Firm behind controversial Dartmouth infilling plan says project will improve habitat

The civil construction firm behind the controversial proposal to infill part of Dartmouth Cove in Halifax harbour says the project will convert a contaminated zone into fish habitat that will support efforts to resurrect the ecosystem of a nearby river.

Bruce Wood, the chief financial officer of Atlantic Road Construction and Paving Ltd., detailed the plan during an interview this week at the company's office in Dartmouth, N.S., acknowledging the project to dump 100,000 cubic metres of rock faces steep opposition.

"When it's done, the environment in Dartmouth Cove will be much better off than it is now," he said.

The project is an attempt by the company to deal with an issue that's grown during Halifax's construction boom — where to safely put enormous amounts of acid-producing pyritic slate dug up when excavating sites for the foundations of new buildings.

The infilling project has been opposed by a neighbourhood group, the local councillor and the area MP. They've raised a variety of concerns, including how it will affect the views into Dartmouth Cove and a popular walking trail along the water.

Pyritic slate, which is common in Halifax, releases acid when it is exposed to oxygen. Piling it on land is environmentally dangerous, as runoff washes acid into streams and rivers where it can kill fish. It can also contaminate groundwater.

One solution often used in the Halifax region is to dump it into the ocean. Submerging it in the sea greatly cuts down its exposure to oxygen, according to a 2022 report by Halifax municipal officials, while the alkalinity of the water helps neutralize the small amount of acid that is produced.

Atlantic Road Construction said bottom samples from the Dartmouth Cove infill site and videos taken by divers show the area is contaminated with heavy metals and other pollution from decades of nearby industrial activity and sewage, and there is little life on the sandy bottom, aside from a few crabs.

A report prepared for the company by an environmental engineering firm, and submitted to the federal Department of Fisheries and Oceans (DFO), concluded the "majority of the proposed infill area is poor quality habitat."

The proposed infill will stretch for more than three football fields in length along the shoreline, and will be roughly 90 metres wide. But crucially, the company said, about a third of that width will be taken up by a new rocky intertidal beach meant to spur the growth of rockweed seaweed.

The purpose is to provide a "staging ground" for gaspereau fish before they swim up Sawmill River, which empties into Dartmouth Cove and is being reworked to restore fish passage to Sullivan's Pond, Lake Banook and into the connecting watershed.

The infill will be built in stages, starting with a stone perimeter that will become the beach and which the company said will cap the contaminated sediment. The infilling is predicted to take two years, however Wood said there will be periods of inactivity.  

"It's not going to be dump trucks running down there all day, every day for two years," he said.

But while the company said it will keep an adjacent walking trail open, eventually looping it along the shoreline of the infill, Wood said it is not yet sure what the new land will be used for, although he suggested it would be ideal for future development and a boardwalk.

That lack of a firm plan for the site is at the heart of some of the opposition, according to Sam Austin, the municipal councillor for the area. There's concern the area will be saddled with a "moonscape rock wasteland."

"It's not part of some bigger public project or vision or anything, it's just 'We need to dump our fill somewhere,'" he said.

There is currently no municipal planning around where pyritic slate should or should not be dumped, Austin said. The engineering firm Stantec has studied the issue for the municipality, according to a city spokesperson, however the report is not being released until it goes to the regional council.

The Dartmouth Cove project received an approval from Transport Canada last month, although that is being challenged in court by COVE, a neighbouring not-for-profit research and development organization that worries the infill will impede vessels at its docks.

Atlantic Road Construction is also seeking approval from DFO. In an email to CBC News, a spokesperson said the department reviews information on predicted impacts on fish, habitat and aquatic species at risk, and examines "mitigation and offsetting measures."

Pyritic slate is routinely dumped into Halifax harbour, such as at a container terminal in the city's south-end. Other sites have included Mill Cove in Bedford and the King's Wharf development, located on the far side of Dartmouth Cove from the Atlantic Road Construction proposal.

The company, Wood said, is trying to plan ahead. Current disposal sites can become backlogged, and will one day reach capacity, prompting Atlantic Road Construction to seek out its own alternatives.

In 2022, the Port of Halifax's Ocean Terminals began accepting pyritic slate, part of a three-to-five-year plan to infill 3.2 hectares with 500,000 cubic metres of rock in order to create new yard space. At the same time, it stopped taking slate at the terminal in Fairview Cove.

Lori MacLean, a spokesperson for the Port Authority, said it will be a "number of years" before the Ocean Terminals site can no longer take more rock. She said there have been no delays at the site, although there is a booking system for contractors seeking access.