Gerhard Schaefer

Gerhard Schaefer
University of Strasbourg | UNISTRA · Faculté de Physique et Ingénierie; Institut Terre et Environnement de Strasbourg (ITES)

PhD

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101
Publications
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Publications

Publications (101)
Article
Full-text available
This study focuses on a detailed analysis of the errors introduced by two quasi-analytical approaches based on either Fick’s first law or a combination of Fick’s and Darcy’s laws to evaluate the vapour flux of chlorinated solvents from a source zone located in the unsaturated zone towards the atmosphere. A coupled one-dimensional numerical flow and...
Article
We report on results from primary drainage experiments on quasi-two-dimensional porous models. The models are transparent, allowing the displacement process and structure to be monitored in space and time during primary drainage experiments carried out at various speeds. By combining detailed information on the displacement structure with global me...
Article
In disordered porous media, two-phase flow of immiscible fluids (biphasic flow) is organized in patterns that sometimes exhibit fractal geometries over a range of length scales, depending on the capillary, gravitational and viscous forces at play. These forces, as well as the boundary conditions, also determine whether the flow leads to the appeara...
Article
A rare dataset of in‐situ 10Be from high‐resolution depth profiles, soils, rock outcrops and stream sediments is combined with geochemical analysis and modeling of regolith evolution to understand the variability of denudation rates in a mountain watershed (Strengbach critical zone observatory). High‐resolution depth profiles are key to detect the...
Conference Paper
Full-text available
Coastal areas around the Mediterranean basin concentrate population, multi-sector economic activities and agricultural activities. This induces an important need in fresh water and high solicitation of coastal aquifers, which can lead to salt water intrusion. This issue, added to contaminated surface water percolating towards the aquifer, and along...
Conference Paper
Full-text available
The PRIMA Sustain-COAST European project aims at exploring innovative governance for sustainable coastal groundwater management and pollution reduction in the context of a changing climate by involving researchers, local citizens, water stakeholders, and policy makers in interactive dialogue. Four study sites have been selected, among them the Wadi...
Article
Relatively little is known about the deep water circulation and the role of deep weathering processes on the Critical Zone (CZ) evolution. In this study, major fractures from four deep boreholes and water collected from these fractures (20-60 m of depth) were studied to improve our understanding of the deep CZ in a granitic headwater watershed (Str...
Article
Full-text available
We experimentally and numerically study the influence of gravity and finite-size effects on the pressure-saturation relationship in a given porous medium during slow drainage. The effect of gravity is systematically varied by tilting the system relative to the horizontal configuration. The use of a quasi two-dimensional porous media allows for dire...
Article
The predictions of two recent and two classical mathematical models are compared with experimentally measured three-phase relative permeabilities. Experimentally determined constitutive relationships in two-phase systems were used as model input parameters to numerically predict relative permeabilities (kr) in three-phase systems. Then the estimate...
Research Proposal
Full-text available
Every two years, the JEMP, which were initiated in 1993 at Toulouse, France (see their history here) are the ideal meeting place for scientific and industrial communities whose common purpose is the understanding of the complex behavior of porous media. The fifteenth edition of JEMP will be held at Le Palais Universitaire at Strasbourg (France) fro...
Article
This paper presents a new modelling approach to quantify the hydraulic diffusivity of low‐permeability unconsolidated porous media under confined saturated‐flow conditions in the laboratory. The derived analytical solution for the transient variation of the hydraulic head after flow interruption was applied to experimental data obtained from contin...
Article
Full-text available
The Soultz-sous-Forêts geothermal plant in northern Alsace (France) is under consideration for a campaign to actively stimulate the low-permeability granitic reservoir. The operation of the enhanced geothermal system requires the re-injection of fluid into the geothermal reservoir, which can cause a strong disequilibrium between the fluid and the g...
Article
We study the effects of connectivity enhancement due to film flow phenomena on the drainage of an artificial porous medium and the relative influence of gravity for such effects. The medium is initially fully saturated with a liquid (wetting phase), which is displaced by air (nonwetting phase). Our setup allows us to directly visualize the dynamics...
Article
In the present study, indigo blue dye removal efficiency of activated carbon (AC) and natural clay (NC) was evaluated and compared, firstly in an adsorption unit, and then in an adsorption coupling ultrafiltration (A/UF) system. Effect of operating variables like pH, contact time, adsorbent dosage, initial dyes concentration during the adsorption w...
