A rising acid tide

Published by MAC on 2005-04-12

A rising acid tide

12 April 2005

Melissa Fourie, Johannesburg Mail & Guardian, South Africa

The name "Witwatersrand" has come to haunt the people who live along this ridge - the source of so much wealth from gold and other minerals. But with many mines nearing the end of their productive lives or already closed, the water table is recovering after being driven down by decades of pumping water out of mineshafts.

In 2002, polluted water from certain mines started to decant onto the surface and into dolomite rocks below the surface, with long-term and potentially devastating consequences for the environment and the health of humans and animals. It is also threatening to drown the Sterkfontein caves.

The start of the decant

In August 2002, an extraordinary event took place near Krugersdorp on the West Rand. Although this was predicted by several geologists, geohydrologists and environmental scientists in 1996, neither government nor mining conglomerates seem to have anticipated it.

Two years later, scientists, mining companies and government remain reluctant to discuss the event and its impact publicly. And yet it is the start of a problem of such magnitude that it will affect our environment and health for decades to come.

August 2002 was the first incident of decanting, or "acid mine drainage", which started when polluted water from an old mine shaft on the property of Harmony Gold Mine (Pty) Ltd (Randfontein Operations), began to flow out or "decant" on to the surface, first through a borehole upstream of the Krugersdorp Game Reserve, and then through an old vent shaft pushed open by the force of the water.

Sulphur compounds in the water gave it the pH of orange juice. It also had toxic levels of heavy metals, and oxidising iron pyrites tinged the water bright red.

At first, the problem seemed only that of a dramatic increase in the volume of water. In the Krugersdorp Game Reserve, two ancient springs began to flow for the first time in living memory.

The hippo dam in the reserve was called the "dry dam" until as recently as two years ago, and never retained inflowing water for more than a few days. Now, this "dry" dam is constantly filled with water, even overflowing in July 2003 into streams that feed the Tweelopiesspruit. The rising water table has also reactivated an old swamp.

Between seven and 15 megalitres of water are decanting daily. Monitors for water quality in Tweelopiesspruit inside the reserve show increased sulphates and reduced pH levels in both surface and groundwater since 2000.

Acid mine drainage

Why is this mine water so acidic and so polluted?

Acid mine drainage (AMD) has been described as the largest single environmental problem facing the mining industry, particularly because it is persistent and costly, and tends to be a liability for mines long after they cease to operate.

AMD is a worldwide problem, and has been the topic of extensive research in North and South America. In South Africa, the National State of the Environment Report calls AMD a "recognised threat", but reliable data on its extent and the volume entering water courses is not easily available. The report suggests that AMD from the 15 working and 29 closed gold mines on the northern side of the Vaal Barrage catchment (which supplies water for the whole of Gauteng) is already affecting the receiving water sources.

The end of subsidised water pumping

Why did the first instance of decanting of acid mine water only happen in 2002?

After almost 120 years of mining in the Witwatersrand basin, mining has created a gigantic, interconnected subterranean warren stretching from Roodepoort in the west to Boksburg in the east, in some places as deep as 3 000 metres.

To reach such deep levels, millions of megalitres of groundwater had to be pumped out, which has been going on for decades. At its peak, as much as 35 megalitres a day were pumped from the western mining basin, and discharged into both the Upper Wonderfonteinsspruit, flowing south into the Vaal, and Tweelopiesspruit, flowing north into the Crocodile river.

By the 1970s, government paid "pumping subsidies" to mines that showed that this cost was the difference between profitability and demise, with concomitant loss of jobs. Today, these pumping subsidies can amount to R2-million a month for a single mine.

But since the 1990s, many Reef mines began to close as they reached the end of their productive lives - today, in the central Witwatersrand, only three major mines still operate.

As a result, much less water is pumped out than before, and the water table is recovering faster than consumption from the surface. Undisturbed, the water table began to rise from the deepest defunct mines into the vast network of tunnels. The old ridge of tumbling waters is coming back to life, but the water is tainted.

What is in the water?

