REV01106

• Permit No: M1980244
• IBM Index Class Name: Revision
• Doc Date: 5/21/1997
• Doc Name: MEMO REVIEW OF TR CRESSON PROJECT PN M-80-244
• From: DMG
• To: BERHAN KEFFELEW
• Type & Sequence: TR25
• Media Type: D
• Archive: No

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DIVISION OF MINERALS AND GEOLOGY
Depanmenl of Natural Resources
131 J Sherman St., Room 215
Denver, Colorado 80203
Phone: 1J031 8fib-J567
FAX: [phone]
STATE OF COLORADO
MEMO
Roy Romer
Governor
lames 5. Lochhead
E Kecutive Director
Date: May 21, 1997
To: Berhan Keffelew
From: James Dillie
Re: Review of T hnical Revision, Cresson Project, Permit No. M-80-244
Per your request, I reviewed the technical revision submittal from CC & V regarding the
expansion of Phase II heap leach facility.
~~~~~
DEPARTMENT OF
NATURAL
RESOURCES
Michael B. Long
Division Director
With one exception, it appears the design and contraction specifications for the expansion azea
are identical to those which were approved for Phase 11 construction so they were not reviewed in
any great detail. The only difference is the requested modification to the structural fill material.
The operator proposes to increase the percentage passing the No. 200 sieve from the approved
25 percent or less to 50 percent or less and increase the plasticity index to 30 or less( from less
than 10).
Structural fill is used primarily for slope reduction and other miscellaneous site grading projects
in order to prepare an adequate base for placement of [he soil liner fill. Increasing the amount of
fines will, generally, increase the plasticity index which, in tutu, will probably increase cohesion
at the optimum moisture content, reduce cohesion when saturated and reduce the internal friction
angle. If slope stability is not deemed a problem than the proposed modified material would be
acceptable.
The operator completed slope stability analyses for two portions of the proposed expansion area.
Section 5.0 of the T.R, submittal presents the data, and results, of the geotechnical analyses for
leach pad stability. All failure modes considered in the study were evaluated according to the
Spencer Method. A seismic coefficient of 0.14g was used in all pseudo-static analyses
(consistent with that used for Phase II). Except for the proposed modified structural fill, material
design properties used in the stability analyses were previously approved. The proposed
modified structural fill was assigned an internal friction angle of 26 degrees with no cohesion.
Factors of safety were determined for two sections of the northern leach pad area. As noted on
drawing No. 10, a static factor of safety of 2.1 was calculated for section A-A~. The pseudo-