Multi-species Transport Research Articles

A Practical Modeling Framework for Non-Fickian Transport and Multi-Species Sequential First-Order Reaction.

Many studies indicate that small-scale heterogeneity and/or mobile-immobile mass exchange produce transient non-Fickian plume behavior that is not well captured by the use of the standard, deterministic advection-dispersion equation (ADE). An extended ADE modeling framework is presented here that is based on continuous time random walk theory. It can be used to characterize non-Fickian transport coupled with simultaneous sequential first-order reactions (e.g., biodegradation or radioactive decay) for multiple degrading contaminants such as chlorinated solvents, royal demolition explosive, pesticides, and radionuclides. To demonstrate this modeling framework, new transient analytical solutions are derived and are inverted in Laplace space. Closed-form, steady-state, multi-species analytical solutions are also derived for non-Fickian transport in highly heterogeneous aquifers with linear sorption-desorption and matrix diffusion for use in spreadsheets. The solutions are general enough to allow different degradation rates for the mobile and immobile zones. The transient solutions for multi-species transport are applied to examine the effects of source remediation on the natural attenuation of downgradient plumes of both parent and degradation products in highly heterogeneous aquifers. Results for representative settings show that the use of the standard, deterministic ADE can over-estimate cleanup rates and under-predict the cleanup timeframe in comparison to the extended ADE analytical model. The modeling framework and calculations introduced here are also applied for a 30 year groundwater cleanup program at a site in Palm Bay, Florida. The simulated plume concentrations using the extended ADE exhibited agreement with observed long concentration tails of trichloroethene, cis 1,2 DCE, and VC that remained above cleanup goals.

Self-similar solutions for multi-species plasma mixing by gradient driven transport

Multi-species transport of plasma ions across an initial interface between DT and CH is shown to exhibit self-similar species density profiles under 1D isobaric conditions. Results using transport theory from recent studies and using a Maxwell–Stephan multi-species approximation are found to be in good agreement for the self-similar mix profiles of the four ions under isothermal and isobaric conditions. The individual ion species mass flux and molar flux profile results through the mixing layer are examined using transport theory. The sum over species mass flux is confirmed to be zero as required, and the sum over species molar flux is related to a local velocity divergence needed to maintain pressure equilibrium during the transport process. The light ion species mass fluxes are dominated by the diagonal coefficients of the diffusion transport matrix, while for the heaviest ion species (C in this case), the ion flux with only the diagonal term is reduced by about a factor two from that using the full diffusion matrix, implying the heavy species moves more by frictional collisions with the lighter species than by its own gradient force. Temperature gradient forces were examined by comparing profile results with and without imposing constant temperature gradients chosen to be of realistic magnitude for ICF experimental conditions at a fuel-capsule interface (10 μm scale length or greater). The temperature gradients clearly modify the relative concentrations of the ions, for example near the fuel center, however the mixing across the fuel-capsule interface appears to be minimally influenced by the temperature gradient forces within the expected compression and burn time. Discussion considers the application of the self-similar profiles to specific conditions in ICF.

Chemical reaction-transport model of diethylzinc hydrolysis in a vertical MOCVD reactor

ZnO thin film has many uses as a semiconductor material. It can be fabricated by chemical vapor deposition with diethylzinc (DEZn) and water vapor. The present study employs density functional theory to examine reaction complexes of DEZn with 1–2 molecules of water, which may occur in the gas phase according to previous studies. The kinetic and thermodynamic data provide a better understanding of the ZnO deposition process. A computational fluid dynamics analysis was carried out using the kinetic parameters to simulate the deposition rate of ZnO in a reaction chamber, showing the dependence of the film growth rate on temperature. The simulation data agreed with the experimental one within 8%, proving the feasibility of the current chemical reaction-transport model of diethylzinc hydrolysis. Furthermore, the fields of the flow, the temperature, the multi-species transport, and the chemical reaction were analyzed. These insights could reveal the reaction kinetics of ZnO thin film fabrication in the metal-organic chemical vapor deposition chamber. The results show that the pathway involving nucleation and growth of oligomers from trimers, and ultimately particle formation, is consistent with the decreased growth rate at increasing temperatures. The maximum growth rate of ZnO film was obtained at 573–773 K when ZnO is grown by DEZn and H2O in a horizontal chamber rotating at high speed. When the temperature is above 773 K, parasitic reactions lead to a rapid decline in the ZnO deposition rate. These insights could reveal the reaction kinetics of ZnO thin film fabrication; and help with the reactor design, optimization, and process parameter adjustment in the metal-organic chemical vapor deposition process.

