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F > Former Beacon Station No. 474 May 15,2000 Stockton California Results of Additional Subsurface Investi ation Control Board document (RWQCB) Tri-Regional Board Staff Recommendations for Preliminga Investigation and Evaluation of Underground Tank Sites. SITE DESCRIPTION AND BACKGROUND The site is an operating gasoline service station located on the southwestern corner of the intersection of East Main Street and Broadway Avenue in Stockton, California. Site facilities include a station building, two gasoline product dispenser islands, and three underground gasoline storage tanks (USTs). These installations and other site features are shown on the Site Plan (Figure 2). Previous environmental investigations at the site have been performed by Acton, Mickelson, van Dam, Inc. (1995), El Dorado Environmental Inc. (1997), and Horizon (1996), and others. Three soil borings (SB-1 through SB-3) were advanced prior to removal the UST's. The UST's were removed and replaced in September 1993. In December 1993, three additional soil borings were advanced and converted to groundwater monitoring wells (MW- 1 through MW-3). In May 1996, Horizon advanced soil borings B-1 through B-4 and installed two off-site groundwater monitoring wells (MW-4 and MW-5). In September 1997, Horizon advanced six soil borings at the site. Three of the soil borings i were located adjacent to monitoring wells MW-1, MW-2 and MW-3 and were completed as monitoring wells MW-6, MW-8, and MW-9. The wells were constructed with higher and slightly overlapping screened intervals because of rising groundwater levels. One soil boring was completed as monitoring well MW-7 located in the southeast corner of the site to provide lateral definition. Two soil borings (B-5 and B-6)were drilled at the north end of the two dispenser islands and were completed with three nested soil vapor extraction wells, VW- 1, VW-2, VW-3, and VW-4, VW-5, VW-6, respectively. Gasoline-range hydrocarbons were reported in soil and groundwater samples collected during the previous investigations. Depth to groundwater has risen from approximately 80 feet 1474.22rpt 2 HORIZON ENVIRONMENTAL INC.