Application of Geophysical Tools in the Assessment of Aquifer Quality and Heavy Metal Contamination Risk at Ikenyi Area of Southeastern Nigeria

Groundwater development in Ikenyi area of the Southeast Nigeria is plagued by poor borehole yield and heavy metal contamination due to its dominant lithology and intense historical mineralization. To mitigate these challenges, water boreholes in the area often target fracture zones, metamorphic aureoles and areas with low risk of mineralization. To identify these choice locations for the water borehole a cluster of geophysical methods comprising Magnetics, Resistivity, Induced Polarization (IP) and Normalized Induced Polarization (NIP) has been strategically deployed. The study revealed the presence of lineament associated with a fault and four geoelectrical layers namely Layer-1, Layer-2a layer-2b and Layer-3 between 0 m and 100 m. The geoelectric layers were correlated to both stratigraphic units identified in a well lithology log in the area and published literature on stratigraphy of the area. Subsequently, composite rock maps highlighting the spatial distribution of dominant lithology of the corresponding four geoelectric units were generated. Combined interpretation of water quality test, the stratigraphy derived from the geoelectric layers and composite rock maps suggest that except for wells in the Southeast, other wells are producing water from stratigraphic unit associated with geoelectric layer-2a. Water produced from aquifer in geoelectric layer 2b and layer 3 tend to be better quality. The study showed that wells sited in the Northwest area will have low chance of contamination but may have poor yield. However, wells producing from geoelectric layer-3 occurring at depths of about 50 m in the west and 10 m in the east and also within the mapped fault corridor will most probably have a good yield with low risk of heavy metal contamination.