The Science of the Total Environment 317 (2003) 189–200 0048-9697/03/$ - see front matter  2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0048-9697(03)00337-1 Generation of humic and fulvic acid from Callovo-Oxfordian clay under high alkaline conditions Francis Claret, Thorsten Schafer, Andreas Bauer, Gunnar Buckau* ¨ Forschungszentrum Karlsruhe, Institut fur Nukleare Entsorgungstechnik, Karlsruhe D-76021, Germany ¨ Received 23 September 2002; received in revised form 20 March 2003; accepted 30 April 2003 Abstract Low-carbon-containing clay from four different depths (447 to 516 m) of the Meuse Haute Marne (MHM) site is kept in contact with alkaline solution simulating conditions expected from cement dissolution in the near-field of a nuclear waste repository. Original organic material in the clay consists mainly of aliphatic hydrophobic compounds basically without oxygen-containing functional groups. After contact with ‘solid young fluid’ (mimicking cement dissolution, initial pH 13.22) for approximately one and a half years, high concentrations of hydrophilic organic matter are found (243–355 mg DOCyL). Characterization by solubility behavior, UVyVis absorption, IR and fluorescence properties show that the dissolved hydrophilic organic matter has the characteristic features of humic and fulvic acids. Estimation of humic and fulvic acid content via UVyVis spectroscopy results in 97.5 ("9.7)% of DOC being humic and fulvic acid. The results indicate that this could be an important source of complexing mobile organic matter influencing the mobility of radionuclides in a nuclear waste repository under consideration for this site. Investigations were conducted under oxic conditions representing the situation in the excavation disturbed zone (EDZ) of an underground facility. Sample amounts were very small and thus some characterization results are partly of preliminary character.  2003 Elsevier Science B.V. All rights reserved. Keywords: Clay organic matter; Humic substancesl; Disposal; Radioactive waste; High pH 1. Introduction Geologic disposal of radioactive waste is under consideration for a number of different geological settings. These include clay, salt and crystalline rock. Within these different types of basic host rocks, great individual variations are found. One site under consideration in France is at the Meuse *Corresponding author. Tel.: q49-7247-824461; fax: q49- 7247-82-4308. E-mail address: buckau@ine.fzk.de (G. Buckau). Haute Marne (MHM) in the Eastern Paris basin, where the French nuclear agency (ANDRA) is currently setting up an underground laboratory. The sedimentary host formation is an approximate- ly 130 m thick clay-rich Callovo-Oxfordian for- mation at approximately 350–550 m depth below ground surface in the selected area. The origin of the clay organic matter, identified by biomarkers, in the Oxfordian series is mainly terrestrial-derived (type III kerogen), whereas organic carbon in the Callovian series is mainly of marine origin (type