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S'I ORMWATER SITG PL:\N DEC[MDFR 19,2005 <br /> N[\V C[NTURI'VILLAG[ PAGL S <br /> V. AN�.t,YSIS AN�D DESIGN OF RUNOFF �ONTROL BNiP'S <br /> � DRAINAGE BASIN AN,�LYSIS <br /> The site contains three drainage basias. ��he new reo�areas ancl Nic :ot lot �vill be collected and <br /> � directed to an intiltration trendi (Basin !), while thc rcmaining la�vn, parking and frontage will <br /> be directed to a second storm system that includes a trcatment s}�stem and an infiltration trench <br /> (Basin 2). This basin also includes the existino 6-plex located on the northeast portion of the <br /> � property. The tinal basin is thc arca of the cxisting access and parking for the previously <br /> mentioned 6-plex (Basin 3). This area currenUy drains to a drywell that no longer functions. Wc <br /> propose to add ar� infiltration trench and replacc the dry wcll with a sedimentation structure. Sec <br /> IFigure 3: Developed Site. <br /> �� HPDROLOGIC ANALYSIS <br /> The drainage desi�;n foi thc site was prepared using thc rcyuiremcnts of the City of Evcrctt <br /> Stormwatcr Management Manual, (C�M Manual) as wcll as the 2005 Department of Ecology <br /> i Stunmvater Management Manual, (DOE Manual). Use of the DOE Manual is duc to some of thc <br /> (unding Housing Hope has received for this project. In general, the most restrictive of cach <br /> manual has been used whcre there were discr�:pancies in ihe requirements. SCS curve numbers <br /> � were taken from the CEM Manual. The WWi;M2 softwarc by the DOE was used to calculatc <br /> rwioff. Stonnshed by Engenious, Inc was uscd �vhere SCS calculations wcre made. <br /> Thc rainfa(1 evenis used in the calculations are the SCS type lA distribution of the 24 hour <br /> ruinfall cvcnt for thc 2, 10 and 100 ycar rcturn pciiods. Total prccipitation, t'rom the Tablc 1-5.4 <br /> of thc CEM Manual, is as follows: <br /> Rcturn Period Rainfall <br /> 3 1'car L55 inchcs <br /> 10 Yenr 2.25 inches <br /> 100 Ycar 3.25 inchcs <br /> �� RairSall for thc WWHM2 softwarc is intcrnally calcu!ated buscd on sitc location. <br /> SOIL DESCRIPTION <br /> A geotechnical analysis from RMI Associates, LTD «as prepared. Their im�estigation indicates <br /> �hat the site is generally underlain by 1 finc to mcdium sand. They have detennined that <br /> infiltrations rates in Ihc medium sand will be 3.33 inchcs per hour. <br /> � ��i�.;�.:rq�r.coe��,e,,,�e,�,�in�,_,�-,ca.uao��o�q�ssarvrNc«.��ryooc DWHlsrm <br />