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Marschall P.,National Cooperative for the Disposal of Radioactive Waste | Giger S.,National Cooperative for the Disposal of Radioactive Waste | de la Vassiere R.,Andra Inc | Shao H.,Federal Institute for Geosciences and Natural Resources | And 7 more authors.
Swiss Journal of Geosciences | Year: 2017

The excavation damaged zone (EDZ) around the backfilled underground structures of a geological repository represents a release path for radionuclides, which needs to be addressed in the assessment of long-term safety. Additionally, the EDZ may form a highly efficient escape route for corrosion and degradation gases, thus limiting the gas overpressures in the backfilled repository structures. The efficiency of this release path depends not only on the shape and extent of the EDZ, but also on the self-sealing capacity of the host rock formation and the prevailing state conditions, such as in situ stresses and pore pressure. The hydro-mechanical and chemico-osmotic phenomena associated with the formation and temporal evolution of the EDZ are complex, thus precluding a detailed representation of the EDZ in conventional modelling tools for safety assessment. Therefore, simplified EDZ models, able to mimic the safety-relevant functional features of the EDZ in a traceable manner are required. In the framework of the Mont Terri Project, a versatile modelling approach has been developed for the simulation of flow and transport processes along the EDZ with the goal of capturing the evolution of hydraulic significance of the EDZ after closure of the backfilled underground structures. The approach draws on both empirical evidence and experimental data, collected in the niches and tunnels of the Mont Terri rock laboratory. The model was benchmarked with a data set from an in situ self-sealing experiment at the Mont Terri rock laboratory. This paper summarises the outcomes of the benchmark exercise that comprises relevant empirical evidence, experimental data bases and the conceptual framework for modelling the evolution of the hydraulic significance of the EDZ around a backfilled tunnel section during the entire re-saturation phase. © 2017 Swiss Geological Society

Marti B.S.,ETH Zurich | Bauser G.,ETH Zurich | Bauser G.,Camille Bauer AG | Stauffer F.,ETH Zurich | And 3 more authors.
Water Science and Technology: Water Supply | Year: 2012

Well field management in urban areas faces challenges such as pollution from old waste deposits and former industrial sites, pollution from chemical accidents along transport lines or in industry, or diffuse pollution from leaking sewers. One possibility to protect the drinking water of a well field is the maintenance of a hydraulic barrier between the potentially polluted and the clean water. An example is the Hardhof well field in Zurich, Switzerland. This paper presents the methodology for a simple and fast expert system (ES), applies it to the Hardhof well field, and compares its performance to the historical management method of the Hardhof well field. Although the ES is quite simplistic it considerably improves the water quality in the drinking water wells. The ES knowledge base is crucial for successful management application. Therefore, a periodic update of the knowledge base is suggested for the real-time application of the ES. © IWA Publishing 2012.

Wetter O.,University of Bern | Pfister C.,University of Bern | Weingartner R.,University of Bern | Weingartner R.,Institute of Geography | And 3 more authors.
Hydrological Sciences Journal | Year: 2011

The magnitudes of the largest known floods of the River Rhine in Basel since 1268 were assessed using a hydraulic model drawing on a set of pre-instrumental evidence and daily hydrological measurements from 1808. The pre-instrumental evidence, consisting of flood marks and documentary data describing extreme events with the customary reference to specific landmarks, was "calibrated" by comparing it with the instrumental series for the overlapping period between the two categories of evidence (1808-1900). Summer (JJA) floods were particularly frequent in the century between 1651-1750, when precipitation was also high. Severe winter (DJF) floods have not occurred since the late 19th century despite a significant increase in winter precipitation. Six catastrophic events involving a runoff greater than 6000 m 3 s -1 are documented prior to 1700. They were initiated by spells of torrential rainfall of up to 72 h (1480 event) and preceded by long periods of substantial precipitation that saturated the soils, and/or by abundant snowmelt. All except two (1999 and 2007) of the 43 identified severe events (SEs: defined as having runoff > 5000 and < 6000 m 3 s -1) occurred prior to 1877. Not a single SE is documented from 1877 to 1998. The intermediate 121-year-long "flood disaster gap" is unique over the period since 1268. The effect of river regulations (1714 for the River Kander; 1877 for the River Aare) and the building of reservoirs in the 20th century upon peak runoff were investigated using a one-dimensional hydraulic flood-routing model. Results show that anthropogenic effects only partially account for the "flood disaster gap" suggesting that variations in climate should also be taken into account in explaining these features. © 2011 Copyright IAHS Press.

