GEOPHYSICAL AND HYDROCHEMICAL CHARACTERIZATION FOR QUANTITATIVE AND QUALITATIVE ANALYSES OF GROUNDWATER WITHIN ILORIN NW, SHEET 223 SOUTHWESTERN NIGERIA
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Date
2022-06
Authors
Journal Title
Journal ISSN
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Publisher
School of Post Graduate Studies, Kwara State University, Malete
Abstract
The study area covers parts of Ilorin Northwest Sheet 223 which is underlain by the
Basement Complex rocks of southwestern Nigeria. The need for groundwater system
evaluation within the study area arises to provide a standard database for consumption and
Agrarian purposes. The study aims at determining the quantity and quality of the groundwater
in the area. The objectives of the study are to determine the groundwater time-dependent
variations to obtain the perennial groundwater level fluctuation, analyze the magnetic
anomalies to derive lineaments’ distribution, investigate the geophysical study of vertical
electrical sounding to establish the potentiality of the groundwater, and, conduct the
hydrochemical analysis of groundwater samples of 35 sampling points within the area to
determine their quality for human and agrarian usability. The methodology adopted for this
research includes; (i) Peizometric measurement of water level in the area for perennial
groundwater level fluctuation determination, (ii) analyzing aeromagnetic dataset to obtain
magnetic anomalies of the underlain rocks within the area (iii) vertical electrical sounding of
Schlumberger array techniques to investigate resistivity changes of the underlying lithologies
and, (iv) assessment of groundwater quality through in-situ and laboratory methods. The
findings from this study revealed that the area is underlain by lithologies comprising;
migmatite gneiss, banded gneiss, augen gneiss, granite gneiss, quartz-mica-schist, and fine grained granite. The time-dependent variation studies show higher groundwater levels in the
southern part of the study area than in the rest parts. The magnetic anomalies are also higher
in the southern part, while they are moderate and low in the western and the eastern parts
respectively. The vertical electrical sounding (VES) identified three to five geo-electric
layers; the topsoil, the lateritic horizon, the weathered basement, the sandy clay/clayey sand,
and the underlying fractured basement rock with the depth varying from 1.05 to 41.8 m. The
range of concentrations of the measured physical parameters; including turbidity (50-470
NTU), pH (3.7-7.9), temperature (29-35 °C) and electrical conductivity (50-940 µS/cm) and
average of chemical parameters (mg/l) Ca (0.85), Na (1.23), K (0.35), Mg (0.56), Cu (0.03),
Fe (0.03), Mn (0.1), Zn (0.02). Pb (0.03), Cd (0.05), SO4
3-
(0.02), PO4
2-
(0.11), Cl-
(1.43),
HCO3
-
(65), CO3
-
(157), and NO3
-
(0.47), fall below the World Health Organization (WHO)
standards. The study concludes that the crystalline rocks within the Ilorin Northwest Sheet
223 have a moderate to low permeability, therefore, are aquiferous with modest groundwater
potential, especially in the southern part. The high lineament density mapped also confirms
the above deductions. The physio-chemical assessment of groundwater samples revealed
values that fall below the maximum desirable and permissible limits of the WHO standard,
which suggest that the groundwater in the study area is good for human consumption and
suitable for Agricultural purposes