2007-12-03_PERMIT FILE - C1980004A ‎(2)‎

• Permit No: C1980004A
• IBM Index Class Name: Permit File
• Doc Date: 12/3/2007
• Section_Exhibit Name: 2.0 General Description of Mining Operations
• Media Type: D
• Archive: Yes

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 40 acres. Pages 11-12 in Appendix N shows the
required runoff volume of 1.2 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. Grand Valley 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.
The sediment drying area will be expanded in late 2007 or early 2008. Run-off from the
"Collector Ditch" is diverted around the sediment drying area. The design for the collector ditch
diversion is shown on Table 4.2-13, Page 3.

M`Clane - MR-44 Volume I 11/07