http://hdl.handle.net/2117/3290 2013-05-19T12:56:36Z http://hdl.handle.net/2117/19028 Title: Multi-isotopic study (15N, 34S, 18O, 13C) to identify processes affecting nitrate and sulfate in response to local and regional groundwater mixing in a large-scale flow system Authors: Puig, Roger; Folch Sancho, Albert; Menció, Anna; Soler Gil, Albert; Mas-Pla, Josep Abstract: The integrated use of hydrogeologic and multi-isotopic approaches (d15N, d18ONO3, d34S, d18OSO4 and d13CHCO3) was applied in the Selva basin area (NE Spain) to characterize NO -3 and SO-2 -4 sources and to evaluate which geochemical processes affect NO -3 in groundwater. The studied basin is within a basinand-range physiographic province where natural hydrodynamics have been modified and different scale flow systems converge as a consequence of recent groundwater development and exploitation rates. As a result, groundwaters related to the local recharge flow system (affected by anthropogenic activities) and to the generally deeper regional flow system (recharged from the surrounding ranges) undergo mixing processes. The d15N, d18ONO3 and d34S indicated that the predominant sources of contamination in the basin are pig manure and synthetic fertilizers. Hydrochemical data along with d15N, d18ONO3, d34S, d18OSO4 and d13CHCO3 of some wells confirmed mixing between regional and local flow systems. Apart from dilution processes that can contribute to the decrease of NO -3 concentrations, the positive correlation between d15N and d18ONO3 agreed with the occurrence of denitrification processes. The d34S and d18OSO4 indicated that pyrite oxidation is not linked to denitrification, and d13CHCO3 did not clearly point to a role of organic matter as an electron donor. Therefore, it is proposed that the mixing processes between deeper regional and local surface groundwater allow denitrification to occur due to the reducing conditions of the regional groundwater. Thus, isotopic data add useful complementary information to hydrochemical studies, especially in those areas where hydrochemical data is not conclusive. 2013-04-29T09:00:29Z http://hdl.handle.net/2117/19018 Title: Granulometry and surfactants, key factors in desorption and biodegradation (T. versicolor) of PAHs in soil and groundwater Authors: Rodriguez-Escales, Paula; Borras, Eduard; Sarra, Montserrat; Folch Sancho, Albert Abstract: High hydrophobicity of polycyclic aromatic hydrocarbons (PAHs) is the most limiting factor for the remediation of polluted soils and aquifers. The present study analyzes the effect of three nonionic surfactants (Tween 80, BS-400, and Gold Crew) and the granulometry of soil (1%, 5%, 10%, and 20% of clay and silt) on desorption of a PAH mixture (fluorene, phenanthrene, anthracene, and pyrene). As a general trend, decrease of fine material content and increase of surfactant concentration raises desorption. However, some particularities have to be considered depending on granulometry together with the surfactant applied. Furthermore, increase of fine material content tends to reduce the importance of the PAH properties, e.g., K ow and solubility, in desorption. To complete the remediation process, biodegradation by Trametes versicolor was tested with the surfactant Tween 80. Results indicate that a high concentration of surfactant does not affect the efficiency of fungus bioremediation. Nevertheless, high fine material content in soil/aquifer can reduce the degradation rate. Moreover, desorption and biodegradation used synergically guarantee better overall results in the remediation of soils polluted by PAH mixtures than other methods that separate desorption and remediation. 2013-04-26T13:31:32Z http://hdl.handle.net/2117/19003 Title: Semianalytical solution for CO2 plume shape and pressure evolution during CO2 injection in deep saline formations Authors: Vilarrasa Riaño, Víctor; Carrera Ramírez, Jesús; Bolster, Diogo; Dentz, Marco Abstract: The injection of supercritical carbon dioxide (CO2) in deep saline aquifers leads to the formation of a CO2 rich phase plume that tends to float over the resident brine. As pressure builds up, CO2 density will increase because of its high compressibility. Current analytical solutions do not account for CO2 compressibility and consider a volumetric injection rate that is uniformly distributed along the whole thickness of the aquifer, which is unrealistic. Furthermore, the slope of the CO2 pressure with respect to the logarithm of distance obtained from these solutions differs from that of numerical solutions. We develop a semianalytical solution for the CO2 plume geometry and fluid pressure evolution, accounting for CO2 compressibility and buoyancy effects in the injection well, so CO2 is not uniformly injected along