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been approved by San Joaquin County. The purpose of the work was <br /> to determine "clean zones" within the current excavation and to <br /> explore the extent of petroleum hydrocarbon occurrence <br />' The locations of the slots are illustrated in Figure 1-3, Appendix C <br /> Soil samples were collected from depths of a pp <br /> p approximately 17 feet <br />' below the grade (2 feet below the bottom of the excavation) and 32 to 35 <br /> feet below grade (17 to 20 feet below the bottom of the excavation ) The <br /> samples were analyzed for TPH as diesel and gasoline, as well as <br />' BTEX Most of the samples collected had diesel concentrations in the <br /> two to ten mg/kg range The data from this investigation is <br /> summarized in Table 1-2 In general, contaminated soil encountered <br /> during this investigation appeared to be largely confined to the <br /> northeast sector of the excavation (slot 6) at a depth of 33 feet below <br /> grade Some contaminated soil also was detected at a depth of 17 feet <br /> below grade in slot 2 The extent of contamination around slot 2 <br /> appeared to be relatively limited The absence of gasoline detections, <br /> Iow diesel detections, and low detections of benzene, toluene, and <br /> xylenes suggest that little contaminated soil remains on the west, <br />' north, and southeast sides of the excavation (sample locations S3, S5, <br /> and S1 respectively) at 15 to 35 foot depths <br />' The results of this investigation are contained in the letter report <br /> submitted by ERM-West to Mr Dean Willis of O'Melveny and Myers <br /> on October 15, 1990 This letter report is contained in Appendix C to <br /> this report <br /> J <br /> Geologic Setdng <br />' The following sections briefly address soil and groundwater <br /> characteristics at the facility <br /> Ground surface elevation at the site is approximately 15 feet above <br />' mean sea level (MSL) Information supplied by the City of Stockton <br /> Public Works Division reported the elevation of the first unconfined <br /> groundwater in the spring of 1990 at 20 feet below MSL This <br />' unconfined groundwater was not encountered during drilling at the <br /> site It is likely that this unconfined groundwater was present at <br /> shallow depths until recent years Irrigation districts in the area <br />' and the California Department of Water Resources (DWR) have <br /> documented reduction in unconfined groundwater levels of several <br /> feet per year during the last five years <br /> During drilling at the site, first water was encountered at depths of <br /> between 43 and 48 feet below grade Water levels quickly rose to <br /> 1-4 <br /> 1 <br />