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White et al (2003) reported EPA data showing a half-life of about 22 minutes at pH=1 and 80°C, and about 154 minutes at pH=2 and 80°C Within the limits of the data, this roughly represents an order of magnitude difference in rate with a difference of one pH unit These data indicate that under conditions of pH near 2 and temperature near 80°C, hydrolysis of MTBE in samples is possible These conditions will not occur in the subsurface, nor during sample storage As noted (White et al , 2003), some analytical procedures may include a step of heating an acid-treated sample to about 80°C for between 3 to 30 minutes, depending upon the specific method If the sample is at pH=1, this could potentially be a cause for concern Given this review, it is apparent that hydrolysis can occur in storage and heating of aqueous MtBE samples under low pH conditions and high temperature Additional testing with field and controlled samples would be required to establish a range of measured hydrolysis data with a sufficient accuracy to predict MtBE hydrolysis under a broad range of arbitrary conditions Within the scope of this project, however, we have instead focused directly on examining and testing the range of conditions and analytical methods commonly used for analysis of groundwater samples 7.9. Potential Conversion of MtBE to TBA Under Storage Conditions: Studies done to date indicate that there is no significant contribution to formation of TBA from hydrolysis of MtBE under normal sample preservation and storage conditions (pH <2 and 4°C) A recent study performed by Shell indicates no conversion of MtBE to TBA during the time of the study (14 days) A modest conversion of MTBE to TBA (-0 4%) was observed when the sample was kept below pH I The study was done with an MtBE concentration of 20,000 mg/L It must be emphasized that samples are acidified in the field directly by having the acid already placed in the laboratory provided Volatile Organic Analysis (VOA) vials, or by adding the acid in the field Typically, 4 drops of 1 1 hydrochloric acid water are added for this purpose The pH achieved by this acid addition is in the range of 1 5 to 2 It is our experience that to reach a pH level less than 1, more than twice the number of drops would be required It is unlikely that the pH would be near 1 in groundwater samples preserved using this method 7.2. Potential Conversion of MtBE to TBA During Analysis Because alcohols such as TBA are not readily stripped (or volatilized) from water, it is common for laboratories to heat samples to improve detection sensitivity This raises the concern for potential hydrolysis of ethers such as MtBE while heating under acidic conditions It is expected that MtBE can hydrolyze and form TBA at low pH and high temperature Because of this conversion possibility and the observance of TBA in groundwater, there has been a great deal of speculation and interest in this issue 20