Chapter Viii Closure and Reclamation
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108 TOWARDS ZERO HARM – A COMPENDIUM OF PAPERS PREPARED FOR THE GLOBAL TAILINGS REVIEW TOWARDS ZERO HARM – A COMPENDIUM OF PAPERS PREPARED FOR THE GLOBAL TAILINGS REVIEW 109 MANAGEMENT OF TAILINGS: PAST, PRESENT AND FUTURE CHAPTER VIII CLOSURE AND RECLAMATION Gord McKenna, Geotechnical Engineer and Landform Designer, McKenna Geotechnical Inc, Adjunct Professor, University of Alberta Dirk Van Zyl*, Professor of Mining Engineering, Norman B. Keevil Institute of Mining Engineering, University of British Columbia 1. INTRODUCTION 2. OVERVIEW OF CURRENT PRACTICE Tailings landforms are an enduring legacy of many Worldwide, many mines have one or more active or mining landscapes – the design and construction inactive tailings facilities. Each tailings facility is a of these facilities to perform well for the next mining landform that is already part of the permanent millennium is just as great a challenge and effort landscape, and which will require reclamation as as is maintaining operational dam safety. This part of mining’s commitment to be a temporary chapter provides an overview of leading practices use of the land and to enable individual mines to for design, construction, deposition, stabilisation, leave a positive mining legacy. Each of these tailings decommissioning, capping, reclamation, and aftercare landforms must be sited, designed, constructed/ for tailings facilities. It builds on the work detailed in filled, decommissioned, stabilised, reclaimed, Sustainable design and post-closure performance of and deregulated as dams, relinquished and then tailings dams (ICOLD 2013). maintained over the long-term by landowners or regulatory agencies. Where the relinquishment cannot An important advance in mine closure design is the be accomplished, ongoing maintenance will be framework of landform design — a new concept that responsibility of the mine owner. is breaking out internationally under different names by various groups and practitioners. Landform design Tailings facilities typically occupy 10 to 40 per cent of entails a paradigm shift away from the practice the area of a reclaimed mining landscape, with pits of separating construction and operations from and waste rock dumps responsible for most of the closure and reclamation. Instead, it calls for a fully rest. Typically, regulators require reclaimed facilities integrated approach that provides design, support, to meet agreed-upon land uses and performance and stewardship throughout the life of the mine and standards that sustain landscapes for the benefits of beyond. local communities (e.g. Brazilian Mining Association [IBRAM] 2014). After mining, the sites are commonly A new Landform Design Institute (LDI 2020) was used as natural areas or wildlife habitat (especially recently formed, which provides ‘how-to’ advice for remote mines). Near cities, they may be used on designing, constructing, and reclaiming mining for agricultural, recreational, or industrial activities landforms and landscapes that are easy to reliably (Pearman 2009). reclaim. The Institute helps mines meet their commitment to be temporary users of the land. Most tailings facilities are difficult to stabilise Effective reclamation of tailings facilities requires and reclaim to the point where they meet societal sound design and planning before construction of the expectations of only an extremely low risk of mining landform even begins. Globally, there are tens catastrophic failure, acceptable residual impacts on of thousands of mining landforms that are partially the environment, and access for agreed-upon land constructed and in need of improved reclamation uses. Many dams cannot be deregulated (i.e. where practices. Sections 5 and 6 of this chapter provides they are no longer regulated as a dam but as a mine a more complete discussion of the landform design waste storage facility). In particular, it is very unlikely approach to overall mine (and specifically tailings) that a dam will be deregulated if it contains ponded closure for both existing and new mining landforms. water or potentially mobile materials, due to concerns *Member of the GTR Expert Panel 110 TOWARDS ZERO HARM – A COMPENDIUM OF PAPERS PREPARED FOR THE GLOBAL TAILINGS REVIEW TOWARDS ZERO HARM – A COMPENDIUM OF PAPERS PREPARED FOR THE GLOBAL TAILINGS REVIEW 111 regarding catastrophic dam failure even after closure. damage the reclamation below. • regulatory requirements often straightforward to reclaim and perform well, as In practice, most tailings landforms need regular do tailings sand beaches. However, tailings facilities • mining company corporate closure criteria monitoring and maintenance, perhaps in perpetuity. Currently, most mines have a ‘conceptual closure plan’ typically present several challenges for closure and that details what needs to be done for the mine site • commitments made by the company to regulatory reclamation: Historically, tailings dam design has focussed on (landscape scale) and for each mining landform (such agencies and communities during the mine life safely containing hydraulically placed tailings during as waste rock dumps, tailings facilities, open pits, and cycle Sand dams, comprised of fine sand and silt mine operations. More recently, designing these plant sites). The plan applies to decommissioning, tailings, are highly erodible. Even when capped and • leading international practices for projects in tailings landforms to be safe, stable, and useful after regrading / stabilisation, mine reclamation, and water revegetated, gullies can penetrate the cover, leading similar climates, with similar physical and chemical filling and reclamation has become a parallel but management and water treatment. Excellent guidance to erosion of mine waste, fan deposition, and elevated conditions and environmental settings, and in not necessarily integrated focus (ICOLD 2013). But for development of modern closure plans is provided suspended sediments in downstream watercourses, similar socio-economic settings. improvements are needed. Most tailings facilities by IBRAM (2014), Government of Western Australia necessitating ongoing maintenance. owners and users still face one or more significant (2015), Asia Pacific Economic Cooperation (APEC, These criteria are captured and addressed in the geotechnical, safety, geo-environmental, or financial 2018) and ICMM (2019). However, at most mines, the Tailings and the tailings pore-water (the water that design basis memorandum (DBM) as described risks related to operational reclamation activities and design and operation of tailings facilities is conducted fills the porosity between the grains of tailings) may below, and then reviewed periodically. For existing long-term landscape performance (McKenna 2002). separately from closure and reclamation. contain elevated levels of metals and may be prone to tailings facilities that have no or too simplistic closure acid rock drainage. Both can affect groundwater and criteria, a DBM should be developed as a high priority. Reclamation practices vary widely according to Mines are required to post financial assurances surface water, creating unacceptable water quality climate, commodity, and regulatory environment. to cover the costs of reclamation and long-term and toxicity to plants, animals, and aquatic life. 3.2 IDENTIFY ALTERNATIVE TECHNOLOGIES Most mines employ conventional reclamation care in most jurisdictions, but depending on the techniques, including regrading of slopes, placement regulatory framework, the assurances can end up The next step is to identify the alternative tailings and • Tailings dam internal drainage systems of cover materials (usually a growth medium), being a small fraction of the eventual requirements. closure technologies and practices that will satisfy (underdrains, gravel drains within the dam, and and planting with site-appropriate, ideally native, In some jurisdictions the land may be abandoned the closure criteria. An options analysis is undertaken socked-slotted drainage pipe) can be prone to vegetation. Reclamation is often conducted while only partially reclaimed, and must be managed using mine plans that incorporate each of the leading clogging, fouling, or collapse, affecting the long- progressively, whereby mine areas, especially mine by the state, with little or no funding available for the tailings technologies. (See Consortium of Tailings term groundwater table and the geotechnical and waste landforms such as tailings facilities and waste remaining work. Management Consultants [CTMC] 2012, for a list erosional stability of dams. rock dumps, are reclaimed soon after bulk material of nearly 100 tailings technologies). This requires • Potentially mobile materials (soft tailings, placement is completed. At some mines, each lower considering the climatic and topographical location liquefiable tailings, or water) stored behind dams bench of dams and dumps is reclaimed as the next of the tailings facility and the feasibility (technical and 3. TAILINGS CLOSURE: WHAT IS GOOD PRACTICE? may pose elevated risks of sudden catastrophic bench above is placed. This approach cannot be used economical) and constructability of different options.1 dam failures and outflows that threaten lives, the for most downstream and centerline constructed Good practice tailings closure development and environment, and property downstream. facilities which can generally only be reclaimed once design starts during the initial stages of the mine Technology developments during the facility mine life all lifts have been