ARCHIVED REPORTS_SEMI-ANNUAL GROUNDWATER MONITORING REPORT AUGUST 2010

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ame&y 2.2 SITE SPECIFIC Site-specific lithologic and hydrogeologic information for the Facilities is presented in the following subsections. 2.2.1 Lathrop Facility At the Lathrop facility, soil was reported to be composed of interbedded silty sand, sandy silt, and clayey silt from ground surface to a depth of approximately 20 feet. During the installation of groundwater monitoring wells LPW-1, LPW-2, and LPW-3, groundwater was reportedly encountered in the well borings at depths between 19 and 21 feet in sand (borings LPW-1 and LPW-3) and clayey sand (boring LPW-2). Below the sandy soils, a clayey silt and silty clay was reported at depths of approximately 22.5 feet (boring LPW-3) and 26 feet (boring LPW-2). Sediments encountered during the November 2007 investigation in borings LP-G8, LP-G9, LP-G10, and LP-G11 consisted primarily of sand, clayey sand, clay, and silt to depths ranging from 20 to 25 feet (Geomatrix, 2007a). During the November 2007 investigation, groundwater was observed at depths of 18.5, 19.0, 16.0, and 16.0 feet bgs in borings LP-G8, LP-G9, LP-G10, and LP-G11, respectively (Geomatrix, 2007a). A summary of the static groundwater level measurements collected during previous groundwater monitoring events and calculated groundwater elevations for the Lathrop facility is provided on Table 1. Historic groundwater monitoring data at the Lathrop facility has indicated a groundwater flow direction generally to the north-northeast at a gradient between 0.002 feet/foot (ft/ft) and 0.005 ft/ft, with an increase in the calculated gradient to 0.008 ft/ft in May 2006 (Geomatrix, 2005b, 2006b, 2006c, 2007b; URS, 2004b). In November 2007, the calculated gradient (0.001 ft/ft) was less than the historical gradients but the groundwater flow direction (northeasterly) was consistent with historical flow directions (Geomatrix, 2007c). In August 2010, the calculated gradient (0.004 ft/ft) and the groundwater flow direction (north- northeasterly) were consistent with historical gradients and flow directions. 2.2.2 French Camp Facility Soil was reported by URS to be composed of interbedded silty sands, clayey silts, and silty clays to a depth of approximately 28 feet. During the installation of groundwater monitoring wells FCW-1, FCW-2, and FCW-3, groundwater was reportedly encountered in the borings at depths of approximately 26 and 28 feet in a sand to silty sand zone. Sandy clay and clayey silt were encountered at a depth of approximately 28.5 feet in well boring FCW-3. Sediments encountered during the January 2006 investigation in borings FC-G8, FC-G9, and FC-G10 consisted primarily of sand, silty sand, clay, and silt to a depth of 31 feet (Geomatrix, 2006a). During the January 2006 investigation, groundwater was observed at depths of AMEC Geomatrix, Inc. P:\10626.000.0\Docs\Semi-Annua1 Groundwater Monitoring&Sampling\Semi-Annual 1-10 4