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The Ore Mountains (Erzgebirge) and Vogtland are low-mountain regions in the East German state of Saxony. Here, silver deposits were found in 1168. Mining began shortly after, continues at varying intensity to this day, and has left numerous galleries and shafts. Today, eight companies with about 250 miners carry out maintenance at more than 40 small and frequently changing underground construction sites throughout the year. Miners are protected against high radon exposure by radiation protection measures such as ventilations, stoppings made of wood, foil, and expanding foam, and staff rotations. However, some of them still show high annual exposure levels; for example, in 2015 up to 14.4 mSv measured by passive radon dosimeters. Reasons for this include the high radon potential in old mining and the natural density driven mine air current through the galleries. Mine air currents can change directions during the day depending on outdoor temperatures. This paper presents the experiences of the Saxon Radiation Protection Authority in monitoring miners in old mining. For this purpose, the paper looks at seven examples of miners’ critical exposures based on measurement curves of radon activity concentration and derives respective radiation protection measures. These encompass, for example, to activate mine fans, erect stoppings, extend ventilation pipes, and change the locations of mine fans. Conclusions are drawn for the operative and strategic radiation protection in old mining.

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Fachbeiträge Kurzfassung Das natürlich vorkommende Isotop Radon-222 kann wegen deutlicher Konzentrationsunterschiede in Grund-und Oberflächenwässern als natürlicher Tracer zur Bestimmung der Aufenthaltszeiten von infiltriertem Oberflächenwasser und der Infiltrationsgeschwindigkeit eingesetzt werden. Für das Untersuchungsgebiet in der Torgauer Elbaue wurde eine Korrelation zwischen der Radonaktivitätskonzentration des Grundwassers und dem lithologischen Aufbau des Grundwasserleiters gefunden. Niedrige Radonaktivitätskonzentrationen im Grundwasser in der Nähe eines Oberflächengewässers können geogen bedingt sein und dürfen nicht als Folge eines Fließweges von Uferfiltrat im Grundwasserleiter fehlinterpretiert werden. Das Verhalten von Uferfiltrat einer Hochwasserwelle derElbe im Grundwasserleiter wurde mit Hilfe von Messungen der Radonaktivitätskonzentration beobachtet. Außerdem konnte die Aufenthaltszeit des Uferfiltrats im Grundwasserleiter an einer unter dem Flußbett der Elbe angeordneten Kolmationsmeßstelle ermittelt und daraus die Infiltrationsgeschwindigkeit des Flußwassers berechnet werden. AbstractOwing to its different concentrations in groundwater and river water, the naturally occuring isotope radon-222 can be used as a natural tracer to determine the residence time of freshly infiltrated water and the infiltration velocity. In the study area, predominant correlation was found between the radon activity concentration of groundwater and the lithologic structure of the aquifer. Misinterpretation of low radon activity concentration measured near surface waters due to geological inhomogeneities can result in false assumptions about groundwater flow paths. The infiltration of river water into the adjacent aquifer during a flood wave was also ascertained by measuring radon activity concentration. Further the residence time of infiltrated water was determined at a sampling point installed beneath the river Elbe and infiltration velocity was calculated.