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The fate of selected UV filters (UVFs) was investigated in two soil aquifer treatment (SAT) systems, one supplemented with a reactive barrier containing clay and vegetable compost and the other as a traditional SAT reference system. We monitored benzophenone-3 (BP-3) and its transformation products (TPs), including benzophenone-1 (BP-1), 4,4'-dihydroxybenzophenone (4DHB), 4-hydroxybenzophenone (4HB), and 2,2'-dihydroxy-4-methoxybenzophenone (DHMB), along with benzophenone-4 (BP-4) and avobenzone (AVO) in all involved compartments (water, aquifer sediments, and biofilm). The reactive barrier, which enhances biochemical activity and biofilm development, improved the removal of all detected UVFs in water samples. Among monitored UVFs, only 4HB, BP-4, and AVO were detected in sediment and biofilm samples. But the overall retained amounts were several orders of magnitude larger than those dissolved. These amounts were quantitatively reproduced with a specifically developed simple analytical model that consists of a mobile compartment and an immobile compartment. Retention and degradation are restricted to the immobile water compartment, where biofilm absorption was simulated with well-known compound-specific Kow values. The fact that the model reproduced observations, including metabolites detected in the biofilm but not in the (mobile) water samples, supports its validity. The results imply that accumulation ensures significant biodegradation even if the degradation rates are very low and suggest that our experimental findings for UVFs and TPs can be extended to other hydrophobic compounds. Biofilms act as accumulators and biodegraders of hydrophobic compounds., This work was financially supported by the Spanish government (project CONMIMO, TED2021-131188B-C32 and TED2021-131188B-C31), the Catalan Research Project RESTORA (ACA210/18/00040) and SGR (2021-SGR-00609), and by EU project MARADENTRO (PCI2019-103425 and PCI2019-103603). IDAEA-CSIC is a Center of Excellence Severo Ochoa (Grant CEX2018-000794-S funded by MCIN/AEI/10.13039/501100011033). The authors also thank the Consorci d’Aigües de la Costa Brava Girona (CACBG) for the access to the WWTP, and to BEKOlut for the provision of the QuEChERS used. Pedro Chamorro is acknowledged for his help in the UVFs analysis., Peer Reviewed, Postprint (published version)

Wormholes are highly conductive channels that develop in high solubility rocks. They are especially important for environmental and industrial sustainability in saline karst aquifers (e.g. Salar de Uyuni, Salar de Atacama). Wormholes dynamics (i.e., the space and time evolution of these preferential flow paths) depends on the hydrodynamic and geochemical conditions during formation, as well as on wormholes competition for flow. Despite the importance of wormholes interaction for their development, experimental efforts have focused on the evolution of a single flow-path. Direct observation and quantification of wormholes dynamics is still lacking. We propose an experimental set-up to visualize and characterize the dynamics of multiple wormholes, which may help to understand the changes in flow and transport behaviour of aquifers. We performed a dissolution experiment in a 2D synthetic evaporitic aquifer, and simultaneous fluorescent tracer tests before and during wormhole growth. We visualized the growth by sequential photographs, with the fluorescent tracer highlighting the evolving structures. We quantified wormholes dynamics by measuring pressure and mass changes of the aquifer, and by image analysis. On the one hand, results show that wormholes tend to form along areas where flux was fastest prior to dissolution. They also show clear evidence of competition for water between wormholes and represent the first quantitative evidence of the amplifying factor that drives the self-organization in wormhole growth. On the other hand, we found that the competition is slower than predicted by current analytical and numerical theories, but consistent with other laboratory results. We conjecture that the discrepancy between theory and experiments can be attributed to the combined effect of non-linear kinetics and particle dragging during dissolution. We then compared experimental tracer breakthrough curves before and during the formation of preferential flow paths. They refl, The final version of the paper has greatly benefitted from comments by Piotr Szymczak. The authors thank the financial support provided by the Sociedad Química y Minera de Chile S.A. through project “Proyección de la evolución SOP – Salar de Atacama. Fase II: ensayos de campo y laboratorio” (SA 9500001785) and by AGAUR (Agència de Gestió d'Ajuts Universitaris i de Recerca, Generalitat de Catalunya, Spain), through project AGAUR- 2017-SGR1485. Michela Trabucchi acknowledges the financial support from AGAUR through the FI fellowship (2018FIB200079)., Peer Reviewed, Postprint (author's final draft)

Denitrifying woodchip bioreactors (DWBs) have proven to be an efficient nature-based solution for nitrate removal. Modeling DWBs is required for improving their design and operation, but is hindered by the complexity of the modeled system where numerous chemical species and model parameters are needed. Reactions inside the woodchips are different from those at the edges, causing chemical localization (i.e., apparent simultaneous occurrence of incompatible reactions). We used the Multi Rate Mass Transfer (MRMT) approach to overcome these problems when simulating reactive transport processes in a DWB located at Kiruna, Sweden. Besides denitrification, other nitrogen-cycling processes (e.g., nitrification, dissimilatory nitrate reduction to ammonium, anammox) and alternative electron donors (e.g. oxygen, sulfate) were also considered. Biomass concentration is incorporated into the biochemical reaction rates, including growth and decay, to characterize microbial catalysis. We found that the MRMT model: 1) can account for the heterogeneity of the porous woodchips; 2) was capable of reproducing the nitrogen species evolution in the DWB with kinetic parameters from the literature; and 3) allows reproducing localized biochemical reactions (e.g., aerobic reactions on the woodchip edges, near the DWB entrance and anaerobic reactions inside); and 4) reproduces the full denitrification reactions sequence, but with the different reactions occurring in different portions of the woodchip (e.g., nitrate to nitrite near the edges and nitrite to nitrous oxide further inside). The latter observation suggests that increasing woodchip size may reduce the outflow of these undesired species., The authors acknowledge the financial support of projects NITREM, RESTORA (Agència Catalana de l'Aigua, ACA210/18/0040), and ConMimo (Spanish Research Agency, AEI, number TED2021-131188B-C31). NITREM (project number 17013) has received funding from the European Institute of Innovation and Technology (EIT). This body of the European Union received support from the European Union's Horizon 2020 research and innovation programme. Additional funding was obtained from the Generalitat de Catalunya (2017 SGR1485) and the Spanish Ministry of Science and Innovation (Centre of Excellence Severo-Ochoa, CSIC-IDAEA, CEX2018-000794-S)., Peer Reviewed, Postprint (published version)

Submarine Groundwater Discharge (SGD) is recognized as a relevant source of pollutants to the sea, but little is known about its relevance as a source of chemicals of emerging concern (CECs). Here, both the presence and distribution of a wide range of CECs have been evaluated in the most comprehensive manner to date, in a well-characterized Mediterranean coastal aquifer near Barcelona (Spain). Samples from coastal groundwater and seawater allowed for the unique spatial characterization of the pollutants present in the land-ocean interface, an outstanding research gap that required attention. The main goals were (1) to determine CECs in the aquifer, so as to evaluate the SGD as a relevant source of marine pollution, and (2) to identify new tracers to improve our understanding of SGD dynamics. To this end, 92 CECs were located in the aquifer by using wide-scope analytical target methodologies (>2,000 chemicals). Among them, the perfluoroalkyl and polyfluoroalkyl substances (PFAS), along with the pharmaceuticals carbamazepine and topiramate, were revealed to be good markers for tracing anthropogenic contamination in ground- and seawater, in concrete situations (e.g., highly contaminated sites). Additionally, non-target analysis expanded the number of potential tracers, making it a promising tool for identifying both the source and the fate of pollutants., This work was funded by the project “Mixing and dispersion in the transport of energy and solutes (MEDISTRAES)” coded as PID2019-110212RB-C21 of the Spanish Government (I+D+I Retos Investigación). We acknowledge the contribution of all the members of the MEDISTRAES I, II and III project, from the Groundwater Hydrology Group of the Technical University of Catalonia (UPC) and the Spanish National Research Council (CSIC), the Autonomous University of Barcelona (UAB), the University of Barcelona (UB), the Geosciences Montpellier Laboratory, CNRS and the University of Rennes, for their support during experimental laboratory tests, the Argentona site creation, the setup of the electrodes during piezometer installation and for ensuring site maintenance. IDAEA-CSIC authors would like to express their gratitude to The Spanish Ministry of Science and Innovation through the support received as “Centro de Excelencia Severo Ochoa 2019–2023″. P. Gago-Ferrero acknowledges his Ramón y Cajal fellowship (RYC2019-027913-I) from the AEI-MICI. V. Rodellas acknowledges financial support from the Beatriu de Pinós postdoctoral programme of the Catalan Government (2019-BP-00241)., Peer Reviewed, Postprint (published version)

V.V. acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Programme through the Starting Grant GEoREST (www.georest.eu) under grant agreement No. 801809. A.V. acknowledges funding from Spanish Ministry of Science and Innovation grant CGL2017-88864-R. IDAEA-CSIC and ICM-CSIC are Centres of Excellence Severo Ochoa (Spanish Ministry of Science and Innovation Grants CEX2018-000794-S and CEX2019-000928-S, respectively, funded by MCIN/AEI/ 10.13039/501100011033)., Peer Reviewed, Postprint (published version)

We describe a formulation to solve reactive transport (RT) problems. The basic idea is to represent transport as mixing water instead of individual solute concentrations, hence the Water Mixing Approach (WMA) name. This conceptual representation simplifies RT calculations as it decouples transport from chemistry. Transport is first solved in terms of water mixing ratios (¿), which we show is feasible for any transport formulation. Chemical calculations can then be written as a set of reactive mixing calculations, which are local, so that they do not need to iterate with transport. We have implemented the WMA for a mixed Eulerian-Lagrangian transport solver with streamline-oriented grid and constant travel time between sequential cells (isochronal grid), which is free of numerical dispersion. We test the WMA on three RT cases. First, a binary system case is used to test the accuracy of the method. Second, a calcite dissolution case is used to compare the WMA to the Direct Substitution Approach to test both accuracy and computational cost (CPU). Third, the accuracy and simplicity of the proposed approach is tested on a reactive pulse injection case, solved in 2D on a spreadsheet. Results confirm the accuracy, simplicity and efficiency (low CPU cost) that result from decoupling transport and chemical steps. Transport through highly heterogeneous media remains a challenge, but the definite separation and simplification of mixing processes in WMA opens a new path for reactive transport modeling in general, and for the search of an effective transport equation, Postprint (published version)

The presence of low permeability regions within porous media impacts solute transport and the distribution of species concentrations. Therefore, (bio)chemical reactions are equally affected. Multirate Mass Transfer (MRMT) models can be used to represent this anomalous transport process. MRMT conceptualizes the medium as a set of multiple continua: one mobile zone and multiple immobile zones. It simulates species transport in mobile and immobile zones simultaneously, which are related by first-order mass exchange. Numerical modeling of reactive transport in this kind of multicontinua media is complex and demanding because of the high dimensionality of the problem. In this paper, we establish the governing equations of reactive transport in multicontinuum media incorporating chemical kinetics into the governing equations. We propose a general numerical solution of reactive transport with MRMT by applying direct substitution approach (DSA) based on Newton-Raphson method. The efficiency of the proposed algorithm benefits of the block structure of the system, which allows us to eliminate immobile zones equations and leads to significant savings in CPU time. We test the validity of the developed solution by comparison with other numerical and analytical solutions., The authors acknowledge the support of project NITREM initiated and funded by EIT (European Institute of Innovation and Technology), and the Water-JPI European Union project MARadentro, project number PCI2019-103425-WW2017., Peer Reviewed, Postprint (published version)

Reactive transport (RT) couples bio-geo-chemical reactions and transport. RT is important to understand numerous scientific questions and solve some engineering problems. RT is highly multidisciplinary, which hinders the development of a body of knowledge shared by RT modelers and developers. The goal of this paper is to review the basic conceptual issues shared by all RT problems, so as to facilitate advancement along the current frontier: biochemical reactions. To this end, we review the basic equations to indicate that chemical systems are controlled by the set of equilibrium reactions, which are easy to model, but whose rate is controlled by mixing. Since mixing is not properly represented by the standard advection-dispersion equation (ADE), we conclude that this equation is poor for RT. This leads us to review alternative transport formulations, and the methods to solve RT problems using both the ADE and alternative equations. Since equilibrium is easy, difficulties arise for kinetic reactions, which is especially true for biochemistry, where numerous challenges are open (how to represent microbial communities, impact of genomics, effect of biofilms on flow and transport, etc.). We conclude with the basic eleven conceptual issues that we consider fundamental for any conceptually sound RT effort., This work is part of grants MEDISTRAES III funded by MCIN/AEI/ PID2019-110212RB-C22 and MCIN/AEI/PID2019-110311RB-C21 and Water JPI project MARadentro (PCI2019-103603), and by the Catalan Water Agency through the project RESTORA (CA210/18/00040). IDAEA-CSIC is a Center of Excellence Severo Ochoa (Grant CEX2018-000794-S funded by MCIN/AEI/ 10.13039/501100011033)., Peer Reviewed, Postprint (published version)

