Beneath the streets of Minneapolis, a handful of tiny robots are on a mission to ensure the city’s underground pipes remain intact.
City crews regularly dispatch the tube-shaped rovers, outfitted with video cameras, to check on the status of sanitary sewers, averting potentially disastrous problems. But the city is also pursuing a three-year, $7 million project to take a snapshot of its less messy cousin – the storm sewer.
The city’s 560 miles of storm sewer collect precipitation from all corners of Minneapolis and funnel it to local bodies of water. The freeze-thaw cycles puts stress on the pipes, some of which date to the 1920s, causing cracks that can eventually create street-level problems.
A backup could cause a localized flood, for example, or a pipe crumbling can create a sinkhole in the road. It can even cause a mini-geyser under the right circumstances, as can be seen at startribune.com/a1965.
That’s why the city is paying outside contractors to hunt for fractures and debris. It’s the first comprehensive assessment of the storm sewer system in a long time.
“Without this data, we’d just go out and clean the whole system,” said Kevin Danen, a public works engineer. “And that’s not efficient. With this data, we can clean targeted areas.”
Cleaning can involve plugging fractures with a tubular lining, or dislodging debris with giant corkscrew devices and jet-propelled hoses.
On a recent morning, public works staffers demonstrated the underground surveillance process at the city’s Hiawatha Maintenance Facility on 26th Street.
Tethered to a large van, the rover itself is about two feet long with an LED light and camera adorning the front end. It has rugged rubber wheels to handle the wet, sometimes unpredictable terrain.
City staffers lowered the rover into a manhole while public works employee Andy Meyer, sitting in the van’s mobile office, watched a screen and used a joystick to maneuver it through a 12-inch diameter pipe — a process the city calls “televising.”
Meyer marks each fracture on the computer, which then gives each section of pipe a quality rating. The pipes are generally made of reinforced concrete, clay or PVC.
But the job isn’t done when all the pipes are televised, Danen said. Up next? Inspecting each of the city’s 36,000 manholes.