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    HIG 79 9

    CHLORIDE MAGNESIUM

    RATIO

    OF SHALLOW GROUNDWATERS

    AS A

    REGIONAL GEOTHERMAL INDICATOR

    IN HAWAII

    MALCOLM E COX

    nd

    DONALD

    M.

    THOMAS

    Assessment

    of Geothermal

    Resources

    in Hawaii:

    Number 3

    1

    f

    NOVEMBER 1979

    Prepared for

    WESTERN

    STATES

    COOPERATIVE

    DIRECT

    HEAT

    RESOURCES ASSESSMENT

    under rant no

    DO

    E I 1 713 4

    H W II

    INSTITUTE

    OF

    GEOPHYSICS

    UNIVERSITY OF HAWAII

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    HIG 79 9

    CHLORIDE MAGNESIUM RATIO

    OF SH LLOW

    GROUNDW TERS

    S A REGIONAL GEOTHERM L INDICATOR

    IN

    HAWAII

    Malcolm

    E Cox

    and

    Donald M

    Thomas

    Assessment

    o f

    Geot he rma l Re sou rc es

    in

    Hawai i :

    Number

    November

    1979

    Prepared fo r

    Western

    S ta t e s

    ooperat ive

    Direc t

    Heat Resou rc e A ss es smen t

    under

    gran t

    no

    DOE/ID/017l3 4

    har les

    E Hels ley

    Di rec to r

    Hawaii I n s t i t u t e of

    Geophysics

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    STR CT

    Because of

    th e

    complex

    geo log i c a l and hyd ro log i c a l

    cond i t ions

    and

    th e

    v i r t u a l

    l ack

    of

    t h e rma l

    s p r i ng s r e g i on a l

    geothe rmal

    i nve s t i g a t i on s in Hawai i r equ i r e th e

    use

    o f

    t echn iques

    s u b s t an t ia l l y d i ff er en t from

    those conven t iona l ly

    app l i ed in

    o the r

    g eo th e rma l e n vi ro nment s. The l a r ge number

    of

    h y dr ol og ic al w e lls

    in th e

    s t a t e prov ides an app re c i ab l e

    sou rce of gro undw ater ch em ica l da t a .

    However

    l a rge ly

    because

    of

    th e i s l and

    env i ronment i n t e r p r e t a t i o n

    of

    much of

    th e se d a ta

    as

    geo thermal i nd i ca t o r s becomes ambiguous .

    I n i t i a l l y Si02 and

    t empera tu re

    o f g ro un dw ate rs were used

    to i d en t i fy

    t h e rma l l y

    anomalous zones bu t on

    a

    r eg iona l

    ba s i s

    has been found

    t h a t t h e se

    c r i t e r i a

    a re

    no t a lways

    s u c c e s s f u l .

    s a f u r t h e r c r i t e r i o n fo r as ses smen t th e Cl/Mg

    r a t i o

    of

    th e

    groundwate r

    has been

    used .

    On a

    s t a t e -w ide

    ba s i s t h i s

    r a t i o

    has been succes s fu l

    in

    f u r t h e r

    s c reen ing

    th e

    Si02 - t empera tu re

    s e l ec t ed

    s i t e s and

    in

    de f i n i ng more

    s pe c i f i c a rea s

    which

    war ran t fu r t he r

    i n v e s t i g a t i o n .

    Tempera tu re

    Si02

    and Cl/Mg va lues

    fo r

    nea r ly 400 groundwate r

    samples a re

    i nc luded .

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    TABLE OF CONTENTS

    ABSTRACT

    LIST OF TABLES

    LIST OF FIGURES

    INTRODUCTION

    OCCURRENCE

    OF

    GROUNDW TER

    IN

    HAWAII

    Dike impounded

    Sedimenta ry and a l l u v i a l

    asa l

    SILICA TEMPERATURE CRITERIA

    S i l i c a

    Tempera ture

    CHLORIDE/MAGNESIUM RATIOS

    Genera l

    Theory

    hlor ide

    Magnesium

    COMPARISONS

    OF

    Cl Mg

    RATIOS

    IN

    OTHER

    THERM L W TERS

    APPLICATION OF

    Cl Mg IN

    HAWAII

    Kauai

    Molokai

    Oahu

    Maui

    Hawai i

    CONCLUSIONS

    KNOWLEDGMENTS

    REFERENCES

    APPENDIX

    v i i

    ix

    1

    2

    2

    2

    3

    5

    8

    8

    9

    9

    11

    12

    16

    18

    18

    23

    23

    23

    30

    30

    31

    35

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    LIST TABLES

    Table

    Comparison of d i f f e r e n t

    a n a l y s e s

    2 Averaged va lues of

    known

    thermal

    and o the r

    waters

    6

    1

    3

    Chemical da ta of va r ious geo thermal waters 13

    Appendix

    Table

    Kauai

    37

    Mo1okai

    39

    Oahu 4

    Maui

    44

    Hawaii

    48

    v i i

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    LIST O

    FIGUR S

    Figure

    1

    Log log p lo t of

    Cl versus g fo r

    a va r i e t y

    of

    geothe rmal

    wate r s from d i f f e r e n t

    envi ronments

    15

    2 Charac t e r i s t i c s

    of

    I Mg

    r a t i o s

    fo r d i f f e r e n t

    wa

    t

    e r types in Hawai i

    17

    3

    Tr i ang l e diagram

    of

    Cl

    and g

    concen t r a tons

    from Kauai 19

    4 Locat ion

    of

    groundwater wel l s on Kauai 20

    5

    Tr i ang l e

    diagram

    of

    Cl

    and

    g

    concen t r a t i on s

    from

    Molokai 21

    6 Locat ion o f gro und water wel l s on

    Molokai 22

    7 Tr i ang l e diagram

    of

    Cl

    and

    g concen t r a t i on s

    from

    Oahu

    24

    8 Locat ion of g ro und water wel l s on Oahu 25

    9 Tr i ang l e

    diagram of

    Cl

    and g concen t r a t i on s

    from

    Maui

    26

    1 Locat ion of

    groundwate r

    wel l s on Maui

    27

    11 Tr i ang l e

    diagram

    of Cl

    and

    g concen t ra t ions

    from Hawai i 28

    12 Locat ion of groundwater wel l s

    on Hawai i 29

    ix

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    INTRODU TION

    Geothermal i nve s t i g a t i on s conducted dur ing

    th e 1973-

    1977

    Hawai i

    Geothermal Pro j e c t ,

    which

    led

    to the

    succes s fu l

    d r i l l i ng

    s i t e

    of geo therm al

    wel l

    HGP-A,

    were

    l a rge ly

    r e s t r i c t ed to

    s eve r a l

    spec i f i c

    a r ea s .

    To gain a more comple te

    unders tand ing

    of

    th e

    geo thermal po t en t i a l

    in

    Hawai i ,

    the

    cu r r en t

    geo thermal

    i nve s t i g a t i on Hawaii Geo th erma l Resource

    Assessment Program

    i s

    conduct ing

    a sys t ema t i c s tudy

    of th e

    Hawaiian I s l ands on a s t a t e -w ide ba s i s .

    The i n i t i a l phase of the r eg iona l

    survey

    has been th e

    compi la t ion and assessment of a l l ava i l ab le groundwater

    chemis t ry

    wi th in th e

    s t a t e .

    T his app ro ach to

    geo thermal

    exp lo ra t ion in Haw aii has

    l a rgeLy

    been o f nece s s i t y . Thermal

    sp r ings

    occur only in

    a

    sma l l

    number

    o f

    c oa sta l lo ca tio ns

    because

    of

    th e b a sa lt ic t e rr a in and the

    complex

    hyd ro log i c a l

    cond i t ions

    in t h i s i s l and env i ronment . Consequent ly many of

    th e r ec on na is sa nc e

    i nve s t i g a t i on

    t echn iques

    employed

    in

    con t i nen t a l , or o lde r env i ronments ,

    a re

    u nsu ita ble in Hawai i .

    The use

    o f ex i s t i ng

    groundwater chemis t ry da ta has

    prov ided

    an

    exce l l en t

    f i r s t s t age reconnai s sance too l

    because

    o f th e

    l a rge

    number

    of groundwater wel l s

    d r i l l ed

    in

    Hawai i . Most

    chemica l ana lyses used in t h i s

    r epo r t

    a re

    from

    th e

    f i l e s of

    the

    Honolulu of f i c e of th e

    U

    S.

    Geolog ica l

    Survey.

    w

    bas ic

    c r i t e r i a

    were i n i t i a l l y es t ab l i s hed to asse ss

    the

    water

    chemis t ry

    da ta :

    t empera tu re

    and Si02 concen t r a t i on s .

    Tempera tures of g rea t e r than 26C o r Si02 concen t r a t i on s

    g rea t e r than 55

    ppm

    fo r Oahu and 30

    ppm

    fo r th e o the r i s l ands

    H .G.R.A.P ., 1978; Thomas e t

    al

    1979 were

    cons idered

    to

    be an om alo us.

    S tud ies in the

    Puna

    a rea

    on th e

    i s l and

    of

    Hawai i

    McMurtry

    e t al

    1977 showed t h a t th e Si02 con t en t

    o f g rou nd water in t h i s ac t ive

    area

    was i nd i ca t i v e o f zones of

    high subsu rface tem pera tu re . F ur the r app l i ca t ion of t he se

    c r i t e r i a fo r use on a r eg iona l bas i s has shown

    t h a t many

    va r i ab l e s

    ex i s t

    which

    lead to ambigu i t i e s

    in

    i n t e rp r e t a t i on ,

    t h e r e fo r e ano ther geochemica l parameter was sought in

    an

    a t t empt

    to c l a r i f y o r r e i n fo rce

    the

    S i02 - t empera tu re

    c r i t e r i a .

    Examinat ion

    of

    th e chemical

    ana lyses

    ava i l ab le showed

    t ha t

    under

    Hawaiian

    cond i t i on s ,

    d i f f i c u l t i e s

    a r i s e

    in

    using

    the major i ty

    of

    e l emen t s ,

    o r

    r a t i o s of e lements , as

    geo thermal

    i nd i c a to r s .

