Broder J. Merkel

Britta Planer-Friedrich

To understand hydrochemistry and to analyze natural as well as man-made impacts on aquatic systems, hydrogeochemical models have been used since the 1960’s and more frequently in recent times. Numerical groundwater flow, transport, and geochemical models are important tools besides classical deterministic and analytical approaches. Solving complex linear or non-linear systems of equations, commonly with hundreds of unknown parameters, is a routine task for a PC. Modeling hydrogeochemical processes requires a detailed and accurate water analysis, as well as thermodynamic and kinetic data as input. Thermodynamic data, such as complex formation constants and solubility-products, are often provided as databases within the respective programs. However, the description of surface-controlled reactions (sorption, cation exchange, surface complexation) and kinetically controlled reactions requires additional input data. Unlike groundwater flow and transport models, thermodynamic models, in principal, do not need any calibration. However, considering surface-controlled or kinetically controlled reaction models might be subject to calibration. Typical problems for the application of geochemical models are: • speciation • determination of saturation indices • adjustment of equilibria/disequilibria for minerals or gases • mixing of different waters • modeling the effects of temperature • stoichiometric reactions (e.g. titration) • reactions with solids, fluids, and gaseous phases (in open and closed systems) • sorption (cation exchange, surface complexation) • inverse modeling • kinetically controlled reactions • reactive transport Hydrogeochemical models depend on the quality of the chemical analysis, the boundary conditions presumed by the program, theoretical concepts (e.g.

A Practical Guide to Modeling of Natural and Contaminated Aquatic Systems

Groundwater Geochemistry

Christian Wolkersdorfer

Broder Merkel

Preface Uranium is a radioactive element and a heavy metal which is naturally occurring in ground and surface water. Although uranium is enriched in granites and gneiss ground water from these host rocks often shows low to intermediate uranium con centrations, while some ground waters from sandstone and carbonate aquifers show elevated uranium concentrations up to several hundred mg/1 without man made impact. On the other side, surface water contains increased anthropogenic uranium concentrations due to the intensive use of phosphate fertilizers and in mining areas due to mining and milling activities. Saxony and Thuringia both be ing states of the reunified Germany are probably an area where uranium mining activities have impacted the environment more severely than in any other part of the world. Thus, the federal government of Germany allocated huge amounts of money for the rehabilitation work, a unique proceeding without precedent in min ing history. In October 1995 the first international conference on Uranium Mining and Hydrogeology (UMM I) was held in Freiberg being organized by the Department of Geology at the technical University Freiberg by the support of the Saxon State Ministry of Geology and Environment. Due to the large scientific interest in the topic ofuranium a second conference (UMH II) took place in Freiberg in Septem ber 1998.

Proceedings of the International Conference Uranium Mining and Hydrogeology III and the International Mine Water Association Symposium Freiberg, Germany, 15-21 September 2002

Uranium in the Aquatic Environment

This book addresses scientists and engineers involved in the areas of uranium mining and milling sites, clean-up measures, emissions of nuclear power plants and radioactive waste disposal, as well as political decision-makers. The topics covered are: impact on groundwater from radionuclide emission, analytical speciation techniques, chemical toxicity, radioisotope plant uptake, microbiology catalyzing U(6+) to U(4+) reduction, geochemical and reactive transport, case studies on abandoned uranium mines and milling sites, long-term storage of radioactive waste, passive in situ treatment techniques and risk assessment studies.

proceedings of the International Conference [on] Uranium Mining and Hydrogeology III and the International Mine Water Association Symposium, Freiberg, Germany, 15-21 September 2002 : with 453 figures, 151 tables and a CD-ROM

Britta Planer-Friedrich

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