Chapter 1

The GARD Guide

Introduction

This Version of the GARD Guide

• Version Number: 0.7
• Last Updated: December 12, 2008
• Property of the International Network for Acid Prevention (INAP)
• For further information or to provide comments and contributions to updates of the Guide, please contact: INAP at terrence.chatwin@inap.com.au

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 link to disclaimer.

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.)
• Consultants
• Researchers/Educators/ Academia
• Community/Communities of interest
  • Bankers
  • NGO’s
  • 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).

“The document assumes the reader to be a scientist or engineer with a reasonable background in chemistry and the basics of engineering, albeit with no specific knowledge of acid rock drainage. The underlying science and technology of ARD are discussed in sufficient detail that the reader can understand their application, but the discussion stops short of being a formal scientific treatise on the relevant aspects of, for example, geochemical kinetics and solute transport hydrodynamics. Rather, the document guides the reader through the logical framework of ARD management enabling them to quantify the nature of the problematic drainage, and the potential for management that exists on the site, leading to the selection of the most appropriate form of prevention and remediation.”

Acid Rock Drainage

Acid rock drainage (ARD) is formed by the natural oxidation of sulphide minerals in 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 they increase the exposure of sulphide minerals to air and water. The drainage produced from the oxidation process may be acidic, with or without dissolved heavy metals, but always contains sulphate ions.

In addition to ARD, neutral mine drainage (NMD) or saline drainage (SD) may be formed from the oxidation process. Neutral mine drainage is characterized by metals in solution at near neutral pH. Saline drainage contains high levels of sulphate at neutral pH without significant metal concentrations; saline drainage’s principle constituents then are – sulphate, magnesium and calcium ions.

Although mine-water quality does not lend itself to precise compartmentalization, the accompanying chart illustrates the various types of drainage. Neutral mine drainage and saline drainage can occur together (ie. 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 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.

1.1 ARD Management - The Business Case

ARD formation is difficult to stop once initiated because it is a natural process. 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 (eg. soil covers on mine wastes – see photo at left)

The cost of ARD remediation at primarily abandoned and “orphaned” mines in North America has been estimated in the tens of billions of US 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 life. Put simply, ARD can make a mine project uneconomic and present mine owners with technically challenging, expensive and difficult long-term management problems.

Addressing ARD can impact a company’s “social license to operate” through financial, political and management issues such as:

• Unbudgeted reclamation costs with little or no internal resources (i.e., manpower, equipment, infrastructure, utilities and management)
• Contaminated water resources with adverse impacts on flora and fauna
• Unbudgeted increases of environmental remediation
• More stringent regulatory requirements
• Loss of corporate image, public acceptance and stakeholder trust due to unexpected contamination
• Loss of future mining opportunities
• Commitment of corporate resources to a mine that has long since ceased to provide economic value.

“Treating acid drainage once it has occurred, or mitigating environmental impact after it has occurred, is usually an admission that something has gone wrong either in the characterisation, planning, design or operation of a mine. It is Newmont’s belief that acid drainage can be prevented if some key principles are followed throughout the life of a mine, from exploration through to closure.” Paul Dowd, former Managing Director, Newmont Australia (Dowd, 2005)

Proper mine characterization, drainage quality prediction and mining 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.

A comprehensive approach to ARD management as promoted by the GARD Guide will reduce liabilities for the mining industry and governments, reduce adverse environmental impacts and build public support for mining.

1.2 Scope and Objectives of the GARD Guide

Scope

The potential for acidic drainage to form from mining has been known since at least 1556. ARD was observed as early as 1698 associated with coal mining in Pennsylvania (BC ARD Technical Guide, 1989).

Research into the process of ARD formation and methods to minimize its impact has been ongoing for over 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 body of scientific and engineering guidance available on ARD already through INAP, MEND, BC ARD, BC MEMPR, ADTI, ACMER, WRC, PADRE and other programs. The research however is in disparate references, not easily accessible and tends to be issue, commodity or geographically centric. The objective of this Guide is to consolidate and summarize the information on ARD management and be up-to-date and global in scope. This Guide focuses on mining and applies to ores, wastes (overburden, waste rock and residues/tailings) and mine workings (including in-situ mining). The Guide applies to the entire mining industry and all commodities produced by mining including base metals, coal, iron ore, gold, diamonds and uranium where the ores contain sulphide minerals. The GARD Guide is applicable to the complete mine life cycle and to existing and historic ARD issues as well as new mines.

However, the Guide does not specifically address:

• 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 (eg. jarosites and other hydroxyl-sulphates) that are produced by pyrometallurgical or hydrometallurgical processes. However, jarosites or other salts produced as intermediate products during ambient temperature sulphide oxidation are considered.

The technology described in this Guide may be of value to those encountering or managing acid sulphate soils and pyrometallurgical or hydrometallurgical sulphate salts.

