TITLE:
Geoelectric Evaluation of Groundwater Potential and Vulnerability of Overburden Aquifers at Onibu-Eja Active Open Dumpsite, Osogbo, Southwestern Nigeria
AUTHORS:
Nicholas U. Ugwu, Rubeni T. Ranganai, Rapelang E. Simon, Ghebrebrhan Ogubazghi
KEYWORDS:
Southwestern Nigeria, Crystalline Rocks, Electrical Resistivity, Groundwater Potential, Vulnerability Mapping
JOURNAL NAME:
Journal of Water Resource and Protection,
Vol.8 No.3,
March
23,
2016
ABSTRACT: Electrical resistivity method was used to assess groundwater potential and
vulnerability of overburden aquifers at Onibu-Eja active open dumpsite, Osogbo,
Southwestern Nigeria. Eighteen Vertical Electrical Sounding (VES) points and five
2-D imaging profiles established in five traverses at the periphery of the dumpsite
were surveyed and analysed. The subsurface comprised of thin topsoil (resistivity
65 - 998 Ωm); heterogeneous weathered layer with resistivity 63 - 333 Ωm and thickness
0.7 - 8.5 m; weathered basement (resistivity 31 - 1253 Ωm and thickness 0.7 - 27.0
m) and fractured/fresh basement (resistivity 36 - 6213 Ωm). The 2-D inverse model
of the profiles delineated low resistivity values ranging from 5 to 100 Ωm at a
depth range of 10 - 20 m along traverses TR1-TR3 which is attributed to leachate
percolation close to the dumpsite. The weathered basement was inclined relative
to the dumpsite. The total overburden thickness varies from 6.9 to 33.7 m, with
20 and 40 m generally recommended as productive for groundwater abstraction in Southwestern
Nigeria occurring in 61% of the area. Further, about 85% of the weathered layer
resistivity values fall within medium groundwater potential (100 - 250 Ωm) and high
groundwater potential (>250 Ωm). The ranking of groundwater potential as a function
of saprolite (weathered basement) resistivity showed that 72% of the study area
is characterized by optimum weathering (20 - 100 Ωm) and is classified as good groundwater
potential. Fractured basement covered