2009-08-06_PERMIT FILE - M2009018

• Permit No: M2009018
• IBM Index Class Name: PERMIT FILE
• Doc Date: 8/6/2009
• Doc Name: Review of Slope Stability Analysis
• From: DRMS-acs
• To: DRMS-mac
• Email Name: MAC
• Media Type: D
• Archive: No

STATE OF COLORADO
DIVISION OF RECLAMATION, MINING AND SAFETY
Department of Natural Resources
1313 Sherman St., Room 215
A D O
C O
PL
Denver, Colorado 80203 Q
D I V N O F

e: [phone]
Phon
RECTION
FAX: [phone] M I N I N G

SAFETY
Bill Ritter, Jr.
DATE: August 6, 2009 Governor
Harris D. Sherman
Executive Director
TO: Michael Cunningham
Ronald W. Cattany
'
FROM: Allen Sorenson Division Director
Natural Resource Trustee

RE: Review of Slope Stability Analysis, Varra Companies, Inc.,
Heintzelman Pit, File No. M-2009-018
The Division of Reclamation, Mining, and Safety (DRMS) engineering staff has reviewed the above
referenced permit application and has determined that the following issues remain to be addressed relative to
the stability of proposed excavations.
1. The geotechnical stability exhibit included in the application states that the "average" thickness of the
sand and gravel deposit is "estimated" at 45 feet. The stability analysis provided incorporates the
"assumption" that the maximum height of any excavated pit wall will be 50 feet. The Applicant must
describe the basis for the determination of a 50 foot maximum depth, as excavation depth is critical to
evaluation of the sufficiency of proposed setbacks.
2. The stability analysis is based on temporary excavation slopes no steeper than 1.25H:1 V. The
application states throughout that the excavated pit slopes will be mined at no steeper than 1.25H:1 V.
Mining at that slope angle is not amenable to bulk mining methods typically employed in gravel pits.
Therefore, the Applicant must respond to the following issues:
a. If the Applicant chooses, as is the case thus far, to predicate the stability analysis and the protection
of nearby property and structures on a 1.25H:1 V pit wall, then the Applicant must provide a
confirmatory statement of recognition that the DRMS will find any instance of mining to a steeper
slope to be a serious violation of a critical permit condition.
b. If the Applicant chooses to continue with the condition that pit slopes will be mined at no steeper
than 1.25H:1 V, a description must be provided in terms of the mechanics of earthmoving as to how
the prescribed slope angle will be maintained. The Applicant must further describe the surveying and
monitoring controls that will be employed to check the slope and the frequency of the surveying and
monitoring.
c. The Applicant must state definitively that the 1.25H:1 V slopes will be maintained throughout the
excavation, regardless of the distance from the working face to a protected structure, or must provide
a plan for where and at what distance from structures the working face will transition from steeper
slopes to the prescribed 1.25H:1 V slope.
d. If the Applicant chooses the flexibility to mine steeper than 1.25H:V, a stability analysis of vertical
pit walls must be provided.
3. Shear strength parameters and stability analyses:
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