U.S. DEPARTMENT OF THE INTERIOR
U.S. GEOLOGICAL SURVEY
MAP SRFIES NO. 132
FLORIDA DEPARTMENT OF NATURAL RESOURCES
published by FLORIDA GEOLOGICAL SURVEY
9go 8. 870 860 850 840 830 820
TRANSMISSIVITY AND WELL YIELDS
OF THE UPPER FLORIDAN AQUIFER IN
William J. Andrews
Prepared by the
U.S. GEOLOGICAL SURVEY
in cooperation with the
FLORIDA DEPARTMENT OF ENVIRONMENTAL REGULATION
FLORIDA DEPARTMENT OF NATURAL RESOURCES,
FLORIDA GEOLOGICAL SURVEY
The Floridan aquifer system, one of the most productive sources of ground water in
the United States, underlies the entire Stale of Florida and parts of Georgia, Alabama, and
South Carolina. In Florida, the Floridan consists of a thick sequence of highly permeable
limestone and dolomites of Tertiary age, with minor amounts of plastic and evaporate
deposits, that is hydraulically interonnectedin varying degrees (Miller, 1986, p. B44-48).
The Floridan aquifer system, particularly the Upper Floridan aquifer, is an important
source of water supply for many areas of Florida due to its abundant quantity of stored water,
its proximity to the surface, its generally suitable water quality for most uses, and its high
hydraulic conductivity. The area in which the Upper Floridan aquifer is used as the principal
source of supply is shown in figure 1. In some coastal areas and in the southern part of
Florida, where the Upper Floridan aquifer is overlain by surficial aquifers that have more
accessible and purer waters, the Upper Floridan aquifer is not tapped as a source of potable
water. The Upper Floridan aquifer is the most productive unit in the Floridan aquifer system
because it is highly solution riddled and, consequently, very permeable and highly
transmissive throughout much of the State, whereas the Lower Floridan aquifer generally
contains saline water.
This report describes transmissivity distribution and probable well yields of the Upper
Floridan aquifer in Florida. The transmissivity information in this report was developed by
the U.S. Geological Survey from Regional Aquifer Systems Analysis (RASA) project of the
- Floridan aquifer system (Bush and Johnston, 1988).
Transmissivity (T) is defined as
T= Kb, (1)
where K = hydraulic conductivity (the capacity of rocks to transmit water
in a unit time under a unit hydraulic gradient through a unit area
measured at right angles to the flow direction), and
b = thickness of the material through which the water flows.
Further information on the derivation of hydraulic conductivities of porous media can be
found in Lohman and others (1972, p. 4-5). The relation between transmissivity and specific
capacity (the rate of discharge of water from a well divided by drawdown of the water level
within a well), is discussed at length in Heath (1983, p. 60-61). Transmissivity, specific
capacity and well yields, given certain simplifying assumptions, are proportional to each
other, thus, knowledge of Iransmissivity of the Upper Floridan aquifer is useful for planning
the development of water supplies from the aquifer.
DESCRIPTION OF THE UPPER FLORIDAN AQUIFER
The Floridan aquifer system generally consists of an Upper and a Lower Floridan
aquifer separated by less permeable beds of highly variable properties, termed the middle
confining unit (Miller, 1986, p. B53). In parts of north Florida and southwest Georgia, there
is little permeability contrast within the aquifer system. Thus, in these areas, the Floridan is
effectively one continuous aquifer (Johnston and Bush, 1988, p. A7).
Where the middle confining unit is present, the Upper Floridan aquifer consists
principally of limestone and dolomite of the following geologic formations: the Suwannee
Limestone (Oligocene), the Ocala Limestone (upper Eocene), and the upper part of the Avon
Park Formation (middle Eocene).
The top of the Upper Floridan aquifer generally coincides with the absence of
significant thicknesses of clastics from the section and with the top of the vertically persistent
permeable carbonate section. For the most part, the top of the aquifer coincides with the top
of the Suwannee Limestone, where present, orthe top of the OcalaLimestone. Insmallareas
of central peninsular Florida and in southeastern Florida, where the Suwannee Limestone
and Ocala Limestone are missing, the Avon Park Formation forms the top of the Upper
The Upper Floridan aquifer is underlain by the middle confining unit of the Floridan
aquifer system, where present, which consists mostly of the lower part of the Avon Park
Formation. The middleconfining unit is underlainby the LowerFloridan aquifer thatconsists
of middle Eocene to upper Paleocene rocks of the Avon Park, Oldsmar, and the upper part
of the Cedar Keys Formations. Where the middle confining unit is absent, the Upper and
Lower Floridan aquifers merge and are considered together as the Upper Floridan aquifer
(Miller, 1986, p. B46).
