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Regional Distribution and Geochemical Characteristics
of Hot Springs Detecting Methane Based on“the Revised Hot Spring Law” in Hokkaido
Eiji UCHINO+, Naoki AOYANAGI+ and Kenji NAKAYAMA+

Abstract
In June ,**1, a tragic gas explosion which took - lives, occurred by methane released
from hot spring water in a spa facility, Shibuya-ku, Tokyo. Therefore, the Ministry of theEnvironment revised, the laws regulating hot springs to prevent further accidents like
this, issued in November ,**1, and coming into force in October ,**2. Immediately, determinations of methane in the ﬁeld with portable gas detectors were started, based on
o$cial manuals. This study reports the detection rate, regional distribution, geochemical
characteristic, and stratums of gas reservoirs etc. of hot spring released methane measured in 02/ samples from all parts of the Hokkaido area. The results can be summarized
as follows ;+) There were 23 samples that exceeded the A test for methane detection and where
it was needed to take measures to protect against disasters from methane. ,) There were,* samples where the B test for methane detection showed it to be necessary to provide
facilities to separate methane from the hot spring water. -) Communities where at least
one sample was detected, distributed widely across Hokkaido. .) The hot spring watertypes were 0-ῌ of Na-Cl and +3ῌ of simple spring waters. These two accounted for morethan 2*ῌ of all hot springs where methane was detected in Hokkaido. /) There were --ῌ
of moor type hot spring water containing humic substances. 0) Among the main anions
in hot springs where methane was detected, the composition and concentration of SO.,
was very low. 1) Most Na/Cl concentration ratios in hot spring waters where methane
was detected were similar to that of sea water. 2) Many B/Cl mol ratios in hot springwaters where methane was detected showed a strong contribution of sea water. 3) The
main reservoirs of hot spring water were : 2*ῌ from sedimentary rocks, and +/ῌ fromvolcanic or igneous rocks. +*) Although the origins of the methane in the hot spring+282  *0* ῌ *2+3  +3  +,   + Hokkaido Institute of Public
Health, North +3, West +,, Kita-Ku, Sapporo, Hokkaido *0*ῌ*2+3, Japan.

/3  ,*+*

  

waters were uncertain, it may be assumed to originate in decomposition by bacteria oforganic matter accumulated on the bottom of the sea or in wetlands in the ancient period
from the main stratums where the hot spring water is pumped up, or from the chemical
characteristics such as pH, temperature, SO., concentration, Na/Cl ratio, B/Cl ratio, etc.
Key words : Revision of hot spring law, methane, ﬂammable natural gas, hot spring water,
portable gas detector, hot springs in the Hokkaido Area

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Detection rates of methane gas from hot spring waters in Hokkaido
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.3.2)0..-* /Z' 5·}-!ºq»7/,¼OE½B8!9Fig. 0 The proportion (meq., ῌ) of main anion CI, SO.,, and HCO- of hot spring waters
where methane was detected in Hokkaido
 : concentration data for sea water are quoted from Nishimura (+32-).
 0 
 CI  SO., HCO-  m   ῌ!
 : 
+32- 289

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Fig. 1 Relationship between SO., and Cl concentrations of hot spring waters with
detected methane in Hokkaido 1 
 SO.,  Cl 

Fig. 2 Relationship between Na and CI concentrations of Hot Springs where methane
was detected in Hokkaido
 : concentration data for sea water are quoted from Nishimura (+32-).
 2 
 Na  Cl 
 : 
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