2009-05-19_REVISION - M1977416 (37)

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Hydrogeological Evaluation of Sunday Mines Group Geologic and Hydrologic Conditions . As discussed in Section 2.3.3, groundwater generally flows westerly from the areas of surface disturbance towards the Dolores River. Therefore, the gradient can be estimated by comparing the elevation of groundwater observed in exploration drill holes at the Carnation/ Sunday and Topaz Mines with the elevation of the Dolores River at potential groundwater discharge points in Big Gypsum Valley. Exhibit 2-3 shows the observed groundwater elevations at the Carnation/ Sunday Mine and Topaz Mine affected areas and the potential discharge point at the Dolores River, the distance from the mines to the potential discharge points, and the estimated hydraulic gradients. The distance used in this estimate is the direct line of site distance between the mine affected areas and the Salt Wash Member outcrops along the Dolores River in. Big Gypsum Valley. This provides a conservative estimate of the hydraulic gradient, because the actual groundwater flow paths are likely longer than assumed. In addition, groundwater may be compartmentalized within relatively isolated fault blocks in some areas, which would affect the actual groundwater flow rate. Additional information regarding the exploration drilling program is presented in Appendix A. r7vti;h;f ?-I Fcfimnfvd hudmulic aradivttt • Mine Observed Elevation of Distance from Estimated Groundwater Potential Mine to Hydraulic Elevation Discharge Potential Gradient (feet) Point Discharge (feet) (feet) Point feet Carnation/ West 5,490 5,360 20;431 0.006 Sunda Topaz 5,403 5,360 10,582 0.004 The porosity of the sandstone is unknown; however, Freeze and Cherry (1979) describe an empirical relationship developed by Chilinger (1963), which allows estimation of sandstone porosity based on the textural classification and the intrinsic permeability. Craig et al. (1955) describe the texture of Salt Wash Member sandstone as ranging from fine grained to medium grained, which is supported by visual observations collected during the course of this investigation. Based on the empirical relationship developed by Chilinger (1963) and the intrinsic permeability data provided by Jobim (1962), the porosity of the Salt Wash member sandstones is estimated to range from approximately 11 to 14 percent. In this estimation of average linear groundwater velocity, this estimated porosity is assumed to be equivalent to the estimated effective porosity of the Salt Wash member sandstones. Groundwater observed in the West Sunday and Topaz Mines occurs within the Salt Wash member of the Morrison Formation. A hydraulic conductivity of 1.1 x 10-4 centimeters per second (cm/ sec.) is estimated for this unit based on intrinsic CM 2-18 T:\64986-Denison Mines\Task Older 3 - DMO Sampling and Analysis Plan\Task 3.14 - Hydrogeology Repodl8nal sunday hydro reporNextTINAL Sunday Hydrogeology Report.doc