UNH Scientists Test Geotextile Mats on Sediments

Scientists from the University of New Hampshire's Contaminated Sediments Center are testing an innovative way to treat polluted sediment in coastal waterways, specifically in a mud flat at the edge of the Cocheco River, just outside downtown Dover.

They've created a patch of black geotextile mats designed to cap and stabilize pollution in place. Over the next two years, UNH associate professor Kevin Gardner, research assistant professor Jeffrey Melton, and a team of UNH students will monitor these mats to evaluate the effectiveness of this new approach.

"We need to know how these mats behave when they're buried under mud for a few years, compared to how they performed in the lab," says Melton. "What will happen to them in this intertidal zone with boats, waves, birds, and weather? How will they impact bugs and other aquatic life in the sediment?"

The mats are six-feet square and one-inch thick. They consist of a mixture of reactive materials sandwiched between two layers of geotextile fabric, creating a sort of quilt that traps pollutants but allows water to flow through. The reactive "filling" of this quilt contains three different substances that bind and stabilize different pollutants. One such substance -- a UNH-patented technology based on a natural form of phosphorus -- treats toxic heavy metals associated with industrial pollution such as lead, copper, zinc, and cadmium.

"But you don't just find one pollutant at a site," says Melton. "Everything is all mixed up in the sediment." So he and his colleagues added organoclay and activated charcoal, which adhere to and treat toxic chemicals such as polychlorinated biphenyls (PCBs), polyaromatic hydrocarbons, (PAHs), and petroleum products that routinely enter waterways through stormwater runoff.

The project is funded by the Cooperative Institute for Coastal and Estuarine Environmental Technology (CICEET), a partnership of UNH and the National Oceanic and Atmospheric Administration, and NH Sea Grant.

Melton admits that even as Americans grow increasingly aware of environmental woes, sediment pollution does not score high on the "green glamour" scale. Yet, he points out, everyone is already feeling its impact through regular advisories that close shellfish beds or warn of eating fish contaminated by heavy metals and persistent organic pollutants like PCBs or PAHs.

"You can enjoy a great day of fishing, but if you can't eat the catch, there's a problem," says Melton. It's estimated that 20 percent of the top six inches of all sediment in U.S. rivers, lakes, streams and estuaries is contaminated. In 2004, the U.S. Environmental Protection Agency reported there were 3,221 fish consumption advisories in state waters.

Melton and Gardner chose the Cocheco not because its sediment is especially polluted, but rather because its characteristics as a well-used tidal river and its proximity to UNH make it an ideal laboratory. They plan to compare the performance of the mats in the Cocheco to those they've laid in Cottonwood Bay in Grand Prairie, Texas, adjacent to the Dallas National Air Station, in a demonstration funded by the Department of Defense's Strategic Environmental Research and Development Program.

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