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Engineering Solutions: Leachate, liners, landfills, and learning

Engineering Solutions: Leachate, liners, landfills, and learning

September 24, 2019
Tim Lougheed
September 24, 2019
Teaser: 

Human beings have undoubtedly been throwing things away for as long as we have had things to throw. These ancient middens – the predecessors of our modern landfills – provide a treasure trove of artefacts for archaeologists, who sift through discarded items for clues to how people once lived.

Deck: 

Human beings have undoubtedly been throwing things away for as long as we have had things to throw. These ancient middens – the predecessors of our modern landfills – provide a treasure trove of artefacts for archaeologists, who sift through discarded items for clues to how people once lived.

Today’s dump sites may well offer up similar insights to future investigators, but they are already revealing a great deal about how our environmental sensibilities have evolved over the last 60 or 70 years. What were once little more than stable excavations to hold large amounts of bulk material have become meticulously designed containers that respect key topographical and hydrogeological features of the surrounding landscape. A crude philosophy that once deemed garbage to be out of mind as soon as it was out of sight has been replaced by sophisticated strategies for considering the complex physical interactions that might take place in a landfill over the course of many decades. The goal is not just to make our unwanted items disappear from view but to ensure that they do not remind us of their presence in some unpleasant way, perhaps by contaminating local soils or water sources.

Inspiration from disaster

The full scope of such unpleasant reminders became clear in the late 1970s when the impact of industrial waste dumping near Niagara Falls New York prompted President Carter to declare a state of emergency around an area known as “Love Canal”, which caused 700 families to be relocated and the closure of the adjacent school. This contamination catastrophe, and a number of others, marked a milestone in the way the American federal government came to regard the practice of placing potential toxic substances into the ground, which would subsequently be controlled by an entirely new body of legislation to deal with pollution before and after the fact.

The environmental tragedy at Love Canal also captured the imagination of Kerry Rowe, Canada Research Chair in Geotechnical and Geoenvironmental Engineering and professor in the Department of Civil Engineering, and set his career on a path quite different than he might otherwise have envisioned for himself. At the time, he was a geotechnical engineer at Western University, where he was contacted by a colleague who was studying a landfill near Sarnia, Ontario, that had been built in much the same way as the one at Love Canal. However, the Canadian site had not experienced the same problem because the soil surrounding the landfill  consisted of a natural clay.

“Although nobody gave much thought to it, this landfill actually had a natural lining,” recalls Rowe, pointing to the need for a barrier that can prevent a dump’s contents from leaching out in sub-surface water. “But because there had been no thought given to it, there was no leachate collection system — it was a bathtub that could overflow.”

Kerry Rowe: Engineering Solutions for Landfills

Kerry Rowe: Engineering Solutions for Landfills

Kerry Rowe, Canada Research Chair in Geotechnical and Geoenvironmental Engineering and professor in the Department of Civil Engineering, explains his ongoing research on landfill management and how he is developing techniques that work with nature rather than fighting nature.

"Although nobody gave much thought to it, this landfill actually had a natural lining,” recalls Rowe, pointing to the need for a barrier that can prevent a dump’s contents from leaching out in sub-surface water. “But because there had been no thought given to it, there was no leachate collection system — it was a bathtub that could overflow."

As he analyzed why this structure had worked and how it could still fail, Rowe began to wonder if there might be a better, more systematic way in which this essential piece of infrastructure could be planned and constructed. This inspiration became the genesis of his work for the past 40 years, which integrates natural environmental components along with engineering principles to improve our ability to safely discard materials with more confidence that they will not come back to haunt us.

Designing a landfill

Rather than view a landfill as a static entity –   little more than a hole in the ground – newer designs are conceived as being highly dynamic and undergoing long-term changes that might affect their performance. These changes are often driven by the movement of water, which makes the assessment of a landfill’s hydrogeology crucial to how it should be designed and constructed.

“Historically, you would have a hydrogeologist come in and evaluate a site and a civil engineer come in to design it,” says Rowe. “The civil engineer would not pay much, if  any, attention to the hydrogeology, but these two things are intricately linked, particularly in Ontario where we have a high water table.”

