HYDRUS Software Applications to Subsurface Flow ...

Czech University of Life Sciences, Prague and

PC-Progress, s.r.o., Prague

Proceedings

of the 4 International Conference th

HYDRUS Software Applications to Subsurface Flow and Contaminant Transport Problems March 21-22 2013 Prague, Czech Republic

Czech University of Life Sciences, Prague Faculty of Agrobiology, Food and Natural Resources Kamýcká 129 165 21 Praha 6 – Suchdol Czech Republic http://www.af.czu.cz/en/ PC-Progress s.r.o. Korunní 2569/108a Prague, 101 00 Czech Republic http://www.pc-progress.com/en/Default.aspx

ISBN: 978-80-213-2380-3

Table of Content Preface................................................................................................................................................5 Papers (Invited Presentations) 1. Jacques, D., J. Šimůnek, D. Mallants, and M. Th. van Genuchten, The HPx reactive transport models: Summary of recent developments and applications.....................................7 2. Šimůnek, J., M. Šejna, D. Jacques, G. Langergraber, S. A. Bradford, and M. Th. van Genuchten, New features of the HYDRUS computer software packages. ...............................17 Papers (Volunteered Presentations) 3. Abramson, A., E. Adar, and N. Lazarovitch, Investigating the impact of irrigation method on profitability of smallholder gardening: Incorporating HYDRUS-1D into a decision support system. .........................................................................................................................27 4. Anlauf, R., and P. Rehrmann, Simulation of water and air distribution in growing media. .....33 5. Antonov, D., D. Mallants, J. Šimůnek, and D. Karastanev, Application of the HYDRUS (2D/3D) inverse solution module for estimating of the soil hydraulic parameters of a quaternary complex in Northern Bulgaria. ...............................................................................47 6. Bezerra Coelho, B., C. R., M. S. Batalha, D. Jacques, M. C. Barbosa, and M. Th. van Genuchten, Using HYDRUS-HP1 to estimate 226Ra transport in soils following the use of phosphogypsum in agriculture. .................................................................................................53 7. Dabach, S., J. Šimůnek, A. Ben-Gal, J. Shi, and N. Lazarovitch, Optimization of triggered irrigation using a system-dependent boundary condition in HYDRUS (2D/3D). ....................63 8. Diamantopoulos, E., S. C. Iden, and W. Durner, Modeling non-equilibrium water flow in multistep outflow and multistep flux experiments. ..................................................................69 9. El-Nesr, M. N. B., A. Alazba, and J. Šimůnek, Dual-drip subsurface irrigation system: Can it act as a hydraulic barrier? ......................................................................................................77 10. Filipović, V., R. Kodešová, and D. Petošić, Numerical modeling of water flow and nitrate dynamics in zero tension plate lysimeters using HYDRUS-2D. ..............................................87 11. Glæsner, N., and H. H. Gerke, Single- and double porosity modeling of solute transport in intact soil columns – effects of texture, slurry placement, and intermittent irrigation. ............95 12. Grinevskiy, S. O., and S. P. Pozdniakov, The use of HYDRUS-1D for groundwater recharge estimation in boreal environments. ............................................................................107 13. Haile, S. S., and B. J. Merkel, Simulation of uranium tailing leaching using VS2DRT. .........119 14. Hlaváčiková, H., V. Novák, and M. Rodný, Infiltration into stony soil: modeling of the process using HYDRUS codes. ................................................................................................127

