2006-06-02_PERMIT FILE - C1980007A (3)

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West Elk one • Interburden between the E Seam and overlying F Seam ranges from 60 to 190 feet (Map 20). The average interburden thickness between the E and F Seams where the E Seam is mineably thick is 100 to 130 feet. Lithologies within the interburden consist of shales, siltstones, generally lenticular sandstones, and local thin coals. Shales and siltstone intervals often occur as thinly interbedded sequences showing distorted bedding. Cazbonaceous plant debris occurs within all lithologies in the interburden. The interburden between the E Seam and the underlying B Seam ranges in thickness from 170 to 300 feet (Map 15), and is described in more detail in the previous section entitled "B-Seam Overburden and Interburden". Representative samples of the E Seam coal, overburden, roof, and floor strata have been collected and analyzed from core holes drilled within the mine permit area, and elsewhere around the lease holdings. Samples of all interburden rock types have also been sampled in drill hole SOM-U3, located in the mine near the B Seam access slopes. These samples have been analyzed for chemical and toxicity pazameters as required by state and federal regulations. The locations of these holes are shown on Map 8 and the analytical results are presented in Exhibit 13. Stratigraphic cross-sections and geochemical analyses indicate that these results aze representative of the existing conditions throughout the West Elk Mine permit area and that the B, E, and F coal seams and associated roof and floor materials do not contain potential acid- ortoxic-forming materials. E Seam Roof and Floor In the West Elk Mine coal lease area, the E Seam roof lithology is highly variable in composition. As seen in drill holes, the E Seam roof usually consists of a sequence of thinly bedded, carbonaceous shales, which are frequently silty to sandy in nature. Locally, thick fluvial sandstones form the immediate roof or closely overlie it. The sharp erosional basal contact of the lazger sand bodies suggests that scouring into the underlying E Seam coal may occur beneath. Along the margin of the channel deposits, thin overlying coal beds or "rider seams" occur that could contribute to poor roof conditions. Because of the variable nature of the overlying lithologies, E Seam roof conditions aze expected to range from good to poor. Current mine plans are to leave top coal un-mined and in place where sufficient seam height allows, to improve roof control. The E Seam floor conditions will likewise be variable, depending upon location within the reserve. Where the upper EO coal bench is merged with the underlying El coal bench, the resulting thick seam will allow for several feet of coal to be left un-mined in the floor (Figure 7). As a result, floor conditions within the central reserve should be excellent. Where the EO and El coal benches split, the mining interval must be raised into the upper seam to avoid mining the thick parting. hi these azeas, floor conditions may be poorer because of the thinner mined bench and the immediately underlying parting, which will become the mine floor. Where the soft claystone parting thickens, it may become more coazse-grained (silty to sandy) and form a more competent floor, • 2.04-31 Revised Nmember 1004 PRIO