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48 <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. <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 />potentially lead to acidic runoff or adversely affect groundwater quality. The <br />mine has a long history of stockpiling coal without encountering spontaneous <br />combustion. <br />The development waste, ditch cleanings, and pond cleanings will be permanently <br />stored in the new DWDA #2 located south of Highway 12 (DWDA #2). This <br />area was previously permitted as the clean coal stockpile area as shown on Map <br />11 Surface Facilities and Roads East Portal. As part of TR -66, the design <br />configuration for DWDA #2 will change. The storage capacity of the revised pile <br />will be about 125,000 BCY. Refer to Figure 13 for the plan and section view of <br />the proposed DWDA #2. The overall pile height will be 50 feet tall. Each 10 -foot <br />bench will be placed in up to 1 foot lifts and compacted with a track dozer. <br />Setbacks of 20 feet for each bench will result in an overall slope of 2.0(H): 1(V) <br />during construction. A stability analysis for the TR -66 revised configuration can <br />Section 2.05 TR -68 12/10/2014 <br />