TAILING DAMS
RISK ANALYSIS AND MANAGMENT
Pavel Danihelka
Eva Červeňanová
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CONTENT:
•
•
•
•
Examples of historical accidents
Introduction to risk theory
Risk analysis principles
Basics of application of risk analysis
to tailing dams safety
• Conclusion
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EXAMPLES OF HISTORICAL
ACCIDENTS
At least 221 serious tailing dams accidents
reported by UNEP*:
Mine name/
Location
Incident
Date
Impact
Baia Mare,
Romania
30.01.2000
100,000 m3 cyanide contaminated water with
some tailings released
Baia Borsa,
Romania
10.03.2000
22,000 t of tailings contaminated by heavy
metals released
Merriespruit,
South Africa
22.02.1994
17 deaths, 500,000 m3 slurry flowed 2 km
* http://www.mineralresourcesforum.org/docs/pdfs/Bulletin121.PDF
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Major tailing dams review – cont.
Mine name/
Location
Incident
Date
Impact
Buffalo Creek,
USA
26.02.1972
125 deaths, 500 homes destroyed
Mufilira,
Zambia
25.09.1970
89 deaths, 68,000 m3 into mine workings
Omai, Guyana
19.08.1995
4.2 million m3 cyanide slurry released
Placer,
Philippines
02.09.1995
12 deaths, 50,000 m3 released
Los Frailes,
Spain
24.04.1998
released 4-5 million cubic meters of toxic
tailings slurries
Stava, Italy
19.07.1985
269 deaths, tailings flowed up to 8 km
Aitik mine,
Sweden
09.08.2000
1.8 million m3 water released
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History of major tailing dams accidents
Source: „ICOLD Bulletin 121“
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Case study:
BAIA MARE
January 30, 2000 in Baia Mare (Romania)
the biggest freshwater disaster in Central
and Eastern Europe.
Nearly 100,000 m3 of cyanide and heavy
metal-contamined liquid spilled into the
Lupus stream, reaching the Szamos,
Tisza, and finally Danube rivers and killing
hundreds of tones of fish and poisoning
the drinking water of more than 2 million
people in Hungary.
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LOS FRAILES
April 25, 1998
tailings dam failure of the Los Frailes
lead-zinc mine at Aznalcóllar near
Seville, Spain,
released 4-5 million cubic meters of
toxic tailings slurries and liquid into
nearby Río Agrio, a tributary to Río
Guadiamar.
The slurry wave covered several
thousand hectares of farmland, and it
threatens the Doñana National Park, a
UN World Heritage Area.
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STAVA
On July 19, 1985, a fluorite
tailings dam of Prealpi
Mineraia failed at Stava,
Trento, Italy. 200,000 m3 of
tailings flowed 4.2 km
downstream at a speed of
up to 90 km/h, killing 268
people and destroying 62
buildings. The total surface
area affected was 43.5
hectares.
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AITIK
On September 8, 2000, the
tailings dam of Boliden's Aitik
copper mine near Gällivare in
northern Sweden failed over a
length of 120 meters. This
resulted in the spill of 2.5
million cubic meters of liquid
into an adjacent settling pond.
Boliden subsequently released
1.5 million cubic meters of
water from the settling pond
into the environment to secure
the stability of the settling pond.
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VARIABILITY OF CAUSES OF
ACCIDENT
•
•
•
•
Inadequate management
Lack of control of hydrological system
Error in site selection and investigation
Unsatisfactory foundation, lack of stability of
downstream slope
• Seepage
• Overtoping
• Earthquake
MAIN ROOT CAUSE:
RISK ANALYSIS AND MANAGEMENT NEGLECTED
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Distribution of causes of tailing dams accidents
Source: ICOLD Bulletin 121
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VARIABILITY OF CONSEQUENCES
• Flooding, wave of slurry
• Contamination of surface water, living organisms
(biota), intoxication
• Drinking and irrigation water contamination
(surface)
• Drinking and irrigation water (underground)
contamination
• Soil contamination
• As consequence of 2),3),4)ad.5 : Food chain
contamination
» FREQUENTLY TRANSBOUNDARY EFFECT
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Conclusion:
• Tailing dam is a risky installation able to
cause major accident and so we have to
treat it as major risk
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2. INTRODUCTION TO RISK THEORY
• Definition of
– Hazard
– Risk
• Risk and its quantification (measurement)
• Principles of risk reduction/management
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DEFINITION OF TERMS
SOURCE OF DANGER
=
POTENTIAL TO CAUSE
DAMAGE
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RISK
=
PROBABILITY x GRAVITY
OF ACCIDENT (EVENT)
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RISK
DANGEROUSITY
IDENTICAL
RISK
DIFFERENT
DIFFERENCE: MANAGEMENT OF RISK
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FLUX OF DANGER
Initial
event
Other
conditions
Source
system
Flux of danger
Target
system
DOMINO EFFECT:
SYSTEM 2
INITIAL
EVENT
SYSTEM 3
SYSTEM 1
CATASTROPHE
Example: Stava accident
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• Flux of danger:
 Movement of
material
 Flux of energy
 Flux of
information
• Targets system:
 Population around tailings dam
 Environment
• Surface water
• Underground water
• Soil
• Living organisms
 Material and financial losses
(direct)
 Functioning of enterprise
(including indirect losses)
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• Sources of danger:
– Having potential (energy) to cause damage
– Having potential to weaken structure, resistance,
resilience of our system (tailing dam and its
environment)
• Direct to dam stability
• Indirect including human error
• To consequences
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• RISK MATRIX
A – banal case
B – frequent accident with low
consequences (minor injury,
small contamination, ...)
