Driving over abandoned mines: Shocking map shows NJ is ‘Swiss cheese’

🚨A large sinkhole developed on Route 80 east in the center lane in Wharton

🚨Abandoned mines that caused an adjacent sinkhole in December could be to blame

🚨Old maps provide inaccurate information about the mines

WHARTON — As work continues repairing the second sinkhole in two months on Route 80, one geologist says abandoned mines in the area are affecting the interstate.

William Kroth, the executive director of the Sterling Hill Mining Museum, told New Jersey 101.5's Eric Scott that during the Revolutionary War there were 400 iron mines in northern New Jersey. The sinkhole on Route 80 is right over one of those mines but it's hard to accurately determine how deep it is or how many there because the maps are old.

A New Jersey Department of Environmental Protection map shows the Huff Mine in Wharton was active between 1855 and 1910.

"A lot of them have been lost, they're not that accurate. The ground is Swiss cheese, gravity never sleeps," Kroth said. "We hope that the mines don't collapse, but they are supported by timbers as the timbers get older, they rot and they lose their bearing capacity so we have a sinkhole develop. It's that simple."

Kroth says many of the mines around Route 80 were never capped but only brushed over and things like highways and buildings were constructed over them.

"And now we're paying the price for not properly taking care of the voids that we made in that area," Kroth said.

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Voids, organic material is bad

The mines being located near an interstate highway present a a delicate balance between safety and the ability to move traffic to find a long-term solution, according to Kroth. There is a process to determine the expanse of the sinkhole.

"You have to kind of take a biopsy underground by using a drilling rig. So you drill down and you take samples. You gauge the strength of the soil, where the water table is, if you hit any voids or organic material. Those are bad things," Kroth said.

The New Jersey Department of Transportation said a sinkhole opened up Monday night in the center lane while crews conducted boring tests on what started as a depression. It is 75 feet from the December sinkhole in the right lane and shoulder.

Transportation Commissioner Fran O’Connor said that repair work will continue 24/7 until the road is reopened to traffic. There was no timetable for the completion of the repair.

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