Abstract
Groundwater inflows showing notable natural radioactivity have been found at the northern end of the Holešovice cable tunnel close to the Čimice Grove. This groundwater originates from the Barrandian Neoproterozoic slates of the Blovice accretionary complex, Belt I (Šárka-Zbiroh Belt) at depths approximately 100 meters below the surface, occurring along 50 meter profile of the cable tunnel.
Water springs are dispersed in the spring area, with the total discharge of 2 L/s. Groundwater is cold (T ~ 11.1 - 12.3 °C), neutral (pH ~ 6 - 7.48), suboxic to oxic (Eh (ORPH) ~ 177 up to 418 mV), of a hydrochemical type CaMgHCO3, total mineralization being around 702 mg/L.
Radon activity ((222)Rn) varies between 415 and 1195 Bq/L and radium activity ((226)Ra) ranges between 0.18 and 5.3 Bq/L. Activities of Rn and Ra are relatively high.
Currently, this is the most radioactive water within Prague agglomeration. This water is relatively aggressive as well, causing damage to the concrete lining of the cable tunnel and also allowing formation of calcite precipitates with an increased radium ((226)Ra) activity.