journal of hydrology 14 (1971) 93-128; © north-holland...

Journal of Hydrology 14 (1971) 93-128; © North-Holland Publishing Co., Amsterdam

Not to be reproduced by photoprint or microfi lm without written permission f rom the publisher

S E A S O N A L F L U C T U A T I O N S IN T H E C H E M I S T R Y OF L I M E -

S T O N E S P R I N G S : A P O S S I B L E M E A N S F O R C H A R A C T E R I Z I N G

C A R B O N A T E A Q U I F E R S

EVAN T. SHUSTER

Department of Geology

and

WILLIAM B. WHITE

Department of Geochemistry and Mineralogy and Materials Research Laboratory, The Pennsylvania State University, University Park, Pennsylvania 16802, U.S.A.

Abstract: The dissolved carbonate species were analyzed in the waters of 14 carbonate springs in the Central Appalachians at 2-weck intervals during water year 1967-68. The springs were classified into diffuse-flow feeder-system types and conduit feeder-system types by hydrogeologic evidence. Comparison with the chemical parameters showed that the conduit springs were very variable in hardness throughout the year (coefficient of variation 10-24 %) whereas the diffuse flow springs had a rather constant hardness (coefficient of variation < 5 %). The variation in hardness is a better index of aquifer type than is hardness itself. Diffuse flow springs were, on the average near saturation; the conduit springs were undersaturated by factors of 2 to 5. Ca/Mg ratios were near unity for springs fed by dolomites or dolomite-related rocks; Ca/Mg ratios for limestone springs were 3-8 times higher. Aquifer systems of quite different flow mechanics can exist in the same hydrogeologic environment and can be distinguished by their chemical behavior.

Introduction

Carbonate aquifers often discharge their water through large-capacity

springs. In regions where the ground water lies at shallow depths and where

there is much localized recharge through sinking streams, the springs often

show considerable seasonal var ia t ion in their characteristics. Discharge may

vary over more than two orders of magnitude. The water may become turbid

dur ing periods of high runoff. Other springs show much smaller var iat ions;

their observable characteristics tend to remain constant in spite of f luctuations

in discharge.

Our purpose in this paper is to investigate the variations in the chemical

parameters of carbonate springs and to relate these variations to the type of

flow system in the carbonate aquifer. Our emphasis, therefore, is on the geo-

93

94 EVAN T. SHUSTER AND WILLIAM B. WHITE

chemistry of carbonate species and their variation with season. The study area is a limestone valley of Central Pennsylvania where many limestone springs of varying characteristics occur.

The precursor to this work was the study of three springs in Brush Valley 1) during the water year 1961-1962. There it was shown that the concentration of C a C O 3 in the ground water exhibited pronounced minima at times of high discharge. This was attributed to rapid flow-through times and sub- sequent lack of equilibrium between the water and the wall rock. The present data were collected mainly during the water year 1967-1968 from 14 springs of well established hydrogeology. These springs were selected to illustrate a wide variety of discharge ranges and behavior.

There has been much research on the geochemistry of carbonate waters in recent years. Most of this research such as that of Back and Hanshaw 2) is concerned with the spatial rather than the temporal variations in carbonate ground water. A few seasonal variation studies have been published. ZStl 3) was able to use chemical variations to establish the flow system in the Austrian alpine karst. Gams 4) followed the seasonal variations in water chemistry in the Slovene karst. Most pertinent to the present study is a series of papers by Pitty 5 s) which relate chemical variations in karst waters to flow-through time and to source area. The chemistry of some of the same area used for the present study has been discussed by Jacobson and Langmuir 9).

Models for carbonate aquifers

The gross behavior of a carbonate aquifer is determined in large part by the regional geology. The stratigraphic position of the carbonate rocks with respect to non-permeable capping or perching beds, and large structural features which control the position of recharge and discharge areas and the position of the carbonate rock outcrop determine the broad-scale picture 10,11). Within a particular hydrogeologic setting, ground water systems may consist of minor secondary porosity in the forms of fractures, joints, and bedding planes largely unmodified by solution12), or there may be a well integrated system of pipes and conduits. In a structurally and stratigraphically complex area such as Central Pennsylvania it is possible that both such flow systems could exist side by side.

Realizing the existence of a wide variety of possible flow systems, the two end members were assumed to be l) diffuse flow along joints, fractures, partings, bedding planes, and other small interconnected openings measured in centimeters or less and 2) flow through integrated conduit systems with water flowing, often turbulently, through solution passages measured in centimeters to meters (Fig. 1).

THE CHEMISTRY OF LIMESTONE SPRINGS 95

The diffuse flow tends to behave as laminar flow in a porous medium, although it is an extremely anisotropic medium. The water table is usually well defined because of the high degree of interconnectivity of the secondary porosity. The hydraulic conductivity is uniformly distributed throughout the rock. Natural discharge from such a system is usually through a large number of smaller springs and seeps, or a few large springs that exist because of stratigraphic or structural features.

On the other hand, the conduit system approximates flow through irregular pipes. Conduit systems result from the localization of ground water flow paths by solutional modification. Large flows take place in the conduit

DIFFUSE FLOW SYSTEM

Approaches "Darcy" Flow

Approaches Pipe Flow Fig. 1. The two end-member flow systems of carbonate aquifers.

while nearby rock may and usually does, have a very low hydraulic conductivity. Flows may be on the order of feet per second velocity and frequently are in a turbulent regime. The drainage pattern (as opposed to the water table concept) should be viewed as a network of solutional passages con- tributing flow to the major conduits. The discharge is usually through a single large spring. The gradients of the major pipes are typically low. The pipe system may contain intermittent air spaces. It carries a bed load of clastic sediment and even has a stream bed in many places which may prevent the water from coming in contact with the carbonate wall rock.

96 EVAN T. SHUSTER A N D W I L L I A M B. W H I T E

Geologic framework

The study area lies within the Nittany Arch, a major anticlinorium forming one of the broadest valleys of the folded Appalachians, Nittany Valley (Fig. 2). The valley trends generally N 40 ° E and is flanked by Bald Eagle Mountain, Tussey Mountain, and their extensions. Nittany Mountain and Brush Mountain are major synclinal ridges within the anticlinorium. Minor folded structures influence the topography between the bordering ridges. These structures are generally parallel to the axis of the anticlinorium, and are asymmetrical with the northwest limbs of the anticlines having steeper dips than the southeast limbs.

SPRING L O C A T I O N | C~'"

NITTANY VALLEY /__~ , .,~\ c,, CENTRAL PA. / . 0 ~ r~...a..~

STATE COLLEOE

i hSlN

3 o 6 i~ ts

SCALE IN MILES

EXPLANATION M A J O R S T R E A M S

" - " ~ - - S U R F A C E D R A I N A G E D I V I D E S

~"~',',',',',',',',',',';~ M O U N T A I N B O U N D A R I E S

. @ ~ M A J O R TOWNS

• S P R I N G S IN T H I S S T U D Y

Fig. 2. Sketch map of the study area with spring locations, adapted from "The Stream Map of Pennsylvania" by H. W. Higbee, 1965.

A few major thrust faults are present in the central part of the study area. The Birmingham fault in Buffalo Run valley parallel to Bald Eagle Mountain is a major overthrust with a stratigraphic displacement of about 5000 ft near Birmingham la).

At the northeast and, Nittany Valley splits into Brush Valley, an anticline,


Brush Mountain, a syncline, and Penns Valley, another anticlinal structure 14). No large faults have been mapped, although a series of thrust faults are suspected along the south flank of Nittany Mountain. No published maps on a quadrangle basis exist for Brush and Penns Valleys.

The topography at the study area demonstrates fairly well the underlying geology. The major ridges are topped by the Lower Silurian Tuscarora Quartzite. The slopes of the ridges are in the Upper Ordovician Juniata Formation (shales and sandstones), with the Oswego Sandstone forming secondary ridges, and the Reedsville Shale forming the lower slopes. The edges of the valleys are underlain by a series of Middle Ordovician limestones about 1200 ft thick. ~fhe limestones generally have moderate to steep dips into the mountains. The Lower Ordovician sequence of thick dolomites and somewhat thinner limestones with a total thickness of about 3200 ft is exposed in the center of Nittany Valley. The oldest important aquifer is the Gatesburg Formation made up of dolomites, sandy dolomites, and dolomitic sandstones15). The floors of Brush and Penns Valleys are underlain by the Middle Ordovician limestones.

