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• Well Installation Report - Former Unocal Service Station No 0187 October 21, 1997 PREVIOUS ENVIRONMENTAL WORK Two 1,000-gallon gasoline and one 550-gallon waste oil USTs were removed from the southeast corner of the subject site in 1967 Data related to soil conditions beneath the USTs at the time of removal is not available These USTs appear to have been replaced with two 10,000-gallon gasoline and one 280-gallon waste oil USTs situated in a common excavation in front of the station building. The two 10,000-gallon gasoline, one 280-gallon waste oil USTs, associated product piping, hydraulic lifts, and oil/water separator were removed and the station facilities demolished in January, 1992 Petroleum hydrocarbons were not detected in soil samples collected beneath the USTs, hydraulic lifts, or oil/water separator. Total Petroleum Hydrocarbons as Gasoline (TPHg) and benzene were detected in one soil sample collected from the product piping trench between dispenser islands D-1 and D-3 at concentrations of 150 and 0 81 parts per million (ppm), respectively This trench area was overexcavated, and a confirming soil sample collected from the base of the excavation Petroleum hydrocarbons were not detected in this soil sample A second 130-gaIlon waste oil UST was removed from the eastern portion of the property in May 1992 Petroleum hydrocarbons were not • detected in the soil sample collected from beneath this UST Results of the UST removal investigation were presented in GSI Report No 782701-1, Tank Removal Observation Report, dated September 11, 1992 In October 1993, GSI drilled eight exploratory soil borings (U-A through U-H) in the locations of the former USTs, the former product dispenser islands, and the former hydraulic lifts in anticipation of site closure During this investigation, TPHg were detected in soil samples analyzed from borings U-G, drilled within the former gasoline UST pit, and U-D, drilled adjacent to former dispenser island D-4 TPHg concentrations in four of the soil samples analyzed ranged from 1,600 to 2,900 ppm Benzene was not detected in these soil samples. Results of this subsurface investigation are presented in GSI Report No. 782702-3, Exploratory Soil Boring Report, dated December 15, 1992 In July 1994, GSI drilled five additional onsite soil borings (U-I through U-M) and installed three onsite groundwater monitoring wells (U-1 through U-3) TPHg were detected in soil samples analyzed from borings U-J (1 7 ppm at 26 5 feet bgs) and U-K (130 ppm at 41 5 feet bgs) TPHg were detected in soil samples analyzed from borings U-3 (330 ppm at 46 5 feet bgs), U-L (19,000 ppm at 45 5 feet bgs), and U-M (510 ppm at 45 5 feet bgs) Results of this subsurface investigation are presented in GSI Report No 4827.703-5, Well Installation and Exploratory Soil Boring Report, dated September 21, 1994. 4827 21-2 2