Laserfiche WebLink
• Sedimentation Ponds 008 through 013 Design Parameters <br />In accordance with 4.05.2 and NPDES regulations, WFC will use Ponds 008 through 013 to <br />prevent, to the extent possible, additional contributions of sediment to stream flow or runoff outside <br />the permit area due to mining disturbance. Ponds 008 and 009 are as-built designs, 010 through <br />013 have yet to be constructed. The pond designs are found in Attachments 2.05.3(3)-4, <br />2.05.3(3)-5, and 2.05.3(3)-6. Map 2.05.3(3)-1 shows the locations of the as-built and yet-to-be built <br />ponds. <br />The sedimentation pond is designed, constructed, and maintained as follows: <br />a) Pond 010 has been designed to provide storage for the runoff or inflow entering the pond as a <br />result of a 10-year, 24-hour precipitation event and to meet all applicable State and Federal <br />regulations for all effluent limitations before discharge from the permit area. Ponds 008, 009, 011, <br />012 and 013 have been designed to contain the 25 year 24 hour event with no discharge from the <br />emergency spillway. Pond 010 design includes routing the 25 year event through the emergency <br />spillway. <br />b) The sedimentation ponds are designed to provide adequate sediment storage volume in <br />compliance with the CDMG regulations. The actual designs are based on 3 year sediment volumes <br />• based on USLE calculations. Actual construction may cut more volume below the dam level <br />(incised storage) to lessen expensive cleanout during the operation. <br />c) The principal spillway design is an 18-24"diameter CMP or other pipe which will have a valve <br />on the entrance. This pipe will be stopped down in the inlet side to a 6" valve which will be <br />controlled by a wheel on the pond embankment. During normal conditions, the valve will be cracked <br />slightly open to provide the equivalent cross-sectional area of a 2" diameter orifice opening. This <br />opening has been evaluated and is known to provide 24 hour detention time for each pond during <br />the large events while allowing dewatering of the pond within a reasonable amount of time. If <br />clogging occurs, the valve will simply be opened (at least 24 hours after a large storm) and <br />maintained from the spillway inlet side. The valve will then be screwed back to a set position to <br />provide the above mentioned cross-sectional area. <br />d) Appropriate combinations of principal and emergency spillways to safely contain or discharge <br />the runoff from a 25-year, 24-hour precipitation or larger event, as required by the CDMG's <br />2.05.3(3) -13 <br />• <br />