DEGRADATION OF CHLORINATED HYDROCARBONS AND GROUNDWATER GEOCHEMISTRY - A FIELD-STUDY

Published laboratory studies suggest that certain chlorinated hydrocarbons are subject to chemical degradation in groundwater through abiotic and biologically-mediated processes. However, relatively few field investigations have been conducted on the degradation of these compounds. We examine the issue of degradation with regard to several chlorinated aliphatics dissolved in groundwater at the Lawrence Livermore National Laboratory in California. The highly oxidized state of the local groundwater, as indicated by geochemical observations suggests that reductive degradation reactions of chlorinated ethenes and ethanes are not thermodynamically or microbially favorable. In contrast, it is known that certain chlorinated compounds, such as 1,1,1-TCA, may degrade through redox-independent elimination or hydrolysis reactions. Indeed, statistical analyses and numerical modeling have provided evidence for the nonredox-driven transformation of 1,1,1-TCA to 1,1-DCE and to possibly acetic acid at the site. Similar analyses conducted for PCE and TCE failed to indicate any evidence for reductive dehalogenation.