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    Diederik Jacques

    ... The LLNL-database (ie Lawrence Livermore National Laboratory-database) incorporated in PHREEQC was the thermodynamic database used to determine the ... 4. K. Lemmens, M. Aertsens, P. Lolivier, N. Malangreau, V. Pirlet, P. De Cannière... more
    ... The LLNL-database (ie Lawrence Livermore National Laboratory-database) incorporated in PHREEQC was the thermodynamic database used to determine the ... 4. K. Lemmens, M. Aertsens, P. Lolivier, N. Malangreau, V. Pirlet, P. De Cannière and P. Van Iseghem, SCK•CEN, R ...
    The objective of this study was to include the nutrient uptake deficiency stress in the generic multicomponent transport model, HP1 (the geochemical code PHREEQC coupled to the transient water and solute transport model HYDRUS-1D). The... more
    The objective of this study was to include the nutrient uptake deficiency stress in the generic multicomponent transport model, HP1 (the geochemical code PHREEQC coupled to the transient water and solute transport model HYDRUS-1D). The first step was the incorporation of a combined passive-active root nutrient uptake model in HP1 (Jacques et al., 2006). The nutrient uptake model is based on the model of Silberbush et al. (2005). For example, Ca is taken up by passive and active processes, in which the parameters of the Michaelis-Menten active uptake model depend on the solution chemistry. Simulations were compared with experimental data from four irrigation treatments with different Na(-Cl) concentrations. The results are a preliminary attempt to predict uptake of different ions under varying conditions of salinity. Results for Na and K are promising.
    In this study we provide an analysis of the subsurface transport of radionuclides released from phosphogypsum (PG) when used as a fertilizer or amendment in agriculture. PG (dihydrated calcium sulfate), a residue of the phosphate... more
    In this study we provide an analysis of the subsurface transport of radionuclides released from phosphogypsum (PG) when used as a fertilizer or amendment in agriculture. PG (dihydrated calcium sulfate), a residue of the phosphate fertilizer industry, can contain relatively high amounts of impurities from the host rock, including heavy metals and radionuclides such as 238U and especially 226Ra. It is important to assess the environmental risks caused by the long- term use of PG in agricultural operations. The natural uranium and thorium decay chains in the phosphate host rock are in equilibrium. During the phosphate production process, however, this equilibrium is disrupted and radionuclides migrate to both the fertilizer (especially 238U and 234U) and phosphogypsum (226Ra and 210Pb). Our study focused on the transport of 226Ra when PG is applied annually to a typical soil profile in the Brazilian Cerrado. Expected water flow and solute transport processes were estimated first using ...
    Within the scope of the SNOWMAN network, a study was performed on the fate and transport of mercury in soil systems in order to improve characterization and remediation. This report summarizes the main findings with respect to (i)... more
    Within the scope of the SNOWMAN network, a study was performed on the fate and transport of mercury in soil systems in order to improve characterization and remediation. This report summarizes the main findings with respect to (i) enhanced knowledge on mercury fate leading to a reactive transport model, (ii) best practices in mercury characterization, (iii) state-of-the art risk assessment, and (iv) current practices in site remediation
    Research Interests:
    ABSTRACT Nonequilibrium surface complexation reactions have been found to substantially affect U(VI) transport in natural porous media both in laboratory and field scale experiments. Nonequilibrium sorption behavior occurs on multiple... more
    ABSTRACT Nonequilibrium surface complexation reactions have been found to substantially affect U(VI) transport in natural porous media both in laboratory and field scale experiments. Nonequilibrium sorption behavior occurs on multiple time scales and is a result of diffusion-limited transport in immobile intra-grain and intra-aggregate pore water. Experimental data on U(VI) transport was success- fully described with a recently developed reactive transport model that accounted for the nonequilibrium adsorption processes through the formulation of a multi-rate sur- face complexation model treating surface complexation as kinetic reactions. In the present work, a benchmark problem set has been developed for testing existing or newly devel- oped reactive transport codes on their capability to simulate multi-rate surface complexation and dual-domain multi- component reactive transport of U(VI). The benchmark problem consists of three individual component problems on the basis of previous studies investigating the desorption of U(VI) from radionuclide-contaminated sediment from the Hanford 300A site, Washington, USA. Starting with a single-domain model considering constant hydrochemical conditions (component problem 1), the complexity of the model was stepwise increased. In the component problem 2 dual-domain first-order mass transfer was added. The prin- cipal problem also included dual-domain mass-transfer, but was further extended for changing hydrochemical condi- tions in the column’s inflow water, which resulted in drastic changes in the U(VI) desorption pattern due to surface complexation reactions. For the three individual compo- nent problems, the corresponding simulation results agree very well among four well-known and thoroughly tested independent reactive transport codes, indicating that the proposed benchmark problem set is a suitable test case.
