2016-07-21_REVISION - M1980244 (4)

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Technical Memorandum Cripple Creek&Victor Gold Mine ■ Stability Evaluation for Arequa Gulch VLF—Mill Solution Injection Program NewFields Job No.475.0106.008 July 12,2016 ➢ Baseline condition— No active solution injection Solution injection with a saturation plume initiating 10-feet below the ore surface and percolating downward with either a 50-feet or 100-feet width Although wicking of mill solution upwards around the wells is highly unlikely give the particle size characteristics of the ore, we evaluated the saturation level at only 10-feet below the surface as an added level of conservatism. The width of the saturation plume was selected based on the results of the Hydro-JexT"" injection program evaluation (AMEC, 2009). The evaluation indicated that pressurized injection of solution at half of the overburden pressure resulted in a vertical saturation plume from the injection point to the base liner with an approximate 50-feet in width. The saturation plumes considered for this evaluation are reasonable, and likely conservative, for a non-pressurized injection program. 2.4 Results Results of the stability evaluation are listed in the following table and output graphics from the stability models are included as attachments. SCENARIO FACTOR OF SAFETY No Injection 1.56 50-foot Wide Plume 1.45 100-Foot Wide PluT±_j 1.36 The results indicate the facility slopes are stable, and the calculated factors of safety are acceptable considering the minimum acceptable factor of safety for static conditions has been established as 1.3 for the project site. The results confirm that the spatial extent of the saturation plume from the injection program influences the calculated factor of safety; as the saturation plume expands towards the exterior slope the factor of safety decreases. Although the ore was modeled as saturated at approximately 10-feet below the existing surface around the injection wells, this scenario is highly unlikely given the perforations in each well initiate at 20-feet below the surface and actual factors of safety are probable slightly higher. 3.0 DISCUSSION The current stability evaluation addressed the influence of the proposed mill solution injection program on the stability of the AGVLF Phase IV slopes. The impact of introducing solution into the heap under hydrostatic conditions reduces the calculated factors of safety, but does not result in unacceptable or unsafe conditions. Page 3