BANGOR, Maine — Jerry Linscott doesn’t know where along the city’s 150 miles of underground sewers the next lightpost-swallowing sinkhole will be.

But on Friday, he checked one spot off the list: The line under Penobscot Street near John Bapst High School.

It’s an odd place, too, considering its age. The line was built in 1875, but its bricks shined bright red, almost like new, on one of the two computer screens Linscott’s eyes flicked between. It had no big inward bulges, no large cracks or seams, no cave-ins, and contained no debris.

“This is one of our older sewer lines in town, one of our better ones, actually,” the 32-year-old collection technician said as he sat inside a van on Friday and steered a remote-controlled camera up the underground sewer toward Broadway. “It’s in really good shape.”

Friday was likely a light day for the four-man crew. Assigned with the responsibility of scoping about 10 percent of the 150-mile system annually, the Sewer Department crew often gets called out to emergencies. But when they’re aren’t any, like on Friday, the crew looks for damaged lines that might need repair, or where collapses are likely, City Engineer John Theriault said.

The city aims to fund nearly $63 million in infrastructure projects during the next 15 years to stop raw sewage and contaminated stormwater from spilling into the Penobscot River and Kenduskeag Stream. And that’s just for the jobs it knows about — not the work that arises from emergencies or natural wear-and-tear.

With most of its infrastructure at least a century old, and some of it pre-Civil War, it’s not an exaggeration to say that sinkholes could occur along many roads or sidewalks in the Queen City. Officials know the older sections, but as with Penobscot Street, they really don’t know what they will find until they find it.

The scoping crew members “give us the information we need to know the condition of the sewer line and then they help us prioritize the project schedule to see what needs to be done,” Theriault said.

Driving the camera is “a stressful job,” said Lead Technician Jim Grant, a 54-year-old Glenburn man and the crew’s foreman. “At any time of the day you can get that machine stuck down there — and then you have to dig.”

Built by hand, one brick at a time, the Penobscot Street sewer lines’ masonry was done well. The bricks were straight. Water trickled along the bottom of the oval-shaped structure. The structure looked almost too clean, but that, Grant said, is deceptive.

Like the fired red clay, the white of the mortar between the bricks shined brightly through the monitor, but that was because the masonry hadn’t seen sunlight in 141 years. The sun bleaches bricks of color, Grant said.

These days, sewer pipes are not brick, but PVC pipe — as durable as brick but far less expensive, Grant said. Brickwork as fine as that under the streets would be far too expensive today.

Sinkholes are also expensive, like the one caused by an ancient wooden culvert’s collapse that swallowed a light pole and some paved walkway in November on the Bangor Waterfront and cost about $200,000 to replace. The culvert is part of the underground Davis Brook Storage Facility, which stores stormwater flows and sewer overflows from nearby Main Street and neighborhoods to the west.