A Review of the Software Resources in Modeling Groundwater Contamination Transport: Case Studies in Iraq

Abstract

Modeling of groundwater resource is important for predicting the future behavior of the aquifer and studying the future effect of contamination in the aquifer. The objective of this chapter is to concentrate on MODFLOW Packages used to model groundwater flow and contamination transport and learn more about the capabilities and limitations of MODFLOW Packages, and then some case studies were used to concentrate on the ability of MODFLOW packages. Some MODFLOW Packages were reviewed to check the limitations and strengths of each. Most of the software was developed over time to include the many options to make the user work with it effectively. The results indicated that most MODFLOW Packages are useful for modeling groundwater and predicting the future effect.

1. Introduction

Groundwater is a renewable resource that, when adequately managed, ensures a long-term water supply and mitigates the consequences of anticipated climate changes. It can be used to determine how groundwater might respond to possible stressors brought on by climate change and the impact of human activity. The interdependence between groundwater and other environmental factors has led to the development of simulation models that provide a predictive capability. A vital supply of water for household, industrial, and agricultural purposes is groundwater. Due to fast population expansion, development in all fields of life, urbanization, and industry, as well as a lack of surface water, the usage of groundwater has expanded significantly [1, 2, 3, 4] About 30% of the world’s population uses groundwater for drinking [4, 5]. Groundwater models are utilized to evaluate various conceptual models and determine hydraulic characteristics. They can also be utilized for managing water resources and forecasting aquifer behavior [6]. Using a variety of groundwater models is an effective approach for gathering more thorough information about the issue being studied. Groundwater models can aid in developing a mental knowledge of this phenomenon when properly developed. Furthermore, they must be proven to be valid to accurately recreate the historical behavior of groundwater. They can use these data to forecast future water conditions and recommend the most effective management strategies. They can predict future groundwater behavior, aid decision-making, and facilitate the investigation of different management strategies. However, a “mainstream” model does not automatically indicate that it is the definitive truth, and it is not always totally dependable, as model results are always associated with uncertainty. Thus, the models’ outputs received by decision-makers improve when the modeling incorporates a range of the modeler’s confidence in the outcomes. A model is used to analyze the system underneath water. Numerical models are computationally intensive and more complex than analytical models, yet the analytical models do not require a computer [7]. The initial step is to conduct a formal software selection process to choose the best proposal from a range of options. This transitory phase is often bypassed. Some modelers have quickly adopted MODFLOW [8, 9, 10, 11, 12, 13, 14], a model developed by the USGS, with the primary goal of creating their projects without considering other options. Recently, advanced and powerful modeling tools have become available in numerous user-friendly commercial software packages that are now frequently utilized [7, 15]. A groundwater flow model estimates the water flow rates both within and across the boundaries that are of concern, as well as producing optimal hydrostatic heads and water table levels for unconfined aquifers. It can determine the overall water balance and display the flow rates of a river or stream. In essence, a solute transport model replicates the material confinements that arise during groundwater extraction. The solutes’ (or heat’s) passage through the subsurface (and the system’s boundaries, respectively) can be modeled. Groundwater models can be used to compute the fluxes of water and solutes between the groundwater system under consideration and the neighboring surface water, rivers, lakes, and pumping bores that are associated with source and sink features within the groundwater domain. When it comes to simulating groundwater models, MODFLOW modeling software—rated highly by Hatari Labs—outperforms the competition. The capabilities of MODFLOW allow for the modeling of groundwater movement at the local or large-scale level as well as its interactions with the bodies of water on top of it. Due to MODFLOW’s open-source code (no fees associated with it), false beliefs have been spread regarding the program’s age or lower capacity compared to its counterparts with commercial bases. Every numerical computation aids in simulating and depicting the complex behavior of processes that are observed in nature. Additionally, there is no such thing as the best modeling software; input data and the modeler’s criteria determine the quality of the simulation. A true open-source program permits the unrestricted free download of software for any purpose and at no cost, such as MODFLOW. In the MODFLOW example, the price is not the primary factor in the decision, but this is not to say that it should not be taken into consideration. I signed up for MODFLOW because of its computing power for information conveyance, its seeming simulation method, and its improved discourse on the management of water resources. The following are the main benefits of MODFLOW:

1. Even though it is free, there will not be any costs to you. Being produced by an open-source American government organization, MODFLOW is provided without charge.

