Interdisciplinary approach for the hydrogeological characterization of the Chalk aquifer: application on perchlorate transfer in the Champagne Chalk ; Approche interdisciplinaire pour la caractérisation hydrogéologique du milieu crayeux : application au transfert de perchlorates dans la craie de Champagne

Perchlorate (ClO4-) has frequently been detected in groundwater at concentrations relevant to human health. Analyzes in Champagne-Ardenne have highlighted the presence of ClO4- in groundwater for drinking water supply. The ClO4- has two suspected sources: a military source related to World War I (WWI) and an agricultural source related to past use of Chilean nitrate fertilizers. The objectives of the study are to determine the sources and behavior of ClO4- in the Champagne Chalk aquifer and to explain the heterogeneities observed by specifying the aquifer functioning.The study area is located east of Reims. A methodology involving historical, hydrodynamic, geochemistry, groundwater dating and isotope analysis has been developed. High spatio-temporal heterogeneities are observed in the Chalk aquifer. A conceptual model of aquifer functioning is proposed, highlighting main factors governing the Chalk groundwater geochemistry. ClO4- is detected throughout the area with high concentrations (> 4 μgL-1) detected mainly downgradient the Champagne Mounts, where large quantities of ammunition were used, stored and destroyed during and after WWI. A post- WWI military origin of ClO4- is inferred from isotopic analysis and groundwater ages. Different tendencies of ClO4- variation are observed and interpreted by a combination of ClO4- concentrations, aquifer functioning and historical investigations, revealing major sources of ClO4- (e.g., unexploded ammunitions, ammunition destruction sites) and its transfer mechanisms in the aquifer. ClO4- contamination in the Champagne Chalk seems unlikely to decrease in the short- to medium-term due to the long persistence time of major sources. ; Des analyses ont mis en évidence la présence de perchlorate (ClO4-, suspecté d’être un perturbateur endocrinien) dans des captages d’eau potable de Champagne-Ardenne. Deux sources sont suspectées : une source militaire liée àla Grande Guerre et une source agricole liée àl’utilisation passée de nitrates chiliens. Les objectifs de l’étude ...