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Report on Additional Site Assessment and First Quarter 2000 Groundwater Monitoring 4 <br /> 7-Eleven Inc Store#17647, 1048 W Yosemite Avenue,Manteca CA February 22 2000 <br /> 40 RESULTS <br /> ' 41 Geology and Hydrogeology <br /> ' The site is located in the central part of the San Joaquin Valley The shallow stratigraphy in the area <br /> consists of Quaternary alluvium and lake deposits The materials encountered during recent drilling at <br /> the site generally consisted of silty fine sand grading downward to medium-grained sand to a depth of <br /> about 15 -20 feet below grade, with scattered interbedded clay strata (Appendix A) <br /> During drilling, groundwater was encountered at approximately 15 feet below grade Equilibrated <br /> ' groundwater levels are about 13 feet below grade On January 25,2000, the groundwater flow was to <br /> the west, at a hydraulic gradient of 0 0025 foot per foot(Table 2, Figure 2) <br /> ' 42 Results of Soil Sample Analyses <br /> ' Sall analytical data collected during well installation are summarized in Table 1 Soil benzene <br /> concentrations were non-detectable Soil TPH-G concentrations ranged up to 0 005 mg/kg Soil MTBE <br /> levels ranged up to 0 0233 mg/kg Highest sod hydrocarbon concentrations were detected at depths of <br /> 15-20 feet below grade Copies of the analytical results and chain-of-custody documents are included <br /> in Appendix D <br /> ' 43 First Quarter 2000 Groundwater Analytical Results <br /> Quarterly groundwater monitoring well analytical data are summarized in Table 2, and shown on <br /> ' Figure 2 Only well MW-3 contained detectable hydrocarbon concentrations benzene at 0 94 pglL, <br /> TPH-G at 81 hglL, and MTBE at 108 pg/L Dissolved D1 PE, ETBE,and TAME were not detected in any <br /> of the samples collected, dissolved TBA was found in well MW-3 at 111 hglL Copies of the analytical <br /> ' reports and chain-of-custody forms are included in Appendix D <br /> ' Dissolved oxygen levels ranged between 0 7 and 1 0 milligrams per liter(mg/L), which is indicative of <br /> generally anearobic conditions <br /> I } <br /> r 1 <br /> 1 1 I i <br /> I <br /> i <br /> l li <br /> ' ' E <br /> E fl <br /> k I l t i l i <br /> ,I," I II Ili I" iii ILII , <br />