2017-01-05_REVISION - M1977300

• Permit No: M1977300
• IBM Index Class Name: Revision
• Doc Date: 1/5/2017
• Doc Name: Returned Mail
• From: USPS
• To: DRMS / Cotter Corporation
• Type & Sequence: TR23
• Email Name: MAC
• Media Type: D
• Archive: No

ATCOLORADO
Division of Reclamation,
Mining and Safety
Department of Natural Resources
1313 Sherman Street, Room 215
Denver, CO 80203
December 23, 2016
Ken Mushinski
Cotter Corporation
P.O. Box 1750
Canon City, CO 81215
RE: Schwartzwalder Mine; DRMS File No. M-1977-300; Technical Revision (TR -23)
Dear Mr. Mushinski,
The Division has identified several other comments and questions that must be addressed prior to the
Division's decision due date.
1. The design drawings provided in Attachment C for the storm water diversion ditches are not stamped
by a licensed professional engineer. As required by Rule 6.4.21(10)(a), please provide design
drawings which have been certified by a licensed professional engineer for all Environmental
Protection Facilities.
2. The Operator has indicated the storm water diversion ditches have been designed to accommodate a
100 -year flood event with a peak discharge of 60 cfs. Appendix E (pg. 51) of the 1983 Amendment,
states the estimated peak discharge above the east/south Waste Rock Pile (WRP) is 119 cfs for the
100 -year flood event. The peak discharge for the west/north WRP was not analyzed. Please provide
the Division with a hydrologic analysis which demonstrates 60 cfs is the appropriate peak discharge
for the design of the storm water diversion ditches.
3. The design drawings show the storm water diversion ditches terminate several feet above the toe of
slope of the WRP's. The design should include a means to safely convey the diverted flow from the
base of the diversion ditches to Ralston Creek. Please describe how storm water will be safely
conveyed to Ralston Creek so that erosion of the W RP's or the access roads does not occur.
4. The design drawings show weep drains will be placed vertically in the storm water diversion ditches.
In the Division's experience, horizontal weep drains are less subject to plugging and sediment
deposition. Please provide a technical justification for constructing vertical weep drains.
5. The design drawings for the storm water diversion ditches do not address freeboard. Please indicate if
the design of the storm water diversion ditches accounts for freeboard. If so, specify the freeboard.
The Division recommends the design provide for one foot of freeboard or half the velocity head.
6. The Southern WRP Ditch Typical Section on Sheet No. 27 of the design drawings shows placement
of fill adjacent to the storm water diversion ditch. Please specify the nature of the fill and describe
how it will be compacted.
of coto
1313 Sherman Street, Room 215, Denver, CO 80203 P 303.866.3567 F 303.832.8106 http://mining.state.co.us
John W. Hickentooper, Governor I Robert W. Randall, Executive Director I Virginia Brannon, Director * 4':- i
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