The CDS system is entirely self-operating, relying on water hydraulics and gravity. Raw stormwater enters the diversion chamber where a weir guides the flow into the unit's separation chamber. A vortex is formed that spins the water. The floatable and most suspended solids settle into the sump at the bottom of the separation chamber. The trash and suspended solids remain in the sump until they are removed, typically once or twice a year. The water that is now free of floatables and suspended solids then passes through a self-cleaning screen that removes any remaining debris and then is discharged to Poplar Creek.
Buehler was the lead designer of the Streamwood system. Working with White and the subdivision's developer Pulte Homes, she created a system design calling for 14 CDS devices, each one measuring 6 or 8 feet in diameter.
“We've become very familiar with the CDS technology,” said Buehler. “It is a simple technology with a relatively small footprint, and by all accounts it works very well. We heard a lot of good things about it before using it on this project.”
Experienced public works directors know that stormwater runoff from certain areas such as lawns and parking lots may contain high concentrations of nitrogen and phosphorous, as well as trash and suspended solids. Removing these chemicals is important in protecting local surface waters but it is not easy to do. According to Buehler, CDS Technologies worked with her in designing modifications in several of the units, fitting them with additional infiltration chambers to trap nitrogen and phosphorous. These special units were placed in strategic locations to filter out the unwanted contaminants.
The CDS units, each weighing in excess of 20,000 pounds, were manufactured nearby at local precaster Welch Brothers in Elgin, Ill. When the units become fully functional this fall, White and his colleagues can evaluate their effectiveness. White seems relatively confident that his system will deliver stormwater that is free of debris to the area's streams.
— Gibbs is a freelance writer in Germantown, Tenn.