Daniel Fernàndez-Garcia

Daniel Fernàndez-Garcia
Universitat Politècnica de Catalunya | UPC · Department of Civil and Environmental Engineering

PhD Environmental Science and Engineering

About

104
Publications
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2,295
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Publications

Publications (104)
Article
Random walk particle tracking methodologies to simulate solute transport of conservative species constitute an attractive alternative for their computational efficiency and absence of numerical dispersion. Yet, problems stemming from the reconstruction of concentrations from particle distributions have typically prevented its use in reactive transp...
Article
Mixing is increasingly recognized as a critical process for understanding and modeling reactive transport. Yet, mixing is hard to characterize because it depends nonlinearly on concentrations. Visualization of optical tracers in the laboratory at high spatial and temporal resolution can help advance the study of mixing processes. The solute distrib...
Article
We review the basic mathematical concepts of random walk particle tracking (RWPT) and its advantages and limitations. Three different numerical approaches to overcome the local mass conservation problem of the random walk methodology are examined: (i) the interpolation method, (ii) the reflection principle, and (iii) the generalized stochastic diff...
Article
The reconstruction of smooth density fields from scattered data points is a procedure that has multiple applications in a variety of disciplines, including Lagrangian (particle-based) models of solute transport in fluids. In random walk particle tracking (RWPT) simulations, particle density is directly linked to solute concentrations, which is norm...
Preprint
Full-text available
The reconstruction of smooth density fields from scattered data points is a procedure that has multiple applications in a variety of disciplines, including Lagrangian (particle-based) models of solute transport in fluids. In random walk particle tracking (RWPT) simulations, particle density is directly linked to solute concentrations, which is norm...
Article
Full-text available
Soil moisture measurements are needed in a large number of applications such as hydro-climate approaches, watershed water balance management and irrigation scheduling. Nowadays, different kinds of methodologies exist for measuring soil moisture. Direct methods based on gravimetric sampling or time domain reflectometry (TDR) techniques measure soil...
Article
The particle support volume is crucial for simulating reactive transport with Lagrangian methods as it dictates the interaction among particles. Assuming that it is constant in space, the particle support volume can be selected by means of kernel density estimation theory, an approach that has been shown to provide accurate estimates in simple setu...
Article
Full-text available
Pumping tests are performed during aquifer characterization to gain conceptual understanding about the system through diagnostic plots and to estimate hydraulic properties. Recovery tests consist of measuring head response in observation and/or pumping wells after pumping termination. They are especially useful when the pumping rate cannot be accur...
Article
Full-text available
Soil moisture measurements are needed in a large number of applications such as climate change, watershed water balance and irrigation management. One of the main characteristics of this property is that soil moisture is highly variable with both space and time, hindering the estimation of a representative value. Deciding how to measure soil moistu...
Article
https://authors.elsevier.com/a/1W~Jt16J1mlPA9 . A better understanding of microbial dynamics in porous media may lead to improvements in the design and management of a number of technological applications, ranging from the degradation of contaminants to the optimization of agricultural systems. To this aim, there is a recognized need for predicting...
Article
In recent years a large body of literature has been devoted to study reactive transport of solutes in porous media based on pure Lagrangian formulations. Such approaches have also been extended to accommodate second-order bimolecular reactions, in which the reaction rate is proportional to the concentrations of the reactants. Rather, in some cases,...
Article
Measured (or empirically fitted) reaction rates at groundwater remediation sites are typically much lower than those found in the same material at the batch- or laboratory-scale. The reduced rates are commonly attributed to poorer mixing at the larger scales. A variety of methods have been proposed to account for this scaling effect in reactive tra...
Article
Improving degradation rates of emerging organic compounds (EOCs) in groundwater is still a challenge. Although their degradation is not fully understood, it has been observed that some substances are preferably degraded under specific redox conditions. The coupling of Managed Aquifer Recharge with soil aquifer remediation treatment, by placing a re...
Article
The accumulation of biofilms in porous media is likely to influence the overall hydraulic properties and, consequently, a sound understanding of the process is required for the proper design and management of many technological applications. In order to bring some light into this phenomenon we present a mechanistic model to study the variably satur...
Article
Most methods for hydraulic test interpretation rely on a number of simplified assumptions regarding the homogeneity and isotropy of the underlying porous media. This way, the actual heterogeneity of any natural parameter, such as transmissivity (T), is transferred to the corresponding estimates in a way heavily dependent on the interpretation metho...
Article
When laboratory-measured chemical reaction rates are used in simulations at the field-scale, the models typically overpredict the apparent reaction rates. The discrepancy is primarily due to poorer mixing of chemically distinct waters at the larger scale. As a result, realistic field-scale predictions require accurate simulation of the degree of mi...
