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  • Geochemical modeling of arsenic release from a deep natural solid matrix under alternated redox conditions

     Molinari, A.; Ayora Ibañez, Carlos; Marcaccio, M.; Guadagnini, Laura; Sanchez Vila, Francisco Javier; Guadagnini, Alberto
    Environmental science and pollution research
    Date of publication: 2014-02
    Journal article

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    Dissolved arsenic (As) concentrations detected in groundwater bodies of the Emilia-Romagna Region (Italy) exhibit values which are above the regulation limit and could be related to the natural composition of the host porous matrix. To support this hypothesis, we present the results of a geochemical modeling study reproducing the main trends of the dynamics of As, Fe, and Mn concentrations as well as redox potential and pH observed during batch tests performed under alternating redox conditions. The tests were performed on a natural matrix extracted from a deep aquifer located in the Emilia-Romagna Region (Italy). The solid phases implemented in the model were selected from the results of selective sequential extractions performed on the tested matrix. The calibrated model showed that large As concentrations have to be expected in the solution for low crystallinity phases subject to dissolution. The role of Mn oxides on As concentration dynamics appears significant in strongly reducing environments, particularly for large water-solid matrix interaction times. Modeled data evidenced that As is released firstly from the outer surface of Fe oxihydroxides minerals exhibiting large concentrations in water when persistent reducing conditions trigger the dissolution of the crystalline structure of the binding minerals. The presence of organic matter was found to strongly affect pH and redox conditions, thus influencing As mobility.

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

     Barahona Palomo, Marco
    Defense's date: 2014-02-28
    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.

  • 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
    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.

    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.

  • 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
    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.

  • 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
    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.

  • 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
    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.

  • 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
    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.

  • Arsenic release from deep natural solid matrices under experimentally controlled redox conditions

     Molinari, Antonio; Guadagnini, Laura; Marcaccio, Marco; Straface, S.; Sanchez Vila, Francisco Javier; Guadagnini, Alberto
    Science of the total environment
    Date of publication: 2013-02
    Journal article

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  • Mobility and interaction of heavy metals in a natural soil

     Bianchi Janetti, Emanuela; Ishai, Dror; Riva, Monica; Guadagnini, Alberto; Sanchez Vila, Francisco Javier; Berkowitz, Brian
    Transport in porous media
    Date of publication: 2013-04
    Journal article

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    We study the mobility and interaction under competing conditions observed for copper ( Cu2+) and zinc ( Zn2+) ions in the context of laboratory-scale experiments performed in natural soil columns. The experiments focus on the analysis of solute breakthrough curves (BTCs) obtained after injection of an aqueous solution containing similar concentrations of the two metal ions into a soil column fully saturated with double deionized water. Transport of the competing ions is tested for the same soil under aerobic and anaerobic conditions. Measurements show that the species with lower affinity for the soil, Zn2+, migrates occupying all available adsorption sites, and is then progressively replaced by the ion with higher affinity, Cu2+. The two ions are displaced in the system with different effective retardation. The slowest species replaces the sorbed ions, resulting in observed Zn2+ concentrations that display a non-monotonic behavior in time and which, for a certain period, are larger than the concentration supplied continuously at the inlet. In the absence of a complete geochemical characterization of the system, we show that the measured concentrations of both metals can be interpreted through simple models based on a set of coupled partial differential and algebraic equations, involving a small subset of aqueous and adsorbed species that are present in the system. Depending on the model considered, the relationship between aqueous and adsorbed ion concentrations is described at equilibrium by a Gaines¿Thomas (GT) formulation, a competitive Sheindorf¿Rebhun¿Sheintuch (SRS) isotherm, or an Extended Langmuir (EL) isotherm, respectively. The GT formulation provides the best interpretation of the observed behavior among the models tested. We find that employing these simple models, which account only for the main governing reactive processes, allows reasonable estimation of the observed BTCs in experiments where only partial geochemical datasets are available.

    We study the mobility and interaction under competing conditions observed for copper (Cu2+) and zinc (Zn2+) ions in the context of laboratory-scale experiments performed in natural soil columns. The experiments focus on the analysis of solute breakthrough curves (BTCs) obtained after injection of an aqueous solution containing similar concentrations of the two metal ions into a soil column fully saturated with double deionized water. Transport of the competing ions is tested for the same soil under aerobic and anaerobic conditions. Measurements show that the species with lower affinity for the soil, Zn2+, migrates occupying all available adsorption sites, and is then progressively replaced by the ion with higher affinity, Cu2+. The two ions are displaced in the system with different effective retardation. The slowest species replaces the sorbed ions, resulting in observed Zn2+ concentrations that display a non-monotonic behavior in time and which, for a certain period, are larger than the concentration supplied continuously at the inlet. In the absence of a complete geochemical characterization of the system, we show that the measured concentrations of both metals can be interpreted through simple models based on a set of coupled partial differential and algebraic equations, involving a small subset of aqueous and adsorbed species that are present in the system. Depending on the model considered, the relationship between aqueous and adsorbed ion concentrations is described at equilibrium by a Gaines–Thomas (GT) formulation, a competitive Sheindorf–Rebhun–Sheintuch (SRS) isotherm, or an Extended Langmuir (EL) isotherm, respectively. The GT formulation provides the best interpretation of the observed behavior among the models tested. We find that employing these simple models, which account only for the main governing reactive processes, allows reasonable estimation of the observed BTCs in experiments where only partial geochemical datasets are available.

