Uranium mill tailings ponds represent the highest potential risk of all legacies from the former uranium mining and milling industry in Germany. Taking into consideration their large volumes and amounts of pollutants, one should principally look for the on-site remediation of such objects. Due to the specific features of the tailings and especially the fact that older plants were created without any consideration for their long-term stability, the radiological, chemical-toxic and geomechanical impacts and risks must be analysed. This is the basis for selecting the most appropriate remediation option. To analyse the success of counter-measures and, if necessary, to conduct any respective follow-up measures, it is essential to carry out long-term safety assessments based on relevant site-specific information.

To fulfil this task, GRS developed a universal conception and methodology of prospective safety reports for uranium mill tailings ponds on behalf of the Saxonian Board for Environment and Geology (LfUG). This conception has been applied to the Lengenfeld tailings pond.

This document comprises:

1. An integral description of the facility and its environment (including data sheets).

2. An assessment of the existing risks (including the basis of assessment) and an analysis of the main deficiencies.

3. A description of the measures conducted and their effects on the magnitude of risks.

4. A description of the nature, extent and an assessment of the monitoring programme and data.

5. A long-term site forecast and safety analysis.

The safety assessment is based on recommended and control values specified in or derived from laws, guidelines, norms or standards. All information necessary for the safety analysis has been compiled in a GIS-coupled database.

This paper includes a short description of the plant and its environment, an evaluation of the present safety status of the Lengenfeld tailings pond and a forecast on contaminant distribution in the downstream groundwater flow by means of a three-dimensional site-specific model. Finally, proposals for restoration strategies and long-term monitoring are presented.

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