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See detailDirect measurement of groundwater flux in aquifers within the discontinuous permafrost zone: an application of the finite volume point dilution method near Umiujaq (Nunavik, Canada)
Jamin, Pierre ULiege; Cochand, Marion; Dagenais, Sophie et al

in Hydrogeology Journal (in press)

Permafrost thaw is a complex process resulting from interactions between the atmosphere, soil, water and vegetation. Although advective heat transport by groundwater at depth likely plays a significant ... [more ▼]

Permafrost thaw is a complex process resulting from interactions between the atmosphere, soil, water and vegetation. Although advective heat transport by groundwater at depth likely plays a significant role in permafrost dynamics at many sites, there is lack of direct measurements of groundwater flow patterns and fluxes in such cold-region environments. Here, the finite volume point dilution method (FVPDM) is used to measure in-situ groundwater fluxes in two sandy aquifers in the discontinuous permafrost zone, within a small watershed near Umiujaq, Nunavik (Quebec), Canada. The FVPDM theory is first reviewed, then results from four FVPDM tests are presented: one test in a shallow supra-permafrost aquifer, and three in a deeper sub-permafrost aquifer. Apparent Darcy fluxes derived from the FVPDM tests varied from 0.5×10-5 to 1.0×10-5 m/s, implying that advective heat transport from groundwater flow could be contributing to rapid permafrost thaw at this site. In providing estimates of the Darcy fluxes at the local scale of the well screens, the approach offers more accurate and direct measurements over indirect estimates using Darcy’s law. The tests show that this method can be successfully used in remote areas and with limited resources. Recommendations for optimizing the test protocol are proposed. [less ▲]

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See detailGroundwater and contaminant mass fluxes monitoring in heterogeneous aquifers
Jamin, Pierre ULiege

Doctoral thesis (2019)

Groundwater is one of the most important natural resources of our planet and it requires appropriate management and protection in order to guarantee its availability for future generations. From a water ... [more ▼]

Groundwater is one of the most important natural resources of our planet and it requires appropriate management and protection in order to guarantee its availability for future generations. From a water quality point of view, old industrial activities and modern accidental releases have locally impacted groundwater resource. Management of these contaminated aquifers has historically relied on comparison between measured contaminant concentrations in groundwater and threshold values. This approach is a necessary early characterization step but is totally insufficient to fully investigate the contaminants behavior in groundwater and to quantify the associated risks. Since the beginning of the years 2000, a consensus has been growing among the scientific, technical and decision makers’ community on the fact that management of contaminated aquifers should be performed in terms of contaminant flux metrics. Accordingly, it has become necessary to dispose of techniques able to accurately measure mass fluxes and mass discharges of contaminants in aquifers. Contaminant mass flux usually relies on measurements of both groundwater flux and contaminant concentration in monitoring wells drilled in the aquifer of concern. Research efforts must lead to the proposition of new solutions, methodologies and techniques, in particular for measuring groundwater fluxes. In this work, the Finite Volume Point Dilution Method (FVPDM), is proposed as an innovative single-well method for monitoring groundwater fluxes in aquifers. Mathematical basis and a first analytical solutions allowing to interpret FVPDM experiments performed in steady state groundwater flow conditions were already developed and validated on a few field applications. In this research, a generalized FVPDM interpretation framework for monitoring groundwater fluxes over time is proposed, based on a new finite difference expression proposed to calculate groundwater fluxes from FVPDM experiments performed in transient groundwater flow fields. In a first step, the FVPDM technique was successively applied in various laboratory and field experiments allowing to define its accuracy, precision and resolution under transient groundwater flow conditions. A first lab-scale flow tank experiment demonstrated the accuracy of the FVPDM for groundwater fluxes measurements in both steady and transient state flow conditions. Difference between the prescribed water flux in the flow tank and the measured water flux using FVPDM was as low as 0.15 %. In a second experiment the FVPDM was applied to measure groundwater fluxes on several fractured zones of an open well installed in a crystalline rock aquifer. This constitutes the first successful application of the FVPDM technique in a fractured aquifer, using straddle packers. The classical point dilution method (PDM) was also applied during this experiment, under the same groundwater flow conditions to compare the sensitivity and uncertainty of both methods. It demonstrated that FVPDM generally provides a better precision than PDM but it may require longer experimental durations. A third FVPDM experiment undertaken in an alluvial aquifer allowed to validate in the field the method for monitoring rapidly changing groundwater fluxes. This first series of experiment allowed to validate the FVPDM as a fully operational method for measurements of groundwater fluxes for a wide spectrum of experimental and flow conditions. In a second step, three field-scale applications of the method were performed. The first relates to direct groundwater fluxes measurements in a sub-permafrost aquifer located in the remote territories of northern Quebec. These measurements came in support to a thermo-hydrodynamic model of a watershed where permafrost thaw occurs. This specific application demonstrated the robustness and versatility of the FVPDM. In a second field application, the FVPDM was used to monitor, under controlled conditions a solute mass discharge experiment undertaken in a heterogeneous alluvial aquifer at a series of control planes in order to compare different methods for calculating the total mass discharge based on discrete groundwater fluxes and concentration measurements. In a third application, the FVPDM was successfully used in a groundwater pollution investigation to characterize highly transient groundwater flows and pollutant mass fluxes within a coastal aquifer influenced by marked tides. The results of this experiment allowed to improve and refine the conceptual site model and provided crucial information for optimizing further investigations and risk mitigation measures at this polluted site. The FVPDM was applied in a wide range of environmental contexts, of application scales, of experimental setups, of aquifer types, of time scales, of groundwater flow conditions, and for both research and consultant-type purposes. The FVPDM was proven to be a robust and versatile method that provides high-quality reliable groundwater flux data for general hydrogeological characterizations and for contaminant mass fluxes monitoring, even under highly transient flow conditions. From a more general perspective, this research demonstrated the great importance and the huge benefits of having direct and reliable in situ measurements of groundwater fluxes for any kind of hydrogeological studies. This research proves once more the value of undertaking mass flux measurements for characterization of contaminated sites, risk assessment and design of risk mitigation measures. [less ▲]

