[in Japanese]

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On the underground of the MIbi plain, the sedimentary layers exist over 1,500m thick. In the lowest part of these layers, there is the ultra underground water which temperature is about 50° C. We determined quality and Radon contents of the waters of 11 wells situated in the left bank of Kiso river. For the seasonal variation study one of these wells was continuously observed once a month during one year.
As the result, quality of this ultra underground water was higher concentration than ordinary ground water in the shallow layers, and belonged to NaC1 type or NaCI + NaHCO₃ type. According to the results of Tritium concentration in this water, the NaCl component in this water was suggested not to originate from recent sea water but from fossil water.
The amounts of Radon in the ultra underground water were excesivly higher level than those level which was calculated from radioactive equilibrium with Radium, and therefor it was suggested that Radon was supplied from the basements.
Results of the continuous observation of one well were that water quality was stable and did not change during one year and also Radon contents were unchanged. This suggested that the basements around this well were unchanged.

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Tobishima, a small island on the Sea of Japan, is situated thirty-nine kilometers northwest of Sakata. Along the eastern and the northeastern coasts, such types of ground water as seepage spring and fissure spring are distributed.
The major constituents dissolved in the ground water are the sodium and chloride ions which originate from sea-spray and airborne salt emitted from the sea surface and dispersed over the island. The primary source of the the ground water is atmospheric precipitation, the washout by which over the island ultimately determines the quality of the ground water.
Hohki area where the coast faces northeastwards and an eastwardly wind prevails is characterized by the high content of sodium and chloride ions.

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