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�r � <br />���IT�x S,e¢ (,vn lfrn ccry�rnr;,� ,nd���hnj iFrry,s '�G��f 3fi //.'ucca� <br />l� < a�id�,�ss.�c�1. �'m5 ��. �t� a✓ d�u- Ci� �� - <br />i�.�s � <br />TO: <br />FROM: <br />DATE: <br />SUHJECT: <br />Detention• <br />bt E M O R A N D II M <br />Gordon Witcher <br />Jane Zimmerman <br />January 11, 1994 <br />�� ji . <br />l/i <br />I j i <br />� `' i <br />��� y <br />Plan Review, SEPA ,�60-93, Taco Bell <br />� <br />C� ��. <br />J� jz��� ¢-- <br />✓ A completed City of Everett Drainage Calculation Form is <br />required for appz•oval of detentior. calculations. <br />�� �,uc��� Orifice calculations are required for the control <br />��' N���� � structures. <br />��I��`� ��j�� �;�1 <br />rr'�' „�� stormwater treatment svstem: <br />-,;M ri�,� <br />Z'�r The SEPA decision document requires an oil/water separator <br />� to be provided in series with the vegetated (biofiltration) <br />swale. <br />City standards require high flow bypasses for both oil/water <br />✓ separators and vegetated swales. When these facilities are <br />in series, a single bypass system can be utilized upstream <br />of the separator and swale by sizing each facility for the <br />larger of the two design flows, either the baffle-type <br />separator desiqn flow or the vegetated swale design flow. <br />� When an oil/water separator and a vegetated swale are <br />located in series downstream of a detention system, the <br />separator and swal.e may be sized for the allowable release <br />from the detention system, with 25 year storm detention <br />overflows bypassed around the separator and swale. <br />oil/water seoarator/arit resoval vault: <br />�. <br />�.c� s�� City standards call for ttie oi.1/water separator vaults to <br />��c�`� <<��� .�j.have a minimum design flow determined by using the rational <br />�"U y�t ��;��� formula with a rainfall intensity of 0.5 inches per hour <br />,t �,F� over the contributing area, unless the separator is located <br />�,ou`�V �:.� ��s downstream of a detention system as discusred abev�. The <br />vi�"'� }C� vault ie required to be sized to provide a 15 minuLe <br />��;,�r ��h, detentica� time for the desiyn flow. <br />� ��� <br />�� m <br />