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The REPRO-TDE test was performed at a depth of about 400 m in the ONKALO underground research facility in Finland. Synthetic groundwater containing radionuclide tracers [tritiated water tracer (HTO), 36Cl, 22Na, 133Ba, and 134Cs] was circulated for about 4 years in a packed-off interval of the injection borehole. Tracer activities were additionally monitored in two observation boreholes. The test was the subject of a modeling exercise by the SKB GroundWater Flow and Transport of Solutes Task Force. Eleven teams participated in the exercise, using different model concepts and approaches. Predictive model calculations were based on laboratory-based information concerning porosities, diffusion coefficients, and sorption partition coefficients. After the experimental results were made available, the teams were able to revise their models to reproduce the observations. General conclusions from these back-analysis calculations include the need for reduced effective diffusion coefficients for 36Cl compared to those applicable to HTO (anion exclusion), the need to implement weaker sorption for 22Na compared to results from laboratory batch sorption experiments, and the observation of large differences between the theoretical initial concentrations for the strongly sorbing 133Ba and 134Cs, and the first measured values a few hours after tracer injection. Different teams applied different concepts, concerning mainly the implementation of isotropic versus anisotropic diffusion, or the possible existence of borehole disturbed zones around the different boreholes. The role of microstructure was also addressed in two of the models., Funding was provided through the Task Force partner organizations participating in this modeling exercise (POSIVA OY, Finland; SKB, Sweden; SÚRAO, Czech Republic; KAERI, Republic of Korea; NUMO, Japan). JAEA’s modeling study was performed as a part of “The project for validating near-field assessment methodology in geological disposal system” funded by the Ministry of Economy, Trade and Industry of Japan (grant no. JPJ007597). The modeling studies by TUL, UJV, CTU, and PROGEO were performed as part of the Radioactive Waste Repository Authority (SÚRAO, Czech Republic) project, “Research support for the safety assessment of a deep geological repository.” IDAEA-CSIC is a Centre of Excellence Severo Ochoa (Spanish Ministry of Science and Innovation, Project CEX2018-000794-S). The helpful comments on an early version of the paper by Kersti Nilsson, Johan Byegård, and Lasse Koskinen, and the constructive comments by the editorial office and by two anonymous reviewers are gratefully acknowledged.

Modelling fluid flow and water-rock interaction in fractured crust using a Discrete Fracture Network approach Groundwater accounts for around 25% of the world’s fresh water supply. Due to the increasing anthropogenic pressure on shallow aquifers as well as climate change that is impacting global groundwater recharge, there is an increasing need to access deeper groundwater resources, which are frequently hosted in fractured-rock formations. The migration of groundwater (and other types of fluids, in general) in fractured rocks allows the contact between fluids in geochemical disequilibrium with the host rocks (i.e., large geochemical gradients) promoting water-rock reactions inside the fractures. These reactions may influence the permeability and porosity, as well as they may lead to fracture sealing. So, a thorough understanding of the coupled hydro-chemical processing that occur in fractured media is important for applications such as the sustainable exploitation of the afore-mentioned reserves, the protection and remediations of aquifers used for drinking water production or the safety analyses of deep geological repositories for spent nuclear fuel. In fractured rocks, groundwater flows in specific pathways and interacts with the host rock which may lead to the change in the hydro-geochemical conditions. The prediction of these interactions become critical for a proper management of the different applications. Therefore, the understanding and modelling of fluid-fracture interaction is of high scientific and commercial interest. Using the software dfnWorks, it is possible to model the fluid transport using a non-reactive Lagrangian method (particle tracking). In this contribution, we intend to implement geochemical reactions in dfnWorks to quantify the impact of these reactions in the fracture network. In fact, flow of water through Discrete Fracture Networks leads to interaction between water and the minerals occurring in the fracture plane and thus alters the underlying groundwater flow patterns. Thus, using these DFN-based reactive transport simulations, we aim at predicting the effect that chemical reactions have on flow and channeling. Besides presenting a proof-of-concept set of calculations, we will also present preliminary results of a real-case application, where fracture filling is produced as a result of a chemical imbalance.

