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United States Environmental Protection Agency Region 1

Decision Document

Central Impact Area

Soil and Groundwater Operable Units

Camp Edwards

Massachusetts Military Reservation

Cape Cod, Massachusetts

March 2012 r

V SDMS DocID 497072

TABLE OF CONTENTS •••'- PAGE

vi (•

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PART I: DECLARATION FOR THE SDWA DECISION DOCUMENT 1

" A . SITE NAME 1

B. STATEMENT OF BASIS AND PURPOSE 1

C. ASSESSMENT OF THE SITE 1

D. DESCRIPTION OF COMPREHENSIVE RESPONSE ACTIONS 2

E. DETERMINATIONS.......,.; 5

F. SUPPORTING DATA 6

G. AUTHORIZING SIGNATURE 7

PART II: THE DECISION SUMMARY 8

A. SITE DESCRIPTION...., 8

B. SITE HISTORY AND ENFORCEMENT ACTIVITIES 8

1. History of Site Activities . 8

2. History of Investigations and Response Actions 9

3. History of Relevant Federal and State Enforcement Activities 16

C. COMMUNITY PARTICIPATION 17

D. SCOPE AND ROLE OF OPERABLE UNITS 20

E. SITE CHARACTERISTICS .20

F. CURRENT AND POTENTIAL FUTURE SITE AND RESOURCE USES 24

G. SUMMARY OF SITE RISKS 24

H. RESPONSE ACTION OBJECTIVES FOR GROUNDWATER 26

I. DEVELOPMENT OF ALTERNATIVES FOR GROUNDWATER. 27

J. DESCRIPTION OF ALTERNATIVES, SUMMARY OF COMPARATIVE ANALYSIS

AND THE SELECTED RESPONSE ACTION 30

Decision Document

Massachusetts Military Reservation

•March 2012

Page ii of iv

TABLE OF CONTENTS PAGE

K. RESPONSE ACTION IMPLEMENTATION 40

L DETERMINATIONS 50

M. DOCUMENTATION OF NO SIGNIFICANT CHANGES :..51

N. STATE ROLE 51

PART III: THE RESPONSIVENESS SUMMARY 52

List of Figures

Figure 1 MMR Location and General Site Use

Figure 2 Central Impact Area Location and Site History

Figure 3 Locations of Investigations

Figure 4 Extent of RDX in Groundwater 2010

Figure 5 Source Investigations and Excavation Areas

Figure 6 Private Wells Downgradient of the Central Impact Area Plume

Figure 7 Configuration of Alternative 4 (Modified)

Figure 8 Conceptual UXO Source Removal Plan

Figure 9 Central Impact Area 2011 Land Use Control Area

List of Tables

Table 1: Summary of Alternatives

Table 2: Regulatory Considerations

Decision Document Central Impact Area Massachusetts Military Reservation

Page iii of iv

List of Appendices

A: Massachusetts Department of Environmental Protection Letter of Concurrence

B. Glossary of Terms and Acronyms

C. Index of Key Supporting Documents

D: Soil and Groundwater Screening

Decision Document Central Impact Area Massachusetts Military Reservation

Page iv of iv

PART I: DECLARATION FOR THE SAFE DRINKING WATER ACT DECISION DOCUMENT

A. SITE NAME

The subject site is the Central Impact Area (also referred to as "the Site"), which is located at

Camp Edwards at the Massachusetts Military Reservation (MMR).

B. STATEMENT OF BASIS AND PURPOSE

This Decision Document presents the selected response actions for the Central Impact Area.

The selected response action was chosen in accordance with Section 1431(a) of the Safe

Drinking Water Act (SDWA), 42 USC § 300i(a), as amended, and the Administrative Order (AO) concerning response actions issued there under, U.S. Environmental Protection Agency

Region 1 (EPA) Administrative Order No. SDWA-1-2000-0014 (A03). The authority to select the necessary response action(s) has been delegated to EPA Region 1's Regional

Administrator pursuant to EPA Delegation No. 9-17 (1200-TN-350) dated May 11, 1994 and further delegated to EPA Region 1's Director, Office of Site Remediation and Restoration, pursuant to a redelegation of authorities dated April 6, 2010.

This decision is based on the Administrative Record, which has been developed in accordance with A03 and with a previous EPA Administrative Order, SDWA 1-97-1019 (A01), including consideration of the substantive cleanup standards of the Massachusetts Contingency Plan

(MCP) 310 CMR 40.0000. The Administrative Record is available for review at the Impact Area

Groundwater Study Program (IAGWSP) office, PB0516 West Outer Road, Camp Edwards, MA.

C. ASSESSMENT OF THE SITE

On July 13, 1982, EPA determined that the Cape Cod Aquifer is the sole or principal source of drinking water for Cape Cod, Massachusetts, and that the Cape Cod Aquifer, if contaminated, would create a significant hazard to public health (47 Fed. Reg. 30282). Contaminants from the

Training Ranges and Impact Area at MMR are present in and may enter and migrate in the aquifer. The response actions selected in this Decision Document are necessary to protect the

Cape Cod Aquifer, an underground source of drinking water on which the public relies.

