Intrinsic bioremediation of diesel-contaminated cold groundwater in bedrock

In 1982 diesel fuel migrated from a well lease site into underlying fractured bedrock contaminating the,groundwater-bearing zone approximately 30 m below ground surface. Historical contaminant concentrations, geochemical indicators, and microbiological data were analysed to evaluate natural attenuation, specifically intrinsic bioremediation. Evidence of microbial activity was provided by most probable number (MPN) and commercial biological activity reaction tests (BART (TM)). Laboratory microcosms using groundwater from the site were incubated under aerobic and anaerobic conditions with electron acceptor and nutrient amendment to assess microbial activity. Aerobic biodegradation rates were determined by measuring mineralization of C-14-dodecane. Nutrient amendment combined with a higher temperature (28 degrees C) increased the first-order aerobic biodegradation rate to 0.0066 d(-1) from 0.0002 d(-1) at 10 degrees C. Anaerobic biodegradation rates were calculated from depletion of total extractable hydrocarbons (TEH) over 717 d at 10 degrees C. Nutrient addition increased the anaerobic first-order biodegradation rate to 0.0016 from 0.0005 d(-1). Data from these laboratory microcosms indicate that the current slow rates of intrinsic bioremediation may be enhanced with nutrient addition.