Characterizing managed aquifer recharge systems with state-of-the-art tritium and noble gas measurement techniques and integrated surface-subsurface hydrological modelling

The broad focus of this research project is the improvement of the conceptual and quantitative understanding of surface water-groundwater interactions via state-of-the-art tritium measurement techniques and integrated surface-subsurface hydrological modelling. The specific goal is the development of a dissolved gases and water stable and tritium isotopes based method for the continuous monitoring of managed aquifer recharge (MAR) systems, which are considered the most important mitigation measures against the negative impacts of climate change on water availability. The field site is Switzerland's largest managed aquifer recharge (MAR) site Hardwald in Muttenz, Basel. Continuous analysis of the spatial and temporal distribution of tritium in the river Rhine and in the groundwater wellfield is achieved with the deployment of portable mass spectrometers for dissolved gas analyses and automated sampling devices for the sampling for water for isotopic analyses. In addition, within the framework of the project a new state-of-the-art tritium enrichment line is being built within Eawag's environmental tracer laboratory. The new enrichment line is combining recent methodological developments of IAEA's isotope hydrology laboratory and of Eawag's environmental isotope tracer group. The measurement of low-level tritium concentrations will thus be made possible via an improved electrolytic enrichment method for tritium in small volume water samples, followed by low level liquid scintillation counting. The efficient measurement system for natural to ultra low level tritium concentrations, the online monitoring of dissolved gases and the integrated modelling method will provide a new toolbox for the near real-time quantification of the flow and mixing of different groundwater sources in MAR systems. The numerical modelling is based on a high resolution 3-D geological model incorporated into an integrated surface-subsurface hydrological model (ISSHM). The modelling software HydroGeoSphere, the inverse modelling software PEST++ and the data assimilation software PDAF will be used for model construction, model calibration and real time modelling.