE ANALYSIS OF ALTERNATIVES

................................................................................................THRESHOLD CRITERIA 39

PRIMARY BALANCING CRITERIA

MODIFYING CRITERIA

SUMMARY COMPARISON OF ALTERNATIVES

.............................................................................................THE SELECTED REMEDY 41

...........SUMMARY OF THE-RATIONALE FOR SELECTION OF ALTERNATIVE 6 41

Description of Alternative 6 ...................................................................................Summary of Costs for Alternative 6 47 ...................................................................................Expected Outcome of Alternative 6 47

................................................................................STATUTORY DETERMINATIONS 47

..................STATUTORY DETERMINATIONS FOR REMEDIAL ALTERNATIVE 6 48

.....................The Selected Remedy is Protective of Human Health and the Environment 48 ....The Selected Remedy Attains Applicable or Relevant and Appropriate Requirements 48

The Selected Remedial Action is Cost-Effective The Selected Remedy Utilizes Permanent Solutions and Alternative Treatment or Resource

............................................Recovery Technologies to the Maximum Extent Practicable 49 The Selected Remedy Satisfies the Preference for Treatment as a Principal Element Five-Year Review Requirements

DOCUMENTATION OF SIGNIFICANT CHANGES

STATE ROLE

Tables

Figures

Summary of Chemicals of Concern and Medium-Specific Exposure Point Concentrations Cancer Toxicity Data Summary Noncancer Toxicity Data Summary Summary of RME Cancer and Noncancer Risks Screening-level Ecological Hazards Under No Action Synopsis of Federal and State ARARs for Remedial Alternative 6 Lnterim Groundwater Cleanup Levels Derivation of Risk-Based Concentrations for Manganese and Iron Based on Child Residents Interim Porewater Cleanup Levels Comparison of Remedial Alternatives Comparative Analysis of Cost Detailed Cost Backup and Sources of Cost Information Present Value Calculation for Remedial Alternative 6

Site Location Source Area PCE Plume Delineation

Appendices A Administrative Record Index B Declaration of State Concurrence C Responsiveness Summary

Glossary

ABB-ES

AOC

ARAR

AWQC

bgs

BRAC

BTEX

CAA

CAC

c c c s

CERCLA

Cis-1,2-DCE

CMC

CMR

COC

CPC

cvoc

CWA

cY 1,l-DCE

1,2-DCE

1,2-DCP

DNAPL

EPA

EPC

ERA

ERD

FFA

FOST

FS

ft

HI

HHRA

HLA

HQ

IC

IRIS

IRZ

IWS

LTMP

MAAF

MADEP

MCL

MCLG

ABB Environmental Services, Inc.

Area of Contamination applicable or relevant and appropriate requirement Ambient Water Quality Criteria below ground surface Base Closure and Realignment Act benzene, toluene, ethylbenzene, xylene

Clean Air Act Citizens Advisory Committee Criterion Continuous Concentrations Comprehensive Environmental Response, Compensation, and Liability Act cis 1,2-dichloroethene Criterion Maximum Concentration Code of Massachusetts Regulations chemical of concern chemical of potential concern chlorinated volatile organic compound Clean Water Act cubic yard(s)

1,1-dichloroethene 1,2-dichloroethene 1,2-dichloropropane dense nonaqueous phase liquid

Environmental Protection Agency exposure point concentration ecological risk assessment Enhanced Reductive Dechlorination

Federal Facilities Agreement Finding of Suitability to Transfer Feasibility Study feet or foot gallons per minute hazard index human health risk assessment Harding Lawson Associates Hazard quotients

Institutional Controls Integrated Risk Information System In-situ Reactive Zones In-well Stripping long-term monitoring plan

Moore Army Airfield Massachusetts Department of Environmental Protection Maximum Contaminant Level Maximum Containment Level Goals

G loaary

MCP

mg/kg

MMCL

NAPL

NCP

NIPDWR

NPL

O&M

OPS

O W

OSWER

PCE

pH

PID

PP

RAE3

R40 R A W

RCR4

RD

Rf

RfD

RFTA

RI

RME

ROD

SA

SARA

SDWA

SI

SMCL

SVE

TBC

TCE

TPH

TRC

TSCA

VC

VPGAC

VOC

Massachusetts Contingency Plan milligrams per kdogram Massachusetts Maximum Contaminant Level nonaqueous phase liquid National Oil and Hazardous Substances Pollution Contingency Plan National Interim Primary Drinking Water Regulation National Priorities List

Operation and Maintenance Operating Properly and Successfully oxidation reduction potential Office of Solid Waste and Emergency Response tetrachloroethene negative log of the hydrogen ion concentration photoionization detector Proposed Plan

Restoration Advisory Board remedial action objectives Remedial Action Work Plan Resource Conservation and Recovery Act Remedial Design retardation factor reference dose Reserve Forces Training Area Remedial Investigation Reasonable maximum exposure Record of Decision

