Montreal sewage dump: How it's going to work

Mayor Denis Coderre has announced that Montreal will go ahead with its controversial sewage dump at midnight tonight. Here's how it's going to work.

8 billion litres of sewage to go into St. Lawrence River over a maximum period of 7 days

Mayor Denis Coderre shows how much a piece of the southeast interceptor has deteriorated and is in need of replacement.

Mayor Denis Coderre has announced that Montreal will go ahead with its controversial sewage dump at midnight tonight.

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Here's how it's going to work:

Wednesday, 12:01 a.m.: Valves are shut off

The valves bringing wastewater to the 30-kilometre-long southeast interceptor — a major sewer pipe that collects the effluent from a network of other sewer lines on its way to the water treatment plant — will be shut off.

The sewage will be diverted through discharge points along the St. Lawrence River. 

The diverting of the water will last until work on the interceptor is completed.

Wednesday, approx. 6 p.m.: Crews begin work

This is an example of arches in the southeast interceptor that have deteriorated and are in need of being replaced. (City of Montreal)

The southeast interceptor is expected to have dried out, allowing work crews to enter and start work on 14 deteriorating arches. The arches will be replaced to increase the capacity of the interceptor.

Crews will also inspect areas of the interceptor, looking at layers of sediment and the degree of concrete degradation.

Work crews will work in shifts, 24 hours a day, until work is completed.

Sewage diverted from boroughs, cities

While the southeast interceptor valves are shut off, the sewage will be diverted to discharge points along the river.

The boroughs and cities which had their sewage diverted to the southeast interceptor include:

  • Lachine 
  • LaSalle
  • Verdun 
  • South West
  • Ville-Marie 
  • Outremont 
  • Mercier-Hochelaga-Maisonneuve
  • Montreal West
  • Côte-St-Luc
  • Town of Mount Royal
  • Westmount​

Five other boroughs and three cities will have some of their discharge points used.

During the sewage dump, the city is asking citizens not to go into the St. Lawrence River and not to flush certain items down the toilet.

Hover over borough or city to see what percentage of the sewage from each is to be diverted.

The City of Montreal is asking citizens to not flush these items in their toilets during the sewage dump. (City of Montreal)


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