1. Hydrochemical Consultant, Valeriusstraat 11, NL 1071 MB Amsterdam, The Netherlands, Arcadis, P.O. Box 264, NL 6800 AG Arnhem, The Netherlands, LGIT, Université de Grenoble, P.O. Box 53, F-38041 Grenoble, France, and Environmental Service Department South East Utrecht, P.O. Box 461, NL 3700 AL Zeist, The Netherlands