Mine closures: planning for a century of maintenance

Regulations make it mandatory for mining companies to remediate their tailings after the closure of their operations. This can be a costly and time-extensive activity, tying the mining company to an obligation of maintenance that lasts forever.

Walking away from an abandoned mine used to be common practice. However, that is no longer allowed, and mining companies are obligated to address their former operations and manage the residual infrastructure and tailings. “Historically in some Canadian jurisdictions, mining companies had the ability to walk away post-operation and assume land ownership back to the Crown, including all associated environmental liabilities,” says Adam Waltho, Senior Engineer at GHD.

In the US, there are cases of historical mines on government land that were abandoned. Many states have legacy mine programs to try to mitigate contamination and manage waste from these mines. In the case where legacy mines are owned by companies that exist today, or where a company that owned a legacy mine was purchased by another company, the current owner is now responsible for the environmental liability.

Now, regulations require that mines establish closure plans to ensure an environmentally conscious way of closing the mine, completing site reclamation, and managing the mining waste. Planning and deploying strategies that address liabilities early on is key to saving costs and reducing environmental liabilities in the long run.

Incorporating mine waste management — considering closure — in the planning and design stages is essential for sustainability and long-term liability control.

Government regulators require financial assurance to guarantee the site's reclamation post-closure. By changing waste management processes now, we can help address these future liabilities. Leaving waste management until the end of the mine’s life can be costly for managing the tailings site and the amount of financial assurance needed for reclamation. Planning and finding solutions that minimize mine waste can mean less work involved post-closure, and therefore often decreases the amount of financial assurance required.

Tailings facilities represent a long-term, ongoing financial and environmental liability that can be mitigated. “Very often, the amount of metal extracted from ore is less than a fraction of 1%, with the balance of material discharged to a tailings facility,” says Brandon Hurl, Project Director and GHD Associate. Mining waste with sulfide minerals can create acid, which lowers the pH of water and dissolves metals, resulting in water quality that exceeds regulatory standards. Subaqueous mine waste disposal (placing tailings directly underwater) can be an effective way of handling acid production by limiting exposure to oxygen, but it involves managing the body of water. Managing water can include active strategies such as constructing dams, pH adjustment, and ensuring a minimum depth of water cover. The problem is when the operations stop, the water level must still be maintained, and the water must be treated often. So, this becomes an ongoing liability because the tailings will need to remain submerged in perpetuity to prevent them from generating acid. This is a very long and expensive option to manage, tying up capital for financial assurance of the long-term management of the tailings facility post-operation of the mine.

That’s why developing an integrated management plan incorporating passive treatment options and limiting, or eliminating, long-term maintenance requirements can improve a mining company’s balance sheet. For example, wetland treatment of drainage for areas affected by tailings disposal checks all the boxes of being self-contained, low maintenance, reduces bioavailability of metals and allows environmentally friendly blending in with the natural landscape. When adding this type of passive treatment to the mining waste management system, operators can see the benefits in real-time and compare them to traditional solutions. 

Wetlands can produce alkalinity through natural processes, increasing the pH in the water and creating an anoxic (low oxygen) environment. This controls acid production from mine waste and provides an environmentally friendly habitat full of vegetation that can thrive under acidic conditions. This passive, naturalized way of addressing metal contamination often fits in with the surrounding natural character of the mine area, which is a bonus for the community. “Treatment wetlands can blend seamlessly with the natural wetlands in the area,” Hurl notes.

Understanding mine waste in advance of construction, what the constituents are, the quantities, and how it could affect the outside environment is the starting point for developing options for closure. “Investigation is an important first step in determining optimal strategies for managing un-impounded mining waste. Developing plans for closure involves evaluating different criteria that balance the mining company’s overall objectives, priorities, and desired benefits, whether that’s aesthetics, community, chemical stability, [or] minimizing long-term liability. Cost-benefit and regulatory demands are included in a typical analysis. Alternatives are presented in a way that helps facilitate informed decisions and ultimately leads to sustainably managed post-closure solutions that minimize liability. So, for instance, if the current system involves a dam, we will look for options to potentially reduce long-term liabilities by removing those dams and manage waste differently, along with providing a cost-benefit analysis of alternatives,” says Waltho. 

Contact us to discuss mine closure project options that will help you balance your organization’s priorities.