Decision Document Central Impact Area Massachusetts Military Reservation

D. DESCRIPTION OF COMPREHENSIVE RESPONSE ACTIONS

This Decision Document sets forth the selected response actions taken and to be taken for addressing the source areas contributing to groundwater contamination, and the groundwater contamination at and emanating from the Site. The source areas include both soil contamination and unexploded ordnance (UXO), also referred to in this Declaration and Decision Document as unexploded ordnance/discarded military munitions/munitions constituents, or UXO/DMM/MC, or

UXO that may be in or on the soil. There may be additional areas on the site where UXO and the soil beneath may pose public safety risks, ecological risks, dermal contact risks, and/or soil ingestion risks. These potential UXO-related risks are not addressed by this Decision

Document, which was issued pursuant to Administrative Order No. SDWA-1 -2000-0014 and

Section 1431(a) of the SDWA, and which focuses on potential endangerment to the health of persons deriving from contaminants present in or likely to enter the underground source of drinking water.

While the response actions taken to date have addressed known areas of soil contamination and varying degrees of UXO removal have occurred over 56 acres of the CIA source area, there is an estimated 4,000 to 9,000 UXO items remaining within Central Impact Area. These remaining munitions items pose a potential long term threat to the groundwater and require a

Long Term Source Area Response Plan to address this threat. This Long Term Source Area

Response Plan will be developed by the EPA, the Army, the NGB and MassDEP and will be implemented by the Army/NGB in a phased approach.

Based on groundwater sampling results, EPA, in consultation with the Massachusetts

Department of Environmental Protection (MassDEP), deemed it necessary to develop and evaluate a range of potential response actions to address contaminants detected in groundwater associated with the Central Impact Area. The feasibility study identified the explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and perchlorate as the Contaminants of

Concern (COCs) for groundwater.

Decision Document Central Impact Area Massachusetts Military Reservation

These COCs were used to develop and evaluate a range of potential response actions for the

Site. Groundwater modeling was used to determine the feasibility of the alternatives and because the perchlorate and RDX plumes are co-located, the selected response action was based on the remediation of the RDX plume. The cleanup objectives for the Central Impact

Area are to restore the useable groundwater to its beneficial use, wherever practicable, within a timeframe that is reasonable given the particular circumstances of the site; to provide a level of protection in the aquifer that takes into account that the Cape Cod Aquifer, including the

Sagamore Lens, is a sole source aquifer that is susceptible to contamination; and to prevent the ingestion and inhalation of groundwater containing the COCs, in excess of federal Maximum

Contaminant Levels (MCLs), Health Advisories (HA), Drinking Water Equivalent Levels

(DWELs), applicable State standards or unacceptable excess lifetime cancer risk or non-cancer

Hazard Index (HI).

There currently is no federal drinking water standard for perchlorate. However, in December

2008, EPA issued an Interim Drinking Water Health Advisory for exposure to perchlorate in water of 15 pg/L. Also, the Massachusetts Department of Environmental Protection (MassDEP) has promulgated a Massachusetts Maximum Contaminant Level (MMCL) for perchlorate of 2

M9/L.

The lifetime federal Health Advisory for RDX in drinking water is 2 pg/L, the Massachusetts

Contingency Plan (MCP) GW-1 standard is 1 pg/L, and the 10"6 risk-based concentration that results in an increased lifetime cancer risk of one in a million is currently 0.6 pg/L.

The EPA, in consultation with MassDEP, has selected a response action in the Central Impact

Area groundwater plumes under which the aquifer, that has been designated a Sole Source

Aquifer by the EPA and a Potentially Productive Aquifer by the MassDEP, will be restored. The groundwater response actions will ensure that the groundwater containing RDX at concentrations greater than the IO"6 risk-based level and/or perchlorate greater than 2 pg/L is restored to protective levels.

Decision Document Central Impact Area Massachusetts Military Reservation

The selected response action of Focused Extraction with Monitored Natural Attenuation, with source controls and Land Use Controls (LUCs) provides the best balance of the criteria used to evaluate cleanup alternatives.

The selected alternative (Focused Extraction with Monitored Natural Attenuation, and Land Use

Controls for groundwater and a phased approach for UXO removal) achieves cleanup goals in a reasonable timeframe and protects human health through the use of extraction and groundwater monitoring to ensure that groundwater modeling predictions regarding the reduction and migration of contamination are correct and that contamination levels continue to decline.

Human health will be further protected through the implementation and verification of LUCs.

These LUCs will prevent use of contaminated portions of the aquifer at the Site for drinking water purposes until groundwater data confirms that contamination has been reduced to below risk-based levels.

The major components of the source and groundwater response actions are:

o The development and implementation of a Long Term Source Area Response Plan to address the estimated 4000 to 9000 munitions items and related soil contamination located throughout the CIA. The plan will be developed by the EPA, the Army, the NGB and

MassDEP and will be implemented by the Army/NGB in a phased approach. The first phase will consist of UXO clearance of an additional 30 acres of the CIA over a 3 year period followed by a second phase consisting of UXO clearance of an additional 20 acres of the

CIA. The development and implementation of additional phases, if necessary, will be based on the results of these first two phases. A Work Plan for the first phase shall be developed by the Army/NGB within sixty (60) days of the issuance of this Decision Document and submitted to the EPA and MassDEP for review. The work plan shall be approved by EPA, in consultation with MassDEP. A Work Plan for the second phase shall be developed by the

Army/NGB within sixty (60) days of the completion of the first phase. The work plan for the second phase will take into account information gathered from the first phase and will be submitted to the EPA and MassDEP for review. The work plan shall be approved by EPA, in consultation with MassDEP. The plans for the first two phases will employ techniques to minimize habitat destruction while maximizing the reduction of UXO with a goal to remove

Decision Document Central Impact Area Massachusetts Military Reservation

75% to 95% of the UXO within the fifty acres covered by the first two phases.

