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West Elk Mine <br />• Impacts Beneath the Mined Coal Seam <br />Based on mapping and observations by Mr. Dunrud in the B Seam of the Somerset Mine, impacts to <br />the coal and rocks below the mined coal bed are expected to be limited to about one mining <br />thickness. There is no expected mining impact to the underlying D Seam coal because its top <br />commonly occurs at least a mining thickness below the base of the E Seam. Furthermore, <br />impacts to the floors of the mine workings are expected to be limited to the chain pillars, because <br />the floors of the longwall panels are loaded with caved roof rocks and overlying strata before <br />deformation in the floor can occur. <br />Floor heaving, pillar punching (the pillar punches into the floor and roof rocks), and squeezing <br />(plastic flowage, see Dunrud 1976 for more details) are the only expected deformation in the <br />immediate mine floor, which consists of impure coal, shale, sandstone and claystone. Deformation <br />in the floors of the chain pillars is expected to occur after the longwall panel is mined and the pillars <br />begin to yield. <br />Possible Subsidence Consequences <br />Apache Rocks and Box Canyon Mining Areas - The greatest surface impacts are expected to occur <br />along the precipitous slopes and cliffs that flank West Flatiron and in the steep canyon slopes of the <br />Box Canyon mining area (Box Canyon, Sylvester Gulch tributaries to the east, and the unnamed <br />drainage to the west of Box Canyon). Though unlikely, the worst possible consequences foreseen <br />are that: <br />• 1. Cracks as much as 50 to 100 feet deep may develop above the chain pillars common to the <br />first three northern panels and may divert intermittent flow in Box Canyon and the unnamed <br />canyon to the west of Box Canyon to the mine through local fractures or to permeable rocks <br />in the overburden (see Map 14 for details). Flow, in this unlikely event, would likely be <br />through linear zones of structural weakness (i.e., fractures, joints) which may have caused <br />the canyon to form initially. It is believed, however, that fractures and joints will terminate <br />in the soft, ductile shale and claystone units. <br />2. Cracks could locally form and be as much as 75 to 200 feet deep above chain pillars and <br />barrier pillars on the precipitous slopes, ridges, and/or cliffs that flank West Flatiron and <br />may accelerate the naturally-occurring rock fall and landslide process. <br />The worst possible, but again very unlikely, underground impacts in the Apache Rocks and <br />the Box Canyon mining areas may be that: <br />3. Interconnected fractures in the fractured zone may form in the Marine Sandstone that <br />underlies the D Seam and impact isolated groundwater that may be present. Any grater <br />present in these lenticular sand units of the Marine Sandstone might therefore be dig: e:-tad tn <br />the smile ? orkinas. <br />Though unlikely, fractures filled with water and methane that were reported in the <br />abandoned Oliver No. 2 Mine (Dum-ud 1976, p. 30-34) might be encountered or iintersected <br />• by the B Seam fractured zone that may divert the water and methane to the B Seam <br />workings. <br />2.05-158 Revised Jane 2005 PRIO, Rev. Alm•ch 2006; Allay 2006 PRIO, Nov. 2006TR707,Ap7-il 2007TRI08; Sep. 2007 PR12, Feb. 2008 PR-12