ModBack – Simplified contaminant source zone delineation using backtracking
K. Thielsch, M. Herold, T. Ptak
Applied Geology, Geoscience Centre, University of Göttingen, 37077 Göttingen, Germany, [email protected]
ModBack enables a simplified delineation of contaminant source
zones and zones free of contamination sources in saturated aquifers
following the approach by Jarsjö et al. (2005).
1 Geographical data view / input
Main menu & Toolbar
ModBack
TOC
Input data required:
 referenced data sets with
coordinate information in x,y format
Data frame
Coordinates
It uses a GIS-based interface comprising four steps: geographical
data view / input, analytical and numerical groundwater modeling,
ana-lytical and numerical backtracking, result illustration / output.
Combination of directly controlled modeling tools:
 PMWin© (WebTech 360, Inc., Processing Modflow Pro), ArcGIS®
(ESRI®, ArcMap, ArcCatalog), CSTREAM (Bayer-Raich et al., 2003),
Surfer® (Golden Software), Excel© (Microsoft ®)
4 Result illustration / output
ModBack
 convert the pathlines (results
num. model) matrix to x,y data
 add theses pathlines as points
 convert the points to polylines,
 change color
 add .dxf files (results
backtracking CSTREAM)
Add geographical data, vector data
(Esri .shp format)
2a Analytical approach
Investigation of max.
radius of contribution
(Control Plane)
Creation of conceptional
IPT pumping duration
Standalone anlaytical
approach,
Rothschink, P. (2002)
Analytical
2a
Analytical
Result illustration /
output
3b
Paste results from 2a
Open, create, run
PMWin projects
Create pathlines in
PMPath
Create, run
CSTREAM projects
Edit results in Golden
Software Surfer
Convert pathlines matrix to
x,y data, add as Points
Copy
Results
Source zone / Source
zone absence
4
2b
Numerical
Backtracking model
3a
Cut pathlines
Numerical
Groundwater model
Plume length statistics
2b Numerical groundwater model
Create new ArcGIS projects
(ESRI .mxd format)
Geographical data view/
input
1
Copy
Results
Estimation of the required pumping
duration of an integral pumping test
(IPT, Teutsch et al., 2000) using Excel
following Rothschink, 2002:
 enter RC (red box)
 define model parameters (blue box)
 pumping time is calculated
automatically (green box)
Editable inside of Data frame
Maximum radius of contribution (RC)
is defined as half distance between
two neighboring wells
 within ModBack by measuring tool
Open ArcGIS projects
(ESRI .mxd format)
Convert points to polylines
Save results as shapefile
Groundwater model set up using
PMWin (example data):
 hor. hydraulic conductivity: 0.032 [ms -1 ]
 specific storage: 0.01 [m-1]
 eff. porosity: 0.15 [-], aquifer thickness:
2m
 mesh size: 5x5m, around wells: 1x1m
 layer type: transmissivity varies
 period length equal to pumping time (RC)
 define the max./min. plume
length using analytical equations
 or use plume length statistics
(Schiedek et al., 1997)
 cut pathlines to specific length
Inert compounds
Source zone
3 IPT evaluation
CSTREAM
 create possible zones
containing contamination
sources and zones free of
contamination sources from the
pathlines directly within ModBack
 reactive and inert compounds
 based on results of numerical
groundwater model (PMWin)
Creation of pathlines using PMPath:
 two pathlines (red lines), one at each
end of the control plane for one well
 backtracking, simulation time is entire
duration transient flow simulation
 export data
 needs concentration-time
series of a pumping well, IPT
Jarsjö et al. (2005)
no pathline cutting
Inert compounds
Source zone absence
Reactive compounds
Source zone
Jarsjö et al. (2005)
consideration of plume length statistics
max:4500m, min: 20m
 export of results as shapefile or
DXF (Surfer)
Reactive compounds
Source zone absence
 analytical IPT evaluation
possible as well
References: Jarsjö, J., Bayer-Raich, M., Ptak, T. (2005), Monitoring groundwater contamination and delineation source zones at industrial sites: Uncertainties using integral pumping test, J. Contam. Hydrol., 79, 107-134; Rothschink, P. (2007): IPV-TOOL. http://www.lubw.baden-wuerttemberg.de/servlet/is/47957/; Schiedek, T., Teutsch, G. and Gratwohl, P. (1997), Literaturstudie zum natürlichen Rückhalt / Abbau von Schadstoffen im
Grundwasser. Landesamt für Umweltschutz, Baden-Württemberg, Germany (in German); Teutsch, G., Ptak, T., Schwarz, R., Holder, T. (2000), Ein neues integrales Verfahren zur Quantifizierung der Grundwasserimmission: I. Beschreibung der Grundlagen, Grundwasser 4 (5), 170–175 (in German).
Acknowledgements: The authors greatly acknowledge the support by the Slovenian INCOME project partners and by Fugro GmbH, Braunschweig, Germany as well as the financial contribution by the EU, LIFE+ program.