the aquifer thickness. We formulate the problem in terms of a CO2 potential that facilitates solution in horizontal layers, with which we discretize the aquifer. Capillary pressure is considered at the interface between the CO2 rich phase and the aqueous phase. When a prescribed CO2 mass flow rate is injected, CO2 advances initially through the top portion of the aquifer. As CO2 is being injected, the CO2 plume advances not only laterally, but also vertically downwards. However, the CO2 plume does not necessarily occupy the whole thickness of the aquifer. We found that even in the cases in which the CO2 plume reaches the bottom of the aquifer, most of the injected CO2 enters the aquifer through the layers at the top. Both CO2 plume position and fluid pressure compare well with numerical simulations. This solution permits quick evaluations of the CO2 plume position and fluid pressure distribution when injecting supercritical CO2 in a deep saline aquifer. 2013-04-26T10:43:49Z http://hdl.handle.net/2117/18815 Title: Mobility and interaction of heavy metals in a natural soil Authors: Bianchi Janetti, Emanuela; Dror,Ishai; Riva, Monica; Guadagnini, Alberto; Sánchez Vila, Francisco Javier; Berkowitz, Brian Abstract: 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. 2013-04-16T12:32:46Z http://hdl.handle.net/2117/17800 Title: Claves y oportunidades para un pacto del agua en España Authors: Garrido, Alberto; Custodio Gimena, Emilio 2013-02-15T15:50:03Z http://hdl.handle.net/2117/17530 Title: Stochastic evaluation of mixing-controlled steady-state plume lenghts in two-dimensional heterogeneous domains Authors: Cirpka, Olaf; Rolle, Massimo; Chiogna, Gabrielle; Barros, Felipe de; Nowak, Wolfgang Abstract: We study plumes originating from continuous sources that require a dissolved reaction partner for their degradation. The length of such plumes is typically controlled by transverse mixing. While analytical expressions have been derived for homogeneous flow fields, incomplete characterization of the hydraulic conductivity field causes uncertainty in predicting plume lengths in heterogeneous domains. In this context, we analyze the effects of three sources of uncertainty: (i) The uncertainty of the effective mixing rate along the plume fringes due to spatially varying flow focusing, (ii) the uncertainty of the volumetric discharge through (and thus total mass flux leaving) the source area, and (iii) different parameterizations of the Darcy-scale transverse dispersion coefficient. The first two are directly related to heterogeneity of hydraulic conductivity. In this paper, we derive semi-analytical expressions for the probability distribution of plume lengths at different levels of complexity. The results are compared to numerical Monte Carlo simulations. Uncertainties in mixing and in the source strength result in a statistical distribution of possible plume lengths. For unconditional random hydraulic conductivity fields, plume lengths may vary by more than one order of magnitude even for moderate degrees of heterogeneity. Our results show that the uncertainty of volumetric flux through the source is the most relevant contribution to the variance of the plume length. The choice of different parameterizations for the local dispersion coefficient leads to differences in the mean estimated plume length. 2013-01-30T09:46:31Z http://hdl.handle.net/2117/17235 Title: A hypothesis-driven approach to optimize field campaigns Authors: Nowak, Wolfgang; Rubin, Y.; Barros, Felipe de Abstract: Most field campaigns aim at helping in specified scientific or practical tasks, such as modeling, prediction, optimization, or management. Often these tasks involve binary decisions or seek answers to yes/no questions under uncertainty, e.g., Is a model adequate? Will contamination exceed a critical level? In this context, the information needs of hydro(geo)logical modeling should be satisfied with efficient and rational field campaigns, e.g., because budgets are limited. We propose a new framework to optimize field campaigns that defines the quest for defensible decisions as the ultimate goal. The key steps are to formulate yes/no questions under uncertainty as Bayesian hypothesis tests, and then use the expected failure probability of hypothesis testing as objective function. Our formalism is unique in that it optimizes field campaigns for maximum confidence in decisions on model choice, binary engineering or management decisions, or questions concerning compliance with environmental performance metrics. It is goal oriented, recognizing that different models, questions, or metrics deserve different treatment. We use a formal Bayesian scheme called PreDIA, which is free of linearization, and can handle arbitrary data types, scientific tasks, and sources of uncertainty (e.g., conceptual, physical, (geo)statistical, measurement errors). This reduces the bias due to possibly subjective assumptions prior to data collection and improves the chances of successful field campaigns even under conditions of model uncertainty. We illustrate our approach on two instructive examples from stochastic hydrogeology with increasing complexity. 