Ž . Journal of Contaminant Hydrology 47 2001 127–137 www.elsevier.comrlocaterjconhyd Solute transport properties of compacted Ca-bentonite used in FEBEX project M. Garcıa-Gutierrez a, ) , T. Missana a , M. Mingarro a , J. Samper b , ´ ´ Z. Dai b , J. Molinero b a CIEMAT, Ed. 20, AÕenida Complutense 22, 28040 Madrid, Spain b E.T.S. Ingenieros de Caminos, UniÕersidad de La Coruna, La Coruna, Spain ˜ ˜ Received 18 August 1999; received in revised form 25 February 2000; accepted 31 March 2000 Abstract The present Spanish concept of a deep geological high level waste repository includes an engineered clay barrier around the canister. The clay presents a very high sorption capability for radionuclides and a very small hydraulic conductivity, so that the migration process of solutes is limited by sorption and diffusion processes. Therefore, diffusion and distribution coefficients in Ž . compacted bentonite i.e. in ArealisticB liquid to solid ratio conditions are the main parameters that have to be obtained in order to characterise solute transport that could be produced after the canister breakdown. Ž . Ž . Through-Diffusion TD and In-Diffusion ID experiments with HTO, Sr, Cs and Se were carried out using compacted FEBEX bentonite, which is the reference material for the Spanish concept of radioactive waste disposal. Experiments were interpreted by means of available analytical solutions that allow the estimation of diffusion coefficients and, in some cases, distribution coefficients. Analytical solutions are simple to use, but rely on hypotheses that do not hold in all the experiments. These experiments were interpreted also using an automatic parameter estimation code that overcomes the limitations of analytical solutions. Numerical interpretation allows the simultaneous estimation of porosity, diffusion and distribution coefficients, accounts for the role of porous sinters and time-varying boundary concentrations, and can use different types of raw concentration data. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Diffusion; Sorption; Bentonite; Radionuclides ) Corresponding author. Tel.: q 34-91-3466542; fax: q 34-91-3466139. Ž . E-mail address: michel@ciemat.es M. Garcıa-Gutierrez . ´ ´ 0169-7722r01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. Ž . PII: S0169-7722 00 00143-1