Contaminant Transport Model Research Articles

Analytical modeling of contaminant transport along sloping coastal beaches in presence of tidal waves and exponential rainfall infiltration

Coastal beaches are the most important part of the marine environment and are highly influenced by the interactions taking place between groundwater and surface water of any form. Generally, the purity index of the groundwater is based on the concentration of Total Dissolved Solids (TDS) in it. Analytical solutions are the best tools for groundwater flow and transport modeling. However, contaminant transport along the sloping coastal beaches with complex boundaries cannot be addressed with available analytical solutions. In the present study, new analytical models are developed for groundwater flow and contaminant transport for sloping coastal beaches with continuity and tidal boundary conditions. To assess the performance of the new analytical solution and to validate the range of aquifer parameters, numerical simulation is performed using Du-Fort Frankel (DFF) Scheme. Numerical experimentation is carried out using the Tchebycheff and L2 norms. It is observed that the new analytical solution for the contaminant transport gives acceptable results over the wide range of the aquifer parameters. To show the effectiveness of the developed models, two case studies from Indian coastal aquifers namely, Kalpakkam, Tamil Nadu, and Bhavnagar, Gujarat are considered. The profiles of the contaminant concentration are obtained to study the TDS behavior along these complex coastal beaches in the spatiotemporal directions. The results are compared with numerical model results and found to be satisfactory. The combined effect of the initial rainfall and rainfall decay constants showed a significant impact on the concentration of TDS. TDS concentrations are observed to be varying highly with the variation in the tidal constituents and bed slope.

Groundwater contaminant transport modeling using MODFLOW and MT3DMS: a case study in Rajshahi City

Abstract Rapidly growing urbanization and industrialization processes including man-made activities result in groundwater contamination that becomes unsafe for human use. In this study, the groundwater flow and contaminant migration through aquifers in Rajshahi City were modeled using MODFLOW and MT3DMS codes. ModelMuse, a graphical user interface (GUI), is used to run the codes and the hydrological and geological data of the region are used as the input parameters for the model. The travel distance of five selected contaminants such as chromium (Cr), copper (Cu), manganese (Mn), lead (Pb), and zinc (Zn), from the source (e.g. landfill site), were simulated corresponding to travel times of 1, 3, 5, 10, 15, 20, and 50 years. The study results showed that the migration distance of the contaminants increases over time and follows a logarithmic trend. Among the contaminants, the model-predicted results show that the concentration of Cr and Pb in the groundwater varies more than 90% from their standards over the period of 50 years, which suggests that these two pollutants are the prime contaminants polluting groundwater in the coming future. This model can be used as an effective decision-making tool for the monitoring of groundwater contaminant transport for a specific location.

Effects of groundwater flow on the distribution of bitumen contaminants in a shallow coastal plain sand aquifer of the Nigerian Dahomey basin

In situ bitumen seeps within the shallow subsurface of a section of the coastal Dahomey basin of southwestern Nigeria act as a geogenic source of polycyclic aromatic hydrocarbons (PAHs), which contaminates soil and groundwater resources in the area. This study focuses on a hydrogeochemical characterization of PAHs contaminants from the bitumen seeps and assesses their distribution using a groundwater flow and transport model. To do this, we used geophysical results from a previous study to determine the location of three water wells drilled to depths of 15 m each. Soil and groundwater samples were retrieved from different depths during drilling and used for sedimentological and geochemical analysis. We also performed pumping tests on all 3 wells to determine the hydraulic properties of the aquifer in the area and, lastly, developed a MODFLOW-based groundwater flow and transport model to simulate the distribution of the contaminants. Bitumen-bearing sediments retrieved during the groundwater well installation confirmed earlier interpretations of geophysical results, which mapped subsurface lithologies that host the bitumen seeps. These lithologies, which act as PAH contaminant sources, occur at depths below 11 m towards the southern part of the study area. Hydraulic conductivity and porosity of the sandy aquifer were estimated to be 0.25 m/day and 46%, respectively. The United States Environmental Protection Agency's priority PAHs, including Naphthalene, Acenaphthylene, Fluorene, and Pyrene of geogenic sources, were identified with concentrations ranging from Below Detection Limit (BDL) to 5 ppm in both sediment and groundwater samples. We simulated the distribution of Naphthalene in groundwater in the area using the contaminant transport model, considering its high dissolution tendency. Hydrodynamic dispersion was observed as the dominant transport mechanism of the contaminants in groundwater. A distribution rate at the concentration of significant risk to human exposure was predicted to be 0.022 m/day and 0.015 m/day in the horizontal and vertical directions, respectively. This study confirmed groundwater contamination by PAHs from in situ bitumen seeps and provided a framework for future groundwater remediation within the area.

