Of International Council on Mining and Metals (ICMM) participating members, North America has the most forecasted mine closures within the next 50 years1. Greater awareness of government, regulators, and the public has driven an increased focus on environmental, social, and governance (ESG) considerations for mining companies around the world. The global mining industry is having to shift and evolve its previous approaches to mine closure and implement a more “sustainable closure” vision. One of the most challenging elements of mine closures are tailings storage facilities (TSFs), largely due to the physically and chemically complex materials that could pose significant risks to not just the environment but also downstream communities.
Sustainable mine closure addresses TSFs, pits, waste rock piles, and other disturbed areas—and requires meeting physical, chemical, ecological, and social objectives. Sometimes, however, these objectives come into conflict with each other and pose challenges to mine-closure planning. Over the years, the approach to closure, landform design, and reclamation of an inactive tailings facility has evolved and now incorporates dam safety and integrated mine closure best practices. A robust multi-staged closure plan recognizes that environmental stewardship is more than just minimizing potential impacts.
Four pillars of sustainable mine closure
Achieving sustainable closure relies on four components—physical stability, chemical stability, social stability, and ecological stability—with physical and chemical stability being the critical pillars upon which objectives pertaining to other aspects can be accomplished. These four terms (among others) appear in several regulatory documents from jurisdictions across North America, such as the following definition for closure defined by the Government of Alberta in the Alberta Dam and Canal Safety Directive2:
"Closure means a process of modifying and establishing a configuration for a dam or canal with the objective of achieving long-term physical, chemical, ecological, and social stability, and a sustainable, environmentally appropriate after-use ..."
Physical and chemical stability form the foundation for achieving sustainable closure, because they are critical to safety and serve as a platform for long-term ecological and social stability. These four aspects sometimes conflict with each other, making planning for closure even more challenging. For example, a tailings or waste dump that contains potentially acid-generating (PAG) wastes often becomes the subject of debate for wet versus dry closure. One of the best ways to achieve chemical stability in this situation is to isolate the material from air by keeping the material saturated; however, this can be at odds with achieving physical stability, where saturated conditions can pose significant risks, such as liquefaction, slope failures, and other geotechnical risks. Other physical risks, such as erosion, can have significant consequences if not appropriately managed and planned for, particularly given these closure landscapes are expected to function over the long term. The relationship between these four critical aspects of sustainable closure is illustrated in the figure below:
Achieving physical and chemical stability nearly always involves a multi-staged approach. It is most successful when completed over extended periods of time—ideally while the mine is still in operation—and should be considered before the mine even opens. Lack of equipment and lack of funding pose additional challenges to closure for legacy facilities. This is why so many have been left to the public, which then must absorb the closure cost and associated risks. This cost is usually greater than if it had been done gradually during active mining. Interests can also differ significantly, so engaging with stakeholders early and often in the planning process is critical to successful and sustainable closure outcomes.
Closure vision
The MVLWB (2013)3, ICMM (2019)4, and the more recent Society of Mining, Metallurgy & Exploration (SME) Tailings Management Handbook (2022)5 all reference having a “closure vision” to guide closure planning. The closure vision should consider:
Ideally, the closure vision would initially be developed by the mine owner, incorporating stakeholder input to reach a shared vision of the final end land use and outcome. Each mine and each element/component within it is unique and has specific needs and challenges that necessitate a tailored closure planning approach.
Too often, closure visions crafted early in a mine’s life cannot be reasonably achieved, due to external and internal factors. While these plans often answer the “what” of closure, they neglect to answer enough of the “why” and “how” questions. Closure plans are then presented to regulators and stakeholders as specific, defined actions; however, a mine may operate for decades, meaning the mine plan and closure plan will inevitably shift with time. It is critical to communicate the closure vision’s intent with stakeholders so that any implementation changes still satisfy the overall objective; otherwise, it could result in significant regulatory challenges and pushback from local communities.
Mines have a significant impact on the environment and surrounding communities, and while these impacts benefit global society and local economies, these benefits are usually temporary and come at a sometimes significant environmental cost. While successful closure can include terrestrial reclamation that sets the land on a trajectory toward its pre-mine condition, it may also prescribe an end land use that provides function and value to all stakeholders.