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See detailDynamics of greenhouse gases in groundwater: hydrogeological and hydrogeochemical controls
Nikolenko, Olha ULiege; Orban, Philippe ULiege; Jurado, Anna et al

in Applied Geochemistry (2019), 105

In this study the variability of greenhouse gases (GHGs) concentrations along lateral and vertical dimensions of the chalk aquifer located in the eastern part of Belgium was examined in order to ... [more ▼]

In this study the variability of greenhouse gases (GHGs) concentrations along lateral and vertical dimensions of the chalk aquifer located in the eastern part of Belgium was examined in order to understand its dependence on hydrogeological and hydrogeochemical conditions. Groundwater samples from 29 wells/piezometers were analyzed for concentrations of nitrous oxide (N2O), carbon dioxide (CO2), methane (CH4), major and minor elements and stable isotopes of nitrate (NO3−), nitrous oxide (N2O), sulfate (SO42−) and boron (B). For lateral investigations, four zones with different environmental settings were identified (southern, central, north-eastern and northern). Groundwater was oversaturated with GHGs with respect to its equilibrium concentrations with the atmosphere in all zones, except the northern one, undersaturated in N2O (0.07 ± 0.08 μgN/L vs. 0.3 μgN/L). Vertical dimension studies showed the decrease in CO2 concentration and significant changes in both isotope signatures and concentration of N2O with depth. The production of N2O could be attributed to a combination of nitrification and denitrification processes occurring at different depths. CO2 concentration is controlled by the process of dissolution of carbonate minerals which constitute aquifer geology. CH4 is produced due to methanogenesis in deeper parts of the aquifer, though its thermogenic origin is also possible. Differences in hydrogeochemical settings and changing intensity of biogeochemical processes across the area and with depth have considerable effect on GHGs concentrations. Thus, before estimating GHGs fluxes at the groundwater–river interface insights obtained from larger-scale investigations are required in order to identify the representative spatial zones which govern GHGs emissions. [less ▲]

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See detailTowards a subsurface predictive-model environment to simulate aquifer thermal energy storage for demand-side management applications
Robert, Tanguy ULiege; Hermans, Thomas ULiege; Lesparre, Nolwenn et al

in Proceedings of SSB 2018, 10th International Conference on System Simulation in Buildings (2018, December 12)

