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Hydrogeological Evaluation of Van 4 Mine <br />Geologic and Hydrogeologic Conditions <br />Several confining units and leaky confining units are present within the Mezozoic <br />sandstone aquifer, which restrict movement of water from individual sandstone <br />aquifers within the lager Mesozoic sandstone aquifer. The Summerville shale is a <br />confining unit within the aquifer that restricts movement of water between the Salt <br />Wash aquifer and an underlying aquifer including the Chinle Formation, Wingate <br />Sandstone and the Navajo Sandstone. In addition, the Carmel Formation and the <br />Kayenta Formation contain interbedded shale. These formations are likely leaky <br />confining layers, which are less permeable than the adjacent sandstone layers but <br />more permeable than confining layers such as rock salt and shale. In summary, the <br />Mesozoic aquifer is a layered aquifer with individual sandstone aquifers separated by <br />confining and/or leaky confining units. <br />The Tertiary to Upper Cretaceous aquifer is similar to the Mesozoic aquifer, but it <br />occurs in sandstones that are higher in the stratigraphic sequence. This aquifer is <br />bounded at lower contact by shale of the Brushy Basin Member of the Morrison <br />Formation. The Tertiary to Upper Cretaceous aquifer contains a lower dominantly <br />sandstone aquifer hosted by the Burro Canyon Formation and the Dakota Sandstone, <br />and an upper sandstone aquifer hosted by the Mesaverde Formation, which is not <br />present in the Van 4 Mine area. The Mancos shale is a confining unit that separates the <br />upper and lower sandstone aquifers. <br />Alluvial aquifers are locally present in valley bottoms that contain significant <br />accumulations of unconsolidated alluvial deposits. Weir et al. (1983) maps an <br />extensive alluvial aquifer within Paradox Valley, which overlies outcrops of the <br />Pardox Member of the Hermosa Formation. Interaction of alluvial groundwater with <br />the Paradox Member contributes to naturally elevated total dissolved solids <br />concentrations in the Dolores River (Chaffin 2002). <br />The principle direction of groundwater flow within the Mesozoic and Tertiary to <br />Upper Cretaceous aquifers are lateral, because the confining layers restrict <br />groundwater flow between the individual sandstone aquifers. Groundwater within <br />these aquifers is both unconfined and confined in areas of the Dolores Basin. <br />Groundwater generally moves towards the Dolores River based on water level <br />contours provided by Weir et al. (1983). This is supported by observations of <br />generally gaining flows in the Dolores River as discussed previously in Section 2.2.2. <br />Jobim (1962) analyzed intrinsic permeability within rock units of the Mesozoic and <br />Tertiary to Upper Cretaceous aquifers in relation to the distribution of uranium <br />deposits in the Colorado Plateau. This work included measurement of intrinsic <br />permeability at numerous localities within the Uravan Mineral District, which <br />contains the project area. Jobim developed a series of isopermeability contour maps <br />that provide intrinsic permeability data for the general vicinity of the Van 4 Mine <br />Group area. Intrinsic permeability data from Jobim (1962) are provided for the <br />various sandstone units within the Mesozoic and Tertiary to Upper Cretaceous <br />aquifers in Exhibit 2-1. In addition, Exhibit 2-1 provides hydraulic conductivity data <br />for the rock units, which were calculated from the intrinsic permeability data. <br />2-7 <br />draft final van 4 hydrogeology report.doc