FOR REVIEW ONLY NOT FOR
Preliminary Report of the
Committee on Ground Water
FLORIDA WATER RESOURCES STUDY COMMISSION
Dr. Robert 0. Vernon, Chairman
W. P. Still
M. I. Rorabaugh
Nevin D. Hoy
Theodore B. Jenson
Dr. B. F. Buie
Dr. A. M. Buswell
C. A. Black
Paul H. Shea
E. C. Weichell, Jr.
Florida Geological Survey
Florida Geological Survey
U. S. Geological Survey
U. S. Geological Survey
Florida Engineering Society
Florida State University Geology Department
University of Florida, Chemistry Department
Florida Section, American Water Works
U. S. Corps of Engineers
Associated Industries of Florida
GROUND WATER OF FLORIDA
Nearly the entire State of Florida is underlain by porous and permeable limestones
which provide very large supplies of ground water. At present, more than 86 percent of
t'b State's population depends on ground water for domestic use. In addition, large
dnatts are used for industry and for irrigation of vegetables and fruit.
in the past few years, the problems of water supply, water quality, and drainage
have increased substantially. The population of Florida is growing at a rate greatly
above the average for the country, the growth being due to retired people moving to a
warm climate and partly to industrial growth. Florida is rapidly gaining new industry as
theresult of the trend for industry to move into the South. Many of the industries are
of the chemical type and use very large amounts of water. These uses, combined with the
use of water in a mineral production that has increased tenfold in the past ten years,
has resulted in heavy withdrawals from ground water.
The principal water problem in the State has been salt-water contamination. Most
of the large cities are located on the coast and the majority of these have had salt-
water encroachment problems. The rapid development of the water resources has created
many problems for municipal officials, and interference of wells and local over-
development are becoming apparent in the industrialized areas.
During six of the last seven years, Florida has experienced a severe drought. De-
clining water levels are causing great concern to cities and to individual well owners.
Data collected in the past should be analysed to determine the interrelationship of
rainfall, temperature, and water levels and to determine if low water levels might be
The topography of Florida is extremely flat and most of South Florida is less than
50 feet above sea level. Heavy rainfall results in extensive flooding, and during dry
periods there is a problem of obtaining fresh water for irrigation. At present, the
Corps of Engineers, U. S. Army, and the Central and Southern Florida Flood Control District
are engaged in a $300,000,000 project designed to eliminate floods and provide fresh
water during droughts. The construction of canals, levees, and control structures
changes water conditions day by day and makes evaluation of the hydrology difficult.
Health problems are of concern. In some areas, sewage is disposed of through
drainage wells or permitted to seep into surface sand. In several areas, badly needed
FHA and GI housing has been deemed unsafe by the State Board of Health because of its
concern with health standards and the quality of water supplies.
Large strip mines in parts of Florida are responsible for additional problems.
dewatering of the pits threatens drainage of several large natural lakes. To what
extent the excavations will alter the hydrology in the recharge area is important.
Ground water occurs in almost all rocks of Florida. The State is underlain by a
thick section of sands and limestones and most of these rocks yield some water but some
of them yield large quantities. Figure 1 lists the formations of the Cenozoic Era of
Florida and figure 2 illustrates generally the altitude of these beds. Usable fresh
ground water is confined to the upper few thousand feet of rock. The two principal
aquifers are the Floridan, which is artesian, and the Biscayne, in which the water is
under water-table conditions.
The Biscayne aquifer is composed of the Fort Thompson formation, the Caloosahatchee
marl, the Tamiami formation, and younger sediments. Insofar as the Floridan artesian
aquifer is concerned, the cover, or aquiclude, is composed largely of the Miocene sediments,
whereas the artesian water is contained in basal Miocene, Oligocene, and Eocene beds.
Thick columns of fresh water, present under recharge areas, may fill the pores of
sediments as old as the Paleocene.
Above the Floridan aquifer, linestones, some of which are very permeable and porous;
sands; and shell marls of Pleistocene and Miocene ages contain large quantities of
potable water of high quality under water-table conditions. These aquifers are utilized
along the coastal areas in southern peninsular Florida and in the western Panhandle,
where artesian water is salty or unavailable.
Artesian water occurs in a series of porous, coquinoid limestone. The water in
this widely spread, copiously producing group of rocks is held under pressure by the
clays, dense limestone, and sands of Miocene age, principally those of the Hawthorn
formation. The aquiclude covers the aquifer except for limited areas along the western
Peninsula and north-central Panhandle, where the limestones are exposed, as illustrated
in figure 2. In these areas heavy discharge occurs, but the development of more porosity
and permeability along essentially horizontal bedding planes than that developed ver-
tically maintains the hydrostatic head across the exposures. Because of the differential
in porosity and permeability, water moves slowly upward and leaks most rapidly as the
exposure is approached. Therefore, it will be found that in such discharge areas water
pressures are greater in the deeper wells.
Deep wells drilled for oil penetrate very salty water below fresh water over most of
the State. This water is commonly much more salty than sea water. From these records,
it is inferred that the entire State is underlain by the heavily mineralized waters and
that the fresh artesian water is floating upon the salty water because fresh water has a
lower density. The artesian water of Florida forms a series of dome-shaped lenses that
rest on an irregular surface of salt water. The depth to the contact of fresh and salt
water is roughly 40 times the height of water table or piezometric surface above sea
level. It would require a column of 40 feet of fresh water in the subsurface to raise
the water table one foot above sea level and 41 feet to balance a 40 foot column of salt
water of normal salinity and keep sea water out of the formations.
The shape of the upper surface of the mass of fresh water in the artesian system
is illustrated in figure 2. The thickness of fresh water is roughly 40 times the
piezometric surface, and in Jacksonville it is known to be about 2,400 feet, the original
piezometric pressures in the area having been about 60 feet above sea level.
The artesian aquifer in the southern part and in thin areas along the coasts of the
Peninsula contains salty water that is thought to have entered the aquifer in the geolo-
gic past and which is now being flushed from the rocks by fresh water.