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See detailMonitoring transient groundwater fluxes using the Finite Volume Point Dilution Method
Jamin, Pierre ULiege; Brouyère, Serge ULiege

in Journal of Contaminant Hydrology (2018), 218

Classic estimates of groundwater fluxes are usually based on the application of Darcy's law, which can lead to large imprecisions in transient groundwater flow cases. There is a need for direct, in situ ... [more ▼]

Classic estimates of groundwater fluxes are usually based on the application of Darcy's law, which can lead to large imprecisions in transient groundwater flow cases. There is a need for direct, in situ measurement techniques able to monitor time-variable groundwater fluxes. The investigation presented here demonstrates that the Finite Volume Point Dilution Method (FVPDM) is a promising technique for the continuous monitoring of groundwater fluxes. The experimental configuration consisted of monitoring transient groundwater fluxes generated by a multiple step pumping test, which was undertaken in the alluvial aquifer of the River Meuse, Liège (Belgium). Additionally, two FVPDM tests were simultaneously performed in two piezometers screened at two different depths in the alluvial aquifer. Tracer concentration changes during the FVPDM tests were interpreted as the consequences of Darcy flux changes in the alluvial aquifer, which was related to changes in the applied pumping rate. Piezometric levels were also monitored in piezometers located around the pumping well. The pumping test was interpreted using classical analytical solutions, and the FVPDM tests were interpreted using a new mathematical solution, which allows for calculating changes in Darcy fluxes based on the FVPDM tracer concentration evolution during transient groundwater flow conditions. The experiment demonstrated the FVPDM's ability to monitor, as well as be sensitive to changes in transient groundwater fluxes. The FVPDM interpretation also showed contrasting results between the upper part of the aquifer, which is made of loam and sand and slow groundwater flows prevail, and the lower part of the aquifer, which is made of gravels and pebbles and intense groundwater flows prevail. [less ▲]

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See detailCaractérisation des eaux souterraines par des approches centrées sur les flux : concepts et applications
Brouyère, Serge ULiege; Jamin, Pierre ULiege

Conference (2018, September 20)

Les procédures les plus courantes visant à définir l’état pollué des eaux souterraines reposent sur des mesures de concentrations en polluants en différents points d’accès à la nappe. Cette manière de ... [more ▼]

Les procédures les plus courantes visant à définir l’état pollué des eaux souterraines reposent sur des mesures de concentrations en polluants en différents points d’accès à la nappe. Cette manière de procéder est relativement simple et, si le réseau d’échantillonnage est suffisamment dense, elle permet assez rapidement de cartographier l’étendue de la pollution et de comparer cet état pollué aux normes sanitaires et environnementales en vigueur. Cependant, les polluants se déplacent dans et avec l’eau souterraine. Mettre en évidence et quantifier ces flux de polluants est essentiel pour établir le diagnostic de l’état pollué, tant dans sa compréhension générale que pour évaluer les risques potentiels pour les récepteurs exposés et pour dimensionner correctement le plan d’assainissement. Dans ce contexte, l’objectif de l’exposé est dans un premier temp de revenir sur les concepts de base des approches de caractérisation de l’eau souterraine centrées sur les flux de polluants et comment elles s’articulent et complètent celles qui sont centrées sur les concentrations en polluants, aux différents stades des études de pollution des eaux souterraines (caractérisation, étude de risque et plan d’assainissement). Dans un deuxième temps, différentes techniques d’investigation et de mesure des flux de polluants dans les eaux souterraines seront décrites et illustrées par des exemples pour en tirer quelques perspectives en matière de caractérisation de l’état pollué des eaux souterraines. [less ▲]

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See detailThe double porosity of the chalk and its influence on solute and heat transport
Hoffmann, Richard ULiege; Goderniaux, Pascal; Jamin, Pierre ULiege et al

Conference (2018, September 13)

Fractured rock aquifers like the Belgium chalk can act as important drinking water suppliers and for protection an advanced imaging of double porosity effects is important for transport predictions with ... [more ▼]

