Laserfiche WebLink
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 />4. Evaluation of Impacts to Fish and Foldel Creeks and Their Alluvial Vallev Floors (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 5 -Right (Drawing 5). From the <br />sub - mains, it flows south across 5 -Right and then east across 4- Right, northeast across 5 -Right <br />(Drawing 6), 6 -Right and 7 -Right (Drawing 7). Fish Creek eventually leaves the planned mining area <br />over the ribside of 7- Right. <br />Foidel Creek runs east of the start room for 1 -Right and across the south eastern corner of 2 -Right <br />exiting over that panels start room (Drawing 8). <br />4.1. 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 and Foidel Creek AVFs during Wolf Creek Seam coal <br />extraction. The following issues were investigated and resolved: <br />1. Will subsidence cause Fish or Foidel Creek to overtop their existing high 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 or Foidel Creek <br />due to subsidence. and /or how much of the Fish Creek or Foidel Creek AVFs will be <br />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 />4.2. 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 />and the immediate. surrounding area. <br />2. Developing an excel spreadsheet that contained each of the data points for approximately <br />18,000 linear feet of Fish Creek. <br />3. Importing approximately 100;000 data points, representing the ground surface over the <br />mining area from AUTOCAD and adding these data to the AVF data in the spreadsheet. <br />4. Numerically subsiding this data set in the spreadsheet_ <br />5. Exporting the numerically subsided data set back to AUTOCAD and creating a new <br />subsided topography. <br />9 PN: 2013 -26 <br />