Environmental geohydrological investigation : focusing on the Onderstepoort landfill site, Gauteng, South Africa

Abstract

The Onderstepoort landfill facility is in the City of Tshwane (CoT) and has been operational since 1996. The facility was developed following the Environmental Conservation Act (ECA) 73 of 1989 and classified as G:M:Bwhich means that the facility accepts general waste (G), medium in size (M), and with no significant generation of leachate (B-). Onderstepoort landfill facility has reached its full capacity and is in the process of being closed.Tshibalo,(2017) also revealed that the Onderstepoort landfill facility was established without bottom liners and lacked a leachate collection system. Thus, it was necessary to conduct a study to investigate the physical, chemical, and microbiological quality of groundwater samples collected from the three existing boreholes in the facility. A limited pilot water quality study involved the analysis of water from two boreholes in August 2015 for pH, electrical conductivity, colour, and total coliform count. After a third borehole was drilled, a more comprehensive four-week study was conducted in August, October, and November 2016. Groundwater samples were collected and analysed in an accredited laboratory for comparison against the World Health Organisation (WHO) and SANS 241: 2015 drinking water quality standards. Physical parameter analysis showed that the sample water colour and electrical conductivity were within both water quality standards of WHO (2017) and SANS (2015). Although the water pH decreased since the 2015 study, the pH of the water samples collected in 2016 still exceeded the WHO (2017) water quality standard. The chemical parameter analysis showed that chloride, fluoride, cadmium, calcium, lead, sodium and zinc were within the water quality standards but higher than standard concentrations of copper, sulphate, nitrate nitrogen, magnesium and manganese determined. The parameters such as sulphate, copper and iron are within the acceptable limits since the 2015 study. The microbiological analysis also showed high numbers of E.coli and total coliforms that had increased since 2015. Based on the results of this study, the leachate from the decomposed waste material may be responsible for groundwater contamination due to the lack of bottom liners and it might make the groundwater unsafe for human consumption or domestic use. As a consequence, there is a need for continuous monitoring of the groundwater quality within and outside the facility.