Fractured rock aquifers like the Belgium chalk can act as important drinking water suppliers and for protection an advanced imaging of double porosity effects is important for transport predictions with reduced uncertainty. Between two adjacent 50 m-deep 7.55 m distant boreholes a with flowmeter tests and optical imagining figured out open main fracture is for multiple tracer tests isolated using an inflatable double packer system. Injecting in a dipole configuration continuously 50 °C hot water for 70 h jointly with two pulse fluorescent dye tracer (uranine) shows a 12.5 hours arrival delay of the heat compared to the solute. Stopping heat injection shows a strong direct temperature decrease followed by slow temperature rebound over several days. Stored heat around the injection well is pulled and the matrix reacts slowly by contribute stored heat to the colder water drawn from the surroundings. [less ▲]

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See detailExperimental assessment and prediction of short-term aquifer thermal energy storage for energy demand-side management applications
Robert, Tanguy ULiege; Hermans, Thomas; Lesparre, Nolwenn et al

Conference (2018, September 10)

Groundwater heat pump (GWHP) systems are now widely used for space heating and cooling and domestic hot water production. On one hand, GWHP systems are considered as a renewable energy and on the other ... [more ▼]

Groundwater heat pump (GWHP) systems are now widely used for space heating and cooling and domestic hot water production. On one hand, GWHP systems are considered as a renewable energy and on the other hand, their increasing use impacts electrical grid balancing. Since the coupling of electrically-driven heating, ventilation, and air-conditioning (HVAC) systems with thermal energy storage (TES) is seen as a promising tool for demand-side management (DSM) in the low-voltage grid, experimental validation of aquifer thermal energy storage (ATES) capabilities at demand side management (DSM) frequencies (real time, intraday, interday, and interseasonal) is needed for the sector to adopt it. We demonstrated here that hourly to daily ATES can be efficient in terms of energy recovery rate and exergy whereas weekly to seasonal ATES bears the risk of lower recovery rates and presents almost always low exergy. Moreover, energy recovery rates are improved with the increasing use of storage and recovery cycles. To formulate this demonstration, we emulated the operating conditions of GWHP systems with ATES in several well-characterized experimental pilot sites in Wallonia. The standardized experiment we used to estimate the different hydrodynamic parameters and energy recovery at the pilot sites was based on push/pull tests with the injection of heated water, its storage for different DSM periods, and finally its recovery. Fluxes were either measured in-situ by means of the finite volume point dilution method or estimated with the local hydraulic conductivity and gradient. We report here a direct relationship between the energy recovery rate and natural groundwater fluxes. [less ▲]

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See detailDirect single well measurement of groundwater flux in permafrost-impacted aquifers in Nunavik, Canada
Jamin, Pierre ULiege; Cochand, Marion; Dagenais, Sophie et al

Poster (2018, September 10)

Permafrost dynamics in high latitude territories is a complex process resulting from atmospheric, soil, water and vegetation interaction. Advective heat transport by groundwater has been identified as ... [more ▼]

Permafrost dynamics in high latitude territories is a complex process resulting from atmospheric, soil, water and vegetation interaction. Advective heat transport by groundwater has been identified as potentially playing a significant role in permafrost dynamics. However, there is a lack of direct measurements of groundwater parameters such as hydraulic head and hydraulic conductivity for determining flow patterns and groundwater fluxes in permafrost environments due to difficulties in accessing these remote territories and associated high costs of field work in such remote areas. Existing monitoring wells are often insufficient to allow the assessment of representative hydraulic gradients and realistic groundwater flow rates. Here, the Finite Volume Point Dilution Method (FVPDM) is applied to measure in-situ groundwater fluxes in a supra- and sub-permafrost sandy aquifer within a small watershed in Umiujaq, Nunavik, Canada. The advantage of the FVPDM method is to provide direct measurement of groundwater flux using a single well technique. The tests show that this method can be successfully applied in remote conditions and with limited resources. Darcy fluxes derived from the FVPDM tests varied from 0.577 to 0.840 m/d, implying that advective heat transport from groundwater flow could be contributing to permafrost thaw at this site. These data are important since very few estimates of groundwater fluxes are available in the discontinuous permafrost zone and that such a significant groundwater flux can have a major impact on heat exchange between groundwater and permafrost. Moreover, they are essential for building and calibrating realistic groundwater flow and heat transport models required for better understand permafrost dynamics and sustainable groundwater management in cold environments. [less ▲]

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See detailRecent advances for monitoring groundwater and pollutant fluxes using single-well applied tracer techniques
Jamin, Pierre ULiege; Orban, Philippe ULiege; Verreydt, Goedele et al

