The 6,600-acre Beltsville Agricultural Research Center (BARC) has been addressing environmental problems at several locations since being placed on the National Priorities List (NPL) under the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) in 1994. The Beaver Dam Road Landfill (BDRLF) is one such site investigated as part of the BARC environmental program, and groundwater was found to be contaminated with elevated concentrations of trichloroethylene (TCE) originating within the landfill. In consultation with EPA Region III a Feasibility Study resulted in selecting a “permeable reactive barrier” (PRB) remedy with the objective of treating groundwater to achieve remedial goals. A PRB is a biofilm associated with a stationary substrate that treats contaminated groundwater anaerobically via reductive dechlorination. Commonly referred to as a “biowall,” TCE is degraded sequentially to cis, trans, and 1,1 dichloroethylene (DCE), vinyl chloride, and ethane/ethene. Establishing the composition of the biowall substrate was technically challenging. Microbial sources, groundwater residence time, and the ability of the system to maintain anaerobic conditions were studied. Through research completed by the ARS and University of Maryland (UMD) research organizations, an optimum composition was selected to be a mixture of compost, woodchips, and sand. The biowall at BDRLF is designed to capture and treat contaminated groundwater along a 1,000 foot front, is 2 feet wide, and extends 20 feet below ground tying into an impermeable underlying clay. Since its installation in 2013, biowall performance has been closely monitored. In addition to reductions in contaminant concentrations, key indicators of the biological activity include temperature, pH, total organic carbon, oxidation reduction potential, dissolved oxygen, and other indicators of reductive processes such as methane and ferric/ferrous iron concentrations. This paper examines biowall implementation challenges, applied research completed to address those issues, performance attributes to date, and future efforts aimed at improving and enhancing performance.

Implementing a biowall to induce microbial reductive dehalogenation of volatile organics in groundwater

254th National Meeting (2017)

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