Enbridge says the pipeline and pumping station were safely shut down after the spill, which occurred Tuesday night.
It says the release occurred entirely within the pumping station and was contained on-site in designated catchment areas.
"There are no impacts to the public, wildlife or waterways," the pipeline company said in a release issued Wednesday.
"Nearby residents and businesses may detect a faint odour," it said, but added that air monitoring has shown "levels are well within safety limits."
Enbridge said a cleanup of the oil was expected to be completed Thursday, but there was no estimate for when Line 4 would be restarted.
The company said initial estimates put the volume of the release at approximately 1,350 barrels, although that was subject to change.
Meanwhile, all regulatory, municipal and provincial officials have been informed and an investigation is underway.