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EPA Superfund Record of DecisionEPA/ROD/R03-04/607 2004 EPA Superfund Record of Decision: ABERDEEN...

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EPA/ROD/R03-04/607 2004 EPA Superfund Record of Decision: ABERDEEN PROVING GROUND (EDGEWOOD AREA) EPA ID: MD2210020036 OU 21 EDGEWOOD, MD 09/30/2004
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Page 1: EPA Superfund Record of DecisionEPA/ROD/R03-04/607 2004 EPA Superfund Record of Decision: ABERDEEN PROVING GROUND (EDGEWOOD AREA) EPA ID: MD2210020036 OU 21 EDGEWOOD, MD 09/30/2004

EPA/ROD/R03-04/6072004

EPA Superfund

Record of Decision:

ABERDEEN PROVING GROUND (EDGEWOOD AREA)EPA ID: MD2210020036OU 21EDGEWOOD, MD09/30/2004

Page 2: EPA Superfund Record of DecisionEPA/ROD/R03-04/607 2004 EPA Superfund Record of Decision: ABERDEEN PROVING GROUND (EDGEWOOD AREA) EPA ID: MD2210020036 OU 21 EDGEWOOD, MD 09/30/2004

GRACES QUARTERS (OPERABLE UNIT A) PRIMARY TEST AREA RECORD OF DECISION Final September 2004

U.S. Army Garrison Aberdeen Proving Ground, Edgewood, Maryland

DISTRIBUTION RESTRICTION STATEMENT APPROVED FOR PUBLIC RELEASE:

DISTRIBUTION IS UNLIMITED

6143-A-6

Page 3: EPA Superfund Record of DecisionEPA/ROD/R03-04/607 2004 EPA Superfund Record of Decision: ABERDEEN PROVING GROUND (EDGEWOOD AREA) EPA ID: MD2210020036 OU 21 EDGEWOOD, MD 09/30/2004

RECORD OF DECISION

ABERDEEN PROVING GROUND, EDGEWOOD GRACES QUARTERS (OPERABLE UNIT A: GROUNDWATER)

PRIMARY TEST AREA

FINAL

Directorate of Safety, Health and Environment Environmental Conservation and Restoration Division

Installation Restoration Program U.S. Army Garrison Aberdeen Proving Ground, Edgewood, Maryland

September 2004

Page 4: EPA Superfund Record of DecisionEPA/ROD/R03-04/607 2004 EPA Superfund Record of Decision: ABERDEEN PROVING GROUND (EDGEWOOD AREA) EPA ID: MD2210020036 OU 21 EDGEWOOD, MD 09/30/2004

Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page ii of vi

TABLE OF CONTENTS Section Page TITLE PAGE ................................................................................................................................................................................ i LIST OF FIGURES .....................................................................................................................................................................ii LIST OF TABLES .......................................................................................................................................................................ii LIST OF ACRONYMS AND ABBREVIATIONS ..............................................................................................................iv 1 DECLARATION .............................................................................................................................................................. 1 1.1 SITE NAME AND LOCATION ....................................................................................................................1 1.2 STATEMENT OF BASIS AND PURPOSE ................................................................................................1 1.3 ASSESSMENT OF THE SITE .......................................................................................................................1 1.4 DESCRIPTION OF THE SELECTED REMEDIES ..................................................................................1 1.5 STATUTORY DETERMINATIONS ............................................................................................................2 1.6 DATA CERTIFICATION CHECKLIST ......................................................................................................2 2 THE DECISION SUMMARY ...................................................................................................................................... 4 2.1 SITE NAME, LOCATION AND DESCRIPTION .....................................................................................4 2.2 SITE HISTORY AND ENFORCEMENT ACTIVITIES ...........................................................................6 2.3 COMMUNITY PARTICIPATION ................................................................................................................9 2.4 SCOPE AND ROLE OF THE OPERABLE UNIT ...................................................................................10 2.5 SITE AND OPERABLE UNIT CHARACTERISTICS ...........................................................................11 2.6 CURRENT AND POTENTIAL FUTURE SITE AND RESOURCE USES .........................................21 2.7 SUMMARY OF SITE RISKS .......................................................................................................................21 2.7.1 Human Health Risk Assessment ........................................................................................................................21 2.7.2 Ecological Risk Assessment ...............................................................................................................................24 2.8 REMEDIAL ACTION OBJECTIVES ........................................................................................................25 2.9 DESCRIPTION OF ALTERNATIVES ......................................................................................................26 2.9.1 Alternative 1: No Action .....................................................................................................................................27 2.9.2 Alternative 2: Institutional Controls/LTM .......................................................................................................28 2.9.3 Alternative 3: Vitamin B12-catalyzed reductive dehalogenation in areas greaterthan 1,000 µg/L; MNA at all other locations .............................................................................................................................28 2.9.4 Alternative 4: Vitamin B12-catalyzed reductive dehalogenation in areas greater than 1,000 µg/L; pump-and-treat at all other locations ..........................................................................................................29 2.9.5 Alternative 5: Vitamin B12-catalyzed reductive dehalogenation in areas greater than 1,000 µg/L in the surficial aquifer; pump-and-treat at all other locations ...............................................................29 2.9.6 Alternative 6: Vitamin B12-catalyzed reductive dehalogenation in areas greater than 100 µg/L (both aquifers); MNA at all other locations ................................................................................................30 2.9.7 Alternative 7: Pump-and-Treat at all locations .............................................................................................31 2.9.8 Alternative 8: Pump-and-treat in areas greater than 1,000 µg/L (both aquifers); LTM at all other locations ............................................................................................................................................................31

Page 5: EPA Superfund Record of DecisionEPA/ROD/R03-04/607 2004 EPA Superfund Record of Decision: ABERDEEN PROVING GROUND (EDGEWOOD AREA) EPA ID: MD2210020036 OU 21 EDGEWOOD, MD 09/30/2004

Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page iii of vi 2.9.9 Alternative 9: ERH in areas greater than 1,000 µg/L in the surficial aquifer; pump-and-treat at all other locations ..................................................................................................................................................32 2.10 COMPARATIVE ANALYSIS OF ALTERNATIVES ................................................................................33

2.10.1 Threshold Criteria ................................................................................................................................................33 2.10.2 Primary Balancing Criteria ...........................................................................................................................35 2.10.3 Modifying Criteria ...............................................................................................................................................38

2.11 SELECTED REMEDY 39 2.12 STATUTORY DETERMINATIONS 43

2.12.1 Protection of Human Health and the Environment ........................................................................................44 2.12.2 Compliance with ARARs Requirements ............................................................................................................44 2.12.3 Cost Effectiveness .................................................................................................................................................44 2.12.4 Utilization of Permanent Solutions and Alternative Treatment Technologies (or Resource Recovery Technologies) to the Maximum Extent Practicable ...................................................................................46 2.12.5 Preference for Treatment as a Principal Element ...........................................................................................46 2.12. 6 Five-year Review Requirements .......................................................................................................................46

2.13 DOCUMENTATION OF SIGNIFICANT CHANGES FROM PREFERRED ALTERNATIVE OF PROPOSED PLAN ........................................................................................................................................................46 3 RESPONSIVENESS SUMMARY .............................................................................................................................47 3.1 OVERVIEW ...............................................................................................................................................................47 3.2 BACKGROUND ON COMMUNITY INVOLVEMENT .................................................................................47 3.3 SUMMARY OF COMMENTS RECEIVED DURING THE PUBLIC COMMENT PERIOD AND AGENCY RESPONSES ......................................................................................................................................................48 4 REFERENCES ................................................................................................................................................................ 55

LIST OF FIGURES

Figure 1. Graces Quarters location map .....................................................................................................................................5 Figure 2. Topographic and site location of the Primary Test Area, Graces Quarters (APG, 1999b) ...............................8 Figure 3. Primary Test Area, Graces Quarters (APG, 2002) ................................................................................................12 Figure 4. Graces Quarters Primary Test Area Conceptual Model of the Aquifer System (APG, 2002) .......................13 Figure 5. Graces Quarters Primary Test Area, Groundwater flow in the surficial aquifer (APG, 2002) ......................14 Figure 6. Graces Quarters Primary Test Area, Groundwater flow in the middle aquifer (APG, 2002) ........................15 Figure 7. Conceptual groundwater discharge areas, Graces Quarters (APG, 2002)..........................................................16 Figure 8. Isopleth map showing the horizontal extent of the total VOC plume in the surficial aquifer beneath the Primary Test Area, Graces Quarters (APG, 2001c) ...........................................................................................19 Figure 9. Isopleth map showing the horizontal extent of the total VOC plume in the middle aquifer beneath the Primary Test Area, Graces Quarters (APG, 2001c) ...........................................................................................20 Figure 10. Conceptual diagram of a recirculation well ..........................................................................................................41

Page 6: EPA Superfund Record of DecisionEPA/ROD/R03-04/607 2004 EPA Superfund Record of Decision: ABERDEEN PROVING GROUND (EDGEWOOD AREA) EPA ID: MD2210020036 OU 21 EDGEWOOD, MD 09/30/2004

Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page iv of vi

LIST OF TABLES Table 1. Areas and volumes of contaminated groundwater in Graces Quarters Operable Unit A-Primary Test Area (APG. 1999) ..............................................................................................................................................................18 Table 2. Primary constituents contributing to carcinogenic risk or noncarcinogenic hazard under future military multi-use scenario (APG. 1998a) ..........................................................................................................................23 Table 3. COC maximum concentrations. MCLs. and RAO concentrations (APG. 2004) ...............................................26 Table 4. Comparative Analysis of Alternatives ......................................................................................................................34 Table 5. Alternative 3 cost summary ........................................................................................................................................40 Table 6. Action-Specific Applicable or Relevant and Appropriate Requirements ...........................................................45

Page 7: EPA Superfund Record of DecisionEPA/ROD/R03-04/607 2004 EPA Superfund Record of Decision: ABERDEEN PROVING GROUND (EDGEWOOD AREA) EPA ID: MD2210020036 OU 21 EDGEWOOD, MD 09/30/2004

Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page v of vi

LIST OF ACRONYMS AND ABBREVIATIONS

APG Aberdeen Proving Ground

APGSCC Aberdeen Proving Ground Superfund Citizens Coalition

ARAR Applicable or relevant and appropriate requirement

bgs Below Ground Surface

BRA Baseline Risk Assessment

CA Chloroethane

CAHs Chlorinated Aliphatic Hydrocarbons

CERCLA Comprehensive Environmental Response, Compensation, and Liability Act

COCs Constituents of Concern

COPCs Constituents of Potential Concern

CS Ortho-chlorobenzolmalonoitrile

CWM Chemical Warfare Materiel

DSERTS Defense System Environmental Restoration Tracking System

DNAPL Dense Non-Aqueous Phase Liquid

DOD Department of Defense

EM Electromagnetic Conductivity

EPA U.S. Environmental Protection Agency

ERA Ecological Risk Assessment

ERH Electrical Resistance Heating

°C Degree Celsius

FFA Federal Facilities Agreement

FS Feasibility Study

ft Feet

GB Isopropylmethylphosphonofluoridate

GD Pinacolylmethylphosphonofluoridate

GMS Groundwater Modeling System

GPR Ground-Penetrating Radar

HD 2,2'-dichlorodiethyl Sulfide (mustard gas)

HEAST Health Effects Assessment Summary Tables

HI Hazard Index

IRIS Integrated Risk information System

kW-hr Kilowatt Hour

Page 8: EPA Superfund Record of DecisionEPA/ROD/R03-04/607 2004 EPA Superfund Record of Decision: ABERDEEN PROVING GROUND (EDGEWOOD AREA) EPA ID: MD2210020036 OU 21 EDGEWOOD, MD 09/30/2004

Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page vi of vi

LIST OF ACRONYMS AND ABBREVIATIONS (cont'd)

LECR Lifetime Excess Cancer Risk

LTM Long-term Monitoring

LUC Land Use Controls

MCL Maximum Concentration Level

SIDE Maryland Department of the Environment

ULNA Monitored Natural Attenuation

NCP National Contingency Plan

NGVD National Geodetic Vertical Datum

NPDES National Pollutant Discharge Elimination System

NPL National Priorities List

O&M Operation and Maintenance

ppb Part Per Billion

PVC Polyvinyl Chloride

RA Risk Assessment

RAB Restoration Advisory Board

RAGS Risk Assessment Guidance for Superfund

RAO Remedial action objective

RBC Risk Based Concentration

RCRA Resource Conservation and Recovery Act

RfDs Reference Doses

RI Remedial Investigation

ROD Record of Decision

SARA Superfund Amendments and Reauthorization Act

SFs Slope Factors

µg/L Microgram per Liter

USGS U.S. Geological Survey

UXO Unexploded Ordnance

VOC Volatile Organic Compound

VX o-ethyl-s-(2-diisopropylaminoethyl) methylphosphonothioate

Page 9: EPA Superfund Record of DecisionEPA/ROD/R03-04/607 2004 EPA Superfund Record of Decision: ABERDEEN PROVING GROUND (EDGEWOOD AREA) EPA ID: MD2210020036 OU 21 EDGEWOOD, MD 09/30/2004

Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 1 of 56 1 DECLARATION 1.1 SITE NAME AND LOCATION Graces Quarters, Operable Unit A (Groundwater), Primary Test Area. Aberdeen Proving Ground (APG), Edgewood, Maryland (EPA Superfund Site ID number MD2210020036). 1.2 STATEMENT OF BASIS AND PURPOSE This Record of Decision (ROD) presents the selected remedy for Operable Unit A; Groundwater at Graces Quarters, Primary Test Area, APG, Edgewood, Maryland. The remedial action is chosen in accordance with the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), as amended by the Superfund Amendments and Reauthorization Act (SARA), and to the extent practicable, the National Oil and Hazardous Substances Pollution Contingency Plan (NCP). The information supporting the decisions on the selected remedy is contained in the administrative record for APG. The U.S. Department of the Army (the site owner) is the lead agency for this action with coordination from the State of Maryland Department of the Environment (MDE); the U.S. Environmental Protection Agency (EPA) is the lead regulatory agency and together the Army and EPA issue this ROD. 1.3 ASSESSMENT OF THE SITE Actual or threatened releases of hazardous substances from this site, if not addressed by implementing the response action selected in this ROD, may present an imminent and substantial endangerment to public health, welfare, or the environment. 1.4 DESCRIPTION OF THE SELECTED REMEDIES Groundwater beneath the Primary Test Area at Graces Quarters has been impacted by chlorinated solvents, which were used during activities conducted formerly at the site, including development and testing of chemical agent munitions. A groundwater plume of chlorinated volatile organic compounds (VOCs) with localized concentrations of 1,1,2,2-tetrachloroethane, carbon tetrachloride, and trichloroethene greater than 1,000 micrograms per liter (µg/L), exists beneath a portion of the Site, posing a potential threat to human health and the environment. The selected remedial action includes treatment technologies to eliminate principal threats and stimulation of natural attenuation to address non-principal threats, as well as institutional controls (land use restrictions) that were already in place at the site. The major components of the selected remedial action are as follows: • In-situ treatment of chlorinated VOCs in areas having concentrations greater than 1,000 µg/L of 1,1,2,2-

tetrachloroethane, carbon tetrachloride, and trichloroethene using injection of vitamin B12 amendment into the aquifer through recirculation wells to stimulate catalyzed reductive dehalogenation, followed by Monitored Natural Attenuation (MNA);

• MNA at all other locations containing low levels of chlorinated VOCs; and,

Page 10: EPA Superfund Record of DecisionEPA/ROD/R03-04/607 2004 EPA Superfund Record of Decision: ABERDEEN PROVING GROUND (EDGEWOOD AREA) EPA ID: MD2210020036 OU 21 EDGEWOOD, MD 09/30/2004

Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 2 of 56 • Land use controls on the use of groundwater in the surficial and middle aquifers until MCLs are met. 1.5 STATUTORY DETERMLNATIONS This remedy attains the mandates of CERCLA Section 121 and, to the extent practical the NCP. The selected remedy is protective of human health and the environment, complies with Federal and State requirements that are legally applicable or relevant and appropriate to the remedial action, is cost effective, and utilizes permanent solutions and alternative treatment technologies to the maximum extent practicable. This remedy also satisfies the statutory preference for treatment as a principal element of the remedy (i.e., reduces the toxicity, mobility, or volume of hazardous substances, pollutants, or contaminants through treatment). Because this remedy will not result in hazardous substances, pollutants, or contaminants remaining on-site above levels that allow for unlimited use and unrestricted exposure, but will take more than five years to attain remedial action objectives (RAOs) and cleanup levels, a policy review may be conducted within five years of construction completion for the site to ensure that the remedy is, or will be, protective of human health and the environment. 1.6 DATA CERTIFICATION CHECKLIST The following information is included in the Decision Summary section of this ROD. Additional information can be found in the Administrative Record file for this site. • Constituents of concern (COCs) and their respective concentrations. • Baseline risk represented by the COCs. • Cleanup levels established for COCs and the basis for these levels. • Current and reasonably anticipated future land use assumptions and current and potential future beneficial uses

of groundwater used in the baseline risk assessment (BRA) and ROD. • Potential land and groundwater use available at the site as a result of the selected remedy. • Estimated capital, annual operation and maintenance (O&M), and total present worth costs, discount rate, and

the number of years over which the remedy cost estimates are projected. • Key factor(s) that led to selecting the remedy (i.e., a description of how the selected remedy provides the best

balance of tradeoffs with respect to the balancing and modifying criteria, highlighting criteria key to the decision).

