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2.2. Sediment Control System Gravel Minine <br />.' The gravel operation will employ one fairly lazge sediment cleanout pond and two smaller ponds <br />that will handle the slurry dischazge from the processing operations. These ponds aze labeled Willits <br />Ponds #1, #2 and #3. These ponds will be cleaned out on an as needed basis. The sediment from the <br />ponds will be dug out with an excavator and will be either placed on regraded azeas for reclamation <br />or stockpiled in the designated stockpile azeas for later reclamation. The stockpiles will have a <br />minimum of 2.SH:1 V sideslopes and will be seeded with a temporary mix designated as Mix A in <br />the reclamation plan. As of April, 2003, approximately 2500 cP of silt has already been stockpiled <br />from recent gravel operations in Fines Pile #4. <br />Willits Ponds #2 and #3 will overflow into Pond A, which should always contain relatively clean <br />water. This pond is hydrologicaly sealed and will be used for recirculating water during drought <br />periods when sufficient water is not available from the River or the Columbia Ditch. <br />Willits Pond #4 will handle all surface runoff from the plant azea and stockpile area. This is <br />approximately 7 acres in size. The calculations to demonstrate that this pond is adequate to contain <br />., the 100 yeaz 24 hour event are shown below: <br />Design Volume Calculations <br />Willits Pond #4 <br />Area (acres) 7.0 <br />Design Event 100 yr. storm <br />Design Precipitation 2.8 Calculated S <br />Average CN 67 4.92537313433 <br />Description Porous Gravel <br />Topsoil Piles <br />Calculated Runoff Volume (Q) 0.4886955832 <br />Calculated Runoff Volume (acre-ft.) 0.28507242353 <br />A-ma Placer 7/03 26 <br />