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3.0 SITE INVESTIGATION RESULTS 3.1 Geology and H dro Bolo Y 9 gY In general, soil to a depth of 20 feet beneath the site consists of a fining-upward sequence of fine-grained siliciclastic sediments The uppermost soil is a light brown silty clay that grades into a light brown clayey silt at approximately 7 feet bgs This clayey silt unit grades to a light brown silty fine sand with some clay at approximately 12 feet bgs With depth, the clay content of this silty fine sand diminishes to the total observed depth of 20 feet bgs Saturated soil was first encountered at approximately 8 feet bgs Static groundwater was measured in each of the boreholes at approximately 7 feet bgs Groundwater was extracted easily and found to be sediment-laden and cloudy 32 Analytical Results Based on the investigation results, soil and groundwater beneath the site has been impacted by diesel and gasoline hydrocarbons The soil sample analytical results are summarized in Table 1 and the groundwater analytical results are presented in Tables 2 and 3 The laboratory reports are included as Appendix D Results of the soil sample analyses and inspection of continuous core indicate that diesel and gasoline hydrocarbons are concentrated vertically at or near the water table at a depth of approximately 7 feet bgs and that impacted soil extends to a depth of approximately 12 feet bgs Soil samples collected from 5 feet bgs from within and immediately east of the former UST excavation contained concentrations of TPH-as-diesel of up to 18 ppm and TPH-as-gasoline of up to 2 ppm Soil samples collected from 10 feet bgs contained up to 1,800 ppm of TPH-as- diesel and 400 ppm of TPH-as-gasoline At 10 feet bgs, benzene was detected at a maximum concentration of 54 ppm MTBE was not detected in any of the sod samples analyzed Soil samples collected at a depth of 15 feet bgs from within and around the former UST excavation did not contain detectable concentrations of either diesel or gasoline hydrocarbons One soil sample collected at a depth of 20 feet bgs from within the former UST excavation only contained 0 006 ppm of xylenes Since no other diesel or gasoline hydrocarbons were detected in this sample, this detection of xylenes is probably not significant Laterally, impacted soil at 10 feet bgs is concentrated near the former UST excavation but extends to the north of the site under the city of Tracy right-of-way The soil sample collected at 10 feet bgs from SB-8 indicates that soil on the north side of Hamilton Alley contains 390 ppm of