Radon levels in dwellings in chalk terrain : development and analysis of distributional and causal models
This thesis investigates the range, distribution and causes of high radon levels in
dwellings in the Brighton area of Southeast England. Indoor radon levels were
measured in more than 1000 homes. The results show that high radon levels can arise
in an area previously considered to offer low radon potential from local geological
sources. Climate and building-related factors were found to affect significantly the
radon levels in dwellings. Multiple regression was used to determine the influence of
the various factors on indoor radon levels and an empirical model developed to
predict indoor radon levels.
The radon hazard, independent of building-related effects, was determined for each
surveyed location by adjusting the radon measurement to that expected on the ground
floor of a 'model' dwelling. This standardised set of radon levels was entered into a
geographical information system (GIS) and related to surface geology. The geometric
mean radon level for each lithological unit was plotted to produce a radon hazard map
for the area. The highest radon levels were found to be associated with the youngest
Chalk Formations, particularly where they meet overlying Tertiary deposits, and with
Clay-with-Flints Quaternary deposits in the area.
The results were also converted to the radon activity equivalent to that expected from
the NRPB's standard dual-detector dwelling survey method and analysed by
lognormal modelling to estimate the proportion of dwellings likely to exceed the UK
Action Level of 200 Bq/m3 for each lithological unit. The likely percentages of
dwellings affected by radon thus obtained were mapped to lithological boundaries to
produce a radon potential map.
The radon hazard map and the empirical radon model facilitate the prediction of radon
levels in dwellings of comparable construction and above similar geology and should
further the understanding of the behaviour of radon gas in buildings to allow indoor
radon concentrations to be controlled. The radon potential map is directly comparable
with those produced by NRPB and BGS and can be used to assist in environmental
planning and development control.