Radon is a naturally occuring radioactive gas released by the breakdown of uranium in soil in rock. And yes, you guessed it, Ottawa sits on above average radon desposits.
Radon gas enters homes by seeping through foundations, particularly through foundation cracks, sump pits, floor drains, pipe penetrations, and other openings that allow higher concentrations of radon to accumulate indoors.
Even if you have no openings or cracks in your foundation, radon levels can still be found in your basement.