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Memo to Applegate Group, Inc. 2 January 10, 2013 <br />Slope Stability Review File No. M- 1982 -131 <br />The Operator has provided the Division with structure agreements between the Operator and the <br />surrounding property and structure owners, except for the following: <br />• Weld County - N 17 and N 21 Avenues <br />The eastern edge of N 21st Avenue is located approximately 20 feet from the top of the mined pit slope <br />and was identified by Applegate as the critical section for the stability analysis. Based on the Division's <br />stability analysis this critical section is not stable and must be addressed by the Operator, by either <br />obtaining a structure agreement with Weld County, providing site specific soils properties for a more <br />accurate stability analysis or backfilling the area to address the stability concerns. <br />Weld County Road — N 21 Avenue, Critical Location — Mined Slope <br />The Mined Slope critical cross section was duplicated using the Applegate soil properties and the standard <br />DRMS soil properties. The DRMS soil property analysis produced a potential failure surface with a lower <br />safety factor (0.96) than the Applegate identified critical slip circle and the Division's required factor of <br />safety of greater than 1.0. The accuracy of the Operator's analysis is not confirmed and must be <br />addressed and corrected by the Operator. The Division's stability analysis results are attached. <br />Weld County Road — N 21 Avenue, Critical Location — Reclaimed Slope <br />The Reclaimed Slope critical cross section was duplicated using the Applegate soil properties and the <br />standard DRMS soil properties. The DRMS soil property analysis produced a potential failure surface with <br />a lower safety factor (1.99) than the Applegate identified critical slip circle. However, the factor of safety <br />was greater than the Division's required factor of safety of greater than 1.0. The accuracy of the <br />Applegate analysis is confirmed for the proposed reclaimed slope. The Division's stability analysis results <br />are attached. <br />Conclusion <br />The Division will require the Operator to justify the road surcharge load and the soil parameters used in <br />the analyses. Additionally, the Operator must address the potential mined slope failure surface with an <br />unacceptable factor of safety lower than 1.0. <br />Enclosure — copies of the Division's Galena stability analysis results <br />