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SEDIMENT CONTROL RESPONSES CONTD. • 6) Tables 6.1 and 6.5 show the flows, velocities and depths of the ditches for the 100-year event. It should be noted that as shown on this table riprap is not necessary for the ditches until Phase V. At this point, velocities become excessive (over 6 feet per second) and the ditch bottom must be protected. Also, at this point, the ditches become permanent structures. The peak discharge for the ditches for each phase for the various ditches were calculated to obtain the true peak discharge which the individual ditch will carry. 7) The riprap size required for the sediment control and clear water ditches are shown on Tables 6.1 and 6.5. The size shown on these tables is the 50% gradation. Based upon recommended gradation requirements from the U.S. Bureau of Reclamation, the maximum size of the riprap will be three times the 50% size. Available sandstone in the area will be utilized for the riprap. TOPSOIL -RULE 4.06 1) Visual monitoring of the topsoil pile and subsoil pile will be peformed on a monthly basis to assure that any possible slumping will be repaired as soon as possible. It should be noted, however, that West Elk Coal Company personnel will observe the stockpiles during the course of regular operations on an almost daily basis and if any problems are noted, corrective action will be taken. 2) West Elk Coal Company does not feel, for several reasons, that the subsoil stockpile warrants the use of a survey monumentation monitoring system. We • request that CMLRD review our reasoning for not installing the survey monitoring system. The major points are as follows: 1) The subsoil pile is relatively small, at maximum capacity it will contian approximately 45,000 cubic yards. 2) A state of the art stability analysis was performed for the subsoil stockpile at maximum capacity and in the planned configuration. The safety factor was calculated to be 1.7 which is greater than the required 1.5. 3) The subsoil stockpile is located near Sylvester Gulch, however, the relocated road is between the stockpile and the gulch. The most likely problem, if any were to occur, would be small surficial slumps in response to snowmelt and spring runoff. These would be kept from entering Sylvester Gulch by the road. 4) If a major movement of the pile were to occur, it could be identified in a short period of time since it would affect the Sylvester Gulch Road, which is used on a daily basis to inspect the main fan. •