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1 Report on Additional Site Assessment and First Quarter 2000 Monitoring and Sampling Report 6 7-Eleven Inc Store#19976 1399 N Main St,Manteca California February 4 2000 1 Sensitive receptor survey results were reported to the SJCPHS in April 1999 Land use in the Immediate site vicinity Is generally light commercial State Department of Water Resources data Indicated twelve water supply wells within 2,000 feet of the subject site, five of which are within 1,000 feet of the site According to a telephone conversation between the City of Manteca Engineering Division and IT Corporation personnel, there are no municipal water supply wells within 1 mile of the site The nearest municipal supply well is located at the corner of Northgate Drive and Hoyt Lane, approximately 1 25 Imiles west (crossgradient) of the site 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 I the wells identified are located along Joseph Road south/southwest (upgradient) of the site The nearest well 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 Iaware of the well or its condition The nearest downgradient/crossgradient wells are located at 152158 State Highway Route 99 and at 1726 North Main Street approximately 1,550 to 1,600 feet northeast of I� 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 Review 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 42 Results of Soil Sample Analyses Table 1 summarizes the laboratory analytical results for soil samples collected on December 22, 1999 from well MW-6 Benzene was non-detectable Soil TPH-G concentrations ranged up to 15 4 mg/kg, with highest levels detected at 20 feet below grade Soil MTBE levels were non-detectable Copies of the analytical results and chain-of-custody documents are included in Appendix D The summary of recent and historical soil analytical data indicates that the lateral and vertical extent of the soil hydrocarbon plume has been sufficiently delineated No further assessment is considered to be . warranted at this time 1 ' 19976 3SA