Tidal analysis is an aquifer scale testing that is a low-cost alternative to pumping tests for evaluating aquifer hydraulic parameters without groundwater extraction. Many analytical solutions may be used to assess aquifer head fluctuations in response to tidal fluctuations. Nonetheless, they are rarely used in practice. Aside from that, most analytical solutions are based on a conceptual model that typically consists of an unconfined aquifer and a confined aquifer separated by an aquitard, where hydraulic head fluctuations in the unconfined aquifer part are commonly neglected. Additionally, the frequent confined aquifer short response time to sea-level fluctuations cannot rely on hydraulic connection of the confined aquifer to the sea through the aquitard. As a consequence, when analytical solutions are applied to real-world cases, the hydraulic diffusivity is overestimated. In this study, we investigate through different numerical simulations the fluctuations of the phreatic surface by considering the delayed yield. Numerical results demonstrate that the mechanical effect generated by the load over the sea bottom exerted by sea-level fluctuations is a key factor when determining aquifer parameters. We further show that in multilayer systems, head fluctuations in various aquifer layers can cause interferences and, consequently, increased attenuation of the tidal signal, resulting in an overestimation of the inferred hydraulic diffusivity. Our results provide guidance on how to properly reproduce tidal responses in coastal aquifers., Peer Reviewed, Postprint (published version)

Modeling solute transport in heterogeneous porous media faces two challenges: scale dependence of dispersion and reproducing mixing separately from spreading. Both are crucial since real applications may require km scales whereas reactions, often controlled by mixing, may occur at the pore scale. Methods have been developed in response to these challenges, but none has satisfactorily characterized both processes. In this paper, we propose a formulation based on the Water Mixing Approach extended to account for velocity variability. Velocity is taken as an independent variable, so that concentration depends on time, space and velocity. Therefore, we term the formulation the Multi-Advective Water Mixing Approach. A new mixing term between velocity classes emerges in this formulation. We test it on Poiseuille’s stratified flow using the Water Parcel method. Results show high accuracy of the formulation in both dispersion and mixing. Moreover, the mixing process exhibits Markovianity in space even though it is modeled in time, Peer Reviewed, Postprint (published version)

Reactive transport (RT) through heterogeneous media, may cause chemical heterogeneity if water flux is slow through portions of the medium. In such cases, chemical localization (i.e., the occurrence of reactions that would not occur in well mixed media) may develop, which is especially relevant for biochemical reactions occurring in biofilms. The objective of this work is to study the conditions for chemical localization. We represent the impact of heterogeneity by means of the non-local multirate mass transfer (MRMT) model, which views the porous media as consisting of one mobile and many immobile zones. A dimensional analysis of the governing equations shows that the problem is characterized by reaction times and the distribution of residence times in immobile zones, relative to transport time. To analyze the interplay between them, we simulated simple RT problems in multicontinuum media. Results indicate that immobile zones with residence times much smaller than transport can be lumped together with the mobile zone by modifying the reaction rates, which reduces computations. More importantly, reactions driven by species that are not present in the inflowing water but are the result of previous reactions will take place preferentially in immobile zones, whose residence time is comparable to or larger than reaction times. In fact, daughter species may take a long time and distance to build up. That is, daughter species will not be largest near the inflow, where parent species display largest concentrations, but further downstream at isolated (long residence times) immobile zones., The authors acknowledge the financial support of project NITREM (European Union, European Institute of Innovation and Technology, project number 17013, PA2021/EIT/EIT Raw Materials GA2021 EIT RM) and the project RESTORA (Agència Catalana de l’Aigua, ACA210/ 18/0040). Additional funding was obtained from the Generalitat de Catalunya (2017 SGR1485) and the Spanish Ministry of Science and Innovation (Centre of Excellence Severo-Ochoa, CSIC-IDAEA, CEX2018–000794-S)., Peer Reviewed, Postprint (published version)

S'ha realitzat un assaig de traçadors al laboratori de camp a l'interior de l'EDAR de Palamós, que consisteix en sis rèpliques de sistema de recàrrega SAT que imiten la infiltració i el flux d'un aqüífer, cada sistema compta amb barreres reactives de diferent composició . L'objectiu de l'assaig és analitzar l'eficàcia dels materials que componen les barreres reactives quant a eliminació de contaminants, aquests han estat simulats mitjançant traçadors conservatius, amb capacitat d'adsorció diferent a la matèria orgànica i amb capacitat de biodegradació. S'han fet corbes d'arribada en concentració vs. volum recarregat acumulat i s'ha dissenyat un model numèric que simula el transport de soluts amb els processos d'advecció, dispersió, adsorció, intercanvi entre la zona mòbil i immòbil i reaccions de degradació. Mitjançant l'ajust de les dades de les corbes d'arribada amb les corbes del model, s'han obtingut el valor dels paràmetres de capacitat d'emmagatzematge, de constant de desintegració i d'intercanvi de flux màssic entre les zones mòbil i immòbil. Amb la comparació d'aquests paràmetres i la interpretació de les corbes d'arribada per a cada traçador i en cada sistema, es distingeixen les diferents respostes que han tingut les barreres reactives i que n'ha influenciat tant la composició., Se ha realizado un ensayo de trazadores en el laboratorio de campo en el interior de la EDAR de Palamós, que consiste en seis réplicas de sistema de recarga SAT que imitan la infiltración y flujo de un acuífero, cada sistema cuenta con barreras reactivas de distinta composición. El objetivo del ensayo es analizar la efectividad de los materiales que componen las barreras reactivas en cuanto a eliminación de contaminantes, estos han sido simulados mediante trazadores conservativos, con distinta capacidad de adsorción a la materia orgánica y con capacidad de biodegradación. Se han elaborado curvas de llegada en concentración vs. volumen recargado acumulado y se ha diseñado un modelo numérico que simula el transporte de solutos con los procesos de advección, dispersión, adsorción, intercambio entre la zona móvil e inmóvil y reacciones de degradación. Mediante el ajuste de los datos de las curvas de llegada con las curvas del modelo, se han obtenido el valor de los parámetros de capacidad de almacenamiento, constante de desintegración e intercambio de flujo másico entre las zonas móvil e inmóvil. Con la comparación de estos parámetros y la interpretación de las curvas de llegada para cada trazador y en cada sistema, se distinguen las distintas respuestas que han tenido las barreras reactivas y que tanto ha influenciado la composición de estas., A tracer test has been carried out in the field laboratory inside the Palamós WWTP, which consists of six replicas of the SAT recharge system that mimic the infiltration and flow of an aquifer, each system has reactive barriers with different composition. The aim of the test is to analyze the effectiveness of the materials that compose the reactive barriers in terms of contaminant removal, these have been simulated using conservative tracers, with different adsorption capacity to organic matter and biodegradation capacity. Breakthrough curves in concentration vs. accumulated recharged volume and a numerical model has been elaborated that simulates the transport of solutes with the processes of advection, dispersion, adsorption, exchange between the mobile and immobile zone and degradation reactions. By adjusting the data of the breakthrough curves with the curves of the model, the value of the parameters of storage capacity, disintegration constant and mass flow exchange between the mobile and immobile zones have been obtained. With the comparison of these parameters and the interpretation of the breakthrough curves for each tracer and in each system, the different responses that the reactive barriers have had and how much they have influenced their composition are distinguished

Reactive transport modeling is a methodological tool to study the coupled physical, chemical and biological processes in Earth system. It is complex not only because of the nature of the equations, but also because of the effects of the porous medium heterogeneity on reactive transport. This thesis aims to deepen the understanding of reactive transport processes in order to explain the biochemical degradation process in porous media, with special emphasis on the role of biofilm and its growth. First, we propose a general and efficient numerical solution of reactive transport in multicontinuum media using Multirate Mass Transfer (MRMT) approach. To overcome the non-linearity of the problem, induced by non-linear kinetics, we use the Newton-Raphson method to get the global solution. We solve the system of equations in block form, which allow us to reduce the unknowns to those of mobile zones and to, thus improving efficiency. The solution is validated by comparison with analytical solution for linear kinetics. The code is developed in Object-oriented way, which enables the code reusability and data polymorphism. Second, we investigate the conditions for chemical localization (i.e., the occurrence of reactions that would not be possible in single continuum media). To this end, we write the multicontinuum transport equations in dimensionless form to find that reactive transport in multicontinuum media is governed by three characteristic times: the distribution of residence times in immobile zones, and the characteristic reaction and transport times. To study the interplay between these three characteristic times, we simulate three chemical systems: conservative, single reaction and sequential reaction. Results demonstrate that reactions driven by species that result from previous reactions will localize in immobile zones whose residence time is comparable to reaction times. Furthermore, immobile zones with residence times much smaller than those for transport can be lum, El modelado de transporte reactivo es una herramienta metodológica para estudiar los procesos físicos, químicos y biológicos acoplados en el sistema terrestre. Es complejo no solo por la naturaleza de las ecuaciones, sino también por los efectos de la heterogeneidad del medio poroso sobre el transporte reactivo. Esta tesis tiene como objetivo profundizar en el conocimiento de los procesos de transporte reactivo para explicar el proceso de degradación bioquímica en medios porosos, con especial énfasis en el papel del biofilm y su crecimiento. En primer lugar, proponemos una solución numérica general y eficiente de transporte reactivo en medios multicontinuum utilizando el enfoque de Transferencia de Masa Multivelocidad (MRMT). Para superar la no linealidad del problema, inducida por una cinética no lineal, utilizamos el método de Newton-Raphson para obtener la solución global. Resolvemos el sistema de ecuaciones en forma de bloque, lo que nos permite reducir las incógnitas a las de zonas móviles y a, mejorando así la eficiencia. La solución se valida por comparación con la solución analítica para cinética lineal. El código se desarrolla de forma orientada a objetos, lo que permite la reutilización del código y el polimorfismo de los datos. En segundo lugar, investigamos las condiciones para la localización química (es decir, la ocurrencia de reacciones que no serían posibles en un medio continuo único). Con este fin, escribimos las ecuaciones de transporte multicontinuum en forma adimensional para encontrar que el transporte reactivo en medios multicontinuum se rige por tres tiempos característicos: la distribución de los tiempos de residencia en zonas inmóviles, y los tiempos de reacción y transporte característicos. Para estudiar la interacción entre estos tres tiempos característicos, simulamos tres sistemas químicos: conservador, reacción única y reacción secuencial. Los resultados demuestran que las reacciones impulsadas por especies que resultan de reacciones p, La modelització del transport reactiu és una eina metodològica per estudiar els processos físics, químics i biològics acoblats en el sistema terrestre. És complex no només per la naturalesa de les equacions, sinó també pels efectes de l’heterogeneïtat mitjana porosa sobre el transport reactiu. Aquesta tesi té com a objectiu aprofundir en la comprensió dels processos de transport reactiu per explicar el procés de degradació bioquímica en medis porosos, amb especial èmfasi en el paper del biofilm i el seu creixement. En primer lloc, proposem una solució numèrica general i eficient de transport reactiu en medis multicontinuos mitjançant l'enfocament de transferència de massa multirata (MRMT). Per superar la no linealitat del problema, induïda per cinètiques no lineals, fem servir el mètode de Newton-Raphson per obtenir la solució global. Resolem el sistema d’equacions en forma de blocs, que ens permeten reduir les incògnites a les de les zones mòbils i a, millorant així l’eficiència. La solució es valida comparant-la amb una solució analítica de cinètica lineal. El codi es desenvolupa de manera orientada a objectes, que permet la reutilització del codi i el polimorfisme de dades. En segon lloc, investigem les condicions per a la localització química (és a dir, l’aparició de reaccions que no serien possibles en un mitjà continu). Amb aquest objectiu, escrivim les equacions de transport multicontinu en forma adimensional per trobar que el transport reactiu en mitjans multicontinuos es regeix per tres temps característics: la distribució dels temps de residència en zones immòbils i els temps de reacció i transport característics. Per estudiar la interacció entre aquests tres temps característics, simulem tres sistemes químics: conservador, de reacció única i reacció seqüencial. Els resultats demostren que les reaccions impulsades per espècies que resulten de reaccions anteriors es localitzaran en zones immòbils el temps de residència és comparable als temps de reacció. A, (Xinès) 反应运移模型是地球系统中研究物理、化学和生物耦合过程的一种方法工具。反应运移是复杂的，不仅在于其控制方程本身的复杂性，而且受多孔介质非均质性的影响。本论文旨在加深对反应运移过程的理解，以解释多孔介质中的生物化学降解过程，尤其是生物膜的生长及其作用。 首先，我们利用多速率传质(MRMT)方法提出了多连续介质中反应运移的一种通用且高效的数值解。为克服非线性动力学反应导致问题的非线性，我们采用牛顿-拉夫森方法迭代求得全局解。利用分块的形式求解方程组，将未知量的个数减少为可移动区域的个数，从而提高计算效率。通过与线性动力学解析解的比较，验证了该方法的正确性。采用面向对象的方式开发程序，实现了代码的可重用性和数据多态性。 其次，我们研究了局部化学反应的条件，即在单一连续介质中不可能发生的反应的发生。为此，我们推导了多连续介质中的反应运移方程的无量纲形式，发现多连续介质中的反应运移受控于三个特征时间:不可移动区停留时间的分布，反应时间和运移时间。为研究这三种特征时间之间的相互作用，我们模拟了三种化学体系:保守反应、单反应和顺序反应。结果表明，由前一的反应导致的物种驱动的反应将定位于停留时间与反应时间相当的不可移动区域。此外，可将停留时间比运移时间小的多的不可移动区域视作可移动区域（假设非常快的反应处于平衡状态），从而很大的减少了计算。 最后，我们模拟了有微生物参与的反应运移，涉及的生物化学反应不仅能够氧化有机碳，而且能够为微生物的生长提供碳源，从而导致生物膜的生长。众所周知，生物膜的生长会导致生物堵塞（即渗透性的降的），大多研究致力于该方向。但生物膜的生长也会导致孔隙几何形状和连通性发生显著变化，不仅导致不可移动区域平均停留时间的增加，而且改变其分布。如上所述，这对于研究局部（生物）化学过程至关重要，特别是在考虑微生物介导的反应时，其往往集中在生物膜中。我们提出了一个停留时间在不可移动区域中随生物膜生长的演化模型。通过与文献中提取的实验数据进行对比，在生长的不同阶段进行示踪实验，来测试该模型。结果表明，该模型能够较好地再现实验的显著性特征。, Postprint (published version)

