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material. Using techniques developed by the U.S. Bureau of Reclamation (USBR, 1974), a <br />• grain size distribution was developed that optimized permeability and protected against <br />clogging. The calculated grain size distribution is as follows: <br />Mesh or Sieve °~ Passing <br />Size <br />4-inch 100 <br />1 1 /2 inch 70-85 <br />3/4 inch 40-60 <br />No. 4 10-20 <br />No. 40 4-12 <br />No. 200 < 5 <br />The drain itself will be constructed above and within the limits of the central ridge excavation. <br />The excavation will be sloped to route water reaching the bottom to a central 2-foot wide by <br />2-foot deep box-type cut as shown in Drawing 95266-01. The box-cut will be filled with the <br />drain material, creating the underdrain. This underdrain will exit at the toe ditch where <br />discharge is routed to the sediment pond. <br />4.1.3 Haul Roads <br />Haul roads will be constructed similar to the details on Drawing 95266-03. The average <br />grade has been designed to be a maximum of 10 percent, consistent with Rule 4.03.1(31. <br />The haul roads on the benches at EI. 6,035 ft, EI. 6,085 ft and EI. 6,135 ft are at a 2 percent <br />grade. On the outside of the haul road will be a small safety berm approximately 2 to 3 feet <br />high. On the inside of the haul road is a ditch sized to convey a 100-year, 24-hour storm. <br />On haul roads constructed at 10 percent grades, a minimum ditch depth is 1 foot. Ditches <br />on 2 percent haul roads need to be a minimum of 1.5 feet deep. The ditch side slopes should <br />be constructed at 2:1. Flow rates of water transported by the design storm will require scour <br />protection in the form of riprap. Riprap and filter material requirements are shown on <br />Drawing 95266-04, and are based on procedures developed by the Office of Surtace Mining <br />IOSM) (OSM, 1982). <br />• <br />To keep collected runoff water within the disturbed area, corrugated metal pipe (t'.MP) <br />culverts or optional highway-grade corrugated polyethylene (PE) pipe culverts will be needed <br />86266/1424.RPT Coel Mine Waste Bank Final Design for the Bowie No. 2 Mine <br />June 1896 WESTEC 8 <br />MCUUACY-Ol <br />