  • Occurrence and fate of emerging contaminants in urban groundwater. A case study: Barcelona.

     Jurado Elices, Anna
    Defense's date: 2013-10-21
    Universitat Politècnica de Catalunya
    Theses

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  • Sediment- water interaction in a water reservoir affected by acid mine drainage: experimental and modeling.

     Torres Sánchez, Ester
    Defense's date: 2013-11-15
    Department of Geotechnical Engineering and Geo-Sciences, Universitat Politècnica de Catalunya
    Theses

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  • A methodology to assess the combined effect of climate change and groundwater overexploitation over the Upper Guadiana basin, Spain

     Sapriza Azuri, Gonzalo
    Defense's date: 2013-12-20
    Universitat Politècnica de Catalunya
    Theses

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    AzuriEl efecto conjunto del cambio climático y la sobreexplotación de las aguas subterráneas podría llegar a ser crítico para la disponibilidad de recursos hídricos en la cuenca del Alto Guadiana (CAG) en el centro de España. Los modelos de circulación general del clima (GCM) son utilizados para evaluar el impacto del cambio climático. La salida de estos modelos no puede usarse directamente en modelos hidrológicos porque: (1) la resolución espacial es demasiado grande, y (2) el gran sesgo con que simulan la precipitación. Por tanto, se desarrolló un modelo para el downscaling diario de campos espaciales de precipitaciones. El modelo denominado Stochastic Rainfall Generating Process (SRGP) incorpora dos no-estacionaridades: (1) cambios en la frecuencia de los mecanismos de generación de precipitación (frontal y convectivo), y (2) no estacionaridades espaciales causadas por la interacción de patrones de circulación atmosférica (ACP) con la topografía (efecto orográfico). El SRGP se diseñó para que incorpore variables simuladas por los GCMs con sesgo reducido (ACP), así como observaciones. Estas prestaciones permiten: (1) utilizar el SRGP como un método de downscaling en el estudio del cambio climático, (2) generar campos estocásticos de precipitación condicionando a estaciones meteorológicas. Esta última función se utilizó para investigar el efecto de la variabilidad espacial de la precipitación (RSV) en la respuesta hidrogeológica en la CAG. Se constató que la RSV afecta fuertemente la respuesta hidrológica especialmente para la recarga de agua subterránea y las respuestas asociadas al acuífero. GCMs utilizados en el quinto informe del Panel Intergubernamental del Cambio Climático fueron empleados para evaluar el efecto del cambio climático. En todos los casos se consideraron las simulaciones correspondientes al periodo histórico (GCMH) y el escenario futuro de emisiones RCP8.5 (GCM-RCP8.5). El cambio climático se evaluó como el efecto acumulado en el incremento de las temperaturas, cambios en la frecuencia de los ACP y cambios en la probabilidad y volumen de lluvia. Se aplicaron transformaciones para corregir el sesgo en la temperatura, probabilidad y volumen de lluvia, mientras que se utilizó de forma directa los ACP. Se aplicó el SRGP como método de downscaling. El GCMH se utilizó para evaluar la respuesta hidrológica obtenida, introduciendo el concepto de equivalencia estocástica. Esta evaluación se basó en comparar la respuesta hidrológica obtenida al aplicar como forzantes la salida transformada (corrección del sesgo y SRGP) de los GCMH, en relación a la obtenida con observaciones. Se comprobó que no se alcanza una respuesta estocástica equivalente exacta para todas las respuestas, pero sí, reproducir variaciones estacionales.El efecto conjunto del cambio climático y la sobreexplotación por bombeo en la CAG se realizó en dos etapas: (1) Se simuló en condiciones naturales (sin bombeo) comparando la respuesta hidrológica obtenida de aplicar como forzantes GCMH y GCM-RCP8.5. (2) con los mismos forzantes se incorporó los bombeos y se compararon las respuestas. Se determinó que el efecto del cambio climático produce una reducción de 14% y 25% en el número de días de lluvia y en el volumen de lluvia respectivamente. Mientras que un incremento del 20% en la evapotranspiración potencial. En condiciones naturales esto se traduce en una reducción del 20% para la humedad de suelo y la evapotranspiración real. En tanto que, para la recarga de agua subterránea, escurrimiento, intercambio río-acuífero y caudal en el río la reducción fue del 40%. Finalmente, el efecto conjunto de los bombeos y cambio climático, resultó en una reducción para todas las variables, siendo de un 20% tanto para la humedad del suelo y al evapotranspiración real y del 50% para la recarga. Para el las respuestas asociadas al acuífero, la reducción llega hasta el 60 %. Los resultados mostraron un incremento de la estación seca extendiéndose de Abril a Octubre.

