Optimization of water quality monitoring in a typical quaternary catchment in Mpumalanga, South Africa

Abstract

Water is a scarce and precious natural resource in South Africa. The Department of Water and Sanitation (DWS) has been appointed as the custodians of the water in South Africa with Catchment Management Agencies (CMA’s) assisting in this cause. A management measure used for the protection of the water resources in South Africa is water quality monitoring, a process that can be very complex and difficult within a quaternary catchment. This study was undertaken to investigate optimization of water quality monitoring within a typical quaternary catchment in the Mpumalanga Province of South Africa. The study area is the C12D quaternary catchment and consists of several 1st to 4th order tributaries with the geology consisting of ultramatic / mafic intrusive rocks arenaceous rocks consisting of sandstone. The optimization of placing surface and groundwater monitoring points were investigated in the study area through identifying pollution sources and establishing a correlation between groundwater flow and surface water flow directions. A desktop study and a site visit to the study area identified five main pollution sources, namely gold mining, coal mining, agriculture, town of Secunda and a sewage treatment plant. To establish a correlation between groundwater levels and surface topography, a Bayesian correlation test was performed. The test showed a significant positive correlation between the groundwater levels and surface elevation within the study area, r2 = 0.9437, p < 0.001. As a result, the surface water flow direction was used to determine the direction of groundwater flow in the study area. Identifying specific water quality variables to be monitored for each pollution source was also investigated as a means for optimizing water quality monitoring. Historic water quality data were assessed for significant variation between upstream and downstream monitoring points. A literature review was used to supplement historic water quality data where absent or lacking. The results showed significant variations in Total Dissolved Solids (TDS), Sodium (Na), Electrical Conductivity (EC), Calcium (Ca), Chloride (Cl), Sulphates (SO4), Fluoride (F) and Magnesium (Mg) concentrations for the gold mining activities, Ca, Nitrates (NO3), Na, Cl, F, EC, TDS and NH4 concentrations for the sewage treatment plant, Cl concentrations for the town of Secunda, no variation for the agricultural activities and SO4, Ammonium (NH4) and NO3 concentrations for the coal mining activities.