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Beacon Station No.474 December 23, 1997 Sto-ckton. CalifQrniai cInvestigation e the SJC PHS/EHD, preparing a site-specific safety plan, scheduling drilling, drilling six ' borings, completing four of the borings as groundwater monitoring wells, completing the remaining two borings as nested vapor extraction wells, performing well development, ' groundwater sampling, and preparation of this report. The work was accomplished as outlined in Horizon's Work Plan No. 1474.12, dated August 1, 1997. ' 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 located toward the northern property boundary, and three underground gasoline storage tanks (USTs) ' located toward the northeastern property boundary. Locations of these and other pertinent site features are shown on the Site Plan (Figure 2). Previous environmental work at the site was performed by Horizon and others. This previous work included drilling three onsite soil SB-I borings through - g ( gh SB 3) prior to removing the USTs, the removal and replacement of the USTs in September 1993, and drilling three additional soil borings and installation of three groundwater monitoring wells ' (MW-1 through MW-3) in December 1993. in May 1996, Horizon drilled soil borings B-I through B-4, and installed offsite groundwater monitoring wells MW-4 and MW-5. ' Detectable concentrations of gasoline-range hydrocarbons were found to be present in the soil and groundwater during these previous site investigations. Locations of the soil borings ' and groundwater monitoring wells are shown on Figure 2. Groundwater was found to be present at a depth of approximately 80 feet below surface grade (bsg) in 1993, and had risen ' to approximately 68.feet._bsg in 1996. Quarterly-monitoring on June 13 1997 has indicated- the depth-to-water beneath the site to be approximately 63 feet bsg (see Table 1). ' 1474-12.rpt 2 HORIZON ENVIRONMENTAL INC.