Navy Aims to Chemically Degrade Contaminated Groundwater

Contractors for the U.S. Navy have begun planning a $1 million project to deter a contaminated underground aquifer from potentially releasing vapors into residences east of the former Naval Weapons Industrial Reserve Plant site on Hartwell Road.

The measure has an official label of “time-critical removal action,” under provisions of federal policy requiring response to “actual or potential exposures to nearby human populations, animals, or the food chain from hazardous substances or pollutants.”

The wooded area is on the east hillside of the 46-acre site, which for many years was the location for the design, fabrication, and testing of weapons equipment. The area has been inactive for more than 20 years. The Navy began investigating environmental issues in the 1980s; in 1984 new town wells were closed by pollutants traced to the site. Efforts to remove groundwater contaminants began in 1997.

The “time-critical” plans call for installation of a “permeable reactive barrier,” 100 feet long and 40 feet deep, in the northeast part of the property, before the end of the year.

It’s a chemical process, as the barrier will be injected with “colloidal activated carbon.” The Navy memo says the hope is to sequester volatile organic compounds “on the soil matrix to prevent further downgradient migration.” The contaminants would be degraded through an abiotic process.

The project is under the direction of the Naval Facilities Engineering Systems Command Mid-Atlantic, based in Norfolk, VA. According to a memorandum from Eric Ross, remedial project manager, the action will lower risks for residences “by reducing the potential for chlorinated volatile compounds to migrate offsite in the uppermost groundwater bearing unit, thus mitigating risks of vapor intrusion.”

The report says, “Long term monitoring has identified increasing trichloroethene concentrations in the plume at the northeast property boundary. Low levels of cis-1,2-dichloroethene are also present.”

Following completion, “performance monitoring will be conducted by collecting confirmation groundwater samples to ensure effectiveness,” the document said.

According to the memorandum, any alternative approach “could require a planning period of at least two years, during which time such residential receptors may be inadvertently exposed to solvents through vapor intrusion into residences.”

Heidi Porter, director of Bedford’s Health and Human Services Department, commented that state and federal environmental officials urged the Navy to respond to the situation. Even though no testing has indicated a problem off the site, “modeling they used seemed to indicate that there potentially could be a problem.”

Remedial action has been ongoing in the area of the barrier project since 2010, including conventional efforts to contain the underground plume and bioremediation by using emulsified vegetable oil. On the western portion of the site, 23 extraction wells and treatment of contaminated groundwater began in 1997.

According to the Navy memo, a predesign investigation will “define the vertical profile of the plume, hydraulic properties of the target treatment zones, and movement of the mass flux along  the proposed barrier transect. Monitoring wells will be installed in and around the barrier during the investigation and baseline sampling will be performed.”

The carbon injections will follow, scheduled for the fall. The site will require a water source and storage pods; the staging area will be cleared of brush and trees as needed. A Navy consultant will coordinate, including monitoring groundwater to assess distribution of activated carbon within the aquifer.

Further monitoring will include monthly water quality analysis three times, then quarterly three more times. Near the end of 2024 there will be a decision on future frequency.

Porter emphasized that the first thing the agencies check is drinking water, but that wouldn’t be affected by the plume being addressed.