Monitored Natural Attenuation of MTBE Introduction When gasoline is spilled from under ground storage tanks, methyl tertiary butyl ether (MTBE) and its degradation product, tertian butyl alcohol (TBA), are among the most important contaminants released to ground water. The state agencies that regulate spills of gasoline from underground storage tanks need information on the behavior of MTBE and TBA in spills of gasoline. Background Most MTBE plumes in ground water are anaerobic and the organisms that naturally degrade MTBE in these plumes must be anaerobes. Unfortunately, it has been difficult to isolate anaerobic MTBE degrading microorganisms for study in the laboratory. As a consequence, risk managers often fail to consider in their exposure evaluation the contribution of the natural biodegradation of MTBE in ground water. They also fail to recognize the hazard from the accumulation of TBA that is produced from biodegradation of MTBE. Recent laboratory work has shown that the ratio of stable carbon isotopes is shifted during biodegradation. MTBE molecules with the lighter isotope (12C) are preferred, and the residual MTBE accumulates more molecules with the heavy isotope (13C). The extent of degradation can be predicted from the change in the ratio. Objectives • Determine the contribution of natural biodegradation of MTBE to natural attenuation of MTBE at gasoline spill sites • Develop and evaluate the use of stable carbon isotope ratios as a tool to recognize natural biodegradation of MTBE when it occurs at a particular gasoline spill site • Isolate microorganisms that are capable of anaerobic biodegradation of MTBE and characterize the pathways of MTBE metabolism and the requirements for MTBE metabolism under anaerobic conditions Approach • Conduct detailed case studies at representative plumes of MTBE to document the rate and extent of natural attenuation of MTBE at field scale • Analyze water samples from a large number of sites for the concentration of TBA and MTBE to determine the co-distribution of MTBE and TBA • Compare the ratio of concentrations of TB A to MTBE to determine whether the TBA was produced by biological action on MTBE • Evaluate the usefulness of the analysis of stable carbon isotope ratios to determine whether MTBE has been biologically degraded in ground water Accomplishments The survey data show much higher concentrations of TBA at gasoline spill sites than would be expected from the small amounts of TBA that are present in the gasoline. In Orange County, California, and in selected gasoline stations in eastern United States, the amount of TBA in ground water is equivalent to the amount of MTBE. The National Risk Management Research Laboratory's mission is to advance scientific and engineering solutions that enable EPA and others to effectively manage current and future environmental risks. NRMRL possesses unique strengths and capabilities and is dedicated to providing credible technological information and scientific solutions that support national priorities and protect human health and the environment. ------- At a gasoline spill site in New Jersey, the attenuation of MTBE along the flow path in ground water was directly related to an increase in the stable carbon isotope ratio in the residual gasoline in the plume. The increase in ratio of stable carbon isotope was confirmed in a microcosm study done with core material from the site. Ground water at gasoline spills in Orange County, California, has a particularly high concentration of TBA. A completed survey compares the changes in the stable isotope ratio of MTBE to the attenuation of MTBE and accumulation of TBA. At most stations, the high concentration of TBA was caused by natural biodegradation of MTBE. When the stable isotope ratios for MTBE were measured at 13 gasoline spills in Orange County, they revealed that there had been extensive biodegradation of MTBE in at least one well at each site. In 11 of the 13 stations, the TBA in the well with the highest concentration of TBA was produced in the ground water from biodegradation of MTBE The following articles have been published: Wilson, J.T. (2003). "Fate and Transport of MTBE and Other Gasoline Oxygenates." In: Handbook for Managing Releases of Gasoline Containing MTBE. Edited by E. Moyer and P. Kostecki. Amherst Scientific Publishers, pp. 9- 61. Kolhatkar, R., T. Kuder, P. Philp, J. Allen, and J.T. Wilson. (2002). "Use of Compound-Specific Stable Carbon Isotope Analyses to Demonstrate Anaerobic Biodegradation of MTBE in Ground Water at Gasoline Release Site." Environmental Science and Technology, 26, 24: 5139-5146. Wilson, J.T., J.A. Vardy, J.S. Cho, and B.H. Wilson. Natural Attenuation of MTBE in the Subsurface Under Mcthanogcnic Conditions (PDF). (59 pp, 1.53 MB) (EPA/600/R-00/006) January 2000 Wilson, J.T. and R. Kolhatkar. (2002). "Role of Natural Attenuation in the Life Cycle of MTBE Plumes." Journal of Environmental Engineering, 128, 9: 876-882. Future Tasks A journal article, entitled "Contribution of Biodegradation of MTBE to High Concentrations of TBA at Gasoline Spill Sites in Orange County," is in preparation. Investigators Cherri Adair, Phil Kaiser, and John Wilson U.S. EPA Ground Water and Ecosystem Restoration Division Ada, Oklahoma 74820 580-436-8534 Collaborators American Petroleum Institute Committee Health Care Agency of Orange County, California University of Oklahoma, Department of Geology and Geochemistry The National Risk Management Research Laboratory's mission is to advance scientific and engineering solutions that enable EPA and others to effectively manage current and future environmental risks. NRMRL possesses unique strengths and capabilities and is dedicated to providing credible technological information and scientific solutions that support national priorities and protect human health and the environment. ------- |