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SubTerra, Inc. Peabody Twentymile Coal, LLC 03/16/2015 <br />Foidel Creek Mine <br />Permit Revision for Longwall Mining in the Wolf Creek Seam - Subsidence Evaluation <br />6. Evaluation of Potential Impacts to Powerlines <br />The layout of the Wolf Creek Seam Panels in relation to the Archer -Hayden, Craig -Hayden - <br />Steamboat, and Foidel Creek -Steamboat power transmission lines is shown in Drawings 14,15 and <br />16. The "H" frame structures of the Foidel Creek -Steamboat line will be sequentially undermined by <br />Panels 7 -East, 6 -East, then 5 -East over a period of several years. <br />For structures on the parallel Archer -Hayden and Craig -Hayden -Steamboat lines, mining will proceed <br />from the east towards the west in a direction that is almost parallel to the alignment of the power lines, <br />with undermining of the power lines by panel 12 -East. The 985 -foot wide longwall panel will retreat <br />between 40 and 60 -feet per day under normal conditions (subject to market demand), affecting each <br />structure for from 25 to 35 days. <br />6.1. Scope of Work <br />The scope of work covered by this report included predicting transverse and traveling subsidence <br />associated with coal extraction and determining the effects of these predicted movements on the <br />power lines. As noted above, this work followed on from previous work covering subsidence <br />prediction, planning, and observation of power line response when the Archer -Hayden and Craig - <br />Hayden -Steamboat power transmission lines were undermined by Panel 19 -Right in the Wadge <br />Seam. <br />Tasks included: <br />• Digitizing topography along the power line routes (for input to clearance calculations). <br />Twentymile Coal, LLC supplied the topographic map and aerial photographs for the area. <br />• Inputting pylon location coordinates to prediction tables. <br />• Estimating time phased surface and pylon foundation subsidence using the traveling <br />subsidence curve. <br />• Reviewing prior pylon subsidence data (from the eastern mining district) and dummy pylon <br />foundation test (from the southwest mining district) for input to this study. <br />6.2. Approach <br />Our approach included developing a subsidence prediction for mining the Wolf Creek Seam in the <br />Northern Mining district as noted in Section 2. Predicted transverse and traveling subsidence profiles <br />were subsequently used to estimate the time phased movements along those portions of the Foidel <br />Creek -Steamboat lines that cross Panels 7 -East to 5 -East and those portions of the Archer -Hayden <br />and Craig -Hayden -Steamboat lines that cross Panel 12 -East. <br />6.3. Subsidence Prediction <br />6.3.1. Foidel Creek -Steamboat Transmission Line <br />Figure 9 shows predicted subsidence along the Foidel Creek -Steamboat line and Table 6 shows the <br />p f & iiit6d subsidcilGe chid pernianerit tilt at each "H" flame struGtuiu. Individual otructufes will subside <br />by up to 6 -ft with a maximum of 2.5 -in differential settlement between the legs on each structure. <br />13 PN: 2013-26 <br />