Evaluating Intrinsic Bioremediation at Four Sour Gas Processing Facilities in Alberta

Mass attenuation through intrinsic bioremediation of the aromatic hydrocarbons-benzene, toluene, ethylbenzene, and xylene isomers (BTEX)-was studied at four natural gas processing facilities in Alberta. These compounds are commonly found in hydrocarbons associated with the natural gas processing industry, and their environmental behaviour and fate are relatively well understood. This study used four techniques to assess whether intrinsic bioremediation could attenuate BTEX-contaminated groundwater plumes at the four sites. Source mass data was not available at any site.At each site, historical data indicate that BTEX plumes were delineated and show no evidence of extensive migration. Geochemical evidence was reviewed to compare the distribution of dissolved BTEX concentrations to distributions of common electron accepters (dissolved oxygen, nitrite+nitrate and sulphate) and metabolic byproducts of biodegradation (iron and manganese).Analysis of the data suggests that BTEX biodegradation is occurring at all four sites. Electron acceptors were depleted and metabolic byproducts were enriched within the BTEX plumes.Bacterial plate counts were generally higher in BTEX-impacted wells versus unimpacted wells at three of the sites. The opposite case was found at the other site. Microcosm experiments indicated aerobic biodegradation at three sites, while anaerobic biodegradation was interpreted at only two sites after incubation periods of approximately four to five months.Theoretical estimates of the biodegradation potential were calculated for each site, and indicate intrinsic biodegradation to have remediation potential at three locations. More field research-is required to examine the relative role of biodegradation compared to other attenuation mechanisms (volatilization, sorption, and dispersion and chemical oxidation).