DISTRIBUTION, TRANSPORT, AND BIODEGRADATION OF TCE IN FRACTURED SEDIMENTARY ROCKS OF THE NEWARK BASIN AT THE NAVAL AIR WARFARE CENTER, WEST TRENTON, NJ

The U.S. Geological Survey and the U.S. Navy are conducting a multidisciplinary investigation of the distribution and fate of trichloroethene (TCE) in dipping fractured mudstones of the Triassic Lockatong Formation that underlie the former Naval Air Warfare Center (NAWC), West Trenton, NJ. TCE has been partially transformed to cis-1,2-dichloroethene (DCE), vinyl chloride (VC), and ethene by natural microbial reductive dechlorination. Although a pump and treat system has operated since the mid-1990's, maximum dissolved concentrations of TCE, DCE, and VC remain high: about 200,000; 16,000; and 1,200 micrograms/liter, respectively. TCE was released in aqueous and non-aqueous phases, but has not been observed in non-aqueous phase in the subsurface.

Extensive characterization of the hydrogeology and of dissolved concentrations in more than 70 wells indicates that bedding-plane fractures and thin fissile or laminated strata are major transport paths. Persistently high concentrations of TCE in wells suggest that a large amount of contaminant mass lies in low-permeability fractures and/or the primary rock porosity. Methanol extraction of contaminants from cores collected in a 52 meter deep borehole confirms that TCE occurs in the primary porosity of core samples near fractures. TCE detection generally is correlated with mudstone lithology, with the highest concentrations in fissile and laminated strata, and with low concentrations or nondetects in unfractured massive strata. These results are consistent with TCE concentrations in water pumped from packer-isolated zones of the borehole.

Natural and enhanced biodegradation of TCE, DCE, and VC at NAWC also is being investigated, through measurement of the spatial and temporal distribution of redox conditions and indigenous microbial DNA, and through a bioaugmentation pilot study conducted with the U.S. Navy and GeoSyntec, Inc. These field studies are designed to reveal the mechanisms controlling anaerobic biodegradation of TCE and its daughter products in fractured-sedimentary-rock aquifer systems.