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  • 1
    In: Groundwater, April 2015, Vol.53(S1), pp.139-148
    Description: Numerical and laboratory studies have provided evidence that combining hydraulic tomography with tomographic tracer tests could improve the estimation of hydraulic conductivity compared with using hydraulic data alone. Field demonstrations, however, have been lacking so far, which we attribute to experimental difficulties. In this study, we present a conceptual design and experimental applications of tracer tomography at the field scale using heat as a tracer. In our experimental design, we improve active heat tracer testing by minimizing possible effects of heat losses, buoyancy, viscosity, and changing boundary conditions. We also utilize a cost‐effective approach of measuring temperature changes in situ at high resolution. We apply the presented method to the 8 m thick heterogeneous, sandy gravel, alluvial aquifer at the Lauswiesen Hydrogeological Research Site in Tübingen, Germany. Results of our tomographic heat‐tracer experiments are in line with earlier work on characterizing the aquifer at the test site. We demonstrate from the experimental perspective that tracer tomography is applicable and suitable at the field scale using heat as a tracer. The experimental results also demonstrate the potential of heat‐tracer tomography as a cost‐effective means for characterizing aquifer heterogeneity.
    Keywords: Hydrogeology ; Aquifers ; Tracers (Biology) ; Tomography;
    ISSN: 0017-467X
    E-ISSN: 1745-6584
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  • 2
    In: Groundwater, January 2014, Vol.52(1), pp.37-49
    Description: Oxygen transfer in the capillary fringe (CF) is of primary importance for a wide variety of biogeochemical processes occurring in shallow groundwater systems. In case of a fluctuating groundwater table two distinct mechanisms of oxygen transfer within the capillary zone can be identified: vertical predominantly diffusive mass flux of oxygen, and mass transfer between entrapped gas and groundwater. In this study, we perform a systematic experimental sensitivity analysis in order to assess the influence of different parameters on oxygen transfer from entrapped air within the CF to underlying anoxic groundwater. We carry out quasi two‐dimensional flow‐through experiments focusing on the transient phase following imbibition to investigate the influence of the horizontal flow velocity, the average grain diameter of the porous medium, as well as the magnitude and the speed of the water table rise. We present a numerical flow and transport model that quantitatively represents the main mechanisms governing oxygen transfer. Assuming local equilibrium between the aqueous and the gaseous phase, the partitioning process from entrapped air can be satisfactorily simulated. The different experiments are monitored by measuring vertical oxygen concentration profiles at high spatial resolution with a noninvasive optode technique as well as by determining oxygen fluxes at the outlet of the flow‐through chamber. The results show that all parameters investigated have a significant effect and determine different amounts of oxygen transferred to the oxygen‐depleted groundwater. Particularly relevant are the magnitude of the water table rise and the grain size of the porous medium.
    Keywords: Groundwater – Analysis;
    ISSN: 0017-467X
    E-ISSN: 1745-6584
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  • 3
    In: Groundwater, January 2015, Vol.53(1), pp.57-70
    Description: We performed quasi‐two‐dimensional flow through laboratory experiments to study the effect of a coarse‐material inclusion, located in the proximity of the water table, on flow and oxygen transfer in the capillary fringe. The experiments investigate different phases of mass transfer from the unsaturated zone to anoxic groundwater under both steady‐state and transient flow conditions, the latter obtained by fluctuating the water table. Monitoring of flow and transport in the different experimental phases was performed by visual inspection of the complex flow field using a dye tracer solution, measurement of oxygen profiles across the capillary fringe, and determination of oxygen fluxes in the effluent of the flow‐through chamber. Our results show significant effects of the coarse‐material inclusion on oxygen transfer during the different phases of the experiments. At steady state, the oxygen flux across the unsaturated/saturated interface was considerably enhanced due to flow focusing in the fully water‐saturated coarse‐material inclusion. During drainage, a zone of higher water saturation formed in the fine material overlying the coarse lens. The entrapped oxygen‐rich aqueous phase contributed to the total amount of oxygen supplied to the system when the water table was raised back to its initial level. In case of imbibition, pronounced air entrapment occurred in the coarse lens, causing oxygen to partition between the aqueous and gaseous phases. The oxygen mass supplied to the anoxic groundwater following the imbibition event was found to be remarkably higher (approximately seven times) in the heterogeneous system compared with a similar experiment performed in a homogeneous porous medium.