Simulation of Groundwater Flow and Migration of the Radioactive Cobalt-60 from LAMA Nuclear Facility-Iraq

This study provides a simulation of groundwater flow and advective-dispersive migration of radioactive Co-60 through an aquifer with three layers, which release or leak to groundwater from the Active Metallurgy Testing Laboratory (LAMA) Nuclear Facility-Iraq due to the nuclear accident scenario. Processing Modflow for windows (PMWIN) and Modular Three-Dimensional Multispecies Transport (MT3DMS) Models were used for this purpose. The study area and the contaminated area were 12.7 km2 and 0.005625 km2, respectively. Water levels of the groundwater have been measured in six monitoring wells. The simulation time was assumed to have started in 2016. The PMWIN model simulated the flow for two scenarios of water level in Tigris River (average and minimum water levels). The MT3DMS model simulated 10 years of plume travel, beginning in 2016. The simulated Co-60 concentrations after five years of travel were 32.34 and 34.44 μg/m3 for the two scenarios. The maximum predicted Co-60 concentrations at the end of Year 10 were 34.86 and 37.31 μg/m3, respectively. The sensitivity analysis showed that the simulated hydraulic heads in the observation wells and the simulated plume of Co-60 were highly sensitive to changes in the effective porosity but less sensitive to changes in other parameters of the dispersion and chemical reaction processes. The time necessary to reach steady state condition was predicted to be approximately 16 years. The contaminated area was isolated by using remedial process which is represented by three fully penetrating pumping wells with a suitable flow rate (0.045 m3/s) for controlling the movement of Co-60 pollutant.

Groundwater Modeling Under Variable Operating Conditions Using SWAT, MODFLOW and MT3DMS: a Catchment Scale Approach to Water Resources Management

This paper presents an integrated modeling approach by linking soil and water application tool (SWAT), modular finite difference groundwater flow (MODFLOW) and modular 3-dimensional multi-species transport (MT3DMS) models capable of predicting a groundwater system response, in terms of flow and salt concentrations, to current and future development conditions. SWAT, a semi-distributed hydrologic model, estimates the spatio-temporal distribution of groundwater recharge rates. These rates are then input to MODFLOW using an interface module developed that maps the HRU-based spatial resolution of SWAT outflows into the cell-based spatial structure of inputs to MODFLOW and MT3DMS. The integrated SWAT-MODFLOW-MT3DMS model is used in modeling Dehloran aquifer system located in the arid western region of Iran, experiencing changes in land-use, irrigation system and pumping locations and loads. The results illustrate the significance of the developed integrated modeling tool in quantifying the impact of changes in land and surface water resources on its subsurface water system.

Modelling the influence of interaction between injection and formation brine salinities on in-situ microbial enhanced oil recovery processes by coupling of multiple-ion exchange transport model with multiphase fluid flow and multi-species reactive transport models

