If you need to travel through Kuma, the township outside
Stilfontein, on a windy winter’s day you will probably have to stop
periodically, waiting for the blustering wind to abate somewhat, as the dust in
the air makes it impossible to continue driving.
The situation is caused by 15 old tailings dams in and
around Stilfontein, all relics from the old Buffelsfontein and Hartbeesfontein
gold mines, whose surfaces become so dry in the winter months that Kuma
residents live in a perpetual uranium-bearing dust cloud. The situation in Stilfontein
itself is slightly better, but not much.
The Kareerand mega tailings dam being built by First
Uranium 15km outside Stilfontein will resolve the problem, but is in danger of
being kyboshed – ironically enough because of opposition from environmental
groups, pressure groups and unreasonable demands from landowners.
From an engineering viewpoint the mega tailings dam is
a pioneering project that would make a dramatic difference to the quality of
air and water in the mine-polluted area.
The techniques being applied to the design and
building of the enormous tailings dam, which will hold 450 tonnes of processed
mine tailings in the first stage of its lifetime, have never been used
elsewhere.
The walls of tailings dams are always built at a
45-degree slope, but the Kareerand Dam’s slope is 15 degrees. This is to reduce
the wind resistance on the wall. The final wall is also being constructed with
scalloped inlets to retain the rainwater that runs down and thus prevent
erosion, said Fraser Alexander engineer Beric Robinson, who designed the
tailings dam. He is regarded as a worldwide expert in tailing dam design.
“We try to imitate nature, but managing to do so is not
a daydream. The techniques being used are based on comprehensive analysis and
years of observing tailings dams,” said Robinson.
“The challenge to the question as to whether the dam
will improve current conditions is not scientific. Rather, it is an economic
challenge to construct the tailings dam and operate it economically.”
In building the dam, surface soil from the 2km terrain
was collected in an outside weir right around the dam. When the dam wall has
finally set, this will be pushed up and positioned against the final wall.
Unlike other tailings dams, Kareerand’s drainage system
has a discharge point right in the middle of the dam, which feeds water to
smaller supplementary dams beside the big dam, for recirculation from those
points. The water will then be used in a sophisticated water irrigation system.
This system, which consists of different batteries of
sprinklers, will be controlled by a wind-monitoring system so that dust is
spread across the tailings dam when the wind speed reaches particular levels.
The old tailings are first fed through a gold and
uranium plant which was built in Stilfontein at a cost of about R3.2bn over
the past three years. It involves the extraction of 57% gold and 33% uranium
from the tailings.
Dumping on the Kareerand mega dam will put an end to
the residual leaching of uranium, salts and sulphates into the Vaal River. In
time, when the uranium plant is in full production, it will also remove the
sulphates from the mine tailings.
The Kareerand tailings dam will not permanently solve
the problem, but assumptions developed from scientific models indicate that it
will take about 200 years before contaminated water from the Kareerand Dam will
reach the Vaal River.
Geological changes and the quality of underground
water will be continuously monitored through boreholes around the Kareerand Dam.
In future years the findings will be continuously tested in line with
projections developed from scientific models to predict the future soil and
water quality in the area around the dam. If ecological weathering veers outside
these criteria, steps will be taken to rectify the situation.
It took two years of research before a decision was reached
to build the mega tailings dam on the current site. Seven different sites were
considered in collaboration with the Department of Water Affairs before the decision
was taken for the current site some 15km south-east of Stilfontein.
First Uranium preferred a site 2km to the north-east
of Stilfontein, but the Department of Water Affairs turned this down because it
was, like the other 15 old tailings dams, over a dolomite formation. It's
precisely this porous dolomite that results in water containing uranium, heavy
metals and sulphates filters down from the tailings dam and into the
groundwater and ultimately into the nearby Vaal River.
The choice of terrain pushed up the project costs by R200m. The
pipes to convey the tailings along the increase distances cost an additional R154m and
the pipes constructed around the tailings dam on the new site cost another
R200m-odd.
The total cost of building the dam is around R400m.
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