2012-07-03_REVISION - M1984014

• Permit No: M1984014
• IBM Index Class Name: REVISION
• Doc Date: 7/3/2012
• Doc Name: RESPONSE TO ADEQUACY REVIEW #2
• From: COTTER
• To: DRMS
• Type & Sequence: AM1
• Email Name: GRM
• Media Type: D
• Archive: No

Parameter
Catchment
1 -2 -3
Catchment
4 -5 -6
Tsh (sheet flow) (hr)
0.16
0.14
T (shallow concentrated) (hr)
0.03
0.04
Tch (channel) (hr)
0.00
0.00
Tc (hr)
0.19
0.18
Q. (cfs)
490
520
Q 100 (cfs)
1.5
3.7
Response to DRMS Adequacy Review #2 — Cotter JD -8 Mine Reclamation Plan Amendment
Table 1. Mine Site Current Conditions - Peak Discharge (Qloo)
The revised peak flows shown in Table 1 are within the existing design capacity of
the proposed structures. However, the pond and spillway freeboard would be
reduced to 0.4 ft during the 24 -hour 100 -year event. To retain a 0.5 -ft freeboard on
all ponds and spillways and maintain the remaining design parameters shown in the
Drainage Design Plan, the spillway widths will be increased to 2.0 ft and 5.0 ft on
Pond 1 and Pond 2 respectively.
REFERENCES:
NRCS, 1986. Urban Hydrology for Small Watersheds - TR -55, United States
Department of Agriculture, Natural Resources Conservation Service,
Technical Release 55. June 1986.
6. Culverts: The culverts presented in Attachments 1 a and lb are 12- and 15 -inch diameter
pipes. Common practice is to use a minimum culvert diameter or (sic) 18 inches to
reduce the potential of plugging with wind -blown debris and animal denning activities.
Please commit to using at least 18 -inch diameter culverts.
Cotter response: All culverts installed by Cotter for stormwater management will
be a minimum of 18 inches in diameter. The Drainage Design Plan has been
modified to show both the calculated minimum hydraulic requirement and the
design requirement of 18 inches.
On the DD -19 Road, Montrose County installs culverts to fit their requirements.
There remain outstanding review issues that must be addressed that do not allow sufficient time
for completion prior to the 365 day limit per Rule 1.4.1(9) of June 8, 22012 (sic). The Division
and operator agree that an additional sixty (60) days, July 15, 2012, will allow completion of
review so a decision can be issued on the EPP submittal. The additional time also allows for
addressing the requirements of the public participation process as an objection has been
received on the EPP. A hearing will be scheduled before the Mined Land reclamation (sic)
Board for the August 8 -9` 2012 MLRB meeting. The objecting party has been notified of the
extension request and has verbally indicated no issue with it.
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