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Section 7 <br />Groundwater Information <br />7.4.2 Surface Affected Areas <br />This section addresses the direction and rate of groundwater flow in the vicinity of <br />the affected areas of the Sunday Mines Group. In these areas, the rate of groundwater <br />flow cannot be estimated empirically and therefore, this section presents estimates <br />based on analytical evaluations of available data. The rate of groundwater flow is <br />discussed here in terms of the average linear groundwater velocity. The average <br />linear groundwater velocity is a function of the hydraulic gradient, the effective <br />porosity, and the hydraulic conductivity (Dominico and Schwartz 1980). Data <br />presented in Exhibit 7-2 for estimated hydraulic conductivity is based on the intrinsic <br />permeability analyses of Jobim (1962). This section presents estimates of the rate of <br />groundwater flow using the estimates of Jobim (1962), estimates of hydraulic gradient <br />based on relative observed water elevations in exploration drill holes and the Dolores <br />River, and values for effective porosity that are estimated using empirical <br />relationships described by Chilinger (1963). <br />Groundwater generally flows westerly from the areas of surface disturbance towards <br />the Dolores River. Therefore, the gradient can be estimated by comparing the <br />elevation of groundwater observed in exploration drill holes at the Carnation/ Sunday <br />and Topaz Mines with the elevation of the Dolores River at potential groundwater <br />discharge points in Big Gypsum Valley. Exhibit 7-2 shows the observed groundwater <br />elevations at the Carnation/ Sunday Mine and Topaz Mine affected areas and the <br />potential discharge point at the Dolores River, the distance from the mines to the <br />potential discharge points, and the estimated hydraulic gradients. The distance used <br />19 in this estimate is the direct line of site distance between the mine affected areas and <br />the Salt Wash Member outcrops along the Dolores River in Big Gypsum Valley. This <br />provides a conservative estimate of the hydraulic gradient, because the actual <br />groundwater flow paths are likely longer than assumed. In addition, groundwater <br />may be compartmentalized within relatively isolated fault blocks in some areas, <br />which would affect the actual groundwater flow rate. <br />EAhihit 7-2_ Estimated Hydraulic Gradient <br />Mine Observed Elevation of Distance from Estimated <br /> Groundwater Potential Mine to Potential Hydraulic <br /> Elevation Discharge Point Discharge Point Gradient <br /> (feet) (feet) (feet) (feet) <br />CarnationiWest 5,490 5,360 20,431 0.006 <br />Sunda <br />Topaz 5,403 5,360 10,582 0.004 <br />The porosity of the sandstone is unknown; however, Freeze and Cherry (1979) <br />describe an empirical relationship developed by Chilinger (1963), which allows <br />estimation of sandstone porosity based on the textural classification and the intrinsic <br />permeability. Craig et al. (1955) describe the texture of Salt Wash Member sandstone <br />as ranging from fine grained to medium grained, which is supported by visual <br />observations collected during the course of this investigation. Based on the empirical <br />relationship developed by Chilinger (1963) and the intrinsic permeability data <br />provided by Jobim (1962), the porosity of the Salt Wash member sandstones is <br />estimated to range from approximately 11 to 14 percent. In this estimation of average <br />7-8 <br />T:184988-Denison Mines\Task Order 4 - EPP Sunday Mines GroupTINAL EPPTINAL - Environmental Protection Plan Sunday Mines.doc