A Winnipeg couple is living in a government-owned house, managed by the Department of National Defence, that exposes them to potentially deadly radon gas at levels exceeding the government's own guidelines, CBC News has learned.

"They wouldn't put their family members in this house, so why would they put ours?" Lindsay Olafson said. "It's very disappointing and very unethical."

Olafson and her husband, who serves in the military, moved into the home in 2012.

Three years earlier, the department had discovered that the home's radon levels were five times the Health Canada guideline, and it performed some mitigation to bring the levels down.

But Olafson said they weren't told about any of this when they moved in.

CBC News arranged to test the Olafson home, and the result revealed a level of 481 becquerels per cubic metre — about 2½ times the government guideline for radon exposure.

"It's an awful feeling trying to fall asleep at night," she said. "My husband and I could get sick from this and possibly die."

Radon is a radioactive gas that seeps into homes from decaying uranium found in rocks and soil beneath houses.

Long-term exposure to radon is the second leading cause of lung cancer.

Mitigation does not always work

The Winnipeg couple may not be alone. Starting in 2007, the federal government began testing its buildings for radon and found that nearly four per cent have readings above Health Canada guidelines.

Some buildings have since been modified to reduce the radon levels, but the process hasn't always been successful.

Lindsay Olafson with radon test results

Lindsay Olafson reviews the results of radon testing on her Winnipeg home, which is owned by the federal government and managed by the Department of National Defence. (CBC)

Data obtained by CBC News on 489 affected federal buildings from 16 departments show at least six of those buildings went through radon mitigation that didn't bring levels below the guideline.

The federal departments responsible told CBC News the vast majority of the buildings have been mitigated or that mitigation and retesting were underway.

Some departments now need to go back a second time to solve the problem.

One residence used by the Canada Border Services Agency in Yukon shows an original radon reading of more than twice the guideline when tested, but two years later, that reading was still 366 becquerels per cubic metre​. More mitigation is planned.

An RCMP detachment in Doaktown, N.B., had a level of 1,438, which only dropped to 1,383 post-mitigation, but more work is planned for that building.

Dozens of buildings have not begun mitigation at all. Some are slated for disposal and some are no longer owned by the government.

Effectiveness of mitigation varies

The Department of Defence told CBC News it mitigates military houses using proven methods that include sealing cracks and installing a heat recovery ventilator.

The department's website indicates the ventilation unit would lower the radon level between 25 to 75 per cent.

Radon expert Bob Wood of Toronto said that in most cases his first choice wouldn't be a heat recovery ventilator.

"With radon being a radioactive gas in a home, we want to make sure that the system that goes in is simply the best and takes little or no maintenance," he said.

He adds that ventilators need weekly, monthly and yearly maintenance to ensure that the system is effective.

Health Canada agrees. Its own guide for radon mitigation states that continued effectiveness of a heat recovery ventilator depends on regular maintenance and that "dilution is expected to be able to reduce average radon concentrations to only about 50 per cent of the initial value."

Olafson said she wasn't told the heat recovery ventilator in her house was to prevent radon exposure, and at times she left it off.

"If they don't tell people what they are for, then what's the use?" she said. "Your house is supposed to be a safe haven, not a silent killer."

Post-mitigation testing not done

Some government departments provided full results to CBC News, including post-mitigation test results, while others either declined to answer specific building information or indicated they haven't done followup testing.

Health Canada's guidelines recommend post-mitigation testing and so does Wood.

"Days after the mitigation has been completed you are supposed to perform a short-term radon test to establish what the levels now are, to make sure that the system has been effective," Wood said.

Advice to people exposed to high radon levels

Dr. Ray Copes, chief of environmental and occupational health at Public Health Ontario, said nothing can be done about past exposure to radon, but workers can protect themselves by limiting future exposure.

"It's even more important for people to give up smoking where there are high levels of radon," he said.

"There's an interaction between radon and smoking."

Copes adds that workers have a right to know about hazards they are facing in the workplace.

"I would expect that if workers wanted to know what levels of radon were present in their workplace, and those results were available," he said.

The union that represents federal workers, the Public Service Alliance of Canada, told CBC News it will be advising its health and safety committees how to get the necessary information about past tests and how to get current tests done.

Many departments stated they've already passed on that information to their workers and health and safety committees.

Kelley Bush, head of Health Canada's national radon program, told CBC News in May the department plans to retest federal buildings.

"What we are going to do next is follow up and find out what was done from a mitigation perspective," she said. "And understand the percentage of buildings that were actually mitigated."

Olafson said that regular testing should be done in all military houses and that the department should fix her home's radon problem.

"My husband helps keep the country safe, and in turn [Canadian Forces Housing Agency] isn't keeping us safe," she said. "It should be fixed so we can live here safely."

The Department of National Defence declined an interview and would only say it planned further testing on Olafson's house in the fall of 2014.

Olafson said the military has not told her what it will do to fix her house.

With files from Joseph Loiero