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Page 4 of 7 <br />control plans shall be revised as needed based on current site conditions and to <br />comply with all applicable requirements. <br /> <br /> <br />3. Temporary Sediment Basins <br />A. A temporary sediment basin (or permanent) shall be provided when 10 or more <br />acres of disturbed soil drain to a common location prior to the runoff leaving the <br />site or entering surface waters. The Permittee is also encouraged, but not <br />required to install temporary sediment basins in areas with steep slope or highly <br />erodible soils even if the area is less than 10 acres and it drains to one common <br />area. The basins shall be designed and constructed according to the following <br />requirements: <br />a. The basins must provide storage below the outlet pipe for a calculated <br />volume of runoff from a 2 year, 24 hour storm from each acre drained to <br />the basin, except that in no case shall the basin provide less than 1800 <br />cubic feet of storage below the outlet pipe from each acre drained to the <br />basin. <br />b. Where no such calculation has been performed, a temporary (or <br />permanent) sediment basin providing 3,600 cubic feet of storage below <br />the outlet pipe per acre drained to the basin shall be provided where <br />attainable until final stabilization of the site. <br />c. Temporary basin outlets will be designed to prevent short-circuiting and <br />the discharge of floating debris. The basin must be designed with the <br />ability to allow complete basin drawdown (e.g., perforated riser pipe <br />wrapped with filter fabric and covered with crushed gravel, pumps or <br />other means) for maintenance activities, and provide a stabilized <br />emergency overflow to prevent failure of pond integrity. Energy <br />dissipation must be provided for the basin outlet. <br />d. Temporary (or permanent) basins must be constructed and made <br />operational concurrent with the start of soil disturbance that is up <br />gradient of the area and contributes runoff to the pond. <br />e. Where the temporary sediment basin is not attainable due to site <br />limitations, equivalent sediment controls such as smaller sediment <br />basins, and/or sediment traps, silt fences, vegetative buffer strips or any <br />appropriate combination of measures are required for all down slope <br />boundaries of the construction area and for those side slope boundaries <br />deemed appropriate as dictated by individual site conditions. In <br />determining whether installing a sediment basin is attainable, the <br />Permittee must consider public safety and may consider factors such as <br />site soils, slope, and available area on site. This determination must be <br />documented in the SWPPP. <br />f. The Permittee shall maintain the sedimentation basins and will remain <br />functional until an acceptable vegetative cover is restored to the site, <br />resulting in a pre-development level rate of erosion. The city will not <br />issue building permits for lots containing sediment basins until they have <br />been removed or relocated based on the projects restoration progress.