The Department of Defense (DoD) has responsibility for many large plumes with dilute concentrations of tetrachloroethene (PCE), trichloroethene (TCE), dichloroethene isomers (cDCE, tDCE, 1,1-DCE) and vinyl chloride (VC) in groundwater. Many of the aquifers that harbor these plumes are water-supply aquifers, and in the absence of a mechanism for the degradation of the chlorinated alkenes, computer models predict that the plumes will continue to expand over time. Many water supply aquifers are aerobic. In aerobic groundwater, PCE and TCE are not subject to biodegradation, and there are limited prospects for biodegradation of cDCE in groundwater. The only plausible mechanism for degradation in aerobic groundwater is abiotic degradation associated with reactive iron minerals in the aquifer matrix material. The overall objective of this project is to develop a deeper understanding for the role of magnetic materials (MM) in mediating abiotic degradation of chlorinated ethenes in aquifers.

This project will be divided into the following four tasks.

• Task 1 will develop a ¹⁴C assay that can be used to measure the rate of abiotic transformation of chlorinated ethenes in contact with core samples of aquifer materials.
• Task 2 will determine the effect of magnetic materials in aquifer materials, naturally occurring magnetite in aquifer materials, and Fe²⁺ that is sorbed to the surface of magnetite on the rate of abiotic transformation of chlorinated ethenes in aerobic and anaerobic groundwater.
• Task 3 will gain insight into the mechanisms of abiotic transformation of chlorinated ethenes by using dual-element compound specific isotope analysis (CSIA) to determine the fractionation of carbon (C) and chlorine (Cl) during abiotic degradation, and by determining the effect of a hydroxyl radical scavenger on the rate of abiotic degradation of chlorinated ethenes.
• Task 4 will interpret the results in a manner that facilitates incorporation of a quantitative understanding of the abiotic transformation processes into an improved site conceptual model.

This research project will provide DoD remedial project managers with a microcosm approach that will be more affordable and can provide a rate constant in as little as two months. Because the rate constants are directly measured on aquifer sediments rather than derived solely from monitoring data from wells at a site, they should be more credible, and will facilitate the acceptance by regulators of improved site conceptual models that incorporate abiotic transformation of chlorinated ethenes. The improved site conceptual models will provide a basis to determine if it is appropriate to stop pumping at a site and transition to passive measures, or when in the future it may be appropriate to make the transition. The improved understanding of the mechanisms of abiotic degradation, particularly in aerobic groundwater, will add to the credibility of the new site conceptual models, and facilitate acceptance by regulators and other stakeholders.  (Anticipated Project Completion - 2024)

Theses and Dissertations

Dunn, O.F. 2023. Evaluating the Role of Magnetic Materials in Mediating Abiotic Degradation of Chlorinated Ethenes at TCAAP-A Using a 14C-Assay (Master's Thesis). Clemson University.