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Title: MULTICOMPONENT GEOCHEMICAL TRANSPORT MODELING USING THE HYDRUS-1D COMPUTER SOFTWARE PACKAGE

Author
item SIMUNEK, JIRKA - UC RIVERSIDE, CA
item JACQUES, DIEDERIK - SCK CEN, MOL, BELIGUM
item Van Genuchten, Martinus

Submitted to: American Water Resources Association Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 2/2/2005
Publication Date: 6/27/2005
Citation: Simunek, J., Jacques, D., Van Genuchten, M.T. 2005. Multicomponent geochemical transport modeling using the HYDRUS-1D computer software package. American Water Resources Association Conference Proceedings. In: Institutions for Sustainable Watershed Management: Reconciling Physical and Management Ecology in the Asia-Pacific. June 27-29, 2005. Honolulu, HI. 7 p.

Interpretive Summary: The transport of reactive solutes in soils is the result of the physical processes of water flow and solute transport, and chemical interactions between solutes and the soil solid phase. When multiple solutes are present, they may undergo chemical reactions with each other, or could be competing for available sorption sites on the solid phase. These processes cannot be modeled with traditional approaches that treat solutes as chemically independent constituents and use simplified linear or nonlinear adsorption isotherms. In this paper we briefly describe two recently developed models for reactive transport that are both based on the HYDRUS-1D software package simulating water, heat and solute movement between the soil surface and the groundwater table. One model resulted from coupling HYDRUS-1D with the UNSATCHEM major ion chemistry module. This model, restricted to major ions such as sodium, calcium and magnesium, enables analyses of the effects of salinity on plant growth and the amount of water and amendments needed to reclaim salt-affected soil profiles. The second model, HP1, resulted from coupling HYDRUS-1D with the popularly used PHREEQC biogeochemical code. The latter program accounts for a wide range of equilibrium and kinetic reactions. Two HP1 example applications are discussed in this paper: the leaching of heavy metals (zinc, lead and cadmium) from a contaminated soil colum, and the transport of the explosive TNT and its degradation products. The latter example shows that groundwater may be more vulnerable to the leaching of TNT degradation products, than of the parent compound itself.

Technical Abstract: ABSTRACT: The transport of reactive contaminants in the subsurface is generally affected by a large number of nonlinear and often interactive physical, chemical and biological processes. Simulating these processes requires a coupled reactive transport code that couples the physical processes of water flow and advective-dispersive transport with a range of biogeochemical processes. In this paper we summarize two recently developed coupled geochemical models that are both based on the HYDRUS-1D software package for variably saturated flow and transport. One model resulted from coupling HYDRUS-1D with the UNSATCHEM module. While restricted to major ion chemistry, this program enables quantitative predictions of such problems as analyzing the effects of salinity on plant growth and the amount of water and amendments required to reclaim salt-affected soil profiles. The second model, HP1, resulted from coupling HYDRUS-1D with the PHREEQC biogeochemical code. The latter program accounts for a wide range of instantaneous or kinetic chemical and biological reactions, including complexation, cation exchange, surface complexation, precipitation-dissolution and/or redox reactions. The versatility of HP1 is illustrated in this paper by means of two examples: the leaching of toxic trace elements and the transport of TNT and its degradation products.