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CURSO BÁSICO DE MODELAGEM COM VISUAL MODFLOW FLEX Cursos Profissionais WST Apostila Prática Maio de 2021 © Waterloo Hydrogeologic Page 1 Visual MODFLOW Flex Exercise – Intro 1 An Introduction to Groundwater Flow and Contaminant Transport Problem Description The site is in an industrial park that has a leaky underground storage tank (UST) holding unleaded gasoline (illustrated in the figure below). The site is 200 meters by 150 meters by 30 meters deep, with the groundwater flow direction from left to right (west to east). Exercise Objectives • To create a groundwater flow model using Visual MODFLOW Flex and visually examine the results of your model using contours of hydraulic head, particle pathlines, and velocity vectors • Use Visual MODFLOW Flex to build a contaminant transport simulation and view the results using contours, color shading, and a concentration breakthrough curve from an observation well that you will add to the model. • Assign a remediation pumping well to assess the option of a pump and treat remedial measure. • Examine model results using state-of-the-art 3D graphics technology. Utilizing Visual MODFLOW Flex, you will create 3D volumetric shapes that represent contaminant plumes changing over time. H e a d = 2 6 .5 m H e a d = 2 9 .5 m X = 200m, Y = 150m ➔ X = 0m, Y = 0m © Waterloo Hydrogeologic Page 2 Visual MODFLOW Flex Exercise: Intro1 Terms and Notations For the purposes of this tutorial, the following terms and notations will be used. (This assumes you are using a right-handed mouse.) type - type in the given word or value ↔ - press the <Tab> key - press the <Enter> key - click the left mouse button where indicated - double-click the left mouse button where indicated Starting Visual MODFLOW Flex On your Windows desktop, you will see an icon for Visual MODFLOW Flex Visual MODFLOW Flex to start the program. The following Visual MODFLOW Flex window will appear: © Waterloo Hydrogeologic Page 3 Visual MODFLOW Flex Exercise: Intro1 PART 1: CREATING A GROUNDWATER FLOW MODEL Section 1: Project Settings To create a new project: File / New Project… from the top menu bar A Create Project dialog box will be displayed prompting you to enter the project name of the new Visual MODFLOW Flex project. Type: Intro1 as the project name Browse button under Data Repository Select a directory on the hard drive (or use the default location) Note: By default, new Visual MODFLOW Flex projects will be saved to the following location - [C:\Users\<username>\Documents\Visual MODFLOW Flex\Projects] The default units are appropriate and do not need to be changed. OK button in the lower right corner of this window The following window will then appear: © Waterloo Hydrogeologic Page 4 Visual MODFLOW Flex Exercise: Intro1 The Select Modeling Scenario allows you to choose whether to proceed with the Conceptual or Numerical modeling workflow. The conceptual modeling workflow allows you to import all data objects into Visual MODFLOW Flex and to build a conceptual site model (CSM). The CSM can then be used as a starting point for several different numerical models. In other words, numerical model (i.e. with different grid types, engines, etc.) can be quickly and easily created based on the same conceptual modeling. This makes it easy for the user to manage several different numerical models with slight variations. Conceptual modeling is not covered in this exercise, so we will proceed with the numerical modeling workflow: Numerical Modeling Proceeding with the numerical modeling workflow will bring you to the first step in the that workflow, which is to define your model objectives. This step allows you to specify whether you will be running a fully saturated or variably saturated model, whether contaminant transport will be included, which flow/transport engines will be utilized, etc. You will see the following window open: © Waterloo Hydrogeologic Page 5 Visual MODFLOW Flex Exercise: Intro1 We will retain most of the default settings in this step, but we will change the start date: Wednesday, January 1, 2014 (select from dropdown menu) We will keep the default flow parameter values. [Next Step] proceed to the next step in the workflow The Define Numerical Model workflow step will appear, allowing you to select whether to import an existing grid or create a new one. We will create a new grid in this exercise: Create Grid This will bring you to the ‘Create Grid’ step in the numerical modeling workflow. At this step you will specify the boundary/extents of your model and the structure of your model’s grid. Your screen should look like the image below: © Waterloo Hydrogeologic Page 6 Visual MODFLOW Flex Exercise: Intro1 Section 2: Define Model Grid Now you will specify the number of rows, columns, and layers to be used in the model. Under the ‘Grid Definitions’ frame, enter the following model rows, columns, layers and depth information in the appropriate boxes: Rows = 30 Columns = 40 Xmin = 0 Xmax = 200 Cell width = calculated this value can be adjusted as per project requirements Ymin = 0 Ymax = 150 Cell height = calculated this value can be adjusted as per project requirements For this exercise, you will ignore the option “Calculate extents from a polygon object”. Next, specify the parameters for the vertical grid discretization: Type: 10 For the Number of Layers Specify the layer Elevations (typing the values directly into the grid): © Waterloo Hydrogeologic Page 7 Visual MODFLOW Flex Exercise: Intro1 Layer1 - Top: 30 (replace 100) Layer2 - Top: 27 Layer3 - Top: 24 Layer4 - Top: 21 Layer5 - Top: 18 Layer6 - Top: 15 Layer7 - Top: 12 Layer8 - Top: 9 Layer9 - Top: 6 Layer10 - Top: 3 Layer10 - Bott: 0 The screen should now look like the image below: Create Grid Click the ‘Create Grid’ button at the top-right © Waterloo Hydrogeologic Page 8 Visual MODFLOW Flex Exercise: Intro1 [Next Step] proceed to the next step in the workflow Visual MODFLOW Flex will then construct a 40 columns x 30 rows x 10 layers finite difference grid with uniform grid spacing in both the X and Y directions, and will automatically create the model run Input tree structure. By default, you will be taken to the View Grid step as shown in the following image: The ‘View/Edit Grid’ portion of the workflow allows the user to make any necessary changes to the grid structure. This is particularly useful if you are following the conceptual modeling workflow and would like to test slight variations in the grid structure. Since we’ve just created this grid and do not require any changes we will proceed to the next step in the workflow, ‘Define Properties’. Section 3: Define Properties [Next Step] proceed to the next step in the workflow Under the ‘Toolbox’ in the main working window, ensure that conductivity has been selected from the first dropdown menu. © Waterloo Hydrogeologic Page 9 Visual MODFLOW Flex Exercise: Intro1 Conductivity from the list menu under the Toolbox Edit option under the Toolbox The default property values will be displayed in the Conductivity dialogue box. For this simple model, we will assume all grid cells have the same hydraulic conductivity (values are defined in m/s) Type: 2e-05 for Kx under Layer 1, Row 1, Column 1 (or F2) to assign this value to the entire column Type: 2e-05 for Ky under Layer 1, Row 1, Column 1 (or F2) to assign this value to the entire column Type: 2e-06 for Kz under Layer 1, Row 1, Column 1 (or F2) to assign this value to the entire column OK to exit the dialogue window Now we will change the storageparameters of the model. Storage from the list menu under the Toolbox Edit option under the Toolbox Change the storage parameters as follows; Type: 0.15 for Sy Specific Yield (dimensionless) (or F2) to assign this value to the entire column Type: 0.001 for Ss Specific Storage (1/m) (or F2) to assign this value to the entire column Type: 0.15 for Ep Effective Porosity (dimensionless) (or F2) to assign this value to the entire column Type: 0.20 for Tp Total porosity (dimensionless) © Waterloo Hydrogeologic Page 10 Visual MODFLOW Flex Exercise: Intro1 (or F2) to assign this value to the entire column The edit property dialogue box should look like the figure below: OK to accept these storage values Now is a good time to save the project. File/Save Project from the main menu Section 4: Add Basemap You will select a shapefile to be used as a background base map for your model. File / Import Data… from the main menu A ‘Data Import’ window will open, Select ‘Dxf’ in the ‘Data Type’ list menu […] button next to ‘Source File’, to browse to the data import file Browse to the location where you downloaded the ‘Supporting Files’ folder ‘basemap.dxf’ in your project directory Open to open the data file Next >> to accept default settings Next >> to accept default settings Finish to import the map object The new data object will appear as the last item in the data tree. We can view the basemap in a new 2D Viewer window: Right-click on ‘Basemap’ in the ‘Data Tree’ 2D Viewer from the menu © Waterloo Hydrogeologic Page 11 Visual MODFLOW Flex Exercise: Intro1 The basemap will become visible in a new view window which appears as a new tab. To change the background colour of the 2D viewer: Right-click anywhere within the window Background colour from the pop-up menu Select: Grey OK Your display should look like the figure below: Close the