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. Former Unocal Service Station #0187 October 9, 1995 (Figure 1) The subject site is situated in an area of retail stores and hotels Topography in the site vicinity is flat-lying, at an elevation of approximately 15 feet above mean sea level (MSL) McLeod Lake and the Stockton Deep Water Channel are situated approximately one-half mile to the west The site was an operating Unocal Service Station from 1922 until 1992 The most recent service station consisted of a three-bay service station building, three product dispenser islands (D-1 through D-3), and two gasoline and one waste oil USTs in a common excavation. 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 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-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 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-C, 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 • 482704-3 2