Such conditions make it possible to take advantage of hydraulic containment, where the external pressure of water from outside the landfill prevents any contaminants or leachate from escaping. Rowe and his colleagues in the field have devoted a great deal of effort to demonstrating the practical success of such transport mechanisms, which have already proved their value. By way of example, he points to the Halton landfill in the Niagara Escarpment, where no fewer than four years’ worth of study went into ensuring that the ongoing hydrological behaviour of the region was well understood before anything was built. 
Nor is such prior research enough to guarantee success, he adds.
“You have to design it not for what’s there today, but what will be there after you build the site,” he argues. “Depending on the size of a landfill, it will immediately begin to affect the local hydrogeology and continue to do so, as will any population growth in nearby areas served by the landfill. We are also realizing that the pace of climate change could alter conditions over the life of a facility, with seasonal temperatures and water flow patterns becoming significantly different over the next 50-100 years or more.”

Rowe with Governor General Julie Payette

In recognition of his pioneering research in geoenvironmental engineering, Kerry Rowe was invested as an Officer of the Order of Canada by The Right Honourable Julie Payette, Governor General of Canada, in November 2018.

Rowe with students examining a clay liner

Kerry Rowe along with graduate students Jiying Fan, Ti-Kang Li, and Farhana Jabin examine a clay liner in his lab in Ellis Hall.

Installation of a liner

The team works on installing a liner at the Queen's University Environmental Liner Test Site in Godfrey, Ontario.

Rowe with student assessing compression

Kerry Rowe and graduate student Ti-Kang Li assess the compression ability of a liner sample in his lab in Ellis Hall.

The team at the testing site

Students work on the installation of a liner at the Queen's University Environmental Liner Test Site in Godfrey, Ontario.

Inside Rowe's lab in Ellis Hall sit row upon rows of simulations testing the integrity of different types of landfill liners.
[Rows of simulations testing the integrity of different types of landfill liners]

Preventing leakage

Another innovation has been the development of geomembranes, long thin sheets of  plastic material that can line a landfill and enhance its ability to prevent the release of liquids or gases into the ground. Such liners have a similar net effect as a barrier to contaminants as natural clay but they have a finite lifespan determined by elementary physical factors such as pressure and temperature, which can eventually cause deterioration and ultimately lead to a containment failure unless the system has been designed to address this fact.

Much of Rowe’s research has focused on determining the service life of various geomembrane products, a pursuit that combines abstract modelling with some very rudimentary destructive testing. Tucked away in various corners of Ellis Hall on Queen’s campus are liner samples being subjected to the many different forms of abuse they would suffer in a working landfill, such as being crushed under heavy weights or simmered in warm water baths. As he stands in front of several primitive-looking stacks that simulate the effect a pile of garbage would have on a geomembrane, he emphasizes that there are no shortcuts in such experiments, which must regularly run for years at a time.

Testing technology

For further testing of this technology Rowe and his colleagues and students turn to the university’s landfill field station about 40km north of Kingston in Godfrey, where they can study the behaviour of a full-scale geomembrane installation. Here they have recorded daytime temperatures as high as 60C on the lining surface, which can create pockets filled with moisture that condenses when they cool overnight, a cycle that could eventually erode the soil underneath to create an escape path for liquid from the landfill.

As such findings have been confirmed, they are slowly but steadily making their way into regulations and engineering practices that govern landfills across North America and Australia where Rowe has acted as a consultant. However, these policies can still vary widely from one jurisdiction to another. That is understandable, Rowe acknowledges, as the conditions affecting a liner can also vary widely, from say a mining tailings pond in the geology of the American southwest to a municipal garbage dump operating in the boreal forest soil of Northern Ontario.

And while the toxic output of mines or factories are obvious hazards, Rowe cautions that what we send out of our own homes can be just as threatening.

“Sometimes it’s trace elements that make the difference, not high concentrations of something,” he warns. “We’ve looked at highly-acid mining solutions and they can be more benign than standard landfill leachate. Two of the most damaging things in standard landfill leachate are soap and common salt. It’s not horrible solvents, it’s soap and salt. These are things you don’t expect until you do the testing.”

Centres and Institutes

GeoEngineering Centre

Core research: 

The GeoEngineering Centre is a collaborative venture between 18 faculty members and approximately 100 graduate students and post-doctoral students led by Queen's University and the Royal Military College of Canada. Drawn from three different engineering departments at the two universities, the Centre's members are dedicated to innovation and advancement of knowledge in geotechnical, geohydrological, geochemical, geomechanical, and geosynthetics engineering.

Researcher Profile
Canada Research Chair in Geotechnical and Geoenvironmental Engineering

R. Kerry Rowe

Developing new guidelines and techniques for building waste-disposal sites that provide long-term environmental protection: this research will lead to the development of better methods for protecting the environment from contamination by waste.