Delineation of saline water intrusion to safe-guide inland groundwater resources

Abstract This work is intended to study the groundwater potential of Lagos Island in Nigeria and delineate appropriately, the depth at which saline water intrude into the groundwater resources of the area. Saline intrusion into groundwater resources of Lagos Island has rendered potable percentage of undergroundwater undrinkable. Better understanding and proper delineation of the saline water will proffer efficient household use of the resource. A direct current electrical resistivity method of geophysical prospecting using the Schlumberger electrode configuration was adopted. Electrical resistivity with natural gamma was carried out to accurately delineate prolific sand aquifer(s), determine the exact lithology of the well and nature of saturated fluid at Lagos Island. The same test was repeated at Lagos Inland in order to proffer engineering control techniques that will be necessary for controlling saline intrusion into inland groundwater. Quantitative interpretation of curve types obtained from the field data of the sounding curves revealed that the site is underlain by topsoil, clay, sandy clay and saline water sand intercepted at a depth of 136 m. Groundwater development through deep borehole drilling is recommended to a minimum depth of 220 m; the borehole depth should not exceed 250 m. Technique for controlling seawater intrusion into inland groundwater should include construction of subsurface barrier in excess of 136 m deep perpendicular to the coastal creeks and lagoons.