References of "Brouyère, Serge"
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See detailHow heterogeneity of the K-field influences a heat plume in a shallow alluvial aquifer: responses from a heat tracer test
Klepikova, Maria; Jamin, Pierre ULg; Orban, Philippe ULg et al

in Abstract book (2016, January 26)

Simultaneous solute and heat tracer test provides essential information for a reliable assessment of low temperature geothermal systems. The actual efficiency of ‘open systems’, including heat storage ... [more ▼]

Simultaneous solute and heat tracer test provides essential information for a reliable assessment of low temperature geothermal systems. The actual efficiency of ‘open systems’, including heat storage projects, is strongly affected by the heterogeneity of the hydraulic conductivity field (K-field). It could be also useful for assessing the cumulative impacts of numerous projects in urban areas on the groundwater resources. Using field data from a solute and heat tracer test conducted in the alluvial aquifer of the Meuse River (Belgium), an inverse problem of parameter estimation is solved. The tracing experiment consisted in simultaneously injecting heated water and a dye tracer in a piezometer and monitoring the evolution of groundwater temperature and tracer concentration in the recovery well and in monitoring wells. To get insights in the 3D characteristics of the heat plume, an arrangement of three transects of observation wells was used. The breakthrough curves measured in the recovery well showed that heat transfer in the alluvial aquifer is slower and more dispersive than solute transport. Recovery is very low for heat while in the same time it is measured as relatively high for the solute tracer. This is due to the fact that heat transport is a thermal diffusion dominated process. For conditions corresponding to high Peclet numbers, the hydraulic conductivity is the primary calibration parameter for predicting heat plume distribution. Heat diffusion is larger than molecular diffusion, implying that exchange between groundwater and the porous medium matrix is far more significant for heat than for solute tracers. [less ▲]

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See detailHeat tracer and solute tests in an alluvial aquifer: field experiment and inverse modelling
Dassargues, Alain ULg; Klepikova, Maria; Jamin, Pierre ULg et al

Poster (2015, December 18)

Using heat as an active tracer in different types of aquifers is a topic of increasing interest. In this study, we investigate the potential interest of using heat tracer tests for characterization of a ... [more ▼]

Using heat as an active tracer in different types of aquifers is a topic of increasing interest. In this study, we investigate the potential interest of using heat tracer tests for characterization of a shallow alluvial aquifer. A thermal tracer test was conducted in the alluvial aquifer of the Meuse River, Belgium. The tracing experiment consisted in simultaneously injecting heated water and a dye tracer in a piezometer and monitoring the evolution of groundwater temperature and tracer concentration in the recovery well and in monitoring wells. To get insights in the 3D characteristics of the heat transport mechanisms the space-filling arrangement of observation wells was used. The breakthrough curves measured in the recovery well showed that heat transfer in the alluvial aquifer is slower and more dispersive than solute transport. Recovery is very low for heat while in the same time it is measured as relatively high for the solute tracer. This is due to the fact that heat diffusion is larger than molecular diffusion, implying that exchange between groundwater and the porous medium matrix is far more significant for heat than for solute tracers. Temperature breakthrough curves in other piezometers are contrasted with what would be expected in an ideal layered aquifer. They reveal strongly unequal lateral and vertical components of the transport mechanisms. The observed complex behavior of the heat plume was explained by the groundwater flow gradient on the site and heterogeneities of hydraulic conductivity field. By using numerical model of heat and flow coupled with pilot points inverse approach main preferential paths were characterized. [less ▲]

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See detailUse of dual carbon-chlorine isotope analysis to identify degradation pathways of 1,1,1-trichloroethane in groundwater
Palau, Jordi; Jamin, Pierre ULg; Badin, Alice et al

Conference (2015, September 17)

The high susceptibility of chlorinated aliphatic hydrocarbons (CAHs) like 1,1,1-trichloroethane (1,1,1-TCA) to be transformed via different competing pathways (biotic and abiotic) complicates the ... [more ▼]

