Authors:

Rodrigo Tonidandel , Total Meio Ambiente Ltda - Geógrafo, M.Sc. em Geologia, MG - Brasi l

Hernani M. de Lima, Professor Associado, Escola de Minas, UFOP, MG - Brasi l

Maria G. Parizzi , Professora Associada, Departamento de Geologia, IGC/UFMG, MG - Brasi l

Pietro V. Cota, Total Meio Ambiente Ltda - Engenheiro Ambiental , MG - Brasi l

ÇLegal and Environmental Aspects on the

Closure of Tailings Dams in the State of Minas

Gerais, Brazil

In Minas Gerais like for Brazil, people who live here are called by their profession. The suffix “eiro” is related to occupation.

Brasileiros (Brazilians), people that worked with the Brazilian wood. Mineiros (Miners) people that work in the mines.

Mining is one of the most important industry in Minas Gerais

Minas Gerais accounts for more than 50% of the Brazilian Mineral production;

So Minas Gerais holds the main mines and consequently the higher number of TSF. Most of them located in the Quadrilátero Ferrífero Region.

INTRODUCTION

Address the results from the programme

developed by FEAM (the main recommendations

of the technical standards),

Evaluate the current state of the main legal and

environmental aspects related to dams, and

Discuss some of tailings dam design criteria and safety requirements applicable to the closure phase.

My agenda today …

In Minas Gerais there are four records of major incidents

involving tailings dams:

1986 – rupture of the tailing dam of Mina de

Fernandinho, owned by Itaminas (Itabirito-MG);

2001 – rupture of a saddle dam from a mining pit owned

by Mineração Rio Verde Ltda. (Nova Lima-MG);

2006 – leak of tailings by a partial rupture of the tulip

type spillway from a dam of Mineração Rio Pomba

Cataguases Ltda. In January 2007 occurred the rupture of

this same dam (Miraí-MG);

Rupture of a saddle dam from a mining pit owned by Mineração Rio Verde Ltda.

Fonte: FEAM, 2008.

Rupture of the São Francisco dam – Mineração Rio Pomba Cataguases

Fonte: FEAM, 2008.

In 2001, the rupture of a saddle dam in Nova Lima

was a new milestone on environmental policies

related to the mining industry, especially on

standards that regulates dams, giving rise to the

Normative Resolutions nº. 62/2003, 87/2005 and

124/2008 of the State Board of Environmental

Policies (COPAM), all related to dam safety.

In general, these Normative Resolutions managed by Feam

requires a dam registration,

propose a system that classifies the structures and

determine the presentation of the Report of the

Technical Audit of Dams’ Safety (RATSB), as well as

requires a declaration of the stability status of a dam, by

an independent and recognised consultant according to

the periodicity related to the class of dam’s potential

environmental damage.

DAM’S MANAGEMENT PROGRAM IN THE STATE OF MINAS GERAIS

Upon completion of the registration forms, it was

possible to quantify and locate the tailings dams in

the state. This made possible to generate a spatial

representation of the structures, as well to identify

to which hydrographic basin the tailings dams

belongs.

REGISTERED DAMS

Distribution of mining dams by hydrographic basins in Minas Gerais (2013).

0

50

100

150

200

250

300

DoceRiver

GrandeRiver

JequinhonhaRiver

MucuriRiver

ParaíbadoSulRiver

ParanaíbaRiver

PardoRiver

SãoFranciscoRiver

125

24

81 10 18

2

266

59%

27%

Nu

mb

er

of

dam

s

DISTRIBUTION BY HYDROGRAPHIC BASINS

Hydrographic basins which drain the Quadrilatero Ferrífero region.

The Quadrilátero Ferrífero covers 34

municipalities and is inserted into a region

that is home to the largest urban

concentration in the state of Minas Gerais,

with an estimated population of 4,305,826

inhabitants (IBGE, 2010).

According to COPAM Normative Deliberations, the classification of the potential for environmental damage from dams is associated with two technical criteria related to the characteristics of the structures and three environmental criteria, receiving each a score (V) ranging from zero to four, depending on the characteristics of the dam.

