References of "Brouyère, Serge"
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See detailInteractions between groundwater and the cavity of an old slate mine used as lower reservoir of an UPSH (Underground Pumped Storage Hydroelectricity): A modelling approach
Bodeux, Sarah ULg; Pujades, Estanislao ULg; Orban, Philippe ULg et al

in Engineering Geology (2017), 217

In the actual evolving energy context, characterized by an increasing part of intermittent renewable sources, the development of energy storage technologies are required, such as pumped storage ... [more ▼]

In the actual evolving energy context, characterized by an increasing part of intermittent renewable sources, the development of energy storage technologies are required, such as pumped storage hydroelectricity (PSH). While new sites for conventional PSH plants are getting scarce, it is proposed to use abandoned underground mines as lower reservoirs for Underground Pumped Storage Hydroelectricity (UPSH). However, the hydrogeological consequences produced by the cyclic solicitations (continuous pumpings and injections) have been poorly investigated. Therefore, in this work, groundwater interactions with the cyclically fill and empty cavity were numerically studied considering a simplified description of a slate mine. Two pumping/injection scenarios were considered, both for a reference slate rock case and for a sensitivity analysis of variations of aquifer hydraulic conductivity value. Groundwater impacts were assessed in terms of oscillations of piezometric heads and mean drawdown around the cavity. The value of the hydraulic conductivity clearly influences the magnitude of the aquifer response. Studying interactions with the cavity highlighted that seepage into the cavity occurs over time. The volume of seeped water varies depending on the hydraulic conductivity and it could become non-negligible in the UPSH operations. These preliminary results allow finally considering first geological feasibility aspects, which could vary conversely according to the hydraulic conductivity value and to the considered groundwater impacts. [less ▲]

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See detailStatistical description of hydrogeological parameters for the main aquifer contexts in Wallonia
Briers, Pierre ULg; Dollé, Fabien ULg; Orban, Philippe ULg et al

Conference (2017, January 20)

The Walloon Region Soil decree proposes a series of guidance documents associated to the procedures for site remediation operations. Among others, one of these documents describes methodologies and tools ... [more ▼]

The Walloon Region Soil decree proposes a series of guidance documents associated to the procedures for site remediation operations. Among others, one of these documents describes methodologies and tools for risk assessment of pollutant leaching from soil to groundwater and for pollutant dispersion through groundwater. These tools require using estimates of hydrogeolocial parameters such as hydraulic conductivity, effective (transport) porosity etc. In this context, an inventory of hydrogeological studies (regional characterization studies, groundwater protection zones…) was performed to identify and collect available field-based measurements for a statistical description and analysis of such data. Complementary to that, a simple geodatabase has been developed to manage and process these data. As expected, these results show contrasted parameter distributions per geological contexts and regions. The objective of the presentation is to describe the methodology followed for the statistical treatment of hydrogeological data and to present the results and associated database. It is believed that such results can be very useful for different hydrogeological studies, in particular as a first referential for groundwater modelling applications and any other studies where statistical descriptions of hydrogeological data are relevant. [less ▲]

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See detailDynamics and emissions of N2O in groundwater: A review
Jurado Elices, Anna ULg; Borges, Alberto ULg; Brouyère, Serge ULg

in Science of the Total Environment (2017), 584-585C

This work reviews the concentrations, the dynamics and the emissions of nitrous oxide (N2O) in groundwater. N2O is an important greenhouse gas (GHG) and the primary stratospheric ozone depleting substance ... [more ▼]

This work reviews the concentrations, the dynamics and the emissions of nitrous oxide (N2O) in groundwater. N2O is an important greenhouse gas (GHG) and the primary stratospheric ozone depleting substance. The major anthropogenic source that contributes to N2O generation in aquifers is agriculture because the use of fertilizers has led to the widespread groundwater contamination by inorganic nitrogen (N) (mainly nitrate, NO3−). Once in the aquifer, this inorganic N is transported and affected by several geochemical processes that produce and consume N2O. An inventory of dissolved N2O concentrations is presented and the highest dissolved concentration is about 18.000 times higher than air-equilibrated water (up to 4004 μg N L-1). The accumulation of N2O in groundwater is mainly due to denitrification and to lesser extent to nitrification. Their occurrence depend on the geochemical (e.g., NO3−, dissolved oxygen, ammonium and dissolved organic carbon) as well as hydrogeological parameters (e.g., groundwater table fluctuations and aquifer permeability). The coupled understanding of both parameters is necessary to gain insight on the dynamics and the emissions of N2O in groundwater. Overall, groundwater indirect N2O emissions seem to be a minor component of N2O emissions to the atmosphere. Further research might be devoted to evaluate the groundwater contribution to the indirect emissions of N2O because this will help to better constraint the N2O global budget and, consequently, the N budget. [less ▲]