Study Area Superfund Amendments and Reauthorization Act Safe Drinking Water Act Site Investigation Secondary Maximum Containment Level soil vapor extraction to be considered trichloroethene total petroleum hydrocarbons Technical Review Committee Toxic Substances Control Act micrograms per gram micrograms per kilogram micrograms per liter U.S. Environmental Protection Agency underground storage tank vinyl chloride vapor-phase granular activated carbon volatile organic compound

Glossary

ZVI zero-valent iron

Part 1:The Declaration

PART 1: THE DECLARATION

SITE NAME AND LOCATION

Area of Contamination 50 Devens Reserve Forces Training Area Devens, Massachusetts

CERCLIS ID MA72 10025154

STATEMENT OF PURPOSE AND BASIS

This decision document presents the U.S. Army's and U.S. Environmental Protection Agency (USEPA) selected remedial action alternative for Area of Contamination (AOC) 50 at the Devens Reserve Forces Training Area (RFTA) (formerly Fort Devens), Devens, Massachusetts (Figure 1). It was developed in accordance with the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA), 42 USC $ 5 9601 et seq., as amended by the Superfund Amendments and Reauthorization Act (SARA) of 1986, and, to the extent practicable, the National Oil and Hazardous Substances Pollution Contingency Plan (NCP) 40 CFR Part 300, et seq., as amended. The Chief Base Realignment and Closure Office (BRACO) and the Director of the Office of Site Remediation and Restoration, USEPA Region 1, have been delegated the authority to approve this Record of Decision (ROD).

This decision is based on the Administrative Record that has been developed in accordance with Section 113(k) of CERCLA. The Administrative Record is available for public review at the Devens BRAC Environmental Office, Devens, Massachusetts, and at the Ayer, Harvard, Lancaster, and Shirley Town Libraries. The Administrative Record Index (Appendix A) identifies each of the items considered during selection of the remedial action.

STATE CONCURRENCE

The Commonwealth of Massachusetts concurs with the selected remedy. Appendix B contains a copy of the Declaration of State Concurrence.

ASSESSMENT OF SITE

The response actions selected in this ROD are necessary to protect public health or welfare or environment from actual or threatened releases of hazardous substances to the environment.

DESCRIPTION OF THE SELECTED REMEDY

The selected remedy for AOC 50 is Alternative 6: Soil Vapor Extraction, Enhanced Reductive Dechlorination (with solubilized inorganic controls), In-Well StrippingIAerobic Bioremediation, Monitoring, and Institutional Controls (IC). In addition, Geochemical additives and In-situ Chemical Oxidation are included as contingencies to address inorganics and volatile organic compounds, respectively, in the event that monitoring data indicate that implementation of these contingencies is warranted. This remedy is a comprehensive approach that addresses all current and potential future risks caused by groundwater contamination and mitigates residual soil contamination in the source area.

The AOC 50 Source Area comprises less than 2 acres and surrounds Buildings 3803 (the former parachute shop), 3840 (the former parachute shakeout tower), 3824 (a gazebo), and 3801 (the former 1 0 ~ Special Forces airplane parachute simulation building). Sources of groundwater contamination within AOC 50 include two World War I1 fueling systems, a drywell, and the tetrachloroethene (PCE) drum storage area; these sources are collectively referred to as the Source Area (Figure 2). Other potential sources of contamination may include a former cesspool and floor drain associated with Buildings 3801 and 3840. Although these sources have been removed or taken out of commission, groundwater underlying AOC 50 contains elevated concentrations of volatile organic compounds (VOCs) most notably

PCE.

Site investigations and a risk assessment indicate that soil does not pose an unacceptable risk and there are no complete exposure pathways to the groundwater plume at AOC 50 under the current land use.

However, soil contamination in the Source Area is a continuing source of groundwater contamination and will therefore be mitigated. Exposure to contaminated groundwater would only occur if the land use changes or if groundwater associated with the AOC is used in the future. Based on the results of the human health risk assessment (HHRA), the following future site and groundwater uses are associated with health risks that exceed USEPA target cancer-risk ranges and non-cancer thresholds:

Potable use of the groundwater associated with the Source Area and the Southwest Plume by a full-time commercial/industria1 worker.

Use of the groundwater associated with the Source Area in an "open" industrial process (e.g., washing and spraying) by a full-time cornmercial/industria1 worker.

Unrestricted potable use of the groundwater associated with the Source Area, and North and Southwest Plumes (e.g., consumption by residents).

Construction and occupation of residential dwellings over the Source Area (vapor intrusion).

Based on the results of the screening-level ecological risk assessment (ERA), the following potential risks are associated with groundwater discharging to the Nashua River:

Low risk predicted for benthic organisms under current conditions.

Low to moderate risk predicted for benthic organisms under future conditions.

Risks for pelagic organisms were determined to be negligible under all scenarios.

The chemicals of potential concern (CPCs) contributing to potential future human health risk greater than the benchmarks of 1x10-~or a hazard index of one at the site include PCE, trichloroethene (TCE), 1,l-dichloroethene (1,l -DCE), cis-1,2-dichloroethene (cis-1,2-DCE), vinyl chloride (VC), 1,2-dichloropropane, methylene chloride, 1,2-dichloroethane,benzene, arsenic, lead, nitrate, and manganese.