Riva M.,Polytechnic of Milan | Guadagnini A.,Polytechnic of Milan | De Gaspari F.,Polytechnic of Milan | De Gaspari F.,Polytechnic University of Catalonia | And 2 more authors.
Water Resources Research | Year: 2010

We present novel equations for the exact sensitivity matrix of the (ensemble) mean hydraulic head under steady state groundwater flow conditions. These equations are embedded in a geostatistical inverse procedure to condition approximations of stochastic moment equations of flow on measured hydraulic conductivities and heads. Our formulation allows considerable improvement of the methodology proposed by Hernandez et al. (2003, 2006) and renders the inversion of moment equations feasible for a large number of unknown hydraulic parameters. The spatial distribution of the natural logarithm, Y, of conductivity is parameterized within the pilot points framework. Whereas prior values of Y at pilot points are obtained by a variant of kriging, posterior estimates at pilot points are obtained through a maximum likelihood fit of computed to measured heads. The maximum likelihood function also includes a regularization term. By means of a synthetic example and upon adopting formal model information criteria we explore the influence of (1) the number of pilot points and (2) the order of approximation of the governing mean flow equation on our ability to properly estimate the log conductivity and head fields and identify the relative weight of the regularization term and the parameters of the underlying Y variogram. We find that none of the adopted information criteria can identify the optimum number of pilot points and the plausibility weight and variogram parameters values can be determined by the Kashyap's Bayesian measure. Copyright © 2010 by the American Geophysical Union.

Pool M.,CSIC - Institute of Environmental Assessment And Water Research | Pool M.,Polytechnic University of Catalonia | Carrera J.,CSIC - Institute of Environmental Assessment And Water Research | Carrera J.,Polytechnic University of Catalonia | And 2 more authors.
Journal of Hydrology | Year: 2015

Inversion of the spatial variability of transmissivity (T) in groundwater models can be handled using either stochastic or deterministic (i.e., geology-based zonation) approaches. While stochastic methods predominate in scientific literature, they have never been formally compared to deterministic approaches, preferred by practitioners, for regional aquifer models. We use both approaches to model groundwater flow and solute transport in the Mar del Plata aquifer, where seawater intrusion is a major threat to freshwater resources. The relative performance of the two approaches is evaluated in terms of (i) model fits to head and concentration data (available for nearly a century), (ii) geological plausibility of the estimated T fields, and (iii) their ability to predict transport. We also address the impact of conditioning the estimated fields on T data coming from either pumping tests interpreted with the Theis method or specific capacity values from step-drawdown tests. We find that stochastic models, based upon conditional estimation and simulation techniques, identify some of the geological features (river deposit channels and low transmissivity regions associated to quartzite outcrops) and yield better fits to calibration data than the much simpler geology-based deterministic model, which cannot properly address model structure uncertainty. However, the latter demonstrates much greater robustness for predicting sea water intrusion and for incorporating concentrations as calibration data. We attribute the poor performance, and underestimated uncertainty, of the stochastic simulations to estimation bias introduced by model errors. Qualitative geological information is extremely rich in identifying large-scale variability patterns, which are identified by stochastic models only in data rich areas, and should be explicitly included in the calibration process. © 2015 Elsevier B.V.

