2010-02-02_REVISION - M1980244

• Permit No: M1980244
• IBM Index Class Name: REVISION
• Doc Date: 2/2/2010
• Doc Name: Submittal
• From: CC&V
• To: DRMS
• Type & Sequence: TR57
• Media Type: D
• Archive: No

amecoAy
December 17, 2009
Mr. Timm Comer
Manager, Environmental Resources
Cripple Creek & Victor Gold Mining Co.
P.O. Box 191
Victor, CO 80860
Re: Hydro-JexTrm Program Review
Dear Timm:
AMEC Earth and Environmental (AMEC) has prepared this letter for the Cripple Creek & Victor Gold
Mining Company (CC&V) presenting a stability review for the Hydro-Je)Jm program being proposed by
Metal Recovery Solutions, LLC (MRS). The program, as outlined in the MRS letter dated 27 November
2009, will consist of drilling several cased borings into the Valley Leach Facility (VLF) ore heap. Fluids will
then be injected into the borings at different intervals. In all cases, the borings will be completed a
minimum of 100 feet above the liner surface.
According to the preliminary layout of the borings provided by CC&V, the borings are to be located along
the 9925 bench, with a crest set-back of approximately 20 feet. According to the MRS letter, the injection
pressures into the ore heap are to be varied to be at or just below the overburden pressure.
There are several case studies of injecting fluids into ore heaps to enhance recovery. From a stability
standpoint, injecting fluids into ore heaps can be safely done without risking stability by carefully
monitoring injection pressures. In general, the most critical conditions for fluid injection occur with
injection at shallow depths. This is because of the low in situ stresses in the ore heap, which may be
exceeded if injection pressures are not monitored closely. Exceeding the in situ stress at or near an ore
slope, may lead to localized instability.
As part of the review of the proposed injection program, AMEC analyzed the injection pressure and extent
of saturation at several locations in the VLF ore heap. These data were then used to assess stability of
the VLF ore slopes. To assess the injection pressures and extent of saturation, the numerical model
TOUGHV2 was used. TOUGHV2 (Pruess et al, 1999) is a multi-dimensional numerical model for
simulating the coupled transport of water, vapor, air, and heat in porous and fractured media. TOUGHV2
takes account of fluid flow in both liquid and gaseous phases occurring under pressure, viscous, and
gravity forces according to Darcy's law. Interference between the phases is represented by means of
relative permeability functions. The ore slope stability was analyzed using the program Slide 5.0
(RocScience, 2008).
Figure 1 presents a plan map of the VLF showing the 9925 bench. Figure 2 presents a section through
the VLF that was used to assess injection and stability. It is important to note that the focus of the
analyses was on the upper 115 feet of the ore heap from the 9925 bench. Fluid injection at depths greater
than 115 feet, would have no effect on stability due to the large, unsaturated ore section.
Prior to assessing the effect of injection on stability, a stability analysis was conducted on the section
shown in Figure 2, under a no-injection scenario. The stability analysis was conducted using the same
ore strength parameters that have been used for the VLF design (e.g. friction angle of 40 degrees and
zero cohesion). The results of the stability analysis are presented in Figure 3, indicating a Factor of Safety
(FOS) of 1.62, under a no-injection scenario.
AMEC Earth & Environmental, Inc.
304 Inverness Way South, Suite 490
Englewood, Colorado 80112
Tel: [phone]
Fax: [phone] www.amec.com
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