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• face of the slope to the east and west- southwest to the main drainage ditch around the CRDA. The ditches <br /> are designed with an approximately 1.5% to 4% slope. <br /> The proposed refuse pile is not classified as a valley fill according to the Regulations. The steepest side <br /> slopes in the reclaim area are on the order of 10 to 15 degrees. The existing coal refuse area that is located <br /> along the west side of the proposed CRDA is constructed at an overall slope configuration of 3 (H) to 1 (V). <br /> The CDRA configuration was developed to provide long -term stability working with the landforms at the <br /> site. The pile expansion will be contained by the existing coal refuse pile to the west and the existing <br /> hillsides to the south and east. An underdrain is planned to control water levels from reaching a level where <br /> the pile stability could be affected. <br /> The CDRA is designed as a non - impounding embankment fill. A permanent drainage ditch is designed <br /> above the site and around the east and south sides of the pile and then tying into the existing ditch situated <br /> along the south and west sides of the existing refuse pile. The existing ditch currently flows into Pond D. <br /> The ditch should be constructed prior to starting construction of the refuse pile. Temporary diversion <br /> ditches should be constructed and maintained a maximum of 50 vertical feet above the refuse pile to control <br /> surface drainage between the permanent ditch and the back of the pile. As the waste pile progresses in <br /> height, the temporary diversion ditches should be moved up the slope. <br /> Slope Stability Analysis <br /> • A stability analysis of the proposed slope configuration was completed to determine the potential for slope <br /> movement. The analysis involved the evaluation of the geotechnical properties of the coal refuse and <br /> foundation conditions. A typical cross - section of the north side of the proposed configuration was used in <br /> our analysis. The soil properties and analysis are outlined below. The results of the stability analysis are <br /> outlined below and presented in Appendix C. <br /> The properties of the coal refuse materials were determined using results from the previous investigations, <br /> as well as data collected from the compaction testing and observation of the construction of the existing <br /> coal refuse disposal area. For this evaluation we have assumed that the coal refuse materials will be a <br /> granular, non - cohesive material. Values of 25, 30 and 35 degrees for the internal angle of friction, values of <br /> 95, 105 and 115 pcf for the unit weight and a cohesion value of 0 psf were used in the analysis of the <br /> proposed slopes. <br /> Based on the laboratory and triaxial shear test results for the reclaim spoils encountered at the site, values of <br /> 34 and 38 degrees for the internal angle of friction, values of 110, 120 and 130 pcf for the unit weight and a <br /> cohesion value of 0 psf were used in the analysis of the proposed slopes. It should be noted that the larger <br /> particle size materials (larger gravels, cobbles and boulders) were not used in the triaxial shear test; <br /> therefore, the values for the angle of friction are conservative. <br /> We have assumed that claystone or sandstone bedrock will be encountered below the reclaim spoils at a <br /> depth of approximately 85 to 100 feet below the existing ground surface. We have assumed a value of 25 <br /> • <br /> Job Number: 08 -7915 NWCC, Inc. Page 6 <br /> Revised 10/12/09 <br />