The committee met Aug. 14-15 at EPA headquarters in Washington, D.C. to discuss and refine the first draft of its report, which it presented to EPA Administrator Carol Browner. Natural attenuation is a form of site remediation that allows naturally occurring or added microbes to break down and resolve the contamination. Natural attenuation is one of the least expensive forms of site remediation. Relatively little is known about the biodegradability of MTBE, in comparison to the BTEX chemicals, according to the report. Areas most susceptible to MTBE contamination, such as subsurface soil and groundwater, generally can have anaerobic conditions.
Natural attenuation is more effective if it can take place in both aerobic and anaerobic conditions.
Specifically, the committee suggested studying MTBE biodegradation, plume behavior and site history, and conducting MTBE microcosm studies. The committee found that enough research and knowledge is available to accurately predict the migration of BTEX chemicals from petroleum contamination, and therefore the scope of site cleanup, but not enough research is available to accurately predict the migration of MTBE plumes. If plume migration is not accurately gauged, site contamination may travel beyond the area in which cleanup efforts are focused. Because MTBE travels more quickly through soil and water and behaves differently than the more common BTEX chemicals, requirements and guidelines for natural attenuation that were developed for BTEX will likely need to be changed and revised in order to be used for MTBE cleanup, according to the report.