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i Iin Boring B4 at 300 mg/kg (ppm). The highest concentrations of benzene, toluene, ethyl- benzene, xylene (BTE&X) and TPH as gasoline were detected in Boring B4 at a depth of 60 feet at 370 ppm, 1,200 ppm, 330 ppm, 980 ppm, and 16,000 ppm, respectively. BTE&X and TPH as gasoline were not detected at 60 feet in Boring B1 Benzene was detected at 0 43 ppm in Boring B5 at 55 feet The laboratory reports and chain of custody forms are Iincluded in Appendix B 4.4 Relative Groundwater Elevation and Flow Direction The average depth to groundwater at the site is 55 26 feet bgs. The relative groundwater ' elevation is highest in MW-2 at 42 62 feet The average hydraulic gradient was calculated to be 0 0023 ft/ft with the flow direction ranging from N 25°E to N 70°E (Figure 5) I4.5 Groundwater Sample Analysis When MW-4 was sampled on February 22, 1994, no free product was present however TPH ' as gasoline and diesel were detected at concentrations of 420 mg/L (ppm) and 12 ppm, respectively BTE&X components were also detected in MW-4 at concentrations of 56 ppm, 83 ppm, 8 3 ppm, and 27 ppm, respectively BTE&X and TPH as gasoline were also ' detected in MW-1, MW-2, and MW-3 A summary of the analytical results for groundwater samples is presented in Table 4 The laboratory results and chain of custody form is included in Appendix C 5.0 CONCLUSIONS & RECOMMENDATIONS I 5.1 Vadose Zone Contamination IOne objective of this investigation has been to delineate the lateral extent of the vadose- zone contaminant plume Relatively high concentrations of volatile hydrocarbons detected in Borings B1, B2, and B4 All components were below detection levels in Boring B1 at 60 feet Low to trace levels of BTE&X were detected in Boring B3 which was installed in Grant Street, west of former tank A Only trace levels of BTE&X were detected in Boring ' B5, located west of former tanks B and C Based on the concentrations of contaminants present, GeoAudrt believes the San Joaquin PHS/EHD will require further assessment of the vadose-zone contamination GeoAudrt recommends additional bonngs will be located ' in the areas adjacent to all former tanks Two slant bonngs, north of Boring B1 and east of Boring B1, will assess if the contaminant plume is present below the structure which houses Larry's Auto Repair and the adjacent warehouse A slant soil boring should be ' drilled below the structure north of 134 5.2 Groundwater Contamination IHydrocarbons were detected in samples obtained from all monitoring wells As the extent 06s-1 A4&s.,I.e. 11 li11Y.A.b gip.��QM 9017 9