OCCURRENCE AND DEFINITIONS
Ground water represents one phase of the hydrologic cycle. A part of the rain
that falls upon the earth enters the voids between rock particles and moves downward
to saturate the pores of the subsurface to a level depending upon the balance of the
amount of water entering from rainfall and surface seepage with that escaping from the
ground by leakage. Several belts or zones are present, see figure 3. In descending
order, the water present in rocks of the subsurface occurs with air in the voids of the
soil belt, where it is available for use in plant metabolism; in an intermediate belt
mixed with air and beyond recall by plant roots; and below the water table, where the
water saturates the subsurface. These belts are present under water-table conditions
where the surface of the ground water is free to rise and fall with the water supply,
unconfined by a covering bed.
Throughout much of Florida, water moves downward along pores in the rock and is
trapped below impervious water-tight beds. Wells that are drilled through this cap,
called an aquilude, produce large quantities of water. Water rises in the wells to the
hydraulic gradient and the wells are called artesian. If the gradient projects above
the ground surface, the water will flow from well orfices. Most of the State's larger
springs are artesian. Water wells basically are of two types: (1) water table, and
(2) artesian, both of which are dependent upon rainwater for recharge of the aquifer.
An artesian well is one in which the water level rises above the point of penetration
into the aquifer and, as such, it is similar to a water distribution system. In the
simplified illustration, in figure 3, the hydraulic gradient of a city distribution
system is diagrammed as the height that water will rise in vertical tubes along a line
projected from the tank water surface to the open end of the pipe, These principles of
hydraulics are the same whether in a city distribution system or in nature, but in the
latter the porosity and permeability of the formations and the distribution of recharge
and discharge areas complicate the flow.
a ral a e-- s
Aturt in Florida vary in area exeant froa statowi to local cootrrae se
fige 4, and inala e apprastately 20 fonations ranging fta m Doae to moent in age.
b r atter my be divAd into two types (1) that gas y knu as aat r iab and
(2) t1ha in wlich the water occurs under wnter-able condities. BaWpl of those
Sa tUapN s ae the Floridn aq r i ad tre ad tmqui~er, rerpeotivel. A brief
atIWS tf these aquifers and other principal sources of gromad-aber awLiAs is given
te Foridan aquifer, also komn as "the prince el. aeresian quieter tderlies
Spaottiely all of Florida and is the principal momrce of g mriA-toar sqpIues, acept
ia oeaOMs and Sauta Ros cemties, in easten eseo area autL h of Sft. Atustine,
Nat isn at of the ara south of Lake Okeeabobi. In these ashe te d fte' is either
ssitng or eaita water which is too higb y dnaeralised tO ms ams.
She aquifer CoaS it of limestone formbiaons a fetea d aos i b aides of feet in
tckneas. T major part of the limestone seefion Is sene in ai Ith ewlylang
liAeetemos of CLi eome and MLoce.ne a oecurring in sonm parts of the Skta. Those
sMral liesones feautioas act more or leas a sing a e .lo oaogic dit. The top of
the loAdan aquifer is at or near the land swrfae in the amh-efttrl. and nWrbusetrn
Ihe reas of recharge in the artesian aquifer can be whtiamad from a msp of the
pitmetric surface, see figure 5, which represents by contour lines the hetibt to which
the artoetan water will rise with relation to sea level. Generally, recharge to the
aretsan aetxa occurs where the pieoetric surface is high; for example, the hig area
rl.:~,ri-,r8:;u~l~*;i~~,_,~~.~.---~---; -------- ......LUYY1~-~--
centered around Polk County, from which most of the artesian water in central and
southern Florida is derived. Likewise, discharge from the aquifer generally occurs
where the piesometric surface is low.
The Floridan aquifer is the source of most of the large springs, of which, each of
17 has an average flow of more than 65 million gallons per day. The aquifer as a whole
is' very productive and wells which penetrate it yield from several hundred to several
thousand gallons of water per minute by natural flow or by pumping.
Wherever the piezometric surface stands higher than the land surface, wells will
flow under natural artesian pressure. The areas of artesian flow from the Floridan
aquifer cover roughly a third of the State, see figure 5. However, in most of the areas
of artesian flow the artesian water is relatively highly mineralised.
The Piesmetric Surface. The shape of the upper portion of Florida's artesian water is
illustrated by the piesometric surface, see figure 5. Such a surface is constucted by
measuring the water pressures in numerous wells that bottom in the artesian water-
bearing formations, referring these pressures to sea level, locating the wells upon a map
and connecting the pressures that are equal by smooth contours. In parts of Florida
these contours pile up to heights as much as 120 feet above sea level, as in Polk County.
In other areas and along the coasts these contours are lower in elevation and fewer
It is by means of such diagrams that the direction and distribution of flow of our
ground water can be determined, and combined with the elevation of the land surface; the
depth of the well, the amount of casing, and the height of water life can be forecast.
Where the contours pile up, water must be entering the aquifer at a recharge area and
where these contours decrease and approach sea level, the water must be leaking from the
aquifer in discharge areas. Large recharge areas are present in Polk, Hillsborough, and
Clay counties, Florida, and one is centered in southern Georgia. The saddle across the
central Peninsula, a large discharge area, is the site of many of the State's large
In the areas of the State where the ground surface is lower than the piezometric
surface, flowing wells can be developed.
The Biscayne aquifer of Dade and Broward counties is one of the most highly pro-
ductive water-bearing formations ever investigated by the Geological Survey. This
aquifer is a wedge-shaped mass of highly permeable limestone and sand, mainly of
Pleistocene age, underlain by relatively impermeable marl and clay of late Miocene age.
