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  • The use of kernel density estimators in breakthrough curve reconstruction and advantages in risk analysis

     Siirila, Erica; Fernandez Garcia, Daniel; Sanchez Vila, Francisco Javier
    American Geophysical Union Fall Meeting
    Presentation's date: 2014-12-19
    Presentation of work at congresses

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    Particle tracking (PT) techniques, often considered favorable over Eulerian techniques due to artificial smoothening in breakthrough curves (BTCs), are evaluated in a risk-driven framework. Recent work has shown that given a relatively few number of particles (np), PT methods can yield well-constructed BTCs with kernel density estimators (KDEs). This work compares KDE and non-KDE BTCs simulated as a function of np (102-108) and averaged as a function of the exposure duration, ED. Results show that regardless of BTC shape complexity, un-averaged PT BTCs show a large bias over several orders of magnitude in concentration (C) when compared to the KDE results, remarkably even when np is as low as 102. With the KDE, several orders of magnitude less np are required to obtain the same global error in BTC shape as the PT technique. PT and KDE BTCs are averaged as a function of the ED with standard and new methods incorporating the optimal h (ANA). The lowest error curve is obtained through the ANA method, especially for smaller EDs. Percent error of peak of averaged-BTCs, important in a risk framework, is approximately zero for all scenarios and all methods for np =105, but vary between the ANA and PT methods, when np is lower. For fewer np, the ANA solution provides a lower error fit except when C oscillations are present during a short time frame. We show that obtaining a representative average exposure concentration is reliant on an accurate representation of the BTC, especially when data is scarce.

  • Probabilistic human health risk assessment of chemical mixtures: hydro-toxicological interactions and crontolling factors

     Henri, Christopher; Fernandez Garcia, Daniel; De Barros, Felipe P.J.
    American Geophysical Union Fall Meeting
    Presentation's date: 2014-12-16
    Presentation of work at congresses

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    Improper disposals of hazardous wastes in most industrial countries give rise to severe groundwater contamination problems that can lead to adverse health effects in humans. Therefore risk assessment methods play an important role in population protection by (1) quantifying the impact on human health of an aquifer contamination and (2) aiding the decision making process of to better manage our groundwater resources. Many reactive components such as chlorinated solvent or nitrate potentially experience attenuation processes under common geochemical conditions. Based on this, monitored natural attenuation has become nowadays an attractive remediation solution. However, in some cases, intermediate degradation products can constitute noxious chemical compounds before reaching a harmless chemical form. In these cases, the joint effect of advection-dispersion transport and the species-dependent kinetic reactions and toxicity will dictate the relative importance of the degradation byproducts to the total risk. This renders the interpretation of risk a non-trivial task. In this presentation, we quantify, through a probabilistic framework, the human health risk posed by a chemical mixture in a heterogeneous aquifer. This work focuses on a Perchloroethylene contamination problem followed by the first-order production/biodegradation of its daughter species Trichloroethylene, Dichloroethylene and Vinyl Chlorine that is known to be highly toxic. Uncertainty on the hydraulic conductivity field is considered through a Monte Carlo scheme. A comparative description of human health risk metrics as a function of aquifer heterogeneity and contaminant injection mode is provided by means of a spatial characterization of the lower-order statistical moments and empirical probability density functions of both individual and total risks. Interestingly, we show that the human health risk of a chemical mixture is mainly controlled by a modified Damköhler number that express the joint effect of contaminant mean travel times, reaction kinetics and chemical toxicity. From this, connectivity is shown to produce a significant and non-trivial impact on risk measures. The impact of connectivity can be potentially beneficial or detrimental on the magnitude of human health risk depending on the modified Damköhler number

  • Mathematical equivalence between time-dependent single-rate and multi-rate mass transfer models

     Fernandez Garcia, Daniel; Sanchez Vila, Francisco Javier
    American Geophysical Union Fall Meeting
    Presentation's date: 2014-12-16
    Presentation of work at congresses

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    The observed non-Fickian tailing in solute breakthrough curves is often caused by a multitude of mass transfer processes taking place over multiple scales. Yet, in some cases it is convenient to fit a transport model with a single-rate mass transfer coefficient that lumps all the non-Fickian observed behavior. Since mass transfer processes take place at all characteristic times, the single-rate mass transfer coefficient derived from measurements in the laboratory or in the field vary with time, ß(t). In this context, we present a mathematical equivalence between the Multi-Rate Mass Transfer Model (MRMT) and an effective time-dependent single-rate mass transfer model (t-SRMT). In doing this, we provide new insights into the previously observed scale-dependence of mass transfer coefficients. The memory function, g(t), which is the most salient feature of the MRMT model, determines the influence of the past values of concentrations on its present state. We found that the t-SRMT model can also be expressed by means of a memory function f(t,s). In this case though the memory function is non-stationary, meaning that in general it cannot be written as f(t-s). Nevertheless, the concentration breakthrough curves obtained using an effective single time-dependent rate ß(t) is analogous to that of the MRMT model provided that a simple equality holds. This relationship suggests that when the memory function is a power law, g(t)~ t1-m, the equivalent mass transfer coefficient scales as ß(t)~ t-1. A result that explains the scaling exponent of the mass transfer coefficient reported by the literature review and tracer experiments of Haggerty et al. [2004] of -0.94.

  • Connecting bacterial colonization to physical and biochemical changes in a sand box infiltration experiment

     Rubol, Simonetta; Freixa, Anna; Carles Brangari, Albert; Fernandez Garcia, Daniel; Romani Cornet, Anna Maria; Sanchez Vila, Francisco Javier
    Journal of hydrology
    Vol. 517, p. 317-327
    DOI: 10.1016/j.jhydrol.2014.05.041
    Date of publication: 2014-09-19
    Journal article

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    Infiltration through sediments is linked to complex biogeochemical processes occurring at small spatial scales, often leading to a progressive reduction in infiltration rates due to microbial growth and/or mechanical clogging. Unraveling the linkage between microbial dynamics and water infiltration in a heterogeneous medium is of concern in artificial recharge ponds and natural infiltration systems. We present an 84-day laboratory infiltration experiment that aims at studying the temporal variation of selected biogeochemical parameters at different depths along the infiltration path. The experimental setup consists of a 1.2 m high tank packed with a heterogeneous soil and instrumented with arrays of sensors as well as soil and liquid samplers. Results indicate that: (i) microbial processes are responsible for infiltration reduction, enhancing the spatially heterogeneous distribution of infiltration rates with time, (ii) bacteria and extracellular polymeric substances (EPS) are present at all monitored depths, indicating the potential for deep biological clogging, (iii) bacteria functioning and richness exhibit depth zonation after the system reaches a mature state and (iv) the retention curve changes towards highest saturation by the end of the experiment. The increase in water holding capacity is largest at depth, where the presence of EPS is noticeable. The reduction in time of the quantity of water infiltrating along the tank can only be accounted for with a truly interdisciplinary approach involving physical, chemical and biological processes

  • Caracterización hidrogeológica y modelización hidrodinámica del emplazamiento monitorizado de Ódena (Barcelona)

     Folch Sancho, Albert; Pijuan, Gemma; Rodriguez Fernandez, Diana; Rosell, Monica; Domenech, Cristina; Fernandez Garcia, Daniel; Soler, Albert
    Congreso Ibérico de las Aguas Subterráneas
    p. 327-328
    Presentation's date: 2014-09-10
    Presentation of work at congresses