Article
Full-text available
This study aims to investigate the hydrochemical behaviour of a shallow aquifer of a semi-arid environment in central-eastern Tunisia. It is based on a combined approach of multivariate statistical tools and a geostatistical analysis. The analysis of 49 groundwater samples underlined the heterogeneity between water classes. The factor analysis and...
Article
This paper presents a new modelling approach to describe and explain the temporal variation of oil thickness in well due to groundwater table fluctuations. This new model, which intends to be simple and easy to implement, was compared to field data obtained by continuous measurements of vertical LNAPL position in wells. Two scenarios have been stud...
Article
To quantify water-rock interactions and forecast their spatiotemporal evolution in the shallow aquifer of Sidi El Hani located in central-eastern Tunisia, the numerical code KIRMAT was used. Based on available geological, mineralogical, thermodynamic, kinetic and hydrodynamic data, the model was built and calibrated on two transects of the aquifer...
Article
Full-text available
Biomass as a renewable energy source has become increasingly prevalent in Europe to comply with greenhouse gas emission targets. As one of the most efficient perennial bioenergy crops, there is great potential in the Upper Rhine Region to explore biomass utilization of Miscanthus to confront climate change and land use demand in the future. Yet, th...
Article
In the Sidi El Hani basin, located in central-eastern Tunisia, a shallow aquifer is the main water source for agricultural practice. However, in the last few decades, it has undergone saline pollution. In this context, this study is carried out to identify the origin of the dissolved species and the processes involved in the increase of groundwater...
Article
A numerical simulator based on the discrete network model approach has been developed to simulate drainage processes in a water-saturated porous medium. To verify the predictive potential of the approach to simulate the unstable migration of a dense nonaqueous phase liquid (DNAPL) at the pore scale, the numerical model was applied to laboratory exp...
Article
Full-text available
The use of groundwater for irrigation is considered as the key asset of agricultural development in the plain of Sidi Bouzid. Consequently, the sustainability of groundwater resources requires a good estimation of groundwater extraction. This work aimed to assess the groundwater volume pumped for irrigation during the hydrological year 2013-2014, b...
Conference Paper
Full-text available
Central Tunisia is characterised by a semi-arid to arid climate where groundwater is taken as the main resource of water supply. Sidi Bouzid Plain is among the most available water resource in this region. To cope with, the artificial recharge of the groundwater has been favored in this aquifer by the development of gabion structures on the Wadi El...
Article
The (001) orthoclase surface was dissolved at 180 °C and at far from equilibrium conditions with an alkaline solution (pH180°C = 9) in a titanium open flow reactor. Vertical scanning interferometer (VSI) and atomic force microscope (AFM) surface monitoring were periodically used during the reaction process in order to quantify the surface topograph...
Article
Full-text available
This work reports new findings on the physisorption of Foron Blue 291 on natural bentonite under both static and dynamic flow conditions of the aqueous solution that may prove important when using the adsorption technique for wastewater treatment. The quantity of dye retained by the solid matrix under both ideal exchange conditions between dyes and...
Conference Paper
Full-text available
This work deals with the cleanup of textile effluents using natural clay, which is less expensive and easier to handle than traditionally used adsorbent [1]. It reports new findings on the physisorption of Foron Blue 291 (FB) on natural bentonite under dynamic flow conditions of the aqueous solution (Figure 1), that may important when using adsorpt...
Article
Full-text available
Dense nonaqueous-phase liquids (DNAPLs) spilled on the soil migrate vertically depending upon gravity and capillary forces through the unsaturated zone of the porous aquifer, forming a vapour plume. These volatile organic compounds (VOCs) can be transferred by advection-diffusion to the groundwater or to the atmosphere. Evaluating DNAPL vapour flux...
Article
In this paper we study the influence of sample geometry on the measurement of pressure-saturation relationships, by analyzing the drainage of a two-phase flow from a quasi-2D random porous medium. The medium is transparent, which allows for the direct visualization of the invasion pattern during flow, and is initially saturated with a viscous liqui...
