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• Haul roads at the mine site were designed with appropriate ditches, grades and culverts to con- <br />trol erosion and runoff. All haul roads were constructed basically "on-grade". The existing haul <br />road profiles and typical cross section are shown on Figures 13-1, 13-2, 13-3, and Exhibits 13- <br />20 and 13-21. Construction summaries and certifications are presented in Attachment H. <br />Drainage. Each haul road not within areas disturbed by mining and reclamation activities was <br />designed, constructed and maintained to have adequate drainage using ditches and culverts to <br />safely convey the peak runoff from a 10-year, 24-hour precipitation event while maintaining a <br />minimum of one foot of freeboard to the top of the road embankment (see Exhibits 13-4 and 13- <br />5 and for general locations and Exhibit 13-20 for typical details of drainage sWCtures). <br />Drainage ditches were placed at the toe of all cut slopes formed by the construction of haul <br />roads. Water will be intercepted before reaching a large fill and drained safely away in <br />accordance with the requirements of 4.03.1. Water from a fill will be released below the fill <br />through conduits or in adequately lined channels and will not be discharged onto the fill. <br />When drainage ditches discharge onto open terrain, a number of measures were taken to protect <br />the terrain from erosion. Temporary measures to reduce erosion were employed while the area <br />was undergoing revegetation such as straw dikes, containment ditches, etc. Peabody typically <br />• constructed ditches on the inside of roadway cuts and safety berms for drainage. Atypical V- <br />ditch section is a minimum of two feet deep with side slopes 1.5:1 or flatter. As most road cuts <br />are into resistant bedrock-type material, ditches normally do not require lining. Culverts were <br />designed and installed to minimize the runoff volume conveyed in each ditch. Culverts and <br />ditches were designed using SEDIMOT II to predict the peak runoff and Manning's equation to <br />determine the peak velocity and flow depth (see Attachments I and J). <br />Drainage from haul roads within the areas disturbed by reclamation activities (see Exhibits 12-2 <br />and 12-3) was constructed to meet the requirements of 4.05.2 and such haul roads at a <br />minimum were constructed and maintained to minimize erosion of the disturbed area. Erosion <br />control measures used singly or in combination include: <br />a. Stabilizing all exposed surface areas to promote a reduction in the rate and <br />volume of runoff; <br />b. Using straw dikes, riprap, check dams, berths, geotextile materials, mulches, <br />vegetation sediment filters, contour furrows or other measures that reduce <br />overland flow velocity, reduce runoff volume, or frap sediment; or <br />• <br />13-11 <br />