Groundwater Quality Assessment of Eket Local Government Area, Akwa Ibom State, Nigeria: Physicochemical Profiling, WHO-Referenced Suitability, and a Multivariate Assessment of Saline Intrusion and Petroleum Related Impact

Abstract

Groundwater is the primary domestic water source for communities in Eket Local Government Area (LGA), a coastal, oil-producing area of Akwa Ibom State located along the Qua Iboe River estuary near the Atlantic Ocean. This study assessed the quality and drinking-water suitability of groundwater from eight hand-dug wells and boreholes across Eket LGA using physicochemical profiling of pH, electrical conductivity (EC), total dissolved solids (TDS), oxidation-reduction potential (ORP), salinity, iron (Fe), sodium (Na), potassium (K), total hardness, and total alkalinity. Drinking-water suitability was evaluated against World Health Organization (WHO) guideline values and quantified using the Weighted Arithmetic Water Quality Index. A complementary Integrated-Weight Water Quality Index (IWQI), based on entropy-derived weights, was combined with Pearson correlation analysis, Ward’s hierarchical cluster analysis, one-way ANOVA, great-circle distance analysis, and Moran’s I spatial autocorrelation analysis to distinguish localised saline intrusion from broader groundwater-quality problems. Statistical analyses were performed in Python using pandas and SciPy. The results show that groundwater across the LGA is predominantly acidic (pH 4.0–6.6; seven of the eight sites below the WHO lower limit of 6.5) and iron-enriched (0.89–1.26 mg/L; all eight sites above the 0.3 mg/L guideline). Weighted Arithmetic WQI values ranged from 291 to 412, classifying all sampled sources as “very poor” to “unsuitable for drinking” without treatment. EC, TDS, and salinity were nearly perfectly intercorrelated (r = 1.00) and varied by more than an order of magnitude across sites (20–258 µS/cm). Cluster analysis separated a high-conductivity/high-salinity group (E3, E5, and E8) from a lower-conductivity group, with ANOVA confirming significant differences for EC, TDS, and salinity (p = 0.001), but not for pH, iron, hardness, or alkalinity. Spatial analysis showed that the saline-influenced sites were geographically closely clustered (mean separation 1.21 km, compared with 5.36 km among the remaining sites), indicating a localised intrusion hotspot rather than a uniform LGA-wide gradient; however, Moran’s I tests did not show statistically significant LGA-wide spatial autocorrelation at the current sample size (n = 8). Overall, the findings indicate a localised saline-intrusion signature superimposed on a broader acidity and iron problem. Groundwater across Eket LGA therefore requires treatment, including pH correction and iron removal at minimum, before consumption; sources nearer the estuarine and coastal fringe also require additional safeguards against saline intrusion.