1.0 The Global Acid Rock Drainage Guide
- 1.1 Introduction
- 1.2 Acid Rock Drainage Management – The Business Case
- 1.3 Scope and Objectives of the Global Acid Rock Drainage Guide
- 1.4 Relation to Other Guides
- 1.5 Approach of the Global Acid Rock Drainage Guide
- 1.6 Application to Mine Phase
- 1.7 The Sustainable Development Approach
- 1.8 Layout and How to Use the Guide
- 1.9 Chapter References
- List of Figures
- List of Appendices
The GARD Guide
Development of this Global Acid Rock Drainage Guide (GARD Guide) was sponsored by the International Network for Acid Prevention (INAP) with the support of the Global Alliance. It is the property of INAP. Access and use of the GARD Guide is granted by INAP under certain conditions.
This GARD Guide deals with the prediction, prevention, and management of drainage produced from sulphide mineral oxidation, often termed “acid rock drainage” (ARD), “saline drainage” (SD), “acid mine drainage” or “acid and metalliferous drainage” (AMD), “mining influenced water” (MIW), and “neutral mine drainage” (NMD). The GARD Guide also addresses metal leaching caused by sulphide mineral oxidation. While focused on mining, the technology described will be helpful to those practitioners that encounter sulphide minerals in other activities (e.g., rock cuts, excavations, tunnels). Some of the approaches in the GARD Guide are also relevant to issues arising from reactive non-sulphide minerals.
The GARD Guide is intended as a state-of-practice summary of the best practices and technology to assist mine operators, excavators, and regulators to address issues related to sulphide mineral oxidation. The GARD Guide will be of interest to the following:
- Mining and mining service companies
- Governments (national regulatory or land management agencies, IFC, World Bank, regional development agencies etc.)
- Community/Communities of interest
- Non-governmental organizations (NGOs)
- Indigenous Peoples
The GARD Guide is a technical document designed primarily for a scientist or engineer with a reasonable background in chemistry and the basics of engineering with little specific knowledge of ARD. The target audience is adapted from a model developed by the PIRAMID Consortium (2003).
1.1.1 Acid Rock Drainage
Acid rock drainage is formed by the natural oxidation of sulphide minerals, together with reactions of the base minerals in the rock, which are exposed to air and water. Activities that involve the excavation of rock with sulphide minerals, such as mining, accelerate the process because such activities increase the exposure of sulphide minerals to air, water, and microorganisms. The drainage produced from the oxidation process may be neutral to acidic, with or without dissolved heavy metals, but such drainage always contains sulphate.
ARD results from a series of reactions and stages that usually progress from near neutral to more acidic pH conditions (see Chapter 2). In addition to ARD, neutral mine drainage or saline drainage may result from the oxidation process where there are sufficient base minerals to neutralize the ARD. NMD is characterized by elevated metals in solution at near neutral pH. SD contains high levels of sulphate at neutral pH without significant metal concentrations and saline drainage’s principal dissolved constituents then are sulphate, magnesium, and calcium ions.
Although the water quality resulting from sulphide mineral oxidation does not lend itself to precise compartmentalization, the accompanying chart illustrates the various types of drainage (Figure 1-1). Neutral mine drainage and saline drainage can occur together (i.e., near neutral pH with elevated metals and sulphate).
The GARD Guide addresses ARD, NMD, and SD where contaminants are released from solid to liquid phase by the oxidation of sulphide minerals. For simplicity in the GARD Guide, drainage produced by sulphide mineral oxidation is referred to simply as ARD except where specific aspects of ARD, NMD, and SD formation or drainage characteristics are important to the application of a particular technology or management approach. In those cases, the specific terms NMD and SD are used.
1.2 Acid Rock Drainage Management - The Business Case
ARD formation is difficult to stop once initiated because it is a process that, if left unchecked, will continue (and may even accelerate) until one or more of the reactants (sulphide minerals, oxygen, water) is exhausted or no longer available for reaction. The process can continue to produce contaminated drainage from mining and other sulphide bearing rock wastes for decades or even centuries after mining has ceased. In temperate or tropical climates with high rainfall, large volumes of ARD can be produced requiring large and expensive collection systems, treatment plants and civil works (e.g., covers on mine wastes).
