Understanding Calibration Steps in Transport Modeling: Adjusting Parameters for Transport Simulation

1. Calibration step (calibrate flow model & transport model) Steps in Transport Modeling Adjust parameter values (Z&B)

2. Input Parameters for Transport Simulation Flow hydraulic conductivity (Kx, Ky Kz) storage coefficient (Ss, S, Sy) recharge rate pumping rates All of these parameters potentially could be estimated during calibration. That is, they are potentially calibration parameters. Transport porosity () dispersivity (L, TH, TV) retardation factor or distribution coefficient 1st order decay coefficient or half life source term (mass flux)

3. Comparison of measured and simulated concentrations

4. Perfect match A GWV calibration plot Model Value Observed value

5. Average calibration errors (residuals) are reported as: Mean Absolute Error (MAE) = 1/N  calculatedi – observedi Root Mean Squared Error (RMS) = 1/N  (calculatedi – observedi)2½ Sum of squared residuals =  (calculatedi – observedi)2

6. Example listing of residuals in head targets in GWV

7. Calibration of a flow model is generally straightforward: • Match model results to an observed steady state flow field • If possible, verify with a transient calibration • Calibration to flow is non-unique. • Calibration of a transport model is more difficult: • There are more potential calibration parameters • There is greater potential for numerical error in the solution • The measured concentration data needed for calibration • may be sparse or non-existent • Transport calibrations are non-unique.

8. Simulated: smooth source concentration (best calibration) Simulated: double-peaked source concentration (best calibration) Borden Plume Calibration is non-unique. Two sets of parameter values give equally good matches to the observed plume. Z&B, Ch. 14

9. R=1 R=3 observed R=6 Assumed source input function “Trial and error” method of calibration

10. Case Study: Woburn, Massachusetts Modeling done by Maura Metheny for the PhD under the direction of Prof. Scott Bair, Ohio State University TCE (Trichloroethene)

11. Common organic contaminants Source: EPA circular

12. fraction of organic carbon Spitz and Moreno (1996)

13. Spitz and Moreno ( 1996)

14. 0 1000 feet Woburn Site TCE in 1985 Geology: buried river valley of glacial outwash and ice contact deposits overlying fractured bedrock Aberjona River W.R. Grace Municipal Wells G & H Wells G&H operated from October 1964- May 1979 Beatrice Foods The trial took place in 1986. Did TCE reach the wells before May 1979?

15. Five sources of TCE were included in the model: • New England Plastics • Wildwood Conservation Trust (Riley Tannery/Beatrice Foods) • Olympia Nominee Trust (Hemingway Trucking) • UniFirst • W.R. Grace (Cryovac) Woburn Model: Design MODFLOW, MT3D, and GWV 6 layers, 93 rows, 107 columns (30,111 active cells) Simulation run from Jan. 1960 to Dec. 1985 using 55 stress periods (to account for changes in pumping and recharge owing to changes in precipitation and land use) Wells operated from October 1964- May 1979 The transport model typically took two to three days to run on a 1.8 gigahertz PC with 1024K MB RAM.

16. Calibration step (calibrate flow model & transport model) Steps in Transport Modeling Adjust parameter values (Z&B)

17. Calibration of a flow model is generally straightforward: • Match model results to an observed steady state flow field • If possible, verify with a transient calibration • Calibration to flow is non-unique. Calibration Targets: Heads and fluxes • Calibration of a transport model is more difficult: • There are more potential calibration parameters • There is greater potential for numerical error in the solution • The measured concentration data needed for calibration • may be sparse or non-existent • Transport calibrations are non-unique. Calibration Targets: concentrations

18. Source term input function Used as a calibration parameter in the Woburn model Other possible calibration parameters include: K, recharge, boundary conditions dispersivities chemical reaction terms From Zheng and Bennett

19. Woburn Model: Calibration • Flow model (included heterogeneity in K, S and ) • Water levels • Streamflow measurements • Groundwater velocities from helium/tritium groundwater ages Transport Model(included retardation) The animation represents one of several equally plausible simulations of TCE transport based on estimates of source locations, source concentrations, release times, and retardation. The group of plausible scenarios was developed because the exact nature of the TCE sources is not precisely known. It cannot be determined which, if any, of the plausible scenarios actually represents what occurred in the groundwater flow system during this period, even though each of the plausible scenarios closely reproducesmeasured values of TCE. A trial and error calibration

20. Automated Calibration Case Study Codes: UCODE, PEST, MODFLOWP From Zheng and Bennett

21. source term recharge Sum of squared residuals =  (calculatedi – observedi)2 Transport data are useful in calibrating a flow model From Zheng and Bennett

22. Comparison of observed vs. simulated concentrations at 3 wells for the 10 parameter simulation. From Zheng and Bennett

23. Sensitivity Analysis Sensitivity Coefficients p. 343, Z&B

24. Example of a sensitivity analysis of a flow model From Zheng and Bennett

25. Normalized sensitivity coefficient of travel time with respect to hydraulic conductivity From Zheng and Bennett

26. TMR (telescopic mesh refinement) TMR is used to cut out and define boundary conditions around a local area within a regional flow model. From Zheng and Bennett

27. GWV option for Telescopic Mesh Refinement (TMR)

30. Multiple Species – MT3DMS RT3D

31. RT3D