Derivation of natural background values for groundwater in conjunction with the remediation of a sandstone-hosted uranium mine

摘要

The former uranium underground leach operation at Konigstein, Germany is related to a sandstone-hosted uranium deposit situated in the lowermost of four Cretaceous aquifers. Since 2012 the mine is closed and partially flooded, mine water is controlled by a pump-and-treat-operation. In conjunction with the further prospects of mine water management the derivation of groundwater background values for uranium and radium deemed necessary for the deposit area. Since reliable information could not be derived from regional data sets due to the limited extension of the deposit (2.5 km ×10 km) and its geological setting in a deeper aquifer, local background values had to be generated by a combined evaluation of historical records and data from recent groundwater monitoring. Background values were calculated for the 3~(rd) and 4~(th) aquifer based on the determination of observation point related arithmetic means and a test for Gauss distribution. The calculated local uranium background values were found to be 20 μg/L for the 3~(rd) aquifer and 140 μg/L for the deposit-hosting 4~(th) aquifer. Those values differ significantly from data reported in the literature. For radium natural background values of 1,000 mBq/L for the 3~(rd) and of 17,800 mBq/L for the 4~(th) aquifer were derived. The information gathered will have to be thoroughly considered in the ongoing licensing procedure regarding the long-term water management strategy at the Konigstein mine site.