UNITED STATES DEPARTMENT OF THE INTERIOR
GEOLOGICAL SURVEY


FLORIDA DEPARTMENT OF NATURAL RESOURCES
published by BUREAU OF GEOLOGY


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SPECIFIC CONDUCTANCE OF WATER IN
FLORIDA STREAMS AND CANALS

By
Larry J. Slack and Matthew I. Kaufman

Prepared by
U.S. GEOLOGICAL SURVEY
in cooperation with
FLORIDA DEPARTMENT OF NATURAL RESOURCES
DIVISION OF INTERIOR RESOURCES
BUREAU OF GEOLOGY

Tallahassee
1973


INTRODUCTION

This report presents in concise form, information on the nature and
significance of the specific conductance of water and its area
distributions and variations with time and discharge. Specific
conductance is frequently used as an indicator of inorganic chemical
quality of a particular water body, and is useful for rapid estimation of
chloride and/or dissolved solids content.
Changes in environmental quality with time, pollution and/or
environmental degradation problems, and definition of the origin and
history of waters may be evaluated through the application of specific
conductance information.

NATURE AND SIGNIFICANCE OF SPECIFIC CONDUCTANCE

Specific conductance or "electric conductance," as it is sometimes
called, is a measure of the ability of a water to conduct an electrical
current. It is the reciprocal of the resistance in ohms measured between
opposite faces of a centimeter cube of an aqueous solution and is often
expressed in micromhos per centimeter at 25 degrees C (umhos/cm).
(For background discussions, see Hem, 1970, pp. 96-102.)
The ability of water to conduct an electrical current depends upon
the presence of ionic species (charged particles) in solution. As ionic
concentration increases, conductance of the solution increases. Because
of this relation and the fact that specific conductance determinations
are relatively inexpensive and can be quickly made, they are widely
used as an index of inorganic water quality. A common example of this
important relationship is a plot of specific conductance versus chloride
concentration. Often this curve is so well defined for a given stream
that chloride concentrations can be estimated accurately from
conductance data alone, as shown in figure 1.
The relation between ionic concentration and specific conductance is
linear in dilute solution. As a solution becomes more concentrated, the
relation deviates from a straight line as further increases in
concentration cause progressively smaller increases in specific
conductance. The slope of the straight-line part of the curve depends on
the dominant salts present in the solution and differs for natural waters
of different chemical type, as shown in figure 2. Since changes in
concentrations of the dominant ions would obscure changes in
concentrations of minor ions (such as fluoride), the specific
conductance versus minor ion relationship is unreliable and highly
variable.
The dissolved solids content of natural waters is commonly estimated
by multiplying the specific conductance by a factor ranging from 0.55
to 0.75. This factor is equivalent to the dissolved solids/ specific
conductance ratio. However, for Florida streams, this factor ranges
from 0.28 to 0.75. Because the relation between dissolved solids and
specific conductance is affected by the nature of the solids in solution,
this factor must be determined separately for each set of stream
conditions. For example, as shown in table 1, the Sopchoppy River
near Sopchoppy during high flow is mostly acidic swamp drainage and
has a dissolved solids/specific conductance ratio of 0.28. During low
flow the stream is predominantly alkaline ground water and has a
dissolved solids/specific conductance ratio of 0.53.
The chemical composition of a water depends on the water's origin
and history (Table 1). For many streams within the State, base flow is
essentially alkaline ground water-alkaline because of its passage
through a limestone aquifer. Industrial and municipal wastes,
agricultural drainage, swamp drainage, and tides also influence the
chemical composition and specific conductance of streams and canals.

