The Rusutsu plateau covered with volcanic ash forms table-lands of 300-400m in elevation, being bounded by Mts. Yotei and Shiribetsu in directions of N. W. and S. E. In this area, no underwater and any river were found and men have never lived.
After the 2nd World War, the government researched the underground wa-ter for a purpose of reclamation. Numbers of wells were excavated to 20-40m in depth through volcanic ash stratum to comply with the result of research. But before long, the wells were dried out due to the underground water-level being lowered below the bottom of wells. The reason was that the wells had not been reached to the impermeable layer.
The writer engaged in the research works in this area since 1961 and concluded the followings.
(1) No underground water exists in volcanic ash but it flows in lava under the ash stratum.
(2) Test borings were made in 1963 after geological investigation. Next year, to follow the result, a deep well was excavated to 100m at the same site, obtaining more than the water of 400m3/day to fall down 10 cm of the waterlevel. This means that in case where the water-level falling down to 50cm, 1, 800m3/day of the water can be resulted.

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This paper is principally concerned with the geochemical problem of dissolved minerals transported by the Asahi-gawa River in Yamagata Prefecture. Survey was conducted during the period 1959 to 1960.
Regarding the quality of water, the concentration of anion is in the order: HCO₃->Cl^->SO₄^2- for several samples taken from the drainage system. In the rivers contaminated by mineral deposit in the drainage basin, the relationship: SO₄^2->HCO_3->Cl^- or HCO₃->SO₄^2->Cl^- is found to exist.
In Figs. 4-7 are presented the results of the measurement on the transportation of some ions in solution. From the statistical treatment of these data, the following equations are obtained :
Ca²⁺ : Q_d=11.6Q^0.61
Cl^-:Q_d=15.4 Q^6.62
SO₄^2-:Q_d=7.8Q_0.85
Si0₂:Q_d=9.1 Q^1.05
wher Q_d is dissolved mineral discharge in g/sec, Q flow rate in m³/sec. For COD, the equation : Q_d=aQⁿ is established by the same procedure where a is 0.21 and n 1.45. Moreover, the relation between evaporation residue and flow rate was studied. The results are expressed as follows :
Q>6m³/sec : Ré=25 Q^0.36
Q<6m³/sec : Ré=105-13.8Q
in which Ré is evaporation residue in mg/1.

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