It attains a maximum thickness of about 200 feet in eastern Broward County and about 120
feet in the coastal area of Dade County. It underlies all the coastal areas of the two
counties and most of the Everglades and is everywhere highly productive. The aquifer is
composed predominantly of limestone in the Everglades area of Dade County, but it becomes
increasingly sandy toward the coast. It is the sole source of fresh ground water in the
area, yielding water that is very hard but of excellent quality for irrigation, and with
the exception of the hardness, it is of excellent quality also for industrial as well as
Ground water in the Biscayne aquifer occurs under water-table conditions. The water
table fluctuates in response to rainfall and is highest during September and October
and lowest in spring and early summer. The highest water levels of record occurred in
October, 1947, as the result of a hurricane causing extensive property damage in flooded
areas of Dade and Broward counties. The lowest water levels occurred in June, 1945, after
three years of deficient rainfall, and resulted in the accelerated movement of salt-water
inland along most of the coastal areas of Dade County. Salinity-oontrol dams installed
in the major canals of Dade County in 1946 have alleviated the salt-water encroachment
problem in most of the tidal canals.
Very large quantities of fresh water are available in the Biscayne aquifer. It is
estimated that 30 million gallons a day was utilized in 1950 in Broward County and about
100 million gallons a day in Dade County. These quantities represent only a small per-
centage of the potential yield of the aquifer. Withdrawals have increased appreciably
since 1950, but the over-all effect on water levels is negligible.
In addition to the above aquifers there are several other aquifers in Florida which,
like the Bisca'ne aquifer, are limited in area extent. These aquifers which are utilized
in localized areas occur under both water-table and artesian conditions. No attempt will
be made here to describe all of these aquifers in Florida, rather they will be grouped
by general areas.
The principal source of ground water in the Escambia-Santa Rosa County area is from
sand and gravel formations, in which the water occurs under artesian conditions. These
formations are principally Niocene in age and, geologically, are younger than the forma-
tions comprising the Floridan aquifer. The aquifer ranges in thickness from about 100
to 300 feet and occurs within 500 feet of the land surface.
Wells penetrating this aquifer, and properly developed, will yield over 1,000 gallons
of water per minute. Industries and municipalities are currently withdrawing large
quantities of ground water from this source.
Whereas, the hydrologic and geologic characteristics of this aquifer differ to some
extent from other aquifers in the State, perhaps the outstanding difference is in the
quality of water. The water from the aquifer in Escambia-Santa Rosa area is markedly
lower in mineralization as compared with the water from other aquifers. For example,
the total hardness of water from the municipal supply wells in Pensacola is less than
12 ppm and for the supply wells in Jacksonville (Floridan aquifer) the total hardness is
approximately 300 ppm.
Along the coastal ridge areas from St. Augustine to Stuart ground-water supplies are
generally obtained from shallow deposits of sands, shells, or limestones which make up
the many localized aquifers of relatively small areal extent. These aquifers range from
10 to 100 feet in thickness and occur within 150 feet of land surface.
The ground water occurs under water-table conditions and the aquifers are recharged
by local rainfall. The water-bearing properties of these aquifers will vary considerably;
but on the whole well yields are small in comparison to those obtained from either the
Floridan or Biscayne aquifers.
In southwestern Florida the principal source of ground water is from shallow aquifers
(water-table and artesian) and in parts of the area from the Floridan aquifer for
irrigational use only.
The formations making up the various shallow aquifers range in age from late Miocene
to Pleistocene. These formations are principally limestones and shall beds ranging in
thickness from a few feet to approximately 50 feet. Most of the aquifers occur within
100 feet of the land surface and with a few exceptions have a very limited areal extent.
Even though the aquifers have limited extent there are relatively few areas where shal-
low wells will not provide an adequate source of water supply for domestic use. In
several areas the aquifers are suitable for the development of relatively large water
supplies for municipal and irrigational uses.
The water-bearing properties of the various aquifers will vary considerably but well
yields generally range from 10 to 200 gallons per minute. In some cases wells are
purposely pumped at rates below the maximum to minimize the possibility of inducing salt-
water contamination; for example, the municipal wells at Naples.
Cone of Depression and Interference
When a well is pumped or allowed to flow, water levels in the area around the well
are lowered. The water-table surface, or the pressure surface for artesian conditions,
arranges itself in the shape of an inverted cone. This cone of depression may extend
from a few feet from the pumped well to several miles. When the cones of depression of
two or more wells overlap, well interference develops. For this condition the pumping
lifts will be increased or the well yields will be diminished. Figure 6 illustrates the
cone of depression for one pumping well, and the interference effects when two and three
wells are pumped.
The shape of the cone of depression is controlled by the nature of the openings in
the rocks. Where the openings are large the cone is flat; where the openings are small,
the flow is restricted and the cone is steep. The amount of drawdown depends on the
pumping rate and on the rate of release of water from storage. Drawdowns can be pre-
dicted for any distance from a pumped well if the hydraulic characteristics of aquifer
are known. These constants can be determined by making a controlled pumping test. Such
tests are an important part of a ground-water investigation of an area.
To achieve proper economic development of the ground-water resources of an area,
well interference must be considered in planning well fields. During the last war when
many large industrial plants were built in areas where adequate ground-water data were
not available, costly failures in water supply resulted. In some cases plants were
located too close to one another or too close to city well fields. Within a few months
the cones of depression overlapped and the yield of both fields was diminished. Florida
is presently undergoing increased industrialization. There is a strong possibility that
an industry might locate a well field close enough to a city well field to cause reduction
in yield, or to locate so as to seriously reduce the flow of springs. In one instance
the flow of a large spring has been reduced to zero.
At the present time there is not enough dat a available in most areas to determine
the proper spacing of well fields. Even if technical data were collected, there is no
legal method of preventing a new installation from being located unreasonably close to
an existing well field.
