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Étude du suivi des injections des lixiviats dans les massifs de déchets: combinaison entre méthodes géophysiques et simulation hydrodynamique

Abstract : Operators of non-hazardous waste landfills have to ensure that the waste biodegrades uniformly and rapidly, to shorten the costly post-operation period. Leachate (liquids resulting from biodegradation) must be injected into the waste while controlling the volumes used, in order to maintain the correct moisture level to ensure better biodegradation and limit the piezometric level to 50 cm above the bottoms, in accordance with regulations. To achieve these requirements, operators need tools for characterising and modelling leachate circulation. The aim of this work is to study leachate recirculation in industrial waste sites using combined geophysical data and hydrodynamic modelling. We aim to contribute to define a conceptual model of leachate circulation in an industrial waste site using an approach combining simulation and hydrogeophysics. The first stage in this work involved methodological development of geophysical ERT and MRS in order to adapt them to waste characterisation. In the case of ERT, several authors have shown that there may be false variations in the electrical resistivities calculated from inversions of data obtained during infiltration monitoring. This must be ascertained in order to establish whether they are artefacts of inversion or real resistivity variations. To validate the proposed solutions, the field ERT inversion results are compared with independent measurements (hydrological measurements, electrical resistivity measurements using buried probes, surface geophysical measurements). In the case of MRS One of the major problems of using MRS is the heterogeneous nature of waste, which affects the saturated water content distribution. Usually, MRS provides a 1D water content distribution. However, a 2D spatialised representation would be much better suited to the case of waste. For this reason it was decided to test a 2D inversion code developed at LTHE, based on a simple geometry medium, before carrying out experiments on real waste. The results of this 2D water content measurements are compared with other geophysical methods validate the 2D inversion code. The second stage involved analysing the geophysical results obtained from monitoring of leachate injection into the waste using the electrical resistivity method. The analysis of the ERT results provided information on the structure and hydrodynamic properties of the medium. The MRS results provided information on the hydraulic conductivity ranges in the waste mass studied.On the basis of this information and by combining the geophysical results with the hydrodynamic simulation (HYDRUS-2D), a conceptual model of leachate circulation in waste is proposed. The simulation results show that:  waste cannot in any circumstances be compared to a homogeneous porous medium at the industrial scale;  the medium is similar to a two-phase medium with a porous matrix of low hydraulic conductivity crossed by drains with a very high conductivity. Finally we found that combining geophysical tools with simple hydrodynamic simulation could open new perspectives for developing simulation tools applicable to industrial sites. This approach, and the methodological improvements proposed in this work, indicates that the research may be widened to include two other types of hydrological problem such as applied to infiltration in the top soil layers or identification of aquifer recharges systems.
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Submitted on : Thursday, November 25, 2010 - 11:30:38 AM
Last modification on : Monday, November 23, 2020 - 7:00:07 PM
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Rémi Clement. Étude du suivi des injections des lixiviats dans les massifs de déchets: combinaison entre méthodes géophysiques et simulation hydrodynamique. Géophysique [physics.geo-ph]. Université Joseph-Fourier - Grenoble I, 2010. Français. ⟨tel-00538155v2⟩

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