AN INTEGRATION OF GEOPHYSICAL AND GEOCHEMICAL DATA IN EVALUAT- ING GROUNDWATER RESOURCES IN SAPELE METROPOLIS, WESTERN NIGER DELTA

An integration of geoelectrical and geochemical data was used in Sapele metropolis to delineate the aquifer unit(s) and evaluated the geochemical parameters of the groundwater in the area. Ten (10) water samples were collected from hand-dug wells for geochemical analysis. The geochemi- cal parameters showed average values of 6.20 pH; 156.0μs/cm EC; 7.60mg/l TH; 4.50mg/l, Ca2+; 4.20mg/l Mg2+; 0.95mg/I K+; 1.00mg/l Na+; 0.87mg/l ∑Fe; 0.03mg/I Cu2+; 0.04mg/I Cr2+ ; 28.68mg/l Cl- ; 5.40mg/I HCO3-; 2.41mg/l NO3-; 0.80mg/l SO42- and average sodium absorption ratio (SAR) of 1.36. The relative abundance of cations using these concentrations is in the order of Ca2+> Mg2+ > Na+> K+ > ∑Fe > Cr2+ > Cu2+ while those of anions are in the order Cl- > HCO3- > NO3- >SO42+. Fifteen (15) vertical electrical soundings were carried out in the study area using Schumberger electrode configuration. The result of the interpretation of the VES curves showed that the area is made up of four and five geoelectric layer. The third and fourth layer made up of medium, coarse and gravelly sand constitutes the aquifer unit(s), the average depth to the aquifer is 35.2m. The concentration of the various parameters determined in the groundwater were relatively in accordance with WHO recommended standard for domestic and agricultural purposes except pH and ∑Fe in Okirighwre , Ajogodo and Ogorode. Cr2+ concentrations generally were below stipu- lated standard in most of Sapele metropolis, except at Ugbeyiyi and Ugberikoko where concentra- tions exceeded WHO maximum allowance limit of 0.05mg/l.