Identification of contaminant source and hydraulic conductivity field based on an ILUES-SOM surrogate model

Contaminant source identification and hydraulic conductivity estimation are of great significance for contaminant transport model in the subsurface media, but their actual values are difficult to obtain and can usually be inversely identified and estimated by sparse observations. In order to reduce computational cost in the process of estimating groundwater model parameters, the surrogate model was often used. This study addresses this challenge by proposing a modified self-organizing map (SOM) based surrogate model, named ILUES-SOM. The proposed model combines a modified iterative ensemble smoother method (SGSIM-ILUES) and the SOM algorithm to simultaneously identify contaminant source parameters and hydraulic conductivity field. Considering the characteristics of the proposed method (ILUES-SOM), a comparison of parameter estimation accuracy and computational efficiency is performed with the original SOM and SGSIM-ILUES inversion model. Moreover, the robustness of ILUES-SOM model for inversion was illustrated by proposing varying degrees of observation errors and missing early observation data. The results indicated that ILUES-SOM model can successfully retrieve unknown contaminant source simultaneously with heterogeneity hydraulic conductivity field in the groundwater system.

Cover Image, Volume 47, Issue 3

The cover image is based on the Short Communication An analytical model for contaminant transport in landfill liner with fluctuating leachate head by Haijian Xie et al., https://doi.org/10.1002/nag.3478.

Moving Aircraft River Velocimetry (MARV): Framework and Proof‐of‐Concept on the Tanana River

AbstractInformation on velocity fields in rivers is critical for designing infrastructure, modeling contaminant transport, and assessing habitat. Although non‐contact approaches to measuring flow velocity are well established, these methods assume a stationary imaging platform. This study eliminates this constraint by introducing a framework for moving aircraft river velocimetry (MARV). The workflow takes as input images acquired from an airplane and involves orthorectification, frame overlap analysis, image enhancement, particle image velocimetry (PIV), and aggregation of the resulting velocity vectors onto a prediction grid. We also use new metrics to quantify the agreement between image‐derived and field‐measured velocity vectors in terms of both orientation and magnitude. The potential of MARV was evaluated using data from two Alaskan rivers: a large, highly turbid channel and its smaller, clearer tributary. Sediment boil vortices on the mainstem provided natural features trackable via PIV and estimated velocities corresponded closely with field measurements (R2 up to 0.911). We compared an exhaustive approach that evaluates overlap for all frame combinations to a simpler rolling window implementation and found that the more efficient algorithm did not compromise accuracy. Sensitivity analysis suggested that the method was robust to window parameterization. Comparing PIV output from different flying heights and imaging systems indicated that larger pixels led to higher accuracy and that a more advanced dual‐camera system provided superior performance. Results from the tributary were less encouraging, presumably due to a lack of trackable features in visible images. Testing across a range of rivers is needed to assess the generality of MARV.

