7800 EVERGREEN WAY HYUNDAI Drainage Report 2025-04-28

MINIMUM REQUIREMENT 2: CONSTRUCTION STORMWATER POLLUTION PREVENTION (CSWPP) Temporary Erosion and Sediment Control (TESC) best management practices (BMPs)will be implemented during construction per the DOE Manual and City of Everett requirements to prevent sediment-laden runoff from entering adjacent downstream conveyance systems. TESC BMPs are anticipated to include silt fence, temporary swales, check dams, catch basin inserts, and sedimentation tanks. See Appendix D for Erosion Control Plans and Details. MINIMUM REQUIREMENT 3: SOURCE CONTROL OF POLLUTION The project will provide source control BMPs as required by the DOE Manual. See Appendix I for a summary of both Source Control BMPs applicable to all sites and site specific source controls from the DOE Manual. Note: Due to mid-page page breaks in the DOE Manual, non-applicable BMPs appearing on the same page have been crossed out. MINIMUM REQUIREMENT 4: PRESERVATION OF NATURAL DRAINAGE SYSTEMS AND OUTFALLS All existing drainage patterns will be maintained with the exception of capturing and treating the NW basin, which currently drains offsite to the north. Stormwater runoff from the site will be collected and conveyed to the existing municipal system in Evergreen Way, matching the existing drainage outfall. 4.1 Downstream Analysis Per the City of Everett Surface Water Comprehensive Plan, Volume III Port Gardner Bay Watershed Plan, downstream capacity issues are noted along Evergreen Way between 75th St SE and Madison St. Water flow and water quality issues are identified with planning level projects at 75th St SE, which is greater than 0.25 miles downstream. Per DOE Manual Requirements, redeveloped and remodeled areas are subject to flow control measures that will match or reduce runoff rates compared to existing conditions.As a result, no adverse downstream effects are anticipated. See Appendix B for modeling results showing no increase in stormwater runoff duration or peak flows. MINIMUM REQUIREMENT 5: ON-SITE STORMWATER MANAGEMENT Per DOE Manual Flow Chart for Determining MR#5 Requirements, this project is required to either meet the LID performance standard or implement BMPs per List#2 to the maximum extent feasible. This project is choosing to meet the LID performance standard through planned flow control BMPs.Additionally, post- construction soil quality and depth will be provided for all landscaped areas as required by the City of Everett. See Figure 3-3 for DOE Manual Flow Chart below. KPFF Consulting Engineers 4