UNITED STATES DEPARTMENT OF THE INTERIOR
UNITED STATES DEPARTMENT OF THE INTERIOR
published by BUREAU OF GEOLOGY
THE SHALLOW AQUIFER OF SOUTHWEST FLORIDA
UNITED STATES GEOLOGICAL SURVEY
in cooperation with
BUREAU OF GEOLOGY
FLORIDA DEPARTMENT OF NATURAL RESOURCES
An extensive shallow aquifer underlies the Big Cypress Swamp and
adjacent areas of southwest Florida (fig. 1). This aquifer represents a
principal factor in the present and future growth and development in
southwest Florida. The shallow aquifer beneath the west part of the Big
Cypress Swamp is the source of municipal and irrigation water for most
of that area. The section of aquifer beneath the central part of the Big
Cypress will probably be the prime potential source of water for future
municipal demands along the rapidly urbanizing coastal and adjoining
interior areas. Important as the Biscayne aquifer is to the hydrologic
system in southeast Florida, equally important is the shallow aquifer to
the hydrologic system in southwest Florida and the future growth of
the area. The purpose of this report is to describe pertinent hydrologic
aspects of the shallow aquifer determined from data collected during 1
year of investigation in the central part of the Big Cypress Swamp and
from data collected during several years in perimeter areas of the Big
Cypress Swamp. The data contained in the report were obtained in
cooperation with the Florida Department of Natural Resources and
The Big Cypress Swamp comprises nearly all of Collier County and
parts of southern Hendry and western Monroe counties. (See fig. 1.) It
is a prime source of water supply to maintain the aquatic biologic
communities of the northwest part of the Everglades National Park and
the adjoining estuaries, and it is also a potential area from which fresh
water for the expanding urban area of the lower Gulf coast will be
obtained. The seasonal southward overland flow through the east and
central parts of the Big Cypress Swamp nourishes the Park estuaries,
which are nursery grounds and feeding areas for many marine animals
(Klein and others, 1970, p. 12).
Acknowledgment is extended to the Florida Department of
Transportation, Tallahassee, for granting permission to drill exploratory
holes along the Everglades Parkway, and to the G.A.C. Corporation,
who gave permission to drill on its property in central and western
The prime source of fresh-water supplies in Collier County and
adjoining parts of Lee and Hendry counties is the shallow aquifer.
According to McCoy (1962, p. 24-25), the shallow aquifer has a
maximum thickness of about 130 feet in western Collier County, where
it comprises the Pamlico Sand and the Anastasia Formation of
Pleistocene age, and limestone of the Tamiami Formation of Miocene
age. The aquifer thins eastward, and it wedges out near the Dade and
Broward county boundary. The patterns in figure 1 show,
approximately, the areal extent of the shallow aquifer within and
adjacent to the Big Cypress Swamp and the areas where limestone of
the aquifer is within 10 feet of the land surface.
The approximate real extent of the aquifer was determined from
well logs and well inventory work by Klein and others (1964, Table 8)
in Hendry County, and from McCoy (1962, p. 61-82) in Collier
County. Information concerning the approximate depth to the top of
the limestone of the shallow aquifer was obtained from well logs and
drillers' reports, from exploration holes along roads traversing Collier
County, and from inspection of spoil material along canals and roads.
During 1969-70, exploratory rotary holes were drilled along the
Everglades Parkway from the Collier County east boundary westward
nearly to Naples. The locations of those holes and other exploratory
drill holes are shown in figure 1. They were drilled to determine the
real extent, continuity, depth and thickness of limestone sections and
the relative permeability of the limestone in the shallow aquifer m the
central part of the Big Cypress Swamp area. The hydrologic and
geologic data obtained from those holes are shown graphically in figure
Although the shallow aquifer is nonartesian, it contains beds and
lenses of sandy clay and fine sand of low permeability, which tend to
retard the circulation of water within the aquifer (McCoy, 1962, p.
24-31). Generally, the limestone parts of the aquifer are the important
water-yielding sections because they are solution riddled and, therefore,
are highly permeable. However, nearly everywhere the upper part of the
limestone section is hard and dense and of lower permeability than the
lower part. The low permeability of the upper part is important in that
it affects the ability of shallow canals to drain water from aquifer
Most of the interbedded sand and sandy clay of low permeability
within the shallow aquifer is in the west, north, and east-central parts of
the Big Cypress Swamp. In the central and south parts, generally south
of the Everglades Parkway. the aquifer is composed predominately of
nearly continuous sections of limestone to depths ranging from 60 to
at least 85 feet. The lithologic logs in figure 2 show that a
continuous section of limestone ranging in thickness from 40 feet to
more than 80 feet occurs along the Everglades Parkway from the
Turner River Canal westward nearly 20 miles. At test hole 5, (west of
the intersection of the Barron River Canal) the limestone is at least 80
feet thick. In this test hole, it is a continuous section, the top of which
is immediately below the land surface. Limestone sections south of the
Everglades Parkway generally range in thickness from about 55 feet to
70 feet. Klein (1964, p. 44) indicated that at the Collier County
boundary east of Immokalee the top of the permeable limestone of the
shallow aquifer is 22 feet below the land surface and extends at least to
54 feet in well 131 (fig. 1). The limestone is similar in character to that
penetrated along the Everglades Parkway.
