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Water Quality Management Plan (WQMP) <br />Mainplace Mall Specific Plan <br />IV.3.4 Biotreatment BMPs <br />If the full Design Storm Capture Volume cannot be met with infiltration BMPs, and/or <br />evapotranspiration and rainwater harvesting BMPs, describe biotreatment BMPs included. <br />Include sections for selection, suitability, sizing, and infeasibility, as applicable. <br />Name Included? <br />Bioretention with underdrains <br />❑ <br />Stormwater planter boxes with underdrains <br />Rain gardens with underdrains <br />❑ <br />Constructed wetlands <br />❑ <br />Vegetated swales ❑ <br />Vegetated filter strips ❑ <br />Proprietary vegetated biotreatment systems <br />Wet extended detention basin ❑ <br />Dry extended detention basins ❑ <br />If infiltration is infeasible on any of the development sites after site -specific infiltration testing, <br />biotreatment BMPs are anticipated. Due to the density proposed on -site, proprietary <br />biotreatment BMPs are the likely feasible biotreatment BMP. Proprietary BMPs shall be those <br />that are independently certified and tested by public agencies, including the State of <br />Washington or an equivalent nationally recognized certification. The sizing of biofiltration <br />BMPs shall accommodate the treatment flow rates outlined in Section IV.2 of this report. <br />IV.3.5 Hydromodification Control BMPs <br />Hydromodification is not a concern since the proposed condition volume and peak runoff <br />during the 2-year storm will not exceed the existing condition. The hydromodification analysis <br />only pertains to the area of the master plan that is tributary to Santiago Creek. See Appnedix 4 <br />for calculations on volumes and flow rates and a summary in the table below: <br />Hydromodification - Flow Rate Analysis <br />Drainage <br />Area <br />Existing 2-Year Peak <br />Flow Rate (cfs) <br />Proposed 2-Year Peak Flow <br />Rate (cfs) <br />Percent Increase <br />C <br />18.88 <br />19.32 <br />2.3% <br />D <br />10.01 <br />10.42 <br />4.1 % <br />Centennial Section IV <br />Conceptual Specific Plan WQMP Page 26 <br />