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  • Ground Water
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  • 1
    In: Water Resources Research, July 2015, Vol.51(7), pp.5855-5868
    Description: This work reports numerical stability conditions in two‐dimensional solute transport simulations including discrete fractures surrounded by an impermeable rock matrix. We use an advective‐dispersive problem described in Tang et al. (1981) and examine the stability of the Crank‐Nicolson Galerkin finite... The von Neumann number ≥ 0.373 is required to avoid undershooting in the matrix The Courant number has a lower bound in the fracture for low dispersivity...
    Keywords: Discrete Fracture ; Solute Transport ; Numerical Stability
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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  • 2
    Language: English
    In: Journal of Environmental Management, 01 March 2015, Vol.150, pp.420-426
    Description: This report focuses on the enhancement in trichloroethylene (TCE) removal from contaminated groundwater using xanthan gum (XG)-modified, microscale, zero-valent iron (mZVI). Compared with bare mZVI, XG-coated mZVI increased the TCE removal efficiency by 30.37% over a 480-h experimental period. Because the TCE removal is attributed to both sorption and reduction processes, the contributions from sorption and reduction were separately investigated to determine the mechanism of XG on TCE removal using mZVI. The results showed that the TCE sorption capacity of mZVI was lower in the presence of XG, whereas the TCE reduction capacity was significantly increased. The FTIR spectra confirmed that XG, which is rich in hydrophilic functional groups, was adsorbed onto the iron surface through intermolecular hydrogen bonds, which competitively repelled the sorption and mass transfer of TCE toward reactive sites. The variations in the pH, Eh, and Fe concentration as functions of the reaction time were recorded and indicated that XG buffered the solution pH, inhibited surface passivation, and promoted TCE reduction by mZVI. Overall, the XG-modified mZVI was considered to be potentially effective for the remediation of TCE contaminated groundwater due to its high stability and dechlorination reactivity.
    Keywords: Microscale Zero-Valent Iron (Mzvi) ; Xanthan Gum (Xg) ; Trichloroethylene (Tce) ; Groundwater Pollution ; Environmental Sciences ; Economics
    ISSN: 0301-4797
    E-ISSN: 1095-8630
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  • 3
    Language: English
    In: Journal of Hydrology, January 2016, Vol.532, pp.90-101
    Description: Ground water flow systems of shallow sedimentary basins are studied in general by analyzing the fluid dynamics at the real world example of the Thuringian Basin. The impact of the permeability distribution and density differences on the flow velocity pattern, the salt concentration, and the temperature distribution is quantified by means of transient coupled simulations of fluid flow, heat, and mass transport processes. Simulations are performed with different permeabilities in the sedimentary layering and heterogeneous permeability distributions as well as with a non-constant fluid density. Three characteristic numbers are useful to describe the effects of permeability on the development of flow systems and subsurface transport: the relation of permeability between aquiclude and aquifer, the variance, and the correlation length of the log-normal permeability distribution. Density dependent flow due to temperature or concentration gradients is of minor importance for the distribution of the flow systems, but can lead to increased mixing dissolution of salt. Thermal convection is in general not present. The dominant driver of groundwater flow is the topography in combination with the permeability distribution. The results obtained for the Thuringian Basin give general insights into the dynamics of a small sedimentary basin due to the representative character of the basin structure as well as the transferability of the settings to other small sedimentary basins.
    Keywords: Subsurface Flow and Transport ; Fluid Dynamics in Sedimentary Basins ; Heterogeneity in Permeability ; Density Dependent Flow ; Thuringian Basin ; Opengeosys ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 4
    Language: English
    In: Water Research, 01 September 2016, Vol.100, pp.80-87
    Description: Application of microscale zero-valent iron (mZVI) is a promising technology for in-situ contaminated groundwater remediation; however, its longevity is negatively impacted by surface passivation, especially in saline groundwater. In this study, the aging behavior of mZVI particles was investigated in three media (milli-Q water, fresh groundwater and saline groundwater) using batch experiments to evaluate their potential corrosion and passivation performance under different field conditions. The results indicated that mZVI was reactive for 0–7 days of exposure to water and then gradually lost H -generating capacity over the next hundred days in all of the tested media. In comparison, mZVI in saline groundwater exhibited the fastest corrosion rate during the early phase (0–7 d), followed by the sharpest kinetic constant decline in the latter phases. The SEM-EDS and XPS analyses demonstrated that in the saline groundwater, a thin and compact oxide film was immediately formed on the surface and significantly shielded the iron reactive site. Nevertheless, in fresh groundwater and milli-Q water, a passive layer composed of loosely and unevenly distributed precipitates slowly formed, with abundant reactive sites available to support continuous iron corrosion. These findings provide insight into the molecular-scale mechanism that governs mZVI passivation and provide implications for long-term mZVI application in saline contaminated groundwater.
