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The equivalent of about 265 Olympic swimming pools full of overflow sewage entered the Ottawa and Rideau rivers from the City of Ottawa during last year’s above-average rainy season, according to a city report
The report, which was sent to Ontario’s Ministry of the Environment last month and released yesterday, said an estimated 730,000 cubic metres of sewage mixed with stormwater overflowed from 18 pipes between April 15 and Nov. 15. That represents two per cent of all sewage in the part of downtown served by combined sewers. Elsewhere in the city, storm sewers and sanitary sewers are separate systems.
The information was released as four probes continue into a massive 2006 sewage leak that spilled the equivalent of 350 Olympic pools into the Ottawa River that only recently became public knowledge.
Under normal circumstances, downtown’s combined sewers carry their contents to the city sewage treatment facility, near the Ottawa River in Gloucester. During heavy rains, however, the system is overwhelmed, and the city pumps storm water and raw sewage into the river through five pipes.
The city doesn’t directly measure most of the outflow, but relies on computer models to calculate the releases. According to the models, the Rideau Canal collector emitted 352,319 cubic metres in 46 separate overflows, making it the busiest site by far. Nearly 90 per cent of the 2007 overflow was from gates at the canal, the Rideau River, Booth Street, Cave Creek collector and Bolton Street.
Rainfall between April and November 2007 was slightly above average in volume and intensity. This normally leads to higher sewage overflows, according to the report filed by Barrie King, the city’s program manager for wastewater collection. The yearly average is about 405,000 cubic metres. A massive storm on July 19 and 20, with more than 85 millimetres of precipitation, accounted for 30 per cent of last year’s overflow.
The city is spending $25 million to upgrade the sewer system, including more real-time control at overflow gates to capture more sewage and reduce emissions into area rivers. Controls at the Rideau Canal and Rideau River are expected to be ready by the second half of 2009, said Dixon Weir, the city’s director of water and wastewater services.
The city’s 2009 budget should make further investments in protecting the Ottawa River, said Alta Vista Councillor Peter Hume, chairman of the planning and environment committee.
“It won’t happen overnight, but there will be a push to increase resources,” he said yesterday.
Mr. Hume said public willingness to spend tax dollars on sewers after years of debate has increased with news of a 2006 leak that saw 960,000 cubic metres of raw sewage and storm water expelled directly into the Ottawa River in one spill.
“It’s created an opportunity,” he said.
“We want to eliminate the effects of the City of Ottawa on the Ottawa River.”
An overflow pipe near 24 Sussex Drive got stuck open during a large rainstorm on July 31, 2006, and continued to dump raw sewage into the river until the problem was detected 15 days later.
The event went unreported to provincial environment officials for eight months and to senior city staff, city council, the public health department and the public for almost two years.
It offered a partial explanation for high E. coli counts at Petrie Island Beach in 2006. The federal and provincial environment ministries, along with the city, have launched investigations.