Contaminated sediment management needs better assessment tools


Contaminated sediment management needs better assessment tools, NRC says. Vincent LeClair ... Click to increase image size Free first page. View: PDF ...
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Contaminated sediment management needs better assessment tools, NRC says A new report by the National Research Council (NRC) on contaminated marine sediments recommends upstream source controls, sophisticated cost and risk analysis for managing existing contaminants, and more research and development funding for monitoring technologies to pinpoint underwater contamination. Dredging and construction projects in U.S. harbors and waterways can be delayed for as long as 15 years because of complications surrounding contaminated sediments, according to Contaminated Sediments in Ports and Waterways, published in March. The study was funded by the U.S. Navy, the Army Corps of Engineers, EPA, the Maritime Administration, and the U.S. Geological Survey. Understanding the risks and costs associated with contaminated sediment cleanup is critical to speeding up this process, according to the report, which noted the six major federal laws that govern dredging do not adequately address risks associated with contaminated sediment management. For complex cleanups, the report recommends a "decision analysis" approach that would weigh risk, cost, ciricl benefit on the basis of numerous variables and options The committee said rppprit

advances in pnmniiter software and hardware facilitate this kind of analysis "Decision analysis could be especially valuable because it can accommodate more variables than techniques such as costbenefit analysis that measure single outcomes," NRC writes. The result is a more comprehensive picture of a problem that can serve as a consensus-building tool among involved parties. To lower the cost of managing contaminated wastes, the report recommends more research and development on site characterization technology, which can reduce the volume of material requiring remediation. The cost of most current characterization technologies, such as physical profiling and chemical testing, has "limited the precise definition

of either horizontal or vertical contaminant distributions, which may have led to the removal and remediation of large quantities of uncontaminated sediments at unnecessarily high costs," according to the report. Acoustic profiling, which uses high-resolution mapping of the acoustic reflectivity of sediments to define the thickness and distribution of disparate sediment types, may prove cost-effective, according to the report. By easily identifying fine-grain sediments to which contaminants easily hold, this method can lead dredgers to hot spots and steer them away from areas not likely to be contaminated. Another promising characterization technology is fiber-optic chemical sensors for in situ use said the report. One example is fiber-optic-guided fluorescence which measures trations of polyaromatic hydrocarbons and other compounds that fluoresce at the wavelength sent down the fiber Trace metals, hydrophobic organics such as dioxin, and polychlorinated biphenyls are the major contaminants in sediments. Although contamination is usually diffuse, extending no more than a meter deep, it is sometimes concentrated in hot spots. The United States annually dredges 14 million to 20 million cubic yards of contaminated marine sediments, which amounts to between 5 and 10% of all sediments dredged.

Dredgers clear out channels in Boston Harbor, where a new project will bury contaminated sediments on site in deep underwater pits. (Courtesy Save the Harbor/Save the Bay)

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"By and large, you're dealing with large volumes of relatively lightly contaminated sediments," said Henry Bokuniewicz, a professor at the State University of New York at Stony Brook and co-chair of the NRC report committee. "The most successful projects have been burial, usually near the site." He said projects that had practical uses, such as island construction or habitat foundation construction for wetlands, also have been politically palatable. In the case of Boston Harbor, where a major dredging project is planned, dredgers will dig deep underwater pits where the most contaminated surface sediments could be dumped and capped with sand. Clean sediments will be dumped at an ocean site. "On the positive side, you're not spreading the contamination, you're keeping it in the area where the impacts are already felt," said Peter Shelly, senior attorney with the Conservation Law Foundation. But the down side is that other contaminated sites in the harbor will go untouched because Congress will only fund dredging for shipping lanes, he said. These remaining contaminated sediments will eventually shift back into the dredged lane, said Shelly. The report notes that current treatment technologies available for large volumes of sediments generally are too costly, averaging more than $100 a cubic yard—as compared to $20 for removing and transporting sediments and $5 for conventional navigational dredging, which does not require special disposal procedures. "When it became clear there was no magic bullet to solve the treatment problem, it became more important to look at upstream sources," said attorney Kenneth Kamlet, co-chair of the committee. The report says that states and EPA could address upstream pollution sources by expanding the Clean Water Act's total maximum daily load prowhich sets limits on pollution sources based on total pollution levels in a water bodv It also recommends that states and EPA use legal and enforcement tools such as Superfund to get uppolluters to help pay for contaminated sediment management.— VINCENT LECLAIR