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3.0 SUBSURFACE CONDITIONS 31 Geologic Conditions The geology beneath the site consists predominately of dry, hard, silty soils to 202 feet bgs, the maximum depth explored beneath the site Weak to moderate caliche cement was encountered within much of the silty stratum Two intervals of sandy stratum, that appear to be laterally continuous, are generally interbedded within the fine grained soils The upper sandy interval (sand zone 1) was observed with thicknesses ranging from approximately 2 to 6 5 feet in the continuously logged soil borings, at depths ranging from approximately 48 to 64 feet bgs Sand zone 1 does not appear to extend to the boring B-47 and B-48 areas of the site The lower sandy interval (sand zone 2) was observed with thicknesses ranging from approximately 12 to 23 feet, at depths ranging from approximately 68 to 104 feet bgs Select strata within sand zone 2 were cemented Approximately 5 to 18 feet of fine grained soils (predominately silt) appear to separate sand zone 1 and sand zone 2 At boring locations B-47 and B-48, sandy strata were identified between approximately 110 and 125 feet bgs (B-47) and 118 to 134 feet bgs (B-48) Based on the soil types observed at borings B-33 through B-38, these sandy soils do not appear to extend beneath the site, across Patterson Pass Road Interpreted geologic relationships are illustrated on cross sections A to A' (Figure 3), B to B' (Figure 4), C to C' (Figure 5), and D to D' (Figure 6) The surface trace of each geologic cross section is included on Figure 2 Increased soil hardness was generally observed in the fine grained strata encountered below approximately 140 feet bgs Soil samples collected from 152 feet bgs and 202 feet bgs in boring B-32/MW-1 were previously submitted for physical analysis Relatively low permeability values of 6 5 x 10-' centimeters per second (cm/s) and 2 4 x 10-6 cm/s, respectively, were reported for these samples In a previously submitted SCM, Stratus reported that strata beneath the site do not appear to be horizontal Strata beneath the site were likely tilted from horizontal due to orogenic uplift in the Coast Range Mountains immediately west of the site Stratus previously calculated a strike of N17°E, with a 5° dip towards the east-southeast, using correlative sand stratum encountered in borings B-33, B-35, and B-38 (the upper contact of sand zone 2) as a marker bed for the calculation The strike and dip at a sandstone outcrop located approximately 1 mile west of the site were measured at N15°E and 19° east-southeast, respectively 3.2 Hydrogeology Based on information collected during the drilling of boring B-32, the regional water table appears to be deeper than approximately 202 feet bgs at the site A water supply well situated on-site is screened from approximately 396 to 416 feet bgs and from 496 to 536 feet bgs, with a gravel pack installed from approximately 35 to 540 feet bgs The static water level in the water K SBp Arco for URS16100VReports16100 assessment rpt&scm update doe Page 8 5TKA TU5