Chemical Parameters for the UNSATCHEM module.

The following chemical parameters and selections for the UNSATCHEM module are specified in the Chemical Parameters dialog window:

-        Whether the kinetic or equilibrium model for the precipitation and dissolution of calcite and dissolution of dolomite is to be used (the Kinetic Precipitation/Dissolution  check box).

-        Whether the silica content in the solution is to be calculated based on the solution pH, or whether the effect of pH is to be neglected (the Silica in Solution (pH Dependency) check box).

-        The Critical Ionic Strength, i.e., the ionic strength, below which the extended Debye-Hückel equation is used to calculate ion activity coefficients. Pitzer virial-type equations are used above this value.

-        The Maximum Number of Iterations allowed during any time step between the solute transport and chemical modules. When the maximum number of iterations is reached then the code proceeds to the new time level. The recommended value (if the iterative approach is to be used; from our experience) is 5. Set equal to one if no iteration (we recommend this non-iterative approach) is required (this, in general, leads to significantly lower computational time without significantly altering the results in most cases).

-        Whether the hydraulic conductivity is to be modified depending on the solution chemistry using the McNeal [1968] semi-empirical approach (the Conductivity Reduction due to Chemistry check box).