The high susceptibility of chlorinated aliphatic hydrocarbons (CAHs) like 1,1,1-trichloroethane (1,1,1-TCA) to be transformed via different competing pathways (biotic and abiotic) complicates the assessment of their fate in groundwater. This knowledge is necessary to evaluate contaminant degradation and potential formation of toxic intermediates. Identifying pathways is further complicated in sites contaminated by mixed CAHs because some degradation products of 1,1,1-TCA can be formed from different precursors. Here, identification of pathways based solely on substrate-product concentration relationships may lead to ambiguous interpretations. This study investigates, for the first time, dual C−Cl isotope fractionation as a means of identifying and assessing degradation pathways of 1,1,1-TCA in groundwater. Distinctly different dual isotope trends (L = Δδ13C/Δδ37Cl) were observed for 1,1,1-TCA transformation via oxidation with heat-activated persulfate (L = ∞), reduction with zerovalent iron (L = 1.5 ± 0.1), hydrolysis and dehydrohalogenation (HY/DH, L = 0.33 ± 0.04) in laboratory experiments, illustrating the potential of a dual isotope approach. This approach was evaluated in an aerobic aquifer impacted by 1,1,1-TCA and trichloroethylene (TCE) with concentrations of up to 20 mg/L and 3.4 mg/L, respectively. For 1,1,1-TCA, the dual isotope slope determined from field samples (L = 0.6 ± 0.2, r2 = 0.75) was close to the slope observed for HY/DH in the laboratory (L = 0.33 ± 0.04), indicating that HY/DH was the predominant degradation pathway of 1,1,1-TCA in the aquifer. The observed deviation could be explained by a minor contribution of additional degradation processes. This result, along with the little degradation of TCE determined from isotope measurements, confirmed that 1,1,1-TCA was the main source of the 1,1-dichlorethylene (1,1-DCE) detected in the aquifer with concentrations of up to 10 mg/L. This study demonstrates that a dual C-Cl isotope approach can strongly improve the qualitative and quantitative assessment of 1,1,1-TCA degradation processes in the field. [less ▲]

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See detailTowards processes-based groundwater vulnerability assessments
Dassargues, Alain ULg; Popescu, Cristina; Brouyère, Serge ULg

Conference (2015, September 15)

Various groundwater vulnerability methods have recently been developed. Considering groundwater quality issues, the most common techniques are based on calculation of an index expressing the protective ... [more ▼]

Various groundwater vulnerability methods have recently been developed. Considering groundwater quality issues, the most common techniques are based on calculation of an index expressing the protective effect (i.e. in terms of solute contaminant transport) of underground formations overlying the groundwater resource (Gogu & Dassargues, 2000, Gogu et al., 2003)). However, there is a strong need for new methods giving more emphasis on the processes-based calculation of vulnerability indicators. As a first alternative, a method is proposed based on three factors describing a pollution event (Brouyère et al., 2001): (1) the transit time from the source to the target, (2) the duration of the contamination breakthrough at the target, (3) the ratio between the maximum concentration at the target to the released concentration at the contamination source. The method can feature the impact of surface runoff to preferential infiltration points. Practically, the assessment can then be based on the simulated breakthrough curves at the ‘target’ corresponding to Dirac-type solicitations (Popescu et al., 2008). Different vulnerability maps can be built according to the relative importance conventionally given to each of the three factors. This concept allows a clear distinction between conventional aspects and processes-based results in the building of a final vulnerability indicator. A second proposal consists in reframing the groundwater vulnerability assessment in a Pressure-State-Impact causal chain that is familiar to decision makers (Beaujean et al., 2013). The method is here based on the calculation of sensitivity coefficients for a user-defined groundwater state for which several physically-based indicators are proposed. The sensitivity coefficients reflect the easiness with which the groundwater state transmits pressures into impacts. They are converted to vulnerability, using the concept of ‘transgressing a given threshold’ (Luers et al., 2003). While the methodology is general and can be applied in quantity as quality issues, the choice of causal chains has to be made prior to the calculation. The vulnerability is also related to a damaged state and is related to the ‘distance’ between the current state and a given threshold. Here also, the method allows a clear distinction between conventional choices (threshold) and scientific work (Dassargues et al., 2009). [less ▲]

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See detailA new hybrid approach for modelling groundwater flow in karst aquifers
Willems, Thibault ULg; Hakoun, Vivien ULg; Renard, Philippe et al

Conference (2015, September)

Groundwater flow modelling in karst aquifers represents a real challenge that requires adapted methods. The applicability of an innovative hybrid approach for modelling groundwater flow in karst aquifers ... [more ▼]

