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Alaska Section, American Water Resources Association Michael R. Lilly, Alaska Section AWRA Northern-Region Director The September Brown-Bag presentation was by Kathy McCarthy. Kathy's talk should be of interest to hydrologists and environmental professionals working in the both arctic and subarctic conditions. September 1996 Kathy McCarthy, U.S. Geological Survey. Accidental releases of more than 1,300 cubic meters of fuel have resulted in subsurface contamination adjacent to Imikpuk Lake, a drinking-water source near Barrow, Alaska. A study is being conducted to determine the efficacy of in situ biodegradation as a remediation scheme at these sites, which are underlain by continuous permafrost. Hydrologic and microbial processes are largely confined to the thaw season, which constrains ground-water flow and significant biodegradation of contaminants to a short period (ca. 90 days) each year. Hydrocarbon-degrading microorganisms have been enumerated in soil and ground-water samples. The rates at which these microorganisms mineralize selected hydrocarbons has been measured in the laboratory using radiorespirometry, and the effects of nutrient amendments on these rates have been measured in the laboratory and in the field. Field measurements of dissolved oxygen, nitrate, ammonia, ferrous iron, sulfide, and hydrocarbon concentrations in ground water at one site indicate that biodegradation of hydrocarbons is occurring in situ. At another site, where contamination occurs in the unsaturated zone, laboratory data showed that microbial activity was limited by nitrogen. Nutrient amendments to field mesocosms at this site showed that the greatest stimulation in microbial activity occurred at the lowest, rather than the highest, level of nutrient addition. At the highest level of nutrient addition, hydrocarbon concentrations were higher after treatment than in unfertilized controls, indicating that microbial activity was inhibited rather than enhanced at the higher nutrient application rates. |