Hazmat crews were called to Tarentum after 44 people were evacuated from their homes on the 300 block of West Sixth Street.
Homeowners waited for hours after neighbors reported they smelled gas in the area, but were allowed back in their homes around 9:45 p.m. when crews deemed the situation safe.
Firefighters used gas detection meters to track down where they thought the leak started.
“It’s in the sewer system. Once it’s in the sewage system it will get in everyone’s house, and if your traps aren’t filled with water, that odor is going to come up through your traps and fill your house up,” said Mike Remper, assistant fire chief.
Allegheny County Hazmat crews were called to the scene to shut off valves to stop any potential leak.
The Department of Environmental Protection investigated the cause assuring residents that it was not gas, but just an issue with sewer lines. The lines are being checked, authorities said.