An advisory group wants to bury contaminated soil dredged from the Portland Harbor waterfront under the muddy shallows near the Coast Guard Station in South Portland.

The group of municipal and harbor officials and a team of grant-funded consultants chose the South Portland site as the preferred location of Maine’s first confined aquatic disposal – or CAD – cell from among a half-dozen candidates, concluding the 5-acre spot sandwiched between two other dredged areas was the only viable alternative, said Bill Needelman, Portland’s waterfront coordinator.

Over the last year, other potential sites have been rejected for various reasons, such as their value as a clam seeding, migratory bird nesting or lobster fishing territory; their proximity to a navigational channel; or their too-shallow depth, which might leave too much of the site exposed at low tide, said Needelman. “All the other sites faced opposition,” Needelman said. “The (Coast Guard) site was the last one standing.”

A cell is essentially an underwater hole filled with dredged material, then capped. Such disposal facilities have been dug across southern New England from New Bedford, Massachusetts, to Boston, but Maine has none. The soil removed in other Maine dredging projects has been clean enough to be dumped at sea, but a dredge of the Portland and South Portland waterfront won’t be clean enough for that.

The sediment that has built up between the wharves and piers of Portland and South Portland’s oldest sections of waterfront is tainted by decades of runoff from dockside and upland industry. The cost of hauling the dredged material to an upland landfill for hazardous waste has been so expensive that most wharf owners have simply put off dredging, reluctantly giving up a few inches of usable pier every year, with dozens of berths lost over the decades.

The Portland Harbor Commission and the city of Portland joined forces a few years ago to tackle the dredging issue, securing state and federal grants to hire a team of consultants to study the soil that needs to be dredged and design an affordable but safe way to dispose of the contaminated soil. The advisory group has met with potentially impacted groups, like lobstermen and Friends of Casco Bay, to study potential solutions.

Economic and environmental groups have joined forces to support the plan as relief from falling profits, gentrification, and degradation of water quality.

Wharf owners say they have had to look for other sources of income, like leasing to restaurants or offices, because they can’t attract marine businesses to their piers without deeper berthing spaces that can be used even at low tide. Environmental groups worry about the decades of pollutants that have built up between the undredged wharves, and what happens when big storms or boat propellers disturb the tainted soils.

Federal tests of CAD cells built in Boston Harbor a dozen years ago have found the buried toxins stay put, even during big storms.

The group briefed the South Portland City Council this winter. Claude Morgan, a South Portland councilor who sits on the Waterfront Alliance of Portland Harbor, said he has no major concerns with the cell being on the South Portland side of the Fore River. South Portland pier and marina owners could use it to dredge their facilities, he said, including the city-owned Portland Street Pier.

“I’m satisfied with the caution that’s been taken in reviewing several potential sites and choosing this one,” Morgan said Tuesday. “I’m satisfied that CAD cells have been proven safe over the last 50 years and that the material placed in them does not drift.”

The advisory group settled upon the Coast Guard location in February after ruling out all the other potential sites, but it is “far from a done deal,” said Needelman. Now that it has been chosen as the group’s preferred location, additional tests can begin to make sure there is enough sediment atop the bedrock to dig a hole big enough to bury the 300,000 cubic yards of sediment likely to be dredged.

A drilling barge is scheduled to begin a two-day test of the proposed cell location on Wednesday, Needelman said. It should be visible from Casco Bay Bridge.

Piling tests will follow the drilling if the initial test results prove encouraging, Needelman said. The group hopes to have all the tests completed, along with sediment tests of the areas likely to be dredged, by the end of the summer, so it can get permits from the Maine Department of Environmental Protection and apply for additional grants to proceed with its proposal.

The U.S. Army Corps of Engineers, the regulatory agency that would permit a CAD cell, told the advisory group that designing, permitting and building this kind of disposal facility is a “two-to-10-year adventure.” The total cost of dredging and disposal could run to $8 million to $14 million.

Penelope Overton can be contacted at 791-6463 or at:

poverton@pressherald.com

Twitter: PLOvertonPPH