Investigation of hydrogeological conditions of a fractured shale aquifer in Yala Area (SE Nigeria) characterized by saline groundwater

Geological, hydrogeological and geophysical investigations were carried out in Yala Area (SE Nigeria) to delineate potential zones for future groundwater development. The area is underlain by Turonian fractured shale rock intruded by basaltic rocks and saline water. High lineament density (> 30 km −1 ) recorded in the north suggest high permeable zone, compared with low lineament density (< 10 km −1 ) in the south and east. Geophysical results reveal four types of aquifers: an upper weathered, fractured shale aquifer with mean resistivity and thickness in the range 27–40 Ω m and 20–28 m and a lower fractured shale aquifer with mean resistivity in the range 28.5 to 36.0 Ω m and unresolved thickness; fractured saline shale aquifer with mean resistivity and thickness of 21 Ω m and 50 m; fractured silty shale aquifer with mean resistivity and thickness of 54.4 Ω m and 10 m and basaltic intrusive fractured shale aquifer with mean resistivity and thickness of 135.6 Ω m and 6 m. A broad range of aquifer parameters were obtained from resistivity data and pumping test. Groundwater quality on the mean indicated alkaline and good fresh water for drinking and irrigation use with minor level of salinization. Concentration of dissolved ions in the area are enhanced through weathering and ion exchange. On the basis of these data, the potential zones for groundwater harnessing have been delineated in Yala Area.