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See detailUnderground pumped hydro-energy storage in Wallonia (Belgium) using old mines – Potential and challenges
Erpicum, Sébastien ULiege; Archambeau, Pierre ULiege; Dewals, Benjamin ULiege et al

in Shaping the future of hydropower (2017)

Pumped Storage Hydroelectricity (PSH) is a well-known and efficient technology to store various amounts of electricity. In most parts of Europe, appropriate sites for new classical PSH plants are getting ... [more ▼]

Pumped Storage Hydroelectricity (PSH) is a well-known and efficient technology to store various amounts of electricity. In most parts of Europe, appropriate sites for new classical PSH plants are getting scarce. An alternative consists in using underground volumes as lower reservoirs to build so-called Underground Pumping Storage Hydroelectricity (UPSH) plants. The paper presents the main results of a research project currently investigating the potential and feasibility of such innovative plants in the context of Wallonia, where numerous abandoned mines and quarries are located all over the territory. After a description of the main types of reservoir configurations existing in the considered region and the evaluation of their expected energy storage potential, the tools and methodology developed in the scope of the project are presented. Their application to the case of an underground slates quarry and an open pit chalk mine helps in identifying the remaining challenges [less ▲]

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See detailHydrogeochemical mechanisms governing the mineralization and elevated fluoride (F -) contents in Precambrian crystalline aquifer groundwater in central Benin, Western Africa
Tossou, Yao Yelidji Joel ULiege; Orban, Philippe ULiege; Gesels, Julie et al

in Environmental Earth Sciences (2017), 76(20),

In the central part of Benin (Western Africa), high fluoride (F -) contents have been reported in groundwater from Precambrian crystalline bedrock aquifer which is the main source of drinking water. The ... [more ▼]

In the central part of Benin (Western Africa), high fluoride (F -) contents have been reported in groundwater from Precambrian crystalline bedrock aquifer which is the main source of drinking water. The hydrogeochemical mechanisms leading to such elevated fluoride concentrations are usually not fully understood. In this context, the objective is to identify the hydrogeochemical processes governing groundwater mineralization and the origin of the high fluoride concentrations. A dataset of 162 groundwater samples was collected from the aquifer consisting of a thin altered bedrock layer (shallow aquifer) and a deep fractured crystalline bedrock (deep aquifer). Geochemical approaches and multivariate statistics have been used to explore the data. Fluoride concentrations vary between 0.00 and 7.19 mg/L in groundwater. Samples collected in the southern part of the investigated area, close to Dassa-Zoumé, show the highest concentrations, with more than 75% greater than the guideline value of 1.5 mg/L. The deep fractured aquifer shows higher concentrations of fluoride than the shallow regolith reservoir. Results reveal that groundwater mineralization is derived mainly from the hydrolysis of silicate minerals, but it is also influenced by anthropogenic effects, particularly in the shallow reservoir. However, fluoride has a geogenic origin, primarily from the weathering of silicate minerals, primarily biotite. Ca 2 +/ Na + cation exchanges and F -/ OH - anion exchanges between groundwater and the rock matrix also occur as minor processes. Saturation of the water with respect to calcite and the precipitation of this mineral, which reduces calcium activity, also favor the release of fluoride from rocks. © 2017, Springer-Verlag GmbH Germany. [less ▲]

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See detailPROPOSITION D'UN SUPPORT D'AIDE À LA DÉCISION POUR L'AMÉLIORATION DE L'ACCÈS À UNE EAU SOUTERRAINE DE MEILLEURE QUALITÉ DANS UN CONTEXTE DE CONTAMINATION GÉOGÉNIQUE AU FLUORURE AU BENIN (AFRIQUE DE L'OUEST)
Tossou, Joël; Hermans, Thomas ULiege; Orban, Philippe ULiege et al

in Geo-Eco-Trop : Revue Internationale de Géologie, de Géographie et d'Ecologie Tropicales (2017)

Les eaux souterraines des aquifères de socle cristallin de la partie centrale du Bénin (Département des Collines) présentent des concentrations élevées en fluorure, allant jusqu'à 7 mg/L alors que la ... [more ▼]

