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require review and approval. When approved, the chemical treatment systems must be included in the Construction Stormwater Pollution Prevention Plan (SWPPP). Design and See Appendix II-B for background information on chemical treatment. Installation Specifications Criteria for Chemical Treatment Product Use: Chemically treated stormwater discharged from construction sites must be nontoxic to aquatic organisms. The Chemical Technology Assessment Protocol (CTAPE) must be used to evaluate chemicals proposed for stormwater treatment. Only chemicals approved by Ecology under the CTAPE may be used for stormwater treatment. The approved chemicals, their allowable application techniques (batch treatment or flow -through treatment), allowable application rates, and conditions of use can be found at the Department of Ecology Emerging Technologies website: http ://www. ecy.wa. gov/programs/wq/stormwater/newtech/technologi.es.bt MI. Treatment System Design Considerations: The design and operation of a chemical treatment system should take into consideration the factors that determine optimum, cost-effective performance. It is important to recognize the following: • Only Ecology approved chemicals may be used and must follow approved dose rate. • The pH of the stormwater must be in the proper range for the polymers to be effective, which is typically 6.5 to 8.5 • The coagulant must be mixed rapidly into the water to ensure proper dispersion. • A flocculation step is important to increase the rate of settling, to produce the lowest turbidity, and to keep the dosage rate as low as possible. • Too little energy input into the water during the flocculation phase results in flocs that are too small and/or insufficiently dense. Too much energy can rapidly destroy floc as it is formed. • Care must be taken in the design of the withdrawal system to minimize outflow velocities and to prevent floc discharge. Discharge from a batch treatment system should be directed through a physical filter such as a vegetated swale that would catch any unintended floc discharge. Currently, flow -through systems always discharge through the chemically enhanced sand filtration system. • System discharge rates must take into account downstream conveyance integrity. • Volume II— Construction Stormwater Pollution Prevention -August 2012 4-111