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West Elk Mine <br />are filled by processes of mass wasting and sedimentation. However, their location on steep slopes <br />and cliffs relative to hydrologic resources is such, that these cracks will cause minimal impacts. <br />Cracks are projected to be widest and deepest on the steep slopes, cliffs and ridges adjacent to <br />and on either side of Minnesota Creek and its tributaries, as well as Lick Creek. Maximum crack <br />depth on these steep slopes and cliffs is estimated to locally be from 15 to as much as 35 feet <br />deep. Due to the lack of lateral constraint, these cracks may remain open until they are filled by <br />processes such as sheet wash and sedimentation. <br />Oliver No. 2 Mine Considerations <br />Mack Glide <br />This type of movement occurs where the shear strength, or frictional resistance, along a plane or <br />planes of weakness (commonly bedding planes) is less than the shear stress generated by the block <br />mass above them. The material above the plane of weakness then slides as a block (block glide; <br />decollement-type movement). <br />Block Glide Potential in the Oliver No. 2 Mine Area <br />The Oliver No. 2 Mine was an E/D Seam coal mine operated east of Sylvester Gulch during the <br />1940s and early 1950s (See Map 5). Based on information contained in the Oliver No. 2 Mine <br />closure report dated October 1953, water-and methane-filled fractures within the mine E/DO Seam <br />were encountered in the floor of the Oliver No. 2 Mine. (Both water and methane were reportedly <br />under high pressure). The fractures (with a reported trend N77°E) were encountered during pillar <br />development before any fractures produced by floor-heave would likely have occurred. For block <br />glide to occur, the shear strength must be less than the shear stress generated by overburden load <br />and any unbalanced lateral stresses. At the very gentle dip of 2.2 to 3.2 degrees, a high pore-fluid <br />pressure would be necessary to cause the shear strength to be less than the shear stress. <br />It is very unlikely that shear strength along bedding planes in the coal seam (or seams) mined at <br />Oliver No. 2 could be reduced to this extent because: <br />1. There is no high pre-fluid pressure; the water can drain out the Oliver No. 2 Mine portals <br />even though seals of cinder blocks, arranged in double rows, were constructed 700 to 800 <br />feet south of the portal area. This is evidenced by the lack of spring development in the <br />overburden. <br />2. The dip of bedding is 2 to 3 degrees-much less than the 8 to 17 degree angle of friction for <br />any clays that might be present in the coal-bearing rocks of the Mesaverde Fornlation. <br />3. No indication of block glide has been observed in the 42 years since the mine was closed. <br />4. All of the Oliver No. 2 Mine workings are outside the angle of draw of plainned B Seam <br />mining, with the exception of the first Box Canyon panel. <br />5. State Geologists from most coal-producing states were contacted regarding the known <br />occurrence of any block glide in such gently-dipping rocks as in the Oliver No. 2 Mine area. <br />Not one could recall an occurrence of block glide, including those from eastern states where <br />2,05-139 Revised June 2005 PRIO, Rev. March 2006; May 2006 PRIO, A'ov. 2006TRIOTApri12007TRIO&Sep. 2007 PR12; Feb. 2008 PR-12