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TAB 7 <br />HYDROLOGIC DESCRIPTION <br />Regional Hydrogeology <br />Introduction. Topography, lithologies, and geologic structures are important factors <br />affecting the occurrence, movement, and quality of ground vra tees near Peabody's Seneca <br />II-W Mine. Each of these factors have been examined in order to characterize the local <br />and regional ground water systems so that the effects of mining (if any) at the Seneca <br />II-W Mine can be determined. <br />Topography. The Seneca II-W Mine permit area is located in the rugged Williams Fork <br />Mountains of northwestern Colorado. Topography is the primary factor controlling the <br />movement of ground water within shallow, unconfined aquifers; recharge occurs in areas of <br />higher elevation, and discharge occurs in lower areas along drainages. Unconfined <br />ground water flow directions generally coincide with topographic slopes. The movement of <br />confined ground waters is controlled by geologic structures, although the attitudes of <br />topographic slopes and geologic structures may be similar (i .e. dip slopes are often <br />present). <br />Lithology, Aquifer characteristics and water quality are primarily determined by <br />lithol ogy. The permit area is underlain by structurally deformed sedimentary rock strata <br />that range in age from late Cretaceous to Oua ter nary. <br />A sumana ry of the physical and hydrological character of the lithologies affected or <br />potentially affected by mining activities at Seneca II-W is presented in Table 7-1, <br />Sources of information for this table are Bass et al. (1955), Steele et al. (1979), <br />Brogden and Giles (1977), Stewart (1983), and the results of Peabod y's hydrological <br />monitoring and testing at Seneca II-W. Although the Trout Creek sandstone will not be <br />directly disturbed by mining, a well completed in this strata rri 11 provide water for the <br />mine facility. Detailed geologic descriptions of these lithologies can be found in Tab 6 <br />("Geology") of this permit application package (PAP), <br />It Should be noted that Ure characters sties presented in Table 7-1 are r,eneralizations. <br />The physical and hydrolonical properties of these lithologies ran va rv :.i gnilicantly both <br />laterally and vertically, <br />1 <br />