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SUNDAY MINE COMPLEX-HYDROGEOLOGIC REPORT <br /> salinity and sediment (BLM, 2015). The RMP lists the Lower Disappointment Valley as rated <br /> high for salinity control potential in the Colorado River Basin Salinity Control Act of 1974 (BLM, <br /> 2015). <br /> 7.0 HYDROGEOLOGY <br /> 7.1 Regional Hydrogeology <br /> The regional hydrogeology of the Colorado Plateau, western Colorado, and southeastern Utah <br /> has been studied by several researchers including Jobin (1962), Cooley and others (1969), Weir <br /> and others (1983), Avery (1986), and Lowe (1996). Early authors simplified hydrogeologic <br /> descriptions by lumping packages of water-bearing geologic formations and units into aquifers <br /> bearing a single letter of a primary formation. Using this convention as described by Avery <br /> (1986), Table 7-1 summarizes the main hydrogeologic units and their hydraulic characteristics in <br /> the region. <br /> As shown in Table 7-1, the geologic units described in Section 4.0, either individually or <br /> combined, exhibit hydrogeologic properties of interest in the region. Key aquifers, as shown on <br /> Figure 4-3, include the quaternary alluvium and the bedrock D, M, and N aquifers, where the <br /> main confining units are the Mancos Shale, the Morrison Formation Brushy Basin member, the <br /> Summerville Formation, and the Chinle Formation. Because of their great depth, the geologic <br /> units older than the Chinle Formation are not noted as having hydraulic properties of interest in <br /> the region. They are also not included in the discussion below, as there are several hundreds of <br /> feet of aquicludes between the N aquifer and the C aquifer, which is next deeper aquifer in the <br /> region, and the C aquifer cannot realistically be impacted by mining operations at the SMC. <br /> Alluvial Aquifers <br /> Alluvial aquifers are commonly made up of unconsolidated alluvial and colluvial sediments <br /> including gravel, sand, silt, clays and mixtures of these materials. The aquifers are restricted to <br /> main drainages as valley fill adjacent to intermittent and perennial streams; the most prolific <br /> being associated with the latter stream type. These aquifers typically have a limited amount of <br /> water storage as their lateral width and vertical thickness may be measured in a few hundred ft <br /> and commonly less than 150 ft, respectively. Few alluvial aquifers in the region can support <br /> commercial development, but locally serve as excellent domestic water sources for remote <br /> residences and ranches. Areas where alluvial aquifers are used include the Naturita area on the <br /> San Miguel River and areas at, and upstream of, Dolores on the Dolores River(Topper and <br /> Western Water 8 Land, Inc. 15 <br />