viewer window by selecting the ‘X’ in the tab labelled ‘2DViewer -1’. Section 5: Input of Boundary Conditions The following section of the exercise describes some of the steps required to assign the various model boundary conditions. Ensure that you return to the ‘NumericGrid1-Run’ tab and close the 2D viewer tab to continue. Assigning Constant Head [Next Step] proceed to the next step in the workflow © Waterloo Hydrogeologic Page 12 Visual MODFLOW Flex Exercise: Intro1 To view the model grid in relation to the basemap, check mark the basemap data object from the tree. Basemap activate the basemap by clicking from the ‘Data Tree’ Right-click anywhere within the window Background colour from the pop-up menu Select: Grey OK To assign a constant head boundary ensure that this boundary condition type is selected from the ‘Toolbox’: Constant Head under the toolbox You will use a constant head boundary to represent the heads along the east and west sides of the model. From the toolbox menu: Assign under the toolbox Polyline from the menu that appears You will assign a vertical line coinciding with the equipotential of 29.5 m on the left side of the domain. Move the mouse-pointer to the upper-left corner of the grid Left-click the center of the cell Move the mouse-pointer to the lower-left corner of the grid (you should see a red line being drawn) Right-click the center of the cell. A small menu will appear after completion of drawing the line: Click Finish from the menu that appears. The Define Boundary Conditions dialog will appear. Next >> we will keep the default name Enter the following values: Starting head = 29.5 (or F2) to assign this value to the entire column Ending head = 29.5 (or F2) to assign this value to the entire column Since the model is steady-state (boundary condition values do not change over time), no time values are required. The Define Boundary Condition window should look like the figure below: © Waterloo Hydrogeologic Page 13 Visual MODFLOW Flex Exercise: Intro1 Finish to confirm and create this constant head boundary condition A set of red points will now fill the selected cells, indicating that a constant head boundary value has been applied. Now assign a constant head boundary to the right (east) side of the model in a similar fashion. Assign under the toolbox Polyline from the menu that appears Move the mouse-pointer to the upper-right corner of the grid Left-click the center of the cell Move the mouse-pointer to the lower-right corner of the grid (you should see a red line being drawn) Right-click the center of the cell. A small menu will appear after completion of drawing the line: Click Finish from the menu that appears. The Define Boundary Conditions dialog will appear. Next >> Enter the following values: Starting head = 26.5 (or F2) to assign this value to the entire column Ending head = 26.5 (or F2) to assign this value to the entire column Finish to confirm and create this constant head boundary condition © Waterloo Hydrogeologic Page 14 Visual MODFLOW Flex Exercise: Intro1 The constant head cells on the right edge were automatically moved down to the second model layer (Layer 2). Visual MODFLOW Flex’s "smart" interface recognizes that the assigned head (26.5 m) is below the bottom of the first model layer (elevation = 27.0 m), which is not permitted by MODFLOW. Visual MODFLOW Flex takes care of this automatically. Type: 2 under Layer to display You will see the line of constant head cells on the right side of the model domain. Now you will examine the model in cross-section to verify the location of these boundary condition cells: Row from the list of available views By default, Row 1 will be shown in the cross-section view. You can see that the constant head has been assigned to the cells in the second layer (red cell on the right side). To view the model in more detail, you can apply a vertical exaggeration factor. The following screen will appear: © Waterloo Hydrogeologic Page 15 Visual MODFLOW Flex Exercise: Intro1 Assigning Recharge The annual recharge to the water table at the site is approximately 150 mm/year. Recharge must be assigned in the Layer view, specifically to Layer1. □ Row from the list of available views (remove the checkbox) Type: 1 under the Layer to display Follow the steps below specify the annual recharge in layer 1. Change the Boundary condition type to Recharge under the Toolbox Recharge from the list of available boundary conditions Assign button, under the Toolbox Entire Layer from the menu that appears The Define Boundary Condition window will appear. Next >> Recharge (mm/yr) = 250 (or F2) to assign this value to the entire column Ponding (m) = 0 © Waterloo Hydrogeologic Page 16 Visual MODFLOW Flex Exercise: Intro1 (or F2) to assign this value to the entire column Static select this from the menu for ‘Schedule’ The Define Boundary Condition window should look like the figure below: Finish to confirm and create this recharge boundary condition Upon completion, you should see a set of white points in all the cells in layer 1, indicating that the cells belong to RechargeZone1; feel free to click on the Database button, to see the list of Recharge zones and corresponding values. Now is a good time to save the project. File/Save Project from the main menu Section 6: Adding Particles [Next Step] proceed to the next step in the workflow The next step in the workflow is to select a type of run (single or PEST run), but there are a few optional tasks to complete beforeselecting the run type, such as assigning tracking particles, ZoneBudget zones or observation wells. You will be presented with a choice screen with several options. Define Particles First, turn on the basemap in the viewer window © Waterloo Hydrogeologic Page 17 Visual MODFLOW Flex Exercise: Intro1 Basemap from the data tree You will place particles in a vertical line down-gradient of the contaminant source in order to examine their pathlines later. Particle pathline analysis is a useful tool in rapidly assessing the risk potential to down-gradient receptors from a groundwater contamination plume. There are several ways of assigning particles. The user can manually select points where particles will be placed, place a circle of particles around a single point, or use an imported data object to specify the origin of the particles. We will use the imported data object option in this exercise. First you must import the particles from XYZ points defined in an excel file. File a dropdown menu will appear Import Data… from the menu Point from the data type dropdown menu […] to browse to the correct file A dialogue box opens that allows you to browse for the appropriate file. In the project directory choose the following file: Particles.xlsx Open Next >> from the Data Import window Next >> accept the defaults in the Data Import Window Next >> accept the defaults in the Data Import Window Next >> accept the defaults in the Data Import Window Finish You should see a new ‘particles’ data object appear in the data tree, in the top left corner of the window. From the main window, under the “Toolbox” Assign Using Data Object from the pop-up menu The following window will appear: © Waterloo Hydrogeologic Page 18 Visual MODFLOW Flex Exercise: Intro1 At this step, you choose the desired points data object and convert these into particles. Particles select the points data object from the data tree under ‘Select Point Object’ Forward select forward as the particle type The window should appear as follows: OK to accept the default settings and create the particles The particles should now appear as points, in the layer view. These are located along column 11 in the grid, as shown below: © Waterloo Hydrogeologic Page 19 Visual MODFLOW Flex Exercise: Intro1 Now is a good time to save the project. File/Save Project from the main menu Section 7: Running MODFLOW and MODPATH You are now ready to perform the groundwater flow and particle pathline simulation by running MODFLOW 2005 and MODPATH. From the top of the main workflow window, [Next Step] proceed to the next step in the workflow You will be presented with an option to Select Run Type Single Run You will be prompted to select which engines to run. By default, MODFLOW-2005 should already be selected; you also need to include MODPATH in the model run: MODPATH from the list of available engines © Waterloo Hydrogeologic Page 20 Visual MODFLOW Flex Exercise: Intro1 [Next Step] proceed to the next step in the workflow The translation settings will appear; this allows you to adjust solvers and their parameters (number of iterations, head-change criterion, damping factors), package settings, output control, etc.. In the future, you might wish to increase the maximum number of iterations if the model does not converge. For now, we will simply use the default settings. The model run is setup as a steady-state simulation. You can see this defined as follows: Settings under MODFLOW-2005, in the settings tree Type: 3650 for steady-state simulation time The MODFLOW-2005 settings tree should look like the figure below: Note: The ‘Steady-State Simulation Time’ is not used if you have selected Transient Flow. However, a number must still be entered. Although the simulation will always be run to the same equilibrium solution in Steady State, the total amount of water passing through boundary conditions depends on the amount of time simulated. For example, Zone Budget analysis of a Steady State solution would be affected by the simulation time, whereas regional head values would not. You are now ready to create the input files (packages) for MODFLOW and MODPATH. button located on the workflow toolbar Visual MODFLOW Flex will now create the files necessary to run the USGS MODFLOW and MODPATH programs. You will see a progress of the Translation, which should take approximately 5-10 seconds. Once complete you will see ‘Translation Finished’ at the bottom of the translation log details window. [Next Step] proceed to the next step in the workflow button located on the workflow toolbar © Waterloo Hydrogeologic Page 21 Visual MODFLOW Flex Exercise: Intro1 The numeric engines will start running and display progress in the main window. MODFLOW-2005 will run first followed by MODPATH. Each engine will have an information window that displays simulation results and progress. Clicking on the tab of the respective window will enable you to view detailed results of each run. The model run should take approx. 