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15. Izadi, F. T., A. M. Damuchali, G. A. Fardi, and A. Khodadadi, Simulations of the impact of different rainfall intensities on reactive transport of metal contaminants from mine tailings. ..................................................................................................................................................135 16. Izadi, F. T., G. A. Fardi, A. Khodadadi, and M. Faridzad, Investigating the effect of acidic rain on reactive transport of metal contaminants in groundwater. ...........................145 17. Kalin, J., B. Petkovšek, P. Montarnal, A. Genty, E. Deville, and J. Krivic, Comparison of two numerical modeling codes for hydraulic and transport calculations in the near field. ......155 18. Kanzari, S., M. Hachicha, R. Bouhlila, and J. Battle-Sales, Characterization and modeling of water movement and salts transfer in a semi-arid region of Tunisia. ...................................165 19. Kanzari, S., I. Bâ, M. Hachicha, and R. Bouhlila, Characterization and modeling of water and salt dynamics in a sandy soil under the effects of surface drip irrigation. .........................175 20. Karlsson, S. C., S. Dalahmeh, C. Lalander, and H. Jönsson, Hydraulic properties and reduction of COD, phosphorus and nitrogen in a sand filter used for greywater treatment – simulation and verification. ......................................................................................................183 21. Kato, C., T. Nishimura, H. Imoto, and T. Miyazaki, Predicting soil CO2 dynamics in arable land of Andisol in western suburb of Tokyo. ...........................................................................191 22. Kébré, M. B., F. Cherblanc, F. Ouédraogo, Jean-Claude Bénet, and F. Zougmoré, Flow at low water contents: A simple approach for inverse estimation of van Genuchten-Mualem soil hydraulic parameters. .........................................................................................................203 23. Léger, E., A. Saintenoy, and Y. Coquet, Estimating saturated hydraulic conductivity from surface ground-penetrating radar monitoring of infiltration. ....................................................215 24. Leterme, B., and D. Jacques, Modeling Hg reactive transport in soil system using HP1. .......225 25. Leterme, B., M. Gedeon, and D. Jacques, Groundwater recharge modeling in the Nete catchment (Belgium) with HYDRUS-1D – MODFLOW package. .........................................235 26. Morvannou, A., N. Forquet, M. Vanclooster, and P. Molle, Which hydraulic model to use for vertical flow constructed wetlands? ....................................................................................245 27. Nakhaei M. and J. Šimůnek, Estimating the soil hydraulic and thermal properties of unsaturated porous media using HYDRUS-2D. .......................................................................257 28. Phogat, V., M. A. Skewes, M. Mahadevan, and J. W. Cox, Simulation of water and salinity dynamics under different irrigation applications to an almond tree in pulsed and continuous mode..........................................................................................................................................267 29. Pontedeiro, E. M., V. Ottoni, and M. Th. van Genuchten, HYDRUS-1D modeling applications to waste disposal problems in Brazil. ...................................................................277 30. Pozdniakov, S., P. Wang, S. Grinevskiy, and J. Yu, Simulation of groundwater evapotranspiration with HYDRUS-1D in desert environments. ..............................................289 31. Raij, I., N. Lazarovitch, A. Ben-Gal, U. Yermiyahu, and D. Jacques, Accounting for solution composition in a plant roots active nutrient uptake model. ........................................299

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32. Ramos, T. B., J. Šimůnek, M. C. Gonçalves, J. C. Martins, A. Prazeres, and L. S. Pereira, Modeling water and nitrogen fate in plots with sweet sorghum irrigated with fresh and blended saline waters using HYDRUS-2D. ..............................................................................307 33. Ružičić, S., Z. Kovac, M. Mileusnic, and K. Posavec, Longitudinal dispersivity determination using conservative tracer in the field. ................................................................315 34. Sandhu, C., T. Fichtner, I. Hasan, and P.-W. Gräber, Predicting the impact of treated wastewater infiltration on groundwater recharge by simulating reactive transport in the unsaturated zone. ......................................................................................................................323 35. Schwen, A., G. Bodner, and W. Loiskandl, Temporal variations of soil hydraulic properties and its effect on soil water simulations.....................................................................................333 36. Šimůnek, J., D. Jacques, and M. Šejna, HP2/3: Extensions of the HP1 reactive transport code to two and three dimensions. ............................................................................................345 37. Thaysen, E. M., E. Laloy, and D. Jacques, CO2 fluxes to aquifers beneath cropland: Merging measurements and modeling. .....................................................................................355 38. Toride, N., and DaiWen Chen, Fate and transport of nitrogen in soils based on a coupled nitrogen-carbon cycling model using the HP1 code. ................................................................365 39. Valdes-Abellan, J., J. Jiménez-Martínez, and L. Candela, HYDRUS application to assess possible impacts of non-conventional water irrigation under two different vadose zone monitoring strategies.................................................................................................................377 40. Xiao, H., J. Böttcher, and J. Šimůnek, Simulation of the heavy metal transport in unsaturated soils: Use of scale factors to quantify variable sorption isotherms. ......................385 41. Yurtseven, E., J. Šimůnek, S. Avci, and H. S. Öztürk, Comparison of HYDRUS-1D simulations and ion(salt) movement in the soil profile subject to leaching..............................395

