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dam-l Toxic silt in SA Lake/LS

http://www.suntimes.co.za/1999/11/28/news/gauteng/njhb06.htm
Sunday Times - Gauteng
DAM NUISANCE
Disgruntled borehole owners in Centurion say council's 'toxic' silt is causing
them a ...
MICHAEL SCHMIDT

THE town council of Centurion near Pretoria has come under fire for pumping
"toxic" silt into an unlined dam, allegedly poisoning the groundwater on which
borehole users rely.

Though experts say there is no risk of poisoning, the R2-million project has
been the subject of an expensive court battle between residents and the
council.

Of particular concern to residents is the recent 440-plus percent rise in the
levels of toxic manganese found in test boreholes surrounding the dam into
which the waste is being pumped. In lower concentrations, manganese can stain
laundry and bathroom ceramics. In higher concentrations it has been linked to
Parkinson's disease.

Local businesses in the Highveld Technopark next to the dam have already spent
R500 000 in legal fees trying to force the council to clean up its act.

The problem started in 1982 when the then Verwoerdburg council dammed the
Hennops River, creating what is today called Centurion Lake. But the dam was
badly designed and the lake silted up frequently. In 1995 the council decided
to build a dam on a wetland bordering the Technopark into which silt dredged
from the lake could be pumped.

The plot-owners in the park objected to the dam, the issue becoming more acute
a year or two later when the sewage treatment facility at Tembisa failed,
dumping thousands of litres of raw sewage downstream into Centurion Lake.

About 18 months ago, the Highveld Technopark Association took the council to
court, claiming that the silt dredged from the lake was hazardous waste and
should not be dumped in the dam. The judge ruled against the association,
saying that though the silt contained raw sewage, it did not legally constitute
waste.

But the residents stood by their objections, so the Gauteng Department of Water
Affairs and Forestry stepped in, the council hired consulting engineers and a
"gentlemen's agreement" was struck that no pumping would go ahead until the
results of groundwater tests from a series of boreholes was completed.

But last week, said the association's Fred Joubert, it was discovered "the
council had broken the agreement and had been secretly pumping silt into the
dam since September 19".

"We found the manganese in one of the test boreholes had risen by about 444
percent," he said. But manganese is a common element in soil and the source of
the higher concentration has not been determined.

Petrus Venter, deputy director of water quality management in Water Affairs'
Gauteng North region, said a letter had been sent to the council demanding that
it stop the pumping.

"The council didn't do it secretly," Venter said. "It wrote us a letter saying
it was doing it, but the problem was there was an agreement it wouldn't go
ahead until we were satisfied."

Venter said residents were mistaken about the possibility of the groundwater
being poisoned, saying: "As far as we know there is no risk of pollution. We
ran two models and the more conservative one showed that the whole risk of
groundwater pollution is sub-zero. But now, after a full year of investigation,
we're back to square one."

The council has dumped 90 tons of lime into the dam to neutralise the manganese
and other metals and form a protective lining. It plans to add another 250 tons
periodically.

Centurion town engineer, Ansen Lamprecht, said the council would apply this
week for a permit to resume pumping. He said council tests had shown "there is
no connection between the silt dam and the groundwater".

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      Lori Pottinger, Director, Southern Africa Program,
        and Editor, World Rivers Review
           International Rivers Network
              1847 Berkeley Way, Berkeley, California 94703, USA
                  Tel. (510) 848 1155   Fax (510) 848 1008
                        http://www.irn.org
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