The regulator says 27,000 litres of crude bitumen were released underground on Jan. 3 at the company's troubled Primrose field.
But agency spokesman Darin Barter said the leak has been stopped.
"There was no release to surface," Barter said Friday. "There's no aquifers that have been impacted by this incident."
Barter said the release has been definitively attributed to a failed well casing, setting this leak apart from an earlier one in the same field last summer that also remains under investigation.
In that leak, more than a million litres of bitumen has so far seeped to the surface. The spill continues, although cold weather has slowed the amount to almost nothing.
CNRL has said the earlier leak was also due to a well failure.
"We don't necessarily share that view of the incident," said Barter.
The regulator is investigating whether the bitumen escaped through cracks in the rock above the deposit and was driven to the surface by high-pressure steam pumped underground to soften it before being extracted. The company has been ordered to reduce the pressure of the steam it uses.
The first leak remains the subject of a $40-million cleanup effort from CNRL.
Barter said there's no indication when the regulator's report on that leak will be complete.
There were also bitumen leaks at the Primrose field in 2009. The regulator concluded those leaks were at least partially caused by high volumes and high pressures of steam.
Mike Hudema with Greenpeace Canada said it is "incredible" that CNRL is still allowed to continue its operations.
"If the Alberta government is serious about protecting Alberta's environment, it has to pull CNRL's approval for their Cold Lake operations," Hudema said in a release.
"How many more spills will it take before we see real action?"
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