The cost of ARD remediation at primarily abandoned and “orphaned” mines in North America has been estimated in the tens of billions of U.S. dollars. Individual mines can face post-closure liabilities of tens to over a hundred million dollars for ARD remediation and treatment if the sulphide oxidation process is not properly managed during the mine’s life.
Put simply, ARD can make a mine project uneconomic and present mine owners with technically challenging and expensive long-term management issues.
- Unbudgeted reclamation costs with little or no internal resources (i.e., manpower, equipment, infrastructure, utilities and management) at the time of closure
- Contaminated water resources with adverse impacts on human health, flora, and fauna
- Unbudgeted increases of environmental remediation
- More stringent regulatory requirements which evolved over time
- Loss of corporate image, public acceptance, and stakeholder trust
- Loss of future mining opportunities
- Commitment of corporate resources to a mine that has long since ceased to provide economic value
Proper mine characterization, drainage quality prediction, and mine waste management can prevent in most cases, and minimize in all cases, ARD formation. However prevention of ARD must begin at exploration and continue throughout the mine-life cycle. The mining industry recognizes that continuous ARD planning and management is imperative to successful ARD prevention. Proper planning and management of ARD can prevent environmental impacts from occurring.
Many mines will not produce ARD because of the inherent geochemical nature of their mining wastes or very arid climatic conditions. Also, mines that have implemented well founded prediction and, where required, prevention and monitoring programs should also be able to avoid significant ARD issues. For example, Placer Dome Inc., a large gold and copper mining company, published information on the ARD and metal leaching potential and management plans for its 22 operating and closed mines (Placer Dome Inc, 1998 and 2003). Of the 22 mines, eight (36%) exhibited a potential for ARD and five others (23%) a potential for NMD (metal leaching), requiring that prevention and monitoring plans be developed and implemented. Only three (14%) mines actually produced ARD or NMD where water treatment of drainage was necessary; none of those mines had implemented ARD prevention measures from the start of operations.
A comprehensive approach to ARD management, as promoted by the GARD Guide, will reduce environmental risks and subsequent costs for the mining industry and governments, reduce adverse environmental impacts, and build public support for mining. The extent and specific elements of the ARD management approach that should be implemented at a particular mine or project will vary based on the potential to produce ARD and other site-specific factors.
1.3 Scope and Objectives of the Global Acid Rock Drainage Guide
The potential for acidic drainage to form from mining has been known since at least 1556 and ARD was observed as early as 1698 associated with coal mining in Pennsylvania (BC Acid Mine Drainage Task Force, 1989).
Research into the process of ARD formation and methods to minimize its impact have been ongoing for more than 50 years. Much progress has been made, in the last 20 years in particular, through a number of research consortiums. As such, there is a considerable scientific and engineering guidance available on ARD through organizations such as INAP, MEND, the British Columbia AMD Task Force (BC AMDTF), the British Columbia Ministry of Energy, Mines and Petroleum Resources (BC MEMPR), ADTI, the Australian Centre for Minerals Extension and Research (ACMER), the South African Water Research Commission (WRC), The South African Department of Water Affairs and Forestry (DWAF), the Partnership for Acid Drainage Remediation in Europe (PADRE), and other programs. However, this research is generally available through disparate references and is not easily accessible. The research tends to be issue, commodity, or geographically (climate) centred. The objective of this GARD Guide is to consolidate and summarize the current information and to use global thinking on ARD management.
Many examples and case studies of ARD prediction and mitigation have been studied for the last 20 years that buttress and corroborate the more fundamental scientific research. The knowledge gained from both positive and negative field results contributes greatly to current and future ARD management plans and enhances the credibility of consultation processes on ARD. Also, application of ongoing science and engineering research supports continual improvement in ARD management.
This GARD Guide focuses on mining and pertains to ores, wastes (overburden, waste rock and residues/tailings), and mine workings (including in situ mining). The GARD Guide applies to the entire mining industry and all commodities produced by mining, including base metals, coal, iron ore, precious metals, diamonds, and uranium where the ores contain sulphide minerals. The GARD Guide is applicable to the complete mine life cycle and to existing and historical ARD issues as well as future mines.
While much of the science in the GARD Guide is more broadly applicable, it does not specifically address the following:
- Acid sulphate soils, although reference is made to approaches and technologies from the acid soil literature where relevant to the management of sulphide mineral oxidation
- Dissolution of sulphate salts (e.g., jarosites and other hydroxyl-sulphates) that are produced by pyrometallurgical or hydrometallurgical processes (However, jarosites or other salts produced as intermediate products during sulphide oxidation under ambient conditions are considered.)
