APPLICATION OF 2D DIPOLE IMAGING IN GROUNDWATER CONTAMINATION STUDIES OF SABON-LAYI AND ITS ENVIRONS, KEFFI, CENTRAL NIGERIA

The long-time practice of careless disposal of commercial, electronic and domestic wastes especially along stream channels in Sabon-Layi and its environs, in the ancient city of Keffi, Central Nigeria could lead to groundwater contamination from leachates of some dangerous heavy metals emanating from the open wastes, thereby rendering it unsafe for use since majority of the inhabitants of the area depend on groundwater from shallow hand dug wells. The area comprises of low lying schist and weathered gneissic ' ocks exposed on the surface, with presence of mainly joint, faults and exfoliations. A . oundwater contamination study was conducted with a total of nine water samples - five n hand dug wells and four from boreholes, collected within the area for chemical alysis of some harmful heavy metals. Results obtained revealed the presence of As, j, Cd, Cu, Fe, Mn, Pb and Zn with range values of 0.21-0.80, 0.51-0.80, 0.05-0.33, . .70-4.90, 0.95-1.00, 0.05-1.37, 0.10-0.74 and 2.10-3.90 respectively in five hand dug wviis samples, implying that except for Cu and Zn, other metals analyzed are present in amounts above the WHO and NSDWQ quality standards making the water unsafe for consumption. However, heavy metal contents in the four borehole water samples all fall below the WHO and NSDWQ standard with range values of 0.001 - 0.008, 0.02- 0.40, 0.002-0.005, 0.008-0.017, 0.44-1.05, 0.16- 0.52, 0.001-0.014, and 0.038-0.138 for As, Ba, Cd, Cu, Fe, Mn, Pb and Zn respectively which means they are safe for consumption. Results of calculation of contamination status indicate slight heavy metal contamination for waters in shallow wells in the area under investigation. 2D electrical resistivity tomography using dipole configuration was conducted on two profile lines spread across the area to depict plume locations and extent. Results show the presence of plumes in Sabon-layi and Kofar Kokona indicated as areas of appreciably low resistivity values ranging from 1.0 ohm/m to 20 ohm/m at shallow depths of 3 m to 7 m. These areas should be avoided during water well constructions and groundwater should be obtained from wells with depth of 25 m and above in the area.