Montreal sewage spill proceeds and what are the implications!

Go back to main page

Montreal sewage spill proceeds and what are the implications!

Posted on 18 November 2015 by Nadia Koukoui
Posted in FluksAqua insights, Sewage dump, Utility management, Wastewater Management,


The newly elected government in Ottawa has given Montreal permission to proceed with a short-term release of untreated sewage, amounting to one third of the city’s total sewage production. The release will send an estimated eight billion litres into the St. Lawrence River.

Members in FluksAqua’s forum for wastewater managers have been following the issue for some time. In fact, a request for clarity on the best practices under consideration by the city of Montreal for the planned spill prompted us to take a closer look at this issue.

This #Flushgate saga has attracted much attention in Canada, and also worldwide, led by the public and fueled by community outrage, that is amplified by the media. How is it possible for a city to spill untreated sewage in this day and age?


The answer is not as simple as it might appear. The reality for wastewater managers is very different from what the public perceive. While there are many spills of untreated sewage in all regions of Canada, as well as other regions of the developed world, wastewater managers are working hard to reduce the effects, or to eliminate such spills.

There are a number of issues to be considered in assessing the merits of this decision. These include the depth of the assessment and consultation processes, the responsiveness of a mitigation plan to deal with aging infrastructure, and the importance of knowledge in managing competing interests.

The Montreal municipal government originally announced its intentions in 2014 to federal and provincial authorities, although it became public knowledge in September 2015. The municipal government argued the temporary dumping of untreated sewage was necessary because a new snow chute was needed. As well, the existing South interceptor needed repairs and cleaning of obstructions, to avoid potentially more serious overflows in the future.

After a series of protests, the municipal government had to suspend the planned spill. Quebec’s provincial government authorized the undertaking and imposed a rigorous supervision plan. However, near the end of the federal election campaign, the Conservative government withheld its approval and ordered an independent panel of scientists to investigate the potential impact of the sewage spill on the water quality and for the wildlife along the river, even though many of the most prominent university scientists and environmental engineers in Quebec had already added their voices to calm the public with reasoned arguments in favor of the Montreal solution.


In one of her first acts as the newly appointed Minister for the Environment and Climate Change, Catherine McKenna approved the Montreal plan while imposing further requirements to mitigate the impact of the spill. These requirements included:

  • Strengthening the city’s emergency management plan;
  • Improving the visual surveillance of the discharge plume;
  • Creating a more comprehensive cleanup plan for affected areas;
  • Monitoring the discharge’s impact on the river’s ecosystem throughout the spilling process, including before and after; and
  • Undertaking a comprehensive review of the process leading up to the city’s decision to dump the raw sewage.

The planned release of raw sewage started on Nov. 11. Although the municipal government had said the spill would not last longer than seven days, engineers were able to reopen the lower half of the South Interceptor only three days later on Nov. 14.

Media outlets reported that McKenna described the city’s plan as “far from ideal,” and noted the planned spilling was a balancing of risk between a planned release versus an accidental discharge arising from Montreal’s aging sewer system. Even so, McKenna also recognized the importance of consulting meaningfully with affected towns and suburbs as well as with specific stakeholders, such as the region’s First Nations.



The City of Montreal has said all along that the spill was necessary so it could complete essential infrastructure work including repairs to a key sewer interceptor. With the aging sewer systems in place around the world, temporary and ongoing dumping of untreated sewage continues to occur. Quebec still has 45,000 sewage spills every year, and other Canadian jurisdictions face similar challenges. Winnipeg, Manitoba, for example, has seen almost 185 million litres of raw sewage dumped into its rivers since 2004, and the province needs an estimated $4 billion upgrade to its system.

The lesson Montreal can offer wastewater managers worldwide is how to best manage such releases carefully to reduce their negative impacts. Using best practices in wastewater management, the expertise of scientists, engineers and technicians, and ongoing consultation with stakeholders are essential to protect the water environment.

Montreal identified the late fall as the best time because spawning season ends, and the cooler temperatures reduce the proliferation of bacteria. As well, the city’s water engineers say the flow rate of the river supports rapid dilution. The river flows an average at 7,000 cubic metres per second in the region, while the expected release rate will be 13 cubic metres per second during the one-time, maximum seven-day period.


The greater risk of damage caused by deteriorating infrastructure means wastewater managers have to make decisions that appear counter-intuitive to the environmental protection measures cities have implemented in recent decades. It is worth emphasizing that their job is to treat wastewater to the best of their facilities’ capacity.

In Montreal’s case, the city has also brought in protective measures such as restrictions against water activities, including fishing, kayaking and surfing, to ensure public safety while the dump is underway. There will also be additional monitoring of water quality to ensure public safety.

There were alternative options put forth, and considered, including the suggestion from Environment Canada’s panel of experts to pump the untreated sewage into special tankers. Two hundred tankers would be needed – at most there may be a total of 20 such ships available in Eastern Canada* – and there was no viable solution with respect to the disposal of the liquid sewage.

Montreal also faced an urgent need to build the new snow chute before the first snowfalls occurred. Further delays would have stressed the system, posing other challenges. If the panel of experts had included construction experts as well, the panel members could have identified alternative construction methods – ones adapted to active sewer conditions – that would have mitigated, if not eliminated, the need to spill the untreated sewage.

There are two lessons we can take from Montreal’s experience. The first is that releasing untreated sewage has become a very sensitive issue in the public eye, and the second is that careful planning with wastewater engineers and managers is not just an option when it comes to releasing untreated sewage into our water systems. We need to build on their expertise in relation to the most adapted construction, maintenance and repair methods, timing, monitoring and evaluation of the situation, so we can reduce the negative effects of such a release. As well, consultation with key stakeholders such as river communities, downstream municipalities and First Nations is critical to communicating the plan in advance. Ensuring the proper information is shared with all parties in a timely and comprehensive manner is needed for understanding the rationale of such dumping.


FluksAqua is an online community dedicated to fostering open discussion on the issues and priorities of water and wastewater management professionals globally. Managing the only website dedicated to sharing information for the primary benefit of the urban water facilities user community, the members of FluksAqua represent organizations and communities who contribute key indicators to measure and compare the performance of networks globally.

Join our forum where your peers who started the conversation on what the best practices for a planned sewage discharge are.


About the author

Nadia Koukoui is passionate about water, people and bikes. She actively supports the FluksAqua community of practice by engaging with members and industry partners.

To connect with Nadia, share your comments, feedback, or if you would like to suggest a blog topic you can send her an email her at

Nadia est une passionnée du domaine de l'eau qui s'engage activement auprès de la communauté de pratique.

Communiquez avec Nadia à pour tout commentaires, suggestions ou si vous êtes intéressé à partager un article de blogue.