Seawater intrusion (SWI) consists in the movement of seawater (SW) into freshwater (FW) aquifers, contaminating drinking water resources. SWI, along with the parallel reduction of Submarine Groundwater Discharge may lead to ecological impacts beyond the reduction of FW resources. Water salinity is the critical physical property to identify SWI. The salinity contrast between FW (~1g/L) and SW (35g/L) is high enough for salinity and, therefore, water electrical conductivity (ECw), to be indirectly measured using geophysical techniques such as geophysical logs (e.g. induction) or electrical and electromagnetic methods (e.g. electrical resistivity tomography, ERT). Although the context of SWI sounds ideal for the use of geophysics, ERT displays poor resolution in depth. We propose using cross-hole ERT (CHERT) to enhance resolution, placing the electrodes in depth along the boreholes. We tested it for the first time in a SWI context, at the Argentona experimental site, some 40 km NE of Barcelona. Results of the 2-years time-lapse CHERT monitoring showed that the use of CHERT and surface ERT increased the model resolution, and the bulk EC (ECb) values from CHERT were validated with induction logs from the site. We were able to image the seasonal fluctuations of groundwater flux that cause the SW-FW interface to move seawards during periods of high flux or landwards during periods of low flux; as well as the salinization of the aquifer due to an intense drought in the study area during the monitoring period. Two short-term events were also imaged: a decrease in ECb related to a heavy rain event, and an increase in ECb in the beach area related to storm surges. We built a hydrogeophysical model to characterize the Argentona site using all available data types. The model couples a density-dependent flow and transport simulator with a geoelectrical solver through a petrophysical relation. This model was calibrated by minimizing the misfit between observed and simulated hydrau, La intrusión salina (SW) es el flujo de agua de mar (SW) hacia acuíferos de agua dulce (FW), contaminando las reservas de agua potable. La SWI, más la disminución de la Descarga de Agua Submarina, tiene impactos ecológicos más allá de la reducción del agua potable. La salinidad del agua es clave para identificar la SWI. El contraste entre el FW (~1g/L) y el SW (35g/L) es tan alto que la salinidad, y la conductividad eléctrica del agua (ECw), puede ser medida usando técnicas geofísicas como los sondeos (e.g. inducción) o los métodos eléctricos y electromagnéticos (e.g. tomografía de resistividad eléctrica, ERT). Aunque el contexto de la SWI suene ideal para el uso de la geofísica, la ERT tiene baja resolución en profundidad. Proponemos el uso de ERT entre pozos (CHERT) para mejorar la resolución, con los electrodos a lo largo de los piezómetros. Se ha testeado el CHERT por primera vez para la SWI en el sitio experimental de Argentona, a 40 km al noreste de Barcelona. Los resultados de los dos años de monitoreo muestran que el uso del CHERT y del ERT mejora la resolución del modelo, y los valores de la EC del medio (ECb) se validaron con los sondeos de inducción. Se logró visualizar las fluctuaciones temporales de los flujos de agua subterránea que causan que la interfaz FW-SW se mueva hacia el mar en periodos de alto flujo, o hacia el interior en periodos de bajo flujo; al igual que la salinización del acuífero debido a una sequía intensa en el área durante el periodo de monitoreo. Dos eventos de corta duración también se detectaron: una disminución en la ECb por un evento de lluvia intensa, y un aumento de la ECb en el área de la playa por las mareas de tormenta. Se construyó un modelo hidrogeofísico para caracterizar el sitio de Argentona usando todos los datos disponibles. El modelo acopla dos simuladores a través de una relación petrofísica: el de flujo y transporte con densidad variable y el de geoeléctrica. El modelo se calibró minimizando la distancia entre la, Postprint (published version)

Aplicat embargament des de la data de defensa fins el 31/12/2021, Freshwater quality and availability in coastal areas are affected by seawater intrusion into coastal aquifers. While coastal water quality and coastal ecosystems can be significantly affected by pollutants discharged into the sea. In this thesis we investigate: (i) the use of sea level periodic fluctuations (e.g. tides) to characterize coastal aquifers hydrodynamic parameters; (ii) the chemical reactions that occur in the mixing zone between freshwater and seawater; and (iii) the impact of high-frequency fluctuations (e.g. storms) on the mixing zone and chemical reactions. Thus, the Argentona experimental site allowed us to apply and validate the investigated methods. The results show that thanks to the tidal method we have been able to clarify the technique and make its application easier. In addition, we make one of the first applications to a real aquifer where we detail the entire process from the acquisition and filtering of head data to finally obtain the hydrodynamic parameters by numerical modeling. This allowed refining the conceptual model and observing the pronounced impact of aquitard on the propagation of inland tidal fluctuations. In addition, we have investigated the chemical reactions that occur by the mixing between freshwater and saltwater. The results show that coastal aquifers are a fairly complex system with many chemical reactions. We observe the predominance of cationic exchange reactions, but also quite a few redox reactions using organic matter as electron donors and molecules such as dissolved oxygen, nitrates, iron, or manganese oxides as electron acceptors. We have observed that quite a few reactions associated with the rocks that form the reservoir also occur. But we go beyond identifying them, we present a method to quantify these reactions, which allows us to observe the spatial distribution of the reactions. Furthermore, by quantifying them, it is possible to estimate the chemical composition of the water that is discharged into the s, La calidad y la disponibilidad del agua dulce en las zonas costeras está afectada por la intrusión marina en los acuíferos costeros. Del mismo modo, la calidad de las aguas costeras y los ecosistemas costeros pueden ser afectados significativamente por la descarga de agua subterráneaal mar. En esta tesis investigamos: (i) el uso de las fluctuaciones periódicas del nivel del mar (como las mareas) para caracterizar los parámetros hidrodinámicos de los acuíferos costeros; (ii) las reacciones químicas que ocurren en la zona de mezcla entre el agua dulce y el agua salada; y (iii) el impacto de las fluctuaciones temporales de alta frecuencia (por ejemplo las tormentas) sobre la zona de mezcla y las reacciones químicas que ocurren en el acuifero. Los metodos estudiados han sido aplicados y validados en el campo experimental de Argentona. Consideramos el acoplamiento hidromecanico sobre la respuesta del acuifero a las fluctuaciones de las mareas. El método de las mareas se aplica por primera vez a un acuífero real donde detallamos todo el proceso desde la adquisición y el filtrado de datos a la obtención de los parámetros hidrodinámicos por modelación numérica. Esto permitió refinar el modelo conceptual y observar el impacto pronunciado de las capas poca permeables sobre la propagación de las fluctuaciones de mareas hacia tierra dentro. Además, hemos investigado sobre las reacciones químicas que ocurren a lo largo de la mezcla entre el agua dulce y el agua salada. El estudio se realiza utilizando el analisis de mezcla acaplado a una herramienta de mezcla reactiva. Los resultados muestran que los acuíferos costeros son unos sistemas bastante complejos con muchas reacciones químicas. Observamos una preponderancia de las reacciones de intercambio catiónico, pero también bastantes reacciones redox usando la materia orgánica como donador de electrones y las moléculas tipo el oxígeno disueltos, los nitratos, los óxidos de hierro o de manganeso como aceptor de electrones. Hemos ob, La qualité de l’eau et sa disponibilité dans les zones côtières sont affectées par l’intrusion marine dans les aquifères côtiers. De même, la qualité des eaux côtières et les écosystèmes côtiers peuvent être considérablement affectés par les polluants rejetés dans la mer. Les travaux de cette thèse étudient : (i) l’utilisation des fluctuations périodiques du niveau de la mer (par exemple les marées) pour caractériser les paramètres hydrodynamiques des aquifères côtiers ; (ii) les réactions chimiques qui se produisent dans la zone de mélange entre l’eau douce et l’eau salée; et (iii) l’impact des fluctuations temporelles de hautes fréquences (par exemple les tempêtes) sur la zone de mélange et les réactions chimiques. Par conséquent, le site expérimental d’Argentona nous a permis d’appliquer et de valider les méthodes étudiées. De plus, nous faisons l’une des premières applications à un aquifère réel où nous détaillons l’ensemble du processus depuis l’acquisition et le filtrage des données jusqu’à l’obtention des paramètres hydrodynamiques par modélisation numérique. Cela a permis d’affiner le modèle conceptuel et d’observer l’impact prononcé des couches peu perméables sur la propagation du signal marées dans l’aquifère. De plus, nous avons étudié les réactions chimiques qui se produisent au cours du mélange entre l’eau douce et l’eau salée. Les résultats montrent que les aquifères côtiers sont des systèmes assez complexes avec de nombreuses réactions chimiques. On observe une prépondérance des réactions d’échange cationique, mais aussi pas mal de réactions redox utilisant la matière organique comme donneur d’électrons et des molécules comme l’oxygène dissous, les nitrates, les oxydes de fer ou de manganèse comme accepteurs d’électrons. Nous avons également observé que de nombreuses réactions associées aux roches qui forment le réservoir se produisent. Mais nous allons au-delà de leur identification, nous présentons une méthode pour quantifier ces réactions, qui nous, Postprint (published version)

We measure groundwater flux and thermal parameters around a borehole performing a heat dissipation test by heating the armor of a single fiber-optic cable and interpreting the resulting heating curves with a new analytical method. The procedure is similar to thermal response tests, but benefitting from the high spatial and temporal resolution of distributed temperature sensing and lasting longer, so as to measure advective dissipation. Field installation relies on an innovative method in hydrogeology, which is based on the installation of the FO cable in the annular space of the well, close to the aquifer matrix. The proposed new analytical method, expands the traditional Moving Infinitesimal Line Source Model to account for the effects of the field set up and cable materials. In fact, we show that the resulting temperature build-up goes through four periods easy to identify using the log derivative of temperature (dT/d (ln(t))): Initial response, skin (cable insulation), conduction dominated and advection dominated. We test the proposed method in an unconsolidated shallow aquifer with controlled pumping. Results are of the same order of magnitude of independent estimates of groundwater velocity., This work was funded by the projects CGL2016-77122-C2−1−R / 2-R and PID2019-110212RB-C22 / C21 of the Spanish Government. We would like to thank SIMMAR (Serveis Integrals de Manteniment del Maresme) and the Consell Comarcal del Maresme in the construction of the research site. We would like to acknowledge Sensornet (UK) for their support and collaboration. We would also like to thank Dr. Javier Benitez Buelga for his collaboration in designing and setting up the fiber-optic field installation. The author Albert Folch is a Serra Húnter Fellow., Peer Reviewed, Postprint (published version)

The drawdown response to a hydraulic stress contains crucial information to characterize an aquifer. Modeling drawdowns is far easier than modeling heads because they are subject to homogeneous (zero) internal sink/sources, and boundary and initial conditions. The problem lies on the fact that drawdowns are not measured directly but derived from measurements of head fluctuations. Resulting drawdowns may suffer persistent inaccuracies in complex systems with uncertain long-acting external stresses, so that they are affected not only by errors in head measurements, but also in estimates of the natural head evolution. This hinders the use of drawdowns in groundwater models, and forces modelers to employ absolute heads and soft information. In this context, we present a method to filter systematic errors in drawdown data during the calibration of a groundwater model. To do this, we introduce a bias correction term in a composite inverse problem that combines a natural head model with a drawdown model. Since these two models share the same parameters, a two-stage iterative optimization algorithm is developed to jointly estimate the bias, natural trends, and parameters. The method is illustrated by a synthetic example in a heterogeneous aquifer. The example shows that the method converges to the best conditional estimate even when absolute head data is strongly biased. In the same example, we demonstrate that the use of biased absolute head data in the traditional inverse problem can also provide good fittings but, in this case, the bias leads to an incorrect estimation of the transmissivity field., The final version of the paper has greatly benefitted from comments by Keith Halford and two anonymous reviewers. The authors acknowledge the financial support provided by the Sociedad Química y Minera de Chile S.A. through project “Proyección de la evolución SOP, Salar de Atacama. Fase II: ensayos de campo y laboratorio” (SA 9500001785) and by the AGAUR (Agència de Gestió d'Ajuts Universitaris i de Recerca, Generalitat de Catalunya), through project AGAUR-2017-SGR1485. M. Trabucchi acknowledges the financial support from the AGAUR through the FI fellowship (2018FIB200079)., Peer Reviewed, Postprint (published version)

