Publication Date:
2018-04-24
Description:
A soil radon-deficit survey was carried out in a site polluted with kerosene (Rome, Italy) in winter 2016 to
assess the contamination due to the NAPL residual component in the vadose zone and to investigate the
role of the vapor plume. Radon is indeed more soluble in the residual NAPL than in air or water, but
laboratory experiments demonstrated that it is also preferentially partitioned in the NAPL vapors that
transport it and may influence soil radon distribution patterns. Specific experimental configurations
were designed and applied to a 31-station grid to test this hypothesis; two RAD7 radon monitors were
placed in-series and connected to the top of a hollow probe driven up to 80-cm depth; the first instrument was directly attached to the probe and received humid soil gas, which was counted and then
conveyed to the second monitor through a desiccant (drierite) cylinder capturing moisture and eventually the NAPL volatile component plus the radon dissolved in vapors. The values from the two instruments were cross-calibrated through specifically designed laboratory experiments and compared.
The results are in agreement within the error range, so the presence of significant NAPL vapors, eventually absorbed by drierite, was ruled out. This is in agreement with low concentrations of soil VOCs.
Accordingly, the radon-deficit is ascribed to the residual NAPL in the soil pores, as shown very well also
by the obtained maps. Preferential areas of radon-deficit were recognised, as in previous surveys. An
average estimate of 21 L (17 Kg) of residual NAPL per cubic meter of terrain is provided on the basis of
original calculations, developed from published equations. A comparison with direct determination of
total hydrocarbon concentration (23 kg per cubic meter of terrain) is provided.
Description:
Published
Description:
138-147
Description:
6A. Geochimica per l'ambiente
Description:
JCR Journal
Keywords:
Soil radon
;
NAPL contamination
;
Radon de fi cit
;
04.04. Geology
;
05.04. Instrumentation and techniques of general interest
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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