ABSTRACT

This study focuses on the analysis of groundwater quality and direction of flow in Ehime Mbano South-Eastern Nigeria with the aim of minimizing cases of abortive water well projects in the area. Ehime Mbano is located within Anambra-Imo sedimentary basin of South-Eastern Nigeria. The study area is underlain by Benin Formation (miocene-recent), Bende-Ameki Formation (Eocene) and Imo Shale Formation (Palocene). It is located from latitude 5o 37' N to 5o 46' N; and longitude 7o 14' E to 7o 21' E. Elevation, Vector Grid and 3-D surface maps were used to ascertain the direction of water flow which slopes in two directions: North-West to South-East and North-West to South-South West with a point of convergence noticed at Umunakanu, Umuezeala 1, Umuakagu and Umunumo. A total of 60 vertical electrical soundings, using Schlumberger configurations with AB/2 = 400m was undertaken to estimate aquifer parameters within the study area. The VES data were interpreted using state of the art soft wares e.g. IP12WIN and Surfer 12 to obtain the final model for each VES. Isoresistivity studies were carried out in the area and contoured at specific distances of AB/2 = 1m, 8m, 15m, 50m, 150m, 200m, 250m, 300m and 350m. Results revealed significant variations of electrical resistivity with depth. Regions of low resistivities such as Nzerem, Lowa,and Agbaja were identified. Places of high resistivities were also observed in the Southern and South- regions especially around Ikperejere and Ibeafor. The results of this study using electrical resistivity method to characterize the aquifer revealed various aquifer parameter values within the area. The resistivity values indicate the presence of clay, top soil, sand and sandstone lithologies. The average resistivities of rock units within the study area vary between 1000Ωm and 10,000Ωm. The central and southern parts of the study area like Ikperejere, Ibeafor have relatively higher resistivity values making them more viable for groundwater exploitation than the Northern parts which have relatively low resistivity values like Agbaja, Nzerem and Lowa. The most abundant resistivity curves are with KK, KHK and HK types with a percentage abundance of 21.7%, 18.3% and 16.7% respectively revealing major sustainable aquifers and their depth of occurrence. Majority of the locations have transmissivities between 50m2/day and 500m2/day while few places have high values of 501m2/day to1100m2/day especially at Umuchienta in the southeast, Umueleke and Umuawuchi. Aquifer vulnerability assessment carried out revealed areas with high, low and moderate vulnerability based on the DRASTIC Index. Locations with high vulnerability rating of 126 -165 include: Umuokiri Umunumo and Ikperejere. Locations with moderate vulnerability rating of 86-125 include: Ikpem, Ikweii Nzerem while locations with low vulnerability rating of 70-85 include: Umuokara Uzinomi and areas close to Umueze II. Water quality analysis was conducted for fifteen water samples within the study area. Analysis of physicochemical, heavy metals and microbiological characteristics (pH, Conductivity, Turbidity, Total Dissolved Solids (TDS), Acidity, and Alkalinity), was carried out using standard laboratory techniques. The results were compared with World Health Organization (WHO) Standard and Nigerian Standard for Drinking Water Quality (NSDWQ). Some water samples had concentration of five parameters being clearly above both WHO and NSDWQ permissible limits. This raises concern of contamination and health risk, hence the need for periodic treatment and monitoring of ground water in the area. It is recommended that a regional water scheme should be established at locations such as Ezeoke Nsu with possible high yield so that it can serve other communities where groundwater prospect is slim. In all, a good aquifer characterization has been presented which can serve as a guide to hydrogeophysical and hydrogeological information for groundwater in the area.