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• Sun Coal Company considered removing culverts or reducing culvert widths prior to <br />decommissioning the road; however, it was determined that disturbance to these <br />structures would not be environmentally beneficial. The existing culverts are designed <br />to convey the peak flow runoff from the design storm across the road without adverse <br />erosion or downstream sedimentation impacts. The decision to leave the culverts is <br />also related to providing adequate drainage of the road surface and to avoid <br />indiscriminately concentrating runoff into areas prone to erosion that are located outside <br />of the natural drainage. The culverts control concentrated runoff to selected areas <br />where energy capable of eroding erosive soils would be appropriately dissipated. <br />Culvert design and supporting calculations are presented oa Table 2.05.3-5 and <br />Appendix 2.05.3-5. All culverts, as recommended by EPA (1977), have a minimum <br />diameter of 18 inches. <br />Culverts to 1 to 10, Map 8, as the road drainage is designed, are capable of conveying <br />the peak flow from the 100-year, 24hour storm. All culverts are capable of being self- <br />. cleaning (velocities greater than two feet per second). However, debris or rocks have a <br />tendency to block culvert entrances; and as a result. Sun Coal Company installed trash <br />racks on all culvert inlets. <br />Sun Coal Company was released from liability and reclamation bond obligations for the <br />entire haul road in 1989. <br />• <br />Mid-Term Review -181- Revised 4/96 <br />