10-30 seconds. Once completed, you should see a few new objects appear in the model explorer tree, under “Outputs / Flow” • Heads • Drawdown • Fluxes • Water Table • Forward Pathlines Section 8: Output Visualization [Next Step] proceed to the next step in the workflow You will be presented with an option to View Results, and select the desired results type © Waterloo Hydrogeologic Page 22 Visual MODFLOW Flex Exercise: Intro1 View Maps The head equipotential lines for your simulation will be displayed initially by default. Take a moment to review the range of calculated head values over layer 1; note that as you mouse over the Layer view of the grid, the values in the status bar at the bottom of the window, will display the X,Y position of the mouse cursor, along with the layer, row, and column for the cell and the calculated head value for that cell. Notice the olive-colored cells on the right of the model, which indicate cells that are “dry”. Dry cells occur when the calculated hydraulic head is below the bottom of that particular cell (thus representing the unsaturated zone). To better visualize and understand what is meant by dry cells, we will view the model in cross-section. Row from the list of views Type: 15 under the Row, to display row 15 □ Layer to remove from the list of views © Waterloo Hydrogeologic Page 23 Visual MODFLOW Flex Exercise: Intro1 Also, we will turn on the calculated water table location for the model. Locate the Model Explorer, and the items under “Outputs/Flow” in the lower right corner of the window: Water Table from the model explorer tree, under Outputs/Flow The water table will appear as a solid blue line. Now decrease the Vertical Exaggeration of the Row view to improve the display: Type: 5 under Exaggeration (located above the 2D View) We can now see the equipotential lines from 29.5 m on the left to 26.5 m on the right. Examination of column 38 shows that the water table near the down-gradient boundary, is located entirely below the bottom of Layer 1, thus causing MODFLOW to treat these cells in Layer 1 as dry. You can see that in the adjacent cell, Layer 1, Column 37, the calculated head is 27.1, which is just above the cell bottom of 27.0 m (you can see these values in the status bar by placing the mouse cursor in the cell to the left of the dry cell, in layer 1.) Section 9: Viewing Particle Pathlines To see the results of the particle tracking pathline simulation, you must set the Pathlines visible in the model tree: © Waterloo Hydrogeologic Page 24 Visual MODFLOW Flex Exercise:Intro1 Forward Pathlines from the model explorer tree, under Outputs/Flow This will display the pathlines of the forward tracking particles that you specified. You may scroll through the various rows of the model domain, by using the up/down arrows under rows. In addition, you may turn on the 3D view, to see the color maps of heads and pathlines. This completes Part 1 of the Intro exercise. In Part 2 of this exercise, you will set up and run a contaminant transport simulation using MT3DMS. Now is a good time to save the project. File/Save Project from the main menu © Waterloo Hydrogeologic Page 25 Visual MODFLOW Flex Exercise: Intro1 PART 2: RUNNING A TRANSPORT SIMULATION USING MT3DMS In this section, you will simulate the transport and fate of a dissolved-phase groundwater contaminant plume. The evolution of the contaminant plume will be simulated for a ten-year period. Section 10: Setting Up a Transport Model Define Modeling Objectives from the workflow tree In the right side of the window, you can define the settings for the Transport Model run. Transport Active add a check box beside this setting Next you will define the sorption and reaction options. Using the settings in this window, you can: 1. Select the desired sorption and reaction options 2. Add and remove chemical species 3. Set the initial concentration of those species 4. Set transport and reactive parameters used in the transport calculations. In this example MT3DMS v.5.3 will be used as the transport engine. By default, you will be viewing the ‘Species Parameters’ tab. Under default initial concentration (SCONC), you will see this is set as 0 mg/L. This means that the initial concentration in every cell is zero. If you wanted to alter this value it could be done at this time. Otherwise you can define spatially distributed initial concentrations at the Define Properties step. For this simulation, you will use the default value of 0 mg/L. Section 11: Creating a Refined Grid Before assigning the concentration source, it is important to create a more refined grid in our area of interest, where predictions will be made of plume concentration. This will allow us to improve the accuracy of the simulated plume and therefore better predict the ultimate fate of the groundwater contaminant. Fortunately, Visual MODFLOW Flex allows us to create multiple numerical representations for the site, and derive the inputs for each numerical model from the conceptual objects that were generated while drawing the property zones and boundary conditions in Part 1 of this exercise. From the model explorer tree, locate the ‘Simulation Domain’ folder. Under this, find the item Model Domain. Right-click on NumericGrid1 from the workflow tree Edit Numerical Grid… from the menu that appears © Waterloo Hydrogeologic Page 26 Visual MODFLOW Flex Exercise: Intro1 A Grid Refinement window will appear. Enter the following values, under the ‘Grid Edit Details’ tab: Type: RefineGrid for the New Grid Name Type: 10 for From Type: 20 for To Type: 2 row(s) with Apply grid edit to apply this row refinement Once finished, the display should appear as below. © Waterloo Hydrogeologic Page 27 Visual MODFLOW Flex Exercise: Intro1 The rows between the 2 selected gridlines will automatically double. Now, we must perform the same task to the columns in the model. Edit Columns from the top left of the window Enter the following values, under the ‘Settings’: Type: 10 for From Type: 20 for To Type: 2 row(s) with Apply grid edit to apply this row refinement The number of columns between these 2 gridlines should automatically double. Once completed, your grid should look like the following figure: OK to apply the grid edits and close the window Please note that a whole new file structure has been generated within the Model Explorer, as shown in the image below: © Waterloo Hydrogeologic Page 28 Visual MODFLOW Flex Exercise: Intro1 The new refined grid will be automatically populated with the property zones and boundary conditions as defined in the original model run. You will also notice that a new tab is generated within the Visual MODFLOW interface, named ‘RefineGrid-Run1’. This new tab contains the workflow associated with the new refined grid. This tab will open automatically and you should be redirected to the Define Model Objectives step associated with the new workflow. We won’t make any changes to the grid structure, so let’s proceed to the Define Boundary Conditions step: Define Boundary Conditions from the Worflow menu Now is a good time to save the project. File / Save Project from the main menu Section 12: Adding the Contaminant Source Concentration You are now ready to represent the contaminant source by assigning a constant concentration to the cell where the storage tank is located (in Layer 3). Change the Boundary condition type to Constant Concentration under the Toolbox Constant Concentration under the Toolbox Type: 3 under Layer to view layer 3 © Waterloo Hydrogeologic Page 29 Visual MODFLOW Flex Exercise: Intro1 This is the model layer associated with the location of the leaking storage tank. We will need to view the basemap in order to assign the contaminant source to the correct location. Basemap under the Data Tree You should now zoom into the storage tank area using the tools at the top of the 2D viewer window. to zoom to a box Digitize a box around the storage tank so that this becomes more visible. Left-click in the region of row 17, column 8 While holding the button: Pan the mouse to row 24, column 15 Release the button. The viewer window should look like the following: Assign button under the Toolbox Polygon from the menu that appears © Waterloo Hydrogeologic Page 30 Visual MODFLOW Flex Exercise: Intro1 Assign the constant concentration boundary condition by