    ABSTRACT The use of the subsurface for CO2 storage, geo- thermal energy generation, and nuclear waste disposal will greatly increase the interaction between clay(stone) and concrete. The development of models describing the mineralogical... more
    ABSTRACT The use of the subsurface for CO2 storage, geo- thermal energy generation, and nuclear waste disposal will greatly increase the interaction between clay(stone) and concrete. The development of models describing the mineralogical transformations at this interface is complicated, because contrasting geochemical conditions (Eh, pH, solution composition, etc.) induce steep concentra- tion gradients and a high mineral reactivity. Due to the com- plexity of the problem, analytical solutions are not available to verify code accuracy, rendering code intercomparisons as the most efficient method for assessing code capabil- ities and for building confidence in the used model. A benchmark problem was established for tackling this issue. We summarize three scenarios with increasing geochemical complexity in this paper. The processes considered in the simulations are diffusion-controlled transport in saturated media under isothermal conditions, cation exchange reac- tions, and both local equilibrium and kinetically controlled mineral dissolution-precipitation reactions. No update of the pore diffusion coefficient as a function of porosity changes was considered. Seven international teams participated in this benchmarking exercise. The reactive transport codes used (TOUGHREACT, PHREEQC, with two different ways of handling transport, CRUNCH, HYTEC, ORCHESTRA, MIN3P-THCm) gave very similar patterns in terms of predicted solute concentrations and mineral distributions. Some differences linked to the considered activity models were observed, but they do not bias the general system evo- lution. The benchmarking exercise thus demonstrates that a reactive transport modelling specification for long-term performance assessment can be consistently addressed by multiple simulators.
    A general description of the mathematical and numerical formulations used in modern numerical reactive transport codes relevant for subsurface environmental simulations is presented. The formulations are followed by short descriptions of... more
    A general description of the mathematical and numerical formulations used in modern numerical reactive transport codes relevant for subsurface environmental simulations is presented. The formulations are followed by short descriptions of commonly used and available subsurface simulators that consider continuum representations of flow, transport, and reactions in porous media. These formulations are applicable to most of the subsurface environmental benchmark problems included in this special issue. The list of codes described briefly here includes PHREEQC, HPx, PHT3D, OpenGeoSys (OGS), HYTEC, ORCHESTRA, TOUGHREACT, eSTOMP, HYDROGEOCHEM, Crunch-Flow, MIN3P, and PFLOTRAN. The descriptions include a C. I. Steefel () · B. Arora · S. Molins · N. Spycher high-level list of capabilities for each of the codes, along with a selective list of applications that highlight their capabilities and historical development.
    Research Interests:
    ABSTRACT The HPx reactive transport codes were developed to simulate flow and transport processes in variablysaturated porous media subject to a variety of low-temperature geochemical processes. The codes combine the HYDRUS models for... more
    ABSTRACT The HPx reactive transport codes were developed to simulate flow and transport processes in variablysaturated 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.
