How a tiny sinkhole may become a big problem at St. Clair County's airport

KIMBALL TWP. — Most days the crew that inspects infrastructure at the St. Clair County Airport doesn’t find much to be alarmed about on site.

But on the morning of June 4, something was amuck on the airport’s crosswind runway.

A 3-foot-wide and 2-foot-deep hole had unexpectedly appeared midway down its 4,000-foot length.

“It’s small for a sinkhole, yes, but for a runway, anything above 5 inches, we have to shut (it) down,” Airport Director Catie Fiore said during an interview on Friday.

Typically, the crosswind runway accommodates planes when they need to land at an angle versus head-on with the wind. That means it provides two extra directional options — and safer ones — for pilots.

Now, the primary runway at 5,100 feet long and 100 feet wide is the only option that remains. And Fiore said the airport — averaging around 2,5000 operations a year — may be seeing roughly a third of its business in areas like dolling out fuel affected by the shutdown as the county gathers resources and works with the Michigan Department of Transportation and engineering consultants to figure out how to address the sinkhole itself.

The tiny phenomenon is having a big impact.

And for the foreseeable future, giant Xs laid out in bright-colored snow fencing are marking the closure at either end of the runway.

How did this happen?

The primary runway was part of a massive $4.6 million rehabilitation that repaved it and installed new edge lighting in 2019. The crosswind runway, however, hasn’t been touched in decades, and while the runaways are subject to maintenance just like public roads, the last time crack-sealing was done was in 2022.

Soon after the inspection crews’ sinkhole discovery last month, Fiore said they determined a drain built during a 1990s expansion of the crosswind runway could be the culprit.

“We found the drawing that said there was a drain that was put underneath it,” she said. “And it looks very close to the drain.”

Fiore said pipe inspectors the following week televised the entire drain — a piece section of concrete infrastructure that has a 30-inch diameter and is 325 feet across.

The runway is 75 feet wide, and the sinkhole is off to one side, currently marked by cones and a metal cover. Fiore said they found “a void roughly 20 feet away from the hole,” where dyed water helped confirm a leak had traveled the distance.

“We don’t know how long it’s been going,” she said. “It’s one of those (things) where as much as I would like to say just fill the hole in, I don’t know what’s been compromised beyond just face value. Because had we filled it and not looked at that drain, this could have (happened again).”

What comes next?

Most major airport infrastructures have traditionally been federally funded at a rate over 90%.

But St. Clair County Administrator Karry Hepting referenced the sinkhole and potential cost concerns in her report before the county board of commissioners on June 20.

“Kind of a parallel path, we are working with the state on what we need to do on the needs assessment or the justification. Because as you may recall, our crosswind funding has been pulled,” Hepting told board members. “… So, depending on what happens in this justification study, this runway is no longer eligible for funding."

“The board will have to make a decision if this is a runway we want to continue to maintain at 100% of our cost or if we just want to take that runway out of service.”

Fiore said they may be able to utilize some three years of airport funding delivered in the $290,000 range in 2022, 2023, and this year as part of President Joe Biden’s 2021 infrastructure bill to help fill the cost gap.

For now, she said they’re waiting on a study to help determine if they’re “justified” or eligible to be reimbursed out of another funding pot.

Involved in the airport industry since her teens, Fiore on Friday referenced her own support the role the airport can play in the community — engaging with kids at events they host, such as its fly-in event that returns this August, and accommodating the everyday people utilizing their services.

Still, she said they hope to be able to address the crosswind runway soon.

Contact reporter Jackie Smith at (810) 989-6270 or jssmith@gannett.com.