• A 550 gallon-per-minute (gpm) pump and treat system consisting of three extraction wells to contain groundwater with concentrations of RDX greater than 2 ppb at Burgoyne Road which will use the Demolition Area 1 treatment system and injection wells

• Development and implementation of a long-term monitoring program to verify that the groundwater is being restored as predicted and to determine if additional source removal work is needed. Implementation of land use controls to prevent access to and use of the contaminated portions of the aquifer for drinking water, and maintain the integrity of any current or future groundwater monitoring wells and treatment systems,

• Five year reviews to determine if the groundwater treatment system is still protective and achieving the goals established, to determine if additional or more expedited source response actions are necessary to protect groundwater and to determine if improved technologies are available.

E. DETERMINATIONS

The response actions selected in this Decision Document will protect the public health from any endangerment which may be presented by the presence or potential migration of COCs from the Site into the underlying Sole Source Aquifer. The response action selected in this Decision

Document, issued pursuant to A03 and Section 1431 of the SDWA, addresses the unacceptable threats to the groundwater aquifer from the Site. In this Decision Document, EPA is making no determination regarding any remaining public safety risk, ecological risk, dermal contact risk, and/or soil ingestion risk posed by any remaining contamination at the Site.

As required by A03, the selected alternative for the Site (Focused Extraction with Monitored

Natural Attenuation, and Land Use Controls for groundwater and a phased approach for UXO removal) provides a level of protection to the aquifer underlying and downgradient of the Site commensurate with the aquifer's designation as a Sole Source Aquifer and a Potentially

Productive Aquifer and is protective of human health.

In addition to annual reports on groundwater monitoring and verification of land use controls, the selected response actions include periodic reviews at frequencies not to exceed five years. The

Decision Document Central Impact Area Massachusetts Military Reservation scope of each review will include, but not be limited to, sampling data, modeling data, and other relevant data. EPA, in consultation with MassDEP, will review this and any other relevant information to determine if additional measures are necessary for the protection of human health. This will include information acquired after the implementation of the selected response actions (such as new regulatory requirements or changes in the environmental conditions of the

Site).

F. SUPPORTING DATA

Detailed information on the Site is included in the Final Central Impact Area Feasibility Study dated July 20, 2011 and the Final Central Impact Area Source Report dated July 20, 2011. An overview of the Site, including decision factor(s) that led to selecting the groundwater and source response actions, is included in the Decision Summary section of this document. The

Decision Summary section also includes information on RDX, the respective concentrations, the baseline risk, the cleanup levels established and the basis for the levels, current and future land and groundwater use assumptions used in the baseline risk screening and Decision Document, land and groundwater use that will be available at the Site as a result of the selected response action, and decision factor(s) that led to selecting the remedy. Additional information can be found in the Administrative Record for the Site.

Decision Document Central Impact Area Massachusetts Military Reservation

G. AUTHORIZING SIGNATURE

This Decision Document documents the selected response actions for remediation of the

Central Impact Area within Camp Edwards at the MMR. These response actions were selected by EPA under the authority of the SDWA. The MassDEP concurs with this decision.

U.S. Environmental Protection Agency

Da.e:-3/?//Z, tes T. Owens, Irector, Office of Site Remediation and Restoration

Region 1

Decision Document

Massachusetts Military Reservation

PART II: THE DECISION SUMMARY

A. SITE DESCRIPTION

The Impact Area is located on Camp Edwards on the Massachusetts Military Reservation on

Cape Cod in Massachusetts (Figure 1). The Central Impact Area is a 330-acre portion of the

Impact Area where targets were concentrated. The delineation of the 330 acres was based on historical and current site use, a review of historical aerial photographs, airborne magnetometer

(AIRMAG) results, firing fans and unexploded ordnance discoveries, groundwater plumes and particle backtracks, and explosives detections in soil.

The site is generally comprised of scrub oak barrens (Quercus ilicifolia), reforestation of previous cleared areas, and the remnants of burned areas. The remainder of the Impact Area that surrounds the site includes vegetated pitch pine (Pinus rigida) and scrub oak forest. The ground surface is relatively flat and generally slopes from the northwest to the south and east.

B. SITE HISTORY AND ENFORCEMENT ACTIVITIES

1. History of Site Activities

The Central Impact Area has been used as an impact area for artillery and mortar firing from the late 1930s until 1997 (Ogden 1997). During the late 1940s, the Central Impact Area also contained Navy air-to-ground rocket ranges that utilized inert 2.25-inch rockets. Various types of munitions including 37 millimeter (mm), 40mm, 75mm, 90mm, 105mm, and 155mm artillery projectiles and 50mm, 60mm, 70mm, 81mm, 3-inch, and 4.2-inch mortars have been fired into the Central Impact Area (USAGE 2001). These munitions include high explosives (HE) charges designed to explode upon impact, and practice rounds, which do not contain an HE charge but may contain a spotting charge designed to emit smoke upon impact.

The predominant HE charge used in pre-World War II munitions contained 2,4,6-trinitrotoluene

(TNT). Post World War II artillery and mortar munitions used Composition B for the HE charge, which is a mixture of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and TNT. The low-intensity training round (LITR) is an artillery practice projectile that was introduced in 1982 to reduce the

Decision Document Central Impact Area Massachusetts Military Reservation noise associated with HE explosions. The LITR includes a spotting charge containing perchlorate. The use of HE artillery projectiles ceased in 1989, and the firing of all munitions into the Central Impact Area was discontinued in 1997.

