2022-02-22_PERMIT FILE - C1980007 (5)

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West Elk Mine 2.04-36 Rev. 11/04- PR10, 04/06- PR10, 09/07- PR12, 10/08- PR14; 01/22- MR459 occur locally within all seams, but none are projected in the mineable areas. The burned areas are generally small (about 4 percent) and occur mainly near the coal outcrops. Projections of weathered areas are based on core hole data, topographic relief, and topographic slope orientation. The lateral extent of weathering is assumed to be greatest where topography is gentle, such as adjacent to broad, shallow valleys. Depth of weathering on north-facing slopes is assumed to be greater than on south-facing slopes, everything else being equal. Floor and roof conditions will deteriorate in areas of lower cover where weathering has progressed far enough to weaken clays and shales. Effects of Slopes Most of the high relief terrain is located in the northern and eastern portions of the lease area where slopes of 30 to 70 percent are common between the Dry Fork of Minnesota Creek, Deep Creek, and the North Fork. Within the Box Canyon permit area, the very steep topography prevents vehicular access and even makes pedestrian access difficult. Total topographic relief of the area exceeds 3,000 feet. South of the Dry Fork of Minnesota Creek in the South of Divide and Southern panels permit area, the topography generally exhibits less vertical relief, but gradually increases in elevation to 9,100 feet. There is a marked asymmetry of the valley side profiles in the area. This asymmetry is caused by micro-climatic differences on opposite sides of the valley. This results in variation of soil development, which in turn influences erosion rates. The interbedded shales of the Mesaverde Formation, when moist, are susceptible to movement and weathering which promotes erosion, mass-wasting, and downslope movement of the overlying sandstone materials. This increased mobility of the moist shales leads to a gradual decline in slope angle. Thus, the northerly-facing slopes generally are not as steeply inclined as the southerly-facing slopes. Map 31 and Map 31A are slope maps in which the topographic inclination has been broken down into categories. Note that over 90 percent of the area has slopes steeper than 15 percent and, therefore, is unsuited for most activities except general recreation or engineered structures. Some of the narrow valleys on the property could be used for building sites, but relatively steep slopes adjacent to these valleys are subject to soil movement or slump and rock falls. Steep Topography The effects of steep topography on mining conditions have been difficult to define and quantify. Geotechnical theory holds that rapid topographic change over a significant area causes stresses related to differential load, and that these stresses can cause roof control problems in mining. Areas of steep topography have been defined by using arbitrary guidelines of 33.3 percent slope over a minimal slope width of 500 feet. Topographic slopes in excess of 70 percent are limited to the cliff faces along Minnesota, Dry Fork, and Lick Creeks and on the perimeter of West Flatiron Mesa. About 11 percent of the mine area has been defined as steep topography. The greatest effect of topography was in the northern and eastern one-third of the property, where topography is generally the steepest.