GEOELECTRICAL EXPLORATION FOR GROUNDWATER IN CRYSTALLINE BASEMENT ROCKS OF FOBUR AND ITS ENVIRONS, JOS-PLATEAU, NORTHCENTRAL NIGERIA

Abstract

Fobur and its environs are underlain by crystalline rocks in the north-central sector of the
Nigerian Basement Complex. A geophysical investigation involving electrical resistivity was
carried out with the aim of evaluating the groundwater potential for alternative water supply due
to inadequate surface water and low yield boreholes in the area. Thirty-three (33) Vertical
Electrical Soundings (VES) were acquired from Fobur and its environs adopting Schlumberger
electrode configuration with current electrode separation (AB) varying from 1.5 to 125 m. The
acquired field data were interpreted and iterated using “RESIST” software. The total transverse
resistance value (219.8 - 26721.50 Ωm2) was adopted in the classification of the area into poor,
weak, moderate and very good transmissivity zones. The groundwater potential of Fobur and its
environs are classified into poor, low and good groundwater potential zones based on the
integration of geo-electric and Dar-Zarrouk parameters. The VES data indicate two (2) to five (5)
geo-electric layers namely: topsoil/lateritic, clayey soil, weathered layer, fractured unit and fresh
basement. The Overburden comprises of the topsoil, laterite, and weathered basement with
thickness ranging from 3.6 to 42 m. The zones with overburden thickness of 20m and above are
viable for groundwater abstraction and constitute about 50 % of the area. The aquifer protective
capacity of the area was classified into good (> 0.7 mhos), moderate (0.2 – 0.69 mhos), weak
(0.1 – 0.19 mhos), and poor (< 0.1 mhos), based on the longitudinal conductance value (0.00192
- 1.587868 mhos). The basement resistivity ranges from 43.7 to 27717.3 Ωm and was used to
classify the area into good, medium, low and negligible aquifer potential zones. Hence, the result
of this research will form the tools for groundwater improvement, management and
structural/infrastructural development planning of the study area.