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

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 Ω-1 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.