Sewage to flow directly into St. Lawrence for 8 days

Call it Flushgate 2.0.

More than 4,700 South Shore homes will flush their toilets straight into the St. Lawrence River over eight days this month so the Longueuil agglomeration can replace sections of a sewage pipe that carries effluent to a water treatment plant.

About 162 million litres of untreated waste is expected to be dumped starting Nov. 15, Longueuil said Thursday. That includes waste water from toilets, sinks, showers and commercial and industrial drains in an area that straddles Highway 20 and includes parts of the cities of Longueuil and Boucherville.

Residents of the area are being asked to use less water as of Nov. 15 to reduce sewage that ends up in the river. And Longueuil is warning the public to avoid contact with the river water south of Îles-de-Boucherville.

The dump is smaller than Montreal’s 2015 discharge. Dubbed Flushgate, it made international headlines.

Montreal poured five billion litres of effluent into the St. Lawrence as it carried out infrastructure repairs to one of its main sewage collectors. If Longueuil dumps 162 million litres as expected, its discharge will be about three per cent the size of Montreal’s.

In June, Longueuil discovered a leak in a 90-centimetre-diameter pipe at the bottom of the St. Lawrence. It carries effluent from mainland homes and businesses to a water-treatment plant on Île Charron.

It patched the hole but must now replace two six-metre-long sections of the pipe near the bridge part of the Lafontaine tunnelbridge.

The pipe will not be able to carry sewage for eight days during the work, which will cost $700,000.

Scuba divers working shifts that cover 24 hours a day, operating with almost zero visibility, will remove and replace the old sections of pipe, said Longueuil spokesperson Louis-Pascal Cyr.

The work will not affect the quality of drinking water in Longueuil or in other municipalities that get their water from the river, Cyr said.

Longueuil decided to do the work now because water levels are higher, and at this time of the year fewer people use the river and fish aren’t spawning.

Water quality will be tested before, during and after the work and riverbanks will be monitored, Cyr said. A system will be put in place to capture solid materials from the sewage.

“There is very, very little (environmental) impact on a long-term basis because the river has a very high capacity of dilution,” Cyr said.

After Montreal’s 2015 dump, the city said drinking water was unaffected in downstream municipalities. Water quality was back to regular levels within four to 10 days of the dumping. Fecal coliform levels there were 30 times the acceptable limits four days after the end of the sewage dumping, but back to normal six days after that.

Raw sewage is dumped in the river more often than people may think, said water expert Sarah Dorner, an associate professor at École Polytechnique. It happens when sewer networks and treatment plants are overflowing due to heavy rainfalls and snow melting, for example.

Dorner said governments should do more to prevent such unplanned dumps as well as planned ones.

“There’s a lot we can do to retain the water on the surface instead of having so much of it go to the sewer system,” she said.

“Anything that makes the city like a sponge. Tree-planting, for example, can be really good for capturing more of the rain before it lands on the ground.”

To avoid discharges during sewage system repairs, “long-term, it’s really a good idea to create more redundancy in these systems” so municipalities have more than one way to send raw sewage to treatment plants, she said.