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Estimation of Groundwater Residence Time Using the 36 Cl Bomb Pulse
Author(s) -
Tosaki Yuki,
Tase Norio,
Sasa Kimikazu,
Takahashi Tsutomu,
Nagashima Yasuo
Publication year - 2011
Publication title -
groundwater
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.84
H-Index - 94
eISSN - 1745-6584
pISSN - 0017-467X
DOI - 10.1111/j.1745-6584.2010.00795.x
Subject(s) - groundwater , residence time (fluid dynamics) , environmental science , hydrology (agriculture) , groundwater recharge , geology , aquifer , geotechnical engineering
We propose a methodology for estimating the residence time of groundwater based on bomb‐produced 36 Cl. Water samples were collected from 28 springs and 2 flowing wells located around Mt. Fuji, Central Japan. 36 Cl/Cl ratios in the water samples, determined by accelerator mass spectrometry (AMS), were between 43 × 10 −15 and 412 × 10 −15 . A reference time series of the above‐background (i.e., bomb‐derived) 36 Cl concentration was constructed by linearly scaling the background‐corrected Dye‐3 data according to the estimated total bomb‐produced 36 Cl fallout in the Mt. Fuji area. Assuming piston flow transport, estimates of residence time were obtained by comparing the measured bomb‐derived 36 Cl concentrations in spring water with the reference curve. The distribution of 36 Cl‐based residence times is basically consistent with that of tritium‐based estimates calculated from data presented in previous studies, although the estimated residence times differ between the two tracers. This discrepancy may reflect chlorine recycling via vegetation or the relatively small change in fallout rate, approximately since 1975, which would give rise to large uncertainties in 36 Cl‐based estimates of recharge for the period, approximately since 1975. Given the estimated ages for groundwater from flowing wells, dating based on a 36 Cl bomb pulse may be more reliable and sensitive for groundwater recharged before 1975, back as far as the mid‐1950s.