Evolution of groundwater hydrogeochemistry and assessment of groundwater quality in the Anayari catchment

The quality of groundwater in the Lower Anayari Catchment was assessed for its suitability for drinking, domestic and irrigation purposes. The Lower Anayari Catchment lies in a semi-arid region in Ghana and covers an area of about 253 km². The area is predominantly an agricultural area and groundwater is the main source of water for domestic and agricultural purposes. Sixty-six groundwater samples were collected from boreholes and hand-dug wells. The samples were analysed for their physico-chemical properties. Calcium (Ca²⁺) and bicarbonate (HCO₃⁻) were the most abundant cation and anion respectively. The major water types in the study area are of Ca–Mg–HCO₃ and the mixed Ca–Mg–Cl type. The water chemistry is mainly controlled by reverse ion exchange, dissolution of minerals and evaporation. The quality of groundwater for drinking and domestic use was assessed using the weighted arithmetic water quality index (WQI) approach and the values showed that 94% of the samples were of ‘good’ quality while 6% were of poor quality. The groundwater was generally good for drinking except for some few samples which showed elevated F and NO₃⁻ concentrations above the WHO guideline values of 1.5 mg/L and 50 mg/L respectively. The quality of groundwater for irrigation was also assessed and the EC, %Na, SAR and RSC ranged between 240 and 710 μS/cm, 23.54–38.93, 0.47–1.04 and −1.9 to −0.09 respectively. The groundwater in the area has low sodicity with medium salinization and can generally be used for irrigation without prior treatment. Groundwater quality in the Anayari catchment is influenced by geology with little anthropogenic influence. Hence, proper groundwater management strategies and policies are needed to protect the aquifers.