HP2 Module

HYDRUS-1D, as well as HYDRUS (2D/3D), was recently coupled also with the PHREEQC geochemical code (Parkhurst & Appelo, 1999) to create a new comprehensive simulation tool, HP1 (acronym for HYDRUS1D-PHREEQC) (Jacques and Šimůnek 2005; Jacques et al., 2006; Šimůnek et al., 2006a) and HP2 (acronym for HYDRUS2D-PHREEQC). This new code contains modules simulating (1) transient water flow in variably-saturated media, (2) the transport of multiple components, (3) mixed equilibrium/kinetic biogeochemical reactions, and (4) heat transport. HP1/2 is a significant expansion of the individual HYDRUS-1/2D and PHREEQC programs by preserving most of their original features. The code still uses the Richards equation for simulating variably-saturated water flow and advection-dispersion type equations for heat and solute transport. However, the loosely coupled program can simulate also a broad range of low-temperature biogeochemical reactions in water, the vadose zone and in ground water systems, including interactions with minerals, gases, exchangers and sorption surfaces based on thermodynamic equilibrium, kinetic, or mixed equilibrium-kinetic reactions. HP1/2 uses the operator-splitting approach with no iterations during one time step (a non-iterative sequential modeling approach). Jacques et al. (2006) evaluated the accuracy of the operator-splitting approach for a kinetic reaction network (i.e., sequential and parallel kinetic degradation reactions) by comparing HP1/2 with an analytical solution for TCE-degradation, as well as for mixed equilibrium and kinetic reactions involving different flow conditions (steady-state and transient).

Jacques and Šimůnek (2005), Šimůnek et al. (2006a), and Jacques et al. (2008a,b), demonstrated the versatility of HP1/2 on several examples, which included a) the transport of heavy metals (Zn2+, Pb2+, and Cd2+) subject to multiple cation exchange reactions, b) transport with mineral dissolution of amorphous SiO2 and gibbsite (Al(OH)3), c) heavy metal transport in a medium with a pH-dependent cation exchange complex, d) infiltration of a hyperalkaline solution in a clay sample (this example considers kinetic precipitation-dissolution of kaolinite, illite, quartz, calcite, dolomite, gypsum, hydrotalcite, and sepiolite), e) long-term transient flow and transport of major cations (Na+, K+, Ca2+, and Mg2+) and heavy metals (Cd2+, Zn2+, and Pb2+) in a soil profile, f) cadmium leaching in acid sandy soils, g) radionuclide transport, and h) long term uranium migration in agricultural field soils following mineral P-fertilization.

References:

Appelo, C. A. J., and D. Postma, Geochemistry, Groundwater and Pollution, 2nd ed., A. A. Balkema Publ., Leiden, The Netherlands, 649 p., 2005.

Jacques, D., and J. Šimůnek, User Manual of the Multicomponent Variably-Saturated Flow and Transport Model HP1, Description, Verification and Examples. Version 1.0, SCK•CEN-BLG-998, Waste and Disposal, SCK•CEN, Mol, Belgium, 79 pp., 2005.

Jacques, D., J. Šimůnek, D. Mallants, and M. Th. van Genuchten, Operator-splitting errors in coupled reactive transport codes for transient variably saturated flow and contaminant transport in layered soil profiles. J. Contam. Hydrology, 88, 197-218, 2006.

Šimůnek, J., D. Jacques, M. Th. van Genuchten, and D. Mallants, Multicomponent geochemical transport modeling using the HYDRUS computer software packages. J. Am. Water Resour. Assoc., 42(6), 1537-1547, 2006.

Jacques, D., J. Šimůnek, D. Mallants, and M. Th. van Genuchten, Modeling coupled hydrological and chemical processes in the vadose zone: a case study on long term uranium migration following mineral p-fertilization, Vadose Zone J., Special Issue “Vadose Zone Modeling”, 7(2), 698-711, 2008a.

Jacques, D., J. Šimůnek, D. Mallants, and M. Th. van Genuchten, Modelling coupled water flow, solute transport and geochemical reactions affecting heavy metal migration in a podzol soil, Geoderma, 145, 449-461, 2008b.

Jacques, D., and J. Šimůnek, Notes on HP1 – a software package for simulating variably-saturated water flow, heat transport, solute transport and biogeochemistry in porous media, HP1 Version 2.2, SCK•CEN-BLG-1068, Waste and Disposal, SCK•CEN, Mol, Belgium, 113 pp., 2010.

Jacques, D., C. Smith, J. Šimůnek, and D. Smiles, Inverse optimization of hydraulic, solute transport, and cation exchange parameters using HP1 and UCODE to simulate cation exchange, J. Contaminant Hydrology, (in press).