Article
Full-text available
In this paper, we develop an implementation of gravity effects within a Global Pressure formulation in a numerical scheme based on the implicit pressure explicit saturation (IMPES) approach. We use the Discontinuous Galerkin Finite-Element Method (DGFEM) combined with a generalised Godunov scheme to model an immiscible two-phase flow with predomina...
Article
Full-text available
The purpose of this study was to determine whether a bentonite from the Gafsa deposit (western Tunisia) could be used to remove the Foron Blue 291 (FB) azo dye from wastewater. Batch adsorption and desorption experiments were conducted using untreated and purified bentonite and the influence of contact time, pH, adsorbent mass and temperature of th...
Book
Full-text available
Die Anwendbarkeit numerischer Transportmodelle in der Grundwasserwirtschaft ist eingeschränkt durch die Schwierigkeit, den dispersiven Charakter der Grundwasserströmung naturnah zu beschreiben. Dies liegt im wesentlichen an der Heterogenität des Untergrunds. Ziel der hier dargestellten systematischen Untersuchungen an inhomogenen Modellaquiferen wa...
Article
One-dimensional flow simulations were conducted at four locations of the shallow alluvial aquifer of the upper Rhine River (at the Erstein polder) to quantify the time-dependent moisture distribution, the water flux and the water volume infiltrated in the unsaturated zone as a function of soil heterogeneities during a five-day-long flooding event....
Article
Full-text available
Industrialization during the 19th and 20th century led to the use of chemical products such as chlorinated solvents, e.g., trichloroethylene (TCE). At locations where volatile organic compounds were accidentally spilled on the soil during transport or leaked from their storage places, they could have migrated vertically through the unsaturated zone...
Article
In disordered porous media, two-phase flow of immiscible fluids (biphasic flow) is organized in patterns that some times exhibit fractal geometries across a range of length scales, depending on the capillary, gravitational, and viscous forces at play. These forces, as well as the boundary conditions, also determine whether the flow leads to the app...
Article
Full-text available
To quantify the vertical diffusive mass transfer of trichloroethylene (TCE) in a low water-saturated porous medium, diffusion experiments were conducted in soil columns using a medium-size quartz sand at two different water saturations; namely, completely dry and at irreducible water saturation. Advective transport of TCE vapors was mainly generate...
Article
Les recherches portent sur une quantification des instabilités de déplacement d’un DNAPL en milieu poreux homogène et saturé. L’approche expérimentale repose sur la mesure des vitesses d’arrivées du DNAPL dans une colonne de laboratoire à différents points d’une section de contrôle au moyen des fibres optiques et sur la cartographie in situ des sat...
Article
Full-text available
A pore-scale network model based on spherical pore bodies and cylindrical pore throats was developed to describe the displacement of water by DNAPL. The pore body size and the pore throat size were given by statistical distributions with user-specified values for the minimum, mean and maximum sizes. The numerical model was applied to a laboratory e...
Article
Multiphase flow modelling is a major issue in the assessment of groundwater pollution. Three-phase flows are commonly governed by mathematical models that associate a pressure equation with two saturation equations. These equations involve a number of secondary variables that reflect the fluid behaviour in a porous medium. To improve the computatio...
Article
We describe the construction of Total Differential (TD) three-phase data for the implementation of the exact global pressure formulation for the modeling of three-phase compressible flow in porous media. This global formulation is preferred since it reduces the coupling between the pressure and saturation equations, compared to phase or weighted fo...
Article
We study various types of biphasic flows in quasi-two-dimensional transparent porous models. These flows imply a viscous wetting fluid, and a lowly viscous one. The models are transparent, allowing the displacement process and structure to be monitored in space and time. Three different aspects will be presented: 1. In stationary biphasic flows, we...
Article
Full-text available
In this study we present a pore-scale network model to simulate gravity dominated displacement of a wetting fluid (water) by a lower-viscosity DNAPL (trichloroethylene) in homogenous porous media. A typical geometric representation of the network model includes a regular cubic lattice structure with pore bodies corresponding to the vertices of the...
Article
Full-text available
In this paper, we discuss the results of a Partitioning Interwell Tracer Test (PITT) performed in a large scale experiment with a well-defined TCE spill, and present a novel combined analytical-numerical inverse modelling approach using measured concentration profiles within a TCE plume to predict the distribution of the DNAPL in a virtual vertical...