HE munitions that did not explode or that partially functioned (low order) have accumulated within the Central Impact Area during its use. Unexploded ordnance located along roadways or at other locations that presented a safety hazard due to human access have historically been blown-in-place (BIP) using an explosive donor charge. BIP operations were also used to clear areas for site investigation starting in 1997.

Historical information indicates that in the past, several portions of the Central Impact Area have undergone a variety of uses and in some cases have been mechanically cleared of vegetation.

Among the previously developed areas within the Central Impact Area are the following (Figure

2 ) : •

• Sub-Caliber Aircraft Rocket (SCAR) Sites - two approximately 10-acre sites used by

Naval aircraft in the 1940s for target practice with inert 2.25-inch rockets.

• Eastern Test Site - a 4.5 acre area in the northern portion of the Central Impact Area believed to have been used for artillery and mortar targeting.

• Tank Alley - a cleared area which developed around 1965 and afterward used extensively as a target area.

« Chemical Spill 19 (CS-19) - an area in the west-central region of the Central Impact

Area where ordnance testing and disposal activities occurred.

Investigations of the CS-19 area were conducted under the Installation.Restoration Program

(IRP) by the Air Force Center for Engineering and the Environment (AFCEE).

2. History of Investigations and Response Actions

Remedial investigations were conducted at the Central Impact Area to investigate the nature and extent of contamination in soil and groundwater resulting from past military activities (Figure

3). Data collected as part of these investigations were used to characterize the nature and extent of groundwater contamination emanating from the site, any continuing sources of

Decision Document Central Impact Area Massachusetts Military Reservation contamination including soil contamination and potential contamination from unexploded ordnance (UXO), and to provide a basis for the evaluation of risk(s) posed by the site.

A brief summary of the investigations and response actions performed is provided below. A more detailed discussion can be found in Sections 3.0 and 4.0 of the July 2011 Feasibility

Study.

Source Investigations and Results

Approximately 3,800 soil samples were analyzed for explosives. Approximately 3,724 (98%) were analyzed by EPA Method 8330 while approximately 76 (2%) ofthe samples were collected and analyzed using EPA Method 8330B. In addition, approximately 671 samples were analyzed for perchlorate by EPA Method 314. Among the explosives compounds, discussion is focused particularly on RDX considering its dominant impact on groundwater. The number of samples analyzed for explosives was about seven times greater than the number analyzed for perchlorate, since the latter became a chemical of interest after RDX.

Perchlorate and the 18 explosives analytes measured by EPA Method 8330 were detected in one or more soil samples. Thirteen analytes had maximum concentrations exceeding a Soil

Screening Level (SSL). Three of these compounds (2,4-dinitrotoluene, RDX, and HMX) were detected at concentrations exceeding MassDEP MCP S-1/GW-1 Soil Standards. As previously stated, approximately 3,800 soil samples were analyzed for explosives (not including semivolatile organic compound [SVOC] samples, which also have three explosives analytes reported) and about 671 were analyzed for perchlorate. The highest frequencies of detection were observed for perchlorate (19.2%), RDX (5.2%), 2A-DNT (4.6%), TNT (4.0%), 4A-DNT

(3.9%), and HMX (2.5%).

The types and frequencies of contaminants observed are believed to reflect the munitions fired into the Central Impact Area and munitions release mechanisms, contaminant fate and transport, and soil characterization methods. Perchlorate is an ingredient in the spotting charge used in LITR projectiles fired from 1982 to 1997. RDX and TNT are the main ingredients in HE

Decision Document Central Impact Area Massachusetts Military Reservation charges used after World War II. 2A-DNT and 4A-DNT are breakdown products of TNT, and

HMX is an impurity typically present in RDX.

Detections of total explosives, RDX and perchlorate appear to be scattered throughout the

Central Impact Area areas sampled, and relatively high detected concentrations are frequently co-located with non-detects. The maximum RDX detection, and a series of smaller co-located detections, was observed at a low order mortar with exposed filler at High-Use Target Area 2

Transect 2. Apart from this detection, and detections at Targets 9 and 11, RDX detections were focused on the areas near Turpentine Road and Tank Alley. Therefore, RDX was determined to be most prevalent in soil in the area where groundwater impacts have occurred.

The results of investigations indicated that explosives contamination in Central Impact Area soils predominantly consists of perchlorate, RDX, TNT and the two amino-DNTs, and HMX.

Most of the detections for explosives are located adjacent to non-detects, i.e., contaminant particles are scattered and heterogeneously distributed in soil. RDX levels are higher and more frequently detected in target areas than in other areas. In the immediate vicinity of a target, RDX and other explosive levels generally declined and were less frequently detected with increasing distances from the target. Explosives concentrations and detection frequencies in soil immediately beneath intact unexploded ordnance were generally similar to detections in surface soil. Explosives were generally detected less frequently and at decreasing concentrations with increasing depth.

The predominant HE charge used in pre-World War II munitions fired at MMR contained TNT.

Post-World War II artillery and mortar munitions used Composition B for the HE charge, which is a mixture of RDX and TNT. It should be noted that HMX is a common impurity in RDX and therefore is implicit in the formulations of Composition B. The LITR [also used at the Central

Impact Area] is an artillery practice projectile that contains perchlorate and was fired starting in

1982. As previously discussed, RDX is the most widespread contaminant in the Central Impact

Area and the most persistent contaminant in the current groundwater contaminant plume.

