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Pacific Gas and Electric Company Technical and Ecological.Services �Er1- j 3400 Crow Canyon Road San Ramon,CA 94583 510/820-2000 November 8, 1995 15 San Joaquin County Public Health Services Environmental Health Division i P.O. Box 388 Stockton,CA 95201-0388 RE: PG&E's Tracy Service Center, 502 East Grant Line Road, Tracy CA Mr. Steven Sasson: This letter is in response to your October 17 request for(1)analytical results of soil samples collected during tank removal, and(2)a work plan for the investigation and possible over excavation and confirmatory groundwater sampling of the former UST location. In November 1986(prior to tank removal), two soil borings were drilled to determine whether soil and/or groundwater had been impacted in the vicinity of the tank. Five subsurface soil samples and two groundwater samples were collected for laboratory analysis. The laboratory analytical results were provided to you, along with a copy of the original report, in a package sent March 1, 1995. They showed the presence of gasoline hydrocarbons and BTEX in concentrations up to 43 mg/kg,4.8 mg/kg, 7.4 mg/kg, 7.4 mg/kg, and 12 mg/kg, respectively, in the soil samples; and up to 190 mg/L, 31 mg/L,49 mg/L, 21 mg/L, and 22 mg/L, respectively, in the groundwater samples. In June 1987, a soil vapor survey was performed to evaluate the distribution of volatile organic compounds in the vicinity of the tank. The results indicated that VOCs were confined to an area no further than 50 feet(in the downgradient direction)from the tank. This data was provided to you in a June 1988 report, "Characterization of the Tracy Service Center Underground Tank Site",prepared by PG&E's Technical and Ecological Services Department No soil or groundwater samples were collected from the tank excavation when the tank and pump island were removed on October 22, 1987. An unknown quantity of soil was removed from the tank and pump island excavations, and replaced with clean fill. The excavated soil was disposed of off-site in an approved landfill. Quarterly groundwater monitoring has shown steadily decreasing gasoline concentrations in the well located downgradient and within 10 feet of the former tank location, and consistently non-detectable gasoline concentrations in the three wells located downgradient and within 80 feet of the former tank location. The most recent two quarters of groundwater monitoring events suggest that, even at the well located within 10 feet and downgradient of the former tank location, intrinsic bioremediation has resulted in reductions in groundwater concentrations of TPHG and BTEX to levels below laboratory detection limits. We anticipate obtaining four consecutive quarters of non-detect data in the near future, and look forward to receiving closure from your office and the Central Valley Regional Water Quality Control Board shortly thereafter.