The Ashumet Valley plume originates at the former Firefighter Training Area 1 (FTA-1), with contribution from the decommissioned MMR sewage treatment plant (CS-16/CS-17) about 1,000 feet to the south.

Treatment of contaminated soils at FTA-1 began in June 1995 and was completed in September 1997. A total of 42,531 tons of soil was treated using a thermal treatment process. Soil cleanup objectives were met, the area was restored, and the source area no longer contributes to the Ashumet Valley groundwater plume. For the former sewage treatment plant, the remedial investigation, which defines the nature and extent of contamination, has been completed. A feasibility study, which outlines options for addressing the contamination, is being reviewed. A proposed plan, which describes AFCEE’s preferred alternative for addressing the former sewage treatment plant (CS-16/CS-17), will be released for public comment in September 1998. Following public comment, a record of decision describing the final decision will be released; it is scheduled for December 1998. Once the record of decision has been signed, design and construction of the selected remedy will begin.

Primary Contaminants

The primary contaminants of the Ashumet Valley plume are TCE, PCE, and 1,2 dichloroethylene (1,2-DCE). TCE has been found as high as approximately 50 ppb; average concentrations of TCE and PCE are less than 20 ppb. The safe drinking water standards, or maximum contaminant levels, for these contaminants are 5 ppb for each. PCE and TCE are common solvents associated with cleaners, solvents, paint thinners, and other wastes. Other inorganic contaminants associated primarily with the former sewage treatment plant, such as phosphorus and nitrates, also have been detected.

Affected Area

The Ashumet Valley plume is roughly 10,000 feet long, a maximum of 4,500 feet wide, and averages 30 to 50 feet thick. In general, the plume is more than 60 feet below ground and 50 feet below the water table along most of its length.

The plume extends from the southern base boundary past Ashumet Pond and Carriage Shop Road in Falmouth, toward Route 28.

Plume Cleanup

A pilot test of recirculating well technology began in the eastern lobe of the Ashumet Valley plume in March 1997. The purpose of the test was to determine whether recirculating well technology could effectively capture the plume and reduce contaminant concentrations in the groundwater. The test was completed in August 1997. The test results enabled AFCEE to determine that recirculating well technology could successfully capture groundwater contaminants. The system will be removed in mid-1998 and the site reclaimed.

The Ashumet Valley plume was one of four plumes to undergo the "decision criteria" process in 1997, a public process that enabled the remedial project managers and the public to compare and evaluate cleanup alternatives.

In September 1997, after careful consideration of the advantages and disadvantages of each plume response alternative and comments received during the public comment period, the remedial project managers from AFCEE, EPA, and MassDEP decided on an alternative to treat the Ashumet Valley plume.

The selected alternative uses ETR technology to achieve a significant degree of plume capture. To help restore the Falmouth well field within a reasonable time, an axial fence will be placed within the plume, in the vicinity of the Crane Wildlife Area, to capture and treat VOCs to background levels. To help protect Ashumet Pond, an ETR fence to capture phosphorus and VOCs will be located along the northwest shore of the pond.

The decision also features provisions to relieve nitrate loading in surface waters south of the plume, to investigate the southeast part of the plume, to minimize the effects of construction in neighborhoods, and to reduce adverse effects on natural resources.

Next Steps