Comparative Hydrogeochemical Assessment of Groundwater Quality in Ajaokuta and Okene: Implications for Contamination, Aquifer Dynamics, and Sustainable Water Management

Abstract

This study presents a comparative hydrogeochemical evaluation of groundwater systems 
in Ajaokuta and Okene, two rapidly developing urban centres within the Basement 
Complex terrain of North-Central Nigeria. The investigation aims to assess groundwater 
quality, identify potential sources of contamination, and elucidate the dominant 
geochemical processes controlling groundwater evolution in the area. A total of twenty
three (23) groundwater samples were systematically collected and analysed for major 
ions, trace metals, and key physicochemical parameters using standard analytical 
procedures based on APHA (1995) guidelines and Atomic Absorption Spectrometry 
(AAS). Multivariate statistical techniques—including correlation analysis and Principal 
Component Analysis (PCA)—together with pollution assessment indices such as the Metal 
Index (MI), Contamination Factor (CF), and Enrichment Factor (EF), were applied to 
characterize hydrogeochemical controls and distinguish between natural and 
anthropogenic influences. The results reveal marked spatial variations in groundwater 
chemistry between the two locations. Groundwater in Okene is dominated by Ca–HCO₃ 
hydrochemical facies, characterized by low electrical conductivity, low total dissolved 
solids, and negligible concentrations of potentially toxic metals, reflecting largely pristine 
conditions governed by natural water–rock interaction processes. In contrast, 
groundwater in Ajaokuta displays elevated electrical conductivity, total dissolved solids, 
and increased concentrations of iron and mercury in some samples, with hydrochemical 
facies transitioning from Ca–Cl to mixed types. These characteristics indicate significant 
anthropogenic influence, particularly from industrial activities, urban runoff, and waste
related inputs. PCA results further corroborate these findings, identifying mineral 
dissolution as the primary geochemical driver in Okene, while Ajaokuta groundwater 
chemistry reflects additional contributions from industrial emissions and leachate 
migration. Although most measured parameters fall within the permissible limits set by 
the World Health Organization (WHO) and the Nigerian Standard for Drinking Water 
Quality (NSDWQ), the enrichment of mercury in Ajaokuta poses a notable environmental 
and public-health concern. Overall, the study highlights the sensitivity of Basement 
Complex aquifers to land-use changes and industrialization, emphasizing the need for 
continuous groundwater monitoring, improved waste management, and stricter regulatory 
enforcement to ensure sustainable groundwater resources in emerging industrial regions.