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

     Sanchez Vila, Francisco Javier
    Participation in a competitive project

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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
    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
    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
    Date of publication: 2012-01-27
    Journal article

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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
    Date of publication: 2012-04-02
    Journal article

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  • Fate of ß-blockers in aquifer material under nitrate reducing conditions: Batch experiments

     Barbieri, Manuela; Licha, Tobias Walter; Nödler, Karsten; Ayora Ibañez, Carlos; Sanchez Vila, Francisco Javier; Carrera Ramírez, Jesús
    Chemosphere
    Date of publication: 2012-11
    Journal article

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    The fate of the three environmentally relevant β-blockers atenolol, metoprolol and propranolol has been studied in batch experiments involving aquifer material and nitrate reducing conditions. Results from the about 90 d long tests indicate that abiotic processes, most likely sorption, jointly with biotransformation to atenololic acid were responsible for the 65% overall removal observed for atenolol. Zero order kinetics, typical of enzyme-limited reactions, controlled the transformation of this beta blocker to its corresponding carboxylic acid. The mass balance evidences that no mineralization of atenolol occurs in the biotic experiment and that atenololic acid is more stable than its parent compound under the studied conditions. This finding stresses the importance of considering atenololic acid as target compound in the environmental studies on the fate of atenolol. For metoprolol and propranolol the results from the experiment suggest a slower sorption to be the dominant removal process, which led to final decreases in concentrations of 25–30% and 40–45%, respectively. Overall, the removals observed in the experiments suggest that subsurface processes potentially constitute an alternative water treatment for the target beta-blockers, when compared to the removals reported for conventional wastewater treatment plants.

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

     Pedretti, Daniele
    Defense's date: 2012-12-21
    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.

  • Premi ICREA Acadèmia

     Sanchez Vila, Francisco Javier
    Award or recognition

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  • AJUT ICREA ACADEMIA 2011

     Sanchez Vila, Francisco Javier
    Participation in a competitive project

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  • Formation of diclofenac and sulfamethoxazole reversible transformation products in aquifer material under denitrifying conditions: batch experiments

     Barbieri, Manuela; Ayora Ibáñez, Carlos; Sanchez Vila, Francisco Javier; Licha, Tobias Walter; Nödler, Karsten; Osorio, Victoria; Pérez, Sandra; Köck Schulmeyer, Marianne; López de Alda, Miren; Barceló Culleres, Damià; Carrera Ramírez, Jesús
    Science of the total environment
    Date of publication: 2012-06-01
    Journal article

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  • Assessing and forecasting the impacts of global change on Mediterranean rivers: the SCARCE Consolider project on Iberian basins

     Navarro Ortega, A.; Acuña, Vicenç; Batalla, R.J.; Blasco, J.; Conde, C.; Elorza, Francisco Javier; Elosegi, A.; Frances, F.; La-Roca, Francesc; Muñoz, I.; Petrovic, Mira; Picó, Y.; Sabater, Sergi; Sanchez Vila, Francisco Javier; Schumacher, Marta; Barceló Culleres, Damià
    Environmental science and pollution research
    Date of publication: 2012-05
    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
    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.

  • Inferring spatial distribution of the radially integrated transmissivity from pumping tests in heterogeneous confined aquifers

     COPTY, N.K.; Trinchero, Paolo; Sanchez Vila, Francisco Javier
    Water resources research
    Date of publication: 2011
    Journal article

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  • Microcosm experiments to control anaerobic redox conditions when studying the fate of organic micropollutants in aquifer material

     Barbieri, Manuela; Sanchez Vila, Francisco Javier; Ayora Ibañez, Carlos; Cama Robert, Jordi; Carrera Ramírez, Jesús; Koeck Schulmeyer, Marianne; López de Alda, Miren; Barceló Culleres, Damià; Tobella Brunet, Joana; Hernández García, Marta
    Journal of contaminant hydrology
    Date of publication: 2011-11-01
    Journal article

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  • A divide and conquer approach to cope with uncertainty, human health risk, and decision making in contaminant hydrology

     Pereira Jorge de Barros, Felipe; Bolster, Diogo; Sanchez Vila, Francisco Javier; Nowak, Wolfgang
    Water resources research
    Date of publication: 2011-05-10
    Journal article

