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b. The sedimentation ponds are designed to provide adequate sediment storage <br />volume in compliance with the DRMS regulations. The actual designs are based <br />on 3 year sediment volumes based on USLE calculations. Actual construction <br />may cut more volume below the dam level (incised storage) to lessen expensive <br />cleanout 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 left slightly open to provide 24 hour <br />detention time for each pond during the large events. This is accounted for as <br />weep holes in the SEDCAD design runs. When a large event occurs, the operator <br />will wait until the Imhoff cone test shows that the water meets effluent standards <br />prior to discharge. If an Imhoff cone shows that the water meets the effluent <br />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 left slightly open to allow <br />detention time for subsequent storms. For Ponds 008, 012 and 013, SEDCAD <br />analysis has shown that the effluent from a slightly cracked open valve <br />(equivalent of a garden hose) still meets effluent requirements. For these ponds, <br />the operator can decide to leave the valve cracked or shut as described above. <br />d. Appropriate combinations of principal and emergency spillways to safely contain <br />or discharge the runoff from a 25 -year, 24-hour precipitation or larger event, as <br />required by the DRMS'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 <br />dam will still be installed. <br />e. Pond freeboard will be a minimum of 1.0 feet from the highest level of water <br />allowed 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 <br />of dam width will be at least 10.0 feet in all areas. <br />g. All ponds except Pond 018 will have a keyway cut along the entire width of the <br />dam. This keyway will be filled with competent material and compacted to the <br />same standards as the dam foundation. <br />Page 2.05.3(3)-13 January 2016 (TR -70) <br />