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Posted on: April 25, 2017

City & Harbor Commission Make Progress on Dredging Solution, Select CAD Cell Site Location


The City of Portland and the Portland Harbor Commission, working with a team of consultants from Stantec, Apex, and Campbell Environmental Group, have identified a primary site for evaluating a potential confined aquatic disposal cell (CAD Cell) in Portland Harbor. CAD Cells have been used in many US harbors and around the globe and are considered an environmentally and financially responsible way to dispose of dredged materials determined to be inappropriate for disposal at offshore sites. The dredge and CAD Cell project goals are to provide the testing, engineering, and permitting required to dredge materials currently filling in the harbor’s wharfs.

The CAD Cell project has undergone an extensive site selection process involving public input from a diverse range of stakeholder groups. The process included evaluation of multiple sites in Portland Harbor. After thorough review, the project team has identified a primary site for further evaluation. The site is located near the US Coast Guard station in South Portland, in shallow water just to the south of the federal navigation channel (map attached)

All other potential sites were rejected due to either construction feasibility, fisheries impacts, habitat disturbance, or navigational constraints. Bill Needelman, Waterfront Coordinator for the City of Portland, notes, “Locating a feasible site is a big step for this process. Dredge projects aren’t easy and we’ve worked hard to be responsive and inclusive in dealing with our constituencies. It appears to come down to this last site near the Coast Guard.”

Next steps for the project include continued scientific investigations that will gather data needed for environmental permitting and design of the CAD Cell. To collect this data a barge will mobilize at the proposed site later this week to drill a test boring near the center of the CAD Cell. The boring data will be utilized to verify that there is enough sediment thickness above the bedrock to accommodate the CAD Cell. The data will also be utilized to determine geotechnical properties of the sediments for the design of the CAD Cell.

The results of the Dredging and CAD Cell projects to date have been presented to the South Portland City Council and the Portland City Council Sustainability and Transportation Committee.  


While the federal channels of Portland Harbor receive regular maintenance dredging, paid for by the Federal Government, the many public and private pier owners must pay for their own dredging. Most private and public wharfs and marinas have not been dredged in decades because the sediment accumulating around Portland’s piers contain “legacy contaminants” from long departed industries and current storm water outflows. As a result, the presence of these contaminants likely prohibits sediment disposal at sea and the alternative upland disposal method is very expensive. 

It is anticipated that public and private piers and marinas would have access to the CAD Cell, while larger industrial piers, such as the petroleum terminals, would continue to use open water disposal.  Like the federal navigational channels, many larger terminals have been continually dredged and their sediments are clean enough to dispose of at sea.

The dredging stalemate in Portland Harbor has had significant economic and environmental consequences. To maintain their piers, owners have been forced to look at other uses for revenue, such as restaurants, and office tenants, which potential competes for traditional working waterfront industries. One local pier owner, Charlie Poole, from Union Wharf notes, "Without a reliable, well-maintained berth, with proper water depth at all tides, we do not have anything to offer the marine businesses." 

Accumulating sediments are also impacting the environment when disturbed by boat propellers and big storms, degrading water quality in the Fore River. Cleaning up contaminated sediments and isolating them in a CAD Cell will result in a cleaner harbor. Ivy Frignoca, Casco Baykeeper, Friends of Casco Bay, has stated: “Our priority is to protect and improve the water quality of Casco Bay. CAD cells have been used successfully around the world, including in Massachusetts and Rhode Island. The plan here is to remove sediments from around Portland’s and South Portland’s wharves and place it in a much smaller, confined space, which will be capped with clean fill. This measure should keep the polluted sediments underground so they cannot contaminate shellfish and other aquatic life. This solution will help clean up the harbor and benefit our economy.”

About the project: The CAD Cell siting and permitting process is managed by the City of Portland Economic Development Department and funded through the Maine Department of Transportation.  A companion US EPA Brownfields grant to the Portland Harbor Commission is funding a related study to assess the sediments around the contributing piers and wharfs.

Contact Bill Needelman, Waterfront Coordinator:

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