digitizing a polygon on top of the circular storage tank, using the left mouse button to assign vertices where necessary. Double-click to close the polygon and then right-click in the polygon. A small menu will appear after completion of drawing the polygon: Finish from the menu that appears The Define Boundary Condition dialog will appear: Next >> Type: 250 for Conc001, replacing the -1 value (or F2) assigns this value to the entire column You will assume that the solubility limit will be maintained for the duration of the simulation. Finish © Waterloo Hydrogeologic Page 31 Visual MODFLOW Flex Exercise: Intro1 You should see a few new points appear on top of the circle in the layer view, which indicates that those grid cells have a Constant Concentration boundary condition assigned to them. Section 13: Adding a Concentration Observation Well [Next Step] proceed to the next step in the workflow The Select the Next Step window will appear Define Observation Wells In order to see how the plume concentration changes over time down-gradient from the source of contamination, you will add a monitoring well. Later, you will use this monitoring well to assess plume concentration at this point by displaying a concentration versus time breakthrough graph. The well location must be imported from an excel file. File / Import Data… from the main menu A Data Import dialog box will appear. Well from the data type drowdown list […] to browse to the correct file A dialogue box opens that allows you to browse for the appropriate file. In the project directory (C:\VMODFlex\Intro1\), choose the following file: Conc_obs_well.xls Open Next >> from the data import window Next >> in the preview window The followingwindow will appear: © Waterloo Hydrogeologic Page 32 Visual MODFLOW Flex Exercise: Intro1 In this window, you define what well data to import. Under the “Select the type of data you want to import” Well heads with the following data from the top left of the window Observation points Observed concentrations Once done correctly, you should have the following options defined © Waterloo Hydrogeologic Page 33 Visual MODFLOW Flex Exercise: Intro1 Next >> from the data import window Next >> in the preview window Observation points tab at the top of the data import window Conc Obs. Map to field for Concentration Time Map to field for Concentration observation data Next >> in the preview window Finish A new data object, conc_obs_well will appear in the model tree conc_obs_well from the Data Tree button under the Toolbox in the main window A concentration observation well will appear as a point down-gradient of the source area. However, it will be displayed in Layer 3 corresponding to the vertical observation point (e.g. screen elevation). Type: 3 under Layer to change view to layer 3 Concentration Observations in the Model Explorer Since well OW-1 is an observation well, you have entered a zero concentration. If this well were used as a calibration point to calibrate (qualify) the results of a contaminant transport simulation, you would enter the actual contaminant concentrations measured at the site, over several periods of time. Now is a good time to save the project. File / Save Project from the main menu © Waterloo Hydrogeologic Page 34 Visual MODFLOW Flex Exercise: Intro1 Section 14: Assigning Dispersion Properties Define Properties option in the Workflow tree Change the Parameter group to Dispersion under the Toolbox Longitudinal Dispersion from the menu under Toolbox Edit… Change the default Dispersion to 2.0. Type: 2.0 in the Dispersion column (or F2) assigns this value to the entire column OK The ratio of the horizontal and vertical dispersivity to the longitudinal dispersivity has default values assigned for this model; default value for Horiz/Long. Dispersivity is 0.1; default value for Vert./Long Dispersivity is 0.01. These values are assigned for all layers in the model and do not need to be adjusted for this exercise. Section 15: Running MT3DMS You are now ready to run MT3DMS. Navigate to the Single Run step in the workflow, Single Run option in the Workflow tree Run Transport Engine to include this engine in the model run Select MT3DMS from the transport engine dropdown menu [Next Step] proceed to the next step in the workflow Settings under the MODFLOW-2005, in the Settings Tree Type: 3650 for Steady-state simulation time © Waterloo Hydrogeologic Page 35 Visual MODFLOW Flex Exercise: Intro1 Next setup the MT3DMS option General under MT3DMS, in the Translation settings tree The first line contains the Porosity options. By default, the “Effective” porosity option is selected. Total for the Porosity option MT3DMS allows you to select the solution method for the advection component of the transport equation. Depending on the situation, each solution method presents advantages and disadvantages. For this exercise, you will select the Upstream Finite Difference, which based on trial- and-error has proven to reduce the amount of numerical dispersion in this exercise. Solution Method under MT3DMS, in the Translation settings tree You will see the Solution Method settings on the right side of the window. Yes for the Use Implicit GCG Solver Although the flow field is steady-state, you will run a transient transport simulation to see the evolution of the plume with time. This requires that you specify the duration of the simulation. Output Control under MT3DMS, in the Translation settings tree The MT3DMS Output Settings will appear. Here you can define the total time of the transport simulation. Type: 3650 under Simulation time length Type: 10000 under Max Number of Transport Steps Next you will define the different times where you want the simulation results to be saved. button to add an additional row to the grid button 7 additional times to add a total of 8 rows Enter the following values in the grid, starting at the first (top) row (values expressed here are in days): 1 30 60 180 365 730 1825 3650 Your screen should look like the image below: © Waterloo Hydrogeologic Page 36 Visual MODFLOW Flex Exercise: Intro1 You are now ready to create the input files (packages) for MODFLOW and MT3DMS. button located on the workflow toolbar Visual MODFLOW Flex will now create the files necessary to run MT3DMS and MODFLOW-2005. You will see a progress of the Translation which should take approximately 5-10 seconds. Once complete, [Next Step] proceed to the next step in the workflow button located on the workflow toolbar The numeric engines will start running, and display progress in the main window. MODFLOW-2005 will run first, followed by MT3DMS. This simulation should take a minute or less to complete, depending on computer speed. MT3D automatically determines the step size for contaminant transport by attempting to minimize numerical dispersion and oscillations as the functions relate to flow velocities and grid size of the model. In this simulation, the optimal time step determined is less than 30 days. Depending on the simulation, the optimal time step may be quite small and result in extremely long run times. Extended run times are common when pumping wells develop high flow velocities in the area around the well screen. © Waterloo Hydrogeologic Page 37 Visual MODFLOW Flex Exercise: Intro1 The engines progress window will once again appear. MODFLOW will run as before, followed by MT3DMS. As MT3D runs, the transport step, step size, and total elapsed time are displayed. The current period and transport step being analyzed is displayed in the progress window. Once the simulation is complete, you should see a line entry “Program completed.” in the progress window. In addition, you will see a new item “Concentration (Conc001)” appears on the model tree, under Outputs / Transport. Section 16: Viewing Concentration Simulation Results [Next Step] proceed to the next step in the workflow You will be presented with an option to View Results, and select the desired results type View Maps The concentration distribution can be visually analyzed in Visual MODFLOW in a variety of ways. One option is to contour and customize the concentration distribution. Contouring simulation results allows you to produce a range of contour plots for your site-specific results. By default, Heads will be displayed in the View Maps step. You will remove Heads from the view, and display Concentrations. □ Heads remove the check box beside Heads in the Model Explorer Concentrations (Conc001) add a check box to Conc001 in the Model Explorer Examine your simulation results in cross-section. Type: 3 under Layer to display layer 3 Row from the list of views Type: 20 under Row, to display row 20 to remove gridlines You will now see a Layer (plan) view of the plume and a cross sectional view, or slice, through the contaminant plume for the first time step (1 day). Adjust the vertical exaggeration as required (ensure you have the Row view selected to enable changes to the vertical exaggeration). Your interface should look like the image below: Note: if your results display a uniform concentration of 0 mg/L across the entire model domain it is likely that your concentration input values were overwritten. If you notice abnormallylow concentrations please revisit your boundary condition inputs to ensure that concentrations have been applied correctly. © Waterloo Hydrogeologic Page 38 Visual MODFLOW Flex Exercise: Intro1 Notice the