Hydrochemistry

Previous studies have shown that river-aquifer connectivity exists. However, an integrated approach that consists of multiple measuring methods to quantify and characterise such connectivity still needs improved scientific understanding due to the underlying principles and assumptions of such methods, mainly when such methods are applied in a semi-arid environment. Three techniques (hydrogeochemistry, stable water isotopes, and baseflow separations) were applied to quantify and characterize river-aquifer interactions.

The response of an alluvial and estuarine deposit aquifer, locally known as the Harbour Beds Formation, located in the coastal area of the Durban Metropolitan District to 48 hours of group well pumping is studied to understand its potential for groundwater supply and consequent seawater intrusion. Groundwater levels were monitored from the three pumped boreholes and piezometers. Similarly, EC, TDS and pH were monitored every hour from the boreholes and piezometers.

This study assessed aquifer-river interaction using a combination of geological, hydrological, environmental stable isotope, and hydrochemical data in a non-perennial river system in the Heuningnes catchment. Results showed the depth to groundwater levels ranging from 3 to 10 m below ground level and aquifer transmissivity values of 0.17 to 1.74 m2 /day. The analytical data indicated that Na-Cl-type water dominates most groundwater and river water samples.

Water resources, including groundwater, are under threat globally from abstraction and pollution, making studies of water flows ever more urgent. South Africa has a growing population, a relatively dry climate and abundant mining activity, all of which increase the importance of water management. Mooiplaas Dolomite Quarry, southeast of Pretoria, has been mining metallurgical grade dolomite since 1969 and is located in the productive karst aquifers of the Malmani Subgroup, Transvaal Supergroup.

Gold mining on the Witwatersrand has started in the late nineteenth century as sporadic open cast mining and ceased in the late twentieth century, leaving a complex network of haulages, tunnels and ultra-deep vertical shafts/sub-vertical shafts. At least three ore bodies (conglomeritic horizons) were mined down to a depth in excess of 3 000 m from surface. Three large mining basins resulted from the mining methodology applied, namely the Western, Central and Eastern (Rand) Basins.

The natural CO2 springs at the Bongwana area emanates from a number of sites along an 80 km long N-S trending fault known as Bongwana fault. CO2 rich groundwater is observed at a shallow depth in a borehole drilled for water supply parallel to the main fault. The geology along the entire fault length is characterized mainly by Dwyka Group sediments. The objectives of this study are to characterize the CO2 springs and assess their impacts on groundwater and surface water quality.

An integrated approach involving multivariate statistical analysis combined with graphical methods (Piper trilinear diagram and δ18O-δ 2H plots), and environmental isotope analyses were successfully applied to characterise the spatial distribution of hydrogeochemical parameters and their controlling factors within the Lake Sibayi catchment located in north-eastern South Africa.

The legacy of mining in South Africa in general and in KwaZulu-Natal (KZN) province in particular, continues to affect the quality of surface water and groundwater resources. Rehabilitation of Northern KZN abandoned coal mines and their discard coal mine dumps had been undertaken by Government in the 1990’s following the emergence of stricter environmental legislation. The purpose of this study was to study the success of the rehabilitation of these abandoned mines in improving the quality of surface water and groundwater resources around the area.

In South Africa and neighboring countries such as southern Zimbabwe, Botswana, southern Angola and Namibia, most river systems are non-perennial due to semi-arid/arid climatic characteristics. In such river systems, the interaction between groundwater and surface water is of significance in terms of developing appropriate methods for determining ecological water requirements among others. However, the interaction is not well understood in terms of the influence on the volume and quality of water on the gaining and losing water bodies.

Well-established engineered systems for depth-discrete monitoring in fractured rock boreholes (referred to as a Multilevel System or MLS) are commercially available and offer much diversity in design options, however, they are used infrequently in professional practice and have seen minimal use in groundwater research. MLSs provide information about hydraulic head and hydrochemistry from many different depths in a single borehole and, therefore, magnify greatly the knowledge value of each borehole.