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GEOMATRIX <br /> 2.1 AREA TOPOGRAPHY <br /> Area topography is portrayed on Figure 1,based on the "Stockton West, California" base map <br /> (USGS, 1968,photo revised 1987). This figure shows a relatively flat topography that <br /> generally grades to the west. The elevation of the HCC facility is shown at about 5 feet above <br /> mean sea level (msl). <br /> ' Based on visual observations West Charter Way and Tillie Lewis Drive are higher in elevation <br /> than the HCC facility and based upon previous observations of rainfall at the site, drainage is <br /> toward the northern portion of the facility. <br /> ' 3.0 GEOLOGY/HYDROGEOLOGY <br /> The HCC facility is located within the San Joaquin River watershed, near Stockton, California, <br /> ' which runs northwest/southeast approximately 2700 feet west from the facility. Geomatrix has <br /> reviewed readily available soil and groundwater references in order to prepare this work plan. <br /> The following subsections summarize that information. <br /> ' 3.1 SOIL <br /> Soil in the vicinity of the HCC facility is described as the Stockton Clay Adobe in the "Soil <br /> Survey, Stockton Area, California" (USDA, 1981). Surface investigation conducted in the <br /> ' vicinity of the site by Geomatrix indicates surficial soils are comprised of primarily clays and <br /> silts with interbedded sand lenses. <br /> t3.2 REGIONAL AND LOCAL HYDROLOGY <br /> ' The facility is located on the lower flood plain of the San Joaquin River near the San Joaquin <br /> River Delta. According to the San Joaquin County Flood Control and Water Conservation <br /> t District, the depth to groundwater is highly variable in the Stockton area, ranging from less <br /> than 10 feet to more than 190 feet below ground surface (bgs). The Stockton area is located <br /> adjacent the San Joaquin River Delta and is influenced by ocean tides and salt water intrusion <br /> ' up San Francisco Bay and into the river delta region. Regional groundwater flow is <br /> predominantly eastward from the river delta area, but is influenced by pumping activities. <br /> ' Results of previous investigation in the site vicinity indicated first groundwater to be present at <br /> ' depths ranging from 4 feet to 16 feet bgs. Groundwater elevation data indicate that <br /> groundwater flow is predominantly eastward. <br /> ' \\fr2\deptdam\PROJECI\C5193\5193.001\5193.001-SAWP.doc 2 <br />