This week, the province announced plans to renew its creosote monitoring program in Calgary's West Hillhurst neighbourhood for the next five years.

The chemical contamination originated from a wood preserving creosote plant on the south side of the Bow River that shut down in 1962 after 38 years in operation. The plant was located just west of the current Greyhound bus station in the West Village.

The creosote leached under the Bow River and the contaminated soil was walled off in the mid-'90s, but never cleaned up.

Larry Bentley, a University of Calgary geoscience professor, was a groundwater management consultant to the province on the contaminated area of the West Village when it was partially remediated in the late '80s and early '90s.

He spoke with the Calgary Eyeopener Thursday about the contamination and why cleaning up the mess for good isn't going to be easy.

Below is an edited transcript of that conversation.

Q. Do we even know where the creosote is now or how it's moving?

A. We have a general idea of where the creosote — the oily part of this contamination — is, but certainly, the specifics of the exact locations are not known.

Q. How does the creosote move?

A. The oily part, which is what we call free product, is denser than water and it will move along the bedrock down slope, like water runs down a driveway, of course very slowly. It also runs into the cracks and fissures within the bedrock.

So it's going down-slope and the down slope direction is to the north in this area

Q. Does it flow into the bow river or does it go under the Bow River?

A. It goes under the Bow River, some of the dissolved components will end up in the Bow River, but the oily part is going to go beneath the Bow River and then move north under West Hillhurst.

Q. Why does this matter? What's the danger?

A. There are two main health risks — if you are digging, like they were in Broadview [Road] back in the '90s, you can encounter the free product itself and then that has certain health risks associated with it.

But to the homeowners in the area, the biggest risk is through the organic compounds that have dissolved into the groundwater and then volatilized into the soil gases. The gases can seep into the basements and into the houses.

Those can have minor irritation to skin and lungs and things like that and in long-term exposures, they can be carcinogenic.

Q. Has creosote contamination been found on the north side of the Bow River?

A. [The CBC building] actually was one of the hot spots. There were three wells drilled there and each of them found oily product beneath the site. All along Memorial Drive, they've drilled a series of wells from west of 19th to east of 16th streets and there were either free product or traces or free product in the soil along there. And of course all the way up in Broadview they found it in 1991 while they were digging a water main.

Q. The creosote contamination has been spreading since 1962, is it even possible for the city to fully clean it up?

A. It's very difficult to clean up because the creosote may not even be moving now that the wall's been put in place, the source has been isolated and the creosote leaves a trail wherever it goes so it gets less and less and less and at some point it becomes stagnant and won't move any further.

But it's tricky to find because it's in these little cracks and crevices in the bedrock and so it's hard to locate. What you see is basically the result of the dissolved compounds in the groundwater to give you an idea of where it is.

It's extremely difficult to clean up completely because it's very tricky and hiding out in all kind of little recesses in the bedrock. In the the drilling programs they found it five metres below bedrock in some locations.

Q. Could you build on the south side of the river without cleaning it up?

A. I think it would be tough. I think there are engineering solutions — like how you can put positive pressure into basements to make sure gases are not leaking into basements. So there probably are ways to engineer the facility, you can immobilize the creosote so it's not moving around anymore.

But to completely clean it up is a tough prospect, although there are some modern technologies, very expensive ones, out there that seem to do a pretty good job of getting most of it.​

With files from the Calgary Eyeopener