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Hydrogeological Evaluation of Sunday Mines Group <br />Geologic and Hydrologic Conditions <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 2-14. 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 hole WS-4 causes the <br />screened interval to be located in an intermediate siltstone and shale of the Salt Wash <br />member rather than the Top Rim Sandstone. The screened interval of monitoring <br />wells located on the south side of the underground mine workings are located in the <br />Top Rim Sandstone, which hosts the uranium-vanadium mineralization as well as the <br />other associated elemental enrichments. <br />Groundwater quality data shown in Table 2-6 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 mg/L to 1,710 mg/L, but the <br />water contains much lower concentrations of sodium, chloride and sulfate. <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 of uranium, vanadium and other elements <br />that are enriched in the ore bodies. Water quality from the underlying unit displays a <br />different chemistry with very high salinity. This suggests that the intermediate <br />siltstones and shales of the Salt Wash Member may contain enrichments of sodium, <br />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 natural enrichments of uranium, vanadium and other <br />elements that comprise the ore bodies. This signature does not extend even locally <br />into the underlying intermediate siltstones and shales of the Salt Wash member. The <br />lateral extent of groundwater with this characteristic chemical signature in the Top <br />cm 2-24 <br />T:\64986-Denison Mines%Task Order 3 - DMO Sampling and Analysis Plan\Task 3.14 - Hydrogeology ReportAnal sunday hydro reporNe tTINAL Sunday Hydrogeology Repon.doc