Joint Estimation of Adsorptive Contaminant Source and Hydraulic Conductivity Using an Iterative Local Updating Ensemble Smoother with Geometric Inflation Selection

The joint estimation of groundwater contaminant source characteristics and hydraulic conductivity is of great significance for reactive contaminant transport models in heterogeneous subsurface media. The accurate determination of the sorption parameters of such contaminants is also a key prerequisite for estimating the parameters of the groundwater system. In this study, to investigate the impact of the sorption parameter field on the accuracy of hydraulic conductivity and source characteristics estimation, numerical experiments were conducted in a synthetic aquifer considering the contaminant sorption process in groundwater models with varying sorption parameter settings. Iterative local updating ensemble smoother with geometric inflation selection (ILUES-GEO) was employed to assimilate hydraulic head and contaminant concentration data to jointly estimate the contaminant source information and hydraulic conductivity in a heterogeneous aquifer. The results indicated that the ILUES-GEO successfully recovers contaminant source information simultaneously with hydraulic conductivity, and its performance improves as more accurate sorption parameters are introduced. Furthermore, the influence of the ILUES algorithm parameters and ensemble size is investigated to improve the estimation accuracy. Additionally, the characterization of contaminant sources and hydraulic conductivity fields is influenced by the number and locations of measurements. This study can help to understand the significance of sorption parameter setting for the joint estimation of reactive contaminant source and hydraulic parameters.

Performance of landfill low-permeability liners for minimizing groundwater contamination

Low-permeability liners are required at the base of municipal solid waste (MSW) landfills to minimize leachate leakage and contaminant migration into groundwater. This paper uses a two-dimensional coupled groundwater flow and contaminant transport model to examine the performance of three types of low-permeability liners specified by the current Chinese landfill standard: (1) a compacted clay liner (CCL), (2) a geomembrane (GMB) overlying a CCL, and (3) a GMB overlying a geosynthetic clay liner (GCL) on a CCL. The model simulates leachate leaking and contaminant migrating over the entire base of the landfill for the CCL and through the holed GMB wrinkles for the GMB composite liners. The performance of each type of low-permeability liners was evaluated and compared in terms of leakage rate and peak impact of chloride on the aquifer. Based on liner cases and conditions examined in this paper, the results show that the three types of low-permeability liners are not equivalent for minimizing the leakage rate and chloride impact on the aquifer. The GMB + GCL + CCL performs the best among the three low-permeability liners, and is effective for limiting the peak chloride impact on the aquifer below the acceptable level in drinking water.

Arsenic and Copper Contaminant Transport Modelling In Xaysomboun Province, LAO PDR

Arsenic and Copper Contaminant Transport Modelling In Xaysomboun Province, LAO PDR

Uncertainty with Varying Subsurface Permeabilities Reduced Using Coupled Random Field and Extended Theory of Porous Media Contaminant Transport Models

To maximize the usefulness of groundwater flow models for the protection of aquifers and abstraction wells, it is necessary to identify and decrease the uncertainty associated with the major parameters such as permeability. To do this, there is a need to develop set of estimates representing subsurface heterogeneity or representative soil permeability estimates. Here, we use a coupled Random Field and extended Theory of Porous Media (eTPM) simulation to develop a robust model with a good predictive ability that reduces uncertainty. The coupled model is then validated with a physical sandbox experiment. Uncertainty is reduced by using 500 realisations of the permeability parameter using the eTPM approach. A multi-layer contaminant transport scenario with varying permeabilities, similar to what could be expected with shallow alluvial sediments, is simulated. The results show that the contaminant arrival time could be strongly affected by random field realizations of permeability compared with a modelled homogenous permeability parameter. The breakthrough time for heterogeneous permeabilities is shorter than the homogeneous condition. Using the 75% confidence interval (CI), the average contaminant concentration shows 4.4% variation from the average values of the considered area and 8.9% variation in the case of a 95% confidence interval.

