This presentation reviews tailings dams and the hazardous waste contained within them. Basic design and the consequenses of design failure will also be reviewed.

1. TAILINGS DAMS
A Review on Failure Rates, Consequences and Solutions
Vanessa Chappell
Physiology Seminar, 2017

2. Worldwide Waste Problem
• Disposal of waste in a crowded world is
becoming more and more of a problem
• Even domestic waste in developed
countries presents complicated disposal
issues as we have seen from previous
landfill presentations

3. What are Tailings Dams?
 Mining is the extraction of minerals and
metals from earth. Manganese, tantalum,
cassiterite, copper, tin, nickel, bauxite
(aluminum ore), iron ore, gold, silver, and
diamonds are just some examples of what is
mined.
 Tailings are the waste product of mining and
consists of ground rock and process
effluents that are generated in a mine
processing plant.
 Tailings Dams are among the largest
manmade structures on Earth!

4. Mining Waste
• Due to the nature of mining and mineral
processing the volumes of wastes from
mining operations are significantly larger
than BOTH domestic and industrial
wastes.
• Around the banks of a tailing lake in
China - seven square miles of toxic
waste shows the extent of this industry's
impact.
• 9,600 to 12,000 cubic meters of waste
gas—containing dust concentrate,
hydrofluoric acid, sulfur dioxide, and
sulfuric acid—are released with every
ton of rare metals that are mined.
• Approximately 75 cubic meters of acidic
wastewater, plus about a ton of
radioactive waste residue are also
produced.
*Vegetation appears red, grassland light is brown,
rocks are black, and water surfaces are green.

5. Mining Waste
 Mining extraction is never 100%
efficient, so it is not possible to reclaim
all reusable and expended processing
reagents and chemicals.
 The unrecoverable and uneconomic
metals, minerals, chemicals, organics
and process water are discharged,
normally as slurry, to a final storage
area, Tailings Storage Facility (TSF).
 Both the physical and chemical
characteristics of tailings and their
methods of handling and storage are of
great and growing concern.

6. How to Store Tailings
• To help determine the design requirements of a
tailings storage facility, the following characteristics
of the tailings will need to be established:
• Chemical composition (including changes to chemistry
through mineral processing) and its ability to oxidize
and mobilize metals
• Physical composition and stability (static and seismic
loading)
• Behavior under pressure and consolidation rates
• Erosion stability (wind and water)
• Settling, drying time and densification behavior after
deposition (getting rid of the water)
• Hard pan behavior (crust formation on top of the
tailings)

7. Structure of Tailings Dams
 Tailings Dams must provide safe and permanent storage of tailings material. This is
achieved by designing tailings embankments to withstand any potential catastrophic
event – such as an earthquake or flood – and by controlling the seepage of tailings
water.
 Unlike water dams, tailings embankments are made of rock and sand, and have a
very wide base. As the volume of tailings material contained in the storage area
grows, so must the height of the tailings embankment and the elevation of the
tailings pipeline.
 Another concern for tailings management relates to the dispersal of tailings dust.
This dispersal can be prevented by keeping the tailings material saturated at all
times.

8. Factors affecting Tailings Dam Stability
 Foundation stability
 Height and angle of outer slope
 Rate of disposition and detailed properties of tailings
 Seismic influences
 Control of hydrology (drainage system)

9. Basic Designs for Tailings Dams
A. Downstream
• successive raising of the embankment
that positions the fill and crest further
downstream.
B. Centerline
• tailings from the embankment crest form
a beach behind the dam wall. When
subsequent raising is required, material
is placed on both the tailings and the
existing embankment.
C. Upstream
• starts with a pervious (free draining)
starter dyke foundation. The tailings are
usually discharged from the top of the
dam crest creating a beach that becomes
the foundation for future embankment
raises

10. Failure
Despite improvements on safe design for tailings dams. There has been reported failure
almost every year for the past 30 years

11. How many? How often do they fail?
 An estimated 3,500 active tailings impoundments stand around the world
 As of 2000 these structures experience known "major" failures of about 2 to 5
annually, along with 35 "minor" failures
 This failure rate is more than twice the failure rate of conventional water retention
dams.
 The records are very incomplete on crucial data elements:
 design height of dam, design foot print, construction type (upstream, downstream, center line), age,
design life, construction status, ownership status, capacity, release volume, runout, etc

12. Results of Failure
• The sheer magnitude and often toxic
nature of the material held within
tailings dams means that their failure,
and the ensuing discharge into river
systems, will invariably affect water
and sediment quality, and aquatic and
human life for potentially hundreds of
km downstream (Edwards, 1996;
Macklin et al., 1996, 2003, 2006;
Anonymous, 2000; Hudson-Edwards et
al., 2003).
• Records indicate that thousands of
people have died from tailings dam
failures (WISE, 2012)

13. Results of Failure
• Over 2000 people lost their lives between 1964-2000 due to tailings dam failures
• Between 2000-2017 tailings dam failures have caused a reported 5000 people to
become homeless, 400 dead, 125 missing, 150 injured, and millions affected as a
result of water and soil contamination

14. Environmental impacts associated with tailings dam failures
Other than the possible heavy loss of life and economic losses, environmental damaging impacts associated with
structural failures in dams include:
• damage or destruction of valuable habitats and ecosystems;
• release of effluent from an impoundment may contaminate surface water
• generation and release of acid mine drainage may occur
• seepage of effluent throughout the base of the structure may contaminate groundwater
• dried tailings may be swept as dust by strong winds into neighboring habitations or ecosystems
• effluent in tailings impoundments may generate toxic gases that may poison birds attracted by water in dry
regions

15. Examples of tailings impoundment failures

16. Failures and Causes

17. Design Failure
 Upstream construction is one of the
earliest construction types and the most
common method used.
 Cheap
 Uses materials on site
 Inactive dams are not immune
 Overtopping (rain coupled with poor
management)
 Seismic changes

18. Common Reason for Active dam Failure
 Seepage
 Weather
 Managemnt

19. Timely Remedial Action
• Timely action when warning signs first
appear can prevent costly and
sometimes fatal consequences
• Responsibility is left to the owner or
operator of the dam but there is no
substitute for a competent engineer in
the construction process
• Regular inspection is a must

20. Conclusion
 There was a lack of design ability, poor construction, poo operation/closur o a
combination in each and every case history
 If basic design and construction requirements are ignore a tailings dams opportunity
as a FAILURE is imminent
Quotes from dam operators after failures:
“A well intentioned corporation employing apparently well-qualified consultants I not adequate
insurance against serious incidents.” (Morgentsern, 1998 after the Spain Dam Failure.)
“Any attempt at construction o a tailings dam that does no ake into account the design-construct
process is in my opinion doomed to great distress.” (D’Appolonia, 1976, after the Virginia disaster)