2017-08-11_PERMIT FILE - C1981028 ‎(2)‎

• Permit No: C1981028
• IBM Index Class Name: Permit File
• Doc Date: 8/11/2017
• Section_Exhibit Name: Appendix K-6 Hydrologic Analysis Sediment Pond & Ditches
• Media Type: D
• Archive: No

September 2, 2016
Mr. Ben Moline
Molson Coors Brewing Company
Water Resources and Environmental Compliance
P.O. Box 4030, Suite 400
Golden, CO 80401
Habitat Management
Environmental & Natural Resource Services
RE: Keenesburg Strip Mine, Permit C-1981-028, DRMS Adequacy Review of Permit Renewal
Application No. 7 (RN7), Permanent Pond & Ditch Capacity Analyses
Dear Ben:
Please find enclosed the hydrologic analyses report for Keenesburg Mine's permanent ponds and
ditches that addresses Colorado DRMS's June 13, 2016 review Rule 4.05 Hydrologic Balance
comment. In their comment the DRMS requested that the detention storage requirement of
Sediment Pond 2 be confirmed, or demonstrate to the DRMS that the data and values presented in
Appendix K-1 of the permit remain valid in 2016 through 2026.
A complete record of the previous modeling for these sediment control structures was not
available in DRMS's files or at the mine site. In light of this informational deficiency, we
contacted Dan Hernandez to discuss the information that would be required to satisfy this
comment. Dan indicated that SEDCAD modeling of the pond and ditches using currently
accepted values and practices would be adequate to address their concerns.
The attached report from Water & Earth Technologies uses SEDCAD and RUSLE2 to model
stormwater runoff and sediment transport fi-om the Keenesburg Mine's watersheds. The design
work uses currently accepted inputs for DRMS's current design requirements for permanent
ponds and ditches including:
I . The 10 -year, 24- hour precipitation event for permanent ponds 1 and 2 volume retention
capacities;
2. The 25 -year, 24-hour precipitation event for pond 2 spillway adequacy evaluation; and
3. The I0 -year, 24-hour precipitation event for the east and west temporary diversion
ditches.
Please review the enclosed report and let me know if we need to make any changes in this
document. After receiving your approval, we will send it to the DRMS for their consideration,
unless you would prefer to send it to them.
/Siinc rely,
Wayne A. Erickson
w/enclosure
,Habitat Management, Inc.
14 Inverness Drive East • Suite A-100 • Englewood • CO.80112
office: 303 -770 -9788 -fax: [phone] • www.habitatmanagementinc.com