Multivariate analysis of seasonal changes of chemical elements in groundwater around Solous lll dumpsite, Lagos, South-West Nigeria

The study of changes in groundwater quality across the study areas became necessary to track the sources of the contamination in the water sources. Assessment of the physiochemical parameters of groundwater samples obtained from both borehole and hand-dug wells were conducted around the Solous III dumpsite, Lagos, South-western, Nigeria. Multivariate statistics such as correlation coefficient analysis, Hierarchical cluster analysis (HCA) and principal component analyses (PCA) were utilised to assess the mode of association of parameters and their interrelationships to establish possible sources of groundwater contamination. Eight groundwater samples were obtained around the dumpsite during the wet and dry seasons for analyses of their physicochemical properties. The results of the analyses of water samples indicated seasonal changes for the various elemental constituents analysed. There was generally an increase in mean concentration of total dissolved solid (TDS), pH, temperature and hardness in the dry season study, and a corresponding increase in the mean concentration of Ca2+, Mg2+, Na+, SO42-, NO32-, Pb, and Cr, when compared with the wet season. On the other hand, there was reduction in the mean concentration of electrical conductivity (EC), K+, Cl-, PO43-, Fe, Zn, Mn, Cu, and Ni in the dry season when compared with the wet season. Some of the water sample parameters exhibited high concentration when compared with the World Health Organisation (WHO)/Standard Organisation of Nigeria (SON) standards, which may be due to the impact of leachate migration from the dumpsite. Five varimax rotated factor loadings and communalities were responsible for 30 % and 35 % of the total variance in the data set during wet and dry seasons respectively. The PCA parameters identified to be influencing the quality of water are perhaps related to anthropogenic activities from the dumpsite, soluble mineral dissolution, rock-groundwater interaction and weathering activities while PCA performed on samples of groundwater during wet and dry seasons indicated 2 and 3 important clusters, respectively. The clusters of parameters as observed in the parameters dendrograms clearly validates the results earlier obtained in the correlation analysis component of this research. The dendrogram was also able to reflect variation in the quality of water with season as indicated in the difference in the number of clusters during both wet and dry seasons. The outcome of this research should help highlight and focus water quality management on key chemical elements of concern and prioritize efforts to mitigate their release into groundwater around the study area. By extension, this research work offers specific contribution to achieving the Africa's Union's Agenda 2063 Goal No. 7 i.e. Environmentally sustainable and climate resilient economies and communities, with Priority Area of Water Security.