Sediment dredging

From WikiCover

At many projects to dredge contaminated sediments from U.S. rivers and other bodies of water, it has not been demonstrated that dredging has reduced the long-term risks the sediments pose to people and wildlife, says a new report from the National Research Council. Many dredging projects have had difficulty meeting short-term goals for reducing pollution levels. Whether dredging alone can reduce long-term risks was difficult to determine at many sites because of inadequate monitoring data and other limitations, the report says. It calls on the U.S. Environmental Protection Agency to improve and intensify its monitoring at dredging and other projects intended to remediate contaminated sediments at the nation's Superfund sites.

Dredging is effective at removing contaminated sediment mass permanently from the environment, the report says. But removing mass may not be enough to achieve desired cleanup levels or long-term goals for reducing risks, because dredging inevitably leaves residual contamination behind.

Contaminated sediments can be found at the bottoms of many U.S. rivers and other water bodies near former mining, agricultural, or industrial sites. Tainted with polychlorinated biphenyls (PCBs), heavy metals, or other toxic substances, the sediments can pose risks to people, fish, and aquatic animals. Many of these sites are slated for cleanup by EPA under federal Superfund legislation, and a minimum of 14 of them are sediment megasites -- sites where the cost of remediating sediments is expected to reach at least $50 million, or has already done so. Decisions about whether to dredge at these sites have proved controversial, so Congress asked the Research Council to evaluate the method's effectiveness. To inform its conclusions, the committee examined 26 dredging projects, five of them at megasites, and evaluated whether they had attained their cleanup and risk-reduction goals.