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discharge pipe extends to the river, additional riprap has been placed to mini- <br />• mize discharge erosion impacts. <br />The top of the impoundment ranges from 10 to 15 feet wide and is accessible <br />for maintenance from the existing access road. <br />After the structure was constructed, topsoil was placed to a depth of 12 <br />inches and fertilized, mulched, and seeded in accordance with specifications <br />outlined in Section 2.05.4. <br />During the bonding period, Sun Coal Company will maintain the structure <br />and monitor discharge in accordance with the approved NPDES permit stipulations <br />(see Section 2.05.6). <br />Additional sedimentation ponds and traps are located on the backfilled mine <br />L~ <br />area as discussed in Section 2.05.4. <br />Water bars, or cross drains, have been incorporated to remove water from <br />the road surface to ditches, runouts, sediment traps, and sedimentation ponds <br />before water is ahle to concentrate and subsequently erode the road surface. <br />Cross drain spacings recommended by Packer (1967) provided guidance on <br />appropriate cross drain spacing in relation to the road grade. <br />All water bar designs are based on "worst-case" road surface water runoff <br />for the areas between road markers 2200 to 2400 feet (Map 8), road grade 0 to 3 <br />percent (0.34 acres); 6500 to 7250 feet, road grade 3 to 6 percent (0.34 acres); <br />and 7250 to 8550 feet, road grade 6 to 9 percent (0.34 acres). <br />The "worst case" 100-year, 24-hour peak runoff cross drain flow (Table <br />2.05.3-4) is .37 cubic feet per second (cfs). Utilizing this peak flow, a water <br />bar with an adequate freeboard was designed with a minimum top width of 5 feet <br />- 178 - (Rev. 5/86) <br />