NEW ORLEANS -- The state Department of Environmental Quality said Thursday that crews continue to clean up after a “slow leak” of diesel fuel from a million-gallon tank at the Sewerage & Water Board’s main plant drained into the 17th Street Canal.

The leak was first reported Tuesday night when people who live near pumping station No. 6 reported smelling diesel fuel near the facility, which sits on the Orleans-Jefferson parish border.

Crews later traced an oily sheen in the canal back to the S&WB plant. Fire Chief Tim McConnell said Wednesday afternoon it appeared the diesel came from the tank and somehow was able to seep out of a containment area designed to stop any fuel from making its way into the canal.

The New Orleans Fire Department on Thursday said it was "confident" the fuel came from that tank.

Neither the state DEQ nor the NOFD could immediately provide an estimate of how much fuel leaked into the canal.

Officials have said the fuel poses no threat to the city’s drinking water since that comes from the Mississippi River.

On Thursday, crews continued to vacuum any fuel they found and were pumping smoke into lines near the containment area to try to find out how it was able to leak into the canal.

McConnell, whose firefighters respond to incidents involving hazardous materials, told The New Orleans Advocate the tank in question hasn't been used in "eons." But if boilers in the plant ever lose their main source of power, the tank would serve as a backup fuel source, so it remains on site.