    The Cl/Mg

    r a t i o

    appeared

    to

    be

    the

    most success fu l

    i nd i ca t o r fo r the

    type of water being

    s tud ied shal low ground

    wate r . It d i s t i ngu i she s between th os e S i0 2- temp er at ur e

    anomal ies most

    l i ke ly to

    be

    caused by

    anomalous geo thermal

    hea t from those

    due to

    o the r cond i t i on s .

    This r epo r t

    di scusse s

    some

    of the

    problems

    in

    us ing

    the

    Si02- tempera tu re

    c r i t e r i a fo r

    sha l low groundwater assessment

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    and

    the

    app l i c a t i on s of th e Cl/Mg r a t i o .

    Also pre sen ted

    a re

    those areas

    with in

    th e

    s t a t e

    t h a t

    a re cons idered to possess

    po t en t i a l on the

    bas i s of t h e i r Cl/Mg r a t i o .

    O URREN E OF

    GROUNDW TER IN HAWAII

    Any

    r eg iona l

    assessment

    of th e chemica l p rope r t i e s of

    groundwater from a

    l a rge number of

    environments

    i s d i f f i c u l t

    due to th e va r i a t i on in such

    parameters

    as dep th of

    wel l

    and

    ca s i ng ) ,

    topograph ic

    and

    geographic

    l o ca t i on and

    the

    type / s

    of

    aqu i f e r which

    each wel l

    pene t r a t e s .

    These va r i a t i on s

    a re majo r prob lems in

    u t i l i z i ng

    th e

    Si02 concen t r a t i on s

    and

    t empera tu re

    va lues o f

    groundwate r

    and

    make r e l a t i v e comparisons

    d i f f i c u l t .

    One

    of

    the

    most

    impor tan t

    f a c to r s

    def in ing

    th e

    cha rac t e r

    of

    the

    groundwate r in a given l o ca l e

    i s th e

    type of aqu i f e r

    from which

    th e

    water

    i s

    drawn. G enera lly , th ree bas ic

    groundwater types can

    be cons idered in

    Hawaii :

    i )

    i i )

    dike- impounded occurs

    with in

    basa l t s

    from

    nea r

    s ea - l eve l to

    high

    e l eva t ions , but i s most

    o f t en

    as soc i a t ed

    with rift zones; usua l ly of l o c a l

    recha rge . Where t h i s aqu i f e r type occurs near

    s e a - l eve l , and

    th e

    dikes

    a re pa r a l l e l to

    the

    coas t ,

    en cro achmen t o f

    s a l i ne wate r i s r e s t r i c t e d ,

    and th e f r esh groundwater

    wi l l not

    nece s sa r i l y

    be

    cont inuous

    to

    th e deeper

    under ly ing

    s a l i ne

    wate r

    S tea rns e t

    al

    1940) .

    Numerous

    dike

    format ions

    can

    form success ive

    r e se rvo i r s

    of

    t h i s

    type

    to highe r e l eva t i on s r e s u l t i ng in a

    s t epped groundwate r g rad i en t .

    sedimentary

    and a l l uv i a l occur a t lower

    e l eva t ions ,

    u su ally w ith in

    the l a rge r

    va l l ey s and

    in

    co a s t a l

    a r ea s . The sed imentary mate r i a l i s

    usua l ly

    of l imi t ed th ickness

    and

    low

    pe rmeab i l i t y ;

    however in la rg e v al le ys the

    sed iments can be

    s eve r a l

    hundreds of meters t h i ck and

    of bo th

    marine

    and

    t e r r e s t r i a l

    o r i g i n .

    These

    sed imentary

    a rea s are of ten

    highly

    popula ted

    and

    con ta in many

    groundwater wel l s ,

    and

    consequen t ly i n f i l t r a t i on

    of s a l i ne water in to a l l u v i a l aqu i fe rs has

    in

    many

    places

    been enhanc ed by

    cont inuous

    pumping.

    Most of the

    groundwater i s of l o c a l r echarge ,

    but

    i s

    of ten

    a l t e r ed

    chemica l ly because

    of

    i r r i g a t i on

    and the

    consequen t

    recyc l ing .

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    i i i bas a l non-a r t e s i an groundwater ;

    unde r l i e s

    a l l

    of

    the major i s l ands

    in the

    Hawaiian cha in , and

    can

    extend

    to

    g rea t

    depth .

    It i s

    usua l ly

    t r a n s i t i ona r y

    through

    a zone

    of

    mixing to deep

    s a l i ne

    water

    in

    permeable

    a rea s

    with

    deep

    l avas

    S tea rns e t

    al 1940 .

    This wate r p ro bab ly

    extends

    to 5

    to

    6

    m below the l a r g e s t

    i s l ands and

    i s th e major

    source of groundwater in

    Hawai i .

    Cumulat ive

    pumping

    of wel l s

    with in

    t h i s

    aqu i f e r

    type

    has

    a lso

    produced

    some

    l oca l

    upwel l ing of

    th e u nd erly in g s a l i ne water

    Swain,

    1973 . In

    much

    of the s t a t e , and e spec i a l l y southern Oahu,

    the Ghyben-Herzberg f r e shwa t e r - s a l i n e water

    i n t e r f a ce i s replaced by a t r an s i t i on zone

    of

    mixing due

    to th e

    a r t i f i c i a l

    and na t u r a l

    dynamic

    s t r e s s e s

    a r i s ing from

    heavy withdrawal

    and

    the

    seasona l na tu re

    of

    th e rech arg e

    imposed

    on

    t h i s

    deep

    groundwater Mink, 1961 . n

    the

    o lde s t

    i s l ands e . g . Maui, Oahu , th e

    bas a l

    aqu i f e r in

    th e co a s t a l

    regions

    i s capped by marine sedimentary

    depos i t s

    which l a rge l y re ta rd inward or outward

    groundwate r migra t ion

    in

    the sha llow

    pa r t s of

    these r e s e rvo i r s Mink,

    1964 .

    Div i s ions

    among

    th e d i f f e r en t

    aqu i f e r s

    a re

    no t always

    wel l def ined , and

    aqu i fe rs with

    in te rmed ia te cha r ac t e r i s t i c s

    a lso ex i s t .

    In

    some a rea s of

    h ighe r

    e l eva t i on , groundwate r

    can be perched on impermeable ash beds . Areas with a low

    dens i ty

    of

    dikes

    and s t r u c t u r a l

    permeab i l i ty

    wi l l

    al low

    more

    e x te n si ve s ub su rf ac e movement of wate r . In a rea s where

    s i gn i f i c an t s ub su rf ac e h ea t

    ex i s t s ,

    the equ i l ib r ium

    of

    the

    Ghyben-Herzberg

    zone

    may

    be

    des t royed by a

    lower ing

    of the

    dens i ty

    of the

    s a l i ne wate r

    thus

    induc ing l o ca l i z ed

    upwel l ing

    of s a l i ne wate r i n to

    th e fre sh w ate r

    l en s . The chemis t ry

    and

    volume

    of

    su r face waters and groundwaters

    in Hawaii i s

    also

    a f fec ted by th e preva i l ing t r ade wind pa t t e r n s . The

    i s l and

    topography produces d i s t i n c t windward and leeward c l ima t i c

    cond i t ions which a f f e c t r echa rge r a t e s and c rea t e

    l a rge

    va r i a t i ons

    in

    e ro s i on , wea the r ing , and

    s o i l t ypes ,

    in

    some

    cases wi th in r e l a t i v e l y

    l o ca l i z ed

    a rea s ; thus

    any r eg iona l

    survey of groundwaters

    in Hawaii must be able

    to d i s t i ngu i sh

    between chem ic al a nomal ie s due to mixing

    o f g eo th erm ally

    a l t e r ed

    groundwate r and those

    caused

    by o the r phenomena

    a r i s ing from the l o ca l i z ed na tu re of the hydrogeo logy .

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    4

    SILICA TEMPERATURE CRITERIA

    S i l i c a

    The

    s i l i c a

    concen t r a t i on in

    thermal

    waters

    i s

    widely

    used

    as bo th

    a qua l i t a t i v e and q u a nt i ta tiv e in d ic ato r of subsur face

    hea t Mahon, 1966; Fourn ie r and Rowe, 1966; E l l i s 1970;

    Fournie r and Truesde l l 1970 .

    On

    the i s l and of Hawaii the

    concen t ra t ipn

    of Si02 was

    also succe s s fu l l y

    app l i ed to sha llow

    the rmal groundwater McMurtry e t

    al 1977 .

    While

    Si02

    concen t ra t ion

    i s reasonably success fu l as

    a broad

    qua l i t a t i v e

    i nd i c a to r of

    anomalous

    subsur face

    t empera tu re cond i t ions

    when

    appl ied to a l l

    groundwaters

    in

    Hawaii ,

    it i s a f f ec t ed

    by

    many

    fac to rs which

    render

    the i n t e rp r e t a t i on of

    th e

    da t a

    ambiguous .

    Two

    areas of uncer t a in ty ex i s t with th e use of th e repor ted

    Si02

    concen t ra t ions .

    One

    i s th a t

    a

    va r i a t i on

    of

    from

    20

    to

    85 ppm

    Si02 can occur

    among

    d i f f e r en t

    aqu i f e r s in

    the same

    re gio n; seco nd ly

    va r i a t i on s of up

    to 5

    have

    been

    noted in

    d i f f e r en t ana lyses

    from th e

    same w ell w ate rs

    Table 1 . The

    l a t t e r

    appears to

    be

    due to both

    ana l y t i c a l

    procedure

    used and

    cond i t ions of co l l e c t i on and s t o rage .

    The ranges of Si02 with in waters from d i f f e r en t aqu i fe rs

    has been summari zed by Davis 1969 .

    He

    notes

    t ha t

    to

    3 ppm

    Si02 wi l l

    a lmo st immedia te ly

    m inutes go in to

    so lu t i on

    as ra in

    comes in

    con tac t

    with

    the ground

    su r f ace . During

    su r face

    and

    subsur face movement of t h i s wate r

    it wi l l reach a Si02

    con ten t

    of

    5

    to

    20

    ppm

    be fore

    en te r ing

    high

    l eve l

    aqu i f e r s .