Closure planning for tailings storage facilities
Due to the challenging physical and chemical properties of the waste materials they store, TSFs are one of the most challenging mine-site elements to close. Most mine closure plans call for some form of land reclamation; however, some mines (such as Alberta’s oil sands surface mines) produce a fluid-like tailings material that is extremely weak and slow to consolidate and strengthen. TSFs often must undergo a transitional step between active operation and final certified landform to achieve chemical and physical stability. This multiple-phased step transitions a TSF from a fluid-containment structure (or “dam”) into a physically stable structure, which behaves more like other mine waste structures (such as overburden dumps).
This phase of TSF closure is generally a technical one with the objective of creating a physically stable structure, applying to both the associated containment structure and the contents contained within. The figure below illustrates the potential progression through closure of a TSF in Canada (modified from Al-Mamun & Small 20186, and Schafer et al. 20197):
Case study
Barr’s mine closure paper, presented at the Mine Closure 2023 conference, examines a closure planning case study for an inactive TSF in North America. Given that mining operations have been ceased for some time and there are no waste dumps or pits to reclaim, the case study focuses on closure and reclamation of the TSF and water management systems still in use. Closure planning for the site primarily addressed placement and isolation of residual waste materials within the TSF, improvements to site-wide water management to remove the need for the TSF, and eventual decommissioning and removal of the existing earthen containment dam to accommodate construction of a new permanent landform, with the goal of achieving physical and chemical stability of the closed facility. This will allow for the establishment of a beneficial end land use for local communities and the site owner, resulting in a sustainable final closure outcome.
Develop and implement a tailored closure approach
Adequate closure planning and implementation during mining and the post-mining transition are becoming a growing focus for government, industry, and the public. With more current and legacy mining facilities expected to enter various stages of closure in the next several decades, investors are favoring ESG-forward companies. Demonstration of good mine closure practices on existing or legacy mines can also improve the likelihood of future approvals with regulators for opening new mines or expanding existing mines.
All mine sites (and even elements of specific sites) are unique and therefore require a unique closure approach. For help developing and implementing a closure approach tailored to your mining facility, contact our team.
Adapted from Barr’s Evolution of closure planning for an inactive tailings facility paper, presented at the 2023 Mine Closure conference in Reno, Nevada, on October 2–5, 2023.
About the authors
Scott Laberge, geoenvironmental engineer, has over four years of geotechnical and geoenvironmental engineering experience at Barr. Scott’s experience includes tailings management; geo-technical and environmental site investigation; construction observation and materials testing; geotechnical instrumentation installation; saturated and unsaturated soil mechanics; critical state soil mechanics; oil sands geology; mine operations; and retainment structures. Scott’s work at Barr has included projects for coal, oil sands, and potash clients across Canada. He also has technical expertise in tailings and mine waste management and mine closure planning and design, including advanced numerical modeling of consolidation and settlement of unconventional tailings materials.
Dale Kolstad, vice president, senior environmental engineer, has two decades of experience with projects involving civil and environmental engineering. He currently leads multidisciplinary teams in solving challenging mine waste and tailings projects across multiple geographies and regulatory jurisdictions. Examples of his work include development of tailings dewatering technologies, contaminant source control within mine rock stockpiles, mine contact water treatment, and conceptual to detailed closure and reclamation plan development. Dale has a background in contaminated site assessment and remediation and is versed in active and passive treatment technologies and waste containment, including the design of liner and cover systems.
Billy Dehler, senior geotechnical engineer, has nearly 15 years of geotechnical engineering and project management experience, most recently in the U.S. and Canadian power and mining industries. He has performed geotechnical engineering for industrial facilities and commercial developments, renewable power generation facilities, and redevelopment of contaminated sites. His work focuses on investigation, analysis, design, instrumentation, and inspections for pollutant-containment dikes, large earthen dams for tailings basins, and slurry wall and seepage collection systems. He also researches geologic hazards, performs site reconnaissance, completes geological mapping to evaluate potential impacts on proposed construction, and provides construction phase services including planning and oversight of QA/QC.
Art Kalmes, vice president, senior civil engineer, has more than three decades of experience in water resources and civil engineering. He specializes in work involving dams and levees, tailings management, civil engineering design, hydrology and hydraulics, floodplain management, and stormwater management. Art has served as principal or project manager for planning, permitting, design, and construction efforts at several large mines spanning five continents. He has managed more than 100 natural resources and stormwater projects and conducted over 70 floodway and floodplain evaluations.
