Modelling the baseline geochemistry of groundwater in a Chalk aquifer considering solid solutions for carbonate phases

The Chalk aquifer of Champagne (France) baseline geochemistry has been determined using a solid solution approach for the modelling of calcite dissolution. The water–rock interactions are modelled by the speciation code CHESS from field data and Ca, Mg and Sr aqueous concentrations in groundwater. The stoichiometries of solid solutions are defined in each stratigraphic unit of the Chalk aquifer from bulk geochemistry and Chalk mineralogy of samples taken from boreholes. The initial mineralisation of water at the bottom of the unsaturated zone and the characterisation of the theoretical evolution of groundwater chemistry along the flow lines associated with incongruent calcite dissolution are calculated from this approach.

Research highlights
► Modelling of water–carbonate interactions using solid solutions.
► The stoichiometries of solid solutions are defined from Chalk geochemistry.
► The initial mineralisation of groundwater is calculated.
► Chemical evolution of groundwater along the flow lines is calculated.
► Modelling of incongruent carbonate dissolution is achieved from experimental data.