These are the input files of the OpenFOAM simulations of case C1

Input files of the OpenFOAM simulations of case C2

Hydrologists routinely analyze pumping test data using conventional interpretation methods that are based on the assumption of homogeneity and that, consequently, yield single estimates of representative flow parameters. However, natural subsurface formations are intrinsically heterogeneous, and hence, the flow parameters influencing the drawdown vary as the cone of depression expands in time. In this paper a novel procedure for the analysis of pumping tests in heterogeneous confined aquifers is developed. We assume that a given heterogeneous aquifer can be represented by a homogeneous system whose flow parameters evolve in time as the pumping test progresses. At any point in time, the interpreted flow parameters are estimated using the ratio of the drawdown and its derivative observed at that particular time. The procedure is repeated for all times, yielding time‐dependent estimates of transmissivityTi(t) and storativity,Si(t). Based on the analysis of the sensitivity of drawdown to inhomogeneities in theTfield, the time‐dependent interpreted transmissivity values are found to be a good estimate ofTg(r), the geometric mean of the transmissivity values encompassed within a progressively increasing radiusrfrom the well. The procedure is illustrated for Gaussian heterogeneous fields with ln(T) variances up to a value of 2. The impact of the separation distance between the pumping well and observation point on data interpretation is discussed. The results show that information about the spatial variability of the transmissivity field can be inferred from time‐drawdown data collected at a single observation point

Waste rock piles are an outcome of open pit and underground mining operations. Unprocessed low‐grade rock is disposed of in piles from several meters high to 100 m+ high. Waste rock piles may still contain sufficient concentrations of metals to be a potential source of pollution. The evaluation of the potential risk involves properly characterizing flow through these piles under unsaturated conditions. The main flow characteristic of the piles is the presence of a large range of grain and pore sizes. Based on data from an instrumented rock pile located in Saskatchewan Canada, unsaturated flow through the pile is modeled as a linear system after separating a fast and a slow component. Water reaching the base of the pile is monitored by 16 contiguous zero‐tension lysimeters. The fast component, flowing through macropores, is assumed to be released instantaneously, while the slow component is simulated using a linear‐reservoir model that assumes the presence of an interconnected porous matrix. An empirical transfer function (TF) is computed as the ratio of the spectra of signals between the output (basal outflow) and the input (rainfall time series). Determination of a parametric transfer function model provides information on the characteristic time of water storage in the matrix and on the fraction of the water within each subsection of the experimental pile that is channeled through the macropores. An analysis of the output signal at different support scales is performed, indicating the nonlinearity of the macropore fraction scaling processes

Heterogeneity of subsurface environments and insufficient site characterization are some of the reasons why decisions about groundwater exploitation and remediation have to be made under uncertainty. A typical decision maker chooses between several alternative remediation strategies by balancing their respective costs with the probability of their success or failure. We conduct a probabilistic risk assessment (PRA) to determine the likelihood of the success of a permeable reactive barrier, one of the leading approaches to groundwater remediation. While PRA is used extensively in many engineering fields, its applications in hydrogeology are scarce. This is because rigorous PRA requires one to quantify structural and parametric uncertainties inherent in predictions of subsurface flow and transport. We demonstrate how PRA can facilitate a comprehensive uncertainty quantification for complex subsurface phenomena by identifying key transport processes contributing to a barrier's failure, each of which is amenable to uncertainty analysis. Probability of failure of a remediation strategy is computed by combining independent and conditional probabilities of failure of each process. Individual probabilities can be evaluated either analytically or numerically or, barring both, can be inferred from expert opinion

