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Geostatistical techniques application to dissolved radon hazard mapping: an example from the western sector of the Sabatini Volcanic District and the Tolfa Mountains (central Italy)
Author(s)
Language
English
Obiettivo Specifico
5A. Energia e georisorse
Status
Published
JCR Journal
JCR Journal
Peer review journal
Yes
Title of the book
Issue/vol(year)
/35 (2013)
ISSN
0883-2927
Electronic ISSN
1872-9134
Publisher
Elsevier Science Limited
Pages (printed)
312-324
Issued date
2013
Keywords
Abstract
Dissolved Rn was determined in 192 samples collected from cold shallow volcanic and sedimentary aquifers,
deep thermal aquifers and from waters associated with bubbling gases in the western sector of the
Sabatini Volcanic District and the Tolfa Mountains (central Italy). Shallow aquifers hosted in the Quaternary
volcanic complexes show values ranging from 1.0 to 352 Bq/L (median value 55 and inter-quartile
distance 62 Bq/L), while waters circulating within the permeable horizons of the sandy-to-clayey sediments
of the Tolfa flysch have values from 1.0 to 44 Bq/L (median value 6.9 and inter-quartile distance
8.1 Bq/L). Thermal waters are hosted in the Mesozoic carbonate formations and move towards the surface
along faults. Here, dissolved Rn values range from 0 to 37 Bq/L (median value 3.0 and inter-quartile distance
9.5 Bq/L). Waters associated with bubbling gases show dissolved Rn contents ranging from 2.0 to
48 Bq/L (median value 6.2 and inter-quartile distance 23 Bq/L). Those results suggest that lithology is
the main factor affecting the Rn contents in shallow aquifers, due to the high levels of Rn progenitors
U and Ra in the volcanic rocks relative to sedimentary units. The influence of other factors such as the
presence of a fracture network, seasonal flow variations, type of discharge (from well or spring) was also
investigated. Radon contents of thermal waters result from mixing with shallow waters (from both volcanic
and sedimentary rock aquifers) and decrease of Rn solubility with temperature, while for bubbling
pools the effects of strong degassing were also considered.
In terms of health hazard from direct ingestion of Rn-rich waters, 20.8% of those circulating within the
volcanic aquifer show values higher than the recommended value of 100 Bq/L, while none of those circulating
within the sedimentary aquifers exceed the threshold value. Geostatistical techniques were used
for the elaboration of contour maps by using variogram models and kriging estimation aimed at defining
the areas where a potential health hazard due to the direct ingestion of Rn-rich waters and to inhalation
of air following degassing of Rn from waters may be expected.
deep thermal aquifers and from waters associated with bubbling gases in the western sector of the
Sabatini Volcanic District and the Tolfa Mountains (central Italy). Shallow aquifers hosted in the Quaternary
volcanic complexes show values ranging from 1.0 to 352 Bq/L (median value 55 and inter-quartile
distance 62 Bq/L), while waters circulating within the permeable horizons of the sandy-to-clayey sediments
of the Tolfa flysch have values from 1.0 to 44 Bq/L (median value 6.9 and inter-quartile distance
8.1 Bq/L). Thermal waters are hosted in the Mesozoic carbonate formations and move towards the surface
along faults. Here, dissolved Rn values range from 0 to 37 Bq/L (median value 3.0 and inter-quartile distance
9.5 Bq/L). Waters associated with bubbling gases show dissolved Rn contents ranging from 2.0 to
48 Bq/L (median value 6.2 and inter-quartile distance 23 Bq/L). Those results suggest that lithology is
the main factor affecting the Rn contents in shallow aquifers, due to the high levels of Rn progenitors
U and Ra in the volcanic rocks relative to sedimentary units. The influence of other factors such as the
presence of a fracture network, seasonal flow variations, type of discharge (from well or spring) was also
investigated. Radon contents of thermal waters result from mixing with shallow waters (from both volcanic
and sedimentary rock aquifers) and decrease of Rn solubility with temperature, while for bubbling
pools the effects of strong degassing were also considered.
In terms of health hazard from direct ingestion of Rn-rich waters, 20.8% of those circulating within the
volcanic aquifer show values higher than the recommended value of 100 Bq/L, while none of those circulating
within the sedimentary aquifers exceed the threshold value. Geostatistical techniques were used
for the elaboration of contour maps by using variogram models and kriging estimation aimed at defining
the areas where a potential health hazard due to the direct ingestion of Rn-rich waters and to inhalation
of air following degassing of Rn from waters may be expected.
Type
article
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