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Other culverts were sized for the maximum discharges from 10-year 24-hour storms (20-year, 24-hour <br />storms for culverts with areas exceeding 35 square feet). The technique used was that presented in <br />SCS-TP-149 (Rev. 1973) and was applicable to watersheds with areas less than 2000 acres. See <br />Section V-B-2 for a discussion of runoff calculations. <br />Drainage ditches along the haul road and plant access road were sized to handle runoff from a 10-year <br />24-hour storm. Where velocities were expected to exceed four feet per second due to steepness of <br />grades, ditches were lined and riprapped. All ditches were seeded along with cut and fill slopes as <br />previously discussed. Straw dikes, rock check dams, and other erosion control methods were field <br />specified to minimize erosion prior to vegetation establishment. <br />All culverts were designed assuming that inlet conditions control, the headwater to diameter ratio is 1:0, <br />and that the culvert ends protrude from the fill. Culverts larger than 48 inches in diameter were designed <br />assuming that inlet conditions control, the diameter ratio was not greater than 1:5, and that rock or <br />concrete head walls were used. <br />Riprap was placed at all culvert entrances and exits. There is a minimum of three feet of compacted <br />material over all culverts. Generally culverts over 36 inches in diameter were installed along with <br />embankment construction. Culverts under 36 inches in diameter were installed after road embankment <br />construction is completed and before the final gravel or crushed rock and finish courses were placed. <br />• Sizes and locations of all culverts are shown on the plan and profile drawings. The drainage areas for <br />the major culverts and typical calculations for ditches and culverts along the haul road and plant access <br />road are included in Illustrations 1, 2 and 3. <br />Haul roads and other unpaved roads are maintained by periodic regrading of the gravel surface and <br />regraveling as required. Ditches and culverts are also cleaned periodically to assure proper drainage. <br />The surface of the road is watered and treated with magnesium chloride or other appropriate additive for <br />dust control. Maintenance complies with Section 4.03.1(6) requirements. <br />The haul road will be completely reclaimed. The culverts will be removed and the gravel surface will be <br />scraped up and buried in an approved fashion. The terrain will then be regraded to approximate original <br />contours, covered with topsoil and reseeded, Typical cross sections showing how the haul road will be <br />reclaimed are shown on Map 69. <br />Refuse is transported from the preparation plant to the Refuse Disposal Area by 35 to 100-ton off-road <br />trucks. These trucks operate at a maximum speed of 30 mph. The speed is restricted to 20 mph on <br />some curves and near the plant site. <br />Mine Permit Renewal #3 (Rev. 8/99) IV-16 <br />