Hydrogeophysical Investigation of Fluoride-Rich Groundwater in Gombe State

This study conducts a hydrogeophysical investigation to characterise subsurface conditions associated with high fluoride concentrations in groundwater in Gombe State, North East Nigeria. Elevated fluoride in drinking water causes dental and skeletal fluorosis, which has been documented in communities across the Nigerian basement complex and volcanic terrain. Understanding the lithological and structural controls on fluoride enrichment is important for identifying safe groundwater sources. This study acquires VES data at 32 stations in Balanga, Dukku, and Nafada local government areas, supplemented by ground magnetic profiling along 12 traverses. VES data are inverted using IPI2WIN software and interpreted in terms of hydrogeological layer models. Magnetic profiles are processed for RTP and analytical signal to map mafic rock bodies associated with the fluorite mineralisation described in the regional geology. Groundwater samples from 28 boreholes and hand-dug wells are analysed for fluoride, pH, TDS, and major ions. Statistical correlation analysis relates geophysical parameters to water chemistry. Findings reveal that high fluoride concentrations above 1.5 milligrams per litre are consistently associated with groundwater from weathered basement zones characterised by low resistivity (5 to 25 ohm-metres) and coinciding with magnetic anomalies attributable to alkali-rich rock bodies. The Na/Ca ratio in high-fluoride wells is significantly elevated, indicating cation exchange processes that promote fluoride release. The spatial coincidence of magnetic lineaments and high-fluoride wells in 73 percent of sampled locations confirms lithological control. The study recommends avoidance of weathered basement aquifer zones in fluoride-risk areas.

Keywords: hydrogeophysics, fluoride, groundwater, Gombe State, basement complex.