3900 BROADWAY BASE FILE 2016-01-01 MF Import

CITY OF EVERETT STORMWATER MANAGEMENT MANUAL 3.3.20 BMP C257: Construction Stormwater Filtration Purpose Filtration removcs sediment from runoff originating from disturbcd areaz of thc sitc. Filtration removcs sediment�am runofforiginaling�om diswrbed areas of the sitc. Condltiorts of Use Traditional BMPs used to cootrol soil erosion and sediment loss from sites under development may not be adequate to ensurc compliancc with the water quality standard for turbidity in the rcceiving water. Filtration may be used in conjunclion with gavity settling to remove sediment as small as fine silt(0.5 µm).The reduction in turbidity will be dependent on the particle siu distribution of the sediment in thc starmwater. in some circumstances,sedimentation and filtration may achieve compliance with the water quality standard for turbidity. Ualike chenucal treahnent,thc use of conswction stocmwater filtratiun does not require approval from Ecolagy. Filhation may also be used in conjunction with polymer treatment in a portable system to assurc capturc of thc Aocculated solids. Traditiooal UMPs used ro wntrol soil erosion and sedimeot loss from sites wder dwelopment may not be adequate to ensure compliance with the water quality standard for hvbidity in the receiving water. Filtration may be used in coujunction with graviry settling to tcmove sedimeat as small as fine silt (0.5 µm). The rcduction in turbidiry will be dependent on the perticle size distribution of the scdiment in the stormwater. In some circumstances,sedimentation and filtration may achieve compliance with thc water quality standard for curbidiry. . 1 The use of conshuctioo stormwatcr filtratian does not require approval Crom Ecology or the Ciry as long as treatment chemicals are not used. Background Informafion Filtration with sand media has been used for over a century to treat�vater and wastewater. The use of sand f Ihatioo for treatment of stortnwater has developed recently,gencrally to treat runofT from streets, parking lots,and residential arcas. 'fhe application of filtration ro cooswction stortnwater is curtently under development. Deslgn and Installation 5pecifications Two types of filtration systems may be applied to construcdon stormwater trcatment: repid and slow. Rapid sand filters are the typical system used for water and wastewater trcatmcnt. They can achicve rclatively hig6 hydraulic flow rates,on the ordcr of 2 to 20 gpm/sf,becausc thcy have automatic backwas6 systems to remove accumuleted solids. In contrast,slow sand filiers have very low hydraulic rates, on the otdcr of 0.02 gpm/sf,because they do not have backwash systcros. To datc, slow sand filtration has generally been used ro treat srotmµater. Slow sand filhalion is mcchanically simple in comparison to rapid sand filtration but requires a much lazger filter area. • Filt;stion Equipment. Sand media filters arr.availablc with automatic backwashing features that can filter to 50µm paRide size. Screen or bag filte�s can filler doun to 5 µm. Fiber wound fltets can remove particles down to 0.� µm. Filtcrs should be sequenced from thc largest to thc smallest pore opening. Sediment removal efficicncy will bc related to particle si2e distribution in thc stortnwatcr. • Treatment Process DescripNon Stormwater is collectedat interception point(s)on the<_ite and is diverted to an untreated stortnw�ter sediment pond or tank for removal ot large sediment and storage of the slortnwater before il is treated by the fiitration systcm. The untreated stortnwater is Volume II—Constrvction Sformwater Pollution Prevention 3-66