8407 BROADWAY SECURE SPACE STORAGE 2025-08-19

Broadway Everett Expansion Storm Drainage Report November 16, 2022 6. Runoff Treatment: The majority of the pollutant generating hard surfaces within the project disturbance boundary is existing and will be ground and overlaid. The pollutant generating surface that will be replaced is 1,373 SF and therefore does not trigger additional water quality requirements. Oil control is not required for the project. The proposed project is a self-storage facility and does not have more than 100 vehicles per 1,000 SF of gross building area, does not equal or exceed 300 trip ends per day, and the area is not subject to 25 or more vehicles that are over 10 tons gross weight. 7. Flow Control: The stormwater discharges of the redeveloped site must match the pre-developed discharges from 50% of the 2-year peak flow up to the 50-years peak flow, with the pre-developed condition being forested land cover. The existing wetvault on-site is to be used for flow control. We used the vault and flow control riser data from the as-built and construction documents from the original development to verify that the size of the wetvault's detention capacity meets current codes. We conducted a WWHM analysis for the proposed project and it was determined that the use of the vault satisfies the flow control requirement and requires no additional provisions. See Appendix B — Flow Control Basin Map, Appendix E—WWHM Report, and Appendix F—Wetvault As- Built. 8. Wetlands Protection: Stormwater on-site does not discharge to a wetland. No wetlands will be impacted by the proposed redevelopment. 9. Operation and Maintenance: See Operation and Maintenance Manual under separate cover. Page 4