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Please reference the proceedings as follows: Šimůnek, J., M. Th. van Genuchten, and R. Kodešová (eds.), Proceedings of the 4th International Conference "HYDRUS Software Applications to Subsurface Flow and Contaminant Transport Problems", March 21-22, 2013, Dept. of Soil Science and Geology, Czech University of Life Sciences, Prague, Czech Republic, ISBN: 978-80-213-2380-3, pp. 404, 2013. Please reference the individual papers as follows (adjust highlighted text as needed): Authors, Title, Proceedings of the 4th International Conference "HYDRUS Software Applications to Subsurface Flow and Contaminant Transport Problems", edited by J. Šimůnek, M. Th. van Genuchten, and R. Kodešová, March 21-22, 2013, Dept. of Soil Science and Geology, Czech University of Life Sciences, Prague, Czech Republic, ISBN: 978-80-213-23803, pp. ??-??, 2013.

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Preface These proceedings document presentations given at the Fourth International Conference on “HYDRUS Software Applications to Subsurface Flow and Contaminant Transport Problems,” held in Prague, Czech Republic, March 21-22, 2013. Previous conferences in this series were held in Utrecht in 2005, in Prague in 2008, and in Tokyo, also in 2008. The conferences focus on the development and application of advanced numerical models simulating variably-saturated flow, heat transport, and the transport of various contaminants or other solutes (such as nutrients, pesticides, heavy metals, radionuclides, and pathogenic microorganisms) in soils and groundwater. The conferences are designed to bring together users of the HYDRUS family of codes, as well as of related software, to review and exchange information on various aspects of the codes, future enhancements of the software, and their application to a range of soil, environmental, hydrological, ecological and agricultural problems. Since the first workshop in 2005, the community of HYDRUS users has been continuously growing as evidenced by the number of downloads (over 10,000 times each of the past several years) and visits to the HYDRUS web pages (on average several hundred each day). Hundreds of journal articles have now been published in which the HYDRUS codes have been used. Feedback from users such as those attending the HYDRUS conference has been extremely important in identifying particular strengths and weaknesses of the codes, and for defining additional processes or features that should be included in the models. Feedback is also continuously obtained from several discussion forums on the HYDRUS website, where users can submit questions or suggestions about the models. These proceedings contain 41 contributions from mostly HYDRUS software users, covering a range of topics from the very fundamental to important practical applications. These proceedings, as well as those of previous HYDRUS conferences, can be downloaded freely from the HYDRUS website at http://www.pc-progress.com. We would like to thank the Czech University of Life Sciences and PC-Progress for hosting the conference in Prague. Our appreciation goes also to the many participants who travelled to Prague from all continents. Special thanks are due to those that contributed to these proceedings. Published studies in which the codes have been used always provide useful information for new users. We believe that the software tools have served, and will continue to serve, an important role in especially vadose zone research. The Editors Jirka Šimůnek Rien van Genuchten Radka Kodešová

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The HPx Reactive Transport Models: Summary of Recent Developments and Applications Diederik Jacques1, Jiří Šimůnek2, Dirk Mallants3, and Martinus Th. van Genuchten4 1

Performance Assessments, Institute of Environment, Health and Safety, Belgian Nuclear Research Centre, Mol, Belgium, [email protected] 2 Department of Environmental Sciences, University of California Riverside, CA, USA 3 Land and Water, CSIRO, Adelaide, Australia 4 Department of Mechanical Engineering, Federal University of Rio de Janeiro, UFRJ, Rio de Janeiro, RJ, Brazil

Abstract The HPx reactive transport codes were developed to simulate flow and transport processes in variably-

saturated porous media subject to a variety of low-temperature geochemical processes. The codes combine the HYDRUS models for flow and transport (HYDRUS-1D version 4.16, and HYDRUS 2D/3D version 2.02) with the generic thermodynamic and kinetic model PHREEQC-2.17. As such, HPx expands significantly the capabilities of the individual codes for multicomponent one-dimensional (HP1) and twodimensional (HP2) transport problems. This paper provides a brief summary of recent developments and applications of HPx, such as (i) the inclusion of gas diffusion, (ii) extension to two-dimensional problems, (iii) inverse optimization, and (iv) feedback between changes in geochemical variables and transport properties. HPx is a flexible tool which can be applied to flow and transport problems involving relatively complex geochemical processes. A typical example is the geochemistry of mercury, which in a contaminated soil may be present in different forms and phases.