Related projects
The pits, mill site, roads, waste-rock dumps, and powerlines at the Pine Point lead-zinc mine—which operated from 1964 to 1988—were reclaimed to the standards in place at the time the mine closed, and the land leases were returned to the government. Nearly 30 years later, when an updated closure and reclamation plan for the tailings area was required based on revised guidelines, Barr developed a multi-year research plan to study metal concentrations as well as the fate and transport of metals across the site. Barr also studied the watersheds and surface-water routing, groundwater conditions, and the water balance and geochemistry at the site, and conducted an assessment of human-health and ecological risks. Barr then revised the larger closure plan with the outcome in mind: long-term closure that is cost-effective, meets regulatory requirements, and addresses community concerns.
A Canadian oil sands mine is demonstrating that water-capped tailings technology can be used to convert a former tailings basin into a lake similar in appearance and function as other regional lakes. Since 2014, Barr has been conducting monitoring and physical assessments of the fluid fine tailings in this demonstration pit lake. Our work includes using data generated from annual sonar surveys to determine the top of the tailings’ surface; estimating water and tailings volumes, water-cap depth, and rate of settlement; and annual reporting on changes over time. Tailings samples are periodically collected throughout the lake and submitted for physical laboratory testing. In addition, we are analyzing tailings characteristics to determine changes in various properties over time.
The Doe Run Company’s former Block P mill and mine sites are located in Montana’s Barker-Hughesville mining district within the Lewis and Clark National Forest. Concerns about environmental impacts associated with historical mining activities at the sites prompted the company to evaluate the impacts of metals leaching and acid rock drainage at six inactive mine sites in the upper Galena Creek watershed, the inactive lead-zinc mill site, and associated tailings basins. Barr assessed groundwater in the bedrock and alluvium, and then evaluated potential sources of inflow to the mine workings. We conducted a geotechnical evaluation of waste-rock piles at the site and assessed potential waste-rock repository locations. Barr designed the repository and stream channel, planned and implemented revegetation and long-term monitoring and maintenance programs, and provided construction observation.
Part of the environmental permitting effort for PolyMet’s proposed copper-nickel and precious-metal mine included tailings-basin closure planning. Barr evaluated both wet and dry closure approaches for the basin. A “wet closure” approach would consist of a large pond surrounded by wetland and meadow areas to cover the basin, limit oxygen intrusion into the tailings, minimize water-quality impacts, and accommodate wetland mitigation at the time of basin closure. A “dry closure” approach would include surface contouring to shed surface water, a hydraulic barrier to limit water infiltration, and a vegetated soil cover. We studied water-quality impacts for both of the closure options, as well as constructability, long-term maintenance, and slope-stability factors of safety for the basin.
Barr assists a potash mining client in Canada with operating its tailings management areas at several facilities by providing long-term deposition planning, new facility design, instrumentation and monitoring assistance, and closure planning. We have investigated alternatives for depositing tailings more effectively to better position the sites for closure and evaluated tailings characteristics for containment and capping. We also identified closure alternatives and are developing designs for one facility that follow the Canadian Dam Association’s guidelines for converting a tailings management area to a landform.
References
1 Brock, D. 2020. “ICMM’s integrated mine closure: Good practice guide—Then and now.” AusIMM. Accessed May 25, 2023. www.ausimm.com/bulletin/bulletin-articles/icmms-integrated-mine-closure-good-practice-guide--then-and-now.
2 Government of Alberta. 2018. “Alberta Dam and Canal Safety Directive.” Government of Alberta. Edmonton, Alberta.
3 MacKenzie Valley Land and Water Board (MVLWB). 2013. “Guidelines for the Closure and Reclamation of Advances Mineral Exploration and Mine Sites in the Northwest Territories.” MCLWB. Yellowknife, Northwest Territories.
4 International Council on Mining & Metals (ICMM). 2019. “Integrated Mine Closure Good Practice Guide, 2nd ed.” ICMM. London.
5 Society for Mining, Metallurgy & Exploration Inc. (SME). 2022. “Tailings Management Handbook.” SME. Englewood, Colorado.
6 Al-Mamun, M. & Small, A. 2018. “Revisions of guidance of landforms in CDA mining dams bulletin—A companion paper with additional details” in Proceedings of the Canadian Dam Association Annual Conference. Canadian Dam Association. Quebec City, Quebec.
7 Schafer, H., Beier, N. & Macciotta, R. 2019. “Closure of the long-term behaviour of tailings dams: Using industry experience to fill the gaps” in Proceedings of the GeoSt. John’s 2019. Geobrugg, Newfoundland.