Groundwater Monitoring in the Gneisso-Basaltic Fractured Rock Aquiferous Formations of Kumba, Southwest Region Cameroon: Seasonal Variations in the Aqueous Geochemistry and Water Quality

摘要

The objective was to determine and monitor seasonal changes during four hydrological seasons: Wet season (September), Wetdry season (December), Dry season (March) and Drywet season (June) in the groundwater aqueous geochemistry and its domestic-agro-industrial quality using physicochemical parameters and hydrogeochemical tools: Temperature, Electrical Conductivity EC, pH, Total dissolved solids TDS, Ionic ratios, Gibbs diagrams, Piper diagrams Durov diagrams, total hardness HT, Water quality index WQI, Sodium adsorption ratio SAR, Percent Sodium %Na, Kelly’s Ratio KR, permeability index PI, Magnesium adsorption ratio MAR, Residual sodium carbonate RSC and Wilcox diagram. Field physicochemical parameters ranged from: Wet season; pH 3.9 - 6.9; Temperature, 23.3°C - 29.1°C; EC, 10 - 1900 μS/cm; TDS, 6.7 - 1273 mg/L; Wetdry, pH, 5.7 - 11.7; Temperature, 23.6°C - 28.3°C; EC, 1 - 1099 μS/cm, TDS, 0.67 - 736.33 mg/L; Dry pH, 5.7 - 13.1; Temperature, 26.3°C - 30.2°C; EC, 12 - 770 μS/cm, TDS, 8.04 - 515.9 mg/L and Drywet, pH, 4 - 7.4; Temperature, 25.8°C - 30.7°C; EC, 10 - 1220 μS/cm, TDS, 6.7 - 817.4 mg/L. Seventy-two groundwater samples, 18 per season were analysed. All ionic concentrations fell below acceptable World Health Organization guidelines in all seasons. The sequence of abundance of major ions are; Wet, Ca~(+) > Mg~(2+) > Na~(+) = K~(+) > NH_(4)~(+), HCO_(3)~(?) > Cl~(?) > NO_(3)~(?) > SO_(4)~(2?) > HPO_(4)~(2?); Wetdry Ca~(+) > K~(+) > Mg~(2+) > Na~(+) > NH_(4)~(+), HCO_(3)~(?) > Cl~(?) > SO_(4)~(2?) > NO_(3)~(?) > HPO_(4)~(2?); Dry Ca~(+) > K~(+) > Mg~(2+) > Na~(+) > NH_(4)~(+), HCO_(3)~(?) > Cl~(?)> NO_(3)~(?) > SO_(4)~(2?) > HPO_(4)~(2?); Drywet NH_(4)~(+) > Ca~(+) > K~(+) > Mg~(2+) > Na~(+); Cl~(?) > HCO_(3)~(?) > NO_(3)~(?) > SO_(4)~(2?) > HPO_(4)~(2?). Groundwater ionic content was due to rock weathering and ion exchange reactions. CaSO_(4) is the dominant water type in Wet and Wetdry seasons; followed by CaHCO_(3), Na + K-Cl Wet, CaSO_(4) and CaHCO_(3) Wetdry; MgCl Dry and Drywet followed by CaCl, CaHCO_(3) Dry and CaSO_(4), CaHCO_(3) Dry-Wet. The dominant hydrogeochemical facies are Ca-Mg-Cl-SO_(4) followed by Na-K-SO_(4) Wet and Ca-Mg-HCO_(3)~(?) in all other seasons. Ion exchange, Simple dissolution and uncommon dissolution are the processes determining groundwater character. The water quality indices; WQI, HT, SAR, %Na, KR, PI, MAR,RSC and Wilcox diagrams, indicate that groundwater in Kumba is 80% - 100% excellent during the Drywet &Wet seasons, 5% - 10% unsuitable during the Wetdry & Dry seasons for domestic use while being excellent-good for Agro-Industrial uses in all other seasons. Physicochemical parameters in some areas exceeded permissible limits for drinking. All hydrogeochemical parameters vary with seasons and these variations show the impact of annual cycles of seasonal changes on the aqueous geochemistry of groundwater in Kumba.