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�sting bc��rfac_Drai��: <br /> T'here are no subsucface drainage problems that we are awaze of. <br /> PR POSAL <br /> � Fre en • <br /> 2 I'ear Storm for Treatment Volume <br /> 10 Year Storm for Storm Sewer Inlets and Gutters <br /> 10 Year Storm for Storm Sewer Laterals <br /> 100 I'ear Storm for Detention Storage Volume <br /> Desian Refer nces <br /> City of Everett Design Standards <br />' Stormwater Management Manual for the Puget Sound Basin <br /> N.O.AA Atlas Z,precipitation-Frequency Atlas of the Western United States, Vol, ]X <br /> Waterwvrky gydrology So�e pa�kaB�_ S��B��a Urba�Hydrograph bfethod <br /> WSDOT Design Manual, ge�on 1210 <br /> WSDOT HydrauGcs Manua! <br /> WSDOT Standard Plans and SpeciBcations <br /> Water Quality Asses�ment Guide M 22-15(HIt) <br /> Pr nocAl: <br /> This suPplement will consider modiScations to the detention and wet ond desi s on! , <br /> fehew of the Hydraulic Report by the District 1 Hydraulics Section and the City of Everett, it was <br /> determined iha�the site needed to be reanal p � Y �er <br /> compute a more accurate stormW,ater runoff ����8 more current hydrologic methods to <br /> compGance with the Crty of Everett's redevelopment mitigation standazds. <br /> ty. The site was also reevaluated to determine <br /> Waterworks FIydrology So�,aze Package and the requirements of the Stormwater Management <br /> After using the <br /> Manual for the Puget Sovnd Basin, ic w�determined that the detention volume calculated in the <br /> original report was not adequate and should be increased. T'he actua� detention volume required <br /> for the site was calculated as 3,982 c.f. instead ofthe original 2,27p c.f. <br /> detention volume the wet pond originally designed for the site was unable o d tain I of the ed <br /> stormwater runoff. The wet pond was also unable to provide the required biofiltration requested <br /> by the City�p� of their rrutigation requirements. <br /> This supplement now proposes to construct an underground detention vauldpump station to <br /> detain the r�noffwhich wi1]then be pumped into a vegetated swale on the site to provide <br /> bioSltration before being released into the City of Everett's storm seWer sy,s�em. The detention <br /> vault will consist of an 8 foot wide by 10 foot higlt reinfarced concrete single box culvert sealed at <br /> both ends. The culvert will be 90 feet long, and wi�1 contain four submersible pumps to drain the <br /> vault. Two of the units will pump a combined 1.26 cfs, the two yeyr storm flow, into the <br /> 2 <br />��;p-:,.- . � � --- - ..-'�`"`.' -...._.-�..,. ' - ' . <br />