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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 <br />pond as a result of a 10-year, 24-hour precipitation event and to meet all applicable <br />State and Federal regulations for all effluent limitations before discharge from the <br />permit area. Ponds 008, 009, 011, 012 and 013 have been designed to contain the <br />25 year 24 hour event with no discharge from the emergency spillway. Pond 010 <br />design includes routing the 25 year event through the emergency spillway. <br />b. The sedimentation ponds are designed to provide adequate sediment storage <br />volume in compliance with the CDMG regulations. The actual designs are based on <br />3 year sediment volumes based on USLE calculations. Actual construction may cut <br />more volume below the dam level (incised storage) to lessen expensive cleanout <br />during the operation. <br />c. The principal spillway design is an 18-24" diameter CMP or other pipe which will <br />have a valve on the entrance. This pipe will be stopped down in the inlet side to a <br />6" valve which will be controlled by a wheel on the pond embankment. During <br />normal conditions, the valve will be cracked slightly open to provide the equivalent <br />cross-sectional area of a 2" diameter orifice opening. This opening has been <br />• evaluated and is known to provide 24 hour detention time for each pond during the <br />large events while allowing dewatering of the pond within a reasonable amount of <br />time. If clogging occurs, the valve will simply be opened (at least 24 hours after a <br />large storm) and maintained from the spillway inlet side. The valve will then be <br />screwed back to a set position to provide the above mentioned cross-sectional area. <br />d. Appropriate combinations of principal and emergency spillways to safely contain or <br />discharge the runoff from a 25-year, 24-hour precipitation or larger event, as <br />required by the CDMG's regulations, will be installed. If a pond is designed to <br />contain the runoff from a 25 year 24 event, an emergency spillway cut into the dam <br />will still be installed. <br />e. Pond freeboard will be a minimum of 1.0 feet from the highest level of water allowed <br />in the pond (or emergency spillway) to the top of dam. <br />f. All pond dams will be designed to have a height of less than 10.0 feet measured <br />from the original ground in the middle of the dam to the top of the dam. The top of <br />dam width will be at least 10.0 feet in all areas. <br />g. All ponds will have a keyway cut along the entire width of the dam as shown on Map <br />2.05.3-13. This keyway will be filled with competent material and compacted to the <br />same standards as the dam foundation. <br />• <br />(Revised 12/01) Attachment 2.05.3(3) -10-3 <br />