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.

VLF-EM and VES: an application to groundwater exploration in a Precambrian basement terrain SW Nigeria

In a hard rock environment with surface or near surface expression of outcrops, the use of VES only becomes difficult due to its associated problems and limitations. However, the use of VLF-EM becomes imperative in mapping basement structures relevant to groundwater development. A total of 2100 VLF-EM data plus selected VES points were covered over 7 traverses with length varying from 3000 to 4500 m. The VLF-EM result mapped basement structures relevant in groundwater development. This is further studied using VES. Results of the investigation indicate that a HKH sounding curve is obtained with a maximum of five subsurface layers comprising: the top soil, clay/sandy clay unit, the fresh basement, fractured basement and the basement bedrock. The fractured basement layer constitutes the main aquifer unit with thickness of 20-25 m. The layer resistivity and thickness ranges are 60-100 ohm-m; 40-80 ohm-m, 1600-2100 ohm-m, 250-420 ohm-m, and 2200-7500 ohm-m; and 0.3-1.2 m, 1.9-2.5 m, 16.5-22.5 m and 22-30 m for the five layers respectively. The geoelectric results compared favorably well with drilling information to above 90%. The yield of the well is 2 L/s with good recharge capability