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Summary 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. [ABSTRACT FROM AUTHOR]

The abandoned, flooded deep salt mine in Stassfurt, Germany has been extensively studied. The mine causes serious uncontrolled salt leaching and mass displacement effects underground that have led to significant regional-scale subsidence. Collapsing mined areas and further large-scale subsidence pose a potential danger to the city of Stassfurt. Comprehensive modeling of the three dimensional (3-D) variable density flow dynamics is required at both large and local scale to assess the stability of the cap rocks and the potential of subsidence due to salt leaching processes, and to better control (minimize) salt leaching. The impact of different engineering solutions and appropriate remedial strategies (e.g. pumping schemes) on the subsurface spatio-temporal distribution of salinity is of specific concern. Coupled variable density flow and transport simulations were performed using FEFLOW, a finite-element simulator, which is capable of both porous media (Darcy-type) flow computations and lower-dimensional discrete elements for laminar or turbulent flow. The geometry of the mine workings is incorporated in suitable detail and resolution in the developed 3-D model. Computational results were successfully compared with field observations and geophysical measurements. Different model scenarios provide better insight into flow and mass transport processes in the study area, which could provide significant information to quantify subsidence potential of the mine site. [ABSTRACT FROM AUTHOR]

Abstract: A popular method for the treatment of aquifers contaminated with chlorinated solvents is chemical oxidation based on the injection of potassium permanganate (KMnO4). Both the high density (1025 gL−1) and reactivity of the treatment solution influence the fate of permanganate (MnO4) in the subsurface and affect the degree of contaminant treatment. The MIN3P multicomponent reactive transport code was enhanced to simulate permanganate-based remediation, to evaluate the pathways of MnO4 utilization, and to assess the role of density contrasts for the delivery of the treatment solution. The modified code (MIN3P-D) provides a direct coupling between density-dependent fluid flow, solute transport, contaminant treatment, and geochemical reactions. The model is used to simulate a field trial of TCE oxidation in a sandy aquifer that is underlain by an aquitard. Three-dimensional simulations are conducted for a coupled reactive system comprised of ten aqueous components, two mineral phases, TCE (dissolved, adsorbed, and NAPL), reactive organic matter, and including ion exchange reactions. Model parameters are constrained by literature data and a detailed data set from the field site under investigation. The general spatial and transient evolution in observed concentrations of the oxidant, dissolved TCE, and reaction products are adequately reproduced by the simulations. The model elucidates the important role of density-induced flow and transport on the distribution of the treatment solution into NAPL containing regions located at the aquifer–aquitard interface. Model results further suggest that reactions that do not directly affect the stability of MnO4 have a negligible effect on solution density and MnO4 delivery. [Copyright &y& Elsevier]

Abstract: Mineral and aqueous geochemical data are combined with a conceptual groundwater flow model, to establish the origin and fate of iron, aluminium and manganese in the groundwater system of a small back-barrier island. The flow model domain consists of an unconfined island fresh groundwater lens overlying a semi-confined hypersaline aquifer. The two aquifers are separated by a discontinuous, clay-rich aquitard and both contain diffusion governed variable density flow fields. High concentrations of dissolved iron and manganese are associated with brackish to hypersaline groundwater, although there is no systematic relationship with salinity. Calculation of S2−/SO4 2− and Fe2+/Fe3+ redox couples and the results of thermodynamic modelling show that redox disequilibrium in the groundwater is widespread. Groundwater samples containing aqueous sulphide and ferric iron complexes are supersaturated with respect to pyrite, goethite and haematite but the prevailing state of redox disequilibrium controls mineral dissolution and precipitation. Aqueous iron in the deeper regions of both aquifers is derived from the dissolution of iron oxide–hydroxides in lateritic palaeosols controlled by seasonal fluctuations in groundwater redox state. Aqueous manganese is potentially derived from the dissolution of ilmenite and amorphous oxide–hydroxides. The oxidation of iron sulphides contributes to the aqueous iron concentration and sulphuric acid production in the shallow groundwater. The solubility of aluminium is also limited by this process, governed by acidity regulation. A significant proportion of aqueous iron is transmitted from the semi-confined to the overlying unconfined aquifer through discontinuities in the aquitard layer. Movement of metals in solution outside the island groundwater system is restricted by the presence of diffusion boundaries within variable density transition zones. [Copyright &y& Elsevier]

