Report lays acid mine drainage bare
Feb 20, 2011 1:35 AM | By LUCKY BIYASE in The TimesThe stark and harsh reality of acid mine drainage (AMD) is laid bare in a report by the Department of Water Affairs.
WHERE'S THE WATER? Aurora mine's No 1 catchment tank used to receive water directly from the mine. Because the pumps have been removed no water is being drained from the mine. The walls are covered with mining sludge Pictures: KATHERINE MUICK-MERE
The document includes the findings of an interministerial committee team of experts on AMD, assembled in September to investigate the issue.
"Urgent reduction of water ingress into mine voids remained a high priority," it says.
The department would neither confirm nor deny ownership of the document.
The document proposes various interventions for three areas: the West Rand (Western Basin), central Johannesburg (Central Basin) and the East Rand (Eastern Basin).
It also notes that recent heavy rain and resultant flooding in Gauteng raised concerns that these conditions would lead to more water flowing into mines and worsening AMD in the province.
"The recent occurrence of flooding is in essence a matter separate to that of AMD; however, cognisance must be taken that flood water has potential to enter mine workings and also increase AMD."
The document points out that water in mine workings is an important environmental concern.
"As mine water levels rise, it contaminates ground water. Further rises lead to decant (overflow) of the polluted water into surface streams, releasing water directly to mine openings," it says.
Turning to the Western Basin, the report says the AMD flow rate during the dry season was either absent or of relatively small volumes, typically averaging two megalitres, or 2000000l, a day. But during the wet season, such as in December, this rose to 15.5 megalitres per day, on average.
It says that after heavy rains last month, the decant further increased to an average of 30 megalitres. This is in addition to 12 megalitres of partially treated mine water a day, making for a total of 42 megalitres a day.
"These episodes of AMD decant are contaminating ... Tweelopies Spruit and Blaauwbank Spruit (which both flow north into the Crocodile River system).
"Western Basin subsurface mine water is considered to be flowing via underground paths to the Wonderfontein Spruit, a river which feeds into the Vaal River."
On the Central Basin, the document says previous evidence shows the rate of water rise ranged from 30cm a day in the dry season to 90cm a day in the wet season (averaging about 55cm a day).
"Presently the water level is at 508m below surface and there is no surface decant of AMD," the report says.
"The latest results indicate the rate of rise fluctuates between 0.37m and 0.47m per day," it adds.
"Despite the recent high rainfall, there is a slower rise than expected, which is possibly due to delayed ingression or a more extensive network of lateral mine workings at the 500m (below surface) level, which is absorbing the ingress of water."
The report has the following to say about the Eastern Basin: "As with the Central Basin, there is no surface decant of AMD ... and the current subsurface mine water level is approximately 700m below surface.
"Recent rainfall has boosted the rate of rise to around 0.4m per day (about seven times the rate during dryer conditions).
"At the prevailing rate, mine water can flood the pump station in as little as 16 days unless the Grootvlei Mine seriously increases pumping output.
"According to information at the department's disposal, Grootvlei Mine is in the process of increasing pumping capacity."
Anthony Turton, a critic of the government's handling of the issue, said the report seemed reasonable. "I see nothing here that speaks of a cover-up. Nothing mind bogglingly new either, but no cover-up."
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