Sediment Dredging at Superfund Megasites: Assessing the Effectiveness (2007)Board on Environmental Studies and Toxicology
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Some of the nation's estuaries, lakes and other water bodies contain contaminated sediments that can adversely affect fish and wildlife and may then find their way into people's diets. Dredging is one of the few options available for attempting to clean up contaminated sediments, but it can uncover and re-suspend buried contaminants, creating additional exposures for wildlife and people. At the request of Congress, EPA asked the National Research Council to evaluate dredging as a cleanup technique. The report finds that, based on a review of available evidence, dredging's ability to decrease environmental and health risks is still an open question. Analysis of pre-dredging and post-dredging at about 20 sites found a wide range of outcomes in terms of surface sediment concentrations of contaminants: some sites showed increases, some no change, and some decreases in concentrations. Evaluating the potential long-term benefits of dredging will require that the U.S. Environmental Protection Agency step up monitoring activities before, during and after individual cleanups to determine whether it is working there and what combinations of techniques are most effective.
- Dredging is one of the few options available for the remediation of contaminated sediment and that it should be considered, with other options, to manage the risks that the contaminated sediments pose.
- EPA needs to centralize and coordinate assessment and management of contaminated sediment megasites to ensure greater consistency in evaluations, greater technical competence, more active leadership at the sites, and an emphasis on what works and why.
- Improved risk assessment that specifically considers the full range and real-world limitations of remedial alternatives is needed to allow valid comparisons of technologies and uncertainties.
- The committee could not generally establish whether dredging alone is capable of long-term risk reduction. That is because monitoring at most sites does not include all the measures necessary to evaluate risk over time, dredging may have occurred in concert with other remedies or natural processes that affect risk, insufficient time has passed to evaluate long-term risk reduction, and a systematic compilation of site data necessary to track remedial effectiveness nationally is lacking.
- The committee found that dredging alone achieved the desired contaminant-specific cleanup levels at only a few of the 26 dredging projects, and that capping5 after dredging was often necessary to achieve cleanup levels.
- The management of contaminated megasites needs to embrace a more flexible and adaptive approach to accommodate unanticipated factors, new knowledge, technology changes, and results of field pilot tests.