Abandoned mines are on the minds of the City of Nanaimo staff as they update development guidelines for geotechnical reports and assessments.
Staff presented refreshed guidelines at a governance and priorities meeting Monday, May 13.
The update is a consolidation of two existing sets of guidelines related to geotechnical reporting documents prepared for re-zoning, development permits, and development variance permits. The update adds guidelines for geotechnical assessments above abandoned mine workings, including background information on historical mining, mining-induced geological hazards, risk of collapses, gas leaks and water contamination.
“It’s not unique to Nanaimo, but it’s a fairly specialized topic and, certainly over the years, we’ve seen practitioners from outside town coming in and not being fully aware,” said Carl Miller, senior principal engineer with engineering consulting firm WSP. “So this sets some historical context and background, so that things aren’t overlooked, because it’s a fairly specialized field.”
Miller said the current development approval process doesn’t consider some aspects of potential environmental impact over time, such as the effects of repeated freeze and thaw cycles or sea level change. He suggested engineering reports need to factor in long-term surveillance of environmental impacts and potential maintenance.
Local examples of the effects of time, weather, erosion and material deterioration include a sinkhole that formed along Old Victoria Road in 2023 and an eight-metre deep coal mine cave discovered under Pine Street in 2013 when exploratory drilling was done ahead of sewer and water infrastructure work.
According to city documents, abandoned coal mine workings lie beneath about 13 square kilometres of the city’s 93 square kilometres, plus another seven square kilometres of old mine workings under coastal waters.
Miller showed images of old mine shafts on Protection Island, including an opening to the shallow Fitzwilliam Mine and the shaft of a second mine that drops 200 metres below the surface. He also included subterranean images taken of the Old Douglas mine workings under Old Victoria Road and the Hudson Bay Company Free Level workings under Hecate Street that lie just five metres below ground.
“[From] Victoria Road down to Trans Canada [highway], a number of shallow workings are in a state of partial collapse,” Miller said. “You can see timber props that were holding the roof have failed. They transfer the load onto adjacent timer props. This is all actively happening right now.”
Coal mining happened in Nanaimo for more than a century from 1852 to 1964. The adoption of the most recent city plan included creation of the ‘abandoned mine workings hazards development permit area,’ which prompted the need for information about abandoned mine workings to be more readily available to the public, land owners, and developers, and ensures land owners are aware of abandoned mines and that geotechnical professionals are aware of information and recommended approaches around assessing the risks above abandoned mines.
Hazards when developing land above old mines, depending on the type of mine, can include potential for collapse, as well as noxious gases and contaminated water. Miller said WSP has worked with city staff to determine areas of high risk, and said a study has identified 55 vertical shafts and 35 inclined or level-slope mine entrances, mostly associated with the New- and Old Douglas mines, Fitzwilliam Mine in south Nanaimo and mines in Wellington.
“It would have included the [downtown] library and adjacent building, but that’s now been mitigated and made good,” Miller said. “At the north end, the Wellington Mine, Biggs Road area, there’s a number of very shallow mines and there are … fairly routinely collapse features that occur.”
Coun. Sheryl Armstrong asked if the latest mine hazard information about mines will be available to the public and realtors, and Claire Negrin, city subdivision manager, said all the new information in the guidelines will be publicly available on the city’s website.
Nanaimo Mayor Leonard Krog asked if there is much land left for development in Nanaimo with old mines beneath it.
“Only a small portion is what I would consider to be a higher risk of some kind of surface breach…” Miller said. “There’s a lot of re-development in older areas that are specifically very much underlain by workings … and I think that’s particularly important because people look to it and say, ‘well that’s been developed, so what’s the problem?’ These things take a long time. Hundreds of years sometimes to propagate.”
Negrin said the geotechnical reports are intended to make land safe for intended use by remediating the hazards and making purchasers and developers aware of risks prior to remediation assessments.
“At the end of the process, construction has completed, the geotechnical remediation has occurred and then we put a covenant on title; it’s for awareness for future owners … or developers or anybody who just needs to understand what remediation occurred,” she said.
Coun. Erin Hemmens, referring to a mine working that settled on Old Victoria Road, asked about a homeowner’s responsibility for remediation, should a mine working collapse underneath a home, and Jeremy Holm, director of planning and development, replied that the impact would be on private property and remediation would be the homeowner’s responsibility.
The committee recommended that council endorse the guidelines for geotechnical reports and assessments.
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