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    El emplazamiento de Òdena (Barcelona) fue desarrollado conjuntamente por la Agencia Catalana de Residus, la Agencia Catalana del Agua y el grupo de Mineralogia Aplicada y Medi Ambient de la UB. Este emplazamiento tiene como objetivo la investigación in situ de nuevas técnicas de remediación de la contaminación por DNAPLs. Se trata de un acuífero contaminado principalmente por cloroetnos, clorometanos, cloroetanos y clorobencenos, con trazas de BTEXs y pesticidas emplazado en un medio fracturado no confinado constituido por una serie sedimentaria Eocena de calizas, mrgas y algunas intercalaciones de areniscas y microconglomerados cementados que c onfiguran una formación geológica de doble permeabilidad con conductividad hidráulica a través de fracturas y fisuras y en menor orden a través de la porosidad interconectada de la matriz. El origen de la contaminación se encontró en las infiltraciones de un tanque de almacenaje de residuos subterráneo y una balsa localizada fuera de una antigua fábrica de productos fitosanitarios y textil (1978-1985). En julio de 2006 se realizaron las primeras tareas de remediación mediante la extracción de las fuentes de contaminacion y de 2000 t de suelo contaminado de sus proximidades y en su lugar se pusieron residuos de construcción formando dos zanjas de intercepción del agua de recarga en la zona no saturada para su descontaminación mediante hidrólisis alcalina (Torrentó et al, 2014).

  • Toward efficiency in heterogeneous multispecies reactive transport modeling: A particle-tracking solution for first-order network reactions

     Henri, Christopher Vincent; Fernandez Garcia, Daniel
    Water resources research
    Vol. 50, num. 9, p. 7206-7230
    DOI: 10.1002/2013WR014956
    Date of publication: 2014-09
    Journal article

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    Modeling multispecies reactive transport in natural systems with strong heterogeneities and complex biochemical reactions is a major challenge for assessing groundwater polluted sites with organic and inorganic contaminants. A large variety of these contaminants react according to serial-parallel reaction networks commonly simplified by a combination of first-order kinetic reactions. In this context, a random-walk particle tracking method is presented. This method is capable of efficiently simulating the motion of particles affected by first-order network reactions in three-dimensional systems, which are represented by spatially variable physical and biochemical coefficients described at high resolution. The approach is based on the development of transition probabilities that describe the likelihood that particles belonging to a given species and location at a given time will be transformed into and moved to another species and location afterward. These probabilities are derived from the solution matrix of the spatial moments governing equations. The method is fully coupled with reactions, free of numerical dispersion and overcomes the inherent numerical problems stemming from the incorporation of heterogeneities to reactive transport codes. In doing this, we demonstrate that the motion of particles follows a standard random walk with time-dependent effective retardation and dispersion parameters that depend on the initial and final chemical state of the particle. The behavior of effective parameters develops as a result of differential retardation effects among species. Moreover, explicit analytic solutions of the transition probability matrix and related particle motions are provided for serial reactions. An example of the effect of heterogeneity on the dechlorination of organic solvents in a threedimensional random porous media shows that the power-law behavior typically observed in conservative tracers breakthrough curves can be largely compromised by the effect of biochemical reactions.

  • GIS-based hydrogeochemical analysis tools (QUIMET)

     Velasco Mansilla, Domitila Violeta; Tubau Fernandez, Isabel; Gaitanaru, Dragos; Vázquez Suñé, Enric; Gogu, Constantin Radu; Alcaraz, M.; Serrano Juan, Alejandro; Fernandez Garcia, Daniel; Garrido, T; Fraile, J; Sanchez Vila, Francisco Javier
    Computers and geosciences
    Vol. 70, p. 164-180
    DOI: 10.1016/j.cageo.2014.04.013
    Date of publication: 2014-09
    Journal article

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    A software platform (QUIMET) was developed to improve the sorting, analysis, calculations, visualizations, and interpretations of hydrogeochemical data in a GIS environment. QUIMET is composed of a geospatial database plus a set of tools specially designed for graphical and statistical analysis of hydrogeochemical data. The geospatial database has been designed to include organic and inorganic chemical records, as well as relevant physical parameters (temperature, Eh, electrical conductivity). The instruments for analysis cover a wide range of methodologies for querying, interpreting, and comparing groundwater quality data. They include, among others, chemical time-series analysis, ionic balance calculations, correlation of chemical parameters, and calculation of various common hydrogeochemical diagrams (Salinity, Schoeller-Berkaloff, Piper, and Stiff). The GIS platform allows the generation of maps of the spatial distribution of parameters and diagrams. Moreover, it allows performing a complete statistical analysis of the data including descriptive statistic univariate and bivariate analysis, the latter including generation of correlation matrices and graphics. Finally, QUIMET offers interoperability with other external platforms. The platform is illustrated with a geochemical data set from the city of Badalona, located on the Mediterranean coast in NE Spain. (C) 2014 Elsevier Ltd. All rights reserved.

  • Deep bioclogging in a multiphase infiltraton system

     Carles Brangari, Albert; Fernandez Garcia, Daniel; Sanchez Vila, Francisco Javier; Rubol, Simonetta; Freixa, Anna; Romani Cornet, Anna Maria
    International Conference on Computational Methods in Water Resources
    p. 243-
    Presentation's date: 2014-06-11
    Presentation of work at congresses

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    Infiltration ponds are bioreactors in which complex biogeochemical processes occurring over multiple scales often leads to detrimental clogging and a reduction of infiltration rates due to microbial growth or mechanical clogging. Understanding the interactions between pore-scale microbial dynamics and a multiphase infiltration system in heterogeneous porous media is crucial for the management of an artificial recharge facility. Such processes are mostly related to biological activity and include mainly the growth and migration of bacterial community, exudation of EPS, precipitation of compounds, and creation of biogenic air bubbles. Such bio-originated products modify the previously existing soil properties, reshaping the pore-space structure. Thus, biological activity products, which are time dependent and controlled by soil moisture and substrate supplies, can ultimately modify the multiphase flow system through changes in grain size distribution and soil texture.

  • On the non-monotonicity and localized peaks of breakthrough curves

     Siirila, Erica Rachel; Sanchez Vila, Francisco Javier; Fernandez Garcia, Daniel
    International Conference on Computational Methods in Water Resources
    p. 216-
    Presentation's date: 2014-06-10
    Presentation of work at congresses

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    We analyze the shape of breakthrough curves (BTCs). In general, monotonicity of the late-time BTC slope is just assumed. We contend that local peaks may exist but are sometimes not reported for a number of reasons: in the field, either by subsampling or associating them measurement errors; in numerical simulations, from numerical dispersion in Eulerian methods, or from the use of a limited number of particles in Lagrangian methods. The presence of localized peaks in BTCs (when, at what magnitude and duration) is imperative in accurately assessing environmental and human health risk, as discrepancies in the environmental concentration at a given time could potentially affect risk management decisions. The presence of multiple peaks in BTCs is assessed from high-resolution numerical simulations with particle tracking techniques and a kernel density estimator. Individual realizations of 3D heterogeneous K fields with varying combinations of statistical anisotropy, geostatistical models, and local dispersivity are utilized to test for mechanisms of physical mass transfer. BTCs of non-reactive solutes are analyzed for the presence of local maxima, and for the corresponding slope of the receding limb of the curve as a function of travel distance and number of integral scales traveled. We show that the number of local peaks and corresponding slopes strongly depend on statistical anisotropy and travel distance, but are less sensitive to the number of integral scales traveled. We also illustrate the sensitivity of BTC shapes resulting from the geostatistical model used, how local peaks may potentially change the apparent overall slope of the curves, and the implications in water quality management decisions.

