A mysterious odor returned to Delaware County over the weekend as residents and town leaders continue to investigate the source.

Several 911 calls were made from Brookhaven, Pennsylvania, Saturday morning reporting an odd smell in the air.

“About 8:30 yesterday morning,” Stan Warfield of Brookhaven told NBC10. “Not a natural gas smell. More like a petroleum smell.”

Brookhaven Fire Chief Rob Montella said his department is investigating but so far they’ve found nothing.

“When we get on scene it only lasts a short period of time,” Montella said. “By the time we get our monitors out it usually dissipates in 10 to 15 minutes.”

The odor was also reported in nearby Aston, Pennsylvania, in late October as well as in Ridley Township on Veterans Day last month.

“No one has been able to figure out where it’s coming from,” State Rep. Leanne Krueger (D-161) told NBC10.

Several oil and gas pipelines are located in Delaware County but it has not yet been confirmed whether or not any of those pipelines are the source.

“If there is a company that is polluting and not reporting what happened they must be held accountable,” Krueger said.

Brookhaven Mayor Michael Hess said he’s leaving no stone unturned and is mainly concerned about schools and senior centers.

“They gotta find a connection,” Warfield said. “Don’t know what it’s gonna be but it’s not a good thing.”

Rep. Krueger is asking for more investigative resources from the state. Delaware County leaders are also putting together a task force in case the odor returns.