Vulnerability assessment of groundwater pollution in the vicinity of a landfill in Nigeria

Abstract: Malfunctioning landfills are a globally sprawled problem. The Olusosun landfill in Lagos, Nigeria is not an exception. It is located in the middle of the city, nearby groundwater resources used to supply drinking water for the inhabitants in Lagos. When solid waste is thrown in a landfill with an inappropriate management, the groundwater may be contaminated by precipitation and surface runoff percolating the solid waste.  This report identifies if the groundwater fulfills both the Nigerian Standards for Clean Drinking Water and the World Health Organization’s International Water Quality Standards. This report also analyzes if precipitation and temperature affects groundwater quality, which later on becomes the inhabitants drinking water. The study focuses on the following water quality parameters: pH, hardness, total dissolved solids, conductivity, sodium, chlorine, sulphate, phosphate, nitrate, potassium, calcium, magnesium, iron, zinc, manganese, copper, lead, nickel and chromium.  Groundwater quality was assessed in 17 different sampling sites, including wells and boreholes, with samples collected once a month during the year of 2020. Further on, a spatial analysis and temporal analysis were made. The temporal analysis for precipitation and temperature in Lagos is analyzed together with the parameters to ascertain if some parameters depend on these two factors. The tables and diagrams in the results were analyzed by visually studying the data to find correlations between the parameters and temperature respectively precipitation. Lastly, a literature study was made to support the found correlations.  The overall groundwater in the vicinity to the Olusosun landfill does not achieve the standards for either the World Health Organization or Nigeria’s Standards for Drinking Water Quality. The results indicate that the Drinking Water Quality Standards for both Nigeria and the World Health Organization lack limits for some parameters. Not all the water quality parameters investigated have an established quality standard for drinking water use. However, none of the sites exceed the guideline values for the parameters for sulphate, conductivity, nitrate, sodium and copper.  The result presents that the locations with the lowest number of fulfilled parameters, and evidently with the least qualified drinking water, were locations 2, 3, 6, 8, 12, 14, 15, 16 and 17. The majority of these locations are situated close to the landfill. The results also presented that the locations with the best water quality standards were locations 9 and 11, which are also the locations situated the furthest from the landfill. The result for the temporal analysis reveals that the temperature has a correlation to all the parameters except for calcium and that all the parameters have a correlation to all the parameters analysed.  The Olusosun landfill affects the groundwater quality negatively. The locations close to the landfill have the poorest water quality and vice versa. It is necessary to improve the water quality to secure the health of the people consuming it in Lagos, Nigeria. To do so, the landfill management must amend the current management directions. The focus should be on a remediation of the Olusosun landfill. Methods that can be used are solid washing, phytoremediation top-soil placement and establishing world leading practices in the area.