Les eaux souterraines des aquifères de socle cristallin de la partie centrale du Bénin (Département des Collines) présentent des concentrations élevées en fluorure, allant jusqu'à 7 mg/L alors que la norme recommandée par l'OMS est de 1.5 mg/L. La consommation de ces eaux à fortes teneurs en fluorure impacte la santé humaine. La population de la région est effectivement largement affectée par la fluorose dentaire. Les investigations hydrogéochimiques révèlent que l’origine de ces teneurs anormales est géogénique avec une forte contribution des minéraux ferromagnésiens, principalement la biotite. Ce travail se propose de réaliser une double cartographie à l'échelle du département des Collines: (i) une carte de l'estimation des teneurs en fluorure dans les eaux souterraines par krigeage ordinaire et (ii) une carte de la probabilité d'excéder la valeur guide de l’OMS (1.5 mg/L) en fluorure dans les eaux par krigeage d'indicatrices. Outre la cartographie en elle-même, l'analyse de la structure spatiale des données (teneurs en fluorure des eaux souterraines) à travers le calcul des variogrammes montre qu'il existe un lien fort entre celles-ci et les structures géologiques dominantes, confirmant l'origine géogénique du fluorure. Ces informations cartographiques serviront de support à la décision pour les décideurs et les gestionnaires de la ressource quant au choix judicieux des zones de captage d'eau potable pour minimiser/éviter les risques de fortes teneurs en fluorure. [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 ULiege; Dassargues, Alain ULiege 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 ULiege; Briers, Pierre ULiege; Orban, Philippe ULiege 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 detailLanduse change and future flood risk: the influence of micro-scale spatial patterns (FloodLand) - 4th progress report
Dewals, Benjamin ULiege; Bruwier, Martin ULiege; El Saeid Mustafa, Ahmed Mohamed ULiege et al

Report (2016)

The goal of the project FloodLand is to investigate the complex interactions between landuse change and future flood risk. Landuse change is assumed to be mainly driven by population growth and socio ... [more ▼]

The goal of the project FloodLand is to investigate the complex interactions between landuse change and future flood risk. Landuse change is assumed to be mainly driven by population growth and socio-economic factors. It affects future flood risk by altering catchment hydrology as well as vulnerability in the floodplains; but the feedback effect of (the perception of) changes in flood hazard on landuse evolution is also considered. The research is based on a chain of modelling tools, which represent parts of the natural and human systems, including: landuse change modelling, transportation modelling as an onset for the estimation of indirect flood damage, continuous hydrological modelling (forced by precipitation and temperature data disturbed according to climate change scenarios), as well as efficient hydraulic modelling of inundation flow in the floodplains. Besides reproducing a broad spectrum of processes, the modelling approach spans over multiple scales, from the regional or catchment level down to the floodplain and building levels. This distinctive feature is reflected both within the individual models and through their combination involving fine-scale detailed analyses (or data) embedded within coarser models at a broader level. [less ▲]

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See detailGroundwater flow and saltwater intrusion modelling in the Continental Terminal (CT) aquifer near the Saloum inverse estuary in Senegal
Dieng, Ndeye Maguette ULiege; Orban, Philippe ULiege; Dassargues, Alain ULiege et al

Conference (2016, September 27)

The Saloum River hypersaline estuary (Senegal) is an ‘inverse estuary’ showing a salinity increasing from the river mouth towards inland. This salinization process is mainly driven by a net loss of ... [more ▼]

The Saloum River hypersaline estuary (Senegal) is an ‘inverse estuary’ showing a salinity increasing from the river mouth towards inland. This salinization process is mainly driven by a net loss of freshwater due to intense evaporation. In this context, interactions between the river and the surrounding aquifer of the Continental Terminal (CT) may lead to local and progressive salinization of this groundwater main resource for water supply. Our study, based on available data and new measured data in 2012 and 2013, is focused on the southern part of the Saloum basin. It confirms that the groundwater resource is threatened by local saltwater intrusions in the vicinity of the Saloum River and along the western coastal part of the aquifer. For a long term water resources management, it is thus essential to predict the future evolution of this process in a context of increasing groundwater pumping rate together with climate variability and changes. A groundwater flow model is developed using MODFLOW. Starting from a conceptual steady-state situation corresponding to the CT aquifer state in 1973 before development of pumping, a transient calibration of the groundwater flow model is performed on data from 1974 to 2012. Despite the low number of measured data, the model can be considered as the current best assessment tool for future predictions. Using the particle tracking technique (MODPATH), a first assessment of the saltwater intrusions in the aquifer is simulated (neglecting the density effect on the hydraulic conductivity) confirming the measured data. Results, for an increased pumping of 20% in 2050 combined with different climatic scenarios, are useful to assess how the saltwater intrusions will evolve in the next years. [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 ULiege; Pujades, Estanislao ULiege; Orban, Philippe ULiege 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 detailInfluence of groundwater exchanges on the efficiency of Underground Pumped Storage Hydroelectricity plants using open pit mines
Pujades, Estanislao ULiege; Bodeux, Sarah ULiege; Orban, Philippe ULiege et al

