Abstract:

The study of hydrochemical facies is particularly relevant in coastal and deltaic environments, where aquifers are shallow, hydraulically connected to surface water systems, and vulnerable to contamination. The absence of a comprehensive facies-based assessment for the study area represents a critical knowledge gap. This study investigated the geochemical characteristics and determined the hydrochemical facies of groundwater in Tombia, Bayelsa State, Nigeria, with the aim of assessing water quality, identifying dominant geochemical processes, and evaluating potential contamination risks. Five groundwater samples were collected from boreholes across the community and analyzed for physicochemical properties, major cations and anions, using standard analytical techniques and results were subjected to statistical analysis. Piper’s trilinear diagram was employed for the hydrochemical facies classification. Results show pH values (6.35–6.95), indicating slightly acidic conditions, likely influenced by organic matter decomposition and acid sulphate soils. Major ion chemistry is dominated by Ca²⁺ (0.391–1.657 mg/L) and HCO₃⁻ (40.0–90.0 mg/L), with ionic dominance sequences of Ca²⁺ > Na⁺ > Mg²⁺ > K⁺ and HCO₃⁻ > Cl⁻ > SO₄²⁻ > NO₃⁻ for cation and anions respectively, reflecting carbonate weathering and rainfall recharge as primary geochemical controls. Piper’s trilinear diagram revealed that 80% of samples fall within the Ca–Mg–HCO₃ facies, characteristic of recently recharged, fresh groundwater, while 20% lie in the mixed Ca–Mg–Cl field, indicating minor ion-exchange processes. The study concludes that while groundwater in the study area remains geochemically fresh and suitable for agriculture and domestic use based on major ion chemistry, slightly acidic groundwater conditions may enhance contaminant mobility. These findings underscore the need for regular monitoring, improved waste management, water treatment interventions, and policy actions to ensure safe and sustainable groundwater use in the Niger Delta region.