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The minimum depth that the underdrain material should be placed is approximately 4 feet in <br />the center of the draw. It is anticipated that runoff control ditches on the surface should <br />transport rainwater away from the coal mine waste material so that infiltration and utilization <br />of the underdrain is minimized. Calculations relating to the underdrain is located in Appendix <br />C. <br />4.1.3 Haul Roeds <br />A haul road will be constructed similar to the details in the drawings. This road will serve two <br />purposes. First, it will provide public access to the Somerset Cemetery. Second, it will <br />provide access to the proposed coal mine waste bank. Because of its secondary use as an <br />access to the waste bank, it will be constructed as a haul road. The average grade has been <br />designed to be a maximum of 10 percent, consistent with Rule 4.03.1(3). On the outside of <br />the haul road will be a small safety berm approximately 2 to 3 feet high. On the inside of the <br />haul road is a ditch sized to convey a 100-year, 24-hour storm. On haul roads constructed <br />at 10 percent grades, a minimum ditch depth is 1 foot. The ditch side slopes should be <br />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 finer material requirements are shown on Drawing <br />• 95255-03, and are based on procedures developed by the Office of Surface Mining IOSM, <br />1982). A plan and profile of this road is presented in Drawing 95255-05. <br />To keep runoff water which accumulates on the haul road within the haul road system a <br />corrugated metal pipe (CMP) culvert or optional highway-grade corrugate polyethylene (PE) <br />pipe culvert will be needed below the haul road at the switchback at EI. 6.090 ft. It is <br />recommended that an 18-inch minimum diameter CMP be used for this culvert. This culvert <br />will convey the maximum 1-foot design depth from the haul roads with 6-inches of dry <br />freeboard. Taking runoff through the switchback at an approximate 10 percent grade, the <br />culvert was calculated to transport water at 14.1 cfs, above the 3.9 cfs design flow rate for <br />the runoff control ditches. The culvert should be covered with a minimum of 1-foot of cover. <br />Regular maintenance should be employed to keep haul road ditches and culverts clean. <br />Road-cuts in the upper portion of the haul road will primarily be done in bedrock. Because of <br />the competent nature of the outcrops and the existing road-cuts near the site, the road-cuts <br />for the haul roads were designed to be at 1.5H:1V slopes. Fills required as part of the haul <br />• <br />96266/1424.RPT Coel Mine Weete Benk DeBiQn for the Sanborn Craek Mine <br />October 1998 WESTEC, Inc. 8 <br />