Page 11: EPA Superfund Record of DecisionEPA/ROD/R03-04/607 2004 EPA Superfund Record of Decision: ABERDEEN PROVING GROUND (EDGEWOOD AREA) EPA ID: MD2210020036 OU 21 EDGEWOOD, MD 09/30/2004

Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 3 of 56

Page 12: EPA Superfund Record of DecisionEPA/ROD/R03-04/607 2004 EPA Superfund Record of Decision: ABERDEEN PROVING GROUND (EDGEWOOD AREA) EPA ID: MD2210020036 OU 21 EDGEWOOD, MD 09/30/2004

Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 4 of 56 2 THE DECISION SUMMARY 2.1 SITE NAME, LOCATION AND DESCRIPTION APG is a 72,500-acre Army installation located in southern Harford County and southeastern Baltimore County, Maryland, on the western shore of the Upper Chesapeake Bay. Graces Quarters is a peninsula located approximately five miles southeast of White Marsh, Maryland, and two miles southeast of Chase, Maryland, as shown in Figure 1. Access to the property is controlled by chain link fences, a locked gate, and patrols by military police. Paved and gravel roads are present on the peninsula. The only current permanent large structure is an emergency radio transmitter and tower originally constructed by the Federal Emergency Management Agency. Graces Quarters covers 414 acres, of which approximately 151 acres (36 percent) are classified as wetlands. The land mass consists of tidal and non-tidal wetlands, open fields, and wooded areas. Maximum elevation is approximately 40 feet (ft) above National Geodetic Vertical Datum (NGVD). Graces Quarters is bordered to the east and south by the Chesapeake Bay; to the west by Gunpowder Falls State Park, and residential areas; and to the north by the towns of Edgewood, Joppa, Magnolia, and Aberdeen. The Bush River divides APG into the Edgewood Area to the west of the river and the Aberdeen Area to the east. Carroll Island and Graces Quarters (Figure 1) are located in the Edgewood Area; both were listed on the NPL (CERCLIS# MD2210020036) in 1990. The Primary Test Area was identified as Site 5 followed by Defense System Environmental Restoration Tracking System (DSERTS) number EAGQ02-D, while the impacted groundwater below the site was evaluated as Operable Unit A in the Remedial Investigation (RI) of Graces Quarters (APG, 1998a). Chlorinated VOCs -- carbon tetrachloride, 1,1,2,2-tetrachloroethene, trichloroethene, chloroform and tetrachloroethene -- are the major contaminants that potentially pose a threat to human health and the environment. Chemical Warfare Materiel (CWM), unexploded ordnance (UXO) and other hazardous substances, may also be encountered at the Primary Test Area and will be managed in accordance with the previously submitted and approved ROD (APG, 2001a) for Operable Unit B (CWM). Remedial Action is required for this site because the potential exists for future exposure of human receptors. Additionally, there is potential for transport of contaminants to wetlands and the Chesapeake Bay. The Army is the Lead Agency which provides the funding for this Remedial Action. This document is issued by the Army (the site owner and lead agency) and the EPA (the lead regulatory agency for site activities), and in coordination with MDE (the State environmental agency).

Page 13: EPA Superfund Record of DecisionEPA/ROD/R03-04/607 2004 EPA Superfund Record of Decision: ABERDEEN PROVING GROUND (EDGEWOOD AREA) EPA ID: MD2210020036 OU 21 EDGEWOOD, MD 09/30/2004

Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 5 of 56

Figure 1. Graces Quarters location map.

Page 14: EPA Superfund Record of DecisionEPA/ROD/R03-04/607 2004 EPA Superfund Record of Decision: ABERDEEN PROVING GROUND (EDGEWOOD AREA) EPA ID: MD2210020036 OU 21 EDGEWOOD, MD 09/30/2004

Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 6 of 56 2.2 SITE HISTORY AND ENFORCEMENT ACTIVITIES

Graces Quarters was acquired as U.S. Army property in 1918 as part of the original Edgewood Arsenal (AEHA, 1989). Little documentation is available on the use of Graces Quarters prior to the 1940's, but it does not appear that there was any Army activity at the site until the 1940's. Records of testing of CWM at Graces Quarters are only available for the period between 1964 and 1971; however, it is known that testing was conducted before this time. Outdoor testing of lethal CWM ceased in 1969. Open-air testing of simulants and non-lethal incapacitants continued at Graces Quarters until 1971, at which time all open-air testing of CWM ceased at the site. Detailed descriptions of the history and land use of Graces Quarters are presented in the Resource Conservation and Recovery Act (RCRA) Facility Assessment (AEHA, 1989) and the RI Report (1998a). Graces Quarters is expected to remain under military authority with limited military training activities currently being conducted. CERCLA activities at APG are being conducted under a Federal Facilities Agreement (FFA) with EPA signed in March 1990. The bulk of the CWM testing took place at the Primary Test Area, which is approximately 22 acres and is classified predominantly as uplands. No structures are present at this site, and it is currently an open, grassy area. The site has gently sloping relief, ranging between 5 to 20 ft above NGVD, and slopes toward the southwest. The Primary Test Area is located near the middle of the Graces Quarters peninsula and is bounded to the east by the Gunpowder River and the Northern Perimeter Dump; to the south by the Southern/Southwest Perimeter Dumps; to the west by the Dugway Proving Ground Test Site and a north-south access road; and to the north by the east-west access road across Graces Quarters (Figure 2). A small amount of testing was also conducted in the small wooded area southwest of the Primary Test Area. The Mustard Gas (2,2'-dichlorodiethyl sulfide or HD) Test Annuli located north of the Primary Test Area were used in decontamination studies with HD, o-ethyl-s- (2-diisopropylaminoethyl)-methylphosphonothioate (VX), and fuming nitric acid. Surveillance testing was conducted in the small area southwest of the Graces Quarters Disposal Area. A small amount of testing was also conducted in the Graces Quarters Disposal Area. Compounds used at Graces Quarters included HD, VX, ortho-chlorobenzolmalonoitrile (CS), isopropylmethylphosphonofluoride (GB), pinacolylmethylphosphonofluoridate (GD), and chlorinated solvents. Wastes from testing activities were disposed of by dumping or burial, primarily at Graces Quarters Disposal Area. Based on historical uses of Graces Quarters, the principal contaminants that could be present include CWM, explosives, and associated degradation products (most likely via hydrolysis reaction). In addition, other contaminants that could potentially be present include VOCs, semi-VOCs, pesticides/polychlorinated biphenyls, and inorganics. During site operations, use of the decontaminating agent DANC (Decontaminating Agent Non-Corrosive) likely resulted in releases to the subsurface of 1,1,2,2 tetrachlorethane and other VOCs. There exists the potential that some wastes associated with testing and support activities may not have been located/identified, due to the difficulty of detecting these wastes with existing technology. Based on the 1998 RI, the VOC contaminated groundwater beneath the Primary Test Area is designated as Operable Unit A, whereas all CWM and other hazardous substances that have not been located and/or remediated at Graces Quarters are designated as Operable Unit B (APG, 1998a). A ROD has been prepared and approved to address combined Operable Units B at Graces Quarters and Carroll Island, both of which are similar in the types of contaminants, environment, and potential remedial actions (APG, 2001a). All of the land and shoreline areas are included

Page 15: EPA Superfund Record of DecisionEPA/ROD/R03-04/607 2004 EPA Superfund Record of Decision: ABERDEEN PROVING GROUND (EDGEWOOD AREA) EPA ID: MD2210020036 OU 21 EDGEWOOD, MD 09/30/2004

Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 7 of 56 within the Operable Unit B of Carroll Island and Graces Quarters, and the Selected Remedy -- Public Access Controls, Land Use Restrictions, and Erosion Controls -- was chosen as the highest level of protection of human health and the environment. A public meeting was held on May 11, 2000 to formally present the Proposed Plan (APG, 2000) for Operable Unit B at Graces Quarters and Carroll Island. EPA and MDE concurred with the Army's preferred alternative, which then became the selected remedy in the 2001 ROD (APG, 2001a). The community also agreed with the selected remedy. Because the selected remedy for Operable Unit B will allow CWM (if any), hazardous substances, and pollutants to remain on site, remedy reviews will be performed every five years, as required by the NCP (APG, 2001a).

Page 16: EPA Superfund Record of DecisionEPA/ROD/R03-04/607 2004 EPA Superfund Record of Decision: ABERDEEN PROVING GROUND (EDGEWOOD AREA) EPA ID: MD2210020036 OU 21 EDGEWOOD, MD 09/30/2004

Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 8 of 56 Figure 2. Topographic and site location of the Primary Test Area, Graces Quarters (APG, 1999b).

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 9 of 56 2.3 COMMUNITY PARTICIPATION Community relations activities that have taken place at APG to date include monthly Restoration Advisory Board (RAB) meetings, APG Superfund Citizens Coalition (APGSCC) meetings, public meetings and site tours, as well as press releases, and public access to the APG website. Administrative Record – Consistent with requirements of CERCLA section 113(k), an Administrative Record containing information associated with CERCLA cleanup activities at APG is available to the public. The locations, contact information and hours of operation for the administrative record file are as follows: Harford County Library – Aberdeen Branch 21 Franklin Street Aberdeen, MD 21001 (410) 273-5608 Hours: Mon., Tues., Thur. - 10 a.m. to 8 p.m. Wed. - 1 p.m. to 8 p.m. Fri., Sat. - 10 a.m. to 5 p.m. Sun. - 1 p.m. to 5 p.m. (Oct-May only) Hanford County Library – Edgewood Branch 2205 Hanson Road Edgewood, MD 21040 (410) 612-1600 Hours: Mon., Tues., Thur. - 10 a.m. to 8 p.m. Wed. - 1 p.m. to 8 p.m. Fri., Sat. - 10 a.m. to 5 p.m. Sun. - closed Kent County – Washington College Miller Library Chestertown, MD 21620 (410) 778-2800 Hours: Mon. to Fri. - 8 a.m. to 12 a.m. Sat. - 10 a.m. to 10 p.m. Sun. - 11:45 a.m. to 12 a.m. Baltimore County Public Library - Essex Branch 1110 Eastern Boulevard Essex, Maryland 21221 (410) 887-0295 Hours: Mon. to Thur. - 10 a.m. to 9 p.m. Fri., Sat. - 10 a.m. to 5:30 p.m. Sun. - closed Mailing List – A mailing list of all interested parties in the community is maintained by APG and updated regularly. Fact Sheet – A fact sheet describing the status of the Installation Restoration Program was last distributed to the mailing list addressees on April 21, 2004.

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 10 of 56 Proposed Plan – The Proposed Plan regarding this remedial action was made available to the public for their comments. The Feasibility Study (FS) and Proposed Plan for Graces Quarters Operable Unit A (Groundwater) were made available to the public in February 2004 and April 2004, respectively. They can be found in the Administrative Record file and the information repository maintained at the EPA Docket Room in Region III and the public libraries in Harford County, Kent County, and Baltimore County. The notice of the availability of the Proposed Plan was published in newspapers, including The Aegis and The Cecil Whig on April 14, 2004; and The Avenue, The East County Times, and The Kent County News on April 15, 2004. A public meeting was held on April 27, 2004 at the Marshy Point Nature Center, 7130 Marshy Point Road, Baltimore, MD 21220 to present the Proposed Plan. At this meeting, representatives from the Army, EPA and MDE answered questions about problems at the site and the remedial alternatives. The Army and EPA also used this meeting to solicit a wider cross-section of community input on the reasonably anticipated future land use and potential water resources at the site. Response to the comments received during this period is included in the Responsiveness Summary, which is a part of this ROD. 2.4 SCOPE AND ROLE OF THE OPERABLE UNIT An Operable Unit is defined by the NCP as "a discrete action that comprises an incremental step toward comprehensively mitigating site problems". Based on the complexity of the problems (i.e., distinctive nature of contaminants in the soil and the groundwater, and different pathways of exposure) two Operable Units associated with Graces Quarters were established for the purpose of managing the site-wide response action (APG, 1998a). • Operable Unit A: Groundwater associated with the Primary Test Area containing primarily chlorinated VOCs. • Operable Unit B: Entire areas of Graces Quarters addressing all CWM and hazardous substances. As previously mentioned, Operable Unit B of Graces Quarters was addressed together with Operable Unit B of Carroll Island due to their similarity in the types of contaminants, environment, and potential remedial actions. A separate ROD was prepared and approved, which addresses all CWM and hazardous substances that have not been located at both Graces Quarters and Carroll Island (APG, 2001a). This ROD addresses only Operable Unit A of Graces Quarters as the concentrations of chlorinated solvents in the groundwater, primarily 1,1,2,2-tetrachloroethane and carbon tetrachloride in the vicinity of the Primary Test Area, warrant remediation. Based on the concentrations of total VOC's, residual dense non-aqueous phase liquid (DNAPL) may exist in localized areas beneath the Primary Test Area. This suspected DNAPL residual is considered to be a principal threat to human health and the environment. A FS has been prepared to evaluate remedial alternatives addressing the contaminated groundwater (APG, 2004). The selected remedy for Operable Unit A is intended to prevent both human exposures to COCs, and to prevent the migration of COCs from the Primary Test Area at Graces Quarters. The selected remedy for Operable Unit A is designed to destroy the principal threat wastes via in-situ