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  • Simplified Approaches to Deal With the Complexities of Seawater Intrusion

     Pool Ramirez, Maria
    Defense's date: 2011-12-22
    Department of Geotechnical Engineering and Geo-Sciences, Universitat Politècnica de Catalunya
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  • Rainfall partitioning in a deciduous forest (Quercus pubescens Willd.) in NE Spain: processes and modelling

     Muzylo, Aleksandra
    Defense's date: 2011-07-19
    Department of Geotechnical Engineering and Geo-Sciences, Universitat Politècnica de Catalunya
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  • Effect of redox conditions on the fate of emergin organic micropollutants during artificial recharge of groundwater: batch experiment  Open access

     Barbieri, Manuela
    Defense's date: 2011-07-22
    Department of Geotechnical Engineering and Geo-Sciences, Universitat Politècnica de Catalunya
    Theses

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    La recarrega artificial de les aigües subterrànies consisteix en infiltrar aigua als aqüífers per mitjà de les instal·lacions dissenyades per a tal fi i representa una eina important en la gestió dels recursos. A més de l’augment dels recursos d'aigües subterrànies, la recàrrega pot suposar una millora natural de la seva qualitat durant el seu pas pel subsòl. Els processos que tenen lloc en el sistema sòl-aqüífer (filtració, adsorció, reaccions de mescla , redox, biodegradació, etc) han demostrat produir una millora integral de la qualitat de l'aigua, eliminant també de manera efectiva una sèrie de contaminants orgànics. En l'actualitat, la qüestió és saber si la contaminació pels microcontaminants orgànics emergents, és a dir, productes farmacèutics, cosmètics, hormones, drogues il·lícites, pesticides i tensioactius, també es poden atenuar de forma natural. Alguns d’aquests compostos no són completament eliminats pels tractaments d'aigua residual convencionals, essent introduïts contínuament en els cursos d’aigua superficials pels efluents de les plantes de tractament. Malgrat la baixa concentració (ng/L i μg/L), la seva presència en el medi ambient és actualment un problema per a la vida aquàtica i la salut humana. En aquest context, la recàrrega artificial pot esdevenir una alternativa potencial o un tractament complementari per a l'eliminació de microcontaminants orgànics de l’aigua. Hi ha evidències que les condicions redox predominants podrien influir en el comportament d’aquests productes en l'aqüífer. No obstant, en el cas dels microcontaminants emergents, el coneixement sobre aquest tema és encara molt limitat. L’objectiu principal d’aquesta tesi és doncs investigar el possible efecte de les condicions redox sobre el destí de microcontaminants orgànics, la majoria dels quals són contaminants emergents. El treball està motivat pels projectes de recàrrega artificial amb aigua del riu Llobregat (Barcelona, Espanya). L’estudi es basa en experiments de laboratori (batch) utilitzant materials naturals de l'aqüífer, microcontaminants en concentracions ambientals (1 μg/L de cada compost), i unes condicions ambientals similars als llocs de recàrrega artificial. Afegint les quantitats adequades d’acceptors i donadors d’electrons s’han obtingut i mantingut les diferents condicions redox anaeròbies en cada conjunt de microcosmos. Els experiments inclouen sèries biòtiques i abiòtiques per separar la biodegradació de contaminants de l’adsorció a la superfície dels sòlids i altres processos abiòtics. També s’ha dut a terme un experiment amb una major concentració de contaminants (1 mg/L de cada compost), per comprovar la representativitat dels estudis convencionals. Els objectius finals del treball són: 1) identificar les condicions redox més favorables per eliminar de l'aigua els compostos seleccionats, a fi de ser promogudes en l’assaig de camp; i 2) mesurar les velocitats de les reaccions de degradació per tal de preveure el comportament dels micrcontaminants en el aqüífer.