TEMPORAL AND FLOW VARIATIONS OF
SPECIFIC CONDUCTANCE

In many instances the low specific conductance of water in a stream
during high flow reflects a dilution of the low streamnflow (ground
water) by storm runoff that is relatively free of dissolved solids and
therefore low in specific conductance. Figure 3 shows this effect for
four streams for which long-term data are available. The dilution effect
may be small for streams with regulated discharge. In other instances,
the immediate effect of a storm is the transporting of soluble minerals
to the stream, thereby simultaneously increasing the water's
conductance and discharge. Later, when storm runoff has less soluble
minerals available, the dilution effect appears.
Figure 4 shows the relation of specific conductance to discharge for
two canals in southeast Florida. A dilution effect is indicated for the
Hillsboro Canal discharging from Lake Okeechobee and for the
Tamiami Canal, whereas an opposite effect is suggested for the
Hillsboro Canal discharging to Lake Okeechobee (negative flow). This
increased specific conductance with increased negative flow is
associated with the backpumpage of drainage and irrigation waters from
agricultural lands into the canal, and then into Lake Okeechobee.
Long-term specific conductance data are useful in assessments of
changes in environmental quality with time and in providing needed
perprspective to short-term changes. Seasonal and long-term variation in
specific conductance for selected Florida streams and canals are
presented in figure 5A through 5C. Seasonal variations often relate to
changes in discharge and are a recurring phenomenon. Little long-term
change in water quality is evident for the Suwannee and Escambia
Rivers in north Florida (fig. 5A) and for the Tamiami Canal in
southeast Florida (fig. 5C). An upward trend in specific conductance is
suggested for the St. Johns and Alafia Rivers in central Florida (fig. 5B)
and the Hillsboro Canal in southeast Florida (fig. SC). For the latter,
this trend is suggested by the increasing minimum values.

AREAL DISTRIBUTION OF SPECIFIC CONDUCTANCE

According to Florida Statutes, 1969 (28-5.05), the specific
conductance shall not be increased more than 100 percent above
background levels or to a maximum level of 500 micromhos per
centimeter for streams considered to be fresh-water streams.
Recognizing that certain waters of the State, due to natural causes,
may not fall within desired or prescribed limitations, the Statutes
provide for exceptions upon presentation of good and sufficient
evidence.


DEPARTMENT OF NATURAL RESOURCES WATER QUALITY DATA STATIONS,
-- V BUREAU OF GEOLOGY FLORIDA STREAMS
----. .. U. S. GEOLOGICAL SURVEY 1940-68
S TARoSA .:: .. This public document was promulgated at a total -
cost of $420.00 or a per copy cost of $.28 for the Minimum of 4 yrs. bimonthly or at least complete
S' purpose of disseminating hydrologic data. analyses, all flow conditions.
WALTO N S Minimum of 2 vrs. pp--- -os anials..all flow co.nditons.
SOKALGADSEN O \inual. c.n to lour compicte .inaly)e. generally

1 -o 1 ,-o -"" .. iptr er.ls | I, l l ow ondlliorns.
.'. .oi.... oNA... -.. Dt' [ plIeci, co.rndujta.nce lalion. mmimum record 1
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The distribution of the maximum specific conductance observed in EXPL.NATON
Florida streams and canals is shown on the large map. (Lake ".. coc .... n
Okeechobee, the second largest fresh-water lake entirely within the" /* I :l' ''" Ii da -.dllibdlti *1 -1lmi I mum Ipe\ific
United States, is also includedd) The values tend to coincide with / : i' ':
periods of low flow. The regional distribution patterns are generalized ,, r "'' dulllac i ale, cI .jio t Floridi E tI.il -iSnd
(based on all available data through 1968) and local variations may be i omho pr enmeer
expected to exist. -i __op.' T C ,.lu.,. --
Water whose specific conductance is relatively low includes streams A K-' JO e1. -2 .- ., ~
in the Florida panhandle and north-central and central peninsular ,1' Le,".n ', :n 750 1- I 1
Florida. Water exhibiting relatively high values includes streams in the
St. Johns and MAla River basins in northeast and west-central / '25." 4<9 .. More th"n 1500
peninsular Florida, respectively, and most of southern peninsular 5,0. c.*,7 u9* .
Florida. The specific conductance of water from Lake Okeechobee falls gx 1 .o 0/c et- J ...'7<
between that of the relatively dilute inflow of the Kissinmmee River and f -- -
the relatively highly mineralized water characteristic of the agricultural I -
areas immediately to the southeast. S i

SELECTED REFERENCES' '

American Public Health Association and others 0 0 '/ "
1971 Standard methods for the examination of water and *
wastewater: New York, Am. Public Health Assoc., Inc., 13 S */ I o0 S,
ed., p. 38-42, 323-327.
Brown, Eugene 10004 ,
1970 (Skougstad, M.W., and Fishman, MJ.) Methods for I 0
collection n ad analysis of water samples for dissolved so -o
minerals and gases: U.S. Geol. Survey Techniques of Water 5a0
Resources Inves., Book 5, Chap. Al, 160 p. ,'
Hem, J.D. 0A'o ., A I
1970 Study and interpretation of the chemical characteristics of 3 400 STi -- '
natural water (Rev. ed): U.S. Geol. Survey Water- Supply 00 SA a