PROBABILITY
QUANTIFICATION OF RISK
B
C
A
D
C – disaster with high probability
(walking in minefield)
D – disaster with low probability
(nuclear power plant, major
incident)
GRAVITY
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• Acceptability of risk
PROBABILITY
NON ACCEPTABLE
ACTION
NECESSARY
RISK
MITIGATION
ACCEPTABLE
ACTION
VOLUNTARY
CONDITIONALLY
ACCEPTABLE
GRAVITY
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ACCEPTABILITY OF RISK
• Decision is socio-politic, not scientific
• Decision should include all stakeholders
• All types of risk should be evaluation
together
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How to decrease risk?
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RISK ANALYSIS PROCESS
Selection of
sources of
danger
Feedback and
control
Scenarios
proposal
Risk assessment
Goals
setting
Barriers of
prevention
ETA
FTA
AMDEC
FMEA
HAZOP
WHAT-IF
Etc.
Risk management
IMPACT
Residual risk
PROBALITY
TECHNICAL
ORGANISATION BARIERS
BARRIERS
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SOURCES OF DANGER
 Direct to dam stability:
•
•
•
•
Active environment (rain, snow, freeze…)
Earthquake
Geological conditions
Domino effect
 Indirect to dam (including human error):
•
•
•
•
•
Wrong conception
Construction failure
Material failure
Bad maintenance
Lack of control
 To consequence:
•
•
•
•
Water and sludge movement
Mechanical contamination by solid particles
Chemical toxicity / ecotoxicity
Radioactivity
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SCENARIO PROPOSAL
• All plausible scenario should be involved in
preliminary conspiration
• All stages of life-time must be considered
• Those having minor impact omitted
• Similar combined to groups
• Described as combination of events in time
• Finally, we are able to compare limited number
of scenarios only
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TOOLS HELPING TO DEFINE
SCENARIO
•
•
•
•
•
•
•
•
•
•
Examples of past accidents
Near-misses and accidents on site
Control list
WHAT-IF
ETA
FTA
AMDEC
FMEA
HAZOP
Etc.
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Past accidents analysis
• In site – during all life of it
• In similar places you operate, including
near-misses. Mind the necessity of
reporting.
• In mine industry generally
– TAILINGS DAMS, RISK OF DANGEROUS OCCURRENCES, Lessons
learnt from practical experiences, ICOLD- UNEP 2001, Bulletin 121,
ISSN 0534-8293
– APELL for Mining: Guidance for the Mining Industry in Raising
Awareness and Preparedness for Emergencies at Local Level,
Technical report No. 41, UN Publications 2001, ISBN 92-807-2035
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SCENARIO DESCRIPTION
CAUSES
CONSEQUENCES
1
2
„TOP“
EVENT
3
4
(DAM
DESTRUCTION)
5
6
7
SCENARIO 1
SCENARIO 2
EACH SCENARIO NUMBERED
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RISK ASSESMENT:
• FREQUENCY x CONSEQUENCES (IMPACT)
FREQUENCY:
•From past accidents (high degree of uncertainty)
•From initial events frequency and FTA by boolean algebra
•Avoid omitting of low frequency events (not to limit only to
100-year water or earthquake)
•Human factor extremely important
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Frequency of „100 year“ flooding
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One mythus:
„We operate it long time without accident, so safety is
prooved“
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CONSEQUENCES:
• Consequences to human lives, health and well
being. Evaluation of consequences with stakeholders
necessary
• Direct costs (remediation, compensation, ...)
