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M12 PM Remediation
(DAR-1117-837675) Laboratory evaluation of chlorinated ethene transformation processes in fractured sandstone.
Darlington, R.1, Freedman, D. 1, 1 Clemson University, Clemson, SC, USA
ABSTRACT- An industrial site underlain by fractured sandstone is contaminated with trichloroethene (TCE). Field data indicates significant transformation of TCE to cis-1,2-dichloroethene (cis-DCE). A laboratory study was conducted to evaluate the extent and type of transformations occurring in situ for TCE, cis-DCE and vinyl chloride, and to determine via molecular analysis the types of microorganisms that are present. Site groundwater and crushed rock samples from depths of ∼531, 568, 732, and 872 ft were used to prepare microcosms. For each depth and each chloroethene, treatments consisted of anaerobic conditions; (′′as-is′′); autoclaved anaerobic controls; oxidized peroxide controls, and distilled water-only controls. In the 872 and 531 ft depth microcosms, 57-75% of the [14C]TCE added was recovered as [14C]cis-DCE in the as-is bottles after 2-5 months. As much as 17% of [14C]TCE accumulated as 14CO2 plus a 14C-labeled soluble, nonstrippable residue (NSR) in the autoclaved controls. In microcosms prepared with [14C]cis-DCE, a maximum of 2% vinyl chloride and 10% 14CO2 was recovered in the as-is bottles. The predominant product in autoclaved bottles was NSR. Little transformation occurred in peroxide controls. In microcosms prepared with [14C]vinyl chloride, no significant transformation occurred in the as-is or autoclaved treatments. Molecular analysis via the polymerase chain reaction, denaturing gradient gel electrophoresis and sequencing of DNA extracts from the as-is TCE microcosms indicates the presence of a microbe closely related to one that anaerobically oxidizes Fe(II). It is not yet known if anaerobic oxidation of Fe(II) plays a role in chloroethene transformation. Overall, the microcosm results confirm the field observations of TCE reduction to cis-DCE and provide additional evidence for anaerobic transformation of cis-DCE to NSR and CO2.
Key words: Chlorinated Ethenes, Reductive dechlorination, Abiotic Degradation, Molecular Analysis
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