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• 4 0 SUBSURFACE CONDITIONS Stratus has developed geologic cross sections based on available historical soil boring logs, and CPT results during this phase of investigation Interpreted geologic relationships are illustrated in geologic cross sections A-A' (Figure 5) and 13-13' (Figure 6) The surface trace of the cross sections is included on Figure 2 Historical soil boring logs and well details are presented in Appendix D 4.1 Geologic Conditions The following summarizes information from available boring logs prepared by previous consultants and the boreholes logged by CPT during this investigation Fine grained soils are generally observed from surface grade to depths ranging from approximately 8 to 17 feet bgs Predominately sandy soils, approximately 10 to 12 feet in thickness, are observed beneath these shallow fine grained soils and extend to depths ranging from approximately 20 to 30 feet bgs Laterally continuous sandy strata, with thicknesses of approximately 5 to 12 feet, were logged by CPT at depths ranging from approximately 35 to 48 feet bgs Silt and clay mixtures were predominately logged by CPT below these laterally continuous sandy strata, extending to approximately 80 feet bgs Sandy soils were observed from approximately 80 to 85 feet bgs at boring CPT-6, and 80 to 94 feet bgs at boring CPT-7 The lateral or vertical extent of these deepest encountered sandy strata is not currently known 42 Hydrogeology Depth to groundwater beneath the site has ranged from approximately 6 to 17 feet bgs (well MW-1) since monitoring was initiated in August 1991 Fine and coarser grained soils encountered at these depths appear to represent a "smear zone" for the petroleum hydrocarbon impact resulting from the variable groundwater elevations Groundwater elevations have generally increased (approximately 10 feet between 1991 and 2005) since the initiation of monitoring Figure 7 illustrates depth to groundwater elevations in select monitoring wells between 1992 and 2005 Seasonal depth to groundwater fluctuations of 2 to 5 feet annually have also generally been observed Figure 8 illustrates seasonal depth to groundwater fluctuations between 2003 and 2005 Depth to groundwater was measured at depths ranging from approximately 6 30 to 8 82 feet bgs during the third quarter 2005 Historical depth to groundwater measurements and groundwater elevations are included in a table presented in Appendix F Northeast and southeast groundwater flow directions have predominately been observed, at consistently low groundwater gradients Northeast groundwater flow directions are predominately observed onsite, southeast groundwater flow directions are predominately observed east of the site, in the vicinity of Ryde Avenue Given the historical groundwater flow direction, the 7-11 facility #14117 appears to be situated immediately upgradient of the site Select historical groundwater elevation contour maps are provided in Appendix G K\USA Gasohne108351Reportslusa835 scm-assessment report doc Page 8 5TRATU5