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ANAEROBIC DEGRADATION OF MTBE TO TBA IN GROUND WATER AT GASOLINE SPILL SITES IN ORANGE COUNTY, CALIFORNIA
WILSON, J. T., R. KILHATKAR, T. KUDER, R. P. PHILP, AND S. J. DAUGHERTY. ANAEROBIC DEGRADATION OF MTBE TO TBA IN GROUND WATER AT GASOLINE SPILL SITES IN ORANGE COUNTY, CALIFORNIA. Presented at 17th Annual UST/LUST National Conference, Seattle, WA, March 16, 2005.
To inform the public
Although tert-Butyl Alcohol (TBA) has not been used as a fuel oxygenate in Orange County, California, the concentrations of TBA in ground water at gasoline spill sites are high compared to the concentrations of the conventional fuel oxygenate Methyl tert-Butyl Ether (MTBE). In the year 2002, in 429 gasoline spill sites that reported concentrations of both TBA and MTBE, the geometric mean concentration of TBA was 839 µg/L compared to 627 µg/L for MTBE. There are two plausible sources of the TBA, biodegradation of MTBE to TBA and TBA originally present in the gasoline. Thirteen spill sites where the concentration of TBA was greater than 10,000 µg/L were selected for detailed studies. Biodegradation was evaluated by determining the stable carbon isotope ratio (δ13C) of MTBE in the ground water at the thirteen sites. If MTBE was biodegraded, the residual MTBE should be enriched in the heavier carbon isotope 13C. At one site, the concentrations of both MTBE and TBA were high (280,000 and 300,000 µg/L respectively), and there was no evidence of biodegradation. At the other twelve sites, at least 52% of the MTBE originally present in the water had degraded. Biodegradation of MTBE could account for most of the TBA at nine of the thirteen sites.