Conference (2018, September 10)

In many different hydrogeological investigations, quantifying groundwater fluxes is essential but often challenging due to the variability of hydraulic conditions in space and time. Traditional approaches ... [more ▼]

In many different hydrogeological investigations, quantifying groundwater fluxes is essential but often challenging due to the variability of hydraulic conditions in space and time. Traditional approaches used to estimate groundwater fluxes are based on hydraulic conductivity obtained from field pumping or slug tests that provide only order-of-magnitude estimates and hydraulic gradients that can also vary, especially in areas of active groundwater discharge or pumping. The Finite Volume Point Dilution Method (FVPDM) is a recently developed applied tracer technology able to measure accurately groundwater fluxes and to monitor continuously their changes with time. We report 10 years of application of the FVPDM in contrasted hydrogeological contexts, from porous alluvial to fractured-rock aquifers, including strong interactions with surface water and contrasting groundwater flow dynamics. The obtained results prove that the FVPDM is able to measure a wide range of groundwater fluxes from a few centimetres per day to hundreds of metres per day. These results also emphases the variability in groundwater fluxes, (1) with time in aquifers influenced by variable hydraulic conditions such as tidal effects and (2) in space where orders of magnitude difference in groundwater fluxes are observed between nearby monitoring wells at a given site. Preliminary results of continuing work have also shown the potential for the FVPDM approach to be coupled with contaminant specific sensors and with passive sampling technologies to quantify contaminant mass fluxes in the subsurface. Recent developments have also investigated the ability to assess groundwater flow directions at the well scale. [less ▲]

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See detailDynamics of nitrous oxide in groundwater under agricultural areas: insights from multi-isotopic studies (15N, 34S, 18O, 13C, 3H)
Nikolenko, Olha ULiege; Orban, Philippe ULiege; Jurado, Anna et al

Scientific conference (2018, April 20)

In the last two decades the biogeochemistry of nitrous oxide (N2O), one of the most important greenhouse gases, in the subsurface has started to draw significant research attention due to the rising ... [more ▼]

In the last two decades the biogeochemistry of nitrous oxide (N2O), one of the most important greenhouse gases, in the subsurface has started to draw significant research attention due to the rising concern about climate change (Clough et al., 2005). The increase in the concentration of N2O in the atmosphere reflects the increase in amount of N2O derived from the anthropogenic sources (Robertson & Vitousek, 2009). Among these sources it is agriculture that contributes nearly 60% of the total anthropogenic emission of N2O (Syakila & Kroeze, 2011). Agricultural N2O emission to the atmosphere could be divided into direct (occurring from soils) and indirect (occurring from groundwater and surface water as a result of N input to aquatic systems) contributions. While the former one has been intensively studied and is relatively well constrained, the latter one requires additional investigations (Beaulieu et al., 2011; Jurado et al., 2017). Our study attempts to acquire additional evidence about the N2O dynamics in the subsurface by studying its distribution across the chalk aquifer of the Geer catchment in Belgium (the area of the basin 480 km2), where previous studies detected the pronounced impact of the agricultural activities on the groundwater chemistry (Brouyère et al., 2004). To this end, the groundwater samples from 32 locations in confined and unconfined parts of the aquifer were collected in order to examine the spatial variability of N2O along the lateral and vertical dimensions of the studied aquifer. The results of the study revealed that the concentration of dissolved N2O in groundwater varied from 0.03 µgN/L to 19 µgN/L. The majority of groundwater samples collected in the unconfined part of the chalk aquifer, were supersaturated with N2O (above 0.3 µgN/L), while confined area was characterized with lower values of N2O concentration (0.02 – 0.12 µgN/L). In order to identify the biogeochemical pathways of N2O, the multiple isotope analysis of NO3-, N2O, SO42-, B, DOC and 3H were conducted. In addition, the dynamics of N2O production/consumption processes was further explored using data about intramolecular distribution of 15N in N2O. Analysis of information about isotopic signals of compounds of interest and isotopomer maps of N2O helps to elucidate the causes of shifting N2O occurrence in the subsurface. [less ▲]

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See detailMONitOring des flux de POLluants dans les Eaux Souterraines
Jamin, Pierre ULiege; Dassargues, Alain ULiege; Brouyère, Serge ULiege

