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~• end underburden, and Lennox coal units. It is assumed that the division between the beset <br />and middle members of the Yilliems Fork Formation lies somewhere within the Lennox <br />overburden, as defined in this report. Laboratory analyses of unf rectured rock samples <br />from the basal Yilliems Fork unit, the Trout Creek sandstone, and the Twentymile sandstone <br />(regional cliff-farming sandstone unit which separates the middle and upper members of the <br />Yilliems Fork Formation) indicate that the basal Yilliems Fark unit is some 10 times more <br />permeable then the Twentymile sandstone end nearly 20 times more permeable than the Trout <br />Creek sandstone based on geometric mean values for the hydraulic conductivity of the 3 <br />units (Robson and Stewart, 1990, P. 64). The difference in the hydraulic conductivities <br />of these three units is thought to be due to the effects of secondary permeability <br />produced by fractures, particularly those within the various coal beds of the basal <br />Williams Fork unit. Unfrectured coal is considered to be relatively impermeable; however, <br />Robson and Steuart (1990, P. '64) state "the results of eight aquifer tests in the Wedge <br />coal indicate that the mean hydraulic conductivity of this coal is 3.Sx10E-01 ft/day - <br />about three times as large es the hydraulic conductivity of the basal Yilliems Fork <br />aquifer as a whole" (refer also to Table 7-11). Aquifer tests performed by Peabody on a <br />total of ten Yadge coal wells, however, indicate that within the area covered by the Yoast <br />. and Seneca II-W leaseholds, hydraulic conductivities do not exceed 4x10E-03 ft/day, end <br />collectively yield a geometric average of 2x10E-03 for this parameter (Table 7-11). <br />wo published hydraulic data were found for the Wolf Creek underburden, but date available <br />for individual sandstone and siltstone layers within the basal Yilliems Fork unit inditete <br />a range in hydraulic conductivities of 9.2x 10E •06 to 3.2x10E-03 ft/day for the sandstones <br />end 4.9x10E-04 to 1.3x10E-02 ft/day for the siltstones, based on laboratory analyses of <br />rock samples (Robson and Stewart, 1990, P. 61, Table 7). The Yolf Creek underburden (as <br />well es a portion of the Yadge underburden) is dry or unsaturated in the area of the Yoast <br />leecehotd. <br />Based on comparisons between published aquifer test data, laboratory permeability <br />analyses, end field date obtained by Peabody, it appears that both hydraulic <br />conductivities end transmissivities of the Yadge overburden, coal, and underburden ere <br />somewhat lower at the Yoest Mine than at The neighboring Seneca II-Y Mine, end ere <br />considerably lower than those determined in regional studies of the surrounding area. <br />Voter level and aquifer test date for the Yadge coal (except Yell YY29) end underburden <br />• (except Yell YVU29), end Yolf Creek coal end underburden inditete that the two coal units <br />ere more highly saturated end are under higher confining pressures then ere their <br />respective bounding units. At Yadge coal Yell TV29 end Yadge underburden Vell YWU29, the <br />37 <br />