Reactive transport modeling is an important approach to understand water dynamics, mass transport and biogeochemical processes from the hillslope to the catchment scale. It has a wide range of applications in the fields of e.g. water resource management, contaminanted site remediation and geotechnical engineering. To simulate reactive transport processes at a hillslope or larger scales is a challenging task, which involves interactions of complex physical and biogeochemical processes, huge computational expenses as well as difficulties in numerical precision and stability. The primary goal of the work is to develop a practical, accurate and efficient tool to facilitate the simulation techniques for reactive transport problems towards hillslope or larger scales. The first part of the work deals with the simulation of water flow in saturated and unsaturated porous media. The capability and accuracy of different numerical approaches were analyzed and compared by using benchmark tests. The second part of the work introduces the coupling of the scientific software packages OpenGeoSys and IPhreeqc by using a character-string-based interface. The accuracy and computational efficiency of the coupled tool were discussed based on three benchmarks. It shows that OGS#IPhreeqc provides sufficient numerical accuracy to simulate reactive transport problems for both equilibrium and kinetic reactions in variably saturated porous media. The third part of the work describes the algorithm of a parallelization scheme using MPI (Message Passing Interface) grouping concept, which enables a flexible allocation of computational resources for calculating geochemical reaction and the physical processes such as groundwater flow and transport. The parallel performance of the approach was tested by three examples. It shows that the new approach has more advantages than the conventional ones for the calculation of geochemically-dominated problems, especially when only limited benefit can be obtained through parallelization for solving flow or solute transport. The comparison between the character-string-based and the file-based coupling shows, that the former approach produces less computational overhead in a distributed-memory system such as a computing cluster. The last part of the work shows the application of OGS#IPhreeqc for the simulation of the water dynamic and denitrification process in the groundwater aquifer of a study site in Northern Germany. It demonstrates that OGS#IPhreeqc is able to simulate heterogeneous reactive transport problems at a hillslope scale within an acceptable time span. The model results shows the importance of functional zones for natural attenuation process. / Modellierung des reaktiven Stofftranports ist ein wichtiger Ansatz um die Wasserströmung, den Stofftransport und die biogeochemischen Prozesse von der Hang- bis zur Einzugsgebietsskala zu verstehen. Es gibt umfangreiche Anwendungsgebiete, z.B. in der Wasserwirtschaft, Umweltsanierung und Geotechnik. Die Simulation der reaktiven Stofftransportprozesse auf der Hangskala oder auf größeren Maßstäbe ist eine anspruchsvolle Aufgabe, da es sich um die Wechselwirkungen komplexer physikalischer und biogeochemischen Prozesse handelt, die riesigen Berechnungsaufwand sowie numerischen Schwierigkeiten bezogen auf die Genauigkeit und die Stabilität nach sich ziehen. Das Hauptziel dieser Arbeit besteht darin, ein praktisches, genaues und effizientes Werkzeug zu entwickeln, um die Simulationstechnik für reaktiven Stofftransport auf der Hangskala und auf größeren Skalen zu verbessern. Der erste Teil der Arbeit behandelt die Simulation der Wasserströmung in gesättigten und ungesättigten porösen Medien. Das Anwendungspotential und die