Groundwater flow modelling in karst aquifers represents a real challenge that requires adapted methods. The applicability of an innovative hybrid approach for modelling groundwater flow in karst aquifers, namely the Hybrid Finite Element Mixing Cell (HFEMC) method, is evaluated. The hybrid approach consists in combining a classical finite element (FE) model, to model slow flow in the rock matrix, with spatially distributed lumped reservoirs, to model fast flow in the karst conduits network. Water exchanges between the rock matrix and the conduits network are accounted for by means of an internal Fourier boundary conditions (BC). This BC (1st order exchange relation) allows to control the magnitude of water transfers between fast and slow flow domains. We tested the applicability of the HFEMC method on a schematic synthetic domain and on a real karst system. In the synthetic case analysis, we discussed dynamic processes of groundwater storage occurring in the karst system during a recharge pulse. The study focuses on the influence of selected parameters on representative variables such as the discharge curve of the karst system or pressure and mass transfers between conduits and rock matrix sub-domains. In this way, an inversion of the hydraulic gradient between karst conduits and the surrounding rock matrix is shown to occur during the recharge pulse. This phenomenon results in a temporary storage of water from conduits to the rock matrix, which impacts the modelled discharge curve. The first test performed on a real study site, the Noiraigue spring karst system (Jura mountains, Switzerland), exemplify the use of two separated lumped reservoirs for describing the conduits network, which allows to consider two base levels in the karst system. It also points out the challenges to face when modelling a complex natural karst system with the HFEMC approach. The results obtained show that the HFEMC approach is a good candidate to model groundwater flow in karst aquifers. [less ▲]

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See detailControlling factors and occurrence of inorganic and organic compounds in groundwater of urban and industrial areas
Gesels, Julie ULg; Dollé, Fabien ULg; Leclercq, Julie et al

Conference (2015, September)

A relatively extensive survey of groundwater contaminants is performed in urban and industrial contexts, at the regional scale (Walloon Region of Belgium), outside spots of contamination related to ... [more ▼]

A relatively extensive survey of groundwater contaminants is performed in urban and industrial contexts, at the regional scale (Walloon Region of Belgium), outside spots of contamination related to contaminated sites. More specifically, the most detected inorganic trace elements and organic contaminants are identified and their levels of occurrence are described statistically. Mechanisms that can explain their occurrence in groundwater are discussed. From a more pragmatic point of view, the data set has been also used to derive upper limits of pollutant background concentrations to be used in decision-making related to the management of contaminated groundwater in urban and industrial environments. The results presented are based on 243 samples from 8 sectors located in different geological contexts and different urban and industrial contexts. Each groundwater sample was analyzed for 19 inorganic trace elements, 61 organic micro-pollutants and 10 major and minor elements. Five physico-chemical parameters were measured in the field, at the time of sampling to determine the environmental conditions prevailing in groundwater. For comparison, existing groundwater analyses in natural context, available for the entire Walloon Region, were compiled from several databases. Cumulative distribution function plots allow comparing the distributions of inorganic trace elements in urban and industrial sectors to those obtained at the scale of the entire Walloon region. Cumulative distribution function plots are also used to compare the distribution of the inorganic trace elements in the different lithologies, in urban and industrial contexts. The composition of groundwater is altered in urban and industrial sectors with increased concentrations for most inorganic trace elements and organic contaminants. Anthropogenic influence is not limited to inputs of pollutants but also to alterations of subsurface environmental conditions, in particular redox conditions, resulting in the mobilization of pollutants. The influence of lithology is also marked in the data set. [less ▲]

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See detailThe use of the Vadose Zone Experimental Setup as an innovative in situ characterization method for the vadose zone: a case study at an industrial contaminated site in Belgium
Fernandez de Vera, Natalia ULg; Beaujean, Jean ULg; Jamin, Pierre ULg et al

Conference (2015, September)

The development of protection and remediation plans for contaminated soil and groundwater require a detailed understanding of the transport of pollutants in the subsurface. However, such understanding is ... [more ▼]

