Determining Seasonal Natural Effects over Isotopic Baselines for CO2 Storage Monitoring

Dissolved carbon stable isotopes in surface waters can be utilized as a monitoring tool of CO2 geological storage and as a good indicator of potential CO2 leakages, since each source of carbon has a specific isotopic signature. The isotopic carbon baseline value and its range will determine whether the situation responds to a leak or a natural modification as part of the system's annual cycle and its seasonal effects. We measured water temperature, pH, dissolved inorganic carbon (DIC) concentration and other geochemical variables, during the different annual stages, in order to characterize the contribution of different sources of carbon to the natural isotopic evolution of DIC in the area of Hontomin. This area is the selected site for the Spanish research facility for CO2 geological storage operated by CIUDEN. The average value for δ13C-DIC at the study site is -10.7 ‰ (V-PDB), which is very different of the CO2 generated during the oxycombustion process (about -28 ‰ vs V-PDB). After statistical analysis of the sampling efforts, we observed light differences on their average isotopic values which imply certain seasonal effects, although we could not find effects over the DIC concentration.