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. LOCAL GEOLOGY AND HYDROGEOLOGY <br /> The excavation created during tank removal revealed a relatively <br /> flat lying sequence of clay, clayey sandy silt, and silty sands to <br /> a depth of 14 feet below the surface. Exploratory borings <br /> performed on site investigated the subsurface to 60 feet below the <br /> surface. These borings revealed a clayey, silty sand <br /> approximately ten feet thick at 25 feet below the surface of the <br /> site. Another silty sand is found to exist at approximately the <br /> 45 foot depth and extends to the 60 foot depth. Ground water was <br /> encountered in this second sand at approximately 47 feet below the <br /> surface. <br /> Ground water was encountered in soil boring SB2 and monitor wells <br /> KWI, MW2, KW3, and MW4 at approximately 47 feet below the surface. <br /> The ground water depth was measured from the surface in the <br /> borings, and from the top of the casing in the monitor wells. <br /> Ground water flow directions were interpreted from the ground <br /> water gradient that was produced from measurements taken from the <br /> monitor wells. The local gradient follows what was Zescribed <br /> earlier in Regional Geology and Hydrogeology in that it flows to <br /> the southeast, towards downtown Stockton. <br /> WELL RECONNAISSANCE <br /> A reconnaissance of all wells within a half mile radius of the <br /> site was undertaken by WEGE. This reconnaissance was performed by <br /> reviewing the State Department of water Resources well files and <br /> visual inspections near the site (see figure 2A and Table 5) . <br /> The ground water sampled from monitor wells at this site is in the <br /> uppermost (shallowest) aquifer of a flood basin and/or alluvium <br /> fan deposit and is most likely associated with the Victor <br /> formation. Due to the limited thickness of this aquifer and the <br /> younger overlaying formations, most wells in the area produce <br /> their water from deeper sources (Laguna and Hehrten formations) . <br /> The quality of the different aquifers situated in the Stockton <br /> area iu depended upon several factors% <br /> A. The area of recharge. <br /> B. Time, length, and route of water migration. <br /> C. The quality of the overlaying aquifer. <br /> D. Man made obstructions, such as wells, drainages, etc. j <br /> There are no true aquitards within the Stockton area that have <br /> shown the capabilty to block the downward movement of ground water <br /> from one aquifer (sand/gravel formation) to the next. lin <br /> overdraft situation in this area has enhanced this downward <br /> migration and is associated with the steady decrease in ground <br /> water quality due to the intrusion of the more saline water of the <br /> Delta infiltrating the various shallow aquifers. <br /> Ground nater in the Stockton area is suitable for domestic, <br /> 17 <br />