Thomas Boving, assistant professor of geosciences at the University of Rhode Island, may have just solved the problem by using a cheap and readily available material: shredded aspen wood.
Boving and graduate student Wei Zhang are evaluating the effectiveness of the storm water detention ponds at the Gano Street ramp to I-195 in Providence, built in 1999 as part of the highways relocation project. During storms, water is carried from the roadway and surrounding urban areas to the three ponds, which are designed to filter out contaminants before the water reaches Narragansett Bay.
"The goal of the project is to find out if the ponds are doing what theyre supposed to do," said Boving. "And during a shower in May, they appeared to capture most of the pollutants well."
But he noted that heavy rains cause more pollutants to run off the road, and the faster flow of water into and out of the ponds during these storms is expected to reduce the ponds effectiveness.
"Most of the contaminants in roadway run-off are attracted to suspended organic material and sediments, which then settle to the bottom of the ponds," he said. "But if the flow rate is too fast, like during a heavy storm, there may not be enough time for the solids to settle before flowing out and into the bay."
So Boving began searching for a material that could be used in conjunction with the ponds to filter out the contaminants that dont settle to the bottom. Knowing that the contaminants cling to organic material, he tested shredded wood, which is available commercially in the southwestern U.S. for use in evaporative cooling systems.