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See detailConvention Région wallonne et HGE-ULg Caractérisation complémentaire des masses d’eau dont le bon état dépend d’interactions entre les eaux de surface et les eaux souterraines - Délivrable D1.8 Rapport final
Brouyère, Serge ULg; Briers, Pierre ULg; Descy, Jean-Pierre et al

Report (2017)

Mechanisms of interactions between groundwater bodies and rivers whose status and anthropogenic use can be detrimental from a quantitative and qualitative point of view to one or the other of these two ... [more ▼]

Mechanisms of interactions between groundwater bodies and rivers whose status and anthropogenic use can be detrimental from a quantitative and qualitative point of view to one or the other of these two compartments of the water cycle. In addition, contamination of groundwater by nitrate remains relevant. Based on these observations, a study financed by the Public Service of Wallonia was carried out over a period of 39 months to investigate (1) the direction, importance and dynamics of water exchange between groundwater and rivers at the scale of a river section; (2) the impact of these interactions on river baseflows and the river ecological status as a function of groundwater withdrawal and recharge at the catchment scale; (3) mechanisms and timing of transfer and abatement of pollutants (nitrate) between groundwater and surface waters at the watershed scale. The consequences of these mechanisms on the medium- and long-term evolution of groundwater and surface water quality were to be determined. To achieve this, the project relied on the implementation of a series of field investigations essentially focused on the interfaces between surface water and groundwater compartments (soil and unsaturated zone and water-table interface), while acquiring additional information on groundwater. The investigations carried out in the watersheds of the upstream Hoyoux and Triffoy watershed in the Condroz region aimed to provide 6 specific responses to water quantity and quality issued associated with groundwater – surface water interactions in the selected basins and generic responses in the form of new knowledge concerning the mechanisms of recharge and groundwater - river exchanges, concerning the evolution of nitrate concentrations in watersheds, data and measurements for the parameterization of models, and water resources management tools in the form of quantitative and qualitative indicators for groundwater - surface water interactions. [less ▲]

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See detailFactors controlling spatial and temporal patterns of multiple pesticide compounds in groundwater (Hesbaye chalk aquifer, Belgium)
Hakoun, Vivien; Orban, Philippe ULg; Dassargues, Alain ULg et al

in Environmental Pollution (2017)

Factors governing spatial and temporal patterns of pesticide compounds (pesticides and metabolites) concentrations in chalk aquifers remain unclear due to complex flow processes and multiple sources. To ... [more ▼]

Factors governing spatial and temporal patterns of pesticide compounds (pesticides and metabolites) concentrations in chalk aquifers remain unclear due to complex flow processes and multiple sources. To uncover which factors govern pesticide compound concentrations in a chalk aquifer, we develop a methodology based on time series analyses, uni- and multivariate statistics accounting for concentrations below detection limits. The methodology is applied to long records (1996–2013) of a restricted compound (bentazone), three banned compounds (atrazine, diuron and simazine) and two metabolites (deethylatrazine (DEA) and 2,6–dichlorobenzamide (BAM)) sampled in the Hesbaye chalk aquifer in Belgium. In the confined area, all compounds had non-detects fractions >80%. By contrast, maximum concentrations exceeded EU’s drinking-water standard (100 ngL-1) in the unconfined area. This contrast confirms that recent recharge and polluted water did not reach the confined area, yet. Multivariate analyses based on variables representative of the hydrogeological setting revealed higher diuron and simazine concentrations in the southeast of the unconfined area, where urban activities dominate land use and where the aquifer lacks protection from a less permeable layer of hardened chalk. At individual sites, positive correlations (up to τ =0,48 for bentazone) between pesticide compound concentrations and multi-annual groundwater level fluctuations confirm occurrences of remobilization. A downward temporal trend of atrazine concentrations likely reflects decreasing use of this compound over the last 28 years. However, the lack of a break in concentrations time series and maximum concentrations of atrazine, simazine, DEA and BAM exceeding EU’s standard post-ban years provide evidence of persistence. Contrasting upward trends in bentazone concentrations show that a time lag is required for restriction measures to be efficient. These results shed light on factors governing pesticide compound concentrations in chalk aquifers. The developed methodology is not restricted to chalk aquifers, it could be transposed to study other pollutants with concentrations below detection limits. Several factors govern pesticide compounds concentrations in the chalk: hydrogeological setting, land use, groundwater level fluctuations and persistence. [less ▲]

