Courtesy / City of Portland, MDOT
Dredging will involve an estimated 244,678 cubic yards of seafloor in an area that’s 2 million square feet or 46.8 acres off Portland and South Portland.
January 23, 2024
Now with $25M in funding, overdue Portland Harbor dredging will finally move forward
Courtesy / City of Portland, MDOT
Sedimentation along Portland Harbor prevents vessels from reaching berths and limits access to the waterfront.
After years of trying, the city of Portland has cobbled together a total of $25 million from various sources to move forward with the dredging of Portland Harbor.
The project has long been considered critical to the future of Portland’s working waterfront.
“This public private partnership is crucial to maintaining the working waterfronts in Portland and South Portland,” said Danielle West, Portland city manager.
The local economy relies on the working waterfront. As of 2020, it was worth an estimated $800 million in total economic output, related directly or indirectly to industrial marine, commercial fishing, recreational and tourism activities, according to a report prepared for the city by California infrastructure consulting firm AECOM Technical Services.
Many Portland Harbor piers have not been dredged in more than 70 years and are slowly filling in with sediment, decreasing water depths and causing a steady decline in available berthing for the working waterfront, according to Portland’s harbor commission.
The piers have not been dredged during that time because the sediment accumulating around them contains modern-day pollution from storm water runoff, and “legacy contaminants” from long-departed factories and shipyards.
The presence of contaminants prohibits sediment placement at sea, which is the most economical method of removal, which necessitated the more expensive alternative CAD cell method.
Dredge and dispose
The project has two components — dredging and disposal. It will focus on three overlapping districts of Portland’s waterfront:
- The western waterfront is exclusively dedicated to freight and industrial uses that need access to the deep water of the harbor's maintained dredged channel.
- The eastern waterfront is home to Portland's passenger port, with the Casco Bay Lines ferry service, international ferry service and cruise ship facilities.
- The central waterfront consists of 19th-century piers and wharves that form the heart of the harbor and support traditional fishing, marine research, tourism and non-marine uses.
Dredging will involve an estimated 244,678 cubic yards of seafloor in an area that’s 2 million square feet, or 46.8 acres, off Portland and South Portland. The area includes 47 properties along the waterfront adjacent to private and publicly owned piers and waterfront areas, including 21 piers, 10 marinas and boatyards, the Portland public boat launch and the Portland commercial barge landing.
Dredging is expected to occur over a three-year period.
The dredged material will be disposed into a “confined aquatic disposal cell,” or CAD cell — basically a deep hole dredged into the harbor into which contaminated material is permanently deposited.
The proposed CAD cell is in South Portland on subtidal lands publicly owned by the state. Construction will involve excavating approximately 376,858 cubic yards of sediment from an area of approximately 386,233 square feet, or 8.9 acres, of shallow subtidal habitat.
The CAD cell will be dredged to a depth below 49 feet of the harbor’s mean lower low water, which is the average of the lower low water height of each tidal day observed over a 19-year tidal cycle, called the National Tidal Datum Epoch.
Sides of the CAD cell are designed with a 3:1 side-slope. CAD cell construction needs to be completed in one dredge season.
The CAD cell will be constructed by digging a deep hole into the harbor bottom, filling it with contaminated sediments, and capping it with a thick layer of clean sand.
According to the U.S. Army Corps of Engineers, CAD cells have been used in multiple locations within New England as the preferred alternative for the disposal of dredged material deemed unsuitable for unconfined open water disposal.
Scaled-back project
Private and public wharf owners have been stymied by the exorbitant costs associated with the testing, dredging and transfer of sediments. Testing and regulatory permitting can cost wharf owners tens of thousands of dollars.
Sediment buildup has made Portland’s central waterfront entirely unusable, including over 3,000 linear feet of commercial berthing — which is parking for a vessel. Additional vessel support space that was previously built for large vessels is now only functional for smaller boats due to decreased water depths.
Similar conditions exist on the South Portland side of the harbor.
In 2020, the Portland Harbor Commission and the cities of Portland and South Portland were rejected in their application for $24 million in federal transportation funds for the project, then budgeted at $30 million.
In 2021, the city reduced the scope of the project in order to reduce the overall cost. The change included the elimination of a portion of the Portland city dredge near Ocean Gateway, which was no longer considered crucial, and to figure out which private and municipal dredge areas were ready to go financially and technically. This led to a project that was pared-down yet shovel-ready.
After the scope of the project was scaled back, the project was able to secure $10 million from the state via the Governor’s Maine Jobs & Recovery Plan. Funding sources also include $1.45 million in U.S. Environmental Protection Agency brownfields services, $6 million from the Maine Department of Transportation, $4 million from the city of Portland, $1 million from the city of South Portland and $2.64 million in private tipping fees from wharf and pier owners participating in the first phase of the project.
Immediate engineering
A majority of the private wharves and piers will see engineering done for their dredge areas immediately, and private owners who are ready to commit to the project financially are included in the first phase of dredge work.
Those who are not ready will have time to evaluate funding avenues and to get in on a Phase 2 dredge initiative, which will be developed as the CAD and Phase 1 are underway.
The city of Portland, with the Portland Harbor Commission, the state of Maine, and the city of South Portland, is working on a detailed scope of work for incorporation into bid documents. A request for proposals for the first phase of the project is anticipated for early summer with the goal of having a dredging firm under contract by autumn.
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