(Z&B)

Steps in Transport Modeling

Calibration step(calibrate flow model& transport model)

Adjust parameter values

Input Parameters for Transport Simulation

Flow

Transport

hydraulic conductivity (Kx, Ky Kz)storage coefficient (Ss, S, Sy)

porosity ()dispersivity (L, TH, TV)retardation factor or distribution coefficient1st order decay coefficient or half life

recharge ratepumping rates

source term (mass flux)

All of these parameterspotentially could be estimatedduring calibration. That is,they are potentially calibrationparameters.

Comparison ofmeasured andsimulatedconcentrations

A GWV calibration plot

Observed value

Mod

el V

alue

Perfect match

Average calibration errors (residuals) are reported as:

Mean Absolute Error (MAE) = 1/N calculatedi – observedi

Root Mean Squared Error (RMS) = 1/N (calculatedi – observedi)2½

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

Simulated: double-peakedsource concentration(best calibration)

Simulated: smoothsource concentration(best calibration)

Z&B, Ch. 14

Calibration is non-unique.Two sets of parameter values give equally good matches to the observed plume.

“Trial and error”method of calibration

Assumed source input function

R=1 R=3

R=6 observed

Modeling done by Maura Methenyfor the PhD under the direction ofProf. Scott Bair, Ohio State University

Case Study: Woburn, Massachusetts

TCE (Trichloroethene)

Common organic contaminants

Source: EPA circular

Spitz and Moreno (1996)

fraction of organic carbon

Spitz and Moreno ( 1996)

1 0 1 0 0 1 0 0 0

C o n c e n t r a t i o n o f T C E i n m i c r o g r a m s p e r l i t e r

0 1000 feet

TCE in 1985

W.R.Grace

•

BeatriceFoods

Woburn Site

MunicipalWells G & H

Aberjona River

Geology:buried river valleyof glacial outwash andice contact depositsoverlyingfractured bedrock

The trial took place in 1986.

Did TCE reach the wells before May 1979?

Wells G&H operated from October 1964- May 1979

MODFLOW, MT3D, and GWV

6 layers, 93 rows, 107 columns (30,111 active cells)

Woburn Model: Design

The transport model typically took two to three days to run on a 1.8 gigahertz PC with 1024K MB RAM.

Wells operated from October 1964- May 1979

Simulation run from Jan. 1960 to Dec. 1985using 55 stress periods (to account for changes in pumpingand recharge owing to changes in precipitation and land use)

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)

(Z&B)

Steps in Transport Modeling

Calibration step(calibrate flow model& transport model)

Adjust parameter values

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.

Calibration Targets: concentrations

Calibration Targets:Heads and fluxes

Source term input function

From Zheng and Bennett

Used as a calibrationparameter in the Woburnmodel

Other possible calibrationparameters include:K, recharge, boundary conditions

dispersivitieschemical reaction terms

Flow model (included heterogeneity in K, S and )• Water levels• Streamflow measurements• Groundwater velocities from helium/tritium groundwater ages

It cannot be determined which, if any, of the plausible scenariosactually represents what occurred in the groundwater flow system during this period, even though each of the plausible scenarios

closely reproduces measured values of TCE.

Woburn Model: Calibration

Transport Model (included retardation)The animation represents one of several equally plausible simulationsof TCE transport based on estimates of source locations, sourceconcentrations, release times, and retardation. The group of plausible scenarios was developed because the exact

nature of the TCE sources is not precisely known.

A trial and error calibration

Automated Calibration

From Zheng and Bennett

Codes: UCODE, PEST,MODFLOWP

Case Study

From Zheng and Bennett

source term

Sum of squared residuals = (calculatedi – observedi)2

Transport data are useful incalibrating a flow model

recharge

Comparison of observed vs.simulated concentrations at3 wells for the 10 parametersimulation.

From Zheng and Bennett

Sensitivity Coefficientsp. 343, Z&B

Sensitivity Analysis

Example of a sensitivityanalysis of a flow model

From Zheng and Bennett

From Zheng and Bennett

Normalized sensitivity coefficientof travel time with respect tohydraulic conductivity

TMR(telescopic mesh refinement)

From Zheng and Bennett

TMR is used to cut outand define boundaryconditions around a local area within aregional flow model.

GWV option forTelescopic Mesh Refinement

(TMR)

Multiple Species – MT3DMSRT3D

RT3D