The report by the team of experts on the management of Acid Mine Drainage (AMD) is available from this morning on the Department of Water Affairs’ website, http://ww.dwa.gov.za. A complete assessment and reappraisal of the situation with respect to AMD, focusing on the Witwatersrand Gold Fields was conducted and recommendations made to address the current situation.
Examination of international and local literature on all aspects of AMD (e.g. its formation, control, management, treatment and impacts) indicates that the subject has been extensively researched and studied. This has resulted in a sound but generic understanding of the process and its processes involved as well as specific information related to the current situation with respect to AMD in South Africa, focusing on the Witwatersrand Gold Fields. A range of solutions to the problems faced have been identified as well as the need to implement appropriate solutions to address problems at specific sites.
The Western, Central and Eastern Basins have been prioritised for immediate action in order to ensure that measures be implemented before problems become more critical. The following risks have been identified with respect to the flooding of the mines in these areas and the subsequent decant of AMD to the environment:
• Risks due to flooding of the mines:
o Increased seismic activity
o Contamination of shallow groundwater resources
o Geotechnical impacts in areas where water rises close to urban areas.
• Risks due to the decant of AMD to the environment:
o Serious negative ecological impacts
o Regional impacts on major river systems
o Localised flooding in low-lying areas.
A generic approach to the management of these risks has been proposed for implementation in all of the priority areas:
• Decant prevention and management: The experience in the Western Basin has shown the severe impacts which can be expected if the mine void is allowed to flood and decant completely. For this reason it is recommended that the water levels within the basins be held at or below the relevant environmental critical levels (ECLs) by pumping of water. (Environmental critical level is defined as the highest water level within the mine void where no AMD flows out of the mine workings into the surrounding groundwater or surface water systems) In the case of the Western Basin this will require pumping to lower the current water level which is already at surface.
• Ingress control – reduction of the rate of flooding and the eventual decant volume: Pumping and treating water into the future will be a costly exercise. It is therefore necessary to reduce the volume of water which is to be pumped and treated as far as possible. The water flooding the mine void comes from a number of sources, including direct recharge by rainfall, groundwater seeping into the workings, surface streams which lose water to mine openings shallow workings, open surface workings, seepage from mine residue deposits and losses from water, sewage and storm water reticulation systems. Where feasible, engineering interventions will need to be implemented to reduce the flow of water into the underground workings. This process has already commenced with the construction of a canal in the Florida area to prevent stream losses to the underlying shallow mine workings. A number of proposals have been made for similar interventions in other areas with the aim of reducing the volume of water flowing into the mine voids and preventing the pollution of water.
• Water quality management: Even if these measures are implemented, some AMD will still be produced and require treatment to a quality which is fit for some use or discharge to surface streams. Various treatment options and technologies, including active, passive and in situ treatment technologies, have been identified and reviewed. Given the variability in water quality between the different basins and the possibility that the water quality in the mine voids will improve over time, it is likely that a suite of different technologies will be required.
“In light of the serious challenges with AMD in the Witwatersrand, the pumping and treatment of mine water is critical and should be implemented in the Western, Central and Eastern Basins as a matter of urgency. Although the partial treatment of mine water to neutralise acidity and remove metals will be accepted in the short-term, it is important that in the medium- to long-term, mine water needs to be treated to a quality suitable for direct or indirect use. The Department of Water Affairs will conduct a feasibility study to determine the most appropriate long term use of the treated water,” said Minister Molewa, the co-chairperson of the IMC.
The following recommendations by the team of experts have been approved by Cabinet:
• Construction of an emergency treatment plant in the Western Basin to partially treat uncontrolled AMD decants and construction of pumping infrastructure to prevent AMD decants to protect the environmental critical level (ECL) at 150 meters
• In order to protect the environment in the Central Basin by maintaining water levels at or below the ECL, pumping infrastructure with appropriate water treatment should immediately be implemented. Discussions with other stakeholders should take place in respect of the possibility of pumping the mine water to a level that will protect the gold reserves. The refurbishment of the existing neutralisation plant should be considered.
• The reinstatement of pumping and treatment of mine water in the Eastern Basin should be investigated as a matter of urgency.
• Steps must be implemented to reduce the ingress of water into the underground workings, as far as is possible. This will reduce the volumes of water which need to be pumped and treated and consequently reduce the operational costs of AMD management.
• Improved monitoring of mine water, groundwater, surface water, subsidence and other geotechnical impacts of mine flooding and seismicity is required. It is recommended that a multi-institution monitoring committee be established to facilitate the implementation of the required monitoring programmes.
• The implementation of an environmental levy to be paid by operating mines to cover the costs of the legacies of past mining needs to be investigated and implemented, if feasible.
Minister Molewa further said, “As part of the implementation plan, which officials are working on, a notice will be published in terms of Section 19 of the National Water Act to previous and existing mining companies in the Central and Eastern basins, preventing these mines from polluting the water resources as a result of their activities. In respect of the Western Basin mines, directives in terms of Section 20 of the National Water Act will be issued and the department will continue to remedy the situation and claim from the responsible mining companies for the expenses incurred in the remedial process as far as is possible.”
The total budget implication is estimated at R441 660 668 for Capital expenditure, R121 255 000 annual operating cost and R626 261 506 for long-term costs related to ingress prevention. Provisional budget of R225 000 000 has been allocated to the Department of Water Affairs.