Das Projekt "Retention capacity of posidonia shale in respect of seepage water containing heavy metals from flue-dust dumps. Modelling of migration mechanisms based on laboratory tests and work on site" wird vom Umweltbundesamt gefördert und von Universität Karlsruhe (TH) durchgeführt. General Information: The dump sites used for the storage of residues from the various phases of steel production have to meet very special criteria. Flue dust and washing-tower sludge contain extremely high proportions of heavy metals and, in accordance with the Council Directive of 20 Match 1978 on toxic and dangerous waste, wastes containing Pb, Cd and As are among those requiring priority consideration. Seepage water in dumps results in the leaching of heavy metals and, if no precautions are taken, in the penetration of pollutants into the earth or groundwater. The base of a dump can act as a barrier against the migration of pollutants into the groundwater and biosphere, if its permeability is low and its sorption capacity high, and if the body of rock has little tendency toward destabilization and is homogenous and thick (20 m). Rocks with these favourable characteristics are generally argillaceous. In order to establish whether a rock would be suitable for a dump base, laboratory tests are normally carried out to check the above characteristics. The laboratory data are then applied to site conditions. However, the modelling of these conditions on laboratory data often involves major uncertainties. In this case we are in the fortunate position of being able to study a flue-dust dump which has been in existence for several decades and is located on a favourable barrier rock, Posidonia shale. A long-term in-situ test which would be very difficult to simulate in a laboratory has been carried out at this dump. When modelling heavy-metal migration the normal process can be reversed. The actual situation is recorded very precisely, and pollutant migration during recent decades reconstructed. Parallel laboratory tests using the same uncontaminated rock and the same pollutants are carried out, and a model is constructed using conventional methods. The validity of such a model can then be checked, and if necessary the model can be corrected so that it corresponds to what has actually happened. In addition to establishing the value of laboratory tests for ascertaining the suitability of a dump site, it will also be possible to show whether Posidonia shale is suitable for flue-dust dumps. Posidonia shale or 'oil shale' (Lias) is often found very near to iron and steel industry works, as it constitutes the under bed of mined dogger ore. From the point of view of infrastructure, Posidonia shale is therefore a favourable site and is in fact often used as such. Furthermore, a better understanding of complex migration processes (hydro-dynamic dispersion, molecular diffusion, ion exchange, adsorption/desorption, solution-precipitation, formation of organometallic complexes, flocculation-peptization, movement of colloid particles, etc) can help to establish whether any pre-treatment of the material to be dumped or the dump base is necessary.