Natural attenuation at upstream oil and gas sites in western Canada

Analysis of groundwater geochemical data for evidence of natural attenuation (NA) has been well documented for processed (downstream) fuel contaminated sites. This study undertakes a similar approach, by reviewing and categorizing relevant case records at sites associated with upstream oil and gas production. A database was constructed to evaluate the occurrence and extent of natural attenuation from existing field monitoring data. Over 200 sites were analyzed for groundwater and plume characteristics. Results indicate desirable characteristics and conditions for successful NA implementation at upstream sites. A case study was also conducted at an upstream diesel contaminated site. Evidence of intrinsic bioremediation included decreasing contaminant concentrations over time, depletion of terminal electron acceptors and increases in microbial metabolic by-products. A laboratory microcosm study investigated the effects of temperature, electron acceptor and nutrient amendment under anaerobic and aerobic conditions. Results indicated that the groundwater was severely nutrient depleted.