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<br />• WEST ENTRANCE HAUL ROAD DRAINAGE DITCH AND CULVERT DESIGN <br />Peabody Energy Twentymile Coal Company (TCC) proposes to construct approximately <br />1,800 feet of heavy haul truck access road from an existing road to County Road 27 located <br />in Routt County, Colorado. This haul road design includes highway entrance and exit ramps <br />and an underpass under County Road 27. The purpose of this analysis is to model the haul <br />road and surrounding area hydrology to determine the sizing of runoff drainage ditches along <br />the haul road and to determine the sizes of haul road culverts required to intercept drainage <br />ditch flows combined with flows through existing culverts under County Road 27. The <br />hydrologic and hydraulic modeling was conducted using SEDCADT"' 4 (Build Date <br />2000.09.07). Watershed soil and cover information were taken from site photos and a soil <br />investigation report (Habitat Management, Inc., October, 2003. Fish Creek Shaft & Access <br />Road Soil Investigation, Routt County, Colorado, Twentymile Coal Company Permit <br />#82056). Information on the material that would be exposed in the road cut drainage ditches <br />was taken from exploratory test-hole data from 6 different holes drilled along the proposed <br />centerline of the access road alignment (Northwest Colorado Consultants, Inc. Januazy 20, <br />2006. Geotechnical Investigation, Proposed South Haul Road, Foidel Creek Mine, Routt <br />County, Colorado). The proposed haul road, watersheds, drainage ditches and existing and <br />new culvert locations are shown in Figure 1. Supporting SEDCADTm 4 modeling results <br />(including input data and final reports) are attached. Atypical road drainage ditch design <br />(Figure 2) and design schematic for a typical culvert installation (Figure 3) are provided. <br />Three (3) new culverts are required to route the combined water from the watersheds above <br />County Route 27, water from existing culverts under County Road 27, the proposed haul <br />• road surface and watersheds between County Road 27 and the proposed haul road. Four (4) <br />drainage ditches are required to carry runoff to the culverts. The ditches are to be designed to <br />limit runoff velocities in the ditches to less than or equal to 4.0 feet per second (fps). This <br />will ensure that the ditches remain stable with no channel scour or degradation during the <br />peak flow event. Modeling results indicate that culverts with minimum diameters of 8, 18 <br />and ] 8 inches for new culverts 1, 2 and 3, respectively, will adequately pass the 100-year, 24- <br />hour design storm peak flows. It is recommended, however, that culverts with a minimum <br />diameter of the up-gradient County Road 27 culverts (36 inches) be used for the haul road <br />culverts so that new down-gradient culverts do not back up flow onto the haul road <br />embankments. The new roadway drainage ditches have been modeled as triangular erodible <br />channels that intercept runoff from the haul road surface and small watersheds between <br />County Road 27 and the haul road, as a conservative approach. Therefore, in some locations, <br />the existing naturally vegetated channels can be used in place of constructed ditches without <br />scour during the peak flow event. A summazy of road drainage ditch and culvert design <br />pazameters and results are presented below. <br />• <br />