Hydrochemical Investigation of Saline Water Intrusion into Aquifers in Part of Eastern Dahomey Basin, Southwestern Nigeria

This study is a major attempt at delineating presence and lateral extent of saline water intrusions into aquifers at the easternmost part of Dahomey basin which falls essentially in the sedimentary terrain of Ondo State of Nigeria. 61 water samples were collected from hand dug wells, shallow boreholes, and ponds across the study area and analyzed for relevant parameters such as pH, conductivity, total hardness, calcium hardness, magnesium hardness, total dissolved solids, alkalinity and concentrations of the following anions and cations; chloride, calcium, Sulphate, bicarbonate, magnesium and sodium. Equivalent salinity was calculated from the water sample analysis results. The hydrochemical analysis results reveals possible saline water intrusion in the coastal area, especially the southeastern part and Agbabu in the north central part of the study area as evident from high concentration values of chloride (372 - 1500 mg/l), alkalinity (105 - 330 mg/l), equivalent salinity (135 - 2808 mg/l), total dissolved solid (181 - 1005 mg/l), high pH values (4.4 - 8.6 pH) and conductivity values (541 - 1500 µs/cm). Keywords: Saline water intrusion, saline-freshwater boundary, hydrochemical and equivalent salinity.

Hydrochemical Investigation of Saline Water Intrusion into Aquifers in Part of Eastern Dahomey Basin, Southwestern Nigeria

This study is a major attempt at delineating presence and lateral extent of saline water intrusions into aquifers at the easternmost part of Dahomey basin which falls essentially in the sedimentary terrain of Ondo State of Nigeria. 61 water samples were collected from hand dug wells, shallow boreholes, and ponds across the study area and analyzed for relevant parameters such as pH, conductivity, total hardness, calcium hardness, magnesium hardness, total dissolved solids, alkalinity and concentrations of the following anions and cations; chloride, calcium, Sulphate, bicarbonate, magnesium and sodium. Equivalent salinity was calculated from the water sample analysis results. The hydrochemical analysis results reveals possible saline water intrusion in the coastal area, especially the southeastern part and Agbabu in the north central part of the study area as evident from high concentration values of chloride (372 - 1500 mg/l), alkalinity (105 - 330 mg/l), equivalent salinity (135 - 2808 mg/l), total dissolved solid (181 - 1005 mg/l), high pH values (4.4 - 8.6 pH) and conductivity values (541 - 1500 µs/cm). Keywords: Saline water intrusion, saline-freshwater boundary, hydrochemical and equivalent salinity.

Assessment of Surface and Groundwater Quality of the Akure Metropolis, Southwestern Nigeria.

Hydrochemical analysis was carried out on surface and groundwater samples collected from Akure metropolis with a view to determining their quality. Hydrochemical data on groundwater samples from fifty six (56) boreholes were sourced from the Ondo State Water Corporation. Twenty five (25) surface water samples from streams and rivers in the study area were collected and analyzed using standard analytical techniques. The analyzed physical parameters include colour, odour, turbidity, conductivity and chemical properties such as pH, dissolved solid, hardness, cations, anions and heavy metals. All the groundwater samples were colourless, odourless and tasteless. Some surface water samples were coloured and turbid in appearance while some had objectionable odour. Although the NO3- concentration levels in both surface and groundwater samples were generally below the WHO threshold value of 10 mgl-1, relatively high concentration range (2.5-6.0 mgl-1) was recorded within the city centre indicating some level of pollution from cumulative anthropogenetic activities. Only few surface water samples contain Pb while Mn was identified in some surface and groundwater samples. The elevated Pb concentration levels (0.41-3.41 mgl-1) and relatively high Mn concentration levels (up to 2.18 mgl-1) (both much higher than the WHO and NIS thresholds) in some surface water samples was an indication of heavy metal pollution. Conductivity values of the groundwater samples generally ranged from 42.0 – 1400.0 µScm-1.  Only surface water sample 17 was moderately saline while other surface water samples were of freshwater type. Based on TDS values, all the groundwater and surface water samples were of freshwater type (TDS < 1000 mgl-1). Keywords: Physico-chemical Analysis, Surface/Groundwater, Quality, Akure Metropolis