Interaction between injection water (IW) and formation water (FW) salinities during microbial flooding critically influences the dynamics of in-situ Microbial Enhanced Oil Recovery (MEOR) processes. However, the lack in understanding of the influence of salinity interactions on MEOR processes had led to unreliable prediction of MEOR performance, and non-development of efficient strategies to improve the MEOR performance. Hence, analysing the influence of salinity interactions on MEOR processes would make the prediction of MEOR processes more realistic, and thereby, it could assist in development of suitable strategies to enhance the oil recovery. Thus, in the present study, a novel mathematical model has been developed by coupling the Multiple Ion (Na, Ca, Mg, Cl, SO4) Exchange (MIE) transport model with the MEOR model, and it has been solved numerically by finite volume technique. The MIE transport model simulates the resultant spatial and temporal salinity distribution within the reservoir due to the mixing of IW and FW salinities during microbial flooding. The MEOR model simulates the coupled multiphase fluid (water-oil) flow and multispecies (microbes-nutrients) reactive transport processes within the reservoir, and finally predicts the oil recovery due to microbial flooding. Subsequently, the influence of IW and FW at different salinities on MEOR processes has been investigated. The present numerical results were validated with the experimental and analytical results. The results clearly suggest that the in-situ FW salinity was completely altered to the externally injected IW salinity, and this IW salinity dictates the entire MEOR processes as against the conventionally assumed FW salinity. Further, it is revealed that lowering the IW salinity from 0.5M to 0.1M had recovered 4.5%–14% of Original Oil in Place (OOIP) higher than that of conventionally used IW (sea water) for microbial flooding. Moreover, the MEOR performance could be enhanced significantly in reservoirs with any initial FW salinity by adopting IW salinity closer to the salinity condition at which the microbial growth and biosurfactant production is maximum. Finally, the present work assists in the selection of suitable reservoir, microbes, and IW salinity for attaining maximum oil recovery by microbial flooding. Thus, the present work helps to enhance the performance of MEOR technique.

(Invited) Multi-Species Electrochemical Transport through Multi-Phase Materials

Most of the solid state ionic conductors typically exhibit high ionic conductivity for only one ion. Examples include yttria-stabilized zirconia (YSZ), rare earth oxide doped ceria, Sr- and Mg-doped LaGaO3 (LSGM), etc. as oxygen ion conductors; Na-beta”-alumina, NaSICON as sodium ion conductors; LLZO, LiSICON as lithium ion conductors; CsH2PO4 as a proton conductor, etc. Alkaline earth cerates and zirconates when doped with rare earth oxides become mixed proton and oxygen ion conductors. In addition some electronic conduction also prevails. Thus, Y-BaZrO3 is an example of a single phase material that transports two ionic species; H+ and O2-. However, it is usually not possible to vary the conductivities for the two species independently; as the H2O content increases, the proton conductivity increases but the oxygen ion conductivity decreases. Multi-species transport in all of these systems can be given in terms of the gradients in electrochemical potentials of the individual species. The same equations can also be given in terms of the gradients in chemical potentials of neutral species if the assumption of local equilibrium is made. The assumption of local equilibrium implies that the electronic conductivity of the ionic conductors cannot be assumed to be identically (mathematically) zero. This is because such an assumption makes the local chemical potential of electrically neutral species indeterminate. Usually an assumption is made that transport of electrically charged species occurs only down their respective electrochemical potential gradients. This means if the transport is described using the Onsager formulation, the cross coefficients are zero (although there are some studies in which the cross coefficients are not assumed to be zero). The same equations, if written for the transport of the corresponding electrically neutral species, the cross coefficients are not zero. This means the origin of coupling lies in the electro-neutrality condition. In such a case, it is possible to write the Onsager coefficients in terms of the individual, partial conductivities. Multi-species ionic conductors containing multiple phases can also be envisioned. For example, one may fabricate a two phase, contiguous mixture of Y-BaZrO3 and YSZ. When hydrated, all of the proton conduction will occur through the Y-BaZrO3 phase and most of the oxygen ion conduction will occur through the YSZ phase. Other examples of multi-species multi-phase ionic conductors include Na-beta”-alumina + YSZ (made by vapor phase conversion of a-Al2O3 + YSZ composite) and Na-rutile-beta-gallate + YSZ (made by vapor phase conversion of Ga2O3 + YSZ composite). Many other multi-species, multi-phase ionic conductors can be envisioned. These materials differ from the single phase materials in that their transport properties can be designed, to an extent, by suitably designing the corresponding microstructure. In Na-beta”-alumina + YSZ, sodium ion transport occurs through the Na-beta”-alumina phase while oxygen ion transport occurs through the YSZ phase. If an electrochemical cell can made with different thermodynamic activities of sodium and oxygen at the two electrodes, one can induce transport of two ionic species. The general transport equations continue to be applicable and electro-neutrality also continues to remain applicable. The difference from single phase materials, however, is that there is a physical separation of ionic fluxes which is on the order of the microstructural details. The typical grain size in these materials is on the order of a few microns. This means, assuming a one dimensional transport, the regions that transport sodium ions are physically separated by a lateral distance on the order of microns from the regions that transport oxygen ions. In single phase Y-BaZrO3, by contrast, the regions that transport protons and oxygen ions are not physically separate (more than at an atomic level). The objective of this talk is to present similarities and differences between single phase and multi-phase ionic conductors capable of transporting two or more ionic species. Also, the objective is to discuss transport coefficients in these materials. Some preliminary experimental work conducted on some multi-phase materials will be discussed. Acknowledgements: This work was supported by the US Department of Energy under Grant Number DE-FG02-06ER46086 and by the National Science Foundation under Grant Number DMR-1407048.

