The Castleisland Radon Survey—follow-up to the discovery of a house with extremely highradon concentrations in County Kerry (SW Ireland)

Abstract

In July 2003, a house with a seasonally adjusted annual average radon concentration of49 000 Bq m−3 was identified near Castleisland in County Kerry (SW Ireland). The possibility that otherhouses with similar extreme radon concentrations could be present in the surrounding areatriggered the setting up of a localised radon survey, the so-called ‘CastleislandRadon Survey’ (CRS). To this end, approximately 2500 householders living in four10 × 10 km2 grid squares from the Irish grid closest to the town of Castleisland were invited toparticipate. Four hundred and eighteen householders responded to the invitation(17% response rate) and 383 home results were used for further analysis. In the400 km2 encompassing the four studied grid squares, 14% of the homes were found to have a seasonallyadjusted annual average radon concentration above the national reference level of200 Bq m−3 while 2% above800 Bq m−3. An average radonconcentration of 147 Bq m−3 was calculated. This can be compared with the average radon concentration of98 Bq m−3 calculated for the same four grid squares on the basis of 80 measurementscarried out during the Irish National Radon Survey (NRS) which wasconducted between 1992 and 1997. The fourth highest radon concentration(6184 Bq m−3) and three of the ten highest ever measured in Ireland were all identified during the CRS.This shows that localised and targeted radon surveys are an invaluable tool for theidentification of homes at highest risk from high radon concentrations. Two of the fourgrid squares investigated during the CRS are currently designated as high radonareas (defined as areas where 10% or more of all houses are predicted to exceed200 Bq m−3) as predicted by the NRS. A thorough statistical analysis of the CRS and NRS data wascarried out and indicated that both datasets could be merged and used to refine theoriginal NRS predictions. The results indicate that two of the four studied gridsquares could potentially be redesignated. The practical feasibility and overallbenefit of updating the Irish radon map in light of this analysis is described.