The key components of the selected remedy at AOC 50 consist of the following:

Soil Vapor Extraction Enhanced Reductive Dechlorination (with solubilized inorganics controls) In-Well StrippingtAerobic Bioremediation Geochemical Additives (contingency) In-SituChemical Oxidation (contingency) Monitoring Institutional Controls o Existing zoning that prohibits residential use o Other applicable regulations and institutional controls to restrict future groundwater use, manage storm-water recharge under development scenarios, manage construction so that it would not interfere with the remedy, and allow site access as outlined below

Institutional Control Inspections Five-year Site Reviews

This remedy relies on existing property zoning, and access and land use control measures with the property owner to ensure the North Plume property remains in non-residential land use, groundwater pumping is restricted, the remedy is protected, and site access is available to the Army. The remedy relies on existing lease terms and future transfer deed restrictions to ensure that the Source Area property remains in non-residential land use, the groundwater is not ingested and groundwater vapors are not inhaled, groundwater pumping is restricted, storm-water recharge is adequately managed under development scenarios, the remedy is protected, and site access is available to the Army. The remedy relies on existing zoning and legal agreements to ensure that the Southwest Plume property remains in non-residential land use, groundwater pumping is restricted, master planning to adequately manage storm-water recharge under development scenarios, the remedy is protected, and site access is available to the Army. These restrictions shall be implemented, monitored, reported on, and enforced by the Army and shall be maintained until the concentration of hazardous substances in the soil and the groundwater beneath have been reduced to levels that allow for unlimited exposure and unrestricted use. If future land use at AOC 50 is inconsistent with these institutional controls, then the site exposure scenarios for human health and the environment would be re-evaluated to assess whether this response action remains appropriate. To the extent practical, remedial activities will be performed with minimal alteration and disturbance to the property. Long-term environmental monitoring will be implemented to assess the success of restoration activities and to monitor for attainment of groundwater cleanup levels.

STATUTORY DETERMINATIONS

The selected remedy for AOC 50 is protective of human health and the environment, attains federal and state environmental and facility siting requirements that are applicable to the remedial action (applicable or relevant and appropriate requirements), is cost effective, and utilizes permanent solutions and alternative treatment technologies to the maximum extent practicable. The NCP articulates nine evaluation criteria to be used in assessing the individual remedial alternative. The selected remedy was based on a comparison of the nine criteria and meets the goals of protecting human health and the environment, maintaining protection over time, and minimizing untreated waste. Because the remedy

Part I :The Declaration will result in hazardous substances, pollutants or contaminants remaining on-site above levels that allow for unlimited use and unrestricted exposure during the period of operation of the remedy, a statutory review will be conducted within five years after initiation of remedial action to ensure that the remedy is, or will be, protective of human health and the environment.

DATA CERTIFICATION CHECKLIST

The following information is contained in the Decision Summary section of this Record of Decision.

Additional information can be found in the Administrative Record file.

Chemicals of concern and their respective concentrations Baseline risk represented by the chemicals of concern Cleanup levels established for chemicals of concern and the basis for those levels The process by which source materials constituting principal threats are addressed Current and reasonably anticipated future land use assumptions and the current and potential future beneficial uses of groundwater used in the baseline risk assessment Potential land and groundwater use that will be available at the site as a result of the selected remedy Estimated capital, annual operation and maintenance, and total present worth costs; discount rate;

and the number of years over which the remedy cost estimates are projected Key factors that led to selection of the remedy

AUTHORIZING SIGNATURES

The foregoing represents the selection of a remedial action by the US . Department of the Army and the U. S. Environmental Protection Agency, with the concurrence of the Commonwealth of Massachusetts Department of Environmental Protection (MADEP).

Concur and recommend for immediate implementation:

U.S. DEPARTMENT OF THE ARMY

ec meA a w e a \ Glynn D. Ryan Chief, Atlanta Field Office Department of the Army Base Realignment and Closure

COL, GS

Chief, Base Realignment And Closure Office

U.S. ENVIRONMENTAL PROTECTION AGENCY

a a .%K!~IOA Susan Studlien A&m@irector Office of Site Remediation and Restoration Region 1

Date

AUTHORIZING SIGNATURES

The foregoing represents the selection of a remedial action by the U.S. Department of the Army and the U. S. Environmental Protection Agency, with the concurrence of the Commonwealth of Massachusetts Department of Environmental Protection (MADEP).