The broad valley floor is a rolling, low relief surface at about 1100-1300 ft elevation into which has been incised the narrow secondary valleys of the present day streams. None of the major streams have extensive flood plains except Penns Creek near Spring Mills. Incised meanders are found in several places, especially where the streams traverse the structural highs of the valley floor. These structural highs are exhibited as valley uplands. Total relief within the Nittany Valley area is 200 to 400 ft, excluding the major ridges.

Ground water in the Nittany Valley area can usually be classified into two types according to the source of recharge. These types are allogenic waters, which result from precipitation on the clastic rocks of the major ridges, and percolation waters which result from precipitation directly on the carbonate rocks of the valley floor.

Allogenic waters reach the carbonate aquifers as down-slope seepage and as mountain runoff16). A generalized sequence of events has the water moving down the mountain slopes often as small streams. All surface waters sink at, or near, the limestone contact at the valley edges. Then, with the down-slope seepage, the water movement is lateral, or parallel to the mountains, toward the major surface streams and karst springs.

Precipitation falling on the valley floor reaches the carbonate aquifers by percolation through the weathered mantle. These waters then move under the influences of topography and lithology. The minor ridges and topographic highs on the valley floor act as the main recharge areas. Movement is generally toward the major surface streams which cross the valley floor. While there are no surface tributaries to the major streams, several large dry valleys


dissect the valley uplands. The dry valleys, which sometimes contain intermittent streams, act as ground water sinks and channel the ground waters toward the major surface streams. As a result these streams such as Spring Creek, Penns Creek, and Elk Creek tend to be gaining, or affluent, streams as they cross the valley uplands 15,17).

Description of the springs

Springs used in this study are located by latitude and longitude, and also by political and geographic position. The descriptions give the physical

Fig. 3.

OSWEGO

z ' - - - - Z "

REEDSVILLE . . . . . ~ - = IO00 o

~ - ANTES ~ - 200 < COBURN ~ 27'5

SALONA _£_,~ 175 NEALMON T ~ ~ __ 70 BENNER 180

MILROY 4 0 0

~ J ~ - TEA CREEK ~ 7 200

~. COFFEE RUN / I000

~) z AXEMANN 400

Z NITTANY 1200 o /

z

(13

STONEHENGE ~ 600

~ i 550- r,- GATESBURG i710

WARRIOR {250

LoE: FORMAT{ON .~ ~c_~ ~

Stratigraphic column for the Ordovician and Cambrian carbonate rocks that make up the central Pennsylvania carbonate aquifer.


appearance of the spring, the topographic setting, the geologic setting, the drainage basin where known, and some idea of the physical flow characteristics of the springs. These features, combined with any karst geomorphic features, were used as evidence for the type of flow system: diffuse flow or conduit flow. The stratigraphy for the spring descriptions was based on Rones 18), Landon17), and Clark15). Figure 3 lists in stratigraphic order the carbonate section used in this work. All units are Ordovician except the Gatesburg and Warrior Formations which are Cambrian in age.

A summary of the hydrogeologic evidence for spring feeder system behavior is given in Table 1. Most of the evidence is circumstantial and does not yield readily to quantification. The decision to classify a spring as a diffuse flow or conduit flow type was based on a careful evaluation of all field evidence. The topographic situations for the conduit springs are sketched in Figs. 4-8.

.- °~ ~ " ILLE ¢ V E $

' UN-NAMEO CAVe.. ~ ~ __~V..- ,, '~ ~ " ............. ) , , , . > , , ' -

Fig. 4. The Rock Spring area based on USGS Pine Grove Mills quadrangle.

Analytical methods

FIELD DATA

The springs were sampled on a two to three week interval. Temperature, pH, and bicarbonate ion concentration were measured in the field. Samples for analyses of calcium ion, magnesium ion, and total hardness were collected in polyethylene bottles. The samples were not acidified or diluted in any way. In all cases an attempt was made to obtain the sample as close to the spring opening as possible. This was not possible at Penns Cave and the samples were collected in a backwater, or eddy.

| 0 0 EVAN T. SHUSTER AND WILLIAM B. WHITE

Estimates of discharge were made, where possible, by one of two methods. At Penns Cave and Arch Spring changes in discharge were observed by measuring changes in stage relative to some local fixed point. Discharge at the other springs was estimated from the cross-sectional area of the channel

Fig. 5.

-.\ ~ ~ . - , ~ ~ - \ \~

.-! . . . . . . oL, \\'t',

The Tippery Cave Spring and Near-Tippery Spring Area based on USGS Spruce Creek quadrangle.

/ V A L L E Y \... U P L A N D S

/~TYTOON A CAVE ~ttll/i WATER-FILLED-.,~.,~' \ f ARCH SPRING CAVE ~ ( / (r l l~/ /

SINKHOLES "" ~lltl ARCH SPRING ~

LOWER ) SLOPE ! OF BRUSH.// MTN

-,% ,. ,~ ~ 1 ~ ~ ~ ~ / ~ ~

o I/2

SCALE IN MIL~

Fig. 6. The Arch Spring area based on USGS Spruce Creek quadrangle.

Spr

ing

Bed

rock

N

o.

TAB

LE 1

Sum

mar

y of

hyd

roge

olog

ic d

ata

for

spri

ngs

Top

ogra

phic

S

truc

tura

l S

itua

tion

C

ontr

ols

Juni

ata

Riv

er B

asin

Ass

ocia

ted

Kar

st F

eatu

res

Dis

char

ge

Cha

ract

eris

tics

1A

2A

Roc

k S

prin

g (c

ondu

it)

40°4

2"19

"N

77°5

8'04

"W

Spr

uce

Cre

ek

Spr

ing

(dif

fuse

) 40

°37'

02"N

78

°07"

54"W

Ben

ner

Ls.

Nit

tany

Do.

Sou

rce

of S

pruc

e S

trik

e-or

ient

ed

Cre

ek.

Hea

ds i

n co

ndui

t sm

all

vall

ey in

cise

d in

mai

n up

land

s

Bas

e of

hil

l at

co

ntac

t w

ith

floo

d pl

ain

Com

plex

fau

lt z

one.

L

ocat

ed b

etw

een

two

map

ped

over

thru

sts.

M

any

smal

ler

faul

ts.

Man

y sp

ring

s al

ong

line

atio

ns o

bser

vabl

e on

air

pho

togr

aphs

Lin

es o

f si

nks

abov

e sp

ring

. S

trea

m-

cont

aini

ng c

aves

nea

r-

by.

Rem

nant

s of

so

luti

on t

ubes

vis

ible

Non

e ob

serv

ed

2-7

cfs

in s

umm

er.

10-2

0 cf

s in

spr

ing.

M

ax.

disc

harg

e ob

- se

rved

75

cfs.

Hig

h fl

ows

typi

call

y tu

r-

bid.

Rap

id r

espo

nse

to s

torm

s

0.5-

4 cf

s N

ot t

urbi

d. F

airl

y ra

pid

stor

m r

espo

nse

:=

rt~

o = t-n

©

r-

O

Z

rrl

3A

Tip

pery

Cav

e S

prin

g (c

ondu

it)

40°3

4'08

" 78

°09'

24"

Ben

ner

Ls.

B

ase

of c

liff

at

head

of

vall

ey

Foo

t w

all

of Y

ello

w

Spr

ings

thr

ust.

Ver

ti-

cal

bedd

ing

Cav

es a

nd s

inks

nea

r-

by.

Sin

king

mou

ntai

n st

ream

s

1-8

cfs.

Occ

asio

nall

y tu

rbid

. O

nce

extr

emel

y m

uddy

Tab

le 1

(co

ntin

ued)

o t,

~

No

. S

prin

g B

edro

ck

To

po

gra

ph

ic

Sit

uati

on

Str

uctu

ral

Co

ntr

ols

Ass

oci

ated

K

arst

Fea

ture

s

Dis

char

ge

Cha

ract

eris

tics

4A

5A

6A

Nea

r-T

ippe

ry

Spr

ing

(con

duit

) 40

o34'

06"

78o0

9'24

"

Arc

h S

prin

g (c

ondu

it)

40°3

6'28

" 78

"12"

18"

Bir

min

gh

am

Cav

e S

prin

g (d

iffu

se)

40°4

8'25

" 78

° 11

'42"

Ben

ner

Ls.

