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rr GeoStrategies Inc. FOURTH QUARTER STATUS REPORT at Unocal Station No 6981 4707 Pacific Avenue Stockton, California Report No 4855 702-2 MMODUCTION This report summarizes field activities performed at the subject site between October and December, 1994 Field activities included quarterly monitoring and sampling of the groundwater monitoring wells, bi-weekly monitoring of VES operational parameters and monthly sampling of the VES influent and effluent vapor streams Location of the subject site is shown on the Vicinity Map (Figure 1) BACKGROUND The subject site is an active Unocal Service Station situated on the northwest corner of the intersection of Pacific Avenue and March Lane in Stockton, California Underground storage tanks (USTs) were replaced in May and June, 1988 Approximately 1,500 cubic yards (yd') of hydrocarbon-impacted soils were excavated and treated onsite during UST replacement A soil vapor survey was performed to assess the extent of residual hydrocarbons in the soil beneath the site Thirteen groundwater monitoring wells, six vapor extraction wells, and one groundwater extraction well have been installed at or near the subject site between January 1990 and August 1992 A vapor extraction test (VET) was performed in March 1992 to evaluate the feasibility of vapor extraction as a remedial option for soil beneath the site An aquifer pumping test was performed in August 1992 to evaluate the feasibility of utilizing groundwater extraction to remediate hydrocarbon-impacted groundwater A VES was installed at the site and operation initiated in September 1994 Locations of the pertinent site features are shown the Site Plan (Figure 2) 4855702-2 6747 Sierra Court, Suite G•Dublin, CA 94568•(510) 551-8777• Fax (510)551-7888 3035 Prospect Park Drive, Suite 80 • Rancho Cordova, CA 95670 •(916)631-1314• Fax(916) 631-1317 �71