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0 • <br />Chapter 4-Site-Specific /ndustria/ Storm Water BViPs <br />When and Where to Use It <br />A temporary sediment basin should be installed before clearing and grading is undertaken. It should <br />not be built on an embankment in an active stream. The creation of a dam in such a site may <br />result in the destruction of aquatic habitats. Dam failure can also result in flooding. A temporary <br />sediment basin should be located only where there is sufficient space and appropriate topography. <br />The basin should be made large enough to handle the maximum expected amount of site drainage. <br />Fencing around the basin may be necessary for safety or vandalism reasons. <br />A temporary sediment basin used in combination with other control measures, such as seeding or <br />mulching, is especially effective for removing sediments. <br />What to Consider <br />Temporary sediment basins are usually designed for disturbed areas larger than 5 acres. The pond <br />should be large enough to hold runoff long enough for sediment to settle. Sufficient space should <br />be allowed for collected sediments. Check the requirements of your permit to see if there is a <br />minimum storage requirement for sediment basins. The useful life of a temporary sediment basin is <br />about 12 to 18 months. <br />Sediment trapping efficiency is improved by providing the maximum surface area possible. <br />Because finer silts may not settle out completely, additional erosion control measures should be <br />• used to minimize release of fine silt. Runoff should enter the basin as far from the outlet as <br />possible to provide maximum retention time. <br />Sediment basins should be readily accessible for maintenance and sediment removal. They should <br />be inspected after each rainfall and be cleaned out when about half the volume has been filled with <br />sediment. The sediment basin should remain in operation and be properly maintained until the site <br />area is permanently stabilized by vegetation and/or when permanent structures are in place. The <br />embankment forming the sedimentation pool should be well compacted and stabilized with <br />vegetation. If the pond is located near a residential area, it is recommended for safety reasons that <br />a sign be posted and that the area be secured by a fence. A well built temporary sediment basin <br />that is large enough to handle the post construction runoff volume may later be converted to use <br />as a permanent storm water management structure. <br />4-89