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•� Soil Remediation Feasibility Study Work Plan - Unocal Station No 0187 April 30, 1996 station facilities have been removed and the site is currently an unpaved vacant lot Pertinent features of the former service station are shown on the Site Plan (Figure 2) 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 1.0,000-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 and 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-gallon 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 Based on the data collected during this investigation, there does not appear to be hydrocarbon-impacted soils in the vicinity of the former UST pit south of the station building, waste oil tank, hydraulic lifts, or dispenser islands In October 1993, GSI drilled eight on-site exploratory soil bonngs (U-A through U-I) 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 collected at 16 5 and 31 5 feet below ground surface (bgs) from boring U-C, drilled within the former gasoline UST pit in the southeastern corner of the site, and from boring U-D, drilled adjacent to former dispenser island D-4 TPHg concentrations ranged from 1,600 to 2,900 ppm Benzene was not detected in these soil samples TPHg or benzene were not detected in soil samples collected from the other bonngs 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 on-site soil bonngs (U-I through U-M) and installed three on-site groundwater monitoring wells (U-1 through U-3). This work was performed to assess the extent of impacted soil in the southeast corner of the site and evaluate whether •� UN0187 SRW aWAS-1 2