The influence of water-rock reactions and O isotope exchange with CO2 on water stable isotope composition of CO2 springs in SE Australia

Monitoring injected CO2 in CCS sites using oxygen isotopes of water has been demonstrated in field and laboratory experiments. Here, we examine natural CO2-rich springs in the Daylesford-Hepburn region, South East Australia, which show water O-18 depletion compared to local precipitation. Geochemical modelling shows that water-rock reactions are unlikely to have a significant effect on the observed delta O-18 values, which can only be explained by isotopic exchange with CO2. The water delta O-18 shift can be used for monitoring CO2 impact on shallow groundwater aquifers, provided that there is sufficient CO2 and distinction between water and CO2 delta O-18 values exists. (c) 2017 The Authors. Published by Elsevier Ltd.