What to Know A stretch of S. 5th Street between Chestnut and Walnut streets in Old City is severely undermined and will be closed until further notice.

The Philadelphia Water Dept. said there are large voids in the layers between the concrete and the fill layer.

The street runs beside Independence Hall and is a main artery to I-676 and the Benjamin Franklin Bridge.

A major artery in the heart of Philadelphia's Historic District is closed as workers worry about a potential road collapse.

The stretch of S. 5th Street between Walnut and Chestnut streets is "severely undermined" and will remain closed "until further notice," Philadelphia Water Department spokesman John DiGiulio said. The street runs beside Old City Hall, which is attached to Independence Hall, and acts as a major artery to Interstate 676 and the Benjamin Franklin Bridge.

Verizon workers were the first to spot the problem as they were digging in the area, DiGiulio said.

According to DiGiulio, a street usually consists of three layers: asphalt, concrete and a bottom fill — usually compacted soil or stone. As the Verizon workers dug, he said, they noticed large voids between the street's concrete layer and the fill, which prompted them to call the water department.

To prevent the possibility of a car collapsing into the street, the department made the decision to close off the stretch of road. "Eventually, something might have happened and we don't want that to be the case," DiGiulio said.

The usual culprit of such a problem is an issue with the sewer, which the water department first has to clean off before it can begin inspecting, DiGiulio said. The other potential culprit is the lateral line, which is the section of pipe that carries waste from a building and into a sewer.

If the cause turns out to be the sewer, the water department will be responsible for the fix. If it's the lateral line, then it's the property owner who will need to foot the bill, DiGiulio said.

DiGiulio didn't know who owns the surrounding buildings, but 5th Street runs through a section of Independence National Historical Park, which is part of the National Park Service.

Independence National Historical Park could not immediately be reached for comment.