Observation Well 1 (OW-1) you specified earlier does not appear in the cross- sectional view. You can show/hide these objects from the model tree, by adding/removing the check box beside the desired data object. The same is true for any raw data you wish to display, such as shapefiles, air photos, etc. Next, step through the model output time steps to examine the evolution of the contaminant plume. Above the Layer and Row views, you will see a toolbar; in the middle, is a combo box, which display all the output times you previously defined. to display the Next Time Step The Layer and Row views should update to reflect the values of concentrations calculated for 30 days. to display the Last Time Step © Waterloo Hydrogeologic Page 39 Visual MODFLOW Flex Exercise: Intro1 Note: if the toolbar for selecting output times does not appear simply deselect/reselect the Concentration output object under the Model Explorer. Refreshing the view in this way typically resolves any display issues relating to the time-step buttons. The Layer and Row views should update to reflect the values calculated for 3650 days (alternatively, you can select a specified time from the combo box adjacent to the time advancer buttons, to proceed directly to the desired time). Note that like the display of heads values, you can move the mouse around the Layer or Row view, and see the calculated values for each cell in the status bar at the bottom of the window. Section 17: Displaying a Concentration versus Time Graph © Waterloo Hydrogeologic Page 40 Visual MODFLOW Flex Exercise: Intro1 Using OW-1, Visual MODFLOW can produce and display a contaminant concentration versus time breakthrough graph. This feature is useful for examining the predicted contaminant concentration at any point you specify in the model. To display the graph, follow these steps: View Charts from the Workflow tree Transport from the Parameter menu Time Series from the Chart Type menu All Obs. check box under Chart Type Apply at the bottom of the window This will display a concentration-versus-time graph. Double clicking on any point or any portion of the plotted curve will display a pop-up, which will give you the exact data pertinent to that point (clicking again will remove it). From this graph, the maximum BTEX concentration after approximately 1460 days of transport is about 76 mg/L. Now is a good time to save the project. File / Save Project from the main menu © Waterloo Hydrogeologic Page 41 Visual MODFLOW Flex Exercise: Intro1 PART 3: DEFINING A REMEDIATION CAPTURE WELL The remedial option to be evaluated in this exercise is a single-well pump-and-treat system to capture the groundwater plume, preventing further contaminant migration and removing the groundwater for treatment. Apart from the contaminant plume that you have calculated in Part 2 of this exercise you will utilize backward tracking particles to determine the area of influence, or capture zone, for this pumping well operating at a specified rate. You will also determine the optimal pumping rate for the single well that maximizes the operational effectiveness of the system by capturing and removing the entire groundwater contamination plume. Design Objectives The design process of a pump-and-treat remediation system focuses on the maximization of both the operational effectiveness and the efficiency of the remediation system, while simultaneously meeting clean-up targets. Visual MODFLOW Flex models can be very powerful tools. Remediation engineers commonly use these models during the initial feasibility study stage of remedial alternative selection, and later in the design process of groundwater remediation systems. The model enables you to develop an initial system design to meet operational goals and clean-up targets. The model also enables you to explore cause-and-effect scenarios to assess overall remediation system sensitivity to local geologic and hydrologic extremes. In this exercise, you will use particles and the calculated contamination plume distribution to evaluate the effectiveness of the pump-and-treat remediation system. You will design the system to hydrodynamically capture and remove all of the contaminant particles in the groundwater with the interceptor well, while trying to minimize the amount of clean water removed for treatment. Section 18: Assigning the Pumping Well Define Boundary Conditions from the workflow tree Wells from the list menu under Toolbox Before you proceed, make sure you are viewing model Layer 1. You can quickly determine your present location in the model by viewing the values for Layer, Column and Row under the Views section. The well must be imported from an excel file. File / Import Data… a Data Import window will open Well from the data type drodown list […] to browse to the correct file A dialogue box opens that allows you to browse for the appropriate file. In the project directory (C:\VMODFlex\Intro1\), choose the following file: Pumping_wells.xls Open © Waterloo Hydrogeologic Page 42 Visual MODFLOW Flex Exercise: Intro1 Next >> from the Data Import window Next >> in the preview window The following window will appear: In this window you define what well data to import. Under the “Select the type of data you want to import” Well heads with the following data Screens Pumping Schedule Next >> from the Data Import window Next >> Next >> fields are mapped automatically Finish A new data object, Pumping_wells will appear in the Model Explorer tree. Pumping_wells select from the Data Tree Assign from the Toolbox in the main window Using Data Object from the dropdown menu for Assign A new window ‘Create Well Boundary Condition’ will open. in the upper left corner, under Select Raw Wells Data Object © Waterloo Hydrogeologic Page 43 Visual MODFLOW Flex Exercise: Intro1 OK The well will now appear in the grid view, located at X=94, Y=86 in layers 3 and 4 – the layers where the well is screened. If the well is not visible, please ensure you have zoomed out to view the full extents of the model. from the toolbar above the Layer view window Type: 3 under Layer to display layer 3 Your display should appear as shown below: © Waterloo Hydrogeologic Page 44 Visual MODFLOW Flex Exercise: Intro1 A circle will appear indicating the location of the interceptor well. The well is screened over the interceptor trench, with a top at 23.6, and a bottom at 18.25 m. The screened interval for PW-1 has been restricted to Layer 3 and Layer 4, which are the numerical model layers most likely to be exposed to contamination. This approach will help minimize problems associated with drying of cells at the pumping well. Specifically, as MODFLOW 2005 attempts to find a solution, it will iteratively assign heads at all cells, including the cells representing the pumping well. If the head falls below the bottom of a cell that represents part of a screen for the pumping well screened over more than 1 layer, the cell is automatically turned off and the pumping rate is decreased proportionately. The well is pumping at a rate of -60 m3/day for a duration of 3650 days (10 years) Note on convention: The pumping rate must be a negative value to establish an extraction well. A positive pumping rate would indicate an injection well. Now is a good time to save the project. File / Save Project from the main menu Section 19: Assigning Particles © WaterlooHydrogeologic Page 45 Visual MODFLOW Flex Exercise: Intro1 The forward particles that you assigned previously will be re-assigned to the refined grid and to Layer 2, 3 and 4 to determine if the water flowing through the contaminated area will be captured by the pumping well. Another aspect of well design is to minimize the amount of uncontaminated water that is being collected. This can be assessed by assigning backward-tracking particles in a circle around the well. These particles will help to delineate the capture zone of that well and we will be defining them in the screened Layers 3 and 4. If the capture zone is significantly larger than the contaminated zone, the design should be modified e.g. lower pumping rate, more wells, etc. First, we need to redefine the particles, in the workflow select: Define Particles from the main Workflow menu Assign from the Toolbox Using Data Object… from the pop-up menu At this step, you choose the particles points data object, and convert these into particles. particles points data object, from the Data Tree from the Create New Particles window Forward as the Particle Type Layers 2, 3 and 4 to assign particles to additional layers The window should appear as follows: OK to accept the default settings, and create the particles The particles should now appear as points, in the layer view. These are located along column 13 in the grid. We will now add a circle of backward tracking particles around the well in layers 3 and 4. Change the layer to layer 3 Type: 3 under Layer to display layer 3 © Waterloo Hydrogeologic Page 46 Visual MODFLOW Flex Exercise: Intro1 You should now be viewing Layer 3. Ensure the pumping well is visible in the model domain. Well1 from the Model Explorer, under Inputs Assign from the Toolbox in the main window Circle from the pop-up menu Left-click on the point representing the pumping well The following window will appear: © Waterloo Hydrogeologic Page 47 Visual MODFLOW Flex Exercise: Intro1 Radius: 1.8 to change the radius of deployment Layer 4 to deploy