2010-12-17_REVISION - C1981019 (94)

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SHANNON MMILSON. INC. • GEOTECHNICAL STUDY COLLOM TEMPORARY SPOIL FILL COLOWYO COAL MINE 1.0 INTRODUCTION This report presents the results of our geotechnical exploration, testing, analyses, and geotechnical recommendations for the proposed Collom Temporary Spoil Fill. The purpose of our study was to evaluate the long -term stability of the proposed fill for use by Colowyo Coal Company ( Colowyo) in the permitting process. Our work included review of previous studies, review of geologic maps and aerial photos, subsurface exploration, laboratory testing, and stability analysis. We also reviewed information provided by Colowyo regarding bedrock orientation below the site and seeps /springs. Our stability analysis was performed in general accordance with our proposal and with the Colorado Mined Land Reclamation Board (CMLRB), Colorado Department of Natural Resources (now Colorado Division of Reclamation, Mining & Safety) "Regulations of the Colorado Mined Land Reclamation Board for Coal Mining" (CMLRB, 2005). To our • knowledge, the regulations do not specifically address temporary spoil fills. Our recommendations diverge from requirements in the regulations related to allowing surface water to drain over the downstream face of the temporary fill and with respect to the underdrain (which we recommended only under the downstream half of the fill). Our scope did not include evaluation or recommendations regarding erosion protection on the spoil fill or surface water control on and around the fill. 2.0 PROJECT DESCRIPTION Our understanding of the project in based on our discussions with Colowyo and plans provided by them; the location of the project components are shown on the Vicinity Map, Figure 1. The temporary excess spoil fill is located in the Little Collom drainage north of the proposed Collom Lite Pit. We understand that the Little Collom X -Seam pit will be mined first; this pit will be relatively shallow and will mine the X4 seam. The crest of the pit shell and the elevation contours of the proposed mining are shown in Figure 2; at the base of the mined area the contours represent the X -Seam floor. Based on these contours, the dip of the coal floor after mining will be about 2 to 4 percent towards the northeast in the area below the spoil fill. Overburden spoil from the X -seam 23 -1 -01101 -400 -R I.docx/wp /Ikn 23 -1- 01101 -400 Exh. 23 -1 -8 Revision Date: 08/05/09 Revision No.: PR -03