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Design For Closure 

 
Authors: Jack Caldwell - Robertson GeoConsultants Inc. ; Gordon McPhail - Metago Environmental Engineers Pty Ltd

Revised: January 2012

Summary

This review describes the design of mines and mine facilities, including infrastructures, open pits, underground mines, tailings facilities, waste rock dumps, heap leach pads and other waste disposal facilities for closure. It lists technology resources, websites, case histories, and consultants that discuss the design of mines for closures. It also includes consideration of the current and future costs of mine reclamation, restoration, and long-term surveillance and maintenance post-closure.

INTRODUCTION

Designing and operating a mine for closure is now almost a commonplace. But if you are new to the concept or seek to refresh your information base, here is our summary of the current state of the technology, art, and thinking on the topic.

THE BEST TEXTS ON THE TOPIC

Though not quite the definitive handbook on mine closure, but it comes pretty close. I refer to Environmental Techniques for the Extractive Industries: Mine Closure Handbook. There are too many authors to list. It comes from Vammalan Kirjapaino Oy in 2008. Explanation of its origin and genesis is in this extract from the foreword:

This handbook has been prepared during the TEKES-funded project "Environmental Techniques for the Extractive Industries" which was undertaken as a joint research project between industry and various agencies during the years 2003-2005. The project was coordinated by Outokumpu Oyj with supporting industry partners being Tieliikelaitos (TLL, the Finnish Roads Enterprise) and Maa ja Vesi Oy (M&V Oy, Soil and Environment Ltd, which has been incorporated into Poyry Environment Oy). Public sector agencies participating in the project were Geologian tutkimuskeskus (GTK, Geological Survey of Finland) and Valtion teknillinen tutkimuskeskus (VTT, Technical Research Center of Finland).

The volume was written for use in Finland. It was not intended to cover mines outside of Finland. So it is "restricted" in a sense. But it is so comprehensive at 170 pages and covers so many topics in satisfying detail, that it is to be recommended to anyone interested in the subject, and to everyone charged with closing a mine.

An old closed mine near Fairbanks, Alaska

Intended for implementation at mines worldwide, The International Council on Mining and Metals (ICMM) publishes Planning for Integrated Mine Closure: Toolkit. August 2008.

If you have not hitherto read about or thought about planning for mine closure, this new volume is an excellent place to start. The first five chapters take you at an even pace through the reasons why you should plan for closure from start to finish of a mine. The chapters set out the steps towards formulating a cost-effective and responsible closure plan. Then you are told how to implement this plan and why you should do so.

This volume emphasizes the fact that:

Mine closure remains a challenging subject, despite clear recognition of good practice by operations and external stakeholder and the technical ability of companies to achieved recognized good practice. Many of the challenges are posed by the context or situation of a mine or mine development rather than by technical challenges and further dialogue on these issues from the users of this document is needed.

Which is a long and convoluted way of saying that engineers and scientists can close mines given time and money, but management and budgets, regulators and their demands for certainty, and hysterical NGOs get in the way.

The most valuable part of this volume is the so-called "toolkit" of Section 6. Here again not much new, but nevertheless a useful collation of ideas, checklists, and best practice approaches. If you do what is inherent in the toolkit, nobody can accuse you of irresponsibility-you can justifiably claim to be mining responsibly.

BASIC PRINCIPLES

McPhail notes: "Detailed consideration for closure during the setting, selection and design of a tailings storage facility in order to manage risks and financial provisions is not only prudent but is fast becoming mandatory in the current era of emphasis on responsible mining, sustainability, and good governance."

Common sense dictates that you have a mine closure plan and update it at regular intervals. Each update should take account of the current status of mine development and should strive to implement mine operating procedures that will facilitate closure.

Robertson and Shaw (2006) note this regarding design for mine closure:

Closure plans should be re-evaluated as the mine site development progresses since the initial plans are based on projected conditions which are expected to change in response to additional ore discoveries, changing conditions of product and mining economics, advances in technology and new regulatory requirements. Once the initial plan has been developed and is accepted, periodic, iterative re-assessments and revisions should be completed to ensure that the plan remains current, relevant and optimized.

MINE CLOSURE LAWS & REGULATIONS

Some countries have laws and regulations governing mine closure. Many do not. A comprehensive examination of mine closure laws and regulations worldwide is provided by Clark and Clark who both appear to reside in Hawaii. They conclude:

Prior to 1985, the issue of mine closure can be said to have been of a low priority for most countries, as evidenced by the large number of abandoned mines that exist in virtually every major mining country. As a result, very few countries had in place, and the majority still do not have in place, mineral policies and legislation that provide for comprehensive mine closure. The basic components of a comprehensive mine closure policy and associated legislation would
(i) provide specific provisions for reclamation and rehabilitations,
(ii) require both Environmental and Social Impact Assessments and associated work plans,
(iii) have a comprehensive bonding and financial surety program,
(iv) provide provisions specifically for abandonment and post-closure activities, and
(v) have specific monitoring and enforcement procedures to ensure compliance.
Ruins at the old Kennicott copper mines, Alaska

In Australia, the general laws provide for the states to take over long-term custodial care of closed mines, based on the following principles set out in Strategic Framework for Mine Closure:

1. A Responsible Authority should be identified and held accountable to make the final decision on accepting closure.

2. Once completion criteria have been met, the company may relinquish its interest.

3. Records of the history of a closed site should be preserved to facilitate future land use planning.

Old gold mine subsidence

We know of no provision in United States or Canadian law for relinquishing title to a mine and passing the long-term responsibility and liability to the state.

