1605 SE EVERETT MALL WAY BOBS BURGER AND BREW 2025-07-25

Bob's Burger and Brew City of Everett,WA Stormwater Site Plan December 21,2009 1 Analysis and Design of Required Erosion and Sediment Control BMPs The site has been designed to prevent sediment laden runoff from leaving the site. A temporary sediment trap has been sized to collect runoff from the construction site. A Large Parcel Erosion and Sediment Control Plan has been included in Appendix A for reference. The sediment trap is designed in accordance with the City of Everett stormwater manual and will trap sediment produced during the 2-year, 24-hour storm. The required surface area is based on 1250 SF per cfs of inflow during the 2 year, 24 hour event. The runoff produced during this event is approximately 0.1245 cfs. The required surface area based on this volume is 155.63 sf. To meet this requirement the temporary trap has been designed with a surface area dimension of 8'x24'. This trap will outlet into the existing catch basin onsite via a gravel cone riser. Construction of this trap will be in accordance with the City of Everett Stormwater Management Manual. Once the existing catch basin has been removed and additional stormwater pipes have been installed, the second phase of the ESC BMPs will be implemented. The ' catch basins and Filterra units will be protected by straw waddles and inlet protection. This will filter out sediment and allow stormwater to enter the existing drainage system. Analysis and Design of Required Runoff Control BMPs Water Quality Treatment BMPs ' The City of Everett Stormwater Management Manual requires the Water Qualit y BMP's to be sized to treat 91% of the runoff volume This was estimated using a continuous runoff model, WWHMv3. The Design criteria for treatment facilities are assigned to achieve the applicable performance goal at the water quality design flow rate (e.g., 80(3/0 TSS removal). Using WWHMv3, three separate basins were created- one for each Filterra unit. WWHMv3 then calculated the flow by which 91% of the runoff can be treated. See Appendix B for WWHMv3 outputs. The Filterra design manual as approved by the DOE (see Figure 4 in Appendix A) explains how to effectively model the Filterra units as sand filters using WWHMv3. Each individual unit was then sized based on the design criteria. Certain parameters were then used (See Appendix B) and the model was run to help compute the exact size needed for each basin. The units were effectively sized when the percent filtered was greater that 91%. The following table represents the amount of on-site PACLAND Project#30182002 Page 4