An unassuming mound of earth buried on the side of a quiet Toronto street for decades held a dark secret, but don't worry yourself too much, as this little-known radioactive waste site present since the '90s was recently carted off as part of a redevelopment project.

Up until a couple of years ago, you might have registered a few extra clicks on the Geiger counter when passing by what was known as the Passmore Avenue Low-Level Radioactive Waste Storage Site near Markham Road and Steeles.

What was until a couple years ago just a mound of landscaped earth in a sparsely-developed area of Scarborough is the product of radium contamination discovered at a housing development site on McClure Crescent in 1980 and again at nearby McLevin Avenue in 1990, remnants of radium recovery operations conducted on a farm at that site in the mid-1940s.

A drawn-out period of legal challenges and negotiations concluded with the federal government agreeing to buy back more than 60 residential and commercial properties in the Malvern neighbourhood across what would become known as the McClure radioactive site.

During the ensuing cleanup in 1995, the Low-Level Radioactive Waste Management Office removed roughly 16,000 cubic metres of soil from the McClure site, transferring 50 cubic metres of contaminated soil to Chalk River Laboratories.

The remaining soil was brought to the Passmore site and buried in a landscaped mound designed to look like a natural feature.

The 985 Passmore site as it appeared in 2009. Image via Google Street View.

It sat undisturbed for almost three decades before real estate investment firm Prologis acquired the site for redevelopment, constructing what is now known as the Prologis Tapscott Distribution Centre, which wrapped up construction in 2022.

A representative of the company tells blogTO that its new Passmore warehouse was built on a site that "was part of a larger clean-up effort that occurred more than 30 years ago."

The Prologis rep explains that, while soil stored on the site "was within acceptable limits for naturally accruing radium" and "was stockpiled on a membrane and capped on the Passmore site," the company opted to remove it for the construction

"While the site never exceeded the guidelines for naturally occurring radioactive materials, Prologis removed all the mound and the membrane, shipping it all to an authorized facility." they Added that "approximately 15,000 cubic metres of material was removed from the site."

Removal of the radioactive contaminated waste involved rigorous safety measures by Prologis, including commissioning tests of the mound and groundwater prior to their purchase of the site, which the company says was done to "validate the existing reports on the mound context and history."

"Tests were taken at the base of the pile to ensure the materials were fully moved off site as well as re-testing groundwater during construction as an added measure," explains the Prologis representative.

"Finally, tests were performed from three separate consultants, each concluding the same result — that the low levels of radiation are within the acceptable normal range of what is commonly found in naturally occurring granite rock formations in the immediate area."

So, if you're an employee at this new warehouse building and are just learning that your place of work is built on a former radioactive waste site, rest assured that authorities have deemed the land safe.