Influence of multi-species solute transport on modeling of hydrated Portland cement leaching in strong nitrate solutions

The differences between the predictions of Fickian diffusion and Nernst-Planck electro-diffusion based reactive transport models are investigated in the context of an important practical problem – leaching of Portland cement in strong nitrate porewater solutions under saturated conditions. Numerical results are presented for three distinct porewater solutions: deionized water, ammonium nitrate solution, and diluted porewater from a cementitious low-activity nuclear waste form. Solute concentrations predicted by the two transport models show significant differences: as much as a factor of two for ammonium nitrate leaching and as much as a factor of four for waste form leaching; whereas, negligible differences are observed for deionized water leaching. The major conclusion is that Fickian diffusion may be accurate enough for deionized water leaching, but electro-diffusion should be considered in the reactive solute transport modeling of ammonium nitrate decalcification and in the degradation modeling of cementitious materials exposed to nuclear waste form solutions.

Source partitioning of anthropogenic groundwater nitrogen in a mixed-use landscape, Tutuila, American Samoa

This study presents a modeling framework for quantifying human impacts and for partitioning the sources of contamination related to water quality in the mixed-use landscape of a small tropical volcanic island. On Tutuila, the main island of American Samoa, production wells in the most populated region (the Tafuna-Leone Plain) produce most of the island’s drinking water. However, much of this water has been deemed unsafe to drink since 2009. Tutuila has three predominant anthropogenic non-point-groundwater-pollution sources of concern: on-site disposal systems (OSDS), agricultural chemicals, and pig manure. These sources are broadly distributed throughout the landscape and are located near many drinking-water wells. Water quality analyses show a link between elevated levels of total dissolved groundwater nitrogen (TN) and areas with high non-point-source pollution density, suggesting that TN can be used as a tracer of groundwater contamination from these sources. The modeling framework used in this study integrates land-use information, hydrological data, and water quality analyses with nitrogen loading and transport models. The approach utilizes a numerical groundwater flow model, a nitrogen-loading model, and a multi-species contaminant transport model. Nitrogen from each source is modeled as an independent component in order to trace the impact from individual land-use activities. Model results are calibrated and validated with dissolved groundwater TN concentrations and inorganic δ15N values, respectively. Results indicate that OSDS contribute significantly more TN to Tutuila’s aquifers than other sources, and thus should be prioritized in future water-quality management efforts.

Coupling flow with nutrient dynamics via BioChemFOAM in the Mississippi River

An enhanced three-dimensional unsteady hydrodynamic, multispecies transport fate model called BioChemFOAM was developed in OpenFOAM-free computational fluid dynamic platform for understanding and predicting nutrient dynamics, namely, transport and transformation, in aquatic ecosystems. The study motivation was to better quantify transport and distribution of nutrient species in the Upper Mississippi River Basin (UMRB), a major source of nutrient contributor from intense agriculture. The study is unique in examining the transport and reactivity rates under complex hydrologic conditions where main conveyance channels and backwaters co-exist. The model has two main components: a new coupling of turbulent flow processes with multiple species to modulate transport and reaction rates simulations at channel/backwater areas and a complex chemical and biological transformation module suited for species reaction rates in backwaters. The coupled model was first tested for an idealistic domain/case borrowed from the literature. The final model was calibrated, tested and verified in the UMRB.

