Three-dimensional Solute Transport Research Articles

Three-dimensional solute transport in finite and curved porous media with surface input sources

In this paper, an analytical solution for three-dimensional solute transport in porous media between two curved surfaces is investigated. It is assumed that the groundwater velocity and dispersion coefficient vary with time and position. Groundwater velocity is not considered to be horizontal. The components of dispersion coefficient along the axes are considered to be proportional to the square of corresponding the position variable. The dispersion coefficient components along axes are proportional to the corresponding component of groundwater velocity in temporal aspects while former is squarely proportional to letter one in position components. It is assumed that the sources originate from two curved surfaces. The nature of the source on the two surfaces is the same, but there may be a variation in potential. Initially, the aquifer's domain is supposed to be uniformly polluted. The Laplace Integral Transformation Technique (LITT) is used to obtain analytical solutions. Numerical examples are given to demonstrate the effects of various factors on the solute concentration profile in a system where advection and dispersion play important roles.In addition, the sub-case of horizontal flow is also discussed. The model is extremely useful in analyzing and dealing with widespread surface sources of groundwater pollution in simulated agricultural fields or urban dumping areas.

Solutions of a three-dimensional multi-term fractional anomalous solute transport model for contamination in groundwater

The study presents a meshless computational approach for simulating the three-dimensional multi-term time-fractional mobile-immobile diffusion equation in the Caputo sense. The methodology combines a stable Crank-Nicolson time-integration scheme with the definition of the Caputo derivative to discretize the problem in the temporal direction. The spatial function derivative is approximated using the inverse multiquadric radial basis function. The solution is approximated on a set of scattered or uniform nodes, resulting in a sparse and well-conditioned coefficient matrix. The study highlights the advantages of meshless method, particularly their simplicity of implementation in higher dimensions. To validate the accuracy and efficacy of the proposed method, we performed numerical simulations and compared them with analytical solutions for various test problems. These simulations were carried out on computational domains of both rectangular and non-rectangular shapes. The research highlights the potential of meshless techniques in solving complex diffusion problems and its successful applications in groundwater contamination and other relevant fields.

Transport of pollutants in groundwater of domestic waste landfills in karst regions and its engineering control technologies

Domestic waste produces leachate with a high concentration of pollutants in the landfill process due to biochemical degradation stages like compaction and fermentation. A large number of cases show that anti-seepage membranes widely used in refuse landfills tend to rupture under long-term tension and corrosion, causing leachate to enter the groundwater system and pollute the environment. To reveal the phenomenon of groundwater contamination in refuse landfills, typical domestic waste landfills in karst regions were examined, on the basis of a summary of hydrogeological conditions and hydrochemical characteristics, a three-dimensional groundwater flow model and solute transport model were constructed to analyze the pattern of pollutant diffusion, and its controlling factors, under the current conditions and massive rupture of anti-seepage membrane. The results show that with a minor rupture of the anti-seepage membrane, the area of the low pollution region increases first and then decreases while that of the slight pollution region continuously increases; When a massive rupture of the anti-seepage membrane appears, the ranges of heavy pollution region and total pollution regions continue to grow; Pollutant migrates along the same direction as the groundwater flow and diffuse from high concentration region to low concentration regions under the differential concentration effect. Based on the temporal-spatial distribution characteristics of groundwater pollutants, two engineering control schemes, namely, curtain grouting blocking and group well pumping, were established. A comparison of the two control schemes shows that group well pumping stably maintains water quality safety over the long term, pollutants overflow from both sides of the curtain after they have accumulated to a certain point of concentration, causing damage to the groundwater environment in the conservation area.

