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NEW JERSEY
6-minute read
NorthJersey.com
Once called the Bergen-Passaic-Delaware Expressway, Interstate 80 in New Jersey was a $387 million mash-up of projects built more than 50 years ago.
One isn't working out.
In early February, a sinkhole 11 feet in diameter opened up along the eastbound lanes just west of the highway's Route 15 overpass. After the collapse, New Jersey Department of Transportation officials said they found 90 spots to check for possible instability or voids in the area. Weeks later, an even larger sinkhole opened there, leading to the full closure of the highway.
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State officials still don't know, or won't say, what exactly has caused the sinkholes. The extent of the problem is unclear, as is a lasting solution.
When was Route 80 built in NJ?
The stretch from Denville to Roxbury was built generally to parallel Route 46 through North Jersey as part of the Interstate Highway System conceived in the mid-1950s. The idea was to use the federal program and its federal dollars to carry Route 46's traffic through Dover, Wharton and other "bottleneck areas," the Paterson Evening News reported in August 1959.
The section appropriately started where Route 46 narrows from four lanes to two heading west.
S.J. Groves and Sons of Woodbridge built the stretch from Mount Hope Road to Route 15 for $5.5 million, The Herald-News reported when it opened in fall 1959. The 3.7-mile section where the sinkholes have appeared, running from Route 15 to Howard Boulevard, opened a year later, in fall 1960. The state Highway Department awarded that $6.7 million contract to George M. Brewster & Son of Bogota, then Bergen County’s largest road contractor and a key builder of the New Jersey Turnpike, the Paterson Evening News reported in May 1958.
George M. Brewster, raised in Alpine, was a county freeholder who became a four-term county sheriff in the early 20th century. His son William J. Brewster later took over the company, which became Bogota's chief taxpayer before it eventually broke up. How it gained its prominence was questionable. In 1938, for example, the company was one of more than a dozen accused of conspiracy to defraud the government by fixing the price of road materials.
Other accusations hurled at various times against the company included breaching soil removal contracts and receiving favorable road construction contracts from the county. The company also received a 25% tax break from a lax county assessor, had its principal take payoffs from at least one union leader and gained an excessively large contract from the Passaic Valley Sewerage Commission in the 1950s that included $355,000 for equipment never used on the job, various newspaper reports said.
Story continues below map of former mines in New Jersey.
What is under Route 80's lanes?
The problem, however, may have far more to do with how and where the highway was built than by whom. Decades before the construction, Wharton was an iron mining town. Its mine district follows a linear trajectory cutting northeast from Mine Hill to Mount Hope.
Dozens of mines were dug there. Some were short-lived and never amounted to much. Others cut more than 1,000 feet into the fault-laden ground in search of iron-bearing magnetite amid belts of dense gneiss. New Jersey's iron mines may be long closed, but development in the northern part of the state continues to run up against the effects of past mining, said the 2024 New Jersey State Hazard Mitigation Plan.
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Subsidence remains a concern, as some abandoned mine locations and their associated shafts, openings and entrances are mapped inaccurately, the plan said. Others have been improperly filled and capped, a situation potentially made worse by the considerable seismic activity in the Tewksbury area in 2024. Roads and buildings have been constructed on or near these sites, adding to the risk, the 2024 plan said.
The state Department of Environmental Protection's GPS-based mapping system pinpoints the location of the Mount Pleasant Mine as south of the highway and west of Route 15, directly under the Avalon Wharton housing complex, which lies just to the south of the sinkhole zone.
A 1924 map complete with underground mapping from the local Replogle Steel Co. and old U.S. Geological Survey records placed the mine's primary shaft in that general area, with underworkings to the southwest and northeast that are hundreds of feet below the highway, down to below sea level. Most of the ore was extracted northeast of the shaft before it closed in 1896, and the shaft itself had "caved" by the time Interstate 80 was constructed, according to survey records from 1958, when the highway was being built through Wharton.
DEP officials have marked the modern geographic information system maps "authoritative," but metadata warns that the map last updated in December 2023 is not verified by DEP officials and is it not authorized or endorsed by the state.
Beyond the questionable accuracy of even modern maps, none are thought to include all the shaft openings, test pits, entrances and even entire mines that were constructed in New Jersey's history as a mining hotspot before westward expansion. Mines are scattered throughout North Jersey’s Highlands, but records — especially those predating the mid-19th century — are often unreliable, said Alexander Gates, a Rutgers-Newark geologist.
Gates said he hasn’t studied Interstate 80's sinkholes specifically but believes the region’s mining history is a likely factor. Towns and oversight officials may have required mapping, but early shafts were lit by candles, and compasses were mostly useless due to magnetite in the rock. As a result, mine tunnels may not run in the expected directions, and older shafts could be closer to the surface than previously thought.
“Miners followed the veins,” Gates said.
New Jersey's history of mining
North Jersey’s rock is particularly hard, but if a mine shaft is near the surface, constant vibration from traffic could trigger a collapse, Gates said. Officials at the DEP would not comment on the sinkholes' possible connection to the area's mines and directed questions to the Transportation Department, which did not respond to questions about the suspected cause of the sinkholes, whether it be mine collapse, construction flaws or a combination of those and other factors.
Officials with the state Geological and Water Survey, a division under the DEP umbrella, in the past have said the area's deep underground mine tunnels and voids are generally safe, apart from shaft openings and entrances.
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There have nonetheless been collapses before. In the 2000s, underground voids associated with the White Meadow Mine in nearby Rockaway Township caused collapses under a public roadway and a home, requiring the use of a boulder-and-concrete matrix to cap shafts and low-mobility grouting to fill voids, local records show. In that case, microgravity geophysical surveying and test drilling helped look for voids, state records show.
In the past 50 years, Rockaway Township and other towns, such as North Arlington and Mine Hill, have spent hundreds of thousands of dollars on remediation, state records show. The problem is not a small one, as nearly 600 abandoned mines — including copper, graphite, iron, lead, mica, manganese, sulfide, uranium and zinc — have been identified in North Jersey. Most are concentrated in Morris, Sussex, Warren, Hunterdon and northern Passaic counties.
The existence of the mine infrastructure in the Wharton area also caused other complications for George M. Brewster & Son Inc. Before Interstate 80, there were well-established transportation arteries to contend with. The company had to build the highway over North Main Street in Wharton, the old Mount Hope Mineral Railroad and Route 15. Retaining walls were built to bolster short-decked spans over the obstacles and hold back the massive amounts of fill used to build up Interstate 80 between North Main Street and Green Pond Brook, a tributary of the Rockaway River, on the other side of Route 15 to achieve the elevations needed to make the crossings.
On Thursday, Timothy Bechtel, a senior geosciences professor at Franklin & Marshall College, told NorthJersey.com that water is a likely factor in North Jersey’s sinkhole problem, pointing to precipitation or leaking underground pipes as common causes. Sinkholes like the ones that opened along Interstate 80 are “usually related” to these conditions, he said.
Past satellite images of the area where the sinkholes have formed show a grass-filled median at the turn of this century. Today, roughly 25 years later, the median between the old railway and the brook is rocks and shrubbery, a clear sign of erosion.
Gates said that if runoff were the cause, however, the ground would likely bow before caving in. He said the way these sinkholes have formed suggests that abandoned mine shafts are to blame. That could be an issue looking west of Wharton on Interstate 80, with more known mining zones near the highway in Roxbury, Mount Olive, Byram and Allamuchy. The nearby Huff mine is also right at the interchange of North Main Street and Route 80 in Wharton on the DEP's geographic information system map.
Staff writers Matt Fagan and Philip DeVencentis contributed to this story.