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© MWH <br />MONTGOMERYWATSON HARZA <br />• <br />August 8, 2003 <br />Mr. Robert J. Shevling P.E. <br />Engineering Manager <br />Seneca Coal Company <br />Re: Seneca II Mine Stock Pond Stability Analysis <br />Deaz Bob: <br />In response to DMG's comment regarding Rule 4.05.9(8)(6) embankment stability demonstration, <br />MWH has prepared the following report related to the slope stability analysis of the existing stock <br />ponds located throughout Seneca II's mine property. <br />Background <br />• <br />As part of SCC's ongoing reclamation activities, SCC has constructed numerous stock ponds to <br />enhance wildlife and stock water access. These ponds aze typically 8 feet high or less with slopes at <br />or less 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 softwaze package. <br />A Moxgensrern 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:1V <br />• Height from Spillway Invert to Upstream Slope Toe: 5 feet <br />• <br />This geometry is illustrated by the SLOPE/W output shown in Appendix A <br />P.ll. Box 774018 Tel: 970 879 6260 Delivering Innovative Projects and Solutions Worldwide <br />7475 Pine Grove Road, Suite 709 Fax: 970 679 9048 <br />Steamboat Springs, Colorado <br />80477 <br />