The city doesn't know how much oil entered the sewer system on the west side at one of the waste water lift stations.
More than 8000 gallons of water that was contaminated to some degree has been collected and disposed off.
The provincial Environment department was immediately notified when the black liquid was discovered. City workers were continuing with the cleanup at the Lancaster Wastewater Lagoon.
The city says your drinking water is not at risk because it's a separate system.