2016-02-04_PERMIT FILE - C1981041 (50)

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The terrace drains on the Operator's refuse piles meet the requirements of the above rules. An important function of the terrace drains is to control erosion. During refuse pile construction the terrace drains intercept run off from the slope above and direct drainage off of the fill. The function of the terrace drains changes after they are seeded and mulched. Run-off from the slopes above the terrace drains decreases as vegetative cover improves and the terrace drains slowly lose their ability to convey water off of the fill. The universal soil loss equation (USLE) is a means of estimating soil loss and evaluating conservation alternatives on a quantitative basis. One factor used in the USLE is the length slope factor. The length of a slope is directly related to soil loss. According to USLE the length of slope ends where the slope decreases to the extent that deposition occurs. A two hundred foot high refuse pile with a 3H:1V slope angle has an overall slope length of 632 feet. The length of slope for a soil loss evaluation on a two hundred foot high refuse pile with horizontal benches on 30 foot vertical centers is 94 feet since the terrace drains function as a point where the slope decreases and deposition occurs. Thus the terrace drains reduce the length of slope and the amount of soil loss from the reclaimed refuse piles. The rationale demonstrates that terrace drains continue to function as important erosion control structures even after their ability to convey water off the fill is diminished. Final reclamation of disturbance associated with the South Lease Exploration Plan was done in 1985-1987. Reclamation of the North Decline area was started during the summer of 1991 and completed in the spring of 1993. Refer to Exhibit CMC Mining Inc, January 20, 1976 for topography and Exhibits 12C and 28 for North Decline Postmining topography. An area of 18.3 acres which included the North Decline, the water treatment ponds and the storage area was regraded in the spring of 1982 and seeded that fall. The Al substation, a powerline between A and Al substations and the water treatment building at the North Decline were removed during the spring of 1993 and minor regrading and seeding was performed. Demonstration that disturbed area sediment controls are no longer necessary at the North Decline is presented in Appendix 14-12. Reclamation work includes backfilling and grading the two small area exemption sediment traps, reclamation of Pond 7 and installing berm breaks along the permanent channel at appropriate locations to allow reclaimed area drainage to enter the channel. The West diversion ditch #1, East diversion ditches #1 & #2, the 12" CMP and 12" V -ditches that flow to the channel will remain as permanent features as depicted on Exhibit 12C. The 12" CMP at the outlet end of East diversion ditch #2 was removed and replaced with a designed riprap segment with the approval of TR -65 in the spring of 2015 (see Appendix 13-2, pages NDEC-9i through NDEC-9v). These ditches are stabilized with well established vegetation and have been constructed to meet the requirements of Rule 4.05.3 (see Appendix 13-2, pages TR -65 14-3i 02/15