1. Introduction The fate and transport of nutrients and contaminants in variably-saturated porous media is influenced by a range of interacting physical, chemical, and biological processes (Jacques et al., 2008). Transport in soil systems is often further complicated by a multitude of coupled biogeochemical reactions, the presence of spatially and temporally variable flow velocities, and spatial heterogeneities at different scales (for a review see Mallants et al., 2011). A numerical tool that integrates these various processes offers unique possibilities for advanced model building and improving process understanding, ranging from sensitivity analyses of processes and parameters, designing experiments, hypothesis testing by running virtual laboratories, conceptual model validation using experimental data, and evaluation of different management or remediation practices. Based on the HYDRUS suite of models for one-dimensional (Šimůnek et al., 2008) and multi-dimensional problems (Šimůnek et al., 2011), and the generic thermodynamic and kinetic geochemical model PHREEQC (Parkhurst and Appelo 1999), the HP1 (Jacques and Šimůnek, 2005) and HP2 (Šimůnek et al., 2012) modules were developed to handle water flow, multi-component solute transport, heat transfer, and biogeochemical reactions for a range of environmental soil quality applications. In this paper we provide a brief summary of recent developments and various applications of the HPx modules.

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2. Conceptual Basis of HPx The HPx codes considerably extend upon the capabilities of the individual codes. For example, the full range of water flow and solute transport formulations available in the standard HYDRUS codes are now combined with the different geochemical models available in PHREEQC. Contrary to the conventional advection-dispersion-reaction equations forming the basis of the standard HYDRUS-1D and HYDRUS 2D/3D codes, the HPx modules account for interactions between different aqueous components to simulate intra-aqueous degradation, transformation or production processes, as well as heterogeneous equilibrium and kinetic processes. Using the capabilities of PHREEQC, HPx allows thermodynamic equilibrium calculations for • aqueous speciation with different activity correction models (Davies, extended TruesdellJones, B-Dot, Pitzer, SIT - Specific ion Interaction Theory), • multi-site ion exchange sites for different conventions (Gaines-Thomas, Vanselow, Gapon, or accounting for different selectivities considering the equivalent fraction occupied by the cation by the Rothmund-Kornfeld or the active fraction model), • multi-site surface complexation sites with a non-electrostatic, the Dzombak and Morel, or the CD_MUSIC model and different options to calculate the composition of the diffuse double layer, • mineralogical assemblages, • solid-solutions consisting of multiple end members in an ideal solid solution or a binary non-ideal solid solution using the Guggenheim approach for determining the activity coefficients of the end members (Glynn and Reardon, 1990), and • gas exchange. Kinetic calculations are furthermore used to describe mineral dissolution/precipitation (e.g., based on transition state theories as shown by Lasaga (1998) and Brantley (2003)), nonequilibrium sorption processes, biogeochemical reactions, including first-order degradation networks (e.g., C-sequestration, see below), Monod kinetics, and Michaelis-Menten kinetics (e.g., solute-dependent plant uptake coupled with root exudation as shown by Raji et al. (2013)). HPx allows one to select uniform or dual-porosity models for water flow, and uniform, mobile/immobile, or dual-porosity models for solute transport (Figure 1), as well as diffusive processes in the gas phase. As opposed to many other reactive transport codes, HPx also provides an option to account for the effects of root water and nutrient or contaminant uptake, including compensated water uptake and root growth (Šimůnek and Hopmans, 2008). Furthermore, the HPx simulators can accommodate complex boundary conditions including water and chemical exchange with streams and groundwater. Because geochemical gradients (e.g. changing redox conditions) are especially strong along such interfaces, only simulators that provide proper coupling between the various hydrological, geochemical and biological processes involved are capable of providing accurate system descriptions.

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Figure 1. Schematic of possible coupled flow–transport–reaction models available within HPx: a uniform water flow and solute transport model (left), a uniform water flow model with a mobile/immobile solute transport model (middle), and a dual-porosity water flow model with a dual-porosity transport model (right). In the figure, εs is the volume fraction of solid phase, θa is the air content, θw is the water content, θw,m is the mobile water content, θw,im is the immobile water content, Sr,w represents root water uptake, Sr,s,i represents root uptake of solute i, Sc,i is a sink or source term for solute i resulting from aqueous degradation or transformation processes, Γi and Γw are solute and water mass exchange terms between the mobile and the immobile water phases, respectively, and Γwa, Γws, Γws,m, and Γws,im are heterogeneous mass exchange terms between the water and air phases, the water and solid phases, the mobile water and solid phases, and the immobile water and the solid phases, respectively (after Šimůnek and van Genuchten, 2008).

