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| Titel |
Dynamics of soil gas radon concentration in a high permeable soil based on a long-term high-resolution measurement series |
| VerfasserIn |
K. Z. Szabó, Á. Horváth, Gy. Jordán, Cs. Szabo |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250062742
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| Zusammenfassung |
| One method of calculating Geogenic Radon Potential (GRP) is to estimate a continuous
variable from the equilibrium concentration of 222Rn in soil gas, in kBq/m3 (C-) and the
effective permeability of soil, in m2 (k). These parameters can be determined during field
work or can be estimated from other available parameters, such as 226Ra concentration in dry
soil (Bq/kg) or porosity, using transfer functions. Assuming short field measurement,
temporal variation of soil gas 222Rn concentration (csoilRn) can cause difference of the
measured value from C- which should be considered during the evaluation. A long-term
high-resolution observation can reveal various temporal features such as seasonality in
csoilRn. The main aim of this study was to determine the dynamics of csoilRn in terms of
trend, periodicity and transient event in a high permeable soil (1.5E-11 m2) during a one year
period.
We measured the csoilRn in 15 minutes periods for one week in every month using RAD7
radon monitor coupled with soil probe (Durridge Company Inc.). The sampling depth was 80
cm. The measurement site was located in a Budapest urban area, Hungary. The underlying
geological formation at the measurement site is Quaternary (upper Pleistocene) fluvial
sediment, a Pleistocene diamicton (fluvial sand, gravel, clay). Robust statistical analysis and
time series analysis were used for the characterization of radon dynamics in the studied high
permeable soil.
Our results of statistical analyses showed seasonality in csoilRn. We have observed
statistically significant differences of csoilRn between winter (from October to March) and
summer measurements (from May to September). Medians of the csoilRn data of summer
weeks are lower than those of in winter. According to the Mann-Whitney (Wilcoxon) Test the
medians of these two groups are significantly different at the 95% confidence level. The
average of the median values for the winter season was 2.5 times higher (7.0 kBq m-3)
than for the summer season (2.8 kBq m-3). The minimum and maximum values
change together with the average value for each week as confirmed by correlation
analysis. The calculated overall relative variability (MAD/median) was lower in the
winter period (0.08) and almost two times higher in the summer period (0.16).
Variability of csoilRn, including the extreme values, also changes consistently with
seasons between well-defined threshold values. Thus, the csoilRn is predictable
quite well from the observed data series. According to the natural breaks in the
csoilRn distributions of the measured periods, homogeneous groups were identified
and their medians were compared using the resistant Mann-Whitney Test. Results
showed that there is no a statistically significant difference between the medians
of csoilRn in May and August, May and June, October and January at the 95%
confidence level, which clearly confirms the differences between the winter and summer
periods.
These results show that in case of a GRP estimate from a single measurement on a high
permeable soil the measured csoilRn value has to be corrected to get the C-. The correction
should be done according to the season considered. |
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