Genauigkeit verschiedener numerischer Ansätze wurden mittels einiger Benchmarks analysiert und miteinander verglichen. Der zweite Teil der Arbeit stellt die Kopplung der wissenschaftlichen Softwarepakete OpenGeoSys und IPhreeqc mit einer stringbasierten Schnittstelle dar. Die Genauigkeit und die Recheneffizienz des gekoppelten Tools OGS#IPhreeqc wurden basierend auf drei Benchmark-Tests diskutiert. Das Ergebnis zeigt, dass OGS#IPhreeqc die ausreichende numerische Genauigkeit für die Simulation reaktiven Stofftransports liefert, welcher sich sowohl auf die Gleichgewichtsreaktion als auch auf die kinetische Reaktion in variabel gesättigten porösen Medien beziehen. Der dritte Teil der Arbeit beschreibt zuerst den Algorithmus der Parallelisierung des OGS#IPhreeqc basierend auf dem MPI (Message Passing Interface) Gruppierungskonzept, welcher eine flexible Verteilung der Rechenressourcen für die Berechnung der geochemischen Reaktion und der physikalischen Prozesse wie z.B. Wasserströmung oder Stofftransport ermöglicht. Danach wurde die Leistungsfähigkeit des Algorithmus anhand von drei Beispielen getestet. Es zeigt sich, dass der neue Ansatz Vorteile gegenüber die konventionellen Ansätzen für die Berechnung von geochemisch dominierten Problemen bringt. Dies ist vor allem dann der Fall, wenn nur eingeschränkter Nutzen aus der Parallelisierung für die Berechnung der Wasserströmung oder des Stofftransportes gezogen werden kann. Der Vergleich zwischen der string- und der dateibasierten Kopplung zeigt, dass die erstere weniger Rechenoverhead in einem verteilten Rechnersystem, wie z.B. Cluster erzeugt. Der letzte Teil der Arbeit zeigt die Anwendung von OGS#IPhreeqc für die Simulation der Wasserdynamik und der Denitrifikation im Grundwasserleiter eines Untersuchungsgebietes in NordDeutschland. Es beweist, dass OGS#IPhreeqc in der Lage ist, reaktiven Stofftransport auf der Hangskala innerhalb akzeptabler Zeitspanne zu simulieren. Die Simulationsergebnisse zeigen die Bedeutung der funktionalen Zonen für die natürlichen Selbstreinigungsprozesse.

Pressure solution creep is a fundamental deformation mechanism in the upper crust. Overburden pressure that acts upon layers of sediment leaves grains densely packed. Nonhydrostatic stress distributed over the contacts between grains brings an enhancement effect on surface dissolution. As surface retreat over the contacts and hence grain repacking squeeze out pore water in the voids, the layers of sediment are deformed to become denser and denser. This work aims to identify what process slows down pressure solution creep over time. For this purpose, a new mechanistic model of pressure solution creep is developed, derived from the reaction rate law for nonhydrostatic dissolution kinetics under the hypothesis of a closed system. The present mechanistic model shows that (1) the creep rate goes down as a combined consequence of stress transfer across expanding contacts and concentration build-up in the interlayer of absorbed water; and (2) solute migration process acts as the primary rate-limiting process of pressure solution creep in the long run. This work then focuses on hydraulic evolution of channelling flow through a single deformable fracture which is simultaneously subjected to pressure solution creep. The developed 1-D reactive transport model is allowed to capture the strong interaction between channelling flow and pressure solution creep under crustal conditions. This numerical investigation provides a justified interpretation for the unusual experimental observation that fracture permeability reduction does not necessarily cause concentration enrichment. Temperature elevation contributes to accelerating the progression of pressure solution creep.

