A former military base near Boston, USA
Senior Remediation Engineer
ISOTEC Remediation Technolgies
Boston Operations, USA
A release of tetrachloroethylene (PCE) at a former military base near Boston, Massachusetts resulted in an impacted plume larger than 3 acres. The area of PCE-impacted groundwater is undeveloped and consists of woods, wetlands, and grassy open space. The overburden geology consists of low permeability silty sand and glacial till. A layer of weathered bedrock starts at approximately 20 feet below ground surface (bgs) that is 5 to >10 feet thick between the overburden and competent bedrock. The groundwater table is shallow across most of the area (3-6 ft bgs).
Bioremediation via enhanced reductive dechlorination (ERD) was the selected remedy for the site. Pilot testing was performed to support remedial design. The full-scale remediation program consisted of injection points were oriented in a grid format for focused source areas and as a series of five permeable reactive barriers (PRB) for plume wide treatment. A total of 74 direct push injection points were completed in the overburden treating intervals between 6 and 20 ft bgs. A total of 51 injection wells were used for treatment of weathered bedrock. A total of 20,670 gallons of a solution of emulsified vegetable oil with added sodium lactate was applied along with 3,035 gallons of anaerobic water and 76 liters of bacteria was applied for treatment of overburden and weathered bedrock during 40 injection days. The cost of the full-scale bioremediation injection program was $235,000.
More than 60 overburden monitoring wells were installed at the site during the Remedial Investigation, Remedial Design, pilot test, and Remedial Action phases. Following full-scale treatment groundwater sampling was focused on wells nearer to injection points. GWSDAT was incorporated into performance evaluation to improve the ability to visualize the site plume and assess effectiveness of the treatment to reduce plume size and residual PCE mass. More than 15 years of sampling data from 40 overburden monitoring wells sampled before and after full-scale remediation were input into GWSDAT. “GWSDAT’s ability to provide a visualization of temporal trends in contaminant concentrations for a large plume is a powerful tool, especially when groundwater sampling did not always use a consistent set of monitoring wells,” said Senior Remediation Engineer Paul Dombrowski, P.E. of ISOTEC Remediation Technologies who implemented the bioremediation injections.