3323 HOYT AVE WHOLE SITE 2020-06-17

Proposed Site Information: 1. How will your project change the existing conditions? This project will replace the existing(864sf) house with a (3,070sf)duplex.The duplex will take vehicle access(264sf)from the existing alley. 2. Please provide the following quantities of proposed hard surfaces in square feet: Proposed Roof Area: 3,070 Proposed Other Hard Surfaces(pavement,gravel,etc.): Sidewalk 807 sf, Driveway 264 sf 3. How will you manage rooftop runoff after the project is completed? Onsite infiltration areas will not be used as the underlying infiltrative capacity of Till soils is minimal.Additionally,the deisgn criteria cannot be met to provide 250sf per 1,000sf of rooftop. Raingardens will also not be able to be used as the low permeability of Till soils will likely create stagnate water. Downspout Dispersion will not be able to be used as there is not a 25ft flow path on the site while still complying with the GMA and City of Everett Code. Downspout perforated pipe stub outs/infiltration trench will be proposed.An infiltration trench is shown to the maximum extent feasible. The trench is connected through the center with a perforated pipe to release un-infiltrated stormwater. This trench measures 26.3 sf and is maximized amongst the setbacks between homes and property lines 4. How will you manage stormwater runoff from hard surfaces(driveways,paved pathways, patios,etc.)?Evaluate each type of hard surface separately. Stormwater will sheet flow from driveways and sidewalks to the street and alley catch basins. Plan for Permanent On Site Stormwater Management: 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 Pa e3of7