Michael Luter says he wasn’t surprised when a sinkhole opened next to his house in Detroit earlier this year. Sure, his elderly next-door neighbor had to edge her car around the crater to get out of her driveway, but Luter, a former contractor, knows what it means to live with aging infrastructure.
“It was probably a sewer pipe that broke,” he explained. “When that happens, the dirt has to go somewhere. You could have put half a car in (the hole).”
In Detroit, sinkholes are practically an everyday occurrence. City officials said they were currently investigating more than 300 sinkholes, or cave-ins, as of late July.
What causes sinkholes in Detroit?
Sinkholes happen when empty space opens up underground and whatever was sitting on top caves in.
In other parts of the U.S. — even in other parts of Michigan — sinkholes are a natural occurrence caused by acidic rain eating into soft bedrock.
But in Detroit, sinkholes have more to do with the built environment. Our sewer and water systems, about a century old, are giving out.
Detroit’s sinkholes “are not natural,” said Mike Wilczynski, a former geologist for the State of Michigan. “They’re caused when you have a sewer collapse. When it collapses, the soil on top of it is going to settle in to fill in that void.”
Sewer collapses aren’t the only cause of sinkholes, but they’re by far the most common, according to Bryan Peckinpaugh, spokesperson for Detroit Water and Sewerage Department (DWSD).
Sinkholes can also be caused by problems with a gas line, problems with road construction or water main breaks.
Detroit’s water mains burst 80% more often than the North American average, according to a 2017 report.
“Take a pressure washer to sediment on your driveway, and it will blast it away,” said Alex Schultz-Spradlin, a civil inspector who previously worked for the City of Detroit. “The same thing applies to erosion from a water main break.”
Alan VanKerckhove, a retired engineer for the City of Detroit, recalled when crews searching for leaks by sound found a large leak in an intersection near downtown.
“There was nothing under the pavement,” he said. “We were amazed a bus or something didn’t (collapse the pavement and) fall through.”
How are sinkholes fixed?
To close a sinkhole, crews start by investigating the problem. Is the hole caused by a broken city sewer pipe or water main? Is a private sewer line or other utility the source of the problem? If the issue is with a city pipe, they repair it and fill the hole with dirt. Problems with private sewer lines can be fixed by many general contractors.
Are sinkholes dangerous?
Yes, though there are few news reports of serious injuries.
Sinkholes sometimes have warning signs. Witnesses who saw a large sinkhole open up on the westside told reporters that it was preceded by a crack in the pavement.
The danger of a sinkhole is not always related to its size, because they can grow quickly. Some can be big enough to trap a dump truck owned by DWSD (yes, that happened). They can also be tiny. “We got one yesterday that was probably the size of a half dollar coin,” Peckinpaugh said.
No matter the size of the sinkhole, Peckinpaugh recommended that people stay back if they see or suspect a sinkhole, and inform DWSD.
What can I do about a sinkhole?
Submit a complaint on the city’s Improve Detroit page. There’s an option to report sinkholes. You can also call DWSD at 313-267-8000.
You might have to call more than once. Luter said it took months and a TV news story for the sinkhole in front of his house to get repaired. That was a sewer break; water main breaks are usually repaired more quickly, within one to three days, Peckinpaugh said.
When reaching out to the city, be aware that some sinkholes, especially in alleyways, are caused by collapsed private sewer pipes. The repair of private lines falls to the homeowner, and the repair cost can run to thousands of dollars.
What can the city do about sinkholes?
Sinkholes would be much less common if the city’s water infrastructure was up to date. New pipes are less likely to collapse or leak.
Most of Detroit’s sewer and water pipes are more than 90 years old, Peckinpaugh said. In 2019, the city began a $500 million project to replace or repair dilapidated pipes over decades.
City engineers use specialized equipment to search for cracks and leaks in underground pipes. They plan to use the data to start fixing the most vulnerable pipes — unless a sinkhole tips them off first.