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' S E C 0 R 4.0 GEOLOGIC AND HYDROGEOLOGIC SETTINGS Generalized geologic cross-sections for the area are presented in Figure 4 and depict the following conditions • Interbedded layers of sand/silt mixtures and clay/silt mixtures encountered from ground surface to approximately 120 feet bgs • Interbedded layers range in thickness from approximately 5 to 20 feet R ' Groundwater is generally encountered at approximately 30 feet bgs and appears to be an unconfined aquifer ; Lithology beneath the site generally consists of fine-grained silts and clay from ground surface to approximately 20 feet bgs, from 30 to approximately 60 feet bgs, 85 to 100 feet bgs, and approximately 115 to 120 feet bgs Silty sands and sands are generally present at the intervals of 20 to 30 feet bgs, 60 to 85 feet bgs, and 100 to 115 feet bgs Depth-to-groundwater has varied from approximately 24 to 34 feet bgs since the installation of monitoring wells began in 2000 Depth-to-groundwater encountered during drilling has been ' approximately 30 feet bgs indicating that the groundwater aquifer is unconfined Soil samples h1 collected from first encountered groundwater to the total depth explored of 120 feet bgs have generally been classified as very moist to wet indicating the presents of a single aquifer No confining layers have been encountered in soil borings advanced at the site Wells have beeng, ' installed in three zones at the site Groundwater elevation contour maps for each groundwater 17 monitoring zone are included as Figures 5 through 7 P� A Monitoring Zone Wells - A monitoring zone wells (MW-1 through MW-4) have been installed to depths of 50 (MW-1) and 45 feet bgs (MW-2, MW-3 and MW-4) and each of the A monitoring zone wells has 20 feet of screen A monitoring zone wells are installed in the upper portion of the aquifer and are generally installed into the silt and clay layer present at 45 to 50 feet bgs with well screens extending into the more coarse grained material (sand and silty sand) present from 20 to 30 feet bgs B Monitoring Zone Wells " Ten B monitoring zone wells (MW-5 through MW-14) have been installed at the site to depths , ranging from 79 to 83 feet bgs with well screens ranging in length from 5 to 10 feet B monitoring zone wells have been installed in the sand and silty sand generally present at 80 feet ' bgs C Monitoring Zone Wells Three C monitoring zone wells (MW-15 through MW-17) have been installed at the site to ' depths ranging from 120 to 121 feet bgs with 10 feet of well screen C monitoring zone wells s4,µ have been installed in the silty sand from 110 to 115 feet bgs and the sandy silt and clay from 115 to 120 feet bgs h 1 �tip1 Updated SCM 2005 doc 95, 77Cp 64409 05 0005 Yyt t