BEHAVIOR OF URANIUM BEARING GROUNDWATER IN NEOGENE SEDIMENTARY ROCKS; OBSERVATION AT THE KANAMARU DISTRICT, YAMAGATA, JAPAN

To study the groundwater flow system bearing uranium, quasi-monthly water quality measurements for traditional-type observation wells and seasonal water quality and pore-pressure measurements using multi-packer system were done in the Kanamaru district, northeastern Japan, where uranium anomaly in Neogene sedimentary rocks was known. Profiles of chemical parameters for water column of observatin wells show clear stratification especially in dry season, that is, stepwise change of lower pH and EC and higher DO and Eh in shallower part, and higher pH and EC and lower DO and Eh in deeper part. This stratification is confirmed much clearly by multi-packer system installed in a reference well. Higher uranium concentrations of around 2 ppb in groundwater are detected in well-waters sampled from the horizon of rock uranium anomaly, which reachs up to 100 ppm. Relatively lower uranium concentrations of around 0.1 ppb in well-waters are observed in deeper horizons in basement pre-Tertiary granitic rocks