    During

    re s idence t he r e the Si02

    i n c r ea s e s

    to a pp ro xim ate ly 15 to 45

    ppm

    and i s ty p i f ied by high l eve l w a ter supply

    tu nn el w ate r .

    Water

    l eaking from t he se aqu i fe rs and from

    s o i l

    to the

    basa l

    aqu i fe rs

    d i s so lve s

    more s i l i c a r e su l t i ng in Si02 concen t ra t ions of 30

    to 60

    ppm. Higher

    l e ve l water which di scha rges as

    streamflow

    has a

    Si02 con ten t of 15

    to 30 ppm. One f e a t u re noted

    by Davis

    1969 i s t ha t th e Si02 con ten t

    of

    f lood

    or ephemera l

    s t ream-

    flow

    from heavy r a i n f a l l

    i s

    not apprec iab ly

    lower

    than

    t ha t

    in

    more con t inuous ly

    f lowing s t reams .

    Water

    en te r ing

    sedimentary aqu i f e r s commonly has a Si02

    con ten t of 5 to

    5

    ppm,

    which i n c r ea s e s

    to 60

    ppm

    whi le

    in

    the

    aqu i f e r . This

    water

    i s e s pe c ia ll y s u sc e pt ib le to

    fu r the r

    inc reases

    in

    Si02 due

    to r ec i r cu l a t i on

    by i r r i g a t i on and

    r e in j e c t i on

    of

    i ndu s t r i a l

    wate r .

    These

    l a t t e r

    occur rences can

    inc rease the range of Si02

    va lues up

    to 50 to 85 ppm. Visher

    and Mink 1964 cons ide r

    t ha t

    the Si02 concen t ra t ion of 40 to

    75 ppm in re tu rn i r r i g a t i on water

    i s der ived

    from acce le ra t ed

    l eaching

    of s o i l and

    rock be cau se

    of th e cumula t ive

    e f f e c t

    of

    a g rea t e r volume of water

    plus the

    s lower

    movement of

    ground-

    water with in t he se low permeab i l i ty mate r i a l s .

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    f u r t h e r

    va r i ab l e in

    Si02

    concen t r a t i on i s th e

    re s idence

    t ime of wate r in aqu i f e r s ; groundwater appears

    to

    con t inuous ly

    d i s so l ve

    av a i l a b l e

    Si02 from

    th e

    rocks

    t h rough

    which it

    pe r co l a t e s .

    The

    high r a i n f a l l

    on

    th e

    windward

    s ide of

    the

    i s l ands

    removes

    s i l i c a

    more

    r ap id ly

    from s o i l

    and

    rock ,

    r e su l t i ng

    in a r e l a t i v e l y

    g r e a t e r

    av a i l a b i l i t y

    o f s i l i c a

    fo r

    d i s so lu t i on t han

    in th e

    l e s s weathe red rocks of

    th e

    leeward

    s i de s . Other f a c t o r s caus ing i n c r e a s e s

    in d is so lv ed

    Si02

    a re

    ag r i c u l t u r a l phosphates Fox e t al 1 96 7 , bu rn in g

    of

    ag r i c u l t u r a l wastes

    and reduc t ion

    o f

    s o i l Davis ,

    1969 .

    f u r t he r cause

    of

    Si02

    va r i a t i o n s i s th e na t u r a l

    d i f f e r ence

    in the

    chemica l

    compos i t ion of th e

    rock types between

    d i f f e r e n t

    a r e a s .

    Table

    compares

    ana l y t i c a l r e su l t s from

    e l even

    wel l s in

    va r i ous l o c a l i t i e s un t i l th e p re s en t . S ix of the se

    we l l s

    have

    average

    t empera tu re s

    of

    30C

    or

    g r e a t e r

    and

    t h e i r

    comple te

    ana ly ses

    a re inc luded

    in

    Table

    2.

    Without engaging

    in

    a

    d e ta ile d d is cu ss io n ,

    th e

    va r i a t i o n s

    in rep or ted

    s i l i c a

    concen t ra t ions

    can

    be a t t r i bu t e d

    to bo th d i f f e r ences

    in

    an a l y t i c a l t echn ique

    as we l l

    as

    in

    th e methods of co l l e c t i on

    and

    s to r age .

    The

    e a r l i e s t

    ana lyses

    by S ta t e

    and Fede ra l

    agencies a re

    more

    con s i s t e n t over

    t ime ,

    but the

    more recen t

    ana ly ses i n d i v i du a l s

    o r

    depar tments of th e

    Unive rs i ty

    of

    Hawai i show g re ate r v a ri at io n

    due

    to

    th e d i f f e r e n t

    s to rage

    and

    an a l y t i c a l

    t e chn iques app l i e d .

    Probab ly

    th e major cause

    of the se v ar i a tio ns i s th e form

    o f

    s to r age . I d e a l l y , ana lyses

    fo r

    s i l i c a shou ld

    be conduc ted wi th in

    s eve r a l days , bu t

    it i s

    l i ke ly

    t h a t

    fo r most

    o f

    th e o lde r an aly se s th e samples

    were

    not

    ana lyzed

    fo r many weeks. This i n c r e a s e s

    th e l i k e l i hood

    of

    polymer iza t ion and many of

    th e e a r l i e r

    repor t ed ana ly ses a re

    lower than more

    r e c en t ones .

    Cu r ren t

    work

    by HIG,

    however,

    sugges t s

    t h a t t empora l va r i a t i on s

    in

    th e Si02

    concen t ra t ion

    do occu r .

    Tempera ture

    The t empera tu re measurement

    o f g ro und water i s

    probab ly

    a more

    r e l i ab le id e n ti fi ca t io n

    c r i t e r i o n fo r a

    t h e rma l

    anomaly

    than i s Si02 ; however , its use i s cu r r en t l y l im i t ed because of

    th e

    r e l a t i v e l y sma l l

    number o f m ea su re men ts and some que s t i on s

    c on ce rn in g th e

    accuracy

    o f th e

    repor t ed

    da t a .

    On

    th e ex t i n c t

    vo l c an i c i s l ands groundwater t empera tu re s

    27C

    and over a re

    cons ide red

    s i gn i f i c an t ;

    those

    g r e a t e r

    than 29C, high ly

    anomalous.

    The

    t empera tu re o f

    groundwater wi th in th e aqu i f e r s

    above

    s e a - l e v e l

    i s r e la te d to bo th t empera tu re o f

    p r e c i p i t a t i on and

    t empera tu re of

    su r f a c e

    wate r as it en t e r s the

    aqu i f e r .

    Mink

    1964 cons ide r s t h a t th e o r i g i n a l wate r en t e r i ng

    an

    aqu i f e r

    can ga in hea t

    from

    i vo l c an i c a c t i v i t y ; i i f r i c t i o n a l f low;

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    6

    Table

    1 Comparison of different analyses

    Well

    Temp. C1

    5i02

    Number Location Date

    OC

    ppm ppm ppm

    C1/Mg

    HAWAII

    2982-01

    Geoth Test 3

    7/75 3410 59

    57 80

    1/75 93 0

    3274 52

    96 6

    62 96

    12/74

    86 0

    4200 184

    12/74

    88 0 3850

    187

    Average 89 0 3684

    55 5

    156 60 38

    2783-01 Ma1ama-Ki

    1/75 52 2

    3811 210

    100 7

    18 15

    1/74 54 0 11000

    90

    9/62

    5850

    324 59

    18 06

    Average 53 1

    6887

    267 83 2

    18 11

    3081-01

    Kaphoho Test

    7/75

    33 5 316

    27 2

    11 62

    1/75 36 8 303.5

    28

    71 3

    10 84

    12/74

    34 0

    750

    53

    1/74 38 0

    560

    56

    1961

    320 17 1

    70 5

    18 71

    Average

    35 6 450

    24 1

    62 7

    13 72

    2881-01

    Allison

    Well

    1/75

    37 8

    281 15

    24 1 18 73

    1/74

    38 1400

    53

    Average

    37 9

    840 5

    15 38 6

    18 73

    6147-01

    Kawaihae 3

    2/74

    31 0

    300

    8

    1974

    31 0

    253

    32

    84 7 91

    6/63

    255 31

    78 8 23

    6/63

    35 8

    250 33

    89

    7 58

    Average

    32 60

    264 5

    32

    64 8

    7 91

    3758-01

    Kailua/Kona

    1974

    25 0 459

    27

    43

    17 0

    6/74

    25 0

    800

    40

    12/58

    440 37

    26

    11 89

    3/55

    485

    35 33

    13 86

    11/49

    450 9 7

    46

    46 39

    9/49

    460

    28 68

    16 43

    Average

    25 0

    515 7

    27 3 42 7

    21 11

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    Table. 1. Comparison of different

    analyses cont.

    Well

    Temp. C1

    Mg

    Si02

    NlD Iber

    Location

    Date

    OC

    ppm)

    ppm)

    ppm)

    C1/Mg

    MAUl

    4835-01

    Ukumehame

    10/78

    33.1

    459

    26 115

    17

    .65

    9/74 32 660 66

    2/70 400

    29

    60

    13.79

    10/69 33.0 354 15

    59

    23.60

    8/69 373 17 58 21.

    94

    4/69

    34.0 432 21 71 20.57

    1/69 33.0 400 24 71 16.67

    7/68

    420 23 68

    18.26

    Average

    33.0

    437.3

    22.1 71.0

    18.93

    O U

    2508-02

    Waianae

    8/78 27.0

    260

    80

    32

    3.25

    8/75

    28.0

    520 101

    10/71 29.0

    292

    102 92 2.86

    10/71

    29.0

    382

    108 89 3.54

    2/54

    520 127

    84

    4.09

    2/39

    250 111

    87

    2.25

    8/39

    360 130

    88

    2.77

    Average

    28.3

    369.1

    109.7 81.9 3.13

    2808-01

    Lua1ua1ei

    8/78 26.5

    138

    7

    38

    5.11

    7/75

    27.0

    430

    74

    2/72 26.7

    160 28 63

    5.71

    9/57

    26.6

    165

    12/56

    164

    34

    Average

    26.7 211.4 27.5

    52.3

    5.41

    2812-01

    Makaha

    8/78 26.0 92

    34

    40

    2.71

    3/71

    82

    6/70 95

    1969

    26.5

    93 4.9

    66 18.98

    2/62

    100 33

    71 3.03

    Average

    26.3

    93.6

    24.0

    66.4

    8.24

    2808-02

    Lua1ua1ei

    8/78

    19.0

    23 6.5

    27

    3.54

    2/72

    18.5

    26

    7. 4 49

    3.51

    2/72

    26

    7.3

    49

    3.56

    6/67

    32

    6.0

    56

    5.33

    1966

    30

    8.2

    62 3.66

    Average

    18.8

    27.4

    7.1 48.6

    3.92

    7

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    8

    i i i ) r e tu rn i r r i ga t i on water and

    r e l a t i v e l y

    l imi t ed recharge

    from r a in

    in

    i r r i ga t ed a reas ;

    i v )

    t e r r e s t r i a l hea t

    f low.

