Principal and Senior Project Manager
In the fifth volume of the Journal of Environmental Solutions for Oil, Gas, and Mining, Golder’s Sue Longo explores the factors that must be considered, and the best practices, for rehabilitating geohazards associated with underground mine workings on historical mine sites.
Rehabilitation of mine hazards (specifically underground mine workings and openings to surface) is not a simple endeavor. And rehabilitating legacy mines, that did not always employ a robust mine closure strategy as mines do today, have geohazards that have only worsened with time.
There are many hazard mitigation techniques that can address any immediate risks on a legacy site. This paper explores techniques to address the problem itself, moving away from simply identifying and managing risks and moving towards long-term solutions that permanently eliminate the hazards in a planned way. This is not a case of a ‘one-size-fits-all’ solution.
On the road to eliminating hazards, there are a few common pitfalls. Time will not solve the problem but going straight to the fix may not be the best approach either. We need to start with investigations. Gathering enough data to identify what the appropriate ‘fix’ is, by understanding the complete site and all its hazards – physical as well as environmental. Since the physical hazards are typically underground, and often no longer safely accessible, the scale of the hazard isn’t always obvious. Typical concerns are the physical stability of the surface land above an underground working, which if left alone could result in subsidence or sinkholes and/or perhaps inadvertent access by the public to an unsafe area. Investigations can include everything from examining old mine plans, reviewing historical logbooks or records, all the way to drilling and drones to confirm and complete the picture.
There, of course, is a trade-off between investigations and uncertainty: the more money spent on investigations, the better the understanding of the situation; however, there is a limit where more investigation yields diminishing returns. Risk tolerance will vary by owner, and the owner’s drivers will have an impact on any rehabilitation options selected.
Selection and prioritization should be done using a risk assessment method. Evaluation of the rehabilitation options is based on the remediation strategy goals with the understanding that not every option will work with every site.
Site specifics (e.g. access, available materials and the underground circumstances) and the performance criteria are essential to making the right decision. Keeping good documentation of the options evaluation process is becoming ever more important in particular as you engage with stakeholders such as surrounding communities who may play a role in the selection process.
Once the investigation, planning and selection are complete, it’s time to execute. You will require an understanding of the known-knowns, known-unknowns, and the unknown-unknowns to be able to respond effectively when circumstances change as you implement your plan (and they will change). Real-time monitoring is required during execution to document the process and the progress of the rehabilitation which will ultimately make its way into the final report used for regulatory sign-off.
Rehabilitating legacy mine hazards is a collaborative process, engaging owners, government, communities, consultants and contractors. The reward for the effort is not only reduced risk for the owner but the potential for future land development for communities in proximity to legacy mine sites, turning the legacy of mining into a positive one.