Doctor of Philosophy / Department of Civil Engineering / David R. Steward / Groundwater contamination with arsenic (As), a naturally occurring metalloid, is a worldwide problem. Over 100 million people are at health risk due to arsenic contaminated groundwater, especially in the Bengal Basin in south-east Asia. Dissolved organic matter (DOM), geology and geomicrobiology are important factors affecting arsenic mobility. This study focuses on interactions of different aspects of natural organic matter in arsenic-contaminated environments. A literature review specifically includes past studies done on fundamentals of arsenic geology, geomicrobiology, DOM characterization and relevant analytical methods and tools. Based on background information already collected, this research is focused on specific research questions and corresponding hypotheses. The overarching goal of this investigation is to better understand the mechanisms by which DOM influences arsenic mobilization. The specific goals of this research are: 1) to evaluate role of oxidized humic quinones in reductive dissolution of Fe-As minerals and subsequent arsenic mobilization via electron shuttling, 2) to quantify the rate of microbially mediated reductive dissolution in the presence of oxidized humic quinones, 3) to evaluate DOM-Fe-As ternary complex formation and its influence on arsenic mobility and 4) to characterize DOM in the arsenic-contaminated aquifers of West Bengal, India and evaluate its role in arsenic mobilization using groundwater flow and contaminant transport modeling approach. Results of this study revealed that oxidized quinone like moieties (such as fulvic acids) serve as an electron shuttle and enhance the reductive dissolution process under reducing conditions, hence mobilize the arsenic in groundwater. Another key result from this study suggested that arsenic binds with non-aromatic portion of the humic-like DOM under reducing conditions and increases its solution concentration. A field study conducted in West Bengal, India revealed that the mechanisms studied in the laboratory exists in reducing aquifer. A groundwater flow and reactive transport model was created to explain multiple interactions of DOM and arsenic spatial scales. Broader impacts of this study include significant addition to scientific knowledge about subsurface biogeochemistry and the role of DOM in biogeochemical reactions in the subsurface.

Reactive Transport Models (RTMs) provide quantitative tools to analyze the interaction between transport and biogeochemical processes in subsurface environments such as aquatic sediments and groundwater flow. A tremendous amount of research has shown the role and impact of scaling behavior of the reactive systems which stems from geologic heterogeneity. Depending on the kinetics of the reactions, different types of formulations have been proposed to describe reactions in RTMs. We introduce a novel quantitative criteria on the range of validity of local equilibrium assumption (LEA) in aquatic sediments with irreversible heterogeneous sorption reactions. Then we present a one-dimensional (1-D) early diagenetic module, MATSEDLAB, developed in MATLAB. The module provides templates for representing the reaction network, boundary conditions and transport regime, which the user can modify to fit the particular early diagenetic model configuration of interest. We describe the theoretical background of the model and introduce the MATLAB pdepe solver, followed by calibration and validation of the model by a number of theoretical and empirical applications. Finally, we introduce a new pore-scale model using lattice Boltzmann (LB) approach. It uses an iterative scheme for the chemical transport-reaction part and recent advances in the development of optimal advection-diffusion solvers within the lattice Boltzmann method framework. We present results for the dissolution and precipitation of a porous medium under different dynamical conditions, varying reaction rates and the ratio of advective to diffusive transport (Pe, Peclet number) for linear reactions. The final set of calculations considers sorption reactions on a heterogeneous porous medium. We use our model to investigate the effect of heterogeneity on the pore-scale distribution of sorption sites and the competition between three different sorption reactions.

Contaminate transport in vadose is a huge concern since the vadose zone is the main passage way for ground water recharge. Understanding this process is crucial in order to prevent contamination, protect and rehabilitate ground water resources. Reactive transport models are instrumental for such purposes and there are numerous solute transport simulation programs for both ground water and vadose zone but most of this models are limited to simple Linear, Langmuir and Freundlich sorption models and first order decay and fail to simulate more complex geochemical reactions that are common in the vadose zone such as cation exchange, surface complexation, redox reaction and biodegradation. So it is necessary to enhance capabilities of solute transport models by incorporating well tested hydrogeochemical models like PHREEQC in to them to be able closely approximate the geochemical transport process in the subsurface. In this PhD research a new reactive transport model called VS2DRT was created by coupling existing public domain solute and heat transport models VS2DT, VS2DH with hydro-chemical model PHREEQC using non-iterative operator splitting technique. VS2DRT was compiled using MinGW compiler using tools like autotools and automake. A graphical user interface was also created using QT creator and Argus ONE numerical development tools. The new model was tested for one dimensional conservative Cl transport, surface complexation, cation exchange, dissolution of calcite and gypsum, heat and solute transport as well as for two dimensional cation exchange cases. Their results were compared with VS2DT, VS2DH, HP1 and HP2 models and the results are in good agreement.

