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' �.r.v pr gV-ar�r"f' ON SLmf' nFTT*t'CTON R�OUSRE`�E� <br /> The sizing of on-site detentsan��i� t'ieal ia= lung duratian - <br /> based an a 2t haur desi,�. �'? <br /> winte= stor�s in Eve=ett. Fc= sites larger �'�an 5.� ac=es, <br /> on-site detentians systems will be sised by City af Everett <br /> verscnnel vith the use ot EPA's comnuter based starwater <br /> management model (5�'t�1) • A copy of the comnuter printout will <br /> be provided ta t7e apnlicant at his/her request. <br /> For sites smalle= than 5 .0 acres, a series of tables shoc.-n . <br /> below allow t::e apnlicant ta dete�ine his ar he: on-site <br /> detention recuire�ent. Thesa tables vere develoned base� upon <br /> a series of cc�puter si�ulations ot stora:ate: runof= frem a <br /> hvpo�'ietieal 20 aere draiaace basi� u�anesand i±e f oa10a25 <br /> basin included ten parcels varyin5 , , <br /> ac:es to 5.0 ac:es. ' <br /> i_ +-t,e t�t�les: <br /> i=v"' - <br /> The Lirs:. step is to �et==�ine the design stor� erite=ia !or <br /> �e site in guestion. T�1e 1 shohs the design s:.or� criteria <br /> for eicht drainace basins/areas in Eve=i�• The lacat_ons ot <br /> the �ainaqe basins are sho•.+n in fi4ur' <br /> ?.�ter the desicln stora criter_a are detez��':ed� t�e alloG-able <br /> release sate tor tha cn-site detention system is dete�'sed �y <br /> using tables 1 .t�`souch 4. To use tables 1 t4rouch 4, the <br /> existi.ng slone and ground cover .canditions oE the site in <br /> cuestion need to be deter�=ned• . <br /> The slope af t:�e site mus� be deterized �=�m a topcg:anhical <br /> su��ey of tie site ar by using the City's 1486 aerial <br /> togoy'�'anhical mans. The slooe re=ers to the slope o: overland <br /> f1oW rzther �Ytan the sloae oi the channel ar saale tha't drains <br /> the site. The existing greund cover can be classi=ied as <br /> aocds or fores�e3; as lawns, �'ass er landsca�ing; as bare <br /> comoacted ezrth or gravel surfacec; or zs an �per�ious <br /> sur:zce. ' <br /> The atiaimtta siz= o:ifice a1loc:ed `o=cart actiontcoegar•cs Zteof <br /> is 2" . 2.ssumir.c a bo:da .;orif:ce ( <br /> o.51) anfl a head o;: ��o fe=t, t'.:e ts aii o� la releasa rateshot <br /> 2" ori:ice is 0 .1] c�s. Therefare, <br /> less than . 1� c�s S�QuSeene�zs Ie �23belo�alculate on-site <br /> fle�ent'on re:ui_e�ents ( <br />