Poster (2017, May 05)

Contaminated aquifers management is currently based on the evaluation of pollutant concentration in the groundwater. This approach is necessary but totally insufficient to evaluate the risk posed by the ... [more ▼]

Contaminated aquifers management is currently based on the evaluation of pollutant concentration in the groundwater. This approach is necessary but totally insufficient to evaluate the risk posed by the contamination to potential receptors. Since the risk is due to the pollutant that are actually moving, and might reach a receptor, this concentration measurement should be combined to a measurement of the groundwater flow velocity (i.e. the driving force of contaminant migration in aquifers), to quantify the contaminant mass flux at which the receptor is exposed. We propose a new point dilution technique able to measure accurately the groundwater flux and to monitor continuously its changes with time. [less ▲]

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See detailTracer Experiment in a Brownfield Using Geophysics and a Vadose Zone Monitoring System
Fernandez de Vera, Natalia; Beaujean, Jean; Jamin, Pierre ULiege et al

in Vadose Zone Journal (2017), 16(1), 1-15

A saline tracer infiltration test across the fractured vadose zone of an industrial contaminated site in Belgium was monitored by combining surface and cross-borehole electrical resistivity tomography ... [more ▼]

A saline tracer infiltration test across the fractured vadose zone of an industrial contaminated site in Belgium was monitored by combining surface and cross-borehole electrical resistivity tomography (ERT) methods with a vadose zone monitoring system (VMS). The VMS provides in situ continuous hydraulic and chemical information on the percolating tracer at multiple depths in the vadose zone. The combination of such high-resolution data with time-lapse geophysical images that capture the spatiotemporal variability of the subsurface improves interpretations of flow and transport, providing a better characterization of infiltration mechanisms and preferential flow paths. The tracer infiltration test was performed over a heterogeneous vadose zone composed of backfilled materials, sands and silts, and unsaturated fractured chalk. Monitoring results during a 5-d period revealed the formation of a tracer plume in the upper backfilled deposits, while some of the tracer migrated laterally following preferential pathways. Slow vertical flow through matrix pores was found to be dominant under dry conditions. Infiltration of small quantities of rain during the test was found to have an influence on the spatial distribution of the plume. Results from long-term monitoring revealed vertical transport of the tracer toward depths that reached 4 m during a time period of 105 d. During that period, fracture and matrix flow mechanisms across the vadose zone were activated as a response to frequent rainfall episodes. The study demonstrates that the interpretation of geophysical images is improved by in situ information from the VMS. [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 detailMonitored tracer experiment using the vadose zone experimental setup (VZES) for studying water and pollutant recharge processes in a brownfield
Fernandez de Vera, Natalia ULiege; Beaujean, Jean; Jamin, Pierre ULiege 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 detailContinuous monitoring of transient groundwater fluxes using the Finite Volume Point Dilution Method
Jamin, Pierre ULiege; Brouyère, Serge ULiege

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 detailHeat tracer test in an alluvial aquifer: field experiment and inverse modelling
Klepikova, Maria; Wildemeersch, Samuel; Hermans, Thomas ULiege et al

in Journal of Hydrology (2016), 540

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

Using heat as an active tracer for aquifer characterization is a topic of increasing interest. In this study, we investigate the potential 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 an injection well and monitoring the evolution of groundwater temperature and tracer concentration in the pumping well and in measurement intervals. To get insights in the 3D characteristics of the heat transport mechanisms, temperature data from a large number of observation wells closely spaced along three transects were used. Temperature breakthrough curves in observation wells 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 is explained by the groundwater flow gradient on the site and heterogeneities in the hydraulic conductivity field. Moreover, due to high injection temperatures during the field experiment a temperature-induced fluid density effect on heat transport occurred. By using a flow and heat transport numerical model with variable density coupled with a pilot point approach for inversion of the hydraulic conductivity field, the main preferential flow paths were delineated. The successful application of a field heat tracer test at this site suggests that heat tracer tests is a promising approach to image hydraulic conductivity field. This methodology could be applied in aquifer thermal energy storage (ATES) projects for assessing future efficiency that is strongly linked to the hydraulic conductivity variability in the considered aquifer. [less ▲]

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