The development of protection and remediation plans for contaminated soil and groundwater require a detailed understanding of the transport of pollutants in the subsurface. However, such understanding is affected by the lack of spatial and temporal coverage provided by the current in situ characterization technologies. A new system has been developed in order to overcome such limitations. The vadose zone experimental setup is a new development combining cross-hole geophysics and the Vadose Zone Monitoring System (VMS). In cross-hole geophysics, an injection of an electrical current using electrodes installed in vertical boreholes is triggered. From measured potential differences, spatial patterns related with subsurface heterogeneities, water content and solute concentrations are inferred. The VMS allows continuous measurements of water content at different depths of the vadose zone, as well as water sampling. The system is formed by a flexible sleeve containing monitoring units along its depth which is installed in a slanted borehole. The system was installed at a former industrial site in Belgium, where soil and groundwater are contaminated with BTEX, PAH, and heavy metals. Two VMS were installed in two slanted boreholes on site, together with four vertical boreholes containing electrodes for geophysical measurements. The site was initially monitored under natural recharge conditions. Water content sensors located along the VMS registered fast wetting and draining reactions to rainfall events followed by the activation of water transport through fractures. Results from soil water samples show continuous evolution of water chemistry with depth, due to disequilibrium between infiltrated water and the hydrochemical conditions in the unsaturated zone. Subsequently, a saline tracer was injected in the surface. The transport of the tracer in the subsurface was monitored via cross-hole and surface geophysics. Results from imaging reflect the evolution of a plume through vertical and lateral transport and dilution. [less ▲]

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See detailRegional occurence of greenhouses gases in groundwater: Initial results in shallow Belgian aquifers.
Hakoun, Vivien ULg; Gesels, Julie ULg; Tseng, Jean Hsiao-Chun et al

Poster (2015, September)

Currently, the lack of robust, context-distributed subsurface greenhouses gases (GHG) concentrations data is a key bottleneck to reduce the uncertainty range of GHG groundwater input to continental ... [more ▼]

Currently, the lack of robust, context-distributed subsurface greenhouses gases (GHG) concentrations data is a key bottleneck to reduce the uncertainty range of GHG groundwater input to continental surface water bodies such as rivers or lakes estimates. Carbon dioxyde (CO2), methane (CH4) and nitrous oxyde (N2O) are likely to be indirectly transferred to the atmosphere through groundwater discharge into continental surface water bodies. We aim to extend regional-scale estimates of indirect GHG emissions by screening, in numerous hydrogeological (such as alluvial, sandstone, chalk and limestone aquifers) and land use contexts (such as industrial and agricultural), the occurence of these gases. Here, we report and discuss CO2, CH4 and N2O concentrations from an initial survey conducted over selected sites (n= 40) within shallow (0-100 m depth) aquifers in Wallonia (Belgium) for the first time. The preliminary results obtained in this study show that the range of GHG concentrations varies between 5160 and 47544 ppm, 0 and 1064 nmol.L-1, as well as 1 and 5637 nmol.L-1 for the partial pressure of CO2, CH4 and N2O respectively. This new and unique regional dataset provides a first step in developping a refined understanding of favorable contexts for GHG occurence in groundwater which may be used to reduce the uncertainties related to indirect emissions of GHG through groundwater-surface water transfers. [less ▲]

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See detailAssessment of climate change effects on groundwater resource in transient conditions
Goderniaux, Pascal; Wildemeersch, Samuel; Brouyère, Serge ULg et al

Conference (2015, June 27)

A sophisticated transient weather generator (WG) in combination with an integrated surface-subsurface hydrological model (HydroGeoSphere) are used for producing a stochastic generation of large numbers of ... [more ▼]

A sophisticated transient weather generator (WG) in combination with an integrated surface-subsurface hydrological model (HydroGeoSphere) are used for producing a stochastic generation of large numbers of equiprobable climatic time series, representing transient climate change, and assess impacts on groundwater resources in a probabilistic way. The modelling approach, involving the catchment-scale fully integrated surface-subsurface model, is described in Goderniaux et al. [2009]. Biased-corrected climate change scenarios are applied as input of the hydrological model to quantify their impact on groundwater resources. In Goderniaux et al. [2011], the integrated model is used in combination with a stochastic daily weather generator (WG). This WG allowed generating a large number of equiprobable climate change scenarios representative of a full transient climate between 2010 and 2085. These scenarios enabled to account for the transient nature of the future climate change, and to assess the uncertainty related to the weather natural variability. The downscaling method considers changes in the climatic means, but also in the distribution of wet and dry days. This new methodology is applied for the unconfined chalky aquifer of the Geer catchment in Belgium. A general decrease of the mean groundwater piezometric heads, has been calculated. The approach allowed also to assess different uncertainty sources: (1) the uncertainty linked to the calibration of the hydrological model, using 'UCODE_2005'; (2) the uncertainty linked to the global and regional climatic models (GCMs and RCMs), by using a multi-model ensemble; (3) the uncertainty linked to the natural variability of the weather, by using stochastic climate change scenarios. 30 equiprobable climate change scenarios from 2010 to 2085 have been generated for each of 6 different RCMs. Results show that although the 95% confidence intervals calculated around projected groundwater levels remain large, the climate change signal becomes stronger than that of natural climate variability by 2085. The WG ability to simulate transient climate change enabled the assessment of the likely timescale and associated uncertainty of a specific impact. This methodology constitutes a real improvement in the field of groundwater projections under transient climate change conditions as it enables water managers to analyse risks and take decisions with full knowledge of projected impact and their degree of confidence. [less ▲]

