Spring flood waters seem to have left something unusual to the cellar of the old Officers' Square building in downtown Fredericton -- heating fuel.

That’s surprising because the building has relied on electric heat for about 50 years.

The oil was found more than a week ago and it's shut down the museum that's housed there. 

The air quality inside hasn't been deemed safe yet, so Scott Brown describes what you'd see.

“So you'd climb down in there and there's a 200-square foot basement that would be underneath the building where the product was found,” said Brown, the manager of building services for the City of Fredericton.

The product is heating oil and the area where it was found -- normally, no one goes down there, even staff at the Fredericton Region Museum who occupy this building in Officers' Square.

An oily sheen was found on the surface of flood waters, but only after staff noticed a petroleum smell.

“It appears that it came with the ground water, so when the groundwater raised as a result of the flood, it looks like it came through the foundation wall,” said Brown. “It's an old rock wall foundation.”

Known as the officers' quarters when it was first built, the building that stands today has pieces that date back to the mid-1800s.

It was in recent years -- in 2016 -- when the province of New Brunswick sold the building to the city of Fredericton. The city says that in the late 60s and early 70s, it was completely converted to electric heat. They say there's no petroleum products whatsoever on site -- at least that they know of.

Oil wasn't found in the storm sewer or sanitary systems and nearby property owners say they haven't found any either.

Air testing resumed Monday and the city has hired a consultant to do some assessment work.

The Department of Environment has been notified and it said in a statement:

“The consultant and city have discussed their approach with our department, which includes non-intrusive surveys and some groundwater monitoring from existing monitoring wells in the area. This work is scheduled to begin soon.”

Said Brown:“We actually pumped the basement last year during the flood and there was absolutely no source of oil and … flood levels basically came to virtually the same height as what they were last year and the product appeared.”

Right now, everyone is stumped on the source.

In the meantime, the museum will remain closed until further notice.

It’s one more aspect of this year's spring flood that has caused so much anguish for so many people.

The museum is respecting the work that's ongoing and staying out of the space, even though, they have their annual general meeting this Thursday.

With files from CTV Atlantic’s Laura Brown.