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to the northwest toward the San Joaquin River. <br /> ' Recharge to the upper water bearing zones occurs primarily by direct infiltration of <br /> water from precipitation,irrigation, and seepage from canals and streams. Recharge to <br /> ' the lower water-bearing zone is caused by infilitration from the upper zones because of <br /> differences in head elevations. <br /> 2.4.2 Local Ground-Water Occurrence and Movement <br /> Two ground-water aquifers have been identified on site: (1) a shallow perched aquifer <br /> within the Corcoran Clay, considered to be unconfined,and(2) a deep regional aquifer <br /> ' which may be semiconfined to confined. <br /> ' The shallow perched aquifer is located in the upper half of the Corcoran Clay. This <br /> shallow perched zone was suspected in October 1987, while drilling deep Monitoring <br /> ' Well MW-1. This shallow perched zone was confirmed by the installation of <br /> Monitoring Well MW-4 in May, 1988. The shallow perched aquifer does not appear to <br /> ' be extensive; rather, it is confined to the eastern half of the landfill (see Drawing 4). <br /> Ground water Monitoring Wells MW-5 and SB-1 are also installed in the shallow <br /> perched aquifer. This aquifer is not present at SB-2. Groundwater in the shallow <br /> ' perched aquifer appears to be mounded near Monitoring Well SB-1; the flow occurs <br /> both northwest and southeast with a gradient of 0.01. Additional water level <br /> 1 measurements are required to confirm this flow direction as there may be significant <br /> seasonal variations. <br /> ' Ground water in the shallowPP erched aquifer a ears to be restricted to the thin 0.01- <br /> P <br /> ' inch) sandy interlayers that occur in the upper portions of the Corcoran Clay. Recharge <br /> to the zone probably occurs by infiltration from the overlying sediments into the <br /> Corcoran along the thin interbedded sand lenses. The absence of the interbedded sand <br /> ' lenses in the lower half of the Corcoran restricts further vertical movement of ground- <br /> water and causes the perched ground-water condition. <br /> Groundwater in the deep regional aquifer on site generally flows southeast (see <br /> 1 Drawing 5). This deviation from the regional trend (toward the northwest) was <br /> i <br /> STL 9390314 1 0 >:TT1eOf10 As��c73o�e <br />