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Acid Rock Drainage Management Plan 

 
Author: Jack Caldwell

Summary

This review discusses the preparation and implementation of an Acid Rock Drainage Management Plan. All parts of the plan are discussed in detail, including facility design, performance assessments, construction and operation, and closure of the facility.

INTRODUCTION

This is a brief piece on a focused topic: Preparation and implementation of an Acid Rock Drainage Management Plan (ARD-MP) for a mine. This piece is intended to set out options and approaches that:
  • You may choose to use at your mine;
  • Which may enable you to engage and manage a consultant to compile and/or implement the plan;
  • As a regulator review the plan for adequacy and potentially approval; and/or
  • As a member of the public, judge a proposed plan to manage acid rock drainage at a mine in your neighborhood.

TECHNICAL BACKGROUND

To use, understand, and benefit from this piece, you will need at least a basic understanding of the technical issues involved in acid rock drainage. There are so many fine writings on this topic that are readily available, that I only provide a few links, as follows:

All of these and the many other resources you may read on acid rock drainage boil down to a few simple facts: some rocks at some mines, when exposed to air and water, generate acidic runoff, and the acidity of the runoff may pollute water resources at and downgradient of the mine. The nature of the rock, the specifics of the chemical reactions, the level of acidity of the resultants solutions, and the severity of the environmental impact are site-specific. Only sampling and testing, modeling and analysis, will tell you how much work you have to do to build, operate, and close mine facilities that will not cause water quality impairment by acid rock drainage.

DEVELOPING AN ARD MANAGEMENT PLAN

We assume that you have established that at your mine there is a potential and/or actual acid rock drainage issue. In brief, at some time, some part of your mine and its associated facilities will generate water that is acid and that exceeds acceptable limits.

Hence we assume that as a mine manager you decide to compile (or have compiled) a plan to manage this unacceptable drainage; or that as a regulator you have demanded a plan so you may be assured the new mine will not exceed regulatory discharge standards; or as a member of the public you seek a plan that demonstrates that the new mine will not pose a perpetual source of acid drainage.

DISCIPLINES, KNOWLEDGE, AND EXPERIENCE

I submit that regardless of your discipline (scientific, technical, and/or engineering), regardless of you current knowledge (before reading this piece), or your experience, you can understand every issue associated with the compilation and implementation of a mine's acid rock drainage management plan.

I make this assertion to reassure you: most of the writings on the topic are so badly written that you may be tempted to conclude it is your lack of training and intellect that renders the topic hard. I assure you, or at least I opine thus: it is the poor quality of the writing, not the nature of the subject, that renders it seemingly impenetratable.

My advice: if you cannot understand a piece on the topic, put it down and ignore it; the author is not worth fretting or fussing over; assign them to the bin of the inept writers who plague our waking moments. Seek out another piece that is better written and provides the information you seek in a readily comprehensible way.

That said, of course it never hurts to get an expert on your side. The first is a geochemist. They are the only people who truly understand the chemistry of the rocks and soils that give rise to acid rock drainage. Then get a surface water hydrologist and a groundwater hydrologist to help you with the surface water issues and the groundwater issues. Next get a learned civil engineer to compile your mine's water balance model. Get somebody skilled in community relations both to keep the public informed and happy and to interact with the regulators. Maybe even a good lawyer to deal with the regulators-a lawyer is better than an unskilled, shrill scientist screaming to support their concepts.

ASSOCIATED WRITINGS

Here are links to some writings that set out technical approaches that are relevant to any mine's acid rock drainage management plan:

THE ACID ROCK DRAINAGE MANAGEMENT PLAN (ARD-MP)

GENERAL
In this section, we discuss the parts, sections, or chapters of a typical Acid Rock Drainage Management Plan (ARD-MP). As we describe the objectives, scope, and contents of each section, you will find that you learn a little about the technical, scientific, and engineering issues involved and what you need to do to compile the necessary technical approaches to actually manage the acid rock drainage at your site.

