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UNITED STATES DEPARTMENT OF THE INTERIOR
FLORIDA DEPARTMENT OF NATURAL RESOURCES
published by BUREAU OF GEOLOGY
THICKNESS OF THE POTABLE-WATER ZONE
IN THE FLORIDAN AQUIFER
L. V. Causey and G. W. Leve
UNITED STATES GEOLOGICAL SURVEY
in cooperation with
FLORIDA DEPARTMENT OF ENVIRONMENTAL REGULATION
Bureau of Water Resources Management
The Floridan aquifer is one of the most productive
aquifers in the world and is one of the most valuable
natural resources in Florida. It supplies potable water to
tens of thousands of industrial, commercial, agricultural,
and domestic wells in the State and also the municipal
supplies for such urban areas as Tallahassee, Jackson-
ville, Ocala, Daytona Beach, Orlando, Gainesville, St.
Petersburg, and the Cape Kennedy area. Withdrawals
from the aquifer in these urban areas and in other areas
are increasing at a high rate due to the rapid increase in
population and industrial development. Thus, information
is needed by water managers and planners to aid them in
establishing practices for the conservation and utilization
of the water in this important aquifer. The purpose of this
report is to show graphically the approximate thickness of
the zone of potable water in the Floridan aquifer
throughout the State. Potable water, as referred to in this
report, meets the Environmental Protection Agency (Nat.
Acad. Sci., 1973) recommended limits of 250 mg/1
(milligrams per litre) of chloride and 250 mg/1 of sulfate
in public water-suppiy sources.
The Floridan aquifer is composed of limestone and
dolomite beds primarily of Eocene and Miocene age. In
northeastern Florida the aquifer also includes limestone
and dolomite beds of late Paleocene age (Leve, 1968). The
altitude of the top of the Floridan aquifer throughout the
State is shown in the inset map. The top of the aquifer
ranges from more than 100 feet (30 metres) above sea
level in the west-central and north-central parts of the
State to more than 1,000 feet (300 metres) below sea level
in the southeastern and southwestern parts. The bottom
of the Eocene limestone and Paleocene dolomite beds
ranges from 1,000 feet (300 metres) below sea level in
north-central Florida to about 4,000 feet (1,200 metres)
below sea level in the Florida Keys (Chen, 1965, p. 16, fig.
9). The Paleocene limestone and dolomite beds extend
downward from about 2,000 feet (600 metres) below sea
level to 2,500 feet (760 metres) below sea level in
northeastern Florida (Chen, 1965, p. 15, fig. 8). The lower
400 feet (120 metres) contains gypsum and only the
uppermost beds yield usable quantities of water.
The aquifer is at or near land surface in much of
west-central and north-central Florida. In the remainder
of the State it is confined by overlying relatively
impermeable beds of sandy clay, clayey sand, and clay,
which may be as much as 600 to 700 feet (180 to 210
metres) thick in southern Florida. Major recharge occurs
where the aquifer is at or near the surface or where
numerous lakes, ponds, and streams are hydraulically
connected to the aquifer. Recharge also occurs by
downward leakage through confining beds where the
water levels of the shallower aquifers are higher than the
potentiometric surface (water level) of the Floridan aquifer.
Rainfall entering the aquifer in the recharge areas
contains little or no dissolved mineral matter. As the
water moves down gradient through the aquifer it picks
up dissolved minerals because of the solvent effect of the
water on the rocks with which it comes in contact. The
quantity and type of dissolved mineral matter depends
upon the chemical and physical composition of the rocks;
the temperature, pressure, and duration of contact; and
the extent of mixing with mineralized water already
present in the aquifer. In Florida, this mineralized water
could be connate water that was trapped when the rocks
were deposited or sea water that entered the aquifer after
the rocks were deposited.
The type of mineralization in water in the aquifer
varies in different parts of the State: calcium-bicarbonate
water occurs in most of northern and central Florida,
calcium-sulfate water occurs in southwestern and south-
ern Florida, sodium-bicarbonate water occurs in extreme
western Florida, and sodium-chloride water occurs in
many of the coastal areas (Stringfield, 1966, p. 134-135).
The concentration of mineralization generally increases
with depth. Generally, if potable water is available in the
aquifer, it will be in the upper part.
The accompanying large map shows the approximate
thickness of the zone of potable water in the Floridan
aquifer in Florida. The map may also be used in
conjunction with other hydrologic data (transmissivity
and storage) to estimate the quantity of potable water
that may be withdrawn from wells in the aquifer in
various parts of the State, and in conjunction with data on
the altitude of the top of the Floridan aquifer (inset map),
to determine the approximate maximum depth to which
wells can be drilled to obtain potable water from the
The map was compiled principally from two hydro-
logic maps-depth to base of potable water in the Floridan
aquifer (Klein, 1975) and top of the Floridan artesian
aquifer (Vernon, 1973). Additional information was
obtained from basic data collected by the U.S Geological
Survey throughout the State and from numerous local
and regional investigations conducted by the Survey in
cooperation with local, State, and other Federal agencies.
