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Bioremediation of chlorinated ethenes in subarctic sediments Sharon Richmond, & Paul Bradley, Frank Chapelle Alaska Department of Environmental Conservation, Fairbanks, Alaska, USA Frank Chapelle Chlorinated ethenes such as perchloroethene (PCE) are among the most prevalent and persistent contaminants in groundwater. Treatment options in cold climates have largely focused on physical removal via excavation or air sparging with soil vapor extraction although these methods are expensive and not uniformly successful. More recently, bioremediation has emerged as a feasible, less costly alternative at some sites although its applicability in cold climates is largely untested. This approach generally involves introducing an electron donor to the subsurface, which, through biological activity, creates the highly reducing conditions that favor complete reductive dechlorination to ethene. Groundwater and sediment at a former dry cleaner in Alaska was highly contaminated with PCE and trichloroethene (TCE). A pilot study was conducted to determine whether injection of Hydrogen Release Compound® (HRC) into this normally aerobic to metals-reducing aquifer would produce the conditions necessary for complete reductive dechlorination of PCE. Following injection, PCE and TCE concentrations decreased while concentrations of cis-dichloroethene (DCE) increased. Vinyl chloride (VC) and ethene were generally not detected and reductive dechlorination appeared to “stall.” Laboratory analysis of aquifer sediments indicated that dehalococcoides-type bacteria were either absent or present in very low numbers in most samples. Following injection of additional HRC, a pilot-scale bioaugmentation study was initiated. After approximately two years of biostimulation and 1 year of bioaugmentation, methanogenic conditions were achieved in the bioaugmentation area and concentrations of VC and ethene increased. Laboratory studies using aquifer sediments and sediment from the adjacent Kenai River indicated that degradation of TCE, cis-DCE, and VC occurred at rates comparable to those observed in more temperate climates. |