Geophysical assessment of vulnerability of surficial aquifer in the oil producing localities and riverine areas in the coastal region of Akwa Ibom state, southern Nigeria

摘要

1D resistivity sounding survey was combined with geological and geohydrochemical information in order to examine the aquifer vulnerability. Ten Schlumberger soundings were executed along one profile on the basis of proximity to functional boreholes. Ten samples of groundwater from nearby boreholes were checked for concentrations of significant trace element in the laboratory. The resistivity and geohydrochemical information were employed to examine the level of protection and the associated possible risk of the groundwater repository in the mapped area. The interpreted overburden parameters (resistivities and thicknesses) of water repositories were deployed to determine the integrated electrical conductivities (IEC) and susceptibility of hydrogeological units to surface contaminations. Based on results, Eket and Onna on the southern part of Nsit Ubium have IEC which reflect medium to poor protection capacity based on slightly protected and vulnerable protective layers above the underlain groundwater within the approximate depth range of 15-30 m. Nsit Ubium, the northern zone of the survey area, has a wide range of resistivity which creates windows or vulnerable pathways for percolation of waste pollutants from the surface which flow at the deeper layer. However, layers within 15-25 m depth provide good protection to their underlying aquifer based on IEC which are >1 Omega(-1). Hydrochemical parameters also show higher values that are beyond the 2006 World Health Organization (WHO) standards. The integration of resistivity data and the hydrochemical data showed that the dominant topmost cover layers of the study areas are grossly vulnerable due to drainable pores in the formation.