La heterogeneidad es una característica saliente de cada formación geológica natural. En las últimas décadas un gran número de trabajos se han centrado en estudiar la influencia de la heterogeneidad en los problemas de flujo y transporte en medios poros. Dichos trabajos han mejorado sustancialmente la comprensión de los mecanismos que gobiernan estos fenómenos, sin embargo aun existen carencias en la caracterización de propiedades importantes de un acuífero. Entre ellas, el flujo preferencial, la conectividad entre dos puntos de un acuífero y la interpretación de ensayos en acuíferos heterogéneos son aspectos importantes que tienen que ser adecuadamente evaluados para obtener modelos predictivos robustos. En este contexto, el objetivo de esta tesis es doble:· mejorar el conocimiento de la influencia de la heterogeneidad en los procesos de flujo y transporte· proporcionar nuevas herramientas para caracterizar la heterogeneidad de los acuíferosEn primer lugar, evaluamos la relación entre dos indicadores de conectividad de flujo y transporte. El indicador de conectividad de flujo utilizado aquí se basa en el tiempo de respuesta hidráulica en un ensayo de bombeo (por ejemplo, el coeficiente de almacenamiento estimado con el método de Cooper-Jacob). Como indicador de conectividad de transporte utilizamos la porosidad estimada de curvas de llegadas (Φest) en ensayos de trazadores con flujo radial. Los resultados obtenidos permiten explicar la poca correlación entre estos dos indicadores ya observada númericamente por Knudby y Carrera (2005).En segundo lugar, se ha desarrollado un marco geoestádistico para delinear mapas de conectividad utilizando un número limitado de medidas hidráulicas. La metodología permite condicionar los resultados a tres tipos de datos medidos a diferentes escalas: (a) tiempos de llegada de ensayos de trazadores en flujo convergente ta, (b) estimaciones del coeficiente de almacenamiento obtenidas de ensayos de bombeo interpretados con el método de Cooper-Jacob, Sest, y (c) mediciones de valores de transmisividad puntuales, T. La capacidad de la metodología para delinear correctamente zonas de captura se evalúa a través de estimaciones (krigeado simple y ordinario) y simulaciones secuenciales gausianas basadas en diferentes conjuntos de medidas.En tercer lugar, se ha desarrollado una metodología, llamada método del doble punto de inflexión (DIP), para la interpretación de pruebas de bombeo en acuíferos semiconfinados. La ventaja de este método (DIP) se observa en acuíferos heterogéneos, cuando se aplica junto a las demás metodologías. En estos casos cada método proporciona información diferente acerca de la heterogeneidad. En particular, la combinación del método DIP y el método de Hantush permite identificar contrastes entre la transmisividad local (cerca del pozo) y la transmisividad equivalente del acuífero.En cuarto lugar, se utiliza el método de Monte Carlo para evaluar el significado de los parámetros hidráulicos estimados de ensayos de bombeo en acuíferos semiconfinados. Dichos parámetros resultan ser espacialmente dependientes y varían en función del método de interpretación, ya que cada método pondera de forma distinta diferentes partes de la curva de descensos. Por último, se muestra que al combinar las estimaciones de los parámetros obtenidos a partir de los diferentes procedimientos de análisis, se puede inferir información sobre la heterogeneidad del sistema.En quinto lugar, se modela el flujo no saturado en un dique de estériles utilizando un modelo basado en funciones de transferencia. La calibración del modelo proporciona información sobre el tiempo característico del flujo a través de la matriz y de la fracción de agua que se canaliza a través de los macroporos. Por último se presenta un análisis de la influencia de la escala en los resultados. A gran escala el comportamiento del sistema tiende al de un sistema-matriz homogéneo equivalente,enmascarando los efectos del flujo preferencial., Heterogeneity is a salient feature of every natural geological formation. In the past decades a large body of literature has focused on the effects of heterogeneity on flow and transport problems. These works have substantially improved the understanding of flow and transport phenomena but still fail to characterize many of the important features of an aquifer. Among them, preferential flows and solute paths, connectivity between two points of an aquifer, and interpretation of hydraulic and tracer tests in heterogeneous media are crucial points that need to be properly assessed to obtain accurate model predictions. In this context, the aim of this thesis is twofold:· to improve the understanding of the effects of heterogeneity on flow and transport phenomena· to provide new tools for characterizing aquifer heterogeneityFirst, we start by theoretically and numerically examine the relationship between two indicators of flow and transport connectivity. The flow connectivity indicator used here is based on the time elapsed for hydraulic response in a pumping test (e.g., the storage coefficient estimated by the Cooper-Jacob method, Sest). Regarding transport, we select the estimated porosity from the observed breakthrough curve (Φ est) in a forced-gradient tracer test. Our results allow explaining the poor correlation between these two indicators, already observed numerically by Knudby and Carrera (2005).Second, a geostatistical framework has been developed to delineate connectivity patterns using a limited and sparse number of measurements. The methodology allows conditioning the results to three types of data measured over different scales, namely: (a) travel times of convergent tracer tests, ta, (b) estimates of the storage coefficient from pumping tests interpreted using the Cooper-a Jacob method, S est, and (c) measurements of transmissivity point values, T. The ability of the methodology to properly delineate capture zones is assessed through estimations (i.e. ordinary cokriging) and sequential gaussian simulations based on different sets of measurements.Third, a novel methodology for the interpretation of pumping tests in leaky aquifer systems, referred to as the double inflection point (DIP) method, is presented. The real advantage of the DIP method comes when it is applied with all the existing methods independently to a test in a heterogeneous aquifer. In this case each method yields parameter values that are weighted differently, and thus each method provides different information about the heterogeneity distribution. In particular, the combination of the DIP method and Hantush method is shown to lead to the identification of contrasts between the local transmissivity in the vicinity of the well and the equivalent transmissivity of the perturbed aquifer volume.Fourth, the meaning of the hydraulic parameters estimated from pumping test performed in leaky aquifers is assessed numerically within a Monte Carlo framework. A synthetic pumping test is interpreted using three existing methods. The resulting estimated parameters are shown to be space dependent and vary with the interpretation method, since each method gives different emphasis to different parts of the timedrawdown data. Finally, we show that by combining the parameter estimates obtained from the different analysis procedures, information about the heterogeneity of the leaky aquifer system may be inferred.Fifth, an unsaturated highly heterogeneous waste rock pile is modeled using a simple linear transfer function (TF) model. The calibration of the parametric model provides information on the characteristic time of the flow through the matrix and on the fraction of the water that, within each section, is channeled through the macropores. An analysis of the influence of the scale on the results is also provided showing that at large scales the behavior of the system tends to that of an equivalent matrix reservoir masking the effects of preferential flow.