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• INTAKE SHAFT FACILITY <br />ACCESS ROAD DRAINAGE DITCH AND CULVERT DESIGN <br />Peabody Energy Twentymile Coal Company (TCC} proposes to construct approximately <br />2,090 feet of access road from an existing fan/shafr pad to a new intake shafr facility <br />within the Twentymile Coal-Foidel Creek Mine located in Routt County, Colorado. The <br />purpose of this analysis is to model the access road hydrology to determine the sizing of <br />up-gradient runoff drainage ditches along the cut slope of the road, and to determine the <br />number, sizes and locations of road culverts required to intercept drainage ditch flows. <br />The 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 <br />soil investigation report (Habitat Management, Inc. October, 2003. Fish Creek Shaft & <br />Access Road Soil Investigation, Routt County, Colorado, Twentymile Coal Company <br />Permit #82056). The access road, watershed, drainage ditch and culvert locations are <br />shown on Figure 1. Supporting SEDCADTM 4 modeling results (including input data and <br />final reports) are attached. Atypical road drainage ditch design is provided on Figure 2. <br />Two (2) culverts are required to remove the flow from runoff ditches to limit runoff <br />velocities in the ditches (resulting from the 10-year, 24-hour precipitation event) to less <br />than 3.75 feet per second (fps). This will ensure that the ditches remain stable with no <br />channel scour or degradation during the peak flow event. A 6-inch culvert will be <br />required to pass the flow from Drainage Ditch ],and an 18-inch culvert will be required <br />to pass the flow from Drainage Ditch 2. However, it is recommended that culverts with a <br />minimum diameter of 18 inches be used so that culverts remain operational should debris <br />• deposition or icing occur. Following is the summary of road drainage ditch and culvert <br />design parameters and results: <br />ACCESS ROAD DRAINAGE DITCH AND CULVERT DESIGN PARAMETERS <br />AND RESULTS: <br />Road Drainage Ditch 1 <br />Design Parameters: <br />Precipitation: <br />Use ] 0-year, 24-hour storm precipitation depth = 1.8 in <br />Land Use: <br />Undisturbed area = 5.248 ac with CN = 63 (sagebrush - hyd. soil gp. C) <br />Road surface (gravel) = 0.548 ac with CN = 89 <br />Maximum road grade = 10.9 <br />Ditch length = 900 feet <br />Ditch design =triangular ditch with 3:1 side slopes (see Figure 2) <br />Ditch surface material is alluvial silts colloidal <br />Limiting ditch velocity = 3.75 fps <br />Results: <br />Peak flow = 0.51 cfs <br />Peak velocity = 3.58 fps <br /> <br />