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.- The positive controls, spiked with a culture known to degrade both MTBE and TBA, provided an indication that procedures would be adequate and able to determine if degradation was occurring in other cases, as well as a qualitative comparison of relative degradation rates 6. Evaluate possible abiotic transformation of TBA from MTBE Task 4 of the work plan included investigation of possible abiotic transformation mechanisms Significant hydrolysis of MtBE to TBA is unlikely at normal environmental conditions The potential for hydrolysis at low pH levels is discussed below as part of Task 5 The potential for other possible abiotic transformations from MtBE to TBA is not likely to be significant No significant changes were noted in the abiotic control tests included in the microcosm tests series 7. Evaluation of the possibility of TBA detections being an artifact of sample collection and/or laboratory analytical methods Task 5 of the work plan included identifying and quantifying the possibility of measured TBA in groundwater originating as a sampling and analysis artifact from conversion of MTBE to TBA White et al (2003) and O'Reilly et al (2001) have indicated the potential for TBA detection as an artifact of sample collection and/or analysis Further comment on these papers is discussed following The aqueous hydrolysis rate of MTBE is dependent upon temperature, pH, and the presence of other ions (i a salts) Roughly, a 10°C increase in temperature increases the rate by a factor of 2 5 A decrease in pH by one pH unit will increase the reaction rate by about one order of magnitude The influence of other ions is little understood, but probably of less significance than temperature and pH O'Reilly et al (2001) examined these variables, but not in enough detail to permit an extrapolation of data for accurate prediction under various conditions However, the data do confirm the existence of hydrolysis at pH = 1 and 20 to 30°C, with half-lives from weeks to months Approximate extrapolation indicates potential half-lives in the range of minutes to hours at approximately pH=1 and 80°C However, a survey of the laboratories doing the majority of MTBE analyses for Shell in California shows that purge temperatures used are actually between 40 to 45°C and purge times are approximately 11 minutes Under these conditions, at pH=1, TBA production would likely be less than 1% of the original MTBE concentration The transformation would be less if dilution of the sample prior to analysis results in a pH increase ID 19