    La recarga artificial de acuíferos, que consiste en la infiltración de agua subterránea en instalaciones diseñadas para tal fin, constituye una importante herramienta en la gestión de recursos hídricos. Más allá de aumentar los recursos de aguas subterráneas, suscita gran interés la capacidad de tratamiento natural que confiere el tránsito sub-superficial a las aguas. Los procesos que tienen lugar en el sistema suelo-acuífero (filtración, adsorción, mezcla, reacciones redox, biodegradación, etc.) permiten una mejora general de la calidad del agua, eliminando incluso diversos contaminantes orgánicos. En la actualidad, el reto es entender si los microcontaminantes orgánicos emergentes, es decir farmacéuticos, productos de cuidado personal, hormonas, drogas ilícitas, plaguicidas y tensioactivos, puedan también ser atenuados. Muchos de ellos no son completamente eliminados en tratamientos de agua convencionales, siendo introducidos constantemente en aguas superficiales por los efluentes de las plantas de tratamiento de aguas residuales. A pesar de sus baja concentraciones (ng/L and μg/L), su omnipresencia en el medioambiente es actualmente causa de preocupación para la vida acuática y la salud humana. En este contexto, la recarga artificial puede representar un tratamiento alternativo o complementario para la eliminación de microcontaminantes orgánicos de las aguas. Hay evidencias de que las condiciones redox dominantes pueden influenciar el comportamiento de contaminantes orgánicos convencionales en los acuíferos. Sin embargo, en el caso de los microcontaminantes emergentes los conocimientos sobre este tema es todavía limitado. El principal objetivo de esta tesis, motivada por proyectos de recarga artificial con aguas del río Llobregat (Barcelona, España), es investigar el efecto potencial de las condiciones redox sobre el comportamiento de microcontaminantes orgánicos seleccionados (la mayoría de los cuales son contaminantes emergentes) durante la recarga artificial. El estudio se basa en experimentos batch de laboratorio usando material natural del acuífero, microcontaminantes en concentraciones ambientales (1 μg/L cada compuesto), y condiciones verosímiles en enclaves de recarga artificial. Añadiendo cantidades adecuadas de aceptadores y donadores de electrones, fueron establecidas y se mantuvieron diferentes condiciones redox anaeróbicas (condiciones nitrato-, manganeso-, hierro- y sulfato-reductoras) en cada grupo de microcosmos. Se llevaron a cabo series bióticas y abióticas para separar la biodegradación de los contaminantes (mineralización biótica o transformación) de los procesos de adsorción y de otros procesos abióticos. También fue realizado un experimento para alta concentración de contaminantes (1 mg/L cada compuesto), para comprobar la representatividad de los estudios convencionales. El objetivo final de este trabajo es identificar 1) las condiciones redox más favorables para la eliminación del agua de los contaminantes seleccionados, para su posterior simulación en el sitio piloto, y 2) las tasas de eliminación de esos contaminantes, para predecir sus comportamientos en el acuífero.

    Artificial recharge of groundwater, consisting in infiltrating water into aquifers by means of properly designed facilities, represents an important tool in water resources management. Beside its quantitative benefits (augmentation of groundwater resources, long term underground storage, etc.), a great interest for this technique is related to the natural treatment provided to water by subsurface passage. The processes occurring in the soil-aquifer system (filtration, sorption, mixing, redox reactions, biodegradation, etc.) have indeed proven to yield an overall improvement of water quality, removing effectively also a number of organic contaminants. At present time, the issue is to understand whether emerging organic micropollutants, i.e. pharmaceuticals, personal care products, hormones, illicit drugs, pesticides and surfactants, can also be removed. A number of these compounds are not completely removed by conventional water treatments, being thus introduced continuously into surface water bodies by the discharge of wastewater treatment plants effluents. In spite of their low concentration (ng/L and μg/L), their ubiquitous presence in the environment is currently a cause of concern for aquatic life and human health. In this context, artificial recharge may represent a potential alternative or complementary treatment for the removal of organic micropollutants from water. Evidences showed that, among the factors influencing the fate of conventional organic contaminants in the aquifer, the predominant redox conditions could play an important role. Yet, in the case of emerging micropollutants the knowledge on this topic is still limited. The main objective of this thesis, motivated by artificial recharge practices using Llobregat river water (Barcelona, Spain), is to investigate on the potential effect of redox conditions on the fate of selected organic micropollutants, most of them being emerging contaminants, during artificial recharge of groundwater. The study is based on batch experiments involving natural aquifer material, micropollutants at environmental concentrations (1 μg/L each compound), and settings feasible at artificial recharge sites. Different anaerobic redox conditions (namely, nitrate-, manganese-, iron- and sulphate-reducing conditions) were promoted and sustained in each set of microcosms by adding adequate quantities of electron donors and acceptors. The experiments included biotic and abiotic series to separate contaminant’s biodegradation (i.e. biotic mineralization or transformation) from sorption and other abiotic processes. An experiment at higher pollutants concentration (1mg/L each compound) was also carried out, to check the representativeness of studies at concentrations easier to be tested and analysed. The ultimate aim of the work is to identify 1) the most favourable redox conditions for the removal of the target compounds from water, for their following stimulation in the field test site, and 2) pollutants’ removal rates, to predict their behaviour in the aquifer.