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 11 of 56 treatment, address the diluted plume via natural attenuation, and restore the aquifers' potential for beneficial use in years to come. 2.5 SITE AND OPERABLE UNIT CHARACTERISTICS The surficial sediments at Graces Quarters are primarily those of the Patapsco Formation, as described and discussed in the RI Report (APG, 1998a). The clay facies of the Patapsco Formation outcrop mainly in the northeastern part of the peninsula (Bennett and Meyer, 1952), and generally are topographically higher than the rest of Graces Quarters. The sand facies of the Patapsco Formation outcrop in the topographically lower areas of Graces Quarters, and directly underlie the Primary Test Area. In the Primary Test Area (Figure 3), a surficial unconfined aquifer composed of yellow, clean, fine-to-medium quartz sand with thin layers of silty clay underlies the site. This surficial aquifer extends to depths approximately 40 to 50 ft below ground surface (bgs) where it is underlain by a discontinuous confining layer that is composed of silty clay. A semi -confined sand unit, termed the middle aquifer, is present from approximately 40 to 80 ft bgs. The middle aquifer predominantly consists of yellow, clean, fine-to-medium quartz sand with thin stringers of silty clay. Beneath the middle aquifer is a continuous clay aquitard. Figure 4 provides a conceptual model of the affected aquifer system beneath the Primary Test Area. Groundwater flow in the surficial aquifer is predominantly south and southwest toward the wetland areas located in the southern portion of the peninsula (Figure 5). Surficial groundwater likely discharges to these wetland areas and the surrounding water bodies, and locally recharges the middle aquifer where the middle confining layer is absent. Groundwater in the middle aquifer flows radially away from the holes in the confining layer. It is probable that groundwater in the middle aquifer discharges to the Gunpowder River or Saltpeter Creek (Figure 6). However, because the middle aquifer is deeper and separated from the surface water bodies by clays and silts, it likely takes a longer time to do so than water from the overlaying surficial aquifer. A conceptual figure showing the likely discharge area for groundwater from these aquifers is provided as Figure 7. Further detailed discussion of the hydrogeology is presented in the Graces Quarters RI (APG, 1998a), the Additional Groundwater Investigations Data Report (APG, 1998b), and the Conceptual Site Model (APG, 2001c). Groundwater in the surficial and middle aquifer at the Primary Test Area is contaminated with VOCs, particularly chlorinated aliphatic hydrocarbons (CAHs). The most frequently detected contaminants include 1,1,2,2-tetrachloroethane, carbon tetrachloride, tetrachloroethee, chloroform, and trichloroethene. The contaminants have formed a plume of contaminated groundwater originating in the surficial aquifer, migrating to the south, and into the middle aquifer.

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 12 of 56

Figure 3. Primary Test Area, Graces Quarters (APG, 2002).

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 13 of 56 Fi

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 14 of 56

Figure 5. Graces Quarters Primary Test Area, Groundwater flow in the surficial aquifer (APG, 2002).

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 15 of 56 Figure 6. Graces Quarters Primary Test Area, Groundwater flow in the middle aquifer (APG, 2002).

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 16 of 56

Figure 7. Conceptual groundwater discharge areas, Graces Quarters (APG, 2002).

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 17 of 56 Groundwater samples were collected from approximately 46 geoprobes, approximately 10 borings, and approximately 42 monitoring wells. Geoprobes are temporary sampling points and are removed after samples have been collected. The compound detected at the highest concentration was 1,1.2.2-tetrachloroethane at 181.000 µg/L in a groundwater sample from a geoprobe. Confirmed peak detections (repeated detections in permanent wells) of 1.1.2.2-tetrachloroethane are much lower and are on the order of 2,000 to 3,000 µg/L. Carbon tetrachloride, trichloroethene and chloroform were detected in the 1,000 to 3,000 µg/L range, although the majority of the positive detections were below 1,000 µg/L. Tetrachloroethene was detected at lower concentrations than the previously mentioned constituents. There are no known specific contaminant source areas at Graces Quarters. It is likely that the contaminants were introduced to the surficial aquifer as multiple non-point source releases of solvents used during the testing of CWM. The contaminants have formed a plume of contaminated groundwater originating in the surficial aquifer and migrating to the south and into the middle aquifer through pathways in the confining layer. Based on the distribution of contaminants and detected concentrations, it is believed that residual DNAPL may exis t in the surficial aquifer in the area where concentrations exceed 1,000 µg/L total VOCs. This presumption is consistent with the EPA current guidance suggesting DNAPL should be considered as the principal threat and be suspected at areas where the concentration levels of individual constituents exceed one or more percent of their effective solubilities. The EPA guidance also advises using treatment to destroy principal threats and to contain or use engineering methods to address non-principal threats (e.g., dilute VOC plume). In 1999 and 2000, pilot scale testing was conducted to assess the efficacy of injecting a vitamin B12 amendment into the subsurface via recirculation wells. This test demonstrated that this technology effectively degraded the contaminants in the aquifer, rapidly reducing the concentrations within an 80 ft radius of the test well. Concentrations did not rebound following shut down of the system indicating the treatment is effective at remediating potential residual, dense non-aqueous phase solvents. During operation of the system, reducing conditions created in the aquifer temporarily mobilizes naturally occurring arsenic in the formation. Concerns regarding this condition raised by EPA were addressed in a 2004 technical memorandum demonstrating that this is a temporary and reversable condition. It is believed that contamination in the middle aquifer has been transported as dissolved phase only and that no residual DNAPL exists in the middle aquifer -- total VOC concentrations in the middle aquifer are typically less than 1,000 µg/L although peak concentrations exceed 3,000 µg/L. Table 1 presents the areal extent and volume of groundwater contamination in the surficial and middle aquifers at various concentration ranges. These estimates are based on calculations using the Groundwater Modeling System (GMS) software, present understanding of contaminant distribution, and a porosity of 20 percent. Figures 8 and 9 show the areal extent of the total VOC plumes in the surficial and middle aquifers, respectively.

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 18 of 56 Table 1. Areas and volumes of contaminated groundwater in Graces Quarters Operable Unit A -Primary Test Area (APG, 1999).

Area (square feet, ft2)

Volume (gallons) Concentration Range

(Total VOCs) Surficial Aquifer

Middle Aquifer

Surficial Aquifer Middle Aquifer

>1,000 µg/L 60,200 14,500 2,230,000 524,000

100 – 1,000 µg/L 183,000 145,000 4,470,000 3,510,000

5 - 100 µg/L 546,000 1,150,000 16,700,000 35,500,000

Bi-annual monitoring of the plumes has been occurring since 1998. Sampling through 2002 suggests that: • The plume in the surficial aquifer remains relatively stable but may be extending into the marshes south of the

Primary Test Area; • Groundwater modeling suggests that although discharge to the surface water bodies surrounding Graces

Quarters may occur in the future, it will not occur for a considerable amount of time; and • The plume in the middle aquifer also appears to be fairly stable.

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 19 of 56 Figure 8. Isopleth map showing the horizontal extent of the total VOC plume in the surficial aquifer beneath the

Primary Test Area, Graces Quarters (APG, 2001c).

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 20 of 56 Figure 9. Isopleth map showing the horizontal extent of the total VOC plume in the middle aquifer beneath the

Primary Test Area, Graces Quarters (APG, 2001c).

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 21 of 56 2.6 CURRENT AND POTENTIAL FUTURE SITE AND RESOURCE USES Graces Quarters is expected to remain under military authority with limited military training being conducted. In addition to limited military activities, future land uses at the site will include a limited-access Natural Resource Management Area for implementation of the selected remedy. Both military personnel and natural resources management workers were considered as the potential receptors for the BRA; the exposure factors for the latter type of worker were conservatively assumed the same as that of an industrial worker. There are currently no drinking water wells at Graces Quarters and the groundwater is not in use. Future use of groundwater at the site will be restricted until the site-specific RAOs have been achieved. The land use within an approximate 5-mile radius of Graces Quarters is generally residential and recreational. Several communities are present within the 5 mile radius, and some industrial/commercial use is also documented. Both the Hammerman Area of Gunpowder Falls State Park and the Dundee Natural Environmental Area are within close proximity to Graces Quarters. The estuaries and creeks around Graces Quarters are an important natural resource and are used for public recreation including boating, fishing, and swimming—although a restriction on these activities is imposed directly around the military property. The water bodies, marshes, and upland areas (particularily on the military installation where development has not occurred) are also an important habitat for waterfowl, fish, and other wildlife species. 2.7 SUMMARY OF SITE RISKS The BRA estimates what risk the site poses if no action is taken. It provides the basis for taking action, if necessary, and identifies the contaminants and exposure pathways that need to be addressed by the remedial action. This section of the ROD summarizes the results of the baseline risk asses sment for this site. 2.7.1 Human Health Risk Assessment The purpose of a human health risk assessment is to determine whether exposure to site-related contaminants could adversely affect human health. The focus of the human health risk assessment is on the possible human health effects that could occur under current or potential future use conditions in the event that contamination is not remediated. The risk is expressed as lifetime excess cancer risk (LECR) for carcinogens, and hazard index (HI) for noncarcinogens. For example, an LECR of 1 x 10-6 represents the probability of one additional cancer, in a population of one million people exposed. The cancer risk range of 1x 10-4 and . l x 10-6 is the "target range" within which the EPA strives to manage risks. A hazard index is the ratio of anticipated exposure of an individual to the reference dose, the dose at which no adverse effects are expected to occur. If this ratio is less than or equal to one, then no adverse non-cancer effects are expected to occur A hazard quotient (HQ), the sum of the hazard indices for all site contaminants and/or routes of exposure, above one presents a likelihood of non-carcinogenic health effects in exposed populations. 2.7.1.1 Identification of Chemicals of Concern The chemicals of concern in groundwater beneath the Primary Test Area include 1,1,2,2-tetrachloroethane, 1,1,2-trichloroethane, 1,1-dichloroethene, carbon tetrachloride, chloroform,

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 22 of 56 tetrachloroethene, trichloroethene, and vinyl chloride (as listed in Table 2 in Section 2.7.1.3). Maximum and average concentrations are provided in Section 2.8 (Table 3). Groundwater plumes range in concentration from non-detect at their boundaries to the peak concentrations (as listed in Table 2) and accordingly a concentration range is not provided by this table. 2.7.1.2 Exposure Assessment As discussed in Section 2.5, Site and Operable Unit Characteristics, the Conceptual Site Model indicates a relatively shallow aquifer system (classified a Type I by the MDE and Type IIB by the EPA) beneath the Primary Test Area. Groundwater from these aquifers ultimately discharges to the surrounding surface water bodies. It was determined that under the current land use conditions (groundwater is not in use and there are currently no drinking water wells) exposure to groundwater is unlikely. However, for future land-use, civilian and military workers involved with "military multiple-use" (periodic training and light equipment testing activities) of the Primary Test Area may potentially have contact with site groundwater. For military multiple-use workers, there is exposure potential via ingestion of groundwater as assumed in the Risk Assessment (the military multiple-use scenario is essentially a light industrial use assessment which has limited groundwater ingestion assumptions inherent in the scenario. Risks calculated under this scenario (as detailed in Section 2.7.1.3) use the standard EPA default parameters for workers with ingestion as the exposure route). Additional risk scenarios were evaluated at the request of the EPA. While residential land use scenarios are considered unlikely, and the reasonable worst case was assumed to be military multiple -use, residential evaluation was included for comparison purposes and to ensure a complete understanding of the spectrum of potential risk at the site. Under the hypothetical residential scenario, ingestion, inhalation, and dermal exposure routes were evaluated per EPA policy. However, it is noted that the industrial use (reasonable worst case) risk assessment is the basis for remedy selection at this site. 2.7.1.3 Toxicity Assessment The human toxicity assessment was performed in order to identify numerical toxicity criteria with which to assess human health exposures. For non-cancer health effects, chemical-specific Reference Doses (RfDs) were compiled. Chronic RfDs were used to assess long-term exposures ranging from seven years to a lifetime. Subchronic RfDs were used to evaluate the potential for adverse health effects associated with exposure to constituents over a period of 2 weeks to 7 years. Subchronic RfDs were used to evaluate the short-term construction worker hazards. Although the exposure duration for children was less than seven years, chronic RfDs were conservatively used. For cancer endpoints, chemical-specific cancer slope factors (SFs) were compiled. Whenever possible, route-specific toxicity values were used. However, toxicity values for dermal exposures have not yet been developed by EPA; therefore, the oral toxicity values and the gastrointestinal absorption efficiency were used to derive adjusted toxicity values (adjusted to the absorbed dose) for use in assessing dermal exposure.Toxicity data used to calculate the risks associated with the chemicals of concern present at the site (as listed on Table 2) under future military multiple -use and residential land use scenarios were obtained from the 1997 Integrated Risk Information System (IRIS), the 1997 Health Effects Assessment Summary Tables (HEAST), or from direct guidance from the EPA risk assessment

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 23 of 56 group. Of the chemicals of concern listed in Table 2, one (vinyl chloride) is a known carcinogen and all of the remaining chemicals with the exception of 1,1,2 – TCA are considered by the EPA to be possible carcinogens. The primary target organs that are affected by long term exposure to the majority of the chemicals listed in Table 2, include but are not limited to the liver, lungs, kidney, and the central nervous system. 2.7.1.4 Risk Characterization For military multiple use scenario, the calculated carcinogenic risk based on total VOCs is 4x10-3 and the noncarcinogenic HI is 30 (this HI is almost exclusively due to carbon tetrachloride). Table 2 presents the constituents that contributed a risk greater than or equal to 1x10-6, or HI greater than or equal to 1.0, and their calculated exposure point concentration. Table 2. Primary constituents contributing to carcinogenic risk or noncarcinogenic hazard under future military

multi-use scenario (APG, 1998a).

Constituent1 RI Exposure Point

Concentration 2, µg/L Contribution to Risk Contribution to HI

1,1,2,2-TeCA 4,400 3x10-3 N/A

1,1,2-TCA 7.21 1x10-6 0.02 1,1-DCE 3.44 7x10-6 0.004

CT 2,000 9x10-4 30

CF 22.9 5x10-7 0.02

PCE 27.7 5x10-6 0.03

TCE 850 3x10-5 N/A

VC 3.8 3x10-5 N/A

Total VOCs 4x10-3 30

1 Acronyms: TeCA, tetrachloroethane; TCA, trichloroethane; DCE, dichloroethene; CT, carbon tetrachloride; CF, chloroform; PCE, tetrachloroethee; TCE, trichloroethene; VC, vinyl chloride. 2 These data are based on RI data collected prior to 1998 that were used to calculate the risk. For residential land use scenario, the calculated carcinogenic risk of 3x10-2 and the noncarcinogenic HI of 100 (which is almost exclusively due to carbon tetrachloride) sugges ted that the groundwater at Graces Quarters would warrant active remedial actions to mitigate risks associated with exposure to the contaminated groundwater under a residential usage scenario. A breakdown of the contribution of individual constituents to the overall residential risk is detailed in the RI (APG, 1998a); the hypothetical residential exposure is unlikely, however. Diverse uncertainties are inherent in the Superfund-type Human Health BRA methodology and in the assumptions on which it is based. Both the Risk Assessment Guidance for Superfund (RAGS) methodology and the Graces Quarter-specific assumptions are conservative. The potential risk and hazard from exposure to site related contamination at Graces Quarters may differ by one or more orders of magnitude from those calculated—probably being lower. That is, where a pathway is judged to be complete and a chemical has a toxicity criterion, the calculated risk or HQ for that chemical is probably higher than the actual potential risk.