    Numerical models are of precious help for predicting water fluxes in the vadose zone and more specifically in Soil-Vegetation-Atmosphere (SVA) systems. For such simulations, robust models and representative soil hydraulic parameters are... more
    Numerical models are of precious help for predicting water fluxes in the vadose zone and more specifically in Soil-Vegetation-Atmosphere (SVA) systems. For such simulations, robust models and representative soil hydraulic parameters are required. Calibration of unsaturated hydraulic properties is known to be a difficult optimization problem due to the high non-linearity of the water flow equations. Therefore, robust methods are needed to avoid the optimization process to lead to non-optimal parameters. Evolutionary algorithms and specifically genetic algorithms (GAs) are very well suited for those complex parameter optimization problems. Additionally, GAs offer the opportunity to assess the confidence in the hydraulic parameter estimations, because of the large number of model realizations. The SVA system in this study concerns a pine stand on a heterogeneous sandy soil (podzol) in the Campine region in the north of Belgium. Throughfall and other meteorological data and water contents at different soil depths have been recorded during one year at a daily time step in two lysimeters. The water table level, which is varying between 95 and 170 cm, has been recorded with intervals of 0.5 hour. The leaf area index was measured as well at some selected time moments during the year in order to evaluate the energy which reaches the soil and to deduce the potential evaporation. Water contents at several depths have been recorded. Based on the profile description, five soil layers have been distinguished in the podzol. Two models have been used for simulating water fluxes: (i) a mechanistic model, the HYDRUS-1D model, which solves the Richards' equation, and (ii) a compartmental model, which treats the soil profile as a bucket into which water flows until its maximum capacity is reached. A global sensitivity analysis (Morris' one-at-a-time sensitivity analysis) was run previously to the calibration, in order to check the sensitivity in the chosen parameter search space. For the inversion procedure a genetical algorithm (GA) was used. Specific features such as elitism, roulette-wheel process for selection operator and island theory were implemented. Optimization was based on the water content measurements recorded at several depths. Ten scenarios have been elaborated and applied on the two lysimeters in order to investigate the impact of the conceptual model in terms of processes description (mechanistic or compartmental) and geometry (number of horizons in the profile description) on the calibration accuracy. Calibration leads to a good agreement with the measured water contents. The most critical parameters for improving the goodness of fit are the number of horizons and the type of process description. Best fit are found for a mechanistic model with 5 horizons resulting in absolute differences between observed and simulated water contents less than 0.02 cm3cm-3 in average. Parameter estimate analysis shows that layers thicknesses are poorly constrained whereas hydraulic parameters are much well defined.
    ABSTRACT Leaching process of cement-based materials is relevant for the long-term durability of cement based barrier materials used in radioactive waste disposal systems. Ca leaching changes the properties by reducing the pH, increasing... more
    ABSTRACT Leaching process of cement-based materials is relevant for the long-term durability of cement based barrier materials used in radioactive waste disposal systems. Ca leaching changes the properties by reducing the pH, increasing the porosity which leads to the variation of transport properties. This process is extremely slow under environmental conditions. To accelerate the leaching kinetics, the use of ammonium nitrate (NH4NO3) solution becomes popular. The use of ammonium nitrate (NH4NO3) solution to accelerate the leaching kinetics has become popular because of the extremely slow nature of the degradation process under environmental condition. In this study, a one-dimensional diffusion-based transport model was proposed to simulate the leaching process of saturated hardened cement paste in contact with a NH4NO3 solution. The model helps to better understand the transient state of leaching which is difficult to be observed by experimental work. This model is based on macroscopic mass balances for Ca in aqueous and solid phases which are linked together by applying solid-liquid Ca equilibrium. The model only considers the leaching of portlandite and calcium silicate hydrates (C-S-H) which are the main hydrated phases in typical CEM I Ordinary Portland cement paste. The hydration during leaching is not taken into account in the model because of the limited time duration of the experiment. Besides the prediction of the leached depth, portlandite and C-S-H contents, and the amount of leached Ca, the model also enables to simulate the variation of water permeability over the domain at different immersion periods in NH4NO3 solution. The model is verified by accelerated leaching experiments in 6 mol/l NH4NO3 solution on CEM I cement paste samples. Preliminary verification with experimental results shows a good agreement.
