Environmental

Site 3 - Northern Plume

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Site 3 - Chlorinated Solvent Groundwater Plume, Northern Plume

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Site Description

Site 3 is a dissolved-phase chlorinated volatile organic compound (VOC) plume in groundwater at the northern portion of NWIRP Bedford (north of Hartwell Road) near the Facility Storage Building (FSB) and the Components Laboratory (Building 1). The plume extends primarily northwest to a wetland area on private property. Only trace levels of chlorinated VOCs have reached groundwater beneath Elm Brook. The plume appears to be migrating primarily in the unconsolidated (overburden) deposits. Chlorinated VOCs are slow to migrate from the area because of the nature of the groundwater aquifer (low permeability of the glacial till layers). Elevated chlorinated VOC concentrations are also present in soil throughout the saturated, silty till unit, generally from 30 to 50 feet below ground surface.

The source area of the plume is located under the paved loading dock associated with Building 1. There has been one documented release of 55 gallons of Axothene, which contains 1,1,1-trichloroethane, in the loading dock area of Building 1 in 1976, but no other releases of chlorinated VOCs to the subsurface have been recorded. Potential sources which may have contributed to the Site 3 northern plume include: the Components Laboratory, the FSB print shop, a storm drain connected to the FSB, the Antenna Range Building, the former Transportation Building, the AMRAD building, the former hazardous waste storage area, and the Old Incinerator. Chlorinated solvents could have been released directly to the ground or into the storm drain system, and then released to the groundwater through cracks in the system.

Remedial Actions

In 1997, the Navy implemented a groundwater extraction and treatment system (GWETS) as an Interim Remedial Action to prevent off-migration of contaminants to the adjacent wetland area and Bedford town wells. Quarterly or semiannual groundwater monitoring has occurred since the treatment system start-up in 1997. The Site 3 ROD was signed in 2010. The remedy for Site 3 included continued operation of the GWETS, and in-situ enhanced bioremediation with injection of emulsified vegetable oil at the Site 3 source area in 2012 and 2017. The current semi-annual groundwater monitoring frequency will continue at Site 3; samples will be analyzed for chemicals of concern (COCs) and natural attenuation parameters. Because of the extent of contamination and the nature of the groundwater aquifer (situated in a tight glacial till and fractured bedrock), the ultimate cleanup of Site 3 is expected to require several decades.

Land use controls (LUCs) were implemented to restrict future use of the site to industrial/commercial scenarios, to prohibit the use of the groundwater aquifer as drinking water, to restrict building occupancy because there is the potential for vapor intrusion from soil, and to require annual inspections of the site to ensure LUCs are continuing to be implemented.

In 2014, the first Five Year Review (FYR) for NWIRP Bedford identified 1,4-dioxane as an emergent contaminant of concern that is potentially present at the site. Groundwater at Site 3 was analyzed for 1,4 dioxane because of the presence of 1,1,1-trichloroethane, which was commonly stabilized with 1,4 dioxane. A groundwater investigation in 2014 determined that 1,4-dioxane was present at Site 3. 1,4-Dioxane was detected in groundwater samples and was also observed in both the influent and effluent streams of the GWETS. Additional groundwater sampling was performed in 2015 to further delineate the extent of 1,4-dioxane at Site 3. A treatability study for 1,4-dioxane in the groundwater treatment system was initiated. The Navy expects to implement a modification to the GWETS to include treatment for 1,4-dioxane in the next few years. The Navy is also planning to initiate further investigation of the extent of the 1,4-dioxane, and plume treatment/containment options. The Navy is planning on optimizing the LTM program as part of the second FYR.

Previous Investigations

Previous investigations, plans and documentation at this site are: RI/RA; FS; Treatability Study; and a ROD.

Current Status

LUCs have been implemented; Semi-annual Groundwater Monitoring is being conducted; Remedial Action is in process.

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