2010-12-17_REVISION - C1981019 (94)

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NON &WILSON, INC. 0 mining will be replaced to backfill the X -Seam mine area before spoil from Collom Lite is placed in the temporary spoil fill toe area. The Collom Temporary Spoil Fill will be constructed from spoil derived from the first several cuts in the Collom pit. Construction of the fill will generally proceed from south to north. Spoil will be placed in horizontal lifts of 50 to 100 feet. The volume of the fill is estimated at 250 million cubic yards. At completion of the Collom Lite pit, the spoil will be used to fill the last cut(s) to restore approximate original contours. It is estimated that the spoil will be in place about 20 years. The configuration of the spoil fill was developed by Colowyo and includes 3H:1 V (Horizontal: Vertical) side slopes around the perimeter (Figure 2). The top elevation is planned at 7625 feet. The northern (downstream) toe of the fill is planned at about elevation 6750 feet; this represents the highest slope face at about 875 feet. The approximate location of sections through the fill used for our stability analyses are shown on Figure 2 and the section views are shown on Figure 5. The fill is confined by the valley sides within in the Little Collom drainage. Section 1.04 of the • CMLRB regulations (2005) indicate that for excess spoil fill, a site is classified as a "Valley Fill" if the side slopes of the valley measured at the steepest point are greater than 20 degrees, or if the average slope of the profile of the valley from the toe of the fill to the top of the fill is greater than 10 degrees. Based on the topographic information provided by Colowyo, the spoil fill site area has side slopes within the valley greater than 20 degrees and would therefore classify as a Valley Fill according to regulations for excess spoil fills. A sedimentation pond and embankment are planned downstream of the toe of the spoil fill (Figure 2). The embankment will be located outside the Little Collom X -Seam mine area in natural ground. Colowyo has indicated that the embankment is not jurisdictional according to the CMLRB regulations (2005). 3.0 SUMMARY OF PREVIOUS WORK CTL /Thompson, Inc. and Shannon & Wilson, Inc. (S &W) have performed several previous geologic /geotechnical studies at the site that included subsurface explorations and evaluation of excess spoil fill and/or surficial soils as listed in the references at the end of the report. S &W and Call & Nicolas, Inc. (CNI) have also performed several studies investigating spoil engineering properties and bedrock structure and engineering properties, which are also referenced. We reviewed and considered information from these previous investigations and 23- 1- 01101- 400- R1.docx/wp /Ikn 2 23 -1- 01101 -400 Exh. 23 -1 -9 Revision Date: 08/05/09 Revision No.: PR -03