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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 />5. Evaluation of Impacts to Fish, Foidel, and Middle Creeks and Their Alluvial Valley Floors <br />(AVFs) <br />Fish Creek meanders northwards across its Alluvial Valley Floor and passes over the worked out <br />Wadge seam, Western Mining District above the sub mains adjacent to 7 -East (Drawing 4). From the <br />sub -mains, it flows south across 7 -East and then east across 6 -East, northeast across 7 -East <br />(Drawing 5), 8 -East and 9 -East (Drawing 6). Fish Creek eventually leaves the planned mining area <br />over the ribside of 9 -East. <br />Foidel Creek runs east of the start room for 1 -East and across the south eastern corner of 2 -East <br />(Drawing 7), across 3 -East and 4 -East exiting between panels 4 -East and 5 -East (Drawing 8). <br />Middle Creek crosses over 1 -East's southern gate and across 1 -East and 2 -East exiting between <br />panel 2 -East and panel 3 -East (Drawing 9). <br />5.1. Scope of Work <br />The scope of work covered by this section of the report involved an evaluation of potential impacts <br />that may result from lowering the Fish Creek, Foidel Creek, and Middle Creek AVFs during Wolf <br />Creek Seam coal extraction. The following issues were investigated and resolved: <br />1. Will subsidence cause Fish, Foidel. or Middle Creeks to overtop their existing high <br />bank(s)? <br />2. If overtopping is likely, what remedial measures are required? <br />3. What will be the time -phased increase in the surface area of Fish Creek, Foidel Creek, or <br />Middle Creek due to subsidence, and/or how much of the Fish Creek, Foidel Creek or <br />Middle Creek AVFs will be flooded? <br />Several assumptions were made to simplify the analysis: <br />• Creek elevation will rise, relative to the surrounding ground, a distance equal to predicted <br />ground subsidence at that point. <br />• The effects of spring run-off on creek elevation would be in addition to the effects of <br />subsidence. <br />5.2. Subsidence Prediction <br />Subsidence prediction followed the methodology successfully applied in 1999 to evaluate the possible <br />impacts to Fish Creek when panels in the Wadge Seam in the Northern Mining District undermined it. <br />The approach involved superimposing estimated subsidence on over 100,000 data points <br />representing Fish Creek and the ground surrounding Fish Creek and comparing the subsided <br />elevations with existing (i.e., un -subsided) creek levels. The following tasks were performed: <br />1. Generating a grid of data points from the detailed, local topographic map of Fish Creek, <br />Foidel Creek, Middle Creek, and their immediate, surrounding areas. <br />2. Developing an excel spreadsheet that contained each of the data points for approximately <br />50.000 linear feet of Fish Creek. 12.000 linear feet of Foidel Creek and 3,000 linear feet of <br />Middle Creek. <br />10 PN: 2013-26 <br />