2. There is strong scientific evidence for it. Every MODFLOW component has a user manual dedicated to it, which implies that every software component has a user manual as well. The actual physical process may exist in real life and cause the imaginary groundwater to flow into the project’s history. Relevant physical processes to groundwater flow are considered in the experiment's simulated setting according to the manual.

3. MOFLOW is widely supported and upgraded, and it is upgradeable. Its ready-to-use modules allow for the presentation of individual packages, for instance, can be thought of as MODFLOW module add-ons; examples include the local refinement module (LGR) and the unsaturated flow module (UFZ).

4. The MODFLOW calculation technique is based on finite differences. The mechanical regulation maintains what may be called a simulation problem where the aircraft rises and falls, possibly because the perceptual differences induced by the movement of the camera are quite good. This gives it the ability to engage in volume-controlled cell division. The integrated circuit is dependable in a dynamic environment since this control can also be satisfied in certain circumstances. The capacity to implement and uphold precise water storage is time-dependent to prevent leaks in the stored water.

5. The MODFLOW model accurately replicates the physical world associated with groundwater saturation or lowering. The evapotranspiration, a longish hydrologic characteristic parameter that was highly appropriate and practically modeled by MODFLOW, was appropriately performed. It could reject roughly 65% of the groundwater balance, without requiring a lot of processing power. You can get the incomplete package for lakes and rivers, called Interaction, at the code later [7]. The weakness in MODFLOW code: The code cannot be used for constructing geological scenarios, such as steep hydraulic variation in rewetting/drying cells, and has certain restrictions [7]. The reasons why this chapter concentrates on Modflow packages are as follows:

Modflow offers a valuable opportunity to execute intricate evaluations about aquifer head, analysis of groundwater flow, migration of contaminants, and management of water resources.

Modflow software is the primary asset of USGS; however, the broader water geology community has also contributed to a substantial number of supplementary advancements. A significant number of these variations are open source or free, indicating an increase in interactions and innovation among relevant experts in the field.

Modflow can be integrated with various application applications to facilitate image creation, data processing, and the generation of commando plots. The interoperability of this tool is what renders it valuable for the development of comprehensive models and the processing of analysis.

The objective of this chapter is to study the ability of MODFLOW packages to model groundwater flow and contamination transport and the features that make it one of the best software for modeling groundwater. Exclusively examining MODFLOW and its variations in a research paper can provide a concise analysis, present a more lucid and concentrated examination of the model’s advantages and limitations, and offer relevant case studies for practical application.

2. Groundwater flow equation

The mechanism of contamination transport relates to the groundwater flow model. The groundwater flow equation depends on Darcy’s Law and the Mass Conservation Law [16]. The Mass Conservation Law indicates that all water entering and leaving the system is equal.

A three-dimensional groundwater flow equation for the heterogeneous and anisotropic conditions is then presented in (Eqs. (1) and (2)):

$$\frac{\partial }{\partial x}\left(K_x\frac{\partial h}{\partial x}\right)+\frac{\partial }{\partial y}\left(K_y\frac{\partial h}{\partial y}\right)+\frac{\partial }{\partial z}\left(K_z\frac{\partial h}{\partial z}\right)=S_s\frac{\partial h}{\partial t}–\mathrm{W}$$E1

Groundwater flow equation at steady state condition, heterogeneous and anisotropic, is presented in (Eq. (2)):

$$\frac{\partial }{\partial x}\left(K_x\frac{\partial h}{\partial x}\right)+\frac{\partial }{\partial y}\left(K_y\frac{\partial h}{\partial y}\right)+\frac{\partial }{\partial z}\left(K_z\frac{\partial h}{\partial z}\right)=0$$E2

Where:

W: is the volumetric flux per unit volume describing sources/sinks of water ($T^{-1}$).

K: is hydraulic conductivity (L/T).

h: is the hydraulic head (L).

