The work required to install an ozone disinfection system at the Jean-R.-Marcotte wastewater treatment plant could lead to greater discharge of wastewater into the St. Lawrence River. However, the City of Montreal assures that it will mainly be rainwater whose environmental impacts will be very limited.
The City has obviously learned several lessons from the flushgate from 2015, a story that had gone around the world. The executive committee awarded a $93.2 million contract to Pomerleau on Wednesday morning for the construction of two giant siphons as part of the installation of an ozone disinfection unit. This system will ultimately make it possible to substantially improve wastewater treatment for the entire island at the Jean-R.-Marcotte wastewater treatment plant.
This time, to avoid the mess of 2015 in terms of communication, the City took the lead in publicly presenting the possible impacts of the work. During the construction of these two siphons, the treatment capacity of the treatment plant will be reduced, which means that in the event of heavy rains and significant snowmelt, surplus water could be discharged. directly into the river.
A different scenario
According to the director of the Service de l’eau, Chantal Morissette, the situation will be very different from that of 2015, when the City had to carry out work in the southeast interceptor. At the time, 4.9 billion liters of untreated sewage had been dumped into the St. Lawrence River in four days.
This time, no interceptors will be closed and the Jean-R.-Marcotte plant will be able to continue to treat wastewater from island residents in dry weather. But its capacity will be diminished. “During heavy rain, we are able to treat up to the equivalent of three Olympic stadiums per day, but during the construction period, we will be able to treat up to two Olympic stadiums per day”, illustrated Mme Morissette. “But it will never be concentrated sanitary water that will be rejected. It’s going to be diluted water with a bit of sanitation and some rainwater thrown around the island”
In order to reduce the risks, the City has chosen to carry out the work during the winter season, a period historically not conducive to heavy rains and nautical activities, which will minimize the impacts. Thus, the first phase of the work will be carried out from November 2022 to April 2023 and the second, from November 2023 to April 2024.
All the same, 13 billion liters of “diluted” wastewater could end up in the river during the two work periods, which are spread over 360 days.
In 2015, the City had carried out numerous analyzes to measure the impact of wastewater discharges into the aquatic environment and found that the effects had been limited. “It is expected that the episodes of spillage of diluted rainwater during the work will not have a significant impact on the waterways around the island,” said Chantal Morissette on Wednesday.
A necessary evil
Discharges of wastewater into waterways are never desirable, but this time it is the lesser evil given the immense benefits that will result from treating water with ozone, believes André Bélanger, Executive Director of the Rivières Foundation. ” It’s inevitable. But the City is taking the necessary measures to avoid the consequences on the environment,” he believes.
The benefits of treating wastewater with ozonation are such that the risks are worth it, he says. “This work will ensure that we will be able to swim all along the north shore of the river between Montreal and Trois-Rivières. It’s major! he says.
According to him, Montreal is showing courage in this file. “The City was a little left to itself to do this. It is a risky and complex project. Usually, cities will choose less efficient and less expensive solutions for operations. »
Ozonation treatment will make it possible to more effectively treat wastewater that is discharged into the St. Lawrence River. In addition to eliminating fecal coliforms and destroying viruses, this process will remove a good part – from 75 to more than 90% – of emerging pollutants such as drugs, ovulants and antibiotics that end up in water. worn out.
When the ozonation project was announced in 2008, Mayor Gérald Tremblay mentioned a cost of 200 million and commissioning for 2013. The many pitfalls encountered mean that the cost of the project has now reached 696.2 million, specified Chantal Morissette. The commissioning of the new disinfection unit is scheduled for mid-2025.