In Situ Accelerated Anaerobic Biodegradation of a Chlorinated Source Area

ABSTRACT: In situ accelerated anaerobic biodegradation (AAB) is being successfully employed to treat chlorinated solvents that were historically released into soil and groundwater beneath Building 719, a mission-critical maintenance facility at Dover Air Force Base (DAFB), Delaware. Contaminants are attributed to engine cleaning activities conducted in the building and include trichloroethene (TCE), 1,1,1-trichloroethane (1,1,1-TCA), and their degradation products. The AAB system was installed to remediate contaminated groundwater in the source area and minimize the continued contribution to the dissolved plume extending approximately one mile downgradient. The AAB system establishes hydraulic control in the source area by recirculating groundwater through injection and extraction wells located outside Building 719. A carbon substrate and metabolic nutrients are added to the recirculated groundwater as it is reinjected to enhance the natural microbial population at the site. This creates and maintains a reactive zone in the vicinity of the injection wells where contaminants are reductively dechlorinated via microbial metabolic processes. An estimated 130 pounds (59 kilograms [kg]) of TCE were degraded to ethene between May 2002 and October 2004. Additionally, during a period of elevated water table conditions (January 2003 to July 2003), an estimated 530 pounds (240 kg) of TCE were dissolved from the shallow soils and made available for biodegradation