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See detailStream-aquifer interactions: a combined field - methodological approach in fractured carbonate catchments
Brouyère, Serge ULg; Briers, Pierre ULg; Orban, Philippe ULg et al

Conference (2016, December 16)

Stream-aquifer studies remain a challenge due to numerous factors impacting these interactions. They play a fundamental role in terms of quantity and quality of water, in particular on the ecological ... [more ▼]

Stream-aquifer studies remain a challenge due to numerous factors impacting these interactions. They play a fundamental role in terms of quantity and quality of water, in particular on the ecological status of rivers. Field quantification of such interactions is a first step but it has to be in relation with the whole budgets of water and transported substances across the catchment in order to represent their importance on overall fluxes. Numerous complementary investigations have to be undertaken to achieve such understanding of catchment behavior, in particular to estimate specific indicators and to achieve representative data for modeling stream-aquifer interactions. From that situation, our study aims to characterize and quantify stream-aquifer interactions to assess reliability of diverse field experiments methodologies. A catchment has been studied for 3 years in quantitative and qualitative ways via a dense instrumentation and monitoring. Numerous complementary investigations (discharge measurements, hydrogeochemistry, distributed temperature sensing, base flow separation…) have been applied to reach the objectives. We achieved a large and diversified measurement dataset of groundwater-surface water interactions and whole water budget. This allowed reaching an improved understanding of the catchment behavior to quantify importance of the groundwater component on the dynamics and chemistry of the stream and on the consequences on river ecological status. The investigations on several subcatchments allows also to propose a general typology of stream catchment in terms of groundwater dependence based on the combination of various groundwater contexts and groundwater-stream interaction indicators. Methodologies applied in this study allow to emphasize strength and weakness of numerous investigations in a stream aquifer project and conclusions can be reproduced and generalized to other contexts. [less ▲]

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See detailAn old slate mine as lower reservoir for UPSH (Underground Pumping Storage Hydroelectricity)- groundwater interactions and limitations
Bodeux, Sarah ULg; Pujades, Estanislao ULg; Orban, Philippe ULg et al

Conference (2016, September 27)

Renewable energy sources have an increasing role to play in the future energy framework but their intermittence cannot afford a stable production according to the demand. Pumped Storage Hydroelectricity ... [more ▼]

Renewable energy sources have an increasing role to play in the future energy framework but their intermittence cannot afford a stable production according to the demand. Pumped Storage Hydroelectricity (PSH) is an efficient technology to store and release electricity. However, the development of new PSH plants is limited by environmental and topographic constraints. An innovative alternative consists in using old underground mines as lower reservoirs of Underground Pumped Storage Hydroelectricity (UPSH) plants. In this configuration, large amount of water is pumped and injected in underground cavities and these cyclic stresses impact the groundwater system. A hybrid 3D finite element mixing cell method is used to numerically simulate the use of an UPSH facility, in the case of an abandoned slate mine. Different scenarios are computed with varying pumping injection time-sequences. In order to assess the impact on the surrounding groundwater conditions, the resulting head evolution in the cavity and at different distances is analyzed in terms of groundwater oscillation magnitude, drawdown, and seepage into the cavity. Results show clearly the influence of the pumping injection time-sequence (rates, regularity, timing and duration of no-activity periods) on the actual head evolution in the surrounding medium and consequently on the magnitude of interactions with the cavity. For a given hydraulic conductivity of the surrounding medium (i.e. slates in this case study), the main conclusion is that the resulting interaction seepage flows (in and out of the cavity) are highly dependent on the chosen pumping injection sequences. The future impact of UPSH operation must be assessed taking this fact into account. [less ▲]

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See detailOccurrence of greenhouse gases (CO2, N2O and CH4) in groundwater of the Walloon Region (Belgium)
Jurado Elices, Anna ULg; Borges, Alberto ULg; Hakoun, Vivien et al

Conference (2016, September 27)

Carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) can be indirectly transferred to the atmosphere through groundwater discharge into surface water bodies such as rivers. However, these emissions ... [more ▼]

Carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) can be indirectly transferred to the atmosphere through groundwater discharge into surface water bodies such as rivers. However, these emissions are poorly evaluated and highly uncertain. The aim of this work is identify the hydrogeological contexts (alluvial, sandstone, chalk and limestone aquifers) and in situ conditions which are most conducive to the generation and occurrence of GHGs in groundwater at a regional scale. To this end, CO2, CH4 and N2O concentrations as well as major and minor elements were monitored (n=37 samples) in two field campaigns (09/2014 and 03/2015) in 15 groundwater bodies of the Walloon Region (Belgium). This preliminary work, which was presented in the 42st IAH conference (Rome, Italy), shown that GHG concentrations range from 5,160 to 47,544 ppm from the partial pressure of CO2 and from 0 to 1,064 nmol/L and 1 to 5,637 nmol/L for CH4 and N2O respectively. Overall, groundwater was supersaturated in GHGs with respect to atmospheric equilibrium, suggesting that groundwater contribute to the atmospheric GHGs budget. A third sampling campaign is carried out in 2016 including around 60 new groundwater samples. The combination of the results of the three campaigns allows: (1) reducing the uncertainties related to indirect emissions of GHG through groundwater-surface water interaction and (2) contributing to a better understanding of the occurrence of GHGs in aquifers. New results will be presented and discussed in detail in the presentation. [less ▲]

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See detailComparison of temperature from DTS and ERT with direct measurements during heat tracer experiments in heterogeneous aquifers
Nguyen, Frédéric ULg; Hermans, Thomas ULg; Jamin, Pierre ULg et al

Conference (2016, September 27)

Geothermal field characterization and heat tracer experiments often rely on scarce temperature data collected in boreholes. Electrical resistivity tomography (ERT) and distributed temperature sensing (DTS ... [more ▼]

Geothermal field characterization and heat tracer experiments often rely on scarce temperature data collected in boreholes. Electrical resistivity tomography (ERT) and distributed temperature sensing (DTS) have the potential to provide spatial information on temperature changes in the subsurface. In this contribution, we show how DTS and ERT have been used to investigate the heterogeneity of a heterogeneous aquifer during a heat tracing experiment under forced gradient conditions. Optic fibers were installed in the heat injection well and in two piezometers intersecting the main flow directions at 8 m from the injection well. These piezometers were also equipped with ERT. The DTS measurement in the injection well clearly shows the two-layer nature of the aquifer. After the end of injection, the temperature in the bottom part of the well decreases faster than in the upper part due to the higher water fluxes. Those results are confirmed by DTS measurements in natural flow conditions during a heating wire test. DTS and ERT in the cross-panel both show the vertical and lateral heterogeneity of the aquifer. Temperatures only increase significantly in the bottom part of the aquifer where advection is predominant. However, strong differences are observed laterally. ERT additionally shows that the hot plume is divided in two main flow paths, which is confirmed by direct temperature measurements. The comparison of DTS and ERT shows that one of the well is suffering from water mixing. Indeed, temperature from DTS are homogeneous over the whole tichkness of the aquifer, whereas ERT temperature, less affected by local variations, are varying. Our study demonstrate the value of spatially distributed measurements for the monitoring of heat tracer experiment and highligths the issue of multilevel sampling. The detailed temperature measurements can be subsequently used in hydrogeological model to better estimates heat flow and transport parameters. [less ▲]

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See detailHow groundwater interactions can influence UPSH (Underground Pumping Storage Hydroelectricity) operations
Bodeux, Sarah ULg; Pujades, Estanislao ULg; Orban, Philippe ULg et al

Conference (2016, July 28)

In the current energy grid, renewable energy has an increasing role to play. However, their intermittence cannot afford to regulate the produced electricity according to the irregular demand (Evans et al ... [more ▼]

