In-situ mines don't need large tailings ponds and don't create vast holes as do open-pit mines, so they are often described as more environmentally friendly—that assumption is not always the case
The results, which are from a University of Ottawa lab and are to be published August 29, suggest government should increase monitoring of oilsands plants that rely on steam injection instead of open-pit mining, said lead author Jennifer Korosi.
“It’s our hope that this study stimulates that kind of work.”
In-situ mining involves injecting high-pressure, high-temperature steam underground to soften bitumen enough that it can be pumped up. Most bitumen in Alberta is extracted using in-situ methods and they will be used in the majority of the industry’s future growth.
In-situ mines don’t need large tailings ponds and don’t create vast landscape disturbances as do open-pit mines, so they are often described as more environmentally friendly. The assumption had to be tested, said Korosi.
That became even more evident in 2013 when a Canadian Natural Resources site was over-pressurized and oozed bitumen to the surface, she said.
“There’s a pressing need to understand how in situ releases contaminants to the environment, because it’s going to be very different than surface mining. At the moment, it’s mostly unknown.”
Korosi and her colleagues took sediment cores from a small lake adjacent to the CNRL site near Cold Lake, Alta. The area has seen in-situ oilsands activity since the mid-1980s.
Their analysis found little trace of heavy metals normally associated with bitumen.
But the sediment cores revealed the presence of polycyclic aromatic hydrocarbons—a class of chemicals considered carcinogenic—beginning in 1985, about the same time as oilsands development in the area began. As well, the specific types of the hydrocarbons they found are closely associated with petrochemicals and not other possible sources such as forest fires.
“There are certain PAH compounds that we know are released by forest fires, from traffic emissions, and we don’t see those compounds increasing,” said Korosi. “We have a number of different ways we can fingerprint hydrocarbons to know where they’re coming from and consistently, the different metrics were suggesting a petroleum-based source.”
The lake sediments showed hydrocarbon levels grew steadily as development increased. They are now 137 per cent higher than in 1985, said Korosi.
The levels are still too low to have environmental impacts. But they are real—and growing—and raise questions about how they’re getting into sediments.
“We have sources of contamination around in-situ drilling wells that are unaccounted for,” Korosi said. “There’s a pressing need to understand where they’re coming from.”
She said they could be from pipeline leaks, leaky well bores, process water, groundwater or underground fault lines.
“It’s why we really need to understand what’s going on below the surface.”
The study area, with its history of surface leaks, might be an extreme example. But Korosi said there might be other “hot spots.”
“You don’t want to have to wait for bitumen to bubble over ground before you figure out what those hot spots are.”
The research, which is being published in the journal Environmental Pollution, was partly funded by the Alberta government’s environmental monitoring agency.