Assessment of seawater intrusion using ionic ratios: the case of coastal communities along the Central Region of Ghana

Seawater intrusion is a worldwide phenomenon resulting in groundwater quality challenges in coastal aquifers, which has prompted many investigations into its occurrence, sources, and age. To identify the origin of saline groundwater in the coastal communities of Central Region, Ghana, a combination of ten (10) different major ionic ratios-viz. Na/Cl, Mg/Cl, Ca/Mg, K/Cl, SO4/Cl, Ca/ (HCO3 + SO4), (Ca + Mg)/Cl, Cl/ (SO4 + HCO3), Na/Ca and Ca/SO4-and Base Exchange Index (BEX) computed from physico-chemical data on sixty-nine (69) boreholes in the communities have been analysed. The results show elevated levels of chloride concentrations in most of the groundwater in the study area, indicating salinization process by seawater intrusion. Also, the concentrations of the major ions (Na+, Ca2+, Mg2+, and SO42-) constituted more than 80% of the total dissolved solids and correlated well with Cl-, indicating they are from a common source. The spatial variation of the combined effect of the different ionic ratios and BEX classifications showed that, most of the groundwater with high salinity may be due to seawater intrusion. Significantly, the study has delineated areas in the communities with poor groundwater quality arising from seawater intrusion; these areas need to be avoided in the development of the resource for water supply.