  • Probabilistic health risk assessment of chemical mixtures: importance of travel times and connectivity

     Henri, Christopher; Fernandez Garcia, Daniel; De Barros, Felipe P.J.
    European Geosciences Union General Assembly
    Presentation's date: 2014-05-01
    Presentation of work at congresses

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    Subsurface contamination cases giving rise to groundwater pollutions are extensively found in all industrialized countries. Under this pressure, risk assessment methods play an important role in population protection by (1) quantifying the potential impact on human health of an aquifer contamination and (2) helping and driving decisions of groundwater-resource managers. Many reactive components such as chlorinated solvents or nitrates potentially experience attenuation processes under common geochemical conditions. This represents an attractive and extensively used remediation solution but leads often to the production of by-products before to reach a harmless chemical form. This renders mixtures of contaminants a common issue for groundwater resources managers. In this case, the threat posed by these contaminants to human health at a given sensitive location greatly depends on the competition between reactive and advective-dispersive characteristic times. However, hydraulic properties of the aquifer are known to be spatially variable, which can lead to the formation of preferential flow channels and fast contamination pathways. Therefore, the uncertainty on the spatial distribution of the aquifer properties controlling the plume travel time may then play a particular role in the human health risk assessment of chemical mixtures. We investigate here the risk related to a multispecies system in response to different degrees of heterogeneity of the hydraulic conductivity (K or Y =ln(K)). This work focuses on a Perchloroethylene (PCE) contamination problem followed by the sequential first-order production/biodegradation of its daughter species Trichloroethylene (TCE), Dichloroethylene (DCE) and Vinyl Chlorine (VC). For this specific case, VC is known to be a highly toxic contaminant. By performing numerical experiments, we evaluate transport through three-dimensional mildly (2Y=1.0) and highly (2Y =4.0) heterogeneous aquifers. Uncertainty on the hydraulic conductivity field is considered through a Monte Carlo scheme, and statistics of the total risk for human health (RT ) related to the mixtures of the four carcinogenic plumes are evaluated. Results show two distinct spatiotemporal behavior of the RT estimation. Simulations in highly heterogeneous aquifers display a lower mean of RT close to the injection and higher further away. We explain this by the distinct ranges of travel times and connectivity metrics related to the two sets of aquifers. A high 2Y trends to decrease the travel time (and increase the connectivity). Early travel times, associated to channeling effects, are intuitively perceived as an indicator for high risk. However, in our case, early travel times lead a limited production of highly toxic daughter species and a lower total risk. Our results reflect then the interplay between the characteristic reactive time for each component and the characteristic travel time of the plume since the production of VC depends on these factors.

  • On the formation of localized peaksand non-monotonic tailing of breakthrough curves

     Siirila, Erica; Sanchez Vila, Francisco Javier; Fernandez Garcia, Daniel
    European Geosciences Union General Assembly
    Presentation's date: 2014-04-28
    Presentation of work at congresses

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    While breakthrough curve (BTC) analysis is a traditional tool in hydrogeology to obtain hydraulic parameters, in recent years emphasis has been placed on analyzing the shape of the receding portion of the curve. A number of field and laboratory observations have found a constant BTC slope in log-log space, and thus it has been hypothesized that a power law behavior is representative of real aquifers. Usually, monotonicity of the late-time BTC slope is just assumed, meaning that local peaks in the BTC are not considered, and that a local (in time) increase or decrease of BTC slope is also not considered. We contend that local peaks may exist but are sometimes not reported for a number of reasons. For example, when BTCs are obtained from actual measurements, sub-sampling may mask non-monotonicity, or small peaks may be reported as measurement errors and thus smoothed out or removed. When numerical analyses of synthetic aquifers are performed, the simulation method may yield artificially monotonous curves as a consequence of the methods used. For example, Eulerian methods may suffer from numerical dispersion, where curves tend to become over-smoothed while Lagrangian methods may suffer from artificial BTC oscillations stemming from the reconstruction of concentrations from a limited number of particles. A paradigm shift in terms of the BTC shape must also accompany two major advancements within the hydrogeology field: 1) the increase of high frequency data and progression of data collection techniques that diminish the problems of under-sampling BTCs and 2) advancements in supercomputing and numerical simulation allowing for higher resolution of flow and transport problems. As more information is incorporated into BTCs and/or they are obtained in more spatial locations, it is likely that classical definitions of BTC shapes will no longer be adequate descriptors for future treatment of contaminant transport problems. For example, the presence of localized peaks in BTCs (when, at what magnitude and duration) is imperative in accurately assessing environmental and human health risk, as discrepancies in the environmental concentration at a given time could potentially affect risk management decisions. In this work, the presence of multiple peaks in BTCs is assessed from high-resolution numerical simulations with particle tracking techniques and a kernel density estimator. Individual realizations of three-dimensional heterogeneous hydraulic conductivity fields with varying combinations of statistical anisotropy, geostatistical models, and local dispersivity are utilized to test for mechanisms of physical mass transfer. BTCs of non-reactive solutes are analyzed for the presence of local maxima, and for the corresponding slope of the receding limb of the curve as a function of travel distance and number of integral scales traveled, a question which has received little to no attention in the literature. This uniquely designed numerical experiment allows the discussion of BTC evolution in terms of not only the number of local peaks in the BTC, but also how knowledge of the number of local peaks in a BTC relates to pre-Fickian transport. We show that the number of local peaks and corresponding slopes strongly depend on statistical anisotropy and travel distance, but are less sensitive to the number of integral scales traveled. We also illustrate the sensitivity of BTC shapes resulting from the geostatistical model used, how local peaks may potentially change the apparent overall slope of the curves, and the implications of these results in water quality management decisions.

  • A geostatistical approach to estimate mining efficiency indicators with flexible meshes

     Freixas Borrell, Genis; Garriga Piferrer, David; Fernandez Garcia, Daniel; Sanchez Vila, Francisco Javier
    European Geosciences Union General Assembly
    p. 15269
    Presentation's date: 2014-04-28
    Presentation of work at congresses

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  • On the formation of localized peaks and non-monotonic tailing of breakthrough curves

     Siirila, Erica Rachel; Sanchez Vila, Francisco Javier; Fernandez Garcia, Daniel
    European Geosciences Union General Assembly
    p. 6923
    Presentation's date: 2014-04-28
    Presentation of work at congresses

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    While breakthrough curve (BTC) analysis is a traditional tool in hydrogeology to obtain hydraulic parameters, in recent years emphasis has been placed on analyzing the shape of the receding portion of the curve. A number of field and laboratory observations have found a constant BTC slope in log-log space, and thus it has been hypothesized that a power law behavior is representative of real aquifers. Usually, monotonicity of the late-time BTC slope is just assumed, meaning that local peaks in the BTC are not considered, and that a local (in time) increase or decrease of BTC slope is also not considered. We contend that local peaks may exist but are sometimes not reported for a number of reasons. For example, when BTCs are obtained from actual measurements, sub-sampling may mask non-monotonicity, or small peaks may be reported as measurement errors and thus smoothed out or removed. When numerical analyses of synthetic aquifers are performed, the simulation method may yield artificially monotonous curves as a consequence of the methods used. For example, Eulerian methods may suffer from numerical dispersion, where curves tend to become over-smoothed while Lagrangian methods may suffer from artificial BTC oscillations stemming from the reconstruction of concentrations from a limited number of particles. A paradigm shift in terms of the BTC shape must also accompany two major advancements within the hydrogeology field: 1) the increase of high frequency data and progression of data collection techniques that diminish the problems of undersampling BTCs and 2) advancements in supercomputing and numerical simulation allowing for higher resolution of flow and transport problems. As more information is incorporated into BTCs and/or they are obtained in more spatial locations, it is likely that classical definitions of BTC shapes will no longer be adequate descriptors for future treatment of contaminant transport problems. For example, the presence of localized peaks in BTCs (when, at what magnitude and duration) is imperative in accurately assessing environmental and human health risk, as discrepancies in the environmental concentration at a given time could potentially affect risk management decisions.