Agency: European Commission | Branch: FP7 | Program: CP-FP | Phase: Fission-2009-1.1.1 | Award Amount: 6.53M | Year: 2010

The main aim of the project PEBS (Long-term Performance of the Engineered Barrier System) is to evaluate the sealing and barrier performance of the EBS with time, through development of a comprehensive approach involving experiments, model development and consideration of the potential impacts on long-term safety functions. The experiments and models cover the full range of conditions from initial emplacement of wastes (high heat generation and EBS resaturation) through to later stage establishment of near steady-state conditions, i.e. full resaturation and thermal equilibrium with the host rock. These aspects will be integrated in a manner that will lead to a more convincing connection between the initial transient state of the EBS and its long-term state that provides the required isolation of the wastes. The work proposed within the project builds on existing knowledge and experience generated during recent years and supported by ongoing nat. and EC research programmes. The project pretends to provide a more complete description of the THM and THM-C (thermo-hydromechanical-chemical) evolution of the EBS system, a more quantitative basis for relating the evolutionary behaviour to the safety functions of the system and a further clarification of the significance of residual uncertainties for long-term performance assessment. The importance of uncertainties arising from potential disagreement between the process models and the laboratory and in situ experiments to be performed within PEBS, and their implications for extrapolation of results will be reviewed, with particular emphasis on possible impacts on safety functions. In addition to the scientific-tech. aim, the consortium will spread the essential results to the european scientific community and Canada, Japan and China, use its expertise for public information purposes, and promote knowledge and technology transfer through training. WP 5 brings together activities concerning dissemination and training.

Farshi D.,TK Consult AG | Jo D.,AF Consult Ltd. | Trosch J.,TK Consult AG | Faust B.,Kernkraftwerk Gosgen Daniken AG
Proceedings of the International Conference on Fluvial Hydraulics, RIVER FLOW 2014 | Year: 2014

After Fukushima, the question arises, how strongly the nuclear power plants could be impacted by the natural extreme flood events in Switzerland. The Swiss Federal Nuclear Safety Inspectorate (ENSI) requires new investigation from all plant operators in Switzerland in this regard. The two-dimensional modeling of the multi-grain sediment transport considering bed load and suspended load during an extreme event, with an annual probability of occurrence of 10 -4, should be considered in such an investigation. The nuclear power plant Gösgen-Däniken AG at the River Aare close to Olten has investigated the impact of the flood event with sediment transport. In order to simulate the sediment transport in the Aare a two-dimensional (2D) model has been adopted. This model is using the finite-volume method based on an unstructured mesh and is performed with the software tool BASEMENT. BASEMENT consists of all necessary modules for such simulations: depth-averaged flow of Shallow Water Equations (SWE) module, 2D bedload transport module and 2D advection-diffusion module for suspended sediment transport. This paper presents the results of the simulations with a special focus on challenges of the modeling and the boundary conditions. © 2014 Taylor & Francis Group, London.

Gischig V.,ETH Zurich | Wiemer S.,ETH Zurich | Alcolea A.,Geo Energie Suisse AG | Alcolea A.,TK Consult AG
Geophysical Journal International | Year: 2014

Fracture shear-dilatancy is an essential process for enhancing the permeability of deep geothermal reservoirs, and is usually accompanied by the radiation of seismic waves. However, the hazard and risk perspective of induced seismicity research typically focuses only on the question of how to reduce the occurrence of induced earthquakes. Here we present a quantitative analysis of seismic hazard as a function of the two key factors defining an enhanced geothermal system: The permeability enhancement, and the size of the stimulated reservoir. Our model has two coupled components: (1) a pressure diffusion model and (2) a stochastic seismicity model. Permeability is increased in the source area of each induced earthquake depending on the amount of slip, which is determined by the magnitude. We show that the few largest earthquakes (i.e. 5-10 events with M ≥ 1.5) contribute more than half of the total reservoir stimulation. The results further indicate that planning and controlling of reservoir engineering operations may be compromised by the considerable variability of maximum observed magnitude, reservoir size, the Gutenberg-Richter b-value and Shapiro's seismogenic index (i.e. a measure of seismic reactivity of a reservoir) that arises from the intrinsic stochastic nature of induced seismicity.We also find that injection volume has a large impact on both reservoir size and seismic hazard. Injection rate and injection scheme have a negligible effect. The impact of site-specific parameters on seismicity and reservoir properties is greater than that of the injected volume. In particular, conditions that lead to high b-values-possibly a low differential stress level-have a high impact on seismic hazard, but also reduce the efficiency of the stimulation in terms of permeability enhancement. Under such conditions, target reservoir permeability can still be achieved without reaching an unacceptable level of seismic hazard, if either the initial reservoir permeability is high or if several fractures are stimulated. The proposed methodology is a first step towards including induced seismic hazard analysis into the design of reservoir stimulation in a quantitative and robust manner. © The Authors 2014. Published by Oxford University Press on behalf of The Royal Astronomical Society.