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See detailA hydrochemical - isotopic approach for assessing factors controlling the regional pollution of an urban aquifer
Gesels, Julie ULg; Orban, Philippe ULg; Popescu, Ileana-Cristina et al

Poster (2015, June 24)

The alluvial aquifer of the Meuse River is contaminated at regional scale in the urbanized and industrialized area of Liège in Belgium, in particular inorganics pollutants such as sulfate, nitrate and ... [more ▼]

The alluvial aquifer of the Meuse River is contaminated at regional scale in the urbanized and industrialized area of Liège in Belgium, in particular inorganics pollutants such as sulfate, nitrate and ammonium. The sources of those contaminants are numerous: brownfields, urban waste water, subsurface acid mine drainage from former coal mines, atmospheric deposits related to former pollutants emissions in the atmosphere ... Sulfate, nitrate and ammonium are both typical pollutants of the aquifer and tracers of the possible pollution sources. In the Water Framework Directive context, a detailed hydrogeochemical characterization of groundwater was performed. The aim is to determine the origin of the inorganic contaminations, the main processes contributing to poor groundwater quality and the spatial extent of the contaminations. A large hydrochemical sampling campaign was performed, based on 71 selected representative sampling locations, to better characterize the different vectors (end-members) of contamination of the alluvial aquifer and their respective contribution to groundwater contamination in the area. Groundwater samples were collected and analyzed for major and minor compounds and metallic trace elements. The analyses also include stable isotopes in water, sulfate, nitrate, ammonium, dissolved inorganic carbon, boron and strontium. Different hydrogeochemical approaches are combined to obtain a global understanding of the hydrogeochemical processes at regional scale. Hydrochemical interpretations are based on classical diagrams, spatial distribution maps, geochemical equations, multivariate statistics such as self-organizing maps and isotopic analyses. With this combined approach, the location of the contaminant sources and most contaminated sectors of the alluvial aquifer together with a better understanding of geochemical processes involved are obtained. Redox processes strongly influence the composition of groundwater, specifically for compounds degrading the quality of groundwater in the area (sulfate, nitrate and ammonium). The highest concentrations of sulfate can be associated with the post-mining stage in the acid mine drainage process. Various reactions involving nitrogen compounds have been identified and allow a better understanding of causes of high concentrations of ammonium and nitrate. Denitrification and sulphate reduction are also demonstrated based on isotopic ratios. [less ▲]

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See detailUncertainty of climate change impact on groundwater reserves - Application to a chalk aquifer
Goderniaux, Pascal; Brouyère, Serge ULg; Wildemeersch, Samuel et al

in Journal of Hydrology (2015), 528

Recent studies have evaluated the impact of climate change on groundwater resources for different geographical and climatic contexts. However, most studies have either not estimated the uncertainty around ... [more ▼]

Recent studies have evaluated the impact of climate change on groundwater resources for different geographical and climatic contexts. However, most studies have either not estimated the uncertainty around projected impacts or have limited the analysis to the uncertainty related to climate models. In this study, the uncertainties around impact projections from several sources (climate models, natural variability of the weather, hydrological model calibration) are calculated and compared for the Geer catchment (465 km2) in Belgium. We use a surface–subsurface integrated model implemented using the finite element code HydroGeoSphere, coupled with climate change scenarios (2010–2085) and the UCODE_2005 inverse model, to assess the uncertainty related to the calibration of the hydrological model. This integrated model provides a more realistic representation of the water exchanges between surface and subsurface domains and constrains more the calibration with the use of both surface and subsurface observed data. Sensitivity and uncertainty analyses were performed on predictions. The linear uncertainty analysis is approximate for this nonlinear system, but it provides some measure of uncertainty for computationally demanding models. Results show that, for the Geer catchment, the most important uncertainty is related to calibration of the hydrological model. The total uncertainty associated with the prediction of groundwater levels remains large. By the end of the century, however, the uncertainty becomes smaller than the predicted decline in groundwater levels. [less ▲]