Pollution prediction for heavy metals in soil-groundwater systems at smelting sites

The spread of heavy metal contaminations originating from polluted industrial sites pose major environmental risks to surrounding areas. However, the migration of heavy metals in the subsurface is a very complex process that requires the coupling of geological, hydrological, solute transport and geochemical data to better understand and predict contaminant flow paths, plume movement in space and time. In this study, a three-dimensional (3D) variable saturated solute transport numerical model of soil-groundwater was developed to understand pollution risks in a large lead–zinc (Pb-Zn) smelting site. Using the calibrated numerical model, risk trends of heavy metal pollution were predicted, and the design and evaluation of a pollution control technology were proposed. The results showed that the risk of heavy metal spillover was extremely high. It could break through the geographical boundary of the site after 60 days and affect the downstream river on the 712th day. By using a permeable reactive barrier (PRB) based on zero-valent iron (ZVI) and bentonite, the time for the Cd pollution plume to reach the river could be effectively delayed by 225 days, and its diffusion range reduced to 10.2%. However, 31–42% of the contaminants continued to spread outwards through lateral flow pathways even with a PRB. Based on these results, a better remediation strategy for the smelting site is to first remove, passivate or solidify the existing pollution sources, and then use PRB technology to block the pollution transmission pathways. The research results have expanded the application of numerical simulation in the study of industrial pollution sites, providing guidance methods and technical support for pollution prevention and control and space utilization at polluted non-ferrous smelting sites.

Efficacy of Permeable Reactive Barriers in Mitigating Tetrachloroethene Ingress into Highway Drainage Concrete Pipe in Saturated Media

Work herein is focused on evaluating factors affecting tetrachloroethene (PCE) contaminant ingress into the subsurface concrete pipe embedded in the saturated soil profile and assessing the efficacy of permeable reactive barriers (PRB) in mitigating PCE concentration. A three-dimensional groundwater flow and solute transport numerical model is established using MODFLOW paired with reactive transport (RT3D) software, in which the model is developed using a finite-difference numerical scheme. The analyses parameters are developed from data for a site in Wilson, North Carolina, at which subsurface chlorinated organic solvents from a dry-cleaning facility occurred in the presence of subsurface highway concrete drainage pipe. Modeling results after 10 years of simulation period indicated that the natural attenuation process taking place in the native soils with coefficients of KPCE=0.00019 d−1, and 0.0033 d−1 reduced the PCE concentrations breaking through the concrete pipe by 30.7% and 34.1%, respectively. On the other hand, with a greater percent of the soil sorption as manifested by organic carbon content, the PCE concentration breaking through the pipe increased by 137% for the same simulation period as a result of the prolonged presence of PCE concentration within the pipe trench. The hydraulic conductivity of the PRB (kPRB) modestly affects the level of PCE breaking through the pipe, while the increase in thickness of the PRB was found to be the most effective in decreasing the level of PCE ingress into the pipe.

Heterogeneity-Driven Hydrodynamics Conditions the Hydrochemistry of Spring Water in Volcanic Islands.

Perched aquifers represent significant unexploited groundwater reserves in volcanic islands and contain valuable freshwater resources. These water reserves provide critical resources to indigenous populations suffering water scarcity. Groundwater discharged from a perched aquifer into two adjacent (14 m) springs in the volcanic summits constituted by basaltic and pyroclastic deposits of Gran Canaria Island (Spain) was examined. Based on springs discharge data, a three-dimensional groundwater flow and solute transport model of the investigated perched aquifer was calibrated to reproduce its hydraulic regime, as well as to explain the hydrochemical and isotopic composition of its main discharge systems, the studied springs. Groundwater flow simulations effectively replicated flow paths of the two springs affected by the existing geological heterogeneities, with differential travel times of 246 and 130 years, respectively, and with a convergent flow toward them partially explaining the averaged differences in electrical conductivity, δ18 O, and tritium observed between the springs. It can be concluded that, although water quality in both springs is similar and homogenous, as they come from the same aquifer system, geological heterogeneities in the upper elevation volcanic areas is likely the cause for the differences in the residence times of the two springs, which suggests that the flow regimes for the two springs are independent. The chemistry of the two springs, however, is essentially the same, with the exception of tritium, which is used to ascertain residence time.