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 24 of 56 2.7.2 Ecological Risk Assessment An ecological evaluation of Graces Quarters was conducted as part of the RI. Chemical analyses were performed on samples of surface soil, surface water and sediment from freshwater ephemeral ponds, and shoreline surface water and sediment from brackish water habitats (i.e., Saltpeter Creek and Gunpowder River). A survey was also conducted of the terrestrial, wetland, and aquatic flora and fauna of Graces Quarters that could be exposed to constituents of potential concern (COPCs). Surface soil, ephemeral pond surface water, and ephemeral pond sediment samples were collected from locations within the Primary Test Area and could thus be directly associated with the site. The connection between the shoreline surface water samples and the Primary Test Area is less clear because COPC, in these samples may originate from sources other than the Primary Test Area or even other than the Graces Quarters peninsula, given the tidal character of the water bodies. Thus there is a qualitative component to the evaluation of the shoreline COPC data with respect to Primary Test Area contribution. Details of the approach used to evaluate each medium are provided in the RI (APG, 1998a). The ecological risk assessment (ERA) results are summarized as follows: • During the RI, none of the chlorinated solvents that comprise the plumes in the surficial and middle aquifers

were detected in surface soil, ephemeral pond surface water, or ephemeral pond sediment associated with the Primary Test Area.

• No chlorinated solvents were detected in shoreline sediment samples, and only one chlorinated solvent

(1,1,1-trichloroethane) was detected in one of the twelve shoreline surface water samples. This detection was five orders of magnitude below the Federal Ambient Water Quality Criteria. The compound 1,1,1-trichloroethane is not a significant component of the chlorinated solvent groundwater plume associated with the Primary Test Area.

• The ERA concluded that based on comparison of the concentrations of chemicals detected in sediment to the

available toxicity values, it is reasonable to conclude that no adverse effects are currently occurring to benthic communities from chemicals in sediments from the Primary Test Area.

• The ERA concluded that based on comparison of the concentrations of chemicals detected in surface water to

the available toxicity values, it is reasonable to conclude that no adverse effects are currently occurring to aquatic life from chemicals in surface water from the Primary Test Area.

However, predictive groundwater model simulation using a starting point of plume configuration in the mid-1990's, and published by the U.S. Geological Survey (USGS) in 2001, suggested that contaminants may spread throughout various parts of the surficial and middle aquifers if no remedial action is taken (no source removal and no stimulated natural attenuation). Potential VOC discharge to the marshes south of the Primary Test Area; the marshes at the end of the Graces Quarters; or just offshore in the estuaries was also suggested by this work (USGS, 2001). Bi-annual monitoring of wells in the marshes just south of the Primary Test Area has been conducted since 1998 with the most recent round of data (December 2002) indicating continuing plume migration toward the marshes south of the Primary Test Area and VOC (1,1,2,2-

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 25 of 56 tetrachloroethane, carbon disulfate, and vinyl chloride) detections for the first time in the marsh piezometers (APG, 2003). 2.7.2 Basis for Action Based on the likelihood of future contaminant discharge to the marshes and surface waters surrounding Graces Quarters; the calculated risks to future military personnel under the reasonable worst case exposure scenario (military multiple use); the degradation of a Type I aquifer in Maryland; and the uncertainties associated with the future migration of the contaminants in the aquifer system beneath the Primary Test Area, a response action has been selected for the site that will mitigate these risks. The response action selected in this ROD is necessary to protect public health or welfare or the environment from actual or threatened releases of hazardous substances into the environment. 2.8 REMEDIAL ACTION OBJECTIVES The selected remedy is expected to meet all of the specific RAOs determined based on a review o f available data and all ARARs. RAOs consist of medium-specific goals for protecting human health and the environment. These objectives can be achieved by reducing exposure (e.g., limiting access) as well as by reducing the level of COCs. There exists the potential for exposure to contaminated groundwater associated with the Primary Test Area, although public access controls and land use restrictions are currently in place. Qualitative and quantitative RAOs are established for Operable Unit A to restore the aquifer for future beneficial use. The RAOs for Operable Unit A are as follows: • Prevent exposure to groundwater from the surficial and middle aquifers until such time as constituent

concentrations decline below levels specified in the selected remedial alternative. • Restore the aquifers' potential for beneficial use by lowering constituent concentrations to acceptable levels that

are established as quantitative RAOs. Quantitative RAOs are developed for groundwater constituents that produce LECRs greater than or equal to 1x10-6, have an HI greater than 1.0, are present at concentrations above their maximum contaminant level (MCL) established under the Safe Drinking Water Act, or are at cleanup levels acceptable to EPA. The maximum and average concentrations, the MCLs, and the RAOs for the COCs in the Primary Test Area groundwater are shown in Table 3.

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 26 of 56 Table 3. Maximum and Average COC Concentrations, MCLs, and RAO Concentrations (APG, 2004)

COCs1 Maximum

Concentrations2 (µg/L)

Average Concentrations2

(µg/L) MCL (µg/L) RAO3 (µg/L)

1,1,2,2-TeCA 4,400 767 N/A 5

1,1,2-TCA 26 9.4 5 5 1,1-DCE 4.2 2.1 7 7 CT 5,710 575 5 5 PCE 120 30 5 5 TCE 963 242 5 5 VC 16 3.5 2 2

1Acronyms: TeCA, tetrachloroethane; TCA, trichloroethane; DCE, dichloroethene; CT, carbon tetrachloride; PCE, tetrachloroethene; TCE, trichloroethene; VC, vinyl chloride. 2The maximum and average COC concentrations are based on the bi-annual monitoring data collected since 1998. RI data collected through 1998 are not included in this table. 3MCLs are identified as the RAOs for those COCs with a final MCL. 2.9 DESCRIPTION OF ALTERNATIVES A summary of the nine remedial alternatives has been developed to provide a conceptual design and cost estimate and allow for evaluation of each alternative with respect to the required evaluation criteria. While this ROD provides the basis for sound estimates for a preliminary evaluation, additional work will be required to fully assess/design a remedial system on-site. The remedial alternatives generated using the remedial action screening process for the Primary Test Area are summarized as follows: • Alternative 1: No action. • Alternative 2: Institutional controls/long-term monitoring (LTM). • Alternative 3: Vitamin B12-catalyzed reductive dehalogenation in areas greater than 1,000 µg/L; MNA at all

other locations. • Alternative 4: Vitamin B12-catalyzed reductive dehalogenation in areas greater than 1,000 µg/L; pump -and-treat

at all other locations. • Alternative 5: Vitamin B12-catalyzed reductive dehalogenation in areas greater than 1,000 µg/L in the surficial

aquifer; pump -and-treat at all other locations. • Alternative 6: Vitamin B12-catalyzed reductive dehalogenation in areas greater than 100 µg/L (both aquifers);

MNA at all other locations. • Alternative 7: Pump -and-treat at all locations.

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 27 of 56 • Alternative 8: Pump -and-treat in areas greater than 1,000 µg/L (both aquifers); LTM at all other locations. • Alternative 9: Electrical resistance heating (ERH) in areas greater than 1,000 µg/L in the surficial aquifer;

pump-and-treat at all other locations. Institutional controls and groundwater compliance monitoring are included for each alternative except Alternative 1. These controls will include appropriate warning signs, and land and water patrols, and will be detailed in the remedial design in a separate design document. Land use restrictions will be used at Graces Quarters to prohibit the unauthorized extraction and use of groundwater in Operable Unit A. Residential or military residential housing will also be prohibited. Annual site inspections will be conducted to ensure these controls are in place. The Graces Quarters groundwater Operable Unit will be included in the regularity scheduled CERCLA 5-year reviews at APG. UXO screening/clearance is required for all intrusive activities occurring at the site, but is not otherwise addressed under Operable Unit A. These issues are addressed by the Selected Remedy for Operable Unit B -- Public Access Controls, Land Use Restrictions, and Erosion Controls -- as detailed in the ROD for Carroll Island and Graces Quarters Operable Unit B (APG, 2001a). In each of the following alternatives present worth O&M cost was listed instead of annual O&M costs because most of the alternatives involve an up-front treatment option. The O&M cost is different in different years for each alternative, and continues for a different length of time in the different alternatives. Consequently, there is no uniform annual O&M cost that could be listed. The details of the O&M annual cost breakdown are given in the FS (APG, 2004) and can be found in the administrative record. 2.9.1 Alternative1: No Action • Estimated Capital Cost: $0 • Estimated Present Worth Operation & Maintenance (O&M) Cost: $0 • Estimated Total Present Worth Cost: $0 • Estimated Time to Achieve RAOs: Will not Achieve RAOs The EPA FS process requires that a "no action" alternative be evaluated as a basis for comparing alternatives. Although security patrols are presently conducted at APG and warning signs exist, no "additional" action is taken. Therefore, no efforts are undertaken to locate or prevent exposure to VOC contaminated groundwater. This alternative is used for comparison purposes to evaluate other alternatives. Under the No Action alternative for Graces Quarters Operable Unit A, no remedial efforts would be made to control risks to human or ecological receptors; treat or remove waste; or reduce the toxicity, mobility, or volume of contaminated media. Institutional actions (such as land use restrictions) specifically pertaining to Operable Unit A would not be implemented and would not continue if in place now. There are no costs associated with capital, O&M and net present worth.

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 28 of 56 2.9.2 Alternative 2: Institutional Controls/LTM • Estimated Capital Cost: $0 • Estimated Present Worth O&M Cost: $400,000 • Estimated Total Present Worth Cost: $400,000 • Estimated Time to Achieve RAOs: undefined With this alternative, no actions are conducted to remediate groundwater contamination at the site. This alternative does include institutional controls that will be implemented at Graces Quarters as part of the Selected Remedy Appropriate access controls will include warning signs, and land and water patrols, the institutional controls will be detailed in the remedial design in a separate design document. Land use restrictions will be placed on the Primary Test Area Operable Unit A to prohibit the unauthorized extraction and use of groundwater. Residential or military residential housing, and extraction/use of groundwater will be prohibited. Annual site inspections will be conducted to ensure the controls are in-place. This alternative also includes LTM of groundwater at the Primary Test Area which will continue as long as exceedances of MCLs are present in the groundwater. Annual groundwater monitoring will be performed to document the plume configuration and concentration. The design workplan will outline the wells to be sampled, sample analysis, contingency plans, and criteria for discontinuation of the monitoring program. As discussed in the FS Report, groundwater monitoring will consist of sampling 20 compliance wells for VOCs annually. An annual report will present the data results and describe the plume configuration, migration, and change in contaminant levels. 2.9.3 Alternative 3: Vitamin B12-catalyzed reductive dehalogenation in areas greater than 1,000 µg/L; MNA at all other locations • Estimated Capital Cost: $2,111,496 • Estimated Present Worth O&M Cost: $3,588,504 • Estimated Total Present Worth Cost: $5,700,000 • Estimated Time to Achieve RAOs: 30 years Alternative 3, which was identified as the Preferred Alternative in the Proposed Plan issued in April 2004, involves treating areas with VOC concentrations greater than 1,000 µg/L with vitamin B12 amendment and using MNA where concentrations are less than 1,000 µg/L. Land use restrictions (described in Alternative 2) will be enforced to prevent exposure to groundwater contaminants until remediation goals are achieved. Institutional controls will be detailed in the remedial design documents. The vitamin B12 treatment technology has been demonstrated during a pilot study conducted at the Primary Test Area from September 1999 to December 2000 (APG, 2001b). The technology introduces a buffered solution of vitamin B12, titaniu m citrate, and other carbon substrates into the subsurface. The vitamin B12 amendment will be introduced into the subsurface via a recirculation well or other alternative methods such as direct injection or injection through standard wells. Vitamin B12 is a transitional-metal coenzyme containing a cobalt atom in the center of the molecule that, in a chemically reducing environment, catalyzes dechlorination of CAHs. The vitamin B12 treatment technology is expected to meet the performance standard of reducing the total VOCs concentrations to below 100 µg/L in the treatment zones within five years. This

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 29 of 56 technology also is consistent with the EPA guidance using treatment to destroy principal threats, particularly at DNAPL areas, in conjunction with MNA solutions Effective treatment of the hot spot areas will facilitate the use of MNA to remediate areas of the plume where concentrations are less than 1,000 µg/L. In addition to source treatment, the addition of vitamin B12 amendment is expected to expand the extent of the chemical reducing zones beyond the immediate treatment area over time as the vitamin B12 is transported through the aquifer beyond the initial treatment areas. Reduction in contaminant concentrations by natural attenuation will be documented and evaluated through a MNA program to be specified in the design workplan. The achievement of MCLs, which were identified as the RAOs, for the COCs allows termination of monitoring and other requirements. It is anticipated that the design and construction will take two years or less, duration of vitamin B12 injections will be for approximately a year, and that the requirement of MNA monitoring will be 30 years or less.LTM will include monitoring for arsenic and the design specifications for such monitoring will be included in the design workplan. Naturally occurring arsenic may be temporarily released from the aquifer matrix (soil) in response to the reducing conditions created by the treatment technology. This is a reversible condition and arsenic concentrations will drop following completion of the active remedy. 2.9.4 Alternative 4: Vitamin B12-catalyzed reductive dehalogenation in areas greater than

1,000 µg/L; pump-and-treat at all other locations • Estimated Capital Cost: $3,324,793 • Estimated Present Worth O&M Cost: $6,075,207 • Estimated Total Present Worth Cost: $9,400,000 • Estimated Time to Achieve RAOs: 20 years Alternative 4 involves treating areas with VOC concentrations greater than 1,000 µg/L with the vitamin B12 amendment as detailed under Alternative 3. Groundwater extraction and surface treatment by conventional technologies will be used where concentrations are less than 1,000 µg/L. To capture the groundwater plume where concentrations are between 5 and 1,000 µg/L, groundwater will be ext racted, treated above ground using air stripping and carbon adsorption, and discharged to the Gunpowder River meeting the requirements of the National Pollutant Discharge Elimination System (NPDES) using MDE approved discharge parameters. Conventional or horizontal extraction wells would be used as needed to capture this groundwater. It is anticipated that the design and construction will take two years or less. The vitamin B12 treatment technology is expected to meet the performance standard of reducing the total VOC concentrations to below 100 µg/L in the treatment zones within five years. The performance standard that triggers a shut down of the pump -and-treat operation will be based upon the achievement of MCLs or residential RBCs for the COCs. A monitoring program will be specified in the design workplan. 2.9.5 Alternative 5: Vitamin B12-catalyzed reductive dehalogenation in areas greater than

1,000 µg/L in the surficial aquifer; pump-and -treat at all other locations • Estimated Capital Cost: $2,471,264 • Estimated Present Worth O&M Cost: $6,128,736 • Estimated Total Present Worth Cost: $8,600,000 • Estimated Time to Achieve RAOs: 30 years.

