Ottawa sewage overflow in 2017 even more than future tunnel could handle
The combined sewage storage tunnel would not have prevented 9 overflows this year
A year of heavy rainfall led to the release of more than two billion litres of untreated sewage into the Ottawa River this year, far more than even a storage tunnel being constructed to mitigate the problem could have handled.
This year about 2.1 billion litres — enough to fill nearly 850 Olympic-sized swimming pools — was dumped into the river from the City of Ottawa, according to the city's data.
Annual overflow numbers have been decreasing in the last decade, according to Scott Laberge, the city's wastewater collection program manager. But due to an abnormal amount of rainfall, this year's overflow numbers increased dramatically, he said.
The heavy rainfall during three days this spring — May 5 to 7 — led to more overflow than the entire period between April 15 and November 15 the previous year, according to yearly historical overflows on the city's website.
To put this year's rainfall in perspective, consider the city's $232 million Combined Sewage Storage Tunnel project currently under construction.
Once completed in 2020, the tunnels will be able to hold up to 43 million litres of surface runoff and wastewater — as much as approximately 18 Olympic-sized pools, potentially mitigating sewage overflow during heavy rainfalls.
And yet, this year's rainfall would have exceeded the tunnel's capacity nine times during the year, including by 470 million litres during heavy rain on Oct. 29 and 30.
The size of the tunnel was increased 72 per cent during the planning stages in order to account for a predicted increase of rainfall due to climate change, according to Louis Julien, a senior engineer with the city's water resources department.
"If we had just used historical averages the volume of the tunnel would be much less," Julien said.
'All but extreme episodes'
While the Ottawa Riverkeeper is not pleased the annual record was broken this year, it commends the city for the investment into the tunnel project.
"When the system is operational in 2020, that should, in theory, help us eliminate all but the most extreme episodes," said Patrick Nadeau, Ottawa Riverkeeper's executive director.
Where the Riverkeeper says more work can be done is in keeping the public informed about when these overflows happen, Nadeau said.
The Riverkeeper has organized a letter-writing campaign to the Mayors of Ottawa and Gatineau, asking them to look into real-time reporting for sewage overflows to let people know when to avoid the river. So far, Nadeau said they have had no official response.
"People are using the river recreationally, and it's when they are using the river that they need to know these are happening. Not a day later, not a month later," he said.