Two workers were found dead Thursday in a sewer manhole in Aldan, Delaware County, police said.

A rescue operation for the pair began about 11:15 a.m. after coworkers reported the two were unresponsive in the manhole at West Rively and South Sycamore Avenues.

Rescuers pulled both workers from the manhole around noon but the men, both believed to be in their early 20s, were pronounced dead at the scene, Aldan Police Chief Kenneth J. Coppola said.

The two were part of a four-man team from A to U Services in Glenolden, who were conducting dye tests in the sewer line, officials said.

A to U did not immediately respond to a request for comment.

The Delaware County Medical Examiner’s Office responded to the scene and is investigating to determine how the men died. Coppola said it appeared they may have been overcome by gas fumes.

The federal Occupational Safety and Health Administration also will investigate the workplace deaths.

“It’s a very heartbreaking situation we got going on here,” Aldan Mayor Carmen Maniaci told reporters at the scene. “We’re going to do our best to recover and move forward.”

There was no impact on utilities in the neighborhood.