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MINIMUM REQUIREMENT #7 • Describe the Flow Control BMPs for each TDA. Indicate if there are any bypasses to flow control. Indicate if there is flow through from upstream runoff. • If the project area totals are below the flow control TDA thresholds for effective impervious surface or converted vegetation, attach modeling results to determine if flow control is required due to a 0.15 cfs increase in the 100-yr flow frequency for the developed project as compared to existing conditions. • Attach modeling results to demonstrate compliance with the Flow Control Performance Standard. Modeling should include bypasses as well as any flow through going to flow control structures. • Additional flow control requirements may be determined by the City on a case-by- case basis if there are downstream capacity issues. For example, the project may be required to provide modeling to show that developed project conditions will not exceed the 100-yr peak flow from existing conditions. • Provide sizing calculations not otherwise addressed by the model (e.g., flow splitters, other calculations indicated in the Manual). • Describe the overflow route for open-air storage facilities when capacity is exceeded or if the facility plugs or fails. • Provide structural plans and calculations as required by the Manual, DCSS, or the City Building Official. • Address detention vault/tank flotation if high or perched groundwater is present. Provide buoyancy calculations, a description of design considerations and related plans, or a geotechnical letter/report addressing this. • Provide pertinent supporting information used to calculate flow control modeling inputs (e.g., infiltration rate testing and calculations, void space calculations for proprietary flow control BMPs). • Stormwater facilities which infiltrate stormwater by means of an underground facility such as an infiltration trench or vault may need to be registered as an underground injection control well (UIC) with the Washington Department of Ecology's UIC Program. If required, a copy of the UIC registration approval notice shall be attached to the SSP. • Infiltration BMPs receiving non-roof runoff shall have upstream Ecology-approved pretreatment. Also, provide runoff treatment as defined in the Manual for UICs. • If any wetlands are filled, the project shall provide equivalent storage capacity to what the wetlands provided. This volume shall be in addition to storage volumes required to meet the requirements of any of the other minimum requirements. Minimum Requirement #1-9 Supplemental Guidance City of Everett Page 17 Aug 2022