The technology described in the GARD Guide may be of value to those encountering or managing acid sulphate soils and pyrometallurgical or hydrometallurgical sulphate salts.
Additional Web links for organizations:
- MEND http://www.mend-nedem.org
- the British Columbia Ministry of Energy, Mines and Petroleum Resources (BC MEMPR) http://www.gov.bc.ca/empr/
- ADTI http://inside.mines.edu/adti/ADTIMAIN.html
- the Australian Centre for Minerals Extension and Research (ACMER) http://www.acmer.uq.edu.au/index.html
- the South African Water Research Commission (WRC) http://www.wrc.org.za/
- The South African Department of Water Affairs and Forestry (DWAF) http://www.dwaf.gov.za/
- the Partnership for Acid Drainage Remediation in Europe (PADRE) http://www.padre.imwa.info/
- West Virginia Coal Mine Drainage Task Force - http://wvmdtaskforce.com/
The overall objective of the GARD Guide is to collate and facilitate worldwide best practice in prediction, prevention, and mitigation of ARD. It is a reference document for stakeholders involved in sulphide mineral oxidation and related waste management issues.
The GARD Guide has been prepared as a road map through the process of evaluating, planning, design, and management of ARD over the life cycle of mining. The GARD guide has also been prepared as a compendium of the concepts, the techniques, and the processes to be considered in successful ARD management over the mine-life cycle. It provides a broad, but not highly detailed, understanding of ARD technologies and management. However, a comprehensive approach to ARD management will be created where the concepts and guidance in the GARD Guide are translated into site-specific actions.
The GARD Guide is also a “compass” to identify more detailed information on ARD as it lists references for those looking for specifics on ARD technologies and approaches.
The GARD Guide will assist the reader to monitor the evolution of the sulphide oxidation process in mine wastes and identify when involvement of more experienced ARD practitioners is required to address a particular issue.
The GARD Guide is not a design document; design requires a high level of understanding and site-specific knowledge of a particular project or mine. Detailed design of ARD mitigation techniques will continue to be conducted by knowledgeable practitioners.
The following are specific objectives of the GARD Guide:
- Articulate the issues associated with sulphide mineral oxidation
- Improve the understanding of best global practice, customized where necessary for special geoclimatic conditions
- Promote a risk-based, proactive, consistent approach by encouraging planning for and implementation of reduction and control of ARD at the source
- Leverage the world’s ARD expertise and share expertise with developing countries
- Support the ‘Equator Principles’ developed by a consortium of lending institutions and the International Council of Mining and Metal’s (ICMM’s) objectives by achieving ‘global best practice’ in future mining projects
1.4 Relation to Other Guides
There is a considerable body of knowledge on ARD management in the scientific and engineering literature. Many technical documents and guidelines have been produced that summarize certain aspects of the state-of-knowledge and in some cases provide guidelines for managing ARD. In addition, the series of International Conferences on Acid Rock Drainage (ICARD), BC MEND, ACMER, and other conferences regularly review ARD research and management. The ICARD proceedings in particular are valuable summaries of ARD technology and the reader is encouraged to review these proceedings, especially case studies.
Some existing compendia of ARD technology are listed above. The GARD Guide summarizes and references these and other key literature and compendia on the assessment, prediction, control, and management of ARD. It refers the reader to more specialized state-of-the-art guides and summaries where they already exist. INAP has commissioned a separate review of the ARD literature (Wolkersdorfer, 2008).
1.5 Approach of the Global Acid Rock Drainage Guide
The GARD Guide is based on a systematic approach to ARD management as shown in Figure 1-2. The approach proceeds from site characterization to preparation, and ultimately implementation of an ARD management plan. It includes a loop for verification and calibration of predictions and assessments as part of evaluating the performance of the ARD management plan.
Specific elements of the approach and appropriate technologies are described in more detail in this GARD Guide.
1.6 Application to Mine Phase
ARD management is applied at all phases of a mine from “cradle to cradle" as part of an environmental management system (EMS), which includes a continuous improvement process (Figure 1-3). (The term “cradle to cradle” characterizes the objective to return land used for mining to biologically productive use after mining is finished.)
