Présentations Colloques

Oral Presentation
8.10
Session 8.10: Recent developments in groundwater modeling and mathematical tools in Hydrogeology
Tafani Dominique
SIMPLIFIED GIS MODEL OF AGRICULTURAL CONTAMINANTS TRANSFERS FROM SOIL TO DRINKING WATER CATCHMENT AREA
For regulatory groundwater agricultural pollutions risk assessment of drinking water catchment, simples models are usually implemented to assess the potential groundwater contamination. These models consist in weighting hydrogeologic parameters which affect transport from soil surface to aquifer. Results from such simulations are not very accurate. It is nevertheless used to implement agricultural pollutions reduction programs on groundwater catchment areas. Recently Agriculture stakeholders have criticized this methodology and expect a more solid scientific one. Complicated models to completely describe groundwater vulnerability could be implemented but are cost expensive and need a lot of data. Therefore such models would not likely be useful for clients needs. **Geo-Hyd Antea Group has developed with the University of Orléans for Chartres Métropole local water utility the so-called DARCI tool which relies on a quantitative simulation of agricultural pollutants transfer from soil to groundwater. Based on a simplification and integration of transport equation in Residence Time Distribution (RTD), the method consists in cutting the watershed into parallel flow threads, each of them corresponding to a pre-determined surface units. When pollutant flows are applied in entry of this simplified model, for each flow thread, concentrations in water table out of this flow thread are calculated. Convolution, or the sum of each single concentrations series, allows to simulate evolution of pollutant groundwater contamination in the catchment area.**In addition, as each water thread is related to a watershed surface unit, it is possible to identify at a time the most contributive geographic zones. DARCI tool has been tested and validated for simulation of nitrates in Chartres catchment area for Chartres Métropole local water utility and for simulation of atrazine transfer in Orléans catchment area for Orléans local water utility.**Finally a dedicated interface was developed which allows clients to run several scenarios of nitrates pesticides surface reduction programs over the water catchment, with a spatial analysis. **
France