The characterization of evaporitic aquifers for a better understanding of hydrodynamics and geochemical processes is of great importance, especially in environments where both the sustainability of unique ecosystems and the economic interests depend on aquifer features. This is the case of the Salar de Atacama (SdA) evaporitic nucleus, the "driving force" of this thesis, which prompt us to pursue two main objectives. First, characterizing the hydraulic behavior of the SdA nucleus, with special attention for the identification of highly connected structures (preferential flow-paths). Second, enriching the knowledge on preferential flow-paths development caused by dissolution processes (i.e. wormholes dynamics) and the corresponding changes in flow and transport behaviour. As a first step, we focused on the interpretation of hydraulic tests for aquifer characterization. Agarwal's method for recovery test interpretation was selected as suitable for analyzing the SdA aquifer response to imposed stresses for hydraulic properties estimation. Thus, we verified the method under ideal and non-ideal condition and we exposed its limitations. The latter were overcome by modifying the existing methodology and proposing an improved equivalent time to deal with variable pumping rates. At the same time we carried out a long-lasting cross-hole hydraulic test in the SdA nucleus. The complexity of system dynamics highlighted the need of seeking for a different methodology for aquifer characterization. We ended up developing a new filtering-corrective method through which aquifer characterization was carried out. The method involves estimating drawdowns, corrected from eventual systematic and structural errors, to be used as observations while automatically calibrating a groundwater model. Once validated the new method, we applied it, jointly with the stochastic inversion, to characterize the SdA nucleus in terms of spatial variability of the hydraulic conductivity at a large scale, wi, La caratterizzazione degli acquiferi evaporitici, atta a comprendere meglio i processi idrodinamici e geochimici, è di grande importanza, soprattutto in ambienti in cui sia la sostenibilità di ecosistemi unici sia gli interessi economici dipendono dalle caratteristiche dell’acquifero. È il caso del nucleo evaporitico del Salar de Atacama (SdA), il "motore" di questa tesi, che ci spinge a perseguire due obiettivi principali. In primo luogo, caratterizzare il comportamento idraulico del nucleo del SdA, con particolare attenzione all’identificazione di strutture altamente connesse (percorsi di flusso preferenziali). In secondo luogo, arricchire la conoscenza sullo sviluppo di zone di flusso preferenziale dovuto ai processi di dissoluzione (in altre parole, le dinamiche dei wormholes) e sui relativi cambiamenti nel comportamento di flusso e trasporto. Per caratterizzare una falda acquifera solitamente vengono eseguite prove di pompaggio, con lo scopo di comprendere il modello concettuale del sistema, attraverso grafici diagnostici, e stimarne le proprietà idrauliche. Tra le varie prove, le prove di recupero consistono nel misurare le variazioni del livello piezometrico nei pozzi di pompaggio e/o monitoraggio una volta completata la prova di pompaggio. Questi test sono particolarmente utili quando la portata non può essere controllata con precisione. Agarwal ha proposto un metodo, diventato standard nell’industria petrolifera, per ottenere la risposta dell’acquifero al pompaggio a partire dai dati di recupero. Tuttavia, il metodo è stato testato e verificato in misura limitata. Nel secondo capitolo di questa tesi analizziamo il metodo di Agarwal per comprenderne i limiti e superarli. I risultati ottenuti mostrano che il metodo di Agarwal fornisce eccellenti grafici di recupero (ovvero la curva di abbassamento che si otterrebbe durante il pompaggio) e buone stime dei parametri idraulici per quasi tutte le condizioni dell’acquifero, a condizione che venga utilizzata una po, La caracterització dels aqüífers evaporítics per comprendre millor els processos hidrodinàmics i geoquímics és de gran importància, especialment en entorns on tant la sostenibilitat d’ecosistemes únics com els interessos econòmics depenen de les característiques de l’aqüífer. És el cas del nucli evaporític del Salar d’Atacama (SdA), "motor" d’aquesta tesi, que ens impulsa a perseguir dos objectius principals. Primer, caracteritzar el comportament hidràulic del nucli del SdA, amb especial atenció a la identificació d’estructures altament connectades (camins de flux preferent). En segon lloc, enriquir el coneixement sobre el desenvolupament de zones de flux preferent causades pels processos de dissolució (és a dir, la dinàmica dels forats de cuc, comunament anomenats wormholes) i els canvis corresponents en el comportament del flux i del transport. Per caracteritzar un aqüífer, se solen realitzar proves de bombament que permeten comprendre el model conceptual del sistema, a través de diagrames de diagnòstic, i estimar les propietats hidràuliques. Entre les diverses proves, les de recuperació consisteixen en mesurar les variacions del nivell piezomètric en pous de bombament i/o de monitorització un cop finalitzada la prova de bombament. Aquestes proves són especialment útils quan el cabal no es pot controlar amb precisió. Agarwal va proposar un mètode, que s’ha convertit en estàndard en la indústria petroliera, per obtenir la resposta de l’aqüífer al bombament a partir de les dades de recuperació. No obstant això, el mètode ha estat provat i verificat de forma limitada. En el segon capítol d’aquesta tesi analitzem el mètode d’Agarwal per comprendre les seves limitacions i superar-les. Els nostres resultats mostren que el mètode d’Agarwal proporciona excel·lents gràfiques de recuperació (és a dir, la corba de descens que s’obtindria durant el bombament) i bones estimacions dels paràmetres hidràulics per a gairebé totes les condicions de l’aqüífer, sempre que s’utilitzi, La caracterización de los acuíferos evaporíticos para comprender mejor los procesos hidrodinámicos y geoquímicos es de gran importancia, especialmente en entornos donde tanto la sostenibilidad de ecosistemas únicos como los intereses económicos dependen de las características del acuífero. Este es el caso del núcleo evaporítico del Salar de Atacama (SdA), "motor" de esta tesis, que nos impulsa a perseguir dos objetivos principales. Primero, caracterizar el comportamiento hidráulico del núcleo del SdA, poniendo especial atención en la identificación de estructuras altamente conectadas (caminos de flujo preferente). En segundo lugar, contribuir al conocimiento sobre el desarrollo de zonas de flujo preferente causadas por procesos de disolución (es decir, la dinámica de los agujeros de gusano, comúnmente llamados wormholes) y los correspondientes cambios en el comportamiento del flujo y del transporte. Para caracterizar un acuífero, se suelen realizar pruebas de bombeo que permiten comprender el modelo conceptual del sistema a través de diagramas de diagnóstico, y estimar las propiedades hidráulicas. Entre las diversas pruebas, las de recuperación consisten en medir las variaciones del nivel piezométrico en pozos de bombeo y/o de monitoreo una vez finalizada la prueba de bombeo. Estas pruebas son especialmente útiles cuando el caudal no se puede controlar con precisión. Agarwal propuso un método, que se ha convertido en estándar en la industria petrolera, para obtener la respuesta del acuífero al bombeo a partir de los datos de recuperación. Sin embargo, el método ha sido probado y verificado de forma limitada. En el segundo capítulo de esta tesis analizamos el método de Agarwal para comprender sus limitaciones y superarlas. Nuestros resultados muestran que el método de Agarwal proporciona excelentes gráficas de recuperación (es decir, la curva de descenso que se obtendría durante el bombeo) y buenas estimaciones de los parámetros hidráulicos para casi todas las condic, Postprint (published version)

The study of transport of reacting solute through aquifers is relevant in many engineering fields. Reactive transport (RT) is complex because it consists of two phenomena, solute transport and chemical reactions, both of which are affected by heterogeneity. Because of this complexity, RT is solved by using numerical methods obtained from mathematical formulations. This thesis seeks to improve these mathematical formulations for RT and, specifically, to (a) provide a formulation that recognizes the heterogeneity of transport and chemistry at different scales and (b) improve the algorithms to solve RT. The thesis proposes using water exchange to describe mixing, which controls fast chemical reactions. This choice leads to a family of formulations. The Water Mixing Approach (WMA) is initially proposed as an efficient formulation equivalent to the Advection Dispersion equation (ADE). Multi-Rate Water Mixing (MRWM) is employed to account explicitly for chemical heterogeneity. Finally, the Multi-Advective Water Mixing Approach (MAWMA) allows distinguishing between dispersion, driven by hydraulic heterogeneity, and mixing, driven by both hydraulic heterogeneity and diffusion. In all these formulations, the entire transport phenomenon may be modeled as water processes. This implies that solute concentration becomes an attribute of water, exclusively relevant for chemical phenomena that become decoupled from transport. The accuracy of these formulations is tested in several cases., L’estudi de transport de soluts reactius en aqüífers és rellevant en molts camps de l’enginyeria. Aquest transport reactiu (TR) és complex perquè és una conseqüència de dos fenòmens (transport de solut i reaccions químiques) i ambdós afectats per l’heterogeneïtat. Donada la seva complexitat, el TR es resol mitjançant models numèrics obtinguts a partir de formulacions matemàtiques. La present tesis busca millorar aquestes formulacions matemàtiques pel TR i, específicament (a) donar una formulació que reconegui la heterogeneïtat del transport i la química implicada a diferents escales i (b) millorar els algoritmes per resoldre el TR. La tesis proposa utilitzar intercanvi d’aigües per descriure la mescla de soluts, la qual controla les reaccions químiques ràpides. La proposta condueix a una família de formulacions. La Water Mixing Approach (WMA) es proposa inicialment com una formulació eficient i equivalent a l’Equació d’Advecció i Dispersion (ADE). La formulació Multi-Rate Water Mixing (MRWM) s¿utilitza per representar explícitament l’heterogeneïtat química. Finalment, la formulació Multi-Advective Water Mixing Approach (MAWMA), permet distingir la mescal (controlada per l’heterogeneïtat hidràulica i la difusió) de la dispersió (controlada únicament per l’heterogeneïtat hidràulica). En totes aquestes formulacions, el fenomen de transport es pot modelar exclusivament com a processos de transport d’aigua. Per tant, la concentració de solut esdevé un atribut de l’aigua i afecta únicament al fenomen químic, que és completament desacoblat del fenomen de transport. Comprovem en repetides ocasions la precisió d’aquestes formulacions, El estudio de transporte de solutos reactivos en acuíferos es importante en muchos campos de la ingeniería. El transporte reactivo (TR) es complejo porque resulta de dos fenómenos, transporte de soluto y reacciones químicas, afectados por heterogeneidad. Dada la complejidad del TR, su solución requiere modelos numéricos obtenidos a partir de formulaciones matemáticas. La presente tesis busca mejorar estas formulaciones para el TR y específicamente: (a) dar una formulación que reconozca la heterogeneidad química y del transporte a diversas escalas y (b) mejorar los algoritmos para resolver el TR. La tesis propone emplear el intercambio de aguas para definir la mezcla, lo que da lugar a una familia de formulaciones. La Formulación de mezcla de aguas (WMA) se propone inicialmente como una forma eficiente y equivalente de la Ecuación de Advección y Dispersión. La formulación de mezcla de aguas Multi-Ritmo (MRWM) se utiliza para representar explícitamente la heterogeneidad química. Finalmente, la formulación de mezcla de aguas Multi- Advectiva (MAWMA), distingue la mezcla de la dispersión. En todas estas formulaciones, el fenómeno de transporte se puede modelar únicamente mediante procesos de transporte de agua. Por lo tanto, la concentración de soluto se convierte exclusivamente en un atributo del agua, que afecta los fenómenos químicos, que quedan desacoplados del fenómeno de transporte. Comprobamos en repetidas ocasiones la precisión de estas formulaciones, Postprint (published version)

Surface electrical resistivity tomography (ERT) is a widely used tool to study seawater intrusion (SWI). It is noninvasive and offers a high spatial coverage at a low cost, but its imaging capabilities are strongly affected by decreasing resolution with depth. We conjecture that the use of CHERT (cross-hole ERT) can partly overcome these resolution limitations since the electrodes are placed at depth, which implies that the model resolution does not decrease at the depths of interest. The objective of this study is to test the CHERT for imaging the SWI and monitoring its dynamics at the Argentona site, a well-instrumented field site of a coastal alluvial aquifer located 40¿km NE of Barcelona. To do so, we installed permanent electrodes around boreholes attached to the PVC pipes to perform time-lapse monitoring of the SWI on a transect perpendicular to the coastline. After 2 years of monitoring, we observe variability of SWI at different timescales: (1) natural seasonal variations and aquifer salinization that we attribute to long-term drought and (2) short-term fluctuations due to sea storms or flooding in the nearby stream during heavy rain events. The spatial imaging of bulk electrical conductivity allows us to explain non-monotonic salinity profiles in open boreholes (step-wise profiles really reflect the presence of freshwater at depth). By comparing CHERT results with traditional in situ measurements such as electrical conductivity of water samples and bulk electrical conductivity from induction logs, we conclude that CHERT is a reliable and cost-effective imaging tool for monitoring SWI dynamics., This work was funded by the project CGL2016-77122-C2-1-R/2-R of the Spanish Government. This project also received funding from the European Commission, Horizon 2020 research and innovation programme (Marie Sklodowska-Curie (grant no. 722028)). The author Albert Folch is a Serra Húnter Fellow., Peer Reviewed, Postprint (published version)

