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Revised, September 10, 1993 In accordance with Rule 4.05.9(2), both the sediment sump and washbay pond will be considered as impoundments and shall be designed and constructed in accordance with the requirements of Rules 4.05.6(2), 4.05.6(3)(d), 4.05.6(3)(e), 4.05.6(6), and 4.05.6(8)-(12). As per Rule 4.05.6(3)(e), a single open channel spillway will be used for both the sediment sump and washbay pond. The sediment sump spillway will be constructed of non-erodible concrete and CMP designed to carry sustained flows. The washbay spillway will be constructed with non-erodible rip rap designed to carry short-term, infrequent flows at non-erosive velocities where sustained flows are not expected. The capacities of the sediment sump and washbay pond will be approximately 0.9 acft. and 19.8 acft. respectively. For comparison, the Work Area Sediment Pond has a capacity of 17.3 acft. with a calculated runoff and sediment requirement of only 4.74 acft. The sediment sump and washbay pond will intercept only a small part of the surface water drainage area which would normally flow into the Work Area Pond, yet their combined capacity of 20.7 acft. greatly exceeds the calculated capacity of 4.74 acft. for the entire Work Area Watershed. With both of the single open channel spillways used for both the sump and pond being built to dimensions which equal or exceed the main northern perimeter sediment control ditch, both spillways will be guaranteed to be adequate to pass the 25 year-24 hour precipitation event. The washbay pond will be constructed up gradient of the northern perimeter sediment control ditch which flows into the Work Area Pond. A single open channel emergency spillway will be placed in the washbay pond built to the same dimensions as the perimeter sediment control ditch which is 2:1 sideslopes, minimum 1 foot bottom width and minimum 2 foot depth. Emergency spillway riprap will consist of a minimum 6 inches of rock filter base course covered by a minimum 1 foot thick riprap layer. A SEDCAD riprap channel design run is enclosed. The 90° intersection of the washbay pond spillway and the existing diversion ditch will be protected from erosion by rip rap protection sized at a minimum to the same dimensions as the emergency spillway. Any infrequent discharge from the pond will flow into the perimeter sediment control ditch and ultimately to the Work Area Sediment Pond. The slopes on both the pond and sediment sump will be constructed at approximately 3:1 for the outside slopes and at approximately 2:1 for the inside slopes. Upon completion of the pond and sediment sump, a certified as built drawing(s) will be forwarded to the Division. The pond will be added to the quarterly pond inspection list. A new topsoil stockpile ~15K is proposed to be built immediately up gradient of the proposed West Pit Pond. Topsoil will be derived from the stripping which will occur prior to construction of the pond. The topsoil pile is shown on Map 28, Topsoil Handling and Map 36, Bond Calculation Map, Regraded Topography, South Sheet.