Concur and recommend for immediate implementation:

U.S. DEPARTMENT OF THE ARMY

chief, ~ t l a n t aField Office Department of the Army Base Realignment and Closure

And Closure Office

U.S. ENVIRONMENTAL PROTECTION AGENCY

Date

8 1 APR 2UU4

Date

Susan Studlien Acting Director Office of Site Remediation and Restoration Region 1

Part 2 : Decision Summary

PART 2: THE DECISION SUMMARY

1.0 SITE NAME, LOCATION, AND DESCRIPTION

This Record of Decision (ROD) addresses past releases to soil and groundwater at Area of Contamination (AOC) 50 at Devens Reserve Forces Training Area (RFTA), Devens Massachusetts (Figure 1). The Devens RFTA, formerly Fort Devens, is located in the Towns of Ayer and Shirley (Middlesex County) and Harvard and Lancaster (Worcester County), approximately 35 miles northwest of Boston, Massachusetts, A Federal Facilities Agreement (FFA) between the U.S. Department of the Army and the U.S. Environmental Protection Agency (USEPA) establishes the Army as the lead agency for developing, implementing, and monitoring response actions at Devens RFTA in accordance with the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) and, to the extent practicable, the National Oil and Hazardous Substances Pollution Contingency Plan (NCP). Fort Devens is identified by the CERCLIS ID number MA72 10025154.

AOC 50 is located on the northeastern boundary of the former Moore Army Airfield (MAAF), within the former North Post portion of Devens RFTA, Ayer, Massachusetts. The AOC 50 Source Area (Figure 2) comprises less than 2 acres and includes Buildings 3803 (the former parachute shop), 3840 (the former parachute shakeout tower), 3824 (a gazebo), and 3801 (the former loh Special Forces airplane parachute simulation building). Sources of groundwater contamination within AOC 50 include two World War I1 fueling systems, a drywell, and the tetrachloroethene (PCE) drum storage area; these sources are collectively referred to as the Source Area. Other potential sources of contamination may include a former cesspool and floor drain associated with Building 3840. Although these sources have been removed or taken out of commission, groundwater underlying AOC 50 contains elevated concentrations of volatile organic compounds (VOCs) most notably PCE. The primary area of groundwater contamination at AOC 50 is referred to as the Southwest Plume, which extends from the Source Area approximately 3,000-feet downgradient to the Nashua River.

2.0 SITE HISTORY AND ENFORCEMENT ACTIVITIES

This section provides a brief description of the historical land use at Devens RFTA, investigative and response history at AOC 50, and enforcement history.

2.1 LAND USE AND RESPONSE HISTORY

Fort Devens was established in 1917 as Camp Devens, a temporary training camp for soldiers from the New England area. In 1931, the camp became a permanent installation and was renamed Fort Devens.

Throughout its history, Fort Devens served as a training and induction center for military personnel, and as a unit mobilization and demobilization site. All or portions of this function occurred during World Wars I and 11, the Korean and Vietnam conflicts, and operations Desert Shield and Desert Storm.

Fort Devens was identified for cessation of operations and closure under Public Law 101-510, the Defense Base Closure and Realignment Act (BRAC) Act of 1990, and was officially closed in September

1996. Portions of the property formerly occupied by Fort Devens were retained by the Army for reserve forces training and renamed the Devens RFTA. Areas not retained as part of the Devens RFTA were transferred to new owners for reuse and redevelopment.

All but approximately 14 acres of the former M A G (approximately 246 acres total) were transferred to Mass Development in 1997 for reuse. Currently, the airfield is closed to aircraft traffic and is used by the Massachusetts State Police for training and vehicle storage. The MAAF is zoned for Special Use I1 and Innovation and Technology Business. Under the Devens Reuse Plan (November 14, 1994), Special Use I1 and Innovation and Technology Business includes a broad range of industrial, light industrial, office, and research and development uses. There are currently no plans for development of the MAAF, although the area can be developed if interested parties are identified. The Devens RFTA retained approximately 9.1 acres of the former airfield for vehicle storage and maintenance and the 4.3 acre parcel which includes the AOC 50 Source Area.

Sources of contamination within AOC 50 include two World War I1 fueling systems, a drywell, the PCE drum storage area and cesspool. Each of these sources is briefly discussed below.

2.1.1 Fueling Systems

During World War 11, two fueling systems were used in the area subsequently designated AOC 50; one system was used for fueling aircraft and trucks (System A), and the other for fueling trucks (System B).

These systems were not used for refueling operations after the late 1940s (Biang, et al., 1992). The two separate fueling systems were filled by gasoline shipments on a Boston & Maine Railroad spur (which no longer exists) located adjacent to Fueling System B ( Figure 2).

Releases of fuel associated with incidental spills at the former aircraft fuel pits, truck-fill stands, and railroad fuel-delivery points were considered possible sources of contamination. Because the systems were approximately 50 years old, the underground storage tanks (USTs) were also considered possible continuing sources of releases. The potential for migration of contaminated groundwater to the Nashua River was a concern. At the time of the initial Site Investigation (SI) in 1992 (ABB, 1993), several fueling-system components were still visible in their original locations.

