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- = ~- ~ ~ Ill Illlllllllllllll <br />DATE: December 10, 1981 <br />TO: Tom Gillis <br />FROM: R.A. Domingue ,~. <br />RE: BLUE RIBBON COAL COMPANY BLUE RIBBON MINE <br />SEDIMENT CONTROL <br />Tom, <br />CO 47-81 <br />I have completed my review of the runoff and sediment control system <br />at the Blue Ribbon Coal Company (BRCC) mine - the slue Ribbon Coal Mine. <br />From drawings given in the application it is apparent that aI1 waters <br />from disturbed areas are treated in sediment ponds. Much of the work <br />for the control system was performed by Ute Engineering & Surveying <br />Company. Problems identified with the discussion are detailed below: <br />(,. Drainage Areas; <br />The map designated as Exhibit H delineates the boundaries of watershed <br />areas used in calculations of flow and volume estimates for each element <br />in the sediment control system. Of concern are the boundaries for watershed <br />areas 1 and 3. Unless there exists a diversion ditch at the upstream <br />boundary suggested for these watersheds the areas as shown are not the <br />complete watersheds. If there are diversion SystcMS in these watersheds-(~1~ec~ <br />complete designs, including contributing areas, peak flows and complete <br />ditch geometries must be presented. BRCC must explain why these <br />boundaries do not conform with the apparent natural watersheds. <br />L. Ditch Designs: <br />The method used for ditch design is not described in sufficient detail. <br />The designs appear to have been generated by use of some variation on <br />the Chezy equation. The values of the Chezy coefficient and the ditch <br />slope are not given. Without slope measurements review of the designs <br />is not possible. In order to provide sufficient information to show <br />conformance with rule 4.05 BRCC must provide all of the following for <br />ditch designs. <br />1. Drainage Area, <br />2. Design Return Period Storm and Peak Flow, <br />3. All Ditch Geometry, <br />4. Estimated Depth of Flow in Reach of Least Slope, <br />5. Estimated Velocity in Reach of Greatest Slope and, <br />6. Existing and Proposed Ditch Lining. <br />BRCC is reminded of the requirement for 0.3 feet of freeboard during <br />passage of the IO year-24 hour storm (4.05,3(6)(b)). <br /> <br />