2011-04-19_PERMIT FILE - M2011001

• Permit No: M2011001
• IBM Index Class Name: PERMIT FILE
• Doc Date: 4/19/2011
• Doc Name: Adequacy Review- Stability Analysis Exhibit
• From: DRMS
• To: Lafarge West, Inc.
• Email Name: PSH
• Email Name: AJW
• Media Type: D
• Archive: No

STATE OF COLORADO
DIVISION OF RECLAMATION, MINING AND SAFETY
Department of Natural Resources
1313 Sherman St., Room 215
Denver, Colorado 80203
Phone: [phone]
FAX: [phone]
DATE: April 19, 2011
TO: Lafarge West, Inc.
FROM: Peter Hays
COLORADO
DIVISION OF
RECLAMATION
MINING
SAFETY
John W. Hickenlooper
Governor
Mike King
Executive Director
Loretta Pineda
Director
RE: Review of Slope Stability Analysis, Lafarge West, Inc., Iverson Mine, File No. M-2011-001
The Division of Reclamation, Mining and Safety (DRMS) staff has reviewed the stability analysis included
with the Iverson Mine, File No. M-2011-001, permit application. The report specifies setback distances
from the edge of mining in the proposed pit to the edge of the permanent man-made structures within
200 feet of the proposed affected area. The report includes technical slope stability analyses in support of
the proposed setback specifications.
The stability analyses were performed in accordance with accepted geotechnical standards and DRMS
requirements for temporary pit slopes. The following list describes the information used by the applicant
to analyze slope stability for the proposed pit:
1. Mine highwalls were modeled as vertical slopes.
2. Residual soil strength parameters were used for the upper 2.5 feet of weathered bedrock.
3. Factor of Safety must be greater than 1.0.
4. Groundwater levels on the profiles were input to portray site dewatering.
5. Laboratory strength tests were not performed on soils from the site. The soil strength parameters
used were based on typical values for the anticipated soils and the applicant's experience working
with DRMS at other sites in the area.
6. The scenarios were modeled with a general section developed from the most conservative
conditions encountered at the site including 6 feet of overburden overlying 33 feet of sand and
gravel. Beneath the alluvium, the section was modeled with 2.5 feet of residual strength bedrock
on top of claystone bedrock.
Using Clover Technology's Galena v5.01 slope stability software, the DRMS conducted further analysis of
the cross sections for the Iverson Mine. The applicant has stated structure agreements between the
applicant and the following structure owners have been completed:
• Noble Energy, Inc.
• The Iverson home and outbuildings
• Weld County - Poudre River Trail and fences
The Division did not perform analysis for these structures. However, the applicant must supply the
Division with copies of the agreements. Specific comments and requirements for each of the cross
sections are provided below.
Office of Office of
Mined Land Reclamation Denver • Grand Junction • Durango Active and Inactive Mines