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SOUTH PORTLAND — Just offshore from Knightville, at the mouth of Mill Cove, there could be a solution to disposal of Portland Harbor silt and sediment long overdue for dredging.
Portland City Hall spokeswoman Jessica Grondin announced in a press release Tuesday that the harbor floor between South Port Marine and the U.S. Coast Guard station will be tested for use as a “confined aquatic disposal cell.”
“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,” Portland Waterfront Coordinator Bill Needelman said in the press release.
Development of a CAD cell is being undertaken by the city of Portland, Portland Harbor Commission and three consultants. Cells are constructed by digging under the basin, dumping silt from dredging and then capping the cell, according to the Portland Harbor Dredge & CAD Cell Project website.
It has been almost a decade since Normandeau Associates studied what could be done about silt and dredging outside the main navigation channels in Portland Harbor. It has been 70 years or more since the areas around many privately owned piers and marinas have been dredged, according to the website.
The harbor ship channels are routinely dredged using federal funding, but the cost of dredging can be exorbitant for pier owners, project organizers said. Though pier and wharf owners may not be responsible for the accumulation of contaminants in the silt and soil, they are responsible for testing and disposal costs.
The dredged materials may be too contaminated to dump at sea, and too expensive to truck away, and the accumulations have piled up at the expense of marine-related uses of the piers.
“Without a reliable, well-maintained berth, with proper water depth at all tides, we do not have anything to offer the marine businesses,” said Charlie Poole, owner of Union Wharf in Portland.
The time-frame for constructing a cell pales in comparison to the decades of silt accumulation, but it is estimated by project staff it will take six years, if test borings taken by barge this week show the site is suitable.
No cost estimates exist; they will be based in part on the level of participation by pier and marina owners.
The proposed site was one of five considered. Others proved unsuitable because of impacts on fisheries, navigation, habitats or the feasibility of construction, Grondin said.
The Portland Economic Development Department is managing the siting and permitting process, using funding from the Maine Department of Transportation, Grondin said. An assessment of the sediments around the piers is being funded with a Brownfield grant from the U.S. Environmental Protection Agency.
The CAD concept was also endorsed by Friends of Casco Bay Baykeeper Ivy Frignoca as safe and cost effective.
“CAD cells have been used successfully around the world, including in Massachusetts and Rhode Island,” Frignoca said in the press release. “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 solution will help clean up the harbor and benefit our economy.”
If plans are approved, the CAD cell is expected to be used by owners of public and private piers and marinas. Larger industries in the harbor would continue to dredge and dump materials on their own, Grondin said.
Consultants looked at five Portland Harbor sites for storage of dredged materials before deciding to test the area marked with a star on April 27 and 28.
Silt and sediment like that visible April 25 between Custom House Wharf and Portland Pier in Portland could be dredged and stored in an aquatic cell across the Fore River in South Portland.