Short-term impact of sulphate mine dump rehabilitation on the quality of surrounding groundwater and river water in Mazowe District, Zimbabwe

Disposal of wastes from sulphate mining operations has been a perennial problem to the environment in many countries, because these waste will continue to produce acid mine drainage (AMD) for a long time after being generated. The aim of this study was to evaluate the impact of rehabilitation of a pyrite waste rock dump, which had accumulated over seventy years and covering about 5000 m2 of land, on the quality of surrounding groundwater and river water. The research was done two years after a waste rock dump rehabilitation exercise had taken place. Groundwater was sampled from monitoring wells installed on the lower side of dump and at the bank of a nearby river, while surface water was sampled from the perennial river. The water samples collected at two month intervals over a year were analysed for pH, electrical conductivity (EC), total dissolved solids (TDS) and sulphate. Results showed a considerable decrease in pH of river water from 7.5 to 3.0 as the river flowed by the dump. One year after the re-vegetation of waste dump, the pH of river water at all sampling points were not significantly different (p > 0.05) from those obtained in the previous four years of monitoring. The EC of river water increased from 0.25 to 3.2 mS cm−1, while TDS increased from 60 to 2000 mg l−1 from the dump going downstream. Results also indicated that sulphate increased from 20 to 1500 mg l−1 from the dump going downstream and it was the chief solute constituent in river water. Groundwater measurements showed that the rehabilitation exercise had not resulted in the improvement of groundwater quality two years after rehabilitation as water pH remains very low, while EC and sulphates were above the acceptable critical limits. It was concluded that two years after the rehabilitation of the mine dump there was no improvement in the quality of groundwater or surface waters of the Yellow Jacket River.