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Case Closure Report Former Tosco(Unocal) SS No 5421,Stockton,California July 8, 1998 Water and selected soil samples from all seven exploratory borings were analyzed by TPH as gasoline by EPA Method 5030/Modified 8015, and BTEX by EPA Method 8020 In addition, water and selected sort samples from EB3 and EB4 were analyzed for TPH as diesel by EPA Method 3550/Modified 8015 (soil) and EPA Method 3510/Modified 8015 (water), total oil and grease (TOG) by Standard Methods 5520 B&F (water) and 5520 E&F (soil), and for EPA Method 8010 constituents Selected soil samples from EB5 and EB6 were also analyzed for TPH as diesel, TOG, EPA Method 8010 constituents, and for TPH as hydraulic fluid by EPA Method 3550/Modified 8015 One soil sample from EB7 was also analyzed by TPH as diesel, TOG, and EPA Method 8240 constituents The results of soil analyses are presented in Appendix A Tables 1D and 2D, and the results of the water analyses are presented in Appendix A Table 3D Sample locations are presented in Appendix A Figure 1D On June 26, 1996, Pacific Environmental Group Inc (Pacific) issued well survey results for the area around the subject site California Department of Water Resources (DWR) files were reviewed to identify active and inactive water supply wells within a 1/4-mile radius of the site A total of twenty documented wells were identified The closest well appeared to be located approximately 500 feet west of the site Monitoring and extraction wells were not included in the file review A copy of the Pacific report dated June 26, 1996 is presented in Appendix C . Underground Storage Tank Removal Activities In April 1998, all onsite equipment and facilities except for the former station budding and canopy were removed from the site GR personnel witnessed removal of two 12,000- gallon gasoline USTs, one 520-gallon waste oil UST, and related product lines, two hydraulic lifts, and one sand/water separator The USTs and related product piping was removed on April 15, 1998 The hydraulic lifts and sand/water separator were removed on April 21, 1998 Equipment removal, soil sampling, and over-excavation activities were observed by Ms L.etitcia Briggs and Mr Harlin Knoll from the SJCPHS The USTs, hydraulic lifts, and related product piping were found to be in good condition with no signs of holes, leaks or cracks Upon removal of the onsite equipment, soil samples were collected Soil sample locations and analytical data are presented in Appendix A Table 1E, Figure 2E Upon removal of the gasoline USTs on April 15, 1998, a soil sample was collected from beneath each end and center of the USTs at depths of approximately 15 5 to 17 feet bgs Each soil sample was analyzed for TPH as gasoline, BTEX, ethyl t-butyl ether (MtBE), and six oxygenate compounds No petroleum hydrocarbons were detected in sample UX-1-16 The remaining samples contained petroleum hydrocarbons concentrations ranging from not detected to 25000 ppm TPH as gasoline, not detected to 270 ppm benzene and not detected to 170 ppm MtBE All samples were reported as not detected for oxygenate compounds Upon collection of the initial UST complex samples, over-excavation was initiated in the northwest corner of the excavation in the vicinity of sample UX-2-15 5 Samples UX-2-22 140162 03 8