A comparison of field and laboratory analytical methods for radon site investigation

Soil-gas radon measurements provide a valuable tool in assessing probable i ndoor radon levels on a regional basis. However, in Great Britain, seasonal weather changes can cause large changes in soil-gas radon concentration. A lthough this does not significantly constrain systematic radon potential ma pping programmes, it does cause difficulties in responding to ad-hoc reques ts for site-specific radon investigations. The relationship between soil-ga s radon and gamma spectrometry measurements made in the field with radon re leased from a representative sample of soil in the laboratory has been inve stigated as part of a program to develop a method of radon potential mappin g and site investigation which can be used at any time of the year. Multipl e soil and soil-gas samples were collected from sites underlain by bedrocks with widely varying radon potentials. For each geological unit, sites both free of and covered by glacial drift deposits were sampled. Soil and soil- gas samples were taken at the same depth of 60-100 cm. The effectiveness of these radon site investigation procedures has been evaluated by studying t he relationship between the soil-gas radon, gamma spectrometry and radon em anation data with an independent estimate of the radon risk. The geologic r adon potential (GEORP), which is the proportion of existing dwellings which exceed the UK radon Action Level (200 Bq m(-3)) for a particular combinati on of solid and drift geology within a defined geographic area, has been us ed for this study as the independent estimate of radon risk. Soil-gas radon , radon emanation and eU (equivalent uranium by field gamma spectrometry) a re all good geochemical indicators of radon risk (GEORP) in Derbyshire but only soil-gas radon correlates significantly with GEORP in Northamptonshire . Radon in soil gas discriminates more effectively between sites with diffe rent radon potential in Northamptonshire if soil permeability is also taken into account. In general, measurement of soil-gas radon in the field provi des the most universally applicable indicator of radon potential. If soil-g as radon concentrations cannot be determined because of climatic factors, f or example when the soil profile is waterlogged, measurement of radon emana tion in the laboratory or measurement of eU can be used as radon potential indicators in some geological environments. This applies particularly in ar eas where the soil composition rather than the composition and permeability of the underlying rock or superficial deposits are the dominant controls o f radon potential. It appears, therefore, that it may be necessary to use d ifferent radon site investigation methods according to the specific factors controlling radon emanation from the ground. In some cases no method will provide a reliable indicator of radon risk under unfavourable climatic cond itions. (C) 1998 Elsevier Science B.V. All rights reserved.