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U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting, Colorado Springs, Colorado, September 20-24, 1993, Water-Resources Investigations Report 94-4015

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Cometabolic Biotransformation of Trichloroethylene and CIS-1,2-Dichloroethylene in Unsaturated-Zone Soil at Picatinny Arsenal, New Jersey

by

Theodore A. Ehlke (U.S. Geological Survey, 810 Bear Tavern Road, Suite 206, West Trenton, New Jersey 08628) and Thomas E. Imbrigiotta (U.S. Geological Survey, 810 Bear Tavern Road, Suite 206, West Trenton, New Jersey 08628)

Abstract

This study determined the feasibility of in situ cometabolic remediation of gas-phase chlorinated ethenes at Picatinny Arsenal, New Jersey. Cometabolic biotransformation of trichloroethylene (TCE) and cis-1,2-dichloroethylene (cis-DCE) was studied in a laboratory experiment with unsaturated-zone soil cores collected within a contaminant plume near the source. Concentrations of TCE and cis-DCE in soil, soil gas, and ground water within the plume also were quantified. At the highest concentrations studied, TCE (3.2 mM) mixed with cis-DCE (4.3 mM) was degraded most rapidly (0.05 mmol TCE/L/d, 0.09 mmol cis-DCE/L/d) in acclimated soils with a 3-percent methane headspace. Degradation of TCE at lesser concentrations (1.3 mM) as the only chloroethene present in fertilized, acclimated soil was much faster (0.12 mmol TCE/L/d) in the presence of 1.2 percent methane. Most of the unsaturated-zone TCE (>99.9 percent) near the contaminant source was sorbed to soil. Results of soil-gas analyses indicate that the concentration of unsaturated-zone TCE near the contaminant source was highest (0.32 mM) in a shallow clay layer, and decreased with depth to the water table. This indicates that the original contamination was mostly from condensed TCE which drained from a degreasing tank to a nearby dry well. The concentration of TCE in unsaturated-zone soil elsewhere throughout the plume increased with depth, indicating that most unsaturated-zone TCE contamination resulted from volatilization losses of TCE from contaminated shallow ground water.

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