Millions of litres of sewage spilled into Montreal rivers

Though water quality has improved enough around Montreal in recent decades to spur plans to develop city beaches, 150 pipes still dump sewage into the the St. Lawrence River and the Rivière-des-Prairies during heavy rains.

During the worst spill in July 2013, the amount of fecal coliform measured in the water on the banks of Verdun was almost 20 times the limit considered safe for swimming.

The problem lies in the fact that 60 per cent of Montreal's sewer network combines waste water from drains and toilets with rainwater collected in the streets.

We have some catching up to do. There were decades during which almost nothing was done.- Chantale Roulea​, Rivière-des-Prairies-Pointe-aux-Trembles mayor

During heavy rains, when the island's sewer network reaches full capacity, valves are opened to allow water to overflow into rivers in order to prevent backups in businesses and residences.

The city says it is not able to estimate the quantity discharged into the river during overflows, however, according to figures from the city's waste water treatment plant, 99.3 per cent of sewage is treated.

Given that up to 76 billion litres of water  — the equivalent of  three Olympic Stadiums full — comes to the plant during a day of heavy rain, that 0.7 per cent spilled is potentially 530 million litres of sewage being emptied along the shores of the island.

No spill warning

The city does not publish warnings of possible contamination — even major spills into the river — which the Société pour vaincre la pollution environmental group says is unacceptable.   

"To have a beach in Montreal, it is imperative that the city make overflows public when they occur so people can safely swim," said the group's co-chair Daniel Green.

Monitoring Montreal's water quality

The city has a data monitoring network to survey Montreal's aquatic environment at various points around the island. They indicate that in 2013, these discharges would lead to closures at the sites of proposed beaches in Verdun.

The City of Montreal recommends waiting 48 hours after the rains to swim in the river, as strong currents carry contaminated water downstream.

The mayor of Rivière-des-Prairies—Pointe-aux-Trembles says the city is aware of the problem and is investing in solutions.

"[The city] has adopted a water plan and has goals for the next 10 years, including a $4.6 billion investment for upgrading our network. We have some catching up to do. There were decades during which almost nothing was done," said Rivière-des-Prairies-Pointe-aux-Trembles Mayor Chantale Rouleau, who is also in charge of Montreal's water dossier. 

The city says it plans to build several underground reservoirs to store excess water during heavy rains and prevent sewage overflows into the river.

In the mean time, the city says that if it does open a beach, it will close monitor the water quality will be necessary to ensure the safety of the swimmers.