S_s: is specific storage of the porous material ($L^{-1}$).

t: is the time (T).

The groundwater flow equation is numerically solved by MODFOW software.

3. Contamination transport equation

The advection-dispersion equation was developed based on Refs. [17, 18]. Darcy’s Law is applicable since it is assumed that the porous material is homogeneous, fluid-saturated, and isotropic.

The one-dimensional advection-dispersion equation can be modified to account for decay and sorption, and two important global phenomena that might change pollutant concentrations over time are presented in (Eq. (3)):

$$\frac{\partial C}{\partial t}=\left(D_L\frac{{\partial }^{2}C}{\partial x^2}\right)-\left(v_x\frac{\partial C}{\partial X}\right)-\left(\frac{B_d}{\theta }\frac{\partial C^{\ast }}{\partial t}\right)+\left(\frac{\partial C}{\partial t}\right)\mathit{rxn}$$E3

Where:

C: is the solute concentration of the liquid phase (M.$L^{-3}$).

t: is the time (T).

$D_L:$ is the longitudinal dispersion coefficient ($L^2.T^{-1}$).

$v_x$: is the average linear groundwater velocity ($L.T^{-1}$).

$B_d$: is the aquifer bulk density (M.L⁻³).

θ: is the volumetric moisture content or porosity for saturated media.

C *: is the amount of solute sorbed per unit weight of solid (M.$M^{-1}$).

rxn: is a biological or chemical response of the solute indicated by the subscript (other than sorption).

4. Resources for groundwater flow and contamination modeling

Many modern packages are created utilizing a graphical user interface (GUI) that facilitates the creation of input files for the model. These input files can be read by the model code and used to display the model output. The underlying concept shared by all the models, such as Visual MODFLOW, Processing MODFLOW, groundwater modeling system (GMS), and others, all the packages that will explain include MODFLOW code. The sole distinction between these two entities lies in their software, whereas their technology is what renders them identical.

4.1 MODFLOW package

The U.S. Geological Survey (USGS) created the modular finite-difference groundwater flow model (MODFLOW), which was initially made available in 1988 [19]. As a result of its continuous evolution, it is currently the most popular groundwater flow representation program worldwide. It computes to produce heads and flows by reading ASCII files containing the input data (recharge, abstraction, aquifer parameters, boundary conditions, etc.). It is designed specifically for flow simulation using a finite difference grid in saturated porous media. With its user-friendly “Parameter” feature, MODFLOW can perform observation, sensitivity analysis, and parameter estimation, making model setup easy and convenient. Using “Packages,” a broad range of conditions, including numerous recently released new packages, can be represented: With units serving as defined dimensions and hydraulic parameters used to fill the framework model with the model grid, the Hydrogeologic-Unit Flow Package facilitates the link between the hydrogeological framework model and Gridded Logging. The Multi-Node Well (MNW) Package models a reduced pump age to those wells that are next to the pumping well and efficiently distributes fluid to wells that have connections to many model layers (e.g., angled or horizontal wells, nodes). Geometric Multi-Grid (GMG) is about solving these heavy-duty processes efficiently and it was the first part that was written in C language rather than FORTRAN. The package of mathematical models called the Stream Flow-Routing (SFR, substitutes STR) Route streams and lakes water in a way that adjusts the river stage when the stream discharge gets lower; consequently, flow to and from the underground water system adjusts to the new stage. The Subsidence and Aquifer-System Compaction (SUB3) Package is specifically designed to simulate the elastic compaction and development of compressible fine-grained layers. Inelastic compaction in the aquifer is also considered. Sustainable flow packages will be delivered on time. The USGS software package includes various basic pre- and post-processing techniques designed to interact with MODFLOW. Manipulations such as GWCHART, a tool for assessing the agreement between a model and empirical data, and sensitivity analysis, as well as MODEL VIEWER, software for visualizing the contours of simulated models, are performed.

