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Field scale mass discharge measurements from a controlled solute plume
Jamin, Pierre; Brouyère, Serge
2019Groundwater Quality Conference 2019
 

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Keywords :
Mass discharge; Groundwater flux; Finite Volume Point Dilution Method
Abstract :
[en] Control planes are currently the most frequently used methods to calculate contaminant mass discharge in aquifers. However, in heterogeneous aquifers, the representativity of mass discharges calculated by the integration of discrete mass fluxes measurements over the area of the control plane is not evident. Risk assessment of contaminated aquifers requires estimates of mass discharge which must include a quantification of uncertainties in order to establish its robustness credibility. Field-oriented studies are not able to validate the accuracy of the mass discharge calculations because the original mass discharge released by the contaminant source is never known a priori. The only option to validate a mass discharge measurement approach on field experiment is to simulate a dissolved contaminant plume based on a controlled-injection tracer experiment in the aquifer medium. The objective of the study was to evaluate the control plane approach for the calculation of a plume mass discharge in a heterogeneous aquifer, under controlled groundwater flow and solute transport conditions. To do so, a fluorescent dye tracer was injected in an alluvial aquifer during 24 days at a constant flow rate in order to create a steady state solute plume. The injection was performed in a well located upgradient from a pumping well where a constant pumping rate was established. Mass discharge measurements were performed at three control planes located between the injection well and the pumping well. The Finite Volume Point Dilution Method was used to accurately measure groundwater fluxes at each well of the control planes. When the solute plume was assumed steady state, classical groundwater sampling was undertaken for the determination of solute concentrations. Results showed a high vertical variation of groundwater fluxes and solute concentrations in the alluvial aquifer. Solute mass discharges calculated using simple rectangular integration of measured contaminant fluxes values at the first, second, third control plane and at the pumping well represented respectively 66, 51, 23 and 88 % of the solute mass discharge injected at the injection well. Despite based on a sampling array of monitoring wells that was not ideal regarding the spatial heterogeneity of the aquifer, solute mass discharge calculated at the 3 control planes were consistent with the solute mass discharges upgradient in the aquifer. The integration method of mass flux data form the multi-level well array of a control plane can have a significant impact on the calculated mass discharge values. Simple rectangular cross sectional flow surfaces generated steep limits between zones of calculated mass discharges and may not be considered as representative of the spatial variability of solute mass fluxes in the plume. At the same time, smoother interpolation methods were also not perfect since they generated artificially high solute mass discharges. Further integration of these mass flux and mass discharge results into a numerical model is planned and will allow for the estimation of the uncertainties and for the illustration of the relevance of groundwater flux, contaminant mass flux and mass discharge measurements for model calibration. Finally, this study showed the interest of the FVPDM for the measurement of solute mass discharge in aquifers. It also illustrated the importance of accurate and precise groundwater flux measurements that are too often disregarded when calculating mass discharge.
Disciplines :
Earth sciences & physical geography
Geological, petroleum & mining engineering
Author, co-author :
Jamin, Pierre ;  Université de Liège - ULiège > Département ArGEnCo > Hydrogéologie & Géologie de l'environnement
Brouyère, Serge  ;  Université de Liège - ULiège > Département ArGEnCo > Hydrogéologie & Géologie de l'environnement
Language :
English
Title :
Field scale mass discharge measurements from a controlled solute plume
Alternative titles :
[en] Mesures de débit massique ai niveau d'un panache de soluté dans un aquifère alluvial
Publication date :
11 September 2019
Number of pages :
A0
Event name :
Groundwater Quality Conference 2019
Event organizer :
Université de Liège - Hydrogéologie et Géologie de l'Environnement
Event place :
Liège, Belgium
Event date :
du 9 au 12 septembre 2019
Audience :
International
Available on ORBi :
since 02 October 2019

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