Natural Attenuation of MTBE at Laurel Bay, South Carolina
Scientists used direct-push technology to investigate the discharge of methyl tert-butyl ether (MTBE) contaminated groundwater into a stream.
The occurrence of methyl tert-butyl ether (MTBE) in groundwater at gasoline spill sites challenges the paradigm of natural attenuation remediation and our understanding of the impact of gasoline spills on the environment.
- The U.S. Geological Survey (USGS) has identified two important pathways that contribute to the natural attenuation of MTBE. The first is volatilization of MTBE from the spill source into the unsaturated zone, and the second is volatilization of MTBE from the water table down gradient from the source through the unsaturated zone. In both cases, MTBE volatilized to the unsaturated zone is subject to more efficient aerobic (with oxygen) biodegradation than MTBE in the anaerobic (without oxygen) saturated zone. These pathways are important, given MTBE's low degradation rates relative to BTEX (benzene, toluene, ethylbenzene, and zylene) compounds in the saturated zone. The USGS has developed methods to determine the magnitude of these natural attenuation pathways for MTBE.
- The USGS has shown that microorganisms indigenous to surface-water sediments are capable of rapidly degrading MTBE to carbon dioxide. This is the first significant microbial process that has been shown to degrade MTBE in natural environments. Previous studies (including our own) had suggested that MTBE was highly recalcitrant to biodegradation in groundwater systems. Based on these past studies, it was thought that MTBE-contaminated groundwater might seep into surface water and accumulate, providing a source of exposure to humans and wildlife. However, this new result shows that MTBE is rapidly degraded in streambed sediments, and suggests that accumulation to environmentally harmful levels is unlikely.
Landmeyer, J.E., Chapelle, F.H., Bradley, P.M., Pankow, J.F., Church, C.D., and Tratnyek, P.G., 1998, Fate of MTBE relative to benzene in a gasoline-contaminated aquifer (1993-98): Ground Water Monitoring and Remediation, v. 18, no. 4, p. 93-102, doi:10.1111/j.1745-6592.1998.tb00168.x.
Bradley, P.M., Landmeyer, J.E., and Chapelle, F.H., 1999, Aerobic mineralization of MTBE and tert-butyl alcohol by stream-bed sediment microorganisms: Environmental Science and Technology, v. 33, no. 11, p. 1877-1879, doi:10.1021/es990062t.
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