Biodegradation of Chlorinated Ethenes at a Karst Site in Middle Tennessee

Organic constituent

Remarks concerning interpretation

Tetrachloroethylene (PCE)

A commonly used chlorinated solvent that can be biodegraded only by reductive dechlorination. PCE was not used at this site and has not been detected in ground-water samples from the study site.

Trichloroethylene (TCE)

A commonly used chlorinated solvent. The most efficient biodegradation mechanisms include reductive dechlorination and methane cometabolism. TCE was the chlorinated solvent spilled at the study site and has been detected in ground-water samples from the study site.

Dichloroethylene (DCE)

cis-1,2-DCE (cDCE)

The most common byproduct of reductive dechlorination of TCE. If the concentration of cDCE is greater than 80 percent of total DCE concentration, then reductive dechlorination is likely to have occurred. Significant concentrations of cDCE have been detected in ground-water samples from the study site.

trans-1,2-DCE (tDCE)

Trans-1,2-DCE is not produced significantly through any biologically mediated process. If tDCE is 50 percent or more of the total DCE, a good possibility exists that tDCE was released. Significant concentrations of tDCE have not been detected in ground-water samples from the study site.

1,1-DCE

This is the least common byproduct of reductive dechlorination of TCE. 1,1-DCE is also produced when 1,1,1-trichloroethane (TCA) undergoes abiotic chloride elimination. Significant concentrations of 1,1-DCE have not been detected in ground-water samples from the study site.

Vinyl chloride (VC)

VC is a byproduct of cDCE reductive dechlorination. VC has been detected in ground-water samples from the study site.

Ethane and ethene

These are strong indicators of complete reductive dechlorination. They have been detected in ground-water samples from the study site.