Handbook of Radon.
9. Areas of the UK affected by radon.
The principal affected counties are Devon and Cornwall. However, large areas of Devon are only marginally affected.
Areas of Northants, Scotland, Derbyshire and Somerset are also known to contain houses at moderate radon levels and with some above 1000 Bq/m3. Many small areas have become known because of Press and media attention. However, it does not follow that these are the only or the worst affected in the neighbourhood: often they were merely the first to be discovered. Some streets are well known to be affected, but there can be marked differences both between neighbouring houses and between rows on opposite sides of the street.
The worst-affected postcode sectors in Devon and Cornwall especially have been published in the UK. Earlier publication of radon data by zip code in the USA caused increased interest amongst homeowners because of possible effects on property values. The author may be consulted for details.
Postcodes are a useful way of delineating areas, if only because they are used already by marketing organisations. Each sector contains between 1000 and 4000 addresses. In sparsely populated areas a sector can cover many square kilometres. However, few if any align with known geological features or mine workings, which have been known for years to be one of the methods of identifying areas or villages likely to contain houses with the highest radon levels. Only recently has detailed mapping of radon in soil gas been started in the UK. However, porosity or diffusion parameters are also important (and probably more important in inhomogeneous ground) in predicting areas most at risk.
Over four years ago, a County Council identified the areas most likely to contain its worst affected schools using maps and mining records.
However, it is important to recognise that even in Cornwall only around 20% (1 in 5) of houses contain more than 200 Bq/m3 of radon, and of these only a small fraction are at levels that need give rise to concern in the short term.
Radon in soil gas could be investigated over wide areas, but it may remain useful only as a broad indicator. This is because of variations over short distances, and the key role of ground permeability. Unfortunately also, airborne measurements of gamma activity (as have been used in seeking uranium deposits) do not correlate well with all known high radon houses. Again, uniformity may be part of the problem.
A few owners of badly affected houses have undertaken detailed study of geological maps, and have confirmed that their home sits astride a fault or junction between rock types.
The combination of broad-scale radon mapping with detailed study of local maps may be a potent and cost-effective method for identifying high-risk areas to fine resolution.
A similar approach was first used in the USA in the mid 1980s and in Sweden well before that: knowledge of local geology was used to predict the location of other high level houses from a few that had been discovered somewhat by chance.
KEY FACTS:
Houses that contain a very high level of radon can be found in many counties, but outside of the principal affected areas are rare.
Within affected counties there can be large areas that are substantially unaffected, but even within a given postcode sector, these can include very small 'hot-spots', owing to changes in the underlying ground.
Neighbouring houses can have genuinely very different radon levels and few houses may exhibit an essentially fixed radon level, independent of occupancy and building factors.