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C \Users\cwsodward1DesMop\Sundays \FINAL - Environmental Protection Plan Sunday Mines Revised January 2012 door <br />Section 8 <br />Groundwater Quality <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 elevated in rocks at the Sunday Mines Group <br />including arsenic, molybdenum and selenium. The presence of these elements in <br />groundwater in close proximity to the underground workings is thought to be related <br />to naturally occurring concentrations of metals, and development of equilibrium <br />conditions between the ore minerals and the local groundwater. As discussed <br />previously, underground mine development activities such as tunneling, excavating <br />rock, and ventilating the underground workings may also affect the concentration of <br />the naturally elevated elements in ambient groundwater. The extent of effects to <br />groundwater quality attributable to naturally occurring geochemical conditions <br />versus anthropogenic effects related to 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 effects 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 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 measured 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 />of groundwater flow in this area is into the underground workings on both the north <br />side where monitoring well WS -4 is located and the south side of the workings where <br />monitoring wells WS -1, WS -2, and WS -3 are located. <br />The groundwater quality data show a marked difference in samples from monitoring <br />well WS -4 as compared to WS -1, WS -2 and WS -3. The locations of the underground <br />monitoring wells are shown in Figure 8 -1. The collars of the wells are located very <br />close to the base of the Top Rim sandstone, and the rock units dip gently towards the <br />south. The collar location and the downward angle of monitoring well WS -4 causes <br />the screened interval to be located in an intermediate siltstone and shale unit of the <br />Salt Wash member rather than the Top Rim Sandstone. The screened interval of <br />8 -4 <br />