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 30 of 56 Alternative 5 combines vitamin B12-catalyzed reductive dechlorination in areas greater than 1,000 µg/L in the surficial aquifer with pump -and-treat for the remaining areas of the plume, including areas in the middle aquifer greater than 1,000 µg/L. The vitamin B12 component of Alternative 5 is similar to that described for Alternatives 3 and 4. However, this alternative only delivers vitamin B12 amendment using recirculation wells in the surficial aquifer plume in areas with total VOC concentrations above 1,000 µg/L. The groundwater extraction and treatment component of Alternative 5 is the same as that described for Alternative 4, capturing groundwater with VOC concentrations between 5 and 1,000 µg/L. For the middle aquifer, this alternative includes groundwater extraction and treatment for all contamination above 5 µg/L. As described in Alternative 4, extracted groundwater will be treated above ground using air stripping and carbon adsorption, and then discharged to the Gunpowder River meeting the requirements of the NPDES using MDE aproved discharge parameters. It is anticipated that the design and construction will take two years or less. The implementation of vitamin B12 treatment technology is expected to meet the performance standard of reducing the total VOC concentrations to below 100 µg/L in the treatment area in the surficial aquifer within five years. The performance standard that triggers a shut down of the pump -and-treat operation in both surficial and middle aquifers will be based upon the achievement of MCLs or residential RBCs for the COCs. A monitoring program will be specified in the design workplan. 2.9.6 Alternative 6: Vitamin B12-catalyzed reductive dehalogenation in areas greater than

100 µg/L (both aquifers); MNA at all other locations • Estimated Capital Cost: $5,304,838 • Estimated Present Worth O&M Cost: $8,995,162 • Estimated Total Present Worth Cost: $14,300,000 • Estimated Time to Achieve RAOs: 20 years The vitamin B12 component of Alternative 6 is similar to that described for Alternative 3. However, Alternative 6 includes vitamin B12 treatment in areas of the plume, in both the surficial and middle aquifers, where total VOC concentrations exceed 100 µg/L. The vitamin B12 system represented here is conceptually the same as for Alternative 3 other than the increased number of wells required to treat the larger area, the increased flow rate, and an increased amount of vitamin B12 amendment used. Additionally, a pipeline installed three feet underground may be necessary to supply the vitamin B12 amendment to the delivery wells under this alternative. MNA will be used to remediate areas of the plume where total VOC concentrations are less than 100 µg/L. Reduction in contaminant concentrations by natural attenuation will be documented and evaluated through a MNA monitoring program to be specified in the design workplan. It is anticipated that the design and construction will take two years or less. The vitamin B12 treatment technology is expected to meet the performance standard of reducing the total VOC concentrations to below 100 µg/L in the treatment areas within five years. Following the termination of the vitamin B12 injections, MNA is expected to meet the MCLs or residential RBCs for COCs within 30 years, and when these levels are reached, monitoring will cease.

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 31 of 56 2.9.7 Alternative 7: Pump-and-Treat at all locations • Estimated Capital Cost: $1,494,890 • Estimated Present Worth O&M Cost: $5,005,110 • Estimated Total Present Worth Cost: $6,500,000 • Estimated Time to Achieve RAOs: Indeterminate length of time due to possible DNAPL Alternative 7 consists of groundwater pump -and-treat for all of the surficial and middle aquifers where VOC contamination exceeds 5 µg/L. The extracted groundwater will be treated above ground using conventional technologies such as air stripping and carbon adsorption, and discharged to the Gunpowder River meeting the requirements of the NPDES using MDE approved discharge parameters. Compliance monitoring (documentation of the plume configuration and concentration) will consist of sampling compliance wells for VOCs, and the groundwater extraction wells for VOCs and iron quarterly during the first two years. Subsequently, the compliance wells and the extraction wells will be sampled annually during years three through five, and bi-annually thereafter. Throughout operation of the system, influent and effluent groundwater samp les will be collected from the air-stripping/adsorption system on a quarterly basis and analyzed for VOCs. Similarly, vapor samples will be collected before and after the granular activated carbon units and analyzed for VOCs to evaluate system performance. It is anticipated that the design and construction will take two years or less. A potential problem with pump -and-treat technology at this site is that contaminants, particularly DNAPL, may continue to desorb from the soil matrix once the treatment is stopped, and rebound to concentrations above the cleanup criteria. Therefore, the time required for the operation of pump -and-treat alone is indeterminate, and the long-term O&M costs may become substantial. The pumping of the diluted plume will continue until MCLs or residential RBCs for COCs are achieved. A groundwater monitoring plan will be specified in the design workplan. 2.9.8 Alternative 8: Pump-and-treat in areas greater than 1,000 µg/L (both aquifers); LTM

at all other locations • Estimated Capital Cost: $801,934 • Estimated Present Worth O&M Cost: $2,208,066 • Estimated Total Present Worth Cost: $3,010,000 • Estimated Time to Achieve RAOs: Indeterminate length of time due to possible DNAPL Alternative 8 consists of groundwater pump -and-treat for all of the surface and middle aquifers where VOC concentrations are above 1,000 µg/L and LTM where concentrations are below 1,000 µg/L. Land use restrictions (described in Alternative 2) will be enforced to prevent exposure to groundwater contaminants until re mediation goals are achieved, if achievable under this alternative. The groundwater extraction and treatment component of Alternative 8 is similar to that of Alternatives 4, 5, and 7, capturing groundwater with VOC concentrations greater than 1,000 µg/L. The extracted groundwater will be treated above ground using conventional technologies such as air stripping and carbon adsorption, and then discharged to the Gunpowder River meeting the requirements of the NPDES using MDE approved discharge parameters. It is anticipated that the design and construction will take two years or less. As described in Alternative 7, evaluation of the system performance will include monitoring of compliance wells, extraction wells, influent and effluent groundwater samples of the air-stripping/adsorption system, and vapor samples after

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 32 of 56 the vapor phase granular activated carbon units. LTM, to be specified in the design workplan, will be instituted to assess the impact on the dissolved phase plume in response to the source control pumping, and any naturally occurring attenuation process. The pumping of the ground water plume would continue until MCLs or residential RBCs for COCs are achieved. As discussed for Alternative 7, pump -and-treat systems are known to potentially fail in areas where residual products and DNAPLs are present, as is suspected at Graces Quarters. In addition, VOCs in areas where their concentrations are below 1,000 µg/L, but still above their regulatory cleanup levels, will remain largely untreated by this alternative and may not be contained during the anticipated long treatment duration. This alternative, therefore, may not meet the performance standard of MCLs or residential RBCs for COCs. 2.9.9 Alternative 9: ERH in areas greater than 1,000 µg/L in the surficial aquifer; pump-and-treat at all other locations • Estimated Capital Cost: $3,038,504 • Estimated Present Worth O&M Cost: $6,861,496 • Estimated Total Present Worth Cost: $9,900,000 • Estimated Time to Achieve RAOs: 30 years Alternative 9 involves using ERH for remediation of the surficial aquifer where VOC concentrations exceed 1,000 µg/L. For areas in the surficial aquifer where VOC concentrations are below 1,000 µg/L, and for the entire plume in the middle aquifer, pump -and-treat will be used. This technology uses low-frequency electricity delivered to three electrodes in a triangular array to uniformly heat the target area to the boiling point of water, converting the subsurface moisture (groundwater) and contaminants to steam and vapor. The steam and vapor are extracted via conventional extraction technologies such as soil vapor extraction and are treated on site. Three-phase electricity can be obtained from the existing power source that runs to the vitamin B12 pilot study building (APG, 2002). The expected maximum temperature in the target area (100,000 ft2) will be 100 to 112 degree Celsius (°C) and the estimated power required to operate the system is 9,250,000 kilowatt hours (kW-hr) over the year of anticipated operations. ERH technology, however, is not suitable for the middle aquifer because of the difficulties involved with placing electrodes in the middle aquifer and collecting the steam and vapors. Possible concerns with ERH are the potential for releases of hazardous vapors to the atmosphere, the potential remobilization of DNAPLs into the aquifer due to decreased viscosity as it is heated by the ERH process, and physical hazards associated with high voltage and high temperatures. The latter may potentially explode the UXO, if present, and melt polyvinyl chloride (PVC) materials that are commonly used for monitoring wells in the subsurface. The pump -and-treat component of this alternative will be similar to that described in Alternatives 4, 5, 7 and 8. The extracted groundwater will be treated above ground using conventional technologies such as air stripping and carbon adsorption, and then discharged to the Gunpowder River meeting the requirements of the NPDES using MDE approved discharge parameters. It is anticipated that the design and construction will take two years or less. Evaluation of the system performance will include monitoring of compliance wells, extraction wells, influent and effluent groundwater samples of the air-stripping/adsorption system, and vapor samples after the vapor phase granular activated carbon units. The monitoring program will be specified in the design workplan. The pumping of the diluted plume will continue until MCLs or residential RBCs for COCs are achieved.

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 33 of 56 2.10 COMPARATIVE ANALYSIS OF ALTERNATIVES In evaluating the remedial alternatives for Operable Unit A, the potential performance of each alternative is evaluated in terms of the nine evaluation criteria required by the NCP: • protection of human health and the environment; • compliance with ARARs; • long-term effectiveness; • reduction of toxicity, mobility, and volume of chemicals through treatment; • short-term effectiveness; • implementability; • cost; • state acceptance; and • community acceptance. The nine criteria are categorized into one of three groups: threshold criteria, primary balancing criteria, or modifying criteria. The alternative selected must satisfy the threshold criteria, which are of primary importance. The primary balancing criteria are used to weigh the major tradeoffs among the alternatives, and the modifying criteria are considered after the public has commented on the Proposed Plan. A summary of the ranking of each alternative is provided as Table 4, Comparative Analysis of Alternatives. 2.10.1 Threshold Criteria Overall Protection of Human Health and the Environment Overall protection of human health and the environment addresses whether each alternative provides adequate protection of human health and environment and describes how risks posed through each exposure pathway are eliminated, reduced, or controlled, through treatment, engineering controls, and/or institutional controls. Alternative 1 (no action) may not provide adequate long-term protection of human health and the environment because no restrictions are assumed to be in place to prevent future use of the contaminated groundwater at the site. Although the site is on Department of Defense (DOD) property, this alternative assumes that land use restrictions will not be enforced. Groundwater monitoring will not be conducted, so no data will be available to evaluate contamination concentrations and migration. Alternatives 2 through 9 are considered protective of human health because land use restrictions will prohibit future use of groundwater from the Primary Test Area and Alternatives 3 through 9 provide for remediation of the groundwater. These alternatives vary, as detailed in the FS Report, with respect to long-term protection of human health and the environment (APG, 2004). Overall, Alternative 6 receives the best rating for this criterion due to its aggressive treatment of almost the entire plume (at a proportionally larger cost). Alternatives 3, 4, 5, 7, and 9 receive a good rating. Alternatives 2 and 8 receive an adequate rating while Alternative 1 a poor rating.

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 34 of 56

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 35 of 56 Compliance with ARARs Section 121(d) of CERCLA and NCP §300.430(f)(1)(ii)(B) require that remedial actions at CERCLA sites at least attain legally applicable or relevant and appropriate Federal and State requirements, standards, criteria, and limitations which are collectively referred as "ARARs," unless such ARARs are waived under CERCLA section 121(d)(4). The MCLs specified in the National Primary Drinking Water Standards are relevant and appropriate requirements. Based on the high formation permeability, the natural water quality and low total dissolved solids, the aquifers beneath the Primary Test Area are classified by the State of Maryland as Type I (COMAR 26.08.02.09). The EPA classifies both the unconfined and middle aquifers as Type IIB based on yield, total dissolved solids, and the quality. Existing contaminants (i.e., 1,1,2,2-tetrachloroethane) must be treated to attain MCLs and risk based standards (in order for the groundwater to serve as a source of water supply. Alternatives 1 and 2 receive the lowest rating for this criterion because it does not meet the Federal ARARs to clean up the groundwater to MCLs. Alternative 8 also receives a low rating because groundwater in areas where LTM is used may still contain VOCs at concentrations above the MCLs. The remaining alternatives all receive an excellent rating. Alternatives 3, 4, 5, and 6 (involving injection of substrates into the ground) are expected to achieve the MCLs for the chlorinated solvents. However, injection may result in temporary increases in arsenic concentrations above the MCL, total dissolved solid concentrations above the Type I groundwater standards, and titanium in groundwater above its RBC in the treatment zone. It is unclear whether groundwater titanium levels will be above the associated RBC. Pilot testing conducted to date indicates each of these effects is localized and temporary (concentrations are naturally reduced over time). Downgradient monitoring for these parameters will be specified in the design workplan. Alternatives 7 and 9 will comply with all pertinent ARARs. It is important to note, however, that if residual product is present in the source areas, pump -and-treat alone will not remediate these areas to MCLs or other approved cleanup criteria. The pump -and-treat component of Alternatives 4, 5, 7, 8 and 9 will need to comply with applicable Maryland Air Quality Regulations, NPDES regulations, and hazardous waste requirements for spent carbon. 2.10.2 Primary Balancing Criteria Long-term Effectiveness and Permanence The long-term effectiveness and permanence criterion considers the magnitude of the residual risk that would remain after the implementation of an alternative, and the adequacy and reliability of the controls instituted. Alternative 1 (no action) may not provide long-term effectiveness and permanence because no treatment or source removal are to be implemented at the site. Although the site is on DOD property, this alternative assumes that land use restrictions will not be enforced. Groundwater monitoring will not be conducted, so no data will be available to evaluate contamination concentrations and migration. Alternative 1 is not evaluated further in this section, as it does not meet the threshold criteria for protection of human health and the environment, long-term effectiveness and permanence, and compliance with ARARs. Alternatives 2 through 9 include land use restrictions to prevent groundwater use and groundwater monitoring to document the size and concentrations of the plumes. Alternative 2, however, does not remediate the groundwater and thus is not considered a permanent solution.

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 36 of 56 The vitamin B12 component of Alternatives 3, 4, 5, and 6 will result in reductive dehalogenation of the contaminants, which is an irreversible process that decreases the degree of chlorination under reducing conditions ultimately to ethene, ethane, or methane. For Alternatives 3 and 6, natural attenuation processes will help ensure that the chlorinated constituents outside the treatment areas are reduced over time to acceptable levels. Natural attenuation processes will lead to permanent reduction in chlorinated solvent concentrations as attenuation progresses. Pump -and-treat systems included in Alternatives 4, 5, 7, 8 and 9 have been used at hundreds of remediation sites with proven long-term effectiveness in terms of hydraulic control and surface treatment. For each of these alternatives the plume will be contained by the extraction wells until RAOs are achieved. A potential problem with pump-and-treat is that contaminants may rebound once the treatment has ceased, or if residual product remains in the subsurface. RAOs may not be achievable with this technology alone. Alternative 9 includes ERH in addition to pump -and-treat. ERH is an irreversible process that volatizes or hydrolyzes contaminants and extracts them via soil-vapor extraction wells. A pilot test, however, will be required to verify the effectiveness of this approach, the design assumptions (e.g., electrode spacing), and the electrical power requirements that may be significant. Overall, Alternatives 6 and 9 receive an excellent rating due to their aggressive treatment of the contaminant plume (at proportional costs). Alternatives 3, 4, 5 and 7 receive a good rating for long-term effectiveness and permanence. Alternative 2 receives a poor rating because no treatment occurs. Alternative 8 also receives a poor rating because contaminants in areas where LTM is applied may still be present at concentrations above their regulatory cleanup levels and remain untreated. Reduction in Toxicity, Mobility, and Volume Reduction of toxicity, mobility, or volume through treatment refers to the anticipated performance of the treatment technologies that may be included as part of a remedy. The vitamin B12 component of Alternatives 3, 4, 5, and 6 will result in reduction of groundwater toxicity from chlorinated solvent constituents, but may temporarily increase arsenic concentrations in groundwater within the treatment zone. The extent to which arsenic is mobilized will be driven by aquifer redox chemistry. Should the soluble, reduced form of arsenic be transported to an aerobic portion of the aquifer, the arsenic will be oxidized and precipitated. Under lower redox conditions, the arsenic may co-precipitate with iron. Thus, the potential extent of arsenic migration will be naturally limited. Monitoring for this metal will be specified in the design work-plan. The pump -and-treat component of Alternatives 4, 5, 7, 8 and 9 will effectively contain and extract the contaminated groundwater hence decreasing its toxicity, mobility, and volume. However, pump -and-treat may have limited effect on areas of the aquifer where residual product remains. The air stripper and carbon adsorption units will remove the strippable and non-strippable contaminants from the groundwater. Constituents transferred to activated carbon will subsequently be destroyed when the carbon is thermally regenerated. The ERH component of Alternative 9 will result in reduction of groundwater toxicity as contaminants are volatilized and extracted by the soil-vapor extraction wells.

