Groundwater Solute Transport Model Research Articles

The New Potential for Understanding Groundwater Contaminant Transport

The groundwater remediation field has been changing constantly since it first emerged in the 1970s. The remediation field has evolved from a dissolved-phase centric conceptual model to a DNAPL-dominated one, which is now being questioned due to a renewed appreciation of matrix diffusion effects on remediation. Detailed observations about contaminant transport have emerged from the remediation field, and challenge the validity of one of the mainstays of the groundwater solute transport modeling world: the concept of mechanical dispersion (Payne et al. 2008). We review and discuss how a new conceptual model of contaminant transport based on diffusion (the usurper) may topple the well-established position of mechanical dispersion (the status quo) that is commonly used in almost every groundwater contaminant transport model, and evaluate the status of existing models and modeling studies that were conducted using advection-dispersion models.

Simulation on forecast and control for groundwater contamination of hazardous waste landfill

The groundwater flow and solute transport models were established by Visual Modflow, which was used to forecast the transport process of Cr6+ in groundwater and simulate the effects of three control measures of contaminants transport after percolation solution leakage happened in the impermeable layer of the landfill. The results showed that the contamination plume of Cr6+ would reach the pool’s boundary in 10 years, and the distance of contamination transport was 1,450 m. However, the contamination plume will not be obviously expanded between 10 and 20 years. While the ground was covered by hardened concrete, the contamination plume would not reach the pool’s boundary in 20 years. When the leakage-proof barrier was set in the bottom of an unconfined aquifer, the concentration of Cr6+ was higher than that of the leakage-proof barrier unset, but the result was opposite when setting the leakage-proof barrier in the bottom of confined aquifer. The range of the contamination plume was effectively controlled by setting drainage ditches in which water discharge was 2,298.05 m3 d−1, which produced monitoring wells which are not contaminated in 20 years. In sum, combining ground hardening with drainage ditches could produce the best effect in controlling contaminants diffusion, and meanwhile, the drainage ditches daily discharge was reduced to 1,710.19 m3 d−1.

Simulation of spatial and temporal trends in nitrate concentrations at the regional scale in the Upper Dyle basin, Belgium

Models are the only tools capable of predicting the evolution of groundwater systems at a regional scale, by taking into account a large amount of information. This study presents the association of a water balance model (WetSpass) with a groundwater flow and solute transport model (SUFT3D, saturated and unsaturated flow and transport in 3D) in order to simulate the present and future groundwater quality in terms of nitrate in the Upper Dyle basin (439 km2) Belgium. The HFEMC (hybrid finite element mixing cell) method implemented in the SUFT3D code is used to model groundwater flow and nitrate transport. Spatially distributed recharge, modelled with WetSpass, is considered for prescribing the recharge to the groundwater flow model. The feasibility of linking the WetSpass model with the finite-elements SUFT3D code is demonstrated. Time evolution and distribution of nitrate concentration are then simulated using the calibrated model. Nitrate inputs are spatially distributed according to land use. The spatial simulations and temporal trends are compared with previously published data on this aquifer and show good results.

Mathematical Modeling of Groundwater Flow and Solute Transport in Saturated Fractured Rock Using a Dual-Porosity Approach

AbstractThe present paper addresses critical issues that describe the transient transfer of stored rock-matrix flow into high-permeable fractures and rate-limited diffusive solute flux into low-permeable rock matrix using a typical dual-porosity approach. An improved mathematical model is suggested that better describes fluid flow through a coupled fracture-matrix system using a dual-porosity approach. The suggested model differs from a conventional model as the fracture flow equation contains a hyperbolic term in addition to the conventional dispersive term. The matrix flow equation contains the coupling term that controls the transient nature of fluid exchange from the stored rock matrix into the hydraulic conductors. The Langmuir sorption isotherm is suggested to describe the limited sorption sites available on fracture walls, while the Freundlich sorption isotherm is recommended to describe the unlimited sorption sites available within the rock matrix. The dispersion mechanism in a coupled fracture-ma...

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.

