PHYSICOCHEMICAL, LITHOLOGICAL AND HYDROLOGICAL FACTORS INFLUENCING THE EVOLUTION OF IRON AND MANGANESE CONCENTRATION WITH THE DISCUSSION OBTAINED ON EXPERIMENTAL FIELDS OF THE ALLUVIAL PLAIN OF THE SAONE, FRANCHE-COMTE, FRANCE

This work deals with the mechanism for the evolution of iron and manganese values in groundwater in the alluvial aquifer of the Saone river during two hydrologic cycles (1983-1984). Correlations between tests holes at the various experimental sites have shown the complexity of alluvial geology. The aquifer, essentially silicious, consists of channels where flow is rapid and finer alluvial deposits where the flow is slower. The alluvial system is recharged from the valley-sides, drained by the river and confined under superficial clay loams. Iron and manganese can be differentiated by their forms in solution: manganese is normally present as the ion (Mn**2** plus ), iron is most often complexed (complexes of iron-silicia and iron-organic matters). Because of this, they react differently in response to physico-chemical variations in the water table.