There's something rotten in Edmonton's Gold Bar Park.

Area residents and park users have been complaining about a noxious smell for years.

The culprit is Hydrogen Sulphide (H2S) gas emitted from the nearby waste treatment plant.

And while EPCOR and Alberta Environment have long considered it to be a simple odour issue, new evidence suggests there could actually be an adverse effect on people's health.

"For many years, the assumption was that it's ok because there was a park there and the city said it was ok, " said David Bennett, a professor of neuroscience at the University of Alberta.

David Bennett, a neuroscience professor and cross country skier, decided to test the air at Gold Bar Park after becoming concerned about the rotten egg smell near the waste treatment plant. (Supplied ) Bennett is an avid cross country skier who's been bringing his family to Gold Bar Park for years to use the trails.

His constant encounters with the pervasive rotten egg smell never sat well.

"Ever since I moved to Edmonton, it's been pretty obvious it's not a great location for cross country ski trails because it's sandwiched between a sewage treatment plant and the refineries on the upper end of it," he said.

Concerned about the health of his family, Bennett decided to perform his own air quality tests using a very sensitive H2S sensor.

He spent the last week of November 2014 monitoring levels several times a day, for an hour each session.

"I would walk along the trail until the peak odour and then measure the levels," Bennett said. "They basically came out the same every day at around 25 parts per billion (ppb) and every day exceeded the levels considered the guidelines for Alberta."

Those guidelines state Alberta's ambient air quality objectives for H2S are just 10 ppb for an hour.

Those levels were originally set to protect people with higher sensitivity like asthmatics and children in addition to helping control the disturbing odour.

"It's a toxic gas so it can accumulate to really toxic levels," Bennett explained. "In fact sewer workers have to monitor it because it can be really lethal."

Bennett wrote a report on his findings and submitted it to the Edmonton Nordic Ski Club last year.

He says that's when Alberta Environment became involved to verify the numbers.

This past winter, they put in a portable monitoring station for several months near the treatment plant.

"Their data basically confirmed my data and further told us that the bad wind days are low wind days when the pollution is trapped there," said Bennett.

Review of guidelines overdue

While he admits he's not an expert on environmental measurements, Bennett says he is an expert on understanding the impact of chemicals like H2S on the brain.

"We study spinal cords and neurons in my lab and it's very clear from my work that the body is very sensitive to hydrogen sulphide and it can be a health issue at very low levels," he said.

"The problem is the Alberta government really hasn't updated their long term health guidelines for many years."

He says the standard for hydrogen sulphide was actually set back in the early 1970s, and there's never been a clear statement from the government saying there's a health risk even at low levels - until now.

Earlier this week, Bennett received a letter from Health Minister Sarah Hoffman pledging to take action.

"This recent letter from Alberta Health finally makes some headway to them at least admitting and looking into the health risks of these low level, long-term exposures to hydrogen sulphide," he said.

"The letter basically says they do admit there could be a problem with these low levels."

Hoffman wasn't available for comment, but her office sent a statement to CBC:

"Alberta Health confirms it will be leading a scientific review of acute and chronic health impacts for substances like H2S – we expect this review to begin this summer. The review's results will be made available publicly upon completion."

In the meantime, Bennett says Alberta Environment has given EPCOR until May to reduce H2S emissions from the plant to keep them below acceptable levels.

"We knew EPCOR was supposed to reduce H2S, but we also knew they hadn't in the past and were unlikely to in the future because their position was it's just an odour issue," said Bennett. "But now we're making some headway into the government admitting that it could be a health risk."

Your nose knows

Bennett says there's an easy way to know if you could be at risk while in the park.

He noted all of the highest levels of H2S were recorded where there was a smell present.

"The actual problem is fairly localized to within 500 metres of the plant, depending on the wind direction. It's easy to use your common sense if it smells," he advised. "My sense of smell is around 10 ppb so I know if I smell it, it's exceeding. And I can easily ski along to another part of the trail where it doesn't smell and pretty much know I'm safe, right?"

Bennett's testing did find the air quality was the best in the park during the noon hour, although he couldn't explain why.

He suggests that might be the best time for people to work out in the area or choose to use Capilano instead.

"You have to be careful every day," he warned. "There is an obvious odour problem down there and no one can deny that. What we now know is that the odour problem can be a health risk."

The hope is all of this will lead the Alberta government to make changes that will ultimately make enjoying Gold Bar Park safer for your health, and more pleasant for your nose.