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Hydrogeological Evaluation of Sunday Mines Group <br />Geologic and Hydrologic Conditions <br />the second well could not be installed because that portion of the mine is no-longer <br />saturated as a result of on-going mine 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 />2008). However, the recharge rate of the newly installed wells was relatively low <br />which resulted in a short delay in the scheduled sampling. The low recharge rate is <br />indicative of relatively low permeability of the aquifer. During the week of December <br />22, 2009, Denison was scheduling to reenter the underground workings to purge the <br />wells and collect groundwater samples. At that time, concentrations of radon gas <br />exceeding permissible levels were again present in the underground workings and <br />sampling activities could not be completed. Again, during the week of January 5, <br />2009, groundwater sampling activities were planned but were delayed due to high <br />concentrations of radon gas in the subsurface. Following modifications to the mine <br />ventilation system, Denison successfully completed well purging and sampling <br />activities during the week of February 23, 2009. A second round of samples was <br />collected during the week of March 17, 2009. <br />Groundwater samples were submitted to Energy Laboratory in Casper, Wyoming for <br />laboratory analysis. Laboratory analytical data is provided in Appendix A, and the <br />data are summarized in Table 2-6. As described in the hydrogeologic work plan, the <br />groundwater samples were analyzed for all parameters requested in the May 9, 2008 <br />DRMS letter to Denison (DRMS 2008b). <br />The groundwater quality data show that the groundwater is relatively saline with <br />total dissolved solids (TDS) content ranging from 1,300 mg/ L to 6,990 mg/ L. The <br />groundwater also contains uranium and vanadium, which are the primary ore metals <br />in the mine, and several other elements that are naturally enriched in rocks at the <br />Sunday Mines Group including arsenic, molybdenum and selenium. The presence of <br />these elements in groundwater in close proximity to the underground workings is <br />thought to be related to naturally occurring enrichments of metals, and development <br />of equilibrium conditions between the ore minerals and the local groundwater. As <br />discussed previously, underground mine development activities such as tunneling, <br />excavating rock, and ventilating the underground workings may also affect the <br />concentration of the naturally enriched elements in groundwater. <br />The location and orientation of the monitoring wells were initially designed to also <br />evaluate the persistence of any mining-related affects to groundwater quality in the <br />down-gradient direction. This was based on an interpretation that the hydraulic <br />gradient in the area was coincident with topography (i.e. a generally southward <br />gradient). However, a mine dewatering pump is located approximately 200 feet west <br />of the well nest within the lower portion of the West Sunday mine workings. <br />Therefore, it is unlikely that any of the wells are measuring direct effects of the <br />underground workings, because a local cone of depression is likely present with an <br />inward gradient surrounding the dewatered mine workings. Therefore the direction <br />cm _ 2-23 <br />7:\84986-Denison Mines\Task Order 3 - DMO Sampling and Analysis Plan\Task 3.14 - Hydrogeology Report\ final sunday hydro reporbleutTINAL Sunday Hydrogeology Report.doc