UNH researchers test new contaminated-sediment cap in D.C. river
Patented dredging alternative neutralizes harmful heavy metals

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DURHAM, N.H. – University of New Hampshire (UNH) researchers recently began the first field-scale test of a patented system for capping and treating contaminated sediment in the Anacostia River in Washington, D.C.

Environmental engineers from the UNH College of Engineering and Physical Sciences and Environmental Research Group deployed a 100 x 80 foot “active cap” at the bottom of the river April 5-8. Near the junction of the Anacostia and the Potomac, the cap is in a stretch of river contaminated with harmful heavy metals, including lead, zinc and cadmium.

The cap consists of a six inch layer of sand over a six inch layer of naturally occurring phosphate-based minerals from the apatite family. The apatite binds with heavy metals to stop or significantly slow the spread of contaminants, essentially acting as a “heavy metal sink.” Capping provides a beneficial use for the low-grade leftovers from phosphate mines, which use only the finest material for fertilizer.

“For heavy metals, apatite is like a vacuum cleaner,” said Jeff Melton, research assistant professor of civil engineering. “The idea is to bind the metals so that they won’t be re-released into the environment,” he said. “This technology provides a new treatment option for situations when traditional techniques may not be appropriate.”

Funded by an Environmental Protection Agency grant to the Hazardous Substance Research Centers/South & Southwest, the demonstration is designed to evaluate the comparative effectiveness of several innovative capping technologies and traditional methods. So far, it has already shown that UNH’s patented system can be deployed successfully.

The reactive phosphate containment system was invented by UNH Research Professor Taylor Eighmy, with support from the Cooperative Institute for Coastal and Estuarine Environmental Technology (CICEET). Created with congressional funding secured by Sen. Judd Gregg (R-NH), CICEET recently awarded Melton a grant to develop the technology’s commercial potential.

Melton is working with Kevin Gardner, research associate professor of civil engineering and director of the UNH Center for Contaminated Sediment Research, to expand the capabilities of the system by incorporating materials that can treat organic contaminants such as PCBs.

PHOTO CAPTION
Heavy Metal Apatite: A barge-mounted crane lowers a load of apatite -- the heavy-metal-binding ingredient of an innovative contaminated-sediment capping system being tested by UNH environmental engineers -- into the Anacostia River in Washington, D.C.

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