| Abstract
| - Microbial communities indigenous to a shallow groundwatersystem near Beaufort, SC, degraded milligram per literconcentrations of methyl tert-butyl ether (MTBE) undernatural and artificial oxic conditions. Significant MTBEbiodegradation was observed where anoxic, MTBE-contaminated groundwater discharged to a concrete-linedditch. In the anoxic groundwater adjacent to the ditch,concentrations of MTBE were >1 mg/L. Where groundwaterdischarge occurs, dissolved oxygen (DO) concentrationsbeneath the ditch exceeded 1.0 mg/L to a depth of 1.5 m, andMTBE concentrations decreased to <1 μg/L prior todischarge. MTBE mass flux calculations indicate that 96%of MTBE mass loss occurs in the relatively small oxiczone prior to discharge. Samples of a natural microbialbiofilm present in the oxic zone beneath the ditch completelydegraded [U-14C]MTBE to [14C]CO2 in laboratory liquidculture studies, with no accumulation of intermediatecompounds. Upgradient of the ditch in the anoxic, MTBE-and BTEX-contaminated aquifer, addition of a solubleoxygen release compound resulted in oxic conditions andrapid MTBE biodegradation by indigenous microorganisms.In an observation well located closest to the oxygen additionarea, DO concentrations increased from 0.4 to 12 mg/Lin <60 days and MTBE concentrations decreased from 20to 3 mg/L. In the same time period at a downgradientobservation well, DO increased from <0.2 to 2 mg/L andMTBE concentrations decreased from 30 to <5 mg/L. Theseresults indicate that microorganisms indigenous to thegroundwater system at this site can degrade milligram perliter concentrations of MTBE under natural and artificialoxic conditions.
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