2009-12-03_REVISION - M1977036

• Permit No: M1977036
• IBM Index Class Name: REVISION
• Doc Date: 12/3/2009
• Doc Name: Adequacy Review #2
• From: DRMS
• To: Tetra Tech
• Type & Sequence: AM1
• Email Name: JLE
• 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: November 6, 2009
TO: Jared Ebert
FROM: Peter Hays
COLORADO
D IV IS I ON OF
RECLAMATION
MINING
SAFETY
Bill Ritter, Jr.
Governor
Harris D. Sherman
Executive Director
Ronald W. Cattany
Division Director
Natural Resource Trustee
RE: Review of Slope Stability Report, Lafarge West, Inc., 35 Avenue — Brown Property, File
No. M- 1977 -036
The Division of Reclamation, Mining and Safety (DRMS) staff has reviewed the stability report included
with the Greeley 35 Avenue Mine permit amendment application. The report specifies setback
distances from the edge of mining in the proposed pit to offsite facilities worthy of protection from
potential for pit wall landslide failure. The report includes technical slope stability analyses in support of
the proposed setback specifications.
The following list describes the information used by the applicant to analyze slope stability for the
proposed pit:
1. Four boreholes were drilled in the area of the proposed pit. The logs of these boreholes provide
information on the stratigraphy of the gravel deposit, the overburden soil, and the bedrock
underlying the deposit. The boreholes also provide water table information.
2. No laboratory strength tests were performed on soils at the site. The soil strength parameters
used were based on typical values for anticipated soils and experience working with DRMS at
other sites in the area.
3. Analyses were performed with the Slope -W 2007 computer program. For each case, the most
critical soil profiles based on exploratory boring data (i.e. the tallest highwall, thickest overburden
layer and associated weaker clay lenses) were analyzed.
4. The stability analyses were run in accordance with accepted geotechnical standards and DRMS
requirements for temporary pit slopes as follows:
a. Mine highwalls modeled as vertical slopes
b. Residual soil strength parameters used for the upper 2.5 feet of weathered bedrock
c. Factor of safety must be greater than 1.0
5. Groundwater levels on the profiles were input to portray site dewatering.
Using Clover Technology's Galena v5.01 slope stability software, the DRMS has conducted further analysis
of the two cross sections for the Greeley 35 Avenue Mine. Specific comments and requirements for
each of the cross sections are provided below.
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Mined Land Reclamation Denver • Grand Junction • Durango Active and Inactive Mines