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• TECHNICAL REVISION N0. 14 Response: The Pond 008 Diversion Ditch is only proposed to be a short-term diversion used to control runoff until proposed Sedimentation Pond 009 is permitted and constructed by the end of 1989. Sedimentation Pond 008 was designed assuming all of the runoff from the watershed would flow into 008; however, this is conservative and until 1990, there will be an open pit, a minimum of four spoils and various haul road ramps which may intercept the runoff and detain the runoff in the upper part of the watershed. Therefore, the additional 42.9 acres contained in this diversion ditch would be offset by the pits, spoils and haul road ramps which occur in the 008 watershed. The 42.9 acres represents "worst case", assuming part of the Wadge Scraper Pit ditch area within the mining area was also included. The most probable watershed would only be below the Wadge Scraper Pit or 17.8 acres; however, for design purposes on the 008 North Ditch, the 42.9-acre watershed was used. In addition, an analysis was performed using the Sedimentation Pond 008 as-built input data and adding the 42.9 acres in the ditch's watershed to the Pond 008 watershed for a total of 290.44 acres (see the attached analysis for the 10-year, 25-year and 100-year precipitation event). The rest of the input data was used as is. The results indicate no change in the basin trap efficiency for the 10-year, 24-hour storm. The peak stage is increased less than 0.5 ft for all three storms and • adequate freeboard remains on Pond 008. The peak spillway discharge rate during the 25-year storm increases less than 2 cfs; therefore, the overall impact of this ditch is insignificant. The diversion ditch was designed using the following input data: Watershed Area = 42.9 ac. CN = 91.0 P10 = 1.6 inches tc = 0.068 hrs. Slope = 1.0% n = 0.025 z = 2:1 (v-ditch) Output Data: Q10 = 36.5 cfs do = 1.9 ft. Froude No.= 0.96 Total Depth = 3.0 ft. In conclusion, the diversion ditch will be utilized for only a short time until Pond 009 is constructed. Pond 008's design is conservative at this time because the 008 design assumed a worst case condition when all runoff will drain into Pond 008. Adding the acreage to Pond 008's • watershed and rerunning SEDIMOT II for each storm event shows insignificant impacts on Pond 008. Exhibit 7-7 has been revised to include the 008 Diversion Ditch watershed.