Ben

ner

Ls.

(G

razi

er M

em)

Gat

esb

urg

Fm

.

Sid

e o

f ra

vine

5 f

eet

abo

ve

floo

d pl

ain.

75

ft

S. T

ippe

ry S

prin

g bu

t ap

par

entl

y n

ot

con

nec

ted

Nea

r Y

ello

w S

prin

gs

thru

st.

Bed

s o

ver

turn

- ed

an

d d

ip 4

0°S

E.

Maj

or

frac

ture

zo

ne

Sou

rce

of

Sin

king

C

reek

. M

ajo

r tr

un

k

drai

n w

ith

basi

n o

f ~

30 m

i 2. D

rain

s fr

om

val

ley

upla

nds

Co

nd

uit

str

ike-

orie

nt-

ed.

Spr

ing

loca

ted

on

in

ters

ecti

on o

f fr

ac-

ture

tra

ce w

ith

ou

t-

cro

p o

f B

enne

r L

s.

Min

or

cave

in

road

cu

t. P

erch

ed 3

0 ft

ab

ov

e ri

ver.

Ben

eath

sm

all

ravi

ne

Str

ike-

orie

nted

in 1

2 °

dipp

ing

beds

Pen

ns

Cre

ek B

asin

Lin

e o

f si

nks

alon

g ra

vine

. D

ry s

trea

m

beds

in

ravi

ne

1000

fee

t o

f co

nd

uit

ac

cess

ible

in T

y-

To

on

a C

ave.

Man

y

sink

s, s

ome

wit

h st

ream

s o

n b

ott

om

No

ne

obse

rved

1-4

cfs.

Som

etim

es

turb

id.

Fee

der

sys

tem

m

ay b

e co

nce

ntr

ated

fr

actu

res

10

~0

0 c

fs. W

ater

us

uall

y tu

rbed

. F

re-

quen

tly

mu

dd

y a

t hi

gh s

tage

0.00

3-0.

009

cfs.

W

ater

alw

ays

clea

r.

Str

eam

dep

osit

ing

trav

erti

ne o

n i

ts b

ed

.<

Z

-]

r~

ze

N

N

,-t

m

1B

Pen

ns C

ave

(con

duit

) 40

°52"

55"

77o3

6'45

"

Nea

lmo

nt

and

U

pp

er B

enn

er

Ls.

Sou

rce

of

Pen

ns

Cre

ek.

Wat

er r

ises

at

en

tran

ce to

P

enn

s C

ave,

flo

ws

thro

ug

h t

he c

ave

and

out

int

o th

e cr

eek.

Str

ike-

orie

nted

co

nd

uit

Pen

ns

Cav

e tr

un

k

chan

nel

its

elf.

Man

y

sink

s an

d s

inki

ng

stre

ams.

Int

erna

lly

dra

ined

bas

ins.

1-70

cfs

. Wat

er

clou

dy.

Fre

qu

entl

y

mu

dd

y,

som

etim

es

carr

ying

lea

ves

and

tw

igs.

Rap

id s

torm

re

spo

nse

2B

Spr

ing

Ban

k (c

ondu

it)

40o5

5'25

',

"7"7

°gQ

'NA

"

Nea

lmo

nt-

B

enne

r co

nta

ct

Bro

ad a

rea

of

spri

ngs

and

see

ps

in l

ow p

lace

in

vn

lla

v f

lnn

r

Str

on

g l

inea

tion

s,

som

e w

ith

offs

et b

eds

inte

rsec

t nea

r S

prin

g R

~n

k

Sin

king

str

eam

s. S

ink-

ho

les

spar

se

0.5

-4 c

fs. W

ater

so

met

imes

turb

id

3B

4B

5B

1C

Elk

Cre

ek R

ise

(con

duit

) 40

055'

35"

77 °2

8'08

"

Nea

lmo

nt-

S

alon

a co

nta

ct

Ben

ner

Ls.

(S

tove

r M

em.)

Ben

ner

Ls.

(S

tove

r M

em.)

Wea

ver

Spr

ing

(dif

fuse

) 40

o55"

41"

77o2

8"02

"

Spr

ingh

ouse

(d

iffu

se)

40o5

2"13

" 77

o27'

16 "

Big

Spr

ing

(dif

fuse

) 40

°54'

33 "

77

°26'

54"

Ax

eman

n L

s.

2C

Par

adis

e S

prin

g (M

ean

der

cut

-off

) 40

o52'

48"

77o4

7,41

-

3C

Th

om

pso

n

Spr

ing

(dif

fuse

) 40

°48'

08"

77o5

0'50

"

Gat

esb

urg

Fm

.

Ax

eman

n L

s.

Kn

ow

n t

o be

und

er-

gro

un

d r

ou

te o

f E

lk C

reek

, a

surf

ace

stre

am w

ith

30 m

i 2

drai

nage

bas

in.

No

r-

mal

ly d

ry s

urfa

ce

chan

nel

carr

ies

floo

d fl

ow

Sm

all

con

du

it i

n bl

uff

belo

w v

alle

y up

land

s. S

wam

py

ar

ea i

ndic

ates

gen

eral

g

rou

nd

wat

er d

isch

arge

Spr

ing

emer

ges

fro

m

smal

l ca

ve a

t ba

se

of

bluf

f at

lev

el

of

Pin

e C

reek

Str

ike-

orie

nted

un

der

- g

rou

nd

ch

ann

el

No

obv

ious

co

ntr

ols

Str

uctu

re c

ompl

ex.

Man

y m

ino

r fo

lds

and

sm

all

faul

ts

Spr

ing

Cre

ek B

asin

Spr

ing

rise

s th

rou

gh

Z

on

e o

f m

ajo

r th

rust

al

luvi

um o

n f

lood

fa

ults

pl

ain

of

Spr

ing

Cre

ek.

Cre

ek h

ere

deep

ly

inci

sed

belo

w v

alle

y up

land

s

On

ban

k o

f S

prin

g F

ract

ure

tra

ce c

ross

es

Cre

ek i

n de

eply

sp

ring

in

cise

d va

lley

Cen

ter

of

shal

low

V

alle

y ax

is p

aral

lel

vall

ey c

ur i

n va

lley

to

str

ike.

May

be

on

u

pla

nd

s fa

ult

Sm

all

cave

s an

d s

inks

gi

ve a

cces

s to

un

der

- g

rou

nd

str

eam

. M

any

si

nks

and

sin

king

st

ream

s

Few

sha

llow

sin

ks i

n va

lley

upl

ands

Up

lan

ds

con

tain

few

sm

all

inte

rnal

ly

dra

ined

dep

ress

ions

. N

o l

arge

sin

ks o

r si

nkin

g st

ream

s. P

er-

cola

tion

rec

harg

e on

ly

No

ne

obse

rved

No

ne

obse

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and the rate of flow. Flow estimates merely give an indication of the response of the aquifer to incremental recharges. No calculations involving discharge, such as flow-through times and denudation rates, were attempted. Tempera- tures were measured to nearest tenth of a degree Centigrade. The bulb of the thermometer was inserted into the flowing water as close to the actual spring opening as possible. The spring opening was considered to be the point, or points, where the water first emerged f rom the rocks. Thermal layering was observed in some of the larger springs. The bulb of the thermometer was placed below the top, warmer layer which was usually less than 2 inches thick.

pH was measured with a Beckman Model G pH Meter using a Fisher Hg glass electrode, - 5 to 80 °C and 0 to 11 pH. The reference electrode was a

X \ //" .~'% ~

O ~ %o °

N ~

,,4

0-" oe~ ,4' "-, Y ~ ' J / l l / ~ ,

\ ( t r , ) , q ~ - - L ~ \ ~ ~ I ,X ~ . . . .

,.. / I 1%% " ~ SHA R E R CAVE

SCALE IN MILES

Fig. 7. The Penns Cave area taken from USGS Centre Hall quadrangle.

