Preliminary results for natural groundwater colloids in sedimentary rocks of the Horonobe Underground Research Laboratory, Hokkaido, Japan

Sasamoto, Hiroshi   ; Onda, Shingo*

Colloid concentration is an important parameter in models of colloid-facilitated transport. The purpose of present study is to characterize colloid concentrations and colloid stability in natural groundwater from the Horonobe Underground Research Laboratory (URL) as for development of a procedure. The particle sizes of colloids in groundwaters from the Horonobe URL range from several nm to ca. 500 nm, with a mode particle size of ca. 120 nm. Evaluation of colloid stability by DLVO theory suggests that larger colloids (i.e., 100 nm in diameter) would be more stable than smaller colloids in some groundwaters. The estimated colloid particle concentrations ranged from 2.3310 to 1.1210 pt/mL, and mass concentrations were estimated to range from 45 to 1540 g/L for diameters greater than 100 nm. Colloids in Horonobe groundwaters appear to be less stable, with a moderate potential for transport, than colloids investigated in similar international studies. This reduced stability may be due to relatively higher ionic strengths and moderate dissolved organic concentrations in Horonobe groundwaters compared to their international counterparts.