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MAP SERIES NO.16 REVISED
87
UNITED STATES DEPARTMENT OF THE INTERIOR
GEOLOGICAL SURVEY
FLORIDA DEPARTMENT OF NATURAL RESOURCES
published by BUREAU OF GEOLOGY
85*
IIIII I I
FLORIDA DEPARTMENT OF NATURAL RESOURCES
BUREAU OF GEOLOGY
This public document was promulgated at a total
cost of $330.00 or a per copy cost of $.13 for the
purpose of disseminating hydrologic data.
30Q--
PRINCIPAL AQUIFERS IN FLORIDA
By
Luther W. Hyde
Prepared by
UNITED STATES GEOLOGICAL SURVEY
in cooperation with the
BUREAU OF GEOLOGY
FLORIDA DEPARTMENT OF NATURAL RESOURCES
TALLAHASSEE, FLORIDA
1965
REVISED 1975
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INTRODUCTION
Ground water, one of Florida's most valuable resources is
also one of its most abundant. The State is fortunate to have
several prolific ground-water reservoirs that yield tremendous
quantities of water to wells and to some of the world's largest
springs. These ground-water reservoirs, or aquifers, are of two
types-artesian and nonartesian. An artesian aquifer is one that
contains water under sufficient pressure to rise above the top of
the containing formation. A nonartesian aquifer is one that
contains water which is not confined, and the upper water
surface (water table) is free to rise and fall.
The principal source of ground water in Florida is the
artesian Floridan aquifer which supplies most of the water users
in the State. Nonartesian sources include the Biscayne aquifer of
southeastern Florida, the sand-and-gravel aquifer of extreme
western Florida, and a shallow aquifer which lies at depths of less
than 100 feet over much of the State.
The accompanying map shows the approximate areas where
these aquifers are the main source of supply; however, the
boundaries do not represent the areal extents of the aquifers. For
example, the Floridan aquifer extends beyond the southern
boundary shown on the map, but it is not of great economic
significance there because the water is highly mineralized.
Aquifers other than the four described occur in the State,
but they are, for the most part, of minor significance.Oneof these
is an artesian aquifer which is formed by permeable zones that
occur locally within the confining beds above the Floridan
aquifer.
FLORIDAN AQUIFER
The thick limestones of the Floridan aquifer underlie all
of the State and supply ground water to all but southernmost and
westernmost Florida. Along most of the Atlantic and Gulf
Coastal areas, the aquifer contains highly mineralized water.
The Floridan aquifer includes the Lake City, Avon Park, and
Ocala Limestones, all of Eocene age; the Suwannee Limestone of
Oligocene age; and the Tampa Limestone and permeable parts of
the Hawthorn Formation of the Miocene age. In some areas the
aquifer is exposed at the surface, but over much of the State it
lies beneath several hundred feet of sediments.
The thick semipermeable beds which overlie the aquifer,
except in its outcrop areas, restrict the upward movement of the
water and cause the aquifer to have artesian pressure. The
altitude to which water will rise in artesian wells generally
ranges from a few feet above mean sea level, in areas near the
coast, to more than 130 feet above mean sea level in Polk County.
In southern Florida, along coastal areas, and in low stream
valleys, the artesian pressure is sufficient to cause wells to flow.
However, in some heavy use areas such as eastern Duval County
and southern Okaloosa County, the water level has been lowered
below sea level.
Water in the Floridan aquifer is replenished by rainfall in
central and northern Florida and in southern Alabama and
Georgia where the aquifer crops out or where it is covered by
permeable materials. Some replenishment in central Florida
occurs where the confining material is breached by sink holes.
The quality of the water in the Floridan aquifer has been
contaminated by the encroachment of highly mineralized water.
Wells developed in the Floridan aquifer vary in size, depth,
and yield. Domestic wells are usually at least 2 inches in
diameter, and the large municipal and industrial wells may be 30
inches or more in diameter. The depth of wells ranges from about
50 feet to more than 1,000 feet depending on the local geologic
and hydrologic conditions and the yield required.
The yield of wells developed in the Floridan aquifer ranges
from a few gallons per minute for small-diameter wells to several
thousand gallons per minute for some of the large-diameter
industrial wells. The amount of water that can be produced from
the aquifer is controlled by the diameter of the well, the capacity
of the pump, and the hydrologic properties of the aquifer.
BISCAYNE AQUIFER SHALLOW AQUIFER
The nonartesian Biscayne aquifer underlies an area of about
3,000 square miles in Dade, Broward and southern Palm Beach
counties. The wedge-shaped aquifer is 100 to 400 feet thick in
coastal Dade and Broward counties but thins to a few feet near
the western boundary of the counties.
The Biscayne aquifer is composed of rock ranging in age
from late miocene through Pleistocene. The rocks, from oldest to
youngest, are the Tamiami Formation of Miocene age the
Caloosahatchee Marl of Pliocene age, and the Fort Thompson
Formation, Key Largo Limestone, Anastasia Formation, Miami
Oolite, and Pamlico Sand of Pleistocene age.
