Transport and Microbial Transformation of Chlorinated VOCs in Fractured Rock at NAWC West Trenton

摘要

The U.S. Geological Survey (USGS) is conducting a multidisciplinary investigation of the transport and microbial transformation of chlorinated volatile organic compounds (VOCs) in fractured dipping mudstones underlying the 60-acre former Naval Air Warfare Center (NAWC), West Trenton, New Jersey. Trichloroethene (TCE) and jet fuel were released during U.S. Navy operations (1951-98), and natural microbial reductive dechlo-rination has transformed TCE to cis-l,2-dichloroethene (cisDCE), vinyl chloride (VC), and ethene. In a network of about 70 bedrock monitoring wells, most with 5 m open intervals, maximum concentrations of TCE, cisDCE, and VC are about 200,000 Lxg/1, 16,000 ixg/1, and 1,200 ng/1, respectively. Extensive characterization of the geology and contaminants indicates that bedding-plane fractures and thin continuous fissile or laminated mudstone strata are major transport paths. Redox conditions within these paths change rapidly in response to recharge events, suggesting a highly dynamic flow system in the permeable parts of the rock. Persistently high concentrations of VOCs suggest that large contaminant mass lies in the less permeable primary porosity of the rock.