An analytical model for contaminant transport in landfill liner with fluctuating leachate head

AbstractLeachate head in municipal solid waste (MSW) landfills can be very high (e.g., >10 m) in some Chinese landfills and can continuously change during the service life of the landfill. Variations of leachate head can induce time‐dependent seepage velocity changes in the liner, which may lead to a change of transport mechanisms of contaminants. An analytical model for contaminant transport through clay liner system considering the effects of leachate head variations is presented. The analytical solution is obtained using the recursive method and the Green's function approach. The proposed analytical solution is verified by numerical results. The model is then applied to investigate the effects of variable leachate head on the transport of contaminants. The results indicated that time‐dependent advection arising from leachate head variations may play a significant part when investigating contaminant transport through a clay liner. The contaminant concentrations at the bottom of the liner predicted by using fixed leachate head may be underestimated compared to the case with variable leachate heads. The bottom concentration of Pb2+ at t = 50 years for the case with HD = 60 m can be 6.6 times larger than that of the case with fixed leachate head. The mechanisms of contaminant transfer may change from a diffusion‐dominated process to an advection‐dominated process. For example, the molecular diffusion is the dominant process in Event 1 (e.g., t < 5 years with Peclet number < 1) while advection induced by the variations of leachate head may play a more important role for contaminant transport when t > 5 years. Increasing leachate head can result in an earlier breakthrough time and steady state for contaminant transport. The breakthrough time of DCM for the case with HD = 60 m can be 1.6 times lower than that for the case with fixed leachate head. Considering the effects of leachate head variations may be critical to design a more stable and reliable landfill liner.

A bibliometric and visual analysis of contaminant transport modeling in the groundwater system: current trends, hotspots, and future directions.

Contaminant transport modeling (CTM) in the groundwater represents the complex bio-geo-chemical processes in the subsurface system and plays a vital role in designing remediation strategies for contaminated sites. Hence, this study evaluated 1955 articles on CTM-based studies published from 2010 to 2022 by utilizing the Scopus® database to provide a quantitative analysis of current trends and future directions. A systematic approach comprised of a bibliometric survey and visualization of various networks was conducted with the VOSviewer and Biblioshiny software for quantitative analysis of progress of CTM research field over the past decade. The hotspots and evolution of themes of CTM were found using Sankey diagrams, and thematic maps. It was observed that articles were published at an exponential rate over past 5years. The analysis of Scopus® database revealed that the average citations per article and the average citations per year per article were 14.7 and 2.225. In the past decade, USA published 489 articles and emerged as the leading country based on mutual collaborations and cooperation with other top 9 most productive countries. Flinders University was ranked in the first position based on the number of articles, followed by Pacific Northwest National Laboratory. The findings obtained from this study can help researchers identify exploitation and core areas, to understand better the direction of research of mathematical model development, and to determine hotspots of CTM research field.

Environmental hazard quantification toolkit based on modular numerical simulations

Abstract. Quantifying impacts on the environment and human health is a critical requirement for geological subsurface utilisation projects. In practice, an easily accessible interface for operators and regulators is needed so that risks can be monitored, managed, and mitigated. The primary goal of this work was to create an environmental hazards quantification toolkit as part of a risk assessment for in-situ coal conversion at two European study areas: the Kardia lignite mine in Greece and the Máza-Váralja hard coal deposit in Hungary, with complex geological settings. A substantial rock volume is extracted during this operation, and a contaminant pool is potentially left behind, which may put the freshwater aquifers and existing infrastructure at the surface at risk. The data-driven, predictive tool is outlined exemplary in this paper for the Kardia contaminant transport model. Three input parameters were varied in a previous scenario analysis: the hydraulic conductivity, as well as the solute dispersivity and retardation coefficient. Numerical models are computationally intensive, so the number of simulations that can be performed for scenario analyses is limited. The presented approach overcomes these limitations by instead using surrogate models to determine the probability and severity of each hazard. Different surrogates based on look-up tables or machine learning algorithms were tested for their simplicity, goodness of fit, and efficiency. The best performing surrogate was then used to develop an interactive dashboard for visualising the hazard probability distributions. The machine learning surrogates performed best on the data with coefficients of determination R2>0.98, and were able to make the predictions quasi-instantaneously. The retardation coefficient was identified as the most influential parameter, which was also visualised using the toolkit dashboard. It showed that the median values for the contaminant concentrations in the nearby aquifer varied by five orders of magnitude depending on whether the lower or upper retardation range was chosen. The flexibility of this approach to update parameter uncertainties as needed can significantly increase the quality of predictions and the value of risk assessments. In principle, this newly developed tool can be used as a basis for similar hazard quantification activities.

