Geothermics (x97o) - SPECIAL ISSUE 2

U. N. Symposium on the Development and Utilization of Geothermal Resources, Pisa ic~7o. Vol. 2, Part x

A Geochemical Investigation of the Strong Acid Water from the Bored Wells in Hakone, Japan K. NOGUCHI *, T. GOTO *, S. UENO * AND M. IMAHASHI *

ABSTRACT

In the Owakidani valley, located on the north slope of Kamiyama cone, 80 km SW of Tokyo, there are many fumaroles emitting a large amount of steam, carbon dioxide, hyarogen sulfide, sulfur dioxide etc.

In april 1960. a strong acid water with steam (H + 1.4 g/l) was emitted from the Senkyoro well No. 6. In autumn 1968, four shallow wells were made at Owakidani by the Pre- fectural Government of KanagaWa to prevent a landslide. From those wells also strong acid water was emitted accompanied by a large amount of steam, hydrogen sulfide and carbon dioxide. The condensate from gaseous matters emitted from well No. 2 showed 1.4 pH and contained 1.96 g/1 C1-- and 1.6 mg/l F - ; the condensate from well No. 4 showed 1.4 in pH, 1.62 g/l C1-- and 3.8 mg/l F--.

This note explains the possible origin of the strong acid- ic waters.

About 80 km southwest of Tokyo, the central cone Kamiyama of the old volcano Hakone rises as high as 1439 m above sea level, as shown in Figure 1. Yumoto, Tonosawa, Miyanoshita and Sokokura are well known as alkaline hot springs, Yunohanazawa as acid hot springs, and Owakidani , Ioyama and Sotmjigoku as a fumarolic area in Hakone. In the valley Owakidani , which is located on the north slope of Kamiyama, there are many fumaroles emitting a large amount of steam, carbon dioxide, hydrogen sulphide and sulphur dioxide etc., as shown in Figure 2. In April, 1960, strong acid water was emitted from the Senkyoro No. 6 well with steam, when boring depth reached 33.4 m. The chem- ical composition of the water was reported by K. WArAr~uI<I in ]ournal o/ the BaIneological Society o/ Japan in 1966.

After that, the authors received a sample of the same strong acid water f rom Mr SUZUKI, manager of Hakone Thermal Water Supplying Company and car- ded out an analysis of it. The chemical composition of the water was as shown in Table 1. In autumn, 1968, four wells were bored at Owakidani by the Prefectur- al Government of Kanagawa to prevent a land slide as shown in Figure 2. The depth of those wells were 65, 68, 68 and 75 m. From those wells, strong acid water again flowed out accompanied with steam, hydro- gen sulphide and carbon dioxide. From gaseous mat-

* Department of Chemistry, Tokyo Metropolitan Univer- sity, Department of Education, lwate University, Japan.

TABLE 1. D Chemical composition (rag~l) o/ the strong acid water from two Senkyoro wells.

Senkyoro's well Senkyoro (well number is N O 6 well unknown)

H + 1,400 pH 1.2 Cl-" 68,800 1,180 SO4--2 84,000 353 N a + 5,000 Ca + 2 400 25.3

Mg÷2 4,000 9.0 Fe + 2 3,770 88

AI + a 7,140 18

Mn+2 1,340 0.I

HBO2 470

Br- 13.5 0.03

I-- O.4

As 6.4 0.75

U 0.038 < 0.0001

Th 0.029 not detected

/

, w ~ A

4 4 ~ -- --

i\\ ---~ / , -" I t, ,-? ,,,,/_,, / /

FIG. I ~ Map o/ old volcano Hakone.

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TAaLE 2. - - Chemical composition o~ strong acid waters and condensed waters obtained /rom the bored wells at Owakidani. Hakone.

Depth Orifice No. of bored of CI- Acidity C1-- F-- F/C1 temp. pH well Sample Date well o C g/1 (N) (N) g/1 × 103

m

Strong acid 1 water November 29, 1968 65 98 < 1.0 13.15 0.362 0.371 0.0042 0.32 2 , December 16, 1968 68 99 < 1.0 66.7 1.825 1.88 0.011 0.16 2 ) November 29, 1968 68 100 < 1.0 49.75 1.358 1.40 0.017 0.34 3 , November 2, 1968 68 98 < 1.0 30.75 0.842 0.886 0.016 0.52 4 J November 22, 1968 75 99 < 1.0 67.25 1.336 1.896 0.097 1.4