Decision Document Central Impact Area Massachusetts Military Reservation

The most common unexploded ordnance items encountered at the Central Impact Area have been 81mm mortars (27%), followed by 155mm projectiles (24%) and 105mm projectiles (15%)

(AMEC 2008). Cumulatively, these three ordnance types account for more than 60 percent of all items discovered. The next three most common items observed have been 60mm mortars, 4.2 inch mortars, and 37mm projectiles, which cumulatively account for approximately 14 percent of all items discovered. The remaining 26 percent of unexploded ordnance items consisted of a range of munitions including: 2.25-inch, 2.36-inch, 2.75-inch rockets; 57mm recoilless rifle rounds; and 30mm, 75mm, and 90mm, 7-inch, and 8-inch projectiles. 60 percent of the HE

UXO were reported to be within the top foot of soil and almost 90 percent within the top 3 feet.

The deepest item reported was at a depth of 68 inches.

A total of 9.8 acres were intrusively surveyed within the Central Impact Area, including targets and other suspected High-Use areas where unexploded ordnance density was expected to be elevated, compared to perimeter transects and low-density test plots where unexploded ordnance density was expected to be low. Beyond the intrusively surveyed areas, unexploded ordnance items have been discovered during a range of investigation activities, including monitoring well pad construction, road/access path construction, and soil sampling. These

'incidental' discoveries account for more than half of the unexploded ordnance items encountered in the Central Impact Area.

As discussed in detail in the 2011 Central Impact Area Source Investigation Summary Report

(Tetra Tech 2011), unexploded ordnance densities have been estimated for several areas including Post Screening Investigation (PSI) Test Plots. For the PSI Test Plots the estimated average density for the medium/high use test plots was 35 items per acre and for the low use plots 12 items per acre. Extrapolation of unexploded ordnance distribution from the 9.8 acres of intrusively surveyed area to the 330-acre Central Impact Area is difficult considering the heterogeneous distribution of unexploded ordnance. In intrusively surveyed areas, observed unexploded ordnance densities were found to be generally consistent with the working conceptual site model for the Central Impact Area, in which unexploded ordnance are expected to be clustered around targets.

Decision Document Central Impact Area Massachusetts Military Reservation

Considerable uncertainty exists regarding the average UXO density for the entire Central Impact

Area. High Use Target Area density is not representative of the Central Impact Area density since the targets represent such a small portion of the area (approximately 0.14%). The test plots better represent an average density since they are distributed throughout the Central

Impact Area. The average density of all the test plots is 27 HE unexploded ordnance per acre.

This would represent a total average number of 8910 HE unexploded ordnance within the entire

330-acre area. The recently completed excavation of the northern area (a higher density area) resulted in the removal of 12 HE UXO from the base of the excavation and it is estimated that an additional 24 HE UXO will be removed. The total estimated number of HE UXO (36) result in a UXO density of approximately 25 per acre. In addition, the excavation of the EM61 Modified

Test Plot (CIA grid 48-55) (a medium density area near Tank Alley), resulted in the removal of 7

HE UXO for a density of 28/acre. Thus the total number of HE unexploded ordnance in the

Central Impact Area is estimated to be 4,000-9,000. This is generally consistent with the UXO density estimated in the Draft UXO/Source Investigation Report for the Central Impact Area

(AMEC 2008) of 7,467 UXO items. Approximately 820 of these have been removed during investigations and response actions.

Groundwater Investigations and Results

Some of the groundwater underlying and downgradient of the Central Impact Area is contaminated by RDX and perchlorate. RDX is the most widespread groundwater contaminant

(Figure 4). The RDX plume, which is comprised of multiple parallel and overlapping plumelets, is oriented in a southeast to northwest direction consistent with the regional groundwater flow direction. Many of the plumelets appear to be detached from historic source areas, while others correlate to continuing shallow detections. The furthest downgradient extent of the main plume is located about two miles from its presumed origin. Most of the plume remains on the installation. There is a narrow RDX plume that originated in the Central Impact Area and now passes under the Northwest Corner and has migrated off the installation. There is currently no known exposure pathway to this plume. This narrow RDX plume is monitored as part of the

Northwest Corner Decision Document (2010).

RDX within the groundwater plume has been reported up to a maximum concentration of 45 ppb in 2005. The 2010 maximum concentration was 21 ppb and most values now are below 10 ppb

Decision Document Central Impact Area Massachusetts Military Reservation

The perchlorate plume is significantly less extensive than that of the RDX contamination. The highest concentration was 10 ppb, detected in 2010.

Because of the inconsistencies of soil detections, potential RDX source areas were identified through water table detections. These source areas determined from water table detections are consistent with other potential source area indicators such as target locations, UXO density, cratering on aerial photographs and particle backtracks from wells with explosives detections.

More recent (post-2007) RDX water table data shows declining concentrations. These data suggest that the source area response actions conducted to date have had a positive effect on the groundwater. However, a significant number of UXO items still remain in the Central Impact

Area and the long term impacts of these items to groundwater as they corrode are difficult to predict.

Response Actions

Several soil response actions have been undertaken in the Central Impact Area to reduce levels of contamination from certain areas (Figure 5). These include soil and UXO removals at the following areas:

• Armored Personnel Carrier (Target 25) - Approximately 330 tons of contaminated soil were removed and treated in September 2000. One leaking HE UXO was removed.