SITE CHARACTERIZATION
In this section of the mine's ARD-MP you will have to describe the site, at least as much as is relevant to the production and management of acid rock drainage at the site.

If you have compiled an Environmental Impact Statement (EIS) (or equivalent) for the mine, you will have established therein that the acid rock drainage is manageable at your site. Thus much of the information that is needed in this section of a mine's ARD-MP should already be in the mine's EIS.

If, however, you have not had to compile an EIS for the mine, or the EIS was compiled and approved a long time ago, you may need to collect afresh all the information needed to prepare a comprehensive site description section for your ARD-MP.

The data will include information about: site and regional location and topography; site and regional geology; geochemistry; climate; surface water; groundwater; and the receiving environment that may be impacted by acid rock drainage.

MINE DESCRIPTION
In this section of your ARD-MP, describe the layout of the mine and its associated facilities. This will involve text and figures that provide information about the mine workings; the underground mine shaft and adits if this is an underground mine; the open pit and its slopes and sequential development if this is an open pit mine; the heap leach pad if heap leaching is undertaken; the tailings impoundment and its operation; the waste rock dumps; and the surface water management facilities, including diversion swales, channels, and ditches, and any ponds and water retention facilities you may plan or have on site.

ARD POTENTIAL
The data about the rock and soils and how they will generate or be precluded from generating acid drainage should be described in this section of your ARD-MP. The link at ARD Sampling provides guidance on sampling and acid rock drainage characterization. See also this link: Acid Rock Drainage Prediction.

Ultimately there is no substitute for test results from laboratory work aimed at establishing the acid generating potential of potentially suspect soils and rock.

You may also need to document the geochemical attenuative capacity of soils and rocks through which seepage for mine facilities generating acid drainage may seep. Again such data is best obtained from laboratory testing of materials that may be affected.

DESIGN

GENERAL
In this section of your mine's ARD-MP, you should describe the design of all facilities that may generate acid drainage. This will involve documenting the layout of such facilities, the size, the operation, and the closure works.

Keep in mind this is not a design report. The objective is to provide a full description that establishes that you have considered all the options and alternatives. You need to establish that you have selected the approach that minimizes acid drainage or that enables you to best (most cost-effectively) manage acid drainage. You should provide enough information to enable those charged with constructing, operating, managing, and closing the acid generating facility to do so in the full knowledge of initial intentions and perspectives.

GENERATING MULTIPLE SOLUTIONS
All design involves the identification and comparison of alternatives. We assume you did or will do a thorough job in this regard. We assume you will have or are identifying a range of alternative approaches to facilities that will contain acid generating materials. Here is where you should describe the alternatives and document the process of identifying and comparing alternatives.

There are many ways to identify and compare alternatives. The United States' EIS process is, in my opinion, the best and most accepted. If you cannot pass EIS muster, there is probably no point in going more sophisticated.

Let us assume, however, that you do decide and are able to go more sophisticated. Basic Decision Making theory may be applied. Alternatively, or in addition, undertake a Value Engineering workshop. I personally like value engineering and have found it always generates new and innovative approaches.

Obvious alternative solutions include: encapsulation of acid generating materials, direct acidic seepage to attenuating materials, and/or collect and treat acidic seepage. But there are surely as many alternatives as there are mines and waste disposal facilities.

ANALYZING AND SELECTING A SOLUTION: WHAT ARE YOUR OBJECTIVES?
Once you have identified a reasonable range of practical alternatives to limiting and controlling acid rock drainage, you should analyze the alternatives and select the best. This part of the process, as documented in your ARD-MP, depends primarily on the criteria applicable to your mine. If you are in the United States, you will probably be faced with NPDES discharge criteria. These are terribly simple: do not discharge water from your mine the quality of which exceeds present limits-generally the discharge water should not be acidic.

If you are in Canada, you may be able to adopt a more subtle approach: dilute by directing the discharge to larger bodies of water, one of the many lakes or swiftly flowing rivers.

