Transformations of Tetrachloroethene and Trichloroethene in Microcosms and Groundwater

Cis- and trans-1,2-dichloroethene were found in well water at a site contaminated with trichloroethene from a leaking storage tank, although neither compound was used in the vicinity nor was present as an impurity in the trichloroethene in the storage tank The use of tetrachloroethene and trichloroethene in dry cleaning and metal refinishing plants is widespread. Several chloroethene compounds that are found in southern Florida groundwater may have been formed from these solvents via microbial metabolism in the groundwater environment. In this study, depletion of tetrachloroethene and appearance of cis- and trans-1,2-dichloroethene and chloroethene were observed following incubation of tetrachloroethene in microcosms containing muck from the aquifer recharge basin. Public drinking water in Dade and Broward counties in southeastern Florida is drawn from wells sunk less than 45 m (150 ft) deep into the Biscayne Aquifer, which is a shallow, unconfined aquifer composed of porous calcareous rock. The aquifer is recharged primarily by rain falling in the Everglades, a graminoid wetland. The collected surface water, which is continuous withgroundwater, enters the rock substratum through a bed of muck, a saprist histosol formed of decomposed indigenous vegetation.’ Organic solutes leached from the muck are present in groundwater at concentrations up to 17 mg/L. Turbidity values of 60 ntu are not uncommon. During the past five years, chloroeth