• Mortar Target 9 - Approximately 577 tons of contaminated soil were excavated in

August 2001. Seven HE unexploded ordnance items also were discovered and there were elevated levels of explosives contamination at these locations. Excavated contaminated soil from Mortar Target 9 was treated on site using soil washing.

• Targets 23 and Target 42 - 885 and 1,100 tons of soil, respectively, were excavated and treated on site using low-temperature thermal desorption. 17 and 11 HE UXO, respectively, were removed during the intrusive investigation.

Decision Document Central Impact Area Massachusetts Military Reservation

• In 2008 the Air Force Research Laboratory (AFRL) conducted a technology demonstration at the Central Impact Area. This was done to evaluate several methods to clear potential unexploded ordnance from the ranges using remotely controlled equipment. During this demonstration, 30 HE UXO were removed from approximately seven acres.

• In 2010 a second technology demonstration was conducted by AFRL. Contaminated

Soil was excavated from a 3 acre area and approximately 12,300 tons of soil were removed. In addition, approximately 140 HE UXO were removed

In summary, soil removal actions have been conducted at several locations and approximately

21,000 tons of contaminated soil has been excavated and treated on-site, disposed of off-site, or is awaiting final disposition.

Major geophysical investigations were also conducted and include an AIRMAG survey, the Sub-

Caliber Aircraft Rocket site, the Eastern Test site, the High Use Target Area Phases I and II, UXO Density Estimation Test Plots, and the Robotics Technology Demonstrations.

During the soil removal actions, munitions were nearly completely removed from approximately

5.5 acres. In addition, the majority of munitions were also removed from an area of approximately 4.3 acres during the above-listed geophysical investigations. Thus, near complete munitions removal has been accomplished over an approximately 10 acre area.

Further investigations were also conducted over an area approximately 14 acres in size, with plans for an additional 8 acres to be completed. These areas have been surface cleared and magnetic anomalies discovered to be munitions items have been removed. When completed, approximately 75% of predicted munitions will have been removed from approximately 22 acres.

Approximately 85% of predicted munitions have been cleared from 16 acres for drill pad sites, roads, buffers around removal actions, and support areas for vehicle traffic.

Decision Document Central Impact Area Massachusetts Military Reservation

Surface clearance has been performed on approximately eight acres along Tank Alley and

Turpentine Road. This surface clearance resulted in approximately 25% of predicted munitions removal from these acres.

In summary, some degree of UXO removal has been completed within approximately 56 acres.

As of 2007, approximately 520 known or suspected UXO items containing high explosives had been removed. Approximately 300 additional items have been recovered during more recent investigations, including the robotics work, for a total of approximately 820 HE UXO. However, it is estimated that there are approximately 4,000 to 9,000 HE UXO items still remaining in the

Central Impact Area.

3. History of Relevant Federal and State Enforcement Activities

In February 1997, EPA Region 1 issued SDWA Administrative Order 1-97-1019 (A01) requiring the investigation of the impact of contamination at or emanating from the training ranges and impact area upon the Sole Source Aquifer.

In May 1997, EPA issued Administrative Order 1-97-1030 (A02), which prohibited all live firing of mortars and artillery, firing of lead from small arms, planned detonation of ordnance or explosives at or near the Training Ranges and Impact Area except for UXO activities, and certain other training-related activities.

In January 2000, EPA issued SDWA Administrative Order 1-2000-0014 (A03), which required implementation of Rapid Response Actions (RRAs) and Remedial Actions (RAs) to address contamination from past and present activities and sources at and emanating from the training ranges and impact area. The RRAs specifically required by A03 addressed elevated concentrations of contaminants in soil and have been completed. The comprehensive response action component of A03 requires that a feasibility study, remedial design and response action be completed for several areas of concern.

Decision Document Central Impact Area Massachusetts Military Reservation

C. COMMUNITY PARTICIPATION

Throughout the Site's history, the IAGWSP, EPA and MassDEP have kept the community and other interested parties apprised of response activities at the Central Impact Area through informational meetings, fact sheets, press releases and public meetings. Below is a brief chronology of public outreach efforts.

The Impact Area Review Team (IART) was a citizen advisory committee established in 1997 by the EPA under A01. The IART served as a technical advisory resource, allowing the EPA, the

Army, the NGB, and MassDEP to be responsive to public concerns related to the ongoing investigation and cleanup effort at Camp Edwards. In 2007, this team was merged with the

Plume Containment Team, the citizens' advisory team for the Air Force Center for Engineering

& Environment's MMR Installation Restoration Program, and renamed the MMR Cleanup Team.

The combined team meets regularly throughout the year to hear updates and provide public input on the MMR investigations and cleanup.

The IAGWSP also briefs the Senior Management Board (SMB), which advises MMR organizations on environmental programs and policies. Members of the SMB include selectmen or their designated representative from the towns of Bourne, Falmouth, Mashpee, and

Sandwich and representatives from the EPA, MassDEP, Massachusetts Department.of Public

Health, Massachusetts National Guard, U.S. Coast Guard, and a representative from the

Mashpee Wampanoag Tribe.

All IART, MMR Cleanup Team, and Senior Management Board meetings related to the investigation and response activities were advertised in the Cape Cod Times and the local edition of The Enterprise newspapers.

In October 2001, the IAGWSP, EPA and MassDEP released a Public Involvement Plan outlining activities to address community concerns and to keep citizens informed about and involved in response activities.

