Groundwater Quality Assessment in Akoko District, Southwestern Nigeria: A GIS-Based Hydrogeochemical and Statistical Analysis

The practice of exclusive rain-fed agriculture may not guarantee food security in today’s rapidly growing and urbanizing Nigerian society due to seasonality of rainfall regimes. This study employed index-based analytical and statistical techniques in GIS environment to evaluate the hydrogeochemical processes influencing groundwater quality in the Akoko area of Nigeria with a view to determining the suitability of the groundwater for drinking and irrigation purposes. On-site pH, TDS, and EC were measured in situ using Hanna meter. While SO4 2+ was determined using a colorimeter, Ca2+, Na+ , and K+ were measured using a flame photometer. Titrimetric approach was adopted for estimating HCO3 - , Cl-, and TH. The predominance of the cations and anions followed Ca2+>Mg2+>Na+>K + and HCO3 ->Cl->SO4 2->NO3 - order respectively. Alkali earth metals (Ca2+ + Mg2+) dominated over alkali metals (Na+ + K+ ), and (CO3 - + HCO3 - ) exceeded (SO4 2- + Cl- ), suggesting continental environment. Negative chloro-alkaline indices suggested exchange of (Ca2+ + Mg2+) in groundwater for (Na+ + K+ ) in the aquifer. Ionic ratios exhibited depletion of Na+ against Cl- , and prevalence of weathering processes. The pH values ranged from 6.4 to 7.8 (slightly acidic to alkaline). The groundwater was moderately hard to hard, signifying a strong influence of bicarbonate ions. The most prevalent water type was Ca-HCO3, indicating silicate minerals dissolution consistent with Gibbs plot. From PCA results, strong correlations existed between DWQI and EC, TDS, Cl- , SO4 2- , Na+ , and K+ . Generally, the groundwater is drinkable and largely suitable for irrigation following WHO standards and FAO benchmarks with possible salinity management.