Article
We address modern topics of Stochastic Hydrogeology from their potential relevance to real modeling efforts at the field scale. While the topics of stochastic hydrogeology and numerical modelling have become routine in hydrogeological studies, non-deterministic models have not yet permeated into practitioners. We point out a number of limitations o...
Article
A GIS-based software platform was developed to arrange all the available hydrogeochemical data into a comprehensive structure and provide support for its proper storage, management, analysis and interpretation. This platform is composed of a geospatial database and a set of analytical instruments integrated in a graphical user interface that coordi...
Chapter
In this chapter we take a look at the presence of emerging organic compounds (EOCs) in groundwater, with emphasis in sources of pollution, processes affecting the spatial and temporal concentration of these compounds as they move through the aquifer and interact with the soil. Emphasis is placed on the combination of transport mechanisms and physic...
Article
The interplay between the spatial variability of the aquifer hydraulic properties, mass transfer due to sub-grid heterogeneity and chemical reactions often complicates reactive transport simulations. It is well documented that hydro-biochemical properties are ubiquitously heterogeneous and that diffusion and slow advection at the sub-grid scale typ...
Article
Random walk particle tracking methods are a computationally efficient family of methods to solve reactive transport problems. While the number of particles in most realistic applications is in the order of 106-109, the number of reactive molecules even in diluted systems might be in the order of fractions of the Avogadro number. Thus, each particle...
Article
Facies delineation is defined as the separation of geological units with distinct intrinsic characteristics (grain size, hydraulic conductivity, mineralogical composition). A major challenge in this area stems from the fact that only a few scattered pieces of hydrogeological information are available to delineate geological facies. Several methods...
Article
While particle tracking techniques are often used in risk frameworks, the number of particles needed to properly derive risk metrics such as average concentration for a given exposure duration is often unknown. If too few particles are used, error may propagate into the risk estimate. In this work, we provide a less error-prone methodology for the...
Article
Full-text available
The increasing presence of toxic chemicals released in the subsurface has led to a rapid growth of social concerns and the need to develop and employ models that can predict the impact of groundwater contamination on human health risk under uncertainty. Monitored natural attenuation is a common remediation action in many contamination cases. Howeve...
Article
We monitored oxygen concentration through the unsaturated zone in a mid-scale (1 m high) laboratory soil lysimeter subject to short wetting and drying cycles simulating a high permeable shallow aquifer recharged by river water. Ten cycles of different duration were performed during a period of 85 days. Measurements of oxygen in the liquid and the g...
Article
The often observed tailing of tracer breakthrough curves is 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 ch...
Article
The analysis of breakthrough curves (BTCs) is of interest in hydrogeology as a way to parameterize and explain processes related to anomalous transport. Classical BTCs assume the presence of a single peak in the curve, where the location and size of the peak and the slope of the receding limb has been of particular interest. As more information is...
Article
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...
Article
Modeling multi-species 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 combinat...
Article
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 artific...
Article
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...
Article
Construction of underground structures (e.g., subway lines, railways and highway tunnels) is inherently hazardous, posing risks to both workers and machinery at the site and to surrounding buildings. The presence of groundwater may increase these risks. We develop a general probabilistic risk assessment (PRA) framework to quantify risks driven by g...
Article
Particle tracking methods to simulate solute transport deal with the issue of having to reconstruct smooth concentrations from a limited number of particles. This is an error-prone process that typically leads to large fluctuations in the determined late-time behavior of breakthrough curves (BTCs). Kernel density estimators (KDE) can be used to aut...
Article
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 re...
Article
[1] 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...
Article
Considering complex physical and reactive processes is necessary to a trustable plume behavior prediction. However, complexity is often synonym of inefficiency and numerical problem for existing model. We present an efficient particle method to simulate plumes evolution moved by advection-dispersion and affected by network reactions and multirate-m...
Article
Breakthrough curves (BTCs) usually show asymmetric shapes, with marked tailing. This is particularly relevant in convergent-flow tracer tests (CFTTs). It is found that late-time BTCs frequently scales as a power-law function with a slope of -1 in a log-log plot. In tests performed in heterogeneous sandy aquifers with conservative tracers, the key l...
Article
Memory functions and mass transfer models have been widely used to simulate non-Fickian transport in naturally occurring heterogeneous formations. Yet, the link between the heterogeneous structure and the memory function parameters is largely unknown under convergent flow conditions driven by a pumping well. In this work we evaluate the impact of a...
Article
For typical solute transport applications using particle tracking algorithms, models are run with a limited number of particles and the estimation of the travel time density becomes an error-prone problem. Densities are however needed in groundwater applications, for instance to understand mixing, reactions and other type of phenomena occurring in...
Article
Full-text available
In this work, we evaluate the value of hydrogeological information on the assessment of the risk of contamination of a pumping well operating in a heterogeneous aquifer. Our aim is to statistically characterize the mass fraction of the contaminant recovered at the well and its corresponding arrival time. We do so by investigating the role of the ke...