From the time the initial investigations at the Site began, through the present, the IAGWSP regularly presented updates on the investigation and response activities at the Site. With

Decision Document Central Impact Area Massachusetts Military Reservation March 2012 http:Department.of respect to this Decision Document, the most important updates were:

• On May 11, 2011, an informational meeting was held at Otis ANGB, MA, to present the findings of the source investigation and remediation work to the MMR Cleanup Team and the public. A display ad regarding the meeting was placed in the May 6, 2011 editions of the

Cape Cod Times and The Enterprise newspapers and a news release regarding the meeting was sent to the local media.

• On July 13, 2011, an informational meeting was held on Camp Edwards to describe the

Groundwater Alternatives in the Feasibility Study and announce the availability of the

Remedy Selection Plan for the Central Impact Area. At the meeting, the IAGWSP presented the alternatives and the proposed additional UXO removal efforts. EPA presented the proposed response and answered questions from the MMR Cleanup Team and Senior Management Board. The IAGWSP notified the public of the meeting and announced the public comment period in a display ad placed in the July 8, 2011 editions of the Cape Cod Times and The Enterprise newspapers and a news release regarding the meeting was sent to the local media.

• From July 25, 2011 through August 25, 2011, a Public Comment Period was held on the

Remedy Selection Plan for the Central Impact Area. The IAGWSP placed copies of the

Remedy Selection Plan in the lAGWSP's information repositories at the Bourne, Falmouth, and Sandwich, MA, public libraries. The repository contains documents on the Central

Impact Area investigations and findings supporting selection of the response action including the FS and Source Investigation reports, along with other relevant documents.

The Remedy Selection Plan was also made available on the IAGWSP Web site. The web site contains the supporting documents and which offered a means of submitting public comments on the Remedy Selection Plan. In addition, the IAGWSP provided copies of the

Remedy Selection Plan to MMR Cleanup Team members and distributed it to individuals in attendance at the public meeting and public hearing.

Decision Document Central Impact Area Massachusetts Military Reservation

• On July 27, 2011, a Public Information Session and Public Hearing were held on the

Remedy Selection Plan for the Central Impact Area on Camp Edwards, MA. The public information session, along with a presentation on the Remedy Selection Plan and EPA's proposed response, was held prior to the opening of the public hearing. Local residents and officials, news media representatives, and members of the public interested in site activities and cleanup decisions were invited to attend both meetings. Representatives from EPA, MassDEP and IAGWSP were available to answer questions. The IAGWSP notified the public of the July 27, 2011 information session and public hearing, and reminded them about the public comment period in a display ad placed in the July 22, 2011 editions of the

Cape Cod Times and The Enterprise newspapers. Comments received during the Public

Comment Period for the Remedy Selection Plan were compiled and answered in the

Responsiveness Summary included in Part III of this document.

All draft and final reports related to the investigation and response activities were made available through the Information Repository at the public libraries in Bourne, Falmouth, and

Sandwich, MA. These documents also were made available to the public through the IAGWSP

Web site: mmr-iagwsp.org and the Administrative Record at 1803 West Outer Road, Camp

Edwards, MA.

Media releases related to presentations and Public Comment Period for the Central Impact Area were distributed to the Cape Cod Times and other area media including newspapers, radio and television media.

General fact sheets pertaining to the IAGWSP investigations and findings and on related issues, such as the COCs, were also published and distributed.

The IAGWSP, EPA, and MassDEP also participated in general information sessions, that included open houses, information sessions, community meetings and annual updates to the local Town Managers, Boards of Selectmen, and Boards of Health on MMR investigation and response activities.

Decision Document Central Impact Area Massachusetts Military Reservation March 2012 http://mmr-iagwsp.org

D. SCOPE AND ROLE OF OPERABLE UNITS

The Site consists of source areas contributing to groundwater contamination (i.e., contaminated soil and the areas known or suspected to contain UXO, DMM or MC) and groundwater operable units. The current source areas contributing to groundwater contamination were addressed through the removal of geophysical anomalies and the excavation and removal of contaminated soils. It is estimated that there are approximately 4,000 to 9,000 munitions items containing high explosives remaining in the Central Impact Area. These remaining munitions pose a potential long term threat to the groundwater. In addition, these remaining munitions, and the soil beneath, may also pose public safety risks, ecological risks, dermal contact risks, and/or soil ingestion risks. However, these potential UXO/MEC-related risks are not addressed by this

Decision Document, which was issued pursuant to Administrative Order No. SDW A-1-2000

0014 and Section 1431(a) ofthe SDWA, and which focuses on potential endangerment to the health of persons deriving from contaminants present in or likely to enter the underground source of drinking water.

E. SITE CHARACTERISTICS

Site Geology

The Central Impact Area is situated within the Mashpee Pitted Plain, a thick wedge-shaped deposit of unconsolidated Late Pleistocene outwash sands and gravels. The Mashpee Pitted

Plain is bounded to the west and north by the Buzzards Bay and Sandwich moraines, respectively. The Mashpee Pitted Plain is an outwash plain formed by streams that drained the

Buzzards Bay and Cape Cod Bay lobes of retreating glaciers. Depositional environments of the

Mashpee Pitted Plain range from glaciofluvial for the coarser deposits to glaciolacustrine for the finer deposits. In the Mashpee Pitted Plain, the glaciolacustrine deposits are discontinuous and commonly overlie basal till or bedrock. Coarse textured basal till, consisting of poorly sorted sands and gravels, occurs sporadically across the top of the bedrock surface. Coarser grained sands and gravels, deposited in glaciofluvial environments, usually overlie the glaciolacustrine deposits and are more continuous across the plain. Overlying these glaciofluvial deposits is a thin veneer of eolian silt. A general description of the geology of Cape Cod and the geology of

Decision Document Central Impact Area Massachusetts Military Reservation the Central Impact Area is provided in the Draft UXO/Source Investigation Report for the Central

Impact Area (AMEC 2008).

