2010-12-17_REVISION - C1981019 ‎(94)‎

• Permit No: C1981019
• IBM Index Class Name: Revision
• Doc Date: 12/17/2010
• Doc Name: Exhibit 23 Item 1 Geotechnical Report -Collom Temporary Spoil Pile & Pond
• Type & Sequence: PR3
• Media Type: D
• Archive: No

NON 6WILSON, INC.
Appendix A for soil and rock. Individual boring logs follow the classification sheets in
Appendix A. These exploration logs represent our interpretation of the contents of the field logs
and the results of laboratory testing.
Upon completion of drilling and sampling, groundwater levels were measured, and the boreholes
were backfilled with cuttings generated during the drilling process with the top ten feet
backfilled with bentonite chips. Groundwater measurements made during drilling are recorded
on the individual boring logs in Appendix A and discussed further in Section 5.0 of this report.
Geotechnical laboratory tests were performed on selected samples retrieved from the borings to
determine index and engineering properties of the materials encountered beneath the site.
Laboratory testing included:
1. Natural moisture content and density;
2. Grain size distribution;
3. Atterberg limits; and
4. Consolidated - Undrained Triaxial strength testing.
The laboratory test results are presented in Appendix B. The natural water contents, Atterberg
limits, and percent fines are also indicated on the individual boring logs in Appendix A. Soil
properties and strength values are discussed in more detail in the following sections.
5.0 GEOLOGIC AND SOIL CONDITIONS
C7
5.1 Geology
Geologic conditions were interpreted from a review of previous studies, a review of geologic
maps, previous visual observations at the mine and in mine pits, and the current borings. We
also reviewed plots of coal structure in this area, provided by Colowyo, indicating the floor
elevations of the X4, D2 and F2 seams.
Bedrock at the mine site consists of interbedded sandstone, siltstone, claystone, shale, and coal of
the Williams Fork Formation. A considerable amount of engineering laboratory testing has been
performed on rock samples in studies related to the Collom mine area and South Taylor Mine
area (CNI, 2005a, 2005b; Shannon & Wilson, Inc. 2006b, 2008a).
The primary geologic structure in the area is a NW — SE trending asymmetric syncline. The
spoil fill will be located SW of the axis, on the flatter limb of the syncline. This location near the
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Exh. 23 -1 -11 Revision Date: 08/05/09
Revision No.: PR -03