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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 indicates 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 <br />1995. The results of this investigation are presented in the report located in <br />Exhibit 30, Geotechnical Study, Coal Processing Waste Bank. Compaction <br />testing in 1995 and 1996 also confirmed construction of the facility to <br />specifications. CTL/Thompson's Supplemental Stability Investigation of the <br />RDA states: "Based upon the sensitivity of the proposed configurations to water <br />and earthquake conditions, we recommend the proposed RDA be constructed <br />with a minimum 2.2: slopes between the benches. For this configuration we <br />believe the factors of safety are adequate and exceed regulatory minimums for all <br />but the worst case water condition. We do not believe the worst case water <br />condition is likely based upon the results of current investigation." <br />CTL/Thompson used a friction angle of 32 degrees and cohesion of 200 psf for <br />the 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 of 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 />Section 2.05 RN -6 10/17/2016 <br />