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Section 7 <br />Groundwater Information <br />7.2 Potentially Water-Bearing Fracture Zones <br />Potentially water-bearing fracture zones range in size from very small-scale features <br />that primarily influence only the permeability of the rock, to large-scale features that <br />extend for miles and could potentially influence groundwater flow paths. This section <br />focuses on identifying large scale fracture zones associated with the faults mapped by <br />Cater (1954), because these features have a potential to influence groundwater flow at <br />a larger scale. These faults are shown on the geological map included previously as <br />Figure 7-1. <br />Situated between low-permeability units, water would only be expected to enter the <br />Salt Wash Member where it is exposed in adjacent slopes or via conduits such as <br />faults. Faults are present in the lower portion of the slope on the northeastern side of <br />Monogram Mesa (Cater 1954). At its closest point, the nearest fault is approximately <br />4,000 ft. from the Van 4 Mine affected area. The fault, which intersects the Salt Wash <br />Member, is generally parallel to the ridgeline and located along the slope 500 to 1,000 <br />feet (ft) northeast of the topographic divide. There are no intermittent or perennial <br />streams mapped as crossing the fault trace indicating that the only surface water <br />expected to cross the fault would occur as overland flow during occasional rain <br />events or as snowmelt. <br />7.3 Direction and Rate of Groundwater Flow <br />7.3.1 Direction of Groundwater Flow <br />On a large scale, groundwater flow in the Van 4 area is towards the Dolores River <br />(Weir et al. 1983). On a smaller scale, topographic variations and structural geology <br />cause local modifications in groundwater flow paths. Groundwater flow in the <br />vicinity of Van 4 Mine is likely towards the southwest following the dip of the <br />hydrogeologic units and the topography of the Bull Canyon area. This interpretation <br />is supported by the presence of Fawn Springs southwest of the Van 4 Mine and the <br />intermittent stream within Bull Canyon. Ultimately, this groundwater would be <br />expected to reach the Dolores River. <br />7.3.2 Rate of Groundwater Flow <br />The rate of groundwater flow is discussed below in terms of the average linear <br />groundwater velocity which is a function of the hydraulic gradient, the effective <br />porosity, and the hydraulic conductivity (Dominico and Schwartz, 1990). Data were <br />presented in Exhibit 7-2 for estimated hydraulic conductivity based on the intrinsic <br />permeability analyses of Jobim (1962). This section presents estimates of the rate of <br />groundwater flow based on the estimates of Jobim (1962), an estimate of hydraulic <br />gradient, and estimated values for the porosity of the Top Rim sandstone. <br />The hydraulic gradient in the area of the Van 4 Mine is estimated to be approximately <br />the same as the dip of the hydrogeologic units, because groundwater flow is primarily <br />lateral as a result of the inter-layered aquifers and confining units. This is an <br />approximation, but it is adequate for the purposes of this estimate given the level of <br />detail of available information. Based on a three-point solution in the upper Bull <br />7-3 <br />7:\64986-Denison Mines\Task Order 4 - EPP Sunday Mines GrouµVan4\Van4TlNAL ReponTINAL - Environmental Protection Plan Van4.doc