2012-05-03_PERMIT FILE - C1992081 (3)

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Appendix 12 -4 Culvert and Ditch Design Tntrnrinrtinn A meeting was held in the field during fall 1992 between the Colorado Division of Minerals and Geology (CDMG) and Hayden Gulch Terminal, Inc. (HGTI) personnel as part of assigning the Loadout facility to HGTI. It was agreed at this meeting that existing (installed during the construction of the Loadout facility circa 1978/1979) hydrologic structures required designs. It was further agreed that those designs would be limited to hydrologic structures within the immediate facilities area (i.e. crusher, conveyor, tipple, etc.) and not extend the entire length of the railroad track. Although numerous culverts extended beneath the railroad embankment, these were constructed (approximately 1979) for flood control and not to route runoff through the transportation network or to sedimentation ponds. Two of the existing railroad ditches (Ditches 7 and 8) fell within this category and were not included in the design process. The existing culverts and ditches have been inplace for a number of years (since the facility was built circa 1978/1979). This design effort is, therefore, a verification that these structures will continue to function properly. Existing ditch shapes and sizes were derived from aerial photography, surveying and topographic maps. This information was used in the SEDCAD+ computer analysis. Although ditch shapes may not be consistent throughout the entire length, the cross - sectional area is more than adequate due to the largely insignificant drainage areas. Design Considerations Most design information is found in the computer analysis outputs. All ditches and culverts were designed to safely pass surface runoff from the 10 -year, 24 -hour precipitation event. Only two different curve number (CN) values were used: • Rangeland: CN = 84 • Dirt Roads: CN = 89 Areas, slopes and land use categories are as stated. The following tables are a list of culverts and ditches that have been designed or at least assessed by HGTI as part of TR- 01. Other ditches and culverts do not have specific designs for the reasons noted above. All existing hydrologic structures and noted in the following tables meet current design criteria. If culverts are replaced in the future due to maintenance problems, larger culverts will generally be employed. New culverts will be designed in accordance with the Colorado Division of Reclamation, Mining and Safety (CDRMS) regulations. TR -08 12 -4.1 Revised 02/12