Sulphates and heavy metals

Mine-polluted water has high acid levels because of the presence of sulphuric acid. Beyond a certain concentration, sulphates are acutely toxic. Drinking this water can cause immediate vomiting, often leading to mild to severe levels of diarrhoea. Sensitive individuals can tolerate up to 600mg of sulphates per litre, but at the point of decant, there is (according to Harmony Gold) up to 4 500mg per litre. At high levels, the water will have a bitter and salty taste, which could stop people from drinking it.

Mine water also contains toxic heavy metals dissolved by the acid water, including manganese, aluminium, iron, nickel, zinc, cobalt, copper, radium and uranium - all with varying degrees of toxicity, and radioactivity in the case of radium and uranium. Harmony reports that the water at the decant point contains iron levels of 1 200mg per litre.

Henk Coetzee, an isotope geochemist at the Council for Geosciences, says the acid mine water also contains about 16mg uranium per litre, exceeding the World Health Organisation's limits by a factor of 1 000. Uranium and radium can cause cancer.

Although Department of Water Affairs & Forestry (DWAF) officials express concern about the presence of radioactive nuclides, to date no analysis has been made because of the extreme expense involved.

Nitrates and pesticides

Mining is not the only water polluter. Commercial agriculture contributes nitrates and pesticides which leach into ground water and, in addition, the Percy Stewart municipal sewage works near the Krugersdorp reserve release more than 11 000m3 of treated sewage and industrial effluent into the Blougatspruit (a tributary west of the Tweelopiesspruit) that feeds into the Blaauwbankspruit.

In turn, the Blaauwbankspruit feeds into the Cradle of Humankind World Heritage Site and hence transports pollutants from upstream. Sources say that the quality of the effluent discharged by Percy Stewart has recently deteriorated, though the reasons are not clear.

In 2004, SABC2 current affairs programme Fokus reported that water tested in the Cradle area showed "dangerously high" nitrate levels. Nitrate levels higher than 15mg per litre cause oxygen deprivation, which can cause spontaneous abortions, still births and infant mortalities. In higher concentrations there is some risk of death in older children and adults, especially from gastric and other cancers.

Action by Harmony Gold

Despite warnings, the magnitude of the first decant at the Randfontein mine in 2002 appears to have taken Harmony Gold by surprise. For the first eight weeks, Harmony Gold worked around the clock to construct a containment dam and power supply, pumping the water into a large unsealed dam - already polluted from other sources - known as Robinson Lake, and began converting the old Randfontein Estates' uranium extraction plant into a water treatment plant. By December 2004, the treatment facility was 90% complete. Currently, the polluted water is treated using a "high density sludge process".

Although Harmony alleges that no polluted water is currently being released into the environment, it intends to discharge the treated water into the Tweelopiesspruit catchment area. It told officials from Gauteng's environmental department (GDACE) that this release was planned for February 1 2005, when all Harmony's treatment and storage facilities would be at full capacity. It was not clear whether government would permit the release.

Despite having spent more than R28-million on infrastructure and R750 000 on monthly operating costs, Harmony concedes that the water still contains sulphates of 250mg per litre after treatment.

It is also alleged that Harmony is not capturing all the decanting water but only treating surface water and not that flowing through underground dolomite. Harmony contends that underground water is pumped out through two boreholes (with a third to be commissioned soon), and is used for farming and irrigation.

In addition, Harmony concedes that toxic sludge being dumped on a disused tailings dam contains uranium, which requires safe disposal authorised by the National Nuclear Regulator. GDACE officials believe this sludge could cause air pollution as it dries and is blown away by the wind. But Harmony says uranium levels in the sludge are well within the NNR's allowable disposal limit, and that the tailings dam is 2.5m below the vegetated surface area, making air pollution an "impossibility".

Animal deaths

For all Harmony's assurances that no water from the decant, treated or untreated, is being released, since August 2002 unusual and tragic events have occurred downstream in the Krugersdorp reserve.

Fish and other aquatic life in the reserve's waterways have all died. "A few years ago, you couldn't hear yourself talk at night because of the frog noise; now you can hear a pin drop after sunset," says Dirk Brink, the reserve's director.

