Groundwater Modeling 4: GW- 3 Tips

1. Groundwater Modeling 4:GW-3 Tips Groundwater Hydraulics Daene C. McKinney

2. Setup – Part (a) • Create the “working directory” • C:\temp\P20a_work • Download the P20a.zip file (from Blackboard) • Un-Zip the P20a.zip file to get the file P20a.gwv • Place the file P20a.gwv in the directory • C:\temp\P20a_work • Open the model P20a (just double click on the P20a.gwv file) • Run the model P20a

3. P20a.GWV • When you open the P20a.GWV file, you should see :

4. P20a.GWV • When you run the P20a.GWV file you should get a solution that looks like:

5. MODFLOW Packages • Select: Model--> MODFLOW --> Packages • Under “Package” • Add unit 44 for “Drain” • Check box for “Drain” • Under “Cell-by-Cell Flow Unit No.” • Add unit 45 for BCF • Add unit 46 for Drain • Add unit 47 for Recharge • When you run the model you can check the mass balance reports.   • Save your model file

6. Solver Options • If “model fails to converge” • Select: Models  MODFLOW  Solver Options • Select: SIP Tab • Increase: Maximum Number of Iterations from 50 to 100

7. Setup – Part (b) • Create a new “working directory” named P20b_work • C:\temp\P20b_work • Keep a separate working directory for each part, so you can back up if you make a mistake • Make a copy of the file P20a.gwv • Place the file P20b.gwv in the directory • C:\temp\P20b_work • Rename the copy P20b.gwv • Open the model P20b (just double click on the P20b.gwv file)

8. Setup – Part (b) – Cont. • Select “MODELS – PATHS TO MODELS” • Set working directory to: C:\temp\P20b_Work

9. Part b – Impermeable Cap • Create the Impermeable Cap: • Select: Props  Recharge • Select: Props  Property Values  Matrix Editor

10. Impermeable Cap • Change the Recharge values for appropriate rows and cells from 6.34e-008 to 0.00e+00 in the cells representing the Impermeable Cap Note the zeros

11. Recharge for Impermeable Cap • You should end up with a Recharge distribution that looks like this:

12. Transient Model Setup • Convert the model to a transient model with 1 stress period

13. Stress period Types • Select: Model  MODFLOW2000 • Select: Stress Period Types  Set all to transient • Select: Model  MODFLOW • Set up the Stress periods • Stress period length = 972,000,000 seconds (= 30.82 years) • 20 time steps • Time step multiplier of 1.5

14. Specific Yield • Set specific yield = 0.28

15. Initial Heads for Part (b) • Copy the file “P20a_Assign.hds” to the directory “P20b_work” • Select: Model  MODFLOW  Package Options • Select: Initial Heads tab • Select: Initial Head Location: Read Heads Directly from Binary Head Save File • Select: Browse • Select: P20a_Assign.hds file Note

16. Result – Last time step – Part (b) • Results for the last time step should look like this. • Next Time Step Ctrl+Shift+N • Previous Time Step Ctrl+Shift+P

17. Setup – Part (x) x= c, d, or e • Create a new working directory “C:\temp\P20x_work” • Make a copy of the file P20x-1.gwv (x-1 = previous version) • Place the file P20x-1.gwv in the directory • C:\temp\P20x_work • Rename the copy P20x.gwv • Copy the file “P20a_Assign.hds” to the directory “P20x_work” • Select: Initial Head Location: Read Heads Directly from Binary Head Save File • Select: P20a_Assign.hds file

18. Part (c) – Slurry Wall • What’s a slurry wall? • Slurry walls are non-structural barriers (Cutoff Walls, Slurry Trenches) that are constructed underground to impede groundwater flow. (www.slurrywall.com)

19. Part (d) – Drain BC • In the table, the elevation is the stage and the last column is the "conductance” • Fll in the "Drain" BC form as: • Stage: Elevation from table • Width: 1 • Length: 1 • Thickness: 1 • Hydraulic Conductivity: 10 • This gives a "Conductance" = 10 ft2/sec cruxper.com

20. Part (x) • What solution does your team recommend? • Feel free to suggest solutions that are • modifications of those suggested here or • have not been discussed in the assignment or these slides.