Premium platforms are producers of retail consumer products with a price. You can find these accessible guidelines by searching for the MODFLOW interface using a Web search engine. The specific programs handle input, setup, and result assessment, but they do not have the most up-to-date MODFLOW features, which can result in incorrect output due to user misinterpretation. Familiarizing yourself with MODFLOW files can assist you in problem-solving, utilizing new MODFLOW features, and managing unique modeling situations. The updated online tutorial on the USGS MODFLOW website serves as a quick way to view the appearance of different options or input types. Access Doucs, source codes, and executables of MF2K and its auxiliary programs are for free from the official website of the product producers. MODFLOW 6, an older model, now includes just the GWF (Groundwater Flow Model) hydrologic modeling framework. The current implementation of the GWF Model for MODFLOW 6 using the CVFD method is found on a generalized control volume finite difference (CVFD) technique, which guarantees hydraulic connectivity between a cell and any number of surrounding cells. The original MODFLOW is integrated into a comprehensive groundwater modeling system that includes features for linking groundwater and surface water, solute transport, variable-density flow (such as salt water), aquifer system compaction and land subsidence, parameter estimation, and groundwater management [10].

4.2 Visual MODFLOW

Visual MODLOW is a graphical user interface for a component of the USGS MODFLOW family of water flow models. The product is designed for commercial usage and is favored among hydrogeologists for its user-friendly interface. The software is designed to model groundwater flow and multiple pollutant transfers in different scenarios. Land and pipeline surveys, airfields, constructed wetlands, climate change studies, drought monitoring, Environmental Impact Assessment (EIA), landfills, mining operations, riparian area and floodplain monitoring, saltwater encroachment, soil profile analysis, watershed assessment, and more have been demonstrated in practical applications. The MODFLOW program was developed by the United States Geological Survey (USGS). The program utilizes the finite difference solution method to predict the rate and direction of water and pollutant migration. The software must fall under the category of “free public domain software” to meet the criteria. Adhering to this principle is crucial for the software to be in the public domain. Graphical user interfaces (GUIs) for MODFLOW are already available and gaining popularity in the industry. They can be categorized as industrial and recreational types. The Graphical User Interface for inputting data into the Water Video on Visual MODFLOW is a commercial product. It was introduced on the market as “Waterloo Hydrogeologic” in August 1994. Visual MODFLOW differs from MODFLOW in that it requires input data in the form of text files, which can make the process more complex and time consuming. Visual MODFLOW utilizes Excel data files, Surfer grids, GIS, and AutoCAD data files as input. Flowcharting is a simple and efficient tool that requires less time to execute than other methods. The code can interpret unreadable text and binary output from MODFLOW, and generate visual representations such as contour maps and charts. You can better understand the model’s results and consider them more effectively using this approach. Visual MODFLOW comes in two primary types: Classic and Flex. The former pattern involves a numerical evaluation, whereas the latter utilizes conceptual analysis. The scope includes evaluating the significance of the work completed with visual MODLOW from its inception to the present. The guide will let the reader explore their imagination and demonstrate their newfound enthusiasm to learn more about the software and future research [20, 21].

4.3 Processing MODFLOW

The originator of Processing Modflow (PM) was used for the initial reprint of Model MODFLOW. The model was derived from MODFLOW-88 and designed to simulate the flooding scenario of an abandoned open-pit coal mine. MODFLOW-88 was just launched, leading to the development of many codes that enhance its functionalities or utilize it as the primary flow equation solver. As a result, PM has released multiple updates that include the latest computer codes to streamline the modeling process and empower computational professionals to think more creatively. The following part will introduce the latest version of Processing Modflow, which includes support for system codes. The PMWIN model uses the MODFLOW constant-radius circular-distance finite-difference approach to simulate groundwater flow in the aquifer, which is based on a block-centered finite-difference approach. Zones can be represented as distinct, unrestricted, or resistant entities. External stresses such as wells, areal concentrations, evaporation with transpiration, green water, and blue water are significant contributing variables to the flows. Instrument flying can be simulated in drains, river channels, and river beds to model water flow. The PMWIN 5.3.1 is a free version, the “Processing Modflow X” that allows running supported models and provides a user interface with a map function. The map function includes logos, map basis, shape files, and grids acquired from the internet, along with results from several models. The interface allows users to construct, refine, and execute models, as well as visualize the results.

