An evaluation of the impact of acid mine drainage on water quality of the lower Olifants River, South Africa

Abstract

Acid Mine Drainage (AMD) is the acidic water emanating from the mine tailing dams into the surrounding environment. AMD is regarded as a major environmental threat associated with mining. The lower Olifants River in the Kruger National Park (KNP) is considered an environmentally sensitive area, which exhibits high levels of aquatic ecosystems and supports a variety of terrestrial ecosystems within and around the KNP. The Phalaborwa mining industries have been discharging the acid mine drainage contaminated-water into the Ga-Selati River, a tributary to the Olifants River. Although the impacts in the upper Olifants River catchment have been well documented, it was the amount of AMD witnessed at KNP and the dying of fish within the lower Olifants River that raised issues of concerns. Hence, the study investigated the impact of acid mine drainage on water quality of the lower Olifants River, modelled the distribution of the dissolved heavy metals in the stream, and evaluated the applied mine wastewater management strategies at Phalaborwa mining industries. In this study, water samples were collected seasonally (winter, spring, and summer) from 2019 to 2020, and the analytical methods and procedures were optimized for the determination of selected elements in the water samples. During the study, ion chromatography (IC) was used to detect chloride (Cl), sulphate (SO4 - ), nitrate (NO3), and fluoride (F), Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) was used to detect pH, turbidity, electrical conductivity (EC), total dissolved solids (TDS), magnesium (Mg), manganese (Mn), sodium (Na), potassium (K), aluminium (Al) and calcium (Ca). Modelling of the distribution of dissolved heavy metals was performed using the inverse distance weighted (IDW) interpolation technique available in ArcGIS 10.8 software. The range of pH across four sampling sites was between 7.77 and 9.11, indicating an alkaline pH. The concentration of measured parameters elevated downstream points with some exceeding the target water quality range (TWQR) for aquatic ecosystems. The elevated concentration of SO4 - at sites 3 and 4 (downstream points) showed that the acid mine drainage is still a matter of concern at the lower Olifants River catchment. However, the GIS models showed a decreasing trend of the concentration of heavy metal towards the KNP.