1600 121ST ST SE 2016-01-01 MF Import

the staqe-storage relaTionrhi�> ot the pond, or the bcrm design must be modifie�l ::o Th,�t �r.�Tor i:; not ret,�ined in the first cell of the pond. Car wash area oil/water s�arator/g rit removal vault_ Calculations for the car wash area oil/water separator must be submitted as part of the draina�a calculations. The �;.�^ �r oil/water sepa-ator must be sized to give a 15 m.inute �� detention time for the anticipated hose flow to the area. �!�� The anticipated hose flow must be stated, and justification �� for the number used must t�e qiven. �i�� .� I �I, �'�' etormwater quali� enhancement svstem: Ueveloped site r_onditions must be used in determining the design flow for the swale and oil/water separator. However, / due to the location of the water quality enhancinq features � downstream of the detention system, the design flow for these features can be the City's allowable detention release (10 year peak discharge for eristing conditions). PLAN REVIEW COMMENTB Diveraion structure: By using the City's allowable detention release as the swale and oil/water separator desiqn flow, overflows from the detention system can be bypassed around the swale and separator at the restrictor manhole to eliminate the need L for a separate diversion structure. However, oil tends to accumulate in restrictor catch basins. Therefore, when detention overflows bypass an oil/water separator, the overflow structure must be modified so that overflows do not contain large amounts of oil. A floatable material separator may be used on the detention overflow if enough clearance exists between the overflow elevation and the roof of the manhole structure (a minimum of 1.5 feet is necessary between the top elevation of the manhole/cb and the crown of the overflow pipe to meet all ✓ city standards reqardinq installation, cover req�irements on the pipe may also be an issue). otherwise, a baffle, made of a larger diameter pipe and welded to the overflow standpipe, must be added to the overflow/bypass structure. The space between the baffle and the overflow standpipe must be large enough to not cause restriction of flows. The baffle should Ue stiffened by welding a"rib" from the standpipe to the baffle, and should extend a minimum of 2 inct�es above and 6 inches below the overflow elevation.