Steps in Transport Modeling Adjust parameter values Calibration

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

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 1 st order decay coefficient or half life source term (mass flux)

Comparison of measured and simulated concentrations

A GWV calibration plot Model Value Perfect match Observed value

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

Example listing of residuals in head targets in GWV

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.

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

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

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

Common organic contaminants Source: EPA circular

fraction of organic carbon Spitz and Moreno (1996)

Spitz and Moreno ( 1996)

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

Woburn Model: Design MODFLOW, MT 3 D, 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 Five sources of TCE were included in the model: • New England Plastics • Wildwood Conservation Trust (Riley Tannery/Beatrice Foods) • Olympia Nominee Trust (Hemingway Trucking) • Uni. First • W. R. Grace (Cryovac) The transport model typically took two to three days to run on a 1. 8 gigahertz PC with 1024 K MB RAM.

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

Calibration of a flow model is generally straightforward: • Match model results to an observed steady state flow field Calibration • If possible, verify with a transient calibration Targets: Heads and fluxes 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 Calibration Targets: concentrations may be sparse or non-existent Transport calibrations are non-unique.

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

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 reproduces measured values of TCE. A trial and error calibration

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

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

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

Sensitivity Analysis Sensitivity Coefficients p. 343, Z&B

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

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

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

GWV option for Telescopic Mesh Refinement (TMR)

Multiple Species – MT 3 DMS RT 3 D

RT 3 D