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GeoStrategies <br /> ctcber 9, 1997 <br /> Mr. Bob Boost <br /> Unocal Corporation <br /> P.O. Box 5115 <br /> San Ramon, California 94583 <br /> Subject: Work Plan and Feasibility Study at Former Unocal Service Station No. 0187, 437 East <br /> Miner Avenue, Stockton, California. <br /> Mr. Boust: <br /> At the request of Unocal Corporation (Unocal), GeoStrategies (GSI) has prepared this Work Plan to <br /> install one groundwater monitoring well and perform a feasibility study at the above referenced site <br /> (Figure 1). The proposed groundwater monitoring well will be installed to delineate the lateral extent <br /> of hydrocarbon-impacted groundwater. The feasibility study will evaluate natural attenuation as a <br /> remedial alternative for this site. <br /> The subject site is a vacant lot situated on the northwest corner of the intersection of East Miner Avenue <br /> and California Street in Stockton, California. The most recent station configuration consisted of a station <br /> building with three dispenser islands, one 280-gallon waste oil and two 10,000-gallon gasoline <br /> underground storage tanks (USTs). Locations of pertinent site features are shown on the Site Plan <br /> (Figure 2). <br /> PREVIOUS ENVIRONMENTAL WORK <br /> Two 1,000-gallon gasoline and one 550-gallon waste oil USTs were removed from the southeast corner <br /> of the subject site in 1967. Data related to soil conditions beneath the USTs at the time of removal is <br /> not available. These USTs appear to have been replaced with two 10,000-gallon gasoline and one <br /> 280-gallon waste oil USTs situated in a common excavation in front of the station building. <br /> The two 10,000-gallon gasoline and one 280-gallon waste oil USTs, associated product piping,hydraulic <br /> lifts, and oil/water separator were removed and the station facilities demolished in January, 1992. <br /> Petroleum hydrocarbons were not detected in soil samples collected beneath the USTs, hydraulic lifts, <br /> or oil/water separator. Total Petroleum Hydrocarbons as Gasoline (TPHg) and benzene were detected <br /> in one soil sample collected from the product piping trench between the dispenser islands at <br /> concentrations of 150 and 0.81 parts per million (ppm). This trench area was overexcavated, and a <br /> confirming soil sample collected from the base of the excavation. Petroleum hydrocarbons were not <br /> detected in this soil sample. A second 130-gallon waste oil UST was removed from the eastern portion <br /> of the property in May 1992. Petroleum hydrocarbons were not detected in the soil sample collected <br /> from beneath this UST. <br /> In October 1993, GSI drilled eight on-site exploratory soil borings (U-A through U-H) in the locations <br /> of the former USTs, the former product dispenser islands, and the former hydraulic lifts in anticipation <br /> 4827.07-1 <br /> 3164 Gold Camp Drive, Suite 240 • Rancho.Cordova, CA 95670 • (916) 631-1314 Fax (916) 631-1317 <br />