Effects of Landfill Leachate on Groundwater Quality in Northern South Africa

Abstract

In many African countries such as South Africa, untreated groundwater is one of the most utilised resources for domestic, agricultural, industrial, and mining purposes. However, with the growing population, there is a concern about the interconnectivity between waste disposal and water quality. The absence of sanitary disposal methods has left most residents of Muledane and Thohoyandou with only one landfill as the main source of waste disposal. The landfill was designed without a membrane liner, thus, landfill leachate seeps into groundwater, leading to contamination. This study’s objective was to investigate the impact of landfill leachate on groundwater quality in the Thohoyandou landfill site, situated in Limpopo Province, South Africa. Eleven (11) groundwater sampling sites and 4 leachate sampling points were considered, and samples were collected in duplicate both in dry and wet periods. For total coliform and Escherichia coli, M-Tec Agar, M-End Agar, and Nutrient Agar were used. Major cations (Ca2+, Mg2+, Na+, K+, and NH4+) and anions (F−, Cl−, PO43−, SO42-, NO3, and NO2) were analysed using Metrohm 850 professional Ion chromatography (IC). Heavy metals (Cr, Cu, Mn, Ni, Zn, Hg, Pb, Co, Al, and Fe) were measured using inductively coupled plasma mass spectrometry (ICP-MS) and their health risk assessment calculated. Mercury in approximately 60% of all borehole samples in the dry season were found to be above the permissible limit of the recommended guidelines by the South African National Standard, World Health Organization, and Department of Water Affairs. Furthermore, analytes such as NO3-N, Cl, Cr, and Hg, were found at levels that can negatively impact consumers, and the health risk analysis revealed that significant non-cancer risk and cancer risk are realistic. Generally, the borehole near the landfill site displays higher contaminant concentration, which is reduced with increasing horizontal distance. This study confirms that the landfill leachate was a potential source of groundwater contamination within the Thohoyandou landfill site, and while an effective remediation method can be a short-term solution, a re-engineering of the landfill can be considered a long-term viable option.