The borough of Verdun is now taking action after a 1,500-tonne pile of dirt containing carcinogenic coal tar dumped on its shores stirred up questions.

How it got there -- and why residents didn't know about it until Tuesday -- are just some of the questions being asked.

“It's almost repulsive. With all the concerns we have in this day and age - with environmental concerns - to keep what we have beautiful, pristine, safe (is imperative),” said Verdun resident Angus Roberts, who spotted the pile of dirt while out for a spring bike ride

The pile is what's left over from excavation work on Lasalle Blvd.

The borough of Verdun said it wasn't illegally dumped.

Borough councillor Pierre L'Heureux said the decision to allow it traces back to the previous administration, but couldn't say how long it's been there and why they only found out about the possible contamination risk two weeks ago.

“There are so many works being done in the city. They don't tell the politicians all their works,” said L’Heureux.

The site is a former snow dump the environment ministry shut down due to the threat of contaminated water seeping into the river.

The dirt pile, however, was considered safe by city engineers because coal tar isn't water soluble, explained L’Heureux.

“It's authorized to put soil on it, and actually, they followed the protocol and put a plastic sheet underneath the soil and a sheet over the soil to make sure the substance, whatever it is, doesn't blow away,” he added.

On Tuesday, the plastic sheet was in tatters.

The borough said it plans to put up a fence, but some say the pile never should have been there in the first place.

“It should have been in Trois-Rivieres where they are equipped to deal with that kind of material,” said biologist Jean-Patrick Toussaint of the David Suzuki Foundation. “This is again quite of concern and we wonder why the minister of the environment was not aware of the situation and not acting on it.”

Toussaint also disputes the fact that coal tar can't contaminate nearby water.

“It will remain to the soil particles - but still with water there's always a little that will go through the soil particle with the sediments and that's what finds its way in the environment in the waterway,” he said.

The dirt pile is expected to be removed in the coming weeks; until then residents are urged to steer clear.