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fE <br /> I <br /> l ' <br /> IV. HYDROGEOLOGIC SETTING <br /> The :site Is located within the Tracy Groundwater Basin, which is part. of the San <br /> I' Joaquin Valley Groundwater Basin. According to the site asset' sment_study for the Tracy <br /> Defense Depot (TDD) about 5 miles southeast of the site, there are two primary aquifers <br /> that have been identified in then <br /> San Joaquin Valley. The upper aquifer is found above <br /> I'k The Corcoran Clay Member of. the Tulare Formation, and the lower aquifer Is found on <br /> the lower section of the Tulare. Groundwater in the upper aquifer is under variable <br /> confinement conditions as a result of the variable nature of the stratigraphy. On a <br /> regional basis, the upper aquifer extends from approximately 15 to 250 feet below ground <br /> surface. Groundwater flow in the upper aquifer is reportedly to the northeast. The lower <br /> aquifer Is approximately 600 feet below ground surface and is confined by the overlying <br /> Corcoran Clay, <br /> We reviewed groundwater data for the properties nearby and adjacent to the site. <br /> Reports for the Interstate 205 corridor, located along the southeast boundary of the site <br /> (Earth Systems Consultants, 1987) and the Lammersvifle School, 2 miles west of the site <br /> (Groundwater Technology Inc. 1987), indicate that groundwater at each site was <br /> encountered at a depth of 8 feet. A hydraulic gradient down to the northeast was <br /> defined at the Lammersvllle School site. Additional information provided by the San <br /> Joaquin County Office of Flood Control and the Department of Environmental Health <br /> indicates groundwater In the study area associated with the upper aquifer Is at a depth <br /> of 5 to 15 feet below ground level. <br /> R:604.09N . - 5 - 6/1/89 <br /> i <br />