FIELD AND LABORATORY EVIDENCE FOR INTRINSIC BIODEGRADATION OF VINYL-CHLORIDE CONTAMINATION IN A FE(III)-REDUCING AQUIFER

Intrinsic bioremediation of chlorinated ethenes in anaerobic aquifers previously has not been considered feasible, due, in large part, to 1) the production of vinyl chloride during microbial reductive dechlorin ation of higher chlorinated contaminants and 2) the apparent poor biod egradability of vinyl chloride under anaerobic conditions. In this stu dy, a combination of field geochemical analyses and laboratory radiotr acer ([1,2-C-14] vinyl chloride)experiments was utilized to assess the potential for intrinsic biodegradation of vinyl chloride contaminatio n in an Fe(III)-reducing, anaerobic aquifer. Microcosm experiments con ducted under Fe(III)-reducing conditions with material from the Fe(III )-reducing, chlorinated-ethene contaminated aquifer demonstrated signi ficant oxidation of [1,2-C-14] vinyl chloride to (CO2)-C-14 with no de tectable production of ethene or other reductive dehalogenation produc ts. Rates of degradation derived from the microcosm experiments (0.9-1 .3% d(-1)) were consistent with field-estimated rates (0.03-0.2% d(-1) ) of apparent vinyl chloride degradation. Field estimates of apparent vinyl chloride biodegradation were calculated using two distinct appro aches; 1) a solute dispersion model and 2) a mass balance assessment. These findings demonstrate that degradation under Fe(III) reducing con ditions can be an environmentally significant mechanism for intrinsic bioremediation of vinyl chloride in anaerobic ground-water systems. Pu blished by Elsevier Science B.V.