    To model complex hydrological problems, realistic models and representative hydraulic properties are needed. In this study we investigate the ability of two different types of process description for water flow to quantify the water... more
    To model complex hydrological problems, realistic models and representative hydraulic properties are needed. In this study we investigate the ability of two different types of process description for water flow to quantify the water balance in a Soil-Vegetation-Atmosphere (SVA) system. A first model description is based on the Richards' equation for which the mechanistic numerical model HYDRUS-1D is used. The second model description is a compartment model assuming a bucket-type water flow process. We present calibrations of these two models performed for a SVA system developed in a podzol soil with Scots Pine vegetation. Due to a high non-linearity of the calibration problem, an efficient optimization technique is needed. Therefore a genetic algorithm, which belongs to the so-called evolutionary algorithms class, was used in this study. Aim of this work is both (i) calibrating the SVA system and (ii) testing abstraction techniques. Examples of both parameter and model structure abstraction will be presented. Calibrations of the soil hydraulic properties have been obtained using soil water content data collected at several depths with time domain reflectometry probes in two distinct lysimeters. All climatic data (throughfall and other meteorological data necessary for estimating the potential evaporation) and water contents at different soil depths have been recorded during one year at a daily time step in two lysimeters. The water table level, which is varying between 95 and 170 cm, has been recorded with intervals of 0.5 hour. The leaf area index was measured as well in order to evaluate the energy which reaches the soil and to deduce the potential evaporation. Ten scenarios have been elaborated and applied on the two lysimeters in order to investigate the impact of both the water balance process description (mechanistic or compartmental) and the number of horizons used for the profile description, on the calibration accuracy. Main results are that: (i) both model process descriptions are able to describe accurately the measured water contents at all depths when a high number of soil horizon was used, (ii) the mechanistic model performs better than the compartment model, (iii) the considered number of soil horizons is the major factor that controls the accuracy of the calibration. Finally, the compartment model is considered as an abstracted model from the reference model based on the mechanistic model. For instance, yearly drainage values predicted by both models are used to evaluate the performance of the abstracted model. It appears that drainages values simulated by the abstracted model were close to those of the reference model, provided that drainage values were averaged over a sufficiently large period (about 9 months). Therefore, this result suggests that values of drainage obtained with an abstracted model could be reliably simulated for sufficiently long time periods, with a significant gain in computational time compared to the mechanistic approach, and without an important loss of accuracy.
    To protect near surface disposal facilities from infiltrating rainfall a multi-layer cover is installed consisting of different materials including soil (usually sand- or loam-based) and clay. The function of such layers is to divert... more
    To protect near surface disposal facilities from infiltrating rainfall a multi-layer cover is installed consisting of different materials including soil (usually sand- or loam-based) and clay. The function of such layers is to divert infiltrating rainwater and hence minimize water drainage from the cover in the underlying disposal facility. However, the soil and clay materials will change the composition of the infiltrating water due to biogeochemical processes. A methodology is developed to assess changes in water composition as the rain water percolates through the soil and clay layers of a vegetated multi-layer cover. The method is based on a steady-state mass balance approach and uses generic soil physical and chemical properties. The approach considers weathering of the soil and clay minerals estimated from a pedotransfer function and accounts for the average temperature, the textural class and the depth of the profile. Soil microbiological activity is taken into account by imposing the soil partial pressure of CO2. The latter value is estimated from an empirical model based on the actual evapotranspiration. Eight scenarios were developed that resulted in eight different solution compositions of the drainage water. This approach resulted in a realistic pH range between 3.4 and 4.4 for the scenarios that consider either absence of all soil and clay layers (thus representing rain composition) or presence of a single soil layer only. Scenarios that considered both soil and clay layers to be present produced rather high pH values (around 9.5), probably due to too high estimates of the base cation weathering rates generated with the pedotransfer functions. Alternative methods for dealing with weathering of the clay layer are proposed. These types of water compositions were used to simulate the chemical degradation process of concrete as to produce a lower and upper bound to the durability of concrete engineered barriers.
