Environmental Engineering Reference
In-Depth Information
Quarrying may continue during mine operation to provide limestone for acid rock drain-
age prevention measures, to acquire material for staged tailings dam construction, to cater
for ongoing road maintenance or to acquire materials needed for primary mineral process-
ing (such as limestone in acid leaching).
4.8 DESIGN FOR CLOSURE
Mine closure activities occur on cessation of mining and benei ciation activities, following
the exhaustion of the ore reserve. The aim of environmentally effective mine closure is to
leave all areas affected by the project, in a safe and stable condition. This usually involves:
(1) decommissioning and removal of mine equipment and facilities; (2) other activities to
ensure safe conditions after mine closure such as sealing shafts, stabilizing slopes, or long-
term acid rock drainage treatment measures; (3) managing the complex social impacts on
the workforce and on the community associated with the closure of the operation; (4) i nal-
izing rehabilitation that commenced earlier in the mine life; and (5) monitoring the success
of rehabilitation and closure activities over the long term.
Ideally, planning for mine closure starts with mine planning. Modern EIA regulation
requires the mine proponent to present a preliminary mine closure plan as part of the
environmental permitting documents. Mine closure planning is then periodically reviewed
and updated during mine operation with an increasing level of detail and accuracy as the
mine reaches the i nal years of operation. In opencast mining, however, mine closure is
a continuous effort: mined out areas are rehabilitated as soon as practical and in parallel
with the mining.
Environmental aspects of mine closure are many and varied. Decommissioning of the
physical mine infrastructure that is of no use for local communities is achieved relatively
easily. One of the main social challenges is to plan for social changes that will occur due
to the absence of the mine. Employment opportunities are gone, and secondary businesses
that may have depended solely on the mine will lose all custom. Community development
programmes run out of funds and cease to exist, unless ongoing funding is generated from
previous initiatives. One of the main environmental challenges is long-term water man-
agement ( Case 4.7 ). Water can be a long-term destructive force on the mine landscape,
particularly open pits, waste rock storages, and tailings disposal areas. Long-term water
quality also is a concern. Large volumes of rocks have been relocated and are exposed
to a new environment with different natural chemical reactions. The formation of acid
drainage with its associated contaminants has been described as the largest environmental
problem facing the US. mining industry (USEPA 2000). Commonly referred to as acid
rock drainage (ARD) or acid mine drainage (AMD), acid drainage may be generated from
mine waste rock or tailings (i.e. ARD) or mine structures such as pits and underground
workings (i.e. AMD).
Finally there is the issue of the long-term integrity of structures left behind by the mine.
Mine openings, both horizontal and vertical, can be a signii cant physical hazard at an
abandoned mine site. In many cases the openings are well known, but are still a poten-
tial threat to the adventurous who may decide to enter and explore. Those who do face a
number of hazards that can injure or kill, including unstable ground that can collapse, or
foul air, either insufi cient in oxygen or containing poisonous gases such as carbon monox-
ide. Mine openings, particularly vertical shafts, where the opening has been covered either
by a collapsed building or by overgrown vegetation, pose a threat to persons or wildlife of
falling, sometimes hundreds of metres (USEPA 2000).
The aim of environmentally
effective mine closure is to leave
all areas affected by the project,
in a safe and stable condition.
Planning for mine closure starts
with mine planning.
The formation of acid drainage
with its associated contaminants
has been described as the largest
environmental problem facing
the US. mining industry.
 
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