Water levels in wells provide a measure of the amount of water in storage in the
aquifer. When water is added to the aquifer, water levels rise. Rainfall is the principal
source of recharge. The water percolates downward through the openings in the rocks, in
some areas, flows down to the aquifer through natural sinkholes. In some parts of the
State drainage wells are used to dispose of excess surface water. Recharge may also occur
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by direct movement of water from streams, ponds, and lakes into the formations. When
water is lost from the aquifer, water levels decline. Water moves from points of
recharge toward points of lower altitude. Most of the discharge occurs as seepage to
the ocean, to lakes, and to streams, or as springs. Water is withdrawn from the
aquifer through wells.
When the total recharge exceeds the total discharge, water levels rise. When dis-
charge exceeds recharge, water levels decline. Thus, water-level records are of prime.
importance as a running inventory of our ground-water resources.
Graphs are presented that show selected records of water levels for water table
and for artesian aquifers, in pumped areas and in unpumped areas, see figures 7-12.
The most prominent feature is the rapid decline in water levels in many parts of the
State during the past three years. This decline results from the meager recharge re-
sulting from abnormally low rainfall. Another prominent feature on most of the graphs
is the high water levels of 1947-48 which were caused by excessive rainfall.
ROLE OF SPECIAL PURPOSE DISTRICTS AND POUNDED WATERS
IN CREATING RECHARGE IN FLORIDA
Florida is one of the several states of the Union that allows and recognizes the
need for, the formation of semi-public corporations with tax powers, to regulate water
levels in specific areas, as opposed to vesting control in branches of the State or
County governments. These drainage, water control, reclamation or conservancy districts,
as the names imply, are formed to construct, maintain and operate facilities to reclaim
selected areas of land for productive use.
Substantial areas of the State have, at one time or another, been incorporated into
one or more of these special districts. Records show that approximately 28,460 square
miles of Florida have in the past or are at the present time, incorporated in one or more
of these special purpose districts. Many parts of this large area have been in more than
one such district at the same time and many of the areas have been incorporated several
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times throughout the years. The significance of this large total area and the repeated
inclusion of many areas points directly to the desirability and the necessity of such
special purpose districts as a positive means of controlling and conserving water in
The largest of these special purpose districts is the Central and Southern Florida
Flood Control District encompassing 15,500 square miles of all or part of 17 counties.
The co-operative program of this district with the Corps of Engineers will provide
860,000 acres of conservation area lands, 730 square miles of Lake Okeechobee, 55 square
miles of LakeIstokpoga as well as large areas in the Kissimmee and Upper St. Johns
basins for the retention and storage of surplus waters. Regulatory powers, funds and
organized planning are thus assured to further the interests of water conservation through-
out an area comprising 25 o/o of the State of Florida.
Indicative of the future trend in regulatory semi-public corporations is the
Oklawaha Basin Recreation and Water Conservation and Control Authority. This organiza-
tion is charged with the responsibility for the control and conservation of waters in
Lake County. The motivating factor necessitating the creation of this authority was the
need for stabilizing water levels in the various streams and lakes of the county and
prevention of extreme low levels. This is significant, as many districts were organized
initially for the purpose of draining lands, and only in recent years have come to recog-
nize the importance of sound control and conservation of water.
Early drainage districts performed their primary functions of draining and re-
claiming land until such time as the combined effect created over-drained conditions
demanding recognition of the vital need for retaining and conserving a maximum amount
of the available water resources. Virtually all recently organized drainage districts
recognize at their beginning, the importance of conserving local water resources as well
as disposing of surplus waters.
This trend toward an awakening and recognition of the need for conservation of water
resources leaves little doubt of the profound effect of this organized effort to con-
- 12 -
serve surface water. It is an incidental but significant factor that conservation of
surface water through ponding and maintenance of high water levels affects the recharge
of ground waters. Were the entire State of Florida subdivided into many geographic
areas, each having jurisdiction and control of water levels within a particular drainage
area, the combined effect of such regulated conservation would be of importance to the
State and would virtually insure the greatest measure of conservation and most judicious
use of water resources.
LOCAL LOWERING OF WATER LEVELS
There has probably been no general permanent lowering of piezometric pressures in
the Floridan aquifer, but in some areas local cones of depression have been formed by
heavy pumping. Localities where local lowering of water levels is most pronounced are
Fernandina, Jacksonville, Foley, Panama City, and Pensacola.
Fernandina. Two industrial plants at Fernandina punp large quantities of water for use
in their processes. The result of the heavy withdrawal has been to lower the piezometric
surface from an estimated 60 feet above sea level, when pumping began, to a present level
which is below sea level at the lowest point in the cone of depression. Figure 13 shows
the decline of the water level in a typical Fernandina well during the period 1946-55.
Jacksonville, Municipal and industrial wells in the vicinity of Jacksonville are
pumped at rates which approach 100 million gallons daily. That pumping has caused a
progressive decline of the water level of about 30 feet in the last 50 years. The de-
cline since 1941 can be seen from the hydrograph of a typical well shown in figure 14.
Foley. The effect of heavy withdrawal from an aquifer is shown quite strikingly by the
well hydrograph in figure 15. A large industry went into full operation at Foley in
1954. Previous to that time water levels in wells fluctuated generally with rainfall.
When heavy pumping began, water levels declined abruptly and within two years had fallen
- 13 -
Il Ii r h
over 20 feet.
Panama City. Heavy pumping of wells in the Panama City area has lowered the piesometric
surface in the vicinity of the wells over 40 feet. The well hydrograph in figure 16 shows
a progressive decline of about 20 feet from 1946 to 1955. Temporary slowing of the
decline was caused by the abnormally heavy rains of 1947, 1948, and 1953.
Pensacola, Wells in the Pensacola area do not penetrate the Floridan aquifer. Water
supplies are obtained from the pervious layers in interbedded sands and clays of Miocene
age. Water in these sediments is under artesian pressure and pumping by industrial
plants has caused a progressive lowering of the head in the vicinity of wells, as shown
by the well hydrograph in figure 17. At Cantonment, about 15 miles north of Pensacola,
pumping by an industry has lowered the head over 35 feet since 1940.