The ARD management plan is based on technical understanding and knowledge but is defined within corporate policies, government regulations, and community expectations. The ARD management plan is based on site characterization and ARD/NMD/SD prediction science and incorporates engineering measures aimed at ARD prevention and control. Water treatment may be included in the plan as a contingency, or as a necessity for existing mines.
Implementation of the ARD management plan requires the use of management systems and communication between stakeholders. The plan’s performance is monitored through a range of metrics usually based on evaluation of mine water quality. The overall performance of ARD management is evaluated against site-specific environmental requirements and the criteria established by corporate policies, government standards, and community expectations. In this way, the ARD management process is a continuous loop.
The level of assessment and planning for each phase of mining varies based on the degree of information available and the extent of rock excavation and the potential environmental impact. For example, relatively little disturbance and excavation of rock containing sulphide minerals usually occurs during exploration. However ARD management plans are required for exploration drilling, bulk samples, and test pits/underground workings. A poorly planned exploration drilling program could cause long-term ARD problems through disturbance of the natural groundwater conditions and provision of new vertical flow paths. In addition, site characterization, including ore and waste characterization and ARD prediction, must begin at the start of mineral exploration.
The approach to ARD management during the phases of mine development is discussed in more detail in Chapter 9.
1.7 The Sustainable Development Approach
With its potentially wide-ranging and multigenerational consequences, ARD is an important "sustainable development” or “sustainability” issue. Environmental impacts of ARD can be serious and enduring. Depending on where a mine operates, ARD can also impact the well-being of people surrounding the mine, now and in the future. Poor management of ARD can not only harm the environment but also the mining industry’s reputation and communities’ acceptance of individual mining operations. Applying the concept of sustainable development, on the other hand, offers an opportunity to involve multiple stakeholders in ARD management, improve risk management, and optimize the socioeconomic and business benefits of a mining operation.
The Minerals, Mining and Sustainable Development (MMSD) Project, an effort initiated by nine of the world’s largest mining companies, describes sustainable development as a goal to:
In practice, sustainable development requires an integrated, balanced, and responsible approach that accounts for short-term and long-term environmental, social, economic, and governance considerations. The economic benefit derived from mining can be an essential contributor to sustainable development. Environmental and social consequences of ARD detract from this significant benefit unless managed appropriately.
Sustainable development requires that the mining company engage stakeholders and find optimal solutions that minimize risk, maximize benefits to multiple stakeholders, and manage trade-offs. Fundamentally, the company must exercise socially responsible practices. As a particular mining project presents an ARD risk, how can the mining company best limit the risk and satisfy the needs of its stakeholders? Sustainable development requires the following:
- Looking for solutions to ARD issues from a whole-society perspective
- Applying proactive pollution prevention rather than reactive mitigation and treatment
- Implementing ARD prevention and mitigation throughout the whole mine-life-cycle perspective
Application of sustainable development principles to ARD management is discussed further in the GARD Guide (Chapters 10 and 11).
1.8 Layout and How to Use the Guide
The GARD Guide is based on a “Wiki” model. Chapters and subchapters are constructed as pages. Internal links are provided for topics where more detail is available. Links to external websites are included to organizations and other more detailed or specific topic references. The application of management technologies is based on the ARD formation process described in Chapter 2. Chapters 3 to 8 build on elements in the ‘knowledge map’ presented in Figure 1-2. Each chapter is “stand alone” with key references and guidance. A Glossary of common terms and description of Acronyms is available. Each chapter contains tools (e.g., lists, tables, and figures) to assist the reader to apply the knowledge.
Most of the technologies and approaches in the GARD Guide are applicable to generic ARD issues. However, the technologies and approaches may need to be modified to address particular aspects of ARD, such as those related to the following:
- Commodities (coal or hard rock)
- Stage in mine life cycle
- Mine planning, feasibility studies, and design (including environmental impact assessment)
- Construction and commissioning
- Mine sources (e.g., in situ leaching, open pit, underground, tailings, waste rock etc.)
- Climate (wet or dry, temperate or hot or cold)
- High/moderate/low technology applications
- Types of drainage – ARD, NMD, or SD
- Sensitive community issues
Information on these special technologies or approaches is provided in the text, side bars, and tables, as appropriate.
