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Mr, Rich Atkinson - 6 - May 12, 1987 velocities. Another alternative would be to present a plan for establishment of channel vegetation to reduce flow velocity and protect the channel, The Division would be pleased to discuss this methodology with Colowyo, Also, the plan for channel stabilization presented in Exhibit 7 requires differing d50 of the riprap bed for various velocities. However, it is not clear whether differing riprap sizes will be~-~ used, or if the maximum d50 of 22 inches will be used for all channel segments. Colowyo should clarify this, and if appropriate provide information on the d50 size requirement for each channel segment. Lastly, velocity calculations for the reconstructed portions of Taylor Creek must he provided, Channel protection must also be provided if the velocity calculations indicate protection is necessary, 3. Examination of the sediment control plan, including Maps 12 and 19, indicate that runoff from disturbed areas in the southern portion of Section 10 would not be routed through a sediment pond. It appears that this flow would be discharged through Prospect Gulch, Colowyo should clarify this situation and modify the plan if necessary to insure that all disturbed areas are routed to a sediment pond. 4. The narratives on pages 4,05-8, 9, and 16 indicate that some or all sediment ponds may be retained as permanent impoundments. If permanent ponds are being proposed at this time, information must be submitted for each proposed pond to demonstrate that the requirements of Rule 4.05-9 can be met. If this proposal is for future consideration only, the narratives should be revised to clarify Colowyo's intentions. 5. On page 4.06-1, the last sentence references Table 2.05-1, However, the next sentence references "this map." Colowyo should rewrite this sentence to clarify which map is being referenced. 6, The discussion of overburden ripping in section 4.06.4 should be expanded to include the reason the practice is not being performed, and the expected effect on root penetration into the spoil, 7, On page 4.11-2 it is stated that used oil is used for dust suppression at the loadout. Colowyo should describe whether this is in addition to the oil sprayed on the stoker coal, and if so what measures have been taken to minimize soil and water contamination resulting from this practice. 8. The rill and gully stabilization plan in section 4.14.6 lacks sufficient specificity to provide the State with alternatives to enforcement action when gully erosion is present on site. The Division's letter of January 21, 1987 sets forth the specific components which must be included in the plan for such alternatives to be possible, Colowyo is not required to revise this plan, but should be aware that the present plan provides no protection against possible enforcement actions.