Unlike municipal water supplies, provincial regulations do not require systematic testing of domestic well water, which may adversely impact local residents should contamination occur. Private wells are typically shallow relative to municipal wells, and thus, are particularly vulnerable to sources of surficial contamination if preferential recharge pathways such as natural fractures or faulty seals are present. In order to determine the relative importance of well seal integrity as a preferential pathway, a practical detection method was developed based on infiltrometry. This method successfully detected faulty well seals in a wide range of geological settings across Canada, including: Hobbema, Alberta; Lindsay, Ontario; and Chelsea, Québec. It was most successful in areas of minimal heterogeneity and where the surficial geology is composed of fine-grained sediments. The community of Chelsea (Québec) was also the primary study site to examine a range of factors affecting water quality including physical characteristics, faulty well seals, other anthropogenic activities and seasonality. Water samples were collected over a period of 14 months and analyzed for bacteria and major-ion chemistry. The results show that the consideration of physical features alone is not enough to predict vulnerability in the study area. Seasonal fluctuations in ionic concentrations (e.g. ionic strength, NO3-N and Cl-) and coliform bacteria are observed and result from disperse and rapid recharge events. Multivariate analysis techniques (e.g. principal components analysis and hierarchical cluster analysis) demonstrate that preferential recharge pathways and anthropogenic activities, such as domestic effluents affect the groundwater quality. The data and findings of this study were used to assist in the design of a probabilistic risk assessment model based on the Poisson distribution. This study demonstrates the complexity and the challenges related to bacterial contamination in drilled wells. In spite of these challenges, this analysis was useful as a baseline to assess the impact of anthropogenic activities, and may be used in future studies to assist municipalities in the evaluation and protection of groundwater supplies.

Unlike municipal water supplies, provincial regulations do not require systematic testing of domestic well water, which may adversely impact local residents should contamination occur. Private wells are typically shallow relative to municipal wells, and thus, are particularly vulnerable to sources of surficial contamination if preferential recharge pathways such as natural fractures or faulty seals are present. In order to determine the relative importance of well seal integrity as a preferential pathway, a practical detection method was developed based on infiltrometry. This method successfully detected faulty well seals in a wide range of geological settings across Canada, including: Hobbema, Alberta; Lindsay, Ontario; and Chelsea, Québec. It was most successful in areas of minimal heterogeneity and where the surficial geology is composed of fine-grained sediments. The community of Chelsea (Québec) was also the primary study site to examine a range of factors affecting water quality including physical characteristics, faulty well seals, other anthropogenic activities and seasonality. Water samples were collected over a period of 14 months and analyzed for bacteria and major-ion chemistry. The results show that the consideration of physical features alone is not enough to predict vulnerability in the study area. Seasonal fluctuations in ionic concentrations (e.g. ionic strength, NO3-N and Cl-) and coliform bacteria are observed and result from disperse and rapid recharge events. Multivariate analysis techniques (e.g. principal components analysis and hierarchical cluster analysis) demonstrate that preferential recharge pathways and anthropogenic activities, such as domestic effluents affect the groundwater quality. The data and findings of this study were used to assist in the design of a probabilistic risk assessment model based on the Poisson distribution. This study demonstrates the complexity and the challenges related to bacterial contamination in drilled wells. In spite of these challenges, this analysis was useful as a baseline to assess the impact of anthropogenic activities, and may be used in future studies to assist municipalities in the evaluation and protection of groundwater supplies.

