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2.4 Geotechnical Design <br />A geotechnical monitoring plan, as presented in Appendix C, has been and will continue to be <br />implemented as part of RPEE operations. This program is conducted to continually monitor waste <br />rock pile conditions. <br />Initial evaluations of refuse characteristics were conducted over the first two years of CPP operations <br />when the waste rock pile was very small and there was less danger of global instability (compared to <br />a fully constructed waste rock pile). Test results have been compared to the results already collected <br />from the field and the laboratory as discussed in Section 2.2.2.1 and used in the geotechnical design <br />presented in this section. <br />2.5 Subsidence <br />The potential for subsidence related to mining activity in the area of the RPEE was examined. <br />Historically, the Oliver Mine was developed in the E -Seam near the current elevation of Highway <br />133 (Elevations 6,130 to 6,300 in the area underneath the RPEE waste rock pile). This mine used the <br />room -and -pillar mining technique in which pillars of coal remained after mining was completed to <br />support the roof. Mining was completed in the Oliver Mine decades ago. More recently, the longwall <br />mining method was utilized to mine the B -Seam of the West Elk Mine at approximately elevations <br />5,940 to 6,050 in the vicinity of the RPEE. Longwall mining typically results in surface <br />manifestation of settlement more quickly and completely than room -and -pillar mining. The longwall <br />panels were located directly beneath the Oliver Mine workings and both mine workings are located <br />directly below the RPEE waste rock pile as shown in Figure 2-15. <br />Completion of longwall mining of the B -Seam panels in the area of the RPEE waste rock pile <br />occurred in 2006, and it is believed that essentially all of the subsidence due to mining of the 13 -foot - <br />thick coal seam was completed within the first year after mining stopped in this area. Therefore, <br />appreciable subsidence at the ground surface in the area of the RPEE waste rock pile is not expected <br />to occur during the life of the waste rock pile. <br />13 <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 />