2008-05-29_PERMIT FILE - C1981019A (4)

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RULE 4 PERFORMANCE STANDARDS • All requirements set forth in Section 4.27 of the Regulations will be followed during operation and reclamation. Drainage plans are shown in Exhibit 7, Item 20, Erosion and Sediment Control Structures. The post-mining topography is shown on Map 19B. The watersheds tributary to Taylor Creek and Good Spring Creek will be improved by having a lower gradient on reclaimed streams and slopes leading into those streams, thereby reducing erosion and total suspended sediment. The lower slopes will also allow greater infiltration of precipitation, which will tend to attenuate surface water flows. The post-mining watershed drainage aeeas will be the same as the pre-mining drainage areas. Highwalls will be completely backfilled with spoil material in a manner which results in a static safety Factor of at least 1.3. No land above the highwalls will be disturbed except as shown on Map 23A, Mine Plan. The highwall will be blended into the backfilled material to result in a natural and gradual slope change. As discussed in Section 4.14.2, final grading will be accomplished such that overall grades will not exceed lv:3h. Rule 4.27 requires that a showing be made which demonstrates a minimum static factor of safety of 1.3 for all portions of the reclaimed land. The following analysis is provided for that demonstration: As a general observation, such a demonstration can easily by made when postmining grades do not exceed lv:3h (approximately equivalent to 18.4 degrees). For example, assuming a cohesionless dumped spoil slope with a 3H:1 V slope composed of 125 Ibs/sq. fr. in-place density and an internal friction angle (phi) of 35 degrees, the safety factor F for this "infmite slope" problem simplifies to: F = tan (35 degrees) /tan (18.4 degrees) = 2.1 • This factor is well above the required safety factor of 1.3. This analysis assumes that no phreatic surface has developed, i.e. no groundwater is present. For the purposes of this analysis, this is a valid assumption. According to the U.S. Army Corp. of Engineers Manual entitled "Engineering Design, Slope Stability, October, 2003" (EM 1110-2-1902), in the case of cohesionless soils, "the critical mechanism is shallow sliding, which can be analyzed as the infmite slope failure mechanism." In this case, a graphical solution from the manual can be used to verify the equation above. The calculated factor of safety shown above is for a shallow surface failure, and that surface is controlling. Adeeper-seated, lazger failure surface would have an even higher factor of safety. It is also generally recognized that such a 2-dimensional analysis is conservative. This is because it does not account for additional soil strength that occurs when 3-dimensional effects aze considered. In addition, each of the spoil pile designs (Streeter Fill, West Pit Fill, and Section 16 Fill) contain further information regazding other stability analyses that have been performed. These include additional information regarding material properties, hydrologic assumptions, and laboratory testing results that have been performed as components of the stability analyses. See Section 2.05.3 and Exhibit 19 for more information. CJ South Taylor/Lower Wilson -Rule 4, Page 31 Revision Date: 3/30/07 Revision No.: PR-02