Characterisation and Protection of Deep Aquifers in South Africa: Potential Resources

The importance of groundwater in South Africa has become evident over the past decades, especially as pressure on surface water resources intensifies in response to increasing water supply demands. Research has significantly progressed on the shallow groundwater resources conventionally used for water supply, and leading on from this deeper groundwater resources have become a focus point as a future water source. This focus on deep aquifers is driven by new developments, such as shale gas development, injection of brines into deep aquifers, carbon sequestration and geothermal energy. The understanding of deep groundwater in South Africa is often limited due to insufficient data at these depths. To develop a body of knowledge on deep geohydrology in South Africa, an investigation on the currently available information was launched to assess potential deep groundwater resources. The investigation formed part of the larger WRC Project K5/2434 (Characterisation and Protection of Potential Deep Aquifers in South Africa). The geology of South Africa was reviewed from a deep groundwater perspective to provide an initial analysis of potential deep groundwater aquifers. The main potential deep aquifers were identified for further investigation using a ranking system, where Rank 1 shows a positive indication, Rank 2 shows some indication, Rank 3 shows a neutral indication, and Rank 4 shows a negative indication for deep groundwater systems. The Rank 1 geological groups include (in no particular order): the Limpopo Belt, Witwatersrand Supergroup, Transvaal Supergroup, Waterberg and Soutpansberg Groups, Natal Group, Cape Supergroup, Karoo Supergroup. In a number of the identified potential deep aquifers, the indicator for deep groundwater flow systems was the presence of thermal springs. Additionally, deep groundwater occurs below the traditionally exploited weathered zone, and the importance of fractured aquifers becomes paramount in the investigation of potential deep aquifers. In conclusion, three main components were considered for the investigation of potential deep aquifers systems, 1) geological groups; 2) thermal springs and 3) depth of fractures. These three components should be used holistically going forward to best characterise the potential deep aquifers of South Africa.