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Mr. E. Peter Mattheis - 3 - April 27, 1990 Rule 2.05.3(4) -Ponds, Impoundments, and Diversions No designs are found for diversions in the application. Peak flow, ditch gradients and capacities, and peak velocity calculations are required for all diversions, designed to pass the runoff from the 10-year, 24-hour precipitation event. A detailed breakdown of the coal slurry transport system is requested, given the potential for damage from a system malfunction. NCEC should address: 1) how the slurry is conveyed on the surface to the separation system, 2) the design, function and capacity of the slurry ponds, and 3) the likelihood and possible impacts of a system overflow. If the settling ponds are intended to contain any overflow from the separation sy stem, NCEC must incorporate such runoff and sediment load into the pond calculations. Rule 2.05.3(8) - Coal Mine Waste and Non-Coal Processing Waste Pages 4-39 through 4-41 give only a text justification for extension of the mine portal benches using underground development waste. The assumption is made that the angle of internal friction is equal to the angle of repose, which is probably not true. NCEC will have to submit an appropriate analytical stability analysis with material strength analysis for the benches' proposed configuration. Further, since underground development waste is to be utilized for the benches NCEC must demonstrate compliance with applicable design and performance criteria in Rules 4.09 and 4.10. In addition, the last paragraph of this section implies that these benches will not be returned to approximate original contour, which is required by Rule 4.14.2(1 ). Additional provisions must be taken if NCEC wishes to temporarily store 15,000 cubic yards of coal processing waste on the surface. Rule 4.10 gives performance standards for such a structure, which must be incorporated into its design. These include quarterly inspections (4.10.2), subdrain installation (4.10.3(1)), drainage ditch designs (4.10.3(2)), and construction in compacted lifts (4.10.4). A coarse refuse storage pit is described on page 4-29 of the application, but is not shown on the surface facilities location map. What will be the dimensions of the pit, and for how long is storage to take place? The same questions are applicable to the speciality coal storage area described on page 4-30.