Article
Full-text available
The inversion method of pumped concentration can be used as an alternative or complementary method to the conventional methods for groundwater pollution evaluation and quantification. This method is useful even when the monitoring wells are few and also when the contamination source is unknown. In a homogeneous-isotropic case, with radially dominat...
Article
In summary, we disagree with the commentary of Bayer-Raich et al. (2007-this issue) that suggests that IPT evaluations in field situations may be unbiased as long as transverse dispersivities are low. As we have shown here, in the case of the very low dispersive Borden aquifer, the observed concentration gradients vary significantly along the flow...
Article
Forecasting the behaviour of chlorinated solvents in aquifers faces various problems in characterising the source area, evaluating the potential of natural attenuation and numerical modelling. Within such context, ADEME (Agence de I'Environnement et de la Maîtrise de I'Energie) started in 2001 a research program (named MACAOH (Modélisation, Atténua...
Article
This study is focussing on a detailed analysis of the errors introduced by a semi-analytical approach based on the Fick's first law to evaluate the diffusive vapor flux of chlorinated solvents from a source zone towards the atmosphere. A one-dimensional numerical model was developed and applied to 3 study cases characterized by different water cont...
Article
Full-text available
Experimental and modeling studies were performed to investigate the simultaneous transport of trichloroethylene (TCE) and perchloroethylene (PCE) in the vadose zone of a large (25 by 12 by 3 m) well-instrumented artificial aquifer called SCERES. The experimental facility, made up of a 1-m-thick saturated zone and a 2-m-thick unsaturated zone, allow...
Article
The goal of this study was to develop an innovative chloroethene biodegradation module based on biological, thermodynamical and mechanistic concepts. The biodegradation scheme was based on the postulate that in each part of an aquifer only one degradation mechanism is dominant: the one involving the most energetic electron acceptor. Thus, the selec...
Article
Full-text available
A modelling approach was developed to quantify the vertical distribution of a source zone placed in a saturated porous aquifer and composed of a chlorinated solvent in residual phase using concentration profiles recorded at different times downstream of the spill. The first and second calculation steps comprise an iterative backward modelling to lo...
Article
Full-text available
Experimental and modeling studies were performed to investigate the simultaneous transport of trichloroethylene (TCE) and perchlo- roethylene (PCE) in the vadose zone of a large (25 by 12 by 3 m) well- instrumented artificial aquifer called SCERES. The experimental facility, made up of a 1-m-thick saturated zone and a 2-m-thick unsat- urated zone,...
Article
When only few monitoring wells are available to assess the extent and level of groundwater contamination, inversion of concentration breakthrough curves acquired during an integral pumping test can be used as an alternative quantification method. The idea is to use concentration–time series recorded during integral pumping tests through an inversio...
Article
Full-text available
Pollution source characterization by the Partitioning Interwell Tracer Test method requires the assessment of the partitioning coefficient of the tracers with the pollutant. Experiments conducted on batch tests (static) and laboratory columns (dynamic) indicated a partitioning kinetics between the reactive tracer (4-methyl 2-pentanol) and the organ...
Article
Full-text available
In this paper, we present a numerical model for simulating two-phase (oil–water and air–water) incompressible and immiscible flow in porous media. The mathematical model which is based on a fractional flow formulation is formed of two nonlinear partial differential equations: a mean pressure equation and a water saturation equation. These two equat...
Article
Monitored Natural Attenuation (MNA) of chlorinated volatile organic compounds (CVOC) is being evaluated in two industrial sites primarily contaminated by trichloroethene (TCE) and tetrachloroethene (PCE). In order to accurately characterize the contamination source, a systematic depth-discrete soil sampling with an on-site extraction procedure was...
Article
A large scale experiment has been carried out on an experimental facility to study the mass transfer of trichloroethylene (TCE) in a partially saturated porous medium. 5 liters of TCE have been infiltrated in the vadose zone of the site. The mass transfer of TCE from the vapor plume in the unsaturated zone towards the top of groundwater was quantif...
Article
Full-text available
A large-scale experiment was conducted to investigate the transport of trichloroethylene (TCE) vapors in the unsaturated zone and to determine the mass transfer to the groundwater and the atmosphere. The experiment involved injection of 5 1 of TCE in the unsaturated zone under controlled conditions, with multidepth sampling of gas and water through...