Assessment of Groundwater Conditions Using Geophysical and Physicochemical Methods in Canal Estate, Okota, Lagos, Southwestern, Nigeria

Abstract

The dearth of potable water supply has made the residents of the Canal Estate
result to providing alternative water for their daily activities. In view of this,
the electrical resistivity (2D Electrical Resistivity Imaging (ERI), Vertical
Electrical Sounding (VES) and physicochemical methods were used to
investigate suitable aquifers that may provide adequately safe water supply
for the residents of the area. Seven Wenner 2D ERI data and forty
Schlumberger VES were acquired. Also, water samples were collected from
existing boreholes and hand dug wells within the study area for laboratory
analysis. Apparent resistivity values were calculated through forward
modelling technique while VES data were partially curve matched. Five to six
geoelectric layers corresponding to the topsoil, clay, sandy clay, clayey sand
and sand were delineated. The low resistivity range (2 Ωm to 300 Ωm) of
shallow sands is an indication of contaminated subsurface layers. In some
cases, parts of the sands between 20 m to 50 m deep are observed to be
polluted through percolation of contaminants from the surface.
Physiochemical analysis of the water samples revealed values above or below
WHO standard especially in the shallow seated sands. The Biological Oxygen
Demand and Total Bacterial Count are well above the required WHO
standard. In addition, the chloride, Iron (Fe), pH and Copper (Cu) contents
are below WHO approved standard. This implies that the sand layer which
constitute the aquifer units within the study area are polluted. Assessing
aquifers with good water quality for domestic and industrial usage will
require investigating deeper aquifers in the study area with dipole dipole or
pole dipole array configuration.