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• 3.0 INVESTIGATION RESULTS <br /> 31 Geology and Hydrogeoiogy <br /> Soils observed in the five soil borings consisted of alternating sand and gravel sequences <br /> interrupted by finer-grained silt and clay intervals The uppermost 18 feet of soil consisted of a <br /> mostly well-graded sand sequence, which became somewhat coarser-grained with depth This <br /> sand sequence is laterally continuous and overlies a silty sand, silt or clayey silt sequence A <br /> laterally discontinuous sand sequence underlies this finer-grained interval at a depth of <br /> approximately 30 feet bgs A well-graded sandy gravel was observed at the bottom depth of two <br /> ' of the three soil borings extended to 43 feet bgs Soil boring logs are included in Appendix C <br /> During drilling, saturated soil was first encountered at approximately 20 feet bgs Groundwater <br /> ' levels measured in each of the soil borings ranged from 18 7 to 21 feet bgs Groundwater does <br /> not appear to be confined and recharge was found to be moderately strong <br /> ' 3.2 Analytical Results <br /> rwBased on the results of the laboratory analyses, soil and groundwater beneath the site has been <br /> impacted by diesel and gasoline hydrocarbons The source of impact appears to be leakage <br /> ' from the former USTs <br /> The highest concentrations of diesel and gasoline hydrocarbons were detected in samples <br /> ' collected from SB-1, located within the former UST excavation In the sod sample collected at <br /> 18 feet bgs from SB-1, TPH-as-diesel was detected at a maximum concentration of 18,000 <br /> mg/kg and TPH-as-gasoline was detected at 1,900 mg/kg <br /> Vertically, the extent of impacted soil beneath the former USTs is defined to a depth of between <br /> t35 and 43 feet bgs Laterally, the vertical extent of impacted sod is concentrated between 15 <br /> and 25 feet bgs, within the capillary fringe and zone of groundwater table fluctuation <br /> Impacted soil at a depth of 15 feet bgs is defined to within approximately 30 feet south and west <br /> of the former USTs As depicted on Figure 3, the lateral extent of impacted sod at 15 feet bgs <br /> remains undefined to the north and east of the former USTs <br /> 1 9 <br />