Poster (2016, September 27)

Underground Pumped Storage Hydropower (UPSH) plants can be used to manage the production of electrical energy according to the demand. These plants consist in two reservoirs, the upper one is located at ... [more ▼]

Underground Pumped Storage Hydropower (UPSH) plants can be used to manage the production of electrical energy according to the demand. These plants consist in two reservoirs, the upper one is located at the surface while the lower one is underground. The energy is stored by pumping water from the lower to the upper reservoir and produced by releasing water from the upper to the lower one. As a result, the hydraulic head in the lower reservoir varies continuously. UPSH plants interact with the surrounding aquifers exchanging groundwater. These groundwater exchanges, which play an important role in the evolution of the hydraulic head inside the underground reservoir, are a fact of concern in the selection of pumps and turbines because their efficiency varies with respect to the head difference between the two reservoirs. Therefore, the aquifer parameters should be considered in the selection of pumps and turbines. In this context, with an UPSH plant made up by an open pit mine, we study numerically (1) the influence of groundwater exchanges on the efficiency and (2) how the hydraulic head evolution varies depending on the aquifer properties. The relation among the groundwater exchanges, the efficiency of pumps and turbines and the aquifer parameters is considered by comparing the numerical results of several simulations. It is shown that groundwater exchanges are not negligible when optimizing the efficiency of UPSH plants. A priori, low hydraulic conductivity geological media were preferred to decrease interactions with the open-pit or the cavity used as lower reservoir. Taking into account the pump/turbine performance curves, it appears that, on the contrary, the global efficiency would be increased if the surrounding medium facilitates large groundwater exchanges because hydraulic head variations are softened. [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 ULiege; Hermans, Thomas ULiege; Jamin, Pierre ULiege 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 detailGroundwater flow and saltwater intrusion modelling in the Continental Terminal (CT) aquifer near the Saloum inverse estuary in Senegal
Faye, Serigne; Ndeye, Maguette Dieng; Orban, Philippe ULiege et al

Conference (2016, September 26)

The Saloum River hypersaline estuary (Senegal) is an ‘inverse estuary’ showing a salinity increasing from the river mouth towards inland. This salinization process is mainly driven by a net loss of ... [more ▼]

The Saloum River hypersaline estuary (Senegal) is an ‘inverse estuary’ showing a salinity increasing from the river mouth towards inland. This salinization process is mainly driven by a net loss of freshwater due to intense evaporation. In this context, interactions between the river and the surrounding aquifer of the Continental Terminal (CT) may lead to local and progressive salinization of this groundwater main resource for water supply. Our study, based on available data and new measured data in 2012 and 2013, is focused on the southern part of the Saloum basin. It confirms that the groundwater resource is threatened by local saltwater intrusions in the vicinity of the Saloum River and along the western coastal part of the aquifer. For a long term water resources management, it is thus essential to predict the future evolution of this process in a context of increasing groundwater pumping rate together with climate variability and changes. A groundwater flow model is developed using MODFLOW. Starting from a conceptual steady-state situation corresponding to the CT aquifer state in 1973 before development of pumping, a transient calibration of the groundwater flow model is performed on data from 1974 to 2012. Despite the low number of measured data, the model can be considered as the current best assessment tool for future predictions. Using the particle tracking technique (MODPATH), a first assessment of the saltwater intrusions in the aquifer is simulated (neglecting the density effect on the hydraulic conductivity) confirming the measured data. Results, for an increased pumping of 20% in 2050 combined with different climatic scenarios, are useful to assess how the saltwater intrusions will evolve in the next years. [less ▲]

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See detailHow groundwater interactions can influence UPSH (Underground Pumping Storage Hydroelectricity) operations
Bodeux, Sarah ULiege; Pujades, Estanislao ULiege; Orban, Philippe ULiege 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 ULiege; Goderniaux, Pascal; Orban, Philippe ULiege 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 ULiege; Schmit, Flore; Orban, Philippe ULiege 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 detailFactors controlling spatial patterns and time trends of multiple pesticides in groundwater (Hesbaye chalk aquifer, Belgium)
Hakoun, Vivien ULiege; Orban, Philippe ULiege; Dassargues, Alain ULiege 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 ULiege; Orban, Philippe ULiege; Gesels, Julie ULiege 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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