Sources of salinization and Investigation of salt water intrusion into coastal aquifers in parts of the Niger Delta, Nigeria

Coastal aquifer salinization which could be due to salt enriched intra-formation trapped seaward marine deposits, fossil sea water, leaching from saline confining beds, saline sea water intrusion, increase in the total dissolved solids, and tidally induced enlargement of salt water zone is a stack reality in the basin. In this study, integrated vertical electrical sounding, 2D electrical tomography and hydrochemical characterization have been evaluated to determine saltwater intrusion and depth to interface. Results shows that all the coastal island aquifers suffer saltwater intrusion and the depths to the interface can be as low as 10- 15m depending on the tidal phase and elevation, and distance to the tidal river. Hydrochemical indices such as TDS, electrical conditivity and salinity as well as ionic ratios (Na+/Cl-, Ca2+/Mg2+, Ca2+/SO42-, Na+/Ca2+, Mg2+/Ca2+, Ca2+/Cl-, K+/Cl-, base exchange index and Simpson ratio indicates that salt water has intruded the groundwater sources in the oceanic coastal island aquifers. Simpson’s ratio classifies the waters as moderately to injuriously contaminated with saltwater. Safe abstraction depths of 10 – 15m are below the recommended minimum 30m for domestic consumption and subjects the groundwater sources to high vulnerability to anthropogenic pollution and water treatment using reverse osmosis is recommended.