Apparent first-order kinetics in the transformation of 1,1,1-trichloroethane in groundwater following a transient release

A transient release of 1,1,1-trichloroethane (TCA) to an otherwise uncontaminated aquifer at a manufacturing facility presented a useful opportunity to validate the results of previous laboratory and field studies on TCA transformation in groundwater. Abiotic TCA transformation to 1,1-dichloroethylene (DCE) and acetic acid at the site exhibited first-order kinetics with half-life of 2.9 years 15° C. Degradation effects were seen to overwhelm chemical retardation effects on the DCE/TCA concentration ratio in groundwater. The kinetic data was sufficient to date the release to within one week of when it actually occurred. A kinetic approach may be applicable to dating the releases on other contaminated sites where a single transient release is indicated. The transformation of dissolved TCA in groundwater with a half-life of several years can be expected at many contaminated sites.