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ARCADIS <br />Prior to conducting the stability analysis, the following reports were reviewed: <br />• Slope Stability Analysis of the Sediment Pond Embankments in the PR -05 Amendment Area New <br />Horizon 2 Mine, Greg Lewicki, PE, January 12, 2000 (Revised March 2006) <br />• Revised Geotechnical Engineering Study for the Proposed Western Fuels Facility, AA Road and <br />2650 Road, Nucla, Colorado, Lambert and Associates, September 7, 2010 <br />In addition to these reports, soils maps prepared by Kent A. Crofts, IME Environmental Consultants in <br />November 2009 were also consulted in order to gain an understanding of the topography and soil <br />conditions present beneath the proposed embankments. <br />Review of the previous stability analysis indicates that with few exceptions, the FOS developed for similar <br />embankments at the project site all exceed 2.0. These analyses were based primarily on soil strengths <br />and unit weights derived from literature sources that generally tended to be the average values for the <br />presumed material proposed for construction (i.e. SM -SC (silty sand and sandy clay soils) for the <br />embankment soils and GC or GM (gravelly clay or silty sandy gravel) material for the foundation soils). <br />Some geotechnical testing (in place density tests) of the onsite material was conducted that yielded some <br />useful information relative to the slope stability analysis. It was assumed that similar material will be used <br />to construct the new embankments for ponds NHN -001, -002, and -003. If this is not the case, then the <br />slope stability models should be revised to account for the use of different materials. <br />The September 2010 geotechnical report prepared by Lambert and Associates provided a significant <br />amount of useful geotechnical data including: results of standard penetration tests (SPT) conducted in the <br />field, results of direct shear testing of several soil samples, swell /consolidation test results, and total unit <br />weight of the subsurface soils. <br />The following table outlines the results of the geotechnical testing that was conducted by Lambert and <br />Associates in September 2010. <br />Embankment and Foundation Soil Properties <br />Sand and Gravel, Clayey Brown 87.9 to 126.2 18 to 44 67 to 279 <br />Average Values 109.5 30 160 <br />Embankment Soils (SM -SC) 137 33 420 <br />Page: <br />wlssnhrNto001537 0001_ sedeadNeMerablesAraft _repoMslopestabilganaloslslope stabifty analysis and rewmmendabon memo 11 -17 -11 d= 2/4 <br />