Radon in soil gas in South-West England
In an EPA/DOE meeting in the U.S. in 1986, concerns on quantifying radon availability and the indoor radon concentration were highlighted (Hopke 1986). This work addressed some of their recommendations in a study on radon levels in S.W. England. This thesis presents: i) investigations into the correlation between indoor and soil gas radon concentrations, by the acquisition of new data from S. W. England. ii) investigations into the influence of geology, meteorological variables, spatial and depth variation on the measured radon levels. iii) a propsed protocol for obtaining soil gas measurements, suitable for use as an indication of potential inddor radon concentrations in S.W. England. iv) a discussion of the applicability of existing prediction models and proposals for the parameters to be included in any models applied to S.W. England. Several geological faults in S.W. England were delineated using radon measurements. Jointing was found to create anomalously high levels of [sup]222 Rn in the soil gas. A previous theory on the movement of ground water in convection cells was found to be unsupported. A dependence of both indoor and soil gas radon concentrations on the local geology was observed. Granite produced the highest levels as expected, and the influence of its metamorphic aureole was clearly detected. The increased fracturing of the rock was found to increase radon concentrations. Significant differences in soil gas radon levels were measured between the various sedimentary rock types. The two factors that were identified as chiefly responsible for any perturbation of a soil gas concentration, associated with a particular geology, are its moisture content and the inhomogeneity of soil permeability. Only a very weak correlation was obtained between the overall [sup]222 Rn concentration in soil gas and inside the home. However, for high soil gas concentrations a stronger correlation with the indoor level was observed. Typically the soil gas concentration was between a factor of 10 and 1000 times greater than that indoors. Levels as low as 10 kBq m[sup]-3 in the soil could produce an indoor concentration above the Action Level of 200 Bq m[sup]-3, The magnitude of influence of the various controlling parameters prevented the construction of a simple algorithm to predict the indoor radon concentration from that in the soil gas. However, in some cases, factors were identified that increased the probability that a house was above the Action Level. For a soil gas concentration in excess of 100 kBq m[sup]-3, it was found that over 70% of homes were above the Action Level, if located above and/or constructed from granite.