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TCE Ground Water Attenuation in Severe Northern Climates

Principal Investigators
R.R. Dupont, D.L. Sorensen, M. Kemblowski, and D. Smith, Utah State University


Goal: The goal of this project is to conduct a detailed investigation of microbially-mediated containment mechanisms taking place near the source of trichloroethene (TCE) and dichloroethene (DCE) plumes at a site in Alaska.

Rationale: Intrinsic remediation represents a highly attractive remediation alternative, particularly for residual phase contaminants located at or below the ground water table. Mechanisms of attenuation of hydrocarbon plumes and general approaches for the assessment of their attenuation rates are at a fairly well developed stage, and this methodology and understanding of process mechanisms has been supported by numerous field studies at hydrocarbon release sites. Chlorinated solvent plume attenuation has been investigated to a much lesser extent. Mechanisms of cometabolic reduction of TCE, as well as TCE anaerobic dechlorination have been evaluated under field conditions. This research will provide additional data near to the source area of the selected site, where rapid TCE attenuation is taking place, to significantly improve our understanding of the fate of TCE under natural aquifer conditions.

Approach: This project will involve integration of field sampling and analysis work with a companion U.S. Air Force Center for Environmental Excellence (AFCEE) field scale study. Field work will be utilized to provide TCE and daughter product transformation rates and additional evidence of the existence and mechanisms involved in the anaerobic degradation of TCE under actual field conditions prevalent at the selected site. An additional 25 soil and ground water sampling probes will provide near field measurements of the apparent rapid transformation of TCE and DCE taking place in the aquifer. These probes will be placed at the site and will be sampled along with all existing locations. Samples from these new probes will be analyzed for TCE, intermediate products, electron acceptor composition, oxidation/reduction potential status and other sources of electron donor that could be driving the anaerobic metabolism of TCE. These data will be instrumental in verifying the current conceptual model for the site and in more precisely quantifying the intrinsic TCE remediation mechanisms taking place in what appears to be a highly reactive zone of the contaminated aquifer system.

Status: In previous complimentary work, investigators have been involved in field measurement of a range of aquifer conditions coupled with an extensive array of laboratory-determined water quality parameters focused on quantifying terminal electron acceptor composition and the nature and distribution of parent compound and intermediate compounds of the ground water system. Monitoring of these parameters has yielded ample evidence that anaerobic TCE degradation, via anaerobic dechlorination, appears to be taking place at the site. However, the sampling grid is not sufficiently fine near the source area to completely delineate the reaction pathways and to yield acceptable mass balance data for intermediate compound production versus parent compound reduction rates observed at the site. This project will provide data near the source area necessary to definitely describe reaction pathways and reaction rates for TCE.

Approach: This study will focus on an abandoned zinc and lead smelter site in southeast Kansas. The investigators propose to begin investigations whose ultimate goal is to immobilize the metals in place. This would be accomplished with grading to 3-5% slope, to encourage runoff without excessive erosion, and the use of rapid growing poplar trees that have a high water demand. This strategy would minimize net p and intermediate product degradation taking place under natural, intrinsic site conditions. This project has begun recently.

Clients/Users: This project will be of interest to the U.S. Department of Defense, U.S. Department of Energy, regulators, and other researchers.

Key words: trichloroethene, dichloroethene, ground water, monitoring probes, northern climate.

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