    The t emperature of sa l ine

    water

    in deep basa l

    aqu i f e r s i s

    inc reased by approximate ly 14C by t e r r e s t r i a l hea t

    flow

    to

    t emperatures

    of

    approximate ly

    23.3C, as

    the

    water

    migra t es

    from the ocean bottom to the aqui fe r

    Mink, 1964) .

    In regard

    to

    the supply

    of hea t

    to

    groundwaters

    fo r

    geothermal cons ide r -

    a t i on , the r e s idua l hea t

    with in

    i n t r u s i v e

    mate r i a l i s

    co ns id ere d to be the

    most s i gn i f i c an t .

    Groundwater

    t emperatures in

    areas

    where sur face

    mani fe s t a t ions

    of vo lcan ic

    or g eo th erm al

    ac t i v i t y

    occur

    such

    as on the

    lower

    eas t

    r t

    of

    Kilauea) have

    b ee n mea su red from

    30C

    to

    approximate ly

    90C

    in sha l low hydro log ica l d r i l l ho l e s .

    In o the r

    a r eas , and espec i a l l y on the

    i s l ands

    where

    t he r e a re

    no

    sur face express ions of cu r r en t a c t i v i t y ,

    t emperatures

    a re

    lower ,

    ranging

    from

    l8 .5C

    as high as

    33C

    Appendix

    I ) .

    Observed groundwater

    t emperatures

    can be

    r e l a t ed

    to d i f f e r en t

    aqu i f e r types . High l eve l usua l ly d ik e- impounded ) g roundwa te r

    ranges from 18

    to

    21C; basa l groundwater from 20 to 24c

    and sed imenta ry groundwater from

    to

    26C. Anomalous

    t emperatures of 27C and above do no t ,

    however,

    neces s a r i l y

    denote

    the

    exi s t ence of a s i gn i f i c an t the rmal anomaly. I t

    appears t ha t in some a re as , lo ca liz ed and r e l a t i v e l y sha l low

    low

    magni tude the rmal

    anomal ies

    may

    ex i s t

    which i nc rease

    groundwater

    t emperatures by

    or 3C.

    CHLORIDE MAGNESIUM RATIOS

    Genera l

    Because

    of

    the numerous f ac to r s

    in Hawaii

    which a f f e c t

    the

    chemis t ry of

    groundwater ,

    t

    i s d i f f i c u l t

    to

    apply

    a

    chemica l geothermal

    i nd i ca to r without

    making a

    complex

    and

    i nd i v i dua l

    assessment

    of the

    da ta

    from each wel l .

    Fu r t he r ,

    the

    ch em i ca l g eo th ermome te rs

    S i02 , Na/K/Ca, Na/K) commonly

    u t i l i z ed fo r the rmal

    waters

    a re no t appl i cab le

    to

    low

    t emperature

    shal low g rou ndw aters of H aw aii.

    Limited

    appl ica t ion

    of

    the

    Cl/Mg

    r a t i o

    to

    low

    t emperature

    groundwaters in New Zealand

    Schof i e ld ,

    1956) was to some

    degree succe s s fu l in

    d i s t i ngu i sh ing between sa l ine

    groundwater

    of marine or ig in and high chlor ide groundwater o f g eo th erm al

    or ig in .

    Appl ica t ion of

    t h i s

    r a t i o to

    those

    groundwaters

    in Hawaii

    t ha t

    have been

    se lec ted as

    anomalous by

    Si02-

    tempe ra tu re ) p ro vid es

    a f u r t h e r , more cont ro l l ed

    c r i t e r i on

    fo r

    s e l ec t i ng anomalous l o c a l i t i e s . Of

    the

    397

    se t s of Si02-

    temperature

    ana lyses s t ud i ed , 53

    se t s

    have a s ign i f i c an t ly

    anomalous Cl/Mg

    r a t i o

    ~ 1 5

    and

    30 se t s have

    a

    marg ina l ly

    anomalous

    r a t i o 12.0

    to 14 .9 ) . The

    Cl/Mg

    r a t i o s of

    an

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    9

    add i t i ona l

    50 ana ly s e s , which

    were

    or ig ina l l y

    r e j e c t ed by

    the

    Si02- tempera ture

    c r i t e r i a ,

    were

    a l so ca l cu l a t ed n ot inc luded

    in t h i s r epo r t ) ; excep t fo r

    6 s l i gh t l y

    anomalous ca se s , a l l

    were

    found to be

    cons i s t en t ly

    very low.

    Theory

    The

    assumpt ion

    in using the CI/Mg r a t i o as a

    geo thermal

    i nd i ca t o r

    i s

    t h a t

    th e

    ch lo r ide

    con ten t of

    seawater and

    g ro undwa te r r ema in s

    l a rge ly

    una f fec t ed

    by

    thermal processe s

    or ion exchange when seawater

    i n f i l t r a t e s

    the i s l and

    aqu i f e r s ,

    or during subsur face

    groundwater

    migra t i on . The

    magnesium i on ,

    however , i s s t r ong ly dep le t ed

    in

    concen t r a t i on where

    ground-

    waters have been a f f ec t ed by thermal

    p roces s e s ,

    thus producing

    a h ighe r Cl/Mg r a t i o . A ssess ing the

    chemica l

    da ta ava i l ab l e

    sugges t s t h a t r a t i o s

    of g r e a t e r

    than

    t h a t of seawater ~ 1 5

    i nd i ca t e t ha t

    anomalous

    thermal

    cond i t ions

    have

    a f f ec t ed

    aqu i f e r rock chemis t ry by

    hydro thermal

    a l t e r a t i on

    o r

    have

    caused an i nc rea sed

    degree of

    r e ac t i on

    between groundwater

    and

    rock inc lud ing sed imentary mate r i a l and c l a y s ) . Heat ing

    of

    s a l i ne

    wate r

    in th e deep

    basa l

    aqu i f e r s

    a l so enhances

    dep le t ion .

    Chlor ide

    Chlor ide i s the major

    ion

    in a l l

    forms of

    water wi th in

    an

    i s l and

    env ironm ent such as Hawaii.

    This

    i nc ludes r a i n , s t reams

    and high l eve l groundwater as wel l as w ate rs of l ower e leva t ion

    aqu i fe rs

    Tab le

    2 ) .

    The

    ch lo r ide

    i s

    a lmos t

    en t i r e l y

    of

    marine

    o r i g i n from a i rborne s a l t s

    o r

    s a l i n e wate r i n f i l t r a t i o n . The

    highe r

    concen t r a t i on s of ch lo r ide

    in

    groundwaters

    can be

    r e l a t ed to th e amount of

    seawate r

    i n f i l t r a t i on by th e

    approx imat ion

    Seawater

    = 100 Cl groundwater Cl

    s t reamwater )

    Cl

    seawater

    The

    s u i t a b i l i t y of ch lo r ide

    as

    a

    s tandard in

    asses s ing

    the amount of seawater

    mixing

    i s t h a t the

    ch lo r ide ion

    i s

    highly

    s t ab l e in th e groundwater

    in

    both ba sa l t i c and

    sed imentary

    rocks m arine

    and

    t e r r e s t r i a l ) . I t

    does

    no t

    en t e r

    in to chemical r e ac t i on

    with

    o the r ion s o r an ion ic

    exchange

    wi th in

    sed iments Scho f i e ld ,

    1956;

    Mink,

    1961; Swain ,

    1973) .

    Fur the r ,

    the Cl con ten t o f seawater i s una f fec t ed

    even

    a t

    t empera tu res of up to

    350C Bischoff

    and Sey f r i ed , 1978) .

    Sources of c hlo rid e o th er

    than

    sea s a l t s to

    groundwaters

    in Hawaii are c on side re d to

    be minimal .

    The

    ch lo r ide

    con ten t

    of Hawaiian

    l avas

    i s low,

    in

    th e

    range

    of

    0 .01

    to 0.2

    Macdonald e t

    al

    1973) .

    Some

    con t r i bu t i on of ch lo r ide from

    rocks to deep , h igh

    t empera tu re

    groundwaters

    in a rea s

    of

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    I

    0

    Tab le 2 .

    Averaged value s o f

    known

    thermal and other

    waters

    Well

    Temp.

    Na

    K

    Ca

    Mg

    Cl Si02 HCO SO.

    F

    NO

    Cu

    Pb Zn

    As Fe

    Mn

    Number

    Name

    OC)

    pH

    ppm) ppm) ppm)

    ppm) ppm) ppm)

    ppm)

    ppm) ppm) ppm)

    p pm ) p pm )

    ppm ) pp m) ppm) ppm)

    HAWAII

    HGP-A

    300

    4 4 800 149

    96

    1. 0

    1150

    501 =45

    =176

    --

    0.13

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    11

    ac t i v e volcanism may occur , however . E l l i s 1966

    exper imen

    t a l l y

    obta ined aqueous so lu t i on s wi th

    60

    and 250 ppm Cl

    from

    r eac t i on s

    with

    d i s t i l l e d wate r and

    ba s a l t a t 200C and

    300C

    r e spec t i v e l y . Exper iments by El l i s and

    Mahon 1964

    showed

    th a t b a s a l t e a s i ly

    l o s t

    about

    75 of

    its

    t o t a l

    ch lo r ide

    to

    wa te r

    a t t empera tu re s

    of 300 to

    350C.