Effect of Local Cones of Depression
Serious depletion of aquifers by pumping is a distinct possibility and lowered
water levels will affect the cost of obtaining water. As the water level is depressed,
it may be necessary to install larger pumps, deepen wells, or drill additional wells to
obtain the same yield. The most serious aspect of the formation of cones of depression
is in areas where the aquifer connects with the sea, or overlies salty water, and the
water level at the pumped wells is drawn below sea level. In such cases, continued
heavy pumping may draw salt water into the wells.
WASTE OF GROUND WATER
Ground-water waste occurs in Florida in all cases where water from an aquifer is
not or cannot be utilized completely; where it is not re-used when economically possible,
or where it is made unfit for use by contamination. As such, these wastes are classified
as 1) excessive development or over-draft in a well field, 2) consumptive uses, and,
Excessive development and overdraft in a well field cause a decline in the piezo-
metric surface (loss of head) with an accompanying increase in costs and loss of yield.
Extreme cases of overdraft may ultimately reduce the hydrostatic pressures to a point
where salt water from depth or from the ocean, if nearby, will migrate into the well
field and contaminate the supply. The porosity and permeability of the formations of
each large well field should be carefully determined by pumping tests and the adjacent
areas of recharge and discharge plotted so that well spacing, well sizes, and pumping
rates can be set to minimize the interference between wells. Then the field can be
safely developed for maximum yield.
The consumptive waste includes excessive irrigation, wild-flowing wells, and the
nonadvantageous use of springs, streams and lakes. Unfortunately, many citizens are
not educated to their responsibilities and allow their wells to flow continuously or
pump them beyond their needs. Ma~y flowing wells have been abandoned, their casings
rotted; and, in some cases, their waters are highly saline. The Florida Geological
Survey is currently engaged in an inventory of the flowing wells of the State. Of two
counties in which this inventory is now completed, 361 flowing wells were tabulated, of
which 80 were flowing continuously, the water unused and wasted. Of these 80 wildly-
flowing wells, the water from 51 had chloride contents of 250 ppm, or more, and water
from nine were not analysed. The chloride content ranges upward to 3,310 ppm, and this
water is contaminating the ground water of shallow aquifers, resulting in waste of
Ground water is made unfit for use and wasted through contamination by industrial
and municipal wastes and sewage, contamination by salt water trapped in the formation
and not eliminated by casing, and water used for cooling but not returned to the aquifer--
even though heating may make the water undesirable for some uses. In the past some cities
and industries disposed of their wastes and sewage through drainage wells and in sink
holes that connect with the aquifers. Although this practice is being discouraged and is
being discontinued, there are many offenders that continue this type of disposal. Large
quantities of sewage and waste have been placed in theaquifer and will be a source of
contamination for years to come.
Definition and Statement of Problem
The problem of salt-water intrusion may be found in many coastal areas where labge
volumes of water must be withdrawn from permeable formations in contact with sea water.
However, salt-water encroachment in Florida involves more than the intrusion of
ocean water into fresh water. The State Board of Health considers 250 parts per
million of chlorides as unsuited for human consumption and if encroaching water exceeds
this concentration it is considered to be saline. Such salinity may originate from
today's sea water, from connate sea water trapped in the rocks of the aquifer at the
time the rocks were deposited, and from residual sea water filling the pores of the rock
at a time when the land was flooded by high seas. In addition to these natural causes,
salt from the disposal of industrial and municipal wastes and the concentration of salts
upon the land during irrigation add considerable salinity to natural waters. Irriga-
tion waters normally contain some salts. Evaporation and transpiration leave these
salts in the soil which may be made unproductive. This problem has been experienced
in some areas of Hillsborough, Seminole, and Manatee counties. Where water flow and
drainage are sufficient to remove the salts, the accumulative effect may be felt in the
lower parts of a drainage basin.
For the purposes of this study, salt-water intrusion is defined as the movement of
saline water into the fresh ground water whether derived from adjacent oceans or from
underlying or entrapped salt waters.
Unconfined ground water has a water table that roughly follows the local topography
in coastal areas and may be exposed in surface basins of low head above mean sea level.
Normally the level in unconfined fresh water aquifers is above sea level and since water
does not flow up hill, sea water does not enter and contaminate the fresh water. But
when the fresh water level is lowered sufficiently by pumping, the sea water will flow
- 16 -
into the aquifer, resulting in salt water intrusion.
In Florida's confined aquifers the salt-water that apparently everywhere underlies
the fresh water is depressed by the artesian head. During withdrawal of water, the
reduction of this head creates a mound in the salt water beneath the well, and overpro-
duction may cause this mound to intrude into fresh water aquifers and even intersect well
Some wells penetrate lenses of rock that contain saline water interbedded with reek
containing fresh water. If these wells are not constructed properly, and the saline
water cased out, aquifers having lower hydraulic heads will be contaminated by the
movement of the saline waters through the well into fresh water aquifers.
The hydraulic principles controlling the relationship of fresh water to salt water
are illustrated in figure 18. Because fresh ground water is lighter than normal sea
water it floats upon the heavier liquid and a column of fresh water 41 feet high will
balance a column of salt water 40 feet high. This is illustrated by the U-tube of
figure 18. In pervious aquifers, therefore, for each foot of head of fresh ground water
above sea level there would be a column of fresh water extending 40 feet below sea level.
This hydrologic factor, expressed originally by Ghyben and Herzberg, states that the
depth of fresh water is equal to a distance of (S-I) times the height of the water above
sea level, where S is the specific gravity of saline water. Recent work by members
of the U. S. Geological Survey indicates that observed field data correspond to this
principle, modified by the depressive force of ground-water flow and by the dissipation
of the water along the leading edge of the saline wedge.
