_GENERAL DOCUMENTS - C1981017 (226)

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6 . Slope Stability of Hishwall Remnant The highwall 1 remnants shown for all portal areas range from 60 feet to 120 feet in height . These remnants are all located in the sandstones , shales and siltstones of the Bowie Shale of the Mesaverde . Any discussion of the stability of the highwall remnants must be based on what period of time is considered and what degree of sloughage is considered acceptable . Inspections of the highwalls show that the strata is competent and does not tend to fail in massive blocks . The shaley nature of the strata prevents water infiltration , hence , most erosion and sloughage is from the exposed surface , and not deep-seated in the mountainside . Also , the bedding of the strata is near horizontal , which is best for stability . There are no indications of major cracks or other problems that would indicate a potential massive failure in the natural ground above the highwalls . See the enc 1 osed pictures . With the exception of Mine #5 , the thicknesses of colluvium at the top of the highwalls are ', ess than 10 feet and as such , do not contribute significantly to highwall instability . This coincides with the historical record since the portal areas were excavated in the 1950 ' s . No massive failure has occurred at any of the portal areas . Occasionally , large rocks do fall to the bench and surface sloughage occurs on an ongoing basis . The partial highwall elimination ( 25% to 40%) for reclamation will lessen the rockfalls and surface sloughage . The surface sloughage after reclamation w i l l probably not be significantly greater than that of the surrounding "natural highwalls" . Over very long periods of time , the remaining benches will tend to disappear as talus from above settles on the flat areas and gradually fills them to blend with the surrounding terrain . As previously stated , the proposed partial highwall reclamation plan is best for the amounts of reasonably available spoil are present .