    The

    conc lus ion of

    El l i s and

    Mahon 1964 was t h a t ch lo r ide i s ea s i l y

    l o s t

    from

    ba s a l t because

    much

    of the

    l eached ch lo r ide

    i s

    held on su r faces

    wi th in

    th e rocks r a t h e r than in s o l id s o lu tio n .

    This

    may mean

    t h a t minor

    amounts

    of ch lo r ide

    cou ld be

    gained by

    groundwate rs

    th rough

    low t empera tu re wate r - rock i n t e r a c t i on and a long

    re s idence

    t ime

    which

    would enhance

    the

    use

    of Cl/Mg

    r a t i o

    as

    a geo thermal i nd i c a t o r .

    Magnesium

    Magnesium

    ion

    concen t r a t i on s

    can

    be

    s u b st an t i a l ly a lt er ed

    by

    high t empera tu re

    r e a c t i o n s . Labora to ry s tud i e s

    of wate r

    rock equ i l i b r i a have

    shown t h a t

    magnesium can

    be e f f e c t i v e l y

    removed

    from

    so lu t i on by the

    fo rmat ion

    of

    high

    t empera tu re

    rock a l t e r a t i on s produc t s E l l i s

    and

    Mahon, 1964; Mahon, 1967 .

    The two pr imary

    removal

    mechanisms a re t h rough fo rmat ion

    of

    ch l o r i t e

    [Mg3 Si4010

    OH 2Mg3 OH 6]

    u nd er extrem e

    cond i t i on s

    and

    illite [ AlMgFe 4 SiAl a02o OH 4] a t lower

    t empera tu re s .

    Another

    high

    t empera tu re

    r eac t i on

    i s t h a t of seawa te r with

    ba s a l t s , which

    produces

    p r e c i p i t a t e s of magnesium oxysu l f a t e s

    B ischof f and

    Sey f r i ed ,

    1978 and hydroxy la ted magnesium

    s i l i c a t e s

    Mackenzie e t

    al.

    1967 .

    Fie ld s t ud i e s in

    Hawai i

    have i d en t i f i e d th e h igh e r

    tempera ture

    magnesium s i l i c a t e s c h l o r i t e

    and

    illite

    in

    both

    ex t i n c t hydro thermal systems

    Fu j i sh ima

    and Fan, 1977 and

    in

    drill core from HGP A geo thermal wel l

    S tone ,

    1977;

    Stone

    and

    Fan, 1978 In t e rmed ia t e t empera tu re 70 to 150C

    r eac t i on s

    can a lso d ep le te magnesium th rough the fo rm ation o f smec t i t e

    c lay s S ey fr ied and Bi scho f f ,

    1979 .

    The

    sequence of low t empera tu re

    r eac t i on s

    undergone by

    magnesium in a

    ba sa l t i c

    env i ronment can be qu i te

    complex.

    Ra in fa ll , e sp ec ia lly on windward s ide s

    of

    th e i s l a nd s ,

    gene ra l l y c a r r i e s sma l l concen t r a t i on s o f sea s a l t and has a

    Cl/Mg ion

    r a t i o of

    app rox ima te ly

    7. This wate r

    pe r co l a t e s

    down

    t h rough

    th e

    i s la nd a qu ife rs

    and very r ap id ly d is so lv es

    enough m agnesium from

    the

    f e r romagnes i an

    minera l s in th e

    ba s a l t

    to lower

    the Cl/Mg r a t i o

    to a pp ro xim a te ly

    2

    to 3 .

    I n f i l t r a t i o n

    of

    s a l i n e wate r i n to

    the

    ba sa l aqu i f e r s invo lves a

    somewhat

    d if f e re n t s er ie s of r e a c t i o n s . The most

    impor tan t

    of

    t he se

    i s

    the

    ca t ion -an ion e xc ha ng e b etwee n th e in t rud ing

    seawa te r

    and

    th e

    ca lca reous

    marine s ed im ents th ro ug h

    which

    it

    must

    pass .

    Obse rva t ions

    on

    Oahu

    Mink,

    1961 sugges t t h a t th e

    i n t r ud ing

    wate r ga ins and Ca and l o s e s Na and K to th e s ed im en ts .

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    12

    Mink 1961)

    exp res ses t h i s

    r e a c t i o n by

    th e

    fo l low ing

    gene ra l i zed

    equa t i on :

    Ca, Mg c lay 2Na+, K 2Na, K c l ay ca++, Mg

    The s a l i n e wa t e r ,

    a f t e r

    en t e r i ng the ba s a l t i c aqu i f e r ,

    undergoes l ttl f u r t h e r exchange and , as a consequence , ba s a l

    wate r s

    t h a t

    have

    been

    mixed w ith sm all amounts o f i n t r ud ing

    seawa te r commonly have

    Cl/Mg

    r a t i o s r ang ing from

    2

    to as

    high

    as

    6.

    Rat io s of

    5 to 8 a re

    common in sed imen ta ry

    aqu i f e r s

    in

    a reas of low topography l a rge

    va l l ey s ;

    coa s t a l

    s t r i p s

    where

    some

    Mg l o s s to c l ays

    produced by

    wea the r ing

    occu r s . Some

    sa l i n e water i n f i l t r a t i o n

    i s a lso common wi th in

    t h e se aqu i f e r s ,

    o f t en having been enhanced by con t inuous pumping of a l a r ge

    number of wel l s .

    Thus

    th e

    o v er al l in d ic a t io n

    and

    assumpt ion

    app l i ed

    i s

    t h a t

    lower

    t empera tu re r eac t i on s

    undergone by magnesium main t a in

    a

    Cl/Mg r a t i o

    in th e

    range o f to 8

    fo r

    most Hawai i groundwaters ;

    however ,

    as

    groundwate r

    t empera tu re s

    i n c r e a s e ,

    magnesium

    concen t r a t i on s

    a re

    seve re ly

    dep l e t ed , r e su l t i n g

    in

    a s ub s t a n t i a l

    i n c r e a s e in th e obse rved Cl/Mg r a t i o s . The dep l e t i on of

    magnesium and

    consequent

    h ighe r Cl Mg

    r a t i o s

    appear to

    con t inue

    to be r e f l e c t e d

    even

    a f t e r th e h ea te d w ate rs have been

    cooled

    to

    nea r -amb ien t t empera tu res

    t h rough

    conduct ion

    or mixing

    with

    coo l e r n o n- sa lin e w a te rs .

    COMPARISONS

    OF

    Cl/Mg

    RATIOS

    IN

    OTHER

    THERM L W TERS

    In o rde r to fu r t he r a s s e s s th e app l i c ab i l i t y of

    th e

    Cl/Mg

    r a t i o

    as

    a t r a c e r fo r the rm al g roundw ate rs , the

    r a t i o s

    have

    been ca l cu l a t ed fo r a number of

    geo the rma l

    system s T ab le 3)

    in

    a va r i e t y of

    t e r r a i n s . Inc luded in t h i s

    t a bu l a t i o n

    a re

    thermal

    wa te r s

    from o the r i s l and

    env i ronmen t s ,

    many of

    which

    a l so have app re c i ab l e

    seawa te r mix ing , as

    wel l

    as t ho se

    t y p i c a l con t i n en t a l geothe rmal sy s t ems .

    The

    Cl

    and Mg va lues

    fo r these

    wate r s have been p lo tte d lo g ar ith m i ca lly F ig .

    1)

    r e l a t i v e

    to

    th e average pa ram ete rs

    of

    t h e se

    i ons

    in

    Hawai ian

    wa t e r s .

    Three

    gene ra l

    group ings emerge: wate r s from vapo r

    dominated

    sys tems , low ch lo r i de thermal wa t e r s , and high

    ch lo r i de wate r s as soc i a t ed

    wi th

    a rea

    of a c t i v e

    volcan ism.

    True vapor -domina ted

    sys tems a re gene ra l l y cha r ac t e r i z ed

    by

    low

    ch l o r i d e , high S ~

    and low pH .

    Water

    discharged

    from

    s t eam-domina ted

    sys tems

    p l o t

    in th e upper

    l e f t - hand quad ran t

    of Figu re I because of th e r e l a t i v e l y low CI/Mg r a t i o

    due

    to

    h ighe r magnesium

    concen t r a t i on s . This i s n ot u ne xp ec te d,

    in

    t h a t l Mg r a t i o s r e f l e c t t empera tu re dependent wate r - rock

    e qu i l i b r i a ; wate r d i scha rged

    from

    t h e se sys tems

    i s

    gene ra l l y

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    Tab le 3.

    Chemical

    data

    of var ious

    geothermal

    waters

    Quartz

    Loc. No.

    Estim.

    on

    Water Temp.

    S04

    Cl Mg

    Fig. 1 Ref*

    Locality

    Type

    OC

    pH ppm

    ppm ppm

    C1/Mg

    VAPOR SYSTEM

    OR STEAM

    HEATED

    1

    A

    White Island,

    N.Z.

    surface

    in 163 acid

    10500

    61840

    7310

    8. 5

    crater

    2 I

    Rabaul, New Britain, P. N.G.

    shoreline

    158 7. 9 1420 9264 550 16.8

    thermal spring

    3 F

    Tatun, Taiwan Hole

    El02

    deep thermal

    180

    3. 5

    825

    149

    6.1

    24.4

    4 D

    Carboli

    A

    Italy

    deep thermal

    --

    --

    137

    42.6

    5. 0

    8. 5

    5

    D

    Matsukawa, Japan Well MR-l

    deep thermal

    244

    4.9

    1780 12 8.7 1. 4

    6

    D

    Yellowstone Mud Vole , Wyo.

    thermal

    spring

    173 7. 0

    65.3

    13.5 16.4

    0.8

    7 D The Geysers, Calif. thermal

    spring

    115 neutral 766 1. 5 108

    0.01

    HIGH

    I ~ O R I E W TER SYSTEMS

    8 A

    Wairakei, N.Z. Hole 20

    deep thermal 239

    8.4

    35 2215

    0.04

    55375

    9 B

    Waiotapu, N.Z. Hole 6 deep thermal 222

    8.9

    52 1450

    0.06

    26167

    10

    D Yellowstone Norris Bas. ,

    Wyo.

    thermal spring 230

    7.5

    38

    744

    0.2

    3720

    11

    A

    Rotorua,

    N.Z. Hole 137 deep thermal

    196 9. 4 30

    632

    0.2

    3160

    12

    D

    Steamboat

    Springs,

    Nev.

    thermal

    spring

    191

    7.9

    100 865

    0. 8

    1081

    K

    HGP-A Hawaii deep thermal

    218 4. 4

    1150

    :1...0

    1150

    14

    A

    Ngawha, N.Z.

