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International Journal of Geophysics and Geochemistry

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Delineation of Saltwater Intrusion Zone in Parts of Eastern Niger Delta Using Resistivity and Geochemical Data

International Journal of Geophysics and Geochemistry
Vol.5 , No. 1, Publication Date: Mar. 23, 2018, Page: 27-39

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Authors

[1]	Choko Chukwuemeka, Department of Geology, Federal University of Technology, Owerri, Imo State, Nigeria.
[2]	Opara Alexander Iheanyichukwu, Department of Geology, Federal University of Technology, Owerri, Imo State, Nigeria.
[3]	Adikwu Onum Stephen, Department of Geology, Federal University of Technology, Owerri, Imo State, Nigeria.

Abstract

Detailed hydro -geophysical and hydro-geochemical studies were carried out in part of the Niger Delta Basin Nigeria. The objectives were to map and provide evidences that the coastal aquifers in the study area have been intruded by saltwater and to establish analytical/empirical relationships between resistivity and geochemical parameters. Twenty three vertical electrical sounding (VES) data employing the Schlumberger electrode configuration were acquired in different parts of the study area, with a maximum electrode separation of 500m. The VES data were modelled with the OFFIX 3.1 software. The interpreted VES curves revealed mainly the QH, KH, KHKH, AK, QQ, KHK, HKH, QQH and HK curve types. Aquifer resistivity across the study area ranges from 39.7Ωm to 19033.9 Ωm while aquifer depth varies between 4.5m and 83.9m. Aquifer thickness is variable in the study area with values ranging between 2.4m and 78.1m. The Dar-zarrock parameters revealed that the longitudinal conductance(S) and transverse resistance(R) have mean values of 0.319 Sm and 55311.74Ωm² respectively. The mean concentrations of the cations including chloride (Cl^-), bicarbonate, nitrate (NO₃^-), and sulphate are given as 90.73 mg/l, 22.33 mg/l, 0.90 mg/l, and 14.70 mg/l respectively. Similarly, analysis of the mean concentrations of the anions revealed that iron (Fe²⁺), potassium (K⁺), magnesium (Mg²⁺), calcium, and sodium of 0.24 meg/l, 0.899348 mg/l,, 8.126783mg/l, 8.528 mg/l, and 3.848783mg/l respectively. The low resistivity values revealed in different parts of the study area is indicative of areas contaminated by saltwater intrusion. In addition, since the average chloride concentration across the study area (which is a major component of saltwater) is greater than 40mg/l and the Cl^- /HCO₃^- ratio is greater than two, it is therefore believed that there is serious salt water encroachment within the study area.

Keywords

Salt Water Intrusion, Coastal Aquifers, Hydrogeophysical, Hydrogeochemical, Vertical Electrical Sounding, Niger Delta

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