GEOELECTRICAL AND DOWN-HOLE INVESTIGATIONS FOR DELINEATING FRESHWATER AQUIFER IN PARTS OF OBIO/AKPOR LOCAL GOVERNMENT AREA, RIVERS STATE, NIGERIA.
Keywords:Geoelectrical, Down-hole, Freshwater, Aquifer, Obio/Akpor, Electro-kinetic.
Geoelectrical and down hole investigations were carried out in some parts of Obio/Akpor local government area of Rivers State Nigeria to evaluate the aquifer parameters, geophysical characteristics of the subsurface, and delineate fresh water aquifers of the study area. The Vertical Electrical Sounding (VES) technique using the Schlumberger array for resistivity and Self potential log were employed. The ABEM terameter SAS 300B and SAS log 200 for resistivity meter and logging tool was used respectively for the survey and down-hole investigations. The interpretation of the geoelectric survey was done using IP12win software, while the down-hole was interpreted using the Microsoft excel package. Fifteen vertical electrical soundings were done which revealed 4 to 6 geoelectric layers, comprising the top soil, lateritic sand, clay, water saturated fine-medium sand, gravely sand and conglomerate. Results of the Vertical Electrical Soundings from the various survey areas show that the aquifer potential depths range from 13 – 85.3 m. The resistivities of the aquifers in the study area vary from 43.1 – 1203 Ωm. The down-hole investigations revealed freshwater occurrence at a depth of 10 – 48 m in three locations and in two separate depths of 34 – 74 m and 110 – 122 m in the fourth location. The aquifer depth in the geophysical log chart is in agreement with the vertical electrical sounding result. From the findings, it is evident that geophysical down-hole result is a confirmatory test for VES result in terms of groundwater prospecting.