The municipality of Beloeil and the Fondation Rivières took on a shared challenge this summer with the pilot project Beloeil en eaux-vives. More than 850 swimmers enjoyed the whitewater pool safely, demonstrating the swimming potential of the Richelieu River through a combination of sampling methods, including real-time water quality monitoring.
Beloeil: a challenge met
Water quality assessment, particularly during heavy rains, was a key challenge. Indeed, sewage overflows occur, making the water temporarily unsafe for swimming for several hours. Such overflows are common in older neighborhoods of cities like Beloeil, Montreal, or Paris, where the sewer system is combined, meaning it carries both rainwater and sanitary wastewater. These overflows cause bacterial contamination, which can be measured by analyzing the presence of fecal coliforms in water samples. The problem is that it takes between 3 and 5 days to know the coliform levels in the water. By the time the exceedance is discovered, it's already too late to close the location. So, what to do?
At Verdun Beach in Montreal, lifeguards are alerted whenever there is a sewage overflow upstream of the beach, and the site is closed until the water is renewed (between 24 and 72 hours). This method requires careful documentation of the impact of the overflow structures upstream and their influence on the swimming area. Unfortunately, this alert system was not available last summer in Beloeil.
The other option is to try to determine how much rain is needed to trigger overflows. This is what we did in Chambly, where, in the absence of an alert system, we conducted intensive sampling campaigns over two summers. This allowed us to establish, among other things, that when the total precipitation exceeds 26 mm over the past 72 hours, there are sewage overflows. This is one of the indicators used to decide when swimming should be temporarily prohibited.
In the case of Beloeil, the City had enough data to conclude that the water is normally of very good quality during dry weather, but it lacked enough data to understand the impact of overflows during rainfall. This is why the option of using a real-time rapid analysis device to quickly detect contamination spikes was chosen. This device, the ColiMinder, is automated (sampling, analysis, and data transmission) and provides results in 15 minutes, unlike traditional analysis methods, which require 2 to 3 days to produce results after sampling.
The combination of traditional data and real-time data from the ColiMinder contributed to the success of the first edition of Beloeil's pilot project. This is also the same method used by the city of Paris to analyze the water quality of the Seine during the 2024 Summer Olympics. Paris had just completed major work to reduce overflows, including a massive retention basin designed to reduce the impacts of rainfall on overflows, but the basin had not yet been tested.
Obtaining data quickly was crucial, especially as historic rainfall hit Paris just days before the opening ceremony of the Summer Olympics. To ensure the health and safety of the triathletes and open-water swimmers, a total of 6 ColiMinders were installed along the banks of the Seine to continuously monitor fecal contamination levels. Decisions regarding the organization of the competitions could be made by combining data from the devices with data obtained through traditional analysis, thus ensuring the safety of the athletes.
The ColiMinders are expensive devices to operate, and unfortunately, these analyses cannot replace traditional analyses, which are the benchmark for water quality.
Very rain-sensitive structures in Beloeil
There are 59 overflow structures in the sewer network operated by the Régie d’assainissement des eaux de La Vallée-du-Richelieu (RAEVR), which includes Beloeil. Of these structures, 30 are located upstream of the swimming area. Our analysis of historical overflow data since 2017 has identified 5 structures that consistently overflow, and these are the ones that need to be monitored.
Preliminary analyses unfortunately revealed that it takes very little rain in Beloeil to trigger overflows. Fortunately, even though the overflows are frequent, their impact on the whitewater pool is short-lived. In this area, the flow rate of the Richelieu River is relatively high, which accelerates the flow speed and provides better dilution of discharges, resulting in a quicker return to good water quality. In the end, the water quality at the whitewater pool in Beloeil was good for 25 days out of 30 in July.
The Fondation Rivières is currently analyzing all the data from the Beloeil pilot project. The results will be presented to the elected officials and will then be shared with the general public by the municipality within a few months. We will share the information at that time.
ColiMinder
The ColiMinder is an automated analysis device that allows for rapid measurement of water bacterial contamination, using enzymatic activity measurements of the E. coli bacterium to determine bacterial concentration directly in a sample. Due to the speed of the analysis time, the ColiMinder can serve as a first-alert system, with the ability to indicate sudden changes in water quality. The Fondation Rivières uses the ColiMinder to locate sources of contamination, as it has done in the past in Témiscamingue and for the L’Assomption and Châteauguay rivers.
However, the ColiMinder measures a different type of contamination. Indeed, the device measures the enzymatic activity of living cells of the E. coli bacterium, which may be accompanied by pathogenic bacteria for humans, but also of latent or "dead" cells, which accumulate over time (e.g., old fecal pollution). It measures different things. The correlation between traditional data and ColiMinder data is therefore difficult to establish and possibly inappropriate. Its usefulness lies rather in tracking the overall evolution of water quality and particularly sudden variations indicating a new pollution source. It remains necessary to rely on traditional analyses to assess the quality of bathing waters according to current standards.