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See detailUse and utility of combined solute and heat tracer tests for characterizing hydrogeothermal properties of an alluvial aquifer
Klepikova, Maria; Wildemeersch, Samuel; Jamin, Pierre ULg et al

Conference (2015, June 05)

Using heat as a tracer together with a solute tracer is interesting for characterizing hydrogeothermal properties of the underground. These properties are particularly needed to dimension any low ... [more ▼]

Using heat as a tracer together with a solute tracer is interesting for characterizing hydrogeothermal properties of the underground. These properties are particularly needed to dimension any low temperature geothermal project using an open doublet system (pumping-reinjection) in a shallow aquifer. The tracing experiment, conducted in the alluvial aquifer of the River Meuse (Hermalle near Liège), consisted in injecting simultaneously heated water at 40°C and a dye tracer in a piezometer and monitoring the evolution of temperature and tracer concentration in the recovery well and in nine monitoring piezometers located in three transects with regards to the main groundwater flow direction. The breakthrough curves measured in the recovery well showed that heat transfer in the alluvial aquifer is slower. All measured results show also that the heat diffusivity is larger than the solute dispersion. These contrasted behaviours are stressed in the lower permeability zones of the aquifer. Inverse modelling is applied for calibrating the numerical simulation of the groundwater flow, heat and solute transport. First results are presented showing that the density effect must be taken into account and that, as expected, the most important parameter to be calibrated accurately is the hydraulic conductivity. [less ▲]

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See detailModélisation de la remontée des eaux dans les anciennes mines de charbon : un outil pour détecter les seuils de risques d’inondation en plaine alluviale de la Meuse près de Liège (Belgique)
Dassargues, Alain ULg; Wildemeersch, Samuel; Orban, Philippe ULg et al

in Des villes et des territoires sobres et sûrs, Synthèse des interventions (2015, June 03)

La plaine alluviale de la Meuse occupe la partie centrale du bassin charbonnier de Liège. Durant les exploitations minières, les niveaux d’eau des aquifères avaient été rabattus par des pompages d’exhaure ... [more ▼]

La plaine alluviale de la Meuse occupe la partie centrale du bassin charbonnier de Liège. Durant les exploitations minières, les niveaux d’eau des aquifères avaient été rabattus par des pompages d’exhaure. Des galeries d’exhaure creusées à partir des pieds de versant dans la vallée de la Meuse contribuaient également à dénoyer le gisement. La fermeture des dernières exploitations minières durant les années 70 et 80 a été le plus souvent assortie d’un arrêt des opérations de pompage qui y sont associées. Ceci a induit une remontée significative des eaux souterraines avec des conséquences indésirables possibles. Les modèles hydrogéologiques peuvent grandement aider à simuler les écoulements des eaux souterraines dans le contexte particulier des travaux miniers. Cependant, les techniques de modélisation classiques ne sont pas adaptées à ce contexte car le milieu est fortement perturbé par les anciens travaux et les réseaux de galeries. Par conséquent, des techniques de modélisation spécifiques ont été développées. Il s'agit d'une combinaison de modèles de boîte (ne nécessitant que quelques paramètres) pour calculer les niveaux d'eau moyens dans les zones exploitées, avec une modélisation physiquement basée et spatialement distribuée représentant explicitement les zones inexploitées et prenant en compte les interactions entre ces deux sous-domaines. Grâce à ce couplage, les échanges d'eau entre les zones exploitées et inexploitées sont explicitement pris en compte. La méthode permet de simuler la remontée des eaux souterraines après la fermeture des mines et des phénomènes associés tels que les 'coups d'eau' produits par les galeries drainantes. Les concepts et équations de la méthode sont présentés et illustrés sur des cas synthétiques, puis sur l'application de la zone de Cheratte-Blégny. [less ▲]

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See detailSensitivity and vulnerability to groundwater overexploitation by a ‘pressure state impact’ and process based approach
Beaujean, Jean; Lemieux, Jean-Michel; Therrien, René et al

Conference (2015, May 26)

A methodology is developed for proposing a groundwater vulnerability assessment in a Pressure-State-Impact causal chain that is familiar to decision makers. The ‘Driver Pressure State Impact Response’ ... [more ▼]