The uppermost 100 feet or more of sediments in the vicinity of
Immokalee are particularly nonuniform in character (McCoy, 1967, p.
7-12), and they are generally of low permeability, except for isolated
thin sections of coarse sand and gravel of relatively high permeability.
Most wells having yields of 100 gpm (gallons per minute) or more are
deeper than 150 feet and are finished in limestone. Because of the
dissimilarity of the shallow sediments near Immokalee to the sediments
of the surrounding areas, the area shown underlain by the shallow
aquifer in figure 1 did not include the vicinity of Immokalee.
The shallow aquifer is underlain by material of low permeability, the
base of which extends to depths ranging from about 400 feet to more
than 700 feet. This thick section also is the confining layer for the
underlying artesian Floridan aquifer, which yields brackish water by
natural flow to wells throughout the Big Cypress Swamp.
The shallow aquifer in southwest Florida is replenished primarily by
the infiltration of local rainfall. Therefore, during the rainy season,
June through October, ground-water levels are high, and by May, the
usual end of the dry season, water levels normally reach annual lows.
The seasonal fluctuations and long-term trend of water levels are shown
in the hydrograiph of well 131 (fig. 3), 8 miles east of Immokalee and
near the north end of the Big Cypress Swamp. The total annual rainfall
at Lake Trafford is shown for comparison. The level in well 131 was
lowest in the spring of 1962, as a result of the 1961 rainfall deficiency.
The level was highest at the peaks of the 1959 and 1960 rainy seasons.
The maximum range of fluctuation was 6.5 feet. Except for the normal
response of ground-water levels to the wet and dry seasons, the 17-year
water-level record in figure 3 shows no long-term trend.
As the rainy season begins, usually in June, ground-water levels rise
correspondingly. In the central and eastern parts of the watershed,
where drainage is poor to nonexistent, levels generally continue an
upward trend until the water rises above the land surface; thereafter.
further replenishment to the aquifer is rejected, and southward
overland flow occurs. Large-scale inundation is generally continuous
through February or March, but the southward flow through outlets
along U.S. Highway 41 stops generally at the end of December or
January. By May most of the Big Cypress Swamp is dry except for the
perennially wet strands and sloughs. The hydrographs for wells 131 and
380 (fig. 4) show the seasonal fluctuation of ground-water levels in the
Big Cypress Swamp and the flow in the Barron River Canal for 1970
and the dry season of 1971.
The differences between the levels in well 131 in the north part of
the watershed and the levels in well 380 in the south part (see fig. 5 for
locations) indicate that an average southward hydraulic gradient of 18
feet in 35 miles (0.5 foot per mile) sustains during the dry as well as the
wet season through the central part of the watershed. Figure 4 also
shows the close relation between the flow of the Barron River Canal
and the fluctuation of level in the two wells. Widespread inundation
and high ground-water levels during the rainy season cause large
gradients toward the Barron River Canal, which result in increased sheet
flow and ground-water contribution to the canal and, therefore, in
increased canal discharge. During prolonged drodght, sheet flow stops,
the gradients toward the canal are low, and correspondingly low canal
Record low water levels in southwestern Florida occurred near the
end of the dry seasons of 1961-62 and 1970-71. The contour map in
figure 5 shows the configuration of the water table in the shallow
aquifer in early May 1971. The pattern of the contours shows that
water levels were highest in northern Collier and southwestern Hendry
counties and that ground water flows generally southward and
southwestward. Water levels in the southwest part of the area are
strongly affected by the Golden Gate Canal and the Fahka Union
Canal. Ground-water levels in the vicinity of the Barron River and
Turner River canals are only mildly affected because the canals are
shallow and generally are cut into the surface limestone of relatively
low permeability. The effectiveness of drainage by the Golden Gate
Canal, as compared with the Barron River Canal, is indicated by their
flows: the highest daily flow of record of the Golden Gate Canal is
2,390 cfs (cubic feet per second), whereas the highest daily of the
Barron River Canal is 292 cfs.
Observations during the rotary drilling of the exploratory 6-inch
holes, whose locations are shown in figure 1, furnished information on
the permeability changes within the area and with depth in the aquifer
and the differences in yield of wells. The rotary machine utilized
compressed air through the drill stem to bring rock cuttings to the
surface. Increasing quantities of water were picked up as the aquifer
was penetrated and the water and cuttings were forced to the surface.
The differences in the amount of water returned indicated differences
in permeability. The largest quantities of water were returned from
wells drilled in the area between well 2 and well 7 along the Everglades
Parkway. The amount of water returned to the surface from each well
in that area exceeded 500 gpm. Designations of relative permeability
along the Everglades Parkway are shown in figure 2.