  • Probabilistic health risk assessment of chemical mixtures: importance of travel times and connectivity

     Henri, Christopher Vincent; Fernandez Garcia, Daniel; De Barros, Felipe P.J.
    European Geosciences Union General Assembly
    Presentation's date: 2014-04-09
    Presentation of work at congresses

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    Subsurface contamination cases giving rise to groundwater pollutions are extensively found in all industrialized countries. Under this pressure, risk assessment methods play an important role in population protection by (1) quantifying the potential impact on human health of an aquifer contamination and (2) helping and driving decisions of groundwater-resource managers.

  • Estimation of aquifers hydraulic parameters by three different tecniques: geostatistics, correlation and modeling.  Open access

     Barahona Palomo, Marco
    Department of Geotechnical Engineering and Geo-Sciences, Universitat Politècnica de Catalunya
    Theses

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    La caracterización de parámetros hidráulicos en acuíferos es una tarea dificil que requiere información de campo. La mayoria de las veces el hidroge61ogo se basa en valores procedentes de diferentes pruebas para interpretar Ia configuraci6n hidrogeol6gica y posiblemente, generar un modele. Sin embargo, obtener lo mejor de esta informaci6n puede ser un reto.Esta tesis analiza tres casos. Primero, se analiza Ia conductividad hidráulica (K) asociada a una escala de medici6n del orden de 10 m"-1 y obtenida durante una campana de campo. Las estimaciones se obtuvieron en puntas coincidentes en el sitio, mediante: a formulación empírica de Kozeny-Carman, proporcionando valores de K, con base en Ia distribuci6n de tamaño de partículas y las pruebas del medidor de caudal de tipo impulsor en el pozo, el cual infiere las medidas de K a partir de los flujos verticales dentro de un pozo. La correlaci6n entre los dos conjuntos de estimaciones es prácticamente ausente. Sin embargo, las estadísticas de algoritmo natural de ambos conjuntos en el lugar son similares en términos de valores medidos difieren en terminas de rangos del vario grama y varianzas de muestra. Esto es consecuente con el hecho de que los dos tipos de estimaciones pueden estar asociadas con escalas de apoyo de medici6n diferentes (aunque comparables). También coincide con los resultados publicados sobre Ia interpretación de Ia variabilidad de los descriptores geo estadísticos de parámetros hidráulicos en multiplex escalas de observaci6n.El análisis refuerza Ia idea de que los valores de K y descriptores geo estadísticos clave asociadas al inferirse de diferentes metodologías yen las escalas de observaci6n similares (en el case del orden de decenas de en) no son fácilmente comparables y deben ser usados con cuidado en Ia modelaci6n de flujo (y eventualmente, el transporte) del agua subterránea.En segundo lugar, un método de regresión kemel adaptado a datos, originalmente desarrollado para el procesamiento yreconstrucci6n de imágenes se modifica y se utiliza para Ia delimitación de facies. Esta metodología no paramétrica utiliza tanto Ia distribuci6n espacial como el valor de Ia muestra, para producir en cada punto de datos una funci6n kernel de direcci6n localmente adaptativo, con ajuste automático del kernel a Ia direcci6n de mayor correlaci6n espacial local. Se demuestra que este metada supera el NNC (por su acr6nimo en Ingles nearest-neighbor classification) en varies cases de acuíferos sintéticos donde el numero de datos disponibles es pequeno y Ia distribuci6n es aleatoria. Sin embargo, en el caso limite, cuando hay un gran numero de muestras, tanto el metodo kernel adaptado a Ia direcci6n local como el metoda de NNC convergen a Ia soluci6n verdadera. Las simulaciones son finalmente utilizadas para explorar cuales parámetros de Ia funci6n kernel dan resultados 6ptimos en Ia reconstrucci6n de resultados en escenarios tipicos de campo. SeDemuestra que, en Ia practica, una regia general puede ser utilizada para obtener resultados casi 6ptimos, los cuales mejoran cuando se utiliza información clave como Ia proporci6n de facies.En tercer Iugar, se modela el efecto de Ia fluctuaci6n de Ia temperatura del agua sobre Ia K de sedimentos gruesos debajo de una instalaci6n de recarga artificial y se compara con datos de campo. Debido a Ia alta permeabilidad, el agua se desplaza a alta velocidad alta, y por lo tanto, agua con temperatura diferente esta presente en el sedimento bajo Ia balsa en diferentes mementos, esto se traduce en diferentes valores de K dentro de Ia misma capa. Se observaron diferencias de casi 79% en Ia K del modelo, para las temperaturas utilizadas (2°C-25°C}. Esta variaci6n de Ia Ken el sedimento por debajo de Ia balsa de infiltraci6n cuando el agua de temperatura variable entra en el sedimento, causa un cambio en Ia velocidad de infiltraci6n con el tiempo y produce las variaciones observadas en las mediciones de campo.

    Characterization of aquifers hydraulic parameters is a difficult task that requires field information. Most of the time the hydrogeologist relies on a group of values coming from different test to interpret the hydrogeological setting and possibly, generate a model. However, getting the best from this information can be challenging. In this thesis, three cases are explored. First, hydraulic conductivities associated with measurement scale of the order of 10−1 m and collected during an extensive field campaign near Tübingen, Germany, are analyzed. Estimates are provided at coinciding locations in the system using: the empirical Kozeny-Carman formulation, providing conductivity values, based on particle size distribution, and borehole impeller-type flowmeter tests, which infer conductivity from measurements of vertical flows within a borehole. Correlation between the two sets of estimates is virtually absent. However, statistics of the natural logarithm of both sets at the site are similar in terms of mean values and differ in terms of variogram ranges and sample variances. This is consistent with the fact that the two types of estimates can be associated with different (albeit comparable) measurement (support) scales. It also matches published results on interpretations of variability of geostatistical descriptors of hydraulic parameters on multiple observation scales. The analysis strengthens the idea that hydraulic conductivity values and associated key geostatistical descriptors inferred from different methodologies and at similar observation scales (of the order of tens of cm) are not readily comparable and should not be embedded blindly into a flow (and eventually transport) prediction model. Second, a data-adapted kernel regression method, originally developed for image processing and reconstruction is modified and used for the delineation of facies. This non-parametric methodology uses both the spatial and the sample value distribution, to produce for each data point a locally adaptive steering kernel function, self-adjusting the kernel to the direction of highest local spatial correlation. The method is shown to outperform the nearest-neighbor classification (NNC) in a number of synthetic aquifers whenever the available number of data is small and randomly distributed. Still, in the limiting case, when the domain is profusely sampled, both the steering kernel method and the NNC method converge to the true solution. Simulations are finally used to explore which parameters of the locally adaptive kernel function yield optimal reconstruction results in typical field settings. It is shown that, in practice, a rule of thumb can be used to get suboptimal results, which are best when key prior information such as facies proportions is used. Third, the effect of water temperature fluctuation on the hydraulic conductivity profile of coarse sediments beneath an artificial recharge facility is model and compared with field data. Due to the high permeability, water travels at a high rate, and therefore also water with different temperature is also present on the sediment under the pond at different moments, this translates into different hydraulic conductivity values within the same layer, even though all the other parameters are the same for this layer. Differences of almost 79% in hydraulic conductivity were observed for the model temperatures (2 °C – 25 °C). This variation of hydraulic conductivity in the sediment below the infiltration pond when water with varying temperature enters the sediment, causes the infiltration velocity to change with time and produces the observed fluctuation on the field measurements.

