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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

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

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

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

Input files of the OpenFOAM simulations of case C2

Input files of the OpenFOAM simulations of case C2

Pumping tests are routinely interpreted from the analysis of drawdown data and their derivatives. These interpretations result in a small number of apparent parameter values which lump the underlying heterogeneous structure of the aquifer. Key questions in such interpretations are (1) what is the physical meaning of those lumped parameters and (2) whether it is possible to infer some information about the spatial variability of the hydraulic parameters. The system analyzed in this paper consists of an aquifer separated from a second recharging aquifer by means of an aquitard. The natural log transforms of the transmissivity, lnT, and the vertical conductance of the aquitard, lnC, are modeled as two independent second‐order stationary spatial random functions (SRFs). The Monte Carlo approach is used to simulate the time‐dependent drawdown at a suite of observation points for different values of the statistical parameters defining the SRFs. Drawdown data at each observation point are independently used to estimate hydraulic parameters using three existing methods: (1) the inflection‐point method, (2) curve‐fitting, and (3) the double inflection‐point method. 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 time‐drawdown data. Moreover, the heterogeneity in the pumped aquifer or the aquitard influences the estimates in distinct manners. 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