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.' SECTION 4 <br />' SITE LITHOLOGY, HYDROGEOLOGY,AND NATURE OF CONTAMINATION <br /> This section describes the subsurface lithology as interpreted from the previous investigations and <br />' updated using 2003 CPT results, local hydrogeology and the extent of contamination in soil and <br /> groundwater <br />' 41 Site Lithology <br />' Site lithology was determined using boring logs from previous investigations and data collected by <br /> the 2003 CPT and geotechnical testing results The lithology below the site consists primarily of <br />' silty sand and sandy silt with interbedded sand, silt and clay <br /> The lithology is shown on cross sections A-A', B-B', and C-C' on Figures 4-1, 4-2 and 4-3 <br />' respectively There are three laterally continuous layers across the site A layer of sand to silty <br /> sand is present from approximately 40-ft to 60-ft bgs, a silt and clay layer is present from <br /> approximately 100-ft to 110-ft bgs and a sand layer is present from approximately 115-ft to 130-ft <br />' bgs These three layers were present at all of the CPT locations The first layer of sand was also <br /> observed in the four monitoring well locations and borings B10 and B11 installed by Leeward <br /> Consultants (Leeward, 1997) The first layer of sand appears to be shallower north and south of <br /> M CPT-1 as shown on A-A', which may be due to a former riverbed oriented east and west The clay <br /> and silt zones and the deeper sand zone appear to be fairly flat across the site as shown on <br /> Figures 4-1 and 4-2 <br /> Four hthologic groups are shown in Figures 4-1, 4-2 and 4-3 sand, silty sand and sandy silt, <br /> interbedded silt and cemented sand, and silt and clay Eight soil samples were collected from <br /> ' boring CPT-1 and were analyzed for particle size by GEOCON Consultants, Inc of Rancho <br /> Cordova Particle size analyses are critical for determining soil vapor extraction feasibility and <br /> design engineering as well as determining relative permeability of similar lithologies within the <br /> ' saturated zones The results of particle size analyses indicate site soil consists of predominately <br /> sandy silt (USCS classification ML) and silty sand The locations of the eight soil samples are <br /> shown on Figure 4-2 Particle size analysis results are included in Appendix A <br /> l <br /> 1'\230W\23954 1`I trucking\CP i Summary Report\HNAL 1&T i rucking DOC <br />