Under the Ghyben-Herzberg principle a lens-shaped body of fresh water will develop
in porous sediments of rock in equilibrium and floating upon a depressed surface of saline
In Florida where the artesian aquifer dips beneath the ocean and gulf there is
usually a hydraulic balance between the fresh and saline waters in a modified G yben-
Herzberg principle. This relationship is illustrated in figure 18. The artesian aquifer
- 17 -
is exposed along the highlands where it is recharged by rainfall. Well number 1 is
under water-table conditions, but downdip the aquifer is covered by poorly pervious
sediments and the confined water rises in wells above the top of the aquifer. Well
number 2 is artesian but will not flow, whereas well number 3 is a flowing artesian well.
Well number 4 is hypothetically drilled at sea to illustrate the decrease of artesian
head in wells cased into the contact of fresh water with saline water.
Factors Contributing to Salt-Fresh Water Equilibrium Adjustments
A. Loss of head through increased demands by municipalities. The demands of
agriculture, due largely to modern irrigation; and by industry with hydraulic mining,
pulp and paper mills, and refrigeration are examples.
A. Excessive drainage. High water levels in the Everglades and under the Atlantic
Coastal Ridge were materially lowered by the digging of the Everglades Drainage Canals
during the first quarter of the current century. The result has been excessive drainage
and a lower water table that no longer holds in check the salt water from the ocean.
C. Lack of protective works against tidewater in bayous, canals, and rivers. This
factor is particularly prevalent in South Florida between Miami and Fort Lauderdale
where numerous canals and old discharge channels cut the Atlantic Coastal Ridge.
D. Improper location of wells. Wells, in an area subject to salt-water intrusion,
should be located as far as economically feasible from the source of possible salt-water
intrusion and properly spaced with respect to each other to prevent interference.
E. Highly variable annual rainfall with insufficient surface storage during
droughts. The most important single problem having to do with water conservation and
control in Florida lies in the fact that the rainfall is highly variable, resulting in
variations in the piezometric surface.
F. Uncapped wells and leakage. Uncapped artesian wells, in many cases flowing to
waste, represent a serious loss of ground water and must inevitably result in lowered
ground water levels. Even when capped, many old artesian wells have broken or corroded
casings that permit highly saline water from salt residuals to contaminate the fresh
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water in overlying strata.
Typical Examples of Salt-Water Intrusion
Those counties west of the Suwannee River are considered to be Panhandle Florida
and the remaining counties are in Peninsula Florida. Areas in which salt-water intru-
sion into fresh water is occurring is shown in figure 19.
Panhandle Florida: The water supplies of Escambia County and a part of Santa Rosa
County are soft and very low in total dissolved solids. These waters are contained,
under artesian pressure, in plastic sediments of Miocene age, but the aquifers are
hydrologically distinct from the Floridan aquifer.
The effect of huge withdrawals by large industries, armed services installations,
and larger municipalities located near the coast in Elcambia and Bay counties should be
carefully watched to prevent further salt-water intrusion.
Salt-water intrusion is local in the sparsely settled coastal areas of Panhandle
Florida. Analyses of water from artesian springs and wells in this area show that the
normal chloride content of these waters is less than 25 ppm except for well-known mineral
springs. Scattered observation wells in Walton and Wakulla counties indicate limited
and local salt-water intrusion in the unconfined aquifer.
No evidence of serious salt-water intrusion is known from Santa Rosa, Okaloosa,
Gulf, Franklin, Jefferson, Taylor, and Dixie counties on the Gulf Coast, or for the
counties of the Panhandle that do not border the Gulf of Mexico.
Peninsula Florida: In 1950, the Cedar Key municipal supply, consisting of five wells,
had a composite analysis showing 675 ppm chloride as evidence of salt-water intrusion,
but elsewhere along the Gulf coastal area of Citrus and Hernando counties no intrusion
has been observed.
Problems of salt-water intrusion are present at Cedar Key, New Port Richey, the
Pinellas Peninsula generally, Tampa, Manatee and Sarasota counties, Punta Gorda, Fort
Myers, Naples, Everglades City, Miami and vicinity, Fort Lauderdale, Cocoa and other
Brevard coastal cities, Daytona Beach and vicinity, and Flagler and St. Johns counties,
see figure 19.
The salt water that contaminates well supplies of Manatee and Sarasota counties is
contained in porous rock, stratified and interbedded with rocks containing fresh water.
The salt-water intrusion in Volusia, Flagler, Seminole, and St. Johns counties is most
likely rising from the salt water that generally underlies the fresh artesian water.
Elsewhere the intrusion is largely from adjacent ocean water.
Except for local recharge areas centered in Volusia and southern Putnam counties,
water in the Floridan aquifer that underlies the coastal area, between the Atlantic
Coast and the St. Johns River and extending from the middle of St. Johns County south-
ward to Lake Okeechobee, westward across Glades and Charlotte and including the coastal
margins of Sarasota, Manatee, Hillsborough, Pinellas, Pasco, Hernando, Citrus, Levy
and Dixie counties has a chloride content of 100 parts per million or more at moderate
depths. It is commonly too salty for human consumption or for most industrial uses.
Some irrigation benefits are obtained through the use of this water to raise the water
levels in canals and thereby elevate local ground-water tables beneath groves and fields.
In general, with the possible exception of geologically entrapped salt water, in-
trusion of salt waters into fresh waters of the State is a direct result of large
withdrawals of water and excessive drainage of low surface areas. Increasing chlorides
and decreasing heads in fresh water aquifers are indicators of approaching salt-water
intrusion. Coastal areas of large withdrawals should be placed under regular observa-
tion and the withdrawals, spacing of added wells, and conservation practices governed
by the data of these observations.
Ground-water investigations are made for the purpose of evaluating the quantity
and quality of the ground water available for use, to provide for orderly development of
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_ II 1 __
this resource, and to provide information for proper planning so as to avoid interference,
waste, and overdevelopment. Information is also necessary in order to solve salt-water
encroachment problems and to protect supplies from contamination.
