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Section 8 <br />Groundwater Quality <br />Investigation of Groundwater Quality Near the Underground Workings <br />This investigation evaluated groundwater quality in close proximity to the <br />underground mine workings. Additional data will be collected from wells installed in <br />this investigation, and only preliminary data analyses are presented here. The <br />primary purpose of this investigation is evaluation of ambient groundwater quality. <br />The investigation also attempted to evaluate the persistence of any mining-related <br />affects to groundwater downgradient from the underground mine workings. <br />However, this information was not obtained in the investigation as a result of the <br />proximity of the underground monitoring wells in relation to the mine dewatering <br />system. <br />Ambient groundwater quality is defined in HRMMR 1.1(5) as follows: <br />"Ambient Groundwater Quality" for mining operations permitted prior to <br />January 31, 1994, Ambient Groundwater quality shall mean the quality of the <br />groundwater at the mine site as of 1994. For mining operations permitted on <br />or after January 31, 1994, ambient groundwater shall mean the quality of <br />groundwater at the time of submittal of the permit operation. In establishing <br />ambient groundzvater quality, an Operator or Applicant shall use available or <br />collected groundwater data sufficient to characterize the site's ambient <br />groundzvater quality and submit such information in a form suitable to the <br />Office. <br />. The Sunday Mines Group has been in existence since the mid 1950s, and the vast <br />majority of underground mine development occurred prior to 1994. It is unlikely that <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 with 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 the area of planned well installation. Denison worked to improve <br />ventilation in this area of the underground workings to address this issue. Following <br />successful radon gas mitigation, four monitoring wells were installed in the West <br />Sunday underground workings during the week of December 15, 2008. <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 />8-2 <br />TA64986-Denison Mines\Task Order 4 - EPP Sunday Mines Group\FINAL EPP\FINAL - Environmental Protection Plan Sunday Mines.doc