  • 17th Arthur T. Ippen Award. (IAHR 2011 Ippen Awards)

     Sanchez Vila, Francisco Javier
    Award or recognition

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  • Assessing preferential flow through an unsaturated waste rock pile using spectral analysis

     Trinchero, Paolo; Beckie, Roger; Sanchez Vila, Francisco Javier; Nichol, Craig
    Water resources research
    Date of publication: 2011-07-19
    Journal article

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  • Optimal reconstruction of concentrations, gradients and reaction rates from particle distributions

     Fernandez Garcia, Daniel; Sanchez Vila, Francisco Javier
    Journal of contaminant hydrology
    Date of publication: 2011
    Journal article

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  • Quantitative comparison of impeller-flowmeter and particle-size-distribution techniques for the characterization of hydraulic conductivity variability

     Barahona Palomo, Marco; Riva, Monica; Sanchez Vila, Francisco Javier; Vazquez Suñe, Enric; Guadagnini, Alberto
    Hydrogeology journal
    Date of publication: 2011-02-19
    Journal article

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  • Conditional stochastic mapping of transport connectivity

     Fernandez Garcia, Daniel; Trinchero, Paolo; Sanchez Vila, Francisco Javier
    Water resources research
    Date of publication: 2010
    Journal article

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  • An approach to identify urban groundwater recharge

     Vázquez Suñé, Enric; Carrera, J; Tubau Fernandez, Isabel; Sanchez Vila, Francisco Javier; Soler Gil, Albert
    Hydrology and Earth system sciences
    Date of publication: 2010
    Journal article

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  • Nonlinear seismic analysis of industrial steel structures with irregularities

     Gabas Canela, Guillermo
    Defense's date: 2010-07-22
    Department of Construction Engineering, Universitat Politècnica de Catalunya
    Theses

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  • Criterios de trazado para la inserción urbana de tranvías

     Andres Hilarion, Helena
    Defense's date: 2010-07-19
    Department of Transport and Highway Engineering, Universitat Politècnica de Catalunya
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  • A random walk particle tracking methodology to model reactive transport in heterogeneous porous media

     Castro Ledesma, Adolfo
    Defense's date: 2010-01-08
    Department of Geotechnical Engineering and Geo-Sciences, Universitat Politècnica de Catalunya
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  • RIESGO ASOCIADO A LA RECARGA ARTIFICIAL DE ACUIFEROS: UNA VISION INTEGRADA SUELO-ACUIFERO

     Martinez Landa, Lourdes; Barbieri, Manuela; Bolster, Diogo; Guadagnini, Alberto; Riva, Monica; Jódar Bermúdez, Jorge; Valhondo Gonzalez, Cristina; Silva Rojas, Orlando Enrique; Pool Ramirez, Maria; Sanchez Vila, Francisco Javier
    Participation in a competitive project

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  • Computational Methods in Water Resources

     Fernandez Garcia, Daniel; Saaltink, Maarten Willem; Dentz, Marco; Carrera Ramírez, Jesús; Sanchez Vila, Francisco Javier
    Participation in a competitive project

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  • A solution for multicomponent reactive transport under equilibrium and kinetic reactions

     Sanchez Vila, Francisco Javier; Donado Garzón, Leonardo David; Guadagnini, Alberto; Carrera Ramírez, Jesús
    Water resources research
    Date of publication: 2010-07-30
    Journal article

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  • Interpretation of column experiments of transport of solutes undergoing an irreversible bimolecular reaction using a continuum approximation

     Sanchez Vila, Francisco Javier; Fernandez Garcia, Daniel; Guadagnini, Alberto
    Water resources research
    Date of publication: 2010-12-02
    Journal article

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    Coupling of mass transfer and reactive transport for nonlinear reactions in heterogeneous media  Open access

     Willmann, Mathias; Carrera Ramírez, Jesús; Sanchez Vila, Francisco Javier; Silva Rojas, Orlando Enrique; Dentz, Marco
    Water resources research
    Date of publication: 2010-07-01
    Journal article

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    Fast chemical reactions are driven by mixing‐induced chemical disequilibrium. Mixing is poorly represented by the advection‐dispersion equation. Instead, effective dynamics models, such as multirate mass transfer (MRMT), have been successful in reproducing observed field‐scale transport, notably, breakthrough curves (BTCs) of conservative solutes. The objective of this work is to test whether such effective models, derived from conservative transport observations, can be used to describe effective multicomponent reactive transport in heterogeneous media. We use a localized formulation of the MRMT model that allows us to solve general reactive transport problems. We test this formulation on a simple three‐species mineral precipitation problem at equilibrium. We first simulate the spatial and temporal distribution of mineral precipitation rates in synthetic hydraulically heterogeneous aquifers. We then compare these reaction rates to those corresponding to an equivalent (i.e., same conservative BTC) homogenized medium with transport characterized by a nonlocal in time equation involving a memory function. We find an excellent agreement between the two models in terms of cumulative precipitated mass for a broad range of generally stationary heterogeneity structures. These results indicate that mass transfer models can be considered to represent quite accurately the large‐scale effective dynamics of mixing controlled reactive transport at least for the cases tested here, where individual transport paths sample the full range of heterogeneities represented by the BTC.

