US EPA

1437935 

Journal Article 

Processes of radionuclide enrichment in sediments and ground waters of Mont Vully (Canton Fribourg, Switzerland) 

Schott, B; Wiegand, J 

2003 

Yes 

Eclogae Geologicae Helvetiae
ISSN: 0012-9402
EISSN: 1420-9128 

96 

1 

99-107 

10.1007/s00015-003-1079-0 

WOS:000183530400008 

During a survey of radon concentrations (Rn-222) in ground
waters of the Swiss molasse basin carried out by the Swiss Public Health Office, high
concentrations were observed at Mt Vully, which is a small hill. The present study was conducted
to elucidate the processes leading to Rn-222 concentrations, which were several times higher than
those of neighbouring aquifers. Ground waters from 25 water catchments and sediments of the
outcropping Upper Marine Molasse were sampled. These are characterised by radioactive
disequilibria within the U-238 decay series, most pronounced in the sediments. which reveal a
complex history of radionuclide mobility and displacement: A first enrichment in radionuclides
occurred in early diagenetic times. when uranium precipitated on organic materials (bones)
producing a reducing halo during degradation. Since this time, Fe, Mn and Ra-226 have been
mobilised under local reducing conditions and transported with the ground water stream.
Especially along permeable zones like faults and joints, Fe and Mn hydroxides are precipitated
under oxidising conditions, and Ra-226 is adsorbed on the hydroxides. The high Rn-222
concentrations in the ground waters are due to the high Rn-222 emanation coefficients of faults
and joints mineralised with Fe and Mn hydroxides. which act as preferential ground water
pathways. 

radon; radium; uranium; radioactive disequilibrium; radionuclide mobility; molasse sediments; ground water