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• <br /> ' 4 0 GEOLOGIC AND HYDROGEOLOGIC SETTINGS <br /> A regional geologic cross-sections for the area is presented in Figure 4 and depict the following <br /> ' conditions <br /> • Interbedded layers of sand/silt mixtures and clay/silt mixtures encountered from <br /> ' ground surface to approximately 120 feet bgs <br /> • Interbedded layers range in thickness from approximately 5 to 20 feet <br /> • Groundwater is generally encountered at approximately 30 feet bgs and appears to <br /> be an unconfined aquifer <br /> Lithology beneath the site generally consists of fine grained silts and clay from ground surface <br /> ' to approximately 20 feet bgs, from 30 to approximately 60 feet bgs, 85 to 100 feet bgs, and <br /> approximately 110 to 120 feet bgs Silty sands and sands are present at the intervals of 20 to <br /> 30 feet bgs, 60 to 85 feet bgs, and 100 to 110 feet bgs <br /> Depth to groundwater has varied from approximately 24 feet to 34 feet below ground surface <br /> since the installation of monitoring wells began in 2000 Depth to groundwater encountered <br /> ' during drilling has been approximately 30 feet bgs indicating that the groundwater aquifer is <br /> unconfined Soil samples collected from first encountered groundwater to the total depth <br /> explored of 120 feet bgs have generally been classified as very moist to wet indicating the <br /> presents of a single aquifer No confining layers have been encountered in soil borings <br /> advanced at the site Both shallow and deep wells have been installed at the site <br /> Shallow Wells <br /> Shallow wells (MW-1 through MW-4) have been installed to depths of 50 (MW-1) and 45 feet <br /> bgs (MW-2, MW-3 and MW-4) and each of the shallow wells has 20 feet of screen Shallow <br /> well are installed in the upper portion of the aquifer and are generally installed into the silt and <br /> clay layer present at 45 to 50 feet bgs with well screens extending into the more coarse grained <br /> material (sand and silty sand) present from 20 to 30 feet bgs <br /> ' Deep Wells <br /> Ten deep wells (MW-5 through MW-14) have been installed at the site to depths ranging from <br /> 80 to 83 feet bgs with well screens ranging in length from 5 to 10 feet Deep wells have been <br /> installed in the sand and silty sand generally present at 80 feet bgs <br /> The general hydraulic gradient at the site in both the shallow and deep zones has been reported <br /> ' to the northeast Depth to groundwater measurements are included in Tables 3 and historical <br /> gradient table is included as Table 4 <br /> 1 <br /> Updated SCM doc 6 August 13,2004 <br /> ' 77CP 64409 05 0005 <br />