Hydro-Geochemical Studies Of Groundwater In The Southwestern Coastal Districts Of The Central Region, Ghana.

ABSTRACT

The hydrogeochemical data of groundwater of southwestern coastal Districts of the Central Region of Ghana were examined to determine the main factors controlling the groundwater chemistry and study the resultant water type formed in order to determine the suitability of the water for different uses. Different geochemical interpretation methods were used to identify the geochemical characteristics. The pH values of groundwater samples showed that 36 samples had pH values below lower limit of 6.5 WHO (2011). Based on TH, groundwater quality ranges from soft to very hard. The hardness in the study was adduced to be from sedimentary rocks seepage and runoff which may be aggravated by detergents and soaps. The groundwater in the study area falls under fresh (TDS1000 mg/L) types of water. The Ca2++Mg2+ vs. HCO3 - +SO4 2- scatter diagram showed that majority of the samples fall above the equiline indicating that silicate weathering is the dominant process for supply of the magnesium and calcium ions to the groundwater. The concentration of Na+ and K+ in the ground water is a made possible by halite dissolution process (Na+ /Cl- is approximately 1). Also, the relationship between Na+K-Cl and Ca+Mg-HCO3+SO4 showed that there is ion exchange of Na+ and K+ in water for Ca2+ and Mg2+ from rock (aquifer) (Bhat et al., 2013). Concentration of HCO3 - in the study area shows that approximately 9.4% (6 samples) of the sampling stations have values exceeding the allowable limit of 240 mg/L set by the WHO (2011) guidelines for drinking water (Table 4.6). The values of manganese found was between 0 and 3.3 mg/L with as many as 39 samples representing about 60.9% found to be above the WHO (2011) allowable limit of 0.1 mg/L in potable water. The values obtained from the physicochemical analysis of groundwater samples indicated that the dominant cation in the area is Na+ and the anion is Cl- , and the order of dominance ions is Na+ >Ca2+>Mg2+>K+ :Cl- >HCO3 - > SO4 2-. Piper Diagram showes the general dominant water type as NaCl. Sodium measured against Ca2+ and Mg2+ falled outside the permissible limit of 1.0 meq/L and are considered unsuitable for irrigation purposes. The TDS values are with values less than 1000 mg/L and are within the nonsaline category, and are therefore classified as excellent irrigation waters (Robinove et al., 1958).