Fort Devens removed all of these components in 1992. In addition, approximately 450 tons of contaminated soil was removed from under the water-separator, water-control pits, and three 25,000-gallon USTs. The excavation extended to a depth of approximately 18 ft below ground surface (bgs) due to the presence of water in the excavation. All excavations were backfilled to grade. Field screening results and post-excavation sample analyses are presented in the Remedial Investigation (RI) prepared by Harding Lawson Associates (HLA, 2000a).

Part 2: Decision Summary

2.1.2 Drywell, Tetrachloroethene Drum Storage Area, and Cesspool{ TC " 1.4.1.2 Drywell and Tetrachloroethene Drum Storage Area" \f C \I " 4 " }

In 1969, Building 3840 was constructed and attached, via an enclosed walkway, to Building 3803. In addition, two large sinks and a janitors' room were added to Building 3803. The design drawings for Building 3840 indicate that a floor drain was constructed in the center of the concrete floor. This floor drain, the additional sinks in Building 3803, and the roof drains for Building 3840 were piped to a drywell located approximately 20 ft northeast of Building 3840 (Figure 2). The concrete drywell was approximately 5 ft in diameter and 8 ft deep, with an open bottom and a cover on the top. This drywell received wash water, rainwater, and PCE waste associated with parachute cleaning activities.

The drywell near Building 3840 and associated piping were removed for the Army by Roy F. Weston Corporation between November and December 1996 (Weston 1997). The resulting excavation was approximately 9.5-ft deep and covered an area approximately 21 feet (ft) by 30 ft, equating to approximately 225 cubic yards (cy) of soil (in-place). Details regarding the removal activities are documented in a September 1997 report titled Removal Action Report; Dty Well, Cesspool, and Fuel Oil Underground Storage Tank; Area of Contamination (AOC) 50, Moore Army Air Field, Devens, MA (Weston, 1997).

In addition to the removal of the drywell, a 750-gallon fuel storage UST associated with the Building 3840 heating system was also removed. In connection with the tank removal, approximately 787 gallons of oil, water, and residual sludge were recovered from the tank and approximately 25 cy of contaminated soil were excavated. Solid and liquid wastes generated during removal of the drywell and fuel storage UST were taken off-site for proper treatment and disposal.

2.1.2.2 Tetrachloroethene Drum Storage Area

A PCE drum storage area east of Building 3801 was identified during field investigation activities completed in 1992. Historical records and interviews with former Fort Devens personnel indicate this area was used to store single drum quantities of PCE (HLA, 2000a). The PCE was used by Army personnel in Buildings 3803 and 3840 for spot cleaning of parachutes. Parachute cleaning was performed only as needed to maintain the integrity of the parachute material. Unused PCE was either reused or may have been washed down into the drywell system associated with Buildings 3803 and 3840. This information was supported by a review of the historic hazardous waste manifests, which did not include the removal of waste chlorinated solvents from AOC 50 (Mott, 1997). The use of this area for drum storage was discontinued in 1992. The length of time or total number of drums stored in this area of AOC 50 is unknown.

Based on the results of various field investigations, PCE was detected in vadose zone soils beneath the former drum storage area and was likely contributing to PCE impacts in groundwater. An interim removal action for PCE-contaminated soil at the former drum storage area was planned and implemented as a source-control measure while additional investigation activities were conducted across the site. An in-situ soil vapor extraction (SVE) system was installed adjacent to the former drum storage area in December 1993 and January 1994. Five soil vapor extraction wells (SVE-I through SVE-5) were installed, one in the center of the presumed PCE source and four on the periphery (Figure 2).

Operation of the SVE system began in February 1994 and continued through July 1996. Operation & Maintenance (O&M) data collected between February 1994 and July 1996 indicated that approximately 240 pounds (approximately 18 gallons) of PCE were successfully recovered in the vapor phase. Details regarding the installation, operation, and performance of the SVE system between February 1994 and July 1996 are documented in a November 1996 report titled Summary Report, SVE Monitoring, AOC 50 (ABB, 1996a).

The SVE system was operated again for brief periods in December 1998, May and June 1999, and October and November 1999. The brief periods of SVE system operation after the 1996 shut down were conducted to evaluate the concentration of PCE in the soil vapor, under equilibrium conditions. In general, recovered vapor concentrations were either below the detection limits of a photoionization detector (PID), or after a brief peak observed when the system was restarted, quickly attenuated within minutes. No appreciable mass of PCE was recovered during the brief periods of SVE operation between 1998 and 1999.

2.1.2.3 Cesspool

A cesspool associated with the bathroom in Building 3803 was identified on the site drawings; it appears to be the only septic system structure for either building. The concrete and rubble cesspool was approximately 10 ft in diameter and 9 ft deep with an open bottom and a cover on the top. The drywell and cesspool were investigated as potential contaminant sources for the various volatile contaminants, including PCE detected in soil and groundwater during previous investigations.

The cesspool was removed concurrent with the drywell and UST associated with Building 3840. During the cesspool removal activities, a total of 25 cy of soil, sludge, and concrete were excavated and taken offsite for treatment and disposal.

