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Ashb� rn 'fo�� nhomc <br />4. DRAINAGE PROPOSAL <br />"I�hc proposal includcs construction of four duplcx aparunent buildings or cight (8) <br />total units. Drainagc will llow from thc strcct to thc back of thc lot, which is thc lo�v pc�int in <br />the project. Drainagc will entcr a catch b�,s�„ �� a,�s no�m a„a now to an "Aqua-Swirl' , <br />dcsigncd by Vortecnics, whiclt ���ill pic-lrcat runoff from lhc ��roposcd drivcway. Runoff ���ill <br />then Ilow through thc watcr quality de��ice and thence into thc dctention vault. Per City of <br />L'verett standards, the dctention system will bc designed to dctain thc 2-ycar, 10-ycar, and <br />100-ycar (2�1-1 lour) dcvdopcd stonn volumcti and relcasc at '/ of thc prc-cxisting 2-� car. 10- <br />ycar, and 100-ycar frequcncy slorm event ratcs. <br />��s rcquired by the City of I�verclt, a volume corrcction factor of 13G`% lor bank er��sion <br />control has becn applicd to the dctention volume based upon Uic perccnt of the site bccoming <br />impervious. Approaimatcly CO% of ihis sitc will be covcrcd with impervious arca, rclating lo <br />a 36% incrcasc in dc�cntion �'olumc per'fabic I-3.1 of thc li�•crett Slormwatcr �4anagctncnt <br />n-t1„����i. <br />�l�hc final ��.tult sizc (insidc dimcnsians) is I�.3;' X 35� \ 3' ���hich pro��idcs thc total ��i�lnmr <br />rcyuired of 1370 cubic Icet. A ilo��� restrictor/oil pollution control dcvicc (I'ROI'-'I�) �vill <br />control thc dischargc Ilo���s out of thc pipe (Icss than 10,000 ft' of parking and driving <br />surl�ccs are proposcd for thc sitc). <br />n Vortccnics Aqua-Swirl, modcl AS-2 �vill pro��idc thc pro-trcatmcnt for lhe drivc�ca�� <br />r��„on�. �������„�s�,�-�ii n<„�� through thc �\qua-S���irl prc-ircatmcnt devicc bc('orc it is trcatal <br />with ihe 2-cartridge `Storm Piltcr'. 'I'he D.O.E. lias appravcd for the Aqua-S���irl as a <br />"gcncral usc dcsignation" for the prc-trcaUncnt of slorm watcr runoff: <br />"I�hc ���atcr quality providc�l lor this projccl is a 2-cartridgc `Stomi Pillcr' manulacturcd h� <br />Storm���alcr \4�magcmcnt, Ina This dcvicc has bcen approvcd to providc watcr qualily b�. <br />thc VVashington Statc DcpmKment of Lcology. "I'hc mcdia spcciGcd in thc IiL'cr cartridgcs <br />���ill removc oil and similar petrolcum products. <br />Rooltop runot7'will bc convctcd directly to qic detention system bypassing the Storm Piltcr <br />dc� icc. Itoof runoff is considcrcd a non-polluting �urlacc, bul thcsc Ilo���s will bc dctaincd. <br />\V'lil 0-l-�d1-13 <br />