The use of very low-frequency electromagnetic survey in the mapping of groundwater condition in oporoza-gbamaratu area of the Niger Delta

The use of VLF-EM in sedimentary basins has not been fully understood and has not attracted substantial usage in groundwater exploration, specifically in coastal Niger Delta. In the present study, VLF and 2D electrical resistivity imaging (ERI) surveys were combined with hydrogeochemical data to examine groundwater quality. Both interpretations of VLF and 2D ERI uncovered subsurface conductive geologic materials. Eight groundwater and one river water samples as well as static water level were analyzed to complement geophysical data (VLF-EM and ERI). The results suggested that conductive materials detected in the subsurface are unconnected with intrusion of sea water but depicted clay material typical of tidal flat deposits. Furthermore, hydraulic heads estimated from water level and land elevation measurements did suggest that groundwater flows into the Escravos River. Also, the stage of the Escravos River is above water levels in boreholes and hand-dug wells, which is not an indicative of the incursion of salt water into aquifer from the river. The slight level of nitrate loading in groundwater probably suggests contamination emanating from anthropogenic sources such as septic tanks and leachates from diffuse refuse dumps. The study has validated the effectiveness of VLF technique usage in sedimentary basins for the delineation of groundwater quality, but not without important hydrogeochemical data.