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y <br /> lECOR <br /> bFi <br /> .h <br /> 4.0 GEOLOGIC AND HYDROGEOLOGIC SETTINGS <br /> IRegional geologic cross-sections for the area are presented in Figure 3, 4, and 5 and <br /> depict the following conditions: <br /> • Interbedded layers of sand/silt mixtures and clay/silt mixtures encountered <br /> from the ground surface to approximately 75 feet bgs. <br /> Interbedded layers range in thickness from approximately 5 to 35 feet. <br /> • Sand/silt lenses and clay/silt lenses range in thickness from approximately 5 <br /> to 10 feet. <br /> I • Groundwater is generally encountered at approximately 10 to 15 feet bgs and x <br /> appears to be an unconfined aquifer. <br /> Depth to groundwater has varied from approximately 10 feet to 15 feet below ground <br /> I surface since the installation of monitoring wells began in 1998. Soil samples collected <br /> from first encountered groundwater to the total depth explored of 75 feet bgs have <br />' generally been classified as saturated at times even within the fine-grained strata. This, <br /> and the behavior of water levels, suggests the presence of a single aquifer. <br /> ,i <br /> 10 Shallow Wells <br /> Shallow wells (MW-1 through MW-3) have been installed to depths of 26, 26.5, 28 and w <br /> 28 feet bgs, respectively. Shallow wells (MW-5 through MW-19) have been installed to a <br /> z <br /> depth of 25 feet bgs. Each well has approximately 20 feet of screen. The shallow wells <br /> are installed in the upper portion of the aquifer, and are generally installed into the silt <br />' and clay layer present at 15 to 40 feet bgs with well screens extending into the more <br /> coarse grained material (sand and silty sand). <br /> A historical groundwater gradient data is included at Table 6. <br /> PM1 <br /> "R? <br /> R <br /> A}J <br /> ttg <br /> e�I <br /> 1205 SCM.doc <br />