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2.0 Geotechnical Investigation and Design <br />The RPEE has been designed to meet the performance standards set forth in CDRMS Rule 4.10 for <br />Coal Mine Waste Banks, with focused design requirements per Rule 4.10.1(1)(a). The following <br />sections summarize the geotechnical investigation, analyses and design. <br />2.1 Geotechnical Investigations <br />A series of geotechnical investigations have been performed in support of engineering for the RPEE. <br />Investigations were carried out during the initial design phase and during buttress construction and <br />coal refuse placement in the RPEE. These are described in more detail in the following sections. <br />2.1.1 Initial Design Phase Investigation <br />An initial geotechnical investigation was conducted in the vicinity of the RPEE in June 2009 to <br />gather data to provide the basis for the RPEE design. The investigation consisted of 10 soil borings <br />(borings B-1 through B-10) which included rock coring primarily to confirm that bedrock was <br />indeed encountered (rather than individual boulders) upon auger refusal. At locations B-1, B-3, and <br />B-6, rock coring continued to depths of 75 to 100 feet, while bedrock was penetrated for 10 to 15 feet <br />at all other locations. <br />The borings were performed using a truck -mounted drill rig. During the drilling process, the in-situ <br />Standard Penetration Test (SPT) was performed to provide geotechnical information regarding the <br />stiffness and shear strength of the materials encountered. As part of the SPT work, samples were <br />collected using a split -spoon sampler. The samples were logged upon retrieval by a geotechnical <br />engineer or geologist, after which they were sent to Lambert & Associates of Montrose, Colorado, <br />and Soil Engineering Testing of Richfield, Minnesota, for laboratory analyses. The boring logs and <br />laboratory testing data are included in Appendices A and B, respectively. <br />In addition to the exploratory borings, instrumentation was installed at select locations. Vibrating <br />wire piezometers were installed in the following boreholes: B-1, B-2, B-4, B-5, and B-8. These <br />piezometers were installed using the fully -grouted method near the bottom of the colluvium just <br />above the colluvium/bedrock contact. They were intended to measure seasonal fluctuations in the <br />pore water pressures at the bottom of the colluvium, which was deemed to be an important layer for <br />stability of the waste rock pile and associated geotechnical components. <br />PAMpls\06 CO\26\06261003 MCC Refuse Pile Site Review & Permit\WorkFiles\Permit Application\2014 Revision\Exhibit 82 2014-05- <br />29.docx <br />