2013-10-30_REVISION - M1977310 ‎(3)‎

• Permit No: M1977310
• IBM Index Class Name: REVISION
• Doc Date: 10/30/2013
• Doc Name: DRAINAGE DESIGN PLAN FOR THE JD6 MINE
• From: COTTER
• To: DRMS
• Type & Sequence: AM1
• Email Name: TC1
• Email Name: SJM
• Media Type: D
• Archive: No

JD -6 Mine — Drainage Design Plan 43
5.5 Culvert Capacity
Culverts were evaluated to determine the size required to convey the 100 -year 24 -hr peak flow rate (gloo)
based on the parameters shown in Table 25. As shown in Figure 2, the existing culverts are located on
County Road EE 19 and are owned and maintained by Montrose County. Existing culverts are constructed
using 18 -inch diameter corrugated steel pipe. The capacity was evaluated using HY -8 (FHWA, 2012).
On the EE 19 Road, Montrose County installs culverts to fit their requirements.
Any new culverts installed by Cotter within the JD -6 mine area will be installed with adequate capacity to
convey the 100 -year 24 -hour storm, and will be a minimum of 18 -inch diameter.
Table 25. Culvert Capacity for 100 -year 24 -hour Storm Event
Parameter
Culvert C -1
Culvert C -2
Contributing Sub -Basin
N -I
N -H
10 Design Flow cfs
0.31
0.20
100 Max Flow cfs
0.9
0.53
Channel Depth / Culvert Diameter ft
1.5
1.5
Culvert Flow Depth ft
0.34
0.25
Tailwater sloe
0.191
0.075
Velocity ft/s
3.09
2.64
Slope ft/ft
0.02
0.02
6. STRUCTURAL CONTROLS AND ADDITIONAL STORMWATER BMPS
6.1 Summary of Existing Structural Controls for Stormwater
The best management practices (BMPs) for stormwater evaluated above include diversion ditches to
convey upland runoff around the JD -6 Mine site, as well as drainage ditches, berms, and the stormwater
retention pond for the capture, control and treatment of runoff. In summary, existing structural controls on
stormwater flow are shown in Figure 4 and include the following:
• Upper Diversion Structure
• Middle Diversion Structure
• Lower Diversion Structure
• Stormwater and Sediment Retention Pond
• Crest Berm surrounding the waste rock pile
• Perimeter Ditch surrounding the mine facilities area.
• Silt Fence located at the toe of the waste rock pile
6.2 Sediment and Erosion Prevention
Several practices are employed at the JD -6 Mine to reduce erosion and prevent sediment delivery to State
waters. Although no perennial streams or springs have been mapped in the JD -6 Mine area, these sediment
and erosion prevention measures are intended to prevent sediment delivery to ephemeral channels (incised
channels that are mostly dry, but may flow temporarily in response to rainfall or snowmelt).
4148A.131028 Whetstone Associates