Managed aquifer recharge (MAR) is known to increase available water quantity and to improve water quality. However, its implementation is hindered by the concern of polluting aquifers, which might lead to onerous treatment and regulatory requirements for the source water. These requirements might make MAR unsustainable both economically and energetically. To address these concerns, we tested reactive barriers laid at the bottom of infiltration basins to enhance water quality improvement during soil passage. The goal of the barriers was to (1) provide a range of sorption sites to favor the retention of chemical contaminants and pathogens; (2) favor the development of a sequence of redox states to promote the degradation of the most recalcitrant chemical contaminants; and (3) promote the growth of plants both to reduce clogging, and to supply organic carbon and sorption sites. We summarized our experience to show that the barriers did enhance the removal of organic pollutants of concern (e.g., pharmaceuticals and personal care products). However, the barriers did not increase the removal of pathogens beyond traditional MAR systems. We reviewed the literature to suggest improvements on the design of the system to improve pathogen attenuation and to address antibiotic resistance gene transfer., This research was funded by the Spanish Ministry of Science and Innovation CEX2018-000794-S), Water JPI (MARadentro-PCI2019-103603) and Catalan Water Agency (RESTORA-CA210/18/00040)., Peer Reviewed, Postprint (published version)

The processes that control water quality improvement during artificial recharge (filtering, degradation, and adsorption) can be enhanced by adding a reactive barrier containing different types of sorption sites and promoting diverse redox states along the flow path, which increases the range of pollutants degraded. While this option looks attractive for renaturazing reclaimed water, three issues have to be analyzed prior to broad scale application: (1) a fair comparison between the system with and without reactive barrier; (2) the role of plants in prevention of clogging and addition of organic carbon; and (3) the removal of pathogens. Here, we describe a pilot installation built to address these issues within a waste water treatment plant that feeds on water reclaimed from the secondary outflow. The installation consists of six systems of recharge basin and aquifer with some variations in the design of the reactive barrier and the heterogeneity of the aquifer. We report preliminary results after one year of operation. We find that (1) the systems are efficient in obtaining a broad range of redox conditions (at least iron and manganese reducing), (2) contaminants of emerging concern are significantly removed (around 80% removal, but very sensitive to the compound), (3) pathogen indicators (E. coli and Enterococci) drop by some 3–5 log units, and (4) the recharge systems maintained infiltration capacity after one year of operation (only the system without plants and the one without reactive barrier displayed some clogging). Overall, the reactive barrier enhances somewhat the performance of the system, but the gain is not dramatic, which suggests that barrier composition needs to be improved., This study was supported by the Water Joint Programming Initiative (JPI)Water Challenges for a ChangingWorld 2014 through the project ACWAPUR (ACcelerated Water PURification during artificial recharge of aquifers: A tool to restore drinking water sources) and partially funded by the Spanish Ministry of Science, Innovation and Universities through PCIN-2015-245. We are very grateful to the staff of ‘Aguas de la Costa Brava' for their assistance, and to Ma Pau Serra-Roig and Ana Julia Acunha for their contribution to the chemical analysis and to Juli_a Garcia for his effort with the field site work., Peer Reviewed, Postprint (published version)

Aplicat embargament des de la data de defensa fins al 31 de desembre de 2020, Seawater intrusion (SWI) causes not only salinization of coastal aquifers, but also a reduction submarine groundwater discharge (SGD) and nutrient fluxes to marine ecosystems. We have developed a small scale experimental field site to gain insights into both SWI and SGD. The site is located in a coastal alluvial aquifer at the mouth of an ephemeral stream in the Maresme coastline (Barcelona, Spain). Here, we describe our attempts for a detailed site characterization, which was based on the four pillars of hydrogeology: geology (Lithological description and geochemical analysis of core), geophysics (borehole logs, Electrical Resistivity Tomography and thermal monitoring), hydraulics (pumping and tidal response tests) and hydrochemistry (major and minor elements, stable isotopes and Radium isotopes for SGD assessment). As it turned out, all four pillars yielded some surprise. The aquifer consists of alluvial sediments, rather than coastal plain deposits. Tidal loading, rather than hydraulic connection to the sea, appears to drive tidal response, in spite of the aquifer being unconfined. Hydrochemistry suggests an unusually reactive layer, with all cations reflecting some mineral dissolution process, beyond the expected cation exchange. Radium increased with salinity, but the correlation was poor, partly blurred by pH, which was low in the deep portions of the aquifer. These observations were largely explained with the help of geophysics. Both borehole logs and cross-hole ERT helped in identifying silt layers that are frequent in alluvial deposits but proved to play a critical role here. The integration of the different techniques allowed to characterize the different distribution of salt- and freshgroundwater, that in fact yielded an inverse disposition to what is expected in coastal hydrogeology. To improve SGD quantification, we also characterized radium behavior within the aquifer. The recovered sediment during borehole drilling was used to perform both batch and c, La intrusión de agua de mar causa no solo la salinización de los acuíferos costeros, sino también una reducción en la descarga submarina de agua subterránea y en los flujos de nutrientes a los ecosistemas marinos. Para poder entender los efectos que provoca la coexistencia de ambos procesos en acuíferos costeros aluviales, hemos desarrollado un campo experimental a pequeña escala. La zona de campo está ubicada en la desembocadura de una riera efímera en la costa del Maresme (Barcelona, España), en un acuífero aluvial costero. En la presente tesis, se describen los intentos de caracterización detallada del sitio, basada en los cuatro pilares de la hidrogeología: geología (descripción litológica y análisis geoquímico de sedimentos), geofísica (registros de pozos, tomografía de resistividad eléctrica y monitoreo térmico), hidráulica (bombeo y pruebas de respuesta de marea) e hidroquímica (elementos mayores y menores, isótopos estables e isótopos de radio para la evaluación de la descarga de agua submarina). La implementación de los diferentes tipos de técnicas supuso la reconsideración de algunas de las preconcepciones establecidas a priori: la parte del acuífero analizada está constituida por sedimentos aluviales, en lugar de depósitos de llanura costera. A pesar de que el acuífero es libre, parece que la respuesta del acuífero a las mareas está causada por la carga mecánica impuesta por el mar, en lugar de evidenciar la conexión hidráulica con el mismo. La hidroquímica sugiere una capa inusualmente reactiva, con todos los cationes que reflejan algún proceso de disolución mineral, más allá del intercambio catiónico esperado. El radio aumenta con la salinidad, pero no de una manera evidente, debido a que el pH es expecialmente ácido en la zona más profunda del acuífero considerado. La integración de las diferentes técnicas permitió caracterizar la distribución diferentes masas de agua subterránea salada y dulce, que de hecho presentaban una disposición inversa a lo que, Postprint (published version)

The characterization of saline water intrusion (SWI) and its hydrodynamics is a key issue to understand submarine groundwater discharge (SGD) and manage groundwater resources in coastal areas. To test and compare different methods of characterization and monitoring, a new experimental site has been constructed in a coastal alluvial aquifer north of Barcelona city (Catalonia, Spain). The site is located between 30 and 90 m from the seashore and comprises 16 shallow piezometers organized in nests of three with depths ranging between 15 and 25 m and 4 solitary piezometers. The objective of this paper is to combine different recently developed monitoring techniques to evaluate temporal variations in the aquifer hydrodynamics of the site at different spatial scales before and after the dry season of 2015. At the site scale, fibre optic distributed temperature sensing (FO-DTS), for the first time applied to study SWI, and cross-hole electrical resistivity tomography (CHERT) has been applied. At the meter/borehole scale, electrical conductivity of the formation has been applied not only in a repeated manner (“time lapse”), but also for the first time at relatively high frequency (1 sample every 10 min). CHERT has provided a better characterization of the seawater intrusion than electrical conductivity data obtained from piezometers. The combination of techniques has allowed improving the understanding of the system by: 1) characterizing the extent and shape of SWI; 2) differentiating two different dynamics in the aquifer; and 3) identifying preferential flow paths over different time and spatial intervals. Future challenges and the application of these techniques in other areas are also discussed., This work was funded by the projects CGL2013-48869-C2-1-R/2-R and CGL2016-77122-C2-1-R/2-R of the Spanish Government. We would like to thank SIMMAR (Serveis Integrals de Manteniment del Maresme) and the Consell Comarcal del Maresme in the construction of the research site. The authors want to thank the support of the Generalitat de Catalunya to MERS (2018 SGR-1588). This work is contributing to the ICTA ‘Unit of Excellence’ (MinECo, MDM2015- 0552). Part of the funding was provided by the French network of hydrogeological observatories H+ (hplus/ore/fr/en) and the ANR project EQUIPEX CRITEX (grant ANR-11-EQPX-0011). V Rodellas acknowledges financial support from the Beatriu de Pinós postdoctoral program of the Generalitat de Catalunya (2017-BP-00334). M. Diego‐Feliu acknowledges the economic support from the FI‐2017 fellowships of the Generalitat de Catalunya autonomous government (2017FI_B_00365). This project also received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie Grant Agreement No 722028., Peer Reviewed, Postprint (author's final draft)

Geologic carbon storage, as well as other geo-energy applications, such as geothermal energy, seasonal natural gas storage and subsurface energy storage imply fluid injection and/or extraction that causes changes in rock stress field and may induce (micro)seismicity. If felt, seismicity has a negative effect on public perception and may jeopardize wellbore stability and damage infrastructure. Thus, induced earthquakes should be minimized to successfully deploy geo-energies. However, numerous processes may trigger induced seismicity, which contribute to making it complex and translates into a limited forecast ability of current predictive models. We review the triggering mechanisms of induced seismicity. Specifically, we analyze (1) the impact of pore pressure evolution and the effect that properties of the injected fluid have on fracture and/or fault stability; (2) non-isothermal effects caused by the fact that the injected fluid usually reaches the injection formation at a lower temperature than that of the rock, inducing rock contraction, thermal stress reduction and stress redistribution around the cooled region; (3) local stress changes induced when low-permeability faults cross the injection formation, which may reduce their stability and eventually cause fault reactivation; (4) stress transfer caused by seismic or aseismic slip; and (5) geochemical effects, which may be especially relevant in carbonate-containing formations. We also review characterization techniques developed by the authors to reduce the uncertainty in rock properties and subsurface heterogeneity both for the screening of injection sites and for the operation of projects. Based on the review, we propose a methodology based on proper site characterization, monitoring and pressure management to minimize induced seismicity., Peer Reviewed, Postprint (published version)