Identification of Groundwater Contamination using MODFLOW: A Case study of Chhatral Area, Gandhinagar

Abstract: In India, groundwater is a primary source of freshwater and used mainly for agriculture and irrigation purposes. Approximately 80% of the population is dependent on groundwater for household and agricultural purposes in India. The pace of urbanization in Gandhinagar has been accelerated since the capital of Gujarat state was formed; hence a study is carried out to identify the status of groundwater quality in the Chhatral area of Gandhinagar city. In this study, MODFLOW and MT3DMS software are used to identify contaminated groundwater status in particular study areas. MODFLOW software helped in simulating ground water quality under various hydro-geological conditions. After the initial simulation, the area was assigned to MT3DMS, a three-dimensional multi-species solute transport model where arsenic and fluoride concentrated chemicals are figured out above the permissible limit authorized by WHO and BIS for drinking purposes. The results of this study demonstrated that there is need to take necessary steps to control ground water quality in the study area. Groundwater quality modelling will help the stakeholders, government organizations & users to get the exact groundwater quality status for future use. Keywords: Groundwater contamination, Arsenic, Fluoride, MODFLOW, and MT3DMS

Semi-Analytical Three-Dimensional Solute Transport of Sequentially Decaying Species with Mobile-Immobile Regions, Sorption, Decay, and Arbitrary Transient Source

Semi-Analytical Three-Dimensional Solute Transport of Sequentially Decaying Species with Mobile-Immobile Regions, Sorption, Decay, and Arbitrary Transient Source

Adaptation and validation of the ParSWMS numerical code for simulation of water flow and solute transport in soilless greenhouse substrates

Numerical simulation of three-dimensional water flow and solute transport in containerized variably saturated soilless substrates with complex hydraulic properties and boundary conditions necessitates high-resolution discretization of the spatial and temporal domains, which commonly leads to several million nodes requiring numerical evaluation. Even today’s computing prowess of workstations is not adequate to tackle such problems within a reasonable timeframe, especially when numerous realizations are required to optimize the geometry, substrate properties, and irrigation and fertigation management of soilless plant growth modules. Hence, the parallelization of the numerical code and utilization of high performance computing (HPC) are essential. Here, we adapted and applied the ParSWMS parallelized code that is amenable to solving the 3D Richards equation for water flow and the convection-dispersion equation for solute transport subject to linear solute adsorption. The code was modified to allow for nonlinear equilibrium solute adsorption with new boundary conditions and applied to simulate water flow and nitrogen and phosphorus transport in containerized soilless substrates. Multi-solute transport simulations with the modified Linux ParSWMS code were first performed on a workstation and referenced to the Windows-based HYDRUS (2D/3D) numerical code. After confirming the agreement between the modified ParSWMS code and HYDRUS (2D/3D), various preconditioners and iterative solvers were evaluated to find the computationally most efficient combinations. The performance of the modified ParSWMS code and its stability were compared to HYDRUS (2D/3D) simulations for three soilless substrates consisting of horticultural perlite, volcanic tuff, and a volcanic tuff/coconut coir mixture. Considering the solute mass balance error as a stability measure, ParSWMS outperformed HYDRUS (2D/3D). Moreover, simulations with the modified ParSWMS code were about 22% faster than simulations with HYDRUS (2D/3D) on the workstation. Tests of the modified ParSWMS on two HPC clusters with 28 and 94 cores revealed a potential computational speedup of 94% relative to the HYDRUS (2D/3D) simulations performed on the workstation.

Potential impacts of shale and tight gas developments on unconfined aquifers – a chemical screening framework

The Geological and Bioregional Assessment Program examines the potential impacts of shale, tight and deep coal gas development on water and the environment. A key part of the project was quantifying the potential for a decline in the water quality of unconfined aquifers due to unintentional chemical release at the soil surface. To assess this hazard, a quantitative analysis of chemical migration pathways was undertaken, which involved the estimation of contaminant attenuation by dilution and dispersion in soil and groundwater. This provided a conservative screening approach to identify areas for further analysis. Attenuation calculations involved one-dimensional advection-dispersion (AD) simulations through the unsaturated zone, and three-dimensional AD solute transport within the surficial aquifers. Dilution factor (DF) relationships for the combined effect of attenuation in the unsaturated and saturated zone were used to construct spatial maps of the potential for impact on aquifer properties after accidental chemical spills. A higher DF (therefore lower consequence of the surface contamination) was associated with deeper unsaturated zones characterized by heavier soils near the surface, and lower ground water velocities due to lower hydraulic conductivity and/or hydraulic gradient in the saturated zone. The framework was applied across the Cooper Basin and Beetaloo Sub-basin and resulted in two types of maps. The first identified areas being more susceptible to contamination if soil remediation does not occur within a 10-year period. The second map shows the spatially variable combined DFs for a ground water receptor, which may be used to develop site-specific management plans and mitigation measures.