Beckman calomel electrode. Fisher buffers of pH 7 and pH 9 were used as standards. The pH measurement is very sensitive to temperature differences between sample, buffer, and electrode. Errors as large as 0.3 p H unit were observed and there was a great problem with instrument drift. To alleviate these problems, the buffer was immersed in the spring until it cooled to spring temperature, and at the same time the electrode was chilled in a beaker of spring water. Measurements were then made at constant temperature using the pH of the buffer at spring temperature as a standardization point. Measurements made in this way were very reproducible and there was negligible instrument drift.


Bicarbonate ion concentration was determined by field titration using 0.02 N. HC1. The end point was determined potentiometrically using the pH meter. Although this method measures total alkalinity, other carbonate species were assumed to be negligible and the total analysis was assigned to HCO3. The precision of the analysis is _ 2 ppm.

S.ULLTO, Sl CAW

L ° ( " m " CREEK SE~ ~

14

~ X 4 . ~ \ . d' ,o

\ \ *.'

0 I / 2 I 2 3 I I I I

SCALE IN MtLES

Fig. 8. The Elk Creek and Spring Bank areas based on U S G S Mil lheim 15 minu te quadrangle .

LABORATORY ANALYSES

Analyses for calcium ion concentration and total hardness were made in the laboratory using a commercially available Schwarzenbach titration marketed by Hall Laboratories, Calgon Corporation. Hall Laboratories supplied the indicators, buffer solutions for calcium and total hardness determinations, and a standard EDTA titrating solution. Titrations were run in duplicate and results are considered accurate to within l ppm calcium or 1 ppm calcium carbonate. Total hardness was expressed as ppm calcium carbonate. Magnesium was found by difference and the results are considered good to + 2 ppm. The results were expressed as ppm Ca + +, ppm Mg ÷ +, and total hardness as ppm C a C O 3.

The titrations were usually run less than a week after sample collection.


Because bicarbonate ion concentration did not change significantly during the week's delay, it was assumed that no calcium or magnesium was lost by precipitation within the sample bottle.

Results

SEASONAL VARIATIONS IN W A T E R CHEMISTRY

The data are presented as a function of time (Figs. 9-26). Temperature data begin in January, 1967, and end in March, 1968. There are twenty-five temperature data points for springs in the Juniata River basin and twenty- three such points for the remaining springs. Total hardness, calcium ion, and magnesium ion data have the same number of points and span the same time intervals. Bicarbonate ion data are good from February, 1967, through January, 1968. Each spring in the Juniata basin had twenty data points, and each spring in the Penns Creek and Spring Creek basins had nineteen points.

Fig. 9.

.0 12

F.,-

n,- U.I n ~E LU I.-

._ / ; . ' \ - \

,, ...... r ' ~ : ~ ' ~ 7 " -~'~..-,,...-..;,, ,.",, ! '..:....-..-.-.. • ~ - " - 1 -.;~, ' ~ ' " "" ,, . / '

JAN I F I M I A I M I d I d I A I S I 0 I N I D I jANI F I M I A 67 68

ROCK S P R I N G

S P R U C E C R E E K S P R I N G

. . . . . . . . . . . T I P P E R Y C A V E S P R I N G

...................... N E A R T I P P E R Y S P R I N G

A R C H S P R I N G

. . . . . . . . B I R M I N G H A M CAVE S P R I N G

Seasonal variations in the temperatures of six springs in the Juniata River Basin.

The pH data were considered good from April, 1967, through February, 1968. There were eighteen data points for springs in the Juniata River basin and sixteen points for springs in the other two basins. When plotting the data, the successive points for an individual spring were connected by straight lines. In the final drafting the points themselves were not shown. The inflection points of the various lines indicate a data point in that position.

The temperature data give the best indication of the seasonal response of the springs. Some springs show no response. Others show continuous seasonal

T H E C H E M I S T R Y O F L I M E S T O N E S P R I N G S 107

Fig. 10.

12

o

n--

~ 8

r - - .

I I I i I I I I I I I I j A N r JAN F M A M d J A $ 0 N D F I M I A 67 68

P E N N S CAVE

S P R I N G B A N K

. . . . . . E L K C R E E K R I S E

. . . . . . . . . . W E A V E R S P R I N G

S P R I N G H O U S E

Seasonal variations in temperatures of five springs in the Penns Creek Basin.

Fig. 11.

P I0

w ~ 8

w ~ 6

/

A N I F I 67

A I M I j I j I A ~ S ~ 0 I N I D I jANI F---4-~--A" 68

BIG SPRING

. . . . . . . . . P A R A D I S E SPRING

....................... T H O M P S O N S P R I N G

Seasonal variations in temperatures of three springs in the Spring Creek Basin.

response having a high point in summer and a low point in winter. Still others drop to a low point in winter but only rise to a certain temperature level for

the summer months. The total hardness, bicarbonate ion concentration and calcium ion con-

centration data also show that some springs respond to the seasonal influences. These plots, however, show that the ion concentrations of all the springs vary somewhat. These fluctuations are probably based on storm flows. The values of these parameters vary greatly from one spring to another even when they do not show seasonal fluctuation in spite of the fact that all springs are in

similar geologic environments. The magnesium ion concentrations show very little seasonal responses.

Very close examination of the data shows a maximum increase of up to five

108

?ig . 12.

F i g . 13.

E V A N T. S H U S T E R A N D W I L L I A M B. W H I T E

2 2 0

~ - - - " 200 .~ :_ . ,,,.,~..

P, f ' ~ " ~ ~ ...4" " : " ' "~.- .- v 180 . "~ ' .." ..... : : . E - - . J . .-: ".. / i = ,6o ; ,.F~;'~ :"

\ - A /," ", ,',~, ,. ..', t./') '.. - , ' , ~. v ','..'... - "-. ." :

:-= \ - :. ! , , ' ,/:..~ , ! ' / " - - ~ • ~..... / , ....... U',: , o,=o . . . . . ' M " / \ ' " " . . . . . m \ / '~ \ -.- ', " , ' '" cz " , \ , :' - / , , , ~ ~\,.'/~,, , 'A ' , " ~- ,oo \\z"~.~,, ' ,- . :7" I I I \ ',.,V \. ' I ~,, <, "t,--:x',-,; / W \ / v I-- 80 ~ ,' ~ " "

6O ~JANI F I M I A I M I d I ,j I A I S I o I N I D I,.IANI F I M I 67 6 8

R O C K S P R I N G


. . . . . . . . . . T I P P E R Y C A V E S P R I N G

....................... N E A R T I P P E R Y S P R I N G

A R C H S P R I N G

B I R M I N G H A M C A V E S P R I N G

S e a s o n a l v a r i a t i o n s in t o t a l h a r d n e s s o f s ix s p r i n g s in t h e J u n i a t a R i v e r B a s i r

280

o (.9

8 E

t~ LU z

-r

-J

F-

:"'~ . % . A , , , . . ..-"(,. ,~ / ' . \

i / - / " ~ ' - - J " ' " ' ~ ' ~ " "~,. : ........ ;~...-.'

240 - \ . / v' ! V ........... .... i ~. - .....

• ... ......".....: ! j 220 " ' . . . . . . . . . . . . . . ~ . i . ~ ..

E . " " 200 - . . ~ :;

180 ~:

160 ~ . / ~ , . i / ~

I 00 "" " ' " , , ~ " " " /

80 "¢'

~JANi F I M I A I M I J I d i A I S I 0 I N I o IJANI F I M I A 67 6 8

P E N N S C A V E

S P R I N G B A N K

. . . . . . . . . . E L K C R E E K R I S E

....................... W E A V E R S P R I N G


S e a s o n a l v a r i a t i o n s in t o t a l h a r d n e s s o f f ive s p r i n g s in t h e P e n n s C r e e k B a s i n .


Fig. 14.

2 4 (

0 0 2 2 ( 8 E 2 0 0 Q.

u~ 180

bJ Z 160 O n,"

<Z 140 '1"

,-I <t 120 I-- O I--

... " . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . , . . . . .

