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Peabody Sage Creek Mine — Drainage and Sediment Control Plan <br />(1) foot of freeboard. Riprap requirements were determined using the PADER Method and <br />adding three (3) inches to assure a conservative design. <br />A stock pond stability analysis, conducted for the Seneca II Mine (see Tab 13, Appendix 13- <br />9A, Seneca II Mine Stock Pond stability analysis [MWH, 2003]), utilized a worst -case <br />stability scenario, which proved to be stable. In summary, the analysis contains the <br />following: <br />A force limit equilibrium stability analysis was completed using the slope /W software <br />package. A Morganstern Price analysis was used in conjunction with a search routine to <br />estimate the lowest safety factor for the embankment. This method satisfies both <br />moment and force equilibrium of a given analysis. <br />For the worst -case scenario, embankment geometry with the following characteristics <br />was used: <br />• Embankment Crest Width: 5 feet <br />• Downstream Slope Height: 9 feet <br />• Downstream Slope Angle: 2H:1 V <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 />The embankments were constructed from spoil material produced during minimg. This <br />material was placed in controlled lifts and compacted. Based on this fact, observations <br />of the spoil piles, and typical strength values for spoil material, the following strength <br />properties were assigned to the embankment. <br />• Spoil : O = 38 ° ; cohesion = 0 psi <br />• Unit weight = 120 pcf <br />Based on these assumptions, a safety factor of 1.56 was calculated by the limit <br />equilibrium analysis. Rule 4.05.9(8)(b) states that stock ponds shall have a minimum <br />static safety factor of 1.3. <br />Consequently, it is concluded that the proposed stock pond designs will meet or exceed the <br />minimum safety criteria established in Rule 4.05.9. <br />6.0 SMALL AREA EXEMPTIONS <br />The Boneyard and office areas from the Seneca II Mine operations were approved as Small <br />Area Exemptions (SAES) by CDRMS as part of Minor Revisions No. 3 and No. 11 for the <br />Seneca II Permit C- 1980 -005. These areas will be utilized for storage (Boneyard) and office <br />space as part of the Peabody sage Creek Mine operations. The location of the <br />Boneyard /Office SAE is shown on Map 2.05.3 M113, Mine Facilities Area (North End). <br />The SAE consists of the Old Boneyard, the New Boneyard and Office Parking Lot; it covers <br />approximately 5.4 acres. Seneca Coal Company sampled for settleable solids at the areas <br />TR -0/8K 2.05.3 -E2.25 Revised 04/12 <br />