Enhanced In Situ Bioremediation of Chlorinated Solvents (PDF)

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Anaerobic enhancement of a shallow confined silty sand aquifer has resulted in a substantial biodegradation of a dissolved Tetrachloroethene (PCE) plume at a former metal finishing facility in Secaucus, New Jersey. The injection of a time-release hydrogen compound (HRCâ„¢) rapidly converted ambient aquifer aerobic conditions to anaerobic, and maintained such conditions throughout the 6-month monitoring period.  This enhancement effectively induced and facilitated the successive reductive dechlorination of PCE and daughter products Trichloroethene (TCE), cis- and trans-Dichloroethene (c/t-DCE), and Vinyl Chloride (VC).
The pre-test dissolved PCE concentrations of 5 to 8 mg/l and mass declined by 90 to 96% within 2 months of injection. The degradation of both dissolved and adsorbed contaminant mass was maintained even after the temporary rebound of concentrations due to desorption of PCE from soil. Degradation rates of up to 96% and 100% were also obtained for TCE and t-DCE, respectively. The degradation rates of c-DCE were slower and smaller at 30 to 70%. The potential presence of residual product and larger adsorbed solvent mass in the source area resulted in seemingly smaller but faster PCE and TCE overall degradation rates in comparison to downgradient areas. The c-DCE mass degradation during the same period was apparently greater and faster near the source than in the downgradient area.
Of interesting significance was the rapid and near instantaneous degradation of VC under such strong anaerobic conditions. Vinyl chloride was hardly detected during the 6-month monitoring period. The increase by more than one order of magnitude of dissolved carbon dioxide and methane levels, along with the substantial DCE mass degradation, are evidences for the degradation of VC. The relatively high pre-test sulfate levels of about 50 mg/l, which also substantially degraded due to the anaerobic enhancement, did not adversely impact the degradation of PCE and its breakdown daughter products.

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