Hydrogeological and Hydrochemical Assessment of Basin Granitoids in Assin and Breman Districts of Ghana

摘要

Hydrogeological and hydrochemical assessments were carried out in Assin and Breman districts of Ghana. A multi-criteria approach was used in the assessment of the basin granitoids including;electrical resistivity survey, pumping test and water quality analysis. A total of twenty-five (25) representative boreholes were drilled, developed and pumped;obtaining data for aquifer hydraulic parameters estimation. Correlation analysis was used to determine relationships that exist between aquifer hydraulic parameters. Schoeller, Piper, Stiff plot and Gibbs diagrams were used to determine the hydrogeochemical facies, water types and the mechanism that control groundwater quality. The statistical analysis determined that aquifer hydraulic parameters discharge rate (Q), hydraulic conductivity (K) and Transmissivity (T) showed a strong positive correlation with specific capacity (Q/Sw) with R value 0.8462, 0.8738 and 0.8332 respectively. The K and T were respectively between 0.02 - 0.90 m/day and 0.36 - 13.47 m2/day with mean of 0.24 m/day and 3.03 m2/day respectively. The K values indicate a hydrogeological condition of aquiclude with relatively low permeability and medium water bearing capacity. The aquifer T magnitude is very low to low, groundwater potential is adequate for local water supply with limited and private consumption. All physicochemical parameters were within the permissible limits of Ghana Standards Authority (GSA) and World Health Organisation (WHO) except for apparent colour, pH, Fe and Mn. Distribution of major ions in groundwater samples was calculated and the general trend among cations and anions was found to be Ca2+ > Na+ > Mg2+ and Cl? > HCO3? > SO42? respectively. The study area shows five main water types namely;Ca-HCO3, Na-Mg-HCO3-SO4, Ca-SO4, Na-Cl and Mg-Na-Cl. Weathering of rock-forming minerals as the mechanism controlling the groundwater chemistry. Microbiological parameters were above the permissible limits. Groundwater is suitable for drinking after treatment with chlorination, aeration and slow sand filtration methods.