There is a possible exception. Title II uranium mill tailings piles pass into the custodial care of the Department of Energy along with the Title I site when the mine receives a license from the Nuclear Regulatory Agency that they have been closed in accordance with standards. The standards include stability for 1,000 years, so most mining companies are not likely to want to emulate this program.

MINE CLOSURE GENERAL PRINCIPLES & GUIDELINES

GENERAL PRINCIPLES
To design for closure, we need to know what closure involves. The general principles of mine closure are set out in many documents including the following:

UMTRA
Possibly the most stringent mine closure criteria ever implemented are those that governed the Uranium Mill Tailings Remedial Action (UMTRA) Project of the US government. The literature on this project is immense; one example is provided here. The UMTRA Project established that it is possible to close mines in a way that provides stability for long periods. However, the cost of doing so is high and even then there is no cessation of surveillance and maintenance.

CASE HISTORIES
Here are some sites where you can read about closed mine sites:

An old copper mine is closed and filled with water, Butte, Montana

LONG-TERM SURVEILLANCE & MAINTENANCE
In the long term somebody has to look after a closed mine. It is not enough to turn the site over to a local church group and hope they will fix the cover after Sunday services. Here are some sites that deal with the major issues involved with long-term S&M:

DESIGN & OPERATIONAL PROCEDURES TO EXPEDITE CLOSURE

It is all very well to talk about designing and operating for closure. But in practice what does this mean?

This old canal near Sonora, CA still carries water. Well maintained canals like this are now used for local water supplies, stock watering, and so on. Note that it's following the contour line and definitely not flowing straight downhill like a natural stream would.

In this section we list some things you might do to reduce the cost of closure and provide a reclaimed mine site that is not a long-term negative for the environment or society. We do not propose that these approaches are cost-effective. They probably are not.

Points to consider are:

  • the type of mine
  • infrastructure
  • waste disposal facilities
  • financial accountability

MINE TYPE
Choose an underground mine over an open pit mine. This results in the least surface impact, hence reduced closure impact and cost. Fill the underground mine workings with waste rock and/or tailings and/or a mix thereof. This reduces the volume of waste at cessation of mining and reduced the potential for mine-induced subsidence. If you have to have an open pit, provide for backfilling. This is now California law, and we know the world's tendency to emulate Californian fashions. If you cannot backfill the pit, provide for the lake that will develop in all but the world's driest locations.

INFRASTRUCTURE
Roads: I know of no mine where the access roads were decommissioned. There is always somebody who wants to use the roads to get to a house, a graveyard, a hunting ground, a religious site.

Buildings and Other Facilities: Demolish and decommission these. Put unrecoverable or non-recycleable materials into the tailings before putting on the cover. There is not much you can do to design or operate to make this easier or cheaper.

TAILINGS IMPOUNDMENT & WASTE ROCK DUMP & HEAP LEACH PAD
McPhail surveys Australian practice and provides insightful analysis and advice on designing and operating mine waste disposal facilities for closure. His paper and powerpoint presentation are probably the most comprehensive discussion on the topic we know of. You must read them if this topic interests you, regardless of where you practice.

Bonanza Mine, Alaska
  • Site Selection. Find the site with the least permeable foundations. Find a site that is geomorphically stable. Find a site with no groundwater that could possibly be impacted.
  • Layout. Detail to replicate the stable geomorphic forms of the surrounding landscape. To the extent that this is not practical, provide for regrading at closure and for erosion control features and materials.
  • Vegetation. Provide outer surfaces amenable to vegetation and establish vegetation as soon as practical. Where this cannot be done, provide for revegetation at closure.

FINANCE & ACCOUNTING
We believe there is no accepted financial approach that enables one to compare the benefit of money spent on a feature beneficial to closure now with money spent thirty years hence at actual closure. Net present value calculations simply show that it is better to spend money thirty years hence and avoid the expenditure now.

We see no reason to change this. All that needs to be done is to make sure that when the thirty years rolls around there is sufficient money available to do what was postponed until the day of closure. This is best achieved by five year updates of mine closure plans and bonding provisions. An update every year is unrealistic and unnecessary for most mines.

In this regard see the ICMM report Financial Assurance for Mine Closure and Reclamation.

Also see the March 2006 Guidance Paper Financial Assurance for Mine Closure and Reclamation from the ICMM, which concludes:

ICMM recognizes that it is the responsibility of mining companies to provide assurance to governments and the public that closure of facilities will be protective of health, safety, communities and the environment. Financial assurance must be applied in a manner that ensures proper protection but does not place an unnecessary financial burden on the operator which could discourage investment that would stimulate socio-economic development. It is important that the mechanisms put in place serve as far as possible to promote the efficient exploitation of mineral resources and their associated economic benefits while achieving levels of environmental protection and future land use that are acceptable to society. This guidance is intended to help achieve this.

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