Tailings Facilities An Introduction from an Insurance Perspective

1
Tailings Facilities - An Introduction from an
InsurancePerspective

• Some Operational and Closure Considerations

2
Tailings Dam Operation Issues

• Deposit tailings
• Reclaim water
• Plan, engineer and construct rising retention
  dams
• Document all aspects of operation
• Monitor surface and groundwater quality
• Prepare as-built drawings

• Monitor performance of tailings facility
• React to emergencies and incidents
• Prepare and update closure plans
• Prepare tailings dam operation manual

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Tailings Operational Responsibilities

• General Planning and Budgeting
• Siting Overall Design
• Detailed Design - Tailings Retention Dam
• Construction Tender
• Deposit Tailings
• Operate Reclaim
• Monitoring Performance

• Mine Personnel
• Consultant
• Consultant
• Mine and Consultant
• Mine Personnel
• Mine Personnel
• Mine Personnel and Consultant

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Mine Tailings Personnel Requirements

• Need a trained engineer/technician responsible
  for tailings operations at every mine site
• Need commitment from corporate office and mine
  manager to operate tailings impoundment to
  recognized standards
• Need continuity in tailings experience both at
  mine site and with consultants
• Need competent consultants to advise mine and
  corporate office

5
Operational Issues

• Largely trial-and-error methods used for design
  and construction of tailings dams prior to the
  1950s
• Great strides over past 4 decades through
  introduction of soil mechanics in 1960s, lessons
  learnt from experience and continual
  technological advancements
• It is clear that we now have the technology and
  know-how for designing SAFE tailings facilities
• HOWEVER..

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Operational Issues - Contd

• Deficiencies in tailings management practices not
  uncommon
• Deficiencies can severely negate strives for
  technical design excellence
• In most cases, operating personnel lack
  understanding of design background OR
• Lack appreciation of the significance that
  operational deviations from design assumptions
  could impose of safety

7
Operating Issues - Contd

• DME of Western Australia (1998) observed
• It is now clear that while the required degree
  of professionalism is evident in the design and
  construction of tailings structures, many of them
  are not operated in line with all design
  parameters, resulting in particular problems at
  several mine sites. The majority of tailings
  incidents reported to the Department could have
  been avoided if the tailings storage facility had
  been operated within design parameters or had
  been diligently managed.

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Operating Risks - Contd

• Stated commitment and sincere intent needs to be
  backed up by diligent application
• Need to recognize close integration between
  design, construction and operations. all phases
  are inter-related
• Unlike water dams, tailings dams are constructed
  and operated simultaneously

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Operating Risks - Contd
Impacts
Design
Criteria
Criteria and Rules
Construction
Operations
Effects
Effects
Actual
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Operating Risks - Contd

• Recognition and understanding of the interplay
  between design, construction and operations are
  important for mine personnel who manages/operates
  facility
• Staff begins to appreciate potential magnitude of
  effects that actions, or lack of actions, can
  have on performance

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Inspection and Maintenance

• Regular Inspection Very Important Visual
  inspection limited to surficial conditions
• Need conscious effort to question cause and/or
  meaning of any observed deviations from expected
  norms
• Always be aware of design and operating criteria
  during inspection
• Next Figure shows typical visually identifiable
  issues that should be kept in mind
• Table 1 (overhead) provides minimum checklist of
  items

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Inspection and Maintenance Contd
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Inspection and Maintenance Contd

• Inspections should be done regularly by mine
  personnel, and also especially
• During spring freshet
• Mid-summer
• Prior to first snow fall
• Mid-winter (as much as possible)
• Immediately after relatively large natural events
  (e.g. flood)

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Inspection and Maintenance Contd

• Outline routine maintenance measures that can be
  done for example
• Backfill local erosion gullies
• Infill local differential settlement cracks to
  prevent infiltration
• Remove ice formation and/or other debris from
  water conveyance structures (spillways, ditches,
  etc.)
• Grading dam crest surface towards pond
• Upgrade erosion protection as required

15
Inspection and Maintenance Contd

• Document inspection results including any
  maintenance completed, with photographs
• Manual should include organizational chart
  showing a line of communications for reporting of
  incidents or if there is a concern from the
  inspections

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Performance Monitoring for Dam Safety

• Program designed so that development of failure
  modes are identified with lead time for action
• Requires thorough understanding of failure modes,
  and most suitable method of observations/instrumen
  ts to identify them
• Illustration of intricate link between failure
  mode type and monitoring devices on next slide
  (Anderson et al 1999)

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(No Transcript)
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Some Comments on Performance Monitoring...Contd

• It is prudent that every monitoring device have a
  clearly defined function and/or benefit relative
  to safety issues
• Commonly, focus on where additional devices are
  needed.However, where function of existing
  device is not clear, then its maintenance should
  be questioned
• In general, most programs designed for
  construction, then often maintained for long-term
  monitoring, without questioning their
  appropriateness for dam safety needsis it really
  appropriate?