Where the rocks of the Upper Floridan aquifer are not exposed at the land surface, the
aquifer is overlain by varying thicknesses of clastic deposits with some carbonate rocks in
places. For the most part, these rocks are much less permeable than the rocks of the Upper
Floridan and act collectively to confine the Upper Floridan aquifer.
Where surficial deposits are thick, highly permeable, and extensively used as sources
of ground water, they have been given aquifer names, such as the Biscayne aquifer in
southeastern Florida and the sand-and-gravel aquifer in western panhandle Florida (Miller,
1986, p. B40). Permeable carbonate beds in the Hawthorn Formation of Miocene age
constitute important aquifers along the southwestern coast.
The upper confining unit of the Upper Floridan aquifer, known as the intermediate
confining unit (Southeastern Geological Society, 1986, p. 9), generally consists of clastic
rocks of the Miocene-age Hawthorn Formation or equivalent formations, but locally it
contains low-permeability limestone and dolomite of the early Miocene-age Tampa Lime-
stone or the Oligocene-age Suwannee Limestone (Miller, 1986, p. B43-B44). The upper
confining unit, particularly where itis less than 100 feet thick, is locally breached by sinkholes
and other openings that connect the Upper Floridan aquifer with the surface (Miller, 1986,
p. B43). Confinement conditions of the Floridan aquifer system are shown in figure 2.
The Upper Floridan aquifer is separated from the LowerFloridan aquifer byasequence
of low permeability gypsiferous limestone to chalky limestone primarily of middle Eocene
age (Miller, 1986, p. B55). Seven subunits of the middle confining unit were identified and
mapped by Miller (1986).
The rocks composing the Lower Floridan aquifer generally range in age from early
middle Eocene to late Paleocene, but may include rocks as young as late Eocene or as old as
Late Cretaceous. Because it is deeply buried, and in many places contains water that is
unsuitable for public supplies, the Lower Floridan has not been intensively drilled or tested,
and its hydraulic character is not well known.
The base of the Floridan aquifer system in Florida ranges in depth below sea level
from less than 200 feetin the northwestern panhandle to more than 4,100 feet in southwestern
Florida (Miller, 1986, pL 33). The lower confining unit of the Floridan, which separates the
aquifer system from underlying rocks of Cretaceous age, consists of either (1) massive bedded
anhydrite in the Paleocene Cedar Keys Formation in the Florida Peninsula or (2) late Eocene
to late Paleocene glauconitic, calcareous, argillaceous to arenaceous rocks elsewhere in
The thickness of the Upper FloridanaquiferinFloridais highly variable. TheFloridan
aquifer system generally thickens seaward from inland areas in northern Florida. The Upper
Floridan aquifer in Florida is thinnest in the western half of panhandle Florida and in a wide
band parallel to the Atlantic coastline. The greatest thickness of the Upper Floridan is along
the north-central part of the gulf coast of Florida where there is no middle confining unit
(Miller, 1986, p. B54-B55).
NATURE OF THE PERMEABILITY OF THE UPPER
The hydrology of the Upper Floridan aquifer is complex because its porosity and
permeability are due to a combination of factors: (1) the original texture of the rock; (2)
diagenetic processes, such as dolomitization and recrystallization; (3) joints, fractures, faults,
and other structures that provide open channels along which ground-water flow is enhanced;
(4) dissolution of either carbonate rocks or pore-filling evaporites; and (5) precipitation of
pore-filling evaporites (Miller, 1986, p. B82).
To the west of Leon and Wakulla Counties in the panhandle, carbonate rocks of the
Upper Floridan aquifer interfinger with lower-porosity, plastic sediments, causing a sharp
decrease in average permeability of the Upper Floridan aquifer. The amount of low-
permeability, fine-grained carbonate materialin the Upper Floridan generally increases in a
down-basin direction, to the extent that, in areas of southem Florida, the aquifer consists of
low-permeability rocks separated by thin, high-permeability zones (Miller, 1986, p. B65).
The Upper Floridan aquifer is unconfined and has karsticpemreability along sections
of the gulf coastandnorthernFloridawhere the upperconfining unitwas removed by erosion
during the Pleistocene Epoch (fig. 2). The Upper Floridan is confined by low-permnneability,
clayey, Miocene and post- Miocene deposits where it dips genly from its unconfined areas
toward e g coast in the panhale and towa the at nte pe aor the Atlantic Coast. Comparison of
confining conditions (fig. 2) and the thickness of the Upper Floridan tith transmissivity
shous that transmtssivity correlates more closely with confining conditions than wtth the
/ SANTA ROSA
thickness of the aquifer. An explanation for this correlation is that the degree of
confinement of the Upper Floridan has influenced the development of transmissivity by
controlling the rates of recharge to and discharge from the aquifer and, therefore, the
development of solution cavities. Thus, highest transmissivities occur where the Upper
Floridan is unconfined or poorly confined.
