The Shallow Aquifers Vulnerability Investigations using Dar-Zarrouk Parameter in Nnewichi Landslide Site, Nnewi, Anambra State, Nigeria

Abstract

Dar-Zarrouk parameter estimated from vertical electrical sounding
(VES) was executed at the Nnewichi landslide site, aimed at
investigating shallow aquifer vulnerability. The Schlumberger
electrode array, involving twenty soundings, was deployed. The field
data were interpreted qualitatively and quantitatively using
WinResist software. The interpreted geoelectric resistivity and
thickness were used to estimate the Dar-Zarrouk longitudinal
conductance. The results reveal three to four geoelectric units as
loose counteraction material of resistivity 604.8 to 2084.1 Ωm,
regolith/colluvia of resistivity 48.0 to 820.4 Ωm and weathered
sandstone of resistivity 35.2 to 1930.2 Ωm characterized by Q
(60%), QH (35%), and KQ (5%) curve types. The estimated
longitudinal conductance has values ranging from 0.006 to 0.236 Ω1 with an average value of 0.07375 Ω-1
. 70% of the VES points have
poor protective rating (<0.1 Ω-1
), 10% have weak protective rating
(0.1 – 0.19Ω-1) and 20% have moderate protective rating (0.2 –
0.69 Ω-1 ). This implies a poor protective layer rating. Hence, the
overlying counteraction materials and regolith/colluvia units are
permeable to the surface contaminants, thereby making the shallow
weathered sandstone aquifer unit vulnerable to contamination. The
geophysical investigation provides a cost-effective means of probing
aquifer vulnerability in the absence of geochemical analysis.