References of "Dassargues, Alain"
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See detailNumerical simulation of heat transfer associated with low enthalpy geothermal pumping in an alluvial aquifer
Fossoul, Frédérique ULg; Orban, Philippe ULg; Dassargues, Alain ULg

in Geologica Belgica (2011), 14(1-2),

In a context favourable to renewable energies, various aquifers are studied to supply heating and/or cooling systems. The groundwater flow and heat transport are modelled in the alluvial aquifer of the ... [more ▼]

In a context favourable to renewable energies, various aquifers are studied to supply heating and/or cooling systems. The groundwater flow and heat transport are modelled in the alluvial aquifer of the river Meuse in providing an integrated tool for assessing the feasibility of a low energy air cooling/heating system for a large office building by pumping groundwater and discharging it in the river after being heated/cooled by using heat pumps. First, a comparative sensitivity analysis is performed using different codes for assessing the influence of coupling and non linearities on the main parameters due to the temperature evolution in function of time. Then, assuming that the aquifer temperature variation is weak enough to neglect its influence on hydrodynamics and thermal parameters, the MT3DMS and HydroGeoSphere codes are used for modelling the actual case-study. In practice, the worst case scenario considered by the project manager is the cooling of the office building during the hottest summer conditions. So, the influence of the warm water from the river Meuse is computed as it constitutes the major limiting factor. An optimisation of the pumping schema is computed to maximise the efficiency of the system. [less ▲]

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See detailCarte hydrogéologique de Wallonie, Jehay-Bodegnée - Saint-Georges 41/7-8, 1/25.000 : [notice explicative]
Ruthy, Ingrid ULg; Dassargues, Alain ULg

Book published by Service Public de Wallonie, DGARNE - Actualisation partielle : décembre 2010 - Première édition : mai 2003 (2010)

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See detailApplication of a multi-model approach to account for conceptual model and scenario uncertainties in groundwater modelling
Rojas, Rodriguo; Kahunde, Samalie; Peeters, Luk et al

in Journal of Hydrology (2010), 394(3-4), 416-435

Groundwater models are often used to predict the future behaviour of groundwater systems. These models may vary in complexity from simplified system conceptualizations to more intricate versions. It has ... [more ▼]

Groundwater models are often used to predict the future behaviour of groundwater systems. These models may vary in complexity from simplified system conceptualizations to more intricate versions. It has been recently suggested that uncertainties in model predictions are largely dominated by uncertainties arising from the definition of alternative conceptual models. Different external factors such as climatic conditions or groundwater abstraction policies, on the other hand, may also play an important role. Rojas et al. (2008) proposed a multimodel approach to account for predictive uncertainty arising from forcing data (inputs), parameters and alternative conceptualizations. In this work we extend upon this approach to include uncertainties arising from the definition of alternative future scenarios and we apply the extended methodology to a real aquifer system underlying the Walenbos Nature Reserve area in Belgium. Three alternative conceptual models comprising different levels of geological knowledge are considered. Additionally, three recharge settings (scenarios) are proposed to evaluate recharge uncertainties. A joint estimation of the predictive uncertainty including parameter, conceptual model and scenario uncertainties is estimated for groundwater budget terms. Finally, results obtained using the improved approach are compared with the results obtained from methodologies that include a calibration step and which use a model selection criterion to discriminate between alternative conceptualizations. Results showed that conceptual model and scenario uncertainties significantly contribute to the predictive variance for some budget terms. Besides, conceptual model uncertainties played an important role even for the case when a model was preferred over the others. Predictive distributions showed to be considerably different in shape, central moment and spread among alternative conceptualizations and scenarios analysed. This reaffirms the idea that relying on a single conceptual model driven by a particular scenario, will likely produce bias and under-dispersive estimations of the predictive uncertainty. Multimodel methodologies based on the use of model selection criteria produced ambiguous results. In the frame of a multimodel approach, these inconsistencies are critical and can not be neglected. These results strongly advocate the idea of addressing conceptual model uncertainty in groundwater modelling practice. Additionally, considering alternative future recharge uncertainties will permit to obtain more realistic and, possibly, more reliable estimations of the predictive uncertainty. [less ▲]

