Removal of Contaminated Sediment has Begun along Portland Waterfront

What do you do with a big hole in the ground? You fill it, of course.

The first phase of the long-awaited $25 million Portland Harbor dredging project — construction of a 9-acre confined aquatic disposal pit, or CAD cell — was completed early in March, wrapping up after 40 days despite bad winter weather, said Bill Needelman, Portland’s waterfront director. 

“It went exactly as planned,” Needelman said. “The CAD was constructed just as it was designed, and aside from a few routine maintenance shutdowns, everything went very smoothly. Now we can move on to the kind of routine dredging that should be normal for an urban harbor like ours.”

The CAD was dug in a shallow, little-used South Portland cove just downstream from Casco Bay Bridge, near Coast Guard Station South Portland. The trapezoidal, 9-acre burial site is 50 feet deep at its deepest, with sloped sides that run about 800 feet long and 425 feet wide.

The excavated silt, marine clay and glacial till removed to make the hole was dumped 7 miles off Dyer Point in Cape Elizabeth.

The early finish gives the contractor, Cashman Dredging of Massachusetts, enough time to start filling the excavated pit with an estimated 31,780 cubic yards of sediment from the first three dredge sites: Maine State Pier and Ocean Gateway in Portland and Turners Island in South Portland.

These are among the 47 piers, marinas, boatyards, boat launches and barge landings in Portland Harbor that are participating in the project, which will deposit an estimated total of 245,000 cubic yards of contaminated sediment into the CAD pit. Cashman required two transport barges to carry the excavated CAD materials to the open ocean disposal site, but it will only need one to carry the dredged Portland Harbor material to the CAD pit for disposal. But operations are still likely to run round-the-clock. The first three sites were chosen because they are easily accessible, have little or no complicating infrastructure present, and are big enough to be dug out with the large dredge that Cashman used to dig the CAD pit, Needelman said. The soils being removed have also been thoroughly tested.

These are among the 47 piers, marinas, boatyards, boat launches and barge landings in Portland Harbor that are participating in the project, which will deposit an estimated total of 245,000 cubic yards of contaminated sediment into the CAD pit. Cashman required two transport barges to carry the excavated CAD materials to the open ocean disposal site, but it will only need one to carry the dredged Portland Harbor material to the CAD pit for disposal. But operations are still likely to run round-the-clock. The first three sites were chosen because they are easily accessible, have little or no complicating infrastructure present, and are big enough to be dug out with the large dredge that Cashman used to dig the CAD pit, Needelman said. The soils being removed have also been thoroughly tested.

The navigation channel linking Portland Harbor and the Gulf of Maine is dredged every 15 years or so — most recently in 2014, by the U.S. Army Corps of Engineers. But it has been many decades since the sediments have been dredged along the waterfronts. It is up to the owners or the city to remove sediment that shoals up between piers, wharves, marinas or boat launches. And that work has been prohibitively expensive because the sediment requires special handling and disposal.

The sediment deposited in Portland Harbor’s working waterfront by three-quarters of a century of industrialization is too contaminated to be dumped at sea. Tests found it high in remnants of fossil fuels, heavy metals like zinc, mercury, copper and lead, and pesticides. Hauling it to a hazardous waste disposal landfill was too costly for any individual property owner to bear. Local officials have been trying to secure grants for a waterfront dredge for years. The final piece of the puzzle fell into place in January 2024, when the state released $10 million in American Rescue Plan Act funds that state lawmakers had earmarked for the project.