Groundwater sources and geochemical processes in a crystalline fault aquifer

摘要: The origin of water flowing in faults and fractures at great depth is poorly known crystalline media.This paper describes a field study designed to characterize the geochemical compartmentalization adeep aquifer system constituted by graben structure where permeable fault zone was identified. Analysesof major chemical elements, trace dissolved gases stable isotopes reveal theorigin components for each domain provide information on various watersources involved during different seasonal regimes. response induced performinga pumping test fault-zone examined, order quantify mixing processes contributionof domains flow. Reactive enhanced pumped fluxes are alsoidentified discussed.The presents responses related changes hydraulic regime. Theyare interpreted as sources structures within aquifer.During low regime, results suggest recent with clear contribution olderwater inter-glacial (recharge temperature around 7 C), suggesting involvement watertrapped local low-permeability matrix or large scale circulation loops.During high level period, due inversion gradient between permeablefault its surrounding domains, modern predominantly flows down deep bedrockand ensures recharge graben.Pumping induces connections storage-reservoirs. overlaidregolith part flow rate long term (around 20% present case).During late-time pumping, orthogonal coming from fractured majorfault dominant. Storage connected fracture network mainlyensures main (80% case). mixingof transfer conditions. A specific approach applied thereaction along time. Autotrophic denitrification coupled iron mineralsoxidation highlighted rock interaction clearly flux bypumping.