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 37 of 56 Overall, Alternative 2 receives a poor rating in this category, Alternatives 3, 4, and 6 have an excellent rating, while Alternatives 5, 7, 8 and 9, relying heavily on pump -and-treat receive a good rating. Short-Term Effectiveness Short-term effectiveness addresses the period of time needed to implement the remedy and any adverse impact that may be posed to workers, the community and the environment during construction and operation of the remedy until cleanup levels are achieved. Alternative 2 does not include groundwater remediation, and thus, the time required to achieve RAOs is undefined. For Alternatives 3, 4, 5, and 6, the chemical injection of vitamin B12 amendment is estimated to be completed within a year. The rate at which the chlorinated solvent plume not subjected to direct treatment is attenuated under Alternatives 3 and 6, will be dependent on the extent to which reducing conditions are established through transport of the injected chemicals, and the natural rate of attenuation achieved through physical mechanisms in the aquifer following source control activities (vitamin B12 treatment). The natural attenuation portion of Alternatives 3 and 6 are conservatively estimated to take 30 and 20 years, respectively, to achieve the RAOs. Alternative 6 is estimated to take less time than Alternative 3 because the vitamin B12 injection covers a much larger area of the plume for Alternative 6. For Alternatives 4, 5, 7, 8 and 9, the rate at which the pump -and-treat system remediates the aquifers will be controlled by the rate of desorption of the chlorinated constituents from aquifer media. Alternative 4, which includes vitamin B12 treatment for source area reduction in both aquifers and with pump -and-treat, is conservatively estimated to achieve RAOs in 20 years. Alternatives 5 and 9 only include "source area" reduction (via vitamin B12 treatment or ERH) in the surficial aquifer along with pump -and-treat, and are conservatively estimated to achieve RAOs in 30 years. ERH (Alternative 9) is predicted to achieve "source area" reduction within 1 year, however a pilot scale test would be required to verify this estimate. Alternatives 7 (pump -and-treat) and 8 (pump -and-treat along with MNA) are estimated to take at least 30 years to achieve the RAOs and may not be effective in the source areas. Overall, Alternatives 4 and 6 receive the highest short-term effectiveness rating. Alternatives 3, 5 and 9 each receive a good rating, and Alternatives 2, 7, and 8 each receive an adequate rating. Implementability There are three main factors considered for this criterion: technical feasibility, administrative feasibility and availability of services and materials. Alternatives 2 through 9 are administratively feasible and the required services and materials are available. Technical feasibility therefore is the focus of the implementability analysis. Alternative 2 has no implementability considerations because there is no construction associated with this alternative and therefore receives an excellent rating in this category. Installation of the infrastructure for the vitamin B12 treatment, pump -and-treat, and ERH technologies should not be difficult. Proper precautions are necessary when performing any intrusive work due to UXO on-site. The primary technical issue regarding the vitamin B12 treatment component of Alternatives 3, 4, 5 and 6 is the on-site generation of titanium citrate (reducing agent), because it cannot be purchased (assuming titanium citrate is the reducing agent ultimately used). The O&M of the vitamin B12 system will require two full-time operators for

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 38 of 56 one year, and is expected to be more intensive than the other technologies. However, it is expected that treatment with vitamin B12 will be for one year only. Technical issues associated with ERH include the transfer of heat to the subsurface and the collection of steam and vapors. The presence of UXO may result in an explosive hazard due to the high soil temperatures. The shallow depth of the treatment target area may make it harder for the vapor extraction system to capture all of the vapors and prevent hazardous vapor release to the atmosphere. ERH technology can be operated with one part-time operator. However, a pilot test would be required for this technology to demonstrate its implementability. The pump -and-treat components of Alternatives 4, 5, 7, 8 and 9 present no technical implementability issues because this is a well developed technology. Overall, Alternatives 2 and 3 receive the highest rating (excellent) in this category. Alternatives 4, 5, 6, 7, 8 each are classified as good. Alternative 9 may have some implementability issues and was classified as adequate in this category. Cost Alternative 2 provides no remediation but does include LTM and has an estimated total cost of $400,000. Alternatives 3, 7 and 8 each have estimated total net present worth costs of $5,700,000, $6,500,000 and $3,010,000, respectively. Alternatives 9 and 6 are the most expensive with estimated net present worth costs of $9,900,000 and $14,300,000, respectively. The major cost component of the vitamin B12 treatment technology is the labor expense and chemical cost to produce the vitamin B12 amendment. The costs associated with producing the vitamin B12 amendment, the frequency of amendment injections, the number of injection locations, and the duration of the amendment injection period drive the estimated costs for Alternatives 3, 4, 5 and 6. Increasing or decreasing the area to be remediated will significantly affect the cost, and therefore the cost effectiveness, to operate the vitamin B12 treatment. Increasing the number of pumping well locations in the pump -and-treat alternatives would have less of an affect on the pump -and-treat costs. However, the cost effectiveness of the pump -and-treat and ERH alternatives is poor since the time to remediation is indeterminate (since residual DNAPL may remain in the source areas). The number of years required for the pump -and-treat system to achieve the RAOs is a major cost uncertainty for Alternatives 4, 5, 7 and 8. Overall, Alternative 2 receives the highest rating (excellent) in this category because it does not require capital spending. Its effectiveness however is poor. Alternative 3, 7 and 8 each rank as good. Alternatives 4, 5, and 9 are rated adequate, with Alternative 6 ranked poor. 2.10.3 Modifying Criteria State Acceptance The MDE, Waste Management Administration, accepts the selection of Alternative 3 for the site conditions at Graces Quarters.

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 39 of 56 Community Acceptance Based upon the comments received, for the most part, the public concurs with the selection of Alternative 3. Though significantly more expensive, the second most preferred technology was Alternative 6. 2.11 SELECTED REMEDY Based upon the distribution of contaminants and the detected concentrations, residual DNAPL may exist in the surficial aquifer in the area where concentrations exceed 1,000 µg/L total VOCs. DNAPL in the groundwater beneath the Primary Test Area is considered a principal threat waste. Dissolved-phase COCs where concentrations are less than 1,000 µg/L are non-principal threat wastes. Actual or threatened releases of DNAPL and/or greater than 1,000 µg/L total VOCs from the site, if not addressed by implementing the response action selected in this ROD, may present an imminent and substantial endangerment to public health, welfare, or the environment. Alternative 3 is selected because it provides good overall protection of human health and the environment; provides long- and short-term effectiveness; reduces the toxicity, mobility and volume of hazardous constituents through treatment; complies with all ARARs; and has been demonstrated to be implementable. Additionally, Alternative 3 is preferred as it is aggressive and more cost effective than the other alternatives except Alternatives 1, 2, and 8 which are judged to be ineffective at achieving RAOs. The remediation costs ($5,700,000) for Alternative 3, as estimated in the FS (APG, 2004), are presented herein as Table 5. The information in this cost summary was based on the best available information regarding the anticipated scope of the remedial alternative. Changes in the cost elements are likely to occur as a result of new information and data collected during the engineering design of the remedial alternative. This is an order-of-magnitude engineering cost estimate that is expected to be within +50 and -30 percent of the actual project cost. Specifically, Alternative 3 involves treating areas with VOC concentrations greater than 1,000 µg/L with vitamin B12 amendment and using MNA where concentrations are less than 1,000 µg/L. Land use restrictions will be enforced to prevent exposure to groundwater contaminants until remediation goals are achieved. Land use restrictions will include prohibitions of residential or military residential housing, and extraction/use of groundwater. Appropriate access controls will include warning signs, and land and water patrols. Annual site inspections will be conducted to ensure these institutional controls are in place. Alternative 3, is consistent with the EPA's guidance to use treatment to destroy principal threats and stimulated natural attenuation to address non-principal threats (e.g., dilute VOC plume). The vitamin B12 amendment will be introduced into the subsurface via recirculation wells or other alternative methods such as direct injection or injection through standard wells. A vitamin B12 catalyzed reductive dehalogenation pilot test has already demonstrated that the technology is particularly effective in degrading chlorinated solvent concentrations to low levels (APG, 2001b). The vitamin B12 recirculation well conceptual design (Figure 10) presented in this alternative is based on a pilot study conducted at the Primary Test Area from September 1999 to December 2000 (APG, 2001b). The vitamin B12 amendment may be delivered to the groundwater via recirculation wells, direct injection, or other means. The injection systems will be located to treat the extent of the plume with VOC concentrations greater than 1,000 µg/L.

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 40 of 56 Table 5. Estimated Remediation Costs for Alternative 3 (APG, 2004)

DESCRIPTION UNIT QUANTITY RATE/UNIT COST 1. CAPITAL COSTS Vitamin B12 Building/Equipment New Chemical Mixing Building 1s 1 $150,000 $150,000 Primary Mixing Tanks each 4 $12,000 $48,000 Secondary Mixing Tanks each 2 $14,000 $28,000 Pillow Tanks each 2 $10,000 $20,000 Equipment /Piping (New + Upgrade) 1s 1 $200,000 $200,000 Subtotal $446,000 Surficial Aquifer Vitamin B12 recirculation well (plus piezometers) each 13 $34,000 $442.000 vitamin B12 pipe network installation If 1,400 $40 $56,000 Subtotal $498,000 Middle Aquifer Vitamin B12 recirculation well (plus piezometers) each 12 $47,000 $564,000 vitamin B12 pipe network installation If 2,400 $40 $96,000 Subtotal $660,000 Engineering Design (includes MNA, UXO plans) 1s $250,000 Construction Management (5% of subtotal capital costs)

$80,200

PRESENT WORTH OF CAPITAL COSTS $1,930,000 2. O&M COSTS (10-year discount factor 3.1%) Year 1 Operations (During vitamin B12 injection - 25 recirculation wells) Labor (2 people; full time) person-days 520 $320 $166,400 Vitamin B12 amendment for Surficial Aquifer gal conc. 405,600 $3 $1,123,400 Vitamin B12 amendment for Middle AquiferElectrical Costs gal conc 374,400 $3 $1,037,088 Electrical cost kW-hr 336,057 $0 $30,245 Laboratory Analytical (Quarterly) sample 700 $250 $175,000 Sampling Labor (2 people x one day for each recirculation well system/event) person-days 200 $320 $64,000 Reporting/ Technical Support/ Data Analysis 1s 4 $60,000 $240,000

Annual Subtotal $2,836,245 Year 2 Operations (Recirculation wells operation only) Labor (1 person; 1 day/wk) person-days 52 $320 $16,640 Electrical costs kW-hr 333,149 $0,09 $29,983

Annual Subtotal $46,623 Years 1-2 Compliance Monitoring (Quarterly) Labor (2 people x 2 days/event) person-days 16 $320 $5,120 Laboratory Analytical for VOCs and MNA parameters (20 compliance wells)

sample 80 $475 $38,000

Reporting/ Data Analysis event 4 $15,000 $60,000

Annual Subtotal $103,120 Years 3-5 Compliance Monitoring (Annually) Labor (2 people x 2 days/event) person-days 4 $320 $1,280 Laboratory Analytical for VOCs (20 wells) sample 20 $105 $2,100 Reporting/ Data Analysis event 1 $15,000 $15,000

Annual Subtotal $18,380 Years 6-30 Compliance Monitoring (Bi-annually; Yrs. 6, 8, 10, 12, etc.) Labor (2 people x 2 days/event) person-days 4 $320 $1,280 Laboratory Analytical for VOCs (20 wells) sample 20 $105 $2,100 Reporting/ Data Analysis event 1 $15,000 $15,000 Annual Subtotal $18,380 PRESENT WORTH O&M COSTS $3,280,000 SUBTOTAL COST OF ALTERNATIVE 3 $5,210,000 Contigency (10% of net present worth) $521,000 TOTAL COST OF ALTERNATIVE 3 $5,700,000

Note: O&M costs were estimated based on 25 recirculation wells, 20 monitoring wells, and 30 years of compliance groundwater monitoring.

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 41 of 56 Figure 10. Conceptual diagram of a recirculation well

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 42 of 56 The vitamin B12 amendment will be pumped to each recirculation well from a central chemical mixing plant or from mobile tanks/tankers. It is likely that clean water to be used in preparing the vitamin B12 amendment will be supplied from well Q29 which is upgradient of the contaminant plume. This well will be re -sampled before being used as a supply well. Based on pilot test results, vitamin B12 amendment will be generated in batch mode on-site. Tolcide (a bacteriostatic agent) may be added to each well as needed to preclude biological fouling of the injection systems. Redevelopment of wells with carbon dioxide (Aqua Freed) may also be conducted periodically if required. Based on pilot test results, it is likely that source area (i.e., areas with total VOC concentrations greater than 1,000 µg/L) reduction will be achieved within a 1-year period of vitamin B12 amendment injections. MNA will be used to remediate areas of the plume where concentrations are less than 1,000 µg/L. It is important to note that the addition of the vitamin B12 amendment is expected to expand the extent of the strong reducing zone beyond the design treatment area over time as the vitamin B12 amendment is transported through the aquifer beyond the recirculation well capture area. Reduction in contaminant concentrations by natural attenuation will be documented and evaluated through a MNA monitoring program. The results of groundwater monitoring will be used to evaluate the natural attenuation progress and describe contaminant reductions due to natural attenuation. Annual or bi-annual reports will present the data results and describe the plume configuration, migration, and change in contaminant levels. The reports will include an assessment of how effective natural attenuation is in reducing contamination. To provide a baseline to evaluate the effectiveness of natural attenuation, groundwater monitoring will periodically include analyses of groundwater samples for biogeochemical parameters--nitrate, nitrite, sulfate, sulfide, ferric iron/ferrous iron, dissolved oxygen oxidation-reduction potential, hydrogen, carbon dioxide, methane, ethane, ethene, alkalinity, total chloride, and total organic carbon--and VOCs. The results of this data will be used to evaluate the natural attenuation process and make recommendations for further evaluations. Groundwater monitoring during the operation of vitamin B12 amendment addition will consist of sampling injection systems and associated piezometers for VOCs, and other selected parameters. Compliance monitoring (documentation of plume configuration and concentration) will consist of sampling compliance wells for VOCs and MNA parameters (discussed above). Vitamin B12 treatment will produce the fastest remediation of the contaminated plume in both the surficial and middle aquifers. Due to the large cost of producing the vitamin B12 amendment, methods of reducing vitamin B12 use such as pulsed injection will be considered as a means of reducing costs. In addition, carbon sources added to the amendment may potentially accelerate in-situ biodegradation of chlorinated VO Cs and further reduce cost by simplifying the process. Following the introduction of vitamin B12 into the aquifer, highly chlorinated VOCs presented in the vicinity of the vitamin B12 injection area will be reduced to less chlorinated forms, which will subsequently degrade via abiotic or biotic reactions. Evaluation of site data has indicated that MNA used as a follow-up in the lower concentration portions of the contaminant plume, after active remedial actions have been taken in areas with high concentration of VOCs, will be effective (APG, 1999). Therefore, Alternative 3 will significantly reduce the potential for off-site migration of chlorinated hydrocarbons, decreasing the contaminant concentrations in the source areas to below 100 µg/L within a five-year period. The performance standards for the Selected Remedy are: 1) Reduce total chlorinated VOCs in the treatment area (area where VOCs are

