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1 receiving water shall not be taken from the treatment pond prior to decanting. Com- pliance with the water quality standards is determined in the receiving water. Operator Training: Each contractor who intends to use chemical treatment shall be trained by an experienced contractor. Each site using chemical treatment must have an operator trained and certified by an organization approved by Ecology. Standard BMPs: Surface stabilization BMPs should be implemented on site to prevent significant erosion. All sites shall use a truck wheel wash to prevent tracking of sediment off site. Sediment Removal and Disposal: Sediment shall be removed from the storage or treatment cells as necessary. Typ- ically, sediment removal is required at least once during a wet season and at the decommissioning of the cells. Sediment remaining in the cells between batches may enhance the settling process and reduce the required chemical dosage. Sediment that is known to be non -toxic may be incorporated into the site away from drainages. BMP C251: Construction Stormwater Filtration Purpose Filtration removes sediment from runoff originating from disturbed areas of the site. Background Information: Filtration with sand media has been used for over a century to treat water and wastewa- ter. The use of sand filtration for treatment of stormwater has developed recently, gen- erally to treat runoff from streets, parking lots, and residential areas. The application of filtration to construction stormwater treatment is currently under development. Conditions of Use Traditional BMPs used to control soil erosion and sediment loss from sites under devel- opment may not be adequate to ensure compliance with the water quality standard for turbidity in the receiving water. Filtration may be used in conjunction with gravity settling to remove sediment as small as fine silt (0.5 pm). The reduction in turbidity will be dependent on the particle size distribution of the sediment in the stormwater. In some cir- cumstances, sedimentation and filtration may achieve compliance with the water quality standard for turbidity. The use of construction stormwater filtration does not require approval from Ecology as long as treatment chemicals are not used. Filtration in conjunction with polymer treat- ment requires testing under the Chemical Technology Assessment Protocol — Ecology (CTAPE) before it can be initiated. Approval from the appropriate regional Ecology office 2014 Stormwater Management Manual for Western Washington 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Volume 11 - Chapter 4 - Page 404 1