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ABIOTIC NATURAL ATTENUATION OF CIS-DICHLOROETHYLENE AND 1,1-DICHLOROETHYLENE IN AQUIFER SEDIMENT
Citation:
Ferrey, M., R T. Wilkin*, R G. Ford*, AND J T. Wilson*. ABIOTIC NATURAL ATTENUATION OF CIS-DICHLOROETHYLENE AND 1,1-DICHLOROETHYLENE IN AQUIFER SEDIMENT. In Proceedings, Fourth International Conference on Remediation of Chlorinated and Recalcitrant Compounds, Monterey, CA, May 24 - 27, 2004. Battelle Press, Columbus, OH, 4 p., (2005).
Impact/Purpose:
To understand what was responsible for the attenuation observed in the filed, microcosms were made from aquifer sediment collected from three depths near the source of the plume. To distinguish non-biological from biological processes, the sediments in one experimental treatment was heat sterilized. The microcosms were spiked with either cis-DCE or 1,1-DCE, and then incubated at room temperature under anaerobic conditions for 830 days.
Description:
The disposal of TCE and 1,1,1-TCA at the Twin Cities Army Ammunition Plant (TCAAP) in Minnesota produced a plume of contaminated ground water that was over eight kilometers long. Although the size of the plume was consistent with a high ground water velocity in the aquifer and the absence of redox conditions that typically favor reductive dechlorination, fate and transport modeling indicated that contaminant mass was being lost from the ground water over time and distance. A first order decay rate of at least 0.17 per year was necessary to account for the attenuation of the contaminant mass and the observed development of the plume. Vinyl chloride and ethene were not detected.
To understand what was responsible for the attenuation observed in the field, microcosms were made from aquifer sediment collected from three depths near the source of the plume. To distinguish non-biological from biological processes, the sediment in one experimental treatment was heat sterilized. The microcosms were spiked with either cis-DCE or 1,1-DCE, and then incubated at room temperature under anaerobic conditions for 830 days.
In microcosms constructed from sediment samples from the three depths, the first order rate of removal of cis-DCE varied from 0.31 to 2.31 per year. In material from each of the three depths, no significant difference was observed in the rates of removal in the sterilized and non-sterilized sediment. The rate of removal in sterile water controls without sediment was 0.071 per year. For 1,1-DCE, the rate of removal was 1.29 and 1.37 per year in the non-sterilized and heat-killed sediments, respectively, while the rate of removal for 1,1-DCE in the sterile water controls was 0.205 per year. The rates of removal measured in the microcosms are similar to the rates of attenuation observed in the field.
Magnetite was identified in all TCAAP sediment subsamples at similar abundance by X-ray diffraction and optical microscopy. The rates of removal observed in the microcosms are consistent with the rate of abiotic transformation of chlorinated ethylenes that would be expected at the concentration of magnetite in the sediment.