Condensed 2 water November 2, 1968 68 100 1.4 1.96 0.059 0.055 0.0016 0.82 4 , November 29, 1968 75 121 1.4 1.62 0.052 0.045 0.0038 2.3 4 , December 25, 1968 75 131 - - 1.56 - - - - 0.0040 2.6

Well on the opposite side of the valley • November I, 1968 150 2.1 0280 0 . 0 0 7 7 0.0079 0.00061 2.2

Boilin8 Spring November 29, 1968 98 2.0 0.021 0.012 - - 0.00040 19

ters emit ted from the same well , a condensate was ob- t amed by cooling wi th cold running water . The chem- ical composi t ion of the condensates are shown in Ta- ble 2. The eondensates were r emarkab ly lower in acidi- ty, chlor ide and f luor ide content than the above mention-

~,-25 >" -- e'. --._

? g ~ l l l ~ ¢ , ,

I ~ . u , D . . , L~ . ::=.--:~-=.=o iltt,¢ i * ¢ 1 'a~t~'41

FIG. 2 - - A sketch map o/ Owakidani in Hakone.

ed strong acid waters . Between chlor ide and f luoride content in condensed water and wate r emit ted with steam, there exists a l inear re la t ionship as shown in Figure 3. F luor ide content increases wi th increasing chlor ide content . A var ia t ion of orifice temperature , acid- ity and chlor ide content in the s trong acid wate r emit- ted from the wells are shown in Figure 4 and Figure 5

As for the well No. 1, the wa te r which f lowed out first Oc tober 12, 1968, was very rich in chlor ide con- tent and acidi ty, but decreased before Oc tober 15, and then, chlor ide content and acidi ty were almost constant . Moreover , normal i ty of chlor ide in the wate r was al- most equal to the acidity.

In the case of well No. 2, chlor ide content and

acidi ty decreased gradual ly wi th time and the normal i ty

of chlor ide in the wa te r was almost equal to the acid- ity, and s imilar to that of wel l No. 1. In the both wells, it must be not iced that the amount of water grad- ual ly decreased, but the orifice tempera ture rose grad-

ually wi th time.

As for the well No. 4, acid wate r began to f low out f rom the wel l on November 22, but in a short ti-

me, the amount of wate r decreased quickly and only

volcanic gases were emit ted from the well . At the same time, orif ice tempera ture rose dist inct ly. W h e n we col lected a condensate from the well No. 4 on Novem- ber 29, and on December 25, 1968, orifice tempera- tures were found to be 121 °C and 131 °C respectively.

I A c ~ . * s o W*T I ' I o s , . ~Jm I~ ~Tmt ¢

I

el"

FIG. 3 - - Relationship between chloride and [luoride content in condensed water and water emitted with steam.

562

400 t T I ~ t U R I eC 9 8

9 ~

4o I \ C~" 20 - .

"1~. 4g 22 27 ~,t =3 40 4=3 ~-1 2 9

FIG. 4 - - Variation o/ chloride content and acidity o~ water emitted /rom the bored well No. 1.

The content of chloride and fluoride in the conden- sates was remarkably lower than that in the acid wat- ers, and the pH-values of the former were larger than those of the latter.

As for the genesis of such a strong acid water, the following explanation may be possible.

At 65-75 m in depth, if a small amount of ground water mixes with a large amount of volcanic gases ri- sing from deep places, an equilibrium will be establish- ed between volcanic gases and ground water without any distinct change in a composition of volcanic gases. In such eases, a liquid with is remarkably rich in by-

t olmm41 T I I m , m m l ~ 4oo • 0 "C 98

,ao

14 I~ 22 17 ~ 40 20 29 cw.. . ,ou,~ (4,~,8) , , ~ , n w . , o ~

Fro. 5 ~ Variation o/ chloride content and acidity o] water emitted ]rom the bored well No. 2.

drochloric acid will be formed under the ground, prob- ably 65-75 m in depth. It seems that the fact that normality of chloride in the water is almost equal to the acidity, supports such an explanation. Sulphuric acid sometimes contained in a large amount in the wat- er was probably formed from sulphur compound in volcanic gases by the oxidation with air. Moreover, the most part of it was neutralized with the surrounding rocks. Almost all metals such as iron, aluminium, cal- cium, magnesium, sodium, manganese, uranium and thorium in the water may be derived from the surroun- ding rocks by the corrosive action of sulphuric acid.

563