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;. <br />• i <br />required storage capacity of the sediment pond for the designed storm event. Also, the software <br />allows you calculate the flow and retention of the various structures (eg backsloped pit floor) <br />along the flow path. It is also recommended that you estimate the amount of sediment that is <br />anticipated to report to the sediment structure(s). This can be accomplished by using a public <br />domain software called Revised Universal Soil Loss Equation (RUBLE). This information can be <br />used to determine how often the sediment pond will need to be cleaned. Also, the information <br />can be used for other purposes (to estimate the amount of sediment fines that may be carried <br />downstream in the event the sediment pond overtops, etc). <br />You must adequately demonstrate why you select the various criteria for your watershed study. <br />For instance, if you select a SCS curve number, you must provide a legitimate reason for the <br />selection. This applies to the selection of a hydrologic soil group, a storm type, the watershed or <br />subwatershed areas, the retention factor, etc. <br />The revised watershed report must be submitted to the Division within 30 days (by January 21, <br />2000). Again, if the sediment pond is a requirement of the SWMP (and has been approved) the <br />structure must be designed [o contain the 2-year 24 hour storm event and a copy of the approved <br />SWMP must be submitted to the Division along with the revised watershed report. If the <br />sediment pond is not part of the SWMP it must be designed to contain the 10-year 24 hour storm <br />event (DMG policy). <br />If you have any questions, please give me a call. <br />S~ncerely, <br />~~ <br />James Dillie <br />Environmental Protection Specialist <br />cc: James Stevens <br />