A Goal-Oriented Error Estimator for a Class of Homogenization Problems

We present a goal-oriented a posteriori error estimator for finite element approximations of a class of homogenization problems. As a rule, homogenization problems are defined through the coupling of a macroscopic solution and the solution of auxiliary problems. In this work we assume that the homogenized problem is known and that it depends on a finite number of auxiliary problems. The accuracy in the goal functional depends therefore on the discretization error of the macroscopic and the auxiliary solutions. We show that it is possible to compute the error contributions of all solution components separately and use this information to balance the different discretization errors. Additionally, we steer a local mesh refinement for both the macroscopic problem and the auxiliary problems. The high efficiency of this approach is shown by numerical examples. These include the upscaling of a periodic diffusion tensor, the case of a Stokes flow over a porous bed, and the homogenization of a fuel cell model which includes the flow in a gas channel over a porous substrate coupled with a multispecies nonlinear transport equation.

Simulation of Saltwater Intrusion in Coastal Aquifer of Kg. Salang, Tioman Island, Pahang, Malaysia

Numerical models are capable of simulating various groundwater scenarios and relate it towards groundwater management. A mesh based density dependent flow model, FEFLOW is used to simulate groundwater flow and transport for a coastal island aquifer in Kg. Salang, Tioman Island, Malaysia. FEFLOW is designed to simulate 2D and 3D, variable density groundwater flow and multi-species transport. The impacts of pumping and recharge rates represented by three different groundwater scenarios, which were investigated by means of hydraulic heads, TDS concentrations and water balance components. Scenario A showed the standard saturated groundwater flow and the steady state fluid flow. Over pumping and inconsistency in recharge rate are the stresses shown in Scenarios B and C. Scenario B involved in the maximum pumping rate of 96m3 per day and recharge rate of 300mm per year has shown a drawdown of 1.5 m. Scenario C showed the extreme pumping rate of 1000m 3 per day and without recharge has shown a decrease in groundwater levels of 6.3 m.and groundwater storage (50%). Scenario B presented the most promising finding compared with Scenario C. Highest hydraulic heads, lowest mass concentration and positive groundwater storage (2578.6m 3 /day) were obtained in Scenario B. Additionally, and further progress is needed in obtaining the water usage data from each part to determine the best pumping rate. A sustainable groundwater management plan is crucial to maintain the natural resources and social benefits as well as to protect the ecological balance.

On the efficiency of the hybrid and the exact second-order sampling formulations of the EnKF: a reality-inspired 3-D test case for estimating biodegradation rates of chlorinated hydrocarbons at the port of Rotterdam

Abstract. This study considers the assimilation problem of subsurface contaminants at the port of Rotterdam in the Netherlands. It involves the estimation of solute concentrations and biodegradation rates of four different chlorinated solvents. We focus on assessing the efficiency of an adaptive hybrid ensemble Kalman filter and optimal interpolation (EnKF-OI) and the exact second-order sampling formulation (EnKFESOS) for mitigating the undersampling of the estimation and observation errors covariances, respectively. A multi-dimensional and multi-species reactive transport model is coupled to simulate the migration of contaminants within a Pleistocene aquifer layer located around 25 m below mean sea level. The biodegradation chain of chlorinated hydrocarbons starting from tetrachloroethene and ending with vinyl chloride is modeled under anaerobic environmental conditions for 5 decades. Yearly pseudo-concentration data are used to condition the forecast concentration and degradation rates in the presence of model and observational errors. Assimilation results demonstrate the robustness of the hybrid EnKF-OI, for accurately calibrating the uncertain biodegradation rates. When implemented serially, the adaptive hybrid EnKF-OI scheme efficiently adjusts the weights of the involved covariances for each individual measurement. The EnKFESOS is shown to maintain the parameter ensemble spread much better leading to more robust estimates of the states and parameters. On average, a well tuned hybrid EnKF-OI and the EnKFESOS respectively suggest around 48 and 21 % improved concentration estimates, as well as around 70 and 23 % improved anaerobic degradation rates, over the standard EnKF. Incorporating large uncertainties in the flow model degrades the accuracy of the estimates of all schemes. Given that the performance of the hybrid EnKF-OI depends on the quality of the background statistics, satisfactory results were obtained only when the uncertainty imposed on the background information is relatively moderate.