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See detailCaractérisation de l'hétérogénéité de la conductivité hydraulique à saturation au moyen d'essais de pénétration au cône
Rogiers, Bart; Mallants, Dirk; Batelaan, Okke et al

in Bulletin du GFHN n°56 (2010, November)

Dans le cadre du stockage des déchets radioactifs à activité faible et intermédiaire dans une installation de proche surface à Dessel, une caractérisation du site et de ses alentours a été réalisée ces ... [more ▼]

Dans le cadre du stockage des déchets radioactifs à activité faible et intermédiaire dans une installation de proche surface à Dessel, une caractérisation du site et de ses alentours a été réalisée ces dernières années. Les données recueillies contiennent à ce jour 388 mesures de conductivité hydraulique à saturation collectées sur 8 sites de sondage. En outre, des informations secondaires comme la granulométrie, la résistivité électrique, et la porosité ont été recueillies. Pour extrapoler ces informations à toute la région (70 km²), et bâtir un modèle hydrogéologique, plusieurs campagnes géotechniques ont été réalisées avec un total d'environ 260 essais de pénétration au cône. Avec cet ensemble de données, une approche probabiliste à petite échelle peut être utilisée 1) pour valider les modèles déterministes basée sur des paramètres moyens à grande échelle, et 2) pour aider à développer un réseau de surveillance. Parce que les essais de pénétration au cône délivrent une large information sur la variabilité spatiale du sous-sol, ils sont étudiés en détail. Une approche empirique est utilisée pour estimer la conductivité hydraulique à saturation à partir des paramètres des essais de pénétration au cône. En raison de la complexité de la relation entre la conductivité hydraulique à saturation et les variables mesurées sur le terrain, les modèles de régression ne sont pas satisfaisants pour le site investigué. De plus, le nombre de données est insuffisant pour appliquer des méthodes plus complexes comme par exemple les réseaux de neurones artificiels. Par analogie avec les méthodes classique de la classification du sous-sol en fonction des essais de pénétration au cône, une interpolation des données est faite dans le plan de la résistance du cône et le ratio de ce dernier avec la résistance au frottement latéral. Ainsi, une table de conversion est construite pour coupler les paramètres géotechniques à la conductivité hydraulique à saturation. Pour valider la méthode utilisée, les résultats sont comparés avec d'autres informations du sous-sol comme les carottes des sondages et avec des estimations de la conductivité hydraulique à saturation déduites d’analyses granulométriques. Finalement, une réalisation conditionnelle géostatistique de la conductivité hydraulique saturée d'un volume à trois dimensions de 400x175x40 m est proposée, et permet de se rendre compte de l’existence de 2 unités hydrogéologiques contrastées avec de différents modèles structurels. [less ▲]

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See detailEnjeux et défis de l’utilisation des eaux souterraine
Dassargues, Alain ULg

Conference given outside the academic context (2010)

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See detailGroundwater model parameter identification using a combination of cone-penetration tests and borehole data
Rogiers, Bart; Schiltz, Marco; Beerten, Koen et al

in International Groundwater Symposium 2010, IAHR (2010, September)

In the framework of the disposal of short-lived low- and intermediate-level radioactive waste in a near-surface disposal facility in Dessel, Belgium, additional extensive site characterisation has been ... [more ▼]

