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TAB 7 <br /> HYDROLOGIC DESCRIPTION <br /> Regional Hydrogeology <br /> Introduction. Topography, lithology and structural trends each play a principal role in <br /> controlling the quality, quantity and flow characteristics of the regional ground water <br /> regime in the direct vicinity of Peabody Coal Company's Nucla Mine. As seen in the <br /> geology discussion (Tab 6) of the Permit Application Package (PAP), the geology of this <br /> region is complex. Consequently, the ground water system is difficult to interpret. To <br /> understand the extent the Nucla Mine may affect or has affected the local and regional <br /> ground water supply, one must delineate the regional and local ground water systems. <br /> Topography. Topography is the principal element governing shallow aquifers ( 100 feet) in <br /> the Canyon Land Section of the Colorado Plateau Physiographic Province. Topographic highs <br /> act as recharge areas, and lows along streams serve as discharge areas during periods of <br /> high water table. In alluvial and other unconsolidated material, ground water moves for <br /> the most part from high topography to low. This also appears to be the case for the <br /> unconfined portions of the Dakota sandstone and Burro Canyon formations. <br /> Lithology. Lithology governs the water yielding ability, the aquifer characteristics and <br /> the chemical quality of the ground water. As seen in the geology section of the PAP (Tab <br /> 6), the lithology of the Nucla area is extremely variable. Shallow aquifers of the area <br /> consist of unconsolidated valley deposits of the quaternary system and the <br /> stratigraphically variable sandstone, shales and coals of Cretaceous Age (Dakota, and <br /> Burro Canyon Formations). Deeper aquifers consist of the varicolored Morrison Formation <br /> and the Entrada Formation both of Jurassic Age. The variability of lithology within each <br /> of the aquifers creates a complex hydrologic system. <br /> Table 7-1 is a summary chart adapted from Boettcher (1972) describing the physical and <br /> hydrologic character of the water bearing formations mentioned above. Included in Table <br /> 7-1 is water quality which is controlled by the reaction of the ground water and the <br /> aquifer and the ground water retention time (Hem, 1970). in addition, ground water yields <br /> and uses are given. It must be noted that these are generalizations, and these hydrologic <br /> properties can vary greatly within the formations. <br /> 7-1 Revised 04/11/88 <br />