Assessment of aquifer vulnerability in the tectonically deformed sedimentary rocks in Abakaliki area, southeastern Nigeria, using geophysical and geological dataJ

Abstract

A combination of the IEC, AVI, and GOD pollution indices were used to assess the vulnerability of the fractured rock aquifer in the Abakaliki area to pollution from anthropogenic sources. The topsoil ranges from laterite to silt to silty-clay, according to the results of the vertical electrical sounding (VES). The geoelectric sections have varying numbers of layers (1–6 layers) with their resistivity ranges as 29.16–3,949.30 Ω, 4.98–1,630.70 Ωm, 0.35–3,767.20 Ωm,1.76–7926.30 Ωm, and 1.11–3,060.20 Ωm respectively. These have been grouped into four main lithologic units namely the topsoil, indurated/baked shale, fractured shale/sandstone (the aquiferous unit), and the consolidated sandstone units. The thickness of the vadose zone is generally thin (< 18 m), while their hydraulic conductivity is relatively high (0.20–16.11 m/day) for argillaceous rocks. The IEC values (0.003–0.850 S) suggest a weak to fair protective capacity for the vadose zone. The result of the HR (1.01–55.49) indicates that the underlying aquifer is highly to extremely vulnerable, and the GOD values (> 0.7) agree that they are extremely vulnerable.