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3 INVESTIGATION FINDINGS <br /> H dro eolo ical setting, soil sample analytical results and groundwater sample <br /> analytical results are described in the following sections <br /> 3.1 Hydrogeology <br /> Subsurface soils encountered in the vicinity of the Site are primarily <br /> comprised of silt and clay to at least 50 feet (see Figure 3 and Figure 4) <br /> Generally, these silty clay and clayey silt soils are olive or brown in color to <br /> about 35 feet, underlain by a dark gray layer Clayey soils were observed to be <br /> moderately stiff to stiff with moderate plasticity <br /> A relatively thick sequence of fine-grained sand and gravel was observed <br /> from about 20 feet to 35 feet in the MW-3 boring The top of a fine-grained <br /> sand layer was observed at a depth of about 50 feet in probeholes PH-1 and <br /> PH-2 where these borings were terminated Coarser materials were generally <br /> not observed at any other location <br /> A discrete groundwater bearing zone was not readily apparent in any of the <br /> borings, even those continuously cored, with the possibility of those drilled <br /> for MW-1 and MW-3 as reported by GZA Initial groundwater was reported <br /> to be observed in MW-1 and MW-3 borings at about 23 feet However, first <br /> groundwater was observed in most of the borings at a depth of 30 to 35 feet <br /> This groundwater was typically slow to yield from the silty clay matrix <br /> Groundwater eventually rose under pressure within the borings to a depth of <br /> about 23 to 25 feet, suggesting localized confined conditions <br /> Groundwater was not observed in the initial PH-1 and PH-2 probeholes until <br /> about 50 feet It is thought that the driven Geoprobe rods may have smeared <br /> or concealed a higher water-bearing zone Groundwater was never observed in <br /> the PH-3 boring <br /> Based on levels measured on March 28, 2002 (Table 1), groundwater flows <br /> east-southeast, from the former UST area towards the 1725 El Dorado Street <br /> traffic island (see Figure 5), at a gradient of about 0 0026 ft/ft - <br /> 3.2 Subsurface Soil Conditions <br /> Generally, BTEX concentrations in soil samples collected above the <br /> groundwater table were relatively low The highest benzene concentration <br /> measured in soils collected at a depth above the groundwater table was 0 2 <br /> milligrams per kilogram (mg/kg) from the 25 feet sample at PH-1 The highest <br /> II <br /> March 2002 <br /> Subsurface Site Investigation <br /> 1717 South Center Street-Stockton Cahfomia <br /> Prepared by Philip Services Corp <br /> 1 H5£NW240013Z123762£G\Projecu\StockCmt4narch2002mvesttgadon doc May 14,2002 <br />