If you are in a primitive jurisdiction, you may even be lucky enough to establish your own criteria including providing alternative sources of water to those whose primary source is affected by your acidic discharge. This all depends, but you will have to document this as part of a comprehensive statement of objectives and relevant rules and regulations.

Assuming you have established your discharge criteria and assuming you have more than one approach that results in achievement of these discharge criteria-lucky you-you will probably seek to implement the least cost approach. This goes without explanation. Why pay more to achieve the same end? Really this takes us straight back to the US EPA EIS criteria, so I say no more.

DESIGN FOR CLOSURE
This is obvious. I have written extensively about it as have many others. There is no need to delay here repeating the obvious and well-documented. But we must note that easy as it is to write about design for closure, that much more difficult it is to achieve it. Personally I suspect it is impossible. And to the extent that it is, it generally makes little sense: operate to the lowest cost possible today and deal with the inevitable costs of closure when the time comes-meanwhile postponing the day of closure as long as you can.

PERFORMANCE ASSESSMENT

GENERAL
In this section of your ARD-MP, document any performance assessments you have compiled. These may be as simple as a logical train of thought narrative. It may be as complex as a complete mine chemical mass balance model replete with probabilistic inputs.

WATER & CHEMICAL MASS BALANCES
I believe that no mine that has to manage acid rock drainage should be allowed to operate without a comprehensive chemical mass balance. I have written extensively about this at this link. If you cannot access this link, then go to the GoldSim website and get their code and use it.

TESTING ASSUMPTIONS AND DESIGNS
I suggest that you operate your acid generating facilities in accordance with an Observational Method Plan. At this link are extensive writings on the application of the Observational Method to acid mine drainage control and mitigation.

FAILURE AND RISK ANALYSIS
Undertake a Failure Mode Analysis. Also do a Risk Assessment. These two links provide considerable information on these topics and their application in mining situations. Take a look.

CONSTRUCTION & OPERATION

IMPLEMENTING THE ARD-MP
The heart of the ARD-MP are the specifics to be documented in this section about constructing and operating the acid generating facilities. Here follows a re brief description of the major parts of such a plan.

STAFFING
Designate people who are responsible for implementing the plan. The primary responsible person should be a mine or mining company staff person. Ideally they should be a registered professional, if such registrations exist in the jurisdiction of your mine. If not, then the responsible person should be selected on the basis of experience, integrity, and power to effect the right thing.

The mine's responsible person is likely to need the aid of other mine professionals: the chemists, geologists, civil engineers, and other technical and scientific mine staff. Thus the mine's responsible person should have the position, power, and character to invoke and collate such input and assistance.

The mine's responsible person will probably need the input of consultants. But you cannot as a miner, put the ultimate responsibility onto the consultant. Consultants come and go. They are expensive and generally otherwise occupied. Use them for technical and engineering expertise, but not for fundamental activities and the day to day implementation of the mine's ARD-MP.

CONTINGENCY PLANNING & EMERGENCY RESPONSE
Your mine will probably have its own contingency plans and emergency response plans. Make sure these incorporate sections specific to the mine facilities that may generate and control acid drainage.

CLOSURE

You have successfully operated the mine. Now comes the time to close the mine, reclaim the site, and set in place the procedures needed to protect the environment in the long term. If you are lucky, this period will be but a few short years, and then you can walk away from a site that is in equilibrium with the surroundings, and is safe and non-polluting.

If you are unlucky, you will have to be prepared for perpetual maintenance. Or pass the site on to the taxpayer on the basis that they benefitted from the taxes paid by the mine, and now it is time for the body politic to shoulder the perpetual burden.

In strong jurisdictions, you may be held to a bond. In weak jurisdictions, you may be able to leave, and leave it at that.

Regardless, in your mine's ARD-MP, you should describe how this phase of mining is to be dealt with as regards the mine's acid generating facilities. I leave it to you to fill in the blanks.

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