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EVALUATING NATURAL BIODEGRADATION OF MTBE AT MULTIPLE UST SITES
Citation:
Kolhatkar, R., J T. Wilson*, AND L. E. Dunlap. EVALUATING NATURAL BIODEGRADATION OF MTBE AT MULTIPLE UST SITES. Petroleum and Organic Chemicals in Ground Water: Prevention, Detection and Remediation Conference & Exposition (RASA), Anaheim, CA, 11/15-17/2000.
Description:
Until very recently, methyl t-butyl ether (MTBE) was considered non-biodegradable in the subsurface. This has been an impediment in applying remediation by natural attenuation (RNA) as a remedial strategy at MTBE-impacted sites. Although a number of recent studies have demonstrated natural MTBE biodegradation in the field, it is still unknown how prevalent it is and whether the rates of biodegradation are rapid enough to restrict and eventually shrink groundwater plumes. In order to address these questions, BP Amoco, Handex and the EPA have worked together to conduct a groundwater survey at 74 BP retail sites in the US. Groundwater samples were collected during routine monitoring activities in 1999 and were analyzed for a number of volatile organic compounds including MTBE, t-butyl alcohol (TBA), and BTEXTMB as well as a suite of geochemical parameters, including dissolved oxygen, dissolved methane, ferrous iron, total organic carbon (TOC), sulfate, nitrate, alkalinty and pH.
Using dissolved methane as a tracer for the plume, first order biodegradation rate constants were estimated for MTBE, TBA and benzene at a number of these sites. There appeared to be a good correlation between strongly anaerobic plume geochemistry and natural MTBE biodegradation in the subsurface. Another round of groundwater sampling is being undertaken to validate these findings. EPA will initiate laboratory microcom studies in Fall 2000 at two of threse sites to provide an additional line of eveidence for MTBE biodegradation at these sites. These data suggest that naatural biodegradation of MTBE and TBA at some sites may be responsible for attenuation near the source area and may control migration of MTBE and TBA plumes under anaerobic subsurface conditions.
At the sites in this tudy, concentrations and frequency of TBA occurrrence in groundwater are comparable to those for MTBE. TBA is a known intermediate of MTBE biodegradation, although it is also a component in gasoline. Further analyses are underway to ascertain if TBA occurrence in groundwater can be linked to MTBE biodegradation.