Reactive transport modeling is an important approach to understand water dynamics, mass transport and biogeochemical processes from the hillslope to the catchment scale. It has a wide range of applications in the fields of e.g. water resource management, contaminanted site remediation and geotechnical engineering. To simulate reactive transport processes at a hillslope or larger scales is a challenging task, which involves interactions of complex physical and biogeochemical processes, huge computational expenses as well as difficulties in numerical precision and stability. The primary goal of the work is to develop a practical, accurate and efficient tool to facilitate the simulation techniques for reactive transport problems towards hillslope or larger scales. The first part of the work deals with the simulation of water flow in saturated and unsaturated porous media. The capability and accuracy of different numerical approaches were analyzed and compared by using benchmark tests. The second part of the work introduces the coupling of the scientific software packages OpenGeoSys and IPhreeqc by using a character-string-based interface. The accuracy and computational efficiency of the coupled tool were discussed based on three benchmarks. It shows that OGS#IPhreeqc provides sufficient numerical accuracy to simulate reactive transport problems for both equilibrium and kinetic reactions in variably saturated porous media. The third part of the work describes the algorithm of a parallelization scheme using MPI (Message Passing Interface) grouping concept, which enables a flexible allocation of computational resources for calculating geochemical reaction and the physical processes such as groundwater flow and transport. The parallel performance of the approach was tested by three examples. It shows that the new approach has more advantages than the conventional ones for the calculation of geochemically-dominated problems, especially when only limited benefit can be obtained through parallelization for solving flow or solute transport. The comparison between the character-string-based and the file-based coupling shows, that the former approach produces less computational overhead in a distributed-memory system such as a computing cluster. The last part of the work shows the application of OGS#IPhreeqc for the simulation of the water dynamic and denitrification process in the groundwater aquifer of a study site in Northern Germany. It demonstrates that OGS#IPhreeqc is able to simulate heterogeneous reactive transport problems at a hillslope scale within an acceptable time span. The model results shows the importance of functional zones for natural attenuation process. / Modellierung des reaktiven Stofftranports ist ein wichtiger Ansatz um die Wasserströmung, den Stofftransport und die biogeochemischen Prozesse von der Hang- bis zur Einzugsgebietsskala zu verstehen. Es gibt umfangreiche Anwendungsgebiete, z.B. in der Wasserwirtschaft, Umweltsanierung und Geotechnik. Die Simulation der reaktiven Stofftransportprozesse auf der Hangskala oder auf größeren Maßstäbe ist eine anspruchsvolle Aufgabe, da es sich um die Wechselwirkungen komplexer physikalischer und biogeochemischen Prozesse handelt, die riesigen Berechnungsaufwand sowie numerischen Schwierigkeiten bezogen auf die Genauigkeit und die Stabilität nach sich ziehen. Das Hauptziel dieser Arbeit besteht darin, ein praktisches, genaues und effizientes Werkzeug zu entwickeln, um die Simulationstechnik für reaktiven Stofftransport auf der Hangskala und auf größeren Skalen zu verbessern. Der erste Teil der Arbeit behandelt die Simulation der Wasserströmung in gesättigten und ungesättigten porösen Medien. Das Anwendungspotential und die Genauigkeit verschiedener numerischer Ansätze wurden mittels einiger Benchmarks analysiert und miteinander verglichen. Der zweite Teil der Arbeit stellt die Kopplung der wissenschaftlichen Softwarepakete OpenGeoSys und IPhreeqc mit einer stringbasierten Schnittstelle dar. Die Genauigkeit und die Recheneffizienz des gekoppelten Tools OGS#IPhreeqc wurden basierend auf drei Benchmark-Tests diskutiert. Das Ergebnis zeigt, dass OGS#IPhreeqc die ausreichende numerische Genauigkeit für die Simulation reaktiven Stofftransports liefert, welcher sich sowohl auf die Gleichgewichtsreaktion als auch auf die kinetische Reaktion in variabel gesättigten porösen Medien beziehen. Der dritte Teil der Arbeit beschreibt zuerst den Algorithmus der Parallelisierung des OGS#IPhreeqc basierend