The reserve also reports an abnormally high death toll among mammals over the past two seasons, particularly among newly introduced animals. Lions, cheetahs, springbok and red hartebeest have all died within a week of being released. So have hand-reared animals, which showed no health difficulties until they had access to stream water. Since August 2002, at least nine lions have died of disease in the reserve, the first to die of disease since 1965.

The reserve's breeding programmes have also been unusually unsuccessful. Although the foetuses were never found, two rhinoceroses certified pregnant have failed to produce offspring.

The connection between the start of the decant and these animal fatalities may seem obvious, yet scientists have been unable to prove it conclusively, for a variety of reasons.

Some observers blame the animal deaths on a lengthy power failure in 2004 that affected Harmony's pumping and treatment operations, allowing increased volumes of polluted water to flow into the reserve. But Harmony alleges that an earlier five-hour power failure during 2003 had "not significantly affected" the quality of the water flowing to the reserve.

It has been argued that the precautionary principle should apply in such situations, in particular to protect the environment and animals of the Krugersdorp reserve, but to date none of the responsible authorities have helped the reserve.

Long-term risks

Increased water volume

Scientists are unsure where the water table was before mining started around 1886.

In a traditionally dry country, recovery of a water table may seem cause for celebration, but no one was prepared for the volume of water decanting. If nothing is done to address the situation, this water may even flood the Sterkfontein caves, drowning the archaeological and palaeontological heritage of the Cradle of Humankind.

Harmony argues that the artificially lowered water table in fact exposed these deposits in the first place. A recent study predicts that the water table in the caves could rise by as much as 6-8m, although over what period is not stated.

Contaminated mine water is expected to decant into other basins within Gauteng in the next five years, and could, according to GDACE officials, continue to flow for at least 30 years.

Contaminated water

Even if these increased volumes could be accommodated, the levels of pollution, especially heavy metals, are of grave concern. At immediate risk are residents in the decant area, many of whom rely on borehole water, but contamination also flows into several rivers, including those that provide water to Gauteng.

Soil pollution and sinkholes

Another consequence is pollution of soil, which has received little attention, and the increased likelihood of sinkholes, because acid water tends to dissolves dolomite. The first sinkhole directly linked to this decant has already formed, as predicted in July 2004.

More sinkholes in the affected area will no doubt follow. Harmony predicts "uncontrollable ground stability" if untreated mine water contaminates aquifers.

What can be done?

Polluter pays

Under the new Mineral and Petroleum Resources Development Act of 2002, if mining operations cease at an authorised mine, the holder of the mining permit remains liable for compliance with the Act until an unconditional "closure certificate" has been issued by the Department of Minerals and Energy (DME).

DME's closure policy requires that mine closure must safeguard the health and safety of both humans and animals and minimise potential environmental damage. Mines must also make every effort during the life of the mine to minimise costs and work required for the decommissioning and closure phases.

Mines that closed before or during the transitional period provided for in the Act, which do not intend to reopen, must also obtain a closure certificate. As none of the mines in the affected area have been granted closure certificates, mine owners remain legally responsible to take reasonable measures to prevent pollution.

Although Harmony Gold currently takes most of the blame for the AMD because the decant is on one of its mines, all companies that mined in the area from the end of the 19th century contributed to the problem.

In a recent TV interview, DME's acting director-general Jacinta Rocha said, on the basis of the "polluter pays" principle, other mines in the area must also pay clean-up costs.

DWAF said that "efforts are being made", in collaboration with other government agencies, to identify liable mining companies that should assist "in overcoming the challenge of funding the measures that may need to be instituted". DWAF has spent more than R128-million on rehabilitation and the provision of water pollution control works to address AMD in affected catchments.

DWAF officials point out, however, that mine water decanting is a natural process that can never be completely "controlled", because of the fractured nature of our aquifers. Better ways of treating increased water flow to the surface will have to be found, including pumping excessive water elsewhere, although the release of up to 15 megalitres of water per day into other catchment systems could have dramatic consequences for their ecosystems.