2.2 ENFORCEMENT HISTORY

On December 2 1, 1989, Fort Devens was placed on the National Priorities List (M'L) under CERCLA as amended by the Superfund Amendments and Reauthorization Act (SARA) to evaluate and implement response actions to clean up past releases of hazardous substances, pollutants, and contaminants. An FFA to establish a procedural framework for ensuring that appropriate response actions are implemented at Fort Devens was developed and signed by the Anny and the USEPA Region I on May 13, 1991, and finalized on November 15, 1991. AOC 50 is considered a sub-site to the entire installation.

In 1996, the Army initiated an RI for AOC 50. The RI report was issued in January 2000. The purpose of the RI was to determine the nature and extent of contamination at the AOC, assess human health and ecological risks, and provide a basis for conducting a Feasibility Study (FS).

Part 2:Decision Summary

An FS that evaluated remedial action alternatives for cleanup of groundwater was issued in December 2002. The FS identified and screened nine remedial alternatives and provides a detailed analysis of these remedial alternatives to allow decision-makers to select a remedy for cleanup of AOC 50.

In January 2003, the Proposed Plan (PP) detailing the Army's preferred remedial alternatives for AOC 50 was issued for public comment. Technical comments presented during the public comment period are included in the Administrative Record. Appendix C of this ROD, the Responsiveness Summary, contains a summary of these comments and the Army's responses, and describes how these comments affected the remedy selection.

3.0 COMMUNITY PARTICIPATION

The Army has held regular and frequent informational meetings, issued fact sheets and press releases, and held public meetings to keep the community and other interested parties informed of activities at AOC 50.

Community interest in AOC 50 was high throughout this process through the issuance of the PP.

In February 1992, the Army released a community relations plan that outlined a program to address community concerns and keep citizens informed about and involved in remedial activities at Fort Devens.

As part of this plan, the Army established a Technical Review Committee (TRC) in early 1992. The TRC, as required by SARA Section 21 1 and Army Regulation 200-1, included representatives from USEPA, U.S. Army Environmental Center, Devens RFTA, Massachusetts Department of Environmental Protection (MADEP), local officials, and the community. Until January 1994, when it was replaced by the Restoration Advisory Board (RAB), the committee generally met quarterly to review and provide technical comments on schedules, work plans, work products, and proposed activities for the study areas (SAs) and AOCs at Devens RFTA. The RI, FS, and PP reports, and other related support documents were all submitted to the RAB for their review and comment.

The Army, as part of its commitment to involve the affected communities, forms a RAB when an installation closure involves transfer of property to the community. The Fort Devens RAB was formed in February 1994 to add members of the Citizen's Advisory Committee (CAC) to the TRC. The CAC had been established previously to address Massachusetts Environmental Policy ActIEnvironmental Assessment issues concerning the reuse of property at Devens RFTA. The RAB consists of representatives from the Army, USEPA Region I, MADEP, local governments and citizens of the local communities. It meets monthly and provides advice to the installation and regulatory agencies on the Devens RFTA cleanup programs. Specific responsibilities include: addressing cleanup issues such as land use and cleanup goals, reviewing plans and documents, identifying proposed requirements and priorities, and conducting regular meetings that are open to the public.

On January 20, 2003, the Army issued the PP, to provide the public with an explanation of the Army's proposal for remedial action at AOC 50. The PP also described the opportunities for public participation and provided details on the upcoming public comment period and public meeting.

On January 22, 2003, the Army published a public notice announcing the PP, the date for a public information meeting, and the start and end dates of a 30-day public comment period in the Harvard Post and papers of the Nashoba Publishing Company (Groton Landmark, Harvard Hillside, Pepperell Free Press, The Public Spirit, Ayer, Shirley Oracle, and Townsend Times). The Army also made the PP available to the public at the public information repositories at the Ayer Public Library, the Hazen Memorial Library in Shirley, the Harvard Public Library, and the Lancaster Public Library, or by request from the Devens BRAC Environmental Office.

From January 23 through February 20, 2003, the Army held a 30day public comment period to accept public comments on the Proposed Plan. On January 30, 2003, the Army held an informal public information meeting at Devens RFTA to present the Army's Proposed Plan to the public and to provide the opportunity for open discussion concerning the PP.

On February 7, 2003, the Army published a public notice announcing the PP, the date for a public hearing in the Harvard Post and papers of the Nashoba Publishing Company (Groton Landmark, Harvard Hillside, Pepperell Free Press, The Public Spirit, Ayer, Shirley Oracle, and Townsend Times). On February 19, 2003, the Army held a Public Hearing to present the PP and accept formal verbal or written comments from the public. A transcript of this hearing, formal public comments, and the Army's response to comments are included in the attached Responsiveness Summary (see Appendix C). A written request to extend the comment period for the PP from February 20, 2003 to March 7, 2003 was accepted by the BRAC office on February 20, 2003.

All supporting documentation for the decision regarding AOC 50 is contained in the Administrative Record for review. The Administrative Record is a collection of all the documents considered by the Army in choosing the plan of action for AOC 50. The Administrative Record is available for public review at the Devens BRAC Environmental Office and at the Town Repositories. An index to the Administrative Record is available at the BRAC Environmental Office located at 30 Quebec Street.

