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• no discharge from the emergency spillway. Pond 011 will have an expected permanent <br />discharge of 1.34 cfs due to pit pumping, but all sediment pond rules are also satisfied, as <br />shown in Attachment 2.05.3(3)-14. Pond 010 design includes routing the 25 year event <br />through the emergency spillway. Pond 014 excavation has been designed fora 100-year <br />24-hour event with no discharge. Due to its small drainage area and completely incised <br />impoundment, there is no embankment to fail and so only run-off volume calculations have <br />been performed. Only b) below pertains to Pond 014 and volumes were determined using <br />SEDCAD4 instead of SurvCADD software. <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 <br />volumes based on USLE calculations. Actual construction may cut more volume below the <br />dam level (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 <br />valve on the entrance. This pipe will be stopped down in the inlet side to a 6" valve which will <br />be controlled by a wheel on the pond embankment. During normal conditions, the valve will <br />be shut to provide 24 hour detention time for each pond during the large events. When a <br />• large event occurs, the operator will wait a minimum of 36 hours after the storm has ceased <br />to check the water still detained by the pond. If an Imhoff cone shows that the water meets <br />the effluent standard of 0.5m1 settleable solids per liter, the valve will be opened until the <br />water has dissipated to the valve level. It will then be shut to allow detention time for <br />subsequent storms. For Ponds 007, 008 and 011, SEDCAD analysis has shown that the <br />effluent from a slightly cracked open valve (equivalent of a garden hose) still meets effluent <br />requirements. For these ponds, the operator can decide to leave the valve cracked or shut <br />as described above. <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 required by the <br />CDMG's regulations, will be installed. If a pond is designed to contain the runoff from a 25 <br />year 24 event, an emergency spillway cut into the dam will still be installed. <br />e) Pond freeboard will be a minimum of 1.0 feet from the highest level of water allowed in <br />the pond (or emergency spillway) to the top of dam. <br /> <br />(Revised July 2006) 2.05.3(3)-18 <br />