HP2/3: Extensions of the HP1 Reactive Transport Code to Two and Three Dimensions

A large number of interacting physical, chemical, and biological processes determine the fate of major cations and anions, contaminants (e.g., heavy metals, pesticides), and colloids in soil systems. The HP1 simulator (Jacques et al., 2008) is a state-of-the-art model that was specifically developed to evaluate these and similar processes in the unsaturated zone. Although HP1 is a versatile code for implementing different geochemical and transport conceptual models in variably-saturated porous media, one of its main limitations is that flow and transport is restricted to one dimension. Therefore, PHREEQC has recently been coupled also with HYDRUS (2D/3D) (Šimůnek et al., 2011) to handle flow and transport problems, which require a higher dimensionality (HP2/3). Typical examples are flow and transport in soil systems with tiled drains, or with drip and furrow irrigation, or in sloped layered or heterogeneous systems. A typical two-dimensional flow and transport problem illustrating the capability of the HP2 simulator will be presented. The HP2/3 code uses the graphical user interface of HYDRUS (2D/3D) for input and output processing, enabling definitions and finite element discretization of very complex flow domains.