A methodology is developed for proposing a groundwater vulnerability assessment in a Pressure-State-Impact causal chain that is familiar to decision makers. The ‘Driver Pressure State Impact Response’ (DPSIR) framework, for describing interactions between society and the environment, defines a chain of Drivers that exert Pressures on the State of a given resource, such as groundwater, which then generates an Impact that will require an appropriate Response (Kristensen, 2004). The method is here based on the calculation of sensitivity coefficients for a user-defined groundwater state for which several physically-based indicators are proposed. These sensitivity coefficients reflect the easiness with which the groundwater state transmits pressures into impacts. They are grouped into a vulnerability matrix of pressures and impacts that quantify vulnerability for every combination of causal links identified in the DPSIR chain. For that reason, the sensitivity coefficients are converted to vulnerability, using the concept of ‘transgressing a given threshold’, which is commonly used in socioeconomic sciences (Luers et al. 2003). The concept of ‘rising above a given concentration threshold’ can be used for groundwater quality issues. The concept of ‘falling below a given piezometric head threshold’ can be used for groundwater quantity issues as aquifer overexploitation problems. Outside the careful selection of the sensitivity analysis method that can significantly influence the computational effort (Beaujean et al., 2013), emphasis is given to the illustration of the general methodology on a simple groundwater quantity case (of an alluvial aquifer with concerns related to water supply) demonstrating the potential use of this general and physically based vulnerability assessment method. While the methodology is general, the choice of causal chains has to be made prior to the calculation. The vulnerability is also related to a damaged state and is related to the ‘distance’ between the current state and a given threshold. This choice is arbitrary such that the vulnerability is sensitive to the choice of the threshold. [less ▲]

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See detailProcess-based method for groundwater resource vulnerability mapping with regards to solute contamination at the surface
Popescu, Cristina; Brouyère, Serge ULg; Orban, Philippe ULg et al

Conference (2015, May 26)

Numerous groundwater vulnerability methods have been developed taking into consideration a variable number of factors. The most common techniques are based on calculation of an index expressing the ... [more ▼]

Numerous groundwater vulnerability methods 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. However, it has been shown that different overlay and index methods applied to the same system can yield dramatically dissimilar results (among others, Gogu et al., 2003). 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 process-based point of view is proposed and based on three factors describing a pollution event (Brouyère et al., 2001): (1) the transit time from the source to the target, (2) the duration of the contamination breakthrough at the target, (3) the ratio between the maximum concentration at the target to the released concentration at the contamination source. The assessment can then be based on the impulse response at the ‘target’ to a Dirac-type solicitation (point, unit mass, instantaneous source of pollution), considering only physical hydrodispersive processes for intrinsic vulnerability and both physical and biochemical processes for specific vulnerability. The breakthrough curve obtained after a vertical transfer through the overlying layers can be computed pixel by pixel. Automatically processing the columns with identical characteristics, 1D partially saturated flow and solute transport computations are performed. Different maps are obtained for the three above mentioned factors. On the basis of these results, different vulnerability maps can be built according to the weighting coefficients agreed by the local community or decision makers. This concept allows a clear distinction between conventional aspects and process-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. To solve this problem, Popescu et al. (2004 & 2008) and Dassargues et al. (2009) proposed a method for quantifying a lateral “dangerosity” coefficient using runoff coefficients based on land use, slopes, and soil properties. A test application is illustrated on a case-study located in a limestone basin in Belgium. [less ▲]

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See detailContribution of the Finite Volume Point Dilution Method for measurement of groundwater fluxes in a fractured aquifer
Jamin, Pierre ULg; Goderniaux, Pascal; Bour, Olivier et al

in Journal of Contaminant Hydrology (2015)

Measurement of groundwater fluxes is the basis of all hydrogeological study, from hydraulics characterization to the most advanced reactive transport modelling. Usual groundwater fluxes estimation with ... [more ▼]

Measurement of groundwater fluxes is the basis of all hydrogeological study, from hydraulics characterization to the most advanced reactive transport modelling. Usual groundwater fluxes estimation with Darcy’s law may lead to cumulated errors on spatial variability, especially in fractured aquifers where local direct measurement of groundwater fluxes becomes necessary. In the present study, both classical Point Dilution Method (PDM) and Finite Volume Point Dilution Method (FVPDM) are compared on the fractured crystalline aquifer of Ploemeur, France. The manipulation includes the first use of the FVPDM in a fractured aquifer using a double packer. This configuration limits the vertical extend of the tested zone to target a precise fracture zone of the aquifer. The result of this experiment is a continuous monitoring of groundwater fluxes that lasted for more than 4 days. Measurements of groundwater flow rate in the fracture (Qt) by PDM provide good estimates only if the mixing volume (Vw) (volume of water in which the tracer is mixed) is precisely known. Conversely, the FVPDM allows for an independent estimation of Vw and Qt, leading to better precision in case of complex experimental setup such as the one used. The precision of a PDM does not rely on the duration of the experiment while a FVPDM may require long experimental duration to guarantees a good precision. Classical PDM should then be used for rapid estimation of groundwater flux using simple experimental setup. On the other hand, the FVPDM is a more precise method that has a great potential for development but may require longer duration experiment to achieve a good precision if the groundwater fluxes investigated are low and/or the mixing volume is large. [less ▲]