In the current energy grid, renewable energy has an increasing role to play. However, their intermittence cannot afford to regulate the produced electricity according to the irregular demand (Evans et al., 2012). Pumped Storage Hydroelectricity (PSH) is a well-known efficient technology to store and release electricity according to the demand needs but appropriate potential new sites are getting scarce (Steffen, 2012). An innovative alternative consists in using abandoned mines as lower reservoir of an Underground Pumping Storage Hydroelectricity (UPSH) plant. In such configuration, large amount of water will be pumped or injected in underground cavities, creating subsequently head oscillations in the surrounding aquifers. Consequently, this seepage occurring between the considered cavity and the varying groundwater heads in the surrounding geological medium may influence the efficiency of the UPSH plant but also the magnitude of the potential impacts on the groundwater resources. A hybrid 3D finite element mixing cell method (Brouyère et al., 2009) is used to simulate numerically the use of a representative UPSH cavity and calculate the induced changes in groundwater heads in the surrounding geological medium. Different scenarios are computed varying parameter values (hydrogeological and lower reservoir characteristics), boundary conditions, and pumping/injection time-sequences. By analyzing the computed piezometric heads at different distances from the underground reservoir, the magnitude of the aquifer response to pumping storage operations is assessed. The most expected and noticeable effect is the oscillation of groundwater levels. The existence a mean pseudo/ dynamic steady-state and the required time to reach it are also determined. The head difference and its time evolution between the cavity and the surrounding medium is triggering the leakage of groundwater into the cavity or the contrary. The resulting effects on the UPSH plant efficiency can be estimated. Combining these outcomes, some feasibility criteria of this type of projects are identified. Going into practice, further models should include more in de-tails local and specific geometrical and hydrogeolog-ical data of the considered old mine cavities used as lower reservoir. This kind of modelling approach can be used as a first approach for determining how the aquifer will response to short and long term changes in UPSH pumping/injection schemes. [less ▲]

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See detailGroundwater flow and transport modelling at regional scale: lessons learned from different applications in the Walloon Meuse basin
Dassargues, Alain ULg; Goderniaux, Pascal; Orban, Philippe ULg et al

Conference (2016, July 28)

An overview is proposed of the recent groundwater modelling works, at the groundwater body scale, performed by the Hydrogeology & Environmental Geology team of the University of Liège. The developed ... [more ▼]

An overview is proposed of the recent groundwater modelling works, at the groundwater body scale, performed by the Hydrogeology & Environmental Geology team of the University of Liège. The developed modelling tools are built in the general objective of improving our understanding and management, at short, middle and long terms, of the groundwater bodies. The general strategy to be followed implies that conceptualization, parameterization and calibration must be adapted to the actual objectives of each model (Wildemeersch et al., 2014). 3 specific applications are illustrated involving two main groundwater bodies: - application of the HFEMC method (Wildemeersch et al., 2010) within the SUFT3D code for groundwater flow modelling of the ‘Synclinorium of Dinant’ (Orban et al., 2010 and Brouyère et al., 2011); - application of the HFEMC method and the SUFT3D code for the nitrate trends (Batlle-Aguilar et al., 2007) simulations in the Geer basin (Orban et al., 2010) for different scenarios of nitrate inputs; - application of the HGS integrated model for assessing the impact of climate change on the groundwater reserves in the Geer basin (Brouyère et al., 2004, Goderniaux et al., 2009 and 2011) with quantification and comparison of the different uncertainty sources (Goderniaux et al., 2015) Lessons and perspectives are learned and proposed from these modelling experiences at the scale of the groundwater body. [less ▲]

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See detailNitrate dynamic and pathways in fractured limestone aquifers : From soil leaching to groundwater discharge in surface water
Briers, Pierre ULg; Schmit, Flore; Orban, Philippe ULg et al

Conference (2016, July 27)

Fractured – karstified limestone aquifers constitute important, but vulnerable groundwater reservoirs in many areas across the World. Such carbonate systems are highly heterogeneous leading to a high ... [more ▼]