Reply to discussion on ‘Review of groundwater flow and contaminant transport modelling approaches for the Sherwood Sandstone aquifer, UK; insights from analogous successions worldwide’ by Medici and West ( QJEGH , 55, qjegh2021-176)

Sandstone aquifers are challenging to characterize, model and review due to interplays between intergranular porosities, narrow fractures and rock discontinuities enlarged by the groundwater flow (Tellam and Barker 2006; Hitchmough et al. 2007, Bashar and Tellam 2011, Medici et al. 2019). New data collected, and advances in hydraulic testing and modelling techniques should guide the next steps on research on sandstone aquifers worldwide. The contribution of Medici and West (2022) is intended to point the hydrogeological community towards more novel modelling approaches that need to be integrated with all the previous practices for the Sherwood Sandstone aquifer, that have mostly focussed on the Equivalent Porous Medium (EPM), as this is the most widely accepted and practical solution. The focus of the review paper is thus novel approaches to modelling of the flow heterogeneities of the Sherwood Sandstone aquifer as a consequence of a hydraulic characterization project funded by TotalEnergies, which was specific to the Triassic comprising the Sherwood Sandstone Group rather than Permian strata. The flow heterogeneities of sedimentary origin and tectonic origin have also been reviewed in the UK Triassic Sandstone with no angle on groundwater flow modelling (Medici et al. 2019a, b).

Evidence Based Estimation of Macrodispersivity for Groundwater Transport Applications.

The scope of this work is to discuss the proper choice of macrodispersion coefficients in modeling contaminant transport through the advection dispersion equation (ADE). It is common to model solute concentrations in transport by groundwater with the aid of the ADE. Spreading is quantified by macrodispersivity coefficients, which are much larger than the laboratory observed pore-scale dispersivities. In the frame of stochastic theory, longitudinal macrodispersivity is related to the hydraulic conductivity spatial variability via its statistical moments (mean, variance, integral scales), which are generally determined by geostatistical analysis of field measurements. In many cases, especially for preliminary assessment of contaminant spreading, these data are not available and ad hoc values are adopted by practitioners. The present study aims at recommending dispersivity values based on a thorough analysis of tens of field experiments. Aquifers are classified as of weak, medium, and high heterogeneity and for each class a range of macrodispersivity values is recommended. Much less data are available for the transverse macrodispersivities, which are significantly smaller than the longitudinal one. Nevertheless, a few realistic values based on field data, are recommended for applications. Transport models using macrodispersivities can predict mean concentrations, different from the local ones. They can be used for estimation of robust measures, like plumes spatial moments, longitudinal mass distribution and breakthrough curves at control planes.

Evaluating the effectiveness of a geostatistical approach with groundwater flow modeling for three-dimensional estimation of a contaminant plume

