Tailings Disposal - Mining and the Environment: From Ore to Metal - page 717

Where mining takes place underground, backi lling of mine openings with tailings is
an option. Below ground tailings disposal schemes avoid many of the environmental issues
associated with on-land storage. In addition, less tailings are usually produced from under-
ground mining as ore grades are higher and tonnages lower. Potential impacts on water
quality, however, remain.

Potential Risks
Environmental risk and risk to human life from catastrophic failure of tailings impound-
ments as a result of l oods, earthquakes, inadequate engineering design or defective con-
struction are of major concern in tailings management. Little imagination is required to
understand how very large volumes of wet, unconsolidated tailings, contaminated some-
times with toxic reagents, may impose major risks that can induce a fearful public response.
To a large extent, the negative perception of mining in our society originates from past spec-
tacular TSF failures where fear became reality (see ICOLD 2001; USEPA 1995 and UNEP
2001 for a comprehensive listing of past TSF failures). Recent examples include Merriespruit
in South Africa, 1994; Marcopper Project on Marinduque Island in the Philippines, 1996
( Case 18.1 ) resulting in the closure of the mine; Los Frailes in Spain, 1998; and Baia Mare in
Romania, 2000 ( Case 18.3 ). Once released, unconsolidated tailings of low density, may read-
ily l ow for large distances, inundating everything in their path. Phillips, 2000, estimates that
eleven dam failures since 1965 have resulted in 863 deaths.
The risk of catastrophic failure of a tailings impoundment is greatest during the opera-
tional phase. Risk decreases after completion of mining due to drainage of excess water,
consolidation and desiccation which increase the strength of deposited tailings, and a gen-
eral aging of the tailings materials, which reduces chemical reactivity. However, abandoned
tailings storage facilities continue to present considerable risks, which may be compounded
by lack of attention and maintenance. Failures principally occur through over-topping of
the embankment, or water i nding paths of weakness through the containing structures.
Foundation failure may also occur, as at the Los Frailes Mine in Spain. In seismically active
areas, collapse may be due to deformation due to earthquake loading or to liquefaction of the
stored tailings and/or parts of the foundation. Although relatively rare, collapse due to lique-
faction is almost invariably catastrophic. ICOLD and UNEP (2001) concludes that two of the
main causes of TSF failure are lack of control of water balance and construction dei ciencies.
Inappropriate operating procedures have also contributed to many failures.

To a large extent, the negative
perception of mining in our
society originates from past
spectacular TSF failures where
fear became reality.

The risk of catastrophic failure
of a tailings impoundment is
greatest during the operational
phase.

CASE 18.1
Marcopper Tailings Storage Failure 1996

In 1996 a major tailings release occurred at the
Marcopper Mine on Marinduque Island in the Philippines.
The release occurred when the rock around a concrete
plug in a tunnel gave way, releasing approximately
2 million dry tonnes of tailings into the local Boac River
system. The tunnel was connected to the abandoned
Mt Tapian pit being fi lled with tailings (intended as an
interim storage depending on the outcome of a fi nal
sub-sea tailings disposal under study). It is believed that
the rock surrounding the plug failed due to the increasing

hydraulic pressure of the tailings in the pit. The bulk of
tailings discharged in the fi rst 3 days, fl owing down as a
'lahar' for most of the 26 km long river into the sea. The
release caused signifi cant disruption to the lives of the
people in the Boac Valley in one of the poorest province in
the Philippines. Fortunately no lives were lost. The operat-
ing company, Placer Dom, committed itself to rehabilitation
of the river system, the provision of infrastructure,
services and compensation to the people in the valley and
the permanent sealing of the tunnel, a potential fi nancial

commitment up to US$ 80 million (eventually, for
various reasons, not all commitments could be fully fulfi lled
as initially anticipated). More importantly, however, the
incident had a major impact on corporate reputation,
resulted in mine closure, triggered legal proceedings by the
Philippine Government, and continues to infl uence permit-
ting of new mine developments in the Philippines to the
current day.

Source: Based on Brehault (1997)