2009-10-20_PERMIT FILE - C1980004A (2)

Home Browse Search

2-42 As shown on Figure 2.2-3, sub-basins D-1 through D-16 are the major sources of sediment for the sediment pond. The sub-basin area is about 70 acres. Pages 13-17 in Appendix M shows the required runoff volume of 1.7 Ac-ft, and the required sediment storage volume of 0.2 Ac-ft is calculated using the Universal Soil Loss Equation. Discharge from the sedimentation pond is permitted through an NPDES permit issued by the Colorado Department of Health (See Appendix E). The facilities in the mine operations area were designed to convey the runoff from the undisturbed area around the site in buried culverts. Design of all culverts is shown on Table 4.2-13. The design points are shown on Figure 2.2-3. As shown on Table 4.2-10, there is a peak flow of 32.4 cfs at the upstream end of the 42 inch diversion culvert for sub-basin C-3. Table 4.2-13 shows the calculations which indicate that the capacity of the culvert is 117 cfs. The diversion ditch and existing drainage downstream of the culvert have greater than 20 square feet of waterway area to carry the flow at reasonable velocities. Culvert installation practices are contained in Appendix M. The 30 inch culvert on the north side of the mine site carries undisturbed flow from sub-basins C-1 and C-2. Peak flow from C-2 is 14.03 cfs and C-1 is 3.67 cfs. The culverts have adequate capacity of 63 cfs and 32 cfs respectively. This culvert discharges into the same drainage as the 42 inch culvert draining C-3. The discharge area of these culverts are armored with rip-rap to protect against erosion. The Operator has also obtained CMLR approval (MR-15) to extend both of these culverts 50 feet to the bottom of the slope that they discharge onto to further reduce the possibility of erosion. The 42 inch culvert beneath the haul road is designed to safely pass the combined flow from the upstream diversions. The design flow is 52 cfs and the capacity of the culvert is 149 cfs. The other drainage facilities, as depicted on Figure 2.2-3, are adequate to carry surface runoff from the disturbed and undisturbed area, in accordance with applicable regulations. Culverts Q, R, S and T were added at part of the TR-16 Gob pile and associated surface facilities design. Culvert Q will go beneath Light Use Road #1 and has a design flow of 6.8 cfs. Culvert R will go under the Haul Road to the Gob pile and has a design flow of 7.32 cfs. Culvert S will go under Light Use Road #2 and has a design flow of 7.24 cfs. Culvert T will go under Light Use Road #2 and has a design flow of 7.32 cfs. All three culverts will be 24"diameter and provide a capacity of 12 cfs. Rule 4.05.18, `Stream Buffer Zones', requires that surface coal mining operations will not cause or contribute to the violation of applicable water quality standards, and that during and after mining; the water quantity and quality, and other environmental resources of the stream shall not be adversely affected. Therefore, a silt fence will be installed as shown on Figure 2.2-3 in order to control runoff from the disturbed area within 100' of East Salt Creek. The Stream Buffer Zone will be clearly marked with signs in accordance with Rule 4.02.5. TR-16 M`-Volume 1 (Rev 05/08)