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Hydrogeochemistry and isotope studies of groundwater in the Ga West Municipal Area, Ghana

Saka, David, Akiti, Tetteh T., Osae, Shiloh, Appenteng, Michael K., Gibrilla, Abass
Appl Water Sci 2013 v.3 no.3 pp. 577-588
deuterium, evaporation, freshwater, groundwater, groundwater recharge, hills, humidity, hydrogeochemistry, ions, isotopes, minerals, mixing, oxygen, rain, rocks, saline water, salinity, solutes, water supply, wells, Ghana
This paper assesses groundwater in the Ga West Municipal Area of Ghana using hydrogeochemistry and isotope approaches. High salinity groundwaters are obtained in the municipality which poses problems for current and future domestic water supply exploitation. The increase in salinity is related to the dissolution of minerals in the host rocks and the evaporative concentration of solutes. The dominant groundwater composition in both shallow and deep wells sampled is Na–Cl. The concentration of the Na–Cl was observed to increase substantially with well depths. The mixing of freshwater of the shallow hand dug wells with that of saline water of the deep boreholes was noted in the shift from Ca–HCO₃ facies to Ca–Cl facies. Schoeller diagram showed that groundwater in the study area is recharged from a similar source. The Schoeller diagram also showed the gradual increase in concentration of the major ions with depth. This leads to salinization in the deep boreholes. The oxygen and hydrogen isotope compositions in the groundwater samples suggest that groundwater recharge is of meteoric origin with few samples showing evidence of evaporation. An average deuterium excess of rainfall of 14.2 ‰ was observed, which indicates the significance of kinetic evaporation due to low humidity conditions prevalent in the study area. The d-excess also indicates modern recharge along the foothills of the Akwapim-Togo Ranges.