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The Truth About Environmental Dredging
Many
people have been led to believe that dredging
is a sloppy business that will re-suspend PCBs and leave the Hudson
worse than it already is.
In fact, controlled environmental dredging is very different from the navigational dredging that you may have seen. When dredging to keep navigational channels open, the only concern is moving as much sediment in as little time as possible. There's no need to worry about spillage. When dredging to remove contaminated material, controlling spillage is the primary concern. Controlled environmental dredging can be done with either hydraulic or mechanical equipment.
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A hydraulic dredge is like a giant vacuum cleaner with a digger at the front of its hose. The digger loosens the sediments which are sucked up the hose and out of the water.
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A mechanical environmental dredge uses a special clamshell bucket that closes tightly and seals the sediments inside before bringing them to the surface.
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Both systems may also use silt screens or curtains placed in the water to further control the movement of sediments. Environmental dredging is carefully monitored by underwater cameras and other means to ensure that contamination is not being re-suspended.
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