2001-12-11_PERMIT FILE - C1980007A (2)

Home Browse Search

GEOWEST Colorado Springs, Inc. Mardi 31, 1989 • west Elk Coal Company P.O. Box 591 Somerset, Colorado 81434 Attn: Mr. Dennis Conn EXHIBIT 3.4.A.4 Re: Review of B Seam Impacts on Stability of Existing Refuse Pile Dear Dennis: we have examined the factors that we feel are significant to slope stability impacts on the existing refuse pile from the proposed slope construction and mining in the B seam. In summary, we have concluded that there will be no detrimental impacts, rather the anticipated impacts should all favor stability. A summary of our evaluation follows. General Geolooical Environment The B seam lies below the F seam slightly more than 400 feet at most locations within the permit area. It still lies within t}ie Mesa Verde formation above the basal Rollins sandstone member. The geologic environment of the B seam remains very similar to tl~e F seam environment, with rock types in the immediate roof and floor consisting of sedimentary coal measures of predominately sandstone, siltstone and shale. In examination of the logs and stratigraphic cross. sections, we feel there will be no major changes in the general geological environment. Rock Mechanics Testino and Shear Strenoth As part of this evaluation we reviewed all available rock mechanics testing data provided both by the Tucson Research Center of Anaconda Minerals Company (1983), and by J.F.T. Agapito Associates (1988). Although variabilities exist from test to test, mean unconfined compressive strengths remain high for all lithologies, falling in the range of 7,000 to 14,000 psi. Some of the finer grained lithologies (primarily shales) do have a potential to slake, or deteriorate, with regard to strength over time. Therefore, the single most important factor regarding the strength of the refuse material is the relative percentage of the durable lithologies (the sandstone), versus the less durable lithologies (i.e., the siltstones/shales).