High‐level dike‐confined groundwaters and high‐level perched groundwaters on Oahu, Hawaii, were analyzed for tritium, radiocarbon, carbon 13, and several chemical constituents. Discharges from several tunnels that tap dike compartments contain postbomb tritium, indicating the presence of modern (since 1954) recharge. The amount of postbomb tritium in samples taken inside one of the tunnels is a function of the distance between sampling point and overlying surface. Chemical and carbon isotopic compositions of dike waters, established in the soil zone of the overlying ground surface, remain unchanged while the water is passing through the basaltic carbonate‐free compartments. Dike water carbon isotope data are sufficiently consistent to serve as initial values for the dating of water in the Honolulu basal aquifers. The radiocarbon and carbon 13 data for perched waters are similar to those for the dike waters, in spite of the much larger bicarbonate concentrations in the former.
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Hufen et al. (1974) studied this question.
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