    La caracterización de los parámetros hidráulicos de los acuíferos es una tarea difícil que requiere información de campo. La mayoría de las veces el hidrogeólogo se basa en un grupo de valores procedentes de diferentes pruebas para interpretar la configuración hidrogeológica y posiblemente , generar un modelo . Sin embargo, obtener lo mejor de esta información puede ser un reto. En esta tesis se analizan tres casos. Primero, se analizan las conductividades hidráulicas asociadas a una escala de medición del orden de 10 m− 1 y obtenidas durante una extensa campaña de campo cerca de Tübingen, Alemania. Las estimaciones se obtuvieron en puntos coincidentes en el sitio, mediante: la formulación empírica de Kozeny - Carman, proporcionando valores de conductividad, con base en la distribución de tamaño de partículas y las pruebas del medidor de caudal de tipo impulsor en el pozo, el cual infiere las medidas de conductividad a partir de los flujos verticales dentro de un pozo. La correlación entre los dos conjuntos de estimaciones es prácticamente ausente. Sin embargo, las estadísticas del logaritmo natural de ambos conjuntos en el lugar son similares en términos de valores medios y difieren en términos de rangos del variograma y varianzas de muestra. Esto es consecuente con el hecho de que los dos tipos de estimaciones pueden estar asociados con escalas de apoyo de medición diferentes (aunque comparables). También coincide con los resultados publicados sobre la interpretación de la variabilidad de los descriptores geoestadísticos de parámetros hidráulicos en múltiples escalas de observación . El análisis refuerza la idea de que los valores de conductividad hidráulica y descriptores geoestadísticos clave asociados al inferirse de diferentes metodologías y en las escalas de observación similares (en el caso del orden de decenas de cm) no son fácilmente comparables y debe ser utilizados con cuidado en la modelación de flujo (y eventualmente, el transporte) del agua subterránea. En segundo lugar, un método de regresión kernel adaptado a datos, originalmente desarrollado para el procesamiento y la reconstrucción de imágenes se modificó y se utiliza para la delimitación de las facies. Esta metodología no paramétrica utiliza tanto la distribución espacial como el valor de la muestra, para producir en cada punto de datos una función kernel de dirección localmente adaptativo, con ajuste automático del kernel a la dirección de mayor correlación espacial local. Se demuestra que este método supera el NNC (por su acrónimo en inglés nearest-neighbor classification) en varios casos de acuíferos sintéticos donde el número de datos disponibles es pequeño y la distribución es aleatoria. Sin embargo, en el caso límite, cuando hay un gran número de muestras, tanto en el método kernel adaptado a la dirección local como el método de NNC convergen a la solución verdadera. Las simulaciones son finalmente utilizadas para explorar cuáles parámetros de la función kernel localmente adaptado dan resultados óptimos en la reconstrucción de resultados en escenarios típicos de campo. Se demuestra que, en la práctica, una regla general puede ser utilizada para obtener resultados casi óptimos, los cuales mejoran cuando se utiliza información clave como la proporción de facies. En tercer lugar, se modela el efecto de la fluctuación de la temperatura del agua sobre la conductividad hidráulica de sedimentos gruesos debajo de una instalación de recarga artificial y se compara con datos de campo. Debido a la alta permeabilidad, el agua se desplaza a alta velocidad alta, y por lo tanto, agua con temperatura diferente también está presente en el sedimento bajo el estanque en diferentes momentos, esto se traduce en diferentes valores de conductividad hidráulica dentro de la misma capa, a pesar de que todos los demás parámetros son los mismos para esta capa. Se observaron diferencias de casi 79 % en la conductividad hidráulica en el modelo, para las temperaturas utilizadas (2 º C - 25 º C ). Esta variación de la conductividad hidráulica en el sedimento por debajo de la balsa de infiltración cuando el agua de temperatura variable entra en el sedimento, causa un cambio en la velocidad de infiltración con el tiempo y produce las fluctuacciones observadas en las mediciones de campo.

  • Apparent directional mass-transfer capacity coefficients in three-dimensional anisotropic heterogeneous aquifers under radial convergent transport

     Pedretti, Daniele; Fernandez Garcia, Daniel; Sanchez Vila, Francisco Javier; Bolster, Diogo; Benson, David
    Water resources research
    Vol. 50, num. 2, p. 1205-1224
    DOI: 10.1002/2013WR014578
    Date of publication: 2014-02
    Journal article

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    Aquifer hydraulic properties such as hydraulic conductivity (K) are ubiquitously heterogeneous and typically only a statistical characterization can be sought. Additionally, statistical anisotropy at typical characterization scales is the rule. Thus, regardless of the processes governing solute transport at the local (pore) scale, transport becomes non-Fickian. Mass-transfer models provide an efficient tool that reproduces observed anomalous transport; in some cases though, these models lack predictability as model parameters cannot readily be connected to the physical properties of aquifers. In this study, we focus on a multirate mass-transfer model (MRMT), and in particular the apparent capacity coefficient (), which is a strong indicator of the potential of immobile zones to capture moving solute. We aim to find if the choice of an apparent can be phenomenologically related to measures of statistical anisotropy. We analyzed an ensemble of random simulations of three-dimensional log-transformed multi-Gaussian permeability fields with stationary anisotropic correlation under convergent flow conditions. It was found that apparent also displays an anisotropic behavior, physically controlled by the aquifer directional connectivity, which in turn is controlled by the anisotropic correlation model. A high hydraulic connectivity results in large values. These results provide new insights into the practical use of mass-transfer models for predictive purposes.; Key Points; Convergent radial transport is modeled in random anisotropic formations Apparent capacity coefficient follows the same anisotropic patterns of ln(K) This behavior is linked to transport connectivity and stratification

  • Efectos del crecimiento de biomasa sobre la distribución de poros y la curva de retención en procesos de infiltración

     Carles Brangari, Albert; Sanchez Vila, Francisco Javier; Rubol, Simonetta; Romani Cornet, Anna Maria; Fernandez Garcia, Daniel
    Congreso Ibérico de las Aguas Subterráneas
    p. 161-162
    Presentation of work at congresses

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    Una amplia gama de fenómenos multidisciplinares relacionados con los procesos hidrodinámicos, fisico-quimicos se interrelacionan a distintas escalas espaciales y temporales durante procesos de infiltración natural, artificial o inducida. En este trabajo se presenta un ensayo a escala intermedia en el que se simula la infiltración a través de la capa superior de una balsa de recarga con agua de río que contiene una fracción de materia orgánica. El experimento se realiza en una caja de arena de aproximadamente un metro en dirección vertical. El objetivo principal es proporcionar un modelo físico pero simplificado para predecir los efectos de la modificación del espacio de poros durante el proceso de infiltración, con especial énfasis en los procesos biológicos, ya que se encontró que la actividad bacteriana afecta altamente el flujo a través de los suelos no saturados. Entre otros parámetros, se mide el crecimiento, la acumulación y la distribución espacial de las células vivas y muertas con la profundidad, la formación de burbujas de gas biogénico y la producción de sustancias polisacáridas extracelulares, y se observa cómo la evolución de estos parámetros puede estar relacionada con la modificación observada de la curva de distribución de espacio de poros, que a su vez es el principal factor que controla la conectividad hidráulica. Utilizando un modelo del suelo simplificado de tubos capilares, donde el crecimiento bacteriano puede taponar físicamente dichos poros, la evolución en la curva de retención se puede modelar adecuadamente

