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Hydrogeochemical Investigation of Groundwater in the Tono Area, Japan

Published online by Cambridge University Press:  15 February 2011

T. Iwatsuki ,
K. Sato ,
T. Seo  and
K. Hama
T. Iwatsuki
Affiliation:
Power Reactor and Nuclear Fuel Development Corporation (PNC), Tono Geoscience Center, 959-31, Jorinji, Toki, Gifu, 509-51, Japan.
K. Sato
Affiliation:
Power Reactor and Nuclear Fuel Development Corporation (PNC), Tono Geoscience Center, 959-31, Jorinji, Toki, Gifu, 509-51, Japan.
T. Seo
Affiliation:
Power Reactor and Nuclear Fuel Development Corporation (PNC), Tono Geoscience Center, 959-31, Jorinji, Toki, Gifu, 509-51, Japan.
K. Hama
Affiliation:
Power Reactor and Nuclear Fuel Development Corporation (PNC), Tono Geoscience Center, 959-31, Jorinji, Toki, Gifu, 509-51, Japan.
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Abstract

Measurements of chemical compositions of groundwaters, carbon isotope analysis of dissolved inorganic carbon and batch experiments on water-rock interaction have been carried out in order to evaluate the chemical evolution of groundwater in the sedimentary rocks of the Tono area, Japan. The activities of Na and Ca ions in the groundwater plotted along the boundary between Na- and Ca-montmorillonite stability fields on a diagram of 2pH+log[Ca2+] vs. pH+log[Na+], which indicates that the two mineral phases are in equilibrium. Groundwater samples, rich in Ca ions (14.8 ppm Ca ions and 16.3 ppm Na ions), were collected from the shallow zone of the Tono area, and were reacted with the sedimentary rocks in the batch experiments. The experiments have revealed that ion exchange occurs between Na ions in the rock samples and Ca ions in the groundwater samples, and the final solutions became rich in Na ions (1.2 ppm Ca ions and 35.2 ppm Na ions). The results of the batch experiments are in agreement with the variation of Na and Ca concentrations in the groundwater in the sedimentary rocks. The carbon isotope data showed that the fraction of HCO3 derived from the dissolution of calcite increases from 25% to 75% of the total HCO3 content with increasing depth. The molality of Na ions in the groundwater was measured to be twice that of HCO3 ions derived from calcite, which supports the Na and Ca ion exchange in the groundwater. The results suggest that the chemical evolution of the groundwater is characterized by the variation in Na, Ca and HCO3 concentrations, and that ion exchange and dissolution of calcite are dominant reactions in the evolution of groundwater in the Tono area.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 353: Symposium – Scientific Basis for Nuclear Waste Management XVIII , 1994 , 1251
Copyright
Copyright © Materials Research Society 1995

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