Could turning waste into aggregate save farmland from becoming gravel pits?

If approved, Wilmot Township may soon be home to a new gravel pit, which would be built on about 57 hectares of farmland despite resistance from local activists, but one Guelph, Ont., researcher says that turning waste into aggregate may offer an alternative to losing farmland in the future. 

Rafael Santos, an environmental engineering professor at the University of Guelph, is researching how to use products like recycled concrete, mining waste or residue from making steel as an aggregate alternative. 

He says it's not perfect — but it has potential. 

"There are still a lot of uncertainties," said Santos. "Whenever you try to replace a natural material that has been for many, many years optimized for a certain application, now you come in with something that is similar but not quite the same, it generates [some] challenges." 

He said they're still working on how much of recycled materials can be used, the recipe of the mixture, and how long it will last once applied.   

According to the Province of Ontario's interactive pits and quarry map, there are over 80 aggregate pits in Waterloo region that amount to approximately 3,122 hectares of land. That's over 5,900 football fields, but only 0.7 per cent of prime farmland in Ontario have an aggregate license.

The majority of aggregate pits in Waterloo region are in North Dumfries – the township has over 40. There are also pits in Kitchener, Wellesley, Wilmot and Woowich.

Current use of recycled aggregate 

Products like recycled brick and concrete are currently being used as aggregate, but Santos said applications are limited.  

"Basically what ends up happening is that with materials that are less certain, you'll find less resistance to use them for non-structural applications than for structural applications," he said citing examples like sidewalks versus apartment complexes. 

Waterloo region has rules for how recycled aggregate can be used. It can only be used for road base or subbase, and asphalt base, which would be under the surface of a road or asphalt.

Santos explained that the engineering of new forms of aggregate is still improving, and he hopes that as it does regulations will change to permit its use in more applications.

"It's an inherent issue with construction," he said. "There's always a big safety margin just because of the types of applications of these materials we're building, you know, bridges and tunnels and skyscrapers and so the safety margin has been put quite large."

"I think as more pressure builds on when old infrastructure needs to be taken down and recycled, I think they'll build pressure on finding more uses for it. As the science progresses and we understand better the durability and other factors of these materials, things will also move forward more."

Other options?

Mark Reusser, vice president of the Ontario Federation of Agriculture, says another alternative to converting prime farmland to aggregate pits would be to get gravel from somewhere else.

"All over Ontario wherever there's a limestone bedrock for goodness sakes, or glacial till on top of it," Reusser told CBC. 

"Is it more expensive perhaps to bring it a longer distance to where it's needed? It might be, but the only reason there's aggregate here in Ontario in the first place is because of the providence of the glacier that happened 10,000 years ago." 

Sharon Armstrong, a vice president with the Ontario Stone, Sand and Gravel Association doesn't think going long distances is the answer.

"We need balance because aggregate — to be environmentally responsible — has to be close to market," she said. "So that means that some of those sites are going to be on agricultural lands and we need to be able to take the aggregate out, have it close to market to reduce truck traffic, but then return that land to productive producing agriculture when we're done."

Rehabilitation

The Ontario Aggregate Resources Act makes it mandatory for aggregate pits to undergo "progressive rehabilitation"  as companies extract raw materials. That means farmland needs to be resorted back to a farmland, and companies must do it as they go along versus waiting until all the aggregate has been extracted. 

Reusser says that's a good plan — if followed through on. 

"In all the time that I have spent visiting sites, on tours by the [Ontario Stone, Sand and Gravel Association] … I have never seen a site that has been rehabilitated back to its original productive capacity. They don't do it," Reusser said.

"It's farmland. You take out the gravel, you restore it back to farmland. That's not being done. It's never been done. I question whether one can even do it."

There isn't a deadline for when a licensee must rehabilitate the land, which Reusser said he'd like to see. 

"For goodness sakes, farmland is a non-renewable natural resource," Reusser added. "If you treat it well, it is a perpetual resource in that it can continue to produce food forever if you treat it well. Aggregate resource is a one time deal. You take it out, it's gone forever."

North Dumfries Mayor Sue Foxton, said that her township is the third biggest aggregate producers in the province. She's also noticed that few aggregate pits are being turned back into farmland.

"Some of them are quite good at rehabilitating and do wonderful things," she. "But that's not the norm."

But Armstrong insists gravel pit rehabilitation is the standard.

"I would say it's 100 per cent or close to 100 per cent of any of the aggregate sites that have been licensed in the last 30 years will eventually be rehabilitated," she said.

"It's really important that all of the material be extracted because otherwise you're just going to have more sites," she added. "So it's really important that the site remain open until all of that material is gone, so that's the reason why sites stay open."