Dredging contaminated sediments from many waterbodies in the U.S. has not reduced long-term risks posed by the sediments to people and wildlife, concludes a new report by the National Research Council. Many dredging projects have not met short-term goals for reducing pollution levels. Inadequate monitoring data and other limitations make it difficult to determine if dredging alone can reduce long-term risks. The report urges EPA to improve its monitoring at dredging and other projects to remediate contaminated sediment at Superfund sites. Authors of the report include Charles O’Melia of Johns Hopkins University and Richard Luthy and Perry L. McCarty of Stanford. They point out that the success of dredging to meet cleanup goals depends on the characteristics of a site. For example, if a site has unfavorable conditions, such as boulders, cables or bedrock beneath the contaminated sediments, dredging alone will probably be insufficient. The presence or absence of such conditions should be important factors in deciding whether to dredge. At least 14 Superfund sites are sediment mega-sites, requiring $50 million or more to clean up.

The authors conclude that dredging is effective at removing contaminated sediment mass permanently from the environment. However, dredging invariably leaves residual contamination. Therefore, removing mass may not be sufficient to achieve cleanup goals or long-term goals to reduce risks. Out of the 26 dredging projects examined, the authors found only a few sites where dredging alone achieved cleanup goals. Capping at many sites was required to contain the residual contamination. The report concludes that the dredging process itself releases contaminants into the water with short-term adverse effects on fish and aquatic animals and, potentially, on humans. EPA should consider dredging as one of several methods available for cleaning up contaminated sediments. A combination of methods should be considered, particularly if a site has any characteristics unfavorable to dredging. The authors point out that cleaning up megasites requires long time frames and there are many unknowns. EPA should apply adaptive management, which uses monitoring data to review progress and adjust plans when needed, instead of its usual method of conducting an investigation and a feasibility study and then deciding on a set approach to remediation. Also, dredging and other remediation projects should be designed to achieve long-term goals to reduce risks to humans and wildlife, as opposed to simply removing a specific amount of contaminated sediment. In addition, adequate monitoring is essential both before and after dredging. The report “Sediment Dredging at Superfund Megasites: Assessing the Effectiveness” is available at http://www.nap.edu