Soils encountered during installation of the numerous borings and monitoring wells within the

Central Impact Area are consistent with the descriptions of the Mashpee Pitted Plain stratigraphy, and depths to the bedrock surface. The top 260 feet consists predominantly of poorly graded medium to coarse sands with intervals of fine gravelly sediments and is classified using the Unified Soil Classification System as SP. Between 260 and 330 feet, soils are principally classified as finer sands and silts. These deposits are representative of a sandy basal till. Crystalline bedrock was encountered at a depth of approximately 320 to 380 feet below grade.

Site Hydrogeology

Surface water is not significantly retained due to the excessively drained sandy soils of Camp

Edwards. No large lakes, rivers, or streams exist on the property; only small, marshy wetlands and ponds exist. Most of the wetlands and surface waters in the Sandwich and Buzzards Bay

Moraines on Camp Edwards are considered to be perched (MAARNG 2001).

The aquifer system is unconfined (i.e., it is in equilibrium with atmospheric pressure and is recharged by infiltration from precipitation). The sole source of natural fresh water recharge to this groundwater system is rainfall and snow meltwater that averages approximately 48 inches per year. Except on extreme slopes, surface water runoff at Camp Edwards is virtually nonexistent due to the highly permeable nature ofthe sand and gravel underlying the area.

The top of the groundwater mound within the westem Cape Cod groundwater system is located beneath the ranges on the southeast side of MMR. Groundwater flows radially outward: north to either the Cape Cod Canal or the Cape Cod Bay, east to the Bass River, south and southeast to

Nantucket Sound, and west and southwest to Buzzards Bay (ANG 2001). The height of the water table in and around the MMR can fluctuate up to 7 feet annually due to seasonal

Decision Document Central Impact Area Massachusetts Military Reservation variations in groundwater recharge and pumping demand (USGS 1996). Groundwater levels are highest in the spring when recharge rates are high and pumping demand is low; levels are lowest in the late summer/early autumn when rainfall is minimal and pumping demand is at its maximum. The total thickness of the aquifer varies from approximately 80 feet in the south to approximately 350 feet in the north. The variation in thickness is due to the episodes of glacial advance and retreat, the underlying bedrock geology, and the presence of fine-grained materials in the deeper sediments beneath the southern portion of the aquifer (ANG 2001).The groundwater flow direction from the Central Impact Area is predominantly to the northwest ( and the hydraulic gradient steepens with increasing distance from the top of the regional potentiometric groundwater mound. Within the Central Impact Area, groundwater elevations typically range between 65 and 70 feet National Geodetic Vertical Datum, and depth to groundwater ranges from approximately 100 to 140 feet below ground surface (bgs). Based on the observed response of the water table relative to recharge events, the hydraulic travel time through the vadose zone is expected to be three to six months. The thickness of the saturated zone varies between 180 and 280 feet.

A hydraulic conductivity value of 155 feet per day for the saturated zone was calculated from the results of an aquifer test performed within the Central Impact Area on well P-1 (AMEC 2003a).

This value is consistent with the estimated range of 125 to 350 feet per day based on grain size

(Masterson et al. 1996) and is approximately double those calculated in the moraine material.

The hydraulic conductivity of the 5- to 20-foot thick basal till on top of bedrock is estimated at one foot per day (Masterson et al. 1996). Bedrock occurs at a depth of approximately 320 to

380 feet bgs beneath the Central Impact Area and can be considered impermeable. Therefore, the bulk of regional groundwater flow is transmitted through the upper outwash units. The effective porosity of the saturated zone, which was determined from several past MMR studies

(AMEC 2003b; AFCEE 2003; LeBlanc et al. 1991; Barber et al. 1988; Morrison and Johnson

1967), is assumed to be 0.39.

Groundwater flow calculations for different Central Impact Area well pairs using measured gradients and assuming relatively constant hydraulic conductivity and effective porosity values

Decision Document Central Impact Area Massachusetts Military Reservation yield mean and median velocities of 0.32 and 0.29 feet per day, respectively and compare well to the aquifer test derived groundwater flow velocity of 0.48 feet per day (AMEC 2003a).

Movement of Contaminants in Groundwater

RDX leaches from soil to the groundwater. Movement of RDX is slightly retarded in the soil and the aquifer due to limited sorption to soil particles. Therefore, RDX will generally move at a velocity slightly less than that of normal advective flow. Longitudinal dispersion is a significant transport process for RDX and a factor in natural attenuation.

Estimate of the Contaminant Volume and Mass

The estimated volume of RDX-contaminated water emanating from the CIA is 2.57 billion gallons. The estimated mass of RDX within this volume is 22.5 kg (49.6 lbs). The estimated volume of perchlorate-contaminated water emanating from the CIA is 153 million gallons. The estimated mass of perchlorate within this volume is 2.9 Kg (6.4 lbs).

Current Exposure Pathways

There are currently two known private residential water supply wells located downgradient of the Central Impact Area on Route 6 (see Figure 6).