The aim of this study is the impact of climate change on groundwater quality in the Val of Orléans (France). First, geochemical studies made on Loire River and related spring with isotopic composition and major elements revealed a mixing between Loire river water and older karst water in the aquifer. Calcite precipitation and Fe-Hydroxydes formation in the karst play a major role on the behaviour and fate of trace elements. Then, geochemical studies on contaminants like pesticids and pharmaceuticals showed that their occurrence and behaviour vary for each component, according to : the capacity of adsorption on soil/sediment, the degradation rate in waste water treatment plant (for pharmaceuticals) and in natural waters, seasons and climatic conditions, mixing of Loire river water with residual waters in the karst. These chemical investigations allowed us to fix the groundwater quality during our samplings. The threat of local river backflow in the karst system can lead to a degradation of its quality, so the future occurrence of backflow events in the Val was calculated : using a link between backflow events and results of a climatic model downscaling, we found that these events would decrease in frequency in the future. Thus groundwater quality would remain stable, without mixing with contaminated local freshwaters.
