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West Elk Mine <br />observed from the highway construction. Subsidence causes horizontal and vertical displacement <br />of the ground with attendant tilt, curvature, and strain, which may increase landslide activity on <br />slopes that aze already unstable. But subsidence does not remove material from the lower parts of <br />deposits. Subsidence processes therefore do not affect the mass distribution of the deposit as did <br />the highway construction near the northern boundary of the Box Canyon permit revision area. <br />Highwav I33 Landslides in Relation to Angle of Draw Prolertwns <br />The northernmost longwall panel of the Box Canyon mining area, as currently planned, is located <br />about 650 to 2,700 feet south of the landslides on the south side of State Highway 133. Projecting <br />to the surface an angle of draw of 21 degrees, which is the maximum angle measured in the <br />Somerset-West Elk mining area, the closest State Highway 133 landslides are located <br />approximately 600 feet north of the mining area of influence, and therefore should not be affected <br />by longwall mitring. <br />~" Imtlacts Beneath the Mined Coal Bed <br />~J <br />Based on mapping and observations by Mr. Dunrud, in the B-Seam of the Somerset Mine, <br />impacts to the coal and rocks below the mined coal bed are expected to be limited to about one <br />mining thickness. There is no expected mining impact to the Rollins Sandstone because its top (or <br />upper tongue) lies 20 to 50 feet below the base of the B-Seam. Furthermore, impacts in the floors <br />of the mine workings are expected to be limited to the chain pillars, because the floors of the <br />longwall panels aze loaded with caved roof rocks and overlying strata before deformation in the <br />floor can occur. <br />Floor heaving, pillaz punching (the pillar punches into the floor and roof rocks), and squeezing <br />(plastic flowage, see Dumud 1976 for more details) are the only expected deformation in the <br />immediate mine floor, which consists of impure coal, shale, and claystone. Deformation in the <br />floors of the chain pillars is expected to occur after the longwall panel is mined and the pillars <br />begin to crush out under the increased overburden load. <br />Possible Subsidence Consequences <br />Predicted subsidence impacts for the Apache Rocks and the Box Canyon mining azeas have been <br />described in detail above. The greatest surface impacts are expected to occur along the <br />precipitous slopes and cliffs that flattk West Flatiron and in the steep canyon slopes of the Box <br />Canyon mining azea (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 tray develop above the chain pillars common to the <br />fast three northern panels and tray divert intermittent flow in Box Canyon and the <br />unnamed canyon to the west of Box Canyon to the mine through local fractures or to <br />permeable rocks in the overburden (see Map 14 for details). Flow, in this unlikely event, <br />• <br />2.05-131 RevisedJw. /995 PR06; //96 RN03; RevisedJmr. /998 PROS <br />