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Pacific Gas and Electric, Company Enkonmental Services <br /> P.O.Boz 7640 <br /> February 18, 1999 San Francisco, CA 94120 <br /> 415/973-7000 <br /> Direct Dial 415/973- <br /> Telecopy 415/973-9201 <br /> James L. Tjosvold, P.E. <br /> Chief, Site Mitigation Branch <br /> California Environmental Protection Agency <br /> Department of Toxic Substances Control <br /> 10151 Croydon Way, Suite 3 <br /> Sacramento, CA 95827 <br /> Attention: Mr. Fernando Amador <br /> Re: Docket#HAS 90/91-08-Stockton Former Manufactured Gas Plant Site <br /> Subject: Evaluation of 7PH and Benzene Soil Verification Concentrations <br /> Dear Mr. Tjosvold: <br /> Attached for your review and approval is a technical memorandum which describes soil <br /> verification concentrations for Total Petroleum Hydrocarbon (TPH)-gasoline, TPH-diesel <br /> and benzene to be used during soil remediation at Pacific Gas and Electric Company's <br /> (PG&E's) Stockton Former Manufactured Gas Plant Site (site). The Remedial Design <br /> and Implementation Plan (RDIP) for the site includes soil verification concentrations for <br /> polynuclear aromatic hydrocarbons (PNAs) to be taken at the bottom and sides of soil <br /> source area excavations. The soil source areas planned for excavation were defined by <br /> modeling the future transport of PNAs to groundwater (as described in the Feasibility <br /> Study for this site). During his review of the RDIP, Phillip Isorena of the Central Valley <br /> Regional Water Quality Control Board requested that PG&E develop soil verification <br /> concentrations for TPH-gasoline, TPH-diesel, and benzene in addition to the soil <br /> verification concentrations for PNAs. <br /> The attached memorandum discusses how soil verification concentrations for TPH- <br /> gasoline, TPH-diesel, and benzene were developed as well as what concentrations are <br /> proposed: namely, 50 mg/kg for TPH-gasoline, 770 mg/kg for TPH-diesel, and <br /> 1.8 mg/kg for benzene. <br /> If you have any questions or require additional information, please call me at (415) 973- <br /> 6254. <br /> Sincerely, <br /> Patricia E. Sullivan <br /> Project Manger <br /> Stockton Former Manufactured Gas Plant Site <br /> Attachment <br />