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actually contain the runoff for the 11.19 acre drainage area for the 100 year 24 hour event, <br />therefore, no spillway is needed. A principal and emergency spillway are installed in the pond and <br />past calculations show that the pond will route large storms through the spillway structures while <br />providing detention time for sediment and greatly lowering the peak flows. <br />Collection Ditches and Channels <br />Two collection ditches and one collection channel route surface runoff to the sediment ponds. The <br />East Collection Ditch collects runoff from an area south and west of the gravel operations and <br />conveys flow to Sediment Pond No. 1. A compacted berm was constructed below the east <br />collection ditch to prevent any disturbed area runoff escaping from the northeast corner of the <br />surface facilities area. The West Collection Ditch collects surface drainage from the northwest <br />segment of the haul road, and a small area of the Permanently Reclaimed Spoils Area and conveys <br />the runoff to Sediment Pond No. 2. Runoff from Topsoil Pile No. 2 is contained within a small <br />berm constructed around the toe of the pile. No significant amount of water is ever retained by this <br />berm. The culvert crossing for this ditch under the access road is unchanged from the approved <br />plan. After final bond release is granted, this ditch and culvert will remain to provide drainage for <br />the development site. <br />The bench in the North Pit was reduced to a width of 30 feet during reclamation, and the bench <br />itself and all areas above it will drain to an SAE, as described below. The north bench and the <br />disturbed slope above it will drain to the North Pit access road and road ditch. Downslope drainage <br />from the outslope of the North Pit below the bench will be directed to Sediment Pond #1 through <br />the collection ditch system. <br />Alternative Sediment Control (SAE) Topsoil Stockpile # 2 <br />Once topsoil is removed from this stockpile and while the area is final - graded, a berm of 24" height <br />will be placed around the former pile area (2.69 acres) to prevent erosion from the area. This berm <br />will be placed with a small dozer and will have 2H:1 V sideslopes. Once final bond release is <br />granted, this berm will be regraded into the surrounding terrain. <br />Alternative Sediment Control (SAE) South Half of North Pit <br />Once the North Pit has been backfilled, topsoiled and seeded, approximately the south half of the <br />North Pit will flow onto a grassed terrace prior to flowing offsite into undisturbed drainages. To <br />verify the adequacy of sediment control, a calculation using the SCS Curve Number Method was <br />employed. Based on the post mining topography map of the North Pit, approximately 2.9 acres will <br />flow from the reclaimed area onto the terrace from the reclaimed North Pit. The volume of runoff <br />from this area was calculated assuming precipitation of 2.4 inches from a 10 year -24 hour event, a <br />curve number of 90, an S factor of 1. 11, accumulated runoff of 1.442, and accumulated runoff <br />without abstractions of 2.400. The accumulated volume of runoff would be 0.47 acre -feet of <br />runoff. The size of the terrace at the foot of the south half of the North Pit was calculated to be 300 <br />feet long, 20 feet wide and adequate to control sediment from the area above. <br />Abridged Permit Document 5-6 Feb 2008 <br />