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March 10, 2015 <br />Revised November 3, 2015 <br />Colowyo Coal Company, L.P. <br />5731 State Highway 13 <br />Meeker, Colorado 81641 <br />Attn: Mr. Juan Garcia <br />RE: ADDENDUM TO GEOTECHNICAL STUDY FOR THE REVISED COLLOM <br />TEMPORARY SPOIL FILL <br />This report presents our opinions and recommendations for the revised Collom temporary spoil <br />fill. We completed a geotechnical study for the previous Collom temporary spoil fill (Shannon <br />& Wilson, 2009). The previous study included: <br />• Investigation of subsurface conditions, <br />■ Laboratory testing, review of previous testing, and evaluation of engineering properties <br />of the spoil and foundation materials, <br />■ Parametric stability analyses, and <br />■ Recommendations for spoil placement, drain, surface water control, sedimentation pond <br />embankment, and monitoring. <br />This addendum presents our opinions regarding the validity of our previous analyses and <br />additional recommendations for the revised spoil fill. <br />40113 iu El.�•1 <br />In our opinion, the stability analyses and recommendations for the previous temporary spoil fill <br />slope remain valid for the revised temporary spoil fill. These analyses indicated a long term <br />Factor of Safety (FS) of 1.5 or more. In this addendum, we provide revised drain locations and <br />size recommendations. Additional recommendations and details in our previous study remain <br />valid. <br />1321 BANNOCK STREET, SUITE 200 <br />DENVER, COLORADO 80204 <br />PHONE 303.825.3800 <br />FAX 303+825.3801 <br />www shannonwllson com <br />23-1-01403-002 <br />`A ALASKA "'A <br />"' <br />SHANNON 6WILSON INC. <br />FLORIDA <br />_ <br />GEOTECHNICAL AND ENVIRONMENTAL CONSULTANTS <br />MIS OURIIO <br />OREGON <br />WASHINGTON <br />WISCONSIN <br />March 10, 2015 <br />Revised November 3, 2015 <br />Colowyo Coal Company, L.P. <br />5731 State Highway 13 <br />Meeker, Colorado 81641 <br />Attn: Mr. Juan Garcia <br />RE: ADDENDUM TO GEOTECHNICAL STUDY FOR THE REVISED COLLOM <br />TEMPORARY SPOIL FILL <br />This report presents our opinions and recommendations for the revised Collom temporary spoil <br />fill. We completed a geotechnical study for the previous Collom temporary spoil fill (Shannon <br />& Wilson, 2009). The previous study included: <br />• Investigation of subsurface conditions, <br />■ Laboratory testing, review of previous testing, and evaluation of engineering properties <br />of the spoil and foundation materials, <br />■ Parametric stability analyses, and <br />■ Recommendations for spoil placement, drain, surface water control, sedimentation pond <br />embankment, and monitoring. <br />This addendum presents our opinions regarding the validity of our previous analyses and <br />additional recommendations for the revised spoil fill. <br />40113 iu El.�•1 <br />In our opinion, the stability analyses and recommendations for the previous temporary spoil fill <br />slope remain valid for the revised temporary spoil fill. These analyses indicated a long term <br />Factor of Safety (FS) of 1.5 or more. In this addendum, we provide revised drain locations and <br />size recommendations. Additional recommendations and details in our previous study remain <br />valid. <br />1321 BANNOCK STREET, SUITE 200 <br />DENVER, COLORADO 80204 <br />PHONE 303.825.3800 <br />FAX 303+825.3801 <br />www shannonwllson com <br />23-1-01403-002 <br />