When assessing the risk from an underground environment that is contaminated by radioactive nuclides and hazardous chemicals and planning for remediation, the contaminant plume distribution and the associated uncertainty from measured data should be estimated accurately. While the release history of the contaminant plume may be unknown, the extent of the plume caused by a known source and the associated uncertainty can be calculated inversely from the concentration data using a geostatistical method that accounts for the temporal correlation of its release history and groundwater flow modeling. However, the preceding geostatistical approaches have three drawbacks: (1) no applications of the three-dimensional plume estimation using concentration data from multiple depths in real situations, (2) no constraints for the estimation of the plume distribution, which can yield negative concentration and large uncertainties, and (3) few applications to actual cases with multiple contaminants. To address these problems, the non-negativity constraint using Gibbs sampling was incorporated into the geostatistical method with groundwater flow modeling for contaminant plume estimation. This method was then tested on groundwater contamination in the Gloucester landfill in Ontario, Canada, using three-dimensional contaminant transport model and concentration data from multiple depths. The method was applied to three water soluble organic contaminants: 1,4-dioxane, tetrahydrofuran, and diethyl ether. The effectiveness of the proposed method was verified by the general agreement of the calculated plume distributions of the three contaminants with concentration data from 66 points in 1982 (linear correlation coefficient of about 0.7). In particular, the reproduced peak of 1,4-dioxane corresponding to the large disposal in 1978 was more accurate than the result of preceding minimum relative entropy-based studies. The same peak also appeared in the tetrahydrofuran and diethyl ether distributions approximately within the range of the retardation factor derived from the fraction of organic carbon.

Discussion on ‘Review of groundwater flow and contaminant transport modelling approaches for the Sherwood Sandstone aquifer, UK; insights from analogous successions worldwide’ by Medici and West ( QJEGH , 55, qjegh2021-176)

A thorough review paper on hydrogeology topics is challenging, as since the 1990s there has been a substantial increase in published papers and reports. It appears that Medici and West (2022), in keeping a reasonable length to their paper, have only reviewed selected parts of the sandstone stratigraphy comprising the principal sandstone aquifers of the UK. Much of the focus of their review is on the Triassic Sherwood Sandstone aquifers of the north-west of England.

Two-dimensional model of flow and transport in porous media: Linking heterogeneous anisotropy with stratal patterns in meandering tidal channel deposits of the Venice Lagoon (Italy)

Understanding the internal structure of permeable and impermeable sediments (e.g. point-bars and tidal-flat deposits) generated by the evolution of meandering tidal channels is essential for accurate modeling of groundwater flow and contaminant transport in coastal areas. The detailed reconstruction of stratal geometry and hydraulic properties from measurements must be accompanied by depositional history information. In this work, we use high resolution reconstructions of ancient tidal channels of the Venice Lagoon (Italy) to drive 2D simulations of groundwater flow and transport, showing the importance of incorporating information on the sediment accumulation processes into the hydraulic characteristics and how horizontal anisotropy emerging from these processes significantly influences transport. Effective hydraulic conductivity is modeled with a heterogeneous 2D anisotropic tensor with principal directions aligned with observed sedimentation sequences. Comparison of flow and solute dynamics simulated using reconstructed and theoretical hydraulic properties show drastically different pathways of solute propagation.

Contaminant Transport from a Deep Geological Repository: Lumped Parameters Derived from a 3D Hydrogeological Model

A model of contaminant transport from a repository to the biosphere is one of the major needs in the safety assessment of the geological disposal of spent nuclear fuel. This work deals with the development of a procedure that obtained characteristic data from the transport path by postprocessing the results of the 3D flow and transport models, according to the repository concept for the Czech Republic. Postprocessing was used to map the entire transport pathway, which included the smallest tracer flows; therefore, it is called the “integral method”. The results are the characteristics of the storage system, such as: transport path length, flow time, total dilution, groundwater flow, longitudinal dispersivity, porosity, etc. These acquired characteristics can be used directly in safety analyses or to narrow the selection of candidate sites. Furthermore, these parameters were used to set up a model with lumped parameters (in this case, created in the GoldSim SW environment). Even only one “Pipe” component, after being properly set up, shows almost identical results to the entire 3D model. Based on the results of the 3D model, it is possible to set up a lumped parameter model that accurately simulates the transport path and can perform further calculations of a larger number of contaminants in repeated runs, e.g., with stochastic input data, which would be very laborious (or not possible at all) with the 3D model.

Groundwater contaminant transport modeling using Visual MODFLOW: a case study of corporation sewage farm in South Madurai, Tamil Nadu, India

Groundwater contaminant transport modeling using Visual MODFLOW: a case study of corporation sewage farm in South Madurai, Tamil Nadu, India