APPCOR11586 - Laserfiche WebLink

Home Browse Search

D. The application must contain analyses describing potential effects on the structures, sediment ponds and diversions, from subsidence of the subsurface strata resulting from past underground operations. 2. Railroad Loadout Sediment Control Comments A. The perimeter ditch which was designed for a 5 year event must be redesigned for a 10 year 24 hour event. This ditch is a collection ditch, not a diversion ditch. A11 runoff from disturbed areas as the result of a 10 year 24 hour event must be passed through a sediment pond. if a 10 year event occurred at the loadout, the perimeter ditch would overflow and runoff would leave the permit area without passing through a sediment pond. This will not be allowed. The ditch must be redesigned using a slope adjustment factor and basin shape correction factor. The ditch must also include 0.3 feet of freeboard as required under Section 4.05. 3(6)(b). The Mannings 'n' used in ditch calculation is 0.040. This would require a channel lining with material greater than 4" diameter cobbles. The application must indicate the size and type of lining to be used in ditch construction to justify this value of Mannings 'n'. B. Pond Design: The sizing of the spillway takes into account head Loss due to the trash rack, but does not consider bend loss, friction loss, and tail water conditions. These losses must be taken into account in the spillway design. In addition, the design should consider the use of an anti vortex baffle or justify why one is not needed. General: A. For aI1 sedimentation ponds; the Division suggests that markers be placed in all ponds to indicate the 60~ sediment storage level. The marker should be durable and easily identifieable. B. A11 ponds must be certified by a qualified registered professional engineer after construction as required by Section 4.05.6(7). The application needs a statement that certification will be done and a copy of the certification sent to the Divi- sion within 30 days of aI1 pond completion. C. The application must indicate that all sedimentation ponds will be inspected quarterly for structural weakness, erosion, clogging of spillways and dewatering devices, and filling of the 60~ sediment storage volume. D. A copy of the report must be submitted to the Division quarterly. (This is required under Section 9. 05.6 (11(c).) (~)