  • Characterization of mixing and spreading in a bounded stratified medium

     Zavala-Sanchez, V; Sanchez Vila, Francisco Javier; Dentz, Marco
    Advances in water resources
    Date of publication: 2009-05
    Journal article

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  • Application of a mixing-ratios based formulation to model mixing-driven dissolution experiments

     Guadagnini, A; Sanchez Vila, Francisco Javier; Saaltink, Maarten Willem; Bussini, M; Berkowitz, B
    Advances in water resources
    Date of publication: 2009-05
    Journal article

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  • Probabilistic risk analysis of groundwater remediation strategies

     Bolster, Diogo; Dentz, Marco; Fernandez Garcia, Daniel; Sanchez Vila, Francisco Javier
    Water resources research
    Date of publication: 2009-05
    Journal article

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  • Characterization of Spatial Heterogeneity in Groundwater Applications.  Open access

     Trinchero, Paolo
    Defense's date: 2009-02-20
    Department of Geotechnical Engineering and Geo-Sciences, Universitat Politècnica de Catalunya
    Theses

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    La heterogeneidad es una característica saliente de cada formación geológica natural. En las últimas décadas un gran número de trabajos se han centrado en estudiar la influencia de la heterogeneidad en los problemas de flujo y transporte en medios poros. Dichos trabajos han mejorado sustancialmente la comprensión de los mecanismos que gobiernan estos fenómenos, sin embargo aun existen carencias en la caracterización de propiedades importantes de un acuífero. Entre ellas, el flujo preferencial, la conectividad entre dos puntos de un acuífero y la interpretación de ensayos en acuíferos heterogéneos son aspectos importantes que tienen que ser adecuadamente evaluados para obtener modelos predictivos robustos. En este contexto, el objetivo de esta tesis es doble:· mejorar el conocimiento de la influencia de la heterogeneidad en los procesos de flujo y transporte· proporcionar nuevas herramientas para caracterizar la heterogeneidad de los acuíferosEn primer lugar, evaluamos la relación entre dos indicadores de conectividad de flujo y transporte. El indicador de conectividad de flujo utilizado aquí se basa en el tiempo de respuesta hidráulica en un ensayo de bombeo (por ejemplo, el coeficiente de almacenamiento estimado con el método de Cooper-Jacob). Como indicador de conectividad de transporte utilizamos la porosidad estimada de curvas de llegadas (Φest) en ensayos de trazadores con flujo radial. Los resultados obtenidos permiten explicar la poca correlación entre estos dos indicadores ya observada númericamente por Knudby y Carrera (2005).En segundo lugar, se ha desarrollado un marco geoestádistico para delinear mapas de conectividad utilizando un número limitado de medidas hidráulicas. La metodología permite condicionar los resultados a tres tipos de datos medidos a diferentes escalas: (a) tiempos de llegada de ensayos de trazadores en flujo convergente ta, (b) estimaciones del coeficiente de almacenamiento obtenidas de ensayos de bombeo interpretados con el método de Cooper-Jacob, Sest, y (c) mediciones de valores de transmisividad puntuales, T. La capacidad de la metodología para delinear correctamente zonas de captura se evalúa a través de estimaciones (krigeado simple y ordinario) y simulaciones secuenciales gausianas basadas en diferentes conjuntos de medidas.En tercer lugar, se ha desarrollado una metodología, llamada método del doble punto de inflexión (DIP), para la interpretación de pruebas de bombeo en acuíferos semiconfinados. La ventaja de este método (DIP) se observa en acuíferos heterogéneos, cuando se aplica junto a las demás metodologías. En estos casos cada método proporciona información diferente acerca de la heterogeneidad. En particular, la combinación del método DIP y el método de Hantush permite identificar contrastes entre la transmisividad local (cerca del pozo) y la transmisividad equivalente del acuífero.En cuarto lugar, se utiliza el método de Monte Carlo para evaluar el significado de los parámetros hidráulicos estimados de ensayos de bombeo en acuíferos semiconfinados. Dichos parámetros resultan ser espacialmente dependientes y varían en función del método de interpretación, ya que cada método pondera de forma distinta diferentes partes de la curva de descensos. Por último, se muestra que al combinar las estimaciones de los parámetros obtenidos a partir de los diferentes procedimientos de análisis, se puede inferir información sobre la heterogeneidad del sistema.En quinto lugar, se modela el flujo no saturado en un dique de estériles utilizando un modelo basado en funciones de transferencia. La calibración del modelo proporciona información sobre el tiempo característico del flujo a través de la matriz y de la fracción de agua que se canaliza a través de los macroporos. Por último se presenta un análisis de la influencia de la escala en los resultados. A gran escala el comportamiento del sistema tiende al de un sistema-matriz homogéneo equivalente,enmascarando los efectos del flujo preferencial.