Objectives

The overall objective of the GARD Guide is to facilitate world-wide best practice in prediction, prevention and mitigation of acid-rock drainage. It is a reference document for stakeholders involved in sulphide mineral oxidation and related waste management issues.

Specific objectives of the Guide are to:

• Articulate the issues associated with sulphide mineral oxidation
• Reference and improve the understanding of best global practice, customized where necessary for special geo-climatic conditions
• Promote a risk-based, pro-active, consistent approach by encouraging reduction and control of ARD at the source
• Leverage the world’s ARD expertise and share expertise with developing countries
• Support the ‘Equator Principles’ and ICMM’s objectives by achieving ‘global best practice’ in future mining projects

The Guide is a “how to” document based on proven, field tested technologies. It is not a literature review, regulatory tool, case study review or design manual.

1.3 Relation to other guides

Some Existing ARD Compendia

• Acid Rock Drainage At Enviromine, Enviromine
• ARD Test Handbook, AMIRA International, May 2002
• MiMi – Results and Synthesis Report for Phase 1 1998-2001, MiMi, April 2003
• MiMi – Performance Assessment Main Report, MiMi,, December 2004
• Guidelines for Metal Leaching and Acid Rock Drainage at Minesites in British Columbia, Ministry of Energy and Mines, August 1998
• Draft Guidelines and Recommended Methods for Prediction of Metal Leaching and Acid Rock, Ministry of Energy and Mines, 1998
• Draft Acid Rock Drainage Technical Guide Volume 1, British Columbia Acid Mine Drainage Task Force Report, August 1989
• MEND Manuals, MEND, January 2001
• List of Potential Information Requirements in Metal Leaching/ Acid Rock Drainage Assessment and Mitigation Work, MEND Report 5.10E, January 2005
• Environmental Regulation of Mine Waters in the European Union, ERMITE
• Field and Laboratory Methods Application to Overburdens and Minesoils, Industrial Environmental Research Laboratory Office of Research and Developments U.S. Environmental Protection Agency, March 1978
• Risk Assessment Framework For the Management of Sulfidic Mine Wastes, Australian Center for Mining Environmental Research, September 1999
• Industry Liaison Officer Report for the Management of Sulfidic Mine Wastes Project, Australian Center for Mining Environmental Research, February 2000
• Management of Sulfidic Mine Wastes and Acid Drainage, Australian Center for Mining Environmental Research, September 2000
• Manual of Techniques to Quantify Processes Associated with Polluted Effluent Form Sulfidic Mine Wastes, Australian Center for Mining Environmental Research, February 2000
• Comparison of Oxidation Rates of Sulfidic Mine Wastes Measured in the Laboratory and Field, Australian Center for Mining Environmental Research, February 2000
• Management of Sulfidic Mine Wastes – Current Australian Practice and Available Knowledge and Techniques, Australian Center for Mining Environmental Research, May 2000
• Determining the Toxicity Potential of Mine Waste Piles, USGS, June 2003
• Acid Drainage Technology Initiative, ADTI Workbook Chapters: Introduction (in draft), Mitigation (in draft), Sampling and Monitoring, Pit Lake and Prediction (in preparation)
• On-site and Laboratory Investigations of Spoil in Opencast Collieries and the Development of Acid-Base Accounting Procedures, Usher BH, Cruywagen LM, de Necker E, Hodgson FDI, South African Water Research Commission Report Number 1055/1/03, 2003
• Acid –Base Accounting, Techniques and Evaluation (ABATE), Usher BH, Cruywagen LM, de Necker E, Hodgson FDI, South African Water Research Commission Report Number 1055/2/03, 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 "Passive in-situ remediation of acidic mine / industrial drainage" (PIRAMID). University of Newcastle Upon Tyne, Newcastle Upon Tyne UK. 166pp.) (PIRAMID Consortium (2003)
• ASTM Method E-1915 Standard Test Methods for Analysis of Metal Bearing Ores and Related Materials by Combustion Infrared Absorption Spectrometry, Annual Book of ASTM Standards volume 03.06 (also standard method for humidity cell testing, SPLP (vol 11.04) and MWMP (vol 03.06))

As discussed above, there is already a considerable body of knowledge on ARD management in the scientific and engineering literature. Many compendiums have already been produced that summarize aspects of the state-of-knowledge and in some cases provide guidelines for managing ARD. In addition, the series of ICARD, BC, 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 the proceedings from those conferences, especially case studies.

Some existing compendia of ARD technology are listed at right. This 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 detailed state-of-the-art guides and summaries where they already exist.

1.4 Approach of the GARD Guide

The GARD Guide is based on a systematic approach to ARD management as shown in the Figure below. The approach proceeds from site characterization to preparation, and ultimately implementation of an ARD management plan. Specific elements of the approach and appropriate technologies are described in more detail in the chapters of the Guide.

