The Development of Techniques for the Evaluation and Effective Management of Surface and Groundwater Contamination in the Orange Free State Goldfields
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The Development of Techniques for the Evaluation and Effective Management of Surface and Groundwater Contamination in the Orange Free State Goldfields VE Cogho,LJ van Niekerk, HPJ Pretorius and FDI Hodgson WRC Report No.224/1/92 THE DEVELOPMENT OF TECHNIQUES FOR THE EVALUATION AND EFFECTIVE MANAGEMENT OF SURFACE AND GROUND-WATER CONTAMINATION IN THE ORANGE FREE STATE GOLDFIELDS BY V.E. Cogho, L.J. van Niekerk, H.P.J. Pretorius and F.D.I. Hodgson January 1992 Institute for Ground-water Studies University of the Orange Free State WRC Report No. K5/224 Obtainable from: Water Research Commission P O Box 824 PRETORIA 0001 ISBN 1 874858 42 X ACKNOWLEDGEMENTS The research described in this report resulted from a project funded by the Water Research Commission entitled: "The development of techniques for the evaluation and effective management of surface and ground-water contamination in the Orange Free State Goldfields" The Steering Committee responsible for this project, consisted of the following persons: Mr A G Reynders Water Research Commission (Chairman) Mr H M du Plessis Water Research Commission Mr F P Marais Water Research Commission (Secretary) Mr Z M Dziembowski Directorate of Geydrology, Dept of Water Affairs and Forestry Mr SAP Brown Directorate of Pollution Control, Dept of Water Affairs and Forestry Dr G Tredoux CSIR Dr C Frick Geological Survey Prof H J Potgieter University of the Orange Free State Prof F DI Hodgson Institute for Ground-water Studies Mr J Easton Chamber of Mines of S A Dr H N S Wiechers Eskom The financing of the project by the Water Research Commission and the contributions of the members of the Steering Committee are acknowledged gratefully. This project was only possible with the cooperation of many individuals and organizations. The authors therefore wish to thank the following: Loraine Gold Mine, Freegold North and South, St Helena Gold Mine, Unisel Gold Mine, Harmony Gold Mine, Oryx Gold Mine, Beatrix Gold Mine and H J Joel Gold Mine, in particular: Mr J Caulkin (Freegold North), Mr A Howard (Freegold South), Mr H C Morkel (Freegold South), Mr E H Bekker (Harmony Gold Mine), Mr C N O'Connor (Oryx Gold Mine), Mr B J Pretorius (Loraine Gold Mine) and Mr A F Janse van Rensburg (St Helena Gold Mine) for collecting and providing crucial data. The members of the Mining Subcommittee: Mr D R Fleming (Freegold South), Mr D R Young (H J Joel Gold Mine), Mr J C Steenkamp (Loraine Gold Mine), Mr K Eick (Harmony Gold Mine), Dr H N S Wiechers (Chamber of Mines), Mr \V Pulles (Chamber of Mines), Mr J D Wells (Rand Mines), Mr D A Parfitt (Unisel Gold Mine) and Mr A F Janse van Rensburg (St Helena Gold Mine) for their time spent and their valuable contributions to the outcome of the study. The municipalities of Welkom, Odendaalsrus and Virginia and in particular Mr P Bezuidenhout (Welkom) for the storage and other facilities at the Theronia Sewage Works. All the farmers in the study area, who willingly provided important information to the outcome of the study. Mmes M Botha and C le Roux of the Institute for Ground-water Studies, who worked on the project with patience and thoroughness. EXECUTIVE SUMMARY INTRODUCTION Water can be regarded as a scarce commodity in South Africa and one cannot rely solely on the discovery of new water resources to meet the ever-increasing demands. As the industrial and mining activities on the Witwatersrand increased from the turn of the century, so did the contamination of the Vaal River. Repetition of this situation in other drainage basins must, as far as possible, be prevented. As the Orange Free State Goldfields occur in an area isolated from many of the pollution sources found within, for example the Vaal River Catchment, its impact on the environment can therefore be investigated more easily and the results obtained can be used to elucidate ground-water quality problems in areas of diverse mining and industrial activities. The area under investigation stretches from Allanridge in the north to just north of Theunissen in the south, covering approximately 2 100 km2. Many of the possible pollution sources have been present in the area since mining commenced in the early fifties, while other sources have only been ongoing for a few years. The Sand River crosses the study area from east to west, eventually draining into the Bloemhof Dam. This is regarded as a major seasonal stream in the region and its water quality presently deteriorates from 140 mg/1 (TDS) to 700 mg/1, as it passes through the Orange Free State Goldfields. Many chemical elements detrimental to humans, animals and vegetation occur in surface effluent water and leachates from solid waste disposal sites. As those elements may eventually find their way into ground water and subsequently surface water resources, quantification