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Some Comments on Performance Monitoring...Contd

• Some failure modes cannot be monitored to provide
  warning as easily as other failure modes (e.g.
  cannot forewarn a seismic event)
• Monitoring is best suited for ductile behavior
  where shear failure normally takes time to
  develop
• Failure by brittle behavior provides little
  warning (be careful if changes to operations
  result in increased loading)
• Only defense where monitoring not suitable, is
  good design against reasonably worse conditions

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Some Common Problems

• Instruments not read or available readings not
  validated
• Abnormal readings often viewed as error but
  apparently normal readings could also be
  error
• Misinterpretation or ignored - cause and effect
  not appreciated, deviations from historical
  trends not appreciated
• Trigger levels for action not established or, if
  established, no clear action plan
• Without diligent execution, monitoring program
  simply provides a false sense of security

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Illustrative Case Histories

• Uncertainties due to dynamics of mining
  development
• Hydrological conditions differ from assumed
  often in remote areas with no or little data
• Change in mill water balance (more or less water
  to pond)
• Changes in pit geology and/or mill grind
• Change in ore body - greater storage or faster
  dam raises
• Unexpected shutdown - continued rising pond level
• Unexpected high clay in tailings - beach slopes,
  settled densities, sedimentation rates, storage
  capacity, water balance

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Case History 1

• Dam on permafrost
• Key requirement to develop long tailings beach
  against dam
• Actual operations created large free water pond
  against dam, leading to eventual thawing and
  degradation of permafrost.
• Design background unknown or lack of appreciation
  of design deviation

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Case History 2

• Cycloned sand tailings dam at Gibraltar Mine,
  British Columbia
• Extensive under-drain system, cyclone underflow
  discharged directly onto downstream slope
• Design done in late 1960s, assumed average 4H1V
  slopes
• Construction began 1972, performance excellent
• See Figure on Next Slide

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Case History 2 Figure
Gibraltar Tailings Dam
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Case History 2 Contd

• 1991, downstream slope much steeper at 2H1V to
  3H1V, compared to original designexcellent sand
  quality (clean) and increasing dam height reduces
  runout. Prompted a re-evaluation of long-term
  seismic stability of tailings dam, completed
  1992/93.
• KEY POINT
• Review of as-built surveys from mid-1980s onward
  already showed propensity for slope to
  progressively steepen, but significance not
  appreciated.
• Original design done decades ago becomes distant
  memory need effort to maintain continual
  awareness

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Case History 3

• Mineral Kings tailings facility, southeastern
  British Columbia
• Overtopping occurred sometime in March 1986 when
  ice was allowed to form and block spillway
• Even though spillway design was likely adequate,
  lack of attention to operational details was main
  culprit

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Case History 4

• Tailings dam in central interior of Queensland,
  Australia
• Typical practice in Australia is
  upstream-method-of-construction dam raises
  constructed on spigotted beach
• Key requirement is to ensure thin lifts to
  promote drying of tailings, by rotating
  spigotting around dam perimeter
• Drying is required for strength gain to support
  next raise
• INCIDENT
• Recent change in ore type and mill grind
  tailings much finer and cohesive compared to
  previous
• Precluded adequate drying of tailings
  difficulties in meeting design dam raising
  schedule

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Case History 5

• Tailings dam in Indonesia designed on Australian
  practices
• Australia arid (negative water balance) and low
  seismic Indonesia high rainfall (positive water
  balance) with areas of high seismic activity
• Assumption of drying not appropriate
• Water balance management difficulties resulted in
  most of tailings being deposited subaqueously.
  Lower densities was key factor in requiring
  another unplanned dam raise
• Upstream construction led to concerns of long
  term seismic stability due to liquefaction of
  tailings issue currently being addressed

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Case History 6

• Mine in British Columbia
• Piping developed in sand beach of large tailings
  dam discharging some 10,000,000 gallons of water
• Large downstream damage, but fortunately no loss
  of life
• Dam well-designed, rockfill section with graded
  filter
• FINDINGS
• Filter zones not built as specified rather,
  constructed by end-dumping from heights of 6 to
  10 m, causing much segregation
• Also, free water was allowed to pond too close to
  the dam

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Case History 6 Contd

• Poor construction negated effects of design
  features that were specifically incorporated to
  prevent this failure mode
• Remedial measures included filling the pipe with
  gravel and fine rockfill, and spigotting tailings
  from a new dyke constructed over soft tailings
  and located well upstream of main dam
• See Figure on Next Slide

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Case History 6 Figure
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Case History 7

• Acid rock drainage precipitates plug drains along
  toe of tailings dam- reduce stability

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Case History 7 Contd

• Solution place drains below groundwater level
  with a pipe to surface for collection/treatment

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TAILINGS SLURRY TRANSPORT
RAINFALL
RUNOFF
EVAPORATION
WATER RECLAIM
MILL
MILL
SEEPAGE RECOVERY
FREE WATER POND
FLOOD FREEBOARD
RECLAIM PUMP
DAM
TAILINGS
GROUNDWATER SEEPAGE
SCHEMATIC OF TAILINGS DISPOSAL SYSTEM
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What is the purpose of a Closure Plan?

