Hydrogeochemical Relationships between Spring and Subsurface Waters in the Dindefello Area of South Eastern Senegal

The analytical results of water samples collected from the Dindefello Plain area revealed the dominant major ions of bicarbonate, silica, calcium, magnesium and sodium, in order of decreasing relative abundance. Spring water exhibited a very low, Le. similar to rainwater, mineralization status, unlike groundwater. To better understand the origin of mineralization, the data were further analyzed for interrelationships between parameters and for mineral-water relationships using speciation calculations. This provided various tenuous lines of evidence for speculating various modes of groundwater mineralization. Hydrochemical evaluation of major ions suggested an early stage of mineralization which could be attributed to mineral breakdown driven by pH in the vadose zone under the leaching action of H super(+). Conceivably the soil in recharge areas supplies CO2 to infiltrating rainwater, thus adding to the amount of aqueous CO2 (H sub(2)CO sub(3)) already entrapped from the atmosphere. Then, H super(+) ions, produced from the dissociation of aqueous CO2 (H sub(2)CO sub(3) [hArr] H super(+) + HCO super(-) sub(3)), reacts along groundwater flow paths with the carbonaceous-sulfated and silicated minerals, resulting in the observed major ion chemistry. The spatial variations in the groundwater chemistry indicated that the type of bedrock aquifer has an effect on the water chemistry.