2013-01-09T13:02:54Z http://hdl.handle.net/2117/17203 Title: Emerging organic contaminants in groundwater in Spain: A review of sources, recent occurrence and fate in a European context Authors: Jurado Elices, Anna; Vázquez Suñé, Enric; Carrera Ramírez, Jesús; López de Alda, Miren; Pujades Garnes, Estanislao; Barceló, Damià Abstract: This paper reviewed the presence of emerging organic contaminants (EOCs) that have been found in the groundwater in Spain in both, rural and urban areas. The list of compounds included pesticides, pharmaceutical active compounds (PhACs), selected industrial compounds, drugs of abuse (DAs), estrogens, personal care products and life-style compounds. The main sources of pollution and possible pathways have been summarised in this review. EOCs are likely to enter to the aquifer mainly through the effluents of waste water treatment plants (WWTPs) and are present in groundwater at concentrations of ng/L to μg/L. The most studied compounds in Spanish groundwater were pesticides followed by industrial compounds and PhACs. It is important to mention that compared to other water bodies, such as rivers, groundwater is considerably less contaminated, which may be indicative of the natural attenuation capacity of the aquifers. However, some EOCs have sometimes been detected at higher concentration levels in the aquifer than in the rivers, indicating the need for further research to understand their behaviour in the aquifers. For a wide array of compounds, their maximum concentrations show values above the European groundwater quality standard for individual pesticides (0.1 μg/L). Therefore, to preserve groundwater quality against deterioration it is necessary to define environmental groundwater thresholds for the non-regulated compounds. 2013-01-07T19:21:41Z http://hdl.handle.net/2117/17202 Title: Barrier effect of underground structures on aquifers Authors: Pujades Garnes, Estanislao; López, Ander; Carrera Ramírez, Jesús; Vázquez Suñé, Enric; Jurado Elices, Anna Abstract: Impervious structures below the water table modify the natural groundwater flow in aquifers. They act as barriers, causing heads to rise upgradient and to fall downgradient. We define the barrier effect as the increase in head loss across the barrier with respect to the natural conditions prior to construction. We distinguish between regional (the minimum head loss observed at long distances) and local (the maximum head loss observed close to the structure) barrier effects. We use numerical and analytical methods to derive semi-empirical equations to quantify the two barrier effects for semi-permeable, partially penetrating (or fully penetrating but finite in length), and barriers with a by-pass in confined aquifers. The resulting equations depend on the barrier geometry and on the natural head gradient in the aquifer and they are easy to apply. We test their validity at two construction sites, obtaining excellent agreement between the computed and observed barrier effects. 2013-01-07T18:58:35Z http://hdl.handle.net/2117/17041 Title: Bacterial transformation and biodegradation processes simulation in horizontal subsurface flow constructed wetlands using CWM1-RETRASO Authors: Llorens Ribes, Esther; Saaltink, Maarten Willem; Poch, Manel; García Serrano, Joan Abstract: The performance and reliability of the CWM1-RETRASO model for simulating processes in horizontal subsurface flow constructed wetlands (HSSF CWs) and the relative contribution of different microbial reactions to organic matter (COD) removal in a HSSF CW treating urban wastewater were evaluated. Various different approaches with diverse influent configurations were simulated. According to the simulations, anaerobic processes were more widespread in the simulated wetland and contributed to a higher COD removal rate [72–79%] than anoxic [0–1%] and aerobic reactions [20–27%] did. In all the cases tested, the reaction that most contributed to COD removal was methanogenesis [58–73%]. All results provided by the model were in consonance with literature and experimental field observations, suggesting a good performance and reliability of CWM1-RETRASO. According to the good simulation predictions, CWM1- RETRASO is the first mechanistic model able to successfully simulate the processes described by the CWM1 model in HSSF CWs. 2012-11-27T17:25:43Z