LAUSR

We developed a simple 35S separation method that requires relatively small sample volume (about 5 L) and an analysis method that uses a large sample volume counting vial (145 mL) to reduce the sample volume and simplify pretreatment procedures. Laboratory experiments showed that sulfate concentration had no significant effect on 35S measurement. The recovery was 93.0 ± 0.1% and the minimum detectable activity was determined to be 1.0 mBq L−1. Using our method, the measured 35S activities in the spring and rain waters ranged from 19.2 ± 0.6 to 69.5 ± 3.7 mBq L−1 and from 9.9 ± 0.2 to 54.4 ± 1.8 mBq L−1, respectively. Our results suggest that the long-term monitoring data of 35S in rain water and groundwater are needed for the quantitative and accurate estimation of groundwater residence time.