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Flushgate a success but lacked 'social acceptability:' Denis Coderre

A City of Montreal report concludes the four-day sewage dump that spewed almost five billion litres of wastewater into the St. Lawrence River caused no long-term damage, however, an environmental group dismisses the report as "misleading."

Better communication to educate public needed, report on sewage dump notes

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Montreal's communication plan during the sewage dump included signs by the water, pamphlets and media interviews, but it could have been better, a report concluded. (Paul Chiasson/Canadian Press)

The sewage dump that spewed almost five billion litres of untreated wastewater into the St. Lawrence River over four days last November was a success, causing no long-term environmental damage and taking less time than expected, Montreal officials have concluded.

However, the project suffered from a lack of "social acceptability" caused by ineffective communication with the public, their report finds.

"There was lack of communication, and it's important to recognize it," Mayor Denis Coderre told reporters Wednesday.

"But we worked with science, with facts, with experts ... and the facts say that there was almost no impact," he added.

Support arches inside the sewage interceptors were badly deteriorated and had to be replaced. (City of Montreal)

Some of the conclusions of the report, available (in French) on the city's website [PDF]:

  • The water quality of the St. Lawrence River returned to normal four to 10 days after the dump ended.
  • The quality deteriorated in a 250-metre-wide corridor of the river up to 10 kilometres downstream from Montreal.
  • Uptake points for drinking water were not affected.
  • There was no change in the chemical levels of river sediments and plants.
  • No genotoxicity (the presence of toxins that can mutate living DNA) was detected.
  • The city got no official complaints from residents.

City scientists also exposed rainbow trout to different concentration of sewage over four days, and none of them died.

The report suggested that city departments increase their sensitivity to the "social acceptability" of projects to prevent the same level of public outrage that the dump incited.

It also said that better communication plans are needed to improve understanding of technical issues among the general public.

Aerial photos during the sewage dump shows the plume of sewage coming out of the McGill regulator pipe in Old Montreal. (City of Montreal)

Report unrealistic, environment group says

The report was dismissed as "jovial" and misleading by Fondation Rivières, a non-profit advocacy group for the protection of waterways.

It said the city overlooked the non-organic solid waste that was also dumped out.

While the city said that only three cubic metres of solid waste was fished out of the river — about the volume of a backyard jacuzzi — the foundation challenged that figure.

"[More waste] was carried by the current, and a good part will settle at the bottom of Lake St. Pierre, where the current is slower," said Catherine Huard, executive director of Fondations Rivières.

Huard said Quebec's environment ministry should have done its own independent report, and the the city should publish all the information from the project for public scrutiny.

The sewage dump was necessary in order to empty and repair a 30-kilometre-long sewage interceptor.

The dump, dubbed Flushgate, made international news for its immense scale: City officials had expected to dump 8 billion litres of raw effluent into the river, the equivalent of 3,200 Olympic-sized pools.

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