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

the stage-storage relationship of the pond, or the berm �esiqn must be modified so that water is not retained in the first cell of the pond. Car wash area oil/water a�arator/arit removal vaultt Calculations for the �ar wash area oil/water separator must be submitted as part of the drainage calculations. The oil/water separator must be sized to give a 15 minute detention time for the anticipated hose flow to the area. The anticipated hose flow must be stated, and jusYification for the n'umber u�ed must be gi�en. etormwater auality enhancement system: Developed site conditions must be used in determining the design flow for the swale and oil/water separator. However, due tu the location of the water quality enhancing featnres downstream of the detention system, the design flow for these features can be the City's allowable detention release (10 year peak discharqe for existing conditions). PLAN REVIEW COMMENTS Diveraion atructure: By using the City�s allowable detention release as the swale and oil/water separator desiqn flow, overflows from the detention sysLem can be bypassed around the swale and separator at the restrictor manhole to eliminate the need for a separate diversion structure. However, oil tends to accumu:ate in restrictor catch basins. Therefore, when detention overflows bypass an oil/water separator, the overflow structure �ust be modified so that overflows do not contain larqe amounts of oil. A floatable material separator may be used on the detention overflow if enougti clearance exists Uetween the overflow elevation and the roof of the manhole structure (a minimum of 1.5 feet is necessary betwr:en the top elevation of thc manhole/cb and the ciown of the overflow pipe to meet all city �tandards r�garding installation, cover requirements on ti�e 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 be stiffened by welding a"rib" from the standpipe to the baffle, and should extend a minimum of 2 inches above and 6 incl�es below the overflow elevation.