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Appendix B Cone Penetration Test Boring Investigation Phase lI ESA Multi-Modal Station"Six-Block Project" January 6,2003 Page 3 of 3 t. 3.0 DISCUSSION OF RESULTS The geologic logs from borings CPT I through CPT5 were compared in order to evaluate the lateral continuity of the subsurface lithology beneath the site Representative geologic cross-sections depicting the subsurface lithology of the site were prepared by integrating the Information contained In each of the CPT logs and selected Geoprobe and detection boring logs Geologic cross-section locations are shown in Figure 5, Appendix A Geologic cross-section A-A' (Figure 12, Appendix A) was constructed along an east/west orientation, looking to the north, and geologic cross-section B-B' (Figure 13, Appendix A) was constructed along a northwest/southeast orientation, looking to the northeast The CPT bonngs indicate the subsurface geology beneath the site is generally homogeneous below the six-block area Eolian sands, represented in the area on published geologic maps, were not noted in any of the borings completed during this investigation Soils encountered in the CPT borings were predominantly interbedded clays and silts with sporadically occurring thin beds of stiff fine-grained material and sand From the surface to a depth of approximately 27 5 feet bgs (CPT1) to 36 5 feet bgs (CPT4), the subsurface lithology is generally composed of interbedded layers of clay and silt with transitional layers of clayey silt and silty clay With the exception of the soils encountered in CPTI, the silt and clayey silt soils are more prevalent in this zone than the clay-rich soils In CPTI, primarily silty soils and clayey soils were encountered in roughly equivalent abundance Sand and silty sand layers that may correspond to water-bearing zones were generally encountered at or near the basal portions of this uppermost subsurface zone Sand and silty sand layers encountered between approximately 27 5 feet and 39 feet bgs in the CPT borings appear to represent a continuous sand and silty sand unit and likely correspond to the first groundwater at depth across the site Sand and silty sand layers were encountered at approximate depths . of 28 to 32 feet bgs and 108 to 115 feet bgs in CPT1, 30 to 31 feet bgs and 43 feet bgs In CPT2, 28 to 33 feet bgs in CPT3, 36 to 39 feet bgs and 115 to 120 feet bgs in CPT4, and 34 to 36 feet bgs, 95 to 97 feet bgs, 109 to 115 feet bgs, 119 to 121 feet bgs, 134 to 137 feet bgs, and 170 to 174 feet bgs in CPT5 The detection and hydropunch borings were advanced to approximate depths of 45 feet bgs to collect groundwater samples from this shallow zone Interbedded silts, clayey silts, silty clays, and clays comprise the majority of the subsurface between approximately 39 feet and 110 feet bgs With the exception of CPT2, the primarily silty soils and clayey soils were encountered in roughly equivalent abundance to a depth of approximately 110 feet bgs The soils encountered in CPT2 were predominantly silts and clayey silts with sparsely interbedded clay-rich soil layers A semi-continuous sand layer was encountered at an approximate depth of 117 to 119 feet bgs in borings CPT4 and CPT5 In CPT5, this sand layer was separated from another sand layer between approximate depths of 109 feet and 115 feet bgs by a predominantly silty layer This upper member of the lower sand unit was also encountered in CPTI at an approximate depth of 108 to 115 feet bgs Boring PAI and hydropunch boring HBK4-730-1 were advanced to approximate depths of 114 feet bgs and 110 feet bgs, respectively, to collect groundwater samples from the deeper zone The logs for borings CPT2 and CPT3 do not indicate the presence of a potentially water-bearing semi-contmuous sand unit at these depths Other discontinuous sand and/or silty sand layers were encountered at approximate depths of 43 feet bgs in CPT2 and 95 to 97 feet bgs in CPT5 I Based on the soils encountered in CPT5 at depths greater than 120 feet bgs, the site subsurface is comprised primarily of interbedded silts, clays, and transitional soils between these types to an approximate depth of 170 feet bgs Additional deep sand and silty sand layers were encountered in CPT5 • at approximate depths of 134 to 137 feet bgs and 170 to 173 feet bgs