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United States Department of Agriculture

Agricultural Research Service

Title: Coupled Reactive Transport Modeling Based on the New Biogeochemical Code Hp1

item Jacques, D - SCK CEN, MOL, BELIGUM
item Simunek, Jirka - UC RIVERSIDE, CA
item Mallants, D - SCK CEN, MOL, BELIGUM
item Van Genuchten, Martinus

Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: August 1, 2005
Publication Date: October 1, 2005
Citation: Jacques, D., Simunek, J., Mallants, D., Van Genuchten, M.T. 2005. Coupled reactive transport modeling based on the new biogeochemical code HP1. In: S. Torkzaban and S. Majid Hassanizadeh (eds.), Proceedings of Workshop on HYDRUS Applications, p. 15-17, October 19, 2005, ISBN 90-39341125, Department of Earth Sciences, Utrecht University, Utrecht, The Netherlands.

Interpretive Summary: The transport of many organic and inorganic contaminants (including heavy metals and radionuclides) in the subsurface is generally affected by a large number of physical, geochemical, and microbiological processes. Simulation of these processes requires a coupled reactive transport code that integrates the physical processes of water flow and solute transport with a range of biogeochemical processes. This paper summarizes a new coupled model for reactive transport based on two existing models: (1) HYDRUS-1D and PHREEQC. HYDRUS-1D is a one-dimensional numerical model simulating the movement of water, heat and multiple solutes in unsaturated layered soils between the soil surface and the groundwater table, while PHREEQC is a computer program simulating the behavior of complex chemical systems including such reactions as ion exchange and mineral precipitation/dissolution. This paper summarizes two example applications of HP1: long-term transient flow and transport of major cations and heavy metals (notably cadmium) in a soil profile, and the long-term leaching of uranium from agricultural field soils following repeated mineral fertilizer application. HP1 is a public domain software package that can be downloaded freely from

Technical Abstract: The migration of many naturally occurring elements and contaminants in the subsurface is affected by a multitude of complex, interactive physical, chemical, mineralogical, geological, and biological processes. Recently, a new comprehensive simulation tool HP1 (HYDRUS1D-PHREEQC) was developed by coupling the HYDRUS-1D one-dimensional variably-saturated water flow and solute transport model with the PHREEQC geochemical code. This paper gives a brief summary of the various processes that can be considered with the combined software such as (1) transient water flow in variably-saturated media, (2) the transport of multiple components, and (3) mixed equilibrium/kinetic geochemical reactions. The program can simulate a broad range of low-temperature biogeochemical reactions in water, soil and ground water systems including interactions with minerals, gases, exchangers, and sorption surfaces, based on thermodynamic equilibrium, kinetics, or mixed equilibrium-kinetic reactions. The coupled transport and reaction equations were solved by means of a non-iterative sequential approach. Several studies dealing with typical coupled transport phenomena have demonstrated HP1’s capabilities for environmental problems such as the transport of heavy metals (Zn, Pb, and Cd) subject to multiple cation exchange reactions, cadmium leaching in acid sandy soils, and the subsurface transport of organic contaminants such as TNT or PCE and their degradation products. In this paper we give two examples: the long-term transient flow and transport of major cations and heavy metals in a soil profile, and the long-term leaching of uranium from agricultural field soils following mineral fertilizer application.

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