1991-11-18_REVISION - C1981035 (2)

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1. Purpose This Technical Revision presents both an update and modifications to Technical Revision 1, Waste Bank Design, dated April 1991. Although most of the basic design features remain the same, the pile configuration has been modified. Any design features presented in TRl (April 1991) and not specifically changed or made obsolete by proposed changes in this report remain as stated in TR 1. In addition, the stability analysis for the waste bank design presented in TR1 (April 1991) was based on assumed waste material properties. As stated on pages 3 and 4 of that document, values were assumed so that the technical revision could be submitted for review in a timely manner. It further states that laboratory measurements on field samples would be completed and submitted with any necessary modifications to the bank design. This revision reports on the results and impacts of the soils tests. 2. Coal Waste Pile Configuration The basic shape and location of the waste pile remains the same as presented in TR1 (April 1991). The waste pile will begin at section 1, figure 3 in TR1(April 1991), and extend to about 30 feet beyond section 4. The required volume is achieved by extending the pile laterally to the east across the eastside drainage channel and up the hillside approximately to the existing natural tree line. Since this fills in the existing drainage for this reach, runoff from above the pile must diverted around the pile. By extending laterally the available volume is greatly increased thus minimizing the upvalley length of the pile. This configuration results in a total pile length of about 430 feet. The upstream end of the proposed pile is about at the upper end of the existing disturbed area. Thus, only mimimal further disturbance of the natural environment is anticipated. Figure 1 shows the cross sections for the waste pile. Figure 2 is a typical schematic cross section. The surface slope as originally proposed in TR1 (April 1991) is shown (inside line) for reference. Section 1 remains the same as in TRl (April 1991) while the fill area of sections 2, 3, and 4 are dramatically increased. The intended design slope of the pile is 3:1, however because of the new geometry the surface slope of sections 2, 3, and 4 actually decrease to 4.5:1, 3.7:1 and 4.5:1 respectively. The slope facing the mine yard on the west side of the waste pile will have a 3:1 slope. The road will traverse the pile on the north side. 3. Stability Analysis The limit equilibrium stability analysis used to design the waste bank is dependent on three soil properties, effective cohesion, effective friction angle, and the unit weight of the material. To determine field estimates of these properties, soil samples and testing were completed by Lambert and Associates Inc.