Présentations Colloques

Oral Presentation
Session 8.04: Isotopic and residence time tracers
Moeck Christian
Estimating amount and spatial distribution of artificial groundwater infiltration in a highly complex environment based on different tracers
Drinking water supply in urban areas is challenging due to different kinds of water use and potential groundwater contamination and is recognised as a very complex issue encompassing different spatial and temporal scales. In order to protect drinking water production sites in an effective and sustainable way, knowledge about flow, transport and mixing processes of different water types in the heterogeneous subsurface is crucial. Although isotopes, organic micropollutants and hydrochemistry data such as main cations and anions are known to be powerful tools to refine conceptual groundwater models, an important question is how the drawn conclusions will change if only a subset of these tracers is used. It is of critical importance to understand how the choice of tracers will affect the conceptual understanding of processes because this provides the basis for a sustainable and robust water resources management.**In this study, we first estimate artificial infiltration rates along an artificially constructed infiltration system and classify different water types based on hydrochemistry data. Those were obtained from a drinking water production area in Switzerland, where water quality is under pressure due to different potential contamination pathways. To avoid drinking water contamination, artificial groundwater recharge with surface water into an aquifer is used to create a hydraulic barrier between potential sources of contaminated groundwater and drinking water extraction wells. Here, we provide mixing ratios of different water type endmembers based on i) stable isotopes (18O and 2H), ii) organic micropollutants, iii) hydrochemistry data as well as iv) noble gas concentrations and isotope ratios, coupled with 3H 3He water residence times. We systematically investigate the effects of using different tracers to study mixing processes and identify the spatial distribution of artificial infiltrated water. We compare the information content from the applied tracers and illustrate the differences in mixing ratios and distribution. Furthermore, the dating of groundwater using noble gas isotopes and 3H is used to further constrain the conceptual understanding of the groundwater dynamics and to validate the calculated groundwater mixing ratios.**