A northeast Calgary Dairy Queen owner is breathing a sigh of relief after technicians were able to locate the source of a mystery smell that had been plaguing his eatery since it opened three years ago.

"There is no smell, my misery is over," said an elated Sujad Bandali. "It's such a relief. I am so, so happy."

A smell of natural gas — described as being like rotten eggs — had been lingering since 2015 when Bandali first opened the Dairy Queen in the 11100 block of 14th Street N.E.

Hours before the grand opening, Bandali smelled natural gas near the entrance, so he called in the Calgary Fire Department and ATCO, but tests all came up negative.

The smell persisted, however, to the point some customers would complain, and more than one called the fire department to report a possible natural gas leak.

But each time, tests came back negative.

Desperate for an answer, Bandali put up a sign on the door last week assuring customers it was safe to go inside, and even offering a free Blizzard each week for a year to whoever could find the source of the smell.

Some customers suggested the smell could be from Freon coming from the cake freezer, but that was ruled out by the building's landlord. (Submitted by Sujad Bandali)

The response was swift, with people calling and emailing ideas from across Canada — and even as far away as Egypt.

"We had from one end of Canada to the other end, people were responding," said Bandali. "They were leaving us voicemails and emails. Our phone hasn't shut off, we finally had to modify the message. We almost had to hire a full-time person to answer the calls."

ATCO crews went back to the store on Tuesday to do another check — their third in three years — but again came up empty handed.

Then one of the technicians got the idea to do what's known as a "dead check."

"Essentially what it is, is you turn off everything in the building that uses natural gas, then you can confirm if the meter is still turning," said Ryan Germaine, ATCO's vice-president of operations for the Calgary and Edmonton regions.

"If it looks like you're still using gas, it's possible you have a small leak in the building somewhere."

That was done Wednesday morning and a small leak was detected in the building's ceiling.

"I would say this case is quite unusual," said Germaine. "Credit to the individuals who were there, they took multiple steps to do what they could to help figure it out. They didn't give up."

Because natural gas is colourless and odourless, an additive is put in to give it a distinct smell.

Natural gas is also lighter than air, which added to the difficulty of finding the leak in the ceiling, said Germaine, adding ATCO receives about 20,000 calls per year of possible gas leaks in Alberta.

Bandali said he's just relieved the smell is no longer there.

"Finally, I proved it to everybody, I was not losing my mind," he said.