APPCOR11232

• Permit No: C1981034
• IBM Index Class Name: Application Correspondence
• Doc Date: 2/6/1984
• Doc Name: UNDERGROUND DEVELOPMENT WASTE MATERIAL COMPACTION COMMENTS BY GRAND MESA COAL CO
• From: MLRD
• To: DAN MATHEWS
• Media Type: D
• Archive: No

~: .
Richard D. Lamm
Governor

DEPARTMENT OF NATURAL RESOURCES
David H. Getches, Executive Director
MINED LAND RECLAMATION
DAVID C. SHELTON, Dlroctor
February 6, 1984

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999
DIVISION
T0: Dan Mathews
FROM: Jim Pendleton \ ~ ~"`
RE: Underground~Develo nt Waste Material Compaction Comments by
Grand Mes~ ompany
Pursuant to your request, I have reviewed the comments concerning compaction
of underground development waste material currently being placed within the
Grand Mesa Coal Company's Red Canyon Mine's underground development waste
disposal pile. These comments are contained within Volume 11 of the
company's permit application, submitted in response to your draft findings
document of March 14, 1983. The company's response was submitted January
17, 1984.
The company's comments regarding compaction of underground development waste
are two-fold, First, the operator includes a copy of the waste material
shear strength data utilized in completing the stability analysis
accompanying their original design analysis. These results, prepared by
Rocky Mountain Geotechnical, Inc., are presented in compliance with the
prudent state-of-the-art of material strength analysis and show material
strengths complementary with the original pile design.
Secondly, however, the operator submits a letter prepared by the same
consultant on January 10, 1984, which discusses potential effects of
variance from the original compaction standards (density = 78.7 lbs. per
cubic foot) upon the final underground development waste pile's slope
stability. The consultant observes that, based upon their general experience,
they do not believe that substandard compaction would reduce the pile's
factor of safety below the required 1.5 (Rule 4.09). However, Rocky Mountain
Geotechnical's letter observes that this projection is not based upon
" ... either specific shear strength testing or rigorous computer analysis."
The disposal of underground development waste is carefully controlled by
Rule 4.09. Rule 4.09 requires that the waste be compacted to that degree
required to achieve slope stability. In order to determine what specific
minimal degree of material compaction will result in the required degree
of slope stability, it is necessary to complete an appropriate geotechnical
analysis of the waste structure and underground development waste material.
Without such an analysis, it is not possible for either the operator or
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