812 35TH ST 2022-03-07 - Laserfiche WebLink

• Rucker Hill Short Plat Minimum Requirement #5 On-Site Storm Water Management • The project is required to infiltrate,retain, and disperse runoff to the maximum extent feasible. Infiltration of stormwater runoff is infeasible due to the project being within the City's non-infiltration map area. Dispersion of stormwater runoff is not recommended due to most of the on-site slopes consisting of 15% or greater slope. Due to the project proposing more than 5,000 sf of new/replaced effective impervious surfaces,proposed • site runoff will be collected to the maximum extent feasible by a new on-site stormwater conveyance system and detained within a new on-site detention pipe. The detention pipe is desired to discharge into the combined sewer/stormwater conveyance system within the 35'11 Street right-of-way. • Minimum Requirement# 6: Runoff Treatment Runoff treatment is not required for the site as it drains to a City of Everett combined sewer/storm system which directs combined flows to the City's Treatment Plant for treatment prior to discharge to the Snohomish River/Puget Sound. • Minimum Requirement # 7: Flow Control Due to the site proposing more than 5,000 sf. of new effective impervious surfaces, and, flow control is required. Due to project being located in a combined sewer/storm area of the city, flow control is to be designed to match developed runoff rates at or below • existing conditions runoff rates. Flow control for the project is to be provided by the installation of a 40 lineal foot, 5 foot diameter detention pipe with a control riser manhole located in the northern portions of lots 1 and 2. Note that new detention system contains a minimum 6" sediment storage depth in base of system. Refer to the Calculations below and following WWHM flow rate calculation for detention pipe sizing. 1 Existing and Developed Site Summary Total Property Area =30,698 sf. (0.705 Ac.) On-Site Disturbance Area = 18,400 sf. (0.422 Ac.) Adjacent Property Disturbance Area = 7,450 sf. (0.171 Ac.) • Frontage Disturbance Area = 4,150 sf. (0.095 Ac.) Total Disturbed Area =30,000 sf. (0.688 Ac.) Total Site Area =42,298 sf. (0.971 Ac.) Existing Site Site Hardscape area: 0 Existing Main House &Patio = 2,760 sf. (To Remain) Existing Driveway = 4,700 sf. (1,300 sf. Undisturbed) Existing Front Walkway = 217 sf. (To Remain) Total = 7,677 sf. (0.176 Ac.) • Site Pervious area: Existing Tree Canopy(3,481 sf. Undisturbed) = 11,703 sf. (0.269 Ac.) Existing Lawn =22,918 sf. (0.526 Ac.) WESTERN ENGINEERS,INC. 12 PROJECT:16-1584-A