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 43 of 56 greater than 1000 ppb at start) to below 100 ppb within five years; 2) Restoration of the aquifer to beneficial reuse (COCs at or below MCLs) at the conclusion of the MNA portion of the remedy, estimated at 20 to 30 years. The monitoring requirements, including frequency, to measure the progress of the remedy will be specified in the design workplan. Land use controls that prohibit consumption of the groundwater during the implementation of the remedy will also be specified in the design workplan for Operable Unit A. The Army is responsible for implementing, inspecting, reporting and enforcing the Land Use Controls (LUCs) described in this ROD in accordance with the approved LUC Remedial Design document. Although the Army retains ultimate responsibility for the performance of these obligations, the Army may arrange, by contract or otherwise, for another party(ies) to carry them out. Should any LUC remedy fail, the Army will ensure that appropriate actions are taken to reestablish the remedy's protectiveness and may initiate legal action to either compel action by a third party(ies) and for to recover the Army's costs for remedying any discovered LUC violation(s) If the Army transfers property in the areas addressed by this ROD, the Army shall ensure a deed notification is placed in the local property records that describes the restriction on military housing or residential use and that this notification is filed with appropriate agencies, so that the current and future property owners will be aware of this restriction. Specific deed notification language and the appropriate agencies will be identified in the approved LUC Remedial Design document. Under this selected remedy, institutional controls will be implemented to prevent military housing or non-military residential use of the property. These institutional controls will be documented in a LUC Remedial Design document. The LUC Remedial Design will be developed as part of the design phase, and will be submitted to EPA and MDE for review as part of the remedial design and will be subject to approval by the EPA. As part of the Army's inspection and reporting responsibilities, periodic reviews of the restrictions and objectives outlined above will be undertaken and a review report will be submitted every two years after approval of the remedial design. The report will not be subject to approval or revision by the EPA or MDE. 2.12 STATUTORY DETERMINATIONS Based on information currently available, the Army, the EPA, and the MDE believe the selected remedy, Alternative 3, meets the threshold criteria and provides the best balance of tradeoffs among the other alternatives with respect to the balancing modifying criteria. The Selected Alternative is expected to satisfy the following statutory requirements of CERCLA 121 (b): 1) is protective of human health and the environment; 2) complies with ARARs; 3) is cost-effective; 4) utilizes permanent solutions and alternative treatment technologies to the maximum extent practicable; and 5) satisfies the preference for treatment as a principal element. Under CERCLA §121 and the NCP, the lead agency must select remedies that are protective of human health and the environment, comply with ARARs (unless a statutory waiver is justified), are cost-effective, and utilize permanent solutions and alternative treatment technologies or resource recovery technology to the maximum extent practicable. In addition, CERCLA includes a preference for remedies that employ treatment that permanently and significantly reduces the volume, toxicity, or mobility of hazardous wastes as a principal element and a bias against off-site disposal of untreated wastes. The following sections discuss how the Selected Remedy meets these statutory requirements.

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 44 of 56 2.12.1 Protection of Human Health and the Environment Implementation of Alternative 3 will provide a moderate to high level of overall protection to human health and the environment by source area reduction via vitamin B12-catalyzed reductive dechlorination, MNA throughout the groundwater plumes, and institutional controls to prevent groundwater use before RAOs have been achieved. Additionally, this alternative will significantly reduce the potential for off-site migration of COCs. Regardless, the ecological risk assessment concluded that the groundwater contaminants are currently not impacting ecological receptors; virtually no volatile constituents have been detected in surface water or sediment samples. 2.12.2 Compliance with ARARs Requirements This alternative is expected to achieve the MCLs for the chlorinated solvent constituents, which is the ARARs that formed the basis for most of the constituent RAOs. To protect workers, onsite activities will be conducted in accordance with the OSHA requirements for workers at remedial action sites (29 CFR Part 1910). Table 6 describes the primary ARARs associated with the potential remedies for the site. There are several groundwater ARARs issues associated with this alternative. The issues include the temporary increase in arsenic concentrations above MCLs that may occur because of the reduction in aquifer redox conditions, and the increase in total dissolved solid concentrations possibly above Type I standards. The extent to which the arsenic is mobilized will be driven by aquifer redox chemistry. Should the soluble, reduced form of arsenic be transported downgradient to an aerobic portion of the aquifer, the arsenic will be oxidized and precipitate from the solution. Thus, the potential extent of arsenic migration will be naturally limited. Nevertheless, the concentrations of arsenic and total dissolved solid are expected to drop to their background levels following the completion of a 1-year period of vitamin B12 injections. Regulatory approval for the chemical injection will be required for implementation of this alternative. 2.12.3 Cost Effectiveness In the lead agency's judgment, the Selected Remedy is cost-effective and represents a reasonable value for the money to be spent. In making this determination, the following definition was used: "A remedy shall be cost-effective if its costs are proportional to its overall effectiveness." [NCP §300.430(f)(1)(ii)(D)]. This was accomplished by evaluating the "overall effectiveness" of those alternatives that satisfied the threshold criteria (i.e., were both protective of human health and the environment and ARAR-compliant). Overall effectiveness was evaluated by assessing the three of the five balancing criteria in combination (long-term effectiveness and permanence; reduction in toxicity, mobility, and volume through treatment; and short-term effectiveness). Overall effectiveness was then compared to determine cost-effectiveness. The relationship of the overall effectiveness of this alternative was determined to be proportional to its costs and hence this alternative represents a reasonable value for the money to be spent. The estimated present worth cost of the Selected Remedy is $5,700,000 (Table 5 in Section 2.11). Although Alternatives 1, 2, and 8 are less expensive, they are judged to be ineffective at achieving RAOs—therefore, the Selected Remedy (Alternative 3) is cost-effective.

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 45 of 56 Table 6. Action-Specific Applicable or Relevant and Appropriate Requirements

Environmental Laws and Regulations

Action Status Consideration as an ARAR

Federal Federal Clean Water Act - Water quality standards.

(40 CFR Part 131)

Discharges of treated effluent from pump &

treat alternatives

Relevant and Appropriate

Water quality standards may be considered relevant

standards for surface water. Safe Drinking Water Act - Maximum contaminant

level (MCL) (40 CFR 141, 143)

Remedial action objectives

Applicable The unconfined aquifer at the site may be a potential source of potable water.

RCRA - Land disposal restrictions (40 CFR 268)

Management of non- hazardous wastes

during the remediation

Applicable Sludge from manufacturing processes associated with the

injection of vitamin B12 amendment may be

subjected to land disposal restrictions and treatment

requirements. Underground injection control (40 CFR 144-

147)

Management of injection of

amendments during remediation

Applicable In-situ treatment of groundwater may involve

injection.

Maryland Maryland Pollution

Discharge Elimination System (COMAR

26.08.04)

Discharges of treated groundwater and

process water

Applicable Alternatives resulting in discharge to surface water will be in compliance with

the substantive requirements of an NPDES permit.

Underground injection control (COMAR

26.08.07)

Management of injection of

amendments during remediation

Applicable In-situ treatment of groundwater may involve

injection.

Maryland Water Appropriation or Use Regulation (COMAR

26.17.06)

Control and reporting of extracted

groundwater during remediation

Applicable Remedial technologies may include well construction

and groundwater extraction.

Maryland Regulations for Well Drillers (COMAR 26.05)

Compliance with Maryland regulations for well drilling and

installation

Applicable Remedial technologies may include well construction, and will be performed by

licensed drillers. Maryland Erosion and

Sediment Control Regulations (COMAR

26.17.01)

Soil disturbance activities associated

with remediation

Applicable Grading of surface soil for placement of a groundwater

treatment system may increase erosion and

sediment runoff, requiring the application of control

measures during remediation.

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 46 of 56 2.12.4 Utilization of Permanent Solutions and Alternative Treatment Technologies (or Resource Recovery Technologies) to the Maximum Extent Practicable The Army and the EPA, in coordination with the MDE, has determined that the Selected Remedy represents the maximum extent to which permanent solutions and treatment technologies can be utilized in a practicable manner at the Primary Test Area (Operable Unit A). Of those alternatives that are protective of human health and the environment and comply with ARARs, the Selected Remedy provides the best balance of trade-offs in terms of the five balancing criteria, while also considering the statutory preference for treatment as a principal element and bias against off-site treatment and disposal, and considering State and community acceptance. The Selected Remedy will reduce the concentrations of total chlorinated VOCs in the treatment area (Area where VOCs are greater than 1,000 ppb) to below 100 ppb within five years; and restore the aquifer-to beneficial reuse (COCs at or below MCLs ) at the conclusion of the MNA portion of the remedy, estimated at 20 to 30 years. The Selected Remedy satisfies the criteria for long-term effectiveness by destroying chlorinated VOCs in the site groundwater. In addition, there are no special implementability issues that set the Selected Remedy apart from any of the other alternatives evaluated. 2.12.5 Preference for Treatment as a Principal Element By treating the contaminated groundwater through the injection of vitamin B12 amendment followed by MNA, the Selected Remedy addresses principal threats posed by the site through the use of treatment technologies. By utilizing treatment as a significant portion of the remedy, the statutory preference for remedies that employ treatment as a principal element is satisfied. 2.12.6 Five-year Review Requirements Because this remedy will not result in hazardous substances, pollutants, or contaminants remaining on-site above levels that allow for unlimited use and unrestricted exposure, but it will take more than five years to attain RAOs and cleanup levels, a policy review may be conducted within five years of construction completion for the site to ensure that the remedy is, or will be, protective of human health and the environment. 2.13 DOCUMENTATION OF SIGNIFICANT CHANGES FROM PREFERRED ALTERNATIVE OF PROPOSED PLAN There are no significant changes to the Preferred Alternative of the Graces Quarters (Operable Unit A) Primary Test Area, Proposed Plan for Remedial Action (April 2004).

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 47 of 56 3 RESPONSIVENESS SUMMARY The final component of the Record of Decision is the Responsiveness Summary. The purpose of the Responsiveness Summary is to provide a summary of the public's comments, concerns, and questions about the Graces Quarters groundwater remediation and the Army's responses to these concerns. APG held a public meeting on April 27, 2004 to formally present the proposed plan and clean up actions and to answer questions and receive comments. The transcript of this meeting is part of the administrative record for the site. During the public comment period, APG also received written comments. All comments and concerns summarized below have been considered by the Army and EPA in selecting the cleanup method for Graces Quarters. This responsiveness summary is divided into the following sections: 3.1 Overview. 3.2 Background on community involvement. 3.3 Summary of comments received during the public comment period and APG's responses. A sample newspaper notice announcing the public comment period and the public meeting is contained in Appendix A. 3.1 OVERVIEW At the time of the public comment period, the Army had endorsed a preferred alternative (Alternative 3) for the Graces Quarters groundwater. APG proposed treating areas with a higher concentration of VOCs (greater than 1,000 µg/L) with a vitamin B12 amendment, and using MNA for areas with lower concentrations. MDE concurs with the preferred alternative. Generally, the public also agrees with the preferred technologies although some community members prefer using the vitamin B12 amendment to treat areas with VOC concentrations greater than 100 µg/L. 3.2 BACKGROUND ON COMMUNITY INVOLVEMENT APG has maintained an active public involvement and information program for the Installation Restoration Program since the early 1990s. Community members in Baltimore County have actively participated in information sessions, tours, and public meetings, and APG staff has given briefmgs at community association meetings. APG's community relations activities specifically related to the Graces Quarters Proposed Plan included the following: • APG began discussing the Graces Quarters Study Area groundwater remediation plans with the Restoration

Advisory Board in November 2000. Other Board meetings where APG presented information on the groundwater included October 2001 and September 2002.

• APG released the Graces Quarters Proposed Plan for public comment on April 14, 2004. Copies were available

to the public through APG's administrative record locations at the Edgewood and Aberdeen branches of Harford County Library and Miller Library at Washington College in Kent County; in addition, a copy of the Proposed Plan was made available at the Essex branch of the Baltimore County Public Library. A copy of the Proposed Plan also was posted on the Installation Restoration Program's Web Site, and the public was invited to comment through the Web Site.

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 48 of 56 • A 45-day public comment period on Graces Quarters ran from April 14 to May 28, 2004. • APG prepared a news release announcing the availability of the Proposed Plan, the dates of the public comment

period, and the date and time of the public meeting. • APG placed newspaper advertisements announcing the public comment period and meeting in The Aegis, The

Avenue, The Cecil Whig, The East County Times and The Kent County News; the newspaper ads were published on Wednesday, April 14, in The Aegis and The Cecil Whig and on Thursday, April 15, in The Avenue, The East County Times and The Kent County News.

• APG prepared and published a fact sheet on Graces Quarters. On April 21, APG mailed copies of this fact sheet

to more than 2,500 citizens and elected officials on its Installation Restoration Program mailing list. The fact sheet included a form, which citizens could use to send APG their comments.

• On April 27, APG held a public meeting at the Marshy Point Nature Center in Baltimore, Maryland.

Representatives of the Army, EPA and MDE were present. APG representatives presented information on the site and on the proposed clean up actions.

3.3 SUMMARY OF COMMENTS RECEIVED DURING THE PUBLIC COMMENT PERIOD AND AGENCY RESPONSES Comments raised during the public comment period on Graces Quarters are summarized below. The comments are categorized by source. COMMENTS FROM PUBLIC MEETING Comment No. 1: The Director of Science for Baltimore County Schools asked if there was any concern for the children who will take field trips to the area and possibly be in the waters surrounding Graces Quarters. Response No. 1: The solvents detected in the groundwater are approximately fifteen feet deep so there is no current exposure risk. APG has measures in place to discourage trespassing due to potential physical hazards and the potential for ordnance items to still be present and strongly encourages all citizens to obey the trespassing restrictions. Comment No. 2: A community member asked if Hurricane Isabel caused any problems especially with the run off. Response No. 2 : Hurricane Isabel did not have any impact on the groundwater contamination. Past sampling and analysis of the surface water did not detect contamination. Comment No. 3: A community member noted Alternative 6 seemed to have the most "excellent" ratings in the comparison chart shown during APG's presentation. He suggested that the Army consider Alternative 6 instead of Alternative 3 because although Alternative 6 is more . expensive it appears to get the job done faster. Response No. 3: Alternatives 6 and 3 utilize the same technologies with the difference being that under Alternative 6 APG would treat areas with lower levels of contamination with the vitamin

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 49 of 56 B12 amendment instead of allowing monitored natural attenuation to be the primary method of remediating the solvents in the areas of lower concentration. Both alternatives address the higher levels of concentrations immediately with the vitamin B12 amendment which will be completed in approximately one year. The estimated time for monitored natural attenuation to remediate the lower levels of solvents is 20 years with some additional vitamin B12 amendment and possibly up to 30 years without the additional vitamin B12 amendment. However, the cost of the additional vitamin B12 amendment needed is approximately $5 million. APG, EPA and MDE agree that Alternative 3 should be implemented. As required by law, the effectiveness will be fully evaluated during mandated reviews and changes could be implemented as a result of these reviews. The public will be involved in the periodic reviews and have the opportunity to review the results achieved to date and provide comments. Comment No. 4 : A local Baltimore County science teacher questioned whether the Army could actually control people from staying out of restricted areas. He said he had seen a situation where a family was picnicking under a sign that said "Danger" and wondered if there was a mechanism in place to report people that go into restricted areas. Response No. 4: APG has invested substantial time, money, and other resources into enforcing restrictions. Military boat patrols monitor the area and take appropriate action when trespassers are caught. APG strongly urges citizens to obey the restrictions and encourages citizens to call their local police department if they see anyone ignoring the restrictions. Comment No. 5: A community member asked if anyone had ever conducted a study on the number of people who have died of cancer in the area. Response No. 5: Since APG is on EPA's National Priorities List of Superfund sites, the Agency for Toxic Substances and Disease Registry (part of the Centers for Disease Control in Atlanta) is required to conduct a health assessment. The study was conducted in the mid-1990s and concluded that there was no evidence that the contamination issues at APG were impacting cancer rates. Comment No. 6: A community member asked how the total cost for Alternative 3 is allocated over the 30 years and if the majority of the money was spent in the first year and the rest divided up over the next 29 years. Response No. 6: The majority of the cost is related to the implementation of the vitamin B12 technology during the first year. Comment No. 7: A Baltimore County firefighter inquired about the risk of encountering any unexploded ordnance items at Graces Quarters, particularly during the installation of groundwater monitoring wells, and if the Baltimore County Emergency Operations Center would be notified if chemical ordnance items were found or if ordnance items had to be detonated in place. Response No. 7: APG's standard procedure for the installation of monitoring wells is avoidance which means a potential location is first checked with a magnetometer. If a metal object is detected, the monitoring well location would be moved. APG has followed this procedure during the installation of thousands of groundwater monitoring wells without incident. APG notifies the Emergency Operations Centers in neighboring counties when a potential chemical ordnance item is found and keeps them advised of ordnance items that are being detonated in place.

