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Study of Tert-Butyl Alcohol (TBA) at Selected <br /> Underground Storage Tank Remediation Project Sites in <br /> Orange County, California - Final Report <br /> Shell Global Solutions (US), Inc <br /> George DeVaull, Ph D <br /> Paul T Sun, Ph D <br /> Heana A L Rhodes, Ph D <br /> Daniel F Walsh CPG <br /> November 14, 2003 <br /> 1 , Summary of Results <br /> This report summarizes a study concerning the possible ongin of TBA in groundwater at <br /> selected LUST sites in Orange County, California The most plausible explanation for the <br /> anomalous concentrations of TBA in groundwater is that TBA is predominately an <br /> intermediate biological degradation product, produced from MTBE (methyl tert-butyl <br /> ether) primarily in either low-oxygen or methanogenic environmental conditions <br /> Measured soluble concentrations of TBA in groundwater at the investigated sites are also <br /> consistent with estimates of TBA in water in contact with unweathered gasoline <br /> i Dissolution from gasoline as a sole source of TBA in groundwater cannot, however, <br /> explain observed instances of high measured levels of TBA with low (or non-detect) co- <br /> located measurement of either MTBE or BTEX constituents Dilution, partitioning, and <br /> transport alone cannot explain the observed relative concentration levels of these <br /> chemicals Transformation - in this case laboratory confirmation of biological <br /> degradation and transformation - helps explain the measured site data <br /> Other possible sources of measured TBA in groundwater, including abiotic <br /> transformation in the environment, or presence of TBA as an artifact of chemical analysis <br /> methods, for the conditions investigated, are not likely possible explanations for the <br /> elevated levels of TBA observed at the investigated sites <br /> In further results, microcosm analyses conducted on soils (collected below the water <br /> table) as part of this work showed degradation of MTBE and TBA in both aerobic and <br /> anaerobic conditions Investigation of co-metabolism of TBA or MTBE in the presence <br /> of propane was inconclusive, since degradation had been observed without the presence <br /> of the selected(propane) co-metabolic substrate <br /> 2. Introduction <br /> A series of directives issued by Orange County Local Oversight Program (OCLOP) have <br /> been received by Shell, dated from 4 June 2002, indicating a request for study of the <br /> origin of tert-butyl alcohol (TBA) at leaking underground storage tank sites Notification <br /> of approval of the Shell's Proposed TBA Work Plan dated July 19, 2002 was received <br /> 1 <br />