158-Borehole-Mediated Remediation of Contaminated Groundwater within the Vicinity of a Mining Operation in South Africa.

Abstract

Mining of ores involves the excavation of large quantities of waste rock from which the desired mineral ore is extracted. The waste rock forms the major source of most of the pollutions caused by mining. The contaminants, most often, are easily leached out and these have the potential to contaminate the surrounding environment including surface and groundwater. In this project, boreholes were sunk across the pollution plume as remediation measure to reverse the movement of the plume. Direct current (dc) resistivity equipment was used to precisely locate the migration of the plume and the borehole positions cited. The water quality parameters investigated included pH, EC, TDS, Cat', Mg2+, K+, Si, F-, T/alk, Cl- S042-, NO3 and NH4+. Samples were taken after every three months for a period of three years. Base flux assessment was also conducted. Piper hydro-chemical plots were constructed in order to determine whether any significant change in the hydrochemical composition had occurred at a specific sampling locality. Reduction of levels of water quality parameters was achieved over a period of a year after remediation boreholes were strategically sunk along the pollution plume. The following reduction were achieved, 48% S042-, 35.6% Mg2+, 71% Cl- and 95% NO3. The base flux assessment indicated that positive (groundwater gradient from the aquifer towards a nearby river) and negative (groundwater gradient from the river towards the aquifer) gradients occurred along three and two lines respectively. From the Piper plots, all borehole water samples were characterized by Ca/MgCl2 and Ca/MgSO4 groundwater. The results obtained in this study demonstrated that positioning of boreholes strategically along the pollution plume and pumping out contaminated groundwater reversed the plume movement. Consequently, significant reduction in the levels of water quality parameters was achieved. This resulted in the contaminated groundwater meeting the set drinking water quality standards.