Abstract: Verification of numerical models for density dependent flow in porous media (DDFPM) by the means of appropriate benchmark problems is a very important step in developing and using these models. Recently, Infinite Horizontal Box (IHB) problem was suggested as a possible benchmark problem for verification of DDFPM codes. IHB is based on Horton–Rogers–Lapwood (HRL) problem. Suitability of this problem for the benchmarking purpose has been investigated in this paper. It is shown that the wavelength of instabilities fails to be a proper criterion to be considered for this problem. However, the threshold of instability formation has been found to be appropriate for benchmarking purpose. [Copyright &y& Elsevier]

Solute plume subjected to field scale hydraulic conductivity heterogeneity shows a large dispersion/macrodispersion, which is the manifestation of existing fields scale heterogeneity on the solute plume. On the other hand, due to the scarcity of hydraulic conductivity measurements at field scale, hydraulic conductivity heterogeneity can only be defined statistically, which makes the hydraulic conductivity a random variable/function. Random hydraulic conductivity as a parameter in flow equation makes the pore flow velocity also random and the ground water solute transport equation is a stochastic differential equation now. In this study, the ensemble average of stochastic ground water solute transport equation is taken by the cumulant expansion method in order to upscale the laboratory scale transport equation to field scale by assuming pore flow velocity is a non stationary, non divergence-free and unsteady random function of space and time. Besides the stochastic explanation of macrodispersion and the velocity correction term obtained by Kavvas and Karakas (J Hydrol 179:321–351, 1996) before a new velocity correction term, which is a function of mean pore flow velocity divergence, is obtained in this study due to strict second order cumulant expansion (without omitting any term after the expansion) performed. The significance of the new velocity correction term is investigated on a one dimensional transport problem driven by a density dependent flow field. [ABSTRACT FROM AUTHOR]

Abstract: The concepts of homogenization theory are employed to derive a macro-scale brine transport equation for micro-heterogeneous porous medium of layered structure under assumptions of validity of classical Darcy’s law and Fick’s law at the local scale. Derived macro-scale model is analogous to the so-called phase field equations. The obtained results are verified with direct numerical experiment. [Copyright &y& Elsevier]

The farmers of the South-West Punjab, India, lift fresh groundwater for irrigation from the upper layers of the aquifers through interconnected, shallow, and low discharge tube wells. The groundwater of higher salinity usually present at deeper depths remains untouched. Besides permitting irrigation, some control over the water table rise is also achieved during the process. The SUTRA model was used to study the influence of vertical permeability, recharge, pumping rate, and pumping schedule on quality of the pumped water of a well. The results show that vertical permeability, recharge, and pumping rate have significant influence on quality of the pumped water. The influence of pumping schedule is less straightforward. It appears that daily pumping schedules are of limited influence. Seasonal changes in the pumping schedule, however, have significant impact on pumped water quality. [ABSTRACT FROM PUBLISHER]

• A 3-D SEAWAT model is developed to simulate seawater intrusion to a coastal karst aquifer with well-developed conduits. • The simulation results indicate seawater has intruded the aquifer up to more than 3 km through karst conduit networks. • The model quantitatively predicts the severity of seawater intrusion under a changing climate. Seawater intrusion due to sea level rise and climate change could significantly contaminate coastal groundwater resources, particularly in Florida, the flat low-land state in the United States. Based on the field investigation and hydrological measurements, a three-dimensional SEAWAT model is developed to evaluate the groundwater flow cycling and seawater intrusion to freshwater system in the Woodville Karst Plain (WKP), a typical karst groundwater system in the Floridan aquifer. The karst conduit network in the aquifer acts as fast flow pathway for groundwater flow and solute transport, so seawater could deeply intrude into the aquifer. Wakulla Spring, an inland spring 17 km from the coast and a coastal submarine spring, Spring Creek Spring Complex are connected through the conduit network. The flow direction between the two springs switches under various rainfall conditions in this region, thus the discharges at two karst springs are used to estimate the location of seawater/freshwater mixing interface. The SEAWAT modeling results indicate that the mixing interface, defined as 2 PSU (Practical Salinity Unit), intrudes 3 to 5 km through the subsurface karst conduit during the dry season and severely contaminates nearly 1 km width of groundwater around the conduit. The salinity distribution and the distance of seawater intrusion through the conduit system are very sensitive to precipitation variation and the sea level boundary condition. Furthermore, predictions are made for seawater intrusion to the aquifer under various sea level rise, precipitation scenarios and water pumping. The results show that the seawater intrusion could reach and contaminate inland freshwater systems if sea level rises 1.0 m or during a long-term no-precipitation season. This study provides insights for modeling and predicting the vulnerability of a coastal karst aquifer through the simulation of variable-density flow. [ABSTRACT FROM AUTHOR]