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b. All sedimentation ponds are designed to provide adequate sediment storage volurne in <br />compliance with the DMG regulations. • <br />c. An appropriate nonclogging dewatering device will be installed to dewater a 10-year, 24- <br />hour storage volume. <br />d. Appropriate combinations of principal and emergency spillways to safely discharge the <br />runoff from a 25-year, 24-hour precipitation or larger event, as required by the DMG's <br />regulations, will be installed in all ponds. <br />The sediment storage capacity of each sedimentation pond or impoundment will be monitored on an <br />annual basis to ensure that at least one year of sediment storage is available beneath the principal <br />spillway inlet (based on the R.U.S.L.E. or the equivalent sediment storage of one 10-year, 24-hour <br />storm event based on the M.U.S.L.E.1. When adequate capacity is no longer available, sediment <br />removal or other corrective actions will be taken to restore adequate sediment storage capacity to the <br />pond. <br />Peabody will monitor the sediment storage capacity of each pond with one or a combination of the <br />following methods, as applicable: <br />1. Reference Stake - A reference stake will be set at a predetermined clean-out elevation <br />beneath the principal spillway. When sediment storage reaches this elevation, corrective <br />action will be implemented to restore adequate sediment storage. Reference staking will be <br />utilized in ponds that are normally dry and as an indicator for monitoring personnel as to • <br />when a more detailed survey of sediment storage capacity is warranted. <br />2. Cross Sectioning or Grid Method -For the ponds that normally contain water year round, or <br />where a reference stake can not be detected below the water surface, a survey cross <br />section or grid method will be used to determine sediment volume using accepted <br />engineering practices. The survey would be performed when needed to determine sediment <br />storage capacity and to determine when corrective action is required to restore adequate <br />pond capacity. <br />3. Aerial Mapping - An alternative method is photogrammetric mapping that would create an <br />accurate 1" = 50' topographic map with 2 ft. contour intervals to tletermine the remaining <br />storage volume beneath the principal spillway. This method could be used as the sole <br />method for dry ponds or used in conjunction with the surveyed cross section method for <br />ponds partially full of water. Once the topographic map has been generated, accepted <br />engineering methods will be utilized to perform the volumetric calculations. <br />Corrective action required to restore adequate sediment storage capacity may include the following: <br />1. Raise the spillways and redesign the pond in ord~;r to restore adequate storage capacity <br />and to comply with the applicable regulations. <br />2. Excavate the ponding area and enlarge the sediment storage capacity. <br />• <br />4 Revised 9/96 <br />