Biodegradation Rates for Fuel Hydrocarbons and Chlorinated Solvents in Groundwater

Numerous studies presented in the general literature have shown that the key mechanism affecting the rate and extent of migration of a contaminant plume is biodegradation since it removes contaminant mass and reduces average plume concentrations. This paper attempts to address the importance of biodegradation for fuel and chlorinated solvent plumes and to present a comprehensive review of rates of biodegradation obtained from field and laboratory studies. Data from approximately 280 studies are statistically analyzed to determine ranges of biodegradation rates for various contaminants under different redox conditions. A review of 133 studies for fuel hydrocarbons has yielded first-order biodegradation coefficients up to 0.445 day^-1 under aerobic conditions and up to 0.522^-1 under anaerobic conditions in 90% of the cases. A median rate constant for benzene of 0.3% day^-1 was estimated from all studies, while those for toluene, ethylbenzene, and xylenes were estimated to be 4, 0.3, and 0.4% day^-1, respectively. On the other hand, data from 138 studies with chlorinated solvents show that the less chlorinated compounds biodegrade in the 90% of the cases with rate constants lower than 1.35 day^-1 under aerobic conditions and that highly chlorinated compounds biodegrade with decay coefficients up to 1.28 day^-1 in 90% of the anoxic experiments. Median decay coefficients derived from all studies were 4.9, 0.07, 0.42, 0.86, 1.02, 0.44, and 4.7 day^-1 for carbon tetrachloride, dichloroethane (DCA), cis-1,2-dichloroethene (cis-1,2-DCE), tetrachloroethene (PCE), trichloroethane (TCA), trichloroethene (TCE), and vinyl chloride, respectively. The rate constants presented in this study can be used in screening and modeling studies and to guide the assessment of natural attenuation as a viable remedial technology at contaminated sites. represent a compilation of available literature data.