1606 SE EVERETT MALL WAY ANTHEM SELF STORAGE 2025-07-25

The detention facility is private and is located on-site,beneath the private drive aisle. The proposed detention vault will be located on the east side of the building under the driveway, and also acts as a retaining wall. The vault will have six inches of freeboard above the vault riser and a minimum six inches of dead storage. The final interior height of the vault will be 9.5' (measured at the wall face and excluding any height benefit from the"V"bottom). Per COE 2012, this vault has been re-designed to contain a"V"bottom as well as a grated tractor hatch near one of the inlets. This vault contains inlets at either end,both of which are serviceable by a single tractor hatch. Detained flow leaves the control structure and will discharge easterly via conveyance pipe within WSDOT right-of-way to an existing WSDOT catchbasin along I-5. WSDOT has been contacted with respect to this project, and WSDOT permits are underway. Current contacts at WSDOT are headed by Paul Lacy, LacyP@WSDOT.WA.gov The proposed outlet flow control structure will be constructed within the proposed detention vault,but is enclosed in a type-II or similar structure which isolates the control structure from the vault. The control structure is accessible from the proposed private driveway accessing the site. Water quality: Runoff from the drive aisles will treated for water quality prior to detention. The two Contech Stormfilter Catchbasins are filter cartridge style filters with less than one acre of contributing area per filter system. The City of Everett has accepted this style of filter ' system as both a treatment and as a pre-treatment system for installations with less than one acre of contributing pollution generating surface per filter system. As such, we have no additional, pre-treatment specific facilities. The roof runoff is considered non- ' pollution generating water and is not be subject to water quality treatment or pre- treatment. Roof runoff will flow to a downspout system that will bypass the filters and be directed directly into the detention system. The proposed private access drive aisle will be split into two separate drainage sub- basins; the northern system and the southern system. The two sub-basins will flow to two ' separate underground piped storm drain collection and treatment systems that eventually converge in the detention facility. Water quality flow rate was calculated using WWHM2012 as independent WWHM runs for the pollution generating surfaces for the northern area, then again for the southern area.. Water quality treatment will operate as required by the 2012 Stormwater Management Manual for Western Washington. (See the Water Quality Sub-Basin Data Contech StoriuFilter Data in the Appendix) 1