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Record of Decision System (RODS)



City & State:  FALMOUTH  MA  02542
EPA ID:  MA2570024487
EPA Region:  01
NPL Status:  Currently on the Final NPL
ROD Type:  Record of Decision
ROD ID:  EPA/541/R-99/120
ROD Date:  07/06/1999
Operable Unit(s):  10
Abstract:  The Massachusetts Military Reservation (MMR) on Cape Cod, Massachusetts, whose Superfund name is Otis Air National Guard, lies within the boundaries of the towns of Bourne, Mashpee and Sandwich, and abuts Falmouth, Massachusetts. The MMR occupies approximately 22,000 acres and consists of several operating command units. The U.S. Air Force (USAF) managed the base until the end of 1973 when base management was transferred to the Otis
Air National Guard.

MMR is organized into four principal functional areas: Cantonment Area; Range Maneuver and Impact Area; Massachusetts National Cemetery; and Cape Cod Air Force Station. The Cantonment Area occupies 5,000 acres in the southern portion of MMR, this area is the location of administrative, operational, maintenance, housing, and support facilities for the base. This is the most actively used section of MMR. The Otis Air Force Base facilities, including the flight line, are located in the southeast portion of the Cantonment Area. The Range Maneuver and Impact Area occupies 14,000 acres in the northern 70 percent of MMR and is used for training and maneuvers. The Massachusetts National Cemetery consists of 750 acres along the western edge of MMR and contains the Veteran Administration cemetery and support facilities. The Cape Cod Air Force Station occupies 87 acres of the northern portion of the Range Maneuver and Impact Area and is known as the Precision Acquisition Vehicle Entry Phased Array Warning System.

MMR activities that had the potential to contaminate the environment included the storage, handling, and disposal of solvents and petroleum fuels, as well as the leakage of these materials into sumps, leaching wells, storm water drainage systems, and the sanitary sewer system. Landfill operations, firefighter training, coal and ash storage, and numerous chemical and fuel spills also resulted in environmental contamination. The year round population is approximately 2,000 with an additional 800 nonresident employees. Intermittent use of the area for Reserve and National Guard activities increases the MMR population by as many as several thousand people. Both, year-round and seasonal residents live in the towns adjacent to MMR. A single groundwater flow system underlies western Cape Cod, including MMR. The aquifer system is unconfined and is recharged by infiltration from precipitation. It has been classified as a sole source aquifer.

The primary drinking water supply for MMR comes from a groundwater supply well located on the base and installed in glacial outwash. The adjacent towns of Bourne, Falmouth, Mashpee and Sandwich also derive their drinking water from supply wells within the recharge area of this aquifer. Falmouth has a reservoir for storage of drinking water obtained from groundwater. The water supply wells at MMR and the surrounding towns range from 40 to 412 ft deep, with the majority of wells extending to depths of 50 to 100 ft below ground surface, In areas where public water supply lines are not available, residents use private wells for domestic water supplies.

In November 1989, the U.S. Environmental Protection Agency (USEPA) placed MMR on the National Priorities List (NPL). A Federal Facility Agreement (FFA) between the Department of Defense, National Guard Bureau (NGB), U.S. Coast Guard, and USEPA, was signed in 1991 and updated in 1997. The FFA established a procedural framework for ensuring that appropriate response actions are implemented and required the Air National Guard to take the lead in the cleanup activities at MMR. In response to environmental contamination at MM., DOD implemented it multiphase Installation Restoration Program (IPR) at MMR to identify and evaluate problems associated with past releases of hazardous substances. The IPR parallels the USEPA CERCLA investigation and cleanup process. The NGB and subsequently Air Force Center for Environmental Excellence (AFCEE), followed USEPA guidelines for most IRP investigations performed between 1986 and 1989 and for all investigations performed since 1989.

In 1986, an extensive records search and review of available soil and groundwater data identified 73 areas at MMR as having potential for contamination. Four additional areas were later identified through anonymous sources and unrelated base construction projects, bringing the total to 77.
Remedy:  The selected remedy includes excavation and on-site asphalt batching and off-site disposal with a contingency for insitu low flow soil vapor extraction (SVE). The major components of this alternative include excavation, dewatering (if necessary), and temporarily stockpiling of an estimated 1000 cubic yards (cy) of surface soils where contaminants of concern (COC) concentrations exceeded Area of Contamination (AOC) Fuel Spill Number 9 (FS-9) soil cleanup levels; on-site cold-mix asphalt batching of recyclable excavated soils; off-site disposal of non-recyclable excavated soils; and use of the asphalt as sub-base paving material for roadways and parking lots within the Massachusetts Military Reservation (MMR) installation. In addition, where confirmatory sampling indicates COC concentrations in soil that exceed such cleanup levels at depths greater than the practical limits of excavation, an in-situ low flow SVE system will be installed. This SVE system would consist of a single extraction well with passive or active air injection points. The fact that the site is asphalt covered and the depth and thickness of contamination are unknown suggests that ideal air flows would be fostered with injection and extraction points.

Confirmatory sampling would be performed during excavation to verify the extent of contamination exceeding AOC FS-9 soil cleanup levels and to ensure all soils with COC concentrations above such cleanup levels that can be excavated are removed. Samples of excavated materials would be analyzed to determine if concentrations fall below the Resource Conservation and Recovery Act (RCRA) Toxicity Characteristic Leaching Procedure (TCLP) allowable concentrations and state levels. If material is determined to be below these criteria, it would be considered non-hazardous and would be asphalt-batched. If material is determined to exceed these criteria, it would be considered hazardous and would be transported to an off-site RCRA Subtitle C treatment, storage, and disposal facility (TSDF).

If the vertical limit of contamination, as defined by post excavation sampling, were not reached during excavation of the tank pit, additional sampling and remediation would be initiated to establish the extent of contamination. Following the determination of the vertical extent of contamination, a pilot study would be conducted to determine SVE effectiveness and radius of influence. It is probable that the vapor extraction well installed for the pilot study could be incorporated in the operational SVE system. Remedial activities would also be conducted to meet the standards for visible emissions; dust, odor, construction, and demolition; noise; and volatile organic compounds (VOCs). If these standards are exceeded, emissions would be managed through engineering controls.

Following post excavation sampling and confirmation analyses, the excavated areas where SVE is not required would be backfilled with clean soil. The test pit (TP) 11 area would be reseeded. The tank pit area would be covered with asphalt. Site access restrictions at AOC FS-9 would be maintained consisting of restrictions that limit on-site activities that would allow deterioration of the site.

Excavation activities would be performed in a manner designed to minimize release of particulates into the atmosphere, and stockpiled soils would be covered. Erosion control would consist of hay bales and properly maintained silt fencing to prevent runoff. Off-site transportation of contaminated soils would be conducted using covered dump trucks to prevent resuspension of fugitive dusts during transport. The cold-mix asphalt-batching process would minimize the airborne release of VOCs by using a nonvolatile cold asphalt emulsion product. This method also minimizes particulate emission before batching and afterwards. The asphalt paving material generated by the batching process would be used for subpaving of roads and parking lots at MMR. Any stockpili
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