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Developed Condition Event Output: WWHM3 <br /> Peak Flow (cfs) Area (ac) <br /> 2-yr 0.04 0.15 <br /> 10-yr 0.06 0.15 <br /> 100-yr 0.10 0.15 <br /> A. PERFORMANCE STANDARDS <br /> The City of Everett 2010 Stormwater Management Manual as well as the DOE <br /> 2005 Stormwater Management Manual for Western Washington were used in the <br /> design of the stormwater mitigation plan for this project. <br /> C.FLOW CONTROL SYSTEM <br /> By utilizing on-site stormwater management in the form of a swale with check <br /> dams this project will increase the peak 100-year release rate over the existing <br /> conditions by approximately 0.03 cfs. Therefore no further flow control is <br /> necessary since the interim policy requires that the project be designed in such a <br /> manner to not increase the Combine Sewer Overflows and/or basement flooding <br /> in the combined sewer area. This increase in the flow is equivalent to less than <br /> 14 gpm only during the 100-year storm event. Since this flow calculation does not <br /> account for the absorption of runoff within the ponded swale areas the actual <br /> release to the downstream system will be reduced even further. As required by <br /> the interim policy the drainage design for this site has been prepared to maximize <br /> the infiltration of runoff from the project. <br /> Since a significant portion of the existing impervious surfaces (parking and garage <br /> roof) along the alley were directly connected via surface flow to the alley collection <br /> system this project will now nearly eliminate the condition where surface runoff <br /> from the impervious surfaces will drain directly onto the alley pavement. The <br /> proposed impervious surfaces will direct the future runoff to the vegetated swale <br /> and ponding areas prior to collection and conveyance to the Alley system. This <br /> will have a direct effect on the flow rate and durations for the new site compared <br /> with the existing condition. <br /> D. WATER QUALITY SYSTEM <br /> Since this project is in the combined storm/sewer basin treatment of the runoff will be <br /> provided at the COE treatment plant and this project is exempt from runoff treatment per <br /> interim Public Works Policy#2-11. <br /> Hoyt Parking Lot 12-0808 <br /> Oct.2012 Page-13 <br />