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To Dredge Or Not To Dredge

Study recommends alternatives and better monitoring of dredged waterways

by Cheryl Hogue
June 11, 2007 | A version of this story appeared in Volume 85, Issue 24

Credit: EPA
Tar-contaminated sediments were dredged from the Portland Harbor Superfund site in Oregon.
Credit: EPA
Tar-contaminated sediments were dredged from the Portland Harbor Superfund site in Oregon.

A controversial and expensive cleanup method used at some Superfund sites, the dredging of contaminated sediments from waterways, got a tepid review from the National Research Council last week.

EPA uses dredging as the method to clean up a number of Superfund sites. But this costly process is controversial because it leaves some of the pollution behind and because it may worsen some situations, at least in the short-term, by mixing once-buried contaminants back into surrounding water.

Dredging is one of the few options available for removing contaminated sediments, NRC points out in a report released on June 5. The report recommends, however, that EPA consider alternatives to dredging, such as capping the polluted area with clean materials or simply relying on natural processes to break down contaminants.

NRC bases its recommendation on an examination of 26 sediment removal projects at Superfund sites. The study found that dredging, by itself, achieved the desired cleanup levels in "only a few" projects. Capping was often needed in addition to dredging, the report says.

When EPA selects dredging as the method for cleaning up a site, adequate monitoring of pollution levels is essential before and after removal of contaminated sediments, the report says. This will allow EPA, those paying for the cleanup, and the public to determine whether removal of tainted sediments from a waterway has been effective.

The NRC report concludes that monitoring at most Superfund sites has been inadequate to determine whether dredging has lowered the risk of human health or environmental effects from the contamination.

The report, which was requested by Congress, also recommends that EPA deviate from its pattern of selecting and staying with a single method for sediment cleanup at Superfund sites. It says EPA needs to use more adaptive cleanup strategies that can change in response to evolving conditions at these complicated sites.



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