Saint-Hyacinthe, Que., is trying to fix its smelly water treatment plant problem — and it's costly

The City of Saint-Hyacinthe, Que., is putting a moratorium on all new construction near its water treatment plant in an effort to spare potential future residents from the foul odour that's been emanating from the plant for years.

Alain Leclerc, who lives a few hundred metres from the plant likens it to rotten eggs. Others are more blunt; it smells like excrement, especially on hot summer days.

"Everyone in this area learned a new word: H2S," says Leclerc, referring to hydrogen sulfide, a gas produced by the degradation of organic matter such as sewage.

Leclerc says the odour doesn't always reach the house by the Yamaska River where he lives with his wife. 

"But on days when the wind is [blowing] in our direction, it's really disturbing. We almost can't go outside, it's really not pleasant," he says.

City officials revealed at a public meeting on Sept. 10 that the concentration of hydrogen sulfide in the area surrounding the plant is 10 times higher than what is permitted by Quebec's Environment Ministry which is 4.3 parts per billion (ppb)  over a period of four minutes.

Coun. Claire Gagné doesn't want any more residents to be inconvenienced by the odour, she told Radio-Canada.

She said around 700 residents already live in the affected area.

Although hydrogen sulfide can be toxic at high concentrations, public health officials say that's not what's happening in Saint-Hyacinthe.

"This is really a situation where people are dealing with a nuisance and not toxic effects on their health," public health specialist Dr. Julien Michaud-Tétreault told Radio-Canada.

He specializes in environmental health and health risks, and his team was called on by the City of Saint-Hyacinthe to analyze its gas emissions.

"Some may experience stress, fatigue, nausea, stomach aches. Some might complain about experiencing perturbed sleep so it's not benign either as repercussion," he said.

Hydrogen sulfide starts generating serious health risks at a concentration of 100,000 ppb becoming deadly over 500,000 ppb, according to the US Occupational Safety and Health Administration.

The suspension of new commercial and residential development is in place until the end of 2027, as the city upgrades its water treatment facility, expands its capacity and hopefully solves its infamous odour issue.