Analysis of groundwater quality using multivariate and spatial analyses in the Keta basin, Ghana

A holistic assessment of the quality of groundwater from the shallow unconfined aquifers of the Keta strip of the Keta basin has been conducted using multivariate statistical and spatial analyses. A groundwater classification scheme has been developed for groundwater in the area using a robust water quality index (WQI) modified for the case of the Keta basin. On the basis of the WQI so computed, groundwater in the area has been spatially classified into ‘good’, ‘fair’, and ‘marginal’ water types using ordinary kriging developed from a well fitted linear semivariogram function. This study finds that the salinity of groundwater in the basin is largely attributed to mineral weathering and seawater intrusion. Groundwater is stable within kaolinite and Na-smectite field, suggesting the predominance of Na-rich silicate minerals over the high temperature Ca-rich minerals. There are localized influences of domestic waste discharge and agricultural activities on the hydrochemistry of groundwater in the area. Where these effects are high, high nitrate and fluoride concentrations have been noted. Four groundwater clusters have also been distinguished: clusters 1 and 4 are low salinity Ca–HCO3 waters distinguished by differences in pH, whereas clusters 2 and 3 represent high and intermediate salinity Na–Cl waters respectively. This study further finds that clusters 1 and 4 present the best water types for irrigation purposes in the Keta basin. On account of high salinity, cluster 2 members are not suitable for irrigation of any crop in the basin. Sodium adsorption ratio (SAR) appears to display weak seasonal variations due to the influence of seawater intrusion, whose effects vary with the level of the water table relative to sea level. During dry seasons when the water table is low, saline water intrusion elevates the content of sodium in groundwater. This is reflected in the SAR values in some of the wells sampled.