~,NI F I M I A I M I d I d I A I S I O I N I D IJANI F t M I A 67 68

BIG S P R I N G

. . . . . . . . P A R A D I S E S P R I N G

...................... T H O M P S O N S P R I N G

Seasonal variations in total hardness of three springs in the Spring Creek Basin.

?'0

6C

5O

4 c

5C

2O

I0

... .... :11 • = • . .> . . ," , , ~.;, ,..,~ ,,

,,-, , , - . ~ . t ~ ._ . a , -= .~ . / - - '~" ~.x~--.~2~, ~'--.-~..,-¢''~-'. _..~- ;~ ~ . , , t ~ 7 ~ 4 / \ - v , < "~ _',~. ",. '~..,. s t ..> ,,q" \" / \ v ~ ' : x _ , / N " ~ "~k~,, \ . , , ; . / / V ~ v x

,JAN I F I M I A I M I d I d I A I S I 0 I N ~ D I jANI F I M I A 6 7 68

R O C K S P R I N G


. . . . . . . . . . . T I P P E R Y C A V E S P R I N G

...................... N E A R T I P P E R Y S P R I N G

A R C H S P R I N G


Fig. 15. Seasonal variations in calcium ion concentrations of six springs in the Juniata River Basin.

parts per million from the early spring low point for a few springs. Langguth 19) analyzed a karst spring and also found calcium fluctuations to be much greater than magnesium fluctuations.

All springs show some pH response to the increased biotic activity of the

warmer months. A general picture of the results shows that those springs with no seasonal

1 10 EVAN T. SHUSTER AND WILLIAM B. WHITE

tO0

90

80

~ 7o Q .

o 6 0

5O

Fig. 16.

40

30

./%\

:" \ . . . . . . ' " . . - . ..............

.... : .~ . " " . : .~ . , . . . .~:~" ' - , . I !.\ ii ......... -" ........ ',. / !7 /

= I I ~ I I I I I I I I I I I JAN F ,,. A M d a A S 0 N D I jANt F M A 67 68

P E N N S C A V E

S P R I N G B A N K

. . . . . . . . . . . E L K C R E E K R ISE

......................... W E A V E R S P R I N G


Seasonal variations in calcium ion cencentrations of five springs in the Penns Creek Basin.

60

50

o. 40 o .

v

,,~ so

2O

JAN ~ F 67

, o< . - ........ ~:~ ....... ~ : - - ,~ ~.~,~, .......... : ~ ~

M ~ A ~ M t j t j ~ A ~ S t 0 I N I D tJAN~ F t M ~ A 68

BIG SPRING

. . . . . . . . . . P A R A D I S E S P R I N G

................. T H O M P S O N S P R I N G

Fig. 17. Seasonal variations in calcium ion concentrations of three springs in the Spring Creek Basin

fluctuations of their temperatures have the higher total hardness and calcium ion concentrations as well as the higher bicarbonate ion concentrations and

pH.

DIURNAL VARIATIONS

A study was made to see if the springs responded to the diurnal activity of


30

20 E o .

IO

o

Fig. 18.

~ . . . - ' - ~ " - - ~ -':-----~. "~" • " - ' ~ ' - " ~ ' = - ~ " ~ . . ' ~ " ~ ' ~ Z - - -" V

"~'::..~. . . , .~ ~r'" . ' ~ ' ~ ' f ................ ":...~....::..-"~'~,,~.~.=='~

~JAN I F I M I A I M I d I d I A I $ ( 0 I N t D IJANI F I M I A 67 68

ROCK S P R I N G



....................... N E A R T I P P E R Y S P R I N G

A R C H S P R I N G


Seasonal var iat ions in m a g n e s i u m ion concent ra t ions o f six spr ings

in the Jun ia ta River Basin.

20[ ~ -

'JAN ~ I A I S I 0 I I

Fig. 19.

6'7 6 8

P E N N S CAVE

S P R I N G B A N K

. . . . . . . . . . E L K C R E E K R ISE

........................ W E A V E R S P R I N G


Seasonal var iat ions in m a g n e s i u m ion cencentra t ions o f five springs

in the Penns Creek Basin.

3O

=~ '° I | I I I I I I I I I I I I I JAN I F M A M J d A S 0 N O JAN F M A

I

67 68

- - BIG S P R I N G

. . . . . . . . . P A R A D I S E S P R I N G

.................... T H O M P S O N S P R I N G

Fig. 20. Seasonal var iat ions in m a g n e s i u m ion concent ra t ions o f three spr ings in the Spring Creek Basin.


the biota. Since the samples for the seasonal data were collected randomly during the daylight hours, any measurable response by the spring to these cyclic activities could invalidate the seasonal data. The study was made on the waters of two springs, Elk Creek Rise that showed marked seasonal chemical fluctuations and Thompson Spring that showed no seasonal chemical fluctuations.

Fig. 21.

240

220

200

180

E o. 160 ¢:).

140

0 120 "1-

I00

80

60

: . . . . .~

.~.-'-7- ~ - - / - - - - ~ - . _ r " ~ e ' - : -

/ . ,;\i i)i~ "

F t M t A~ M ~ j I d t A I S t 0 I N I D IdAN I F 68

ROCK SPRING

SPRUCE CREEK SPRING

. . . . . . . . . . . T IPPERY CAVE SPRING

...................... NEAR T I P P E R Y SPRING

ARCH SPRING

B I R M I N G H A M CAVE SPRING

Seasonal variations in bicarbonate ion concentrations of six springs in the Juniata River Basin.

The springs were sampled every two hours for a twenty-four hour period. Elk Creek Rise was sampled from 3:00 p.m. September 24, 1968, through 4: 30 p.m. September 25, and Thompson Spring was sampled from 11 : 00 p.m. September 26, 1968, through 7:30 p.m. September 27. The results show that there were no diurnal fluctuations by either spring significantly beyond the error of measurement. As a result, the fact that the seasonal data were collected at random hours during the day is irrelevant to the present use of the data. Any diurnal fluctuations in the carbonate chemistry appear to be below the error threshold of the present techniques.


300 -....

280

- . . , . . , , , 260 ..." ............ : ".,.

:." " , ,

- . , ~ , . . J ' . \ z 4 0 . . - .\..~.j.i :y

- ..... - . / E 200 -; Q .

I 160

,.o , ;t--",,,,.,,-"< ",,,. .i ",, I00 -~7~/ " . . . . ""

80

g I I A IM I d I d I A I S I 0 I N I D IJANIF 68

PENNS CAVE

SPRING BANK

. . . . . . . . . ELK CREEK RISE

......................... WEAVER SPRING

. . . . . . SPRINGHOUSE

Fig . 22. Seasonal va r i a t i ons in b i ca rbona te ion concen t ra t ions o f f i ve spr ings

in the Penns Creek Basin.

260

240

220

"E~ 200 O .

180

"1- 160

140

120

. . ,-".,. 1 . . . . . : ' : '~"~.. / . .~ " ' , . - - - . . . . . . . . , • - , .

1

v

I M I A t M l d I j i A I S 0 I N I D IjANI F 68

- - BIG SPRING

. . . . . . . . . . PARADISE SPRING

........................ THOMPSON SPRING

Fig. 23. Seasonal variations in bicarbonate ion concentrations of three springs in the Spring Creek Basin.


CHEMICAL VARIATIONS IN SURFACE WATERS

A secondary investigation was made to see how long it took the spring water to equilibrate with the atmospheric partial pressure of carbon dioxide and to determine the effect of this change on the equilibrium of the water with calcium carbonate. If the relative ratios of the dissolved species, especially

Fig. 24.

8 . 5 0

8.:50

8 .10

7.90

7.70

7.50

7.50

7.10

\ \ t . \

\ \

/ - . .~ .

/ i,. i

I ~ i

" \ \'\. f .L I,~,// \ ~,. I , : ~ . / ' - - ~ .

~"... ~- \ / - ~ , . . . . . . . "'4.-":"'"'~:.---;<:: _::~,.'...~.,,,.'~" , ' / ' - % : ' 4 " ~ " - ,~,- ,~:, ,~,, /,..'. ........... ....

( M I A I M I d Id IA I S I 0 IN tD IdANI F 68

ROCK SPRING

SPRUCE CREEK SPRING

. . . . . . . . . . . T I P P E R Y CAVE SPRING

..................... NEAR T I P P E R Y SPRING

ARCH S P R I N G


Seasonal variations in p H of six springs in the Juniata River Basin.

