ABSTRACT

Residents of Umueze-Ibeku depend on groundwater abstracted through boreholes for drinking and other domestic purposes. However, the existence of a 15 years old dumpsite having proximity of less than 150m from commercial and private boreholes in the community leaves a lot to be desired. This situation has exposed groundwater in the vicinity to high risk of contamination by leachate from the dumpsite located between Latitude 5.55317⁰ and 5.55344⁰, and Longitude 7.49642⁰ and 7.49650⁰. It is against this background that Geophysical and Geochemical investigation of groundwater contamination by leachate was conducted around the dumpsite to identify the presence of leachate and extent of subsurface contamination. Using the Integrated Geo instrument Services (IGIS) device, Wenner array was deployed to carry out two (2) Electrical Resistivity Tomography (ERT) profiles (one at the dumpsite and the other at a control point). Same device was used to conduct two (2) Vertical Electric Sounding (VES) profiles with Half-Schlumberger (pole dipole) array (one at the dumpsite and the other at a control point). The ERT had a profile length of 100m and an electrode spacing of 5m while the VES had an ABmax of 250m. Res2Dinv software was used to model ERT data, while IPI2WIN was used to process the VES resistivity data. The Geochemical process involved strategic collection of six (6) water samples for analysis at the Soil, Plants and Water Laboratory of the Federal Ministry of Water Resources and Environment, Ahieke, Umuahia, Abia State. Result of Geophysical survey show that a depth of 19.8m was probed by the ERT while VES penetrated a depth of 23.9m at the dumpsite and 31.1m at the control. Presence of leachate with resistivity values ≤ 8.71Ωm and up to 18.8Ωm, having active concentration at between 25m to 75m along the horizontal profile in 2-Dimensions was identified. The identified leachate has penetrated a depth of 11.35m. VES data analyses confirmed the geologic formation which was found to be Bende-Ameki Formation. On the other hand, the lithological unit was seen to be sand, clay and shale. Physicochemical analysis conducted shows that Borehole 6 and stream have Lead (Pb) and Mercury (Hg) concentrations above acceptable limits, while boreholes 1, 5 and stream are hard with stream being highly turbid. However, all water samples are contaminated with more of pathogenic organisms as indicated by the high microbial count and harmful isolates. This can be attributed to drilling of boreholes near residential septic tanks since field experiments have shown that the leachate has not reached the aquifer. It should be noted that from results shown in ERT, leachate will in a short time reach the aquifer to further contaminate the waters as infiltration of the harmful fluid is a continuous process. From literature, harmful effects of pathogenic and metallic contaminants discovered in the sampled boreholes are nervous system disorder, diarrhoea, and lots more. In conclusion, the Umueze dumpsite is a threat to groundwater and human health. Urgent proactive measures such as closure of the dumpsite, mounting of dump stands by Abia State Environmental Protection Agency (ASEPA), treatment of borehole water before use, and strict observance of safe distances of 50ft (borehole to septic tanks) and 1000m (boreholes to dumpsites) are required to forestall future health disasters. This research has provided baseline information for geophysical survey in Umueze-Ibeku.