Fact Sheet # 99-01 Southwest Operable Unit (SWOU) Update The Southwest Operable Unit (SWOU) Remedial Investigation/Feasibility Study (RI/FS) is an investigation focused on the area along and south of the southern MMR boundary. The purpose of this investigation is to:
In July 1997, it was determined that additional data was needed to better assess potential groundwater contamination areas such as Chemical Spill 4 (CS-4), Fuel Spill 13 (FS-13) and Fuel Spill 28 (FS-28). Investigation activities began in January 1998 and included drilling and sampling more than 60 new monitoring wells and sampling 160 existing wells. The Remedial Investigation consisted primarily of sampling groundwater, surface water, and sediment; characterizing the physical site setting; and performing human health and ecological baseline risk assessments. Groundwater within the SWOU is contaminated primarily by organic constituents such as ethylene dibromide (EDB), trichloroethylene (TCE), tetrachloroethylene (PCE), and carbon tetrachloride (CCl4). This study also included information from other source areas and groundwater plumes investigated in the area. This includes Fuel Spills 2, 13, and 28 (FS-2, FS-13, and FS-28); Chemical Spills 4 and 10 (CS-4, CS-10); Landfill 1 (LF-1); private well samples taken since 1986; and ecological sampling. The Draft Remedial Investigation report has been reviewed by the regulatory agencies. A draft Feasibility Study will be submitted for regulatory review in January 1999. The Feasibility Study is a report that will identify and evaluate potential cleanup alternatives for each of the plumes. A Proposed Plan (PP) is a fact sheet that outlines the remedies preferred by the Air Force and how the various cleanup options compare against certain criteria. Once public comment has been heard about the various options, a final decision will be made and documented in a Record of Decision (ROD). The PP is expected to be issued for a 30 day public comment period currently scheduled to occur from May 28 to June 26 1999, and a draft ROD is expected to be issued for regulatory review in August 1999. Introduction Remedial Investigation Primary Contaminants Maximum concentrations found in the groundwater for the primary contaminants are EDB at 18 ppb, TCE at 1,010 ppb, PCE at 140 ppb, and CCl4 at 32 ppb. The highest concentrations of EDB were found within the existing FS-28 groundwater plume. For TCE and PCE, the highest concentrations were found in the existing CS-10 groundwater plume on the base. For CCl4, the highest concentrations found were in wells located along the southern part of the existing LF-1 plume on the base. Plume Cleanup For the CS-4 plume, an extraction, treatment and reinjection (ETR) system consisting of 13 groundwater extraction wells, a carbon treatment facility and an infiltration gallery were installed and started up in November 1993. An evaluation of the system, completed in 1997, recommended several modifications to the treatment system in order to better capture the plume. Treatment system modifications are currently being evaluated in the SWOU Feasibility Study. As part of a Time Critical Removal Action at FS-28, one groundwater extraction well (EW-1) was installed in the area with the highest EDB concentrations, just before the plume upwells into the Coonamessett River system. EW-1 is drawing out groundwater at a rate of 600 gallons per minute (gpm). The extracted water is treated using granular activated carbon and then returned to the river system, meeting the Massachusetts Surface Water Quality Standards. In addition to EW-1, shallow groundwater extraction well points are being proposed for installation as part of the Coonamessett River/Bog Separation Project. The SWOU Feasibility Study will evaluate potential final cleanup alternatives for FS-28. For the CS-10 plume, construction on the Sandwich Road and in-plume remedies are currently ongoing. Further additional work is being conducted for the southwest and southern portions of the CS-10 plume. The FS-13, TCE, PCE, CS-4, FS-28 and CCl4-EDB plumes are being addressed as part of the SWOU Remedial Investigation/Feasibility Study. Source Areas The CS-4 source area displayed exceedences of MCLs, or drinking water standards, for chlorinated solvents in groundwater. The CS-4 source area consists of the West Truck Road area and the CS-4 (North) West Truck Road area. The former area was cleaned up in 1995. Contaminated soils from the former source were treated thermally on site as part of a removal action. For the latter source area, a Site Investigation (SI) was completed and currently is undergoing regulatory review.
Other Activities: Residential Well Sampling Community Involvement AFCEE will present the preferred alternative(s) for addressing contamination in the SWOU study area in a Proposed Plan due to be released for public comment in May 1999. There will be a public meeting and hearing with a public comment period currently scheduled from May 28 to June 26, 1999. Comments received during the public comment period will be addressed in a responsiveness summary, which will be attached to the ROD. The draft ROD is due to be submitted to the regulatory agencies on August 17, 1999. GLOSSARY ethylene dibromide (EDB): a man-made additive that was used formerly in aviation gas to control the buildup of lead in engines. extraction, treatment and reinjection (ETR): a system that extracts groundwater, treats it to reduce or eliminate contaminants, and reinjects the treated water back into the aquifer. Feasibility Study: a report that identifies and screens potential cleanup alternatives for a site that requires further remedial action. maximum contaminant levels (MCLs): the maximum concentration of a given contaminant allowed in drinking water under state and federal regulations. parts per billion (ppb): a measure of concentration. One ppb is comparable to one kernel of corn in a filled, 45-foot silo, 16 feet in diameter. perchloroethylene (PCE): also referred to as tetrachloroethylene; a man-made solvent commonly used for metal degreasing and in dry-cleaning clothes. Proposed Plan (PP): a public document that summarizes the preferred remedial action for a site, presents the rationale for the preference, and is issued for a thirty day comment period. Record of Decision (ROD): final remedial action decision agreed to by all agencies. Remedial Investigation: an investigation to gather and analyze the data necessary to determine the nature and extent of contamination at a site. risk assessment: an evaluation to determine whether adverse impacts to human health and/or the environment are present to warrant an action. secondary drinking water standards: unenforceable federal guidelines regarding the taste, odor, color, and certain other non-aesthetic effects of drinking water. Site Investigation (SI): a technical phase of work that follows a preliminary assessment, or records search, designed to collect more extensive information about a potential hazardous waste site. The information is used to evaluate a site to determine whether further action is required. Southwest Operable Unit (SWOU): an area of study at the MMR roughly between the southern lobe of the LF-1 plume and the CS-10 and Ashumet Valley plumes, encompassing six distinct groundwater plumes. trichloroethylene (TCE): a solvent used to dissolve or disperse another substance such as oil. Time Critical Removal Action: any appropriate removal action taken to abate, prevent, minimize, stabilize, mitigate or eliminate a release or threat of release which endangers or could endanger public health, welfare or the environment. upwell: an area of water table where plume contaminants discharge to a surface water body. For More Information For further information, please contact: Doug Karson Jim Murphy Ellie Grillo
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