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See detailCharacterization of superficial deposits using electrical resistivity tomography (ERT) and horizontal-to-vertical spectral ratio (HVSR) geophysical methods: A case study
Sauret, Elie; Beaujean, Jean; Nguyen, Frédéric ULg et al

in Journal of Applied Geophysics (2015), 121

In developing countries, superficial aquifers are potential water resources for irrigation in agriculture. Cost effective methodologies are required to characterize those deposits in order to identify ... [more ▼]

In developing countries, superficial aquifers are potential water resources for irrigation in agriculture. Cost effective methodologies are required to characterize those deposits in order to identify better locations for groundwater abstraction. This study has investigated the potential use of combined electrical resistivity tomography (ERT) and horizontal-to-vertical spectral ratio (HVSR) to characterize the heterogeneity and thickness of superficial deposits deployed along of a river. The ERT and HVSRmethods are non-invasive geophysical techniques, simple, efficient, robust and easy-to-use in alluvial environment contexts. Using these geophysicalmethods in the Kou basin in Burkina Faso (West Africa), a good correspondence is obtained between ERT images and resonance frequencies determined on theHVSR profiles perpendicular to the Kou River. The superficial deposits and the bedrock depth have been characterized and mapped. The role of faulting andmagmatic intrusions in the accumulation of fractured, deconsolidated andweathered bedrockmaterials and the filling of superficial deposits have been observed and highlighted. Froma hydrogeological point of view, the thickness of (clay-free) superficial deposits presents a relatively important groundwater reservoir and potentially high productivity. The ERT and HVSR were proven to be efficient and complementary methods in superficial deposit environment characterization, and a viable option for exploration of superficial deposits in terms of groundwater reservoir in environments where the bedrock exhibits strong lateral variation due to faulting or volcanic activities. [less ▲]

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See detailVadose zone characterisation at industrial contaminated sites
Fernandez de Vera, Natalia ULg; Dahan, Ofer; Dassargues, Alain ULg et al

in CL:AIRE bulletin (2015)

In order to improve risk characterization and remediation measures for soil and groundwater contamination, there is a need to improve in situ vadose zone characterization. However, most available ... [more ▼]

In order to improve risk characterization and remediation measures for soil and groundwater contamination, there is a need to improve in situ vadose zone characterization. However, most available technologies have been developed in the context of agricultural soils. Such methodologies are not applicable at industrial sites, where soils and contamination differ in origin and composition. To overcome such difficulties, a vadose zone experiment has been setup at a former industrial site in Belgium. Industrial activities carried out on site left a legacy of soil and groundwater contamination in BTEX, PAH, cyanide and heavy metals. The experiment comprises the combination of two techniques: the Vadose Zone Monitoring System (VMS) and cross-hole geophysics. The VMS allows continuous measurements of water content at different depths of the vadose zone, as well as the possibility of water sampling at different depths. The system is formed by a flexible sleeve containing monitoring units along its depth which is installed in a slanted borehole. The flexible sleeve contains three types of monitoring units in the vadose zone: Time Domain Transmissometry (TDT), which allows water content measurements; Vadose Sampling Ports (VSP), used for collecting water samples coming from the matrix; the Fracture Samplers (FS), which are used for retrieving water samples from the fractures. Cross-hole geophysics techniques consist in the injection of an electrical current using electrodes installed in vertical boreholes. From such injections, spatial patterns related with subsurface heterogeneities, water content and solute concentrations are inferred. Two VMS were installed in two slanted boreholes on site, together with four vertical boreholes containing electrodes for geophysical measurements. The site was monitored under natural recharge conditions. Results show the reaction of the vadose zone to rainfall events, as well as chemical evolution of soil water with depth and rainfall infiltration. [less ▲]

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