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1 <br />BMP C241: Temporary Sediment Pond <br />Purpose <br />Sediment ponds remove sediment from runoff originating from disturbed areas of the <br />site. Sediment ponds are typically designed to remove sediment no smaller than <br />medium silt (0.02 mm). Consequently, they usually reduce turbidity only slightly. <br />Conditions of Use <br />Prior to leaving a construction site, stormwater runoff must pass through a sediment <br />pond or other appropriate sediment removal best management practice. <br />A sediment pond shall be used where the contributing drainage area is 3 acres or more. <br />Ponds must be used in conjunction with erosion control practices to reduce the amount <br />of sediment flowing into the basin. <br />Design and Installation Specifications <br />Sediment basins must be installed only on sites where failure of the structure <br />would not result in loss of life, damage to homes or buildings, or interruption of use <br />or service of public roads or utilities. Also, sediment traps and ponds are attractive <br />to children and can be very dangerous. Compliance with local ordinances regard- <br />ing health and safety must be addressed. If fencing of the pond is required, the type <br />of fence and its location shall be shown on the ESC plan. <br />• Structures having a maximum storage capacity at the top of the dam of 10 acre-ft <br />(435,600 ft3) or more are subject to the Washington Dam Safety Regulations <br />(Chapter 173-175 WAC). <br />• See Figure 11-4.2.18 Sediment Pond Plan View (p.391), Figure II-4.2.19 Sediment <br />Pond Cross Section (p.392), and Figure II-4.2.20 Sediment Pond Riser Detail <br />(p 393) for details. <br />If permanent runoff control facilities are part of the project, they should be used for <br />sediment retention. The surface area requirements of the sediment basin must be <br />met. This may require temporarily enlarging the permanent basin to comply with <br />the surface area requirements. The permanent control structure must be tem- <br />porarily replaced with a control structure that only allows water to leave the pond <br />from the surface or by pumping. The permanent control structure must be installed <br />after the site is fully stabilized. . <br />Use of infiltration facilities for sedimentation basins during construction tends to <br />clog the soils and reduce their capacity to infiltrate. If infiltration facilities are to be <br />used, the sides and bottom of the facility must only be rough excavated to a min- <br />imum of 2 feet above final grade. Final grading of the infiltration facility shall occur <br />only when all contributing drainage areas are fully stabilized. The infiltration <br />2014 Stormwater Management Manual for Western Washington <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />�J <br />F] <br />L <br />1 <br />1 <br />1 <br />Volume 11 - Chapter 4 - Page 388 <br />1 <br />