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1999 Yoart Mine * 1942 Drainave and Sediment Cantro! Plan ~ 8 <br />7.0 TOPSOIL STOCKPILE SAE <br />A request for a small area exemption (SAE) has been included in this submittal to cover the planned topsofl <br />stockpiles at the Yoast mine. Runoff From the stockpiles will be controlled by constructing a small <br />containment berm immediately down-gradient of the pIles. The SAE request is presented in Appendix 13- <br />12.4, Topsoil Stockpile SAE, of this Attachment. <br />8.0 STOCK POND DESIGN <br />The constmcdon of stock ponds is proposed in conjunction with the constmction of various postmine <br />channels. Since the stock ponds are relatively small in size and there aze no residential or commercial <br />structures or mining operations immediately below any of the stock ponds, they do not create a threat to <br />public health and safety or tlueaten significant environmental health. <br />SCC has constmcted numerous stock ponds (temporary and permanent) in the Seneca II and II-W <br />reclaimed azeas, which continue to £uncdon as designed and according to the applicable requirements of <br />Rule 4.05.9. Attached aze designs for the proposed stock ponds ST-1 and ST-2. A certified as-built of each <br />stock pond will be submitted following constmcdon. <br />All stock ponds are located in reclaimed areas and are not primary sediment control structures. They are <br />relatively small with a storage capacity of not more than two (2) acre-feet and an embankment height no <br />greater than five (5) feet measured from the invert of the spillway to the upstream toe of the embankment. <br />The combined slope of all the embankments will be less than SH:1V with no slopes greater than 2H:1V. <br />All stock ponds will contain .t single open channel spillway designed to safely pass a 25-yr/24-ltr <br />precipitation event. The spillway will be configured to have a minimum of one (1) foot of freeboazd. <br />Riprap requirements were determined using the PADER Method and adding three (3) inches to account for <br />conservatism. Emergency spillway configurations and tiptop size for each stock pond location is presented <br />in the Table 13-12.8, Stock Pond Spillway Summary. <br />TABLE 13-12.8 <br />STOCK POND SPILLWAY SUMMARY <br />Pond 25-yr Flow <br />(cfs) Bottom Width <br />(ft) Depth of Flow <br />(ft) Freeboard <br />(ft) Riprap <br />Dsa <br />(in <br />ST-1 18.5 10 0.3 1.0 6 <br />ST-2 44.2 10 0.8 1.0 9 <br /> <br />The Colorado Office of the State Engineer was contacted xegazding jurisdiction for the permanent stock <br />ponds at the Seneca II Mine Qanuary 2003). According to the Division Engineer and as stated in Section <br />35-49-107(2) CSR, any dams that are less than five feet high and impound less than two acre-feet of water <br />would not fall under their jurisdiction. <br />The Yoast Mine will incorporate the typical stability analysis for all proposed and future stock ponds based <br />on the worst-case condition experienced and analyzed at the Seneca II Mine. The rationale for using this <br />approach is based on relatively small size of [he impoundments, the construction material consists of the <br />same general strata, and the extremely conservative inputs used in the analysis. <br />A Stock Pond Stability Analysis, conducted for the Seneca II Mine Tab 13, Appendix 13-9A, Volume 12J by <br />MWH, used aworst-case scenario, which proved to be stable. In summary, the analysis contains the <br />following: <br />Montgomery Wahon Mining Grvnp * 765 S. Union Boulevard, Suite 4G0 * Lokemaorl, Colorado 80228 * (303) 763-5740 <br /> <br />TR-30 Revised 03/07 <br />