King, EJ. 7a"E0p0"er p0 i 0 o0 00 o -
1959 Qualitative analysis and electrolytic solutions: New York, C.LOr.DE ILLIGAMPERL.TER4 ~ _- ''" L. I .
Harcourt, Brace and World, Inc., 641 p. Figure 1.-Relation of chloride to sso -- --o' A f uRTI
Rainwater, F.H. specific conductance of composite A l i I' '' i < '
1960 (and Thatcher, L..)Method for collectionand analysis samples of the St. Johns River near Figure 2.-Relation of dissolved solids .
of water samples: U.S. Geol. Survey Water- Supply Paper Deland Florida. 1949 to specific conductance of four I- co .. -_. 9_ "I
1454,301 p. Florida streams of different chemical
U.S. Geological Survey type. 0 ,
Quality of surface waters of the United States, 1940-63: tJp I
U.S. Geol. Survey Water-Supply Paper 942, 950, 970, soo-n-------- i i i OSC --
1022, 1030, 1050, 1132, 1162, 1186, 1197, 1250, 1290, "/t ( -2 .. o.-e _ah v \ -
1350, 1400, 1450, 1520, 1571, 1641, 1741, 1881, 1941, t/ ..
1947. 0o0M
U.S. Geological Surv y *
Water resources data for Florida, pt. 2, Water quality a "
records 1964, 1965, 1966, 1967, 1968. Tallahassee, a -
Florida.o S2
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Figure 5A.-ong-term variations specific conductance of two north
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Figure 5B.-Long-term variations m specific conductance of two central
Florida streams.


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Figure 5C.-Long-term variations min specific conductance of two canals
in southeast Florida.


DISCHARGE, CUBE FEET PER SECOND
Figure 3.-Relation of specific conductance to discharge of four Florida streams.


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HIcLLSBOROCANAL BELOW HG3 4 NEAR SOUTH SAY

ImI114 1111 111


DISCHARGE, CUBIC FEET PER SECOND
Figure 4.-Relation of specific conductance to discharge of two canals in southeast Florid, I' r':.




Table 1. Chemical composition of waters of different spec lie conluciance
Stream Date Spec. Cond. Ratioa Ca Mg Na HCO, SO4 Ci Cr.e.-''
(umhos/cm) (mg/1) (mg/l) (mg/I) (mg/I (mg/ i.- 1 T e.


Sopchoppy River 08-14-67
nr Sopchoppy
Sopchoppy River 06-01-67
nr Sopchoppy
Suwannee River 12-21-67
at Branford
Sliver Springs 05-31-67
nr Ocala
Alafia River 06-03-68
at Lit hila


43 0.28 0.8 0.2


1.4 0 1.6 3 r' ,.: ...: :...T,,. a','.-.o.*


158 .53 26 2.7 2.3 86 0.4


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382 .45 44 8.9 5.4 154 18 0 C-COr.3 6 4 : .. ,...-.i.r.,, a.. a,-e

410 .57 66 8.6 5.6 206 30 I.* C ,Ce .C c .,oc s.. ,u,,r .. ,'

1,460 .40 84 14 56 4 180 78 CaSO4 Acidic Industrial waste, high
In phosphate


HIIIsboro Canal 07-02-68 1,720 .62 142 62 160 536 192 208 Mixed Agrict
below HGS-4
nr South Bay
St. Johns River 06-14-67 2,630 .54 117 39 343 130 141 700 NaCI Base
nr Cocoa salir
Everglades P-35 04-18-68 17,000 .59 278 348 2,950 314 720 5,400 NaCI Tidal
nr Homestead
aDissolved solids in milligrams per liter divided by specific conductance in micromhoS per centimeter.


860


ultural drainage


low, predominantly alkaline,
Ine ground water


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FLORIDA0 GEOLOGIC, SURVEY MA~P SERIEbi


MAP SERIES NO. 58


G 3931
.C1
No. 58
1973
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