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Watersheds of the Mille-Îles River – Update on the status of wastewater treatment systems

Watersheds of the Mille-Îles River – Update on the status of wastewater treatment systems

A new tool to capture sanitation performance in the Mille Îles River watershed

In 2020, Fondation Rivières achieved a first status report on wastewater treatment systems on the territory of the Mille-Îles Watershed Council (COBAMIL), which made it possible to identify issues for the 2017-2019 period.

Since then, new challenges related to wastewater treatment have emerged in the region. In particular, the development of a plan aimed at ensuring the protection of drinking water intakes as well as a craze for swimming at the new Berge des Quatre-Vents beach, suggesting a real need among the population for more of relaxation and refreshment areas along the Mille Îles River.

In response to these challenges, Fondation Rivières offered to update the situation report carried out in 2020 usingAuditEAU, a new tool that it developed to fully exploit data from the Monitoring of Municipal Wastewater Sanitation Works (SOMAEU). Thanks to AuditEAU, it is easier than ever to identify which sanitation systems are on track and those where sanitation performance is stagnating or deteriorating.

Mille Îles River, near Gagnon Island – August 2020


  • Production of an interactive online report for viewing monitoring data
  • Analysis and presentation of findings

Our methodology

Treatment plants
Overflow structures

The raw data from SOMAEU were obtained from the MELCCFP and the works divided into five study areas. However, these steps were carried out using AuditEAU, which greatly facilitated the use of monitoring data, leading to much more in-depth evaluations of the performance of wastewater treatment plants and overflow networks and structures on the site. COBAMIL territory.

Duration of the study

The evaluation of wastewater treatment systems for the period 2020-2021 took place from the beginning of October until the end of November 2022.



The treatment of ammoniacal nitrogen is not very effective in the Mascouche River sector.


There are three places where the intensity of spills per capita stands out from the rest.


The possible gains in phosphorus removal are relatively limited. Stations that exceed their discharge requirements have a low contribution.

There is an improvement for phosphorus removal in certain problem areas. There is also a decrease in sewage overflow frequencies in 2021, but this is due to low rainfall rather than improvements to the networks.

Our mandates for evaluating wastewater treatment systems

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