HP1 reactive transport code A Coupled Numerical Code for Variably Saturated Water Flow, Solute Transport and Biogeochemistry in Soil Systems.

The HP1 code was recently developed to simulate one-dimensional variably saturated water flow and multicomponent transport in soil systems and sediments for a broad range of low-temperature biogeochemical reactions in water, soil and sediments, including aqueous speciation, cation exchange, mineral dissolution/precipitation, and (bio)degradation for mixed equilibrium-kinetic systems.

• One-dimensional transient water flow for different boundary conditions including atmospheric conditions (precipitation, evaporation, transpiration)
• Root water uptake as a sink for water
• Root growth
• One-dimensional transient convective and conductive heat transport for time-variable temperatures at the soil surface
• One-dimensional advective, dispersive and diffusive transport of multiple solutes
• Effect of temperature on transport parameters, thermodynamic constants, and rate parameters
• Different functional forms for the soil hydraulic properties, including hysteresis
• Physical non-equilibrium solute transport
• Physical and chemical spatial heterogeneity
• Equilibrium aqueous speciation reactions and kinetically controlled aqueous reactions such as radioactive decay
• Multi-site cation exchange related to type and amount of minerals present
• Equilibrium and kinetic dissolution/precipitation of primary and secondary minerals
• User-defined kinetic reactions
• Simultaneous presence of different reactions (sequential and parallel kinetic reactions, equilibrium and kinetic reactions, homogeneous and heterogeneous reactions, biogeochemical reactions)