The appearances of significant efflux of carbon dioxide through soil surfaces is a frequent natural phenomena in the wider vicinity of relatively young volcanic fields. These mofettes are often utilised as dry carbon dioxide spas to treat patients suffering from cardiovascular diseases. The carbon dioxide always carries some naturally occurring radioactive radon gas with it. On the one hand this radon gas might pose some radiation risk for the patients and staff of such carbon dioxide spas, on the other hand it may be used as a natural tracer for the study of transport of its carrier gas in the subsurface and in the pools. In this work we have measured the spatial variation of radon activity concentration in the gas phase of the carbon dioxide gas pool of the Cardiology Hospital and in the gas and water phases of the Hell-Mud, which is a wet open pit mofette in the city of Covasna. We have developed a hydro- and gas-geological conceptual and mathematical model with which we were able to describe the measured spatial and temporal behaviour of radon gas concentration. We have found that the relatively low radon concentrations at the bottom of these pools can be explained by removing the radon content of water by intense bubbling degassing of the oversaturated carbonated waters.
Keywords: Carbon dioxide; Model calculation; Mofette; Radon; Subsurface flow.
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