http://hdl.handle.net/2117/17040 Title: CWM1 implementation in RetrasoCodeBright: first results using horizontal subsurface flow constructed wetland data, Chemical Engineering Journal Authors: Llorens Ribes, Esther; Saaltink, Maarten Willem; García Serrano, Joan Abstract: Constructed Wetland Model No. 1 (CWM1) processes were implemented within RetrasoCodeBright (RCB) to simulate hydraulics and reactive transport as well as the main biodegradation and transformation processes in horizontal subsurface flow constructed wetlands (SSF CWs). New values for some stoichiometric and kinetic coefficients were determined in the calibration step in order to obtain more realistic biochemical transformation and degradation processes. The model was checked and then tested for a horizontal SSF CW operating with different hydraulic loading rates [20, 36 and 45 mm/d]. Modifications to the CWM1 formulation had a negligible effect on the good fitting of measured and simulated data. However, changes in stoichiometric and kinetic parameters positively affected performance. Bacterial concentrations defined as initial conditions proved to be a variable requiring attention in the calibration. In terms of pollutant concentrations in effluent, simulated data corresponded well with data measured in most cases evaluated. The quality of the results obtained suggests that CWM1-RETRASO, the resulting model, is a potential tool for studying hydraulics, reactive transport and the main biochemical transformation and degradation processes for organic matter, nitrogen and sulphur in horizontal SSF CWs. 2012-11-27T17:22:47Z http://hdl.handle.net/2117/17038 Title: Experimental and modeling investigation of multicomponent reactive transport in porous media Authors: Katz, Graham; Berkowitz, Brian; Guadagnini, Alberto; Saaltink, Maarten Willem Abstract: We present an experimental and modeling study of solute transport in porous media in the presence of mixing-induced precipitation of a solid phase. Conservative and reactive transport experiments were performed in a quasi-two-dimensional laboratory flow cell, filled with homogeneous and heterogeneous porous media. Conservative experiments were performed by injecting solutions containing sodium chloride and calcium chloride into the domain. In reactive transport experiments, inlet solutions of calcium chloride and sodium carbonate were injected in parallel, resulting in calcium carbonate precipitation where the solutions mix. Experimental results were used as a benchmark to examine the performance of a reactive transport numerical model. Good agreement between model predictions and experimental results was obtained for the conservative transport experiments. The reactive transport experiments featured the formation of a calcium carbonate mineral phase within the mixing zone between the two solutions, which controlled the spatial evolution of calcium carbonate in the domain. Numerical simulations performed on high resolution grids for both the homogeneous and heterogeneous porous systems underestimated clogging of the system. Although qualitative agreement between model results and experimental observations was obtained, accurate model predictions of the spatial evolution of calcium concentrations at sample points within the flow cell could not be achieved. 2012-11-27T17:15:50Z http://hdl.handle.net/2117/16399 Title: Multiphase transport of tritium in unsaturated porous media-bare and vegetated soils Authors: Jiménez Martínez, Joaquín; Tamoh, Karim; Candela Lledó, Lucila; Elorza, F.J.; Hunkeler, D. Abstract: Tritium is a short-lived radioactive isotope (T 1/2=12.33 yr) produced naturally in the atmosphere by cosmic radiation but also released into the atmosphere and hydrosphere by nuclear activities (nuclear power stations, radioactive waste disposal). Tritium of natural or anthropogenic origin may end up in soils through tritiated rain, and may eventually appear in groundwater. Tritium in groundwater can be re-emitted to the atmosphere through the vadose zone. The tritium concentration in soil varies sharply close to the ground surface and is very sensitive to many interrelated factors like rainfall amount, evapotranspiration rate, rooting depth and water table position, rendering the modeling a rather complex task. Among many existing codes, SOLVEG is a one-dimensional numerical model to simulate multiphase transport through the unsaturated zone. Processes include tritium diffusion in both, gas and liquid phase, advection and dispersion for tritium in liquid phase, radioactive decay and equilibrium partitioning between liquid and gas phase. For its application with bare or vegetated (perennial vegetation or crops) soil surfaces and shallow or deep groundwater levels (contaminated or non-contaminated aquifer) the model has been adapted in order to include ground cover, root growth and root water uptake. The current work describes the approach and results of the modeling of a tracer test with tritiated water (7.3×108 Bq m−3) in a cultivated soil with an underlying 14 m deep unsaturated zone (non-contaminated). According to the simulation results, the soil’s natural attenuation process is governed by evapotranspiration and tritium re-emission. The latter process is due to a tritium concentration gradient between soil air and an atmospheric boundary layer at the soil surface. Re-emission generally occurs during night time, since at day time it is coupled with the evaporation process. Evapotranspiration and re-emission removed considerable quantities of tritium and limited penetration of surface-applied tritiated water in the vadose zone to no more than ∼1–2 m. After a period of 15 months tritium background concentration in soil was attained. 2012-08-28T11:58:19Z http://hdl.handle.net/2117/16223 Title: A sensivity analysis of tide-induced head fluctuations in coastal aquifers Authors: Slooten, Luit Jan; Carrera Ramírez, Jesús; Castro, Eduardo; Fernández García, Daniel Abstract: 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 superimposed to describe sea-level fluctuations) decreases exponentially with distance inland. The characteristic length of this decay is Lc= ..., where D is hydraulic diffusivity and P is period. Maximum sensitivity is obtained for distances equal to Lc, which is where maximum information would be obtained if the aquifer is treated as homogeneous. However, sensitivity depends not only on the problem dynamics, but also on parameterization. In fact, if heterogeneity is acknowledged by finely discretizing hydraulic conductivity, we find that connection to the sea (i.e. K near the coast) is what can be characterized best, while the most informative measurements are located at around 0.5 Lc. Thin low conductivity zones near the coast lead to a stepwise decrease in the amplitude of groundwater head fluctuations. We find that the fluctuations are independent of buoyancy effects, so that they can be simulated by constant density codes. High information content and ease of use suggest that they should be helpful in characterizing the aquifer–sea connection, which is important for coastal aquifer protection against seawater intrusion. 2012-07-11T09:18:53Z http://hdl.handle.net/2117/15847 Title: Diffuse and concentrated recharge evaluation using physical and tracer techniques: results from a semiarid carbonate massif aquifer in southeastern Spain Authors: Domingo, Francisco; Alcalá, F.J.; Canton, Yolanda; Contreras, Sergio; Were, Anna; Serrano Ortiz, Penelope; Solé, Albert; Custodio Gimena, Emilio; Puigdefàbregas Sagristà, Joan Abstract: In the high-permeability, semiarid carbonate aquifer in the Sierra de Gádor Mountains (southeastern Spain), some local springs draining shallow perched aquifers were of assistance in assessing applicability of the atmospheric chloride mass balance (CMB) for quantifying total yearly recharge (R T) by rainfall. Two contrasting hydrological years (October through September) were selected to evaluate the influence of climate on recharge: the average rainfall year 2003–2004, and the unusually dry 2004–2005. Results at small catchment scale were calibrated with estimated daily stand-scale R T obtained by means of a soil water balance (SWB) of rainfall, using the actual evapotranspiration measured by the eddy covariance (EC) technique. R T ranged from 0.35 to 0.40 of rainfall in the year, with less than a 5% difference between the CMB and SWB methods in 2003–2004. R T varied from less than 0.05 of rainfall at mid-elevation to 0.20 at high elevation in 2004–2005, with a similar difference between the methods. Diffuse recharge (R D) by rainfall was quantified from daily soil water content field data to split R T into R D and the expected concentrated recharge (R C) at catchment scale in both hydrological years. R D was 0.16 of rainfall in 2003–2004 and 0.01 in 2004–2005. Under common 1- to 3-day rainfall events, the hydraulic effect of R D is delayed from 1 day to 1 week, while R C is not delayed. This study shows that the CMB method is a suitable tool for yearly values complementing and extending the more widely used SWB in ungauged mountain carbonate aquifers with negligible runoff. The slight difference between R T rates at small catchment and stand scales enables results to be validated and provides new estimates to parameterize R T with rainfall depth after checking the weight of diffuse and concentrated mechanisms on R T during moderate rainfall periods and episodes of marked climatic aridity. 2012-05-14T16:12:52Z