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Section 7 <br />Groundwater Information <br />Canyon area using the geologic contacts of Cater (1954), the gradient of the <br />hydrogeological unit is approximately 0.0125 towards the southwest. <br />Groundwater is present at least seasonally in the general vicinity of the Van 4 Mine <br />area within the Salt Wash Member of the Morrison Formation, as evidenced by the <br />presence of Fawn Springs. A hydraulic conductivity of 1.1 x 10-4 centimeter per <br />second centimeters per second (cm/ sec.) is estimated for this unit based on intrinsic <br />permeability values provided by Jobim (1962). <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 />linear groundwater velocity, the effective porosity is assumed to be equivalent to the <br />estimated porosity of the Salt Wash member sandstones. <br />The average linear groundwater velocity is estimated based on a hydraulic <br />conductivity of 1.1 x 10-4 cm/ sec, a hydraulic gradient of 0.13, and the range of <br />effective porosities discussed above. These estimates are shown in Exhibit 7-2. <br />Exhibit 7-2. Estimation of Linear Groundwater Velocity in Van 4 Mine Area for Salt Wash Aquifer <br />Hydraulic Estimated Hydraulic Assumed Effective Estimated Linear <br />Conductivity (cm/sec) Gradient Porosity Groundwater velocity <br /> (ft/ year) <br />1.1 x 10-4 cm/sec 0.0125 0.11 12.9 <br />1.1 x 10-4 cm/sec 0.0125 0.14 10.1 <br />Based on the estimate presented above, the average linear groundwater velocity is <br />thought to be approximately 10.1 ft/year to 12.9 ft/year. <br />• <br />7-4 <br />TA64986-Denison Mines\Task Order 4- EPP Sunday Mines Group-Van4\Van4\PINAL Report\FINAL -Environmental Protection Plan Van4.doc