2010-04-08_REVISION - M1980178

• Permit No: M1980178
• IBM Index Class Name: REVISION
• Doc Date: 4/8/2010
• Doc Name: Second adequacy review
• From: DRMS
• To: Moores Mining, LLC
• Email Name: THM
• Media Type: D
• Archive: No

STATE OF COLORADO
DIVISION .OF RECLAMATION, MINING AND SAFETY
Department of Natural Resources
1 3 1 3 Sherman St., Room 215 C O L O RA D O
Denver, Colorado 80203 D IV] S E ON OF
Phone: [phone] RECLAMATION
FAX: [phone] MINING
SAFETY
DATE: March 17, 2010 Bill Ritter, Jr.
Governor
Harris D. Sherman
TO: Travis Marshall Executive Director
Ronald W. Cattany
FROM: Allen Sorenson Division Director
Natural Resource Trustee
RE: Geotechnical Review, Moores Mining, LLC, Moores Pit,
Conversion Revision CN-01, Permit No. M-1980-178
The Division of Reclamation, Mining, and Safety (DBMS) engineering staff has reviewed the geotechnical
aspects of the above referenced conversion application and has identified the following issues to be addressed.
1. Mine Plan:
The Exhibit C Mine Plan Map includes a cross section that illustrates limits of excavation. In order to comply
with the illustrated limits, the Operator must mine the pit perimeters at slopes no steeper than 3:1 once the
excavation encroaches to within 150 feet of the permit boundaries, assuming a maximum excavation depth of 40
feet. The Operator must make a definitive commitment to this mining method for the stability analyses provided
to be representative of critical stability conditions. Therefore, a definitive written commitment must be provided.
2. Highway 141 Cut Slope:
The Operator has provided analyses to demonstrate that proposed excavation will not destabilize the slope down
to Highway 141. The DRMS accepts the analyses as provided to be conservative and sufficient. However,
further description and analysis of certain other potentially destabilizing activities must be provided. The Exhibit
C Mine Plan Map illustrates overburden stockpiles and runoff detention ponds at the south edge of the mine
property and above the slope down to the highway. The cross section included on the map illustrates a stoney
clay loam layer at the base of the sand and gravel deposit.
a. There is no description or drawings included in the application on the heights or slopes for the overburden
stockpiles. Depending on these parameters, the stockpiles may impose a surcharge load on the highway slope
sufficient to impact stability. The Operator must commit to maximum height and side slopes for the
stockpiles and analyze their impact on slope stability as necessary. Also, the Exhibit C Map illustrates the
stockpiling of overburden onto the slope down to the highway. The Operator must either commit to
stockpiling only in the flatter terrain, or provide a demonstration that stockpiling onto the slope will be stable.
b. The stability analyses provided for the slope down to the highway are for unsaturated conditions within the
main body of materials that make up the slope. Worst case conditions for stability may occur when the
detention ponds are full, and seepage from the ponds infiltrates the slope materials. This is particularly the
case if seepage were to pool at a less permeable interface within the slope, such as may be caused by the
stoney clay loam layer. The Operator must provide an evaluation of the potential for seepage from the ponds
to destabilize the slope.
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