Flow system, physical properties and heavy metals concentration of groundwater: A case study of an area within a municipal landfill site

Abstract

Groundwater within the Olusosun landfill site in Lagos Metropolis was evaluated. Previous research on quality parameters of groundwater in the area made use of equipment of low detection capacity for heavy metals concentrations in water. Also, subsurface flow and significant attenuation of leachate due to horizontal distance between wells and landfill site are yet to be technically elucidated. In the present investigation, priority was given to heavy metals as small quantities may build up in human systems to become a significant health hazard. Then analysis was done with Inductively Coupled Plasma Mass Spectrometry (ICP-MS), while Geographical Information Systems (GIS) technique was used for spatial data analysis and management to illustrate localised flow of groundwater. Digital subsurface model of data from 20 drinking-water wells showed that flow directions are north-south, north-west and south-east. The two extremes of the pH for the groundwater are 4.04 and 8.05, indicating slightly acidic to weakly basic water. Total Dissolved Solids (TDS) are positively-strongly correlated with electrical conductivity (EC) in a line of fit TDS = 29.71 EC - 47.9. From the ICP-MS results, Fe concentrations at locations 1, 3 and 4, and Pb concentrations at locations 1, 5, 7, 8, 14 and 16 did not conform to international human-health benchmarks. Generally, the longer the horizontal distance between a well and the landfill site, the lesser its potential for groundwater contamination. This study better clarifies heavy metals concentrations in water, with GIS for satisfactorily display of positional and attribute for groundwater flow in the area. Key words: Heavy metals, groundwater, landfill, Geographical Information Systems (GIS), Inductively Coupled Plasma Mass Spectrometry (ICP-MS).