2201 EVERETT AVE SEPA 018 - 008 Drainage Report 2025-04-15

Requirement#4-Preservation of Natural Drainage Systems and Outfall The project will maintain and preserve the existing Catch Basins that have been identified on site. A retention/detention pipe facility and infiltration bed facilities have been sized to maintain the storm water runoff to predeveloped site conditions. Tight lining of downspouts and footing drains will be utilized to route storm-water to the storm-water existing pipe facility within Everett Ave and Mcdougall and control structure of the site prior to discharge without causing erosion or drainage impacts to the downstream neighboring properties. UPSTREAM DRAINAGE The site has no upstream drainage onto the property as the land slopes away from the property. DOWNSTREAM DRAINAGE Stormwater runoff from the development area of the site collects onsite and sheet flows to the onsite existing catch basins and conveyance system along the south boundary of the site. Storm runoff is conveyed to the existing 24"combined storm drainage conveyance system flowing south along Mcdougll.The site is within the combined City of Everett stormwater and sewer area for additional information see the Attached Combined System Map and Public Works Policy#:2-11 Attached to this report. Requirement#5-Onsite Stormwater Management The project will provide tightlined connections at all downspouts locations. A solid 6" PVC pipe will direct runoff from the downspouts to the existing catch basin found in the Everett Ave R/W. No flooding or erosion impacts are anticipated with the development of this site. The site is within the combined City of Everett stormwater and sewer area for additional information see the Attached Combined System Map and Public Works Policy #: 2-11 Attached to this report. The site is exempt from Minimum Requirement#6— Runoff Treatment by reducing the impervious surface area. Two Bio retention areas have been provided the developer to reduce flows and water quality requirements and be credited against the project's sewer connection charge (EMC 14.08.135)No additional BMPS are proposed. OPERATION AND MAINTENANCE Maintenance of the downspouts bioretention areas and conveyance system should be on a yearly basis and after heavy rain storms. Pipes and yard/or catch basins that have more than 2 inches of sediment should be cleaned regularly. For additional information see the Attached Operation and Maintenance Manual.