2009-11-13_PERMIT FILE - C1982056 (3)

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Settlement Settlement of the fill and foundation soils will not be excessive and should not affect slope stability or construction. The reclaim spoils and coal refuse are anticipated to behave as granular (non - cohesive) materials and we anticipate settlement to occur rapidly as loads are applied during construction of the CDRA. The top surface of the CDRA is designed to drain to the southeast, away from the slope face, at approximately 2.5 to 3 percent. The elevation of the CDRA at the face is approximately 40 to 50 feet above the elevation at the back of the fill area. This will provide for adequate drainage away from the face of the fill slope, even if some long -term settlement of the coal refuse fill materials occur. Construction Recommendations Initial Construction and Phasing Initial construction of the CRDA Expansion will involve construction of the new haulroad, permanent and temporary ditches and the permanent underdrain to allow for fill placement and approximately 2.8 mcy of the coal refuse in the CRDA. The construction of the CRDA will start at the north end and progress to the south. The initial construction of the CRDA will consist of up to 100 feet of vertical construction, to the second bench, in the northern portion of the fill area. Prior to construction of the CRDA, the existing soil • and cover materials will be stripped and stockpiled near the top of the proposed fill areas. A temporary diversion ditch should be placed a maximum of 50 vertical feet above the initial construction and relocated as the pile advances. Future construction will proceed progressively as dictated by refuse disposal requirements and will involve extension of soil and cover material stripping, perimeter ditches, the underdrain and fill benches to the south, as well as further vertical placement of fill materials to the maximum height of the CRDA area. More detailed discussions of the construction are outlined below. Haulroad Construction A new haulroad will be constructed beginning at the northeast end of an existing haulroad located along the southern edge of Pond D and the northern edge of another existing pond. The new haulroad will be approximately 2,300 feet in length. The haulroad will extend approximately 500 feet to the northeast from the existing haulroad then curve to the south approximately 400 to 500 feet and continue southwest to the proposed CRDA at Station 23 + 00. The haulroad will have a driving surface approximately 30 feet in width. The Haul Road Plan is presented in Figure C -103. We recommend that the gravel/pavement section for the haulroad consist of 18 inches of sub -base sands and gravels overlain by 6 inches of base course materials. The sub -base and base course materials should meet specifications for aggregates outlined by the Colorado Department of Transportation, Standard Specifications for Road and Bridge Construction, Section 703. The sub -base sands and gravels should consist of a pit run material, which meets CDOT Class 3 specifications. The base course materials should • consist of a well - graded aggregate base course, which meets CDOT Class 5 or 6 specifications. lob Number: 08 -7915 NWCC, Inc. Page 8 Revised 10/12/09