Aggravation of licensing procedures by doubtful thermodynamic data

Environmental prognosis by geochemical modelling is a scientific approach t o several open questions of general public interest. Two prominent fields w here geochemical modelling holds an important share are the remediation of contaminated former uranium mining areas and safety assessment of radioacti ve waste repositories in the geosphere. In both fields, application of geoc hemical modelling is stipulated by public authorities. The enormous complex ity of models that can be handled by computers rises the awareness on the m eaningfulness of a modelling result and demands for provision of an estimat e of the dependability of a calculation output by the computers. It is obvi ous that bias, over- and underestimation of uncertainty in input data reduc es the relevance of the calculation output. Chemistry contributes important data to geochemical modelling, both from field analysis and in the fundame ntal physico-chemical quantities enclosed into the thermodynamic data base. Some examples will be given where progress in quality assessment of chemic al data may further the predictive power of geochemical modelling.