Five 30-foot rotary exploratory holes were drilled along the
Henderson Creek Canal, each within 200 feet of the canal, from the
Everglades Parkway southward to U.S. Highway 41, to determine the
shallow geology, the approximate yield of wells, and the general quality
of the shallow ground water. The holes penetrated sand, shelly sand,
and limestone. In November 1970 the wells were tested by pumping at
200 gpm, and water levels were measured in the pumping wells to
determine drawdowns (McCoy, 1972); also water samples were
collected at the beginning and end of pumping. Specific capacity of the
wells ranged from 910 gpm to 35 gpm per foot of drawdown. The
specific capacity for the north wells was the greatest, indicating good
interconnection between the aquifer and the canal near the Everglades
Parkway. The water samples collected at that time from each of these
five wells ranged in chloride content from about 150 mg/1 (milligrams
per liter) to more than 365 mg/l, suggesting that the area of shallow
mineralized ground water inland from Naples, described by Sherwood
and Klein (1961, p. 32-34), also extends southward toward U.S.
Scattered data from specific-capacity tests on other exploratory wells
and from aquifer tests show that the transmissivity of the shallow
aquifer differs widely in Collier and southern Hendry counties. Klein
and others (1964, p. 40-58) showed that the transmissivity of the
shallow aquifer in southern Hendry County ranges from about 250,000
gpd per foot to about 1,000,000 gpd per foot; the highest value was
computed from a test at the Collier-Hendry boundary in the vicinity of
well 131, east of Immokalee. From specific-capacity tests on wells in
the vicinity of the Everglades Parkway and Fahka Union Canal, McCoy
(1972) indicated that the transmissivity of the aquifer there ranges
from about 500,000 to 800,000 gpd per foot. The shallow aquifer
underlying the area eastward to the Turner River Canal would be
expected to be within about the same range, on the basis of the
geologic data shown in figure 2. These transmissivities are markedly
greater than those determined by McCoy (1962, p. 40-41), about
60,000 gpd per foot, 5 miles northwest of Immokalee, and by
Sherwood and Klein (1961, p. 36-39), ranging from 80,000 to 185,000
gpd per foot near Naples.
The water in the shallow aquifer is a typical limestone type, hard,
and high in bicarbonate. It generally meets the standards of the U.S.
Public Health Service (1962) for potable water supplies, except from
areas east of Naples, indicated by Sherwood and Klein (1961, p. 28-34),
and areas along the coast and tidal channels affected by sea-water
intrusion. The ground water in the interior part of the Big Cypress
Swamp generally contains less than 40 mg/I chloride and less than 440
mg/1 dissolved solids.
In view of the good water quality, the relatively large real extent of
permeable limestone, the perennially high water levels, and- the high
yield to wells, the shallow aquifer in the central part of the Big Cypress
Swamp represents a potential source of potable water capable of serving
much, if not all, the expected urban growth along west and south
coasts, provided that good management practices are followed,
overdrainage is prevented, and pollution is minimized in the central Big
Cypress Swamp area.
1964 (Schroeder, M.C., and Lichtler, W.F.) Geology and
ground-water resources of Glades and Hendry Counties,
Florida: Florida Geol. Survey Rept. Inv. 37.
1970 (and Schneider, WJ., McPherson, B.F., and Buchanan,
TJ.) Some hydrologic and biologic aspects of the Big
Cypress Swamp drainage area, southern Florida: US. Geol.
Survey Open-File Report 70003.
1962 Ground-water resources of Collier County, Florida:
Florida Geol. Survey Rept. Inv. 31.
1967 Ground water in the Immokalee area, Collier County,
Florida: Florida GeoL Survey Inf. Circ. 51.
1972 Hydrology of western Collier County, Florida: U.S. Geol.
Survey open-file report, 75 p.
1961 (and Klein, H.) Ground-water resources of northwestern
Collier County, Florida: Florida GeoL Survey Inf. Circ. 29.
US. Public Health Service
1962 U.S. Public Health Service drinking water standards: Public
Health Service Pub. 956; 61 p. See Public Health Repts.
Department of Natural Resources
Bureau of Geology
This public document was promulgated at a
cost of $1177.00 or a per copy cost of
$0.78 for the purpose of disseminating
water resource data.
Figure 2. Hydrogeologic data obtained along the Everglades Parkway.
Figure 1. Approximate real extent of the shallow aquifer and the area where limestone is within 10 feet of the land surface.
.LOCATIO N OFAREA
1952 1955 1960 1965 1968
Figure 3. Hydrographs of well 131 for 1952-68 and rainfall at Lake Trafford, 1953-67.
Figure 5. Low water-level contours for early May 1971.
1970 1971 oAC
Figure 4. Hydrographs of wells 131 and 380 and the discharge of the Barron River Canal for (2 CT 2281
1970 and early 1971.
/'RIDA GEOLOGIC SURVEY MAP SERIES
MAP SERIES NO. 53