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See detailMigration of contaminants through the unsaturated zone overlying the Hesbaye chalky aquifer in Belgium: a field investigation
Brouyère, Serge ULg; Dassargues, Alain ULg; Hallet, Vincent

in Journal of Contaminant Hydrology (2004), 72(1-4), 135-164

This paper presents the results of a detailed field investigation that was performed for studying groundwater recharge processes and solute downward migration mechanisms prevailing in the unsaturated zone ... [more ▼]

This paper presents the results of a detailed field investigation that was performed for studying groundwater recharge processes and solute downward migration mechanisms prevailing in the unsaturated zone overlying a chalk aquifer in Belgium. Various laboratory measurements were performed on core samples collected during the drilling of boreholes in the experimental site. In the field, experiments consisted of well logging, infiltration tests in the unsaturated zone, pumping tests in the saturated zone and tracer tests in both the saturated and unsaturated zones. Results show that gravitational flows govern groundwater recharge and solute migration mechanisms in the unsaturated zone. In the variably saturated chalk, the migration and retardation of solutes is strongly influenced by recharge conditions. Under intense injection conditions, solutes migrate at high speed along the partially saturated fissures, downward to the saturated zone. At the same time, they are temporarily retarded in the almost immobile water located in the chalk matrix. Under normal recharge conditions, fissures are inactive and solutes migrate slowly through the chalk matrix. Results also show that concentration dynamics in the saturated zone are related to fluctuations of groundwater levels in the aquifer. A conceptual model is proposed to explain the hydrodispersive behaviour of the variably saturated chalk. Finally, the vulnerability of the chalk to contamination issues occurring at the land surface is discussed. (C) 2003 Elsevier B.V. All rights reserved. [less ▲]

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See detailComparison of aquifer vulnerability assessment techniques. Application to the Neblon river basin (Belgium)
Gogu, Radu Constantin; Hallet, Vincent; Dassargues, Alain ULg

in Environmental Geology (2003), 44(8), 881-892

Five different methods for assessing intrinsic aquifer vulnerability were tested in a case study and their results compared. The test area was a slightly karstified district in the Condroz region of ... [more ▼]

Five different methods for assessing intrinsic aquifer vulnerability were tested in a case study and their results compared. The test area was a slightly karstified district in the Condroz region of Belgium. The basin covers about 65 km(2) and the karst aquifer provides a water-supply of about 28,000 m(3)d(-1). The methods tested were: EPIK (Doerfliger et al. 1999), DRASTIC (Aller et al.1987), 'German method' (von Hoyer and Sofner 1998), GOD (Foster 1987) and ISIS (Civita and De Regibus 1995). The results are compared and critically examined. From the analysis, it seems that reducing the number of parameters is unsatisfactory, due to the variety of geological conditions. The various methods produce very different results at any given site. As only physically-based methods can be checked for their reliability, it is clear that future vulnerability mapping techniques must incorporate such methods. [less ▲]

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See detailGIS-based hydrogeological databases and groundwater modelling
Gogu, Radu Constantin; Carabin, Guy; Hallet, Vincent et al

in Hydrogeology Journal (2001), 9(6), 555-569

Reliability and validity of groundwater analysis strongly depend on the availability of large volumes of high-quality data. Putting all data into a coherent and logical structure supported by a computing ... [more ▼]

Reliability and validity of groundwater analysis strongly depend on the availability of large volumes of high-quality data. Putting all data into a coherent and logical structure supported by a computing environment helps ensure validity and availability and provides a powerful tool for hydrogeological studies. A hydrogeological geographic information system (GIS) database that offers facilities for groundwater-vulnerability analysis and hydrogeological modelling has been designed in Belgium for the Walloon region. Data from five river basins, chosen for their contrasting hydrogeological characteristics, have been included in the database, and a set of applications that have been developed now allow further advances. Interest is growing in the potential for integrating GIS technology and groundwater simulation models. A "loose-coupling" tool was created between the spatial-database scheme and the groundwater numerical model interface GMS (Groundwater Modelling System). Following time and spatial queries, the hydrogeological data stored in the database can be easily used within different groundwater numerical models. [less ▲]

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See detailLocation of protection zones along production galleries : an example of methodology
Hallet, Vincent; Nzali, Timothée; Rentier, Céline et al

in Dassargues, Alain (Ed.) Tracers and Modelling in Hydrogeology (2000, May)

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See detailCarte hydrogéologique prototype de Wallonie, Modave - Clavier 48/7-8, 1/25.000 : [notice explicative]
Ruthy, Ingrid ULg; Hallet, Vincent; Peters, Valérie et al

Book published by Ministère de la Région wallonne, Direction générale des ressources naturelles et de l'environnement - Edition provisoire: mars 2000 (2000)

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See detailCarte hydrogéologique de Wallonie, Modave - Clavier 48/7-8
Ruthy, Ingrid ULg; Hallet, Vincent; Peters, Valérie et al

Cartographic material (2000)

Detailed reference viewed: 26 (0 ULg)
See detailCarte hydrogéologique prototype de Wallonie, Waremme - Momalle 41/3-4, , 1/25.000 : [notice explicative]
Ruthy, Ingrid ULg; Hallet, Vincent; Peters, Valérie et al

Book published by Ministère de la Région wallonne, Direction générale des ressources naturelles et de l'environnement - Edition provisoire: mars 2000 (2000)

Detailed reference viewed: 7 (0 ULg)
See detailCarte hydrogéologique de Wallonie, Waremme - Momalle 41/3-4
Ruthy, Ingrid ULg; Hallet, Vincent; Peters, Valérie et al

Cartographic material (2000)

Detailed reference viewed: 18 (0 ULg)
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See detailModélisation déterministe des écoulements et du transport de contaminants pour la détermination des zones de protection en Belgique
Dassargues, Alain ULg; Hallet, Vincent

in Milieux poreux et transferts hydriques - Bulletin du Groupe Francophone Humidimétrie et Transferts en Milieux Poreux, Strasbourg (2000)

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See detailAction 'Hydrogéologie de la vallée du Draa' (consolidation du SigmaDraa) (Maroc): rapport d'avancement n°2
Horion, Denis; Hallet, Vincent; Dassargues, Alain ULg et al

Report (1999)

Detailed reference viewed: 15 (1 ULg)
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See detailEffective porosity values used in calibrated transport simulations in a fissured and slightly karstified chalk aquifer
Hallet, Vincent; Dassargues, Alain ULg

in Herbert, M.; Kovar, K. (Eds.) Groundwater Quality 1998, Tübinger Geowissenschaftliche Arbeiten (TGA) (1998)

In fissured and slighly karstified chalks, the main difficulty for modelling groundwater flow and transport consists in finding a good approximation of the highly heterogeneous reality by a REV concept ... [more ▼]

In fissured and slighly karstified chalks, the main difficulty for modelling groundwater flow and transport consists in finding a good approximation of the highly heterogeneous reality by a REV concept. No major problem is encountered for groundwater flow simulations when the high contrast in hydraulic conductivity can be given to the cells/elements of the model. The Darcy’s law is applied in terms of specific flow rate, through the REV. When considering transport, it is often assumed that the calibrated field of hydraulic conductivity should be kept unchanged. Consequently, ‘physically non acceptable’ values of the effective porosity are often needed to obtain a match between modelled and measured breakthrough curves. The model becomes, to some extent, a black-box model. [less ▲]

Detailed reference viewed: 107 (3 ULg)