Devens, Massachusetts and the index is provided as Appendix A.

4.0 SCOPE AND ROLE OF THE RESPONSE ACTION

This ROD documents the selection of the remedial action proposed for control of site risk at AOC 50.

Implementation of Alternative 6 (Soil Vapor Extraction, Enhanced Reductive Dechlorination, In-Well Strippingl Aerobic Bioremediation, Iron Injection [contingency], In-Situ Chemical Oxidation [contingency], Monitoring, Institutional Controls) at AOC 50 will protect possible future commerciaVindustria1 workers and unrestricted use (residents) from exposure to groundwater via ingestion andlor inhalation. Specifically, implementation of Alternative 6 in the following specific areas will:

Source Area Protect potential residential and commercial/industria1 receptors from ingesting contaminated groundwater;

Protect comrnercial/industrial workers from inhaling vapors released from groundwater used as "open" process water;

Prevent potential constructionloccupation of residential dwellings and inhalation of vapors released from contaminated groundwater to indoor air;

Southwest Plume Protect potential residential and commercial/industria1 receptors from ingesting contaminated groundwater;

Prevent low to moderate potential ecological effects to benthic organisms; and

North Plume Protect potential residential receptors from ingesting contaminated groundwater.

5.0 SUMMARY OF SITE CHARACTERISTICS

The following subsections summarize the nature and distribution of contamination presented in the AOC 50 RI report (HLA, 2000a), FS report (ARCADIS, 2002a), and 2001 Groundwater Sampling Report (ARCADIS, 2002b)

5.1 AOC 50 CONTAMINANT CHARACTERIZATION

Contaminated media at AOC 50 previously included surface and subsurface soil and groundwater;

however, because of removal actions that took place between 1992 and 1999, groundwater is considered the medium of concern. The nature and extent of contamination is described in detail in the final RI report and is summarized in the FS report and in the following subsections.

5.1.1 Soil Characterization

Soil contamination at AOC 50 can be divided into two types: 1) petroleum hydrocarbons found in vadose zone soils near the former Fueling System B, and 2) PCE and related compounds in soils above and below the water table in the former drywell and drum storage areas.

5.7.1.1 Fuel-Related Compounds

During the 1992 Site Investigation, soil was collected from 6 borings for laboratory analysis that revealed total petroleum hydrocarbon (TPH) concentrations ranging from less than 27.7 milligrams per kilogram (mgkg) in a surface sample (near the former truck stand) to 162 mg/kg 15-ft bgs south of the former Fueling System B. Xylenes, ethylbenzene, and toluene were detected in soil samples taken from the Fueling System B excavations in December 1992. A soil boring installed in the middle of the former Fueling System B UST grave during the 1996 RI detected benzene concentrations in soil ranging from

0.0046 mg/kg at 18 to 22 ft bgs to 0.020 mg/kg at 10 ft bgs. In this boring, ethylbenzene concentrations ranged from 0.0022 mgkg at 15 ft bgs to 0.0083 mgkg at 18 ft bgs, toluene concentrations ranged from

0.0087 mg/kg at 15 ft bgs to 0.020 mgkg at 18 ft bgs, and xylenes concentrations ranged from 0.0083 mgkg at 20 ft bgs to 0.071 mgkg at 10 ft bgs. During a 1994 Phase I1 Site Investigation, only soil from 4 ft bgs in one boring located in the former PCE drum storage area contained benzene, which was detected at a concentration of 0.002 mgkg.

Two soil/sludge samples were collected from the bottom of the drywell in 1996 and field laboratory results indicated there were no detectable levels of benzene, toluene, ethylbenzene, and xylene (BTEX).

A nearby soil boring, contained toluene at 0.0043 mgkg in the 9-foot soil sample. During the 1998 Benzene and Ethylene Dibromide Assessments (HLA, 2000b), soil samples collected near the dry well and downgradient of the Source Area were analyzed for BTEX. No detectable levels of BTEX were found.

5.1.1.2 PCE and Related Compounds

The highest levels of PCE at AOC 50 were detected in soil samples collected in 1993 beneath the Former Drum storage area. The highest concentration was 3,000 pglg in a 7-foot deep sample. This same boring, as well as others in the vicinity, confirmed the limited spatial presence of PCE in soil both above and below the water table (to a depth of approximately 40 ft bgs) in that area. The SVE system operated between 1994 and 1999 significantly reduced PCE levels in vadose soils in that area, as evidenced by low residual concentrations in soil vapor collected by the SVE system.

Field analytical results for subsurface soil samples collected fiom borings used to assess the former drywell indicated that PCE andlor cis-1,2-DCE was present in the soil fiom the approximate bottom of the former drywell to refusal of the borings (i.e., at the top of the glacial till). Concentrations of PCE in soil were as high as 5.5 micrograms per kilogram (pgkg) at 9-foot bgs and 3.2 pgkg 50-foot bgs. The drywell and associated impacted soil (approximately 225 cy) were removed in 1996.

