Hydro-Geophysical Assessment of Groundwater Potential and Aquifer Vulnerability of the Turonian Makurdi Formation in North Bank area, Makurdi, Middle Benue Trough, Nigeria

Electrical resistivity investigation was carried out in North Bank and its environs in Makurdi, Benue State, with a view to determining the depth to aquifer, aquifer thickmess, groundwater potential of the area and aquifer vulnerability. Twenty-one (21) Vertical electrical sounding (VES) was carried out using the Schlumberger electrode array with the aid of ABEM Terrameter (SAS 3000C) with maximum electrode spacing of 200m. The VES data obtained were interpreted using partial curve matching approach and modelled using WinResist software. Modelled field curves reveal essentially three to four geo-elcetrical layers and two main aquiferous zones corresponding to the upper silty-sandstone and lower medium to coarse grained felspathic sandstones of the Makurdi Formation. The upper silty-sandstone aquifer is characterized by low to moderate resistivity value distribution (37 - 2039 ohm-m) with layer thickness in the range of 3m to 15m. Computed hydraulic and geo-electric characteristics (Zarrouk parameters, hydraulic conductivity and transmissivity) depicts it as unconfined, vulnerable to infiltrating surface 2 -1 2 -1 contaminants, with low groundwater potential (0.63 m day < T 199.65 m day ) and only suitable for small community water supply projects and private consumption. The lower felspathic sandstone aquifer is characterized by relatively thicker sequence of aquiferous materials (3m – 54m). The aquiferous zone is generally unconfined to 2 -1 2 -1 semi-confined in nature, with groundwater potential (30.96 m day < T ≤ 542.73 m day ) seen to be largely moderate. The aquifer is deemed suitable for industrial, irrigational and municipal water supply purposes