particles in layers 3 and 4 The window should appear as follows: OK to create the particles A circle of particles should appear around the well location, colored in maroon red. If you wish, you can zoom into this region to check the particle location. Once you are done, be sure to zoom back out to full extents (click the Zoom Full Extents button from the toolbar). Now is a good time to save the project. © Waterloo Hydrogeologic Page 48 Visual MODFLOW Flex Exercise: Intro1 File / Save Project from the main menu Section 20: Running the Pump-and-Treat Remediation Simulation To run a simulation with the new data set, Single Run from the main Workflow menu You will be presented with an option to Compose Engines. This dialogue will list the numeric models that can be used to simulate groundwater flow, particle tracking, water budgets, contaminant transport, and parameter estimation. For this simulation you should select MODFLOW- 2005 and MODPATH to be run (as indicated by a in the box), uncheck MT3DMS. It is generally a good idea to run a quick MODFLOW & MODPATH simulation prior to running MT3DMS since this will allow you to see if the pumping rate provides suitable capture zone coverage of the plume; in addition, MT3DMS simulations can often require much longer run times (typically several hours) as the model size, complexity and time length increase. □ Run Transport Engine to deselect MT3DMS MODPATH ensure MODPATH is selected [Next Step] proceed to the next step in the workflow The Translate step will appear; there are no changes need for this step, so you are now ready to create the input files (packages) for MODFLOW and MODPATH. button located on the workflow toolbar Visual MODFLOW Flex will now create the files necessary to run the USGS MODFLOW and MODPATH programs. You will see a progress of the Translation, which should take approximately 5-10 seconds. Once complete, [Next Step] proceed to the next step in the workflow button located on the workflow toolbar MODFLOW-2005 will run first, followed by MODPATH. Each engine will have an information window that displays simulation results and progress. Clicking on the tab of the respective window will enable you to view detailed results of each run. You will notice two tabs for MODPATH, one representing the forward tracking particles and one representing backwards tracking particles. The run should take 10-20 seconds. Once the simulation is complete, you should see a summary of the results from the MODPATH run in the MODPATH tab. Section 21: Displaying the Pump and Treat Simulation Results [Next Step] proceed to the next step in the workflow © Waterloo Hydrogeologic Page 49 Visual MODFLOW Flex Exercise: Intro1 You will be presented with an option to View Results, and select the desired results type View Maps button from the main window To determine if the interceptor well was effective in capturing the plume, you will need to display the pathlines. □ Row to view only in plan/layer view Backward Pathlines from the Model Explorer, under Outputs Well 1 from the Model Explorer, under Wells A plot of the head equipotentials and particle pathlines will be displayed as shown in the figure below. You will see that a pumping rate of 60 m3/d is sufficient to capture the plume fully (as indicated by the fact that no pathlines are going beyond the extraction well). If you wish, you can also experiment with more than one extraction well. Using multiple wells in an interception system is generally advisable because it allows the system to continue functioning if one © Waterloo Hydrogeologic Page 50 Visual MODFLOW Flex Exercise: Intro1 of the pumps breaks down or when the wells require maintenance. In the next section, you will re- run the simulation but this time including MT3DMS in the calculations. Section 22: Running the Pump-and-Treat Remediation Simulation with MT3DMS Now let us run MT3DMS to check if the plume is fully captured also for the contaminant transport. To run a simulation with the new data set: Single Run option in the Workflow tree You will be presented with an option to Compose Engines and the dialogue box will list the numeric models. For this simulation you should select MODFLOW 2005, MODPATH and MT3DMS to be run. Run Transport Engine to select MT3DMS [Next Step] proceed to the next step in the workflow button located on the workflow toolbar Once complete the translation is completed, [Next Step] proceed to the next step in the workflow button located on the workflow toolbar The MT3DMS simulation will be completed once you see a message at the bottom of the run log which says ‘***** The run was successful. *****’. To visually analyze the modeling results: [Next Step] proceed to the next step in the workflow View Maps button from the main window To see if the interceptor well was effective in capturing the contamination plume, you will need to display the concentration distribution. □ Heads remove the check box in the Model Explorer Tree Concentration (CONC001) add a check box in the Model Explorer tree Examine your simulation results in cross-section. Row from the list of views Type: 17 under Row to display row 17 A plot of concentration isolines with colors will be displayed. © Waterloo Hydrogeologic Page 51 Visual MODFLOW Flex Exercise: Intro1 Now, step thru the model output time steps to examine the evolution of the contaminant plume. You can also add the pumping well to this view by selecting this in the Model Explorer Above the Layer and Rowviews, you will see a toolbar which controls the output times. to display the Next Time Step The Layer and Row views should update to reflect the values of concentrations calculated for 30 days. To see the concentration distribution after 10 years or 3650 days: to display the Last Time Step Your screen display should look like the figure below. © Waterloo Hydrogeologic Page 52 Visual MODFLOW Flex Exercise: Intro1 The pumping well seems to be capturing the contaminant plume, indicating that the pumping rate is sufficient. However, if you wish to optimise the pumping rate, the model provides a useful tool for designing the number of wells, well location and total pumping rate. The lesson that we can learn from this simulation is that a full simulation of MODFLOW, MODPATH and MT3DMS are necessary to understand the impact of remediation well capture of a contaminated plume. A color map of the results can also be shown in the 3D viewer. 3D from the list of views □ Layer from the list of views □ Row from the list of views This view will show three slices through the model (along the selected layer, row, and column). Ensure the initial particle locations are active and navigate to layer 3. Forward Pathlines add a checkbox in the Model Explorer Tree Backward Pathlines add a checkbox in the Model Explorer Tree Particles add a checkbox in the Model Explorer Tree Type: 3 under Layer to view layer 3 © Waterloo Hydrogeologic Page 53 Visual MODFLOW Flex Exercise: Intro1 Now is a good time to save the project. File / Save Project from the main menu © Waterloo Hydrogeologic Page 54 Visual MODFLOW Flex Exercise: Intro1 PART 4: 3D VISUALIZATION AND INTERPRETATION Viewing modeling results in three dimensions is often the best way to gain insight into the flow and transport characteristics of a site. For example, you may wish to create: • Arbitrary horizontal slices through a model domain; • Vertical cross-sections along or perpendicular to a flowline; • Vertical cross-sections through a set of receptors, such as drinking-water wells; • Three-dimensional isosurfaces that represent migrating contaminant plumes. These types of views allow the hydrogeologist to examine the results in a way that is most relevant to the purpose of the analysis. Furthermore, two and three-dimensional animation techniques can be useful for illustrating time-dependent processes such as contaminant transport or water table drawdown. This section of the exercise will familiarize you with some techniques for assessing your transport modeling results in three dimensions using the 3D Explorer. Section 23: View 3D Contaminant Plume as an Isosurface Next, you will create a 3D volumetric representation of the contaminant plume within the model domain by creating an isosurface for a selected concentration value. A value of 10 mg/l will be used as it represents the maximum allowed concentration for the local water quality guidelines. The isosurface will encapsulate (and draw) any grid cells that have a concentration value greater than or equal to 10 mg/l. Window / New 3D Window from the main menu A 3D visualization window will open in a new tab. Activate elements of your model by using the check boxes in the Model Explorer and Data Tree. Concentration(Conc001) from the Model Explorer, under Outputs The 3D grid of the MT3DMS results will appear, with all cells drawn. Right-click on Concentration(Conc001) from the Model Explorer, under Outputs Settings from the menu that appears © Waterloo Hydrogeologic Page 55 Visual MODFLOW Flex Exercise: Intro1 The Settings dialog will appear. Next you will turn off the Cells view and turn on the desired color map and Isolines. + Style from the settings tree on the left Cells from the settings tree on the left □ Show Cells uncheck box from the top of the settings window Isosurfaces from the settings tree on the left Show Isosurfaces check box from top of the settings window Add click this