Fractured – karstified limestone aquifers constitute important, but vulnerable groundwater reservoirs in many areas across the World. Such carbonate systems are highly heterogeneous leading to a high spatial and temporal variability of fluxes across the soil – vadose zone – groundwater – surface water continuum. One of the main challenges worldwide is to protect such groundwater bodies from diffuse pollutions, in particular agricultural chemicals such as nitrate. To face such problems and to propose adequate pollution mitigation scenarios, the objective here was to better understand and quantify nitrate dynamics and pathways in the subsurface and at the groundwater – surface water interface. The transfer of nitrate was investigated in different ways such as monitoring of concentrations in both groundwater and surface water, tracer experiments in the unsaturated – saturated continuum and regional investigations on groundwater chemistry including stable isotopes of nitrate and other compounds. Results show that nitrate concentrations are relatively stable both in groundwater and surface water during the low flow period (i.e. from spring to autumn). A temporary but significant increase in nitrate concentration is observed in groundwater and rivers during the winter, related to release of residual nitrate from agricultural soils driven by infiltration water. In period of high precipitations and runoff, dilution is measured in the river. Monitoring and tracer test results also highlight the fact that the migration of dissolved contaminants across the unsaturated zone of limestone rocks is very fast and governed by gravitational flows. In the rivers, macroinvertebrates and benthic diatoms were sampled at several sites to assess ecological status and structural and functional response to alteration of water quality (nutrient enrichment) and quantity (current velocity and stream habitats). Diatom indices and community structure indicated good to very good status in both studied streams, indicating that elevated nitrate concentration have no detectable effect on biological quality of the surface waters. The combination of all these results allows developing a detailed conceptual model of the dynamics of nitrate (and other agricultural contaminants) in fractured / karstified limestone aquifers, with improved estimates of nitrate trends and dynamics in both groundwater and rivers. [less ▲]

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See detailMonitored tracer experiment using the vadose zone experimental setup (VZES) for studying water and pollutant recharge processes in a brownfield
Fernandez de Vera, Natalia ULg; Beaujean, Jean; Jamin, Pierre ULg et al

Conference (2016, July 26)

Contaminant transport characterization in the vadose zone of industrial contaminated sites requires in situ technologies that provide information representative of complex heterogeneous systems. However ... [more ▼]

Contaminant transport characterization in the vadose zone of industrial contaminated sites requires in situ technologies that provide information representative of complex heterogeneous systems. However, finding the appropriate methodology is a challenge, as there is a risk of losing data resolution when capturing the spatial variability of the subsurface. An alternative method is provided by The Vadose Zone Experimental Setup (VZES) which combines surface and cross-borehole geophysical methods with a vadose zone monitoring system (VMS). When geophysical imaging is combined with in-situ hydraulic and chemical information at multiple depths of the vadose zone, detailed characterization of contaminant transport in heterogeneous systems is obtained. The system was installed at an industrial contaminated site in Belgium. A saline tracer infiltration test was performed over a heterogeneous vadose zone composed of backfilled materials underlined by unsaturated fractured chalk. Surface and cross-hole Electrical Resistivity Tomography (ERT) measurements were carried out over a 5 day period, following tracer injection. Results from time-lapse imaging reveal high resistivity variations at 0-0.5m depth, indicating that most of the tracer remained in the upper backfilled deposits. This is coincident with the results from sampled waters across the vadose zone, as no tracer was detected below 0.5m depth. Lower resistivity differences were observed laterally, indicating tracer migration in different directions via preferential flow paths. Lateral migration was found to be dominant over vertical transport in the absence of rain events. Three months after the injection, a geophysical survey was performed and combined with in situ continuous hydraulic and chemical information at multiple depths of the vadose zone. Results from geophysical imaging and water sample analyses indicate vertical movement of the tracer, which reached 4 m depth. Information obtained from continuous measurements of water content reveal that the tracer was transferred via preferential flow. The activation of such flow mechanism occurred as a response to rainfall episodes, resulting in water percolation and tracer transport towards higher depths. The results of the investigations demonstrate that the VZES is an effective method in identifying pathways and mechanisms of transport within a heterogeneous conductivity fields. The implementation of this methodological concept at industrial contaminated sites contributes to improve the development of site conceptual models for soil and groundwater protection and remediation. [less ▲]

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See detailFactors controlling spatial patterns and time trends of multiple pesticides in groundwater (Hesbaye chalk aquifer, Belgium)
Hakoun, Vivien ULg; Orban, Philippe ULg; Dassargues, Alain ULg et al

Conference (2016, July 25)

Groundwater contamination by pesticides compounds (parent and degradation by-products) is a well identified environmental issue, however factors influencing their spatial patterns and time trends remain ... [more ▼]