Temporal Moment Analysis of Multi-Species Radionuclide Transport in a Coupled Fracture-Skin-Matrix System with a Variable Fracture Aperture

This paper presents an analysis using temporal moments to study multi-species radionuclide transport along a single fracture with variable fracture aperture in a fracture-skin-matrix system. In the present study, a decay chain having three elements is considered and transport of each member in the decay chain is modeled by solving a coupled system of partial differential equations for fracture, fracture-skin, and rock matrix using explicit finite difference method. Having obtained the concentration distribution, lower order temporal moments of radionuclide distribution are computed to analyze the effective velocity and macro-dispersion coefficient of radionuclides in the fracture. In the present study, effect of varying fracture aperture on transport characteristics of radionuclides is also analyzed. It is found that the fracture aperture variation profile has significant impact on radionuclide distribution along the fracture. Sensitivity analysis is carried out in a fracture-skin-matrix system with sinusoidal fracture aperture to study the effect of various parameters like fracture aperture thickness, fracture-skin porosity, fracture-skin diffusion coefficient, flow rate, radioactive decay constant, and Freundlich sorption isotherm exponent on transport characteristics of radionuclide. The results suggest that the above mentioned parameters significantly influence concentration, distribution, mobility, and effective macro-dispersion coefficient of radionuclides along the fracture.

Dynamic Hybrid Reynolds-Averaged Navier–Stokes/Large-Eddy Simulation of a Supersonic Cavity

A Mach 2 experimental supersonic cavity is simulated using a novel dynamic hybrid Reynolds-averaged Navier–Stokes/large-eddy simulation modeling framework. The model is extended to include multispecies transport and diffusion and is coupled to an advanced low-dissipation numerical scheme. The simulations correspond to a series of experiments for which particle image velocimetry measurements of two velocity components were made within the cavity, as well as fuel concentration measurements. Results are presented and compared with experimental measurements and to simulations made using the improved delayed detached eddy simulation model. The current model is able to predict mean and fluctuating quantities in a manner more consistent with the experiment, suggesting potential improvement over more traditional hybrid models.

Thermo–hydro-ionic transport in sea immersed tube tunnel

This paper investigates the multi-species and multi-fields transport processes in the concrete wall of sea immersed tube tunnel, exposed externally to sea water and internally to road traffic. A thermo–hydro-ionic (THI) model is established for the transport processes, taking into account the heat, mass and electrical charge conservations, the electrical neutrality and solid-solution equilibria in the representative elementary volume (REV) of material. Then, the characteristic lengths for drying and wetting are proposed for the tunnel wall through simplified model of moisture transport to define different durability patterns for tunnel wall, and the associated durability risks are identified. The THI model is applied to the immersed tube tunnel of Hong Kong–Zhuhai–Macau (HZM) sea link project, and the transport processes are simulated for a service life of 120years and different working cases. The analysis shows that: (1) the thermal gradient has more important impact on transport processes than the external sea water pressure on tunnel wall; (2) the drying and wetting extents are overlapped through the wall thickness at 120years, and the internal drying and external leaching condition the multi-species transport; and (3) the corrosion initiation range attains 65cm at 120years but the corrosion current is below the depassivation value (0.1μA/cm2).

Study of flow through a packed bed using discrete element method and computational fluid dynamics

Packed beds find wide applications in chemical industries. In this paper, a Discrete Element Method (DEM) – Computational Fluid Dynamics (CFD) approach has been adopted to predict the flow profile in the bed for different diameter of the bed/diameter of the particle. The randomly packed bed was created using the DEM technique. The radial voidage of the bed was calculated using the Monte Carlo integration method. The radial voidage showed an oscillating pattern up to approximately 4–5 particle diameter from the wall, which was validated with the experimental data reported by several researchers. The flow studies through these packed beds were carried using single-phase laminar flow model. The flow followed a similar oscillating pattern as the radial voidage. The numerical results were validated with experimental data. Preliminary studies to predict the residence time distribution has also been carried out using the multi-species transport model, which was also experimentally validated. The study suggests that DEM and CFD simulation can predict the flow behaviour as well as Residence Time Distribution (RTD) in a packed bed quite satisfactorily without the need to carry out experiments, which would be environmental friendly.

