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/,~ CHAGRIN <br />4/ " RIVER <br />~r7 \YIaTERSHED <br />PARTNERS <br />May 2016 <br />device consistent with Rainwater azzd Lazzd Developmezzt shall be provided to <br />dewater sediment basins. Sediment traps shall also provide both a sediment <br />storage zone and dewatering zone, but the outlet structure shall be constructed <br />consistent with the specifications contained in the latest edition of Raizzwatez• azzd <br />Land Developmezzt. <br />When post-construction detention/water quality ponds are to be used as <br />temporary sediment trapping BMPs, a skimmer discharge device consistent with <br />Rainwater and Land Developniezzt shall be utilized during construction phase and <br />until the site is deemed permanently stabilized by the Village of Mayfield. <br />The skimmer shall be designed per the equivalent requirements of sediment <br />basins and the operator must ensure that the outlet structure of the pond provides <br />an equivalent or better sediment storage zone and dewatering zone. As such, <br />temporarily while the site is under construction, there shall be no discharge of <br />runoff below the elevation required for the sediment storage zone and the <br />discharge of stormwater within the dewatering zone shall only occur through the <br />skimmer. <br />The volume of the sediment storage zone shall be calculated by one of the <br />following methods: <br />Method 1: The volume of the sediment storage zone shall be <br />1000ft3 per disturbed acre within the watershed of the basin. <br />Method 2: The volume of the sediment storage zone shall be the <br />volume necessary to store the sediment as calculated with RUSLE or <br />other generally accepted erosion prediction model. <br />When determining the total contributing drainage area, off-site areas and areas <br />which remain undisturbed by construction activity must be included unless runoff <br />from these areas is diverted away from the sediment settling pond and is not co- <br />mingled with sediment-laden runoff. The depth of the dewatering zone must be <br />less than or equal to five (5) feet. The configuration between the inlets and the <br />outlet of the sediment-settling pond must provide at least two units of length for <br />each one unit of width >_ 2:1 length-to-width ratio; however, a length to width <br />ratio of >_ 4:1 is recommended. Sediment must be removed from the sediment- <br />settlingpond when the design capacity of the sediment storage zone has been <br />completely filled by sediment accumulations. This limit is typically reached <br />when sediment occupies one-half of the basin depth. When designing sediment <br />settling ponds, the applicant must consider public safety, especially as it relates to <br />children, as a design factor for the sediment basin and alternative sediment <br />controls must be used where site limitations would preclude a safe design. The <br />use of a combination of sediment and erosion control measures in order to <br />achieve maximum pollutant removal is encouraged. <br />(3) Silt fence and diversions. Sheet flow runoff from denuded areas shall be <br />intercepted by silt fence or diversions to protect adjacent properties and water <br />resources from sediment transported via sheet flow. Where intended to provide <br />sediment control, silt fence shall be placed on a level contour and shall be <br />capable of temporarily ponding runoff. The relationship between the maximum <br />drainage area to silt fence for a particular slope range is shown in Table 3 below. <br />17 <br />