Groundwater contamination by pesticides compounds (parent and degradation by-products) is a well identified environmental issue, however factors influencing their spatial patterns and time trends remain unclear. In this context, 18 years long time series (1996-2013) of 3 banned (atrazine, diuron, simazine), 2 metabolites (deethyaltrazine –DEA, and 2,6-dichlorobenzamide –BAM) and one regulated (bentazone) pesticides compounds are explored, taking into account concentrations below detection limits. Using a bivariate and multivariate (PCA and hierarchical clustering) statistical framework, these time series are related to nitrate (NO3-) and the fraction of young water recharged since 50 years, land use, to aquifer settings (i.e. confining conditions, thickness of the unsaturated zone) and to groundwater table fluctuations. Results show that pesticides compounds are always below detection limits in the confined area where old groundwater lies. However these compounds are detected every year in the unconfined zone with maximal concentrations exceeding the current European water drinking standard of 100 ng.L-1 every year since 2007 for atrazine. We find the greatest significant (p-value < 0.05) positive correlations between the trio atrazine-DEA (tau=0.62), atrazine-NO3- (tau=0.48) and DEA-NO3- (tau=0.49). We identify positive correlations between most compounds, atrazine (tau=0.44), bentazone (tau=0.36), simazine (tau=0.71); DEA (tau=0.58) and BAM (tau=0.44), and water table fluctuations with periods spanning several years. We determine two groups (6 and 9 sites each) of site which relate to the discharge and recharge areas. Sites from the recharge area where higher diuron, simazine and BAM concentrations occurs correlate with a dense localized urban area. Atrazine and bentazone relates to sites with thin unsaturated zones and high mixing in the wells. Our analysis reveals critical factors affecting 7 pesticides compounds. It improves our understanding of the interplay between land use, aquifer settings and transient processes (water fluctuations) on controlling pesticides concentrations in groundwater. [less ▲]

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See detailHydrogeochemical mechanisms driving the occurrence of elevated fluoride contents in crystalline aquifers in Benin, Western Africa
Tossou, Yao ULg; Orban, Philippe ULg; Gesels, Julie ULg et al

Conference (2016, July 24)

Elevated concentrations of fluoride in drinking water is the source of severe healthy problems such as dental or skeletal fluorosis. High concentrations of fluoride are often observed in fractured and ... [more ▼]

Elevated concentrations of fluoride in drinking water is the source of severe healthy problems such as dental or skeletal fluorosis. High concentrations of fluoride are often observed in fractured and altered crystalline aquifers around the world. However, the hydrogeochemical mechanisms leading to such elevated fluoride concentrations are usually not fully understood. In particular, it is important to make the link between these elevated concentrations and the geological context in order to make efficient recommendations on appropriate locations of further groundwater abstraction wells. This is the case in Benin, Western Africa, where groundwater from crystalline bed-rock aquifers is the main source for drinking-water supply. In this context, this research aims to identify the hydrogeochemical processes governing groundwater mineralization and the origin of the high fluoride concentrations. The investigations are based on groundwater samples collected in the central part of the country (Department of Collines), characterized by hard Precambrian aquifers. The hydrogeological system consists of a thin altered bedrock layer (shallow aquifer) and a deeper fractured crystalline bedrock (deep aquifer). The most significant groundwater quality problems in the area relate to the high fluoride (more than 7 mg / l) and nitrate (over 400 mg / l) concentrations in groundwater. The collected hydrogeochemical dataset was explored using geochemical approaches and multivariate statistics. The results reveal that the water mineralization derives from hydrolysis of silicate minerals, but it is also influenced by anthropogenic effects, particularly in the shallow reservoir. However, fluoride has a natural origin, essentially related to weathering of silicate minerals, mainly from biotite. Ion exchanges between groundwater and the rock matrix also contributes to increase fluoride concentrations in groundwater. Earlier saturation of water with calcite and the precipitation of this mineral due to bicarbonate excess reduce calcium activity are favorable of the release of fluoride by rocks. Further investigations are going on to make the link between crystalline rock types, associated primary minerals and fluoride concentrations in order to identify the geological contexts which are more prone to such problems. [less ▲]

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See detailContinuous monitoring of transient groundwater fluxes using the Finite Volume Point Dilution Method
Jamin, Pierre ULg; Brouyère, Serge ULg

Conference (2016, July)

Groundwater flux is the driving force of solute contaminant dispersion through aquifers. Accurate groundwater flux measurement and monitoring is thus crucial for assessing the fate of contaminants in the ... [more ▼]