Groundwater Migration Modeling and Parameter Sensitivity Analysis on Contaminated Site

Contamination control and remediation of groundwater is one of the hotness points in environmental protection field. Groundwater contamination numerical simulation is widely used for groundwater contamination transportation. In this paper, we constructed an indoor sandbox to conduct hydraulic control experiment and tracer experiment. We also set up groundwater flow model and solute transport model by computer and chose the model's key parameters for sensitivity analysis. The results indicated that the sensitivity of hydraulic conductivity was highest, which was the key parameter in the groundwater flow model. The sensitivity analysis of solute transport model parameters showed that sensitivity from large to small was: longitudinal dispersion, porosity and hydraulic conductivity. This study can obtain the main parameters in groundwater simulation model and is helpful for the construction of groundwater contamination migration model.

Approaches to confirmatory testing of a groundwater flow model for sparsely fractured crystalline rock, exemplified by data from the proposed high-level nuclear waste repository site at Forsmark, Sweden

The Svensk Karnbranslehantering AB (SKB) has proposed the Forsmark site as a future repository for spent high-level nuclear fuel, involving disposal at about 470 m depth in sparsely fractured crystalline bedrock. An essential part of the completed inter-disciplinary site investigation was to develop an integrated account of the site and its regional setting, including the current state of the geosphere and the biosphere as well as natural processes affecting long-term evolution. First, this report recollects the integrated understanding and some key hydraulic characteristics of the crystalline bedrock at Forsmark along with a description of the flow model set-up and the methodology used for paleoclimatic flow modeling. Second, the protocol used for site-scale groundwater flow and solute transport modeling is demonstrated. In order to conduct a quantitative assessment of groundwater flow paths at Forsmark, the standard guide for groundwater flow modeling was elaborated on, to support both discrete and porous media flow approaches. In total, four independent types of data were used to confirm that the final groundwater flow model for the crystalline bedrock was representative of site conditions.

The New Potential for Understanding Groundwater Contaminant Transport

AbstractThe groundwater remediation field has been changing constantly since it first emerged in the 1970s. The remediation field has evolved from a dissolved‐phase centric conceptual model to a DNAPL‐dominated one, which is now being questioned due to a renewed appreciation of matrix diffusion effects on remediation. Detailed observations about contaminant transport have emerged from the remediation field, and challenge the validity of one of the mainstays of the groundwater solute transport modeling world: the concept of mechanical dispersion (Payne et al. 2008). We review and discuss how a new conceptual model of contaminant transport based on diffusion (the usurper) may topple the well‐established position of mechanical dispersion (the status quo) that is commonly used in almost every groundwater contaminant transport model, and evaluate the status of existing models and modeling studies that were conducted using advection‐dispersion models.

Quantitative and Qualitative Assessment of Seawater Intrusion in Wadi Ham under Different Pumping Scenarios

AbstractArid coastal regions are more vulnerable to groundwater deterioration problems. Intensive groundwater abstraction from the coastal aquifer of Wadi Ham, United Arab Emirates, caused a severe saltwater intrusion problem. Given the deterioration of groundwater quality, domestic water supply from well fields have been terminated and replaced by desalinated seawater. In addition, many farms in southeast Fujairah city have been abandoned. This paper develops a two-dimensional finite element groundwater flow and solute transport model to simulate the spatial and temporal variations of the salinity distribution in the coastal aquifer of Wadi Ham, taking into account the transition zone between freshwater and seawater bodies. All simulations were conducted in the horizontal view under transient conditions. The available historical records of the water table levels were used to calibrate and validate the developed model. Emphasis was placed on the response of the transition zone to different pumping scenari...

Analysis for remedial alternatives of unregulated municipal solid waste landfills leachate-contaminated groundwater

A groundwater flow and solute transport model was developed using Visual Modflow for forecasting contaminant transport and assessing effects of remedial alternatives based on a case study of an unregulated landfill leachate-contaminated groundwater in eastern China. The results showed that arsenic plume was to reach the pumping well in the downstream farmland after eight years, and the longest lateral and longitudinal distance of arsenic plume was to reach 200 m and 260 m, respectively. But the area of high concentration region of arsenic plume was not to obviously increase from eight years to ten years and the plume was to spread to the downstream river and the farmland region after 20 years; while the landfill’s ground was hardened, the plume was not to reach the downstream farmland region after eight years; when the pumping well was installed in the plume downstream and discharge rate was 200m3/d, the plume was to be effectively restrained; for leakage-proof barriers, it might effectively protect the groundwater of sensitive objects within an extent time range. But for the continuous point source, the plume was still to circle the leakage-proof barrier; when discharge rate of drainage ditches was 170.26 m3/d, the plume was effectively controlled; the comprehensive method combining ground-harden with drainage ditches could get the best effect in controlling contaminant diffusion, and the discharge rate was to be reduced to 111.43 m3/d. Therefore, the comprehensive remedial alternative combining ground-harden with drainage ditch will be recommended for preventing groundwater contamination when leachate leakage has happened in unregulated landfills.

