Mining expert weighs in on I-80 sinkhole in NJ

WHARTON, N.J. (PIX11) -- Interstate 80 eastbound reopened Monday morning after being closed since Thursday because of a sinkhole in Wharton, New Jersey.

The New Jersey Department of Transportation confirmed the sinkhole was caused by the collapse of an abandoned mineshaft.

The abandoned mine is one of more than 400 throughout Northern New Jersey, which once boasted an active mining industry.

“Northern New Jersey had tremendous numbers of mines,” said Bill Kroth, a geotechnical engineer and president of the Sterling Hill Mining Museum. “We have copper mines in Bergen County. Passaic County [and] Sussex County had iron mines.”

The Sterling Hill Mine was one of two prominent zinc mines in New Jersey and was the last active underground mine in the state.

Kroth said he wasn’t entirely surprised to learn of the Route 80 sinkhole. The area has a dense concentration of abandoned mines and it’s unclear how all of them were sealed shut.

“A lot of the mines weren’t properly backfilled,” said Kroth. “And even if they are properly backfilled, soil settles, they get compacted underground by nature, by moving water - things like that - and you can create a void.”

Kroth said modern-day procedures for closing mines did not exist 100 years ago.

“The old standards are not what they are today,” said Kroth. “So nowadays, there’s a whole procedure step-by-step on what has to be done to make it safe, permanently.”

It’s unknown how or when the mine under Route 80 was closed, but Kroth said work isn’t finished, even though the sinkhole is filled. He expects engineers will take soil samples from the surrounding area to make sure other potential sinkholes aren’t nearby.

“If it was me, I’d be doing angular borings along the shoulder, going down and seeing what’s underneath just to be sure,” said Kroth. “It’s like doing a biopsy of the ground. You get out samples, you can see what’s in it.”

PIX11 News asked Kroth if homeowners in surrounding towns should be concerned about potential issues on their properties. He replied, “I wouldn’t lose sleep over it.”