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31 August 2005 AGE-NC Protect No 96-0232 Page 4 of 30 23 SITE INVESTIGATIONS Based on analytical results of grab ground water samples collected during the UST removals, the UAR reported in May 1993 and due to the necessity to replace well MW-3, a preliminary site investigation was required by the SJCEHD by letter dated 25 January 1996 (Appendix E) prior to obtaining a site closure for the former USTs The following is a brief summary of all site assessment investigations that transpired at the site following removal of the USTs (March 1995) • July 1996- One ground water monitoring well (MW-4) was installed on-site to a depth of 30 feet bsg, a boring log and an as-built well construction description of well MW-4 is in Appendix F Ground water levels were recorded from wells MWA, MW-2 and MW-4 at approximately 15 feet bsg(Table 6),the general ground water flow direction was toward the south-southeast(Appendix H) Laboratory analysis of soil samples collected from MW-4 did not detect any constituents of concern, however, methyl tertiary butyl ether (MTBE) was detected for the first time from wells MW-1, MW-2 and MW-4 concentrations of 310 gg/l, 3 7 pg/1 and 0 74 gg/, respectively Analytical results of soil and ground water samples are summarized in Tables 2 and 7 A report of findings (Closure Summary Report- February 1997, dated 30 April 1997) was prepared by AGE and submitted to the SJCEHD • January 1997 - AGE conducted a sensitive receptor survey to locate potential vertical conduits within a 2,500-foot radius of the site The sensitive receptor survey located two San Joaquin County operational municipal water wells(CSA Nos 1 &2)located approximately 1,600 feet and 700 feet, respectively, southeast of the site, one domestic water well serving Rocky's Restaurant was located approximately 150 feet southwest of the site and a second domestic water well servicing Three B's Truck Plaza was located approximately 450 feet west-southwest of the site One domestic water well serving Flying J's Travel Plaza was located approximately 600 feet north of the site No other sensitive receptors were located Receptor survey results are summarized in Table 10, results of the investigation were previously reported in Closure Summary Report - April 1997, dated 28 April 1997, and submitted to the SJCEHD • August and September 1997- Four soil borings (P1, P2, P3 and P4) were advanced on-site to maximum depths of 70 feet bsg and one soil boring(P5)was advanced off-site at 14659 Thornton Road (Rocky's Restaurant) to a depth of 60 feet bsg Soil boring locations are depicted in Figures 2 and 3,boring logs and as-built construction descriptions for P1through P5 are in Appendix F Analytical results of soil samples detected MTBE from the P 1-3 5 foot soil sample at a concentration of 0 14 mg/kg Grab water samples collected from P 1 detected MTBE and tert-butanol(TBA)at depths between 23 and 27 feet at concentrations of 410µg/l and 25 µg/1, respectively, and at depths between 46 and 50 feet at concentrations of 72 µg/1 and 11 µg/l,respectively A grab ground water sample collected from P5 at a depth between •, 21 and 25 feet bsg contained MTBE and TBA at concentrations of 100 µg/1 and 6 6 µg/1, Advanced GeoEnvironmental,Inc