Fluoride ion and total dissolved solid distribution in Ethiopian Rift valley: The case of Hawassa city aquifer

Abstract

Study region: The Main Ethiopian Rift valley (MER) region, where millions rely on fluoride contaminated drinking water that is by far higher than the WHO standard resulting skeletal and tooth decay. Study focus: Pumping test and drilling lithology data of the already drilled and productive 25 wells (25 m–200 m depth) to characterize the aquifer. Particular emphasis is given to the spatial distribution of fluoride ion (F-) and Total dissolved solids (TDS) applying SPSS (Statistical Package for the Social Scientists) statistical tool. New hydrological insights for the region: The major water bearing formation is of weathered and fractured geologic formation having high porosity and permeability, which resulted in risk of shallow groundwater surface contamination. The concentration of fluoride ion, ranging from 0.65mg/l to 11mg/l is under significance influence by the geochemistry. Higher temperature at the shallow aquifer along with geological process like weathering of rocks and dissolution of CaF2 promotes the concentrated availability of fluoride ions. The deeper the strata along with igneous formation dominated by pumice, the lower the concentration showing strong inverse correlation with depth for both F- and TDS with R2 =0.78 and R2 =0.68 respectively at α< 0.001. Either drilling wells beyond such formations (=60m) or blinding the poor quality strata is recommended to minimize the effect of high fluoride and TDS concentration in drinking water for Hawassa city aquifer.