Cincinnati -- Researchers in the University of Cincinnati College of Engineering have designed a new system to trap dangerous pollutants in highway stormwater runoff. The system is being field tested this fall along the second busiest stretch of interstate in Ohio.
Doctoral candidate John Sansalone developed the new system. Sansalone's adviser is Steven Buchberger, associate professor in civil and environmental engineering at UC. Sansalone calls the system "PET" for partial exfiltration trench. It's a modification of the current systems used to improve drainage under highways, so it's expected to be easy to install and relatively inexpensive.
There are two key components to the system. The first is a bed of oxide-coated sand which attracts and holds onto heavy metals in the storm runoff. Lab-scale experiments demonstrated the special sand can dramatically reduce the concentrations of pollutants such as lead, cadmium, copper and zinc. This component takes care of the dissolved metals.
The second part of the system, a layer of porous pavement concrete block, acts as a giant strainer. "The system is a very effective trap for solids that are washed off the highway," said Sansalone. "Solids are stopped right at the surface of the porous pavement. They can accumulate there, and as a part of routine maintenance, they can be vacuumed back off the surface."
The concrete also neutralizes acidic rainwater and actually raises the pH to the level where the sand layer works best.
Sansalone has spent the last year testing a laboratory version of the PET system. Experimental results reported at the Seventh International Conference on Urban Stormwater Drainage in Germany this month indicate that the system can virtually eliminate nickel, cadmium, lead and zinc from stormwater runoff for up to ten years. And it doesn't matter how bad the storm is.
"Everything was based on peak flows or the heaviest flows, and we're still getting good results," said Sansalone.
The PET system is being installed along I-75 in a heavily traveled and industrial section of Cincinnati. The UC researchers have been trapping rainwater along that stretch of highway for the last two years to determine exactly what pollutants are present. Those same stormwater samples were used to test the lab- scale PET system, so the researchers expect the field-scale model will work effectively and inexpensively.
"Our laboratory work has shown great promise for what we intend to do in the field with this prototype PET installation. We think the system, by the nature of its design, is cost effective. It is not a new component for urban highways. It is essentially an upgrade."
But it will take more than one storm to determine how well the PET prototype works in the real world. The researchers must monitor the system for several months to see how it holds up under the freeze-thaw cycles of winter and spring and to see how road salt and other de-icing chemicals affect it.
The research is funded by the Ohio Department of Transportation.