  • DEMONSTRATING MANAGER AQUIFER RECHARGE AS A SOLUTION TO WATER SCARCITY AND DROUGHT

     Rahbaralam, Maryam; Folch Sancho, Albert; Rodríguez Escales, Paula - Felicitat; Fernandez Garcia, Daniel; Carles Brangari, Albert; Sanchez Vila, Francisco Javier
    Competitive project

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  • Dynamic interactions between hydrogeological and exposure parameters in daily dose prediction under uncertainty and temporal variability

     Kumar, Vikas Jawahar Senthil; De Barros, Felipe P.J.; Schuhmacher, Marta; Fernandez Garcia, Daniel; Sanchez Vila, Francisco Javier
    Journal of hazardous materials
    Vol. 263, num. 1, p. 197-206
    DOI: 10.1016/j.jhazmat.2013.08.036
    Date of publication: 2013-12
    Journal article

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    We study the time dependent interaction between hydrogeological and exposure parameters in daily dose predictions due to exposure of humans to groundwater contamination. Dose predictions are treated stochastically to account for an incomplete hydrogeological and geochemical field characterization, and an incomplete knowledge of the physiological response. We used a nested Monte Carlo framework to account for uncertainty and variability arising from both hydrogeological and exposure variables. Our interest is in the temporal dynamics of the total dose and their effects on parametric uncertainty reduction. We illustrate the approach to a HCH (lindane) pollution problem at the Ebro River, Spain. The temporal distribution of lindane in the river water can have a strong impact in the evaluation of risk. The total dose displays a non-linear effect on different population cohorts, indicating the need to account for population variability. We then expand the concept of Comparative Information Yield Curves developed earlier (see de Barros et al. [29]) to evaluate parametric uncertainty reduction under temporally variable exposure dose. Results show that the importance of parametric uncertainty reduction varies according to the temporal dynamics of the lindane plume. The approach could be used for any chemical to aid decision makers to better allocate resources towards reducing uncertainty. © 2013 Elsevier B.V.

  • On the formation of breakthrough curves tailing during convergent flow tracer tests in three-dimensional heterogeneous aquifers

     Pedretti, Daniele; Fernandez Garcia, Daniel; Bolster, Diogo; Sanchez Vila, Francisco Javier
    Water resources research
    Vol. 49, num. 7, p. 4157-4173
    DOI: 10.1002/wrcr.20330
    Date of publication: 2013-07
    Journal article

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    Anomalous transport in advection-dominated convergent flow tracer tests can occurs due to small-scale heterogeneities in aquifer hydraulic properties. These result in fluctuations of the groundwater velocity field and complex connectivity patterns between injection and extraction wells. While detailed characterization of heterogeneity is often not possible in practice, a proper understanding of what fundamental physical mechanisms can give rise to macroscopic behaviors that are measurable is essential for proper upscaling of solute transport processes. We analyze here how heavy-tailed breakthrough curves can arise in radially convergent flow to a well. The permeability fields are three-dimensional multi-Gaussian fields with varying statistical geometry and degrees of heterogeneity. We consider transport of conservative tracers from multiple injection locations by varying distance and angle from the extraction well. Anomalous power law tailing in breakthrough curves is attributed to a variety of features including the initial vertical stratification of the solute that arises due to a flux-weighted injection, the injection distance to the well relative to the depth of the aquifer, and the statistics of the heterogeneity field as defined by the correlation length and variance of the permeability. When certain conditions cooccur for a given injection, such as strong connectivity contrasts between aquifer layers, injection distances comparable to the horizontal heterogeneity integral scales, and large global variances, breakthrough curves tend to scale as a PL with unit slope at late time. These findings offer new insights to understand what physical processes must be understood to develop and choose appropriate upscaling approaches that might reproduce such anomalous transport in heterogeneous advection-dominated systems.

  • Controlling scaling metrics for improved characterization of well-head protection regions

     De Barros, Felipe P.J.; Guadagnini, Alberto; Fernandez Garcia, Daniel; Riva, Monica; Sanchez Vila, Francisco Javier
    Journal of hydrology
    Vol. 494, num. 28, p. 107-115
    DOI: 10.1016/j.jhydrol.2013.04.040
    Date of publication: 2013-06
    Journal article

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    We addressed the value of hydrogeological information on the assessment of the risk that an operating pumping well is polluted. The work considered a heterogeneous aquifer and focused on the statistical characterization of the contaminant mass fraction from a diffused source recovered at the well and the solute arrival times. We explored the role of the key length scales that characterize and control the well capture region and its probabilistic delineation with respect to the contaminant source location and size. The impact of augmenting the data-base of hydraulic information on the reduction of uncertainty associated with the environmental scenario analyzed was then investigated. It was found that obtaining a robust characterization of the target Environmental Performance Metrics (EPMs) depends on the length scale considered. For the sampling scheme considered, the importance of conditioning on the probability distributions of solute mass fraction and travel times is strongly affected by the location of the contaminant source within the probabilistic well catchment. With reference to the characterization of the travel time distribution associated with the recovery of a given mass fraction, the worth of augmenting the hydraulic parameter data-sets tends to decrease with decreasing solute residence time within the well catchment.

  • Access to the full text
    Optimal reconstruction of non-symmetric travel time density distributions using a new kernel density estimator  Open access

     Pedretti, Daniele; Fernandez Garcia, Daniel
    European Geosciences Union General Assembly
    p. 1
    Presentation's date: 2013-04-07
    Presentation of work at congresses

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  • What controls apparent field capacity coefficients obtained from convergent flow tracer tests in anisotropic randomly heterogeneous formations?

     Fernandez Garcia, Daniel; Pedretti, Daniele; Sanchez Vila, Francisco Javier; Benson, David; Bolster, Diogo
    European Geosciences Union General Assembly
    p. 1
    Presentation's date: 2013-04-07
    Presentation of work at congresses

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  • Breakthrough curves tailing development during convergent flow tracer tests in 3D heterogeneous aquifers

     Sanchez Vila, Francisco Javier; Pedretti, Daniele; Fernandez Garcia, Daniel; Bolster, Diogo
    European Geosciences Union General Assembly
    p. 1
    Presentation's date: 2013-04-07
    Presentation of work at congresses

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  • Quantifying the influence of scaling metrics and hydrogeological data in the statistical characterization of model predictions inwell-catchment regions

     De Barros, Felipe P.J.; Guadagnini, Alberto; Fernandez Garcia, Daniel; Riva, Monica; Sanchez Vila, Francisco Javier
    European Geosciences Union General Assembly
    p. 1
    Presentation's date: 2013-04-07
    Presentation of work at congresses

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  • A relevant coupled particle-tracking solution for network reaction and multirate mass transfer under heterogeneous conditions

