Calibration and Reliability in Groundwater Modelling: Credibility of Modelling

(Proceedings of ModelCARE 2007 Conference, held in Denmark, September 2007). IAHS Publ. 320, 2008, 83-88.

Groundwater vulnerability assessment using physically-based modelling: from challenges to pragmatic solutions

I. C. POPESCU^1,2, N. GARDIN¹, S. Brouyère^1,3 & A. Dassargues^1,4

1 Hydrogeology & Environmental Geology, Geo3 Group, ArGEnCo Dpt, B-52/3, Université de Liège, B-4000 Liège, Belgium

alain.dassargues@ulg.ac.be

2 Groundwater Direction, Water Division, DGRNE, Walloon Region, Belgium

3 Université de Liège, Aquapole, Belgium

4 Hydrogeology & Engineering Geology, Katholieke Universiteit Leuven, Belgium

Abstract Numerous groundwater vulnerability and risk mapping techniques have been developed, taking into consideration a variable number of factors. The most common techniques are based on calculation of an index expressing the protective effect of underground formations overlying the groundwater resource. The limitation of most of these methods is related to their use of a qualitative definition of groundwater vulnerability, as opposed to a definition based on a quantitative description of contaminant migration. A physically-based point of view and definition of the vulnerability is proposed and based on three factors describing a pollution event, which are the contaminant transfer time from the hazard location to the “target”, the contamination duration at the “target”, and the level of contaminant concentration reached at the “target”. This concept allows a clear distinction between conventional aspects and physically-based results in the building of a final vulnerability indicator. This methodology has the further advantage to consider the possible impact of runoff conditions occurring at the land surface and possibly leading to lateral contamination of groundwater through downstream preferential infiltration features. Practically, this method needs to describe and simulate the pollutant migration in the unsaturated zone and possibly in the saturated zone in order to assess the breakthrough curve at the “target”. Preliminary application is illustrated on a case-study located in a limestone basin in Belgium. Perspectives are proposed towards a generalisation of the vulnerability concept for risk assessment within a pressure–state–impact framework.

Key words groundwater vulnerability; susceptibility; sensitivity; contaminant migration; modelling;
preferential infiltration; risk assessment; groundwater protection