12728 19TH AVE SE BASE FILE 2016-01-01 MF Import

15. Stormwater treatment is required when 5,000 square feet or more of hydraulically-connected pavement is created and/or redeveloped by a project. Treatmer�t of stormwater runoff from hydraulically- connected pavement must ucr,ur, per C�ty standards, prior to discharg� of the stormwater from the site, or to a stream, �vetland or underground infiltration system. 16. If suitable soils exist on the site, surface stormwater infiltration systems (e.g. pervious pavers or surface ponding areas and/or swales) may be used to hydraulically disconnect pavement. From a stormwater treatment standpoint, for a pavement area to ba considered hydrauli�ally disconnected, stormtivater runoff from at least the 6-month, 24-hour storm m�st be fully retained and/or infiltrated. 17. The options for treatment of runoff from hydraufcally-connected pavement are: a. Infiitration basin. b. Wetpond. c. Conslructed wetland. d. Stormwater 360 Storm Filter, with pretreatment. e. Alternative treatment technology deemed by the City of Everett to be technically equivalent to the above options. 18. The required stormwater treatment volume for wetponds is the volume of developed runofi iroin the 6- monlh, 24-hour storm. City standards for wetponds allow a maximum of 85% of this volume to be provided as underground dead storage in a wetvault or tank. A minimum of 15% of the stormwater treatment volume, however, must be provided in an open-to-the-air vegetated treatment cell. Please see the City's Stormwater Management Man�al, Chapter 33 for more information. 19. Stormwater detention is required �vhen 5,000 square feet or more of hydraulically connected impervio:�s area is created by a project. 20. If suitable soils exist on the site, underground infiliration systems (e.g., infiltration trenches) or surface siorm water infiltration systems (e.g., splash blocks, pervious pavers, or suri'ace ponding areas and/or sv�ales) n�ay be used to avoid creating hydraulically-connected impervious area from a stormwater detention standpoint. Section 3-2.2 of the City's Stormwater Mar�agement Manual lists site and �esign criteria that must be met. 21. From a storm�,�ater detention standpoint, for an impervious area to be considered hydraulically disconnected, stormwater rGnoff from the 100-year, 24-hour storm must be fully retained andlor infiltrated—without resulting in significant potential for adverse effects from the infiltrated water(such as slope saturation or migration to crawlspaces and/or basements). However, if the on•site soils cannot support full infiltration of the 100-yPar, 24-hour storm partiai ?nfiltration may still be feasible to meet allowable storm water release requirements. 22. An NPDES (National Pollutant Discharge Eliminalion System) permit, administered by Washington State's Department of Ecology, will be required for clearing and grading activities on this site if the site area disturbed by land alteration activities is grea:er than or equal to one acre. 23. Per City policies, due fo the proximity of the site to environmentally sensitive areas, seasonal limitations may be placed on land alteration activities. Land alteration activities are defined in the City's Design and Construction Standards and Specifications as clearing, grubbing, excavafion, filling, grading and stockpiling. Determination of the exact seasonal limitation period requires site-specific information generally not available until the project design stage. However, preliminary analysis using the /� �