auf dem MPI (Message Passing Interface) Gruppierungskonzept, welcher eine flexible Verteilung der Rechenressourcen für die Berechnung der geochemischen Reaktion und der physikalischen Prozesse wie z.B. Wasserströmung oder Stofftransport ermöglicht. Danach wurde die Leistungsfähigkeit des Algorithmus anhand von drei Beispielen getestet. Es zeigt sich, dass der neue Ansatz Vorteile gegenüber die konventionellen Ansätzen für die Berechnung von geochemisch dominierten Problemen bringt. Dies ist vor allem dann der Fall, wenn nur eingeschränkter Nutzen aus der Parallelisierung für die Berechnung der Wasserströmung oder des Stofftransportes gezogen werden kann. Der Vergleich zwischen der string- und der dateibasierten Kopplung zeigt, dass die erstere weniger Rechenoverhead in einem verteilten Rechnersystem, wie z.B. Cluster erzeugt. Der letzte Teil der Arbeit zeigt die Anwendung von OGS#IPhreeqc für die Simulation der Wasserdynamik und der Denitrifikation im Grundwasserleiter eines Untersuchungsgebietes in NordDeutschland. Es beweist, dass OGS#IPhreeqc in der Lage ist, reaktiven Stofftransport auf der Hangskala innerhalb akzeptabler Zeitspanne zu simulieren. Die Simulationsergebnisse zeigen die Bedeutung der funktionalen Zonen für die natürlichen Selbstreinigungsprozesse.

The efficiency to improve the water quality of industrial and municipal wastewater in a constructed wetland/filter basin treatment system was investigated. The wetland system was constructed in a closed phosphate mine used for clay settling and sand tailings in Polk County, Florida. During 18-months of monitoring the chemical/microbiological composition of treated wetland water remained relatively constant, despite significant seasonal variations in temperature, rainfall and humidity. The following changes in water quality between input and output were observed: substantial decrease of water temperature (up to 10°C), reduction of As, SO4, F, Cl, NO3, NO2, Br, Na, K, Ca, and Mg, change in pH from 9 to 6.5-7, increase of H2S (up to 1060 micrograms/L), and a change from positive to negative ORP. There were no exceedances of the primary drinking water standards, volatile organic compounds, synthetic organic compounds, and radionuclides, but a number of exceedances for the secondary drinking water standards (Al, F, Fe, Mn, color, odor, total dissolved solids, and foaming agents). The concentration of fecal and total coliform bacteria in the wetland water was high, but subsequently reduced during filtration in the filter basin from 30 - 730 and 1000 - 7000 count/100 mL to < 2 and < 100 count/ 100 mL, respectively. To resolve the complex hydrogeological conditions a combined isotope/chemical mass-balance approach was applied. The results were the following: (1) the composition of water in the wetland varied throughout the period of the study; (2) a change in isotopic composition along the wetland flow path; (3) the wetland contained mainly wastewater (88 - 100 %) during normal pumping operations; however, hurricanes and inconsistent pumping added low conductivity water directly and triggered enhanced groundwater inflow into the wetland of up to 78 %; (4) the composition of water in monitor wells was mostly groundwater dominated; however periodically seepage from a water body to the north was detected; and (5) seepage from adjacent water bodies into the wetland was not identified during operation, which would indicate a potential water loss from the wetland. To test if the wetland system could be a prospective pre-treatment option for water used in aquifer storage and recovery (ASR) scenarios, a set of bench-scale leaching experiments was carried out using rocks from the Avon Park Formation, the Suwannee Limestone and the Ocala Limestone. Since As in the Floridan Aquifer was mainly present as an impurity in the mineral pyrite the elevated iron and sulfide concentrations in the wetland water were thought to prevent pyrite dissolution. The experiments which covered a range of redox conditions showed that the amount of As released from the aquifer matrix was not perfectly correlated with the bulk rock As concentration, nor the redox state of the water. The following important results were obtained: (1) the highest concentration of As was leached from the Avon Park Formation and the lowest - from the Suwannee Limestone, although the Ocala Limestone had the lowest bulk rock As; (2) minor to no As was released using native Floridan groundwater; (3) Tampa tap water, which chemically and physically