Development of a coupled flow and solute transport modelling for Astaneh-Kouchesfahan groundwater resources, North of Iran

Astaneh-Kouchesfahan Plain is an important source of groundwater in Northern Iran. In the study area, rational management of groundwater resources requires a precise evaluation of groundwater flow and transport components. For this purpose, a 2-dimentional groundwater flow and solute transport model was developed and calibrated using PMWIN 5.3. Simulation results under steady-state and transient conditions show that the horizontal hydraulic conductivity values range from 1 to 23 m/day; and the specific yield values range between 0.03 and 0.25. After construction groundwater flow model, in order to simulate and predict chloride transport in the study area, a 2-D solute transport model for the aquifer has been developed, calibrated and validated using MT3D. The predictive simulation from October 2009 to October 2012 shows that according to present recharge and discharge conditions, groundwater salinities will increase and in the mid and long-term, groundwater consumers will be facing a worse situation than the present.

Use of gaseous tracers (CFCs and SF6) and transit-time distribution spectrum to validate a shallow groundwater transport model

► Pertinent data for validation of catchment solute-transport models are lacking. ► Interests of gaseous tracers and spectrum of transit time distribution are analysed. ► Transit time distribution spectrum is a very relevant validation variable. Catchment-scale solute transport models constitute potentially powerful tools of water resources management for predicting the evolution of water quality in response to land use modifications. Validation of the models remains a crucial step in order to get reliable prediction. However, pertinent data for the validation step are lacking. When catchment solute transport models are applied to shallow groundwater catchments, catchment-scale model validation relies on the validation of the groundwater solute transport model. Here we studied the interests of two approaches for groundwater solute transport model validation: the use of (i) gaseous atmospheric tracers and (ii) of spectral properties of transit time distributions derived from tracer concentration time series of rainfall and stream base-flow. The Kervidy-Naizin catchment, a 5 km 2 catchment in Western France was chosen as case application. Three simulations with a shallow groundwater transport model were performed using three sets of effective porosity, respectively. We then investigated the ability of four gaseous tracers (CFC-11, CFC-12, CFC-113 and SF 6 ) and transit time distribution spectra to identify the most realistic simulations. The three simulations led to mean transit times that varied over a wide range of values, from 1.2 to 12.1 yr. Simulated groundwater mixing ratio differences for the three simulations did not exceed 5% for CFC-11, regardless of the groundwater location. The values of the SF 6 , CFC-12 and CFC-113 mixing ratio differences between the two simulations that contained the two shortest mean transit times were within expected measurement error of the tracer concentrations, regardless of the groundwater location. In contrast, the mixing ratio differences between the two simulations with the shortest mean transit times and the simulation containing the largest one exceeded 28% at all groundwater locations for SF 6 and 9% in groundwater discharging into the stream for CFC-12 and CFC-113. The spectra of the three simulated transit time distributions do not match the transit time distribution spectrum derived from chloride concentration time series. So these results show that transit time distribution spectrum, and in much less extend SF 6 , CFC-12 and CFC-113 mixing ratios are sensitive enough to effective porosity values to be used as validation variables in shallow groundwater transport modelling. Transit time distribution spectrum constitutes an integrative variable able to discriminate between shallow groundwater transport simulations leading to very close mean transit times. In the present work, the discrepancy between the simulated spectra and the spectrum derived from the chloride concentration may come from other catchment processes than groundwater transport process, or from a wrong modelling of the groundwater transport process. Globally, deriving reliable transit time distribution spectrum requires high-frequency and extensive time series of a conservative tracer measured in stream water and rainfall, which is not straightforward to collect. The low sensitivity of simulated CFC-11 tracer mixing ratios to simulated groundwater transit times, and thus to model parameters, constituted a shortcoming to use it as a validation variable of groundwater solute transport models.

Numerical Simulation of Different Schemes’ Influence on Coastal Areas for Groundwater-Source Heat Pump Engineering

More and more people have take more attention on the problem like Seawater intrusion, The same floor recharge and "heat transfixion". This article has established the groundwater flow and solute transport and temperature coupling numerical model,to simulate the underground water temperature’s change by changing the wells’ spacing manner. Simulation results show that the two kinds of disposing Wells solutions are not cause seawater invasion, the second disposing Wells scheme help to prevent the occurrence of seawater invasion.