The PMWIN (Processing Modflow for Windows) model can simulate 1-D and 2-D groundwater flow and pollutants. The model will be simulated using a grid network approach. Additionally, the need to input characteristics for each cell in MODFLOW may result in lengthier processing times compared to other software due to its conceptual nature. PMWIN is recognized for providing comparable results to several other programs [7, 22].

4.4 MT3DMS package

MT3DMS (Modular 3 Dimension Transport Multi-Species) model is a publicly available groundwater model designed for saturated porous media. The current model version incorporates three-dimensional advective-dispersive transport processes along with other basic chemical reactions. Moreover, it serves as the primary module for calculating variable density simulations and running the SEAWAT simulator with sophisticated reaction features. MT3DMS stands out from other solute transport models due to its diverse numerical solution methods for advective transport, as well as the range of boundary conditions and features required to create models that can accurately simulate real flows. The particle-tracking-based solution schemes can achieve nearly dispersion-less results, which has a key benefit compared to other models that may have numerical dispersion due to excessive grid refining.

Since its introduction in the 1990s as the MT3D modular multi-platform simulator for one species, MT3D has become the main tool in the field of transport and fate applications. This approach is quite convenient because it is compatible with MODFLOW. The senses are crucial to us due to their appeal among scholars and daily individuals.

This package prioritizes speed, allowing new users to perform necessary computations quickly. Additionally, it offers comprehensive documentation that includes access to its source code. The MT3DMS source code is written in FORTRAN using a modular up-and-follow coding approach similar to MODFLOW. This model allows for the simultaneous transportation of many species, with each species being exposed to either linear Freundlich or Langmuir sorbents and/or first-order degrading reactions. This excludes reaction periods that are governed by the reaction rates of individual species, which are believed to be unaffected by the concentrations of the other species. The function can be used to calibrate nonreactive traffic models by conducting simulations for different nonreactive species simultaneously. This method is facilitated by a wide array of software programs. Furthermore, a formulation for simultaneous two-phase and multi-phase transport is offered, commonly utilized for simulations of fractured or extremely heterogeneous aquifers. Similar to MODFLOW, MT3DMS does not have a built-in graphical user interface (GUI); hence, the user-friendliness depends largely on the GUI used for data input/output. Conversely, MT3DMS lacks the complete user-friendly functionalities included in the most widely used graphical user interfaces (GUIs) that are compatible with MODFLOW, affecting users [11].

4.5 Groundwater modeling system (GMS) package

GMS is comprehensive software designed for creating computer simulations of groundwater and the movement of pollutants within it. The Groundwater Modeling system (GMS) maintenance is overseen by the Brigham Young University Environmental Modelling Research Laboratory in Utah; however, GMS can be supplied commercially through several suppliers. GMS is used to characterize the site environment, construct models, perform post-processing, calibrate the model, visualize data, and verify the results. The software includes TINs, solids, boreholes, 2D and 3D geostatistics, as well as finite element and finite difference models such as MODFLOW, MODPATH, MT3D, RT3D, FEMWATER, SEEP2D, ART3D, MODAEM, SEAM3D, and UTCHEM for analyzing 2D and 3D domains. Parameter estimates can be conducted using the models such as MODFLOW, PEST, and UCODE.

Users can now select and order individual “modules” to combine them according to their preferences, thanks to this GMS approach. The modules include load, spray, and machine dynamics for pre- and post-processing, optimal model selection, and calibration methods. My expertise is limited to providing summaries of all modules. You may get extensive descriptions of each module and its applications on the commercial vendor’s homepage. Additional users can select a personalized module relevant to their current project and can also incorporate additional ones as their area of interest or job evolves or shifts. The GMS includes a time-saving feature called a “modeling package” that encompasses several applications. It follows the fundamental “conceptual model” approach used by many programs. Upon arrival, you will be presented with a variety of new vocabulary, methods, and protocols that may initially appear challenging to understand. Improving the utilization of easily accessible resources for MODFLOW and FEMWATER modeling programs can be achieved by utilizing higher-quality data sources in water modeling.

