DEVELOPMENT OF HYDROGEOLOGIC FRAMEWORK AND INVESTIGATION OF CONTAMINANT MIGRATION IN FRACTURED BEDROCK BY USE OF GEOPHYSICAL LOGS, WATER LEVELS, AND TCE CONCENTRATIONS, NAVAL AIR WARFARE CENTER, TRENTON, N.J

The U.S. Naval Air Warfare Center near Trenton, N.J., was selected in 2001, as part of the USGS Toxics Hydrology Program, as a site for investigating ground-water contamination in fractured-rock aquifers. The military base is on Triassic age shale and mudstone of the Newark basin. Large quantities of trichloroethylene (TCE) used in jet engine testing leaked at the base during 1950-90’s; ground-water concentrations of TCE, which were detected after sampling began in the early 1990’s, exceeded 100,000 micrograms per liter in two wells.

Natural gamma-ray logs from 40 wells, each log with a signature sequence of anomalies, were collectively interpreted to develop a 3-dimentional structural framework featuring a northwestward dipping synform. Borehole optical- and acoustic-televiewer logs in combination with ambient and stressed heat-pulse flow-meter logs show hydraulically active and passive fractures and partings that are parallel and at high angles to bedding. Water levels measured in wells with 20- to 25-ft open intervals show the 3-dimentional potentiometric surface with discharge to the nearby stream under static conditions and an inclined, elongated cone of depression under stressed conditions. TCE, dichloroethylene (DCE), and vinyl chloride (VC) concentrations appear in 3-dimentions as a plume that is biodegrading and flowing along the strike and around building foundations to a nearby stream in the shallow environment. The plume of contamination in the deep environment has a much lower flow and biodegradation rate than in the shallow environment. TCE, DCE, and VC concentrations in samples collected during 1992-2001 indicate induced movement of TCE caused by the withdrawal of ground water at the recovery wells.