The first thing you notice when standing outside the building at 350 Wentworth Street North is the stench.

There's no mistaking it — a putrid, acrid odor wafting outside, detectable from about 30 feet away.

It's the kind of smell that's unavoidable when you're cleaning up hundreds of barrels of toxic waste. That's exactly what's happening inside the former Currie Tar Products building in the city's north end.

After the burning in your nostrils, the next thing you notice is the for sale sign. "Heavy industrial. Three and a half acres," it reads.

Tests have found the barrels contained coal tar byproducts, industrial solvents and roof tar. (Adam Carter/CBC)

"I also like the 'beware of dog' sign," said Mitchell Gibbs from First Response Environmental.

"It died long ago."

Gibbs, alongside Andre Breberina, are leading a team that is disposing of 800 barrels of toxic waste that were discovered on the site behind a fake wall in April of 2013.

It's painstaking work. Crews had to pull out that wall brick by single brick, as to not damage anything behind it.

Mitchell Gibbs (left) and Andre Breberina are overseeing the cleanup at 350 Wentworth Street North. (Adam Carter/CBC)

Now, there are barrels strewn throughout the site, being prepped to be shipped out by workers in hazmat suits and masks. Those masks aren't optional — without them, the headaches would come. So would the nausea.

"You would just be overcome," Gibbs said.

First Response analyzed the material found in the barrels, and found they contained coal tar byproducts, industrial solvents and roof tar.

Many of the barrels were once hidden behind a false wall on site. (Adam Carter/CBC)

"It's one of the worst we've ever seen — definitely a large scale cleanup," Gibbs said. "There are carcinogens here that will just attack your body."

The Ministry of the Environment has ordered the removal of the waste on site, as well as an environmental assessment. The site has endured years of stalled cleanup efforts through various owners.

The building has changed hands three times in the past couple of decades, and each time the owners have ended up in tax trouble — in some cases owing hundreds of thousands of dollars in back taxes, fees and interest.

The provincial Environmental Review Tribunal signed off on a settlement agreement between current and previous owners of the site to clean it up last year.

First Response expects to be working for the next three weeks. (Adam Carter/CBC)

The property was originally a Currie Products tar facility, which went out of business in the late 1990s. Owner John Currie died in 2013.

First Response Environmental expects to be onsite for about three weeks, preparing the waste to be shipped off to a hazardous waste site in Sarnia — the only one of its kind in the province.

Breberina says it's impossible to know just how much the entire process will cost at this point.

adam.carter@cbc.ca