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Anderson Consulting Engineers DRMS Title 34 Slope Stability Analyses Page 3 conditions. Effective stress parameters alone were used to perform these analyses. According to the analysis for the critical cross section associated with County Road 40 Right -of- Way under long -term steady state conditions, the FOS is 1.2. The FOS associated with Interstate 25 Right -of -Way under long -term steady state conditions is 3.3. Analysis 2: Rapid Draw Down The slope stability for the critical cross sections associated with the County Road 40 Right -of- Way and Interstate 25 Right -of -Way were analyzed under rapid draw down using the staged undrained strength approach. This approach was modeled using a 3 -stage method proposed by Duncan, Wright and Wong (1990). According to the engineering methodology SLOPEM manual, "the first stage involves the stability analysis of the embankment before draw down when the water level is high and the pore pressures in the materials are at a steady state condition. The effective normal stress and shear stress along the slip surface are used to determine the undrained shear strength for materials that do not drain freely. The second stage involves the stability analysis of the embankment after rapid draw down when the water level in the reservoir is low and the pore pressures in the materials are described by the piezometric line after rapid drawdown. The effective normal stress obtained from stage two together with the effective strength parameters are used to compute the drained effective strength along the slip surface. The third stage involves conducting a stability analysis using the computed shear strengths and the final draw down water level ". According to the analysis for the critical cross section associated with County Road 40 Right -of- Way under staged rapid draw down, the FOS is 1.2. The FOS associated with Interstate 25 Right -of -Way under staged rapid draw down is 2.4. Recommendations Due to the conservative material properties and pore water pressure assumptions, Brierley considers a minimum FOS of 1.1 to be appropriate for the project site. The FOS values for each critical cross section under long -term steady state conditions and under rapid draw down were greater than 1.1. Therefore, this stability analysis study is intended to demonstrate that the proposed construction and long -term conditions will not adversely affect the stability of any significant, valuable and permanent man -made structures according to rule 6.4.19 of DRMS Mineral Rules and Regulations of the Colorado Mined Land Reclamation Board for the Extraction of Construction Material. Limitations This memorandum has been prepared for Anderson Consulting Engineers for specific application to the Rigden Reservoir and POE Pit DRMS Title 34 Slope Stability project as understood by our firm at this time, in accordance with generally accepted geotechnical engineering and engineering geologic practices common to the local area. No other warranty, express or implied is made. In the event that changes in the nature, design or location of the planned project are made, the conclusions and recommendations presented in this memorandum should not be considered valid, unless the changes are reviewed by Brierley and the recommendations presented in this memorandum are revised or verified in writing. Our analyses and recommendations are based, in part, upon the data obtained from the reference subsurface investigations performed for a different phase of the subject project, our experience with similar projects and subsurface conditions, and DRMS published soil strength BRIERLEY ASSOCIATES Creating Space Underground