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Hydrogeological Evaluation of Sunday Mines Group <br />Geologic and Hydrologic Conditions <br />. current groundwater quality is significantly different than conditions on January 31, <br />1994. Therefore, the groundwater quality measured in this investigation is thought to <br />best represent ambient conditions at the Sunday Mines Group. <br />Monitoring well installation activities were initially scheduled for September 2008 but <br />were delayed because of the need for additional mine development activities, which <br />improved the ventilation system to address radon concentrations in the area of <br />planned well installation. Denison improved ventilation in this area of the <br />underground workings to address this issue. Following successful radon gas <br />mitigation, four monitoring wells were installed in the underground workings during <br />the week of December 15, 2008. <br />As described in the hydrogeologic work plan (CDM 2008e), the monitoring wells <br />were installed in sub-horizontal underground boreholes. The boreholes were drilled <br />using an underground drilling rig, and were installed at an angle of minus 20 degrees <br />from horizontal. Figure 2-14 is a diagram of the well installations, and Figure 2-15 <br />shows the location of the underground well nest in the West Sunday Mine. The wells <br />were installed to facilitate collection of groundwater from a discrete interval in each <br />bore hole. A packer assembly inflated with nitrogen gas is located at the top of the <br />screened interval to facilitate sampling groundwater from the aquifer at the specified <br />interval. One well was installed north of the underground workings, with a screened <br />interval extending from 43 to 63 ft. Three wells were installed south of the <br />underground workings with screened intervals of 13 to 23 ft., 18 to 28 ft., and 33 to 43 <br />ft., respectively. Dedicated tubing was installed in the wells to facilitate sampling with <br />a peristaltic pump. <br />Minor field modifications of initial designs were necessary to facilitate well <br />installation. The primary modifications included the following: <br />¦ Reduced Well Completion Depths: A reduction in the well completion depths were <br />necessary because of repeated bore hole collapse during installation. The tendency <br />for the borehole to collapse was a result of the orientation being too close to the dip <br />of the rock units and the corresponding bedding plane discontinuities. <br />¦ Installation of Well Heads Above the Water Table: Well heads were installed at an <br />elevation that is several feet above the groundwater table, because of access <br />restrictions within the underground workings. Although the well heads are located <br />in an unsaturated portion of the mine, using the -20 degree installation technique, <br />the well screens for wells WS-2, WS-3, and WS-4 were completed in saturated <br />portions of the subsurface. It appears that the screened interval for well WS-1 is <br />only partially saturated, which adversely affects performance of the well. <br />¦ Installation of One Well North of Underground Workings: The hydrogeologic <br />work plan identified two wells to be installed to assess water quality conditions <br />north of the underground workings. However, during well installation activities, <br />cm 2-22 <br />T:\64986-Denison Mines\Task Order 3 - DMO Sampling and Analysis Plan\Task 3.14 - Hydrogeology Report\linal sunday hydro reporWeXhFINAL Sunday Hydrogeology Report.doc