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VP ARCADIS <br />MEMO <br />To <br />Jerry Koblitz <br />Hugh Roberts, PE <br />Gaston Leone, PE <br />From. <br />Benjamin Black, MS, PG <br />Date: <br />November 17, 2011 <br />Copies: <br />Kristof Fabian, Ph.D., PE <br />ARCADIS Protect No.: <br />C0001537.0001.00001 <br />Subject: <br />Western Fuels — Colorado: New Horizon Mine, Nucla, Colorado <br />Sediment Pond Slope Stability Analysis (Ponds NHN -001, -002, and -003) <br />ARCADIS U.S., Inc. <br />1000 Cobb Place Blvd. <br />Bldg. 500 -A <br />Kennesaw <br />Georgia 30144 <br />Tel 770 428 9009 <br />Fax 770 428 4004 <br />As requested, slope stability analysis was conducted for the three proposed sediment ponds (NHN -001, - <br />002, and -003). Analysis was conducted in order to confirm that the factor of safety (FOS) for the <br />embankments was satisfactory for long term, steady state seepage conditions. <br />The Colorado Division of Reclamation, Mining and Safety (CDRMS), Regulations of the Colorado Mined <br />Land Reclamation Board for Coal Mining (as Revised March, 21, 2001), specifically Sections 4.05.6 and <br />4.05.9 outline in detail the requirements for design and construction of sedimentation ponds and <br />impoundments. Section 4.05.9(8)(b) discusses the minimum required FOS for static conditions with steady <br />state seepage conditions at normal pool elevation and requires a minimum FOS against failure of 1.3. <br />Slope stability sections were developed based on the information contained in the New Horizon North <br />(NHN) Pond Design Memo. It appears from the sections that the proposed ponds will be excavated into <br />the native (or previous fill) soils at the site followed by the installation of an embankment around the partial <br />perimeter of the pond. The embankments will have side slope geometry varying from 2.51-11V (horizontal <br />to vertical) to 3H:1 V, crest width of 10 feet, and a maximum height of 10 feet. Existing soil topography <br />varies, but in no case does it exceed 1 H:1 V. No stability analysis was conducted with regard to the cut <br />slopes in the native /fill soils that will form the remaining perimeter of the ponds. <br />Page: <br />wlsmhmg` co0015370001_ sedcad�d elverablesldraft _repatlsbpestabddyanaVstslsbpe staWGty analysis and reoommendabon memo 11- 17- 11.docx 1/4 <br />