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4. Likelihood of TBA being derived from gasoline product sold at service stations Task 2 of the work plan included quantifying gasoline as a potential source of TBA detected in groundwater There are no known current manufacturing practices for intentional addition of TBA to gasoline TBA was offered commercially as a blending component by ARCO Chemical under the trade name Arconol, which was synonymous with gasoline-grade TBA (GTBA) beginning in 1969 The use of TBA in this application ceased in 1987 The authors of this report have found no available information on the use of GTBA or Arconol in California There are several commercial processes for production of MtBE The processes are based on the reaction of isobutylene with methanol in the presence of catalysts The reaction is selective to isobutylene, allowing for the use of varying refinery streams (steam and fluid catalytic cracker effluent streams, for example) that contain isobutylene Water present in the reaction mixture may lead to the formation of TBA Thus, TBA may be present in MtBE either as a co-product, an impurity, or as an unreacted initial component, depending on the manufacturing process Manufacturing process designs vary depending on product specifications, desired isobutylene conversion, MtBE purity, and the reactant stream composition Typical gasoline-grade MtBE contains 96 to 99% MTBE by weight [Reference CEH Marketing Research Report, Gasoline Octane Improvers — 1999 Chemical Economics Handbook— SRI International] Shell has never manufactured MTBE in any of its California refineries All MtBE added to gasoline in California to meet Federal and State regulatory requirements has been purchased by Shell from commercial sources The MtBE batches are analyzed to determine product quality Review of these data shows detectable TBA levels in many of the MTBE shipments This data set of TBA in MtBE has been used to estimate a range of TBA in gasoline (with MtBE added at required regulatory levels) When mixed into oxygenated gasoline at a nominal regulated concentration of 0 111 g-MtBE/g-gasoline (11 1% by weight), this data indicates a nominal concentration of TBA in MtBE- oxygenated gasoline as follows Fraction of Measured Estimated Concentration of samples at less Concentration of TBA in Gasoline than indicated TBA in MtBE [at 11 11/4w/w MTBE] concentration m -TBAlk -MtBE m -TBA/k asoline 5% 370 40 50% 1300 140 95% 4700 520 99% 8000 890 The California Air Resources Board (CARB) specifies an analysis method for the determination of oxygenates in gasoline [CARB, 1996 Procedure for the Determination 9