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Report on Additional Site Assessment 8 7-Eleven Inc.,Store#19976,1399 N.Main St.,Manteca,California March 5 2001 On March 2 and 3, 1999, IT Corporation personnel conducted a survey of residential units within a 2,000- foot radius of the subject site. The survey identified sixty-five water supply wells within the search radius (not including three wells identified from the State data which have since been capped). Forty-seven of the wells identified are located along Joseph Road south/southwest(upgradient) of the site. The nearest wel to the site is located at the Enterprise Rent A Car facility at 1395 North Main Street approximately 200 feet south (upgradient) of the site. Enterprise personnel at the site at the time of survey were not aware of the well or its condition. The nearest downgradient/crossgradient wells are located at 152158 Stare-Highway Route 99 and at 1726 North Main Street approximately 1,550 to 1,600 feet northeast of the site. Three wells listed as being at the mobile home park about 1,400 to 1,500 feet east/northeast (downgradient) of the site have been capped and are no longer in use. Reiriew of regional geologic and hydrogeologic data indicates the existing dissolved hydrocarbon plume at the site poses relatively low risk to nearby utilized groundwater resources. Based on existing nearby land use,soil types, and soil hydrocarbon plume distribution (generally confined to the upper part of the water-bearing zone at depths of more than 18 feet below grade, or, in vadose zone soils in the immediate vicinity of the hydrocarbon source area),there is apparently low to no risk of vapor migration impact to any potential nearby sensitive receptors. 4.2 Soil Gas,Soil Sample,and Grab Groundwater Sample Analytical Results Table 1 summarizes the laboratory analytical results for the soil gas survey samples. Benzene was non- detectable for all samples except SG-9,which contained 41 ug/L. Concentrations of TPH-G were also non-detectable for all locations except SG-9,which contained 2,500 ug/L. For MTBE, all locations had non-detectable levels except for SG-8,SG-9, SG-10, and SG-11; levels in all of these locations were less than 9 ug/L except location SG-9,which contained 2,200 ug/L. Copies of the analytical results and chain-of-custody documents are included in Appendix D. Soil analytical results are summarized in Table 2. Analytical results were non-detectable for all constituents. Copies of the analytical results and chain-of-custody records are included in Appendix D. Results of analysis of the grab groundwater sample collected from 40 feet below grade in boring SB-2 are included in Table 2A. Analytical results were non-detectable for all constituents except for 1.5 ug/L total xylenes. Copies of the analytical results and chain-of-custody records are included in Appendix D. 199;6ASA