1808 MERRILL CREEK PKY 2016-01-01 MF Import

Because of the proximity of the wet pond/detention pond to the creek corridor, the required permanent srorage could not be provided without further impacting the creek corridor. The permanent storage volume that was able to be provided along with the oiVwater separator and the vegetated swale should adequately provide the water quality necessary to discharge to the creek. The other requirements for the permanent storage volume were able to be met. Over thiRy percent of the wet pond permanent storage volume is provided in the wetland treatment cell: Volume ofwetland treatment cell = 8590 CF Vulume of permanent storage = 27,550 CF Percent provided in weUand trcatment ccll = xsvucr'�=�«oce = 3�•Z PCrcCnt The permanent storage depth in the wetland was designed in the 0-2 foot range (1 foot) and the permanent srorage depth in the open warer cell was designed in the 3-6 foot range (4.5 feet). Oil/Water Separator ** (Deleted during City of Everett Review G/30/94) ** The oil/water separator was designed to the spill containment criteria. A 2500 gallon bat�le-type oil/water separaror is proposed ro treat the design flow before it enters the wet pond. It was not possible to design the oil/water separator for a 15 minute residence time for the design flow. An oil/wlter separator exceeding 25,000 gallons would need to be constructed to provide the 15 minute residence time. An 18-inch bypass line has been provided to convey Flow greater than the design flow around the oilhvater separator. The calculations for the oil/water separnror are �s follows: Total area tributary to the oil/water separator = 9.64 acres Q,,�,= cIA wliere c= 0.9; I = 0.5 in/hr; A= 9.64 acres STORM DILIINAGE REPORT FOR INTRANEST-SEAWAY - YAGE 7