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ig6ETTLER - RYAN INC. <br /> November 7, 2002 <br /> Mr. Michael J. Infurna Jr. <br /> San Joaquin County Public Health Services <br /> Environmental Health Division <br /> 304 East Weber Avenue,Third Floor <br /> Stockton, California 95202 <br /> Subject Response to EHD Letter Concerning <br /> Tosco (76) Service Station No. 11192, <br /> 1403 Country Club Boulevard, Stockton, California. <br /> Mr. Infurna: <br /> At the request of Tosco Corporation (Tosco), a subsidiary of ConocoPhillips, Gettler- <br /> Ryan Inc. (GR) has prepared this letter detailing our responses to the San Joaquin County <br /> Environmental Health Department (EHD) letter to Tosco dated July 22, 2002. This letter <br /> provides responses to questions posed in the EHD letter, GR's proposed modifications to <br /> the Work Plan submitted with the Updated Corrective Action Plan (July 8, 2002), and a <br /> schedule for implementation of the proposed modifications. <br /> RESPONSES <br /> The questions and/or comments detailed in the EHD letter are presented below in italics, <br /> followed by GR's and Tosco's response. <br /> GRI hypothesizes that MtBE rapidly degraded to TBA in response to elevated dissolved <br /> oxygen concentrations. EHD is not aware of any research demonstrating this <br /> phenomenon and would appreciate any applicable documentation. EHD is aware of <br /> research showing reaction pathways for ozone degredation of MtBE, but not for rapid, <br /> partial degradation in the presence of dissolved oxygen. <br /> Although the degradation of MtBE to TBA in the presence of oxygen through natural <br /> bio-activity is not fully understood by the industry, GR believes our hypothesis is the best <br /> explanation at this time. GR does not currently possess data to support our hypothesis, <br /> but recommends that Tosco begin collecting biodegradation parameter data in an effort to <br /> prove the hypothesis. Biodegradation is a more likely explanation than a new release, <br /> since TBA has not been a constituent in Tosco's fuel. Additionally, a new release would <br /> also introduce other typical petroleum constituents into the groundwater, which have not <br /> been detected to date. <br /> 6747 Sierra Court , Suite J • Dublin , California 94568 ( 925) 551 - 7555 <br />