2010 Volume 61 Issue 7-8 Pages 271-287
Uranium series nuclides and their colloidal behavior in groundwater and surface water in Kanamaru area, Niigata and Yamagata Prefectures were studied to elucidate and characterize their behavior in groundwater. Dissolved uranium concentration in granitic basement layer was higher than that in concentrated sedimentary layer although the U content in the latter layer was one order higher than that in the former layer. This may suggest that the U concentrated sedimentary layer adsorbs U rather than dissolves U, and the granitic basement layer dissolves U under dissolving environment. Most of water samples showed U-234/U-238 activity ratios >1, which means that U was dissolved into the groundwater. Several samples taken from subsurface in early stage after boring showed Th-230/U-234 activity ratios >1. As Th-230/U-234 activity ratios over 1 in solution are difficult to be achieved, these high activity ratios may be due to the presence of solid materials such as suspended and colloidal materials. Inclusion of mud and debris by boring, transportation and the colloid formation by the change of pH and Eh are also expected.
