Characterizing groundwater recharge dynamics and response times in large sedimentary basins using 14C age tracer data and a reactive transport modeling approach

Large sedimentary basins represent major groundwater resources vital in sustaining terrestrial ecosystems and the various socio-economic activities essential to modern day society (drinking water supply, health, agriculture, energy, and industry). To address the ongoing and future impacts of climate change and anthropogenic activities on groundwater sustainability a better understanding of groundwater storage and flow dynamics in these multi-aquifer systems is crucial. Groundwater ages in this respect serve as an effective tool, providing valuable insight into rates and sources of groundwater recharge and subsurface heterogeneity. In this study we investigated the well-studied Aquitaine Basin located in Southwest France, the 2^nd largest sedimentary basin in the country, with an extensive repository of hydrologic and geochemical data spanning several decades. A 3D regional numerical flow model was developed and extended to simulate reactive transport of radiogenic, ¹⁴C. An inverse modeling approach using available ¹⁴C activity data is implemented to infer groundwater ages and constrain modern and historic recharge sources and aquifer response times. Preliminary findings from spatial variations in ¹⁴C concentrations and groundwater ages point to the role of aquitards as important sources of recharge in regional scale, multi-aquifer systems.