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 50 of 56 Comment No. 8: A community member inquired how the project is being funded. Response No. 8: Congress allocates funding for the military's environmental cleanup program. COMMENTS FROM QUESTIONNAIRE INCLUDED WITH FACT SHEET As part of its fact sheet on Graces Quarters, APG included a questionnaire that residents could return with their comments. APG received 25 forms. The alternatives preferred by individuals returning comment forms were:

1 Alternative No. 1 - Take No Action. 1 Alternative No. 2 – Institutional Controls & Long-Term Monitoring. 10 Alternative No. 3 – Vitamin B12 Amendment & Monitored Natural Attenuation 2 Alternative No. 4 – Vitamin B12 Amendment & Pump & Treat 0 Alternative No. 5 – Vitamin B12 Amendment in Surficial Aquifer & Pump & Treat 7 Alternative No. 6 – Vitamin B12 Amendment & Monitored Natural Attenuation 1 Alternative No. 7 – Pump & Treat 2 Alternative No. 8 – Pump & Treat & Long-Term Monitoring 0 Alternative No. 9 – Electrical Resistance Heating & Pump & Treat 2 Have no preference on the alternative

Written comments included on the forms regarding the proposed actions are summarized below. Comment No. 9: "Alternative 3 appears to be a good method. I respect your knowledge on the matter." Response No. 9: APG acknowledges the comment. Comment No. 10: (Co mmenter selected Alternative 4) "Alternative 3 is my second choice." Response No. 10: Pump and treat systems have been used at many sites. However, a potential problem with the pump and treat component of Alternative 4 is that contaminants may rebound once the treatment has ceased or if residual product remains in the subsurface. Comment No. 11: (Commenter selected Alternative 1) "With all the other `environmental' restrictions, the area and the water may NEVER be used. Don't waste the money now. Let any developer pay for the cleansing if necessary in decades." Response No. 11: Since APG's studies showed the solvents in the groundwater could pose a risk if the groundwater was needed in the future, APG is required by law to restore the groundwater to beneficial use where possible. Additionally, there is the potential for the solvents to move into wetlands and the Chesapeake Bay in the future. Since the Army envisions retaining ownership of the land, the Army is taking action now to prevent these problems from occurring in the future. Comment No. 12: "Alternative 6 is a more thorough clean up of the area at Graces Quarters in a shorter amount of time – 20 years. The better alternative that we implement in 2005 will be beneficial for our future generations to come."

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 51 of 56 Response No. 12: As discussed in comment 3 above, the times for remediation are estimates, and APG will periodically re -evaluate the effectiveness and coordinate these reviews with the community. Comment No. 13: (Commenter selected Alternative 3) "Please explain; in this alternative what is `for less than 30 years' and how frequently is it monitored?" Response No. 13: As discuss in comment 3 above, the times for remediation are estimates. Once this Record of Decision is signed, the next step in the process will be the development of a plan which will outline in detail how the remediation will be implemented including the frequency of monitoring. APG will make this plan available to the public. Comment No. 14: (Commenter selected Alternative 3) "Please make sure this technology is safe." Response No. 14: APG's initial studies of the technology, as well as available scientific literature, indicate the technology is safe. APG will be monitoring the effectiveness of the technology to ensure it is safe. Comment No. 15: (Commenter selected Alternative 4) "It was difficult to compare `apples to apples' because the estimated rates of success or projected clean up value was not listed within each Alternative. I have to assume that all Alternatives have varying degrees of estimated success, if not, then the least expensive method would be employed with no decisions necessary. Is there any place that would have the information regarding projected success of clean up for each alternative?" Response No. 15: The Feasibility Study, which is part of APG's Administrative Record contains more detailed information on the evaluation of each alternative. APG encourages the public to review the Feasibility Study for more information. The Administrative Record is located at the Edgewood and Aberdeen branches of Harford County Library and Miller Library at Washington College in Kent County. Comment No. 16: (Commenter selected Alternative 7) "First, I apologize for offering comments when I don't understand the details of your pilot study. I don't believe you will get efficient mixing of the groundwater and the B12 solution unless you were injecting at 20 or 30 locations. Next, let's assume the B12 oxidizes the VOC's. Won't we still have organic chemical contamination in the groundwater (even if it is not volatile)? It just seems to me that if you want to get rid of the organics, you should pump the water out, filter it and put it back. Forget all the fancy B12 stuff. It sounds like the goal is to conduct a full scale experiment on the B12 treatment process." Response No. 16: The mixing of the vitamin B12 amendment is effective when recirculation wells are used for mixing and delivery. This was demonstrated during the vitamin B12 catalyzed reductive dechlorination remediation pilot test that was conducted in 2001. The vitamin B12 amendment chemically reduces the contaminants, forming non-toxic organic products such as ethane, ethene, and methane. One reason that a groundwater pump and treat system is not preferred for the Graces Quarters site is because in all groundwater systems there is a "non-migratory" portion of the groundwater; therefore some contaminated groundwater will not be removed by pumping because it will remain between soil pore spaces and/or attached to soil particles. As long is this contaminated

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 52 of 56 groundwater remains in the subsurface, any clean groundwater entering the pore space will be contaminated due to diffusion of contaminants from the non-migratory water. In addition, any residual (bound) separate phase product that may be present in the aquifer may not be removed using a groundwater pump and treat system. APG believes that the most effective way to treat this residual contamination is to use groundwater insitu treatment as proposed with Alternate 3. Comment No. 17: "It's a shame that prior testing has resulted in such contamination. Alternative 3 seems to be a middle of the road approach, but one that is necessary to ensure safety." Response No. 17: APG acknowledges the comments and agrees that Alternative 3 is the best approach. Comment No. 18: (Commenter selected Alternative 3) "I went with your recommendation because of cost - but I believe #6 would be the best." Response No. 18: Cost is only one of the nine criteria mandated by law to be used by APG, EPA and MDE in evaluating possible remediation plans. APG wants to use taxpayer funds in a responsible manner and does evaluate the cost of each alternative, but the most important criteria is the protection of human health and the environment. APG will periodically re-evaluate the effectiveness of Alternative 3 and coordinate these reviews with the community. Comment No. 19: (Commenter selected Alternative 3) "I sincerely hope that you know what you are talking about. The average interested citizen has no way of knowing if you are correct. My question is what impact did Isabel have on this area? Did the flood water flush any of these chemicals to the surface?" Response No. 19: As discussed in comment 2 above, Hurricane Isabel did not have an impact on the groundwater contamination at Graces Quarters. APG has consulted with a number of technical experts on the proposed remedy and will be seeking additional expertise during the bidding of the contract to implement the remedy. In addition, scientists for EPA and MDE have also reviewed the proposed technology and have concurred it is the best alternative. Comment No. 20: (Commenter selected Alternative 3) "Also stabilize the shore line on the Gunpowder side of Graces Quarters like the State Park did with their shore line." Response No. 20: A number of community members commented on a previous proposed plan for Carroll Island and Graces Quarters and requested additional shoreline protection measures. APG amended its proposed plan for Operable Unit B to include shoreline protection measures for areas at greatest risk of erosion for both Carroll Island and Graces Quarters. These measures are in the process of being implemented. Comment No. 21: (Commenter selected no preference) "You people know what is best for us. You are doing a very good job of righting any previous problems." Response No. 21: APG acknowledges the comment. Comment No. 22: (Commenter selected Alternative 8) "Was it not one of the "O" Fields that #8 was used? Would this not work at Graces Quarters?"

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 53 of 56 Response No. 22: APG is utilizing a pump and treat technology as part of the remediation of the groundwater at Old O-Field. However, the groundwater issue at Graces Quarters differs from Old O-Field in that the Graces Quarters groundwater is suspected to contain residual products and dense non-aqueous phase liquids or DNAPLs, and pump and treat systems are known to potentially fail in areas where these types of contaminants are present. Therefore, APG, EPA and MDE did not think Alternative 8 was the best solution for Graces Quarters. Comment No. 23: "I would like to see APG use Alternative 6 for the clean up of Graces Quarters. We need to have the plan that completes the clean-up endeavor swiftly and completely. The money has been appropriated and this community deserves and demands the best and most complete plan available." Response No. 23: As discussed in comment 3 above, the times for remediation are estimates, and APG will periodically re -evaluate the effectiveness and coordinate these reviews with the community. As discussed in comment 18 above, cost is only one of the nine criteria used to evaluate possible alternatives with the protection of the public's health and the environment as the most important criteria. APG receives an annual appropriation of funds for all its environmental projects so money has not been specifically appropriated for the Graces Quarters project. APG has designated a portion of this year's appropriation to begin the work at Graces Quarters. Once a final cost is determined, APG will designate the remaining funding from future years' appropriations. Comment No. 24: "The Oliver Beach Improvement Association, Inc. wishes to go on record as recommending Alternative 6 for the clean up of the ground water problem that exists on the Army property at Graces Quarters. We believe in spite of the added cost for this option that it is money well worth spending in order to correct the problem in a more expeditious manner. We believe the community has lived with these types of problems far too long and thank you for the Army's continuing efforts to correct the problems of years past." Response No. 24: APG appreciates the input the Oliver Beach Improvement Association has provided over the years and respects the desire of the Improvement Association to have the remediation of Graces Quarters completed as soon as possible. As discussed in several comments above, the times in the Proposed Plan are estimates and the highest level of contamination will be addressed with the vitamin B12 solution in the first two years. APG will continue to keep the Association informed of the effectiveness of the remedy as it conducts its periodic reviews and share revised time estimates as they become more fully developed after implementation. Comment No. 25: (Commenter selected Alternative 6) "Fix it right the first time and save money in the long run." Response No. 25: APG agrees with selecting the best solution to a problem from the beginning. The technology used in Alternatives 3 and 6 is the same, and APG, EPA and MDE believe the technology is the correct solution to the groundwater issue at Graces Quarters. APG will periodically re-evaluate the effectiveness and coordinate these reviews with the community. Comment No. 26: (Commenter did not select an alternative) "It's not the cost--it's the idea that we get the environment back to the closest thing to natural, not a "band aid." The military abused the environment—they should get it back to the proper element--at least as much as possible--even if it takes extra years. Take some money from space exploration. Thank you."

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 54 of 56 Response No. 26: In line with EPA policy, APG intends to clean up Graces Quarters to the highest beneficial reuse.

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 55 of 56 4 REFERENCES AEHA. 1989. Resource Conservation and Recovery Act (RCRA) Facility Assessment (RFA), Edgewood Area,

Aberdeen Proving Ground, Maryland, AEAA. APG (Aberdeen Proving Ground). 2004. Graces Quarters, Aberdeen Proving Ground, Edgewood, Maryland.

Feasibility Study, Operable Unit A: Groundwater-Final. Report prepared by URS Group, Inc. for AimTech and Environmental Conservation and Restoration Division of APG. Installation Restoration Program, February 2004.

APG (Aberdeen Proving Ground). 2002. Graces Quarters, Aberdeen Proving Ground, Edgewood, Maryland. Plume

Stability Data Report, Primary Test Area - Working Copy Report prepared by URS Group, Inc. for AimTech and Environmental Conservation and Restoration Division of APG. Installation Restoration Program, January 2002.

APG (Aberdeen Proving Ground). 2001a. Chemical Warfare Materiel and Other Hazardous Substances (Operable

Unit B) and Associated Sites -- Record of Decision. Carroll Island and Graces Quarters, Aberdeen Proving Ground, Maryland. May 2001.

APG (Aberdeen Proving Ground). 200 lb. Graces Quarters, Aberdeen Proving Ground, Maryland. Vitamin B12-

catalyzed Reductive Dechlorination Pilot Test Report. December 2001. APG (Aberdeen Proving Ground). 2001c. Conceptual Site Model, Carroll Island and Graces Quarters, Aberdeen

Proving Ground, Maryland (Draft). Installation Restoration Program, April 2001. APG (Aberdeen Proving Ground). 2000. Proposed Plan for Operable Unit B: CWM and Other Hazardous

substances, and for Removal Actions at the Service Area and Wind Tunnel at Carroll Island and the Service Area and Disposal Area at Graces Quarters-final. Installation Restoration Program, April 2000.

APG (Aberdeen Proving Ground). 1999. Graces Quarters, Aberdeen Proving Ground, Maryland, Natural

Attenuation Evaluation Study-Data Report, Working Copy. Report prepared by URS Group, Inc. for AimTech and Environmental Conservation and Restoration Division. Installation Restoration Program, May 1999.

APG (Aberdeen Proving Ground). 1998a. Graces Quarters, Aberdeen Proving Ground, Maryland, Remedial

Investigation Report-Final. Report prepared by URS Group, Inc. for AimTech and Environmental Conservation and Restoration Division. Installation Restoration Program, January 1998.

APG (Aberdeen Proving Ground). 1998b. Additional Groundwater Investigations Data Report, Aberdeen Proving

Ground, Maryland. Installation Restoration Program, January 1998. Bennet, R. R., Meyer, R. R. 1952. Geology and Groundwater Resources of the Baltimore Area, Maryland

Department of Geology, Mines and Water Resources, Bulletin 4, 573p.

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Record of Decision September 2004 Graces Quarters Operable Unit A: Groundwater Final Aberdeen Proving Ground, Edgewood, Maryland Page 56 of 56 USGS. 2001. Simulation of Groundwater Flow and Transport of Chlorinated Hydrocarbons at Graces Quarters,

Aberdeen Proving Ground, Maryland. Tenbus, F. J., Fleck, W. USGS Water Resources Investigations Report 01-4106, USGS, Denver, Colorado, 51p.

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APPENDIX A

Public Comment Period Sample Newspaper Notice

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