Record rainfall sends raw sewage flowing into the Ottawa River

The view of the Ottawa River from Rideau Falls. (Brad Quinn/CTV News Ottawa)

The record rainfall that soaked Ottawa last Friday sent more raw sewage overflowing into the Ottawa River.

Environment Canada reported 45.5 mm of rain was recorded at the Ottawa Airport on Aug. 9, while 75.8 mm of rain fell at Ottawa's Central Experimental Farm and 83 mm of rain was recorded in Gatineau, Que.

Statistics on the City of Ottawa's website show 155,700 litres of storm water and wastewater overflowed the sewage system and into the Ottawa River on Friday.

Ottawa Public Health issued no swimming advisories at Mooney's Bay Beach and Petrie Island Beaches on Friday, Saturday and Sunday due to high levels of e.coli in the water.

It's the sixth combined sewage overflow reported by the City of Ottawa so far this summer. A total of 51.6 million litres of raw sewage has overflowed the city's sewage system and into the water so far this summer.

The biggest sewage overflow was on June 6, when Ottawa received 44.1 mm of rain. The city's website says 50.1 million litres of combined overflow mixture overflowed the system and into the Ottawa River.

On July 24, when Ottawa received 32 mm of rain, a total of 410,000 litres of raw sewage overflowed the system and into the Ottawa River.

The City of Ottawa built the Combined Sewage Storage Tunnel, designed to intercept and store surface runoff and wastewater until it can be treated at the Robert O. Pickard Environmental Centre and then returned to the Ottawa River. The $232 million project includes six kilometres of tunnels underground designed to stop sewage from flowing into the river during heavy rainfall events.

The underground Combined Sewage Storage Tunnel includes two tunnels: an east-west tunnel through the downtown core from LeBreton Flats to New Edinburgh Park, and a north-south tunnel along Kent Street from Chamberlain Avenue to existing infrastructure behind the Supreme Court of Canada building.

The city reported 11 sewage overflow events in 2023, with 464 million litres of raw sewage overflowing the sewage system. On Aug 10, 2023, 316 million litres of untreated water overflowed the system following heavy rain.