Nature of Ground-Water Investigations
In evaluating ground-water supplies it is necessary: to define the location,
thickness, and lateral extent of the water-bearing formations; to describe the water-
bearing properties of the formations; to evaluate the quantity of water stored in the
formations; to determine the area where water enters the formations from streams or
from rainfall, the direction and quantity of ground-water movement, and the points of
discharge; to map the artesian pressure and water levels; to obtain information on the
chemical properties and temperature of the water; to appraise the quantities available
for use; and to chart the (time) trends in water levels and quality.
A well-balanced program includes the following: collection of basic data, research,
interpretation, and publication of results.
The basic-data program is of two types.
1. Collection of records of factors which change with time. This program includes
the operation of a network of observation wells in which water levels are measured
periodically or on which recording instruments are maintained to obtain a continuous
record of water levels. In areas threatened by salt-water encroachment, samples are
collected periodically and analyzed for chloride content to provide a record of any
changes in salinity. Time records of other factors such as rainfall, temperature of
water, spring flow, river, lake, or pond elevation, barometric changes, ocean tides,
pumpage, and artificial recharge are collected in connection with specific area studies.
Continuing-type records are collected to meet certain needs. The basic network of
observation wells should be continued indefinitely. Long-term records are needed to
evaluate the effects of droughts and wet periods on the availability of water, to
evaluate the effect of long-term pumping on the water levels, to provide a basis for
- 21 -
evaluating the effects of water management and conservation programs on the supplies,
and to provide information for planning efficient use of the available supplies. In
connection with area investigations, records are collected more intensely over a limited
period of time. At the close of the area study, these records are discontinued.
2. Collection of data on factors which do not change with time. This part of the
program includes mapping the geology, determining the position, thickness, and extent
of the water-bearing formations, determining the water-transmitting and storage proper-
ties of the formations. These facts are usually assembled on an area basis. These
studies may include only small areas to meet specific problems, may be county-wide in
nature, or may include several counties. The investigations may be of a reconnaissance
type, perhaps a year per county, or may be comprehensive, in which case three to six
years may be required to study a single county. Where financially feasible it is con-
sidered desirable to include surface water and quality of water in a comprehensive
study. In many cases the relation between streams and ground water, lakes and ground
water, and springs and surface water are such that inadequate conclusions can be reached
if only one phase is studied.
Research is normally carried out in connection with the program. Problems met in
the field are complicated and new methods must be devised to arrive at valid conclusions.
Aside from the salt-water encroachment problem, there are many phases of the work which
have not been adequately evaluated because of limited funds and personnel. Some of the
problems to be worked on in the future are: correlation of rainfall and temperature with
water levels as a means of evaluating recharge and as a method of predicting water levels;
correlation of water levels and stream flow; study of the relation of ground-water levels
and lake levels; study of upward and downward leakage in aquifers and effects of pumping
wells in layered or stratified formations; and effects of jointing and faulting on the
movement and quality of ground water.
Results of investigations are released to the public in formal reports and in open-
file releases. Basic data are available on request. Records of water levels are
- 22 -
published annually. Project or area type studies terminate in an area report which
includes tables of basic data; maps of geology, water pressure, and quality information;
analysis of data; and interpretation of results.
History of Investigations
Formal ground-water investigations in Florida began shortly after the turn of the
;Century. Early work, which was of a reconnaissance nature covering fairly large sec-
tions of the State, was published in reports of the Florida Geological Survey and the
U.S. Geological Survey during the period 1908-1913.
In 1930, cooperative relations were established between the Florida Geological
Survey and the U.S. Geological Survey, a relationship which has continued uninterrupted
to the present time. During the period 1930 to 1939 investigations were very limited
because of the limited funds available to both agencies. Reports were published on the
Sarasota area, Seminole County, and the Lake Okeechobee area, and information was
published on preliminary investigations in Manatee, Orange, Pinellas, Hillsborough,
Seminole, and Duval counties. In 1933, a report on artesian conditions in the peninsular
part of Florida was published. This report included the first published map of the
artesian pressure surface. Quantitative studies were made in the industrial areas at
Pensacola and Jacksonville.
In 1939, the cities of Miami, Miami Beach, and Coral Gables became alarmed about
the encroachment of salt water as related to the increased pumping in the area. An
intensive investigation of the water resources of the area and of the salt-water encroach-
ment problem was begun in the 1940 fiscal year under local and federal funds. By 1943,
the most intensive part of the work was completed and the scope of the program was
reduced. A program of observations of water level and observations on the location and
movement of the salt-water front has continued since 1943 with funds from Miami, Miami
Beach, Dade County, and the Florida Geological Survey, matched with U. S. Geological
Survey appropriations. A part of this work has been research on the mechanics of salt-
In 1940 and 1941, a study was made in the Pensacola area (City, State, and Federal
funds) to determine if pumping by a proposed industry would cause interference with
existing city and military installations. The City of Pensacola has continued financial
support of an observation well program in the area.
During the period 1944 to 1950, rapid growth in population required expansion of
many city water supplies. To partially meet the needs for basic information, the
Florida Geological Survey's contribution was increased from $6,550 in 1944 to $25,000
in 1947. In addition, local funds were furnished by Dade, Nassau, and Pinellas counties,
and by the cities of Pensacola, Miami, Miami Beach, Fort qyers, Fort Lauderdale, Lake
Worth, Delray Beach, St. Augustine, and Dania. Reports were published on the Fort
Lauderdale area, Miami area, and Orlando area. During this period a large part of the
present State-wide network of observation wells was established and equipped with
From 1950 to 1956, the accelerated growth of population and migration of industry
to Florida greatly increased the interest in ground-water investigations. During this
period county investigations were begun in ten counties. Federal funds were matched
with the following cooperating agencies:
Florida Geological Survey
Florida State Board of Conservation
Central and Southern Florida Flood Control District
Santa Rosa Island Authority
Dade Daytona Beach
Hillsborough Miami Beach
Manatee New Smyrna Beach
Polk Port Orange
In the 1956 fiscal year, total funds for theprogram were $194,800 of which $98,000 was
contributed by the U.S. Geological Survey, $49,500 by the Florida Geological Survey,
$14,500 by the Central and Southern Florida Flood Control District, $17,700 by counties,
and $15,100 by cities.
