A stretch of Montreal's $5.5-billion light-rail project will be built on highly contaminated ground, Radio-Canada has learned.

About 500 metres of train track going through the Pointe-Saint-Charles neighbourhood will have to be tunnelled through a former dumping ground.

A study by the City of Montreal found there are close to a million and a half litres of oil contaminated with PCBs in the area, along the St. Lawrence River between the Champlain and Victoria bridges. It was used as a dump for 150 years.

The train's route will bring it over the new Champlain Bridge, along Marc Cantin Street and then underground near the Mel's movie studios.

In order to do that, a 500-metre long part of the tunnel will have to be built right through the contaminated land.

The light-rail project goes through contaminated land in Pointe-Saint-Charles. (CBC)

A spokesman for CPDQ Infra, the Caisse de dépôt subsidiary responsible for the project, said it is aware of the problem but that it's too early to determine how the work will be carried out.

"It's a sector that has been well-studied, all the costs for the specifics in that sector have been calculated in our estimates, so there are no extra costs for that sector," said Jean-Vincent Lacroix, adding they've been working on making sure the tunnel's construction meets environmental requirements for more than a year.

Containing the contamination

Alfred Jaouich, a professor in the department of earth and atmospheric sciences at UQAM, says he is in favour of the train, but that everyone involved will have to be very careful.

He says the rock underneath is not stable and could crack, meaning contamination could easily spread.

Environmentalist and Green Party deputy leader Daniel Green says he isn't against the project either, but he believes there needs to be oversight and control of the waste while it's being excavated.

"It would be disastrous if this allegedly green project ... would pollute the St. Lawrence River by displacing toxic chemicals and all the soil they will be managing and excavating from this trench," he said.

A study by the City of Montreal found there are close to a million and a half litres of oil contaminated with PCBs in the area, along the St. Lawrence River between the Champlain and Victoria bridges. (Radio-Canada)

Green said the documents provided by CDPQ Infra don't mention anything about measures the contractors will have to undertake while working at the site.

He said a third party should be appointed which would have the power to shut down the construction site if pollution is detected.

"We smell these chemicals on the shoreline of the St. Lawrence River next to the Victoria Bridge because of the flow of these oils and chemicals toward the river ... and so the question is by opening up this hazardous waste site to the elements, will the Quebec government essentially pollute the environment even more?"

The city says it is aware of the issue and has been working on cleaning up the site for 25 years.

It says any company hoping to work there will have to respect the provincial laws in place, and that includes CDPQ Infra.

The 67-kilometre rail line would connect 24 stations across Laval, the South Shore and the West Island, with the first trains scheduled to roll by 2020.