PCE was also detected in the one soil boring drilled adjacent to the former cesspool that was associated with the lavatory in Building 3803. Concentrations were low and ranged fiom an estimated concentration of 0.0044 pg/kg in the 20-ft bgs soil sample to 0.011 pg/kg in the 25-ft bgs soil sample. The former cesspool and approximately 25 cy of soil, sludge and concrete were removed in 1996.

The results from the field and off-site laboratory soil samples indicate that soil contamination in the Source Area at AOC 50 appears to be in the saturated zone from approximately 30 ft bgs to 67 ft bgs below and to approximately 60 ft downgradient of the former drywell. This assessment is based on the analytical data collected from soil borings completed in this area of this site. The field and off-site laboratory results of the soil samples collected fiom the soil boring completed at the former drum storage area, and the area between the former drum storage area and the former drywell, indicate that the PCE contamination in soil is limited to the saturated zone from 12 to 35 ft bgs.

5.1.2 Groundwater Characterization

Groundwater contamination at AOC 50 can be divided into two types: 1) petroleum hydrocarbons and 2) PCE and related compounds found throughout the Site.

Based on the October 2001 site-wide groundwater sampling event performed by ARCADIS (2002b), the AOC 50 groundwater plume contains concentrations of PCE, trichloroethene (TCE), 1,2-dichloroethene (1,2-DCE), and 1,2-dichloropropane (1,2-DCP) above their Maximum Contaminant Levels (MCLs). The laboratory analytical results for the October 2001 groundwater samples at AOC 50 indicate that samples collected from 35 of the 51 monitoring wells did not contain PCE at a concentration above the laboratory method detection limit. The VOC analytical results indicate that groundwater samples from 16 monitoring wells contained PCE at concentrations above the 5 micrograms per liter (pg/L) MCL. The highest concentration of PCE detected in a groundwater sample in October 2001 was 4,300 pg/L. PCE concentrations were generally consistent with previous sampling rounds. In October 2001, there were four exceedances of the TCE MCL (5 pg/L), two exceedances of the cis-1,2-DCE MCL (70 pg/L), and one exceedance of the 1,2-DCP MCL (5 pg/L). In October 200 1, benzene and toluene were detected in a limited number of groundwater samples collected across the site including areas adjacent to and downgradient of former USTs; however, the concentrations of benzene and toluene were below their respective MCLs in all cases. More recent data from 2002 confirms previous analytical data and new well data provides additional plume delineation, but also indicates that PCE concentrations in the Source Area have been detected at greater than 30,000 pg/L. The extent of VOCs in groundwater can generally be delineated by the PCE 5 pg/L contour line as shown on Figure 3.

5.2 CONCEPTUAL SITE MODEL

Based on the site history, geology, hydrogeology, surface water hydrology, and contaminant distribution, a conceptual site model was developed for AOC 50 and is outlined in the FS (ARCADIS, 2002a). Field investigation activities indicate that PCE is the primary constituent of concern. The original source of PCE in groundwater is believed to be the former drywell and former drum storage area. This area is considered the Source Area. The Army discontinued drum storage of PCE in 1992 and removed the drywell (and related soils) in 1996. PCE released from these two areas would migrate vertically through the vadose zone to the aquifer.

Dissolved phase PCE has been detected in groundwater at very low concentrations (less than 10 ug/L) north of Route 2A (North Plume) and at elevated concentrations (greater than 1,000 ug/L) southwest of the Source Area (Southwest Plume). Known activities at the site indicate that limited amounts of PCE as product were released to the drywell and to the ground surface near the drum storage area. The releases would be expected to dissipate through dissolution by infiltration to groundwater. Adsorption of aqueous phase contaminants onto soil occurs as a function of equilibrium partitioning as the groundwater plume migrates with the natural groundwater flow direction. The higher silt content of soils in the Source Area provides for higher adsorptive capacity and slower groundwater flow rates in the Source Area.

In addition to partitioning into the aqueous (dissolved) and adsorbed phases, the possibility exists for chlorinated solvents such as PCE to remain in a non-aqueous or free phase depending on a number of factors including the amount and duration of material released and the fraction of organic carbon in the soils. Since free phase chlorinated solvents, including PCE, are typically more dense than water, the non-aqueous phase of PCE and other chlorinated solvents are collectively referred to as dense non-aqueous phase liquid (DNAPLs). The presence of a free or DNAPL phase is important to consider when planning a groundwater remediation program because this phase can present a large portion of the mass of contamination (as compared to the dissolved phase) and also presents a source of ongoing dissolved impacts. As outlined in the FS (ARCADIS, 2002a Section 2.5.1), existing analytical data from the Source

Area do not suggest that a DNAPL exists at the site. Numerous soil borings, soil samples, and screening groundwater samples have been collected in various locations within the Source Area and the concentrations of PCE in these samples are generally lower than would be associated with DNAPL.