    Jubilee Bath

    thermal

    spring

    163 6.4

    347 1250 2. 5

    500

    15 A

    Wairakei,

    N.Z. thermal

    spring

    178 6. 8 72

    1110 4. 2

    264

    16

    J

    Pt.

    Resolution, Tanna, New Heb.

    thermal

    spring

    156

    8.5

    365 1775

    4

    444

    17

    L

    Nakama,

    Savusavu,

    j

    thermal spring

    156

    7. 8

    236

    4762

    3

    1587

    18

    C

    Akrane, Iceland deep thermal

    111 7.1

    60 3017

    12

    251

    19

    C

    Reykjanes, Iceland

    deep thermal

    219 6. 6

    94

    23250 25

    930

    20

    E

    Wilbur Spring,

    California

    thermal spring

    169

    6.9

    9

    9700 38

    255

    21

    J

    W Takara, Efate, New Heb. thermal spring 125

    7. 5

    140

    8670

    47

    185

    22

    E

    Oilf ield brine, Wilbur, Calif.

    deep brine cold 8. 6

    72

    11400

    124

    I

    w

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    T ab le 3 .

    Chemical

    data of various geothermal waters cont.

    I

    Loc. No.

    on

    Fig. 1 Ref*

    Locality

    Water

    Type

    Quartz

    Estim.

    Temp.

    OC

    pH

    S04

    ppm

    C1

    ppm

    Hg

    ppm

    C1/Mg

    WATER SYSTEMS WITH GROUNDWATER MIXING

    23 L

    Waingge1e,

    Fi j

    i

    thermal

    spring

    24 G

    Gran it e Mt ., Alaska

    thermal

    spring

    25

    C

    Hengi11,

    Iceland Well G-3 deep thermal

    26 A

    Hanmer Spring, S. N.Z.

    thermal spring

    27

    H Paraso, Vel la Lave11a, Solomon

    thermal spring

    28 L

    Emperor Gold Mine, iji deep thermal

    groundwater

    29 A Lytte1ton, S. NZ thermal spring

    A Ellis and Mahon, 1964

    B. ~ l l s 1966

    C.

    Arnason

    and Tomasson, 1970

    D vfuite

    et

    a1.,

    1971

    E. White

    et

    a1.,

    1973

    F.

    MRSO

    1974

    G

    Miller

    e t a1., 1975

    H

    Taylor,

    1975

    I Green

    et

    a1. , 1976

    J MacFarlan, 1977

    K Kroopnick e t a 1., 1978

    L.

    Cox

    and

    Hulston,

    in

    press

    110

    6.0

    514

    138 0.02

    6900

    121

    10.1

    62

    9. 3

    0.04 233

    212

    6. 8 89

    153 0.24

    638

    100

    8.0 43

    451 0.2 2255

    126

    7. 0

    224 149 6. 1

    24

    100

    7.25

    667

    404

    23 18

    130

    7. 1

    110 513

    163 3.2

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    15

    0

    0

    0

    0 0

    0 0

    0 0

    0

    0

    0

    0

    0

    N

    0

    0

    N

    CHLORIDE

    ppm

    DEEP SURFACE

    A

    STEAM

    AFFECTED

    WATER

    SYSTEM

    3

    1

    5

    1

    5

    E

    10

    Q

    5

    w

    1.0

    z

    5

    0.1

    5

    0.01

    5

    1

    Fig. 1. Log-log

    plot

    of chloride versus magnesium

    concent ra tion for

    geo

    thermal waters Table 3 from various world environments. The

    t r i ngle

    shows the Cl and parameters

    for

    dif ferent water

    types

    in

    Hawaii.

    The solid p r l le l diagonal l ines represent Cl Mg r t ios

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    6

    s team hea ted ,

    nea r - su r f a ce water

    which o f t en has no t come i n to

    con tac t wi th r e s e r vo i r

    rocks .

    Another

    category

    of the s team

    dominated

    sys tems or systems

    wi th a s team phase , i s found in

    i s l and or coa s t a l envi ronments where s a l i n e

    water

    o f

    marine

    or ig in

    i s

    being

    steam

    hea t ed .

    These

    systems

    have

    high

    ch lo r ide

    and o the r ocean

    s a l t s concen t r a t ions

    and because

    of

    g en era lly s ho rt

    r e s idence t imes ,

    have

    no t

    ach ieved

    equ i l i b

    rium with the hea ted

    aqu i f e r

    rocks . Under these c i r cums tances

    the

    Cl/Mg

    r a t i o

    i s

    even lower because of

    the

    apprec iab le

    c h lo ri de c o nc en tr at io n .

    Low ch lo r ide

    the rmal sys tems

    u su al ly a lso show e leva ted

    CI/Mg r a t i o s . In some i n s t a nc e s , however , pa r t i cu l a r y in low

    t empe ra tu r e

    systems

    and

    in

    thermal waters t ha t

    are

    apprec i ab ly

    d i l u t ed

    by f r e sh groundwate rs ,

    th e

    r a t i o s obse rved

    do

    no t

    conform to

    the

    CI/Mg r a t i o s cha r a c t e r i s t i c of high

    ch lo r i d e

    wate r s ystem s.

    These

    lower

    r a t i o s

    can

    probably

    be

    a t t r i bu t ed

    to non- equ i l i b r a t i on between the l i qu id and mine ra l phases

    of the

    co un try ro ck .

    Thermal

    groundwate rs in Hawaii

    t yp i ca l l y

    f a l l in the

    ca tegory of high ch lo r ide thermal

    sys tems.

    The CI/Mg

    r a t i o s

    in

    these

    systems

    ~ n r l l y inc rease

    with

    inc reas ing t emper

    a tu r e ; however , quan t i t a t i v e e s t ima t e s of t empe ra tu r e based

    on CI/Mg r a t i o s are

    genera l ly

    prec luded due to the

    va r i ab l e

    amounts

    of d i l u t i on and mixing of thermal ly equ i l i b r a t ed

    f lu id s

    with

    non- thermal f l u i d s . The

    deep thermal

    wate r from

    the

    Hawaii geo thermal

    wel l HGP-A

    i s a high ch lo r i d e

    type and

    has

    a Cl/Mg r a t i o

    of over

    1000. CI/Mg

    r a t i o s

    t end ing toward

    the upper r i gh t s i d e of

    the

    diagram

    F ig .

    1 i nd i c a t e

    degrees

    of mixing betw ee n

    th erm al w a te rs

    and

    s a l i ne waters

    see

    Fig .

    2 . The

    su r f a ce d i scharges of

    these

    wate r s a l l have

    Cl/Mg r a t i o s we l l over

    15 ,

    and the deep waters of t h i s type

    have

    a r a t i o of

    grea t e r

    than 400.

    These comparisons

    show

    t h a t

    high Cl/Mg

    r a t i o s

    occur

    in

    o the r

    high

    t empe ra tu r e

    thermal

    wa te r s t ha t have

    s imi l a r

    chemica l ch a r a c t e r i s t i c s to those in Hawai i . More impor tan t ly ,

    e spec i a l ly to

    t h i s

    app l i c a t i on

    in

    Hawa i i ,

    h igh Cl/Mg

    r a t i o s

    occur in high

    ch lo r i d e thermal

    sp r ing waters

    which

    a re

    known

    to have both s a l i ne

    wate r

    and cool groundwater mixing ,

    c i r cums tances

    under

    th i ch

    ne i t h e r

    s i l i c a nor

    Na-K-Ca

    geothermometers can always

    be

    r e l i a b ly

    app l i ed .

    APPLICATION Cl/Mg

    IN

    HAWAII

    Figure presen t s th e CI/Mg paramete rs

    of d i f f e r en t

    types

    of

    wate r in Hawaii .

    The

    common grouping t r ends of non

    thermal ly a l t e r ed groundwaters of d i f f e r e n t types are shown to

    th e l e f t of the

    t r i a ng l e

    boundary. High l e v e l waters

    c lose

    to

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    17

    GROUNDWATER TYPES

    A. Unconfined lower elevation

    B.

    High

    elevation and

    dike impounded

    C. More direct precipitation

    D. Sedimentary. alluvial

    .....

    ,.

    :::>

    .

    V

    w

    A

    --

    ..............

    C>

    ,.

    I

    \

    \

    :E

    Y

    r

    1 1 ,

    C>

    .

    . .

    0

    ....

    =[

    ....

    v.p

    /

    STREAM \

    / --

    ; e- 1

    \

    I

    I

    I

    I

    I

    \

    GRE TER FRESH

    - GROUNDWATER

    LOG CHLORIDE

    Fig.

    2. Character is t ics

    of

    Cl/Mg

    ra t ios of

    dif ferent

    w ater ty pes and of

    groundwaters

    in

    Hawaii.

    The t r iangle

    out l ines

    the

    broad

    parameters

    for

    Hawaii

    conditions. The common groupings

    of

    non-thermal

    water to

    the l e f t

    of the t r iangle are denoted

    by A B C

    and

    A lower

    elevat ion

    uncon

    fined groundwater and basal

    groundwater;

    B

    high

    elevat ion,

    largely

    dike-impounded groundwater; C shallow groundwater, usually

    character

    ized

    by high recharge, and commonly occurring

    on

    windward sides of is -

    lands;

    D

    groundwater in sedimentary aquifers

    usually

    shallow and

    basal groundwater

    with

    sa l ine

    water mixing.

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    18

    t h e i r

    p r e c i p i t a t i on

    source

    tend

    to f a l l a long , or above , th e

    l i ne between th e Cl/Mg r a t i o s of seawa te r and

    stream

    wate r .

