1502 WALL ST IMAGINE CHILDRENS MUSEUM 2022-08-25

• • Proposed Site Information: _ _J 1. How will your project change the existing conditions? The Imagine Children's Museum is expanding to the south, replacing the existing parking lot. Some existing sidewalk and paving in the alleyway will need to be replaced in order to facilitate construction and utility connections. 2. Please provide the following quantities of proposed hard surfaces in square feet: Proposed Roof Area: 12,030 Proposed Other Hard Surfaces (pavement,gravel, etc.): 2270 3. How will you manage rooftop runoff after the project is completed? Existing outfalls for the site will be maintained. The roof drain will connect into the same catch basin that sheet flow from the site currently enters into. 4. How will you manage stormwater runoff from hard surfaces(driveways, paved pathways, patios, etc.)? Evaluate each type of hard surface separately. Under existing conditions the sidewalk within the project area sheet flows into Hoyt Ave, where it flows north along the gutterline before entering the combined sewer system via a catch basin. Those conditions will be matched exactly under proposed conditions. Under existing conditions,the alleyway sheet flows runoff towards a flow line in the center of the alley, where it flows north before entering the combined sewer system. Under proposed conditions, those conditions will be matched exactly. Plan for Permanent On-Site Stormwater Management: _ 1 You are required to "infiltrate, retain, and disperse stormwater" on your site to the maximum extent you can without causing erosion or flooding. The goal is to get stormwater runoff in contact with vegetated surfaces as much as possible before discharging to downstream conveyance systems. See Volume III,Chapter 12 of the 2010 Stormwater Management Manual for stormwater facility requirements: https://everettwa.gov/DocumentCenter/Home/View/1214 1. Determine which options you must use for managing stormwater from rooftops via downspout disconnect by considering the following Best Management Practices(BMPs) in order: • BMP 12.30 On-site Infiltration Areas • BMP 12.40 Raingardens • BMP 12.50 Downspout Dispersion Notes: a. If location criteria can be met, but sizing criteria cannot,you must implement the BMPs to the maximum extent you can without causing erosion or flooding. Pre-sized facilities have been designed to meet 100% mitigation. Facilities may be able to be installed to achieve some stormwater mitigation. b. Other innovative downspout control BMPs such as rain barrels, ornamental ponds, downspout cisterns, dry wells, or other downspout water storage devices may also be used with prior approval by the City of Everett.These are options to consider after the above listed BMPs are evaluated. 2. Determine which options you must use for managing stormwater from hard surfaces(driveways, paved pathways, etc.) by considering the following for each type of hard surface proposed: LPage 3 of 7 CITY OF EVERETT I 3200 Cedar Street Everett, WA 98201 1425-257-8810 everettwa.gov