Anaerobic biodegradation of MTBE at a gasoline spill site

To manage risk or to implement natural attenuation as a remedy, regulatory agencies must understand the processes that attenuate methyl-tert-butyl ether (MTBE) in ground water. Most case studies and laboratory studies in the literature indicate that natural biodegradation is not important; however, recent reports indicate that natural biodegradation of MTBE plays an important role under certain conditions. In an MTBE plume at a retail gasoline station in Parsippany, New Jersey, the long-term monitoring data indicated that the concentration of MTBE was slowly declining over time in the wells that were within the footprint of the plume. The ratio of tert-butyl alcohol (TBA) to MTBE increased with distance from the source area, and the ratio of TBA to MTBE in individual monitoring wells in the plume increased over time. This anecdotal evidence of natural biodegradation of MTBE to TBA at field scale was confirmed with a microcosm study. Core material from the interior of the plume was used to construct the microcosms. Following an initial lag period of 58 d, the concentration of MTBE decreased from more than 1460 micrograms/L to less than 10 micrograms/L within 199 d of incubation. As concentrations of MTBE declined in the microcosms, concentrations of TBA increased. The decrease in concentration of MTBE in the microcosms could be accounted for by an increase in the concentration of TBA.