in terms of time of travel and distance from potential pollution source is vital to managing waste disposal activities. This research project into the water quality of the Orange Free State Goldfields constitutes a three-year contract between the Water Research Commission and the Institute for Ground- water Studies at the University of the Orange Free State. The research commenced on January 1st, 1988. OBJECTIVES According to the agreement, concluded between the Water Research Commission and the Institute for Ground-water Studies, the following aims were proposed for the investigation: • To determine the source of possible pollutants to the surface and ground-water regime. • Quantify the contribution from different sources. • Study the migration rate of pollutants through the aquifers. • Determine chemical alterations to pollutants while on surface and in the aquifer. • Model local and regional movement of pollutants through the aquifer and predict future water qualities. • Enter information into a computerized data base. • Suggest management strategies whereby the influence of disposal can be minimized. POTENTIAL SOURCES OF CONTAMINATION The Orange Free State Goldfields produce many different types of waste (solid or liquid), contributing in varying quantities to the total water quality of the area. A large portion of all the waste generated in the area is associated with mining activities. Wastes found in the study area are: (i) Mine: (a) Solid waste (rock waste, scrap metal and domestic waste). (b) Slimes and return water dams. (c) Evaporation areas, (ii) Municipal: (a) Urban solid waste. (b) Urban liquid waste. (c) Industrial effluent. 1 HYDROLOGY The area forms part of the highveld region and has an average elevation of about 1 360 m above mean sea level. Most of the area has a gentle undulating surface and rarely are any prominent landmarks visible. The Orange Free State Goldfield area is situated in a semi- arid region with a mean annual precipitation of 518 mm. The identification of rainfall cycles as well as a probability analysis for flood occurrence can be important, as excessive unpotable water is one of the major issues in the area. The annual precipitation for the area was 897 mm in 1988. It was observed that the 331 mm recorded in February 1988, has a return period of 100 years. Although high values of annual precipitation do not usually give rise to floods, they should be taken into account when designing effluent disposal facilities. It is, however, the high rainfall of shorter durations that has to be watched closely with respect to floods, as government regulations stipulate water storage capacity requirements on the basis of a balance, which incorporates average monthly rainfall and rainfall with a recurrence interval of 1:100 years of one-day duration. 2 GEOLOGY AND GEOHYDROLOGY The area under investigation is extensively covered by soil and sands of aeolian origin. Outcrops are therefore limited to surface limestone, river terrace gravel, dolerite, kimberlite and sediments of the lower Beaufort Group, the upper Ecca Group and lava sediment of the Ventersdorp Supergroup. In the western and north-western parts of the area, extensive pan development has taken place and may have an effect on the water quality of that specific part of the region. From the reconnaissance and extended sampling, it was found that two basic aquifers exist in the area: (a) A shallow aquifer which lies within the weathered and fractured zone of the Karoo sediments. (b) A deeper aquifer which is developed in the fractured and faulted Ventersdorp and Witwatersrand rocks. Furthermore, it was evident that the occurrence of ground water in the shallow aquifer is geologically controlled. Boreholes with moderate to high yields are associated with the intrusion of dolerite. The average yield of the boreholes in the Beaufort sediments is 3,2 1/s, whereas the average yield in the Ecca sediments is 1,03 1/s. Ground-water levels closely follow the surface topography* implying that ground-water levels are topographically controlled and that vertical leakage to the deeper aquifer is negligible. South and north-east of the Sand River, the slope of the water levels is generally towards the Sand River. In the western and north-western parts of the study area where the surface drainage is poorly developed, ground-water movement is mostly restricted to local vlei and pan systems. The regional ground-water gradient is, however, towards the west of the study area. A model was developed to estimate the salt load that the environment is exposed to, due to the large quantities of water (with a dominant NaCl-character) pumped from the Witwatersrand rocks daily (155 Ml/d) and discharged into evaporation areas and pans. In simulating the water levels for 37 years, about 1 240 x 106 m3 of water was pumped to the surface. If the pumped water has an average electrical conductivity of 450 mS/m, the total dissolved solids in the water are in the order of 3 000 mg/1.