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uitan <br />. hnkd / Environmental Engineering - Matasials Testing <br />July 24, 2009 <br />Seneca Coal Company <br />P.O. Box 670 <br />Hayden, CO 81639 <br />Attn: Roy Karo <br />Job Number. 07-7600 <br />Subject: Supplemental Geotechnical Investigations <br />and Recommendations, Pond 12 Slide, Yoast Mine, <br />Routt County, Colorado. <br />Ladies and Gentlemen: <br />As requested, NWCC, Inc. (NWCC) has prepared this report that outlines the Supplemental Geotechnical <br />Investigations that have been completed for the Pond 12 Slide located at the Yoast Mine in Routt County, Colorado. <br />Also included are additional recommendations regarding the stabilization/reconstruction of the subject slide. Our firm <br />previously submitted a Geotechnical Evaluation and Stabilization/Reconstruction Recommendations report for this <br />project that was prepared under our Job Number 07-7600 and dated September 22, 2008. <br />Supplemental Geotechnical Investigations: NWCC originally advanced 8 test holes and 5 test pits within the <br />existing slide area in June and July 2008. However, to further evaluate the groundwater and underlying bedrock <br />conditions, two additional test holes/monitor wells (TH-9 and TH-10) were advanced to the east of the slide area in <br />November of 2008. In addition, three of the test holes that were previously drilled within the slide area were re-drilled <br />and PVC casing was set in the new test holes so that the groundwater and soil movements could be farther evaluated at <br />these locations. The location of the new test holes/wells are provided in the attached Figure #l along with the test <br />holes and test pits previously advanced at the site. The logs of all of the test holes and field measurements recorded for <br />the water levels and soil movement are provided in Figures #2 and #3. The Legend and Notes associated with the logs <br />are presented in Figures 44 and #5. <br />A test trench/pit was also advanced along the eastern edge of the slide area by the client in July 2009 with a trackhoe so <br />that the underlying bedrock and groundwater conditions could be f uthcr evaluated. The approximate limits of the test <br />trench/pit are shown in Figure #6. The upper (northern) end of the pit was excavated to depths ranging from 15 to 20 <br />feet beneath the existing ground surface. Rig refusal with the trackhoe was encountered in the underlying sandstone <br />bedrock materials in the upper portion of the trench. The lower portion of the trench pit was excavated to depths <br />ranging from 5 to 15 feet below the existing ground surface. <br />Subsurface/Groundwater Conditions: The subsurface conditions/soil profiles encountered in the new test holes <br />(TH-9 and TH-10) were somewhat consistent with the previously drilled test holes and generally consisted of a layer of <br />fill materials, ranging from 15 to 20 feet in thickness, overlying natural clays and/or weathered claystone materials that <br />were underlain by competent claystone-shale bedrock materials. A layer of natural clays was encountered below the <br />• <br />(970) 879-7888 - Fax (970) 879-7891 <br />2580 Copper Ridge Drive - Steamboat Springs, CO 80487