Sensitivity Analysis of a Combined Groundwater Flow and Solute Transport Model Using Local-Grid Refinement: A Case Study

Combining groundwater flow models with solute transport models represents a common challenge in groundwater resources assessments and contaminant transport modeling. Groundwater flow models are usually constructed at somewhat larger scales (involving a coarser discretization) to include natural boundary conditions. They are commonly calibrated using observed groundwater levels and flows (if available). The groundwater solute transport models may be constructed at a smaller scale with finer discretization than the flow models in order to accurately delineate the solute source and the modeled target, to capture any heterogeneity that may affect contaminant migration, and to minimize numerical dispersion while still maintaining a reasonable computing time. The solution that is explored here is based on defining a finer grid subdomain within a larger coarser domain. The local-grid refinement (LGR) implemented in the Modular 3D finite-difference ground-water flow model (MODFLOW) code has such a provision to simulate groundwater flow in two nested grids: a higher-resolution sub-grid within a coarse grid. Under the premise that the interface between both models was well defined, a comprehensive sensitivity and uncertainty analysis was performed whereby the effect of a parameter perturbation in a coarser-grid model on transport predictions using a higher-resolution grid was quantified. This approach was tested for a groundwater flow and solute transport analysis in support of a safety evaluation of the future Belgian near-surface radioactive waste disposal facility.

Modeling Variably Saturated Subsurface Solute Transport with MODFLOW‐UZF and MT3DMS

The MT3DMS groundwater solute transport model was modified to simulate solute transport in the unsaturated zone by incorporating the unsaturated-zone flow (UZF1) package developed for MODFLOW. The modified MT3DMS code uses a volume-averaged approach in which Lagrangian-based UZF1 fluid fluxes and storage changes are mapped onto a fixed grid. Referred to as UZF-MT3DMS, the linked model was tested against published benchmarks solved analytically as well as against other published codes, most frequently the U.S. Geological Survey's Variably-Saturated Two-Dimensional Flow and Transport Model. Results from a suite of test cases demonstrate that the modified code accurately simulates solute advection, dispersion, and reaction in the unsaturated zone. Two- and three-dimensional simulations also were investigated to ensure unsaturated-saturated zone interaction was simulated correctly. Because the UZF1 solution is analytical, large-scale flow and transport investigations can be performed free from the computational and data burdens required by numerical solutions to Richards' equation. Results demonstrate that significant simulation runtime savings can be achieved with UZF-MT3DMS, an important development when hundreds or thousands of model runs are required during parameter estimation and uncertainty analysis. Three-dimensional variably saturated flow and transport simulations revealed UZF-MT3DMS to have runtimes that are less than one tenth of the time required by models that rely on Richards' equation. Given its accuracy and efficiency, and the wide-spread use of both MODFLOW and MT3DMS, the added capability of unsaturated-zone transport in this familiar modeling framework stands to benefit a broad user-ship.

Model Evaluation of Thermal Energy Potential of Hydrogeological Structures with Flooded Mines

A Czech Republic Ministry of Industry and Trade grant (project 2A-2TP1/055) encourages the use of abandoned mines as geothermal energy sources. Mathematical models are being used to evaluate the thermal energy potential. This paper discusses approaches and limitations of using the MT3D code, which is well known as a groundwater solute transport model, for geothermal energy balance calculations. Results showing the potential for geothermal energy abstraction from the abandoned and flooded Krimich II underground coal mine are demonstrated.

Numerical Simulation for Groundwater-Source Heat Pump Engineering Disposing Wells Scheme in the Coastal Region

For analysis the MOMA FengHui residential of BaYuquan area ground- water source heat pump engineering on the influence of seawater invasion，Established the groundwater flow and solute transport and temperature coupling numerical model，Simulated forecast the change tendency of the groundwater flow and solute and temperature of two different disposing Wells scheme. Simulation results show that the two kinds of disposing Wells solutions are not cause seawater invasion, the second disposing Wells scheme help to prevent the occurrence of seawater invasion.