DISTRIBUTION OF TRANSMISSIVITY
The greatest transmissivity values for the Upper Floridan aquifer (greater than
I million ft /d (feet squared per day)) are in the karstic areas of central and northern Flonda
where the aquifer system is either unconfined or where its upper confining unit is less than
100 feet thick. Removal by erosion of the overlying Hawthorn Fonnation during Pleistocene
time is responsible for the distribution of the current karst (Stringfleld, 1966, p. 131).
Where the aquifer is more tightly confined, as it is in areas of the Florida Panhandle
and in southernmost Florida, its transmissivity is generally less than 250,000 ft2/d and
variations in transmissivity are related primarily to textural facese) changes in the carbonate
rocks and are less affected by the thickness of the Upper Floridan aquifer (Miller, I986.
The distribution of transmissivity in the Upper Floridan aquifer can be summarized
as acontinuum-from less than 1,000 ft /d in the confined, micrite-rich limestones of the Fonrt
Walton Beach area in the western panhandle of Florida to more than 1 million ft2/d in the
unconfined karstic areas of central and northern Florida (Bush and Johnston, 1988, p. C201
The areal distribution of transmissivity of the Upper Floridan aquifer in Flonda 1.
shown on the large map (modified from Bush and Johnston, 1988, pL 2). The map portra) s
the most probable ranges of transmissivity based on aquifer tests, digital flow model anal sis.
and geologic information.
The 82 aquifer tests used to prepare the Florida part of the regional map ol
transmissivity (Bush and Johnston, 1988, table 2) are concentrated in areas of heaty
withdrawals. Where the development of ground water has been minimal, the transmissn ir~
estimates used to prepare the large map were based on model calibration and geology The
model was a finite-difference model with 64-square-mile-area grid cells, which was used to
simulate ground-water flow in the Floridan aquifer system in the Southeastern United States
(Bush and Johnston, 1988). The transmissivity values derived from the model are a erage
values forthe grid cells and they donotreflectlocal variations in transmissivity due to solution
features in the rocks--variations which may produce transmissivity changes of an order of
magnitude or more within short distances.
The contrast between values derived from an aquifer test and values derived from the
model is evident in the Jacksonville area where the model indicates a range of transmissi i ry
from 100,000 to 250,000 ftjd, but aquifer-test values for six fully penetrating wells range
from 13,000 to 200,000 ft/d. For karstic areas of the Upper Floridan aquifer, digital
simulation indicates transmissivities ranging from 250,000 ft /d to 10 million ft /d, but lou
net analyses nearmajor springs have yielded transmissivity values from 1 million to 2null ion
ft2/d (Bush and Johnston, 1988, p. (C20).
A qualitative assessment of the reliability of the large map, based on the availability
of field-test data and the sensitivity of the regional flow model to transmissivity, is sho n in
figure 3. Transmissivity values in areas where aquifer-test data are available and where the
model is sensitive to transmissivity are considered to be the most reliable. Transmis is% iN
values in areas where little or no aquifer-test data exist and the model is insensitive to
transmissivity are the least reliable. Nearly one-half of the area of the Upper Floridan aquifer
is in the least reliable category (Bush and Johnston, 1988, p. C20).
In lieu of test information for a particular site, the likely yild of a prospective e II
can be estimated on the basis of the transmissivity of the aquifer. Specific capacity I Q/s|.
which is the yield in gallons per minute divided by the drawdown of the water level in a
well, is estimated from the transmissivity of the aquifer by using a variation of Jacob's
modified nonequilibrium equation (Driscoll, 1986, p. 1021):
where s = drawdown in the well, in feet;
Q = yield of the well, in gallons per minute;
T = transmissivity of the aquifer, in gallons per day per foot;
t = time of pumping, in days, and
S = the storage coefficient of the aquifer.
By assuming a confined aquifer and other assumptions as given in Driscoll (1986.
p. 1021), the specific capacity is:
Q/S = T/2000, or 3
by converting T into feet squared per day:
Q/S = T/267, -41
where T is transmissivity in feet squared per day.
Once specific capacity is known, well yield (Q) can be determined by multiple ing
specific capacity by a limiting drawdown, arbitrarily assumed to be as 50 feet, and taking
into account the efficiency of the prospective well, assumed to be 50 percent. The result is
the well-yield distribution shown on the large map. Further information on the derivat ion of
and factors affecting specific capacity can be found in Heath (1983, p. 60-61).