• Public protection for
• safety, e.g. dams and water
• health, e.g. drinking water quality, vegetation
• environment, e.g. fish, dust
• effective use or rehabilitation of land
• Shareholder protection for
• environmental liability

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The Rules are Changing!

• Regulatory requirements are changing.
• Corporate Accounting is changing to recognize
  Closure Liability.
• International banking rules are changing.
• Social expectations are changing.

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Regulatory Requirements - Closure Plans

• Most plan requirements are similar.
• Differences are more in level of detail, level
  of scrutiny and level of enforcement.
• Examples Peru (PAMA), British Columbia
  (general ), Australia (general), Ontario
  (specific), U.S. (specific varies by state)

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Closure to What Standard?

• .. On closure, returning mine sites and
  affected areas to viable and, wherever
  practicable, self-sustaining ecosystems that are
  compatible with a healthy environment and with
  human activities
• The risk cost (or factor of safety) for
  unknowns has to be reasonable.

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Cover Up Plan versus Closure Plan

• Range of requirements from Cover Up to Closure
• decommission buildings
• reclamation
• physical stability, e.g. dams for seismic and
  erosion
• water management stability, e.g. spillways,
  diversions, etc.
• chemical stability surface , eg. ARD from rock
  dumps and tailings
• chemical stability groundwater, e.g. contaminant
  plumes
• reclamation to productive use, e.g. grazing,
  agriculture, wetland, etc.
• reclamation to acceptable use
• Long term Care and Maintenance or Transfer of
  Liability

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Examples of Financial Assurance

• B.C. Equity silver 30 mil. bond which was
  negotiated on closure for ARD. Bonds required
  on closure to fund long term care and
  maintenance. During operations bonds required
  for cover up plans and financial assurance of
  company for actual closure requirements.
• Ontario Currently being negotiated with the
  mining industry - Government wants Bonds for
  Closure Plans - Mining Industry wants Financial
  Assurance based on Company. Expect to have a
  combination of the two. Smaller operations have
  put up bonds.
• Nevada, Montana Surety company for Closure
  Implementation

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Preparing a Closure Plan

• Steps in a closure plan
• Acceptable land use
• Exit ticket

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Closure Plan Table of ContentsOntario
Legislation

• Legal status, environmental policies and
  regulatory policies
• land ownership, ISO requirements, etc.
• Site characterization baseline and existing
  conditions
• geology, mineralogy, geochemistry
• hydrology, surface water and groundwater
• aquatic and terrestrial biology
• Operations infrastructure
• inventories and as-builts of mill, dams, roads,
  contaminated soils, etc.
• document impacts on groundwater, surface water,
  dust, soils, aquatic/terrestrial
• document environmental management systems, eg..
  Handling hazardous waste, fuel, etc.

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Mine Closure Plan Table of Contents contd

• Develop closure alternatives for both temporary
  and permanent closure
• meet criteria of minimize environment impact
  maximize post closure land use
• comparative cost assessments and risk/impact
  assessments of alternatives
• identify technical issues to be resolved to
  confirm feasibility of closure plan
• identify management issues that could assist
  closure
• identify monitoring requirements
• Selection of preferred alternative(s)
• alternative to meet Owner specific ,
  liability-risk-cost criteria
• cost estimate of preferred alternative(s)
• assessment of liability and legal issues of
  alternative(s)
• develop monitoring program

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Closure Plan Table of Contents

• Identify progressive decommissioning options
• reclaim inactive areas, modify hazardous waste
  and hydrocarbon handling
• modify operations to reduce closure impacts, eg.
  Dust, erosion, seepage, etc.
• Post Closure Land Use
• consider transfer or continued use of
  infrastructure, eg. Power, roads, water supply
• consider future land use that could assist
  socio-economic impact of closure, e.g. resort
  use, agricultural, industrial, etc.
• Closure Plan Review and Update
• annual reviews to reflect changing conditions and
  additional information
• continually work towards reducing risk and cost
  of closure

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Acceptable Land Use?

• No significant human health issues
• safety of structures to standards of other civil
  engineering structures
• healthy sustainable environment

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EXIT STRATEGIES

• Transfer to government
• Transfer to private developer
• Care Maintenance - operated by the mine
• Care Maintenance - Contractor (e.g MWM Inc.)
• Liability transfer to third party