Identifying the source of the Gerhard Minnebron aquifer

MSc (Environmental Sciences with Hydrology and Geohydrology), North-West University, Potchefstroom CampusFresh drinkable groundwater is a very valuable resource, one that needs to be used, developed, managed and conserved. The Gerhard Minnebron (GMB) is such a resource, it is an important resource for the communities and agriculture downstream. The GMB has experienced development and usage without the conservation or protection of the resource. Protecting the GMB from any further pollution and contamination is crucial for the future of the resource. To achieve this the extent of the GMB’s water source should be determined. This study aimed to determine the origins of the water in the Gerhard Minnebron aquifer. One efficient tool to determine surface and groundwater flow is Tracers. There are many different types of tracers, they can be added artificially, or they could occur naturally. Artificial tracers are organic compounds, salts, and fluorescent dyes. Natural tracers are either isotopes or natural gas species. This research made use of a natural tracer namely stable isotopes of Oxygen and Hydrogen. The stable isotopes Deuterium (²H) and Oxygen -18 (¹�O) were chosen because they cause no contamination, they’re inexpensive, already present in the water cycle, and easy to analyse and detect. Making use of the stable isotopes the source of the GMB’s water would be determined. Basic chemical anions and cations analysis were conducted to provide any additional links or aid in determining the source of the GMB’s water. For this study, stable isotope samples were collected at 42 different locations all over the WFS. The samples were collected from different bodies of water, such as groundwater, stream water, dam water and mine water through pipelines and canals. The isotope samples were collected in HDPE bottles and stored out of any direct sunlight preventing evaporation. The samples were analysed with a Picarro L2130-i Isotope and Gas Concentration Analyser. Stable isotopes with chemical analysis of the collected samples were successful in determining the aim of this study in identifying the source of the GMB’s water. The chemical analysis was done on 36 collected samples using ion chromatography. Relevant graphs were created from the chemical and isotope results to identify trends and correlations used to determine the source of the GMB’s water. The isotope analysis revealed three distinct groups. Group one was dominated by groundwater samples displaying very little isotope enrichment and plotted on or close to the local meteoric water line (LMWL). The second group displayed some isotope enrichment and plotted slightly below the LMWL the second group was a mixture of different sources. The third and final group was dominated by surface water samples and plotted well below the LMWL displaying the most isotope enrichment. The chemical concentrations varied with each sample, but high concentrations of bicarbonate and Sulphate was present in most of the samples. Overall groundwater samples displayed low concentrations of all elements. The GMB displayed high concentrations of sulphate and bicarbonate. The chemical signatures in the GMB also correlated with the signatures from surface waters and groundwater samples to the south of the WFS. The stable isotopes Deuterium (²H) Oxygen -18 (¹�O), and the chemistry data provided sufficient evidence to identify the source of the Gerhard Minnebron’s aquifer. The data revealed that the source of the aquifer is the dolomites to the North-East of the GMB with inflows coming from surface water’s, rainwater and groundwater from adjacent aquifers and compartments. To identify the source more accurately, tracers such as CFC’s, additional isotopes, chemical tracers, and physical tracers like dyes are recommended. The area is hydrogeologically very complex and additional research into the aquifer interactions would be very valuable, additional samples collected over a larger sampling area and annual sampling is recommended for future studies.Master