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Hydrogeological Evaluation of Sunday Mines Group <br />Geologic and Hydrologic Conditions <br />aquifer is underlain by rock salt of the Paradox Member and is overlain by bentonitic <br />shale of the Morrison Formation, which are both confining layers. <br />Several confining units and leaky confining units are present within the Mezozoic <br />sandstone aquifer, which restrict vertical movement of water between individual <br />sandstone aquifers. The Summerville shale is a confining unit within the aquifer that <br />restricts movement of water between the Salt Wash aquifer and an underlying aquifer <br />including the Chinle Formation, Wingate Sandstone and the Navajo Sandstone. In <br />addition, the Carmel Formation and the Kayenta Formation contain interbedded <br />shales which are likely leaky confining layers, which are less permeable than the <br />adjacent sandstone layers but more permeable than confining layers such as rock salt <br />and shale. So the Mesozoic aquifer is a layered aquifer with individual sandstone <br />aquifers separated by 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 the lower contact by bentonitic shale of the Brushy Basin Member of the <br />Morrison Formation. The Tertiary to Upper Cretaceous aquifer contains a lower <br />dominantly sandstone aquifer hosted by the Burro Canyon Formation and the Dakota <br />Sandstone, and an upper sandstone aquifer hosted by the Mesaverde Formation. The <br />Mancos shale is a confining unit that separated the upper and lower sandstone <br />aquifers. <br />Alluvial aquifers are locally present in valley bottoms that contain significant <br />accumulations of unconsolidated alluvial deposits. Weir et al. (1983) map an extensive <br />alluvial aquifer within Big Gypsum Valley, which overlies outcrops of the Pardox <br />Member of the Hermosa Formation. Interaction of alluvial groundwater with the <br />Paradox Member outcrops may contribute to the occurrence of high salinity <br />ecosystems in the lower portion of Big Gypsum Valley identified by BLM (2008). <br />The principle direction of groundwater flow within the Mesozoic and Tertiary to <br />Upper Cretaceous aquifers is 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. The <br />anticline in Disappointment Valley causes confined conditions and an artesian well is <br />present in the valley. These wells extract groundwater from the Dakota Sandstone, <br />which is a sandstone aquifer within the Tertiary to Upper Cretaceous aquifer defined <br />by Weir et al. (1983). Groundwater generally moves towards the Dolores River based <br />on water level contours provided by Weir et al. (1983). This is supported by <br />observations of generally gaining flows in the Dolores River as discussed previously <br />in Section 2.3.2. <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 />cm 2-10 <br />T:\64986-Denison Mines\Task Order 3 - DMO Sampling and Analysis Plan\Task 3.14 - Hydrogeology Repomfinal sunday hydro report\text\FlNAL Sunday Hydmgeology Repon.doc