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City of Nanaimo monitoring honeycomb of former mines
The Harbour City’s network of underground coal mines could be slowly collapsing, according to Nanaimo city staff members.
Nanaimo work crews discovered a two-storey deep coal mine cave-in beneath the surface of Pine Street during preparation work for a sewer and water line replacement two weeks ago. They have temporarily closed the street because of the threat of a sinkhole and are investigating options to fill the void without hurting the stability of the mine in other areas.
According to city staff, this is not the first time the City of Nanaimo has come across a collapsed 19th century mine, but it is more extensive. Around 2006, city crews filled a small hole with cement that had broken through the surface after a collapse in the same area.
Susan Clift, the city’s director of engineering and public works, says the municipality believes a lot of the century-old mines are starting to disintegrate, leaving voids beneath the surface.
While most of the mines are on private property, it becomes a concern for the City of Nanaimo when tunnels are shallow and holes open close to the surface in public areas, she said. Caverns only a few metres beneath the surface have the potential to create sinkholes.
Old coal company maps and residents’ accounts of mining activity allows city workers to keep track of mines that need to be monitored.
Road maintenance crews check for signs of sinkholes, like hairline fractures and holes on road surfaces close to known mines, and city officials require drilling to ensure there are no collapsed mines near infrastructure work.
But the information is limited about the state of the mines beneath the surface and remediation is expensive, prompting the City of Nanaimo to only take action on problems it can see. With an anticipation there could be other mine collapses in the future, there are also questions about whether the province should start to bear the cost for helping to repair coal holes.
A representative for the B.C. Ministry of Energy and Mines told the News Bulletin abandoned shafts are covered by the Mine Act, but did not elaborate before press time on if or when the province takes responsibility for remediation.
“As we move forward with the mines, we have to deal with them ... there is not a plan to really deal with them now,” said Stephen Ricketts, the city’s construction manager. “It could be a provincial issue.”
The Harbour City is built on top of a honeycomb of coal mines that have a history of collapsing. Nanaimo resident Pendry Harris, 90, grew up in Nanaimo during the 1930s when a lot of the mines were starting to be decommissioned and recalls his father being ordered to tear down six of his stores on Nicol Street and Victoria Road because a mine had crumbled beneath them. A mine beneath Wharf Street also collapsed, causing the street to cave right in, he said.
“No one paid much attention because everybody in those days were coal miners, you know ... it was just one of those things,” Harris said. “[Mines] were close to the surface, so they’d collapse.”
Residents, like Harris, who have witnessed the early closure and collapse of some mines have been key in helping the City of Nanaimo document the potential state of coal mines. They’ve said, for example, that people went into the mines after they were decommissioned to rob pillars of coal – likely contributing to instability and collapse over time, Ricketts said.
The challenge is “we don’t really know what happened to the mines since then ... the mines could have collapsed [years ago],” he said. “Because it’s underground and none of it’s accessible, we can only deal with the things we find as we do investigations.”
A drilling exercise along Victoria Road and Pine Street earlier this month showed a shallow mine collapsed a couple of metres beneath the surface, creating an eight-metre deep void. City officials are now looking at the best approach to address it, but Ricketts said it will not be as simple as filling the ‘room’ with dirt. With the mine stretching down to the waterfront, the city has to be careful not to hurt the stability of the mine further down the hill, he said.
“We have a geotechnical engineer looking at it and we are formulating a game plan,” Ricketts said. “We’ve reached a point where we need to do something before we put heavy traffic and any sort of vehicle traffic over the road. It’s not thin ice, but we are being precautious.”
As for the rest of the city’s mines, Ricketts said municipal workers will continue to be careful and monitor the situation.