2011-12-28_APPLICATION CORRESPONDENCE - C2010089

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Page 5 of 9 ponds has a notation for a 6 inch valve. However, there is no notation for a gated valve on the 18 inch diameter cmp pipe, which appears to be shown in Figure 5. Please explain and revise, if appropriate. J) In Appendix 2.05.3(4) -1, `ARCADIS Report on Sediment Control ", it is stated on the cross - sections for the three sediment ponds that 18 inch or larger cmp principle spillways will be installed. However, Rule 4.05.9(14)(b) requires that a professional engineer certib, that the pond has been constructed as designed. Therefore, an exact construction design is required. Please revise the three sediment pond cross sections to state the exact diameter of the principle discharge tube. The Division has no further concerns. Text and drawings in Appendix 2.05.3(4) -1 were revised appropriately in the submittal dated November 29, 2011. 5. A) On Map 2.05.3(3) -1, please add a line to connect the SW -FA notation with the SW -FA drainage area. The Division has no further concerns. Map 2.05.3(3) -1 was relabeled as Map 2.05.3(4) -1 and revised in the November 29, 2011 submittal. 9. The May 26, 2011 submittal contained Sedcad designs that demonstrate that the ponds have sufficient volume capacities. However, the response to question number 12 -B of this section may require another review if the elevations of the primary discharge pipes are raised. Pond volumes were revised in the November 29, 2011 submittal. However, the Division has an additional concern. Referring to the pond volume data found in Table 3 of Appendix 2.05.3(4) -1, "ARCADIS Report on Sediment Control ", please explain how the design capacities for all three ponds were obtained. The values do not seem to correlate with the capacities that are listed in each of the elevation- capacity- discharge tables found in the Sedcad designs of Appendix 2.05.3(4) -2. 12. A) In the last sentence of the 3r complete paragraph on page 4 of the Arcadis report in Appendix 2.05.3(4) -1, the sediment storage elevations listed for the three sediment ponds don 't match the sediment storage elevations presented in Table 3 on page 5. Please revise. The text was revised in the November 29, 2011 submittal. However, with the revised Sedcad design submittal, the Division has an additional concern. The elevations of each of the principle spillway risers used in the Sedcad pond designs of Appendix 2.05.3(4) -2 do not correspond to the elevations depicted on the pond profiles and as listed in Table 3 in Appendix 2.05.3(4) -1, "ARCADIS Report on Sediment Control ". The same is true for the emergency spillway elevations for ponds NHN -001 and NHN -003. Please rectify these differences and provide the appropriate revised pages for these two appendices. B) Referring to Table 3 of the Arcadis report in Appendix 2.05.3(4) -1, the invert of the primary discharge pipe elevation for each sediment pond is located just above the maximum sediment storage elevation. The Division is concerned that the sediment ponds may have sediment discharge problems due to this small elevation difference. The Sedcad manual, on page 64, recommends a minimum 2 foot difference between the top of the sediment level and the primary pipe invert. If the release is slow, 0.5 feet to 1.0 feet can be used. Please consider increasing the height between the top of the sediment storage level and the invert of the primary discharge pipe, allowing for the requirement mentioned in question number 9 of this section that the pond capacity between the primary discharge pipe and the emergency spillway must contain the runoff volume from a 10 year -24 hour event.