Technical Report
Full-text available
Technical guide for the evaluation of the subsoil problems associated with organochlorine compounds
Chapter
The area involving the Lower Valley and Delta of the Llobregat River has a long-standing tradition in Managed Artificial Recharge (MAR) activities. For more than 50 years different MAR activities have taken place, and at present the area provides a catalog of methodologies put into practice. This chapter provides an overview of artificial recharge...
Article
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 o...
Article
For risk assessment and adequate decision making regarding remediation strategies in contaminated aquifers, solute fate in the subsurface must be modeled correctly. In practical situations, hydrodynamic transport parameters are obtained by fitting procedures, that aim to mathematically reproduce solute breakthrough (BTC) observed in the field durin...
Article
Facies delineation or reconstruction is defined as the separation of geological units with distinct intrinsic characteristics (i.e. grain size, hydraulic conductivity, mineralogical composition, etc.). It is a major challenge (for scientists, technicians, stake holders, among others) when just a few scattered pieces of information are available. Se...
Article
Since the middle of the previous century, DNAPL contamination is a clear identified problem for the management of urban and suburban groundwater resources quality. Random walk particles tracking methods showed their legitimacy and efficiency for modeling reactive transport especially thanks to the absence of numerical dispersion and computational e...
Article
Capturing the effects of aquifer heterogeneity is key to evaluating risk in groundwater related problems. In this work we analyze the potential failure of remediation due to the rebound of concentrations driven by back diffusion. Withdrawing polluted water from a contaminated aquifer by pumping is one of the most common components of many remediati...
Article
The efficiency of artificial surface ponds (SPs) for managed aquifer recharge (MAR) is mostly controlled by the topmost portion of the soil. The most significant soil property controlling recharge is the infiltration capacity (I-c), which is highly variable in space. Assessing its spatial distribution in detail is prohibitive in practice due to hig...
Article
Aquifer artificial recharge from surface infiltration ponds is often conducted to replenish depleted aquifers in arid and semi-arid zones. Physical and bio-geochemical clogging decreases the host soil’s infiltration capacity, which has to be restored with periodic maintenance activities. We develop a probabilistic modeling framework that quantifies...
Article
Upon their release into the subsurface, non-aqueous phase liquids (NAPLs) dissolve slowly in groundwater and/or volatilize in the vadose zone threatening the environment and public health over extended periods of time. The failure of a treatment technology at any given site is often due to the unnoticed presence of dissolved NAPL trapped in low per...
Article
In this paper the solute retention properties of crystalline fractured rocks due to mixing-induced geochemical reactions are studied. While fractured media exhibit paths of fast flow and transport and thus short residence times for conservative solutes, at the same time they promote mixing and dilution due to strong heterogeneity, which leads to sh...
Article
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 I c 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-...
Article
Despite the fact that the prognoses on the availability of resources related to different climate scenarios have been already formulated, the complex hydrological and biogeochemical reactions taking place in different compartments in natural environmental media are poorly understood, especially regarding the interactions between water bodies, and t...
Article
Decision makers require long term effective hydraulic criteria to optimize the design of artificial recharge ponds. However, uncontrolled multiscale pore clogging effects on heterogeneous soils determines uncertainties which must be quantified. One of the most remarkable effect is the reduction of infiltration capacity over time, which affect the q...
Article
In the framework of safety assessment studies for geological disposal, site-descriptive models are powerful inter-disciplinary tools aiming at supporting regulatory decision making as well as providing input for repository engineering activities. Striking aspects of these kinds of models are their very large temporal and spatial modeling scales and...
Article
Heterogeneity is key in evaluating risk in environmental related problems. In this work we analyze the potential failure of the endpoint of remediation due to a rebound of concentrations driven by back diffusion. Most typically, pumping out the polluted water is one of the main components of any remediation action. Pumping proceeds until concentrat...
Article
Random walk particle tracking methodologies to simulate solute transport of conservative species constitute an attractive alternative for their computational efficiency and absence of numerical dispersion. Yet, problems stemming from the reconstruction of concentrations from particle distributions have typically prevented its use in reactive transp...
Article
The release of non-aqueous phase liquids (NAPLs) such as petroleum hydrocarbons and chlorinated solvents in the subsurface is a severe source of groundwater and vapor contamination. Because these liquids are essentially immiscible due to low solubility, these contaminants get slowly dissolved in groundwater and/or volatilized in the vadoze zone thr...
Article
We provide a quantitative interpretation of the column experiment reported by Gramling et al. (2002). The experiment involves advection-dominated transport in porous media of three dissolved species, i.e., two reactants undergoing a fast irreversible reaction and the resulting product. The authors found that their observations could not be properly...
