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F1r. [dilliam S. Tate -6- February 17, 1982 The result of this discrepancy is that the bench collection system, Pond 2, the haul road ditch, and culvert No. 1 may be inadequate. As all o.f the drainage in areas 1 and 3 is undisturbed, diversion of this flow away from the pond collection system wi.il reduce or eliminate the need for re-design. The following is a series of :suggested solutions to the problems caused by the discrepancies found in Exhibit N: 1. Bench Collection System In the current system, all of the undisturbed drainage in area 3~is collected by the bench collection system and routed to Pond 2. As all of area 3 is undisturbed watershed, it need not be retained in a sediment pond. The existing collection ditch above the mine bench could be extended to collect all of area 3 and divert it into the adjacent ephemeral drainage to the north. This would eliminate the need to design the bench collection system and Pond 2 for the drainage from area 3. 2. Haul Road Ditch and Culvert No. 1 In the existing system, the drainage from area 2, area 1 and area 9 are routed along the haul road ditch through Culvert No. 1 and into Pond 2. Area 9 is small, used only for equipment storage and a Likely candidate for a Small Area Exemption (9.05.2(3)(b)(i)). Area 1 is undisturbed and, therefore, does not require detention in a sediment pond. Of these three areas, only area 2 need be passed through a sediment pond. The nu:ne bench could be graded such that area 2 drains to the north, into the bench collection culvert and through Pond 2 without coursing along the haul road ditch. The haul road ditch would need to be designed to safely handle the 10-year, 24-hour storm peak flow from area 1 and be extended past the switchback to disc)rarge into Ifubbard Creek. This completely eliminates the need for culvert No. I. Some rock riprap at the terminus of this ditch would be alI that would be required for approval as a diversion. 3. Area 8 No discussion of the existing diversion around the coal stockpile in area 8 is included in the application, nor is the upstream drainage area contributing to this diversion shown on Exhibit B. Both a design of this ditch, providing for the passage of 10-year, 2.9-hour storm peak flow and a map showing the entire contributing area must be provided. In summary, Blue Ribbon Coal Company must: A) Provide a revised Ex,Sibit N, showing the correct topography and the entire contributing areas of areas 1 and 3 and the area above the area 8 diversion , B) Provide revised designs of all structures which have a contributing area change, and