The system of geological exploration for possible ISL influence evaluation in the Southwestern forefield of the Straz uranium deposit in the North Bohemian Cretaceous, Czech Republic

The production of uranium ores in the area of North Bohemian Cretaceous significantly influenced the regime of groundwater and its quality. Since 1990, environmental impact assessments of uranium production has rapidly changed. The large amount of contaminated water from ISL is the greatest potential risk. During 1992-1994, a lot of geological exploration was done in the area south-west of the ISL plant (the direction of natural groundwater flow). A complex of exploration methods, between synoptic and detailed scales, was set for qualification and quantification of potential risks. In the first phase, synoptic methods were used (satellite photos, airborne geophysics). At the same time, the re-interpretation of older geological and geophysical data was performed. Also the works for the regional hydraulic mathematical model of groundwater flow began in the whole area of North Bohemian Cretaceous. Based on the results of this work, surface geophysical and geological exploration started. It was first applied to the areas presenting the maximum of risk (faults with significant vertical movement along them). Results of this exploration were gradually put into the regional hydraulic mathematical model. This model was also targeted at the highest risk areas. So far, the first phase of qualification and quantification of risks resulting from the geological structure has been completed. The results from 1992-1994 signal the necessity of stabilizing contaminated groundwater in the production area. This fact determines the next remediation concepts e.g. the stabilization of groundwater in the production area and followed by gradual steps (e.g. minimal recovery of solutions for the depression cone development in the contaminated area, time-spatial course of contaminated water recovery, preliminary setting of limits for contaminants content etc.). (author). 7 figs