Geologic heterogeneity representation using high‐order spatial cumulants for subsurface flow and transport simulations

The effects of geological heterogeneity representation on the hydraulic properties of two‐dimensional flow and transport simulations are studied using various stochastic simulation algorithms. An alternative multiple‐point method (HOSIM) on the basis of high‐order spatial cumulants and Legendre polynomials is used and compared to the multiple‐point FilterSIM method, and the sequential Gaussian simulation (SGS) method. Conditional realizations of a fluvial reservoir system are generated by HOSIM, FilterSIM, and SGS methods. Then, the simulated hydraulic permeability fields (K) are used in a numerical groundwater flow and solute transport models. Numerical results showed that the HOSIM method created greater connectivity in the reservoir/aquifer (channel) network than FilterSIM and SGS realizations. The numerical simulations show that in a reservoir/aquifer system with a strongly connected network of high‐K materials, the Gaussian and FilterSIM approaches are not as effective as HOSIM in reproducing this behavior. The simulations showed a good agreement between HOSIM realizations and the exhaustive reference image.

Anthropogenic changes in a confined groundwater flow system in the Bangkok Basin, Thailand, part II: how much water has been renewed?

AbstractExcessive groundwater pumping from the sedimentary basin underlying the Bangkok metropolitan area, Thailand, has caused not only piezometric level decline but also enhancement of groundwater recharge. Although groundwater renewal has accelerated, it remains unclear how much water in confined aquifers has been renewed owing to the excessive pumping. To reveal the details of the groundwater renewal process, we performed a water budget analysis and virtual tracer experiment using a numerical model of groundwater flow and solute transport. Mean turnover time was 45600 yr prior to the beginning of significant pumping in 1954, which then shortened to 3500 yr in 2001. The renewed water fraction since 1954 was estimated to be only 0·78% in 2007 on average over the whole basin. This is a reflection of the huge storage capacity of the basin, relatively low recharge rate due both to existence of a thick clay (Bangkok clay), and low plain gradient. The spatially distributed renewed water fraction, which was obtained from the virtual tracer experiment, was no more than 1% in most aquifers except for basin margins where the aquifers are exposed, while in the uppermost BK aquifer it exceeded 5% over a wide extent and reached more than 20% at an alluvial fan. The estimated fraction of renewed water was generally consistent with measured 3H concentrations, demonstrating in part the validity of the numerical model used. The results from our studies indicate that modern waters recharged since 1954 have minimal affect on water quality in the main production aquifers. However, water storage and pressure in aquifers respond quickly to increase in pumping rate, potentially affecting land subsidence. Thus, we have to focus on different time‐scales between groundwater quantity and quality management. Copyright © 2011 John Wiley & Sons, Ltd.

Regional transport modelling for nitrate trend assessment and forecasting in a chalk aquifer

Regional degradation of groundwater resources by nitrate has become one of the main challenges for water managers worldwide. Regulations have been defined to reverse observed nitrate trends in groundwater bodies, such as the Water Framework Directive and the Groundwater Daughter Directive in the European Union. In such a context, one of the main challenges remains to develop efficient approaches for groundwater quality assessment at regional scale, including quantitative numerical modelling, as a decision support for groundwater management. A new approach combining the use of environmental tracers and the innovative ‘Hybrid Finite Element Mixing Cell’ (HFEMC) modelling technique is developed to study and forecast the groundwater quality at the regional scale, with an application to a regional chalk aquifer in the Geer basin in Belgium. Tritium data and nitrate time series are used to produce a conceptual model for regional groundwater flow and contaminant transport in the combined unsaturated and saturated zones of the chalk aquifer. This shows that the spatial distribution of the contamination in the Geer basin is essentially linked to the hydrodynamic conditions prevailing in the basin, more precisely to groundwater age and mixing and not to the spatial patterns of land use or local hydrodispersive processes. A three-dimensional regional scale groundwater flow and solute transport model is developed. It is able to reproduce the spatial patterns of tritium and nitrate and the observed nitrate trends in the chalk aquifer and it is used to predict the evolution of nitrate concentrations in the basin. The modelling application shows that the global inertia of groundwater quality is strong in the basin and trend reversal is not expected to occur before the 2015 deadline fixed by the European Water Framework Directive. The expected time required for trend reversal ranges between 5 and more than 50 years, depending on the location in the basin and the expected reduction in nitrate application. To reach a good chemical status, nitrate concentrations in the infiltrating water should be reduced as soon as possible below 50 mg/l; however, even in that case, more than 50 years is needed to fully reverse upward trends.