In a press release at around 6 p.m. today, refinery officials said "surface water and silt, along with entrained oil" was spilled into Placentia Bay.
"This basin is used to collect storm water runoff from the facility and allow the separation of silt before the clean surface water is released into the Bay" the refinery said in a press release.
The refinery said personnel have stopped the release and are working around the clock to implement the valve repair and clean up the oily residue in the affected area, which is limited to the discharge location to the bay.
The Canadian Coast Guard, Environment Canada, and the provincial government have been notified.
Further details will be released as more information becomes available.