button This will produce the Isosurface properties dialogue window, which allows you to specify the concentration value and visual attributes for the isosurface. Type: 10 in the Attribute Value field Visible check box to activate the isosurface Show Border check box to activate border Once completed, your dialogue window should appear as seen below: © Waterloo Hydrogeologic Page 56 Visual MODFLOW Flex Exercise: Intro1 OK to close the window Apply tp update the 3D View with new settings Your screen should now display an isosurface for BTEX equal to 10 mg/L. (you may need to move the settings window to the side to see the main VMOD Flex window in the background) + Time from the settings tree on the left © Waterloo Hydrogeologic Page 57 Visual MODFLOW Flex Exercise: Intro1 You can see that the default output time that is selected is the end of the simulation (3650 days). To show the time label on the 3d view, Show Time Label check box to include time label Select time = 3650 days to display output results at final time step Apply to update the 3D View with new settings OK to close the window Your display should now appear similar to the figure on the following page, as the contaminant plume (isosurface) now displays at 10 mg/L after 3650 days. You may need to adjust the 3D Viewer zoom and rotation in order to get a better perspective of the 3D groundwater model. Left-click near the bottom of the 3D Viewer window. While holding down the button drag the mouse toward the top of the screen, then release the button Zoom out using the button on the 3D viewer toolbar, or by scrolling down on your mouse cursor wheel © Waterloo Hydrogeologic Page 58 Visual MODFLOW Flex Exercise: Intro1 If you wish, you can view the isosurface for other time steps by using the same procedure as outlined above. Section 24: Viewing Input Data The Visual MODFLOW Flex 3D Viewer also allows you to display the model input data in this 3D perspective. Select different model objects from the Data tree and the Model Explorer tree to view these in 3D. Add checkmarks to the objects you wish to view. You may adjust the exaggeration of the viewer at the bottom of the viewer window. The settings of the model objects can also be modified individually to user specification. Please spend time to familiarize yourself with these options. Your viewer window may appear similar to the one below when you are finished. (in this example, the following data objects are set to visible: • basemap and Pumping_wells (from the data panel) © Waterloo Hydrogeologic Page 59 Visual MODFLOW Flex Exercise: Intro1 • Constant Head 1 and Constant Head 2 (from Model Explorer in the model Inputs) • Forward Pathlines and Backward Pathlines (from Model Explorer in the model Outputs) Section 25: Defining Colormap with Isolines The Visual MODFLOW Flex 3D Viewer allows you to plot colormaps and contour maps of selected model properties on any horizontal, vertical, or cross-sectional surface through the model domain. Let’s add a colormap of the calculated head values in the model domain. Heads from the Model Explorer tree, under Outputs The 3D grid of the Heads results will appear, with all cells drawn. Right-click on Heads from the Model Explorer tree Settings from the menu that appears © Waterloo Hydrogeologic Page 60 Visual MODFLOW Flex Exercise: Intro1 + Style from the settings tree on the left Cells from the settings tree on the left □ Show Cells uncheck box from the top of the settings window Colormap from the settings tree on the left Show Colormapcheck box from top of the settings window Type: 10 as the row number Apply to apply changes and add the colormap We will make a few additional changes before closing the settings window. + Isolines from the settings tree on the left Show Isolines check box from the top of the settings window Slice Type to expand this combo box Layer from the list of slice types Type: 3 for the Layer Number Next you will adjust the contour interval from the settings at the bottom half of the window Contour Interval select radio button Type: 0.25 for the Contour Interval The settings should now appear as shown below. © Waterloo Hydrogeologic Page 61 Visual MODFLOW Flex Exercise: Intro1 Apply to apply changes and add the contour intervals OK The 3D Display should now appear as shown below. Note: your display may appear differently, depending on the rotation or zoom level you have set). Use the rotate and pan options to adjust the view as desired. © Waterloo Hydrogeologic Page 62 Visual MODFLOW Flex Exercise: Intro1 3D view is zoomed in view with Exaggeration = 5 You may also export this view to an image file. Right-click in the 3D Viewer window Save As Image from the pop-up menu […] beside the File Name field Browse to the project location (default is C:\Users\<username>\Documents\Visual MODFLOW Flex\Projects\Intro1) Type: 3D Image as the File Name Save OK to save the image The image will be saved as a bitmap for further use in reports, documentation, etc. ***** This concludes the Intro exercise ***** © Waterloo Hydrogeologic Page 63 Visual MODFLOW Flex Exercise: Intro1 References Borden, R.C., et al., 1997. Anaerobic Biodegradation of BTEX in Aquifer Material, Environmental Research Brief, US Environmental Protection Agency, EPA/600/S-97/003 (copy included in course notes) Clement, T.P., C.D., Johnson, Y. Sun, G.M. Klecka, C. Bartlett, Natural attenuation of chlorinated solvent compounds: Model development and field-scale application, vol.42, p.113-140, Journal of Contaminant Hydrology, 2000. Clement, T.P., Y. Sun, B.S. Hooker, and J.N. Petersen, 1998. Modeling multi-species reactive transport in groundwater aquifers, Groundwater Monitoring & Remediation Journal, vol 18(2), spring issue, p. 79-92. Johnson, C.D., R.S. Skeen, D.P. Leigh, T.P. Clement, and Y. Sun, 1998. Modeling natural attenuation of chlorinated ethenes at a Navy site using the RT3D code, Proceedings of WESTEC 98 conference, sponsored by Water Environmental Federation, Orlando, Florida, October 3-7th. Guoping & Clement, Prabhakar & Zheng, Chunmiao & Wiedemeier, Todd. (1999). Natural Attenuation of BTEX Compounds: Model Development and Field‐Scale Application. Ground water. 37. 707-17. 10.1111/j.1745-6584.1999.tb01163.x. McDonald, M.G., and A. W. Harbaugh, 1988. A modular three-dimensional finite- difference flow model, Techniques in Water Resources Investigations of the U.S. Geological Survey, Book 6., 586 pp. Sun, Y. and T.P. Clement, 1998. A decomposition method for solving coupled multi- species reactive transport problems. Transport in Porous Media Journal, 1404, p. 1-20. Wiedemeier, T.H., et al., 1995. Technical protocol for implementing intrinsic remediation with long-term monitoring for natural attenuation of fuel contamination dissolved in groundwater, Volume 1 & 2, Air Force Center for Environmental Excellence, Technology Transfer Division, Brooks AFB, San Antonio, Texas. Zheng, C., 1990. A modular three-dimensional transport model for simulation of advection, dispersion and chemical reactions of contaminants in groundwater systems, U.S.E.P.A. Report. © Waterloo Hydrogeologic Page 1 Visual MODFLOW Flex Exercise: 3D Capture Visual MODFLOW Flex Exercise – 3D Capture 3D Pathline and Capture Zone Analysis Exercise Objectives • Develop a Visual MODFLOW Flex model using a georeferenced Bitmap (BMP) as a basemap • Evaluate effects of vertical anisotropy and recharge on 3D containment volumes and capture zones for wells in multi-aquifer systems • Perform particle tracking, and evaluate two-dimensional versus three-dimensional capture zones • Determine effect of all no-flux boundary conditions on steady-state simulations Problem Description In capture zone and containment volume analysis for groundwater clean-up, the presentation by Larson et al. (1987) is one of the first attempts to illustrate the significant differences between three-dimensional and two-dimensional model results of capture zones and containment volumes. Until that time, and even today, most aquifers were analyzed with two-dimensional models, the majority isotropic in nature. These authors point out how: • Horizontal area of the containment volume at the water table (for a pumping well) is determined by the rate of recharge [Area = Pumping rate/Recharge]; and, • Shape of the containment volume below the water table is determined by the degree of partial penetration, the horizontal to vertical hydraulic conductivity ratio, the rate and direction of groundwater flow and any present heterogeneities. These generalities are valid provided recharge is the major source of water (surface water sources are negligible). For example, homogeneous, anisotropic aquifers show that deeper penetration of the pumping well and/or a higher vertical hydraulic conductivity will increase the depth of containment and decrease the width. The opposite is true for shallow penetrating wells and low vertical hydraulic conductivities. Several examples illustrating these concepts are presented including a three-dimensional, contaminant capture zone problem for an anisotropic [Kh/Kv], multi-aquifer system with recharge. In this example, which models the capture of a contaminant plume, despite a well-placed fully penetrating well at the head of the plume, the resulting three-dimensional containment volume showed most of the plume was not captured. Although not widely cited in the literature, their work is very