    Sedimentary aqu i f e r waters have r a t i o s t h a t f a l l between t h i s

    upper

    l i ne

    and th e Cl/Mg r a t i o l i ne of

    seawate r ;

    t h i s r e l a t i v e

    disp lacem ent to the

    r i gh t

    i nd i ca t e s

    a

    n on- the rma l )

    l o s s

    of

    to c lay mine r a l s . Waters with

    Cl/Mg r a tio s f a ll in g

    to

    the

    r i gh t of th e seaw ater

    r a t i o

    l i ne

    i.e. Cl/Mg

    15

    a re

    co nsid ered to

    be

    anomalous.

    In gene r a l ,

    the h igh e r the r a t i o ,

    the

    g r e a t e r

    i s

    th e

    thermal

    e f f e c t i nd i ca t ed . The degree of

    disp lacement towards seawater

    approx imates th e amount of

    seawater mixing

    based

    on

    ch lo r ide con t en t ) .

    The

    degree of

    disp lacement

    to

    th e l e f t of the t r i ang l e

    i.e.

    dec rea s ing

    ch lo r ide )

    i nd i ca t e s

    r e l a t i v e amounts of f r e sh groundwater

    m ixing . H igh ly anomalous r a t i o s in low t empera tu re ground

    wate r s t h a t p lo t near the ex trem e b ottom

    of

    th e t r i a ng l e

    or po in t s

    t h a t p lo t

    to th e

    r i gh t

    of

    th e t r i ang l e have

    been

    found

    to

    i nd i c a t e

    er roneous

    da t a .

    Erroneous

    concen t ra

    t i ons were

    found

    in

    some

    of th e o ld er a na ly se s; in some of

    t he se cases the wel l s

    were

    resampled and rea na ly ze d fo r

    Mg

    The

    r e ca l cu l a t ed Cl/Mg r a t i o

    fo l lows

    th e

    t yp i c a l

    pa t t e rn and

    p lo t s

    wi th in

    th e

    t r i ang l e .

    In

    cons ide r ing the d i s t r i bu t i on and th e number of po in t s

    in th e se

    t r i ang l e

    diagram s, th e d i s t r i bu t i on of

    the

    l o ca t i on

    of groundwater wel l s

    F ig .

    4, 6 , 8 , and 10 ) , and th e

    ava i l ab i l i t y of chemica l da ta must be

    cons ide red .

    Kauai F igure s

    and 4

    Kauai , th e o lde s t

    major

    i s l and

    in

    the

    Hawaiian cha in ,

    i s

    a

    low t empera tu re env i ronment .

    The

    Cl/Mg r a t i o of ground

    water

    l a rge l y approx imates t h a t of

    s t ream wate r ,

    i nd i ca t i ng

    tha t

    it i s l a rge ly

    unconfined or

    dike- impounded

    groundwater

    con ta in ing an apprec iab le amount of wate r

    from

    sedimentary

    and bas a l aqu i f e r s . Both of t he se

    groundwaters

    have va ry ing

    degrees of seawa te r mixing .

    Many

    of

    the Si02-anomalous

    groundwaters

    on the i s l and

    a re

    found

    with in

    sed iments and probab ly show some

    r e c i r cu l a t i on

    concen t r a t i on

    of d i s so lved s i l i c a . The

    one

    Cl/Mg

    anomaly i s

    cons ide red

    due

    to

    a

    spur ious ly

    low

    ana ly s i s .

    Molokai

    F igure s

    5 and

    6

    Few Si02- t empera tu re

    anomal ies

    occur

    on

    Molokai

    and

    of

    t he se only two have Cl/Mg anomal ies .

    Both

    a re of low order .

    Most wel l s pene t r a t e sedimentary or

    b asa l a qu ife rs

    and

    some

    show s a l i ne

    wate r

    mixing . Well

    1011-01

    in

    the

    w es t , w ith a

    r epor ted

    water

    tempera ture of 33 .9C, has a low Cl/Mg r a t i o

    7 . 3 ) .

    This

    wel l

    i s

    a pp ar en tly w i th in an a rea

    as soc i a t ed with

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    2000

    I

    /

    1000

    KAUAI

    500

    / ;1;

    /

    /

    /

    I Mg

    15 0

    l M g

    S 11.

    1

    E

    50

    )

    w

    Z

    )

    1

    TtU::A

    IC

    5 0

    /

    /

    /

    ?

    1

    J

    _

    0 5

    0 0

    0

    0

    0

    0 0

    0

    0

    00

    v

    V )

    0

    0

    0 0

    0

    00

    V )

    0

    0

    0

    00

    V )

    0

    00

    N M

    CHLORIDE ppm

    Fig

    3 Log log

    t r iangle

    diagram

    of

    chloride and

    magnesium

    concentrations

    of

    groundwater for the island

    of

    Kauai

    A suspect

    rat io i s denoted by ? ; there

    are

    no Cl/Mg

    anomalies in

    these

    data

    I-

    1 0

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    2

    ---

    o

    o

    ---

    - - - ~ - - ~ - - - - -

    0

    / \

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    0 0

    0 0

    00

    00

    N M

    o 0

    o 0

    o 0

    U ) 0

    o

    0

    o 0

    U )

    0

    MOLOKAI

    o 0

    U ) 0

    A

    //

    /

    /

    /

    /

    /

    / 0

    /

    , / /

    /

    /

    /.

    /

    /

    /

    o

    vi

    A C l/Mg 1 2.0

    14 9

    Cl/Mg

    1.0

    50

    05

    1/ /

    I

    I I I I I I I I I

    o

    5.0

    500

    1000

    2000 I

    I I I I I I I

    I

    V

    W

    Z

    E

    CHLORIDE

    ppm)

    N

    I

    Fig

    5

    Log log t r iangle diagram of

    chloride and

    magnesium concentrations of ground-

    water for the island of Molokai

    Solid

    tr iangles indicate low order

    Cl/Mg anomalies

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    N

    N

    - \ -

    .

    \

    /

    ...-

    _ :

    -

    -

    4

    I

    1

    o

    I

    .

    \ ~ ~

    V _

    _ : ~ : : - - - : . : - , r - -

    _- - - - -

    CfJ2 ~ ~

    33 9

    21

    10

    20

    60

    N

    Well location (no chemistry)

    o

    Si0

    2

    or temperature anomalous

    +

    Low order

    CI/Mg

    anomaly

    12 -14.

    9)

    - \ Generalised

    outline

    of

    coastal lowland

    - :::: Approximate trend of

    rift

    zones

    15720 W

    15710

    15660

    15650

    Fig

    6

    Location

    of

    groundwater wells on th e

    island

    of Molokai i nc lud ing those having anomalous chemis-

    try and

    temperatures 30C

    wo

    low

    magnitude anomalous areas

    are enclosed in boxes

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    an anc i en t rift zone .

    The i s l a nd

    i s i nd i c a t ed

    to be

    gene ra l ly

    a low t empera tu re envi ronment

    which

    con t a in s l o c a l i z ed ,

    pos s ib ly

    sha l l ow ,

    low magni tude th erm al zo nes .

    Oahu

    F igu res

    and

    8

    A l a rge

    number

    of wel l s on

    Oahu

    a re w ith in , or

    pass

    t h rough ,

    th e

    sed imentary aqu i f e r . Many of

    th e se a re wi th -

    drawing

    wate r from th e

    ba s a l

    aqu i f e r

    u nd er ly in g th e i s l a nd .

    Of th e w el ls wi th

    anomalous

    Cl/Mg, 1749-18

    and 2054-03 a re

    co ns id ere d to

    have

    su spec t Mg va lue s . The o the r

    anomalous

    r a t i o s a re c on sid ere d r e a l

    and

    worthy o f

    f u r t h e r

    i nve s t i g a t i on .

    Wells

    2409-07 and 2409-23

    in th e

    Lua lua l e i

    Val ley

    a re i nd i c a t ed

    by wate r chem is try to be s i gn i f i c a n t l y

    anomalous .

    A

    de t a i l e d

    i nv e s t i g a t i o n of

    t h i s

    a r e a ,

    wi th in

    which

    i s th e ca l de r a of

    th e

    anc i en t Waianae vo lcano ,

    was

    completed in

    1978

    Cox e t al

    1979 .

    These

    da t a

    s t rong ly

    sugges t

    the

    p resence

    of

    anomalous

    subsu r face

    hea t in

    the wes t , c en t r a l no r t h , sou th and

    pos s ib ly

    sou t h ea s t of Oahu. S ign i f i c an t l y e l eva t ed 30C+ groundwate r

    t empera tu res occur in

    s e v e r a l l o c a l i t i e s ,

    bu t

    do no t

    always

    co r r e l a t e wi th Cl/Mg r a t i o s .

    Maui F igu res and 10

    The d i s t r i bu t i on

    of Maui

    wel l s

    sugges t s t h a t

    a l a rge

    number a re wi th in th e sed imenta ry aqu i f e r . Some s a l i n e wate r

    i n f i l t r a t i o n i s a l so

    i n d i c a t ed . There

    a re

    very few wel l s

    p lo t t ed

    nea r

    th e r a t i o of

    s t ream

    w a te r, su gg es t in g

    t h a t

    only

    a

    l imi t ed

    amount

    of h igh

    e l eva t i on

    wate r

    i s

    p re s en t ,

    probab ly

    because most of

    th e

    w ells a re

    l oca t ed

    on

    th e

    leeward

    low

    r a i n f a l l

    s i de of th e

    i s l a nd .

    The high number of

    Si02

    anomal ies

    in

    the a l l u v i a l i s thmus between west and

    e a s t

    Maui

    i s due to r e c i r c u l a t i on and r e s i dence t ime e f f e c t s caused by

    ex t ens ive a g r i c u l t u r a l i r r i g a t i on in t h i s

    district Based on

    th e data a va il a b le , th is i s l a nd i s i nd i c a t ed to

    be

    a

    medium

    to

    low

    t empera tu re env i ronmen t , however , s e v e r a l

    r eg ions

    show

    de f i n i t e

    i nd i ca t i on s of anomalous

    subsu r face t h e rma l

    cond i t i on s .

    These a r e a s

    of i n t e r e s t

    a re in th e no r th ,

    no r t h -

    wes t ,

    and

    sou thwes t

    F igu re

    10 .

