# Implementation of Environmental Parameters

In general, the technical procedure comprises the following steps:

- Calculation of the updated concentrations for Ca and DIC, as well as updated pH based on transport calculation and possible sources (e.g. microbial DIC formation).
- Check for under- or oversaturated of the solution with respect to calcite.
- a) Precipitation of calcite in case of oversaturation:

- The amount of precipitated calcite, the resulting concentrations of Ca and DIC as well as the new pH-value are then iteratively calculated. Based on the new pH-value the Al concentration is calculated considering the solubility of a generic gibbsite mineral.

- b) Dissolution of calcite in case of undersaturation:

- The amount of dissolved calcite, the resulting concentrations for Ca and DIC, as well as the new pH-value are then iteratively calculated. If calcite is not available for dissolution to reach equilibrium it is assumed that the pH-value is determined by a generic gibbsite mineral which is always available in the system.

- The new equilibrium conditions will be used to select the K
_{d}-value from the multidimensional matrix for each radionuclide and time step. Concentrations of Fe and Si as potential competitive ion or ligand are indirectly considered in the K_{d}-calculation under the assumption that the solution is equilibrated with quartz and goethite. - Calculation of proton and hydroxyl ion concentrations using the equilibrium pH-value (pH*).

Detailed information can be derived from the ESTRAL and WEIMAR final report by HZDR and GRS.