resembled the ASR injection water, caused the As leaching of up to 27 micrograms/L, which was higher than the As drinking water standard; (4) the wetland and filter basin waters caused the highest release of As (up to 68 micrograms/L), which was unexpected because those water types were less oxygenated than Tampa tap water and thus should be less aggressive; (5) the in-situ filtration of the wetland water through a 0.2 micrometer membrane resulted in a reduction of As from 30 microgram/L to 16 microgram/L; and (5) the UV treatment significantly reduced both fecal and total coliform bacteria, but facilitated the increase of DO in initial waters, a change from negative to positive ORP, and the increase of As concentration in leachates. The experiments confirmed that perturbations of native aquifer conditions caused the release of As from the Floridan aquifer matrix, although the reaction may not be as simple as the dissolution of pyrite by oxygen, but additionally governed by a complex set of factors including the ORP of the system, SO4²?/S², Fe³?/Fe²?, dissolved organic carbon and microbial activity. In addition, the trend of As leaching could be governed by a set of factors, such as the porosity and permeability of the aquifer matrix influencing the rate and degree of free water saturation, amount of pyrite to be exposed to the preferential water flow paths, limited surface reactivity of pyrite with favored reactions on fractured mineral surfaces, the concentration and the selective leaching of As from individual pyrite crystals. To characterize and verify the geochemical processes in the column experiments, the Geochemist's Workbench reactive transport models (React and X1t) were developed. Results from the models correlated well to those from the column experiments and confirmed the following: (1) the water-rock reaction between the aquifer matrix and native groundwater was favorable for pyrite stability preventing the release of As into solution; (2) the injection of oxidizing surface water into reducing native groundwater caused a change in redox potential of the system thus promoting the dissolution of pyrite, and (3) 1D reactive transport model of water-rock reaction between the aquifer matrix and surface water indicated a diverse behavior of As along the column, such as the oxidative dissolution of pyrite, mobilization and simultaneous sorption of As onto neo-formed HFO, followed by the reductive dissolution of HFO and secondary release of adsorbed As, and the potential non-oxidative dissolution of pyrite contributing the additional source of As to the solution.

L’eau des circuits d’une centrale nucléaire est purifiée à l’aide de résines échangeuses d’ions. La prédiction de leurs performances constitue une aide importante pour l’exploitation de ces réacteurs. Les méthodes du transport réactif sont particulièrement adaptées pour cela et constituent la base du code OPTIPUR, dédié à la modélisation de ces résines. Le travail présenté comporte trois axes principaux. Le premier est l’intégration d’une limitation au transfert de masse dans une colonne de résines échangeuses d’ions, avec une mobilité spécifique à chaque espèce chimique, dans le cadre d’un découplage des calculs de chimie et de transport. Ce modèle permet, sans paramètre ajustable, de reproduire assez fidèlement une série d’expériences réalisées précédemment par le CEA. Le second axe concerne les aspects numériques du transport réactif, avec l’utilisation de la méthode d’Anderson pour accélérer la convergence du couplage chimie-transport dans un schéma itératif. En utilisant les informations issues des itérations précédentes et sans modification majeure du code, la robustesse et les temps de calcul ont pu être nettement améliorés. La troisième thématique abordée est celle de l’équilibre d’échange d’ions. Les bases d’un modèle prenant en considération l’évolution de l’humidité de la résine, ainsi que son élasticité sont proposées ; les interactions entre groupes fonctionnels, contre-ions et eau sont considérées comme des équilibres chimiques. Les constantes d’équilibre sont ajustées à partir de mesures de la teneur en eau de la résine à différentes pressions de vapeur d’eau. Finalement, des coefficients de sélectivité apparents peuvent être calculés et comparés aux mesures disponibles. / In nuclear power plants, the water contained in different circuits is purified by passing through ion exchange resins. Prediction of the performance of these resins is an important help to