    Hawai i

    F igu res 11 and 12

    The p l o t of th e da t a shows a cons ide rab l e

    spread

    demon

    s t r a t i ng th e r ange of groundwate r

    env i ronmen t s .

    The l a rge

    number

    of

    wel l s p lo t t ed between s t ream

    and

    r a i nwa t e r r a t i o s

    most ly

    l oca t ed on

    th e

    windward

    s i d e ; both

    dike - impounded

    groundwaters

    and

    tho se w ith more d i r e c t p r e c i p i t a t i o n

    a re

    i nd i ca t ed .

    Sedimenta ry aqu i f e r s a re

    much

    more l im i t ed

    on

    Hawai i than on th e o th er i s la nd s

    and

    th e trend towards th e

    seawa te r

    r a t i o

    l i n e

    i s

    commonly

    due to

    t he rmal d i s rup t i on

    o f

    th e

    Ghyben-Henzberg

    l en s caused by anomalous ly high subsu r face

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    N

    -l>-

    00

    00

    00

    60

    NM

    o

    o

    o

    6

    o

    o

    o

    \I )

    o

    o

    o

    o

    o

    \I )

    OAHU

    o

    o

    \I )

    SEAWATER

    / I

    / I

    ,

    I

    /

    /

    /

    /

    .

    /

    /

    . I

    I

    .. .

    I

    .

    ,

    A

    )

    I

    I

    \A

    I

    I

    I

    I

    I

    o

    U

    -

    Cl Ma 15 0

    A

    Cl Ma

    12.0 - 1

    9

    Cl Ma 11.9

    2000

    i I I > I I j

    500

    0 5

    q

    1000

    5 0

    1

    50

    V

    w

    Z

    1

    1

    Q.

    CHLORIDE (ppm)

    Fig.

    7.

    Log log

    t r i ngl

    diagram

    of

    chloride and magnesium concentrat ions of

    groundwaters for

    the

    is land of Oahu A suspect

    r t io

    is denoted

    by ? ;

    s ol id t ri an g le s show

    low order

    Cl/Mg anomalies and sol id squares indicate

    h igh o rd er anoma li es .

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    15740

    5750

    Well

    location no

    chemistry)

    o Si0

    2

    or temperature anomalous

    w order CI/Mg anomaly 12-14.9)

    High order CI/Mg anomaly 15.0)

    /

    Generalised outline

    of

    coastal lowland

    ::::: Approximate

    trend of

    rift

    zones

    15760

    5810

    5820 W

    21

    20

    0

    -

    J

    }

    o

    0

    21

    ~

    ~ ~ I

    0

    e

    08

    0

    o.

    21

    4

    N

    Fig

    8

    Location

    of g roundwater

    wells on

    th e

    i s land of

    Oahu including

    those

    having anomalous

    chemistry

    and temperatures

    > 30C Si x l Mg anomalous

    areas enclosed

    in

    boxes are

    shown

    in order of

    impor-

    tance to

    geothermal studies

    The area

    denot ed 1

    covers t he c al de ra of

    th e

    Waianae volcano

    N

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    N

    o

    o

    o

    o

    o

    o

    o

    II

    o

    o

    o

    o

    o

    II

    o

    2

    o

    II

    .

    o

    ii i

    MAUl

    - < 9 > / _ _

    RAIN

    /

    Cl Mg

    15.0

    Cl Mg 12.0 - 1 .9

    Cl Mg

    SI1 9

    Q

    2000 I , J

    0 5

    5 0

    1

    500

    1000

    [

    Q.

    50

    c.I

    w

    Z

    CHLORIDE ppm

    Fig. 9.

    Log log

    t r i a n g l e

    diagram

    of th e chlor ide

    an d

    magnesium c o n c e n t ra t i o n s

    fo r th e is land of Maui.

    So l i d

    t ri a ng l es i n di c at e lo w order

    Cl/Mg

    anomalies

    s o l i d

    s q u ar es show high

    o rd e r

    anomalies.

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    I

    ~ /

    o

    \

    \

    \

    \

    \

    \

    \

    \

    \

    \

    /

    11//

    / /

    /

    o

    /

    /

    3

    Well location no chemistry)

    o Si 0

    2

    or temperature anomalous, ,

    + oworder C1/Mg anomaly

    12-14.9)

    High order

    CI Mg

    anomaly

    ~ 1 5 . 0

    / -

    Generalised outline of

    coastal lowland

    =Approximate trend of rift

    zones

    2

    20

    40

    20

    50

    20

    60

    N

    15640 15630

    15620

    15610

    15560 W

    Fig 1

    Location

    of groundwater

    wells

    on th e

    island

    of Maui i n clud ing tho se having anomalous chemistry

    and temperatures 3 C Five Cl/Mg anomalous

    areas

    enclosed in boxes

    are

    in order o f i mp or ta nc e to

    geothermal

    studies

    N

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    N

    00

    HAWAII

    SEAWATER

    / .

    /

    ,,

    /

    ,,/

    ,I

    ,, . .

    Cl/Mg 15

    CI/Mg12.0-14.9

    Cl/Mg 11 9

    1

    0 5

    Q

    0

    0

    0

    0

    0

    0 0 0

    vi

    \I

    0

    0

    0

    0

    0

    \I 0

    0

    0

    \I

    0

    0 -

    0 -

    CHLORIDE

    ppm)

    2000 I

    I

    I I I I . :::l

    500

    1000

    5

    1

    Q.

    :E 50

    ::>

    Vl

    w

    Z

    ( )

    :E 10

    Fig. 11. Log-log t r iangle

    of

    th e chloride and magnesium

    concentrat ions

    for

    th e

    is land of

    Hawaii.

    A suspect ra t io

    is denoted by ? . Solid t r iangles

    show

    low order Cl Mg

    anomalies and solid

    squares

    indicate

    high order anomalies.

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    20

    20

    N

    __I

    -

    \

    \\

    2

    /

    ,/

    ~ / /

    . /

    I I

    I I

    I I

    Well location no chemistry)

    o

    Si0

    2

    or temperature anomalous

    + low order CI/Mg anomaly 12-14.9)

    * High order CI/Mg

    anomaly 15)

    ...

    -

    , Generalised outline

    of

    coostal lowland

    -

    :::: Approximate trend

    of

    rift

    lones

    Fig 12 Location of groundwater wells on the is land of Hawaii

    including

    those having anomalous chemistry and temperatures 3 C

    Seven

    Cl/Mg

    anomalous areas enclosed in boxes are in order of importance to geo-

    thermal studies

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    3

    hea t on t h i s

    v o lc a ni ca ll y a c tiv e

    i s l a nd . The

    major i ty

    o f

    we l l s on Hawai i pene t r a t e ba sa l and low

    e l eva t i on

    d ike

    impounded

    aqu i f e r s .

    Seve r a l of t h e se aqu i f e r s show seawa te r

    mixing , which

    i s

    e s p e c i a l l y

    most s i g n i f i c a n t in those we l l s

    w i th in a reas

    of

    known

    high

    subsu r f a c e

    t empera tu res

    such

    as

    th e

    lower eas t ri t of

    Kilauea . The

    ove r a l l a i s t r i b u t i o n

    of po in t s

    i n d i c a t e s th e

    high

    t empera tu re

    envi ronment

    of

    the Big I s l and .

    CONCLUSIONS

    The Cl/Mg

    r a t i o

    o f g ro un dw ate rs i s a su i t ab l e geochemical

    i n d i c a t o r

    fo r

    r eg i ona l r econna i s sance

    assessment

    of a l a r ge

    volume

    of

    da ta in an envi ronment

    where

    much of the o the r

    wate r

    chemis t ry can be ambiguous We be l i e ve t h a t use of

    t h i s

    i nd i ca t o r has succes s fu l l y l oca t ed a rea s in which fo l low-up

    surveys

    a re w arra nte d.

    t

    f u r t h e r

    appears

    t h a t

    t h i s

    r a t i o

    can a lso be

    app l i ed

    in

    a s im i l a r

    way

    in

    o the r

    env i ronment s

    which

    posses s cha r a c t e r i s t i c s

    s im i l a r

    to

    Hawai i and which

    may

    have geo the rmal po t en t i a l

    bu t

    l im i t ed

    s ur fa ce m a n if es ta tio n s

    and a l a r ge

    volume

    o f g ro un dw ater

    chemis t ry .

    The use o f Cl/Mg

    on

    p r ev ious ly ex i s t i ng da ta s e t s , h o w v ~ r i s obvious ly

    no t

    i n f a l l i b l e and shou ld be r e l a t ed to

    o the r

    c r i t e r i a such as

    Si0

    concen t r a t i on

    and t empera tu re .

    Areas

    of

    appa ren t anomalous

    t h e rma l

    cond i t i on s

    have

    been

    de te rmined and a re i nd i c a t ed wi th in

    boxes

    in F igu res 4 , 6 ,

    8 ,

    l a , and

    12 and

    numbered

    in

    o rde r of p r i o r i t y fo r

    each

    i s l and . A

    more comprehensive

    a s se s smen t of the

    po t en t i a l

    of

    the se and o the r a reas on a s t a t e -w ide ba s i s i s presen ted in

    Thomas e t a la 1979 .

    An obvious f ea tu r e in t h i s type of

    a s se s smen t

    i s th e

    l im i t a t i o n placed

    upon it

    by

    the

    l o ca t i on

    of wel l s and th e

    ava i l ab i l i t y

    of chem ical da t a . t i s

    high ly

    l i k e ly th a t

    o the r

    anomalous a reas ex i s t in the

    s t a t e , which

    were

    no t

    r e f l e c t e d

    by

    t h i s s tudy

    because

    o f

    th e l a ck

    of we l l s

    in those a r e a s .

    KNOWLEDGMENTS

    We

    acknowledge

    th e a s s i s t a n c e of

    Dale

    Er landson

    and

    Les l i e Kaj iwara

    in

    th e

    compi la t ion

    and

    s t o r age

    o f

    th e wate r

    chemis t ry da t a . The coope ra t ion of th e

    s t a f f

    a t th e U.S .G.S .

    Honolulu Of f i c e i s

    app re c i a t ed .

    The work was ca r r i ed out

    under

    th e Depar tment o f Energy

    g r an t number

    DOE/ID/017l3 4

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