Tracer visualization in the laboratory at high spatial and temporal resolution can help advance the study of mixing processes. However, grain borders, fluctuations in lighting and non-uniform brightness contribute to produce noisy images of concentrations that cannot be used to directly estimate mixing at the local scale. We present a new methodology to visualize local values of mixing from noisy images of optical tracers based on a nonparametric regression algorithm. The methodology is used to provide a full visualization of the mixing dynamics that occur in a tracer experiment performed in a reconstructed heterogeneous aquifer consisting of two materials with contrasting hydraulic properties. Results show that the method is capable of providing optimal images of mixing of high quality even at complex material edges between bodies of different sand. In transport problems, dispersivity control the mixing. Understand the behaviour of this parameter allow characterizing the mixing. Characterize this parameter is complex due to the heterogeneity and the spatial and temporal fluctuations, in that many assumptions (about the definition of dispersion, how to represent it locally, and how to handle medium heterogeneities or velocity fluctuations) are required to make it tractable. Surprisingly the results go in opposite directions. All agree that fluctuations of velocity transverse to the mean flow direction enhance transverse dispersion; some authors conclude that the enhancement is very large; others conclude that it is not so important. Researchers generally agree the effects of velocity fluctuations on longitudinal dispersion is much smaller than on transverse dispersion. However, they have found it to decrease. Others increase, others remain unchanged ironically, and despite of all the above research, little experimental work has been performed. For this reason, we presents an experiment specifically aimed at evaluating the effect of temporal fluctuations of velocity, El transporte en un medio heterogéneo sometido a actuaciones temporales del campo de velocidades está siendo objeto de varias investigaciones, ya que los flujos de agua subterránea varían naturalmente en el tiempo (ciclos de evapotranspiración, variaciones estacionales en la lluvia, secuencias de años secos y húmedos o fluctuaciones locales por los bombeos, etc.) y por qué es intuitivo que las fluctuaciones temporales de la velocidad deberían mejorar la mezcla y dispersión del soluto. La mezcla se reconoce cada vez más como el proceso crítico para comprender y modelar el transporte reactivo. Sin embargo, como la mezcla está altamente influenciada por la variabilidad espacial de la velocidad y depende no linealmente de las concentraciones, su caracterización por ahora está lejos de ser la óptima. La visualización de un trazador en el laboratorio a alta resolución espacial y temporal puede ayudar a avanzar en el estudio de los procesos de mezcla. Sin embargo, los bordes irregulares de los granos de arena, las fluctuaciones en la iluminación y el brillo no uniforme contribuyen a producir imágenes con ruido en las concentraciones que finalmente no se pueden ser usar para estimar directamente la mezcla a una escala local. Presentamos una nueva metodología para visualizar los valores locales de la mezcla a partir de imágenes con el ruido proveniente de trazadores ópticos basados en un algoritmo de regresión no paramétrico. La metodología se utiliza para proporcionar una visualización de la dinámica de la mezcla que se produce en un experimento con un trazador óptico realizado en un acuífero heterogéneo construido en laboratorio que consta de dos materiales con contraste en sus propiedades hidráulicas. Los resultados muestran que el método es capaz de proporcionar imágenes óptimas de la mezcla de una alta calidad incluso en las zonas donde se localizan los bordes de materiales complejos como entre cuerpos de arena diferente. En los problemas de transporte, la dispersividad, El transport en mitjans heterogenis sota camps de velocitat temporalment fluctuant ha estat objecte de molta investigació tant perquè els fluxos d'aigües subterrànies varien de forma natural en el temps (cicles d'evapotranspiració, variacions estacionals de precipitacions, seqüències d'anys secs i humits o fluctuacions de bombeig) i perquè és intuïtiu les fluctuacions temporals de la velocitat haurien de millorar la barreja i la dispersió del solut. La mesura es reconeix cada cop més com el procés crític per comprendre i modelar el transport reactiu. Tanmateix, atès que la barreja està molt influenciada per la variabilitat espacial de la velocitat i depèn no linealment de les concentracions, la seva caracterització adequada queda lluny de ser òptima. La visualització del traçador al laboratori amb una alta resolució espacial i temporal pot ajudar a avançar en l'estudi dels processos de mescla. Tanmateix, els límits del gra, les fluctuacions de la il·luminació i la brillantor no uniforme contribueixen a produir imatges sorolloses de concentracions que no es poden utilitzar per estimar directament la barreja a escala local. Presentem una nova metodologia per visualitzar valors locals de barreja a partir d'imatges sorolloses de traçadors òptics basats en un algorisme de regressió no paramètrica. La metodologia s'utilitza per proporcionar una visualització completa de la dinàmica de mescla que es produeix en un experiment de traçador realitzat en un aqüífer heterogeni reconstruït que consta de dos materials amb propietats hidràuliques contrastants. Els resultats mostren que el mètode és capaç de proporcionar imatges òptimes de mescla d'alta qualitat fins i tot en vores de material complex entre cossos de sorra diferent. En els problemes de transport, la dispersió controla la barreja. Comprendre el comportament d'aquest paràmetre permet caracteritzar la barreja. Caracteritzar aquest paràmetre és complex a causa de l'heterogeneïtat i les fluctuacions espacials i temporals, Postprint (published version)

Pumping tests are performed during aquifer characterization to gain conceptual understanding about the system through diagnostic plots and to estimate hydraulic properties. Recovery tests consist of measuring head response in observation and/or pumping wells after pumping termination. They are especially useful when the pumping rate cannot be accurately controlled. They have been traditionally interpreted using Theis' recovery method, which yields robust estimates of effective transmissivity but does not provide information about the conceptual model. Agarwal proposed a method that has become standard in the oil industry, to obtain both early and late time reservoir responses to pumping from recovery data. However, the validity of the method has only been tested to a limited extent. In this work, we analyze Agarwal's method in terms of both drawdowns and log derivatives for non-ideal conditions: leaky aquifer, presence of boundaries, and one-dimensional flow. Our results show that Agarwal's method provides excellent recovery plots (i.e., the drawdown curve that would be obtained during pumping) and parameter estimates for nearly all aquifer conditions, provided that a constant pumping rate is used and the log derivative at the end of pumping is constant, which is too limiting for groundwater hydrology practice, where observation wells are usually monitored. We generalize Agarwal's method by (1) deriving an improved equivalent time for time-dependent pumping rate and (2) proposing to recover drawdown curves by extrapolating the pumping phase drawdowns. These yield excellent diagnostic plots, thus facilitating the conceptual model analysis for a broad range of conditions., Peer Reviewed, Postprint (published version)

Groundwater withdrawals are growing in most developing countries, including Mongolia, where freshwater resources are limited and unevenly distributed, and most surface waters are frozen during winter. Groundwater represents some 80% of the water supply in the country. Computation of recharge is important, but is complicated in cold regions, because of phase change and permafrost, which is found on 63 percent of the country, and causes conventional physically-based land surface models to be inaccurate. We have developed a two-compartment water and energy balance model that accounts for freezing and melting and includes vapor diffusion as a water and energy transfer mechanism. It also accounts for the effect of slope orientation on radiation, which may be important for mountain areas. We applied this model to the Upper Tuul River Basin to evaluate recharge under different soil and vegetation types. The basin is divided into 12 zones (models) based on elevation ranges, orientation and slope. Due to the limited number of observation data in this area, precipitation, air temperature and relative humidity were corrected as a function of elevation by means of lapse rates. Results show that recharge is relatively high and delayed with respect to snowmelt during spring, because it is mainly associated to thawing at depth, which may occur much later. Most importantly, we find that vapor diffusion plays an important quantitative role in the energy balance and a relevant qualitative role in the water balance. Except for a few large precipitation events, most of the continuous recharge is driven by vapor diffusion fluxes. Large vapor fluxes occur during spring and early summer, when surface temperatures are moderate, but the subsoil remains cold, creating large downwards vapor pressure gradients. Temperature gradients reverse in fall and early winter, but the vapor diffusion fluxes do not, because of the exponential shape of the saturated vapor pressure as a function of temperat, La extracción de agua subterránea crece en la mayoría de los países en desarrollo y representa un problema en Mongolia, donde los recursos de agua son limitados, están distribuidos de manera irregular, y la mayoría de las aguas superficiales se congelan en invierno. El agua subterránea representa la principal (del orden del 80%) fuente de suministro, lo que hace importante el cálculo de la recarga. El cálculo se complica en zonas frías por los cambios de fase y el permafrost, que cubre el 63% del país, y hace que los modelos convencionales de balance de agua en el suelo sean imprecisos. Hemos desarrollado un modelo de balance de agua y energía de dos compartimentos que incluye sublimación, congelación y fusión, así como la difusión de vapor como mecanismo de transferencia de agua y energía. También reconoce el efecto de la orientación de la pendiente sobre la radiación, que puede ser importante en zonas de montaña. Hemos aplicado este modelo a la Cuenca Alta del Río Tuul. Para incluir el efecto de los distintos tipos de suelo y vegetación, dividimos la cuenca en 12 zonas en función de la elevación, la orientación y la pendiente. Por otro lado, hemos tenido que corregir, en función de la altitud, los datos de precipitación y temperatura y humedad relativa del aire, solo disponibles en estaciones situadas en valles. Los resultados muestran que la recarga es relativamente alta y retrasada respecto al deshielo, ya que una parte se asocia a la fusión del hielo profundo, que ocurre mucho más tarde. Lo más importante es que la difusión de vapor desempeña un importante papel tanto en el balance energético como en el hídrico. Exceptuando algunos eventos de alta precipitación, la mayor parte de la recarga está asociada al flujo difusivo de vapor, que aporta no solo agua sino también energía para fundir el hielo profundo. La difusión de vapor es máxima al final de la primavera y principios del verano, cuando el suelo se calienta, favoreciendo la evaporación, pero el subsuelo p, Цэвэр усны нөөц хязгаарлагдмал, жигд бус тархалттай, гадаргын ус нь өвлийн улиралд хөлддөг онцлогтой Монгол зэрэг хөгжиж буй орнуудад газрын доорх усны хэрэглээ өсөж байна. Усны нийт хэрэглээний 80 орчим хувийг газрын доорх усаар хангадаг. Газрын доорх усны тэжээмжийг тооцох нь чухал боловч нийт газар нутгийн 60 хувьд нь олон жилийн цэвдэг чулуулгийн тархалттай, фазын өөрчлөлттэй, физикд суурилсан газрын гадаргын загварууд нь тодорхой бус байдаг шалтгаанаас хүйтэн уур амьсгалтай бүс нутгуудын хувьд хүндрэлтэй байдаг. Иймд хөлдөлт, гэсэлтийг тооцоолох болон ус ба энергийн шилжилийн механизм болох усны уурын диффузыг (vapor diffusion) багтаасан хоёр хэсэг ус ба энергийн балансын загварыг хийсэн. Уг загварт уулархаг районы чухал хүчин зүйл болох газрын гадаргын налуугийн байрлал, нийлбэр цацрагийн нөлөөллийг тооцож үзсэн. Загварыг янз бүрийн хөрс, ургамалтай нөхцөлд тэжээмжийг үнэлэх зорилгоор Туул голын сав газрын дээд хэсэгт хэрэглэсэн. Тус талбайг газрын гадаргын налуу, байрлал болон өндөржилтөөр нь 12 бүсэд (загварт) хувааж үзэв. Талбайн цаг уурын ажиглалтын мэдээ хязгаарлагдмал тул хур тунадас, агаарын температур болон харьцангуй чийгшил өндөржилтөөс хамаарсан хамаарлыг (lapse rate) ашиглан засварыг гүйцэтгэлээ. Загварын үр дүнгээс харахад, тэжээмж харьцангуй их, ихэвчлэн хөрсний гэсэлтийн гүнээс хамаарч хожуу тохиолдох хаврын цасны хайлалтаас ирдэг байна. Хамгийн чухал нь усны уурын диффузи энергийн балансад тоон чухал үүрэг гүйцэтгэж усны балансад чанарын үүрэг гүйцэтгэдгийг тогтоосон. Нэг удаагийн их хэмжээний хур тунадаснаас бусад тохиодолд газрын доорх усны тэжээмж нь усны уурын диффузын урсацаар бий болно. Газрын гадаргын өнгөн хэсгийн температур өсөх үед (>0°C), хавар болон зуны улиралын эхэн үед их хэмжээний усны уурын диффузи явагддаг ч газрын өнгөн хэсгээс доошхи гүнд хөрс хөлдүү байж доош чиглэсэн их хэмжээний усны уурын даралтын зөрүү бий болдог. Газрын өнгөн хэсгийн болон гүн дэх температурын зөрүү намар, өвлийн улирлын эхэнд эсэргээрээ тохиолдоход ба, Postprint (published version)

Artificial recharge of aquifers through infiltration basins (AR) improves water quality and in- creases groundwater resources, which make of it an appropriate technique for the renaturalization of waters affected directly or indirectly by wastewater effluents. Emerging organic compounds (EOCs), typically present in such waters, are mainly reduced during AR by sorption and biotrans- formation. We installed a reactive barrier in an infiltration basin (5000 m2) to enhance the removal of EOCs in the recharge water. The barrier consisted of sand, vegetable compost, iron oxide and clay. Vegetable compost was aimed at: 1) release organic carbon to be used as a carbon source by the microbial community thus promoting the generation of diverse redox conditions, and 2) to adsorb neutral EOCs. Clay and iron oxides were aimed at increasing sorption sites for cationic and anionic EOCs, respectively. Field application of such a design was tested by comparing the redox indicators and behavior of EOCs prior and after the installation of the reactive barrier. Residence time distributions of the recharge water at the monitoring points were obtained by a pulse tracer test. These distributions were used for calibrating a conservative transport and flow model of the aquifer. Finally, first order rates and retardation factors of several EOCs were estimated by fitting model outputs to observed concentrations. The estimation of the first order decay rates and retardation factors of several EOCs allowed the comparison of such values with values reported from other field sites and column experiments. The reactive barrier succeed in releasing organic carbon and achieving diverse redox condi- tions. The transformation of most EOCs was enhanced after the installation of the reactive barrier. In fact, first order rates and retardation factors were higher in the reactive barrier than in the rest of the aquifer and similar or higher than those from literature. In summary, addition of proposed react, La recarga artificial de acuíferos a través de balsas de infiltración (AR) mejora la calidad del agua y aumenta recursos de aguas subterráneas, convirtiéndola en una técnica apropiada para la renaturalización de las aguas afectadas directa o indirectamente por los efluentes de aguas residuales. En este tipo de aguas la presencia de compuestos orgánicos emergentes (EOCs) es más que frecuente. Durante la recarga artificial este tipo de compuestos es eliminado principalmente debido a la adsorción y a la biotransformación. Para mejorar la eliminación de los EOCs durante la infiltración del agua de recarga se instaló una barrera reactiva en una balsa de infiltración. La barrera consistía en arena, compost vegetal, óxidos de hierro y arcilla. La finalidad del compost vegetal era por un lado la de aportar carbono orgánico disuelto para ser utilizado como principal fuente de carbono por la comunidad microbiana promoviendo así la generación de diversas condiciones redox, y por otro lado la de adsorber EOCs neutros. La Arcilla y los óxidos de hierro se pusieron con la intención de aumentar los sitios de adsorción para los EOCs catiónicos y aniónicos, respectivamente. La efectividad de la barrera en el campo se estudió comparando el comportamiento de los indicadores redox y de los EOCs antes y después de la instalación de la barrera. Mediante un ensayo de trazadores tipo pulso se obtuvieron las distribuciones de los tiempos de residencia del agua de recarga a los puntos de observación. Estas distribuciones se utilizaron para calibrar un modelo de flujo y transporte conservativo del acuífero. Por último, las tasas de degradación de primer orden y los factores de retardo de varios EOCs se estimaron mediante el ajuste de los resultados del modelo con las concentraciones observadas. Las tasas de degradación y los factores de retardo estimados se compararon con valores encontrados en la bibliografía. La barrera reactiva cumple su función aportando carbono orgánico y generando diver, Postprint (published version)

