Investigating High Fluoride Concentrations in Groundwater in the Bongo-Bolgatanga Districts of Northern Ghana by Using Isotopic and Dating Techniques

The goal of this research is to use isotopic and dating techniques to investigate recharge pathways into high fluoride wells in the Bongo-Bolgatanga Districts of Northern Ghana, West Africa. High fluoride wells have concentrations above the World Health Organization's (WHO) drinking water standards of 1.5 mg/L. The geology of the area is dominated by the Bongo granitic suite. Nineteen groundwater and two surface water samples were collected and analyzed for major ions, oxygen and hydrogen isotopes, and tritium concnetration. Eleven samples had fluoride concentrations above the WHO drinking water standard. Most of the groundwater samples plot on the Global Meteoric Water Line (GMWL) and have a δ¹⁸O values between -2‰ and -4‰ consistent with regional values. Three high fluoride samples plot on the GMWL but with δ¹⁸O values between -4‰ and -6‰. Four groundwater and two surface water samples show isotopic evaporative enrichment. All of the evaporatively enriched groundwater samples have high fluoride concentrations. They are Na-HCO₃ type water while the remaining groundwater samples are Ca-Mg-HCO₃ type water. Of the nine tritium samples analyzed to date, eight have concentrations between 2.0 and 3.6 tritium units (TU), indicating they are mixtures of submodern and recent water, and one sample had 0.5 TU indicating it contains submodern water. With respect to the origin of high fluoride concentrations, there appears to be a correlation between evaporative enrichment during prior to recharge and high fluoride. In addition, high fluoride in non-evaporativley enriched samples appears to be due to groundwater in contact with fluoride-rich rocks for an extended period of time.