Large sinkholes could be more the norm as Minneapolis pipes age

As Jeff Berg bicycled past a small hole — 6 inches wide but much deeper below the surface — at a south Minneapolis intersection near his house Monday, he worried that more of the street could collapse when a car passes near it.

"You think, 'How big could this get?' " Berg said, near the sinkhole at 43rd Street W. and Pleasant Avenue S. "Is it going to open up and all of a sudden take up the whole intersection when someone drives by?"

Minneapolis has had a handful of major sinkholes so far in 2023 following the third-snowiest winter on record. Most notable is a large crater at the intersection of 27th Street and Girard Avenue S. that has shut down the road since its collapse April 9. Another small sinkhole opened at the intersection of 40th Street and Nicollet Avenue, which has since been filled with soil and surrounded with caution tape.

The 43rd Street sinkhole was caused by an abandoned storm drain system that collapsed, according to Angie Craft, the surface water and sewers director for Minneapolis Public Works. Below the small opening at the surface, the hole appeared to widen and spread out at least a few feet below the pavement.

The Girard Avenue sinkhole opened up when a 120-year-old sewer pipe collapsed. The heavy snowmelt this spring may also have led to the large sinkholes.

Calvin Alexander, professor emeritus from the University of Minnesota's Earth and Environmental Sciences department, explained that water can enter the soil through road cracks or manhole covers. The water can carry away the ground below the asphalt, creating a void below the street.

"We certainly saw a bump in the number of potholes this spring, and as some of them might have formed, coincidentally, near broken sewer mains or storm sewers," Alexander said.

Craft agreed that last winter's frequent freezing and thawing can "certainly" exacerbate the sinkhole situations.

The cause of the 40th Street sinkhole is still under investigation.

Craft said the Uptown sinkhole at 27th and Girard is expected to keep the road closed at least for a couple of months more before the Metropolitan Council and city workers finish repairs.

Craft did not know cost estimates for the three recent sinkholes, but she said major repairs can grow to more than $1 million. Depending on where the land and pipes collapse, it can vary whether it's the local government or a property owner's job to fix the sinkhole. The city could also decide to replace more of the pipes if necessary.

"Sometimes we might choose then to kind of do some further investigation and maybe repair a longer stretch since we're excavating," she said.

For Berg and his neighbors in south Minneapolis, he said the concern is how far they need to drive around the hole to avoid a similar fate.