The program for the 1957 fiscal year is $205,000. Cooperating agencies are:
Florida Geological Survey
Central and Southern Florida Flood Control District
Dade Daytona Beach
Hillsborough Miami Beach
During the period 1950-56, reports were published on the following areas:
Fair Point Peninsula, Santa Rosa County
Central and Northern Florida
Naples area, Collier County
Palm Beach County
Biscayne Aquifer (Broward-Dade Counties)
Artesian Submarine Springs
Progress reports were published on:
Ground Water in Florida
Ruskin area, Hillsborough County
Volusia County (northeastern part)
A table of well data and maps were released for Brevard County.
Water levels and artesian pressures were published annually in water supply papers.
The scope of the present program is illustrated in figures 20 and 21.
The State-wide network of observation wells shown in figure 22 has 186 locations
where periodic or continuous records of water levels are collected. Of these, 104
are equipped with automatic recorders. In addition, records are being collected at 41
recording and 523 non-recording stations in connection with project investigations,
many of which will be discontinued at the close of the project investigation.
Figure 20 shows the areal investigations now in progress. A large part of the
program is concentrated along coastal areas where threats of salt-water intrusion are
of prime importance. Funds were made available in these areas because of heavy pumping
in the rapidly growing heavily populated areas. Most of northern and Panhandle Florida
have not yet experienced the large water requirements of new industry and rapid
Need for an Expanded Program
Florida is expanding rapidly in population and in industrial development. Nearly
all of the cities have or will have to expand their water facilities. The impact of
new industries is being felt. Many of the new industries, particularly pulp mills and
chemical industries, are users of extremely large quantities of water. Florida has an
abundance of water; however, the quantity and quality of water available at any one
point is not always readily determinable. A comprehensive program to appraise the
ground-water resources for the State is badly needed:
1. To supply information to prospective industries, to help them find locations
which have water of adequate quality and quantity for their purpose.
2. To delineate areas of limited supplies so that overdevelopment and substantial
financial loss will be avoided.
3. To obtain more information on the occurrence and movement of salt water so as
to avoid costly repetition of salting of well fields.
4. To make information available to consulting engineers for planning expansion
of well fields.
5. To provide information on supplies available for irrigation.
6. To provide general factual information needed in resolving legal problems on
water use and water rights.
7. To provide basic geologic and hydrologic information needed to cope with
pollution, drainage problems, and artificial recharge.
8. To make basic data available to Federal, State, and local agencies engaged in
water management and water conservation activities.
9. To provide ground-water data needed to evaluate the over-all hydrology of the
Financing and Responsibility
At the present time, most of the systematic ground-water investigations are made
by the U. S. Geological Survey in cooperation with State and local agencies. The
Florida Geological Survey is the State agency having responsibility for this work.
Under the present cooperative arrangement between the Florida Geological Survey and the
U. S. Geological Survey, the Florida Geological Survey acts as a coordinating agency.
The State agency encourages county and city participation in the program. This arrange-
ment has the advantage of steering State and Federal funds into areas where work is badLy
needed. If a city or county is willing to contribute financially, this fact in itself
shows that the problem is of sufficient interest to the local people that they are
willing to help pay the bill. This method of allotting funds has certain disadvantages.
First, advance planning on a State-wide basis cannot be achieved. By the time a city
or a county requests an investigation the problem has usually become quite serious. In
most cases considerable money would have been saved if the investigation had been made
five to ten years earlier so that the information would have been available before the
problem became critical. If a larger amount of State funds could be made available
the program could be accelerated and could be planned on a State-wide basis rather than
on the present piecemeal problem area basis. Second, the present method of working in
critical areas does not allow for a realistic approach to the study of the hydrology.
- 27 -
Generally, rainfall enters the Floridan aquifer in the central part of the State, seeps
eastward to the Atlantic Ocean or westward to the Gulf of Mexico. This cycle is not
related to city or county boundaries. In order to evaluate properly the quantities of
water involved in this cycle the problem must be studied more broadly than can be done on
a county investigation. Third, the present method of financing does not give assurance
of a continuing program. Operation of a successful program requires special equipment
and trained personnel. Where a substantial portion of the funds comes from cities and
counties there is no certainty from one year to the next that these local agencies will
continue the, program. A well-planned program solidly financed at State and Federal
level is needed.
Relation of Ground-Water Program to Work of Other Agencies
The ground-water program is a part of the U. S. Geological Survey program of water
resources investigation. Because of the many interrelationships between ground water
and surface water, the ground-water program must be planned and carried out by close
coordination with the Surface Water Branch. The work of the Quality of Water Branch
which deals with the chemical quality of both surface and ground water, must also be
closely coordinated in planning and operating a program.
Topographic mapping is a very important program. Topographic maps are needed for
locating wells, mapping the water-bearing formation, and for establishing elevations for
use in drawing water elevation and water pressure maps. The present U. S. Geological Sur-
vey topographic mapping program (all Federal funds) includes new maps for large areas of
the State. However, there are several important areas on which no work is scheduled, and
several areas in which maps are old and are not adequate for present-day needs. A cooper-
ative program between State and Federal agencies to adequately map the State would be
very beneficial to ground-water studies. Good topographic maps will greatly improve
the accuracy of the ground-water maps and reports and would save time and expense on the
Ground-water investigations require a considerable amount of geologic work. The
cooperative relation between the Florida Geological Survey and the U. S. Geological
Survey provides for coordination and exchange of all geologic information. Recent
ground-water work shows that the structure of the formations is of major importance in
governing the movement of water and the salting of aquifers. There is need for an
extended and enlarged program of geologic mapping. All subsurface and surface geological
work done by the Florida Geological Survey will be of considerable value in compiling
and interpreting ground-water data.