News and information for the worldwide dredging industry

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In early May, the U.S. Environmental Protection Agency (EPA) announced the start of the sixth, and final, season of dredging the PCBcontaminated sediments from the bottom of the Hudson River. This is a historic project for EPA and one of the largest and most complex in Superfund history. The cleanup is being conducted by General Electric Company (GE), with EPA overseeing the project. GE says it has invested more than $1 billion on the cleanup since 2009.

EPA and GE estimate that between 1947 and 1975, from 500,000 to 1.1 million pounds of polychlorinated biphenyls (PCBs) were discharged from the Fort Edward and Hudson Falls facilities into the upper Hudson River. An estimated 500,000 to 700,000 pounds of PCBs remain in the river sediments, EPA says.

The EPA-mandated cleanup called for the removal of an estimated 2.65 million cubic yards of PCB-contaminated sediment from a 40-mile stretch of the upper Hudson River. As of May, approximately 2.5 million cubic yards of contaminated sediment have been removed. This was to be the sixth and final year of dredging.

EPA did say this year was full of “logistically challenging areas” to be dredged, including those near dams and shallow waters around islands. Dredging is also continuing this year in a two mile section of river near Fort Miller, located between the Thompson Island Dam and Fort Miller Dam, which is inaccessible by boat. The target removal for this year – 250,000 cubic yards.

Dredging goes from May to November, when the Champlain Canal is open – 24 hours a day, six days a week. Three to five mechanical dredges remove contaminated sediment with clamshell buckets and place the dredged sediment in separate barges.

Of the more logistically challenging work, EPA says, “In the land-locked section of river, where direct water-transport of loaded barges to the processing facility isn’t possible because of dams, loaded barges will be pushed by tugboat to a loading station on a narrow section of land on the east shoreline of the river, south of the Thompson Island Dam. Once there, the material in the barge will be off-loaded into a bin on land and then re-loaded into another barge in the Champlain Canal channel. From there the barges will be pushed by tugboat upriver to GE’s sediment dewatering and processing facility located on the Champlain Canal in Fort Edward, New York.”

The sediment is mechanically dewatered and the water is treated on-site and then returned to the Champlain Canal. That sediment processing facility was scheduled for decommission once the last of the dredged material had been transported off-site. But that might not be this year as planned.

In May, the National Oceanic Atmospheric Administration (NOAA) dealt a blow to the project, at least to its completion.

In 2002, when EPA decided on which remedial action to take, the science used model projections of PCBs in fish to compare alternatives. Since then, findings have shown that the models overestimated the rate of natural recovery in surface sediment and the associated fish levels. The NOAA Office of Response and Restoration presented its findings, which had the following conclusions: the original models about surface sediment recovery were overly optimistic; attaining the needed levels in the fish will take longer than predicted; and additional removal of PCB-contaminated sediment in the Upper Hudson River is needed.

Perhaps this is good news for contractors working on the project (which EPA says employed more than 280 area contractors, subcontractors, vendors and suppliers that provided services and materials to support the remediation work on the Hudson River). Although the river isn’t free and clear of contamination, this could also be a learning experience for the science of dealing with contaminated sediment. It’s a rare opportunity to re-visit old biological model predictions and create new and better models for the future and other remediation projects.

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