• Social disturbance
• Consequence to environment – short time and
long time impacts
• Economical consequences and operability
• Indirect costs
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Costs of Failure
Physical failure: recent large failures $30 to $100 million
in direct costs
Environmental failure: some recent clean-up liabilities to
several $100’s of millions
Closure liability: some recent examples in $ 500 milon to
$ 4 billion range
Industry/investor impacts: Shareholder value losses and
industry imposed constraints and costs amounting to
many billions of dollars
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CONSEQUENCES II:
• The scales of consequences should be defined
before analysis is done (4-6 grades)
• All possible targets should have the same scales
of consequences (e.g. Grade X is comparable in all
target systems)
• The most serious consequence is selected
• Internal values of society/enterprise become to
be clarified
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Severity of impact – an example
(source: Robertson GeoConsultants Inc.)
Consequences Severity Biological Impacts Regulatory Impacts and
(Direct Costs)
and Land Use
Concerns
Public Concern and Image
Health and Safety
Extreme (>$10 M)
Local, international and NGO
outcry and demonstrations, results
in large stock devaluation: severe
restrictions of 'licence to practice';
Local, international or NGO
activism resulting in political and
financial impacts on company
'license to do business' and in
major proceedure or practice
changes,
Occasional local, international
and NGO attention requiring
minor proceedure changes and
additional public relations and
communications
Infrequent local, international and
NGO attention addressed by
normal public relations and
communications
Fatality or multiple fatalities
expected
No international/ NGO attention
No concern
High ($1 - $10 M)
Catastrophic impact
on habitat
(irreversable and
large)
Significant,
irreversible impact
on habitat or large,
reversable
Unable to meet regulatory
obligations or expectations; shut
down or severe restriction of
operations
Regularly (more than once per
year) or severely fail regulatory
obligations or expectations large increasing fines and loss of
regulatory trust
Moderate ($0.1 - $1 M) Significant,
Occasionally (less than one per
reversible impact on year) or moderately fail
habitat
regulatory obligations or
expectations - fined or censured
Low ($0.01 - 0.1 M)
Minor impact on
habitat
Negligible (<$0.01 M)
No measurable
impact
Seldom or marginally exceed
regulatory obligations or
expectations. Some loss of
regulatory tolerance, increasing
reporting.
Do not exceed regulatory
obligations or expectations
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Severe injury or disability likely:
or some potential for fatality
Lost time or injury likely: or
some potential for serious
injuries; or small risk of fatality.
First aid required; or small risk
of serious injury.
RISK ASSESSMENT
PROBABILITY
Following frequency and gravity, scenarios
are put to the risk matrix
1
5
2
4
3
7
6
GRAVITY
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GOALS SETTING:
Non-axeptable (red zone) scenarios: immediate action
PROBABILITY
Conditionally acceptable (yellow zone) scenatios: action envisaged
1
5
1
5
2
4
3
6
2
7
7
GRAVITY
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BARIERS OF PREVENTION / PROTECTION
Initial
event
BARRIER
Other
conditions
Source
system
REMOTION OF SOURCE
Flux of danger
BARRIER
Target
system
PROTECTION OF TARGET
SYSTEM 2
INITIAL
EVENT
BARRIER
SYSTEM 3
SYSTEM 1
BARRIER OF FLUX DOMINO EFFECT
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CATASTROPHE
SAFETY MANAGEMENT
• Prevention part (even three part of bow-tie
diagram)
• Emergency preparedness
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NEAR MISSES:
„HUNTING FOR DEVIATIONS“
ELIMINATED
CATASTROPHE
BIG ACCIDENTS / LOSSES
SMALL ACCIDENTS/ LOSSES
DEVIATIONS
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Emergency preparedness
• Preparedness to accident, even with low
probability
• Training and not only desktop one
• Information of all potentially involved
• Crisis management including training
• Open and honest communication with
municipalities, emergency response
teams, government bodies (inspection…)
• Communication with media
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RECOMMENDATIONS
1) Detailed site investigation by experienced geologists and geotechnical
engineers to determine possible potential for failure, with in situ and
laboratory testing to determine the properties of the foundation materials.
2) Application of state of the art procedures for design.
3) Expert construction supervision and inspection.
4) Laboratory testing for “as built” conditions.
5) Routine monitoring.
6) Safety evaluation for observed conditions including “as built” geometry,
materials and shearing resistance. Observations and effects of piezometric
conditions.
7) Dam break studies.
8) Contingency plans.
9) Periodic safety audits
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And something for thinking…
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DO WE REALLY NEED ACCIDENT
PREVENTION?
•
•
•
•
You've carefully thought out all the angles.
You've done it a thousand times.
It comes naturally to you.
You know what you're doing, its what
you've been trained to do your whole life.
• Nothing could possibly go wrong, right ?
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THINK AGAIN!
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THINK AGAIN!
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• Thank you for your attention !
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