    Keywords: Tracers (Chemistry) ; Groundwater ; Vadose Zone ; Flow (Dynamics);
    ISSN: 0017-467X
    E-ISSN: 1745-6584
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  • 4
    In: Groundwater, May 2019, Vol.57(3), pp.420-429
    Description: The spatial distribution of hydraulic properties in the subsurface controls groundwater flow and solute transport. However, many approaches to modeling these distributions do not produce geologically realistic results and/or do not model the anisotropy of hydraulic conductivity caused by bedding structures in sedimentary deposits. We have developed a flexible object‐based package for simulating hydraulic properties in the subsurface—the Hydrogeological Virtual Realities (HyVR) simulation package. This implements a hierarchical modeling framework that takes into account geological rules about stratigraphic bounding surfaces and the geometry of specific sedimentary structures to generate realistic aquifer models, including full hydraulic‐conductivity tensors. The HyVR simulation package can create outputs suitable for standard groundwater modeling tools (e.g., MODFLOW), is written in Python, an open‐source programming language, and is openly available at an online repository. This paper presents an overview of the underlying modeling principles and computational methods, as well as an example simulation based on the Macrodispersion Experiment site in Columbus, Mississippi. Our simulation package can currently simulate porous media that mimic geological conceptual models in fluvial depositional environments, and that include fine‐scale heterogeneity in distributed hydraulic parameter fields. The simulation results allow qualitative geological conceptual models to be converted into digital subsurface models that can be used in quantitative numerical flow‐and‐transport simulations, with the aim of improving our understanding of the influence of geological realism on groundwater flow and solute transport. : Generate hydrogeological virtual realities and analyze three‐dimensional conceptual models using a flexible open‐source Python package.
    Keywords: Hydrogeology – Analysis ; Hydrogeology – Electric Properties ; Aquifers – Analysis ; Aquifers – Electric Properties ; Ore Deposits – Analysis ; Ore Deposits – Electric Properties ; Geomorphology – Analysis ; Geomorphology – Electric Properties ; Anisotropy – Analysis ; Anisotropy – Electric Properties ; Groundwater Flow – Analysis ; Groundwater Flow – Electric Properties ; Groundwater – Analysis ; Groundwater – Electric Properties ; Sedimentary Structures – Analysis ; Sedimentary Structures – Electric Properties;
    ISSN: 0017-467X
    E-ISSN: 1745-6584
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  • 5
    In: Groundwater, November 2019, Vol.57(6), pp.925-939
    Description: Numerical models for reactive transport can be used to estimate the breakthrough of a contaminant in a pumping well or at other receptors. However, as natural aquifers are highly heterogeneous with unknown spatial details, reactive transport predictions on the aquifer scale require a stochastic framework... : Estimate the time of contaminant breakthrough at a receptor within a stochastic framework without solving reactive transport.
    Keywords: Denitrification ; Stoichiometry ; Particle Tracking ; Transport ; Aerobic Respiration ; Receptors ; Stochasticity ; Aquifers ; Aerobic Respiration ; Aquifers ; Denitrification ; Aerobic Respiration ; Demand Analysis ; Tracking ; Contaminants ; Computer Applications ; Uncertainty Analysis ; Contaminants ; Aquifers ; Denitrification ; Microorganisms ; Transport ; Contaminants ; Receptors ; Numerical Models ; Mathematical Models ; Scaling ; Electrons ; Aquifers ; Aquifers ; Stoichiometry;
    ISSN: 0017-467X
    E-ISSN: 1745-6584
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