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PURPOSE: <br /> BMP C250 applies when using approved stormwater chemicals in a batch or flow- <br /> through treatment process. Turbidity is difficult to control once fine partials are <br /> suspended in stormwater runoff from a construction site. Chitosan-enhanced sand <br /> filtration is a flow-through water treatment technology that utilizes a biopolymer to <br /> increase filtration efficiency. Chitosan is a natural biopolymer, derived from crustacean <br /> shells, that is nontoxic and completely biodegradable. <br /> Chitosan-enhanced sand filtration has been used extensively throughout the United <br /> States to treat storm water and dewatering water with exceptional results. The chitosan- <br /> enhanced sand filtration process is capable of reducing storm water turbidities to less <br /> than 10 NTU on a continuous, flow through basis. <br /> Chemical treatment may be required to meet turbidity stormwater discharge <br /> requirements, especially when construction is to proceed during the wet season, but it <br /> should never be utilized as the primary BMP. Traditional BMP's need to be implemented <br /> and maintained along with the filtration system, to minimize the need for chemical <br /> treatment of stormwater. <br /> CONDITIONS OF USE: <br /> Formal written approval from the Department of Ecology through a "Request for <br /> Chemical Treatment" document is required for the use of chemical treatment regardless <br /> of site size. Chemical treatment system operators and managers must go through a <br /> Dept. of Ecology approved training program and keep that certification current <br /> throughout the project. The Washington State Dept. of Ecology maintains a list of <br /> operators with current certification at: <br /> https://ecology.wa.gov/DOE/files/59/592bd838-f392-4bd7-9179-79e5d4b99901 .pdf <br /> DESIGN AND INSTALLATION: <br /> The design and operation of a chemical treatment system should take into consideration <br /> the factors that help determine optimum, cost effective performance. At a minimum, the <br /> system should consist of the water collection system, untreated holding pond or tanks, <br /> chemically enhanced sand filtration system and water quality monitoring and data <br /> logging equipment. <br /> The attached "Stormwater Chemical Treatment Plan" identifies the system components, <br /> design criteria and operational procedures in compliance with BMP C250, as well as the <br /> General Use Level Designation for Stormklear 1% for this project. <br /> City of Everett 2 <br /> EVERETT Reviewed for Permit 10/20/2021 <br /> WASHINGTON <br />