    Keywords: Microscale Zero-Valent Iron (Mzvi) ; Aging ; Passivation ; Hydrogen Production ; Saline Groundwater ; Engineering
    ISSN: 0043-1354
    E-ISSN: 1879-2448
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  • 5
    Language: English
    In: Journal of Hydrology, August 2017, Vol.551, pp.648-659
    Description: Application of numerical models is a common method to assess groundwater resources. The versatility of these models allows consideration of different levels of complexity, but the accuracy of the outcomes hinges upon a proper description of the system behaviour. In seawater intrusion assessment, the implementation of the sea-side boundary condition is of particular importance. We evaluate the influence of the slope of the sea-side boundary on the simulation results of seawater intrusion in a freshwater aquifer by employing a series of slope variations together with a sensitivity analysis by varying additional sensitive parameters (freshwater inflow and longitudinal and transverse dispersivities). Model results reveal a multi-dimensional dependence of the investigated variables with an increasing relevance of the sea-side boundary slope for seawater intrusion (decrease of up to 32%), submarine groundwater discharge zone (reduction of up to 55%), and turnover times (increase of up to 730%) with increasing freshwater inflow or dispersivity values.
    Keywords: Saltwater Intrusion ; Coastal Aquifers ; Numerical Investigation ; Sea-Side Boundary Condition ; Submarine Groundwater Discharge ; Residence Times ; Opengeosys ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 6
    Language: English
    In: Environmental Earth Sciences, 2015, Vol.74(10), pp.7147-7158
    Description: This paper presents the design and integration of a GIS-based data model for the regional hydrologic simulation in the Meijiang watershed, China. Hydrologic systems (HS) require integration of data and models simulating different processes. Here, an object-oriented approach using Unified Modeling Language (UML) is introduced, which supports the development of GIS-based Geodatabase model—GeoHydro/DataBase (GH/DB). Spatial data, such as basins, stream network, and observation stations are stored in the feature classes. The time series and their attributes are included in the tables. Relationship classes are used to link associated objects. The new development within the scientific program OpenGeoSys (OGS) is the integration of GH/DB into the numerical simulations. The graphical user interface is implemented for the pre- and post-processing of the simulation. As for the case study, a regional hydrologic model is developed in the Meijiang watershed area for the understanding of water infiltration from surface into groundwater via soil layer with various time scales. The integration of databases and modeling tool represents the comprehensive hydrosystems and thus it is a useful tool to understand the different processes and interactions between the related hydrological compartments.
    Keywords: Geographical information system (GIS) ; Unified modeling language (UML) ; GeoHydro/DataBase (GH/DB) ; Hydrologic simulation ; Meijiang watershed ; OpenGeoSys
    ISSN: 1866-6280
    E-ISSN: 1866-6299
    Source: Springer Science & Business Media B.V.
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  • 7
    Language: English
    In: Environmental Earth Sciences, 2013, Vol.70(7), pp.3363-3380
    Description: As part of the HG-A experiment in the Mont Terri Rock Laboratory, large-scale in situ water/gas injection experiments was conducted in a microtunnel. This research work focuses on the numerical analysis of the experimental data and the in situ observations. Concerning a temporary change of the hydromechanical properties of Opalinus Clay during experimental operations, three phases were numerically interpreted. These included the generation of excavation damaged zone during tunnel excavation, in which highly permeable flow paths around the tunnel have been formed; the self-sealing effect during water tests; and the pressure evolution during a long-term gas injection test. A coupled two-phase flow and mechanics model, taking into account the strong anisotropic properties of Opalinus Clay, was developed to interpret the measured data. The hydraulic anisotropy was described by a transversely isotropic permeability tensor. An elasto-plastic model was established to consider both stiffness anisotropy and strength anisotropy. Anisotropic plasticity was studied using the microstructure tensor method.
