Posted on March 6, 2024
Tons of contaminated silt have built up in Greenwich Harbor over decades, but the town may be able to dispose of it by simply burying it deeper underground.
The town, in coordination with state and federal officials, is preparing to dredge the harbor, and burying the silt and other materials in a confined aquatic disposal site, or CAD cell, may be the best option, they said.
Greenwich Harbor, which is a federal channel, is so full of silt that during low tide some places in the harbor are only about seven feet deep, when it should be about 12 feet deep. It was last dredged in 1968.
Geoffrey Steadman, a consultant who works with Greenwich and other Connecticut towns on coastal issues, told the Greenwich Harbor Management Commission that a CAD cell may be the “most economical and feasible way” to deal with the dredged material when the time comes.
If officials chose to use a CAD cell in Greenwich, harbormaster Paul Cappiali told the commission, then the contaminated material — also called spoils — will be dug up and loaded onto a barge in the harbor.
Crews will then dig a deep hole of clean dirt, load that onto a second barge and dump it in a designated location in Long Island Sound. The contaminated spoils will then be taken off the first barge and loaded into the hole before it is “capped” with a layer of clean dirt.
Birds fly over Greenwich Harbor on a sunny day at Roger Sherman Baldwin Park in Greenwich, Conn. Tuesday, Oct. 3, 2023.
Officials have not decided an exact course of action for dealing with the dredged materials just yet, but Steadman detailed the CAD cell option to the HMC on Feb. 21.
“They will dig a CAD cell — a deep hole, in effect — within the footprint of the channel, within which they would place the contaminated material that they dredged from the channel. And then they would place clean dredge material on top of that. So that’s likely to be one of the options that they come up with,” Steadman said.
Steadman noted that the CAD cell procedure was used in Norwalk Harbor about 20 years ago. The Army Corps of Engineers, which works on dredging federal channels like Greenwich Harbor, has also done CAD cell work in New London; Providence, R.I.; Hyannis, Mass.; and other locations around New England.
The exact course of action depends on how contaminated the harbor silt is.
Selectperson Janet Stone McGuigan, who serves as the Board of Selectmen’s liaison to the HMC, said that $500,000 of federal funds for testing the soil had been released as of late February.
McGuigan got the news from U.S. Rep. Jim Himes, D-Conn., who helped secure the funding for the soil testing and has been working to keep the project moving ahead in Washington, she said.
“He also assured me that we are still on schedule to have the dredge tested either this spring or summer,” Stone McGuigan said. “In his opinion, spring or summer really means it’ll shift a little bit to summer or late summer. But we are on our way.”
The silt in Greenwich Harbor may be too contaminated to be dumped in the Sound, but the dirt beneath it, which has not been tainted by decades of runoff, could be clean enough to dump farther out in the ocean, officials said.
It’s still unclear exactly when the dredging itself will happen and exactly how much it will cost, but Steadman said it would be “measured in the millions of dollars.”
The project cost will be shared between the federal government and the town. Greenwich previously set aside $2 million for the dredging, but Stone McGuigan said that they may need to seek an interim appropriation for more funding if their share exceeds $2 million. Steadman said there may be state funding available to help cover the town’s share.