Micro-seismicity, and especially felt seismicity, induced by Enhanced Geothermal Systems (EGS) operations is a matter of scientific interest, not only because of the related risks and concerns, but also because the correspondence between injection and seismic activity still remains unclear. The Thesis aims to deepen the understanding of the involved Thermo-Hydro-Mechanical (THM) processes, in order to explain and manage co- and post-injection seismicity. First, we investigate the HM coupling and its effects on pressure response. Fluids injection exerts a force over the aquifer that causes deformation. This implies that Specific Storage, which reflects the capacity of permeable media to deform, cannot be treated as a single parameter, like in classical groundwater hydrology, because deformation also depends on aquifer geometry and on surrounding formations, which constrain displacements. We demonstrate the non-local nature of storage (i.e., its dependence on the poroelastic response over the whole aquifer) by means of analytical solutions to the transient pressure response to injection into one-dimensional and cylindrical finite aquifers, while acknowledging HM coupling. We find that the pressure response is faster and much greater than predicted with traditional solutions. Second, we consider non-isothermal injection and compare the effects of HM and TM couplings. We present analytical expressions for long-term hydraulic and thermal stresses and displacements for unidirectional and radial geometries. To obtain them, we assume steady-state fluid flow and develop an easy-to-use solution to the transient heat transport problem. The solution is then used to illustrate the poroelastic and thermoelastic response and, in particular, the sensitivity of stresses to the outer mechanical boundary conditions. Third, we perform coupled HM and THM simulations of cold water injection in a fault-intact rock system, which allows us to analyze mechanical stability changes during inje, La micro-sismicitat induïda per operacions relacionades amb els Sistemes Geotèrmics Estimulats ha originat un gran interès científic, no només pel risc i la preocupació que comporta, sinó també perquè la relació entre la injecció de fluids i l'activitat sísmica no s'entén completament. Aquesta tesi pretén avançar en la comprensió dels processos hidro-termo-mecànics (THM) que causen aquesta sismicitat, per poder explicar-la i gestionar-la. En primer lloc, hem investigat l'acoblament hidro-mecànic (HM) i el seu efecte sobre les pressions. En Hidrologia Subterrània clàssica l'emmagatzematge especifico expressa la capacitat de l'aqüífer de deformar-se després d'una variació de pressió. Malgrat això, la sobrepressió generada per la injecció exerceix una força que deforma tot l'aqüífer, depenent de la seva geometria i de les formacions adjacents. Per això, l'emmagatzematge no es pot expressar amb un sol paràmetre, sinó que depèn de la resposta poro-elàstica de tot l'aqüífer, per la qual cosa diem que l'emmagatzematge específic és "no-local", cosa que vam mostrar mitjançant solucions analítiques de la resposta transitòria al problema HM de la injecció en aqüífers de dimensió finita, amb geometria tant unidimensional com cilíndrica. Seguidament, hem considerat una injecció no isoterma i comparat els efectes de l'acoblament hidro-mecànic (HM) i termo-mecànic (TM). Hem obtingut expressions analítiques per a les tensions i els desplaçaments induïts a llarg termini per la pertorbació hidràulica i tèrmica, en el cas de dominis unidireccional i radial. Per a això, hem considerat flux estacionari i desenvolupat una solució analítica senzilla per al transport de calor en règim transitori, la qual cosa ens ha permès calcular la resposta poro i termo-elàstica i en particular la sensibilitat de les tensions a les condicions mecàniques en el contorn exterior. A continuació, hem desenvolupat simulacions HM i THM acoblades de la injecció d'aigua freda en un sistema format per una falla e, Postprint (published version)

Temperature gradients can drive vapor diffusion by controlling vapor pressure in the soil. We studied vapor diffusion for soils in two different climates: A semiarid climate at El Cabril (Córdoba, Spain) and a subarctic climate in the Upper Tuul River basin (Mongolia). For El Cabril vapor diffusive fluxes were studied by means of the measured temperatures and an analytical model. For the second site (Upper Tuul) a physically based soil water and energy balance model was developed accounting for relevant processes such as melting-freezing of water and vapor diffusion in the soil. Results of both sites show that vapor diffuses downwards during summer and upwards during winter, while yearly averaged fluxes diffuse downwards. The overall amount is small for El Cabril, but significant for the Upper Tuul. The latter large values can be explained by the large temperature oscillations of the Mongolian climate and the freezing/thawing of subsoil layer., Postprint (published version)

Reactive transport plays an important role in the development of a wide range of both anthropic and natural processes affecting geological media. To predict the consequences of reactive transport processes on structural and hydrodynamic properties of a porous media at large time and spatial scales, numerical modeling is a powerful tool. Nevertheless, such models, to be realistic, need geochemical, structural and hydrodynamic data inputs representative of the studied reservoir or material. Here, we present an experimental study coupling traditional laboratory measurements and percolation experiments in order to obtain the parameters that define rock heterogeneity, which can be altered during the percolation of a reactive fluid. In order to validate the experimental methodology and identify the role of the initial heterogeneities on the localization of the reactive transport processes, we used three different limestones with different petrophysical characteristics. We tracked the changes of geochemical, structural and hydrodynamic parameters in these samples induced by the percolation of an acid fluid by measuring, before and after the percolation experiment, petrophysical and hydrodynamic properties of the rocks., Peer Reviewed, Postprint (published version)

In recent years, some geological applications like the CO2 storage or the hydraulic fracturing have attracted the attention not only of the scientific community but also of the general public. One of the reasons of the controversy generated by these topics is the ignorance about some processes that can take place during the realization of this kind of operations. In fact, several questions are still unresolved: how long will the fractures propagate?, Will the contaminated fluid or the released gas leak to aquifers or to the atmosphere? Will the injection process induce seismicity? What magnitude? Hence, the aim of this work (developed as a part of the EU - FracRisk project) is to answer some of these questions identifying the parameters which are key in the hydraulic fracturing operation. In order to do that, a new thermo-hydro-mechanical Finite Element code has been developed in the Kratos framework using C++. As part of this code, a different method to solve the shear and the tensile failure has been proposed. In this method, fractures are represented as a zero thickness element, this means that both sides of the element lie together in the initial configuration (it seems a 1D element in a 2D domain, and a 2D element in a 3D domain) and separate as the adjacent matrix elements deform (Figure 1). Since the hydraulic fracturing operations take place in hard, fragile rocks, an elastic matrix can be assumed and irreversible displacements in fractures when rock failure occurs can be imposed. The formulation used to simulate shear and tensile failure is based on the analytical solution proposed by Okada (1992) and it is part of an iterative process. Thus, the fracture failure is calculated in a straightforward manner, avoiding numerical issues and capturing the domino effect that may occur when the failure process is triggered in a zone. In conclusion, the goal of this work is to analyze the main uncertainties related with the thermo-hydro-mechanical behavior of fractur, Peer Reviewed, Postprint (published version)

Hace unos años se decidió descontaminar el embalse de Flix, afectado por vertidos de residuos por un empresa química durante todo el siglo pasado. •Los residuos formaron 4 lóbulos de sedimentos en el río, con elevadas concentraciones de Mercurio, compuestos orgánicos volátiles (COV´s), residuos de producción de acetileno (Ca(OH)2) y pesticidas organoclorados. •Se ha realizado un modelo 0D de transporte reactivo de la concentración en el agua conforme se excavan los sedimentos transitorio y explícito en excel, calibrado hasta Septiembre 2014 con datos semanales de la empresa extractora FCC. •El modelo concluía dos graves problemas al terminar la excavación: Elevada concentración de Hg y pH (12.4), equilibrado con portlandita •Desde Marzo de 2015 se observó un acusado descenso de pH y Hg. Nuestro objetivo ha sido encontrar la causa de estos descensos, para ello se han realizado simulaciones, muestreos y experimentos de laboratorio. La precipitación CaCO3 debida a la difusión de CO2 atmosférico explica una parte de la disminución de pH, pero resulta insuficiente aun considerando la oxidación de materia orgánica. •El Hg se adsorbido en CaCO3 es alrededor de un 30%, otro 60% parece haberse volatilizado. •La electrolisis en laboratorio reproduce un descenso del Hg de 80% en 3 días. Sólo un 10% de Hg ha sido recuperado en el cátodo. • Se cree que el Hg2+ se reduce a Hg0 y volatiliza. •El pH descendió hasta 3.8, se cree que debido a hidrólisis del agua. •Se esta trabajando en comprobar el Hg0 volatilizado en próximos experimentos., Postprint (published version)

Reactive transport modeling involves solving several nonlinear coupled phenomena, among them, the flow of fluid phases, the transport of chemical species and energy, and chemical reactions. There are different ways to consider this coupling that might be more or less suitable depending on the nature of the problem to be solved. In this paper we acknowledge the importance of flexibility on reactive transport codes and how object-oriented programming can facilitate this feature. We present PROOST, an object-oriented code that allows solving reactive transport problems considering different coupling approaches. The code main classes and their interactions are presented. PROOST performance is illustrated by the resolution of a multiphase reactive transport problem where geochemistry affects hydrodynamic processes., Postprint (author's final draft)

Results of reactive transport laboratory experiments often suggest that pore scale heterogeneity induces localization of reactions (the generation of local micro environments favoring reactions that would not occur in a well-mixed Representative Elementary Volume, REV). Multi-Rate Mass Transfer (MRMT), which has been employed to reproduce hydrodynamic heterogeneity, may also be used to simulate geochemical localization. We extended the Water Mixing Approach (WMA) designed for single porosity media, to simulate chemical reactions caused by the mixing of mobile and immobile zones. The method is termed Multi-Rate Water Mixing (MRWM). The MRWM approach was employed to simulate laboratory experiments of CO2-rich brine transport through carbonate rich samples (Luquot et al., 2016, in this issue). Chemical heterogeneity in space was reproduced by varying the mineral assemblages in immobile regions. This enabled us to reproduce the generally low pH environment while allowing for high pH local zones required for the localized precipitation of kaolinite, which has been observed in reality, but cannot be modeled with conventional reactive transport formulations. The resulting model is very rich, in that it can reproduce a broad range of pore scale processes in a Darcy scale model, and complex, in that the interaction between chemical kinetics and immobile zones physical parameters is non-trivial., Peer Reviewed, Postprint (author's final draft)

A method developed for low-permeability fractured media was applied to understand the hydrogeology of a mine excavated in a granitic pluton. This method includes (1) identifying the main groundwater-conducting features of the medium, such as the mine, dykes, and large fractures, (2) implementing this factors as discrete elements into a three-dimensional numerical model, and (3) calibrating these factors against hydraulic data (Martinez-Landa and Carrera 2006). A key question is how to identify preferential flow paths in the first step. Here, we propose a combination of several techniques. Structural geology, together with borehole sampling, geophysics, hydrogeochemistry, and local hydraulic tests aided in locating all structures. Integration of these data yielded a conceptual model of the site. A preliminary calibration of the model was performed against short-term (< 1 day) pumping tests, which facilitated the characterization of some of the fractures. The hydraulic properties were then used for other fractures that, according to geophysics and structural geology, belonged to the same families. Model validity was tested by blind prediction of a long-term (4 months) large-scale (1 km) pumping test from the mine, which yielded excellent agreement with the observations. Model results confirmed the sparsely fractured nature of the pluton, which has not been subjected to glacial loading-unloading cycles and whose waters are of Na-HCO3 type., Peer Reviewed, Postprint (published version)

Artificial recharge of aquifers is a technique for improving water quality and increasing groundwater resources. Understanding the fate of a potential contaminant requires knowledge of the residence time distribution (RTD) of the recharged water in the aquifer beneath. A simple way to obtain the RTDs is to perform a tracer test. We performed a pulse injection tracer test in an artificial recharge system through an infiltration basin to obtain the breakthrough curves, which directly yield the RTDs. The RTDs turned out to be very broad and we used a numerical model to interpret them, to characterize heterogeneity, and to extend the model to other flow conditions. The model comprised nine layers at the site scaled to emulate the layering of aquifer deposits. Two types of hypotheses were considered: homogeneous (all flow and transport parameters identical for every layer) and heterogeneous (diverse parameters for each layer). The parameters were calibrated against the head and concentration data in both model types, which were validated quite satisfactorily against 1,1,2-Trichloroethane and electrical conductivity data collected over a long period of time with highly varying flow conditions. We found that the broad RTDs can be attributed to the complex flow structure generated under the basin due to three-dimensionality and time fluctuations (the homogeneous model produced broad RTDs) and the heterogeneity of the media (the heterogeneous model yielded much better fits). We conclude that heterogeneity must be acknowledged to properly assess mixing and broad RTDs, which are required to explain the water quality improvement of artificial recharge basins., Peer Reviewed, Postprint (published version)

