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SubTerra, Inc. Peabody Twentymile Coal, LLC April 11, 2016 <br />Subsidence Mitigation During 9 -East Undermining of the Energy Spur at the Foidel Creek Mine <br />3. Remedial Actions <br />Two potential remedial schemes have previously been used to mitigate subsidence impacts to the <br />Energy Spur, partial re -leveling with pre -ballasting of the track, and partial re -leveling during track <br />undermining. Planning for both partial re -leveling schemes involves calculating the amounts of <br />ballast required at each Station to partially compensate for the subsidence that will occur. Pre - <br />ballasting further involves the pre -placement of ballast in advance of mining, while "partial re - <br />leveling during track undermining" involves sequential placement of ballast and track tamping, on a <br />daily basis, during track undermining. Both of these methods have been successfully used during <br />prior phases of track undermining. <br />Prior mitigation has involved building out the ballast prism, "flooding" the track with ballast and side <br />dumping ballast alongside the track so that it can be easily placed during undermining. A tamper <br />and regulator were kept in a siding near the project site and used daily during undermining to re - <br />ballast and elevate the track. <br />The above process worked well during non -winter months when the tracks were free of snow and <br />is the preferred methodology from a QA/QC perspective. However, if undermining is planned <br />during the winter months, re -ballasting can be completed prior to mining and the track left flooded <br />with ballast. <br />3.1. Remedial Planning <br />There were two steps involved in remedial planning. The first step was to model the predicted <br />subsided elevation for each railroad Station (e.g., see Table 1, Column 8 and Figure 5). The third step <br />was to model the required track re -elevation required to ensure that differential gradient tolerances <br />can be maintained in the future (e.g., see Table 1, Column 12 and Figure 6). <br />Previous Energy Spur projects involved maintaining gradients below or at 1.5% with a maximum 0.2% <br />differential gradient. However, existing gradients exceed 1.5% through and up -gradient of the mining <br />area. The planning approach was therefore to bring gradients below 1.5% inside the zone affected by <br />mining while improving differential gradients. <br />Table 1, column 11 shows the estimated, partial re -levelling required to bring the section of track <br />above the mining area to less than a 1.5% grade. Maximum subsidence effects with remediation are <br />estimated at: <br />1. Maximum subsided gradient of 1.4%. <br />2. Differential gradients less than 0.3%. <br />Figure 6 and Table 1 present the original elevation, predicted subsided elevation and required re - <br />elevation curves for 9 -East. Drawings 4 and 5 show the existing and required ballast prisms derived <br />in this study. <br />3.2. Field Implementation <br />Field implementation of the re -elevation (or re -leveling) program will involve either (1) pre -ballasting <br />of the Energy Spur in advance of undermining followed by periodic survey of the alignment during <br />undermining, or (2) re -leveling the Energy Spur during undermining. Additional detailed remedial <br />planning work will be carried out prior to undermining the track. Tasks will include: <br />6 PN: 2016-10 <br />