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PC Progress - Version Hydrus-UnsatChem -Add-On Module Software
The geochemical UNSATCHEM module (Šimunek and Suarez, 1994; Šimunek et al., 1996) has been implemented into one-, two-, and three-dimensional computational modules of the HYDRUS-1D and HYDRUS (2D/3D) software packages. The geochemical UNSATCHEM module simulates the transport of major ions in variably-saturated porous media, including major ion equilibrium and kinetic non-equilibrium chemistry. The resulting code is intended for predictions of major ion chemistry, along with water and solute fluxes in soils during transient flow.
The major variables of the chemical system in UNSATCHEM-2D are Ca, Mg, Na, K, SO4, Cl, NO3, H4SiO4, alkalinity, and CO2. The model accounts for various equilibrium chemical reactions between these components, such as complexation, cation exchange and precipitation-dissolution. For the precipitation-dissolution of calcite and dissolution of dolomite, either equilibrium or multicomponent kinetic expressions can be used, which includes both forward and back reactions. Other dissolution-precipitation reactions considered include gypsum, hydromagnesite, nesquehonite, and sepiolite. Since the ionic strength of soil solutions can vary considerably in time and space and often reach high values, both the modified Debye-Hückel and the Pitzer expressions are incorporated into the model to calculate single ion activities. The effect of solution chemistry on the hydraulic conductivity is also considered. Water flow and heat transport modules are similar (almost identical) as in regular HYDRUS. Possible applications include studies of the salinization/reclamation of agricultural soils, sustainability of various irrigation systems, and the disposal of brine waters in mining operations. Applications of the UNSATCHEM module are demonstrated on several examples.