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Estimates of aquifer geo-hydraulic and vulnerability characteristics of Imo State and environs, Southeastern Nigeria, using electrical conductivity data

Ejiogu, B. C., Opara, A. I., Nwosu, E. I., Nwofor, O. K., Onyema, J. C., Chinaka, J. C.
Environmental monitoring and assessment 2019 v.191 no.4 pp. 238
anthropogenic activities, aquifers, data collection, electrical conductivity, equations, groundwater, hydraulic conductivity, models, shale, Benin, Nigeria
Two hundred and twenty-six vertical electrical sounding (VES) data were acquired across the study area that has six geologic formations for the purpose of evaluating the geo-hydraulic potentials and the protective capacity of the aquifers of the study area. Schlumberger array was adopted for data acquisition using the ABEM™ Terrameter SAS 4000. Results of the study revealed four to six geo-electric layers. A variety of geo-electric curve types were identified in the study area with the KK curve type being dominant. The aquifer zones lie between the third and sixth layers with their resistivity values ranging from 101 to 8900 Ωm with a mean value of 1799 Ωm. Estimates of the aquifer hydraulic characteristics using the new set of model equations based on conductivity data revealed hydraulic conductivity range of 0.925 and 13.42 m/day while transmissivity ranged between 16.0 and 887 m²/day. These findings showed that groundwater potential is high in Benin Formation, moderate in Nsukka and Ajali Formations, and generally poor within Ogwashi and Imo Shale Formations. Aquifer vulnerability studies revealed that the values of the integrated electrical conductivity (IEC) of the study area ranged between 28.4 and 2202 mS with a mean value of 403 mS. Results of the IEC revealed that the aquifer protective capacity of most parts of the study area were extremely poor (86.2%) with percolation period of several months while only 1.8% of the study area are fairly good. The aquifers of the study area may therefore be vulnerable to contamination from anthropogenic sources, and adequate aquifer protective strategies are therefore recommended.