DELAWARE COUNTY, Pa. (CBS) — Once again, an unusual odor has been wafting across parts of Delaware County. Investigators on Monday are working to figure out what it is and where it’s coming from.

A mysterious and stinky smell is causing some people to take a double sniff when stepping outside.

“It’s like a sulfur, smokey,” Glenolden resident Terry Pelham said. “As soon as I got out of the car I could smell it.”

Delaware County Emergency Services received more than a dozen calls about the odor, stretching from Tinicum to Glenolden, Lansdowne and even Upper Darby.

“Something from the creek or something or maybe from the sewage,” Glenolden resident Michael Szymanski said.

“It was overwhelming. I was afraid to smoke. I was like, where is this coming from? I literally thought the gas main had broken,” Glenolden resident Diana Delaney said.

Authorities still don’t know the source of the stench but they say it’s consistent with previous odor problems in the area.

“I smell stuff like that all the time,” a resident said.

The Odor Investigation Task Force is helping to figure out what’s going on. It consists of agencies from Pennsylvania, New Jersey and Delaware.

“It’d be nice to know what it is,” one person said.

Whatever it is, the Department of Environmental Protection is also trying to figure out what the smell is.