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Section 8 <br />Groundwater Quality <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 drill holemonitoring well WS -4 <br />causes the screened interval to be located in an intermediate siltstone and shale unit of <br />the Salt Wash member rather than the Top Rim Sandstone. The screened interval of <br />monitoring wells located on the south side of the underground mine workings are <br />located in the Top Rim Sandstone, which hosts the uranium - vanadium mineralization <br />ore as well as elevated concentrations of the other associated natural elemental <br />enrichmcntsoccurring elements such as arsenic, molybdenum and selenium. <br />Groundwater quality data shown in Table 8 -2 display a marked difference between <br />wells screened in the Top Rim Sandstone (WS -1, WS-2 and WS -3) and the well <br />screened in the underlying intermediate siltstones and shales (WS -4). Water quality <br />from WS -4 is very- saline with TDS of 6,990 mg /L and contains high concentrations of <br />chloride, sodium and sulfate. This water also contains relatively lower concentrations <br />of the ore metals uranium and vanadium and associated elements such as arsenic, <br />molybdenum and selenium. The wells screened in the Top Rim sandstone show <br />relatively higher concentrations of the ore metals and associated elements. This water <br />is also relatively saline with TDS ranging from 1,300 to 1,710 mg /L, but the water <br />contains much lower concentrations of sodium, chloride and sulfate. This marked <br />contrast in uranium and vanadium concentrations in groundwater within the <br />underlying intermediate siltstones and shale indicates that potential anthropogenic <br />effects to groundwater in direct proximity to the underground workings has not <br />affected groundwater located only 63 feet from the underground workings. <br />The groundwater data collected to date supports the hydrogeological framework for <br />the area developed by Weir et al. (1983), which describes groundwater flow moving <br />laterally within the sandstone unit. Vertical flow is restricted by interbedded low <br />permeability units such as the intermediate siltstones and shales of the Salt Wash <br />Member, which limits potential vertical migration of groundwater. The groundwater <br />quality data described above show a marked difference in groundwater quality <br />between the units. Groundwater quality in the Top Rim Sandstone displays a <br />signature associated with the enrichments naturally elevated concentrations of <br />uranium, vanadium and other elements that are enriched present in the ore bodies. <br />Water quality from the underlying unit displays a different chemistry with very-high <br />salinity. This suggests that the intermediate siltstones and shales of the Salt Wash <br />Member may contain natural enrichments of sodium, chloride and sulfate. <br />The groundwater quality data collected to date shows that groundwater located <br />within approximately 40 feet of the underground workings shows a characteristic <br />signature associated with the naturally elevated concentrations enrichments of <br />uranium, vanadium and other elements that comprise the ore bodies. This signature <br />does not extend even locally into the underlying intermediate siltstones and shales of <br />the Salt Wash member. The lateral extent of groundwater with this characteristic <br />chemical signature in the Top Rim Sandstone unit is currently unknown. Denison <br />C1Documents ant Settinos\ cwoodward .DMClDesktoMEnvironmental Protection Plan Sunday Mines Revised November 2011 rev l (2111 10 11.docx <br />7 -14 <br />