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Nanaimo reviews stability of former mines
For 100 years, miners chased coal-rich seams beneath the Harbour City in search of black gold, carving a virtual honeycomb of underground tunnels.
Now, decades after the hunt was abandoned, the City of Nanaimo is proposing its first proactive and “high-level” investigation into the stability of the underground network.
The new study – estimated at $50,000 – comes on the heels of the discovery of a two-storey-deep mine collapse and developing sinkhole beneath a south Nanaimo road. It was the first time city officials had encountered a mine that presented an immediate and “serious” safety issue, prompting plans to search for other dangerous and weakened tunnels, said Poul Rosen, the city’s manager of engineering projects.
The city is obligated to ensure roads are safe and “can’t ... knowingly allow these sinkholes to show up,” he said, adding the desktop study is potentially the initial step in a multi-phased project to identify and remediate high-risk mines.
A panel of experts would have to be hired to do the initial investigation, which is reportedly beyond the expertise of city staff members.
“We need to take a step back and see which mines are the biggest concern ... and prioritize which ones we should focus our attention on first,” Rosen said, adding it will be a very high-level and unique undertaking. “Right now we don’t know that much about the mines.”
“We have the maps and know where they are, but we really don’t know what their condition is.”
The city’s coal mining history started in the 1800s and by the time it ended, a maze of tunnels stretched from east Wellington to Protection Island and Cassidy. A seven-metre-long coal mine map at the Nanaimo Museum showcases the vast network and while it comes to no surprise to museum volunteer Norm Swanson that some structures are collapsing, he questions how the city will tackle its search for weakened tunnels.
“You would have to look at everything because the whole city is just a honeycomb ... you can’t pinpoint just one area as being more vulnerable than the other,” he said.
City officials have made no qualms about the challenge ahead, but say it’s necessary after the discovery of the coal hole on Pine Street.
If the city can find vulnerable mine shafts and tunnels before they collapse, it can prevent public safety issues and budget for remediation, said Mayor John Ruttan. The latest costs to repair a coal hole tallied close to $240,000.
“I think everyone understands there are mine shafts underneath Nanaimo, but no one felt it would represent a significant risk until [one] collapsed,” Ruttan said. “We have to make sure we do our due diligence.”
The next step – determining when the mines could collapse – will be the greatest challenge, according to Rosen. While there are structures that have likely already collapsed and present no concern at all, others have remained in the same condition as the day they were abandoned, he said.
“What condition are they in now in 2014?” he asked. “That’s where things get complicated. The subsidence risk potential over any given mine, that’s fairly straightforward to get a handle on. What you can’t say is when it will happen.”