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i <br /> steeper south of the former UST than it is to the north (Figure 3) . <br /> It is also consistent with the previous calculation of 0. 0098 ft/ft <br /> 1 directed N 110 E, and with regional trends (San Joaquin County <br /> Department of Public Works, Flood Control Section, 1990) . <br /> 4. 3 Groundwater Sample Results <br /> TPH as gasoline, benzene, toluene and xylenes were detected in <br /> monitoring well MW-1 at concentrations of 120 gg/L, 8 .9 Ag/L, 0. 36 <br /> ' Mg/L and 0. 68 pg/L (ppb, parts per billion) respectively. Benzene <br /> and toluene were also detected in monitoring well MW-4 at levels of <br /> 1. 2 Ag/L and 0 . 30 Ag/L. No contaminants were detected in the sample <br /> from MW-5 . The water sample analyses are summarized in Table 3 and <br /> illustrated graphically in Figure 4 . The laboratory results and <br /> chain of custody are attached in Appendix A. <br /> 1 5. 0 CONCLUSIONS & RECOMMENDATIONS <br /> 5 . 1 Soil Contamination <br /> As discussed in the Preliminary Investigation and Evaluation Report <br /> (PIER) prepared by GeoAudit in December, 1991, this site was <br /> excavated to a depth of 34 feet, and soil samples collected from <br /> the walls and Floor of the excavation contained no detectable <br /> hydrocarbons above the method detection limits for EPA methods <br /> ' 8015m and 8020. Subsequently, groundwater monitoring well MW-1 was <br /> drilled adjacent to the north wall of the excavation, and soil <br /> samples were collected at 5-foot intervals to a depth of 50 feet. <br /> Moderate to strong hydrocarbon odors were reported in soil samples <br /> ' between 35 and 50 feet, and xylene and/or toluene were detected at <br /> relatively low concentrations in samples at 35, 40, and 45 feet <br /> (Monitoring Well Installation Report, June, 1992) . <br /> Four additional monitoringwells have since been installed, and a <br /> total of ten (10) soil samples from these wells have been analyzed. <br /> 1 ' <br /> ' 8 <br />