Montreal's sewage dump saga explained in 5 key points

The City of Montreal plans to dump one-third of its sewage into the Saint Lawrence River from Oct. 18 to Oct. 25. Here is a sum-up of the entire issue broken down into five key points.

City plans to dump 8 billion litres of sewage into St. Lawrence River from Oct. 18-25

The City of Montreal's plan to dump eight billion litres of untreated wastewater into the St. Lawrence River has stirred controversy. (Thomas Daigle/CBC)

The City of Montreal plans to dump one-third of its sewage into the Saint Lawrence River from Oct. 18 to Oct. 25. The plan has stirred up controversy among politicians and citizens.

To better understand the entire issue, here are five key questions and answers.

1. Why does the city need a plan to divert eight billion litres of sewage?

Major construction work to lower the Bonaventure Expressway to street-level in downtown Montreal requires moving a snow dump, which is connected to a big sewer. This sewer's pipe measures five metres in diameter and normally carries sewage to the city's water treatment plant. However, in order to carry out the work to move the snow dump, the sewer's pipe must be drained.

There's also another reason that the interceptor sewer must be drained: the city must remove old, wooden building hoops that have started to detach from the structure. The pieces breaking loose could jeopardize water treatment.

The eight billion litres of wastewater would flow directly into the Saint Lawrence River via 26 interceptors, which correspond to areas used for sewer overflow during heavy rains.

The interceptors that would be used in the dumping of the sewage are located in the following boroughs:

  • LaSalle
  • Verdun
  • Sud-Ouest
  • Ville-Marie
  • Mercier-Hochelaga-Maisonneuve
  • Rivières-des-Prairies–Pointe-aux-Trembles

According to city officials, the plan, which was approved by Quebec's Environment Ministry, is an exceptional measure. 

2. Does the plan pose a health or environmental risk?

The sewage dump would flow at a rate of 13 cubic metres per second for seven days, compared to the river which flows at a rate of 7,000 cubic metres per second. For one week, eight billion litres — the equivalent of 2,600 Olympic-sized pools — of toilet waste and discharges from hospitals and businesses.

Until the 1980s, it was common to dump sewage into the river.

The chair of Montreal's executive committee, Pierre Desrochers, said there would be no impact on the quality of the city's drinking water. He added that the drinking water of the municipalities located downstream from the dump sites would also not be affected.

"The river has a significant dilution capacity, with a flow rate of 6,000 to 7,000 cubic meters per second. This does not pose a major concern for the environment," said city spokesman Philippe Sabourin.


The city says it will dump the wastewater at the end of October, so that there is the least possible impact on the river's ecosystem. According to Réal Ménard, a member of the executive committee, the fish spawning period is over this time of year, and the cooler water temperature limits the spread of bacteria found in the sewage.

Water activities will be forbidden during the time allotted for the sewage dump.  The city will install signs along the river's banks informing people that no fishing, kayaking or surfing will be allowed.
Montreal Mayor Denis Coderre accused the federal government of playing "cheap politics" on the backs of Montrealers.

What some experts are saying

Sarah Dorner, engineering professor at École Polytechnique, said there's no reason to be alarmed.

"They have disinfection processes and they have the means to monitor the water quality," said Dorner, who released an information booklet on the plan with four of her colleagues.

"If the spill is the only possible and acceptable solution, the effects on water quality and on the communities downstream will be negligible compared to the cumulative effects of having wastewater that is not completely treated in water treatment plants and sewage overflows during heavy rains in the region of the island of Montreal," the research group said.

But Abdelaziz Gherrou, a specialist in wastewater and water treatment processes, believes the city's plan could have a negative impact on the environment — despite the river's strong current.

""It is true that the huge flow of the river will mitigate this impact somewhat but it remains that, over a period of one week, some contaminants have time to affect the flora and fauna," he said.

3. What are politicians saying?

We are not a draining field for the City of Montreal.- Serge Péloquin, Sorel-Tracy mayor 

The mayors of some municipalities situated downstream from Montreal, including Trois-Rivières, Bécancour and Sorel-Tracy, have denounced the city's plan.

"We are not a draining field for the City of Montreal," said Sorel-Tracy Mayor Serge Péloquin.

The federal environment minister, Leona Aglukkaq, questioned the city's plans, saying plans should be put on hold until the ministry gets more information.

Montreal Mayor Denis Coderre accused the federal government of playing "cheap politics" on Montrealers' backs., adding that the Environment Canada had seen the file in September 2014.

Federal campaign trail

The matter even came on the federal campaign trail.

NDP Leader Tom Mulcair said an NDP government wouldn't allow it.

"The idea that in 2015, we would release billions of litres of raw wastewater into the St. Lawrence and its ecosystem: It's so preposterous, it's obvious an NDP government would not permit it," Mulcair said.

The floating spa Bota Bota in Old Montreal is near one of the 26 interceptors where the wastewater will be dumped. (Bota Bota)
Liberal Leader Justin Trudeau did not address the issue, while Bloc Québécois Leader Gilles Duceppe accused the other parties of being hypocritical.

"I have not seen a politician — of the Conservatives, the Liberals, the NDP — denounce the regular spills into Lake Ontario without any warning."

Several Green Party candidates criticized the city's plan, with two candidates calling for an injunction.

4. Is there another option?

According to the City of Montreal, there is no other choice than to dump the wastewater into the river for seven consecutive days.

Sylvain Ouellet, Projet Montréal's spokeman on the environment, wondered if it would have been possible to limit the damage. "Would it have not been possible to pump the wastewater to a temporary detour to avoid contaminating the river?"

Environmental activist Daniel Green, who's also running for the Green Party, believes it would be best to carry out the plan in winter.

"The City of Montreal could, for example, work in February and dump this wastewater when there is no migration of ducks and other migratory birds, and when there are no hunters, fishermen or boaters on the river," Green said.

5. What about elsewhere?

In the past, the City of Montreal has dumped wastewater into the river from the same interceptor sewer.

  • Spring 2003 : 10 billion litres
  • Fall 2003 : 7.6 billion litres
  • Fall 2005 : 770 million litres

Here's a rundown of other Canadian cities where dumps of raw sewage have taken place:


Raw sewage was continuously pumped into the Halifax harbour until a new wastewater treatment plant was constructed in 2008. However, sewage continued to be discharged into the harbor unknowingly, when sewer lines were cut during construction. 


Roughly 185-million litres of raw sewage have been dumped into Winnipeg's rivers since 2004 due to the city's antiquated combined-sewer system. The city says that massive upgrades need to be made to the older sewer system, which could cost the city up to $4 billion.

Mr. Floatie is one citizen's attempt to protest the amount of raw sewage that continues to flow into Juan de Fuca Strait each day. (Mr. Floatie/Facebook)

Victoria and Esquimalt

The region pumps about 130-million litres of raw sewage daily into the Juan de Fuca Strait, a channel leading to the Pacific Ocean. Victoria and Esquimalt have been in a longtime battle with the federal and provincial government concerning their sewage treatment practices and have been struggling to find a site for a new treatment plant for years. 

Esquimalt citizen James Skwarok even created a mascot to protest the sewage dump: Mr. Floatie, the giant turd.


In July 2013, Toronto was pounded with 126 millimetres of rain in under two hours. More than a billion litres of sewage and storm water overflowed onto city streets and cascaded into Toronto's harbour.

Heavy rains often overwhelm Toronto's old sewer system, forcing the city to bypass water-treatment plants and send raw sewage into Lake Ontario.

With files with The Canadian Press


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