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Pagel 2 <br />Konig Drainage Letter.doc <br />offsite basin will cross CR 81 and flow into the pit. Flows within this basin are generally in a <br />sheetflow condition to the southeast over moderately sloping agricultural land. These flows are <br />relatively minor and will be contained within the pit. <br />Basin 03 is approximately 0.9 acres and is located to the west of the pit and west of CR 81. <br />There is a defined roadside ditch in this area, approximately 1 foot deep with a 1% longitudinal <br />slope. Flows within this basin are generally in a sheetflow condition towards the roadside ditch, <br />then becoming concentrated flow. This ditch conveys the 100-yr flow from basin 03 to the <br />south along CR. 81. Therefore 100-yr flows from this basin will not enter the pit. <br />Basin 04 is approximately 0.7 acres and is located to the west of the pit and east of CR 81. There <br />is a defined roadside ditch in this area, approximately 1 foot deep with a 1% longitudinal slope. <br />Flows within this basin are generally in a sheetflow condition towards the roadside ditch, then <br />becoming concentrated flow. This ditch conveys the 100-yr flow from basin 04 to the south <br />along CR 81. Therefore 100-yr flows from this basin will not enter the pit. <br />On-Site Stormwater <br />For both mining phases 1 and 2 there will be two temporary sediment ponds constructed. There <br />will be diversion ditches or berms to capture stormwater and direct flows to each pond. <br />Calculations for pond sizing are attached. <br />With Phase 1 there will be flows entering the pit from the undisturbed phase 2 portion of the pit <br />and offsite basin 02. Both phase 1 ponds have been sized for a volume of 1800 cf per acre of <br />disturbed tributary area within the pit. The flows from the undisturbed phase 2 area and off-site <br />basin 02 will be captured within the pit by a topsoil berm constructed along the east edge of the <br />pit. At the south and north edge of the pit the berm will continue until tying in with the 5067 <br />contour. A pump rated at 150 gpm with a floating suction line will discharge stormwater from <br />the ponds. The discharge rate of 150 gpm is below 1 cfs which will allow sufficient time for <br />settling within the ponds while also draining the ponds within the required 72 hours. <br />With Phase 2 there will be flows entering the pit from off-site basin 02 and captured within the <br />north pond. The phase 2 north pond has been sized for a volume of 1800 c.f. per acre of <br />disturbed tributary area within the pit and the off-site area from basin 02. The phase 2 south <br />pond is sized for the volume from the disturbed tributary area within the pit. There is no off-site <br />flows tributary to the south pond. Again, a pump rated at 150 gpm with a floating suction line <br />will discharge stormwater from the ponds. The discharge rate of 150 gpm is below 1 cfs which <br />will allow sufficient time for settling within the ponds while also draining the ponds within the <br />required 72 hours. <br />Refer to the drainage calculations, Mine Plan Map, Erosion Control Plan, and Stormwater <br />Management Plan Report for more information. <br />Conclusion <br />The proposed Konig Borrow Pit will not have any impacts on existing drainage patterns or <br />adversely affect downstream properties or structures.