In the framework of the disposal of short-lived low- and intermediate-level radioactive waste in a near-surface disposal facility in Dessel, Belgium, additional extensive site characterisation has been performed in 2008. The gathered data now include 388 hydraulic conductivity measurements on samples from 8 cored boreholes. Detailed characterisation of these cored boreholes, together with geophysical logging, enabled to identify various hydrostratigraphical units at 8 discrete locations in the research area. Various analyses were performed on the cores, yielding information on grain size, mineralogy, density and total porosity. Geophysical logging parameters were derived from gamma-ray and resistivity measurements. Subsequently, an extensive geotechnical logging campaign was performed in order to establish a 3D-model of the hydrostratigraphical units, based on a dense network of investigation points. About 180 cone penetration tests (CPTs) were executed and lithology was deduced in detail based on existing soil classi cation charts. As such, a description of the regional subsurface up to depths of nearly 50 m was established, and this information was integrated with the borehole data. Most importantly, the lateral extent, depth and thickness of a hydrogeologically important aquitard was identi fied. Based on the 2008 site characterisation results and their interpretation, an update of a ground- water fl ow model used in safety assessments was made. The CPT-based stratigraphic model and the hydraulic conductivity data determined at different scales were combined into a new 3D hydrostratigraphical model. The small-scale measurements (on 100 cm³ core samples) are compared with hydraulic conductivity values obtained from pumping tests and the large-scale parameters derived by inverse modelling. The performance of the original and the updated flow model are compared. The presented approach was succesfull in substantially decreasing the conceptual model and parameter uncertainty and resulted in an improved calibration of the groundwater flow model. [less ▲]

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See detailDirect multiple-point geostatistical simulation of edge properties for modeling thin irregularly-shaped surfaces
Huysmans, Marijke; Dassargues, Alain ULg

in Cockx, L.; Van Meirvenne, M.; Bogaert, P. (Eds.) et al 8th International Conference On Geostatistics for Environmental Applications, GeoENV’2010 (2010, September)

Thin irregularly-shaped surfaces such as clay drapes often have a major control on flow and transport in heterogeneous porous media. Clay drapes are often complex curvilinear 3-dimensional surfaces and ... [more ▼]

Thin irregularly-shaped surfaces such as clay drapes often have a major control on flow and transport in heterogeneous porous media. Clay drapes are often complex curvilinear 3-dimensional surfaces and display a very complex spatial distribution. Variogram-based stochastic approaches are often also not able to describe the spatial distribution of clay drapes since complex, curvilinear, continuous and interconnected structures cannot be characterized using only two-point statistics. Multiple-point geostatistics aims to overcome the limitations of the variogram. The premise of multiple-point geostatistics is to move beyond two-point correlations between variables and to obtain (cross) correlation moments at three or more locations at a time using "training images" to characterize the patterns of geological heterogeneity. Multiple-point geostatistics is able to reproduce thin irregularly-shaped surfaces such as clay drapes but is often computationally intensive. To capture the thin surfaces, a small grid cell size should be adopted for the training image. This results in large training images and a large search template size and thus a large CPU and RAM demand (Huysmans and Dassargues, 2009). [less ▲]

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See detailGeostatistical analysis of primary and secondary data in a sandy aquifer at Mol/Dessel (Belgium)
Rogiers, Bart; Mallants, Dirk; Batelaan, Okke et al

in Cokx, L.; Van Meirvenne, M.; Bogaert, P. (Eds.) et al 8th International Conference on Geostatistics for Environmental Applications (GeoENV2010) (2010, September)

In the framework of the disposal of short-lived low- and intermediate-level radioactive waste in a near-surface disposal facility in Dessel, Belgium, additional extensive site characterization has been ... [more ▼]

In the framework of the disposal of short-lived low- and intermediate-level radioactive waste in a near-surface disposal facility in Dessel, Belgium, additional extensive site characterization has been performed in 2008. The gathered data now enclose 388 hydraulic conductivity measurements on samples of 8 cored boreholes. Secondary information as grain size analysis, porosity, and borehole geophysical parameters was also gathered. In addition, the geology of the study area has also been thoroughly characterized by a set of 178 cone penetration tests (CPTs) to approximate 50 m depth. This dataset allowed to refine the hydrostratigraphical model of the region. The existing groundwater model, based on large-scale effective hydraulic properties, was updated accordingly. The next step is a small-scale probabilistic approach 1) to validate the current existing deterministic groundwater models and 2) to support design for a monitoring network. In preparation for stochastic realizations of the subsurface, a geostatistical analysis of the available primary and secondary data is performed. [less ▲]

