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amee <br /> Based on the GMP, AMEC Geomatrix conducted the following tasks during the August 2010 <br /> semi-annual groundwater monitoring event: <br /> • measured water levels in the groundwater monitoring wells and assessed the <br /> groundwater flow direction at the Facilities; <br /> • purged the groundwater monitoring wells and collected groundwater samples from <br /> each monitoring well for laboratory analysis; <br /> • analyzed the groundwater samples for diesel-range total petroleum hydrocarbons <br /> (TPH-diesel) by Environmental Protection Agency (EPA) Method 8015M, total and <br /> dissolved Cr by EPA Method 6010B, and dissolved Cr VI by EPA Method 7199; <br /> • compared groundwater laboratory results to the RWQCB WQG for TPH-diesel at <br /> 100 pg/L and the CDPH MCL for Cr at 50 pg/L (as defined in the Order); and <br /> • prepared this semi-annual groundwater monitoring repo,i. <br /> 2.0 BACKGROUND GEOLOGY AND HYDROGEOLOGY <br /> Regional and site-specific lithologic and hydrogeologic information for the Facilities was <br /> presented in the November Semi-Annual 2004 Groundwater Monitoring Report prepared by <br /> URS (2004a). For the purpose of this groundwater monitoring report, this section briefly <br /> describes site-specific geology and hydrogeology conditions as presented by URS (2004a). <br /> 2.1 REGIONAL <br /> The Facilities are located in the San Joaquin Valley of the Central Valley geomorphic province, <br /> which is a large, northwest-trending, asymmetric structural trough composed of interlayered <br /> gravels, sands, silts, and clays derived from the adjacent mountains and deposited in alluvial <br /> fan, fluvial, lacustrine, and marsh environments (USGS, 1986). The San Joaquin Valley is <br /> bounded by the Coast Ranges to the west, the Delta to the north, the Tehachapi Mountains to <br /> the south, and the Sierra Nevada Mountains to the east. <br /> The Facilities are located within the San Joaquin Hydrologic Basin (Department of Water <br /> Resources [DWR], 1975). The hydrogeologic units consist of consolidated rocks of the Victor <br /> Formation, the Laguna Formation, and the Mehrten Formation, and unconsolidated deposits <br /> composed of fluvial, lacustrine, and marsh deposits. The unconsolidated deposits are the <br /> main water-bearing formations in the basin. Regional groundwater flow in this area is <br /> reportedly to the north, northwest, and northeast (San Joaquin County Flood Control and <br /> Water Conservation District, 1999). <br /> AMSC Geomatrix, inc. <br /> PA10626.000.0\Docs\Semi-Annua1 Groundwater Monitoring&Sampling\Semi-Annual 1-10 3 <br />