Groundwater Flow Dynamics in Shallow Coastal Plain Sands Aquifer, Abesan Area, Eastern Dahomey Basin, Southwestern Nigeria.

Thirty hand-dug wells were identified and evaluated to study the groundwater flow dynamics and anionic species distribution in the study area. Topography and water table levels method with the aid of Surfer were adopted in the delineation of six recharge and discharge zones correspondingly. Dissolved anionic species of Cl-, HCO3-, SO42- and NO3- were determined using titrimetric and spectrophotometric method. The prominent anions in order Cl- > HCO3- > SO42- > NO3- at discharge and recharge area are Cl- and HCO3- ranging from 0.22ppm to 3.67ppm and 2.59ppm to 0.72ppm respectively. Analysis of groundwater head distribution and flow vector in Abesan area confirmed that Cl- concentration is higher than HCO3-concentration in recharge zones and conversely in discharge zones. A large percentage of the samples showed that the anions falls within the permissible limit of the W.H.O standard. Water Quality assessment revealed saltwater intrusion imprints in the groundwater of the study area. Potential salinity and SO42-/ Cl- ratios signifies that most of the groundwater in Abesan falls in a water class found to be insuitable for irrigation and not saline. Continuous dissolution of these anionic species may pose a significant threat to the inhabitants of Abesan area in the nearest future.