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collection ditch to prevent any disturbed azea 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 azea of the Permanently Reclaimed Spoils Area and conveys <br />the runoff to Sediment Pond No. Z. Runoff from Topsoil Pile No. 2 is contained within a small berm <br />constructed around the toe of the pile. No significant amount of water is ever retained by this berm. <br />The culvert crossing for this ditch under the access road is unchanged from the approved plan. After <br />final bond release is granted, this ditch and culvert will remain to provide drainage for the <br />development site. <br />Designs for collection ditches and channels aze contained in Appendices 5-2, 5-9, and on Map 5-10. <br />All ditches were constructed to control the design flow and to minimize erosive velocities during <br />design event conditions. <br />Detention Sumps <br />• <br />The bench in the North Pit will be reduced to a width of 30 feet for reclamation, and the bench itself <br />and all areas above it will drain to two sumps, as shown on the Hydrology Map. These two sumps <br />aze called Upper Sump 1 and Upper Sump 2. The north bench and the disturbed slope above it will <br />drain to the North Pit access road and road ditch. A smatl sediment sump (Lower Sump) will be <br />installed to collect the runoff from the 100 year event for the 1.13 acre downspoiled area that does <br />not drain to any other sediment facility. <br />Design Volume Calculations Upper Sump 1 <br />Area Drainage Area (acres) 4.37 <br />Design Event 100 yr. storm <br />Design Precipitation 3.2 <br />Average CN 89 <br />Calculated S 1.23595505618 <br /> <br />Description Exposed gravel and rocky soil before <br />vegetation <br />Calculated Runoff Volume (Q) 2.08 <br />Calculated Runoff Volume (acre-ft.) 0.76 <br />Ponding Percentage 5.00 <br />Actual Runoff Volume (acre/ft.) 0.72 <br />As shown on the Hydrology Map, this sump contains approximately 1.09 acre-feet. This sump will <br />have grip-rapped trapezoidal spillway width of 10 feet and a 0.5 foot depth to pass any overflow <br />• from storms above the 100 yeaz event. <br />TR09, TRll, TR12 (v1,0) S-6 Revised 3/98, 8/02, 9103 <br />