The reports and data used to compile this map span a
period of about 15 years. Therefore, this generalized map
cannot be used to determine the exact thickness of potable
water in the aquifer at any specific location or at any
specific time. In preparing the map, no consideration was
given to seasonal or long-term changes in thickness or
local variations due to pumpage. In many areas in
northern and central Florida, and particularly along the
I 'r -- .
T -1 I'
coast, the thickness of the zone of potable water is affected
by the fluctuation of the potentiometric surface in
response to recharge and discharge. When the potentio-
metric surface (inset map, Healy, 1975) is lowered by a
decrease in recharge or an increase in discharge, highly
mineralized water moves either vertically upward from
the deeper parts of the aquifer or laterally into the zones
of potable water. For example, discharge by thousands of
irrigation wells in St. Johns, Putnam, and Flagler
Counties seasonally lowers the potentiometric surface in
the area and causes highly mineralized water to move
upward into the zone of reduced head (Bermes and others,
1963). This movement of mineralized water reduces the
thickness of the zone of potable water in the aquifer. As a
result, some wells that yield potable water during most of
the year yield nonpotable water during the crop-growing
season. Also, in urbanized and industrial areas in Duval
and Nassau Counties, for example, the potentiometric
surface of the Floridan aquifer is gradually being lowered
because of increased discharge by numerous industrial,
commercial, and municipal wells. The lowering of the
potentiometric surface is causing nonpotable water to
gradually move upward into the upper zones of the
aquifer, thereby decreasing the thickness of the zone of
potable water (Leve, 1968).
The large map shows that there is little or no potable
water available from the Floridan aquifer in southern
Florida and along the east coast as far north as southern
St. Johns County. The maximum thickness of the zone of
potable water is in central Florida where it exceeds 2,000
feet (600 metres). The areas of major thickness generally
conform to the areas of major recharge and highest water
levels. For example, the more than 2,000 feet (600 metres)
of thickness in southern Sumter, Lake, and northern Polk
Counties and the more than 1,000 feet (300 metres) of
thickness in northernmost Florida and in Volusia County
generally outline major areas of recharge to the aquifer.
Throughout most of Florida the mineralized water
below the potable zone may be used for many purposes
including commercial cooling and for various types of
industrial and agricultural uses. With the progress being
made on various desalination methods, the mineralized
water may also become an important source of drinking
water (municipal supplies) in the future, particularly
along the coastal regions and in southern Florida where
little or no potable water is available from the Floridan
Bermes, B. J., Leve, G. W., and Tarver, G. R.
1963 Geology and ground-water resources of Flagler,
Putnam, and St. Johns Counties, Florida: Florida
Geol. Survey Rept. Inv. 32.
Chen, C. S.
1965 The regional lithostratigraphic analysis of Paleo-
cene and Eocene rocks of Florida: Florida Geol.
Survey Geol. Bull. 45.
Healy, H. G.
1975 Potentiometric surface and areas of artesian flow
of the Floridan aquifer in Florida, May, 1974:
Florida Bur. Geology Map Series 73.
1975 Depth to base of potable water in the Floridan
aquifer: Florida Bur. Geology Map Series 42
Leve, G. W.
1968 The Floridan aquifer in northeast Florida:
"Ground Water," Vol. 6, No. 2, p. 19-29.
National Academy of Sciences and National Academy of
1973 Water quality criteria 1972: (U.S.) Environmental
Protection Agency rept. EPA R3 73 003, 594 p.
Stringfield, V. T.
1966 Artesian water in Tertiary limestone in the south-
eastern states: U.S. Geol. Survey Prof. Paper 517.
Vernon, R. 0.
1973 Top of the Floridan artesian aquifer: Florida Dept.
Nat. Resources, Bur. Geology Map 56.
DEPTH TO TOP OF THE
FLORIDANAQUIFER IN FLORIDA
(Adapted from Vernon. 1973.1
- -200 -
Floridan aquifer at or near land surface.
Line of equal depth tc Floridan aquifer. Interval
200 feet. Datum is mean sea level.
'A ~ ..
Thickness of zone of
potable water, in feet.
(Adapted from Healy, 1975.)
I more than 2000
POTENTIOMETRIC CONTOUR. Shows altitude at
which water level would have stood in tightly
cased wells that penetrate the Floridan aquifer.
Contour intervals 10, 30, and 40 feet. Datum is
mean sea level.
SNo potable water
(In this report, water is considered potable if its chloride
or sulfate concentration does not exceed 250 milligrams
per litre.) % t
5 i i
FLOOR IDA GEOtLOGIC SURVEY MAP ,
MAP SERIES NO. 74
89 8o8 87 860 85 84* 83 820
"a 0 % ^ 5 '-*,-