2010-12-09_REVISION - M2008017 ‎(3)‎

• Permit No: M2008017
• IBM Index Class Name: REVISION
• Doc Date: 12/9/2010
• Doc Name: MEMO- Revised Slope Stability Analyses Review
• From: DRMS-tc1
• To: DRMS-mac
• Type & Sequence: TR1
• Email Name: MAC
• Email Name: TC1
• Media Type: D
• Archive: No

STATE OF COLORADO
DIVISION OF RECLAMATION, MINING AND SAFETY
Department of Natural Resources
p O L O RA N OF
1313 Sherman St., Room 215 F
Denver, Colorado 80203 RECLAMATION
Phone: [phone] M
MINING
FAX: [phone] SAFETY
MEMORANDUM Bill Ritter, Jr.
Governor
Mike King
Executive Director
To: Michael Cunningham, Environmental Protection Specialist Loretta Pineda
Director
From: Tim Cazier, P.E., Environmental Protection Specialist
Date: December 9, 2010
Re: Revised Slope Stability Analyses Review for Derr Pit TR-01, Permit No. M-2008-017
The Division of Reclamation, Mining and Safety engineering staff (DRMS) have reviewed the
revised Slope Stability analyses submitted with the December 7, 2010 TR-01 Adequacy Review
- 02 Comment Responses for the Derr Pit, Weld County, Colorado prepared by J&T Consulting
for Broken Arrow Investments, LLC. This reviewed focused on the stability analysis related to
the change from dry mining with a slurry wall in place to wet mining (prior to construction of the
proposed slurry wall).
Based on information provided via email and telephone discussions with J.C. York (J&T
Consulting) on December 6, 2010, and the subject stability analyses results, DRMS has
determined the setbacks and mine slopes proposed for the Derr Pit are protective of nearby
infrastructure and can be approved pursuant to Rule 6.5. Critical to this determination is the
mine plan requirement to restrict wet mining to within the interim mining limit (110 to 120 feet)
from the final mining limit as shown on Sheet 1 of Exhibit C - Mining Plan Map. Therefore, the
Operator must be notified that DRMS will consider wet mining outside the interim mining limit
to be a serious violation of the permit that will initiate an immediate enforcement action.
DRMS appreciates the use of conservative parameters and slope geometry used in the subject
analyses. We further understand that the location representing the proposed dragline loads in the
analyses is not representative of proposed mining practices, nor is it likely the dragline will
actually be located as close to the crest of the excavation slope as represented in the analyses.
However, DRMS encourages the operator to follow safe mining practices, adhere to MSHA
regulations, and follow the equipment manufacturer's recommendations for safe operation of
mining equipment.
Office of Office of
Mined Land Reclamation Denver • Grand Junction • Durango Active and Inactive Mines