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<br />•- ditches. This plan must also include new pit area diversion designs which <br />account for the increased drainage area. We can accept designs based upon <br />the 10 year, 24-hour peak flow, rather than the previously specified 100 year, <br />j~"L`~~• 24-hour peak flow. Include riprap designs where needed, based upon a <br />%'~_~-- verifiable riprap design method, and which Incorporate proper filter blanket <br />i <br />designs. Finally, submit a revised Pond 5/6 design which also accounts for <br />the increased drainage area. <br /> Response: The proposal to retain undisturbed drainage ditches as <br /> permanent diversions is based on the value of existing ditches in <br /> minimizing erosion potential for downgradient reclaimed areas and in <br /> reducing the volume of runoff to be handled by downstream <br />~L sed+mentation structures. Both the rationale and the proposal for <br />~ <br />5 or " <br />S permanent diversion are consistent with applicable provisions of Rule <br />lr <br />~ <br />~~'`~ ~ <br />L~ 4.05.3. <br /> Given the Division's concerns relative to compatibility with natural <br /> drainage patterns and potential maintenance considerations, <br /> Rockcastle will commit to remove the existing upland ditches and <br /> reclaim the associated disturbance areas. Drainage designs for all <br /> downstream structures including ditches, culverts, and Pond 5/6 have <br /> been reviewed and revised as appropriate to reflect any resulting <br /> increase in flow volumes. Revised drainage designs and supporting <br /> documentation accompany these responses as Appendix A, Drainage <br /> Design Information. <br />3) !n accordance with abatement measures specified within Notice of Violation <br />C-89-034, and several previous inspection reports, all disturbed area drainage <br />must be routed to a sediment pond, or a demonstration must be completed <br />to verify that a pond is not needed. Specific areas of concern include the <br />• northeast perimeter of Pit S, where several breaches leave been noted. We <br />recommend that this ditch should be removed, after demonstration that a <br />-2- <br />