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SubTerra, Inc. Peabody Twentymile Coal LLC 09/27/2014 <br />Foidel Creek Mine <br />Permit Revision for Longwall Mining in the Wolf Creek Seam - Subsidence Evaluation <br />5.4.2. Structure Tilt <br />5.4.2.1. Foidel Creek- Steamboat Transmission Line <br />Each structure will start to subside when the longwall face retreats to within 500 -feet of its foundation. <br />At this time, the structure will begin to tilt backwards towards the approaching face and inwards <br />towards the center of the panel. As the face passes by, the structure will tilt back to vertical in the <br />traveling direction but will remain permanently tilted towards the panel center. The maximum <br />estimated permanent tilt is 0.012 ft/ft as shown in Table 4. <br />Structures on the Foidel Creek - Steamboat Transmission line are located between 400 and 600 -ft <br />apart so that two adjacent structures may be subject to subsidence at the same time. The primary <br />impact of this interaction will be a modest increase in line sag over what would be expected if each <br />structure reacted independently. <br />5.4.2.2. Archer - Hayden and Craig- Hayden - Steamboat Transmission Lines <br />Structures on the Archer - Hayden and Craig - Hayden- Steamboat Transmission lines will also be <br />subject to transitional and permanent tilt. The permanent movement will serve to "level out" the <br />permanent transverse tilt induced, during previous undermining, by Panel 19 -Right in the Wadge <br />Seam. <br />The estimated transverse tilts at Pylon 146 on the Archer- Hayden line and Pylon 145 -4 on the Craig - <br />Hayden- Steamboat line are provided in Tables 7 and 8, respectively. Tilt and displacement in the <br />direction of face retreat will be greatest for structures on the Archer- Hayden line as these structures <br />are closer to the panel center and will therefore experience more subsidence. <br />The effective length of the traveling subsidence profile (approximately 1,500 -feet) means that each <br />pole will react to the subsidence wave independently. Thus, as the subsidence at one structure ends, <br />subsidence at the next structure begins. This factor should, for the most part, eliminate the potential <br />for complex interaction allowing the response of each structure to be independently evaluated. <br />5.4.3. Differential Movements across the Structures <br />Horizontal surface strain will result in small displacements between the legs of two legged wooden <br />and four - legged lattice structures as each structure is undermined. These movements are estimated <br />to be lower in magnitude than experienced when these structures were previously successfully <br />undermined. <br />5.4.4. Risk Evaluation <br />Our preliminary evaluation indicates that subsidence risks are lower than when these lines were <br />previously undermined. Additional confidence in the acceptability of subsidence related risk might <br />also be gained by reviewing field - monitoring reports for the Eastern Mining District, earlier tests carried <br />out by Twentymile Coal in the Southwest Mining District, and the results of the initial program when <br />19 -Right in the Wadge Seam undermined these power lines. <br />14 P N : 2013 -26 <br />