PERMFILE66375

• Permit No: M2004022
• IBM Index Class Name: Permit File
• Doc Date: 6/3/2004
• Doc Name: Review of Slope Stability Analyses
• From: DMG
• To: DMG
• Media Type: D
• Archive: No

STATE OF COLORADO
DIVISION OF MINERALS AND GEOLOGY
Department of Natural Resources
1313 Sherman St., Room 215
Denver, Colorado 80203
Phone: [phone]
fAX: [phone]
DATE: June 3, 2004
TO: Tom Schreiner
FROM: Allen Sorensonr~
RE: Review of Slope Stability Analyses, Hilltop Aquatic Investments, LLC,
Raindance Sand and Cravel Mine, File No. M-2004-022 GQ~ ; ~,~-,,~
COLORADO
DIVISION O F
MINERALS
GEOLOGY
RECLAMATION•MINING
SAf ETY•SC IENCE
Bill Owens
Governor
Russell George
Executive Direcor
Ronald W. Cottony
Division Director
Natural Resource Trustee
The Division of Minerals and Geology (DMG) geotechnical engineering staff has completed a review of
the slope stability analyses prepared by the Applicant's consultants for the above referenced proposed
operation. DMG has determined that the proposed mining operation will have no adverse impacts on
neazby structures worthy of protection; these structures aze:
• Town of Windsor water pipeline;
• Poudre River Trail;
• Eaton Ditch;
• Everitt Barn.
This determination relies on the mine operator's strict adherence to the setbacks from these structures that
were input to the stability analyses. The Applicant must understand that these setbacks are enforceable
conditions of the mined land reclamation permit, and that failure to abide by the setbacks will be looked
upon as a serious violation of the terms of the permit.
It should be noted that DMG identified one concern with the inputs to the Applicant's analyses, but found
that this concern was not relevant to the determination of stability due to the magnitude of the mining
setbacks in this particular case. The concern is with the shear strength values assigned to the weathered
bedrock that underlies the sand and gravel deposit. This weathered material behaves as an over
consolidated, stiff fissured clay, and upon unloading caused by mining this clay may degrade to its fully
softened strength and locally to its residual strength, which can be quite low. However, in this case, with
the required and enforceable setbacks, degradation of the weathered bedrock would not result in slope
failure that could impact the neazby structures.
cc: Carl Mount, DMG (via email)
c:\acs\LOANER MACHINEU1y Documents\raindance stability analysis.doc
Office of Office of Colorado
Mined Land Reclamation Active and Inactive Mines Geological Survey