Seasonal Variations in Groundwater of the Phreatic Aquiferous Formations in Douala City-Cameroon: Hydrogeochemistry and Water Quality

Abstract

This study carried out in Douala City, was to determine the seasonal variations of groundwater, the influence of the rock formations on the groundwater solute chemistry and groundwater domestic-agro-industrial quality using hydrogeochemical tools and physicochemical parameters, Ionic ratios, Gibbs diagrams, Piper diagrams, Durov diagrams and water quality indices. From physicochemical parameters, in the rainy season, pH ranged from, 4.6 - 7.1; EC, 0.023 - 1.63 mS/cm, Temperature, 26.3˚C - 29˚C and TDS, 0.015 - 1.09 mg/L, and in the dry season pH ranged from 5 - 7.2, EC, 0.01 - 1.61 mS/cm, Temperature, 24.4˚C - 29.5˚C and TDS, 0.01 - 1.08 mg/L. Forty groundwater samples, 20 per season, wet and dry were analysed. The major ions fell below WHO acceptable limits for both seasons. The sequences of abundance of major ions were, Ca2+ > K+ > Mg2+ > > Na+, > Cl− > > > in wet season and Ca2+ > Mg2+ > K+ > Na+ > , > Cl− > > > in dry season. Ion-exchange, simple dissolution and uncommon dissolution processes determined groundwater character. Groundwater ionic content was as a result of ion exchange from rock-weathering. Water types are; MgCl and MgHCO3 in both seasons. Hydrogeochemical facies are; Ca-Mg-Cl-SO4, characteristic of groundwater some distance along its flow path and Ca-Mg-HCO3, characteristic of freshly recharged groundwater from precipitation. The groundwater indices of Sodium Percent (% Na), Residual Sodium Carbonate (RSC), Kelley’s ratio (KR), Sodium Adsorption Ratio (SAR), Electrical Conductivity (EC), Total Dissolved Solid (TDS), USSL and Wilcox index were determined, evaluated and found to be suitable for agro-industrial uses in all seasons. Permeability Index (PI), Water quality index (WQI) and Magnesium Adsorption Ratio (MAR) were not suitable in some areas and in some seasons.