Delineation of depth to Groundwater in parts of Federal University of Petroleum Resources Effurun, Delta State using One-Dimensional resistivity inversion

Abstract

Geophysical survey using the 1-D electrical method was carried out in a location at the Federal University of petroleum Effurun (FUPRE) campus in Ugbomro Delta State in order to determine the depth to prolific aquiferous layers for groundwater production. The Schlumberger configuration was used with a current electrode separation of about 300m. Five (5) VES profiles were occupied in the surveyed area labelled as VES1, VES2, VES3, VES4 and VES5, with VES2 and VES3 acquired within the same location to check for instrumental coupling in the resistivity meter. The resistivity data was inverted using the resistivity modeling software (IPI2Win.v.2.1) application to generate the layer parameters (resistivity, depth and thickness), from which hydrological properties (transverse resistance) which was taken as transmissivity was extracted from the geoelectric data and geologic sections of the subsurface were drawn. The result of the interpretation showed four to five geoelectric layers and six lithologies namely clay, sandy clay, clayey sand, fine sand, medium sand, coarse sand (which is gravely) and a high resistivity carbonate bed. In the study area, along profiles VES2 and VES4 lies prolific aquiferous layers which are favorable for groundwater development. In VES2 five layers were delineated, it was observed that within the second and fourth layers along this profile lies high resistivity materials (with resistivity >2200Ωm) which depicts coarse sand. The coarse sand observed within the fourth layer in VES2 has a thickness of about 26.9m at a depth of 6.27m below the subsurface and is sandwiched between two low resistivity materials at the third and fourth layers (with resistivity values of about 405Ωm at the third layer) which depicts clayey sand and (resistivity values <50Ωm within the fifth layer) which depicts clay. This shows that the coarse sand observed within the fourth layer in VES2 is a good aquifer zone with high transmissivity value of about 60,444Ωm² making it highly productive and favorable for groundwater abstraction. Also in VES4, four layers were delineated with coarse sand observed within the second layer with a thickness of 1.78m at a depth of about 1.72m which is shallow and medium sand observed within the third layer at a depth of about 3.5m, and considering its thickness (about 43.8m) this layer will be favorable for groundwater abstraction as observed from its transmissivity value (of about 44,150Ωm²). Aquifer zones delineated within the second and third layers for VES1 and VES5 even though they have a reasonable thickness of about 30.83m and 28.3m respectively are not good aquifer zones because they lie within shallow depths of about 0.77m and 1.48m respectively. Therefore, within the surveyed area the aquifer zones of high productivity lies within the third and fourth layers in VES4 and VES2 at a depth of about 3.5m and 6.27m respectively which lies within and below the water table (about 3.0 ± 0.5m) as reported by previous studies.