ASSESSMENT OF HYDRODYNAMIC CONDITIONS WITHIN THE COASTAL AQUIFER AT ARAROMI SEASIDE, SOUTH-WESTERN NIGERIA

Abstract

The project assesses the hydrodynamic conditions within the coastal aquifer at Araromi seaside and Southwestern Nigeria. Water samples were collected from 28 hand-dug wells and 11 points from waterways in the study area. Water table and physico-chemical parameters were measured accordingly on site. Vertical Electrical Sounding was done to determine the thicknesses and depth of freshwater. Major ions and heavy metal concentrations were analyzed for. In the hand-dug wells, the EC, TDS, pH and Temperature had average in-situ values of 346.03 Ωs/cm, 174.10 mg/lCaCO3, 8.02 and 27.80oC, respectively while the waterways had 978.82 ΩS/cm, 475.91 mg/l CaCO3, 7.83 and 28.65°C, respectively. Only one recharge zone (characterized by sodium-chloride facies type) and one discharge zone (dominated by sodium-bicarbonate facies type) were observed in Araromi. The VES results showed that freshwater is 1 m deep and 1m thick. The concentrations of the dissolved major ions in the hand-dug wells were Na+, K+, Ca2+, Mg2+, Cl-, SO4 2-, NO3 2- and HCO3 - with average values of 52.60, 22.75, 8.36, 9.22, 220.22, 12.95, 0.27 and 377.69 mg/l, respectively. The pollution index value for the water samples was 0.206 showing that the groundwater in the study area has an insignificant pollution. Results of heavy metal analysis showed that Pb+, Fe2+, Mn2+, Co+ and Ni+ have average values of 0.27, 0.63, 0.07, 0.46 and 0.44 mg/l, respectively. The dissolved cation concentration dominance was in the order: Na+> K+> Mg2+> Ca2+; anion in the order: HCO3 ->Cl->SO4 2- >NO3 2- and heavy metal in the order: Fe2+>Co+>Ni+>Pb+>Mn2+. In the waterways, the major ions: Na+, K+, Ca2+, Mg2+, Cl-, SO4 2-, NO3 2- and HCO3 - had average values of 52.24, 23.93, 17.43, 100.49, 855.29, 37.51, 0.14 and 236.36 mg/l, respectively while the heavy metals gave average values of v 0.78, 1.77, 0.28, 0.85 and 0.86 mg/l for Pb2+, Fe2+, Mn2+, Co2+ and Ni, respectively. The dissolved cation concentration dominance was in the order: Mg2+> Na+> K+> Ca2+; anion in the order: Cl->HCO3 - >SO4 2->NO3 2- and heavy metals in the order Fe2+>Ni+>Co2+>Pb2+>Mn2+. Results showed that there were steady cyclic shifts in the position of recharge and discharge zones in the area, with the most significant ones observed in the evenings. These shifts are probably due to wave/tidal actions in the area.