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Geosyntec° <br /> consultants <br /> 2. SITE BACKGROUND <br /> This section presents a summary of the regional and local geology, hydrogeology, and a <br /> summary of historical operations. For a more detailed discussion on the history of the <br /> site and the subsurface conditions, refer to the Remedial Investigation Report (LFR <br /> Levine-Fricke [LFR], 1999) and the Revised Draft Feasibility Study(LFR, 2002). <br /> 2.1 GEOLOGY AND HYDROGEOLOGY <br /> This section provides a summary of the geology and hydrogeology at the site and the <br /> surrounding vicinity. <br /> 2.1.1 Regional Geology and Hydrogeology <br /> 2.1.1.1 Regional Geology <br /> The city of Stockton is located within the central portion of the Great Valley <br /> geomorphic province of California. The Great Valley is an asymmetrical, structural <br /> trough that consists of alluvium and flood plain deposits transported from the flanking <br /> Sierra Nevada Mountain Range to the east and Coast Range to the west. Geology in the <br /> Stockton area generally consists of the unconsolidated alluvial and flood plain deposits <br /> of the Modesto Formation. The Modesto Formation consists of a heterogeneous mix of <br /> generally poorly sorted clay, silt, sand, and gravel with some beds of claystone, <br /> siltstone, sandstone, and conglomerate. These units are discontinuous and have <br /> considerable lateral and vertical variability(LFR, 1999). <br /> 2.1.1.2 RegionalHydrogeology <br /> The site is located within the Eastern San Joaquin groundwater basin. Groundwater <br /> elevations within San Joaquin County range from 170 feet above mean sea level (msl) <br /> in the northeastern corner of the county to 50 feet below msl near the center of the <br /> county and east of Stockton. Groundwater throughout San Joaquin County generally <br /> flows towards the central groundwater depression. Within the city of Stockton, <br /> groundwater elevations range from 0 feet above msl to 40 feet below msl and <br /> groundwater generally flows in an east-northeast direction towards the depression <br /> located outside the city limits (San Joaquin County Flood Control and Water <br /> Conservation District, 2012). <br /> Pre-Design Investigation Work Plan 3 18.05.12 <br />