2010-09-03_ENFORCEMENT - C1981019 (5)

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is EXHIBIT 7, ITEM 14, PART R — EAST PIT RECLAMATION SEQUENCING The progression of mining in the East Pit is generally from east to west, climbing upward in topography and moving away from the Prospect Pond. As a result, the watershed tributary to the pond in the early years is intercepted by the inactive East Pit, and grows as backfilling and grading advance westerly. The progress of the backfilling/grading activity is presented on Map 29. The entire watershed tributary to Prospect Pond is ultimately 711.1 acres. As of 2010, approximately 550.7 acres of that total is tributary to the pond, with the remainder being intercepted by the East Pit. The 550.7 acres that drains to Prospect Pond includes 322.3 acres of disturbed land and 228.4 acres of undisturbed land. About half of this total, mostly undisturbed land in Section 15 and the reclaimed land from the Section 16 pit, arrives at the pond by way of the South Collection Ditch in the southern half of Section 15. The remainder of the watershed is intercepted by the East Pit and various diversion ditches described in more detail below. As backfilling progresses westward and up the hill, the tributary area to Prospect Pond will grow until ultimately the entire 711.1 acres of reclaimed and undisturbed watershed reports to the pond. The determination of the worst case condition with respect to sediment pond performance is therefore not obvious. Accordingly, several time frames were separately evaluated, each representing a further progression of the mining activity to the west, as described sequentially on Figures Exh.7- 14R -1/2, 7- 14R -3/4 and 7 -14R- 5/6. The figures are presented in pairs, one with hatching to describe the reclamation status, and the other providing acreages and topography. • In order to assure compliance with effluent requirements at the outlet of Prospect Pond, up to 5 stock tanks will be constructed in the re- established main drainage channels of Prospect Ditch, North Tributary Ditch, and Final East Pit Ditch. Three of these (ET1, NTEP1 and PD 1) will be constructed in 2010, one in 2011 (EP2), and the other (PD2) in 2012. C] The on -line stock tank ponds will be designed in accordance with Fig. 2.05 -6 "Stock Tank Plan/Profile — Typical Design ", and constructed at the locations shown on Figures Exh. 7 -14R -1 through Exh. 7 -14R -6 included in this technical revision. In many cases these stock tanks completely intercept the runoff from their tributary watersheds in the 10 year 24 hour design storm. For the reclamation sequencing of the East Pit, three time frames were evaluated for the drainage to Prospect Pond. The results of the SEDCAD modeling for each are described below. Curve Numbers assigned to each subwatershed in each development stage are as per TR -73. As would be expected, some of the curve numbers vary with the passage of time as the age of the reclamation increases. Spillway design storms for the Prospect Pond were included in Volume 2D, as previously approved. Exh. 7 -14R -1 Revision Date: 09/01/10 Revision No. TR -87