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material around the culvert will be removed and transported for final • disposal at the coal refuse disposal area. The final cross section will have more flow carrying capacity than the original downstream channel. Further reclamation details are in Section 4.4. 4.3.1.7 Coal and Non-Coal Processing Waste The underground development waste, excess spoil, and coal processing waste are placed in a designated disposal area as shown on Drawing D-4-9. Process waste includes solids from the wash plant operation. These solids are deposited in two slurry disposal areas in the permit area, noted as upper settling pond and lower settling pond on Drawing D-4-8. The accumulation of solids is cleaned out of each disposal area about once every 6 months, and deposited on the refuse disposal pile. The configuration of the refuse pile was designed by Chen & Associates, geotechnical consultants, to attain a long-term static safety factor of 1.8 and a seismic safety factor of 1.5. These fac- tors are based on geotechnical testing and engineering analysis as detailed in the Chen & Associates' report in Appendix 4-C. Snowmass Coal will follow the design recommendations contained in Chen's report which have been approved by the State Engineer. A naturally occurring subdrainage system at the disposal area is described in the Chen Report. Basically, this system involves a clay layer that serves to isolate, from the ground water, the drainage water that infiltrates the waste pile. Water from the waste pile is inter- cepted by the refuse disposal pond at the toe of the fill. Geochemical tests indicate that the runoff water does not contain effluents that are harmful to the environment. Coal refuse is hauled to the disposal area, placed in 24-inch lifts, and compacted to a minimum of 90 percent maximum dry density (AASHTO T99-74). This method ensures mass stability and prevents formation of • voids. final configuration of the refuse pile is shown on Drawing D-4-12. 4-21