    Coupling physical and biogeochemical processes within one integrated numerical simulator provides a process-based tool for investigating the fate of contaminants as affected by changing hydrologic regimes and geochemical conditions. The... more
    Coupling physical and biogeochemical processes within one integrated numerical simulator provides a process-based tool for investigating the fate of contaminants as affected by changing hydrologic regimes and geochemical conditions. The numerical simulator HP1 attempts to bridge these two interactive processes. The code is especially geared for variably-saturated conditions, thus serving as a powerful tool for vadose zone research and engineering applications. HP1 extends the capabilities of HYDRUS-1D to simulate physical soil processes by including the capabilities of PHREEQC to account for biogeochemical processes, all embedded in a user-friendly windows interface. The HP1 reactive transport simulator was obtained by weak, non-iterative coupling of HYDRUS-1D and PHREEQC-2. HP1 is free software and can be obtained at http://www.pc-progress.com as part of HYDRUS-1D. A detailed account is given of the new features and processes that were recently incorporated in HP1: (i) full implementation of HP1 into the graphical user interface of HYDRUS-1D, (ii) dynamic changes in porosity, permeability and tortuosity when minerals dissolve or precipitate, and (iii) diffusion of gas components in the gaseous phase. The implementation of the porosity-permeability-tortuosity changes was benchmarked against results from the MIN3P code. HP1 users can implement their own porosity-permeability and porosity-tortuosity relationships using BASIC statements in the input file. Additionally, hydraulic conductivity and pressure head scaling factors can now also vary with time depending upon the geochemical state variables. An example is further presented in which HP1 is coupled with the model-independent optimization tool UCODE_2005 (Poeter et al., 2005) . The resulting software allows thermodynamic, kinetic and geochemical parameters to be estimated from experimental data. The optimization features are illustrated for an experimental data set involving transient water flow, solute transport and cation exchange processes. References Poeter, E.P., M.C. Hill, E.R. Banta, S. Mehl, and C. Steen, 2005. UCODE_2005 and six other computer codes for universal sensitivity analysis, calibration and uncertainty evaluation. U.S. Geological Survey Techniques and Methods 6-A11.
    Research Interests:
    Model abstraction (MA) is a methodology for reducing the complexity of a simulation model while maintaining the validity of the simulation results with respect to the question that the simulation is being used to address. The need for MA... more
    Model abstraction (MA) is a methodology for reducing the complexity of a simulation model while maintaining the validity of the simulation results with respect to the question that the simulation is being used to address. The need for MA is recognized in simulations of complex systems where increased level of detail does not necessarily increase accuracy, but increases computational complexity,
    When a field or a small watershed is repeatedly surveyed for soil water content, sites often can be spotted where soil is consistently wetter or consistently dryer than average across the study area. The phenomenon has been called time... more
    When a field or a small watershed is repeatedly surveyed for soil water content, sites often can be spotted where soil is consistently wetter or consistently dryer than average across the study area. The phenomenon has been called time stability, temporal stability, or temporal persistence in spatial patterns of soil water contents. It was shown that such persistence can be used to optimize monitoring and upscaling of soil moisture. Relatively less is known about temporal persistence of water content at various depths in vadose zone. The objectives of this work are to demonstrate the temporal persistence in soil water contents measured on a vertical two-dimensional grid, and to propose a technique to utilize this persistence to monitor and upscale soil water content. Sixty TDR probes (two-rods) were installed along the trench in loamy soil at 12 locations with 50-cm horizontal spacing at 5 depths (15, 35, 55, 75, and 95 cm). Some probes at a given depth consistently showed water contents below average whereas others show water contents above the average. To quantify the persistence, we computed relative water contents as ratios of individual-probe water contents to average water contents from the same depth. The number of probes could be decreased and the soil water content could be upscaled much more efficiently because the variability ranges of relative water contents were narrow. A numerical experiment showed the efficiency of the proposed technique. Corrections for temporal persistence can be useful to improve estimates of layer-averaged water contents and their uncertainty.
    Research Interests:
    Simulations of soil water flow require measurements of soil hydraulic properties which are particularly difficult at field scale. Laboratory measurements provide hydraulic properties at scales finer than the field scale, whereas... more
    Simulations of soil water flow require measurements of soil hydraulic properties which are particularly difficult at field scale. Laboratory measurements provide hydraulic properties at scales finer than the field scale, whereas pedotransfer functions (PTFs) integrate information on hydraulic properties at larger scales. One way of downscaling large-scale data is to use an ensemble of PTFs to generate hydraulic properties with each of the PTFs and to obtain the ensemble prediction of soil water flow by averaging the simulations results obtained with individual PTFs. Alternatively, the prediction of field-scale soil water flow can be made with the average hydraulic properties obtained from the PTF ensemble. Similarly, the upscaling can be done using an ensemble of hydraulic properties along individual soil profiles to obtain ensemble prediction of soil water flow by averaging simulations results obtained for the individual profiles. Alternatively, the prediction of field-scale soil w...
