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The experimental SCERES facility of the LHyGeS

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Responsable : Olivier Razakarisoa

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Tél : 03 88 10 67 97

A large-scale experimental groundwater model for measuring, modelling and to better understand reactive transfer processes

Site labellisé de l’Observatoire de Recherche H+ en 2008

SCERES, Experimental Controlled Research Site for the rehabilitation of Waters and Soils

Implanted since 1992 to test and validate technological developments in the studies of subsurface hydrosystems and groundwater contamination mechanisms, the experimental SCERES facility arises from the common will of the CNRS (National Center for Scientific Research), the University of Strasbourg, IFP, ‘Générale des Eaux’ group and BURGEAP to finance its construction and also to have a controlled experimental pilot site on the CNRS Campus in Strasbourg-Cronenbourg. In a tight armed concrete basin of 25 m length, 12 m wide and 3 m depth, the facility reconstitutes a realistic scale aquifer with particle size comparable to that of the alluvium of the Rhine ditch. SCERES is at the disposal of scientific collaborations (research institutes, private sector, engineering consulting firms, communities etc.) for the realization of research and development (R&D) projects.

The SCERES platform is equipped with wells, piezometers, a spatial network of water and gas sampling and several instruments of subsurface hydrodynamic parameters measurements (velocity, flowrate, pressures, moisture content profiles, etc.) and meteorological (T °, Hr, Patm., wind, etc.). By its size and its characteristics, this big device is unique in Europe and offers, in controlled conditions and in real-scale situation, the opportunity to allow data acquisitions and scientific results.

To make research works and focusing on SCERES-scale processes are vital actions required by the LHyGeS to be able to approach the concepts which are difficult to access at the reduced-scale of physical laboratory models or for investigations carried out on contaminated industrial site such as the assessment of the role of the capillary fringe or the quantification of exchange mechanisms between the unsaturated zone and the groundwater.

SCERES, what motivations ?

The main approaches available to advance our knowledge in the studies of reactive transfer mechanisms are frequently confronted with complications.

In the approach using physical laboratory models, research works are often handicapped by the limited size of the experimental devices used; For the approach where the intervention is carried out on a real site, the investigation can be tricky because the quantification of the mechanisms involved is often difficult to realize due to the heterogeneity of the site hydrogeology parameters and the uncertainties related to the knowledge of the pollution source area. These difficulties encountered both in laboratory and on real site will have an impact on the performance of the mathematical modelling approach which, for their relevance, requires the acquisition of reliable data.

In front of this situation, the SCERES facility has emerged which embodies the necessary intermediary between the laboratory scale and that of the industrial site in order to approach transfer processes in 3D controlled conditions and to study in a more representative way the hydrosystem and groundwater contamination mechanisms.

SCERES, to do what ?

Among the research works already approached on the SCERES facility, the following studies were examples realized and can be continued :

- Quantification of transfers (concentrations, flux, mass balance, etc.) in the saturated and unsaturated zones, in the capillary fringe, at the soil/air interface and/or through concrete slabs ;

- L’impact des flux d’eaux verticaux (battement de nappe) sur les transferts du polluant (produit pétrolier, solvant chloré, NAPL, etc.) dans la nappe, en zone non saturée et ses interfaces ;

- Impact of vertical water fluxes (water-table fluctuations) on the transfers of pollutant (petroleum product, chlorinated solvent, NAPL, etc.) in the groundwater, in the unsaturated zone and its interfaces ;

- Consideration of meteorological parameters (Patm, T °, humidity, wind) and the soil air pressure field in the evaluation of the transport (diffusive and convective) of the pollutant vapors present in soils to air atmospheric ;

- Continuous measurements of the spatio-temporal variations of water content profiles (capacitive sensors), pressures and soil air temperatures via the acquisition units coupled to the various sensors ;

- Numerical simulations tests on the volatile pollutant vapors transfer to the atmosphere, water-table fluctuations experiments (density effect of gas mixtures, evaluation of relative soil air permeabilities, etc.).

Some highlights

The various actions already carried out on the SCERES platform have strengthened the transfer of scientific knowledge and practical application methods involving operational results for the diagnosis of contamination cases as evidenced by these few highlights :

- In-situ demonstration of the ability of surfactant solutions to remobilize to the pumping well the residual NAPL pollutant trapped in the soil (accidental 480 liters of diesel oil spill subject to water-table fluctuations, surfactant formulation allowing good performance both in terms of surfactant flux (permeability) and in terms of the efficiency of residual pollutant recovery);

- The importance of volatile DNAPL vapor fluxes (TCE and PCE) in soil air (predominance of gaseous contamination, vapor dissolution, role of the capillary fringe, etc.);

- The development of a computational approach to quantify, from dissolved concentrations measured near the suspected source zone, the vertical distribution of residual DNAPL in saturated zone. This innovative approach implemented on SCERES, based on an iterative inversion of concentration profiles and coupled with numerical modelling of transfer and transport, has also been applied to a case of PCE pollution at an industrial site;

- The evaluation of the performance of several methods of DNAPL pollution source zones characterization carried led in the MACAOH-ADEME program (2002-2007), [applicability of the PITT method, representativeness of samples taken in piezometers, development of technical methods and protocols to guide stakeholders and engineering design offices during diagnosis at industrial sites contaminated by chlorinated solvents];

- As part of the R&D FLUXOBAT project, the development and optimization of devices for evaluating the transfer of volatile soil pollution to indoor air and/or atmospheric air;

- The benchmarking of several types of groundwater multilevel water samplers and the design of an innovative multilevel sampler to better take into account the heterogeneities of vertical concentration distributions in groundwater when water samples are taken from the piezometers (PEMN-ADEME project (2011-2016));

Permanent staff currently involved
S. Cotel (IR2 CNRS) ; P. Friedmann (TCN CNRS) ; O. Razakarisoa (IR1 CNRS) ; G. Schäfer (PU1 UNISTRA).