Alcolea Rodriguez A.,GeoEnergie Suisse AG | Kuhlmann U.,TK Consult AG
4th EAGE Shale Workshop 2014 - Shales: What Do They Have in Common? | Year: 2014

The present study focuses on the temporal evolution of hydraulic parameters of the Excavation Damage Zone (EDZ hereinafter). To that end, a hybrid finite/discrete element method (FEMDEM) was first used to simulate the geometry and geomechanical conditions of discrete fracture networks forming the EDZ, which develop in response to the excavation process in the rock mass around the underground structures of a radioactive waste repository (NAGRA, 2013). The simulated geometry and geomechanical properties are mapped onto a finite element mesh, which allows us to solve the fluid motion equations at the near-field. The resaturation of the EDZ causes a pore pressure increase at that zone. This leads to a decrease of the normal effective stress and, correspondingly, to the progressive closure of the fracture. This closure causes fracture hydraulic conductivity to drop in time, while matrix conductivity increases due to swelling. The objectives of this study are: 1) To quantify the temporal evolution of hydraulic properties in response to pressure variations caused by the resaturation of the EDZ after excavation and emplacement. 2) To quantify the temporal evolution of the specific axial flux through the EDZ. 3) To quantify the total time required for a full resaturation of the EDZ.

Alcolea A.,University of Neuchatel | Alcolea A.,TK Consult AG | Renard P.,University of Neuchatel
Water Resources Research | Year: 2010

Connectivity constraints and measurements of state variables contain valuable information on aquifer architecture. Multiple-point (MP) geostatistics allow one to simulate aquifer architectures, presenting a predefined degree of global connectivity. In this context, connectivity data are often disregarded. The conditioning to state variables is usually carried out by minimizing a suitable objective function (i.e., solving an inverse problem). However, the discontinuous nature of lithofacies distributions and of the corresponding objective function discourages the use of traditional sensitivity-based inversion techniques. This work presents the Blocking Moving Window algorithm (BMW), aimed at overcoming these limitations by conditioning MP simulations to hydrogeological data such as connectivity and heads. The BMW evolves iteratively until convergence: (1) MP simulation of lithofacies from geological/geophysical data and connectivity constraints, where only a random portion of the domain is simulated at every iteration (i.e., the blocking moving window, whose size is user-defined); (2) population of hydraulic properties at the intrafacies; (3) simulation of state variables; and (4) acceptance or rejection of the MP simulation depending on the quality of the fit of measured state variables. The outcome is a stack of MP simulations that (1) resemble a prior geological model depicted by a training image, (2) honor lithological data and connectivity constraints, (3) correlate with geophysical data, and (4) fit available measurements of state variables well. We analyze the performance of the algorithm on a 2-D synthetic example. Results show that (1) the size of the blocking moving window controls the behavior of the BMW, (2) conditioning to state variable data enhances dramatically the initial simulation (which accounts for geological/geophysical data only), and (3) connectivity constraints speed up the convergence but do not enhance the stack if the number of iterations is large. Copyright 2010 by the American Geophysical Union.

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