Estimating Discharge of Chlorinated Volatile Organic Compounds from Contaminated Fractured Rock to a Stream

Concentrations of trichloroethylene (TCE), cis-1,2-dichloroethylene (cDCE), and vinyl chloride (VC) and stream base flow discharge measurements were collected at 48 stations in Gold Run, a small brook that passes over contaminated fractured bedrock in West Trenton, N.J.  Surface water-quality data were collected at each station up to 7 times during 1984-98, prior to closure of the Naval Air Warfare Center (NAWC), a former Navy jet engine testing facility adjacent to Gold Run. Water samples were collected at each station up to 48 times during 1999-2012, after closure of the NAWC. Base flow discharge measurements were collected at 12 stations during 2007-12. Mean concentrations of TCE, cDCE, and VC in the brook prior to closure ranged from less than detection to 520, 7,000 and 2,300 micrograms per liter (mg/L) respectively. After base closure, accompanied by contaminated soil excavation, installation of a pump and treat system, and monitored natural attenuation, mean concentrations of TCE, cDCE, and VC in the brook ranged from less than detection to 320, 560, and 37 mg/L, respectively. New Jersey Department of Environmental Protection Agency regulates TCE and VC in surface water with maximum permissible concentrations of 1 and 0.08 mg/L, respectively. Base flow measurements range from zero to 284 liters per minute (L/min). Concentrations of TCE, cDCE, and VC decrease downstream primarily as a result of volatilization, decreasing by 50 percent over every stream reach of 211, 211, and 106 meters respectively. Based on mean concentrations and base flow, 19.8 kilograms per year (kg/yr) of original TCE discharged to Gold Run from an area of highly contaminated bedrock at the NAWC since closure compared to 280 to 6,200 kg/yr prior to closure. This result suggests that contaminated soil excavation, contaminate groundwater withdrawals, and natural attenuation has substantially reduced offsite discharge of contaminants via Gold Run.