Use of Environmental Forensics for Trichloroethylene (TCE) Plume Delineation

The United States Department of Defense (DoD) is responsible for millions of acres across the United States. At some DoD-owned sites (and those known as formerly used defense sites (FUDS)), it has been determined that subsurface contaminants exist. At many of the sites, trichloroethylene is a subsurface soil and/or groundwater constituent. Under aerobic conditions, TCE does not readily degrade and can persist as TCE with its only movement governed by physical hydrologic processes. Under anaerobic conditions, TCE is sequentially reduced primarily through microbial reductive dechlorination. For TCE, this involves the sequential reduction of TCE to DCE (primarily cis-1,2 Dichloroethene, but trans-1,2 Dichloroethene and 1,1-Dichloroethene have also been observed), followed by conversion of DCE to Vinyl Chloride (VC) and finally VC to ethene. As chlorinated solvents biodegrade, the products of the degradation process may or may not be less harmful than the original contaminants. This can lead to an accumulation of these toxic compounds under certain conditions. Investigative experience, sound data collection and a combination of traditional (physical, chemical and biological) information along with isotope composition or “fingerprinting” information are necessary for developing a thorough understanding of the nature and extent of TCE contamination in the subsurface.