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PRE-TANK REPLACEMENT SITE ASSESSMENT WORK PIAN <br /> 1071 North Main Street,Manteca,California <br /> �wr <br /> Cretaceous sandstones and shales overlay pre-Cretaceous ultra basic igneous rocks, <br /> granitic rocks, and metamorphosed sedimentary and volcanic rocks. Sediments <br /> two originating from the Sierra Nevada and the Coast Ranges were deposited in a marine <br /> environment during the Cretaceous and the Pleistocene periods. Interruptions in the pre- <br /> Pleistocene sedimentary depositional cycle occurred several times as volcanic activity, <br /> -• uplift, faulting and/or folding altered the region. From the Pleistocene to the Present, <br /> deposition has been alluvial. <br /> The subject site is situated near the axis of the San Joaquin trough. Recent Alluvium and <br /> the Victor Formation overlay the Laguna Formation. The Laguna Formation consists of <br /> clay and sand units and unconformable overlays the andesitic sediments of the Mehrten <br /> Formation. From the Pleistocene to the present, the depositional environment has been <br /> alluvial. Several thousand feet of unconsolidated silty, sandy and gravelly sediments lie <br /> within the basin (DWR 1967). <br /> V <br /> 2.10 Regional Hydrogeology_ <br /> Three water-bearing formations have been identified beneath the subject area including <br /> the Mehrten Formation, the Laguna Formation and the Victor Formation. Groundwater <br /> occurs in the Mehrten Formation under semi-confined conditions. Wells that penetrate <br /> the Mehrten Formation yield as high as 1000 gallons per minute (gpm). <br /> Groundwater occurs within the Laguna and Victor Formations under both unconfined and <br /> semi-confined conditions. Yields as high as 1500 gpm have been reported from wells <br /> penetrating the Laguna Formation (DWR 1967). <br /> ar <br /> 2.11 Water Well Information <br /> A water well search conducted through the State of California Department of Water <br /> Resources indicates that four water wells exist within a 1/2 mile radius of the site. The <br /> locations of local water and groundwater monitoring wells are shown on Figure 4. <br /> 4 <br /> iwr <br /> rr <br /> low <br /> 91-013A.RPT 5 <br /> v <br />