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• portion of the mine is no- longer saturated as a result of on -going mine <br />dewatering activities. <br />Section 8 <br />Groundwater Quality <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, 2008, Denison was scheduling to reenter the underground workings to purge the <br />wells and collect groundwater samples. At that time, concentrations of radon gas in <br />air 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 />The groundwater quality data show that the ambient groundwater is relatively saline <br />with TDS content ranging from 1,300 to 6,990 mg /L. The ambient groundwater also <br />contains uranium and vanadium, which are the primary ore metals in the mine, and <br />several other elements that are naturally en efl- elevated in rocks at the Sunday <br />Mines Group including arsenic, molybdenum and selenium. The presence of these <br />elements in groundwater in close proximity to the underground workings is thought <br />to be related to naturally occurring enrichments concentrations of metals, and <br />development of equilibrium conditions between the ore minerals and the local <br />groundwater. As discussed previously, underground mine development activities <br />such as tunneling, excavating rock, and ventilating the underground workings may <br />also affect the concentration of the naturally enriched elevated elements in ambient <br />groundwater. The extent of effects to groundwater quality attributable to naturally <br />occurring geochemical conditions versus anthropogenic effects related to <br />underground mine development is unknown. <br />The location and orientation of the monitoring wells were initially designed to also <br />evaluate the persistence of any mining- related affects effects to groundwater quality <br />in the down - gradient direction. This was based on an interpretation that the hydraulic <br />gradient in the area was coincident with topography a generally southward <br />gradient). However, a mine dewatering pump is-was located approximately 200 feet <br />west 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 measuringmeasured direct effects of <br />the underground workings; because a local cone of depression is likely present with <br />an inward gradient surrounding the dewatered mine workings. Therefore the <br />direction of groundwater flow in this area is into the underground workings on both <br />the north side where monitoring well WS-4 is located and the south side of the <br />workings where monitoring wells WS -1, WS -2, and WS -3 are located. <br />C1Documents ant Settings \cwoodward.DMC \ Desktop \Environmental Protection Plan Sunday Mines Revised November 2011 rev1 (2) 11 10 11 .docx <br />7 -13 <br />