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49 <br />As presented, the pile appears to be stable, even in the unlikely event that a water <br />table surface does develop within the spoil. However, there is a potential that <br />excessive water pressures could develop along the interface of the pile and the <br />foundation strata if springs developed within the channel. The potential for this <br />to occur can best be determined by observations of the area over time. If this <br />condition exists, a free draining under drain would need to be installed. The <br />location of any spring would determine the longitudinal extent of the required <br />under drain. <br />The results of this analysis indicate an adequate factor of safety against slope <br />instability for the assumed material properties, slope profile, and ground water <br />conditions outlined in this report. These results will be verified with the actual <br />behavioral characteristics of the waste material once it is available for testing. <br />CTL /Thompson conducted a Supplemental Stability Investigation of the RDA in 1995. <br />The results of this investigation are presented in the report located in Exhibit 30, <br />Geotechnical Study, Coal Processing Waste Bank. Compaction testing in 1995 and <br />1996 also confirmed construction of the facility to specifications. CTL /Thompson's <br />Supplemental Stability Investigation states: "Based upon the sensitivity of the <br />proposed configurations to water and earthquake conditions, we recommend the <br />proposed RDA be constructed with minimum 2.2:1 slopes between the benches. For <br />this configuration we believe the factors of safety are adequate and exceed regulatory <br />minimums for all but the worst case water condition. We do not believe the worst <br />case water condition is likely based upon the results of the current investigation." <br />CTL /Thompson used a friction angle of 32 degrees and cohesion of 200 psf for the <br />RDA stability analysis. NECC plans to haul development waste to the RDA. <br />Exhibit 37, Development Waste Disposal Area Design (AAI 2010) presents the <br />strength properties of the development waste. The strength properties for the <br />development waste are a friction angle of 37 degrees and cohesion of 461 psf. <br />Placing development waste on the RDA will not compromise the stability of the <br />RDA because the strength properties of the development waste are substantially <br />greater than those used for the stability analysis of the RDA. <br />CTL /Thompson also performed a stability analysis of the Lorencito Canyon Mine <br />waste to be processed at the New Elk Mine and stored in the RDA. Results of <br />this study are also presented in Exhibit 30, Geotechnical Study - Coal Processing <br />Waste Bank. <br />The Development Waste Pile (DWP) west of the mine entrance been successfully <br />reclaimed. A new development waste disposal area (DWDA #2) is necessary to <br />accommodate the waste rock excavated during development and preparation of <br />areas incident to underground mining. The refuse material is expected to be <br />identical to the material deposited in the DWP. Experience on -site dictates that <br />the makeup of these materials is not indicative of the components of that would <br />Section 2.05 TR -70 03/02/2015 <br />