1. ModBack – Simplified contaminant source zone delineation using backtracking K. Thielsch, M. Herold, T. Ptak Applied Geology, Geoscience Centre, University of Göttingen, 37077 Göttingen, Germany, kthielsch@gwdg.de 1 Geographical data view / input  define the max./min. plume length using analytical equations  or use plume length statistics (Schiedek et al., 1997)  cut pathlines to specific length 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) Maximum radius of contribution (RC) is defined as half distance between two neighboring wells  within ModBack by measuring tool 2a Analytical approach 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 2b Numerical groundwater model 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) 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). 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 ® )  based on results of numerical groundwater model (PMWin)  needs concentration-time series of a pumping well, IPT  export of results as shapefile or DXF (Surfer)  analytical IPT evaluation possible as well 3 IPT evaluation CSTREAM 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) 4 Result illustration / output  create possible zones containing contamination sources and zones free of contamination sources from the pathlines directly within ModBack  reactive and inert compounds 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. ModBack Input data required:  referenced data sets with coordinate information in x,y format Inert compounds Source zone absence Inert compounds Source zone no pathline cutting Jarsjö et al. (2005) Reactive compounds Source zone absence consideration of plume length statistics max:4500m, min: 20m Reactive compounds Source zone Jarsjö et al. (2005) 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).http://www.lubw.baden-wuerttemberg.de/servlet/is/47957/ Data frame Coordinates Main menu & Toolbar TOC 3a Standalone anlaytical approach, Rothschink, P. (2002) Copy Results Copy Results Create, run CSTREAM projects 3b Edit results in Golden Software Surfer Analytical Numerical Backtracking model Result illustration / output 4 Plume length statistics Source zone / Source zone absence Cut pathlines Convert pathlines matrix to x,y data, add as Points Convert points to polylines Save results as shapefile Editable inside of Data frame 2a Investigation of max. radius of contribution (Control Plane) Creation of conceptional IPT pumping duration Paste results from 2a Open, create, run PMWin projects Create pathlines in PMPath 2b Create new ArcGIS projects (ESRI.mxd format) Add geographical data, vector data (Esri.shp format) Open ArcGIS projects (ESRI.mxd format) 1 Geographical data view/ input Analytical Numerical Groundwater model