Assessment of municipal solid waste leachate pollution on soil and groundwater system at Onderstepoort landfill site in Pretoria

Abstract

This study focuses on determining the quality of soil and groundwater at the Onderstepoort Municipal Solid Waste (MSW) landfill site. The study area is situated in Pretoria North, a jurisdiction of City of Tshwane Metropolitan Municipality (CTMM). Samples were collected from three different spheres (i.e. leachate, soil and water) in the study area, to determine the concentration of metals accumulated in each sphere. The three spheres provided an overview of the contaminants found in leachate, soil and water. The laboratory analyses using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) indicated that soils in the site have been severely contaminated with heavy metals. Higher concentrations of heavy metals occurred in the soils compared to the groundwater surrounding the landfill site and this may be due to the ability of the soil strata to absorb the contaminants caused by the landfill leachate. In essence, the measurements indicated that leachate soil has very high pollutant levels (0.21 to 2505.61 mg/kg); soil was characterised by fairly-high pollutant levels (0.03 to 638.27 mg/kg); leachate solution has given rise to moderate pollutant levels (0.01 to 2.296 mg/L) and water resources have low-moderate pollutant levels (<0.0001 to 0.456 mg/L) depending on the location. Furthermore, the findings indicated that the soil was contaminated with lead, cadmium, copper, zinc and nickel, and the concentration increases particularly where the generation of leachate is taking place. Groundwater, particularly in Borehole 2 has been moderately contaminated with nitrite, calcium and manganese. The findings also indicated that the concentrations of contaminants become high in borehole located close to the waste dump and decrease further away from the waste dump. The chemical analysis of this groundwater indicated that the concentrations of chemical properties have increased since the year 2009. This was determined through the comparison of groundwater study undertaken in 2009 to the current study results obtained. The site geological formation, Rustenburg Layered Suite is known to contain the anomalies of nickel, chromium, vanadium, copper, arsenic, lead and zinc but these are less toxic and less distributed. Therefore, the primary source of pollution at the study area could be the landfill operation through the generation of leachate affecting both soil and water