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Mr.Anthony Adza -2- March 24,2016 EWSD retained RJH Consultants,Inc.(RJH)to perform an engineering evaluation and identify a recommended setback between the property boundary and pit highwall that would provide an acceptable slope stability factor of safety for structures near the pit slope. Stability Analyses GENERAL Two-dimensional stability analyses were performed using limit equilibrium techniques. The software program Slope/WC 2007 was used,which is part of the Geo-Studio software suite. Spencer's method was used, which satisfies both force and moment equilibrium. Critical failure surfaces were optimized using the program, which means the shape of the critical failure surface was adjusted to evaluate if a lower safety factor could be obtained from a non-circular failure surface. EVALUATED CROSS SECTION Subsurface data used to develop the evaluated cross section is presented in Attachment A. Subsurface conditions for the evaluated cross section included 32 feet of overburden clay, overlying 11 feet of sand and gravel, overlying bedrock. The evaluated cross section was based on subsurface conditions at the north side of the east pit(near boring BE-115). This location was selected for analysis because it included the following: • A structure(Highway 50)adjacent to the property boundary • The deepest location of bedrock • The thickest location of overburden clay,which is anticipated to have lower strength than the sand and gravel. The natural groundwater level was considered to be at Elevation(El.)4532,which is about 15 feet below the ground surface at the evaluated cross section. The evaluated cross section considered that the mining highwall was 1 H:1 V and a low-permeable barrier soil-bentonite barrier wall had been installed about 25 feet interior of the property boundary. The evaluated cross section geometry is shown on model outputs in Attachment C. MATERIAL PROPERTIES The material properties used for the stability analyses are presented in Table 1. These properties were based on properties developed by RJH during previous stability analyses at the Site and are consistent with properties provided by the DBMS. Reference material used during development of the material properties is provided in Attachment B. 16109-16-03-10-Engineering Evaluation Letter