    We used the recently developed HP1 coupled geochemical transport code to calculate U-fluxes to groundwater originating from application of inorganic P-fertilizers to an agricultural field. The HP1 code was found to be a very convenient... more
    We used the recently developed HP1 coupled geochemical transport code to calculate U-fluxes to groundwater originating from application of inorganic P-fertilizers to an agricultural field. The HP1 code was found to be a very convenient tool for studying interactions between water content and flow conditions, changes in pH, and retention of U. Results show that U will migrate considerable faster during transient flow conditions as compared to steady-state flow. A steady-state flow approach hence can only partially account for the various coupled physical and geochemical interactions in the vadose zone, whereas short-term variations involving considerable temporal variability require a transient model. Calculations of the radiological impact of U-containing groundwater demonstrate that the annual total dose owing to consumption of groundwater would not lead to values exceeding the natural background dose.
    The supercontainer in the concept of the Belgian geological disposal of high level radioactive waste produces a high pH plume in the Boom Clay. This studies assess both the extend of the alkaline plume perturbation and the effect of the... more
    The supercontainer in the concept of the Belgian geological disposal of high level radioactive waste produces a high pH plume in the Boom Clay. This studies assess both the extend of the alkaline plume perturbation and the effect of the Boom Clay pore water on the geochemical concrete properties. At the laboratory scale, long-term column experiments were modeled using a reactive transport model incorporating cation exchange reactions and surface complexation. Long term modeling at the scale of the geological disposal facility was also performed with the reactive transport model PHREEQC. Parameter and model sensitivity were tested with respect to the spatial extend of the alkaline perturbation. The disturbed zone is limited up to 2 m after 25000 y.
    The objective is on the implementation of a consistent thermodynamic database for cement systems at temperatures different from 25°C in geochemical computer codes based on mass action equation and constants (such as PHREEQC-2). The... more
    The objective is on the implementation of a consistent thermodynamic database for cement systems at temperatures different from 25°C in geochemical computer codes based on mass action equation and constants (such as PHREEQC-2). The implementation of the cement/concrete thermodynamic database was verified first by comparing simulations of chemical detrimental reactions in cement systems using PHREEQC-2 and GEMS. Verification was done for simplified cement systems followed by a further verification addressing complex geochemical simulations of by means of benchmark calculations. The thermodynamic database for cement systems is used in studies to simulate the long-term evolution of geochemical conditions in the concrete in a near-surface disposal facility.
    This is the PHREEQC format of the CEMDATA07 thermodynamic dataset orginally distributed in GEMS format. See: http://www.empa.ch/plugin/template/empa/*/62204/---/l=1
    While the methods involved in the measurement of the saturated hydraulic conductivity of soils are simple arid straightforward, the application of these methods in situ, particular in sloping fields, is often difficult, Unless the... more
    While the methods involved in the measurement of the saturated hydraulic conductivity of soils are simple arid straightforward, the application of these methods in situ, particular in sloping fields, is often difficult, Unless the researcher is thoroughly familiar with the method and the possible sources of error in the measurement, substantial errors can be produced. The foregoing. is illustrated by characterising the saturated hydraulic conductivity of a sloping Vertic Luv1so1,: having an average slope of 19% and an effective root depth of 0 72 m .. The following methods were used: the constant-head permearneter, the double rifrig infiltrometer, the inversed auger-hole technique and an inversed method based on the runoff and . subsurface outflow recorded during a field experiment with constant inflow and a 2-D finite element flow simulation model (HYDRUS-2D). The results of the different methods applièd were compared. The analysis revealed that: (i) local, small scale measurements...
    Cementitious binders are commonly used to solidify/stabilize hazardous wastes prior to disposal in multi-barrier engineered disposal facilities or landfills. Because they are not in equilibrium with other materials in a landfill,... more
    Cementitious binders are commonly used to solidify/stabilize hazardous wastes prior to disposal in multi-barrier engineered disposal facilities or landfills. Because they are not in equilibrium with other materials in a landfill, cementitious materials usually degrade with time. Reactive transport models may be used to estimate the possible effects of changing geochemical conditions on the transport properties of the cementitious materials, the leaching of chemotoxic elements from the waste form, and alterations of the sorption properties of surrounding materials due to leaching of cement components

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