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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 />6. Expanding the 3 -D plane, representing the un- subsided water surface of Fish Creek, to <br />meet the subsided ground surface and determining the new area of this surface. <br />The results of the predictions are shown in Figure 7 and Drawings 9, 10, 11 and 12. Summary <br />data include: <br />• Subsidence ranging from 0 to 74 inches. <br />® Maximum gradient change of 2.4% along the creek bottom. <br />The estimated impacts of this level of predicted subsidence are provided in the following section. <br />4.3. Predicted Impacts to the AVF <br />4.3.1. Increase in Fish Creek's Surface Area <br />Our evaluation indicates that subsidence would result in over - topping of either the north or south high <br />bank over portions of the affected creek length. Over - topping will cause Fish Creek to spread out over <br />the AVF and link up with oxbow lakes that were previously part of the creek. The elevation of these <br />areas is typically within about one foot of Fish Creek's high bank(s) so that, in some cases, the creek <br />level will rise up against the surrounding ground. As shown on Drawings 9, 10 and 11, there is no <br />indication that the creek will occupy areas outside of its AVF. <br />The estimated increase in Fish Creek's surface area is shown on Drawing 8. Under normal flow <br />conditions, subsidence of the AVF is predicted to result in an increase of Fish Creek's surface area of <br />just under 50 acres. <br />The impacted surface area of Fish Creek may expand during peak flow months and during off - normal <br />years when peak flows are experienced. However, the relative expansion is expected to be less than <br />previously experienced by the un- subsided AVF as stream velocities, and hence gradients, will <br />decrease in flows over the undermined areas. This may in turn result in sediment deposition over the <br />mined out areas and scouring in areas where subsidence has been limited by the presence of the <br />rigid -yield pillar pair. The net increase in Fish Creek surface area during peak flow has been <br />evaluated, assuming an associated, estimated increase in creek elevation of 2 feet, using the 3 -D <br />modeling software. The additional flooded area, for high water conditions was estimated to be <br />approximately 20 acres. <br />4.3.2. Increase in Foidel Creek's Surface Area <br />The estimated increase in Foidel Creek's surface area is shown on Drawing 12. Under normal flow <br />conditions, subsidence of the AVF is predicted to result in an increase of Foidel Creek's surface area <br />of about 2 acres. <br />4.3.3. Potential for Fissure Development and Water Loss (or Stream Pirating) <br />Surface cracking or fissuring has previously been confined to areas where the Twentymile sandstone <br />either outcrops or is located relatively close to the surface. In these areas, the blocky nature of the <br />Twentymile sandstone may result in strain concentration at joints, abnormal displacement between <br />adjacent blocks and surface cracking. <br />10 PN: 2013 -26 <br />