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George's Service • <br /> Remedial Action Work Plan <br /> Project No.425.2 <br /> June 30,2011 <br /> 3.4. Hydrology of Site <br /> 3.4.1. Zone Divisions <br /> To define the site more accurately, the aquifer is divided into four zones (Zones A through <br /> D) defined by the screen intervals of the sixteen monitoring wells associated with the Site. <br /> Zone divisions and well construction are summarized in Table 1 of appendix A. <br /> • Zone A <br /> o monitoring wells screened between 5 and 22-feet bgs. <br /> o average groundwater elevation for the April 26, 2011 groundwater monitoring <br /> event was 72.69 feet AMSL. <br /> o Zone A groundwater bearing and slope averages NI PE at 0.0028 ft/ft. <br /> • Zone B <br /> o monitoring wells screened between 32 and 35-feet bgs. <br /> o average groundwater elevation for April 26, 2011 groundwater monitoring <br /> event was 72.99 feet AMSL. <br /> o Zone B groundwater bearing and slope averages northwest at 0.0052 ft/ft. <br /> • Zone C <br /> o monitoring wells screened between 45 to 49.5-feet bgs. <br /> o average groundwater elevation for April 26, 2011 groundwater monitoring <br /> event was 72.78 feet AMSL. <br /> o Zone C groundwater bearing and slope averages N290E at 0.0087 ft/ft. <br /> 0 <br /> • Zone D <br /> o MW-202 screened between 79 and 81.5-feet bgs <br /> o groundwater elevation for April 26, 2011 groundwater monitoring event was <br /> 72.72 feet AMSL. <br /> 3.4.2. Vertical Groundwater Gradients <br /> Several sets of vertical groundwater gradients have been estimated historically: <br /> • MW-2/MW-2X and MW-2X/MW-202 (Table 6A) <br /> Historical vertical groundwater gradient calculations for the area around MW-2 have <br /> been performed at regular intervals since August 25, 1997 and are generally positive. <br /> • MW-6/MW-106 and MW-7/MW-107 (Table 6B) <br /> Historical vertical groundwater gradient calculations north of Durham Ferry Road <br /> suggest that Zone A is not mixing with the lower zones in the aquifer. <br /> • MW-1/MW-101, MW-l/MW-201 and MW-101/MW-201 (Table 6C) <br /> Historical vertical groundwater gradient calculations up gradient of the plume suggest <br /> that Zone A is not mixing with the lower zones in the aquifer. The calculations <br /> indicate there may be mixing between Zones B, C,and D. <br /> Creologfcal recIMICS mc. 6 <br /> 4252 RAP.docx <br />