The interactive section is also designed using the “conceptual model” method. A user inserts model properties such as boundary conditions, hydraulic conductivity values, 2D and 3D model domain, into a GIS interface of a hybrid GIS system that does not need interaction with simulation programs. Model format properties are transmitted to specific grid cells or mesh elements through the GIS interface by clicking a button. This technique enables quick model substitution, applying previously established indexes to fresh simulations, and evaluating the results. In addition to patching GMS for more precise adjustments, users can effortlessly alter the grid and assign the correct value without requiring the final text file, but it is still recommended to refer to the document to confirm the results. GMS 6.0 provides GIS connectivity with ArcGIS, requiring the user to own an independent ArcGIS license. The modeler can transition smoothly from creating conceptual models to finalizing model outcome figures without disrupting its workflow. GMS is a sophisticated hydrological modeling system that combines various products into one purchase. It includes support for multiple models, connections to ArcGIS, conceptual groundwater modeling, and inversion computation inside a unified environment. Each new edition of GMS should be implemented gradually, taking into account that certain features may need further refinement before the full range of capabilities becomes operational [7].

4.6 Case studies

MODFLOW package abilities can be summarized on some case studies to show the capability for modeling the contamination transport, and predict future effects of aquifers and the variants of MODFLOW.

4.6.1 Case 1: Modeling groundwater flow and nitrate transport in study area in Erbil city Kurdistan region - Iraq

To study the direction of groundwater flow and contamination transport a study area was selected which covers about 579.72 square kilometers within the Erbil basin, the aquifer depth is 400 m, the first layer was silty sandy gravel with a 300 m depth, the second was clay with 25 m depth, and the third layer was silty sand with 75 m depth. Groundwater Modeling System (GMS) version 10.6.2. was used for this purpose. Observation groundwater head for 23 was taken for years 2021–2022. MODFLOW is used to predict the direction of groundwater and MODPATH is utilized to study the direction of groundwater flow and tracking of particles. MT3DMS is used to study the movement of contamination. The study area was divided into 500 columns, 156 rows, and three layers with cell dimensions 100×100 m. The boundary conditions were assumed to be constant from three sides of the model and the fourth side (right side of the model) was a Greater Zab River; the river conductance was calculated for this side which was (2.94 (m²/d)/m), and the initial model head was assumed 434, 134, and 109 m a.s.l., respectively for the (first, second, third) layers. The recharge was assumed to be constant, and the discharge from 1980 to 2016 years was 0.08782 m/year. The surface water elevation of Greater Zab River varied between 242.92 and 219.95 m a.s.l. The concentration of nitrate concentration in landfill leachate was 5264 mg/l, which is considered as the source of contamination in the study area, and the initial nitrate concentration for the study area was 50 mg/l.

The model was calibrated by changing the values of hydraulic conductivity and effective porosity for each type of layer, the results indicated a good correlation between the observed and calculated head, the R² of the model was 0.9917, and the R² for model validation was 0.8387. The value of hydraulic conductivity after calibration for the first layer is 1.4 m/d, for the second layer is 0.0025 m/d, and for the third layer is 1.35 m/d. The effective porosity after calibration for 1, 2, and 3 layers are 0.23, 0.095, and 0.37, respectively. Figure 1 presents the direction of groundwater flow in the first layer. The groundwater flows from the eastern side of the study area toward the western side (Greater Zab River). Figure 2 presents the spread of nitrate in the study area from landfill sites. The nitrate contamination can spread to about 2 km from all sides of the landfill site, the effect of diffusion was neglected because of the effect of advection and dispersion, and dispersion has a high effect on the spread of contamination due to the high permeability of the first layer [23].

Figure 1.

Direction of groundwater flow in the first layer.

Figure 2.

The distribution of nitrate in the study area.

4.6.2 Case 2: Simulation transport from Basra landfill using processing MODFLOW

A conceptual approach was used, the study area (Al-Rafdhia aquifer - Basrah city—Iraq) covers 300 km² with a model thickness of 70 m, the aquifer was unconfined, and the model domain was divided into 100 rows and 100 columns and seven layers with vertical direction with constant thickness (ΔZ) 10 m. The layer’s base is positioned at a depth of 50 meters below the water table to guarantee that all wells fully penetrate the model. There are 10,000 uniformly spaced cells in all. The research area limits contain around 120 wells, which are putting pressure on the aquifer by extracting an average of 200 m³/day each. These wells are the primary supply of fresh water for the agricultural areas in the region. Table 1 presented aquifer parameters in the study area [24].

