APPLICATION OF GEOPHYSICAL METHODS IN THE EVALUATION OF VULNERABILITY AND PROTECTIVE CAPACITY OF THE AQUIFER IN ORU AND ENVIRONS, SOUTHEASTERN, NIGERIA

Abstract

Evaluation of Vulnerability and Protective Capacity of Aquifer in Oru and Environs, Southeastern,
Nigeria was conducted applying geophysical methods to ascertain the protective capacity of the
aquifer in the area from possible pollution. Aquifer Vulnerability indices and Hydraulic parameters
have been estimated from DRASTIC (an acronym for Depth to water, net Recharge, Aquifer media,
Soil media, Topography, Impact of vadose zone and hydraulic Conductivity) and surface
geoelectrical data, using data sets from Oru west and Oru east and environs in Southeastern
Nigeria. The study area is underlain by the Benin Formations. Fourteen (14) vertical electrical
sounding (VES) results, using the Schlumberger method were acquired for the study area. A
maximum current electrode spacing (AB) of 1000 meters was used for data acquisition. For
comparative purposes, seven (7) of the soundings were carried out near existing boreholes to
evaluate the interaction of subsurface materials. The layer parameters thus obtained from the
analysis were combined with pumping test data from existing boreholes to estimate aquifer
hydraulic conductivity including those areas without boreholes and vulnerability index assessment,
using the DRASTIC model. From the study, the vulnerability assessment and analysis of the results
of the vulnerability map of the study area indicates that Amagu, Omuma, Umuejike and Umuabiah
areas fall within the moderate vulnerability zone while the other adjoining areas fall within the
high vulnerability zone. The longitudinal conductance of the aquifers range from a minimum of
0.002702 Ω-1 at Akwada axis to a maximum of 0.036396 Ω-1 at Ofor-Uru area with an average
value of 0.015411 Ω-1. The study revealed that the overburden layers within the study area and
environs are poorly protected and highly vulnerable to pollution. The regression line of data points
obtained in this plot yield an equation: DI = 348.82C + 141.2 with R2 = 0.043 and a correlation
coefficient of R = 0.20736, implying relationship between the two variables.