Theory of multi-species electrophoresis in the presence of surface conduction

Electrophoresis techniques are characterized by concentration disturbances (or waves) propagating under the effect of an electric field. These techniques are usually performed in microchannels where surface conduction through the electric double layer (EDL) at channel walls is negligible compared with bulk conduction. However, when electrophoresis techniques are integrated in nanochannels, shallow microchannels or charged porous media, surface conduction can alter bulk electrophoretic transport. The existing mathematical models for electrophoretic transport in multi-species electrolytes do not account for the competing effects of surface and bulk conduction. We present a mathematical model of multi-species electrophoretic transport incorporating the effects of surface conduction on bulk ion-transport and provide a methodology to derive analytical solutions using the method of characteristics. Based on the analytical solutions, we elucidate the propagation of nonlinear concentration waves, such as shock and rarefaction waves, and provide the necessary and sufficient conditions for their existence. Our results show that the presence of surface conduction alters the propagation speed of nonlinear concentration waves and the composition of various zones. Importantly, we highlight the role of surface conduction in formation of additional shock and rarefaction waves which are otherwise not present in conventional electrophoresis.

Seasonality of temperatures and redox zonations during bank filtration – A modeling approach

Bank filtration (BF) is a common technique for supplying drinking water, using the ability of the infiltration zone and aquifer passage to attenuate or degrade undesired substances that infiltrate from surface waters to groundwater abstraction wells. Temporal and spatial changes of temperatures and redox conditions are often the controlling factors for the fate and behavior of micropollutants during subsurface passage and consequently for the extracted raw water quality. A 2-dimensional cross-sectional heat transport and multi-species reactive transport model was set up to simulate the seasonally varying temperatures and redox conditions on the infiltration path at a bank filtration site in Berlin, Germany. The calibrated model was able to capture the observed variations in O2 and NO3− when considering temperature dependence of the redox reaction kinetics. The observed Mn2+- and Fe2+-concentrations were not well replicated by the model, presumably due to mineral reactions that were not accounted for in the simulations. SO42− was found to behave conservative, i.e., the observed concentration could be well simulated without any reactions. The simulations reveal the transience of BF systems with regard to temperatures and redox conditions, which has important implications for the BF quality and should therefore be accounted for.

Modelling of the groundwater flow and of tracer movement in the porous and fissured media: Chalk Aquifer (Northern part of Paris Basin, France)

A groundwater flow model has been developed in order to study the chalk aquifer of Paris Basin, based on most of the geological and hydrological available data. The numerical processes are intended to modelling the groundwater flow in the Senonian (Late Cretaceous) formations and to visualize the tracer movement in groundwater resources in the experimental site of LaSalle Beauvais (northern part Paris Basin). Both objectives were achieved as follows: (i) the comprehension of the spatial distribution of the hydraulic conductivity in the chalk aquifer taking into account the characteristics of the hydrogeological system and (ii) the use of the analytical solution for describing one-dimensional to two-dimensional solute transport in a unidirectional steady-state flow tracer with scale-dependent dispersion. Advection and diffusion mechanisms are taken into account. Comparison between the breakthrough curves of the analytical and the numerical solutions provided an excellent agreement for various ranges of scale-related transport parameters of interest. The developed power series solution facilitates fast prediction of the breakthrough curves at each observation point. Thus, the derived new solutions are widely applicable and are very useful for the validation of numerical transport. The numerical approach is carried out by MT3DMS, a Modular 3-D Multi-Species Transport Model for Simulation of Advection, Dispersion, and Chemical Reactions of Contaminants in Groundwater Systems, and based on total variation-diminishing method using the ULTIMATE algorithm. The estimation of the infected surface could constitute an approach in water management and allows to prevent the risks of pollution and to manage the groundwater resource from a durable development perspective. Copyright © 2015 John Wiley & Sons, Ltd.