Numerical Simulation for Impact of Groundwater Environment in a Chemical Industry Park in the Southwest of Shandong Province Based on GMS

The establishment of chemical industry park can bring great pressure on local groundwater environment, and even cause serious groundwater pollution problems. This study armed at a chemical industry park in southeast of Shandong province and developed a three-dimensional groundwater solute transport model through GMS software, selected dichloromethane as the typical contaminant, simulated and predicated the transport characteristic of groundwater contaminant in different conditions. The results showed that after 20 years, the dichloromethane can separately transport 820m and 1,000m under different hypothetical conditions, the greatest affected area can separately reach 32×104 m2 and 21×104 m2; it indicated that the studied area would be polluted under these simulated conditions, so measures must be done to improve the ability of seepage-proofing of this chemical industry park and to enhance the management and the monitoring of groundwater in this studied area.

Barrier dysfunction or drainage reduction: differentiating causes of CSF protein increase

BackgroundCerebrospinal fluid (CSF) protein analysis is an important element in the diagnostic chain for various central nervous system (CNS) pathologies. Among multiple existing approaches to interpreting measured protein levels, the Reiber diagram is particularly robust with respect to physiologic inter-individual variability, as it uses multiple subject-specific anchoring values. Beyond reliable identification of abnormal protein levels, the Reiber diagram has the potential to elucidate their pathophysiologic origin. In particular, both reduction of CSF drainage from the cranio-spinal space as well as blood–CNS barrier dysfunction have been suggested ρas possible causes of increased concentration of blood-derived proteins. However, there is disagreement on which of the two is the true cause.MethodsWe designed two computational models to investigate the mechanisms governing protein distribution in the spinal CSF. With a one-dimensional model, we evaluated the distribution of albumin and immunoglobulin G (IgG), accounting for protein transport rates across blood–CNS barriers, CSF dynamics (including both dispersion induced by CSF pulsations and advection by mean CSF flow) and CSF drainage. Dispersion coefficients were determined a priori by computing the axisymmetric three-dimensional CSF dynamics and solute transport in a representative segment of the spinal canal.ResultsOur models reproduce the empirically determined hyperbolic relation between albumin and IgG quotients. They indicate that variation in CSF drainage would yield a linear rather than the expected hyperbolic profile. In contrast, modelled barrier dysfunction reproduces the experimentally observed relation.ConclusionsHigh levels of albumin identified in the Reiber diagram are more likely to originate from a barrier dysfunction than from a reduction in CSF drainage. Our in silico experiments further support the hypothesis of decreasing spinal CSF drainage in rostro-caudal direction and emphasize the physiological importance of pulsation-driven dispersion for the transport of large molecules in the CSF.

Assessment of groundwater quality of major industrial city of Central Ganga plain, Western Uttar Pradesh, India through mass transport modeling using chloride as contaminant

Present work deals with the simulation of a three-dimensional groundwater flow and solute transport model of Moradabad city lying between rivers Ramganga and Gagan. Present study is used to predict the response of aquifer and the migration of contaminant (chloride in this case) over a period of time using MODFLOW and MT3D software. A grid system of 500m×500m was designed and the various input parameters such as hydraulic head, layer thickness, recharge, pumping etc. were applied under various packages available in the software. Pumping rates of 500m3/day, 1000m3/day and 1500m3/day were used for the simulation of abstraction. Hydraulic conductivity ranging from 13 to 18m/day was assigned block wise. The model was run for steady state condition until a match between observed and computed heads was obtained. Sensitivity analysis was done by varying hydraulic conductivity and recharge parameters in the model. Solute transport modeling is carried out considering Cl as contaminant. Concentration of chloride is higher in northern, central and southern part of the study area. The data obtained from the water quality analysis of June 2012 was used initially in the steady state simulation. The predictions made from transport model indicate that the concentration of chloride would continue to increase if the current situation is not controlled and this will lead to further deterioration of groundwater quality.

