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Geotechnical Stability Report — Kersey Mine May 24, 2024 <br /> Kersey, Colorado Page 4 <br /> pervious materials, irrigation practices, land use, and other factors. Consequently, any measured <br /> groundwater levels shown on the boring logs only represent conditions at the time the readings <br /> were collected and may thus be different at the time of construction, which can include levels <br /> encountered at shallower depths during periods of heavy precipitation. Static daily and seasonal <br /> groundwater levels and upper (perched) saturation zones would need to be determined through <br /> the installation and long-term monitoring of piezometers. This was outside of TRC's scope of <br /> work. Any changes noted in groundwater levels during the construction process may require a <br /> review of the recommendations presented in this memorandum. <br /> SLOPE STABILITY ANALYISS RESULTS <br /> In an effort to evaluate the global stability of potential slopes that would be created during surface <br /> mining activities, TRC performed a slope stability analysis using SLIDE2, Version 9.024, <br /> developed by RocScience,Inc. SLIDE2 is a slope stability computer modeling program that solves <br /> the stability of the cross-section with a two-dimensional limiting equilibrium method by analyzing <br /> numerous potential failure planes to find the critical failure surface that results in the lowest factor <br /> of safety (FOS) for the slope. <br /> For this analysis, a minimum acceptable value of factor of safety used is 1.5 pursuant to USACE <br /> guidance (Engineering Manual EM 1110-2-1902 Slope Stability) for long term slopes under static <br /> conditions. A minimum acceptable factor of safety of 1.1 was used in the analysis to evaluate <br /> potential effects of earthquake/seismic (pseudo-static) conditions. The FOS against sliding in the <br /> analysis is calculated using Bishop Simplified and Janbu Simplified Methods. <br /> A peak ground horizontal acceleration factor of 0.0643g was used for the approximate Project <br /> Site location based on the USGS Unified Hazard Online Tool <br /> (https://earthquake.usqs.qov/hazards/interactive/). This factor is the peak acceleration with 2 <br /> percent probability of exceedance in 50 years. It should be noted that due to the relatively shallow <br /> depth to bedrock, the horizontal acceleration factor was not adjusted to account for damping or <br /> amplification effects. <br /> A general cross section was developed as part of the slope stability analysis to evaluate proposed <br /> slopes ranging from 2H:1V to 3H:1V in grades. Soil information and shear strength parameters <br /> used were extracted from CTL report dated May 15, 2024, and are summarized in Table 3 below. <br /> Table 3: Soil Parameters <br /> Material Name Unit Weight Saturated Unit Cohesion Phi <br /> (pcf) Weight (pcf) (psf) (deg) <br /> Clayey Sand 120 N/A 25.0 28 <br /> Sandstone 130 N/A 5000 35 <br /> The FOS calculated for the various slopes analyzed are summarized in Table 4 below. <br /> Table 4: Slope Stability Analysis Results <br /> Conditions FOS Minimum <br /> FOS <br /> hji TRc <br />