Unlike municipal water supplies, provincial regulations do not require systematic testing of domestic well water, which may adversely impact local residents should contamination occur. Private wells are typically shallow relative to municipal wells, and thus, are particularly vulnerable to sources of surficial contamination if preferential recharge pathways such as natural fractures or faulty seals are present. In order to determine the relative importance of well seal integrity as a preferential pathway, a practical detection method was developed based on infiltrometry. This method successfully detected faulty well seals in a wide range of geological settings across Canada, including: Hobbema, Alberta; Lindsay, Ontario; and Chelsea, Québec. It was most successful in areas of minimal heterogeneity and where the surficial geology is composed of fine-grained sediments. The community of Chelsea (Québec) was also the primary study site to examine a range of factors affecting water quality including physical characteristics, faulty well seals, other anthropogenic activities and seasonality. Water samples were collected over a period of 14 months and analyzed for bacteria and major-ion chemistry. The results show that the consideration of physical features alone is not enough to predict vulnerability in the study area. Seasonal fluctuations in ionic concentrations (e.g. ionic strength, NO3-N and Cl-) and coliform bacteria are observed and result from disperse and rapid recharge events. Multivariate analysis techniques (e.g. principal components analysis and hierarchical cluster analysis) demonstrate that preferential recharge pathways and anthropogenic activities, such as domestic effluents affect the groundwater quality. The data and findings of this study were used to assist in the design of a probabilistic risk assessment model based on the Poisson distribution. This study demonstrates the complexity and the challenges related to bacterial contamination in drilled wells. In spite of these challenges, this analysis was useful as a baseline to assess the impact of anthropogenic activities, and may be used in future studies to assist municipalities in the evaluation and protection of groundwater supplies.

Unlike municipal water supplies, provincial regulations do not require systematic testing of domestic well water, which may adversely impact local residents should contamination occur. Private wells are typically shallow relative to municipal wells, and thus, are particularly vulnerable to sources of surficial contamination if preferential recharge pathways such as natural fractures or faulty seals are present. In order to determine the relative importance of well seal integrity as a preferential pathway, a practical detection method was developed based on infiltrometry. This method successfully detected faulty well seals in a wide range of geological settings across Canada, including: Hobbema, Alberta; Lindsay, Ontario; and Chelsea, Québec. It was most successful in areas of minimal heterogeneity and where the surficial geology is composed of fine-grained sediments. The community of Chelsea (Québec) was also the primary study site to examine a range of factors affecting water quality including physical characteristics, faulty well seals, other anthropogenic activities and seasonality. Water samples were collected over a period of 14 months and analyzed for bacteria and major-ion chemistry. The results show that the consideration of physical features alone is not enough to predict vulnerability in the study area. Seasonal fluctuations in ionic concentrations (e.g. ionic strength, NO3-N and Cl-) and coliform bacteria are observed and result from disperse and rapid recharge events. Multivariate analysis techniques (e.g. principal components analysis and hierarchical cluster analysis) demonstrate that preferential recharge pathways and anthropogenic activities, such as domestic effluents affect the groundwater quality. The data and findings of this study were used to assist in the design of a probabilistic risk assessment model based on the Poisson distribution. This study demonstrates the complexity and the challenges related to bacterial contamination in drilled wells. In spite of these challenges, this analysis was useful as a baseline to assess the impact of anthropogenic activities, and may be used in future studies to assist municipalities in the evaluation and protection of groundwater supplies.

