Tappan Zee Bridge: Dredged sediment won't be dropped at sea

Apr. 16, 2013

The Tappan Zee Bridge. / File/Peter Carr/The Journal News

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When a clamshell dredge scoops up some of the bottom of the Hudson River this summer to help build the new Tappan Zee Bridge, the sediment it yanks to the surface won’t be deposited out in the Atlantic Ocean as initially planned.

The silt and sand instead will be placed in a yet-to-be-chosen spot somewhere on land. The change, construction officials said, is a result of plans that now call for dredging less than originally expected from the river.

The project’s final environmental study called for digging 1.9 million cubic yards out of the river bottom to make way for barges and other equipment. But Tappan Zee Constructors, the consortium that has a $3.1 billion contract with the state to design and build the new bridge, said it would dredge just 951,000 cubic yards. That dredging will take place over 139 acres instead of at least 164 acres.

The reductions required the consortium to seek a new permit from the Army Corps of Engineers in order to dump the dredged material in the ocean. The mandatory analysis of the sediment that would have been required before ocean dumping can’t be completed in time for dredging to start this year, the consortium said.

Walter Reichert, Tappan Zee Constructors vice president and project manager, said waiting for a Corps of Engineers permit “could cause a delay in the construction calendar” that made that option unfeasible.

While the sediment would be clean enough for ocean disposal, he noted, instead, “We expect to finalize an upland disposal site before the start of dredging season in early August 2013.”

Brian Conybeare, a special adviser to Gov. Andrew Cuomo on the project, declined to comment when asked if the state had any concerns that the search for an on-land disposal site might delay construction.

Dredging can only happen between Aug. 1 and Nov. 1, according to a state permit. The window is meant to provide safe passage to endangered sturgeon swimming in and out of the Hudson for spawning.

Tappan Zee Constructors plans to dredge this year and next, not over the four-year period originally envisioned by the state.

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The consortium said most of the dredging — 80 percent — will happen this year. The consortium said it is considering all disposal options for next year. On-land disposal might require trucks to bring the dredged material to its final destination. The contractor, however — according to the final environmental study — “would not be allowed to transport the dredged material by truck from the waterfront staging areas.” That means barges would haul the material somewhere else before it is transferred to trucks, railroad cars or a disposal facility.

Joshua Verleun, a chief investigator and staff attorney at Riverkeeper, said the reduced amount of dredging “will reduce the impacts on the river.” Both Riverkeeper and Scenic Hudson agreed last month to support the project after the state boosted an environmental mitigation fund and said it would keep the groups informed about construction.

“As long as they find a licensed and approved site and follow all the regulatory requirements, we wouldn’t have any concerns,” Verleun said of the dredging change.