Water ingress and treatment

The Council for Geosciences is currently running a project for the DME to find ways of reducing the ingress of water into the mines and so reduce the volumes decanting. This could allow pumping subsidies to be lowered, and make treatment of polluted water more manageable.

It is also exploring other ways to treat the water, such as artificial wetlands, but there are limits to what plants can do to remove heavy and variable pollutant loads. Artificial wetlands also require large surface areas, which increases water evaporation rates - removing more of an already stressed resource.

Pumping water elsewhere

Harmony's releasing of treated water into Tweelopiesspruit is likely to fill up the dolomitic compartments under the Cradle of Humankind. GDACE officials regard this as a short-term emergency measure, and oppose it on grounds of the potential impact on fossil sites. Harmony may therefore have to conduct a full environmental impact assessment, which could delay water release well beyond the 1 February 2005 deadline.

Harmony has identified three alternatives to Tweelopiesspruit, but each must first be assessed for their potential impact on aquatic and groundwater ecosystems.

First and most expensive is to treat the combined mine water of the western and central Gauteng basin to industrial standards, and pump it 52km to the water-deprived Rustenburg platinum mines. This option would release significant volumes of potable water to residents in the Rustenburg area but would cost an estimated R350-million.

Second is to discharge the water to the Magalies River Catchment via a conduit of canals and pipelines over 8km (R7.5-m). Third and cheapest (R175 000) is to discharge water into the Upper Wonderfonteinspruit, from where it will flow south.

This option may negatively affect the Ventersdorp dolomites underlying the catchment area in question.

Another option is to use treated water for irrigation purposes, but would need substantial investment. GDACE regards this option as too expensive and too complicated.

Harmony is developing a permanent western basin water management and treatment plan, to be finalised early in 2005.

Stakeholder consultation

DWAF and GDACE formed a stakeholder forum after the August 2002 decant to review the problem and make recommendations. The forum consists of a number of task teams, including the Western Basin Void Water Technical Task Team.

Represented on this committee are DME, DWAF, the Department of Environmental Affairs & Tourism, GDACE, Mogale City, the Council for Geoscience, Harmony Gold and other mining companies. To date, affected communities and environmental groups have no representation.

Despite the reluctance to discuss AMD publicly, there is a sense of frustration about government's slow response to dealing with the problem. AMD is a persistent and long-term problem that extends well beyond the current decant. If a comprehensive solution is not found soon, the preservation of the region's ecosystems and the health of millions of South Africans living downstream from the mines are at risk.

Melissa Fourie is an environmental lawyer in the policy & research unit of IUCN-The World Conservation Union's South Africa country office and the project liaison for the IUCN-SA Karst Working Group

AMD in a nutshell

Acid mine drainage (AMD) occurs when water flows over exposed sulphide minerals, which oxidise in the presence of water and oxygen, causing the water to become acidic, which then dissolves other toxic metals. Exposure and oxidation of pyrite and other sulphide minerals occur in mine wall rocks, backfill, waste rock piles, low grade ore stockpiles and tailings deposits. In and around South African gold mines, pyrite (FeS2) present in gold ore dissolves on oxidation and releases iron and sulphuric acids.

The IUCN-SA Karst Working Group

In May 2004, the South African country office of IUCN-The World Conservation Union, in collaboration with the Gauteng Department of Agriculture, Conservation and Environment (GDACE) and the Cave Research Organisation of South Africa (CROSA), established a Karst Working Group, made up of more than 30 individuals from diverse backgrounds and disciplines, including national, provincial and local government, industry, four national universities and a number of voluntary caving organisations.

Their task is to develop a holistic monitoring and management system for karst systems in South Africa, and they have chosen the Cradle of Humankind World Heritage Site as a pilot study, in part to support the Cradle in meeting its reporting obligations to the World Heritage Authority. One of the group's main concerns is the threat of water pollution in the Cradle area, and the effect of such pollution on the karst ecosystems.

The group is supported by the GDACE, the Water Research Commission and the IUCN World Commission on Protected Areas' Cave and Karst Taskforce. It is also establishing partnerships with research institutions in Europe, as well as international NGOs Flora & Fauna International and Earthwatch.