     Henri, Christopher; Fernandez Garcia, Daniel
    European Geosciences Union General Assembly
    p. 1
    Presentation's date: 2013-04-07
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  • A risk-based probabilistic framework to estimate the endpoint of remediation: concentration rebound by rate-limited mass transfer

     De Barros, Felipe P.J.; Fernandez Garcia, Daniel; Bolster, Diogo; Sanchez Vila, Francisco Javier
    Water resources research
    Vol. 49, num. 4, p. 1929-1942
    DOI: 10.1002/wrcr.20171
    Date of publication: 2013-04
    Journal article

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    Aquifer remediation is a challenging problem with environmental, social, and economic implications. As a general rule, pumping proceeds until the concentration of the target substance within the pumped water lies below a prespecified value. In this paper we estimate the a priori potential failure of the endpoint of remediation due to a rebound of concentrations driven by back diffusion. In many cases, it has been observed that once pumping ceases, a rebound in the concentration at the well takes place. For this reason, administrative approaches are rather conservative, and pumping is forced to last much longer than initially expected. While a number of physical and chemical processes might account for the presence of rebounding, we focus here on diffusion from low water mobility into high mobility zones. In this work we look specifically at the concentration rebound when pumping is discontinued while accounting for multiple mass transfer processes occurring at different time scales and parametric uncertainty. We aim to develop a risk-based optimal operation methodology that is capable of estimating the endpoint of remediation based on aquifer parameters characterizing the heterogeneous medium as well as pumping rate and initial size of the polluted area.

  • An analytical solution to study substrate-microbial dynamics in soils

     Sanchez Vila, Francisco Javier; Rubol, Simonetta; Carles Brangari, Albert; Fernandez Garcia, Daniel
    Advances in water resources
    num. 54, p. 181-190
    DOI: 10.1016/j.advwatres.2013.02.004
    Date of publication: 2013-04
    Journal article

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    We provide an approximate analytical solution for the substrate-microbial dynamics of the organic carbon cycle in natural soils under hydro-climatic variable forcing conditions. The model involves mass balance in two carbon pools: substrate and biomass. The analytical solution is based on a perturbative solution of concentrations, and can properly reproduce the numerical solutions for the full non-linear problem in a system evolving towards a steady state regime governed by the amount of labile carbon supplied to the system. The substrate and the biomass pools exhibit two distinct behaviors depending on whether the amount of carbon supplied is below or above a given threshold. In the latter case, the concentration versus time curves are always monotonic. Contrarily, in the former case the C-pool concentrations present oscillations, allowing the reproduction of non-monotonic small-scale biomass concentration data in a natural soil, observed so far only in short-term experiments in the rhizosphere. Our results illustrate the theoretical dependence of oscillations from soil moisture and temperature and how they may be masked at intermediate scales due to the superposition of solutions with spatially variable parameters.

  • Tools and analysis of spatio-temporal dynamics in heterogeneous aquifers: Applications to artificial recharge and forced-gradient solute transport  Open access

     Pedretti, Daniele
    Department of Geotechnical Engineering and Geo-Sciences, Universitat Politècnica de Catalunya
    Theses

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    This thesis deals with the development of tools and analysis to characterize and predict artificial recharge and radial convergent solute transport processes in heterogeneous media. The goal is to provide new insights to understand how heterogeneity, which is the main natural source of uncertainty in decision-making processes related with groundwater applications, can be controlled and its effects predicted for practical purposes in these topics. For hydrogeological applications, accurate modeling of phenomena is needed, but it is uncertain. Uncertainty is derived from the spatio-temporal random distribution of hydrodynamic (physical, chemical and biological) variables affecting groundwater processes, which is translated into random distribution of modeling parameters and equations. Such randomness is of two types: epistemic, when it can be reduced increasing the sample frequency of an experiment; aleatory, when it cannot be reduced when more information is analyzed. Sometimes hydrodynamic processes occur at so small scales that they become impossible to characterize with traditional methods, and from a practical perspective, this is analogous to deal with aleatoric model parameters. However, if some constitutive relationship (either empirically, theoretically or physically based) can be built between processes across different scales, then small-scale processes can be reproduced by equivalent large-scale model parameters. Uncertainty becomes amenable to be treated as epistemic randomness, and large-scale characterization techniques can be used to improve the description, interpretation or prediction of these processes. This thesis deals with these topics. The manuscript is composed by two main parts (the first on artificial recharge and the second on solute transport), each of them divided into three chapters. In chapter 1 of each part, a tool is developed to obtain quantitative information to model a selected variable at coarse grid resolutions. In the case of artificial recharge, satellite images are used to model the spatial variability of the infiltration capacity on top soils with a metric-scale detail. In the case of solute transport, a new method to estimate density from particle distribution is shown. In chapters 2, it is explored what processes occurring at the fine scales can affect the interpretation of artificial recharge and solute transport processes at larger scales. In the first part, a combined method that joins satellite images and field data along with a simple clogging model is used to display the equally-possible spatio-temporal mapping of the infiltration capacity of topsoil during artificial pond flooding activities. In the second part, numerical three-dimensional models are used to simulate transport in heterogeneous media under convergent radial flow to a well at fine scale. It is shown that an appropriate model framework can reproduce similar observations on contaminant temporal distribution at controlling section similar to those obtained in the field tracer tests. It is also provided a physical explanation to describe the so-called anomalous late-time behavior on breakthrough curves which is sometimes observed in the reality at larger scales. In the chapters 3, models are used to define the uncertainty around operating parameters in the optic of prediction and management on artificial recharge and solute transport. In the first case, a probability framework is built to define the engineering risk of management of artificial recharge ponds due to random variability of the initial distribution of infiltration, which controls several important clogging factors based on theoretical approaches. In the case of solute transport, it is discussed how equivalent parameters based on mass-transfer models can be related with the geometrical distribution of hydraulic parameters in anisotropic formation, when convergent flow tracer tests are used.

  • An analytical solution to study substrate-bacterial dynamics in soils

     Carles Brangari, Albert; Rubol, Simonetta; Sanchez Vila, Francisco Javier; Fernandez Garcia, Daniel
    American Geophysical Union Fall Meeting
    p. 1
    Presentation's date: 2012-12-03
    Presentation of work at congresses

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  • Role of length scales on environmental performance metrics for statistical characterization of well-head

     Pereira Jorge de Barros, Felipe; Guadagnini, Alberto; Fernandez Garcia, Daniel; Riva, Monica; Sanchez Vila, Francisco Javier
    American Geophysical Union Fall Meeting
    p. 1454-
    Presentation's date: 2012-12-03
    Presentation of work at congresses

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  • Numerical analysis of anomalous tailing on breakthrough curves during a typical convergent-flow tracer tests

     Pedretti, Daniele; Fernandez Garcia, Daniel; Sanchez Vila, Francisco Javier; Bolster, Diogo
    American Geophysical Union Fall Meeting
    p. 1358-
    Presentation's date: 2012-12-03
    Presentation of work at congresses

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  • A novel approach to investigate the link between natural biofilm growth and soil physical properties in a saturated porous media

     Rubol, Simonetta; Carles Brangari, Albert; Fernandez Garcia, Daniel; Freixa, A.; Romani Cornet, Anna Maria; Sanchez Vila, Francisco Javier
    SCARCE International Conference
    p. 171
    Presentation's date: 2012-11-26
    Presentation of work at congresses

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  • Interactions between hydrogeological and health parameters in probabilistic risk assessment: application to the Ebro River, Spain