Parameter	Value
Hydraulic conductivity Kxy (m/d)	90
Hydraulic conductivity Kz (m/d)	50
Total porosity (%)	32
Effective porosity (%)	28
Specific yield	0.25
ɣs: Average soil dry density (Kg/m^3)	1.78
αL: longitudinal dispersivity (m)	15
αT: transverse dispersivity (m)	1.5
αv: vertical dispersivity (m)	0.15
Fluid viscosity for water (kg.m/sec)	0.001

Table 1.

Original parameters of the aquifer for Al-Rafdhia aquifer.

The model allocated a constant pollutant concentration (15,250 mg/l) to the landfill location as a boundary condition due to the landfill bed level being at or below the constant groundwater levels at the borrow pits. The chloride concentration was selected as the constant concentration source for modeling among the listed pollutant characteristics. Rainfall and return flow are the sources of recharge, with 20% of infiltration coming from rainfall, estimated at 30.4 mm/yr. The simulation prediction for a total of 15 years, from 2016 to 2031, is divided into 15 periods of stress. Figure 3 displays the simulation of groundwater levels as a steady state for the year 2016. The data presented in Figure 3 show a linear drop-in beginning water levels from the southwest to the northeast toward the Shatt-Al-Basrah drain river, with an average hydraulic gradient of approximately 0.0009. The natural groundwater flow in the research area is directed toward the Shatt-Al-Basrah Drain River [24].

Figure 3.

Direction of groundwater flow [24].

The results indicated that pollution transport in the aquifer at 285 m/year, the simulation results reveal that by 2031 the pollutant spread to about 4 km from the landfill site with about 60 m depth as presented in Figure 4, and the three-dimensional transport is presented in Figure 5 [24].

Figure 4.

Spread of contamination after 15 years in the study area [24].

Figure 5.

A three-dimensional model for contamination transport in the study area [24].

4.6.3 Case 3: Simulation groundwater flow and contamination transport of radioactive Cobalt-60 from nuclear facility - Iraq

The Al-Tuwaitha Nuclear Research City is located around 3 km from the city of Baghdad, Iraq. It is situated to the south of the southern edge of Baghdad, across the Tigris River to the east, at a distance of about 0.8 km. A three-dimensional groundwater flow model was utilized for a study area measuring 2925×4350 m at the Al-Tuwaith site in Baghdad, with a grid spacing of 75 m. Three layers of soil, including light brown clay (LB1), gray silt to fine sand (MSG), and gray medium sand (MMS), are being analyzed based on their thickness. The mean ground surface elevation is 31.2 meters above a specific reference point. The aquifer system in the study site area is unconfined. The west side of the city faces the Tigris River, whereas the east side, near the Euphrates, has a definite head border. The data from the Tigris River between 2000 and 2015 show that the upper, average, and lowest water stages were 30.70, 29.15, and 27.60 meters above sea level, respectively. The initial boundary condition assumed the water table was fixed at a level of 25.50 meters above sea level (m.a.s.l.). Table 2 displays the horizontal hydraulic conductivities, bulk densities, and effective porosities of soils corresponding to the soil types of three levels, reflecting the features of each layer.

Layer.	Depth m	Soil	KH cm/s	Bulk density kg/m^3	Effective porosity %
1	16	Light brown clay	10^−8–10^−5	1200–1500	1–18
2	10	Gray silt to fine sand	10^−5–10^−3	1400–1600	1–39
3	24	Gray medium sand	10^−3–10^−1	1600–1700	16–46

Table 2.

Properties of the aquifer in the study area.

The groundwater flow is analyzed in a 12.70 km² study area using a computer model to determine the discharge from the river under two water surface scenarios: Tigris River at 29.20 m.a.s.l. (Scenario 1) and 27.60 m.a.s.l. (Scenario 2).

