Radon levels in the volcanic region of La Garrotxa, Spain

A preliminary survey in the city of Olot, the main town of the volcanic region of La Garrotxa, showed that dwellings built on volcanic formations present higher indoor radon levels than dwellings on non-volcanic materials. The soil of the area is not especially rich in radium. However, some of the volcanic materials present very high permeability and therefore radon entering the houses might have travelled over long distances. In this paper we present indoor radon values measured in a larger survey carried out during April-July 2004. The influence of the volcanic materials found in the preliminary survey has been confirmed. The results obtained suggest the possibility that radon comes from the degassification of mantle through active faults. The values obtained in working places do not constitute a relevant radiological risk for workers.