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Radiogenic helium in shallow groundwater within a clay till, southwestern Ontario
Author(s) -
Sheldon Amy L.,
Solomon D. Kip,
Poreda Robert J.,
Hunt Andrew
Publication year - 2003
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/2002wr001797
Subject(s) - radiogenic nuclide , geology , groundwater , aquifer , pore water pressure , diffusion , geomorphology , hydrology (agriculture) , helium , geochemistry , soil science , mineralogy , geotechnical engineering , mantle (geology) , chemistry , thermodynamics , physics , organic chemistry
Profiles of 4 He in pore water were measured in clay aquitards in SW Ontario. The 4 He distributions are consistent with groundwater velocities that are <6 mm yr −1 , and thus diffusion is the dominant transport mechanism for 4 He. Modeling indicates that the effective diffusion coefficient for 4 He is 6.3 ± 1.6 × 10 −6 cm 2 s −1 . Furthermore, the profiles are consistent with the internal release of 4 He from aquitard sediments at a rate of 0.03–0.13 μcc(STP) kg −1 yr −1 . These rates are also consistent with laboratory release experiments and, on average, are 600 times greater than the production of 4 He from U/Th decay. Modeling and the ratio of 21 Ne to 4 He within the sediments indicate that although the aquitards were deposited about 13 kA BP, the sediments released >70% of initial 4 He for 50 to 60 kA prior to incorporation into the till.