Groundwater flux is the driving force of solute contaminant dispersion through aquifers. Accurate groundwater flux measurement and monitoring is thus crucial for assessing the fate of contaminants in the saturated zone. Unfortunately, classical measurement such as pumping or slug tests based on the Darcy’s law and hydraulic gradient may lead to cumulated errors and provide no more than a snapshot measurement only representative of a given time. There is a need for a technique able to perform a continuous monitoring of groundwater fluxes, and moreover in aquifer where rapid changes of groundwater fluxes occur such as aquifers influenced by surface water, by nearby pumping or by fast precipitation recharge. Alternative methods, such as point dilution tracer tests to obtain a direct measurement of local groundwater fluxes, are promising In this study, the Finite Volume Point Dilution Method (FVPDM) was applied to continuously monitor groundwater fluxes of the alluvial aquifer of the River Meuse, in Liège (Belgium). The experimental setup consisted in the monitoring of a transient groundwater fluxes generated by a step pumping test that lasted 40 hours. Two FVPDM were performed simultaneously in two piezometers screened in two different part of the aquifer. Piezometric heads were also monitored in several piezometer located around the pumping well. Next to this original experimental setup, a mathematical solution has been developed to interpret data from FVPDM performed under transient state in order to deduce the continuous evolution of groundwater flux. The experiment demonstrated the ability of the FVPDM for monitoring transient groundwater fluxes, even if the changes of groundwater flux occurs rapidly. The FVPDM turned out to be very sensitive to small changes in groundwater flux. The FVPDM interpretation also showed that the upper part of the aquifer is affected by slower groundwater fluxes than the lower and coarser part. Furthermore, distinct hydraulic behavior were determined between the upper and lower part of the aquifer. This could not have been revealed by conventional pumping tests using only drawdown data for interpretation. The mathematical solution allowed to determine the groundwater flux at every moment of the test even if the FVPDM had not reached the stabilized phase that usually guarantee its good precision. These results illustrate the great interest of the FVPDM method for monitoring of contaminant fluxes in groundwater if coupled with a real time measurement of contaminant concentration. One of the main perspective is to perform a long term (several months) monitoring of groundwater fluxes in an aquifer influenced by river stages variations in order to prove the ability of the FVPDM for continuous long term monitoring and better characterize the exchanges between groundwater and surface water. [less ▲]

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See detailMulti-species measurements of nitrogen isotopic composition reveal the spatial constraints and biological drivers of ammonium attenuation across a highly contaminated groundwater system
Wells, Naomi S.; Hakoun, Vivien ULg; Brouyère, Serge ULg et al

in Water Research (2016), 98

Groundwater under industrial sites is characterised by heterogeneous chemical mixtures, making it difficult to assess the fate and transport of individual contaminants. Quantifying the in-situ biological ... [more ▼]

Groundwater under industrial sites is characterised by heterogeneous chemical mixtures, making it difficult to assess the fate and transport of individual contaminants. Quantifying the in-situ biological removal (attenuation) of nitrogen (N) is particularly difficult due to its reactivity and ubiquity. Here a multi-isotope approach is developed to distinguish N sources and sinks within groundwater affected by complex industrial pollution. Samples were collected from 70 wells across the two aquifers underlying a historic industrial area in Belgium. Below the industrial site the groundwater contained up to 1000 mg Nl-1 ammonium (NH4 +) and 300 mg N l-1 nitrate (NO3-), while downgradient concentrations decreased to ~1 mg l-1 DIN ([DIN] = [NH4+-N] + [NO3--N] + [NO2--N]). Mean δ1534 N-DIN increased from ~2‰ to +20‰ over this flow path, broadly confirming that biological N attenuation drove the measured concentration decrease. Multi-variate analysis of water chemistry identified two distinct NH4+ sources (δ15N-NH4+ from -14‰ and +5‰) within the contaminated zone of both aquifers. Nitrate dual isotopes co-varied (δ15 N: -3‰ - +60‰; δ18O: 0‰ - +50‰) within the range expected for coupled nitrification and denitrification of the identified sources. The fact that δ15N-NO2- values were 50‰ to 20‰ less than δ15N-NH4+ values in 40 the majority of wells confirmed that nitrification controlled N turnover across the site. However, the fact that δ15N-NO2- was greater than δ15N-NH4+ in wells with the highest [NH4+] shows that an autotrophic NO2- reduction pathway (anaerobic NH4+ oxidation or nitrifier-denitrification) drove N attenuation closest to the contaminant plume. This direct empirical evidence that both autotrophic and heterotrophic biogeochemical processes drive N attenuation in contaminated aquifers demonstrates the power of multiple N isotopes to untangle N cycling in highly complex systems. [less ▲]

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