Considering the sum of the values (V) of the classification parameters presented on Table 1, the dams are classified according to the potential environmental damage into three categories:

Low potential for environmental damage - Class I = (V ≤ 2);

Medium potential for environmental damage - Class II = (2<V≤5);

High potential for environmental damage - Class III = (V> 5).

CLASSIFICATION CRITERIA (DNs 62/2002 e 87/2005)

In 2013 there were 454 registered tailings dams. Of this total, 34% were classified as class III, 36% as class II and 30% as Class I.

120

130

140

150

160

170

ClassIClassII

ClassIII

NumberofDam

s

Classifica onofdamsaccordingtopoten alofenvironmentaldamage-2013

Reduce the likelihood of incidents using a systematic monitoring programme for the dam.

Must be performed by a dam safety specialist that does not belong to the staff of the company.

Must contain at least the expert opinion on the safety of the dam, recommendations for improvement and implementation schedule for works.

The schedule for execution of subsequent audits was established according to the class of the dam:

Every year, for Class II I dams - High Potential for Environmental Damage;

Every two years, for Class II dams - Medium Potential for Environmental Damage

Every three years, for Class I dams - Low Potential for Environmental Damage.

In 2008 was published the DN COPAM nº 124, established that the company must submit to the environmental agency the Statement of Stability ’s Status that allows FEAM to know the results of the technical audit and update information at the Agency database.

REPORT OF THE TECHNICAL AUDIT OF DAMS’ SAFETY (RATSB)

ANALYSIS OF SOME REACHED RESULTS

68%(267)

14%(53)

18%(72)

StabilityCondi ons-2006

StableDams

Damswithoutguaranteeofstability

Damswithnoconclusionsaboutthestability

Feam programme related to tailings dam closure phase Although the works related to compliance to the law and improvements in dams are most often complex and costly, the results obtained in the Dams’ Management Programme have showed satisfactory after the technical security audit.

This programme helps mining companies to undertake more effective control of their dams, in order to minimize the inherent risks associated with the actual design of these structures, allows to predict critical situations and alert to conditions of geotechnical instability and rainfall drainage systems capacity.

However there are very few and largely incomplete guidelines related to dam safety aspects specific to the tailings dam closure phase.

Feam still lacks focus on the tailings dam closure phase considering this phase may last 1000 years or more, as compared with a typical mine production phase lasting some 20 years.

The long closure phase also means that the number of tailings dams will increase with time as new mines are put into production and tailings dams are constructed while few are removed/breached.

Feam programme related to tailings dam closure phase

Which probabilistic flood design criterion as applied to a tailings dam production phase lasting (ex.) 20 years needs should be appropriate for the closure phase that is assumed to last 1000 years or more? Designing for 1000 years is essentially designing for perpetuity.

How to deal with the environmental aspects or environmental performance of dams or consequences related to environmental, social and cultural impacts, as these issues are site-specific and are subject to applicable regulatory approval process?

‘Collect and treat’ (long-term treatment phase) or ‘Water cover’ (closure phase), Which option for decommissioning of a tailings impoundment should be considered?

“While a water cover can create a low oxygen diffusive environment, from a geotechnical perspective a flooded impoundment is certainly of higher risk with regard to essentially every nature of possible physical failure mode”

Some issues that need to be addressed

Should any special consideration be given to the designing of tailings dam because the dam is to function for 1000 years (or perpetuity)?

The question of the degree of long-term structural integrity, or stability margin, of a tailings dam is more complex. It is difficult to believe that the tailings will ‘age’ thus resulting in an increased strength and resistance to liquefaction.

For example, chemical reactions in a tailings impoundment may result in a long-term rise of the phreatic surface and/or perched water table as a result of ‘hardpan’ formation.

Chemical reactions may also result in dissolution of minerals contained in dam or dam foundations materials. Possible cause of Los Fraile dam foundation failure.

How should the minimum design safety factor (shear failure under static conditions) increased from the conventional 1.5?

Some issues that need to be addressed

My tailings dam definition

In Brazil, we “mineiros” (from Minas Gerais), are recognised to have the biggest eye of the word. When we have a dust in our eyes we say that there is a train inside. We use the word train for everything.

“Tailings dam is train that can fail in the future”. Being conservative I do recommended to remove or breach tailings dam.

Conclusion

Thank you all for your attention!

Obrigado pela atenção!