Fig. 25.

"I- Q.

7.80

7.60

7.40

7.20

7.00

6 . 8 0

I M

/

. . ~ . = . . v ' , ~ . ~ .......

~M I d I j I A S I O I N I D IjAN I 6 8

PENNS CAVE S P R I N G BANK

. . . . . . . . . . ELK CREEK R ISE

......................... W E A V E R SPRING S P R I N G H O U S E

SeasonalvariationsinpH offivespringsinthePennsCreek Basin.


pH and bicarbonate ion, change immediately upon the emergence of the water the location of the sampling point becomes critical to this study.

Elk Creek downstream from Elk Creek Rise was chosen. The rise produces between 90~ and 100~ of the flow of Elk Creek for most of the year. At the time of the study the spring water constituted 100~o of the creek's flow. Elk Creek receives no concentrated ground water or surface water for the 1200 m

8.40

8.20

8.00

-r" o. 7.80

7.60

7.40 I

M

.. F - ~ ~ . I.:

I A I M I d I d I A I S t O I N I D IjANI F 68

- - BIG SPRING

. . . . . . . . . P A R A D I S E SPRING

. . . . . . . . . . . . . . . . . . . . . . THOMPSON SPRING

Fig. 26. Seasonal variations in pH of three springs in the Spring Creek Basin.

between the spring and the input from Spring Bank. The contribution from Spring Bank is small compared to the total flow of Elk Creek. For the first 1200 m Elk Creek flows on a small flood plain underlain by Salona-Coburn Limestone. The creek does not appear to be in contact with the bedrock. The water flows in long, fairly quiet pools about 150 m long separated by beaver dams and short lengths of riffles below the dams for the first 1200 m. Then the creek enters the Millheim Narrows, flows over a bouldery bed, and is well aerated.

The creek was sampled at 200 m intervals from zero meters (the first sampling station) at Elk Creek Rise to 1200 m at the confluence with Spring Bank. One more sample was taken at 2000 m: The sampling stations generally coincided with the short sections of riffles.

The sampling was done on November 3, 1968. The results are given in Fig. 27. The temperature increases from the spring (sample taken at 3 : 45 p.m.) and then decreases to the last station (sample taken at 5:45 p.m.). This rise and fall of temperature follows rather closely the rise and fall of ambient air temperature.

The calcium ion concentration shows almost no change, less than two parts per million, over the 2000 m. The bicarbonate ion concentration also


shows no change over the first 1200 m, and only increases by six parts per

million over the whole 2000 m.

The pH, the parameter most sensitive to changes in the partial pressure of carbon dioxide, increases in a smooth curve and becomes stable at 800 m. At the same time the carbon dioxide partial pressure in the water, as calculated from the pH, bicarbonate ion concentration, and temperature drops

from log Pco2 = -2 .462 at the spring to -3 .217 at 800 m. The log Pco2 in the atmosphere is about - 3.5 z0).

Smith21) noticed a similar rise in pH from springs in the Bristol region,

U.K. The change in pH over the first 200 m at Elk Creek was 0.04 pH units, which is not very significant. This indicates that sampling the direct flow of water from a spring will give the same results as sampling the water imme-

diately before it emerges.

Discussion and interpretation

CHEMICAL EQUILIBRIA

The extent of equilibration of the spring waters with the carbonate wall

Fig. 27.

8.50

- r 8.oo

o . 7.5q

A E O. O. 12

v

0 124 0 "1-

1201

I f f

f ® f

E

4C O'~"'O" ~ ' ' = -

e l 10. ? ,o,)- / \

o.1 - . 9-8 F ~ ~ 0

I J I I I I ) L I I I 0 400 800 ,200 1600 2000

DISTANCE DOWNSTREAM FROM SPRING IN METERS

Chemical changes in the discharge of Elk Creek Rise measured downstream from the spring, November 3, 1968. Zero distance is the spring mouth.


rock was calculated. An estimate of the relative extent of equilibration was made as a saturation ratio, which is the ratio of the observed ion activity product to the equilibrium constant for both calcite and dolomite at the temperature of the spring water.

The pertinent chemical equations (see for examples Garrels and Christ 2°) are as follows:

C a C O 3 ~- Ca + + + C 0 3 - (la)

CaMg(CO3) 2 ~ Ca ++ + Mg ++ + 2 C O 3 - (lb)

CO 2 -1- H 2 0 ~- H2CO 3 (2)

H 2 C O 3 ~ H + + HCO3 (3)

H C 0 3 ~ H + + C 0 3 - (4)

H 2 0 ~-- H + + O H - - . (5)

The equilibrium constants for the reactions at twenty-five degrees Centi- grade are

Kca ~ = [Ca ++] [ C O 3 - ] = 10 - s ' ' ° * (6a)

KDo, = [Ca++] 4 [Mg++] 4 [ C O 3 - ] = 10 -8"5°* (6b)

Kco 2 - [ H z C O 3 ] = 10-1.47 ** (7) Pco2

K, [H +] [HCO3] = [ H 2 C 6 3 ] = l 0 - 6 3 s * * (8)

K2 = [H +] [ C O ; - ] = 10 - ' ° ' 33 .* (9) [HCO ]

KH20 = [H +] [ O H - ] = 10 -14.* (10)

To calculate the ion activity products (Kobs= [Ca + +] [ C O l - ] for calcite and Kob s--- [Ca + +]4 [Mg+ +]4 [CO3 - ] for dolomite) for the spring waters, the assumption was made that all of the carbonate species described by Eqs. (4) and (5) existed in solution in equilibrium with each other. This assumption permitted calculation of the ion product without determining by chemical analyses the activity of the carbonate ion, C O 3 - .

The saturation ratios for all samples were calculated from the raw data by a computer program written by Roger L. Jacobson at The Pennsylvania State University. Using the calcium ion, magnesium ion, and bicarbonate ion concentrations, pH, and temperature the program calculated the activities of

* Langmuir (personal communication, 1969). ** Garrels and Christ2°).


the various ions (al =71ml), the ion activity products (Kobs) for calcite and dolomite, and a partial pressure of carbon dioxide. This partial pressure of carbon dioxide is hypothetical. It refers to the gas phase that would be in equilibrium with the solution if the solution were in equilibrium with a gas phase.

The program also interpolated the appropriate equilibrium constants (Kca 1 and Koo0 from values given in five degree Centigrade intervals. The saturation ratio was defined as:

Saturation Ratio (Calcite) -- log (Kobs/Kcal) Saturation Ratio (Dolomite) = log (Kobs/KDo 0.

To convert the concentrations of the various ions to activities the activity coefficient (Yi) was calculated using the Debye-Hfickel equation

Az 4J - log~,i - 1 + diB~/i (11)

A and B are constants characteristic of the water at specified temperatures and pressures. The constant dl relates to the effective diameter of the specified ion in solution. The values for A, B, and di are taken from Garrels and Christ z0). The charge of the ion enters the equation as zi while I is the ionic strength.

The ionic strength was determined indirectly from the bicarbonate ion concentration. Using a total of twenty-two samples from twelve different springs the relationship between bicarbonate ion concentration as parts per million and specific conductance (micromhos) was established

SpC = 1.81 x H C O 3 . (12)

The specific conductance for all samples taken in the seasonal study was calculated and used in Eq. (13) (Jacobson and Langmuirg)).

I = 1.88 × 10-SSpC. (13)

This gives the value of I used in the Debye-H/ickel equation.

CALCITE SATURATION RATIOS

One product of the calculations is the saturation ratio. These, plotted as a function of time in the same manner as the data figures, are given in Figs. 28-30. Zero on the ordinate represents equilibrium between water and wall rock. Positive values indicate supersaturation and negative values indicate undersaturation.

After considering all errors inherent in the analyses, the relationships of

THE C H E M I S T R Y OF L I M E S T O N E S P R I N G S l 19

the various waters to equilibrium are still valid. The variable most liable to measurement errors, and also the most significant in the calculations, is pH. A change in pH of 0.04 pH units (plus or minus) changes the saturation ratio by 0.04 in the same direction (plus or minus). Similarly a pH change of 0.1 pH units changes the saturation ratio by 0.1.