3. Recent Developments and Applications This section describes several recent improvements and applications of HPx. Additional examples are included in these proceedings for mercury transport and fate in soils (Leterme and Jacques, 2013), CO2 production and transport in bare and planted mesocosmos (Thaysen et al., 2013), and active root nutrient uptake accounting for solution composition effects (Raji et al., 2013). The extension of the HPx code to two-dimensional flow and transport problems is described in another contribution to these proceedings (Šimůnek and Jacques, 2013). 3.1. Gas Diffusion Coupled to Organic Matter Degradation A recent addition to HPx is diffusion of components in the gas phase. We present here an illustrative example that includes a process-based soil organic matter degradation model with three immobile organic carbon pools (litter, humus, and biomass), external input of C into the system, and an inorganic pool (CO2). The model is based on previous work by Porporato et al. (2003) as illustrated in Figure 2 (see also Batlle-Aguilar et al., 2011). The model consists of a number of coupled nonlinear ordinary differential equations (see Fig. 2). There are several differences with the original model of Porporato et al. (2003). For example, water flow is modeled using the Richards equation with a root water uptake term (versus a probabilistic modeling approach in Porporato et al., 2003), while heat transport is also considered. Two inorganic pools are further included: CO2(g) and dissolved C, with thermodynamic exchange

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between the two pools. We additionally consider the temperature dependence of rate parameters, and also included transport of inorganic C in the aqueous and gaseous phases.

Figure 2. Schematic of the soil organic matter model (left), the set of coupled non-linear ordinary differential equations, and a list of symbols (after Porporato et al., 2003).

The rate parameters in Figure 2 for first-order decay and decomposition depend on the soil water content (described with the formulations of Porporato et al. (2003) and Manzoni and Porporato (2007)) and soil temperature. The latter effect is described using the temperature stress function from the RothC model of Coleman and Jenkinson (2005). The effects of water content and temperature stress were modeled as a multiplication of both factors. The combined effect of transient variations in the water content and temperature in a soil profile during one year on the stress factors is illustrated in Figure 3. Multiplication of the temperature and water content stress factors leads to considerable variation in organic matter decomposition rates during the year (Figure 3). Decomposition rates, relative to the reference rate value, range from zero (during dry periods near the surface) up to 3.5 (during wet and warm periods). Evolutions of the organic C pools during one year are shown in Figure 4. The different curves follow smoothly the seasonal trends in temperature (and water content). The transformation and decomposition of the organic C pools is also reflected in the general trend of soil CO2 gas. On the other hand, water content changes on the shorter temporal scale seem to influence variations in the soil CO2 partial pressure.

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Figure 3. Temporal variations of water contents (top, left) and temperatures (top, right) in a soil profile during a one year simulation. Resulting stress factors (bottom) for the decay and decomposition rates.

3.2. Inverse Optimisation with UCODE Coupled codes such as HP1 allow simultaneous optimization of various flow, transport, and geochemical parameters using inverse methods. A recent application with HP1 is given by Jacques et al. (2012), who combined HP1 with the general optimization tool UCODE (Poeter et al., 2005). The experimental data resulted from previously published laboratory experiments (Smiles and Smith, 2004) about the transport of major cations (Na, K, Mg, and Ca) during water absorption into horizontal soil columns, which were terminated at different times. Experimental data consisted of spatial distributions of the water content (θ), the Cl concentration, and total aqueous and sorbed concentrations of the major cations. In addition to selected flow and transport parameters (i.e., those describing the water retention and hydraulic conductivity functions, as well as the dispersivity), cation exchange coefficients for the major cations and the cation exchange capacity were estimated. Another new aspect of this study was that two different exchange models could be tested: the Gapon approach and a variable-selectivity model based on the Rothmund-Kornfeld approach. The latter enables stronger binding of a species at lower equivalent sorbed fractions (e.g., Bond, 1995). Calibrated profiles for Mg are shown in Figure 5. The Rothmund-Kornfeld approach was found to perform slightly better than the Gapon approach.

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Exchangeable Mg (mmol/kg soil)

Figure 4. Time evolution of organic C pools (litter: top, left; humus: top, right; and biomass: bottom, left) and of gaseous CO2 concentrations (in atm, bottom, right) in a soil profile during a one year simulation.

