A laboratory experiment for determining both the hydraulic and diffusive properties and the initial pore-water composition of an argillaceous rock sample: A test with the Opalinus clay (Mont Terri, Switzerland)

• Published in: Journal of contaminant hydrology Vol. 128; no. 1; pp. 47 - 57
• Main Authors: Savoye, S., Michelot, J.-L., Matray, J.-M., Wittebroodt, Ch, Mifsud, A.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 01-02-2012; Elsevier
• Subjects: Aluminum Silicates - chemistry; Axisymmetric diffusion; Bromide; bromides; Caesium; Chloride; chlorides; clay; Diffusion; Earth sciences; Earth, ocean, space; Effective diffusion coefficient; Environmental Sciences; Exact sciences and technology; experimental design; Finite Element Analysis; Fluid dynamics; Fluid flow; hazardous waste; hosts; Hydraulic conductivity; Hydraulic tests; Hydraulics; Hydrogeology; Hydrology. Hydrogeology; labeling techniques; Mass Spectrometry; Models, Chemical; Opalinus clay; Porosity; radionuclides; Repositories; Rock; rocks; safety assessment; samplers; Switzerland; Tracers; Water - chemistry; water quality; Water stable isotopes; Central Europe; Switzerland; Europe; Chloride; Opalinus clay; Caesium; Water stable isotopes; Hydraulic conductivity; Axisymmetric diffusion; Effective diffusion coefficient; Bromide; experimental studies; diffusion; reliability; reservoirs; radionucleids; radioactive waste; clay; drill cores; hydraulic conductivity; hydraulics; deuterium; safety; pore water; oxygen; clastic rocks; chlorides; stable isotopes; bromides; tracers; host rocks; argillaceous texture; concentration; samplers; halides; in situ; sedimentary rocks; circulation
• ISSN: 0169-7722; 1873-6009
• DOI: 10.1016/j.jconhyd.2011.09.011

Argillaceous formations are thought to be suitable natural barriers to the release of radionuclides from a radioactive waste repository. However, the safety assessment of a waste repository hosted by an argillaceous rock requires knowledge of several properties of the host rock such as the hydraulic conductivity, diffusion properties and the pore water composition. This paper presents an experimental design that allows the determination of these three types of parameters on the same cylindrical rock sample. The reliability of this method was evaluated using a core sample from a well-investigated indurated argillaceous formation, the Opalinus Clay from the Mont Terri Underground Research Laboratory (URL) (Switzerland).
In this test, deuterium- and oxygen-18-depleted water, bromide and caesium were injected as tracer pulses in a reservoir drilled in the centre of a cylindrical core sample. The evolution of these tracers was monitored by means of samplers included in a circulation circuit for a period of 204
days. Then, a hydraulic test (pulse-test type) was performed. Finally, the core sample was dismantled and analysed to determine tracer profiles.
Diffusion parameters determined for the four tracers are consistent with those previously obtained from laboratory through-diffusion and in-situ diffusion experiments. The reconstructed initial pore-water composition (chloride and water stable-isotope concentrations) was also consistent with those previously reported. In addition, the hydraulic test led to an estimate of hydraulic conductivity in good agreement with that obtained from in-situ tests.
► The diffusion data are consistent with those from lab- and in-situ diffusion experiments. ► Hydraulic test performed at lab led to results comparable with those of field tests. ► The estimate of pore-water chloride and water isotopes contents in agreement with those from lab and field.