2009-06-08_REVISION - M1997032 (25)

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Hydrogeological Evaluation of Van 4 Mine Geologic and Hydrogeologic Conditions the Summerville Formation. The Carmel Formation overlies the Navajo Sandstone and consists of a variety of clastic sedimentary rocks including siltstone, shale, and sandstone. This unit is relatively thin with an estimated thickness of 10 to 25 ft. The Entrada Sandstone overlies the Carmel Formation. This formation consists of a combination of horizontally bedded and eolian-type cross bedded sandstones with a bimodal grain size distribution including very fine grained sandstone (<0.0001 inches (in.) grain size) and medium grained sandstone (0.02 to 0.03 in. grain size). The Entrada Sandstone is 110 to 120 ft. thick. The Summerville Formation overlies the Entrada Sandstone, and consists primarily of sandy and silty shale. This unit also includes local sandstone and limestone layers. The unit is approximately 105 ft. thick. The Upper Jurassic Morrison Formation overlies the Summerville Formation. This formation is important because it hosts the uranium-vanadium mineralization at the Van 4 Mine. The Morrison Formation includes two members: the Salt Wash Member and the Brushy Basin member. The lowermost member is the Salt Wash Member, which consist of sandstone with interbedded red shale and a few local beds of limestone. The uranium-vanadium ore bodies occur within the Top Rim sandstone unit, which is located in the top approximately 100 ft. of the Salt Wash Member (J. Showalter personnel communication 2008). The thickness of the Salt Wash member ranges from 320 to 380 ft. The Salt Wash member is overlain by bentonitic shale of the Brushy Basin member. The thickness of the Brushy Basin Member ranges from 350 to 430 ft. The Lower Cretaceous Burro Canon Formation overlies the Morrison Formation. This formation is heterogeneous and includes conglomerate, sandstone, shale and thin lenses of limestone. The Burro Canyon Member contains some massive beds of up to 100 ft. thick, and the total thickness of the formation is estimated to be 190 to 240 ft. The Cretaceous Dakota Sandstone is a flaggy sandstone unit, which overlies the Burro Canyon Formation. This formation also includes less-abundant conglomerate, carbonaceous shale, and local impure coal. The sandstone ranges from fine grained and thin-bedded to coarse grained and cross-bedded. The Dakota Sandstone is approximately 200 ft. thick. The Dakota Sandstone is overlain by the Cretaceous Mancos Shale. The Mancos Shale is a homogeneous formation of fissile shale that is approximately 1,600 ft. thick. Unconsolidated Quaternary deposits are also present including terrace gravels, wind- deposited material, alluvium, and landslide deposits. These units are local in nature and commonly form a thin veneer of unconsolidated sediments in areas where they are present. 0 cm 2-3 draft final van 4 hydrogeology neportdoc