    Keywords: HM coupling ; Anisotropy ; In situ injection experiment ; Mont Terri Rock Laboratory ; EDZ
    ISSN: 1866-6280
    E-ISSN: 1866-6299
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  • 8
    Language: English
    In: Environmental Earth Sciences, 2012, Vol.67(2), pp.613-632
    Description: The idea of this paper is twofold. On one hand, we propose a general systematic for benchmarking of CO 2 modelling. On the other hand, we integrate material from the CLEAN project into this framework to demonstrate its applicability (Kühn et al. in Environ Earth Sci, this issue 2011). Benchmarks are an important instrument to gain a better understanding of interacting physico-chemical processes and they are a necessary tool to verify the algorithms and the software dedicated to simulate the separated and differently coupled thermo-hydro-mechanical/chemical processes during injecting and storing CO 2 in the subsurface. In general we distinguish between process- and site-related test cases. Process-related benchmarks deal with the required complexity of process coupling as well as equations of state for fluids and constitutive laws for geologic formations. Site-specific benchmarks represent different geological settings for potential CO 2 reservoirs, e.g., depleted gas and oil reservoirs as well as deep saline aquifers. The data basis for benchmarking mainly comes from experimental work in the CLEAN project as well as from literature. The benchmarking systematic is aimed at serving as basis for process studies, experimental design as well as for code inter-comparison purposes not only for numerical tools having used by the CLEAN partners but also for upcoming international benchmarking initiatives as well.
    Keywords: CLEAN ; CO2BENCH ; Benchmarking ; CO modelling ; OpenGeoSys ; Depleted gas reservoirs ; Deep saline aquifers ; Natural analogues
    ISSN: 1866-6280
    E-ISSN: 1866-6299
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  • 9
    Language: English
    In: Environmental Earth Sciences, 2014, Vol.72(10), pp.3795-3802
    Description: Current visualization techniques for computational fluid dynamics applications are sophisticated and work well in simple geometries. For complex geometries such as pore spaces, multiple domain boundaries obstruct the view and make the studying of fluid flow fields difficult. To overcome these deficiencies, we use two-sided materials to render the domain boundaries. Using this technique, it is possible to place the camera inside the domain and have a non-obstructed view of the surrounding flow field without losing spatial reference to the domain boundaries. As a result, a larger part of fluid flow visualization is visible. Two-sided material rendering was successfully applied to display still images with Blender Cycles renderer, in a virtual reality environment, and several implementation techniques were explored for using the Visualization Toolkit.
    Keywords: 3D Graphics ; Virtual reality ; Image generation ; VTK ; OpenGL ; VISLab TESSIN
    ISSN: 1866-6280
    E-ISSN: 1866-6299
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  • 10
    Language: English
    In: Environmental Earth Sciences, 2011, Vol.64(5), pp.1323-1333
    Description: Water shortage and groundwater pollution have become two primary environmental concerns to Beijing since the 1990s. The local aquifers, as the dominant sources for domestic and agricultural water supply, are depleting due to groundwater abstraction and continuous drought in recent years with rapid urbanization and increasing water consumption. Therefore, understanding the hydrogeological system is fundamental for a sustainable water resources management. In this article, the numerical analysis of a 3-D regional groundwater flow model for the Nankou area is presented. The hydrogeological system is reproduced according to sparsely distributed boreholes data. The numerical analysis is carried out using the scientific software OpenGeoSys, which is based on the finite element method. The model calibration and sensitivity analysis are accomplished with inverse methods by applying a model independent parameter estimation system (PEST). The results of the calibrated model show reasonable agreements with observed water levels. The transient groundwater flow simulations reflect the observed drawdown of the last 9 years and show the formation of a depression cone in an intensively pumped area.
    Keywords: Groundwater modeling ; OpenGeoSys ; PEST ; Nankou
    ISSN: 1866-6280
    E-ISSN: 1866-6299
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