Bei der Suche nach einem geologischen Tiefenlager für radioaktive Abfälle müssen alle Risiken für die Integrität des Endlagers und die Sicherheit der umgebenden Biosphäre berücksichtigt werden. Nach der Einlagerung radioaktiver Abfälle kommt es durch verschiedene chemische und physikalische Prozesse innerhalb des Endlagers zur Gasbildung. Die kontinuierliche Gasbildung kann den Gasdruck im verschlossenen Endlager erheblich erhöhen. Das Multibarrierensystem des Endlagers, das häufig aus tonhaltigen Materialien besteht, verhindert, dass sich das Gas verflüchtigt. Die Auswirkungen eines hohen Gasdrucks und die damit verbundenen mechanischen Verformungen können sich negativ auf das Barrieresystem des Endlagers auswirken. Ein genaues Verständnis und die Reproduzierbarkeit der gekoppelten Prozesse ist daher unerlässlich.\\ Experimentelle Ergebnisse deuten darauf hin, dass die Gasmigration bei hohen Gasdrücken über lokal begrenzte, preferentielle Strömungs-pfade erfolgt. In dieser Arbeit wurden verschiedene numerische Ansätze entwickelt, um diese Strömungspfade in numerischen Modellen effektiv zu reproduzieren. Ein entwickelter Ansatz nutzt mikroskalige Eigenschaften, die aus Messungen der Porengrößendichte gewonnen werden. Diese werden hochskaliert und in die Eigenschaften des porösen Mediums integriert. Darüber hinaus ist ein bimodales Porenmodell entwickelt worden, das speziell das dehnungsabhängige Wasserrückhaltevermögen beschreibt und einen verringerten Gaseintrittsdruck und erhöhten Anteil der Makroporosität simulieren kann. Die Simulationsmethoden beinhalten zusätzlich die Verwendung von dehnungsabhängigen Permeabilitätsmodellen für die implizite Darstellung der Strömungspfade. Diese Modellierungsansätze werden dann zur Simulation verschiedener Experimente angewandt, wodurch ein detaillierter Vergleich zwischen berechneten Parametern und experimentellen Ergebnissen ermöglicht wird.\\ Die mit dem Open-Source-Code OpenGeoSys durchgeführten Simulationen zeigen, dass bestimmte Merkmale der Gasmigration durch gesättigten Bentonit oder Tonstein erfolgreich reproduziert werden können. Heterogene Verteilungen der Materialeigenschaften können genutzt werden, um bevorzugte Strömungspfade und plötzliche Gasdurchbrüche zu simulieren. Eine Kombination aus dehnungsabhängigen Modifikationen der intrinsischen Permeabilität und der Wasserrückhalte-kurve ermöglicht eine verbesserte Modellierung impliziter präferentieller Pfade. Das sich daraus ergebende tiefere Verständnis der zugrundeliegenden Prozesse der Gasmigration kann das Sicherheitsanalyse für ein geologisches Tiefenlager für radioaktive Stoffe verbessern.:I Background 1 INTRODUCTION 1.1 Motivation 2 1.2 Objectives 4 1.3 Structure 5 II Theory and Numerics 2 GEOTECHNICAL CONTEXT AND FLUID TRANSPORT 2.1 Deep Geological Repository 9 2.2 Gas production in a DGR 11 2.2.1 Anaerobic metal corrosion 12 2.2.2 Water radiolysis 12 2.2.3 Biodegradation 13 2.3 Fluid transport mechanisms 13 2.3.1 Unsaturated initial conditions 13 2.3.2 Saturated initial conditions 14 2.3.2.1 Advective or diffusive transport of dissolved gas 14 2.3.2.2 Visco-capillary two-phase flow 16 2.3.2.3 Dilatancy-controlled gas flow 18 2.3.2.4 Fracture-controlled gas flow 19 3 NUMERICS AND METHODOLOGY 3.1 Balance equations 21 3.2 Mechanical models 23 3.3 Enhanced permeability functions 24 3.4 Spatial heterogeneity 27 3.5 Bimodal water retention in bentonite 29 4 APPLICATION AND MODEL DESCRIPTION 36 4.1 Application within the DECOVALEX Project 36 4.1.1 Task A – COx claystone 37 4.1.2 Task B – MX-80 Bentonite 38 4.2 Additional gas flow tests 40 III Simulations 5 RESULTS OF GAS FLOW TESTS WITH MX-80 BENTONITE 5.1 Heterogeneous Gas Entry Pressure from Measurements (Paper I) 45 5.2 Bimodal Heterogeneous Gas Entry Pressure (Paper II) 46 5.3 Strain-dependent Bimodal Water Retention Model (Paper III) 47 5.4 Strain-dependent Pore-Model with Heterogeneity 48 6 RESULTS OF GAS FLOW TESTS WITH COX CLAYSTONE (PAPER IV) 51 7 DISCUSSION 53 IV Summary 8 CONCLUSIONS AND OUTLOOK 57 A APPENDIX A 72 A.1 List of Publications 72 B APPENDIX B B.1 Paper I 75 B.2 Paper II 87 B.3 Paper III 109 B.4 Paper IV 121 / In the search for a deep geological repository for radioactive waste, all risks to the integrity of the repository and the safety