Mg (mol/kgw)

0.01

5

0.008

4

0.006

3

0.004

2

0.002

1

0

0

0

0.5 1 1.5 Distance / time0.5 (cm min-0.5)

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0.5 1 1.5 Distance / time0.5 (cm min-0.5)

Figure 5. Simulated profiles of aqueous (left) and sorbed (right) Mg concentrations obtained with the Gapon approach [solid lines] or the Rohtmund-Kornfeld approach [dashed lines], compared with experimental data [symbols: circles - 36 min, triangles - 106 min, and squares - 144 min] from water absorption and solute transport experiments using piggery effluent (Smith and Smiles, 2004) (adapted from Jacques et al., 2012).

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The HP1-UCODE study was supplemented with information content (Hill and Tiedeman, 2007) and surface contour analyses. As illustrated in Figure 6, the parameters of the Gapon exchange approach were better identifiable as compared to the parameters of the Rothmund-Kornfeld approach. Several parameters in the latter approach showed strong correlations. We refer to Jacques et al. (2012) for details. 4

1.5

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1 N CaNa

log KRK CaNa

Log KGCa

3 1

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-1

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Figure 6. Contour plots of the objective function for (left) the exchange coefficient of K and Ca in the Gapon approach (KGK and KGCa), (middle) the exchange constant between K and Na (KRKKNa), and between Ca and Na (KRKCaNa) in the Rothmund-Kornfeld approach, and (right) the exchange constant (KRKCaNa) and the nonlinear coefficient (NCaNa) for exchange between Ca and Na in the Rothmund-Kornfeld approach (adopted from Jacques et al., 2012).

3.3. Coupling Between Geochemical Variables and Transport Properties A useful new feature recently included in HP1 is an option to change the hydraulic and solute transport properties as a function of evolving geochemical state variables. HP1 makes it possible to account for changes in (i) the porosity (and hence the saturated water content), (ii) the hydraulic conductivity, (iii) a scaling factor for the pressure head, (iv) aqueous and gaseous phase pore geometry factors for calculating pore diffusion coefficients, (v) the dispersivity, (vi) the thermal capacity, (vii) the thermal conductivity, and (viii) the thermal dispersivity. HP1 does not provide any pre-defined conceptual or mathematical model to update the flow and transport parameters, but uses the flexibility of the embedded BASIC interpreter for this purpose. This permits users to define any user-specific relationship between the geochemical state variables and the transport properties. A typical example, illustrated in Figure 7, is diffusive leaching from a porous medium in contact with more or less aggressive water. The example concerns leaching of a small concrete beam in contact with three types of water as indicated in the top part of Figure 7: (i) Rain W (wet deposition only), (ii) Rain B (wet and bulk deposition), which has higher ion concentrations, and (iii) Soil water with a higher inorganic carbon content as a result of soil microbiological processes. In terms of concrete performance, the soil water type should be the most detrimental since portlandite (Ca(OH)2) dissolution proceeds rapidly due to leaching and carbonation (i.e., portlandite dissolution followed by calcite precipitation as show by Jacques et al. (2010)). At the same time, chemical dissolution of portlandite and precipitation of calcite change the physical properties such as porosity and tortuosity (e.g., Perko et al., 2010; Jacques et al., 2011).

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Water flux Solute diffusive flux Concrete

1.6

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Rain W - 300 y Rain W - 600 y Rain B - 300 y Rain B - 600 y Soil - 300 y Soil - 600 y

1.2 0.8

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Figure 7. Example showing the effect of coupling transport parameters to geochemical variables. Results are for diffusive leaching of a small concrete beam. Shown are profiles of portlandite (top left), calcite (top right), porosity (bottom left), and the tortuosity factor (bottom right) as a function of the Boltzmann transform λ for three different water types and two different times.

Since calcite has a slightly larger molar volume than portlandite, porosity and tortuosity should decrease if calcite precipitation leads to pore blockage without generation of internal stresses and subsequent fracturing. Some of these processes are clearly evident from the results in Figure 7. The portlandite profiles as a function of the Boltzmann transform (which should collapse to a single curve in case of pure diffusive transport) are different among the three water types. In particular, the portlandite dissolution front has progressed slightly further for water with a presumably less aggressive solution composition (Rain W). On the other hand, enhanced calcite precipitation in the soil water case causes pore clogging and a strong reduction in the tortuosity and the diffusion coefficient. As a result, the portlandite dissolution front is retarded compared to the dissolution fronts when concrete is leached with the other two water compositions. A porosity decrease is also simulated for the Rain B case, mainly due to precipitation of Mgbearing minerals.

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References

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