SITE INFORMATION AND CORRESPONDENCE

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w �\ Mr. Doug Wilson • San Joaquin County Public Health Services September 30, 1991 Page 2 from the walls of the tank excavation and two samples were collected from the bedrock which comprises the floor of the excavation. All the samples were analyzed for TPH-diesel. One bedrock sample and one soil sample were also analyzed for BTEX (Benzene, Toluene, Ethylbenzene, and Xylenes). The two bedrock samples had TPH-diesel concentrations of 7 and 15 ppm (mg/kg). TPH-diesel concentrations in samples from 3 of the 4 walls of the tank excavation were below the detection limit of 0.005 ppm (mg/kg). However, three samples collected from the north wall contained TPH-diesel concentrations ranging from 210 to 5,200 ppm (mg/kg). The analytical laboratory reported observing several unidentified peaks, with a spectrum somewhere between diesel and motor oil. This suggests that much of the contamination remaining in the excavation is a result of the hydraulic line break, and not from the original diesel release. No detectable BTEX concentrations (>0.005 ppm [mg/kg]) were reported. All bedrock in excess of 100 ppm TPH-diesel has been removed from the tank excavation area. During the fourth quarter of 1991 we will enlarge the north wall of the tank excavation until all the soil containing more than 100 ppm TPH-diesel is removed. As the hydraulic fluid is detected using the TPH-diesel analyses, this will ensure that all petroleum products are removed from the excavation. We will then backfill the tank excavation. We anticipate that the excavated soil and bedrock will be bioremediated next summer at Site 300. For additional information, please call Albert Lamarre at (510) 422-0757. Sincerely, Fredric Hoffman Division Leader Environmental Restoration Division FH:JC.jz cc: M. Brown, DOE D. Fisher R. Seraydarian, EPA H. Galles M. Higgins, RWQCB M. Rembaum, DTSC