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Abiotic Removal of TCE and cis-DCE by Magnetite under Aerobic Conditions in Ground Water (Maryland)
Citation:
WILSON, J. T. AND M. Ferrey. Abiotic Removal of TCE and cis-DCE by Magnetite under Aerobic Conditions in Ground Water (Maryland). Presented at The 10th International In Situ and On-Site Bioremediation Symposium, Baltimore, MD, May 05, 2008 - May 08, 2009.
Impact/Purpose:
Disposal of chlorinated solvents
Description:
The former Twin Cities Army Ammunition Plant (TCAAP) is located just north of St. Paul, Minnesota. Disposal of chlorinated solvents at the Building102 site on the TCAAP contaminated groundwater in the shallow, unconsolidated sand aquifer with TCE and cis-DCE. Concentrations of TCE and cis-DCE rapidly attenuate with distance from the source even though the ground water has high concentrations of dissolved oxygen, there is no evidence from geochemical parameters for biological reductive dechlorination, and there is no accumulation of vinyl chloride. Data from the site was used to calibrate a simple transport and fate model. The calibrated rate of degradation of TCE and cis-DCE that was necessary to achieve an acceptable correspondence to the field data was 1.9 per year and 0.8 per year, respectively. To determine whether purely abiotic reactions of TCE and cis-DCE with magnetite in the aquifer matrix could explain the attenuation of TCE and cis-DCE in ground water, sediment from the site was acquired for a microcosm study. The sediment was dried to a powder, then autoclaved overnight to kill organisms capable of reductive dechlorination. Then the sterile sediment was used to construct microcosms. The sediment was wet up with oxygenated reverse osmosis water. Concentrations of dissolved oxygen in the pore water of the sediment were maintained above 3 mg/L over the course of the study. Over 879 days of incubation, vinyl chloride, ethylene, and acetylene were not detected in pore water of the microcosms. Over 879 days of incubation, the first order rate constant for removal of TCE in the microcosms was 0.96 ± 0.277 per year at 95% confidence. The rate constant for removal of cis-DCE was 0.65±0.198 per year at 95% confidence. The rate constants for removal of TCE and cis-DCE in control bottles filled with sterile water was 0.49±0.12 per year and 0.21±0.044 per year respectively. The rates of removal of TCE and cis-DCE in the microcosms corresponded within a factor of two with the rates needed to explain the removal of TCE and cis-DCE in the field scale plume at Building 102 Site. Within a reasonable margin of error, abiotic processes can explain the removal of TCE and cis-DCE in aerobic ground water at the Building 102 site. The sediment collected to construct microcosms had a mass magnetic susceptibility of 9.07 E-07 m3* kg-1. The removal was probably associated with magnetite in the aquifer matrix. This is an abstract of a proposed presentation and does not necessarily reflect MPCA or EPA policy.