In the city of Barcelona and the townships situated in the deltaic area of the Besòs River, groundwater is recognized as an aspect of urban water cycle management. There is groundwater seepage into infrastructure and buildings that in turn require drainage, a part of which is introduced into sewage systems. Sensitized by this issue, city councils have had hydrologic studies carried out to analyze its causes and to plan alternative ways of using these resources while reducing treatment costs, and minimizing the impacts that groundwater and drainage have on infrastructure and vice versa. Based on these studies, and starting in 2000 some of this has been used for municipal practices (garden irrigation and street cleaning). Subsequently, due to a drought that affected the region between April 2007 and January 2009, the government entity in charge of Catalonian water sources (ACA) aims to get greater use out of urban groundwater in this area. This requires a comprehensive understanding of the hydrogeological characteristics of the environment, the availability and quality of these resources, and the appropriate tools for proper assessment and management. This has been the framework of this thesis. Recharge is one of the most relevant aspects of water balance in aquifer systems in urban areas. Urbanization of the area alters the natural hydrological cycle and direct water recharge into aquifers by infiltration is reduced. In turn, evapotranspiration decreases and new recharge sources appear. This thesis presents, first, a methodology that allows for the quantifying of variability in space and time of the recharge in urban areas. Potential sources of recharge that have been considered are: (1) direct infiltration from rain and urban runoff, (2) losses from the sewer system, (3) losses from the water supply system, and (4) other specific sources of recharge (i.e. river infiltration, seawater intrusion, etc.). Recharge calculations are initially performed by applying analyti, En la ciudad de Barcelona y municipios ubicados sobre los terrenos deltaicos del río Besòs, el agua subterránea es un factor que se tiene en cuenta en la gestión urbana del ciclo del agua. La filtración de aguas subterráneas en edificios e infraestructuras obliga el drenaje de estas aguas, parte de las cuáles son vertidas a la red de alcantarillado. Sensibilizados por esta problemática las administraciones implicadas encargaron estudios hidrogeológicos para analizar las causas y plantear alternativas para el aprovechamiento de estos recursos, reducir los costes del tratamiento, así como minimizar los impactos que las aguas subterráneas y drenajes puedan causar a las infraestructuras y viceversa. A raíz de estos estudios y desde el año 2000, parte de éstas se destinan a usos municipales (riego de jardines y limpieza de calles). Posteriormente y debido a un período de sequía que afectó desde abril de 2007 a enero de 2009, la entidad gestora de los recursos hídricos de Cataluña (Agència Catalana de l'Aigua, ACA) planteó un mayor aprovechamiento de los recursos de agua subterránea en este entorno urbano. Esto requiere un buen conocimiento de las características hidrogeológicas del medio, de la disponibilidad y calidad de estos recursos, así como de disponer de las herramientas adecuadas para su evaluación y correcta gestión. Esta tesis se enmarca en este contexto. La recarga es uno de los aspectos más relevantes del balance hídrico en los sistemas acuíferos de zonas urbanas. La urbanización del territorio altera el ciclo hidrogeológico natural, la recarga directa de agua a los acuíferos por infiltración se reduce, disminuye la evapotranspiración y aparecen nuevas fuentes de recarga. En esta tesis se presenta, en primer lugar, una metodología para cuantificar la variabilidad espacial y temporal de la recarga en zona urbana. Las fuentes potenciales de recarga que se han considerado son: (1) infiltración directa de lluvia y de agua de escorrentía, (2) pérdidas del sistema, En la ciutat de Barcelona i municipis ubicats sobre els terrenys deltaics del riu Besòs, l’aigua subterrània és un factor que es té en compte en la gestió urbana del cicle de l’aigua. La filtració d’aigües subterrànies en edificis i infraestructures obliguen el seu drenatge, una part de les quals s’aboquen a la xarxa de clavegueram. Sensibilitzats per aquesta problemàtica els ajuntaments implicats van encarregar estudis hidrogeològics per analitzar les causes i plantejar alternatives per l’aprofitament d’aquests recursos, reduir els costos del tractament, així com minimitzar els impactes que les aigües subterrànies i drenatges poden causar a les infraestructures i viceversa. A arrel d’aquest estudis i des de l’any 2000, part d’aquestes aigües es destinen a usos municipals (reg de jardins i neteja de carrers). Posteriorment i degut a un període de sequera que va afectar des de l’abril de 2007 fins gener de 2009, l’entitat gestora dels recursos hídrics de Catalunya (Agència Catalana de l’Aigua, ACA) va plantejar un major aprofitament d’aquests recursos d’aigua subterrània en aquest entorn urbà. Això requereix un bon coneixement del medi hidrogeològic, de la disponibilitat i qualitat, així com de les eines adequades per a la seva correcta avaluació i gestió. Aquest és el context en que emmarca aquesta tesis. La recarrega és un dels aspectes més rellevants del balanç hídric en els sistemes aqüífers de zones urbanes. La urbanització del territori altera el cicle hidrogeològic natural, la recàrrega directa d’aigua als aqüífers per infiltració es redueix, disminueix l’evapotranspiració i apareixen noves fonts de recàrrega. En aquesta tesis es presenta, en primer lloc, una metodologia per a quantificar la variabilitat espaial i temporal de la recàrrega en zona urbana. Les fonts potencials de recàrrega que s’han considerat són: (1) infiltració directa de pluja i aigua d’escorrentia, (2) pèrdues del sistema de clavegueram, (3) pèrdues de la xarxa d’abastament i (4) altres fon, Postprint (published version)

Unsaturated flow plays an important role in numerous environmental phenomena. It is complex in arid regions, where liquid water fluxes are small and vapor fluxes become relevant, so that heat, water and solute mass transport are needed to understand evaporation. This thesis aims at gaining insight evaporation and vapor flow mechanisms and the relevance of matric potential, temperature and osmotic gradients. These issues are especially relevant for soil salinization, whose mechanisms are poorly understood despite their global impact. We studied them in open soil evaporation column experiments. We found that a water separation process occurs in the soil. Above a very narrow evaporation front, the soil contains high salt concentrations due the solutes transported by the upward liquid flux and concentrated by evaporation. Below, concentrations are lower than the initial ones, because vapor flows downwards below the evaporation front driven by temperature gradients. Condensation of this downward vapor flux dilutes upflowing water, improving soil conditions and providing an area where root plants could live. We modeled nonisothermal multiphase flow and reactive transport during the experiments to quantify the actual processes and to understand the nature of the downward vapor flux. Modeling required modifying the retention curve to represent oven dry conditions. Our model supports the traditional division of soil, by an evaporation front, into a dry region and a moist region. This view may suffice for evaluating evaporation rates and water mass balances, but not for assessing salt processes, which require acknowledging that not only liquid water flow but also vapor diffusion occur below the evaporation front. Unsaturated flow concepts control the design of covers to isolate solid waste. Their goal is to protect the waste from infiltration during long periods of time by promoting surface runoff and lateral drainage and by hindering biointrusion. Two cover designs were buil, La zona no saturada juga un paper important en nombrosos fenòmens ambientals. És complex en zones àrides, on els fluxos d'aigua líquida són petits i els fluxos de vapor adquireixen rellevància. El transport de calor, d'aigua i de soluts és necessari per entendre l'evaporació. Aquesta tesi vol millorar el coneixement sobre l'evaporació i els mecanismes de flux de vapor, i analitzar la rellevància dels gradients de succió, de temperatura i osmòtics. Aquestes qüestions són especialment rellevants per la salinització de sòls, els mecanismes són poc coneguts malgrat el seu impacte global. Hem estudiat experiments de columna d'evaporació on s'ha trobat un procés de separació d'aigua al sòl. Per sobre del front d'evaporació, que és molt estret, el sòl conté altes concentracions a causa dels soluts transportats pel flux ascendent de líquid i la seva posterior evaporació. Per sota, les concentracions són inferiors a les inicials, perquè el vapor flueix cap avall des del front d'evaporació impulsat per gradients de temperatura. Allà condensa, causant la dilució del flux ascendent d'aigua, millorant les condicions del sòl i proporcionant una àrea on les arrels de les plantes podrien viure. Mitjançant un model de flux multifàsic no isoterm i transport reactiu dels experiments, s'han quantificat els processos per entendre la naturalesa del flux descendent de vapor. S'ha modificat la corba de retenció per representar condicions molt seques del sòl. El nostre model és compatible amb la divisió tradicional del sòl, per un front d'evaporació, en una regió seca i una regió humida. Aquest punt de vista pot ser suficient per a l'avaluació de tases d'evaporació i balanços de massa d'aigua, però no per a l'avaluació dels processos de sals, que requereixen no només el coneixement del flux d'aigua líquida, sinó també la difusió de vapor per sota del front d'evaporació. Conceptes de flux no saturat controlen el disseny de cobertures per aïllar residus sòlids. El seu objectiu és protegir els, La zona no saturada juega un papel importante en numerosos fenómenos ambientales. Es complejo en zonas áridas, donde los flujos de agua líquida son pequeños y los flujos de vapor adquieren relevancia. El transporte de calor, de agua y de solutos es necesario para entender la evaporación. Esta tesis quiere mejorar el conocimiento sobre la evaporación y los mecanismos de flujo de vapor, y analizar la relevancia de los gradientes de succión, temperatura y osmóticos. Estas cuestiones son especialmente relevantes para la salinización de suelos, cuyos mecanismos son poco conocidos a pesar de su impacto global. Hemos estudiado experimentos de columna de evaporación en los que se ha encontrado un proceso de separación de agua en el suelo. Por encima del frente de evaporación, que es muy estrecho, el suelo contiene altas concentraciones de sal debido a los solutos transportados por el flujo ascendente de líquido y su posterior evaporación. Por debajo, las concentraciones son inferiores a las iniciales, porque el vapor fluye hacia abajo desde el frente de evaporación impulsado por gradientes de temperatura. Allí condensa, causando la dilución del flujo ascendente de agua, mejorando las condiciones del suelo y proporcionando un área donde las raíces de las plantas podrían vivir. Mediante un modelo de flujo multifásico no isotermo y transporte reactivo de los experimentos, se han cuantificado los procesos, para entender la naturaleza del flujo descendente de vapor. Se ha modificado la curva de retención para representar condiciones muy secas del suelo. Nuestro modelo es compatible con la división tradicional del suelo, por un frente de evaporación, en una región seca y una región húmeda. Este punto de vista puede ser suficiente para la evaluación de tasas de evaporación y balances de masa de agua, pero no para la evaluación de los procesos de sales, que requieren no sólo el conocimiento del flujo de agua líquida, sino también la difusión de vapor por debajo del frente de evapor, Postprint (published version)

A tunnel for the High Speed Train (HST) was constructed in Barcelona with an Earth Pressure Balance (EPB) Tunnel Boring Machine (TBM). The tunnel crosses Barcelona and passes under some famous landmarks such as the Sagrada Familia and the Casa Mill Both monuments are UNESCO world heritage sites and a committee appointed by the UNESCO acted as external observers during the construction. Concerns about soil settlements and the hydrogeological impacts of the construction were raised. These concerns were addressed during the design stage to forestall any unexpected events. The methodology consisted of 1) characterising the geology in detail, 2) predicting the impacts caused in the aquifer, 3) predicting the soil displacements due to water table oscillations produced by the construction, and 4) monitoring the evolution of groundwater and soil settlements. The main estimated impact on groundwater was a moderate barrier effect. The barrier effect, the magnitude of which matched the predictions, was detected during construction. The monitoring of soil settlements revealed short and long term movements. The latter movements matched the analytical predictions of soil displacements caused by the groundwater oscillations. This paper proposes a realistic procedure to estimate impacts on groundwater during tunnel construction with an EPB. Our methodology will considerably improve the construction of tunnels in urban areas. (C) 2015 Elsevier B.V. All rights reserved., Peer Reviewed, Postprint (author's final draft)

We study the fundamental problem of mixing and chemical reactions under a Rayleigh-Taylor-type hydrodynamic instability in a miscible two-fluid system. The dense fluid mixture, which is generated at the fluid-fluid interface, leads to the onset of a convective fingering instability and triggers a fast chemical dissolution reaction. Contrary to intuition, the dissolution pattern does not map out the finger geometry. Instead, it displays a dome-like, hierarchical structure that follows the path of the ascending fluid interface and the regions of maximum mixing. These mixing and reaction hot spots coincide with the flow stagnation points, at which the interfacial mixing layer is compressed and deformed. We show that the deformation of the boundary layer around the stagnation points controls the evolution of the global scalar dissipation and reaction rates and shapes the structure of the reacted zones. The persistent compression of the mixing layer explains the independence of the mixing rate from the Rayleigh number when convection dominates., Peer Reviewed, Postprint (author's final draft)