Laserfiche WebLink
Monitoring well installation within the West Sunday Mine was initially scheduled for <br />September 2008 but was delayed because of the need for additional mine <br />development activities, which improved the ventilation system to address radon <br />concentrations in air within the area of planned well installation. Denison worked to <br />improve ventilation in this area of the underground workings to address this issue. <br />Following successful radon gas mitigation, four monitoring wells were installed in the <br />West Sunday underground workings during the week of December 15, 2008. <br />Section 8 <br />Groundwater Quality <br />These monitoring wells were installed in sub - horizontal underground boreholes. The <br />boreholes were drilled using an underground drilling rig, and were installed at an <br />angle of minus 20 degrees from horizontal. Figure 8 -1 shows the location of the <br />underground well nest in the West Sunday Mine. The wells were installed to facilitate <br />collection of groundwater from a discrete interval in each bore hole. A packer <br />assembly inflated with nitrogen gas is located at the top of the screened interval to <br />facilitate sampling groundwater from the aquifer at the specified interval. One well <br />was installed north of the underground workings, with a screened interval extending <br />from 43 to 63 ft. Three wells were installed south of the underground workings with <br />screened intervals of 13 to 23 ft., 18 to 28 ft., and 33 to 43 ft., respectively. Dedicated <br />tubing was installed in the wells to facilitate sampling with 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 <br />was necessary because of repeated borehole collapse during installation. The <br />tendency for the borehole to collapse was a result of the bore -hole orientation <br />being close to the dip of the rock units and the corresponding bedding plane <br />discontinuities. <br />• Installation of Well Heads above the Water Table: Well heads were installed <br />at an elevation that is several feet above the groundwater table, because of <br />access restrictions within the underground workings. Although the well heads <br />are located in an unsaturated portion of the mine, using the -20 degree <br />installation technique, the well screens for wells WS -2, WS -3, and WS -4 were <br />completed in saturated portions of the subsurface. It appears that the screened <br />interval for well WS -1 is only partially saturated, which adversely affected <br />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 <br />conditions north of the underground workings. However, during well <br />installation activities, the second well could not be installed because that <br />portion of the mine is no- longer saturated as a result of on -going mine <br />dewatering activities. <br />Groundwater samples were initially scheduled to be collected immediately following <br />purging of the newly installed wells in the underground workings (e.g., December <br />C \Users\cwoodward\Desktop \Sundays \FINAL - Environmental Protection Plan Sunday Mines Revised January 2012 docz <br />8 -3 <br />