What to Know Two sewer workers died while working 30-feet underground in Aldan, Delaware County, Thursday.

Two other workers couldn't get a hold of them before finding the duo unresponsive.

It isn't yet known what caused the deaths, fumes are being investigated as a possible cause.

Two sewer workers died 30 feet underground in Delaware County Thursday and what caused their deaths was not immediately known.

The deadly incident took place Thursday morning in Aldan Borough, Pennsylvania.

A four-person sewer crew from the Glenolden-based A to U Services Inc., was performing a dye test to the sanitary sewer line on Sycamore Avenue between Rively and Magnolia avenues.

Two of the workers, Daniel Cleaver and Matthew DiSands, entered a manhole at Sycamore and Rively. At some point Cleaver and DiSands lost contact with the other two workers who were about a block away. Cleaver and DiSands did not respond when the other workers tried to contact them, police said.

The workers then found Cleaver and DiSands unconscious inside the manhole at 11:16 a.m. and they called 911.

Fire rescue located the two men who were already dead and brought the bodies up, Aldan Police Chief Kenneth Coppola said.

One of the men is the son of a police officer in another Delaware County community, according to officials.

Investigators have not yet determined a cause of death but said the lack of oxygen and the presence of sewer gases are suspected.

OSHA and local investigators are working to figure out what happened though at this point they believe it was a tragic accident. The medical examiner was set to perform autopsies.

Investigators were focused on an open manhole with an orange construction cone next to it as they continued to search for clues.

Aldan Mayor Carmen Maniaci called the situation "heartbreaking."

"We are quite shocked this has happened today," he said.

Police said both victims are well known to the community and have close ties to law enforcement and first responders.