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2.0 Geotechnical Investigation and Design <br />The RPE East has been designed to meet the performance standards set forth in CDRMS Rule 4.10 <br />for Coal Mine Waste Banks, with focused design requirements per Rule 4.10.1(1)(a). Per the Rules, <br />the following sections summarize the geotechnical analyses and design, hydrologic water balance <br />analysis, haul road design, and a surface water hydrologic analysis and design. <br />2.1 Geotechnical Investigation <br />A geotechnical investigation was conducted in the vicinity of the proposed RPE East in June 2009 to <br />gather data to provide the basis for the RPE East design. The investigation consisted of 10 soil <br />borings in which rock coring was also performed primarily to confirm that bedrock was indeed <br />reached upon auger refusal rather than a boulder. At locations B -1, B -3, and B -6, rock coring <br />continued to a depth of 75 -100 feet, while bedrock was penetrated for 10 -15 feet at all other <br />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 strength of the materials encountered. As part of the SPT work, samples were collected <br />using a split -spoon sampler. The samples were logged upon retrieval by a geotechnical engineer or <br />geologist, after which they were sent to Lambert & Associates of Montrose, Colorado, and Soil <br />Engineering Testing of Richfield, Minnesota, for laboratory analysis. The boring logs and laboratory <br />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 colluviums /bedrock contact. They were intended to measure seasonal fluctuations in the <br />pore water pressures at the bottom of the colluviums, which was deemed to be an important layer for <br />stability of the proposed refuse pile and associated geotechnical components. <br />Revised July 21, 2011 <br />zCS�cr <br />P <br />P \Mpls�06 CO \26 \06261003 RPE E Permit Mod Support \WorkFlles \Permit Apphcation \Text \Exhibit 82 RPEE design 2011 -07 -21 TR 127 doc <br />