of the surrounding biosphere must be considered. Following the emplacement of radioactive waste, various chemical and physical processes within the repository induce gas generation. Continuous gas generation can significantly increase the gas pressure in the sealed repository. The repository's multi-barrier system, which often consists of clayey materials such as clayrock and bentonite, prevents the gas from dissipating. The resulting high gas pressure and the associated mechanical deformations can have a negative impact on the multi-barrier system of the repository, e.g. by creating fluid pathways. A sufficiently precise understanding and reproducibility of the processes associated with gas migration through clayey materials is therefore essential for the safety analysis of a repository for radioactive waste.\\ Experimental evidence suggests that, under high gas pressure, gas migration predominantly occurs through localized, preferential pathways characterised by spontaneous breakthroughs. In this work, various numerical approaches have been developed to effectively reproduce these pathways in numerical models. One developed approach utilises microscale properties obtained from measurements of pore size density. These are upscaled and integrated into the properties of the porous medium. Additionally, a bimodal pore model is developed specifically to capture strain-dependent water retention, allowing the simulation of gas entry pressure reduction and macroporosity increase within preferential pathways. The simulation methods include the use of strain-dependent permeability models for the implicit representation of these pathways. These modelling approaches are then applied to replicate different experiments, allowing a detailed comparison between calculated parameters and experimental results.\\ The simulations, performed with the open-source code OpenGeoSys, show that certain features of gas migration through saturated bentonite or claystone can be successfully reproduced. Heterogeneous distributions of material properties can be used to simulate preferential pathways and sudden gas breakthroughs. A combination of permeability models as well as strain-dependent modifications of the intrinsic permeability and the water retention curve provide opportunities for improved modelling of implicit preferential pathways. The resulting deeper understanding of the underlying processes of gas migration can strengthen the safety case for a deep geological repository for radioactive materials.:I Background 1 INTRODUCTION 1.1 Motivation 2 1.2 Objectives 4 1.3 Structure 5 II Theory and Numerics 2 GEOTECHNICAL CONTEXT AND FLUID TRANSPORT 2.1 Deep Geological Repository 9 2.2 Gas production in a DGR 11 2.2.1 Anaerobic metal corrosion 12 2.2.2 Water radiolysis 12 2.2.3 Biodegradation 13 2.3 Fluid transport mechanisms 13 2.3.1 Unsaturated initial conditions 13 2.3.2 Saturated initial conditions 14 2.3.2.1 Advective or diffusive transport of dissolved gas 14 2.3.2.2 Visco-capillary two-phase flow 16 2.3.2.3 Dilatancy-controlled gas flow 18 2.3.2.4 Fracture-controlled gas flow 19 3 NUMERICS AND METHODOLOGY 3.1 Balance equations 21 3.2 Mechanical models 23 3.3 Enhanced permeability functions 24 3.4 Spatial heterogeneity 27 3.5 Bimodal water retention in bentonite 29 4 APPLICATION AND MODEL DESCRIPTION 36 4.1 Application within the DECOVALEX Project 36 4.1.1 Task A – COx claystone 37 4.1.2 Task B – MX-80 Bentonite 38 4.2 Additional gas flow tests 40 III Simulations 5 RESULTS OF GAS FLOW TESTS WITH MX-80 BENTONITE 5.1 Heterogeneous Gas Entry Pressure from Measurements (Paper I) 45 5.2 Bimodal Heterogeneous Gas Entry Pressure (Paper II) 46 5.3 Strain-dependent Bimodal Water Retention Model (Paper III) 47 5.4 Strain-dependent Pore-Model with Heterogeneity 48 6 RESULTS OF GAS FLOW TESTS WITH COX CLAYSTONE (PAPER IV) 51 7 DISCUSSION 53 IV Summary 8 CONCLUSIONS AND OUTLOOK 57 A APPENDIX A 72 A.1 List of Publications 72 B APPENDIX B B.1 Paper I 75 B.2 Paper II 87 B.3 Paper III 109 B.4 Paper IV 121

