Undermining Issues

[updated March 2021}

Photo by Gerry Stephenson

Below the surface: 3,000 kilometres of underground roadways and tunnels

In 1979, the Canmore mine closed after 90 years of operations. It's easy to see how much has changed: the town's population has soared with an intentional shift toward tourism, recreation and real estate as the main drivers of its economy.

Underground, however, a complex system of more than 3,000 kilometres of underground roadways and tunnels exists below the western slopes of town on the Three Sisters property. 

To develop infrastructure on disturbed lands such as these requires a whole new level of engineering expertise and mitigation techniques. Even with the brightest people and the best available technology, the opportunity for structural failure on undermined lands is always present.

History has shown us, more than once in Canmore alone, that it's not possible to mitigate undermined land to a 100 per cent level of safety from loss of property, human life, or damage to municipal infrastructure. So what happens if our best mitigation attempts don't last? 

Accidents happen: the Dyrgas Gate shaft collapse

If you know a little about geology, you know that the earth is in a constant state of change. In Canmore, building on the surface is complicated further by the geologic structure of the mountainous environment and the complexity of the underground workings of the former Canmore Mines.

It's no surprise that it's difficult to mitigate perfectly for settling or collapse of the surface.

In 2010, an old mine shaft collapsed, taking out a public trail on Dyrgas Gate, located on Three Sisters lands. Because the sinkhole happened on public property rather than private property (engineered plans intentionally avoided placing any homes directly above the mitigated shaft), the developer responsible for mitigating these collapsed mine workings has considered it "a successful example of mitigation.” [Source: Rocky Mountain Outlook, Nov. 10, 2016].

The open hole was fenced off for seven years, and was found to have a permanent-fix estimated cost of $1,700,000. A $600,000 provincially-funded but temporary fix was applied, and according to the Town of Canmore this “surface” solution will require replacement approximately every 25 years.

The Dyrgas Gate mine shaft, which was temporarily mitigated (or engineered for safety) at a cost to Alberta taxpayers at the time, will be an ongoing cost to the Canmore municipal taxpayers for years to come.

This is a small-scale example of what citizens and long-time local mining experts in the valley are concerned could happen if development is allowed on the unfinished golf course, plans for which have previously been abandoned by developers and unsupported by council because of safety and liability, as well as wildlife corridor viability concerns. The damage, if a sinkhole were to appear, would again leave Canmore citizens footing the bill.

Who pays the bills?

In Canmore's case, history has demonstrated that when developers declare bankruptcy (as they have done three times in the history of these lands, most recently in 2008), local and provincial taxpayers are financially exposed by any accidents that happen on the property.

The new, 2020 Undermining Review Regulation states that the developer must ensure that any engineers they engage to mitigate undermining carry $5,000,000 liability insurance per claim for a ten year period following construction. The same document states the developer carry $5,000,000 liability per occurrence for only a two year post-development period.

Some significant questions remain regarding longterm liability:

• What happens if five million dollars doesn't cover damages that may occur?

• What happens if the developer or engineer goes into bankruptcy again?

• What happens if a sinkhole occurs beyond 10 years post-construction?

According to the 1999 Indemnity Agreement with Province of Alberta, if an undermining-related accident takes place on public property on these lands (sidewalks, roads, etc) beyond ten years time, Canmore taxpayers and the Town of Canmore will be on the hook financially for the resulting damages.

Learning From Experience: A history of mining and development on Three Sisters Lands

This 23-minute video produced by Glen Crawford explores undermining issues and concerns regarding development on the Three Sisters lands. Retired mine engineer and expert on the Canmore Mines, Gerry Stephenson explains the history of what has gone on underground and the potential dangers faced by developing on these lands, before he passed away in 2019.

Evolving technology

Improvements to mitigation techniques are in a constant state of evolution. The best available science, technology and engineering is always being employed by developers and municipalities to make sure people and property is as safe as possible. However, as mentioned above, 100 per cent certainty with any mitigation technique isn't Canmore's reality; unfortunately, unknowns and complications could always exist.

For more on current practices, watch this animated video produced by Three Sisters Mountain Village. Development on much of the Three Sisters lands requires extensive undermining mitigation in order to proceed.

Thanks to all those who provided background for this section, and to the Canmore Museum and Geoscience Centre for sharing illustrations and information.