The aquifer is an interconnected hydrologic unit of per-
meable materials whose boundaries are set by differences in the
hydrologic properties. The permeable limestone of the aquifer is
shielded against upward intrusion of saline water from the
Floridan aquifer by relatively impermeable beds of clay and marl.
However, there is no shield against lateral encroachment of sea
water, the major problem in the area served by the Biscayne
aquifer. Encroachment has resulted from overdrainage by canals.
However, proper control of drainage canals and proper water
management have greatly reduced the threat of sea-water
encroachment.
Water in Biscayne aquifer is derived chiefly from
local rainfall and during dry periods from canals connected to
conservation areas.
The ground water from uncontaminated parts of the aquifer
is fairly uniform in quality. The hardness generally ranges from
200 to 300 mg/1 (milligrams per litre) and the chloride from about
15 to 30 mg/1. Nearly all the water is colored either with organic
material or iron, or both; the color is usually greatest in the
upper part of the aquifer. Excessive amounts of iron are
encountered in some parts of the aquifer.
The Biscayne aquifer is highly productive everywhere along
the coastal ridge and for a considerable distance to the west;
however, its productivity varies considerably from place to place.
Wells developed in the aquifer are as large as 36 inches in
diameter. A typical well is 6 inches in diameter, 50 to 75 feet
deep, and finished with 3 to 10 feet of open hole in highly
permeable limestone. In the northern part of the area, wells may
be as deep as 200 feet. Yield from 6-inch wells ranges from 1,000
to 1,500 gpm (gallons per minute) with less than 4 feet of
drawdown.
SAND-AND-GRAVEL AQUIFER
The nonartesian sand-and-gravel aquifer, the major source
of ground water in extreme western Florida, is a wedge-shaped
deposit extending northward into Alabama. It generally thickens
to the west and southwest from its thin outcrop along the
Walton-Washington County line. In southeastern Escambia
County, the aquifer is 400 to 500 feet thick.
The sand-and-gravel aquifer is composed of sediments
ranging in age from Miocene to Pleistocene. The sediments are
chiefly very fine to very coarse quartz sand which in places is
mixed with granules and small pebbles of quartz and chert.
Lenses and stringers of gravel and clay occur throughout the
aquifer.
Water in the sand-and-gravel aquifer is derived chiefly from
local rainfall and is low in dissolved solids which generally range
from 15 to 40 mg/1; the hardness from 4 to 30 mg/l, the chloride
from 2 to 30 mg/l, the iron less than 0.25 mg/1 and the fluoride
less than 0.2 mg/1. The water is usually acidic.
Wells in the sand-and-gravel aquifer furnish all of the ground
water used in Escambia, most used in Santa Rosa, and a
substantial part of the smaller supplies in Okaloosa County.
Wells may be as large as 30 inches in diameter, the depth varies
from 30 to 500 feet, and the yield ranges from 50 to 2,000 gpm.
A shallow, nonartesian aquifer is present over much of the
State, but in most areas it is not an important source of ground
water because a better supply is available from other aquifers.
However, in rural areas where water requirements are small, the
aquifer is tapped by shallow, small-diameter sand-point wells. The
map shows only those areas where the shallow aquifer is an
important source of water.
In south Florida, the shallow aquifer is the major source of
ground water in Martin, Palm Beach, Hendry, Lee, Collier, Indian
River, St. Lucie, Glades, and Charlotte counties. The shallow
aquifer is an important source of water in some Atalntic and Gulf
coastal areas where the artesian ground water is highly
mineralized.
The lithology, thickness, and hydrologic characteristics of the
shallow aquifer differ from place to place. In southern Florida, the
aquifer ranges in age from Miocene to Recent and is composed of
sands of the Pamlico or older terrace deposits, beds of shell and
sand of the Anastasia Formation, beds of shell and limestone in the
Tamiami Formation, or limestones in the upper part of the
Hawthorne Formation. Northward along the coast the aquifer is
composed primarily of Pleistocene and Recent deposits of sand and
shells, but in come areas it extends downward to include deposits
of Miocene or Pliocene age.
The water in the shallow aquifer is derived chiefly from local
rainfall apd is generally of good chemical quality. The water is
usually low in chlorides except where contaminated by adjacent
salt-water bodies. It ranges from soft to very hard, and it is
commonly high in color and in iron.
Domestic or small public supply wells are generally 1%/ to 2'/
inches in diameter and less than 50 feet deep. Wells of this type are
common in rural areas along the coast. In south Florida, where
permeable shell beds are an important part of the aquifer, larger
wells are constructed. For example, an 8-inch well in northeastern
Martin County yields 500 gpm.
EXPLANATION
4-
Floridan Aquifer
Biscayne Aquifer
S Sand-and-gravel Aquifer
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Shallow Aquifer
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Area where principal aquifer is highly
mineralized
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