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Subsidence Evaluation for the <br />Exhibit 60E Southern Panels, Apache Rocks West, & Sunset Trail Mining Areas Page 41 <br />14.0 SUBSIDENCE CONTROL PLAN <br />Longwall mining has been and is being used for extraction of the B -seam and E -seam in the West <br />Elk Mine. Although longwall mining may initially induce more caving and fracturing of the roof <br />rocks as compared to the room -and -pillar method due to the complete removal of coal in the panel, <br />it offers the advantages of maximizing resource recovery. The longwall method also causes more <br />uniform subsidence (full extraction of panel) and causes equilibrium conditions to be reached in a <br />shorter period of time (i.e., there is no additional, lingering pillar crushing in panels). <br />15.1 Andcipated Effects <br />Long-term impacts on the surface are predicted to be minimal above the longwall panels. The few <br />surface cracks over the mining panels that may occur are expected to close once the longwall face <br />moves past the surface area of influence. Surface cracks present above the rigid chain or barrier <br />pillars or mine boundaries may remain open for many years where permanent tensile strains remain <br />after mining is completed. However, at least several hundred feet of rock will typically exist <br />between any mine -induced surface fractures and the upper part of any mine -induced fractures <br />above the caved zone in the mining panels. Therefore, from a practical standpoint, no <br />interconnection between the surface fractures and the mine workings is anticipated. Again, under <br />a worst-case scenario, if a surface fracture were to occur concurrently within an area controlled by <br />faults or bedrock lineaments, there could be interconnection between adjacent sandstones. <br />However, even under these conditions, the fractures would not extend through the claystones and <br />shales present in the overburden. <br />Minnesota Reservoir is located well outside of the area of mining influence of the projected 13 - <br />seam and E -seam panels for the Southern Panels, Apache Rocks West, and Sunset Trail mining <br />areas and, therefore, will not be affected by longwall mining. <br />15.2 Reduction Measures (Underground) <br />Underground measures that may be taken to reduce surface strains above the chain pillars could <br />include: (1) designing the pillars to yield and crush after mining (thus minimizing humps in the <br />subsidence profile), and/or (2) planning a rapid and uniform mining rate. Any plans to reduce <br />chain pillar dimensions in order to reduce subsidence impacts must, of course, be balanced with <br />health and safety conditions in the mine. Plans for a rapid and uniform mining rate are affected <br />by market demands (or lack thereof) for a constant, high volume of coal. <br />831-032.816 Wright Water Engineers, Inc. <br />October 2018 <br />