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• Drainage and sediment control structures will be maintained so that they are stable and functional <br />at all times, until final bond release is approved. See Section IV.J.1 for the control systems. The <br />consVuction of permanent ditch segments affected by final reclamation in refuse area 2/3 perimeter <br />collection ditches and refuse area 4 perimeter collection ditches will be delayed until final <br />reclamation. Similarly, the revegetation of collection ditches currently subject to deposition of cooly <br />sediment and frequent maintenance wiA be completed after the final revegetation of refuse piles are <br />completed. Interim measures will be taken to control sediment and ditch erosion. Such measures <br />may include some or all of the following: (i) temporary rock check dams (see Figure IV-1 ), (ii) straw <br />bale check dams, (iii) dug out sediment traps (see Figure IV-2), (iv) rip rap or other ditch lining, (v) <br />contour ditching along slopes of refuse areas, (vi) land imprinting using sheep's foot compactor for <br />refuse area slopes and (vii) use of a clarifying agent (Nalco Enact 7888 or equivalent) for <br />decreasing settling lime in sediment ponds. RP-5 perimeter ditches were constructed as <br />permanent ditches and sediment and erosion controls will be installed as appropriate to the ditch <br />design and steepness. <br />Diversion ditches around the perimeter of the refuse disposal sub-areas will intercept runoff from <br />undisturbed areas and either direct it to the sediment ponds or to a natural drainage if the ditch <br />does not collect runoff from waste banks or disturbed areas. Permanent diversion ditches are <br />designed in accordance with the requirements of State Rule 4.10.3(2), 4.09.2(7) and 4.05.4. <br />Permanent diversions are designed to pass the runoff from a 100-year 24-hour storm. Interim or in- <br />• pit refuse area perimeter ditches will also be sized in accordance with the referenced designs to <br />pass the runoff from a 100-year, 24-hour storm. The ditches will be designed to carry the design <br />flow depth and 0.3 feet of freeboard in all areas including the riprap and checkdam sections. See <br />Illustrations 4, 5, and 6. After reclamation has been completed and the sediment ponds have been <br />removed, the permanent diversion ditches will be extended to drain into the natural drainage as <br />shown on Map 81. The ditch design will not apply to the western RP-5 ditch collecting undisturbed <br />area diversion since this ditch area will be a part of the future refuse area 6 (RP-6). <br />The diversion ditches will not be constructed all at once but will be constructed as required as the <br />refuse spoil bank is enlarged. Ditches will be seeded and energy dissipation devices such as <br />cobble dams (Figure IV-1) will be utilized in ditches on steep slopes where water velocity is <br />expected to exceed four feet per second and may cause erosion problems. Temporary diversion <br />ditches will be installed up-slope from the actual working area to catch runoff from the undisturbed <br />area and channel it into the permanent diversion system or away from disturbed areas. <br />Mined material with a specific gravity greater than 1.6 is considered to be coal processing waste. <br />This is known as "sink" material, and samples of it were submitted to commercial laboratories for <br />chemical analyses as required by the Code of Colorado Regulations (2.04.6(2) and 4.09.1(12)(b). <br />The results of the analyses are included in Appendix 9 of Section II.B. <br />• Permit Rev. 4 (07/2002) IV-19 <br />