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A combined model for water flow, solute transport and biogeochemical reactions—HP1. Xuelian Bai Aaron Sawatzky 3 December 2008. Outline. Introduction The combined HP1 model Examples and Applications. Introduction.

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a combined model for water flow solute transport and biogeochemical reactions hp1

A combined model for water flow, solute transport and biogeochemical reactions—HP1

Xuelian Bai

Aaron Sawatzky

3 December 2008

  • Introduction
  • The combined HP1 model
  • Examples and Applications
  • The migration of elements and contaminants in the subsurface is affected by a multitude of complex, interactive physical, chemical, mineralogical and biological processes.
  • All the processes are influenced by precipitation and evapotranspiration, changes of chemical composition or pH of soil and dissolution/precipitation of minerals.
  • The combined HP1 model can simultaneously simulate variably-saturated transient water flow, multi-component solute transport, speciation and geochemical processes, including a variety of mixed equilibrium and kinetic reactions.

Mallants et al., 2008


Simulating water flow, transport and bio-geochemical reactions in environmental soil quality problems


Flow & transport model


Biogeochemical model


Simulating the movement of water, heat and multiple solutes in variably-saturated heterogeneous or layered soils subject to a variety of atmospheric and other boundary conditions

Simulating the behavior of complex chemical systems, such as speciation, ion exchange, surface complexation, and mineral precipitation/dissolution

Mallants et al., 2008

coupling procedure
  • Coupling method: non-iterative sequential approach (weak coupling)
  • Within a single time step:
    • First solve water flow equation and heat transport equation (HYDRUS);
    • Then solve convection-dispersion equation for solute transport for element master/primary species (inert transport) (HYDRUS)
    • Finally solve for each element, calculate speciations, equilibrium reactions, kinetic reactions, … (PHREEQC)

Jacques et al., 2003

hp1 model features
HP1 – model features
  • 1D FE water flow in variably-saturated media
  • 1D FE transport of multiple solutes by CDE
  • 1D heat transport
  • Mixed equilibrium / kinetic biogeochemical reactions
    • Aqueous speciation (reactions in pore-water)
    • Cation exchange (on clay, organic matter, …)
    • Surface complexation (e.g. iron oxyhydroxides)
    • Mineral dissolution / precipitation
    • Any kinetic reactions (oxidation/reduction, (bio)degradation, dissolution/precipitation)

Mallants et al., 2008

hp1 examples
HP1 examples
  • Transport of heavy metals (Zn2+, Pb2+, and Cd2+) subject to multiple cation exchange
  • Transport with mineral dissolution of amorphous SiO2 and gibbsite (Al(OH)3)
  • Heavy metal transport in a medium with a pH-dependent cation exchange complex
  • Infiltration of a hyperalkaline solution in a clay sample (kinetic precipitation-dissolution of kaolinite, illite, quartz, calcite, dolomite, gypsum, …)
  • 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.
  • Kinetic biodegradation of TNT (multiple degradation pathways)

Jacques et al., 2003

typical application and processes involved
Typical application and processes involved
  • Cycling of radionuclides/metals in soil-plant systems
    • Heterogeneous physical/chemical properties
    • Water flow under rainfall - evapotranspiration conditions
    • Root growth and water uptake
    • Microbiological growth
    • Degradation of organic matter with radionuclides/metal release
    • Transport/adsorption/decay
    • Uptake of radionuclides/metals by plants

Mallants et al., 2008

application fields of hp1
Application fields of HP1
  • Process Coupling and InteractionsInvestigate the impacts of multiple coupled biogeochemical reactions in the presence of complex flow fields and spatial heterogeneity.
  • Interpretation of Laboratory and Field DataProvide a useful framework for interpreting experimental results. Understand qualitative and quantitative trends and relationships present in the data.
  • Sensitivity AnalysisPermit the systematic evaluation of the impact of model parameters (both reactive and hydrogeological), initial conditions, and boundary conditions upon the model output.
  • Integration and SynthesisTool for integrating all of the knowledge obtained from simulation, sensitivity analyses, and laboratory and field experimentation.

Mallants et al., 2008

  • www.sckcen.be/hp1
  • J. Šimůnek et al. (2006) Multicomponent geochemical transport modeling using Hydrus-1D and Phreeqc. JAWRA.
  • D. Jacques et al. (2003) The Hydrus-Phreeqc multicomponent transport model for variably-saturated porous media: code verification and application.
  • D. Jacques et al. (2008) Modeling coupled water flow, solute transport and geochemical reactions affecting heavy metal migration in a podzol soil. Geoderma.
  • L. Wissmeier and D.A.Barry. (2008) Reactive transport in unsaturated soil: comprehensive modeling of the dynamic spatial and temporal mass balance of water and chemical components. Advances in Water Resources.