Chapter 9, Acid Rock Drainage Assessment and Management, brings the technologies together and discusses their application while describing in more detail the risk approach, engineering design process, and management systems to ARD. The chapter describes how to prepare and implement the ARD management plan. Chapter 10, Communication and Consultation, describes how to communicate ARD issues within and outside an organization. ARD management must be fully incorporated into geological programs, mining, and milling, so effective communication between disciplines is critical. The chapter also describes the importance of knowledge management given the potential long life of ARD issues. Regulators and local communities must have a clear understanding of the risks of ARD and the effectiveness of approaches proposed to manage it.
Differences in approaches to sustainable development might affect how ARD technologies and management are applied. Sustainable development aspects are briefly discussed in most chapters of the GARD Guide and in more detail in Chapter 11 with respect to the possible future of ARD management. Chapter 11 also identifies research needs and a possible path forward to increase our understanding of ARD genesis, best practice, and management.
1.8.2 How to Use the Global Acid Rock Drainage Guide
The GARD Guide contains 11 chapters, including this one. Readers are encouraged to, in the first instance, progress from one chapter to the next because the approach to ARD management is step-wise. Chapter 4, Characterization, in particular is an important step in implementing the ARD management approach because the application of technology must be based on a thorough knowledge of site conditions.
The tools provided in the GARD Guide will help the reader compile information for use by ARD specialist practitioners. The GARD Guide will also support the reader’s participation in more detailed scientific investigations and engineering studies at a particular mine site (e.g., identify and collect rock and water samples and review the results of analyses). With the help of the GARD Guide and a site-specific ARD management plan, for example, an environmental coordinator will be able to work with other functional groups at a mine site (e.g., mine, mill, and plant services departments) to assist them in implementing the management plan within the overall mine operations and to monitor the plan’s performance.
In general, readers are encouraged to apply the flowcharts and to use the tools in the GARD Guide to address a particular ARD issue. However readers must exercise caution and fully assess the relevance of a tool to their particular situation because ARD issues are often multifaceted and complex; a simple tool, therefore, may not fully apply. References and links in the GARD Guide should be used to access more detailed information on a specific aspect of ARD management relevant to a particular mine project or ARD management issue. An expert ARD practitioner or a suitably qualified person should be consulted in complex cases.
The GARD Guide is also a resource for teaching environmental aspects of mining to science and engineering students.
Finally the GARD Guide is a “living document” and will be updated periodically to reflect the results of ongoing research and advancing knowledge of ARD management technologies. The reader is encouraged to revisit the INAP website to access the most recent version of the GARD Guide and to provide INAP with comments on how the GARD Guide could be improved.
1.9 Chapter References
- British Columbia Acid Mine Drainage Task Force (BCAMDTF), 1989. Draft Acid Rock Drainage Technical Guide – Volume 1. Prepared by Steffen Robertson and Kirsten (SRK), Vancouver, BC.
- Dowd, P.J., 2005. The Business Case for the Prevention of Acid Drainage. Proceedings of the 5th Australian Workshop on Acid and Metalliferous Drainage, ACMER, Brisbane, Australia.
- Mining, Minerals, and Sustainable Development (MMSD), 2002. Breaking New Ground - The Report of the Mining, Minerals and Sustainable Development Project. Earthscan Publications Ltd., London. http://www.iied.org/mining-minerals-sustainable-development
- PIRAMID (Passive in-situ remediation of acidic mine/industrial drainage) Consortium, 2003. Engineering guidelines for the passive remediation of acidic and/or metalliferous mine drainage and similar wastewaters. European Commission 5th Framework, RTD Project no. EVK1-CT-1999-000021, University of Newcastle Upon Tyne, Newcastle Upon Tyne, UK.
- Placer Dome Inc., 1998. It’s about our Future, 1998 Sustainability Report. Vancouver, BC.
- Placer Dome Inc., 2003. Supplementary Sustainability Information and Technical Data. Vancouver, BC.
- Wolkersdorfer, C., 2008. ARD Literature Review. INAP.
List of Figures
- Figure 1-1: Types of Drainage Produced by Sulphide Oxidation
- Figure 1-2: Overall ARD Management Plan
- Figure 1-3: Applying an Environmental Management System to ARD
List of Appendices
- Glossary and Acronyms
- Units and Conversion Factors
- ↑ Although coal is not strictly “ore” as the term is used in hard rock mining, the reader should consider that the term “ore” also applies to coal where found in the GARD Guide.