METABOLIC ADAPTATION AND IN-SITU ATTENUATION OF CHLORINATED ETHENES BY NATURALLY-OCCURRING MICROORGANISMS IN A FRACTURED DOLOMITE AQUIFER NEAR NIAGARA-FALLS, NEW-YORK

A combination of hydrogeological, geochemical, and microbiological met hods was used to document the biotransformation of trichloroethene (TC E) to ethene, a completely dechlorinated and environmentally benign co mpound, by naturally occurring microorganisms within a fractured dolom ite aquifer. Analyses of groundwater samples showed that three microbi ally produced TCE breakdown products (cis-1,2-dichloroethene, vinyl ch loride, and ethene) were present in the contaminant plume. Hydrogen (H -2) concentrations in groundwater indicated that iron reduction was th e predominant terminal electron-accepting process in the most contamin ated geologic zone of the site. Laboratory microcosms prepared with gr oundwater demonstrated complete sequential dechlorination of TCE to et hene. Microcosm assays also revealed that reductive dechlorination act ivity was present in waters from the center but not from the periphery of the contaminant plume. This dechlorination activity indicated that naturally occurring microorganisms have adapted to utilize chlorinate d ethenes and suggested that dehalorespiring rather than cometabolic, microbial processes were the cause of the dechlorination. The addition of pulverized dolomite to microcosms enhanced the rate of reductive d echlorination, suggesting that hydrocarbons in the dolomite aquifer ma y serve as electron donors to drive microbially mediated reductive dec hlorination reactions. Biodegradation of the chlorinated ethenes appea rs to contribute significantly to decontamination of the site.