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Subsurface Investigation December 12, 1990 Former Unocal Station No. 2859, Stockton, California AGS 38012-5 Additional excavation was conducted at the request of Unocal anti with the approval of the San Joaquin Public Health Services (S3PHS). The tank cavity as enlarged to approximately 25 by 35 feet and a bench was cut into the vialls of the excavation to a depth of 7 to 8 feet. An excavator was lowered onto this bench and continued to excavate below the former tanks. The total depth of tb cavity varied from approximately 26 to 30 feet below grade. Soil sample S-0329.9A was collected at 26 feet below grade under the former northern tank; TPHg was detected at 13 ppm. The concentration of BTEX compounds ! ranged from below detection limits to 1.32 ppm. After receiving results of analyses of soil samples collected directly under the former tanks, excavation continued in the area of the southern side wall and under the former tank T-1. Soil sample S-0406-12A was collected at 28 feet below grade from the south side wall and results indicated BTEX concentrations were above 1.0 ppm. The area was excavated further and soil sample S-0406-13A was collected from 30 feet below grade under the former tank. Results indicated the TPfig concentration was 3 ppm and BTEX concentrations were below detection limits for the methods used. 'Me product lines were removed and the trenches were excavated. Soil sarjple S-0330-11 � was collected under the former product piping between the dispenser islznds as shown on Plate P-2. Analyses indicated TPHg at 6 ppm and BTEX compounds were below detection limits for the methods used (Table 2). The former waste-oil tank cavity was excavated to approximately 8 feet below grade and a soil sample wap zollected. Laboratory results indicated the concentrations of TPHg,BTEX, organic lead, volatile organic compounds and polychlorinated biphenyls were below detection, limits for the methods used (Table 2). 6