TTC still looking for source of leak at College Station

An oily substance is seen dripping on the wall of a subway tunnel in Toronto on Tuesday, March 24, 2015. (Brad Ross / TTC)

Transit officials are still searching for the source of the leak the day after an oily substance poured into a tunnel, bringing Toronto's main subway artery to a halt.

Shortly after midnight on Tuesday, a TTC employee noticed some kind of liquid dripping from the ceiling of a tunnel under College Station. Transit officials were forced to shut down the city's busiest subway line, between Bloor and Union Stations, while crews scrambled to stop the leak.

The subway was reopened at approximately 1:30 p.m. on Tuesday, after firefighters applied 300 litres of grout to seal the area where the substance was leaking.

The oily liquid has been tested, but so far officials have not identified its source.

Lab results have confirmed that the substance was not gasoline or diesel fuel, TTC spokesperson Brad Ross said in a message on Twitter on Wednesday.

Ross said it seemed similar to transformer oil, hydraulic fluid, or lubricating oil, but more testing would have to be done.

Officials are still looking for the source, and Ross said it is not known how long the substance may have been in the soil. No spills of any kind had been reported within one kilometre of the area in the past two days, he wrote.

The TTC will meet with representatives of the City of Toronto and Ministry of Environment to determine how best to locate the source.

Officials continue to monitor the subway tunnel, but no issues have been reported so far, Ross said.