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See detailOn the value of conditioning data to reduce conceptual model uncertainty in groundwater modeling
Rojas, Rodrigo; Feyen, Luc; Batelaan, Okke et al

in Water Resources Research (2010), 46(8), 08520

Recent applications of multi-model methods have demonstrated their potential in quantifying conceptual model uncertainty in groundwater modeling applications. To date, however, little is known about the ... [more ▼]

Recent applications of multi-model methods have demonstrated their potential in quantifying conceptual model uncertainty in groundwater modeling applications. To date, however, little is known about the value of conditioning to constrain the ensemble of conceptualizations, to differentiate among retained alternative conceptualizations, and to reduce conceptual model uncertainty. We address these questions by conditioning multi-model simulations on measurements of hydraulic conductivity and observations of system-state variables and evaluating the e ffects on (i) the posterior multi-model statistics and (ii) the contribution of conceptual model uncertainty to the predictive uncertainty. Multi-model aggregation and conditioning is performed by combining the generalized likelihood uncertainty estimation (GLUE) method and Bayesian model averaging (BMA). As an illustrative example we employ a 3-dimensional hypothetical system under steady-state conditions, for which uncertainty about the conceptualization is expressed by an ensemble (M) of 7 models with varying complexity. Results show that conditioning on heads allowed for the exclusion of the two simplest models, but that their information content is limited to further diff erentiate among the retained conceptualizations. Conditioning on increasing numbers of conductivity measurements allowed for a further reffinement of the ensemble M and resulted in an increased precision and accuracy of the multi-model predictions. For some groundwater flow components not included as conditioning data, however, the gain in accuracy and precision was partially o ffset by strongly deviating predictions of a single conceptualization. Identifying the conceptualization producing the most deviating predictions may guide data collection campaigns aimed at acquiring data to further eliminate such conceptualizations. Including groundwater flow and river discharge observations further allowed for a better diff erentiation among alternative conceptualizations and drastic reductions of the predictive variances. Results strongly advocate the use of observations less commonly available than groundwater heads to reduce conceptual model uncertainty in groundwater modeling. [less ▲]

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See detailBayesian Data Fusion for water table interpolation: incorporating a hydrogeological conceptual model in kriging
Peeters, Luk; Fasbender, Dominique; Batelaan, Okke et al

in Water Resources Research (2010), 46(8), 08532

The creation of a contour map of the water table in an unconfined aquifer based on head measurements is often the first step in any hydrogeological study. Geostatistical interpolation methods (e.g ... [more ▼]

The creation of a contour map of the water table in an unconfined aquifer based on head measurements is often the first step in any hydrogeological study. Geostatistical interpolation methods (e.g. kriging) may provide exact interpolated groundwater levels at the measurement locations, but often fail to represent the hydrogeological flow system. A physically based, numerical groundwater model with spatially variable parameters and inputs is more adequate in representing a flow system. Due to the difficulty in parameterization and solving the inverse problem however, an often considerable difference between calculated and observed heads will remain. In this study the water table interpolation methodology presented by Fasbender et al. (2008), in which the results of a kriging interpolation are combined with information from a drainage network and a Digital Elevation Model (DEM), using the Bayesian Data Fusion framework (Bogaert and Fasbender, 2007), is extended to incorporate information from a tuned analytic element groundwater model. The resulting interpolation is exact at the measurement locations while the shape of the head contours is in accordance with the conceptual information incorporated in the groundwater flow model. The Bayesian Data Fusion methodology is applied to a regional, unconfined aquifer in Central Belgium. A cross-validation procedure shows that the predictive capability of the interpolation at unmeasured locations benefits from the Bayesian Data Fusion of the three data sources (kriging, DEM and groundwater model), compared to the individual data sources or any combination of two data sources. [less ▲]

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See detailModelling groundwater pumping and coupled heat transport in a alluvial aquifer: tests using different codes an optimisation
Fossoul, Frédérique ULg; Orban, Philippe ULg; Dassargues, Alain ULg

in Carrera, Jesus (Ed.) XVIII International Conference on Computational Methods in Water Resources, CMWR 2010 (2010, June 24)

Various aquifers are studied in terms of low temperature geothermal potential. The feasibility and impact studies of these systems imply very often a numerical simulation of groundwater flow and heat ... [more ▼]

