THE DEVELOPMENT OF APPROPRIATE PROCEDURES TOWARDS AND AFTER CLOSURE OF UNDERGROUND GOLD MINES FROM A WATER MANAGEMENT PERSPECTIVE Report to the WATER RESEARCH COMMISSION by W Pulles, S Banister and M van Biljon on hehalf of PULLES HOWARD & DE LANGE INCORPORATED RISON GROUNDWATER CONSULTING cc WRC Report No: 1215/1/05 ISBN No: 1-77005-237-2 MARCH 2005 Disclaimer This report emanates from a project financed by the Water Research Commission (WRC) and is approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the WRC or the members of the project steering committee, nor does mention of trade names or commercial products constitute endorsement or recommendation for use. i EXECUTIVE SUMMARY A need was identified by the Water Research Commission to undertake research into the issue of mine closure planning from a water management perspective in the South African gold mining industry. Initially a project was conceived that was based on undertaking a more detailed study on the development of a coherent and integrated closure planning process for a case study region – the Klerksdorp-Orkney-Stilfontein-Hartebeestfontein (KOSH) area. This approach was eventually abandoned due to the unwillingness of the gold mines in this region (other than Anglogold) to participate in the project. The project methodology was subsequently modified and approved by the project Steering Committee to rather study the complete South African gold mining industry and develop a closure planning methodology that would have application throughout the industry. In support of such an industry-wide study, an assessment would be undertaken of the current status of closure planning contained within the mine EMPRs. Review of Mine EMPRs An assessment was made of gold mining EMPRs on the basis of the approved EMPRs as at the end of 2001. It must be recognised that as EMPRs are regularly being updated, a number of the identified shortcomings would possibly be addressed in revised EMPRs that have been submitted since the review was undertaken. However, the conclusions that were reached are considered to be a valid reflection of the status as at the end of 2001. The review focused on those parts of sections 5 and 6 of the EMPRs that describe the decommissioning and closure phases of the mine’s operations and can be summarised as follows: · While most mines recognise the fact that tailings dams generate acid mine drainage, it is generally and incorrectly assumed that the impact will decrease to acceptable levels when mining operations cease. The assessment of long-term risks from tailings dams can at best be described as subjectively qualitative in nature and no proper quantitative assessments were reported in any of the EMPRs. · It appears to be quite widely assumed that the larger particle size of waste rock dumps makes them a minor pollution risk. This view is erroneous as the waste rock dumps have very large inventories of fine material and they are much more permeable to oxygen than tailings dams. The secondary source of contaminants that remain in the soil after a dump has been removed appears to be universally ignored and it is assumed that removal of the dump removes all potential for pollution from that site. · Most mines appear to have some monitoring programme to evaluate shallow aquifer and surface water impacts from the surface residue deposits. However, the monitoring programs are not clearly stipulated in the EMPR documents and hence it is not clear if the extent of contaminant plumes is known. · Very few specialist investigations appear to have been done to identify the status of the geohydrological regime, the extent of contamination, preferential pathways and predictions regarding long – term migration. As a result there are very limited mitigation or management options described in the EMPRs that specifically deal with the containment / rehabilitation of contaminated groundwater. ii · The potential impact on the groundwater from other surface contaminant sources such as the metallurgical plants, domestic and industrial waste sites are not described. Many of the EMPR documents state that these structures will be removed / rehabilitated during decommissioning, but it is not stated if they had an impact and if groundwater rehabilitation is required. · Many of the older mines were subjected to amalgamations and changes in ownership and in many instances the surface infrastructure, including some tailings and rock dumps were sold to 3rd parties. Many of the current mine EMPR documents exclude infrastructure that has been sold and it is not clear if the new owners are required to address groundwater contamination and if it is in fact being done. · All the goldfields and therefore most of the mines are exposed to the inflow of extraneous water into the underground workings. The aquifers affected by the subsequent dewatering vary from one basin to the next, as do the associated environmental problems. The dewatering of the different mining basins is briefly summarised. § Far West Rand and KOSH area. The inflow of water is derived from overlying dolomite aquifers and huge volumes have to be pumped from the mines for work to continue. The groundwater quality is generally good and the pumped water can be discharged into the natural environment. Many of the dolomite compartments have been dewatered over the years, which resulted in sinkhole formation and ground stability problems. This necessitated the establishment of vigorous groundwater and stability monitoring systems that are required to continue for some time after mine closure. After closure, the mine workings will flood and the dolomite aquifers will largely recover to pre – mining levels. Decant is expected to be limited. There are currently no management options in place to cope with contaminated decant water. § Gauteng mines. The three mining basins in Gauteng, i.e. the Eastern, Central Rand and West Rand basin are all at risk of being flooded or are already partially flooded. The water quality in the mine workings is of a poor quality and cannot be disposed into the natural environment without treatment. When mining ceases the basins will flood to the elevations of the lowest topographical shaft, where it will decant. The quality of the decant water is still a matter of debate, as is the ownership of the responsibility for rehabilitation. There is a school of thought suggesting that the water quality will improve over time and that the water can be allowed to decant into the environment. Another school of thought believes that the water quality will be poor and that treatment centres will be required at the decant points. Although some studies have been done, no management options are currently in place. Harmony’s Randfontein Estates Mine has, however, indicated that they may pump and treat water from the West Rand basin until the water quality issue is better understood. § Free State goldfield. The Free State mines are exposed to the inflow of extraneous saline water from a deep connate aquifer. The isolated nature of this aquifer allowed for it to be dewatered effectively and the poor quality water was disposed of through evaporation. Many of the mines are of the opinion that after cessation of mining the workings will flood, but that the water table will stabilise below the Karoo strata and that none of this water will decant from any of the shafts. Although this statement is probably correct there is no reference to any geohydrological investigation iii confirming this. As a result of this perception there are no management plans in place to cope with decant water. · The general conclusion of this situation analysis regarding post closure groundwater management is that not enough work has been done by the mines to fully understand groundwater flow, groundwater contamination and decant potential. As a result the management options to mitigate groundwater contamination after closure are very vague or non-existent. There is a definite need for clear guidance on what type of technical investigations need to be undertaken to provide the following information: · Understanding of the long-term risks (quantity and quality) associated with post- closure decant from gold mines. · Understanding of the long-term risks (quantity and quality) associated with post- closure seepage from waste residue deposits (tailings, waste rock and footprints below removed dumps). · Identification of proactive management measures that can be implemented to minimise the long-term risks associated with decant from mines. · Identification of proactive management measures that can be implemented to minimise the long-term risks associated with seepage from waste residue deposits. It is also clear that, to date, closure planning is not being undertaken on an integrated regional basis, resulting in those mines that have the longest remaining working life in each region being at the highest risk of being held responsible for dealing with the cumulative regional problem. This situation is clearly not equitable and it is therefore urgent that appropriate procedures be developed to ensure that effective closure planning occurs timeously and on an integrated regional basis. Review of regional geology and identification of regional water management areas A detailed review is presented in the report of the geology and geohydrology in the different mining areas. While issues relating to surface water management are taken into account, it was determined that the primary need for regional assessment was dictated by the geohydrological interconnections between mines as whereas surface water interconnections could easily be managed and modified, geohydrological interconnections could not. We have identified ten major gold field regions currently mined in South Africa based on their depositional environment and geohydrological boundaries, rather than their provincial boundaries. The reasons being that in terms of long–term groundwater management systems, it is more sensible in some instances to implement this on a regional basis than an individual mine or provincial basis.