Groundwater Quality Assessment using Integrated Geophysical and Physicochemical Approaches: A Case of Isheri-Oke Estate, Lagos, Southwestern Nigeria

Authors: Ayuk MA

DOI Info: N/A

ABSTRACT

Geophysical and physicochemical investigations of groundwater in Isheri-Oke area of Lagos State were carried out to assess the quality of groundwater due to the presence of a suspected source of contamination of aquifer in the area. 2D electrical resistivity imaging (ERI) and vertical electrical sounding (VES) data were acquired. Five water samples were also collected for Groundwater quality index (GQI) analyses. The results of the 2D ERI revealed three (3) resistivity structures while geoelectric results revealed four to five layers indicating topsoil, clay, clay/peat, clayey sand and sand with resistivity and thickness varying from 2.0 – 1058.9 Ohm-m and 0.4 – 57.1 m respectively. Traverse 1 revealed an elevated case of contamination from the adjacent canal, perhaps due to its proximity. The 2D results from other traverses revealed mild cases of contamination near-surface. The clayey sand/sand at the second and third geoelectric layers showed contamination from the canal which runs perpendicular to traverses 2 and 4 and parallel to 1 and 3 with the impact being maximum along traverse 3. Physicochemical results revealed that all parameters tested are within permissible limits except Iron in BH1. Dissolved oxygen was also below the WHO limits except in BH1. GQI revealed that all water samples tested have values ranging from 50 – 100 signifying “good water quality”. Only the near surface is affected by contamination from the canal as confirmed from the geoelectric investigation and evident in shallow hand dug wells. Continuous geophysical monitoring is recommended for the onset of contamination of the deep-seated aquifers.

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