Various aquifers are studied in terms of low temperature geothermal potential. The feasibility and impact studies of these systems imply very often a numerical simulation of groundwater flow and heat transport. Nowadays, some finite element or finite difference codes are able to deal with such non linear simulations. On a synthetic case study and then on a real case study, a detailed comparative sensitivity analysis is performed using three different codes (MT3DMS, SHEMAT and HYDROGEOSHERE). For low temperatures and relatively small temperature changes, it appears rapidly that the uncertainty affecting values of the main hydrodynamic parameters (i.e. hydraulic conductivity) influences more the results than taking into account any coupling or non linearity. For a case study, the pumping and associated groundwater flow and heat transport are modeled in an alluvial aquifer interacting with a main river in order to assess feasibility of a low energy air cooling /heating system for a large office building. The worst case scenario corresponds to hot summer conditions simultaneously with river maximum temperature and the model leads to an optimization with intermittent pumping in minimum 6 wells. Numerical codes are ready to simulate complex groundwater flow, solute transport and heat transport situations in aquifers, however efforts must be realized to obtain reliable experimental in-situ measured values for the hydro-thermal properties. [less ▲]

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See detailInfluence of natural attenuation and river fluctuations on benzene dispersion in an alluvial aquifer subject to strong interactions with surface water
Batlle-Aguilar, Jordi; Brouyère, Serge ULg; Dassargues, Alain ULg et al

in Schirmer, M.; Hoehn, E.; Vogt, T. (Eds.) Groundwater Quality Management in a Rapidly Changing World (GQ'2010) (2010, June)

A contaminated alluvial aquifer, in a former gasworks factory, discharging to an adjacent river was the object of field and laboratory investigations to assess pollutant attenuation and dispersion ... [more ▼]

A contaminated alluvial aquifer, in a former gasworks factory, discharging to an adjacent river was the object of field and laboratory investigations to assess pollutant attenuation and dispersion. Various organic and inorganic compounds were found in the aquifer in concentrations exceeding regulatory values, among them, benzene, which was presenting the major worry for off-site dispersion, mainly due to its mobility and high concentration, i.e. up to 750 mg L-1 in the source zone. However, benzene could never be detected near the river which is about 160 m downgradient the main source. Due to redox conditions of the aquifer, heavy metals were almost immobile, thus not posing a major risk of dispersion off-site the brownfield. Benzene concentrations together with redox conditions in the aquifer, suggested that benzene degradation was mainly occurring within 100 m distance from the contaminant source under anoxic conditions, and most probably with sulphate as main oxidant. A numerical groundwater flow and transport model, calibrated under transient conditions, was used to simulate benzene attenuation in the alluvial aquifer towards the Meuse River. The mean benzene degradation rate used in the model was quantified in situ along the groundwater flow path using compound-specific carbon isotope analysis (CSIA). The results of the solute transport simulations confirmed that benzene concentrations decreased almost five orders of magnitude 70 m downgradient the source. Simulated benzene concentrations were found to be below the detection limit in the zone adjacent to the river and consistent with the absence of benzene in downgradient piezometers located close to the river. In a transient model scenario including groundwater-surface water dynamics, benzene concentrations were observed to be inversely correlated to the river water levels, leading to the hypothesis that benzene dispersion is mainly controlled by natural attenuation and river fluctuations. [less ▲]

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See detailCarte hydrogéologique de Wallonie, Andenne-Couthuin 48/1-2
Goffinet, Florence; Ruthy, Ingrid ULg; Dassargues, Alain ULg

Cartographic material (2010)

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See detailCarte hydrogéologique de Wallonie, Andenne-Couthuin 48/1-2, 1/25.000 : [notice explicative]
Goffinet, Florence; Ruthy, Ingrid ULg; Dassargues, Alain ULg

Book published by Service Public de Wallonie, DGARNE - Version provisoire : juin 2010 (2010)

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See detailExploratory and structural data analysis of a sandy aquifer at Mol/dessel, Belgium
Rogiers, Bart; Mallants, Dirk; Batelaan, Okke et al

in Geophysical Research Abstracts, Vol. 12 (2010, May 03)

