Assessment of groundwater quality and the controlling factors in coastal aquifers of Ghana: An integrated statistical, geostatistical and hydrogeochemical approach

Coastal aquifers are complex groundwater bearing zones with multiple ways of interacting with seawater. Understanding of the main controls and evolution of such aquifers is essential for effective management of the groundwater. In this paper, a comprehensive study was conducted to characterize and identify the main factors and processes controlling the groundwater quality in some coastal aquifers through an integrated approach of Principal Component Analysis (PCA), Cluster Analysis (CA), geostatistical analysis and information entropy-based groundwater quality index coupled with detailed hydrogeochemical assessments. The PCA and CA yielded four clusters with distinct hydrogeochemical signatures (Cluster 1 and 2: freshwater influenced by rain, Cluster 3 transition zone and Cluster 4 marine influence/seawater intrusion or aerosol spray). Geostatistical analysis showed a wide variation in salinity from the coast to the inland while piper diagram revealed the evolution of the aquifers from Ca-HCO3, Ca-Cl which correspond to natural recharge zone in the north, to mixed Ca-Na-Mg-CI-HCO3 representing transition and Na-Cl towards the coast. The water suitability assessment for drinking using entropy-based groundwater quality index showed that about 59.4%, 20.3%, 7.8%, 2.6%, and 9.9% of the groundwater sample were estimated to be excellent, good, average/medium, poor, and extremely poor water quality. Ion exchange mechanism, dissolution of minerals from the rocks and marine influence are the dominant processes controlling the groundwater chemistry in the area. Recommendations for groundwater resource management and future research needs have also been discussed.