instructive for the implications it has for contaminant plume capture designs and wellhead protection analyses in heterogeneous, anisotropic, three-dimensional aquifers in which recharge plays a significant role. The dotted line in the upper figure of Figure 1 (below) shows the shape of the contaminated containment volume for the middle of the sand layer, predicted by a two-dimensional model that did not account for vertical flow. The lower figure in Figure 1 shows a vertical profile of the true containment zone, using a three-dimensional model that did account for vertical flow. If this clean- © Waterloo Hydrogeologic Page 2 Visual MODFLOW Flex Exercise: 3D Capture up design had been based on a two-dimensional model, it would fail since most of the "expected" containment volume would not be captured. Indeed, in the case of a two-dimensional design, a plot of concentration vs. time would show a decrease until zero was reached, at which point one might erroneously conclude there is no more contamination and the operation was a success. Figure 1 - Simulated 3D Containment Volume for Multi-Aquifer System © Waterloo Hydrogeologic Page 3 Visual MODFLOW Flex Exercise: 3D Capture These results were obtained using the USGS's Trescott and Larson (1976) three-dimensional flow model together with a simple pathline model. The use of the USGS's MODFLOW and MODPATH for the same problem results in very similar, but not equal, results. Let's use Visual MODFLOW Flex (and the USGS MODFLOW-2005 and MODPATH programs) to simulate this problem. References Larson, S.P., C.B. Andrews, M.D. Howland and D.T. Feinstein (1987). Three-Dimensional Modeling Analysis of Ground Water Pumping Schemes for Containment of Shallow Ground Water Contamination. Proceedings of the Conference on Solving Ground WaterProblems with Models, Volumes 1 & 2, Denver, CO. National Ground Water Association, Dublin, OH. pp. 517-530 US EPA, 2002. Elements for Effective Management of Operating Pump and Treat Systems. EPA report 542-R-02-009, OSWER 9355.4-27FS. Can be downloaded at http://clu- in.org/techpubs.htm US Army Corps of Eng., 2000. Operation and Maintenance of Extraction and Injection Wells at HTRW Sites. Engineers Pamphlet EP 1110-1-27. Can be downloaded at: http://www.usace.army.mil US EPA, 2008. A Systematic Approach for Evaluation of Capture Zones at Pump and Treat Systems. EPA Report 600/R-08/003, Office of Research and Development, National Risk Management Research Laboratory, Ada, OK. Terms and Notations For the purposes of this tutorial, the following terms and notations will be used. (This assumes you are using a right-handed mouse.) type - type in the given word or value ↔ - press the <Tab> key - press the <Enter> key - click the left mouse button where indicated - double-click the left mouse button where indicated Starting Visual MODFLOW Flex On your Windows desktop, you will see an icon for Visual MODFLOW Flex Visual MODFLOW Flex to start the program. The following Visual MODFLOW Flex window will appear: http://www.usace.army.mil/ © Waterloo Hydrogeologic Page 4 Visual MODFLOW Flex Exercise: 3D Capture © Waterloo Hydrogeologic Page 5 Visual MODFLOW Flex Exercise: 3D Capture PART 1: CREATING A PROJECT AND GENERATING A GRID The first step to groundwater modeling with Visual MODFLOW Flex is to create your project and generate a grid. Section 1.1: Create Project To create a new project: File / New Project… from the top menu bar A Create Project dialog box will be displayed prompting you to enter the project name of the new Visual MODFLOW Flex project. Type: 3DCapture as the project name Browse button under Data Repository Select a directory on the hard drive (or use the default location) Note: By default, new Visual MODFLOW Flex projects will be saved to the following location - [C:\Users\<username>\Documents\Visual MODFLOW Flex\Projects] Ensure that the correct system of units has been specified. Select the following units: Length: ft Time: day Conductivity: ft/d Pumping Rate: GPM © Waterloo Hydrogeologic Page 6 Visual MODFLOW Flex Exercise: 3D Capture Recharge: in/year Specific Storage: 1/ft Mass: kg (irrelevant – no transport simulation) Concentration: mg/L (irrelevant – no transport simulation) All other values can remain at their default settings. OK button in the lower right corner of this window. The following window will then appear: The Select Modeling Scenario allows you to choose whether to proceed with the Conceptual or Numerical modeling workflow. The conceptual modeling workflow allows you to import all data objects into Visual MODFLOW Flex and to build a conceptual site model (CSM). The CSM can then be used as a starting point for several different numerical models. In other words, numerical model (i.e. with different grid types, engines, etc.) can be quickly and easily created based on the same conceptual modeling. This makes it easy for the user to manage several different numerical models with slight variations. Conceptual modeling is not covered in this exercise, so we will proceed with the numerical modeling workflow: Numerical Modeling Proceeding with the numerical modeling workflow will bring you to the first step in the that workflow, which is to define your model objectives. This step allows you to specify whether you will © Waterloo Hydrogeologic Page 7 Visual MODFLOW Flex Exercise: 3D Capture be running a fully saturated or variably saturated model, whether contaminant transport will be included, which flow/transport engines will be utilized, etc. You will see the following window open, which displays the Define Modeling Objectives step in the numerical modeling workflow: The Define Modeling Objectives step allows you to specify what kind of model will be run (i.e. flow type, whether contaminant transport will be considered, etc.) and to specify some default project settings (i.e. default conductivity, storage values, etc.). For this exercise, the Start Date can be left at the default setting (i.e. today’s date). However, if time- stamped data are to be imported from outside sources, then it is necessary to have the start date fall at or prior to the oldest data point. We will retain most of the default settings in this step, but we will provide new values for the Default Project Property Settings: Type: 8.8 for Kx Type: 8.8 for Ky Type: 0.0628 for Kz Type: 0.001 for Ss Type: 0.27 for Sy We will leave the remaining default flow parameter values as they were: © Waterloo Hydrogeologic Page 8 Visual MODFLOW Flex Exercise: 3D Capture [Next Step] proceed to the next step in the workflow Yes to dismiss the warning regarding model start date Section 1.2: Define Model Grid The Define Grid window will appear, allowing you to select whether to import an existing grid or create a new one. We will create a new grid in this exercise: Create Grid This will bring you to the Create Grid step in the numerical modeling workflow. At this step you will specify the boundary/extents of your model and the structure of your model’s grid. Your screen should look like the image below: © Waterloo Hydrogeologic Page 9 Visual MODFLOW Flex Exercise: 3D Capture Now you will specify the number of rows, columns, and layers to be used in the model. Under the Grid Definitions frame, enter the following model rows, columns, layers and depth information in the appropriate boxes: Rotation = 275 Rows = 21 Columns = 30 Xmin = 15000 Xmax = 21000 Cell height = calculated this value can be adjusted as per project requirements Ymin = 45000 Ymax = 48000 Cell width = calculated this value can be adjusted as per project requirements For this exercise, you will ignore the option “Calculate extents from a polygon object”. Next, specify the parameters for the vertical grid discretization: Type: 10 For the Number of Layers Specify the layer elevations (typing the values directly into the grid): Layer Name Elevation Layer1 - Top: 280 Layer2 - Top: 220 Layer3 - Top: 205 Layer4 - Top: 190 Layer5 - Top: 180 Layer6 - Top: 165 Layer7 - Top: 150 Layer8 - Top: 142.5 Layer9 - Top: 135 Layer10 - Top: 80 Layer10 - Bott: 20 The screen should now look like the image below: © Waterloo Hydrogeologic Page 10 Visual MODFLOW Flex Exercise: 3D Capture Create Grid Click the ‘Create Grid’ button at the top-right [Next Step] proceed to the next step in the workflow Visual MODFLOW Flex will then construct a 30 columns x 21 rows x 10 layers finite difference grid with uniform grid spacing in both the X and Y directions, and will automatically create the model run Input tree structure. By default, you will be taken to the View/Edit Grid step as shown in the following image: © Waterloo Hydrogeologic Page 11 Visual MODFLOW Flex Exercise: 3D Capture The ‘View/Edit Grid’ portion of the workflow allows the user to make any necessary changes to the grid structure. This is particularly useful if you are following the conceptual modeling workflow and would like to test slight variations in the grid structure. Let’s load a site map to ensure that the model extents match-up with our desired model boundary. Section 1.3: Add Basemap You will select a bitmap file (.BMP) to be used as a background base map for your model. File / Import Data… from the main menu Select ‘Map’ in the ‘Data Type’ list menu […] button next to ‘Source File’, to browse to the data import file Browse to the location where you downloaded
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