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• 2-42 <br />As shown on Figure 2.2-3, sub-basins D-1, D-2, D-3, and D-5 are the major sources of <br />sediment for the sediment pond. The sub-basin area is about 17.8 acres. Table 4.2-12 shows <br />the required runoff volume of 0.36 Ac-ft, and the required sediment storage volume of .19 Ac-ft <br />is calculated using the Universal Soil Loss Equation. Discharge from the sedimentation pond is <br />permitted through an NPDES permit issued by the Colorado Department of Health (See <br />Appendix E). <br />The facilities in the mine operations area were designed to convey the runoff from the <br />undisturbed area around the site in buried culverts. Design of all culverts is shown on Table <br />4.2-13. The design points are shown on Figure 2.2-3. As shown on Table 4.2-10, there is a <br />peak flow of 32.4 cfs at the upstream end of the 42 inch diversion culvert for sub-basin C-3. <br />Table 4.2-13 shows the calculations which indicate that the capacity of the culvert is 117 cfs. <br />The diversion ditch and existing drainage downstream of the culvert have greater than 20 <br />square feet of waterway area to carry the flow at reasonable velocities. Culvert installation <br />• practices are contained in Appendix M. <br />The 30 inch culvert on the north side of the mine site carries undisturbed flow from sub- <br />basins G1 and G2. Peak flow from G2 is 14.03 cfs and G1 is 3.67 cfs. The culverts have <br />adequate capacity of 63 cfs and 32 cfs respectively. This culvert discharges into the same <br />drainage as the 42 inch culvert draining G3. The discharge area of these culverts are armored <br />with rip-rap to protect against erosion. Grand Valley has also obtained CMLR approval (MR-15) <br />to extend both of these culverts 50 feet to the bottom of the slope that they discharge onto to <br />further reduce the possibility of erosion. <br />The 42 inch culvert beneath the haul road is designed to safely pass the combined flow <br />from the upstream diversions. The design flow is 52 cfs and the capacity of the culvert is 149 <br />cfs. The other drainage facilities, as depicted on Figure 2.2-3, are adequate to carry surface <br />runoff from the disturbed and undisturbed area, in accordance with applicable regulations. <br />M°Clane Volume 1 Revision 09/05 <br />