2010-01-22_REVISION - C1981019

• Permit No: C1981019
• IBM Index Class Name: REVISION
• Doc Date: 1/22/2010
• Doc Name: Adequacy Review ‎(Memo)‎
• From: Kent Gorham
• To: Jim Stark
• Type & Sequence: TR81
• Email Name: JRS
• Media Type: D
• Archive: No

STATE OF COLORADO
DIVISION OF RECLAMATION, MINING AND SAFETY
Department of Natural Resources
1313 Sherman St., Room 215 C O L O RA D O
Denver, Colorado 80203 D I V IS I ON Of
Phone: [phone] RECLAMATION
FAX: [phone] Interoffice Memo M IN I N G

SAFETY
To: Jim Stark _
' Bill Ritter, Jr.
Governor
From: Kent Gorham Harris D. Sherman
Executive Director
CC: Sandy Brown Ronald W. Cattany
Division Director
Natural Resource Trustee
Date: January 22, 2010
RE: Adequacy review, TR-81, Colowyo Mine, C-81-019
Jim, as per your email dated January 4, 2010, 1 have completed my adequacy review of the
materials submitted for Technical Revision No. 81 (TR-81) for the Colowyo Mine, #C-81-019.
TR-81 proposes changes to the size and construction of the East Taylor and West Taylor
valley fills. These proposed changes resulted in, for one, the need to revisit the design and
performance of the West Taylor pond. The operator included four SEDCAD4 modeling runs
to demonstrate that for the 10-year storm, both the worst case watershed condition and one
intermediate land condition during temporary spoil placement, storm runoff would be
adequately treated to the requirements of Rule 4.05.2. The operator appropriately used curve
numbers approved as a result of TR-73. With the exception of the questions below, I have no
questions or concerns related to the modeling efforts. No physical changes to the existing
West Taylor pond is apparently required based on this modeling. If not already done, I
recommend that the as-built pond certification be reviewed by the Division and compared to
the actual construction completed in the field.
My specific questions are as follows:
1. Please provide a new introductory text section for Part C, West Taylor Pond that
includes new curve number information, etc.
2. Please update the Exhibit 7, Table of Contents, page (Exh. 7-20-ii) to include the
information required by #1 above.
3. Please provide a revised Exhibit 7, Item 20, Table 4 that includes the revised
information for the West Taylor pond for the subheadings watershed area, hydrologic
parameters, and sediment loading parameters.
4. The revised information for permanent drainages in South Taylor based hydrologic
design using the 10-year storm event for the large, main drainages. Given the location
and function of the West Taylor West Tributary Ditch, West Taylor East Tributary
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Mined Land Reclamation Denver • Grand Junction • Durango Active and Inactive Mines