the plant operators. To this end, the method of reactive transport modeling are well suited and is the basis of the OPTIPUR code that was designed to model the resins. The work presented in this manuscript covers three main aspects. The first one is the integration of a limitation to mass transfer in a ion exchange deep bed, taking into account a specific mobility for each chemical species, in the context of separated calculations for chemistry and transport. This model was shown to reproduce experimental data, without adjustable parameters. The second part of this work deals with the numerical aspects of reactive transport modelling. A method developped by Anderson was used to accelerate the convergence of the chemistry transport coupling in an iterative scheme. Using the information from previous iterations, and without major changes in the code, calculation times were largely decreased, as well as the number of calculations failures. The third topic is ion exchange equilibrium. The basis of a model that takes into account the change in the water content of the resin and its elasticity are described. The interactions between the fonctional groups, the counterions and water are considered as chemical reactions. The corresponding equilibrium constants are fitted to measurements of the water content of the resin at different relative humidity. Finaly, the selectivity coefficients can be calculated and compared to litterature values.

No description available.

The transport of contaminants in groundwater system is strongly influenced by various aquifer heterogeneity factors such as spatial aquifer heterogeneity of hydraulic conductivity and reactive substances distribution. The contaminants transport can be simulated by using numerical reactive transport models, and their fate can be possibly even predicted. Furthermore, reactive transport modeling is an essential tool to get a profound understanding of hydrological-geochemical complex processes and to make plausible predictions of assessment. The goal of this work is to improve our understanding of the groundwater contaminants fate and transport processes in heterogeneous aquifer systems, with a focus on nitrate problems. A large body of knowledge of the fate and transport of nitrogen species has been achieved by previous works, however, most previous models typically neglect the interrelation of physical and chemical aquifer heterogeneities on the contaminant fate and redox transformation, which is required for predicting the movement and behavior of nitrate and quantifying the impact of uncertainty of numerical groundwater simulation, and which motivates this study. The main research questions which are answered in this work are how aquifer heterogeneity influences on the nitrate fate and transport and then, what is the most influential aquifer heterogeneity factor must be considered. Among the various type of aquifer heterogeneity, physical and chemical aquifer heterogeneities are considered. The first part of the work describes groundwater flow system and hydrochemical characteristics of the study area (Hessian Ried, Germany). Especially, data analyses are performed with the hydrochemical data to identify the major driving force for nitrate reduction in the study area. The second part of the work introduces a kinetic model describing nitrate removal by using numerical simulation. The resulting model reproduces nitrate reduction processes and captures the sequence of redox reactions. The third and fourth parts show the influence of physical and chemical aquifer heterogeneity with varying variance, correlation length scale, and anisotropy ratio. Heterogeneous aquifer systems are realized by using stochastic approach. Results, in short, show that the most influential aquifer heterogeneity factors could change over time. With abundant requisite electron donors, physical aquifer heterogeneity significantly influences the nitrate reduction while chemical aquifer heterogeneity plays a minor role. Increasing the spatial variability of the hydraulic conductivity increases the nitrate removal efficiency of the system in addition. If these conditions are reversed, nitrate removal efficiency varies by the spatial heterogeneity of the available initial electron donor. The results indicate that an appropriate characterization of the physical and chemical properties can be of significant importance to predict redox contamination transport and design long-term remediation strategies and risk assessment.