Conference Paper
Excavation sites such as those associated with the construction of subway lines, railways and highway tunnels are hazardous places, posing risks to workers, machinery and surrounding buildings. Many of these risks can be groundwater related. In this work we develop a general framework based on a probabilistic risk assessment (PRA) to quantify such...
Article
We studied an irreversible bi-molecular reactive transport experiment performed by Gramling et al. [2002]. In this experiment, colorimetric reactions between CuSO4 and EDTA4- were measured in a laboratory column filled with cryolite. After pre-saturating the system with EDTA4- (denoted as species B), CuSO4 (denoted as A) was injected as a step inpu...
Article
The response of coastal aquifers to sea-level fluctuations, notably tides, is known to contain much information about hydraulic parameters. We performed sensitivity analyses to assess how much, about what and where this information can be best obtained. It is well known that the response to harmonic fluctuations (and many harmonics can be superimpo...
Article
We present a method for the stochastic simulation of point-to-point transport connectivity honoring data from three types of information: (a) travel time estimates obtained from field tracer tests; (b) estimates of flow connectivity indicators obtained from the relatively fast or slow flow response that is observed at a point location given the flo...
Article
The release of non-aqueous phase liquids (NAPLs) such as petroleum hydrocarbons and chlorinated solvents in the subsurface is a severe source of groundwater and vapor contamination. Because these liquids are essentially immiscible due to low solubility, these contaminants get slowly dissolved in groundwater and/or volatilized in the vadoze zone thr...
Article
Many groundwater related problems involve artificial/engineered systems build within a complex natural geological medium. Examples include water supply, tunnels, and remediation efforts. Potential failure of a groundwater system can be defined as insufficient quality or quantity of water available for a given use at a given time. Such failures can...
Article
The storage of contaminant material in superficial or sub-superficial repositories, such as tailing piles for mine waste or disposal sites for low and intermediate nuclear waste, poses a potential threat for the surrounding biosphere. The minimization of these risks can be achieved by supporting decision-makers with quantitative tools capable to in...
Conference Paper
Construction of subterranean excavations in densely populated areas is inherently hazardous. The number of construction sites (e.g., subway lines, railways and highway tunnels) has increased in recent years. These sites can pose risks to workers at the site as well as cause damage to surrounding buildings. The presence of groundwater makes the exca...
Article
The choice of an adequate large-scale conceptual transport model constitutes a major challenge associated with the upscaling of solute transport. Among the different alternatives to the classical advection-dispersion model, the (multirate) mass transfer model has been proposed as a valuable and convenient alternative to model the large-scale behavi...
Article
Full-text available
1] Heterogeneity of subsurface environments and insufficient site characterization are some of the reasons why decisions about groundwater exploitation and remediation have to be made under uncertainty. A typical decision maker chooses between several alternative remediation strategies by balancing their respective costs with the probability of the...
Article
Full-text available
This paper presents an approach conducive to an evaluation of the probability density function (pdf) of spatio-temporal distributions of concentrations of reactive solutes (and associated reaction rates) evolving in a randomly heterogeneous aquifer. Most existing approaches to solute transport in heterogeneous media focus on providing expressions f...
Article
Transport of reactive species in the subsurface is driven by mixing processes. Whenever all reactions can be considered in chemical instantaneous equilibrium, a multiespecies reactive transport problem can be fully defined in terms of mixing driven conservative quantities, termed components, and the spatio-temporal distribution of reaction rates. M...
Conference Paper
The usual observation of anomalous (non-Fickian) transport in the field, manifested by peaked concentration profiles with pronounced tailing, has questioned the use of the classical advection-dispersion equation (ADE) to model transport phenomena at the usual computational scale of a numerical model. In this context, we evaluate the use of (multi-r...
Article
Connectivity of high/low-permeability areas has been recognized to significantly impact groundwater flow and solute transport. The task of defining a rigorous quantitative measure of connectivity for continuous variables has failed so far, and thus there exist a suite of connectivity indicators which are dependent on the specific hydrodynamic proce...
Article
Transport of reactive species in the subsurface is driven by mixing processes. Whenever all reactions can be considered in chemical instantaneous equilibrium, a multiespecies reactive transport problem can be fully defined in terms of mixing driven conservative quantities, termed components, and the spatio-temporal distribution of reaction rates. M...
Article
Chemical species are advected by water and undergo mixing processes due to effects of local diffusion and/or dispersion. In turn, mixing causes reactions to take place so that the system can locally equilibrate. In general, a multicomponent reactive transport problem is described through a system of coupled non-linear partial differential equations...
Article
We analyze the relative importance of the selection of (1) the geostatistical model depicting the structural heterogeneity of an aquifer, and (2) the basic processes to be included in the conceptual model, to describe the main aspects of solute transport at an experimental site. We focus on the res