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• TAB 7 <br />XTDROLOGIC DESCR1Pi ION <br />Rational Nvdrooeolocv <br />Introduction. Topography, lithologies, end geologic structures are important factors <br />affecting the occurrence, movement, end quality of ground waters near Seneca Coal <br />Company's Yoast Mine. Each of these factors have been examined in order to charecterixe <br />the local and regional ground water systems so that the effects of mining (if any) at the <br />Yoast Nine can be determined. <br />Tooogra ohv. The Yoast Mine permit area is Located in the rugged Yilliams Fork Mountains <br />of northwestern Colorado. Topography is the primary factor controlling the movement of <br />ground water within shallow, unconfined aquifers; recharge occurs in areas of higher <br />elevation, and discharge occurs in lower areas along drainages. Unconfined ground water <br />flow directions generally coincide with topographie slopes. The movement of confined <br />• ground waters is controlled by geologic structures, el though the attitudes of topographic <br />slopes and geologic structures may be similar (i.e. dip slopes are often present). <br />litholoov. Aquifer characteristics and water quality are primarily determined by <br />lith ology. The permit area is underlain by structurally deformed sedimentary rock strata <br />that range in age from late Cretaceous to Duaternary. <br />A summary of the physical and hydrological character of [he lithologies affected or <br />potentially affected by mining activities at Toast is presented in Table 7-1. Sources of <br />information for this table are Bess et el. (7955), Steele et al. (1979), Brogden and Giles <br />(7977), Stewart (7983), end the results of Peabody's hydrological monitoring and testing <br />at Yoast. Although the Trout Creek sandstone will not be directly disturbed by mining, e <br />well completed in this strata will provide water for the mine facility. Detailed geologic <br />descriptions of these lithologies can be found in Teb b ("GeoloBY") of this permit <br />application package (PAP). <br />It should be noted that the characteristics presented in Table 7-7 ere generalizations. <br />• The ph ysicel end hydrological properties of these lithologies can vary significantly both <br />lot erelly end vertically. <br />1 <br />