Competitive Inhibition of TCE Degradation by Freons Present in a Regional Plume

摘要

Remediation in urban settings often provides a number of challenges including restricted access for delivery of reagents and competition for electron donors resulting from the presence of regional plumes. At one site, the presence of Freon (chlor-ofluorohydrocarbons) appears responsible for inhibition of TCE degradation and increased consumption of electron donors following addition of HRC~R. This paper will discuss how one regional VOC plume appeared to affect natural attenuation and targeted remediation efforts. This paper will discuss how one might have to account for the additional time or electron donor requirements that will likely be required for reductive dechlorination in cases where a regional VOC plume has commingled with a plume where reductive dechlorination has been implemented.The presence of two Freons in a TCE plume may have been responsible for the limited presence of degradation products prior to treatment. A short term dual phase extraction(DPE)/soil vapor extraction (SVE) system was implemented to largely eliminate the potential of further impact to groundwater due to transport from the vadose zone. Subsequent HRC addition resulted in a relatively rapid depletion of Freons and a reduction in TCE concentrations. The formation of cis-DCE and later vinyl chloride provided evidence of biodegradation and was consistent with geochemical and microbial data. The observations were consistent with inhibition of TCE biodegradation prior to degradation of the Freons. Whether or not Freon-based inhibition was occurring prior to treatment, it is clear that where both Freon and TCE are present, addition of sufficient electron donors can result in efficient degradation of both classes of VOCs.