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Geological Technics Inc. <br /> 1101 7`h Street <br /> Modesto,Califomia 95354 <br /> (209)522-4119/Fax#522-4227 <br /> Additional Site Characterization Work Plan <br /> Soil and Groundwater Investigation <br /> Valentine (Castle Motors) <br /> 2315 N. El Dorado Street <br /> Stockton, CA <br /> Project No. 723.2 <br /> December 10, 2007 <br /> 1.0 INTRODUCTION <br /> In April 1987 the site's two 3,000-gallon gasoline underground storage tanks (UST) and one <br /> 150-gallon waste oil UST were removed (see Figure 1: Area Map & Figure 2: Site Map). <br /> Analyses of soil samples from the UST excavations revealed that a petroleum hydrocarbon <br /> release had occurred. The San Joaquin County Environmental Health Division (SJC/EHD) <br /> subsequently directed Mr. Valentine to begin an investigation to determine the extent of the <br /> petroleum release. <br /> The following is a summary of work performed at the site to date: <br /> • In October 1993 four boreholes (SB-1 thru SB-4) were placed around the location of the <br /> former waste oil tank. Results showed that all soil samples, except for the 36-foot sample <br /> from SB-2,were below detection limits for BTEX and TPH-G. <br /> • In September 1994 monitoring well MW-1 was installed at the site. Soil sample <br /> analytical results indicated the presence of BTEX and TPH-G in the soil to a depth of 56 <br /> feet below grade surface (bgs). Waste oil was detected in the shallow soil samples. <br /> • In June 1995 two additional monitoring wells, MW-2 & MW-3,were installed at the site. <br /> Results showed the presence of high levels. of BTEX and TPH-G in the soil and <br /> groundwater. <br /> • In June 1996 three additional monitoring wells (MW-4, MW-5 & MW-6) and soil boring <br /> "SB-B" were installed at the site. Soil sample analytical results indicated the presence of <br /> significant levels of BTEX and TPH-G. The results also indicated that the pump-island <br /> was a major source of contamination. <br />