    Heterogeneity is a salient feature of every natural geological formation. In the past decades a large body of literature has focused on the effects of heterogeneity on flow and transport problems. These works have substantially improved the understanding of flow and transport phenomena but still fail to characterize many of the important features of an aquifer. Among them, preferential flows and solute paths, connectivity between two points of an aquifer, and interpretation of hydraulic and tracer tests in heterogeneous media are crucial points that need to be properly assessed to obtain accurate model predictions. In this context, the aim of this thesis is twofold:· to improve the understanding of the effects of heterogeneity on flow and transport phenomena· to provide new tools for characterizing aquifer heterogeneityFirst, we start by theoretically and numerically examine the relationship between two indicators of flow and transport connectivity. The flow connectivity indicator used here is based on the time elapsed for hydraulic response in a pumping test (e.g., the storage coefficient estimated by the Cooper-Jacob method, Sest). Regarding transport, we select the estimated porosity from the observed breakthrough curve (Φ est) in a forced-gradient tracer test. Our results allow explaining the poor correlation between these two indicators, already observed numerically by Knudby and Carrera (2005).Second, a geostatistical framework has been developed to delineate connectivity patterns using a limited and sparse number of measurements. The methodology allows conditioning the results to three types of data measured over different scales, namely: (a) travel times of convergent tracer tests, ta, (b) estimates of the storage coefficient from pumping tests interpreted using the Cooper-a Jacob method, S est, and (c) measurements of transmissivity point values, T. The ability of the methodology to properly delineate capture zones is assessed through estimations (i.e. ordinary cokriging) and sequential gaussian simulations based on different sets of measurements.Third, a novel methodology for the interpretation of pumping tests in leaky aquifer systems, referred to as the double inflection point (DIP) method, is presented. The real advantage of the DIP method comes when it is applied with all the existing methods independently to a test in a heterogeneous aquifer. In this case each method yields parameter values that are weighted differently, and thus each method provides different information about the heterogeneity distribution. In particular, the combination of the DIP method and Hantush method is shown to lead to the identification of contrasts between the local transmissivity in the vicinity of the well and the equivalent transmissivity of the perturbed aquifer volume.Fourth, the meaning of the hydraulic parameters estimated from pumping test performed in leaky aquifers is assessed numerically within a Monte Carlo framework. A synthetic pumping test is interpreted using three existing methods. The resulting estimated parameters are shown to be space dependent and vary with the interpretation method, since each method gives different emphasis to different parts of the timedrawdown data. Finally, we show that by combining the parameter estimates obtained from the different analysis procedures, information about the heterogeneity of the leaky aquifer system may be inferred.Fifth, an unsaturated highly heterogeneous waste rock pile is modeled using a simple linear transfer function (TF) model. The calibration of the parametric model provides information on the characteristic time of the flow through the matrix and on the fraction of the water that, within each section, is channeled through the macropores. An analysis of the influence of the scale on the results is also provided showing that at large scales the behavior of the system tends to that of an equivalent matrix reservoir masking the effects of preferential flow.

  • An analytical approach to transient homovalent cation exchange problems

     Sanchez Vila, Francisco Javier; Bolster, Diogo
    Journal of hydrology
    Date of publication: 2009-11
    Journal article

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    Multicomponent reactive transport in multicontinuum media  Open access

     Donado, Leonardo David; Sanchez Vila, Francisco Javier; Dentz, Marco; Carrera Ramirez, Jesus; Bolster, Diogo
    Water resources research
    Date of publication: 2009
    Journal article

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    Multicomponent reactive transport in aquifers is a highly complex process, owing to a combination of variability in the processes involved and the inherent heterogeneity of nature. To date, the most common approach is to model reactive transport by incorporating reaction terms into advection-dispersion equations (ADEs). Over the last several years, a large body of literature has emerged criticizing the validity of the ADE for transport in real media, and alternative models have been presented. One such approach is that of multirate mass transfer (MRMT). In this work, we propose a model that introduces reactive terms into the MRMT governing equations for conservative species. This model conceptualizes the medium as a multiple continuum of one mobile region and multiple immobile regions, which are related by kinetic mass transfer processes. Reactants in both the mobile and immobile regions are assumed to always be in chemical equilibrium. However, the combination of local dispersion in the mobile region and the various mass transfer rates induce a global chemical nonequilibrium. Assuming this model properly accounts for transport of reactive species, we derive explicit expressions for the reaction rates in the mobile and immobile regions, and we study the impact of mass transfer on reactive transport. Within this framework, we observe that the resulting reaction rates can be very different from those that arise in a system governed by an ADE-type equation.