In this study, The MT3D model was used in this investigation to track the movement of the Co-60 plume. The estimated quantity of radioactive waste at the Al-Tuwaitha site in Iraq was around 1.0 metric tons. The dissociation rate of Co-60 into groundwater was determined to be 0.6 × 10 − 6 μg/s/m² due to the recalculation rate of 2.19 × 10⁻⁵ m/day being introduced into the aquifer. The longitudinal dispersivity (αL) of the modeled aquifer in the research area is 5.0 m, while the transverse dispersivity (αT) ranges from 0.05 to 0.5. For this investigation, αT is considered to be 10% of αL. The model’s length was 1200 meters. In this model, the initial state is treated as Co-60 being equivalent to 0 mg/L. After 10 years of simulation, the dispersion of Co-60 concentrations will be taken into account. A simulation using an MT3DMS model will track the regional migration of Co-60 from the LAMA Nuclear Facility over a 10-year timeframe. The study utilized a MOC approach and a first-order Euler solution scheme for the particle tracking algorithm, with a value of 70 for 0.01 cu. m/kg. The time frame was established in the same year, 2016.

Groundwater flow in a 12.70 km² research area was analyzed using two scenarios of water surface change in the Tigris River: Scenario 1 at 29.20 m.a.s.l. and Scenario 2 at 27.60 m.a.s.l. Three fully penetrating wells were developed as a pollution barrier on the southern side of the boundary.

The institution’s model of MODFLOW (PMWIN and MT3DMS) was dominant under the steady state condition for an extended period. The optimal value was obtained by entering (5 × 10⁻⁷, 5 × 10⁻⁴, and 3 × 10⁻² cm/s, respectively) for the vertical hydraulic conductivity of the three layers. The porosity values were 0.16, 0.28, and 0.35, respectively.

The average hydraulic conductivity of sandy deposits varied from 0.05 to 5.0 ft./day, clayey layers ranged from 0.01 to 121 ft./day, and coarse-grained sand, gravel, and boulder deposits ranged from 0.05 to 5.0 ft./day. The estimated net groundwater flow values were 1.34 ft³/s (0.037 m³/s), and the measured value was 5.4 ft³/s (0.144 m³/s). The arithmetical groundwater flow and the steady-state water level matched the calibrated steady-state simulation in their response to the horizontal hydraulic conductivity, which was identified as the main factor influencing the steady-state water levels and flow conditions. Thus, by utilizing a trial-and-error approach and considering aquifer features, each pump was found to provide 0.015 m³/s of water, ensuring that the exclusion region was inside the catch zone surrounding the pumping wells. PMWIN-PRO and PMPATH were the software applications used to execute the model, perform calculations, and identify the capture zone of the wells. Figures 6 and 7 present the groundwater flow direction of Scenarios 1 and 2, respectively, with flow toward the Tigris River [25].

Figure 6.

Groundwater flow equipotential contour lines for scenario 1 [25].

Figure 7.

Groundwater flow equipotential contour lines for scenario 2 [25].

3D model parameters generated nearly identical Co-60 results in the study area using both methods. The average flow velocity of the groundwater was around 3.2 × 10. The final Co-60 maximum level statistic indicates that the primary transport of contaminants is influenced by water velocity in the porous rock. This slow movement is caused by the sorption effect and high retardation factor of Co-60, which is dependent on the partition coefficient. They are the indications of Earth’s history based on the cosmic events that have taken place. The concentration of Co-60 was projected to decrease with time with depth usage, reaching a peak of 37.31 μg/m³ after 10 years as shown in Figures 8 and 9.

Figure 8.

Distribution of contamination in the study area for scenario 1 after 10 years [25].

Figure 9.

Distribution of contamination in the study area for scenario 2 after 10 years [25].

5. Conclusion

Groundwater modeling software is important for the simulation of groundwater flow and contamination, which helps to give estimation for users to predict the behavior of the aquifer. This chapter concentrates on some packages such as MODFLOW, MT3DMS, groundwater modeling system (GMS), Visual MODFLOW, and Processing MODFLOW. Some of them such as groundwater modeling system, and Visual MODFLOW are more popular than other software due to easy use, and learning but most of software developed over time to include different features.