Fig. 28.

8

3¢

g

0 I.-

Z 0 I,,-

I--

o3

+ 1.00

- I . 0 0

-2 ,00

-'--,. A . . _ / /

.. . . . i:- . ; : ~ ? 7 """ " ' " ~ ' ~ ' ' ' % .... :.

I I I I I I I I I M A M d J A S 0 N D IjANI F 68

ROCK SPRING

SPRUCE CREEK SPRING

. . . . . . . . . . T I P P E R Y CAVE S P R I N G

..................... N E A R T I P P E R Y SPRING

ARCH S P R I N G


Seasonal variations in the calcite saturation ratio for six springs in the Juniata River Basin.

+1.00 8

~ 0

o I--

~ - 4 . 0 0

Z 0 p.

I,,," -2 .00

I--

r/)

, .,I .~^---. t r . L ~ - ~ _ ~

I A I M I d I d I A I S I 0 I N I D IdANI F 68

P E N N S CAVE

SPRING BANK

. . . . . . . . . . E L K CREEK RISE

........................ W E A V E R SPRING


Fig. 29. Seasonal variations in the calcite saturation ratio for five springs in the Penns Creek Basin.

120 EVAN T. SHUSTER AND W I L L I A M B. W H I T E

The saturation ratios for calcite of springs in the Juniata River Basin are given in Fig. 28. Only two springs are near saturation, Spruce Creek Spring and Birmingham Cave Spring. Both springs are fed by diffuse flow systems. Birmingham Cave Spring is known to be depositing travertine. It should be noted that both springs are undersaturated with respect to calcite for part of the year. Spruce Creek Spring was undersaturated for the four months of May through August. Its highest saturation ratios were in November and December.

Fig. 30.

v ~ . * 1.00

o v "

0

z - I . 00 0

I--

A I M I d I d J A I S I 0 I N I D IJANI F 6 8

B I G S P R I N G

. . . . . . . . . P A R A D I S E S P R I N G

. . . . . . . . . . . . . . . . . . . . . . . T H O M P S O N SPRING

Seasonal variations in the calcite saturation ratio for three springs in the Spring Creek Basin.

The other springs are associated with conduit flow systems. The waters of these springs are well below saturation at all times of the year and, therefore, are capable of dissolving rock at all times of the year. The relative positions of the springs, one above another, result from the different lengths of time the waters are in contact with carbonate rocks.

Saturation ratios with respect to calcite are given in Fig. 29 for springs in the Penns Creek basin. Weaver Spring and the Springhouse, Coburn, which are the only springs studied in this basin that were identified as having diffuse flow feeder systems, are the only springs to reach saturation with respect to calcite. At no time were these springs highly supersaturated, but for five months during the sampling period they were undersaturated and their waters were capable of dissoNing wall rock.

The springs in this basin fed by conduit flow systems never reached saturation with respect to calcite during the study period. The relative positions of these three springs again indicate the residence time, which here also indicates the size of the conduit.

The saturation ratios with respect to calcite for the springs in the Spring


Creek basin are given in Fig. 30. The three springs studied are apparently in equilibrium with calcite during most of the year. All appear to be slightly undersaturated with respect to calcite during July and August and supersaturated in November and December. Big Spring and Thompson Spring are both supplied by diffuse flow systems. Paradise Spring may be fed by a diffuse flow system, but more likely it is surface water which has traveled a short distance underground. Both possibilities are compatible with the observed saturation ratios.

The raw data show pronounced minima during periods of spring high runoff. These minima are not strongly reflected in the saturation ratios. Although most springs are out of equilibrium with the wall rock, the amount by which they are undersaturated does not vary greatly during the year.

The results of the downstream sampling project at Elk Creek Rise give some idea of what happens to the spring waters as they equilibrate with atmospheric carbon dioxide. Fig. 31 shows that as the water loses carbon

.~ 1.00 o

o~ 0,50 o

~:~ -0 .50 n~

Z I I I I I I l I f C) 400 800 1200 1600 2000

< D I S T A N C E D O W N S T R E A M F R O M S P R I N G I N M E T E R S cir. 22 I---

t~o

Fig. 31. Changes in calcite saturation downstream from Elk Creek Rise, November 3, 1968.

dioxide it approaches saturation with respect to calcite and becomes supersaturated. The saturation ratio remained constant from the 800 m sampling point through 2000 m at which point the water was in equilibrium with atmospheric carbon dioxide. This indicates that ground waters which may be capable of dissolving carbonate rock, rapidly equilibrate with the atmosphere and lose their aggressiveness. This is possible even if the waters are very undersaturated as they reach the surface. The supersaturation, however, is not sufficient to nucleate calcium carbonate since no travertine deposits were observed in the creek bed and the calcium ion and bicarbonate ion concentrations remained constant over the 2000 m sampled.


DOLOMITE SATURATION RATIOS

The seasonal variation in the saturation ratio with respect to dolomite is shown for the three drainage basins in Figs. 32-34. For most part the dolomite saturation curve simply mimics the calcite saturation ratio curve. In general waters which are undersaturated with respect to calcite are also under-

Fig. 32.

"~ + 1.00 v

v ~ 0

0 F- ~ - I . 0 0

Z 0

~ - 2 . 0 0

I--

~ . / ~ , . . j -

...................... S - , ~ : . ~ . . . ' . . , . ~

" ...... ~- - - "2_tv3 ' " . . . . " - , t " . . . ; :~

M I A MI d I d I A I S I 0 I~N D dAN I 68

ROCK S P R I N G



..................... N E A R T I P P E R Y S P R I N G

A R C H S P R I N G

. . . . . . . B I R M I N G H A M CAVE S P R I N G

Seasonal variations in the dolomite saturation ratio for six springs

in the Juniata River Basin.

A ¸ " ~ ÷1.00

2 ~ 0

0 I--

t~ - I .00

Z 0 I--

-2.00

I- <~ ~o

~.,.y- .-3...L---.,,,. / ............. ~ . ~ . . = • ¢ . . , > ~ j < ~ . . . . . l ~ c _ ~ / -

I M I J I d I A I S I 0 I N I D IdANI F 68

- - P E N N S CAVE

S P R I N G BANK

. . . . . . . . . . ELK C R E E K RISE

........................ W E A V E R S P R I N G S P R I N G H O U S E

Fig. 33. Seasonal variations in the dolomite saturation ratio for five springs in the Penns Creek Basin


Fig. 34.

0 o

41.00

0

n . .

z -I .00 O I . -

M I A I M I d I d I A I s I 0 I N I D I jANI F 68

BIG S P R I N G I - - . . . . . . . . . P A R A D I S E S P R I N G

oo ....................... T H O M P S O N S P R I N G

S e a s o n a l v a r i a t i o n s i n t he d o l o m i t e s a t u r a t i o n r a t i o f o r t h r e e s p r i n g s

in the Spring Creek Basin.

saturated with respect to dolomite but the dolomite tends to be farther from equilibrium than calcite. Certain of the constant-chemistry springs are seen to be saturated with respect to both calcite and dolomite.

APPLICATION OF CHEMICAL DATA TO AQUIFER CHARACTERIZATION

The spectra of the seasonal series shown in the figures show in a qualitative way the different responses of the springs. All springs in this study were in much the same hydrogeologic environment and the diversity of the seasonal series is perhaps surprising. Temperature and total hardness seem to be the most valuable of the various parameters for direct application. The springs which can be shown by field evidence to be fed by conduit systems show pronounced minima during periods of high flow. This should be related to rapid flow-through times. The water under high flow conditions moves through the system before it has time to equilibrate with the wall rock. The saturation ratio curves confirm this and further indicate that such waters are rarely or never in equilibrium with the bedrock.