1.5 Application to Mine Phase

ARD management is applied at all phases of a mine from “cradle to cradle“ as part of a continuous improvement process (see Figure below). The ARD management plan is based on technical understanding and knowledge but is defined within corporate policies, government regulations and community expectations. The plan itself is based on site characterization and ARD/NMD/SD prediction science and incorporates engineering to prevention and control. Water treatment may be included as a contingency in the plan.

Implementation of the plan requires management systems and communication between stakeholders. The plan’s performance is monitored using a range of metrics from water and rock sampling and possibly gas testing. The overall performance of ARD management is evaluated against site specific environmental requirements and the criteria established by policies etc. 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 (particularly drill holes that are artesian), bulk samples and test pits/underground workings. In addition, site characterization and ARD prediction must begin at the start of mineral exploration.

The approach to ARD during the phases of mine development is discussed in more detail in the GARD Guide chapters.

1.6 Layout and How to Use

Layout

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 web sites are included to organizations and other more detailed or specific topic references.

The application of management technologies is described in terms of an ARD formation model involving primary, secondary and tertiary factors as described in Chapter 2. This model links ARD production at mineral surfaces to internal and external migration pathways and eventually to potential environmental receptors (eg. aquatic life).

Chapters 3 to 9 build on the ‘knowledge map’ presented in Figure 1 showing in more detail how each step is executed. Each chapter is “stand alone” with key references and specific guidelines. A glossary of common terms and list of references are available. Each chapter contains tools (eg. example tables and figures) to assist the reader apply the knowledge. Standard methods of analysis in external references are identified where appropriate. The majority of technologies and approaches in the Guide are applicable to generic ARD issues. However, they may need to be modified for particular:

• commodities (coal or hard rock)
• mine sources (eg. insitu leaching, open pit, underground, tailing, waste rock etc.)
• climates (wet or dry, temperate or hot or cold)
• high/moderate/low technology applications
• types of drainage – ARD, NMD or SD

Information on these special technologies or approaches is provided in side bars and tables.

Chapter 9, ARD Assessment and Management, brings the technologies together and discusses again the overall logic/process diagram while describing in more detail the application of 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. The chapter includes a set of “FAQ’s” (frequently asked questions) on ARD Management at a basic level suitable for the general public.

Technical chapters end with a section containing “FAQ’s” which are summaries for the chapters.

Differences in approaches to sustainability in developed and developing countries might affect how ARD technologies and management are applied. Sustainability aspects are briefly discussed in most chapters of the Guide and in more detail in Chapter 11 with respect to the possible future of ARD management.

How to Use

This Guide is a reference document and “compass” to further more detailed information on ARD. It might be adequate for readers who desire a broad, but not highly detailed, understanding of ARD technologies and management (eg. mine site environmental staff working with corporate/consultant specialists or regulatory staff coordinating a mine environmental impact assessment). It will assist the reader monitor the evolution of the sulphide oxidation process in mine wastes and identify when more experienced ARD practitioners are required to address a particular issue.

The GARD Guide contains 11 chapters including this one. Readers are encouraged to, in the first instance, progress from one chapter to the next since the approach to ARD management is step-wise. Chapter 3, Characterization, in particular is an important step in implementing the ARD management approach as the application of technology must be based on a thorough knowledge of site conditions.

The tools provided in the Guide will help the reader compile information for use by ARD specialist practitioners. The Guide will also support the reader’s participation in more detailed scientific investigations and engineering studies at a particular mine site (eg. identify and collect rock and water samples and review the results of analyses). With the 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 implement the plan and monitor its performance. An audit tool is provided in the Guide to assist a site environmental coordinator or corporate staff to evaluate the degree of implementation and effectiveness of the ARD management plan.

In general, the reader is encouraged to apply the flow charts and use the tools in the Guide to address their particular ARD issue. However readers must exercise caution and fully assess the relevance of a tool to their particular situation as ARD issues are often multi-faceted and complex; a simple tool may not fully apply. References and links in the 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 should be consulted in complex cases.

The Guide is also a resource for teaching environmental aspects of mining to science and engineering students. An educator’s teaching kit is available here.

Finally this 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 this web site to access the most recent version of the Guide and to provide INAP with comments on how the Guide could be improved.

Chapter References

BC ARD Technical Guide, Volume 1, BC ARD Task Force, 1989. Dowd, P.J. (2005) “The Business Case for the Prevention of Acid Drainage”, in Proceedings of the 5th Australian Workshop on Acid and Metalliferous Drainage.

PIRAMID 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 "Passive in-situ remediation of acidic mine / industrial drainage" (PIRAMID). University of Newcastle Upon Tyne, Newcastle Upon Tyne UK. (166pp.)