Poster (Scientific congresses and symposiums)
Time lapse imaging of water content with geoelectrical methods: on the interest of working with absolute water content data
Dumont, Gaël; Pilawski, Tamara; Robert, Tanguy et al.
2016EGU General Assembly 2016
 

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Keywords :
time-lapse ERT; water content; waste material
Abstract :
[en] The electrical resistivity tomography is a suitable method to estimate the water content of a waste material and detect changes in water content. Various ERT profiles, both static data and time-lapse, where acquired on a landfill during the Minerve project. In the literature, the relative change of resistivity ( Delta rho/rho ) is generally computed. For saline or heat tracer tests in the saturated zone, the Delta rho/rho can be easily translated into pore water conductivity or underground temperature changes (provided that the initial salinity or temperature condition is homogeneous over the ERT panel extension). For water content changes in the vadose zone resulting of an infiltration event or injection experiment, many authors also work with the Delta rho/rho or relative changes of water content Delta theta /theta (linked to the change of resistivity through one single parameter: the Archie’s law exponent “m”). This parameter is not influenced by the underground temperature and pore fluid conductivity ( rho_w) condition but is influenced by the initial water content distribution. Therefore, you never know if the loss of / signal is representative of the limit of the infiltration front or more humid initial condition. Another approach for the understanding of the infiltration process is the assessment of the absolute change of water content ( Delta theta ). This requires the direct computation of the water content of the waste from the resistivity data. For that purpose, we used petrophysical laws calibrated with laboratory experiments and our knowledge of the in situ temperature and pore fluid conductivity parameters. Then, we investigated water content changes in the waste material after a rainfall event ( Delta theta = Delta theta /theta * theta ). This new observation is really representatives of the quantity of water infiltrated in the waste material. However, the uncertainty in the pore fluid conductivity value may influence the computed water changes ( Delta theta =k*m*(rho_w)^1/2 ; where “m” is the Archie’s law exponent). Using these two complementary approaches, we analyzed the effect a major rainfall (20-30 mm in 2 hours) that occurred on the test site, characterized by a vegetalized and relatively dry zone and a devegatelized and humid zone. We intended to prove that most of the information contained in the Delta theta /theta distribution is the initial water content distribution in the ground.Water addition in dry zones resulting in large relative changes. The computation of the Delta theta is necessary to demonstrate preferential infiltration through the capping in a restricted zone of the vegetalized area.
Disciplines :
Geological, petroleum & mining engineering
Author, co-author :
Dumont, Gaël ;  Université de Liège > Département ArGEnCo > Géophysique appliquée
Pilawski, Tamara ;  Université de Liège > Département ArGEnCo > Géophysique appliquée
Robert, Tanguy ;  Aquale SPRL
Hermans, Thomas ;  Université de Liège > Département ArGEnCo > Géophysique appliquée
Garré, Sarah  ;  Université de Liège > Ingénierie des biosystèmes (Biose) > Echanges Eau-Sol-Plantes
Nguyen, Frédéric ;  Université de Liège > Département ArGEnCo > Géophysique appliquée
Language :
English
Title :
Time lapse imaging of water content with geoelectrical methods: on the interest of working with absolute water content data
Publication date :
21 April 2016
Event name :
EGU General Assembly 2016
Event organizer :
European Geosciences Union
Event place :
Vienna, Austria
Event date :
from 18-04-2016 to 22-04-2016
Audience :
International
Available on ORBi :
since 04 April 2016

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