     Kumar, V.; Pereira Jorge de Barros, Felipe; Schumacher, Marta; Sanchez Vila, Francisco Javier; Fernandez Garcia, Daniel
    SCARCE International Conference
    p. 174
    Presentation's date: 2012-11-26
    Presentation of work at congresses

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  • Well capture zone delineation under uncertainity: the value of information for risk assessment

     Sanchez Vila, Francisco Javier; Pereira Jorge de Barros, Felipe; Guadagnini, Alberto; Fernandez Garcia, Daniel; Riva, Monica
    IAHR International Groundwater Symposium
    p. 10
    Presentation's date: 2012-11
    Presentation of work at congresses

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  • A quick and inexpensive method to quantify spatially variable infiltration capacity for artificial recharge ponds using photographic images

     Pedretti, Daniele; Barahona Palomo, Marco; Bolster, Diogo; Sanchez Vila, Francisco Javier; Fernandez Garcia, Daniel
    Journal of hydrology
    Vol. 430-431, p. 118-126
    DOI: 10.1016/j.jhydrol.2012.02.008
    Date of publication: 2012-04-02
    Journal article

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  • Facies reconstruction through the exploitation of a locally adaptive kernel regression: implications in risk evaluations

     Barahona Palomo, Marco; Fernandez Garcia, Daniel; Sanchez Vila, Francisco Javier
    European Geosciences Union General Assembly
    p. 5209
    Presentation's date: 2012-04
    Presentation of work at congresses

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  • Estimating concentration rebounds in pumping wells and their impact on aquifer remediation and risk analysis

     Sanchez Vila, Francisco Javier; Pereira Jorge de Barros, Felipe; Fernandez Garcia, Daniel; Bolster, Diogo
    European Geosciences Union General Assembly
    p. 1
    Presentation's date: 2012-04
    Presentation of work at congresses

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  • On the relationship between connectivity and reaction rates

     SANZ-PRAT, ALICIA; Fernandez Garcia, Daniel
    European Geosciences Union General Assembly
    p. 1
    Presentation's date: 2012-04
    Presentation of work at congresses

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  • Numerical evaluation of apparent transport parameters from forced-gradient tracer tests in statistically anisotropic heterogeneous formations

     Pedretti, Daniele; Fernandez Garcia, Daniel; Bolster, Diogo; Sanchez Vila, Francisco Javier; Benson, David
    European Geosciences Union General Assembly
    p. 601
    Presentation's date: 2012-04
    Presentation of work at congresses

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  • Facies reconstruction through the exploitation of a locally adaptive kernel regression: implications in risk evaluations

     Sanchez Vila, Francisco Javier; Barahona Palomo, Marco; Fernandez Garcia, Daniel
    International Conference on Porous Media & Annual Meeting of the International Society for Porous Media
    p. 1
    Presentation's date: 2012-04
    Presentation of work at congresses

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  • Modeling multicomponent reactive transport with particle tracking and smoothing techniques

     Fernandez Garcia, Daniel; Sanchez Vila, Francisco Javier; Henri, Christopher
    International Conference on Porous Media & Annual Meeting of the International Society for Porous Media
    p. 1
    Presentation's date: 2012-04
    Presentation of work at congresses

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  • Visualization of mixing processes in a heterogeneous sand box aquifer

     Castro Alcalà, Eduardo Francisco; Fernandez Garcia, Daniel; Bolster, Diogo; Carrera Ramírez, Jesús
    Environmental science and technology
    Vol. 46, num. 6, p. 3228-3235
    DOI: 10.1021/es201779p
    Date of publication: 2012-03-20
    Journal article

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  • A bayesian approach to integrate temporal data into probabilistic risk analysis of monitored NAPL remediation

     Fernandez Garcia, Daniel; Bolster, Diogo; Sanchez Vila, Francisco Javier; Tartakovsky, Daniel
    Advances in water resources
    Vol. 36, p. 108-120
    DOI: 10.1016/j.advwatres.2011.07.001
    Date of publication: 2012-02
    Journal article

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  • Mixing induced reactive transport in fractured crystalline rocks

     Martinez Landa, Lourdes; Dentz, Marco; Carrera Ramírez, Jesús; Fernandez Garcia, Daniel; Nardi Ricart, Albert; Saaltink, Maarten Willem
    Applied geochemistry
    Vol. 27, num. 2, p. 479-489
    DOI: 10.1016/j.apgeochem.2011.09.016
    Date of publication: 2012-02
    Journal article

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  • Probabilistic analysis of maintenance and operation of artificial recharge ponds

     Pedretti, Daniele; Barahona Palomo, Marco; Bolster, Diogo; Fernandez Garcia, Daniel; Sanchez Vila, Francisco Javier; Tartakovsky, Daniel
    Advances in water resources
    Vol. 36, p. 23-35
    DOI: 10.1016/j.advwatres.2011.07.008
    Date of publication: 2012-02
    Journal article

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  • Probabilistic analysis of groundwater-related risks at subsurface excavation sites

     Jurado Elices, Anna; De Gaspari, Francesca; Vilarrasa Riaño, Victor; Bolster, Diogo; Sanchez Vila, Francisco Javier; Fernandez Garcia, Daniel; Tartakovsky, Daniel
    Engineering geology
    Vol. 125, p. 35-44
    DOI: 10.1016/j.enggeo.2011.10.015
    Date of publication: 2012-01-27
    Journal article

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  • Combining physical-based models and satellite images for the spatio-temporal assessment of soil infiltration capacity

     Pedretti, Daniele; Fernandez Garcia, Daniel; Sanchez Vila, Francisco Javier; Barahona Palomo, Marco; Bolster, Diogo
    Stochastic environmental research and risk assessment
    Vol. 25, num. 8, p. 1065-1075
    DOI: 10.1007/s00477-011-0486-4
    Date of publication: 2011-05-29
    Journal article

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    The performance of managed artificial recharge (MAR) facilities by means of surface ponds (SP) is controlled by the temporal evolution of the global infiltration capacity Ic of topsoils. Cost-effective maintenance operations that aim to maintain controlled infiltration values during the activity of the SP require the full knowledge of the spatio-temporal variability of Ic. This task is deemed uncertain. The natural reduction in time of Ic depends on complex physical, biological and chemical reactions that clog the soil pores and has been observed to decay exponentially to an asymptotic non-zero value. Moreover, the relative influence of single clogging processes depend on some initial parameters of the soil, such as the initial infiltration capacity (Ic,0). This property is also uncertain, as aquifers are typically heterogeneous and scarcely characterized in practical situations. We suggest a method to obtain maps of Ic using a geostatistical approach, which is suitable to be extended to engineering risk assessment concerning management of SP facilities. We propose to combine geostatistical inference and a temporally-lumped physical model to reproduce non-uniform clogging in topsoils of a SP, using field campaigns of local and large scale tests and additionally by means of satellite images as secondary information. We then postulate a power-law relationship between the parameter of the exponential law, k, and Ic,0. It is found that calibrating the two parameters of the power law model it is possible to fit the temporal evolution of total infiltration rate at the pond scale in a MAR test facility. The results can be used to design appropriate measures to selectively limit clogging during operation, extending the life of the infiltration pond.

  • Spatio-temporal assessment of soil infiltration capacity through physical-based models and geostatistical inference

     Pedretti, Daniele; Fernandez Garcia, Daniel; Sanchez Vila, Francisco Javier; Barahona Palomo, Marco; Bolster, Diogo
    European Geosciences Union General Assembly
    p. 1
    Presentation's date: 2011-04-03
    Presentation of work at congresses

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