2010-11-12_REVISION - M2009076 - Laserfiche WebLink

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Coarse Fractii Before Test - Saturated Wet Density 113.91b/ft3 (1.5 ton/yd" Moisture Content 25.3% Percent Saturation Level 81.7% Dry Density 90.9 lb/ft3 (1.2 ton/yd3) m Consolidation After Test - Under-saturated i 118.5 lb/ft3 (1.6 ton/yd3) 25.5% under-saturated 94.5 lb/ft3 (1.3 ton/yd3) Slimes Fraction Consolidation Before Test - Saturated After Test - Under-saturated Wet Density 110.71b/ft3 (1.5 ton/yd3) 121.4 lb/ft3 (1.6 ton/yd) Moisture Content 43.3% 30.4% Percent Saturation Level 100.5% under-saturated Dry Density 77.2 Lb/ft3 (1.0 ton/yd3) 93.1 lb/ft3 (1.3 ton/yd3) Important Impoundment Stability Measure - The consolidation data above provide for a standard of comparison for evaluating consolidation during operations, utilizing a core sampling procedure that has already been described earlier in this Exhibit. Core samples shall be determined under-saturated when testing reports Alloisture Content data less than the Before Test - Saturated conditions in the above table. This condition demonstrates that the impoundment is consolidating and that saturated, phreatic zones are being mitigated through proper dewatering and drying. Additionally, we have elected to incorporate standpipe piezometers into the design as a simple and effective means of measuring the saturated, phreatic surface level and unstable pore pressures. Standing water will be measured in these standpipes if saturated zones exist and an embankment profile can be mapped. The incorporation of geosynthetics into this design brings forth applying the latest technology and proven engineering practice to bolster the stability of these types of upstream raised tailings impoundments. Applying this technology should eliminate unfounded fears of failure. The potential for liquefaction of this proposed Tailings Impoundment during an earthquake has such a chance risk of occurring; such that, when balanced against the very limited hazard potentials to life and property resulting from such an event at the proposed project location, formulating a rigorous preventive engineering design is extreme. Seismic stability analysis has demonstrated the enhanced stability by incorporating Synteen geogrid. Active and passive dewatering methods have been prescribed using pumped decanting, geocomposite liner underdrains, and a network of "French drains" ("French drains are discussed in the Composite Liner System specifications below). Carefully adhering to the operating and embankment construction parameters previously set forth ensures proper impoundment stability behavior. These parameters prescribe a method of tailings impoundment technique, dewatering practices and embankment geometry relationships. The design was developed based on the preeminent works on this subject: Steven G. Vick's Planning, Design, and Analysis of Tailings Danis, 1990 and the US Army Corps of Engineers (USACE) Slope Stability, EM 1110-2-1902. All of this speaks to diminish seismic liquefaction concerns. This proposed site was chosen because of its remote location. During a site visit to our property on October 27, 2010, we demonstrated to the DRMS the non-populated, non-developed, and limited hazard potential of this proposed project. We feel that this proposed impoundment relates to a "Low Hazard Dam" situation as defined by State Engineer Standards (Rule 2-CCR 402-14.2.14.3) - "'Low Hazard Dam ' is a darn for which loss of human life is not expected, and significant damage to structures and public; facilities as defined for a `Significant Hazard' dam is not expected from failure of the dam." Asa Colorado Professional Engineer it is my job to take into consideration risk and threat levels to life, property and the environment and incorporate that into a safe design - which has been carefully done here. Page 26 of 37