Oil and gas waste is leaking into four lakes in the Northwest Territories, according to a new study.

The waste piles, which are called sumps, were left behind decades ago during oil and gas exploration in the Mackenzie Valley.

The sumps were frozen into the permafrost, and today more than 200 of them dot the region. A recent study tested more than 100 lakes. 20 of which were near sumps. Researchers found four of these lakes had elevated levels of salts, particularly chloride, an important component of drilling waste fluids.

Ed Hoeve, an engineering consultant, says when the man-made sumps were created, they were seen as a permanent and frozen solution. But permafrost in the Mackenzie Valley is two degrees warmer than it was when the waste was frozen into the tundra.

"The Mackenzie Valley in general has experienced greater warming. Up until probably five years ago I think a lot of people would tell you that the Mackenzie Valley was experiencing the most warming in Canada," Hoeve said.

Now, the waste sumps are melting and are altering the chemistry in the lakes.

"Particularly small lakes that have sumps immediately adjacent to them, some of those lakes had very elevated concentrations of salts in them," said Steve Kokelj, a scientist behind the study published Thursday through Queen's University.

"I think we really need to revisit the whole notion of using permafrost as a waste containment medium. We know that the ground is warming and if a primary disposal objective is to freeze materials in the low Arctic, it seems that permafrost is not really a viable option," Kokelj said.

He says the warming trend is amplified by the industrial footprint.

Aboriginal Affairs and Northern Development says it has not yet read the report on the thawing sumps.