2018-09-04_PERMIT FILE - C1980007A (44)

Home Browse Search

West Elk Mine • Weatherise and Burn Weathering and burning of the coal and associated strata occur on the property, Burned areas in all seams aze mapped from drill hole data, by direct observation of burned areas on the surface, and by careful examination of color and color-infrared aerial photographs. Some burned areas occur locally within all seams, but none aze projected in the mineable azeas. The burned azeas aze generally small (about 4 percent) and occur mainly neaz the coal outcrops. Projections of weathered azeas 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 azeas of lower cover where weathering has progressed faz enough to weaken clays and shales. Effects otSloaes 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 aze common between the Dry Fork of Minnesota Creek, Deep Creek, and the North Fork. Within the Box Canyon permit revision area, the very steep topography prevents vehiculaz access and even makes pedestrian access difficult. Total topographic relief of the azea exceeds 3,000 feet. South of the Dry Fork of Minnesota Creek in • the South of Divide permit revision area the topography generally exhibits less vertical relief, but gradually increases in elevation to 9,100 feet. There is a mazked asymmetry of the valley side profiles in the azea. 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, aze 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 aze 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 aze subject to soil movement or slump and rock falls. Steep Toaoeraphv The effects of steep topography on mining conditions aze 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 azbitrary guidelines of 33.3 percent slope over a minimal slope width of 500 feet. Topographic slopes in excess of 70 percent aze limited 2.04-36 Revised Nwem6er 1004 PR/0