Chapter 1

1.0 Chapter 1: The GARD Guide

1.0 Introduction

The GARD Guide

This Version of the GARD Guide

• Version Number: 0.5
• Last Updated: February 16, 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 e-mail address

Development of this Global Acid Rock Drainage (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.

The GARD Guide was created through the contributions of many individuals and organizations. A team lead by Golder Associates Ltd prepared a “beta version” of the Guide. INAP established broad-based Steering and Advisory Committees to direct preparation of this document. INAP also received input from several other contributors, peer reviewers and interested stakeholders. INAP gratefully acknowledges all of this assistance. A list of individuals that contributed to the development of the Guide is available here.

This Global Acid Rock Drainage (GARD) Guide deals with the prediction, prevention and management of drainage produced from sulphide mineral oxidation; often termed “acid rock drainage” (ARD) or “sulphidic drainage”. While focused on mining, the technology described will be helpful to those that encounter sulphide minerals in other activities (eg. rock cuts, excavations, tunnels etc.).

The GARD Guide is intended as a state-of-the-art summary of the best practices and technology to assist operators and regulators to address issues related to sulphide mineral oxidation. This Guide will be of interest to:

• Mining and mining service companies
• Governments (national regulatory or land management agencies, IFC, World Bank, regional development agencies etc.)
• Consultants
• Researchers/Educators/ Academia

PIRIMID Model The document assumes the reader to be a scientist or engineer with a reasonable background in chemistry and the basics of civil 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.

• Community/Communities of interest
  • Bankers
  • NGO’s
  • Indigenous Peoples

The Guide is a technical document designed primarily for a scientist or engineer with a reasonable background in chemistry and the basics of civil engineering with little specific knowledge of ARD. The target audience is adapted from a model developed by the PIRAMID Consortium (2003) (see box at right). The prime reader will typically be an employee of the mining industry, regulatory agency, research organization or consulting company.

It is not a design guide as that requires a higher level of detail and more site specific knowledge of a particular project or mine. Detailed design of ARD mitigation techniques will continue to be conducted by knowledgeable practitioners.

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.

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

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.