Evaluation of the inorganic water chemistry of the Vaal River

Abstract

One of the most essential resources for life on our planet is water. A concern for water resource sustainability has shifted towards the sustainable development of clean water body resource (SWDF, 2009). Data for the Vaal River water chemistry is in abundance. However, research on the historic natural conditions influencing the inorganic water quality, is not as extensive. Inorganic data was obtained from the Department of Water Affairs, for the period 1972 to 2011, for identified monitoring stations along the Vaal River. Water quality was evaluated using various geochemical techniques to analyse the data. The results of the study indicate that the water chemistry of the Vaal River is controlled by: 1. Chemical weathering of siliceous sediment, intrusive igneous rocks and metamorphic rocks (Na+, K+, Mg2+, Ca2+ and (HCO3)-). 2. Anthropogenic influences increasing the sulphate (SO4) concentration There is no major increase in ion concentrations for the stations. However the concentrations of bicarbonate (HCO3)- and SO4 change as it progresses downstream from the first upstream station to the last downstream station. Based on the chemical characterisation, three groups have been identified. (1) Group 1 stations appear to suggest a higher influence in chemical weathering than the group 2 stations. (2) Group 2 stations appear to suggest a greater influence from SO4. (3) Group 3 stations appear to suggest an influence from both the bicarbonate and the SO4 influences. Geographically the chemical weathering is an indication of the three different groups with strong anthropogenic influences in the middle group. The water chemistry for the Vaal River is controlled by two processes, namely chemical weathering and anthropogenic influences. The prominent indication of the difference in these two influences can be seen between group 1 and group 2. A secondary conclusion indicates that a total dissolved solid (TDS) alone is not an accurate representation of anthropogenic influence (or poor water quality) on inorganic water quality of the Vaal River. The natural weathering or geological influences appears to play a more dominant role in certain sections or catchments with lower contributions from anthropogenic influences.