In the framework of the disposal of short-lived low- and intermediate-level radioactive waste in a near-surface disposal facility in Dessel, Belgium, additional extensive site characterization has been ... [more ▼]

In the framework of the disposal of short-lived low- and intermediate-level radioactive waste in a near-surface disposal facility in Dessel, Belgium, additional extensive site characterization has been performed in 2008. The gathered data now enclose 388 hydraulic conductivity measurements on samples of 8 cored boreholes. Additionally, secondary information as grain size analysis, resistivity, porosity, etc. was gathered. With this dataset, a small-scale probabilistic approach can be used 1) to validate the current existing deterministic groundwater models based on large-scale average hydraulic conductivity values, and 2) to support design for a monitoring network. In preparation for stochastic realizations of the subsurface, an exploratory and structural data analysis was performed and is presented here. The exploratory data analysis allows definition of hydrogeological units, independent from the existing lithostratigraphy. It also shows the presence of three conductivity classes within a strongly heterogeneous unit. Currently, only vertical structural data analysis is performed based on vertical data profiles. Semi-variograms and cross-variograms are calculated to characterize the spatial variance of the different hydrogeological units. Additional sampling and measurements will be performed in the future to provide information of the horizontal spatial variance. Together with the current results, these will serve as the basis for conditional stochastic simulation of groundwater flow and contaminant transport. [less ▲]

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See detailA regional flux-based risk assessment approach of contaminated sites on groundwater bodies
Brouyère, Serge ULg; Jamin, Pierre ULg; Dollé, Fabien ULg et al

Poster (2010, April 22)

In the context of the water framework directive, management plans have to be set up about water quality in surface and groundwater bodies in the EU. One of the first steps is to evaluate the risk of ... [more ▼]

In the context of the water framework directive, management plans have to be set up about water quality in surface and groundwater bodies in the EU. One of the first steps is to evaluate the risk of contamination of these water resources, and particularly the risk posed by contaminated industrial sites. From the perspective of water resource management, each of these sites taken individually does not necessary constitute a major threat. However, in heavily industrialised and urbanised areas, the cumulative effect of multiple contaminant sources is likely to present a risk. In order to propose adequate but still economically reliable measures, the calculated risk should be based on a so-called megasite approaches using criteria reflecting the water quality deterioration, in a cumulative way, at the scale of the whole surface water or groundwater body. A GIS-based regional risk assessment approach is developed here for groundwater bodies using the SEQ-ESO currently used within the Walloon Region as indicator to reflect the quality status of the groundwater body. The approach is applied on the groundwater body RWM073 “Gravels and alluvial deposits of the Meuse river between Engis and Herstal”, identified at risk of not reaching a good quality status by 2015. The different steps of this methodology consist of an inventory of proved or potential contaminating industrial sites, a numerical modelling of pollutants behaviour at the scale of the groundwater body and the application of the SEQ-ESO that finally gives a global quality status of the whole groundwater body. This analysis also serves as basis for a socio-economic approach intending to provide indications on costs and benefits generated by total or partial remediation of the contaminated groundwater bodies according to the different management scenarios. [less ▲]

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See detailPhysically-based groundwater vulnerability assessment for groundwater protection and land-use management
Popescu, Ileana-Cristina; Brouyère, Serge ULg; Derouane, Johan et al

Poster (2010, April 22)

Numerous groundwater vulnerability and risk mapping techniques have been developed taking into consideration a variable number of factors. Most common techniques produce maps of indexes based on a ... [more ▼]

Numerous groundwater vulnerability and risk mapping techniques have been developed taking into consideration a variable number of factors. Most common techniques produce maps of indexes based on a relatively empirical combination of weighted factors reflecting the protective effect of underground formations overlying the groundwater resource. The limitation of such 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, such as karstic 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 Néblon limestone basin in Belgium, one of the main groundwater resources for the city of Liège in the Meuse basin. Perspectives are proposed towards a generalisation of the vulnerability concept for risk assessment within a pressure - state - impact framework. [less ▲]

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