Seasonal Variations of Quality and Radon Contents of Ultra Underground Water in the Nobi Plain

概要

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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.
JAPANESE ASSOCIATION OF GROUNDWATER HYDROLOGYの論文