Variations of soil gas radon concentrations in a typical building plot area - preliminary results

The research aimed to analyse variations in soil gas radon concentrations and geogenic radon potential in areas of typical building plots located in regions known for high and low geogenic radon potential. The study was designated to address the following questions:

• Are spatial variations in soil gas radon concentrations and radon potential statistically important in the area of a typical building plot? Are these variations similar in regions known for high and low radon potential?
• How many measurement points should be proposed to properly evaluate geogenic radon potential and radon index on the building plot area?
• Can an in-situ gamma spectrometric survey, combined with soil properties, be useful in the defining radon index at the area of the building plot?
• Are seasonal variations of soil gas radon concentration significant at a depth of 0.8 m?  If so, which season is the most appropriate to evaluate geogenic radon potential?

The research was conducted in two counties: Wrocław and Dzierżoniów located in the Lower Silesian Voivodeship in the southwest part of Poland. Dzierżoniów County is among the counties listed in the Regulation of 18 June 2020 of the Minister of Health where the average radon concentration in a significant number of buildings may exceed the reference level of 300 Bq m⁻³. In both regions, three building plots, each of an area of 300 m² (which is the size of a typical building plot in an urban area in Poland) were identified. At each building plot, five measurement points were designated -  at the four corners and in the middle of each plot. The research at each measurement point included the following procedures:

• Soil gas radon concentration measurements at the depth of 0.8 m using solid nuclear track detectors have been performed. The detectors were replaced at the beginning of each season starting from summer 2023.
• The radionuclides contents in the soil were measured in situ using the gamma-ray spectrometer Exploranium RS-230.
• The ambient gamma dose rate was measured by the radiometer RK-100
• Various soil properties including grain size, permeability, and filtration coefficient were determined.

Additionally, at each building plot, the instantaneous radon concentration and soil permeability measurements were performed using Lucas cells and RADON-JOK.

The preliminary research results indicate that in Dzierżoniów County uranium contents were in the range from 1.6 ppm to 3.3 ppm and thorium from 5.4 ppm to 8.2 ppm, whereas in Wrocław County uranium contents were in the range from 1.6 ppm to 2.5 ppm and thorium from 4.3 ppm to 7.4 ppm. The instantaneous survey of radon concentration revealed that in Dzierżoniów County soil gas radon concentration varied from 10.338 kBq m^-3 to 31,050 kBq m^-3 and soil permeability from 1*10^-12 m² to 1*10 ^-13 m², whereas in Wrocław county the soil radon concentration varied from 0.102 to 0.266 kBq m^-3 and soil permeability form very low (impossible to measure by used equipment) to 2*10^-13m².

Research project supported by program „Excellence initiative – research university” for years 2020-2026 for University of Wrocław