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orado Consult <br />Geotechnical / Environmental Engineering - Materials Testing <br />February 10, 2010 <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 <br />Investigation and Additional <br />Stabilization/Reconstruction <br />Recommendations, Pond 12 Slide, Seneca <br />Yoast Mine, Routt County, Colorado. <br />Ladies and Gentlemen: <br />At the request Seneca Coal Company (Seneca), NWCC, Inc. (NWCC) has prepared this report that outlines <br />a Supplemental Geotechnical Investigation that was recently completed (November 2009) for the Pond 12 <br />Slide located at the Yoast Mine in Routt County, Colorado, as well as provides additional drainage and cite <br />grading recommendations for the stabilization/reconstruction of the subject slide area. NWCC previously <br />submitted a Geotechnical Evaluation and Stabilization/Reconstruction Recommendations report for this <br />project prepared under our Job Number 07 -7600 and dated September 22, 2008, as well as a supplemental <br />report dated July 24, 2009. <br />Supplemental Geotechnical Investigation: NWCC observed the drilling of 4 additional test holes /monitor <br />wells (TH -11 through TH -14) on November 19 and 20, 2009. The test holes were located to the north and <br />east of the subject slide area to further evaluate the underlying bedrock and groundwater conditions in these <br />areas. Locations of the test holes are shown on the attached plans (Sheet 1 of 2). <br />Test holes were advanced by Western American Drilling (WAD), a subcontractor to Seneca, and drilled <br />with a truck mounted Gardner Denver 14W drill rig using 5 -inch diameter rotary core with and both air and <br />water methods to depths ranging from 80 to 180 feet beneath the existing ground surface (bgs). After the <br />completion of the drilling the test holes were cased with 2 -inch diameter (slotted and solid) PVC pipe so that <br />groundwater levels could be monitored. Logs of the test holes /monitor wells and groundwater levels are <br />shown in the attached Figure # 1. The Legend and Notes associated with the logs are presented in Figures #2 <br />and #3. <br />As per NWCC's previous recommendations, the client constructed two north -south test trench/pits within <br />the slide area during July and August 2009. The details for the first trench were discussed in detail in our <br />previous report dated July 24, 2009. The second test pit/trench, which was situated to the west of the first <br />(970) 879 -7888 • Fax (970) 879 -7891 <br />2580 Copper Ridge Drive • Steamboat Springs, CO 80487 <br />