A three-dimensional semi-analytical solution for predicting drug release through the orifice of a spherical device

Three-dimensional solute transport was investigated for a spherical device with a release hole. The governing equation was derived using the Fick’s second law. A mixed Neumann-Dirichlet condition was imposed at the boundary to represent diffusion through a small region on the surface of the device. The cumulative percentage of drug released was calculated in the Laplace domain and represented by the first term of an infinite series of Legendre and modified Bessel functions of the first kind. Application of the Zakian algorithm yielded the time-domain closed-form expression. The first-order solution closely matched a numerical solution generated by Mathematica®. The proposed method allowed computation of the characteristic time. A larger surface pore resulted in a smaller effective time constant. The agreement between the numerical solution and the semi-analytical method improved noticeably as the size of the orifice increased. It took four time constants for the device to release approximately ninety-eight of its drug content.

Use of a Three-Dimensional Reactive Solute Transport Model for Evaluation of Bioreactor Placement in Stream Restoration.

A three-dimensional groundwater flow and multispecies reactive transport model was used to strategically design placement of bioreactors in the subsurface to achieve maximum removal of nitrate along restored stream reaches. Two hypothetical stream restoration scenarios were evaluated over stream reaches of 40 and 94 m: a step-pool scenario and a channel re-meandering scenario. For the step-pool scenario, bioreactors were placed at locations where mass fluxes of groundwater and nitrate were highest. Bioreactors installed over 50% of the total channel length of a step-pool scenario (located to intercept maximum groundwater and nitrate mass flux) removed nitrate-N entering the channel at a rate of 36.5 kg N yr (100 g N d), achieving about 65% of the removal of a whole-length bioreactor. Bioreactor placement for the re-meandering scenario was designed using a criterion of either highest nitrate mass flux or highest groundwater flux, but not both, because they did not occur together. Bioreactors installed at maximum nitrate flux locations (53% of the total channel length) on the western bank removed nitrate-N entering the channel at 62.0 kg N yr (170 g N d), achieving 85% of nitrate-N removal of whole-length bioreactors for the re-meandering scenario. Bioreactors installed at maximum groundwater flux locations on the western bank along approximately 40% of the re-meandering channel achieved about 65% of nitrate removal of whole-length bioreactors. Placing bioreactors at maximum nitrate flux locations improved denitrification efficiency. Due to low groundwater velocities, bioreactor nitrate-N removal was found to be nitrate limited for all scenarios.

Fate of arsenic, phosphate and ammonium plumes in a coastal aquifer affected by saltwater intrusion

A severe groundwater contamination with extensive plumes of arsenic, phosphate and ammonium was found in a coastal aquifer beneath a former fertilizer production plant. The implementation of an active groundwater remediation strategy, based on a comprehensive pump and treat scheme, now prevents the migration of the dissolved contaminants into the marine environment. However, due to the site's proximity to the coastline, a seawater wedge was induced by the pumping scheme. Additionally the groundwater flow and salinity patterns were also strongly affected by leakage from the site's sewer system and from a seawater-fed cooling canal. The objective of this study was to elucidate the fate of arsenic and its co-contaminants over the site's history under the complex, coupled hydrodynamic and geochemical conditions that prevail at the site. A detailed geochemical characterisation of samples from sediment cores and hydrochemical data provided valuable high-resolution information. The obtained data were used to develop various conceptual models and to constrain the development and calibration of a reactive transport model. The reactive transport simulations were performed for a sub-domain (two-dimensional transect) of an earlier developed three-dimensional flow and variable density solute transport model. The results suggest that in the upper sub-oxic zone the influx of oxygenated water promoted As attenuation via co-precipitation with Al and Fe oxides and copper hydroxides. In contrast, in the deeper aquifer zone, iron reduction, associated with the release of adsorbed As and the dissolution of As bearing phases, provided and still provides to date a persistent source for groundwater pollution. The presented monitoring and modelling approach could be broadly applied to coastal polluted sites by complex contaminant mixture containing As.

