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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 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 24 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 /> low diesel detections, and low,detections of benzene, toluene,'and <br /> xylenes suggest:that little contaminated sail remainson the;west, <br /> noith, and southeast aides of the excavation (sample locations S3, S5, <br /> and S1 respectively)at 15 to 35 foot depths. <br /> w 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 /> Geologic Seth <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 Cit,/ oac Stockton <br /> Public Works Division reported the elevation of the first =i_ fined <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 <br /> groundwater levels of <br /> ---feet-per-year-during the last-five-years. ---- - ----- <br /> During drilling at the site, first water was encountered atdepths of <br /> E between 43 and 48 feet below grade. Water levels quickly rose to <br /> i <br /> 1-4 <br />