But industry and government officials responding to the Environment Canada study say it isn't conclusive and more research is needed before action is taken.
"It's going to take some more samples and some more estimates of variability to be able to differentiate what is and what isn't process-affected water," Kelly Munkittrick of Canada's Oilsands Innovation Alliance said Friday.
The alliance co-ordinates collaborative environmental research among oilsands producers.
"It's an indication that this technique might work, but there's a lot more work to be done before it's quantifiable."
But the scientist behind the findings said he's confident in his work.
"With some of the groundwater samples containing chemical profiles similar to tailings ponds, this is the strongest indication to date that process water is reaching the river system," said Richard Frank, lead author of the paper published in Environmental Science and Technology.
That should be enough for the government to start taking action, suggested Alberta New Democrat Rachel Notley.
"Slow down the expansion until they have found a way to stop the leakage that's going on now," she said. "Right now, there's no economic imperative on industry for them to do it."
Eriel Deranger of the Athabasca Chipewyan band, which lives downstream of the oilsands, said Frank's report should persuade the province to implement measures the First Nation has already asked for.
"We've been asking for six years for the government to make it mandatory that these companies put isotopic tracers into their tailings, so that when there is seepage or spillage, we can trace not just to the tailings, but to the tailings of a specific company," she said.
Nor is government forcing industry to do the kind of baseline studies on areas yet to be developed that would allow scientists to track changes, Deranger said.
Alberta Liberal Laurie Blakeman wants an inquiry, complete with power of subpoena, into why it's taken so long for tailings seepage to be addressed.
"It needs to be able to get to the bottom and answer that essential question — why didn't the government notice and why didn't they do anything?" she said.
Erin Flanagan of the Pembina Institute, an environmental think-tank, said the study should push the province to enforce regulations already in place requiring companies to clean up their tailings ponds.
"We need to govern on the precautionary principle," she said. "(The government) needs to take this seriously and there needs to be a response."
Still, Munkittrick advised caution, saying that Frank's paper is only one of a number of scientific attempts to tease out industrial contamination from chemicals in naturally occurring bitumen.
"There's a number of efforts looking at this fingerprinting," he said.
"We'd like to see them come together. If there is a good tool out there, we'd like to use it."
The Alberta government wasn't available to comment on the report, other than to say in a statement Thursday that the research isn't conclusive.
Frank acknowledged his paper is only a first step.
More samples need to be taken from a wider area and from more tailings ponds, he said. He hasn't yet been able to estimate the amount of leakage — although previous studies based on mathematical models have estimated as much as 6.5 million litres a day might be leaking out of a single pond.
Nor is there much understanding of the environmental impact of the seepage, said Frank.
"We don't know what potential impacts —if any — this could have on the receiving environment. Because the chemical mixtures are so similar to what we're seeing naturally, we don't know what those potential impacts could be."
Still, Frank's research should be enough to convince the government to put caution first, said Deranger. Many of the chemicals in tailings water are known to be highly toxic and carcinogenic.
"The big concern in Fort Chip has been the health. This study proves that things are actually happening."
The current response is similar to what the government has done previously when confronted with environmental issues, said Notley.
"What the government and industry are doing is part of a very predictable and long-used pattern. You spend as long as you possibly can denying, then, when you finally get to the point where you can't deny, then you delay.
"Then you spend decades, if possible, questioning the studies and saying, 'That's interesting, but what we need to do is more studies.'"
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