Laboratory and field studies were conducted to determine the magnitude and potential for natural attenuation of chlorobenzenes in a bottomland hardwood wetland located within the Devils Swamp portion of the Petro Processors, Inc. CERCLA site. Studies conducted from 1996-1999 include laboratory and field studies that determined the rates, pathways and extent of HCB degrdation in surface and near surface sediments; identification of parameters that would predict metal inhibition of reductive dechlorination, and the required terminal electron accepting conditions for all reductive dechlorination reaction steps including the final mineralization of monochlorobenzene. Results indicate complete removal of initial DCB concentrations within five weeks of incubation through reductive conversion to monochlorobenzene. Degradation occurred under methanogenic conditions. It was also demonstrated that MCB was slowly transformed to carbon dioxide under methanogenic conditions. Cd and Pb affected the dechlorination rates, appearance of lower chlorinated benzene metabolites and lag times. Inhibition of HCB dechlorination was well correlated to water-soluble Cd. Pb partially inhibited HCB dechlorination at all concentrations tested and inhibition did not correlate to water soluble Pb concentrations or AVS/SEM ratios. based ont hese data, heavy metal inhibition does not appear to be a concern for attenuation of chlorobenzxenes in the wetland.
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