Sulfur Origin and Influences of Water Level Variation on SO4 Concentration in Groundwater of the Transboundary Carboniferous Limestone Aquifer (Belgium, France)

Groundwater of the Carboniferous limestone transboundary aquifer of northern France and Belgium has sulfate concentrations ranging from 20 to more than 1000 mg.l−1, and in some parts of the aquifer a clear increase over several years has been observed.The hydrogeochemical study that was carried out within the whole aquifer highlights a complex geochemical pattern due to the existence of various processes such as water-rock interaction, ion exchange, and different origins of sulfates, such as oxidation of sulfur minerals, and dissolution of secondary and primary evaporites. In some areas, the increase in sulfate concentrations may be linked to a water level increase and to redox processes.