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i '~ <br />~'~L, MU~IH <br /> <br />January 12, 2008 <br />Mr. Rov Karo <br />Reclamation Managet <br />Seneca Coal Company <br />Re: Yoast Mine Stock Pond Stability Analysis <br />Dear Roy: <br />In response to DMG's comment regarding Rule 4.05.9(8)(b) embankment stability demonstration, <br />MWH has prepared the following report related to the slope stability analysis of the existing stock <br />ponds located at Seneca's Yoast mine property. <br />Background <br />As part of SCC's ongoing reclamation activities, SCC has constructed stock ponds to enhance <br />wildlife and stock water access. These ponds are typically 8 feet high or less with slopes at or less <br />than 2H:1V upstream and downstream. SCC requested that a generic stability analysis be <br />completed to assess the stability of the embankments forming the stock ponds. As stated <br />previously, there are numerous stock ponds located on the mine's property. Instead of completing <br />an analysis for each pond, a worst case scenario would be evaluated. If the worst case scenario <br />proved to be stable, then the other embankments with lesser height and shallower slopes should be <br />stable. <br />Stability Analysis <br />A force limit equilibrium stability analysis was completed using the SLOPE/W software package. <br />A Morgenstern Price analysis was used in conjunction with a search routine to estimate the lowest <br />safety factor for the embankment. This method satisfies both moment and force equilibrium of a <br />given analysis. <br />For the worst case scenario, embankment geometry with the following characteristics was used: <br />• Embankment Crest Width: 5 feet <br />• Downstream Slope Height: 9 feet <br />• Downstream Slope Angle: 2H:1V <br />• Upstream Slope Height: 8 feet <br />• Upstream Slope Angle: 2H:1 V <br />• Height from Spillway Invert to Upstream Slope Toe: 5 feet <br />This geometry is illustrated by the SLOPE/W output shown in Appendix A. <br /> <br />