Reducing the ambiguity of karst aquifer models by pattern matching of flow and transport on catchment scale

Abstract. Assessing the hydraulic parameters of karst aquifers is a challenge due to their high degree of heterogeneity. The unknown parameter field generally leads to a high ambiguity for flow and transport calibration in numerical models of karst aquifers. In this study, a distributed numerical model was built for the simulation of groundwater flow and solute transport in a highly heterogeneous karst aquifer in south-western Germany. Therefore, an interface for the simulation of solute transport in one-dimensional pipes was implemented into the software COMSOL Multiphysics® and coupled to the three-dimensional solute transport interface for continuum domains. For reducing model ambiguity, the simulation was matched for steady-state conditions to the hydraulic head distribution in the model area, the spring discharge of several springs and the transport velocities of two tracer tests. Furthermore, other measured parameters such as the hydraulic conductivity of the fissured matrix and the maximal karst conduit volume were available for model calibration. Parameter studies were performed for several karst conduit geometries to analyse the influence of the respective geometric and hydraulic parameters and develop a calibration approach in a large-scale heterogeneous karst system. Results show that it is possible not only to derive a consistent flow and transport model for a 150 km2 karst area but also to combine the use of groundwater flow and transport parameters thereby greatly reducing model ambiguity. The approach provides basic information about the conduit network not accessible for direct geometric measurements. The conduit network volume for the main karst spring in the study area could be narrowed down to approximately 100 000 m3.

A Layer-Integrated Model of Solute Transport in Heterogeneous Media

AbstractThis study presents a numerical solution to the three-dimensional solute transport in heterogeneous media by using a layer-integrated approach. Omitting vertical spatial variation of soil and hydraulic properties within each layer, a three-dimensional solute transport can be simplified as a quasi-three-dimensional solute transport which couples a horizontal two-dimensional simulation and a vertical one-dimensional computation. The finite analytic numerical method was used to discretize the derived two-dimensional governing equation. A quadratic function was used to approximate the vertical one-dimensional concentration distribution in the layer to ensure the continuity of concentration and flux at the interface between the adjacent layers. By integration over each layer, a set of system of equations can be generated for a single column of vertical cells and solved numerically to give the vertical solute concentration profile. The solute concentration field was then obtained by solving all columns of vertical cells to achieve convergence with the iterative solution procedure. The proposed model was verified through examples from the published literatures including four verifications in terms of analytical and experimental cases. Comparison of simulation results indicates that the proposed model satisfies the solute concentration profiles obtained from experiments in time and space.

Generalizing Source Geometry of Site Contamination by Simulating and Analyzing Analytical Solution of Three-Dimensional Solute Transport Model

Due to the uneven distribution of pollutions and blur edge of pollutant area, there will exist uncertainty of source term shape in advective-diffusion equation model of contaminant transport. How to generalize those irregular source terms and deal with those uncertainties is very critical but rarely studied in previous research. In this study, the fate and transport of contaminant from rectangular and elliptic source geometry were simulated based on a three-dimensional analytical solute transport model, and the source geometry generalization guideline was developed by comparing the migration of contaminant. The result indicated that the variation of source area size had no effect on pollution plume migration when the plume migrated as far as five times of source side length. The migration of pollution plume became slower with the increase of aquifer thickness. The contaminant concentration was decreasing with scale factor rising, and the differences among various scale factors became smaller with the distance to field increasing.

Applying Hybrid Heuristic Approach to Identify Contaminant Source Information in Transient Groundwater Flow Systems

Simultaneous identification of the source location and release history in aquifers is complicated and time-consuming if the release of groundwater contaminant source varies in time. This paper presents an approach called SATSO-GWT to solve complicated source release problems which contain the unknowns of three location coordinates and several irregular release periods and concentrations. The SATSO-GWT combines with ordinal optimization algorithm (OOA), roulette wheel approach, and a source identification algorithm called SATS-GWT. The SATS-GWT was developed based on simulated annealing, tabu search, and three-dimensional groundwater flow and solute transport model MD2K-GWT. The OOA and roulette wheel method are utilized mainly to reduce the size of feasible solution domain and accelerate the identification of the source information. A hypothetic site with one contaminant source location and two release periods is designed to assess the applicability of the present approach. The results indicate that the performance of SATSO-GWT is superior to that of SATS-GWT. In addition, the present approach works very effectively in dealing with the cases which have different initial guesses of source location and measurement errors in the monitoring points as well as problems with large suspicious areas and several source release periods and concentrations.