When rain falls on an impervious surface, the runoff carries with it the oils, floatable trash and debris, and sediments that have built up since the last storm.  In the past, some thought that the first ten minutes of a rainstorm mobilized the majority of these oils and sediments.  This phenomenon, known as the "first flush," is what prompted many in the stormwater business today to design BMPs around the low flows associated with this first flush. 

New studies¹, however, indicate that designing a system to treat only the first flush may no longer be valid since these relatively low flows are not strong enough to mobilize a significant amount of the total pollutant load.  At BaySaver Technologies, we designed our BaySeparator product line to treat the runoff not only through the initial first flush, but throughout the entire storm no matter its intensity.

To treat the entire storm, our BaySeparators match the treatment flow rate and path to the incoming flow rate.  During the first flush, BaySeparators treat the entire volume of influent water through both manholes in series.  As flow rates increase, BaySeparator enters into maximum treatment flow.  During this phase, the entire flow is treated in the primary manhole while water containing free oils, fine sediments, and floatables, is diverted to the storage manhole for secondary treatment.  During peak design flow, gravity removes large suspended solids in the primary manhole.  A portion of the flow passes through the storage manhole for further treatment.  The remainder passes straight through the system thus avoiding resuspension of materials previously collected.  This direct flow path of the water assures that BaySeparator will not back up the storm drain.

¹ Studies by University of Alabama; City of Portland, Oregon; City of Austin, Texas; University of Texas.  For more information, please contact BaySaver Technologies.