Yields of wells in the Upper Floridan aquifer range from several hundred to more than
10,000 gal/min (gallons per minute), depending upon construction features, depth, and location
of wells (Conover and others, 1984, p. 37). Wells that tap the Upper Floridan general3 yield
Upper Floridan aquifer wells that yield at least 1,000 gal/min generally tap limestone contanmng
interconnected solution cavities. In northwestern Florida, inland wells have greater yields than
wells along the coast because the Upper Floridan aquifer along the coast contains much
calcareous clay and sand that reduce its transmissivity (Pascale, 1975).
Because the calculations for well yield were based directly on transmissivity and
assumed confined conditions and fully penetrating wells, the ranges of well yield coincide
with the ranges of transmissivity shown on the large map. Pumping more than 10,000 gal/min
from a single well. is impractical; therefore, all areas with transmissivity greater than
100,000 ff/d are shown as having well yields of 10,000 or more gal/min, even though the
calculated yields would be much higher.
Bush, P.W., and Johnston, R.H., 1988, Ground-water hydraulics, regional flow, and
ground-water developmentoftheFloridanaquifersystem in Florida andin parts
of Georgia, South Carolina, and Alabama: U.S. Geological Survey Professional
Paper 1403-C, 80 p.
Conover, C.S., Geraghty, JJ., and Parker, G.G., Sr., 1984, Ground water, in Fernald,
E.A., and Patton, DJ., eds., Water resources atlas of Florida: Tallahassee,
Florida State University, p. 36-53.
Driscoll, F.G., 1986, Ground water and wells (2d ed.,): St. Paul, Minnm., Johnson
Division, 1089 p.
Heath, R.C., 1983, Basic ground-water hydrology: U.S. Geological Survey Water-
Supply Paper 2220,84 p.
Johnston, R.H., and Bush, P.W., 1988, Summary of the hydrology of the Floridan
aquifer system in Florida and in parts of Georgia, South Carolina, and Alabama:
U.S. Geological Survey Professional Paper 1403-A, 24 p.
Lohman, S.W. and others, 1972, Definitions of selected ground-watertenns-revisions
and conceptual refinements, U.S. Geological Survey Water-Supply Paper 1988,
Miller, J.A., 1986, Hydrogeologic framework of the Floridan aquifer system in Florida
and in parts of Georgia, South Carolina, and Alabama: U.S. Geological Survey
Professional Paper 1403-B, 91 p.
Pascale, CA., 1975, Estimated yield of freshwater wells in Florida: Florida Bureau of
Geology Map Series 70, 1 sheet.
Southeastern Geological Society, 1986, Hydrogeological units of Florida: Florida
Geological Survey Special Publication no. 28,9 p.
Stringfield, V.T., 1966, Artesian water in Tertiary limestone in the Southeastern
States: U.S. Geological Survey Professional Paper 517,226 p.
Vecchioli, John, and Foose, D.W., 1984, Florida ground-water resources, in National
Water Summary, 1984-Hydrologic events, selected water-quality trends, and
ground -water resources: US. Geological Survey Water-Supply Paper 2275.
TRANSMISSIVITY, IN POTENTIAL YIELDS, IN
THOUSANDS OF FEET GALLONS PER MINUTE
SQUARED PER DAY (iilh 50 fool drawdown
and 50 percent efficiency )
F LESS THAN 10 D LESS THAN l.O.J
-- \I.O1.,M)0 10.001l AND GREATER
1 .01it ND-) RE TER
(IModified from Bush and Johnsion. 1988)
BISCAh NE -AQUIFER
SAND-AND-.GRA EL QUIFER
iNN 1MED SURFICIAL AQLUIFERS
-%ND INTERMEDI ATE QL IIFERS
I FLORIDAN -AQ)iFER SSTEM
0 50 MILES
I I I ,
Figure I --Principal aquifer, in Florida
i Modified Irom \'ecchioli and Foose. 198-I1
UPPER CONFINING UNIT ABSENT
OR VERY THIN
UPPER CONFINING UNIT IS
LESS THAN 100 FEET THICK,
BREACHED, OR BOTH
UPPER CONFINING UNIT IS
GREATER THAN 100 FEET
0 50 MILES
Figure 2.--Confinement of the Upper Floridan aquifer in Florida
(Modified from Bush and Johnston. 1988).
* MOST RELIABLE--Based on aquifer
test data, model-computed heads
sensitive to transmissivity.
Some aquifer. test data, model-computed
heads insensitive to transmissivity.
Little or no aquifer test data,
model-computed heads sensitive
m LEAST RELIABLE--Little or no aquifer
test data, model-computed heads
insensitive to transmissivity.
0 50 MILES
SIL *U '
- Figure 3.--Reliability of transmissivity distribution
(Modified from Bush and Johnston. 1988).
0 10 20 30 40 5(
I F IR
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GEOJLOGIC SURVEY MAP -S .Cl
No I 3E.
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