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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. 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

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  1. A combined model for water flow, solute transport and biogeochemical reactions—HP1 Xuelian Bai Aaron Sawatzky 3 December 2008

  2. Outline • Introduction • The combined HP1 model • Examples and Applications

  3. Introduction • 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.

  4. Objective • 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

  5. Simulating water flow, transport and bio-geochemical reactions in environmental soil quality problems HP1 Flow & transport model HYDRUS-1D Biogeochemical model PHREEQC 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

  6. Couplingprocedure • 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

  7. 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

  8. 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

  9. 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

  10. 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

  11. References • 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.

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