Geophysical investigation of saline water intrusion into freshwater aquifers: A case study of Oniru, Lagos State

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Adeoti, L
Alile, O.M
Uchegbulam, O
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Scientific Research and Essays
A total of five electrical imaging lines were measured using the wenner configuration. And a total of twelve VES was carried out within the area of investigation. The lines were aligned almost in a linearly NS azimuths, perpendicular to the ocean. The results were presented as profiles, multi-profiles, maps, pseudo sections and inverted sections. Interpretations of these results involve both qualitative and quantitative deductions from 1D and 2D geoelectric models. WingLink software was utilized for plotting, filtering, modeling and iterations of the resistivity data. From the quantitative interpretation and nearby well log data five distinct layers were identified. The layers are dry and unconsolidated sand, clayey sand, saline sand, saline clay and freshwater sand. The resistivity of the topsoil varies from 3259.59 Ohm-m on VES 2 - 67.04 Ohm-m on VES 12. The resistivity of the freshwater sand varies from 1649.76 Ohm-m on VES 6 - 158.28 Ohm-m on VES 10. The resistivity of the saline layer (saline sand/clay) varies from 2.06 Ohm-m on VES 12 - 39.88 Ohm-m on VES 3. The depth to saline/freshwater interface varies from 12.97 m on VES 8 - 63.01 m on VES 5. The quality of groundwater varies from poor polluted saline water saturated sand/clay through intermediate water quality clayey sand/sand to freshwater sand. The interpreted results show saline water plumes where they occur in different part of the area investigated. The 1D and 2D results correlate to a very high degree indicating saline water intrusion between depth interval of 13 and 64 m in the study area. Two major freshwater aquifers (shallow < 6 m and deep > 60 m) where delineated with most of them occurring unprotected. The results showed the effectiveness and usefulness of electrical resistivity and induced polarization method in mapping saline water intrusion problem in coastal areas.
Geophysical investigation , saline water , aquifers , coastal terrain
Adeoti, L., Alile, O. M., & Uchegbulam, O. (2010). Geophysical investigation of saline water intrusion into freshwater aquifers: A case study of Oniru, Lagos State. Scientific Research and Essays, 5(3), 248-259.