Abstract
The tritium concentration of initial groundwater is necessary for groundwater dating. We proposed the equation to estimate tritium concentration of initial groundwater T=R max+(1−R)min, where max is the annual maximum concentration and min is the annual minimum concentration by monthly precipitation sampling, and R is a regional constant. Tritium in precipitation was observed for three years at four sampling sites widely dispersed across Japan. The constant R for each site was calculated to be as follows:0.43 ± 0.18 for Sapporo, 0.45 ± 0.08 for Niigata, 0.23 ± 0.08 for Tokyo and 0.18 ± 0.07 for Matsuyama. The constant R did not depend on the sampling year and the tritium concentration. Utilizing observation data already published, the constant R for these sites can be used to estimate the initial groundwater tritium concentration in the past.
