Sediment dredging falls short on cleaning contaminated rivers

A new US study reveals that sediment dredging may not be an effective means of cleaning contaminated waters, and that better monitoring is needed to assess suitability and results.

The independent report commissioned by the National Research Council looked at 26 superfund ‘megasites’ in the United States – all bodies of water where the cost of dredging cost more than $50 million

“Dredging does take away some of the contaminants, but it does not necessarily lead to reductions in the risk to human health and ecosystem,” Dr Charles O’Melia, chair of the committee that wrote the report, told edie.

“When you have a contaminated site, you can leave it alone and have it take care of itself or cap it by installing clean sediment on top. And then you can decide on dredging.”

According to the new report, many dredging projects have had difficulty meeting short-term goals for reducing pollution levels, and calls on the US 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.

O’Melia told edie that what is needed when tackling a new project is to get data before starting so that appropriate measures can be taken for improvement and clean-up, and an appropriate plan can be developed which may include sediment dredging in addition to using other methods.

Dredging’s ability to achieve cleanup goals depends on a site’s characteristics, the report also concludes. If a particular site has one or more unfavorable conditions – the presence of debris such as boulders or cables, for example, or bedrock lying beneath the contaminated sediment – then dredging alone is unlikely to be sufficient.

The presence or absence of such conditions should be a major consideration in deciding whether to dredge at a site, said the committee that wrote the report.

The report did not study the Hudson River and its proposed plans for PCB cleanup, where the EPA is said to have ordered dredging for a 40-mile stretch north of Albany.

The dredging – scheduled to now begin in 2009 after several delays – aims to remove PCBs dumped into the river at a pair of General Electric plants in Washington County.

Dana Gornitzki

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