Bentonite is regarded as an ideal geomaterial for the engineering barrier system of a deep geological repository (DGR) where nuclear wastes are disposed, as it has several desirable properties for sealing the nuclear wastes, including low permeability, low diffusion coefficient, high adsorption capacity and proper swelling ability. Nevertheless, gas migration in saturated bentonite may undermine the sealing ability of the geomaterial. Previous experimental studies showed that the gas migration process is accompanied by complex hydromechanical (HM) behaviors, such as gas breakthrough phenomenon, development of preferential pathways, build-up of water pressure and total stress, nearly saturated state after gas injection test, localized consolidation, water exchange between clay matrix and developed fractures and self-sealing process. These experimentally observed behaviors should be properly modelled for conducting a reliable performance assessment for the geomaterial over the lifespan of DGR. In this thesis, two different coupled HM frameworks, i.e., one based on double porosity (DP) concept, referred to as coupled HM-DP framework, and the other on phase field (PF) method, referred to as coupled HM-PF framework, are proposed to simulate the gas migration process in saturated bentonite. For the coupled HM-DP framework, the saturated bentonite is assumed as a superposition of a MAcro-Continuum (MAC) and a MIcro-Continuum (MIC). Two-phase flow is only allowed in the MAC, whereas the MIC is impermeable to both water and gas. Nevertheless, the water can transfer between the MIC and the MAC under the water pressure gap. The first coupled HM model in this framework is based on a double effective stress concept. Mechanical behaviors of the MAC and the MIC are respectively governed by Bishop-type effective stress and Terzaghi’s effective stress. The model can well simulate the evolutions of both gas pressure and gas outflow rate, the water exchange between clay matrix and developed pathways, the high degree of saturation and the consolidation of clay matrix. To account for the development of preferential pathways, the damaging effect has been introduced in the framework. In this improved model, Bishop-type effective stress for the MAC is replaced by the independent stress state variables, i.e., net normal stress and suction, since using the net normal stress is beneficial to simulating tensile failure under high gas pressure. Numerical results showed that the damage-enhanced model can well describe the effect of the development of preferential pathways on the build-up of water pressure and total stress. In addition, the proposed hysteretic models for intrinsic and relative permeabilities make the coupled HM framework more flexible to reproduce the experimental results. To explicitly simulate the development of preferential pathways, a coupled HM-PF framework is developed by using Coussy’s thermodynamic theory and the microforce balance law. The coupled HM-PF framework is implemented in the standard Finite Element Method (FEM). To avoid the pore pressure oscillation and enhance the computational efficiency, a stabilized mixed finite element, in which linear shape functions are selected for interpolating all primary variables, is adopted to discretize the whole domain. In the developed framework, swelling pressure (initial stress) is accounted for by introducing a modified strain tensor that is the sum of the strain tensor due to deformation and the strain tensor calculated from the initial stress. The numerical results showed that the developed coupled HM-PF framework can capture some important behaviors, such as the discrete pathways, localized gas flow, built-up of water pressure and total stress under constant volume condition and nearly saturated state in clay matrix. A spatially autocorrelated random field is introduced into the framework to describe the heterogeneous distribution of HM properties in bentonite. The heterogeneity is beneficial to simulating the fracture branching and the complex fracture trajectory. Numerical results showed that some factors, such as Gaussian random field, coefficient of variation, boundary condition and injection rate, have significant influences on the fracture trajectory. At the end of the thesis, the obtained numerical results are synthesized and analyzed. Based on the analysis, the pros and cons of the developed numerical models are discussed. Corresponding to the limitations, some recommendations are proposed for future studies.