Profiles of 4He in pore water were measured in clay aquitards in SW Ontario. The 4He distributions are consistent with groundwater velocities that are <6 mm yr-1, and thus diffusion is the dominant transport mechanism for 4He. Modeling indicates that the effective diffusion coefficient for 4He is 6.3 ± 1.6 x 10 -6 cm2 s-1. Furthermore, the profiles are consistent with the internal release of 4He 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 4He from U/Th decay. Modeling and the ratio of 21Ne to 4He within the sediments indicate that although the aquitards were deposited about 13 kA BP, the sediments released >70% of initial 4He for 50 to 60 kA prior to incorporation into the till.
CITATION STYLE
Sheldon, A. L., Solomon, D. K., Poreda, R. J., & Hunt, A. (2003). Radiogenic helium in shallow groundwater within a clay till, southwestern Ontario. Water Resources Research, 39(12). https://doi.org/10.1029/2002WR001797
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