An overview of the spring data can be obtained by averaging in various ways the individual data points. These averages are shown in Table 2. The springs have been grouped into a diffuse flow set as determined from field evidence described earlier and a conduit flow set. The existence of conduits can be demonstrated positively in the field by the presence of various karst features, caves, and sinkholes. The diffuse flow set is determined largely by the negative evidence of the absence of such features. Classification of a spring into the diffuse flow set is obviously on much shakier ground than classification into the conduit flow set. Paradise spring may be a meander

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bend cutoffon a major surface stream and has therefore been listed separately. The mean total hardness expressed as ppm CaCO3 shows that the diffuse

flow springs contain more dissolved carbonate than do the conduit flow springs but is not particularly informative, since the ranges of data appear to overlap slightly. Comparing the hardness with other data in the table, it seems clear that one should not use hardness itself as a criterion of aquifer behavior.

The fluctuations in the seasonal spectra shown in the figures have been reduced to a single number for each spring by calculating the coefficient of variation of the total hardness (assumed to be the most significant chemical variable). The coefficient of variation, C V= a/~ x 100 where ~r is the standard deviation and )7 is the arithmetic mean. With one exception to be discussed later, the coefficient of variation of the springs classified as diffuse flow types are very low, less than 5~. The variation of the conduit flow springs is much larger. This parameter, determinable from the seasonal series, seems to be a useful index of aquifer type.

Within the seasonal series for a given spring, the ratio of activity (Ca + +)/activity (Mg + +) varies little, thus confirming the observation that the saturation ratio of dolomite mimics the saturation ratio spectrum of calcite. The average Ca + +/Mg + + ratios shown in Table 2 show considerable differences between springs. The two springs whose orifices are in dolomite (although the rocks through which the feeder system passes are unknown) have a ratio near unity. The springs in the upper Ordovician carbonate section, the Champlainian limestones, show high ratios indicating, according to Jacobson and Langmuir 9), that much of the recharge is through limestones. Big Spring and Thompson Spring are in the Axemann limestone but the Axemann is sandwiched between two dolomites (Fig. 3) and this is clearly reflected in the Ca + +/Mg + + ratio. The high calcium content of the conduit- fed springs also reinforces the conclusions of Rauch and White 22) that most of the large cavity porosity is localized in the Champlainian limestones and that there is little cavernous development in the dolomites.

The calculated carbon dioxide pressures show remarkably little systematic variation. All waters seem to contain about an order of magnitude more CO/ than they would if they were in equilibrium with the atmosphere (Pco2=10-3"5). The spring exhibiting the lowest CO2 partial pressure is Big Spring, a diffuse flow system with an unknown recharge area. The spring with the highest CO z pressure is also a diffuse flow spring. It appears that the CO2 pressures are more related to source areas of recharge than to the flow characteristics of the aquifer.

The diffuse flow springs are near saturation, although with respect to quite different CO2 pressures and thus with quite different total hardnesses.


The conduit springs are all highly undersaturated. The flow-through time in these open systems is sufficiently small that water runs through the aquifer and out again before equilibrium is attained. The undersaturation at the spring mouth shows that such conduit water is always capable of dissolving more limestone and that no special mechanism (such as B6gli's 2a) mischungskorrosion) is needed to explain development of solution cavities far from sources of water input.

Two neighboring springs, Tippery and Near-Tippery have quite different chemical characteristics, thus indicating separate sources and little mixing of water above the spring orifices. Both springs are at the same elevation and are only 75 yards apart but are apparently the downstream termini of different conduit systems.

Weaver Spring is interesting in that it is out of context with the other diffuse flow springs. It has a very high hardness, but the hardness shows a considerable variation. Although the CO2 partial pressure is the highest value of any calculated, the water is still somewhat undersaturated compared with the other diffuse flow springs. Weaver Spring flows from isolated rem- nants of valley uplands. The orifice is above nearby creeks and the immediate area does not receive mountain runoff. Most recharge must be received from infiltration through the soil and this perhaps explains the high hardness and high CO2 pressure. It is tempting to argue that this system is in a transition state between a diffuse flow system and a conduit system and that the enlarged solution openings are manifesting themselves in the chemical parameters before surface expressions become obvious.

Acknowledgements

This research was supported by the Mineral Conservation Section, The Pennsylvania State University. We are grateful to Roger Jacobson for the use of his computer program, to Professor Donald Langmuir for discussions and comments on the carbonate geochemistry, and to Henry Rauch for identification of the rock units.

References

1) W.B. White and J. A. Stellmack, Seasonal fluctuations in the chemistry of karst ground water. Proc. of the 4th Internat. Cong. of Speleol. in Yugoslavia, Ljublana, vol. 3 (1968) 261-267

2) W. Back and B. B. Hanshaw, Comparison of chemical hydrogeology of the carbonate peninsulas of Florida and Yucatan. J. Hydrology In (1970) 330-368

3) J. Z6tl, Die Hydrographie des nordostalpinen Karstes. Steirische Beitr/ige Hydrogeo- logie, (1960/1961) No. 2, 183 pp.


4) I. Gams, Factors and dynamics of corrosion of the carbonate rocks in the Dinaric and Alpine karst of Slovenia (Yugoslavia). Geografski Vestnik 38 (1966) 11-68

5) A. F. Pitty, The estimation of discharge from a karst rising by natural salt dilution. J. Hydrol. 4 (1966a) 63-69

6) A. F. Pitty, An approach to the study of karst water. Univ. of Hull, Occasional Papers in Geography No. 5 (1966b) 70 pp.

7) A. F. Pitty, Calcium carbonate content of karst water in relation to flow-through time. Nature 217 (1968a) 939-940

8) A. F. Pitty, Some features of calcium hardness fluctuations in two karst streams and their possible value in geohydrological studies. J. Hydrol. 6 (1968b) 202-208

9) R. L. Jacobson and D. Langmuir, The chemical history of some spring waters in carbonate rocks. Ground Water 8 (1970) No. 3

10) V. T. Stringfield and H. E. LeGrand, Hydrology of carbonate rock terrains - a review with special reference to the United States. J. Hydrol. 8 (1969) 349-417

11) W. B. White, Conceptual models for carbonate aquifers. Ground Water 7, No. 3 (1969) 15-21

12) L. H. Lattman and R. R. Parizek, Relationship between fracture traces and the occurrence of ground water in carbonate rocks. J. Hydrology 2 (1964) 73-91

13) C. Butts, F. M. Swartz and B. Willard, Tyrone quadrangle, geology and mineral resources. Pa. Geol. Survey, 4th Series, Atlas of Pennsylvania No. 96 (1939) 118 pp.

14) C. Butts and E. S. Moore, Geology and mineral resources of the Bellefonte quadrangle, Pennsylvania. U. S. Geol. Survey Bull. 855 (1936) 79-82

15) J. H. Clark, The geology of the Ordovician carbonate formations in the State College, Pennsylvania, area and their relationships to the general occurrence and movement of ground water. The Pa. State Univ. Masters Thesis (1965) 114 pp.

16) L. F. Konikow, Mountain runoff and its relation to precipitation, ground water, and recharge to the carbonate aquifers of Nittany Valley, Pennsylvania. The Pa. State Univ. Masters Thesis (1969) 128 pp.

17) R. A. Landon, The geology of the Gatesburg Formation in the Bellefonte quadrangle, Pennsylvania, and its relationship to the general occurrence and movement of ground water. The Pa. State Univ. Masters Thesis (1963) 88 pp.

18) M. Rones, A litho-stratigraphic, petrographic and chemical investigation of the lower Middle Ordovician carbonate rocks in central Pennsylvania. The Pa. State Univ. Ph .D . Thesis, vol. 1 (1955) 186 pp.

19) H. R. Langguth, On the local and regional mineralization of karst ground waters and their variations from Devonian limestones of the Rhenish Shiefergebirge (Western Germany). In: Hydrology of Fractured Rocks. Internat. Assoc. of Sci. Hydrology, Proc. of the Dubrovnik Symposium 2 (1967) 672-683

20) R. M. Garrels and C. L. Christ, Solutions, minerals, and equilibria (Harper and Row, New York 1965) 74-92

21) D. I. Smith, Some aspects of limestone solution in the Bristol region. Geograph. J. 131 (1965) 44-48

22) H. W. Rauch and W. B. White, Lithologic controls on the development of solution porosity in carbonate aquifers. Water Resources Res. 6 (1970) 1175-1192

23) A. BiSgli, Mischungskorrosion - Ein Beitrag Zum Verkarstungs Problem. Erdkunde 18 (1964) 83-92

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