1500 1ST ST RAIL BARGE FACILITY 2016-01-01 MF Import

Vorlechs` SCormt�aiter Trcatmenl System DESIGN AND OPERATION easfc Oneration The Vortechs�' Sformwater Treatment Sys[em is a hydrodynamic separator designed to enhance gravitational separation of(loating and settling ma[erials from stormwater flows. S[ormwater flows enler the unit tangentially to the grit cliamber, which promotes a gentle swirling motion. As polluted water circles wi:hin the grit chamber, pollutants migrete toward the center of the unit where velocities are the lowes[. The majority of settlah�� solids are left behind as stormwater exits the grit chamber through two apertures on the perimet..�of the chamber. Next, buoyant debris and oil and grease are separated from water flowing under the baffle wall due to their relatively low specific gravity. As s[ormwater exits [he System through the Flow control wall and ultimately through the outlet pipe, it is relatively free of floating and settling pollutants. Over time a conical pile tends to accumulate in the center of the un(t containing sediment and asscciated metals, nutrients, hydrocarbons end other pollutants. Floating debris and oit and grease form a floating layer trapped in front of the baffle wall. Accumulation of these pollu[ants can easily be assessed through access manholes over each chamber. Maintenance is typically pertormed through the manhole over the grit charnber. Desian Process Each Vortechs� System is custom designed based on: • Site size • Slte runoff coefficient • Regional precipitation intensity distribution • Anticipated pollutant characteris[ics These factors are incorporated into the Rational Rainfall Me[hodT", deveioped by Vortechnics, Inc. to estimate ne[ annual pollutant removal e(ficiency. The Rational Rainfall MethodT" Differences in local climate, topography and scale make every site hydreulically unique. It is important to take tiiese factors into consideration when estimafing the long-term pertormance of any stormwater treatment system. To estimate efficiencies as accurately as possible, Vortechn(cs has developed the Rational Rainfall Method'" whlch combines site-specific information with laboratory generated pertormance data (Technical Bulletin No. 1), and local historical precipitation records. Sho�t duration rein gauge records from across the United States and Canada were analyzed by Vortechnics to determine the percent of the total annuai ralnfall that feil at a range of Intensitles. US stations' depths were totaled every 15 minutes or hourly and recorded in 0.01-inch (ncrements. Depths were recorded hourly with 1 mm resolution at Canadlan stations. One trend was consistent at all sites; the vast mzjority of precipitation fell at lo�v in[ensities and hlgh intensity storms contributed relatively little to tlie total annual depth. These intensities, along �vith th� total drainage area and runoff coefficient for each specific site, are translated into flow rates using the Rational Method. Since most sites are relatively small and liiglily Impervious, tlie rational method is appropriate. Based on the Flow rates calculated for each intensity, an operating rate �vithin a proposed Vorteclism System is determined. Finally, a removal efficiency is selected for each operating rate based on anticlpated pollutant characteris[(cs and on full scale laboratory [ests. The relative removal efficiency at each operating rate is addeo to produce a net annual pollutant removal efflcienry estimate. Rev 4-29-04 (WSG)