Modeling of the Contamination in the Alsatian ...

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XVI International Conference on Computational Methods in Water Resources (CMWR-XVI) Ingeniørhuset

Modeling of the Contamination in the Alsatian Aquifer by Chlorinated Solvents
Author:Taef ASWED <> (Institut de mécanique des fluides et des solides de Strasbourg)
Phillippe ACKERER <> (Institut de mécanique des fluides et des solides de Strasbourg)
Presenter:Taef ASWED <> (Institut de mécanique des fluides et des solides de Strasbourg)
Date: 2006-06-18     Track: General Sessions     Session: General

The Alsatian aquifer in the upper Rhine area, north-eastern of France, was contaminated with CCl4 on account of an accident happened on 1970. After several years of the accident, certain concentrations of CCl4, which are far away higher than the acceptable safety norm, have been detected in the underground water aquifer. Measured data have been collected from different locations of the aquifer during the period between 1992 and 2004. To match the history and predict the distribution of the contaminant, one requires knowledge of: (i) the behavior of the contaminant source, (ii) the geophysical parameters that affect water flow and contaminant transfer in the aquifer. In this work, we show the mathematical and numerical modeling of the problem. All measured data collected between 1992 and 2004 were used to validate our model. The chemical CCl4 is modeled as a tracer in water (that is, single-phase flow). Numerical results were obtained with an efficient, 3D single-phase code “TRACES”, developed at the IMFS. This code combines the mixed- hybrid finite element and discontinuous Galerkin methods to solve both the flow and the transport problems. No information is available about the behavior of the contaminant at the source. To estimate the contaminant concentration at the source, the travel time between the source and measurement-wells by the method of moments. Another difficulty one had to overcome was because no measured data of the rock and fluid parameters such as hydraulic conductivity, porosity, longitudinal and transversal dispersivities, were available. Several simulations were thus performed to get the parameters that match best the history. The permeability was calibrated with several runs carried out by changing randomly the permeability of each grid block. Porosity, longitudinal and transversal dispersivities were also fitted to the transport model. We have found that the results are rather insensitive to changes in permeability, while they are sensitive to changes in the longitudinal and transverse dispersivities.