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2 - 42 <br />As shown on Figure 2.2-3, sub-basin D-I, D-2 and D-3 are the major sources of sediment for <br />• the sediment pond. The area is about 2.9 acres. Thus an additional 0.29 acre-feet of storage must <br />be provided, for a total sedimentation pond volume of about 0.54 acre-feet Discharge from this <br />sedimentation pond is permitted through an NPDFS permit issued by the Colorado Department of <br />Health (See Appendix ~. <br />The facilities in the mine operations area were designed to convey the runoff from the <br />undisturbed areas around the site in buried culverts. Design of all culverts is shown on Table 4.2-13. <br />The design pointr are shown on Figure 2.2-3. As shown on Table 4.2-10, there is a peak Flow of 32.4 <br />cfs at the upstream end of the 42 inch diversion culvert for sub-basin C-3. Table 4.2-13 shows the <br />calculations which indicate that the capacity of the culvert is 117 cfs. The diversion ditch and <br />existing drainage downstream of the culvert have greater than 20 square feet of waterway area to <br />carry the flow at reasonable velocities. Culvert installation practices are contained in Appendix M. <br />• The 30 inch culvert on the north side of the mine site carries undisturbed flow from sub-basins <br />C-I and C-2. Peak Flow from C-2 is 14.03 cfs and C-I is about 3.67 cfs. The culverts have adequate <br />capacity of 63 cfs and 32 cfs respectively. This culvert discharges into the same drainage as the 42 <br />inch culvert draining C-3. The discharge area of these culverts are armored with rip-rap to protect <br />against erosion. Grand Valley has also obtained CMLR approval (MR-15) to extend both of these <br />culverts 50 feet to the bottom of the slope that they discharge onto to further reduce the possibility <br />of erosion. <br />The 42 inch culvert beneath the haul road is designed to safely pass the combined flow from <br />the upstream diversions. The design flow is 52 cfs and the opacity of the culvert is 149 cfs. The <br />other drainage facilities, as depicted on Figure 2.2-3, are adequate to carry surface runoff from the <br />disturbed and undisturbed area, in accordance with applimble regulations. <br />Mc <br />Volume 1 <br />10.12-97 <br />