(z&b) steps in transport modeling calibration step (calibrate flow model & transport model)...
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(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
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