REV05731

• Permit No: M1980244
• IBM Index Class Name: Revision
• Doc Date: 4/10/2000
• Doc Name: CC&VG CRESSON PROJECT GEOTECHNICAL ADEQUACY REDVIEW MARCH 2000 AMENDMENT 8
• From: BERHAN KEFFELEW
• To: JIM PENDLETON
• Type & Sequence: AM8
• Media Type: D
• Archive: No

• • III IIIIIIIIIIIIIIII
999
DATE: April 10, 2000
TO: Berhan Keffelew
FROM: Jim Pendleton
RE: CCBVG CRESSON PROJECT - Geotechnical Adequacy Review -
March, 2000 -Amendment No. 8 Application -Volume III,
Appendix 5, Cresson Project Mine Pit Stability Evaluations
(Permit No: M-80-244)
This appendix contains separate mine pit wall stability evaluations and reports for the Main
Cresson Mine, the East Cresson Mine, and the North Cresson Mines. The evaluation for the
Main Cresson Mine was prepared by Itasca Consulting Group. The evaluations for the East
and North Cresson mine areas were prepared by Adrian Brown.
Phase 2 Slope Stability Assessment of the Main Cresson Surface Mine
Amendment No. 8 proposes to deepen, enlarge, and possibly partially backfill the Main
Cresson Pit. Itasca Consulting Group evaluated the anticipated stability of the resulting pit, in
order to recommend pit wall configurations which will be acceptably stable. Itasca's primary
consideration relates to pit wall stability during the operation of the mine. The Division's
primary concern relates to stability of the final reclaimed pit wall configuration.
Itasca had performed an earlier evaluation of the.Amendment No. 7 ultimate configuration of
the Main Cresson Pit (see Appendix A to Appendix 5, Section 1). Their Phase 2 evaluation
benefitted from that earlier evaluation, observations of the existing pit's wall performance, and
considerable additional bore hole, laboratory, and field and core fracture/joint data. Itasca, in
my opinion, has completed a thorough evaluation of the Phase 2 pit wall stability.
In completing it's evaluation, Itasca concludes that the current pit wall configuration should
suffice for the north, south and east walls of the pit. However, further investigation has
determined that the central portion of the west wall when exposed at depth within the area of
the Cresson Pipe may not be stable at the current pit wall configuration and slope. Itasca
concludes on page 38 of it's report; "In order to produce afactor-of-safety of 1.30 against
circular failure in this region of the West wall, the slope of the upper ont-third of the wall will
need to be reduced from the current 60° to 45°, and the lower two-thirds will need to be
reduced from the current 50° to 35°."
Cripple Creek & Victor Gold (CC&VG) reflects Itasca's recommendations within table 5-5 on
page 51 of the "Project Description" in Volume 1 of the Amendment No. 8 application.
However, there appears to be one typographical error and one discrepancy within table 5-5.
First for the typographical oversight, I believe it would clarify table 5-5 to label the bottom box
as "West Wall". Second, for the apparent discrepancy between table 5-5 and Itasca's
recommendations, CCi3~VG presents a proposed overall slope angle for the upper one-third of
the central West wall of 45°, where as table 5-5 presents a proposed overall slope angle for
the portion of 35°-50°. CC&VG should amend table 5-5 to reflect Itasca's