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Group Title: Circular Florida Cooperative Extension Service
Title: Florida's groundwater resource
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00014496/00001
 Material Information
Title: Florida's groundwater resource vast quantity, good quality?
Series Title: Circular Florida Cooperative Extension Service
Physical Description: 5 p. : ill., maps ; 28 cm.
Language: English
Creator: Graham, Wendy D ( Wendy Dimbero )
United States -- Extension Service
Publisher: Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida
Place of Publication: Gainesville Fla
Publication Date: 1991
Subject: Groundwater -- Florida   ( lcsh )
Groundwater -- Quality -- Florida   ( lcsh )
Groundwater -- Pollution -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
Bibliography: Includes bibliographical references (p. 5).
Statement of Responsibility: Wendy D. Graham.
General Note: Cover title.
General Note: "June 1991."
General Note: "This material is based upon work supported by the USDA, Extension Service, under special project #90-EWQI-1-9214."
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Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: ltqf - AAA6936
ltuf - AHY6936
oclc - 24323071
alephbibnum - 001670177
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Table of Contents
    Front Cover
        Front Cover 1
        Front Cover 2
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
    Back Cover
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Full Text

9 June 1991

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Circular 944

Florida's groundwater resource:

Vast quantity, good quality?

Wendy D. Graham

Florida Cooperative Extension Service
Institute of Food and Agricultural Sciences
University of Florida
John T. Woeste, dean


Wendy D. Graham, assistant Professor, Department of Agricultural Engineering, IFAS, University of Florida, Gainesville, Florida 32611-(


SWater is one of Florida's most
valuable resources. Each year
millions of residents and tourists
enjoy the recreational opportunities
and esthetics afforded by thousands
of miles of ocean and marine
waterways along the coasts.
Though scenic and plentiful, this
water cannot be used for drinking,
irrigation, or industrial supply,
because of its salt content. Fresh
water supplies come from extensive
beds of porous rock beneath the
ground called aquifers and from
fresh water lakes, streams and
reservoirs. Figure 1 summarizes the
status of Florida's fresh water
sources and uses in 1980. As this
figure illustrates, over 50% of the
total fresh water used in Florida
comes from groundwater, and over
90% of the public rely on groundwa-
ter supplies for their drinking
water. Thus groundwater is a
particularly important resource for
this state.
Of all the fresh water withdrawn
in Florida, only about one-third is
consumptively used, i.e. consumed
by evaporation, transpiration or
.production processes. The remain-
ing two-thirds are returned to the
environment, either to surface
streams or to aquifers. Because
water comes into contact with a
variety of heavy metals, organic
chemicals, pesticides and fertilizers
during its use, the quality of the
water which is returning to the
environment has become a wide-
spread concern.

Groundwater and
the hydrologic


The continuous circulation of
water from land and sea to the
atmosphere and back again is called
the hydrologic cycle. Figure 2
provides a schematic diagram of the









138 177



Figure 1. Florida's water uses and sources 1980 [7].

Figure 2. The hydrologic cycle [6].

hydrologic cycle for a generalized
Florida setting. Inflow to the
hydrologic system arrives as pre-
cipitation, primarily in the form of
rainfall in Florida. Outflow takes
place as streamflow (or runoff), as
evapotranspiration (a combination
of evaporation from open bodies of
water, evaporation from soil sur-
faces and transpiration from the
soil by plants), and outflow from the
groundwater flow system (to wells,
rivers, springs or oceans). Precipi-
tation is delivered to streams both

on the land surface, as overland
flow to tributary channels, and b3
subsurface flow routes, as interflc
and baseflow following infiltration
into the soil.
Between the land surface and t
groundwater table is the unsatur-
ated, or vadose zone, where both
water and air occur in the soil
pores. In the flatwoods soils of
Florida the unsaturated zone is
typically small. It may occupy the
first 10 to 40 inches below the
ground surface in the dry season,





Figure 3. a) unconfined aquifer, and b) confined aquifer.

and may be non-existent in the wet
season when the water table is at or
above the ground surface. In the
sandy soils of the Central Florida
Ridge however, the vadose zone can
extend 100 feet or more. Water in
the unsaturated zone is either
taken up by plants, evaporated, or
drained by gravity into the satu-
rated zone.
In the saturated groundwater
zone all pores and crevices are filled
with water, and all of the air has
been forced out. Water seeping into
this zone is called recharge.
Groundwater can occur either as an
unconfined (phreatic) aquifer, or as
a confined (artesian) aquifer as
illustrated in Figure 3. In an
unconfined aquifer, the water table
forms the upper boundary of the
aquifer, and the water level in a
well will rest at this level. Water
infiltrating from the surface has the
potential to move rapidly into an
unconfined aquifer, thus there is a
good chance of contamination from
surface activities. In an unconfined
aquifer, groundwater moves by
gravity from areas of high water
table elevation to areas of low water
table elevation. Since the water
table elevation often follows the
surface topography, it can generally

be assumed that groundwater
moves from areas of high land
surface elevation to areas of low
land surface elevation.
Confined aquifers are overlain by
an impermeable, or semi-permeable
confining layer, and are typically
under pressure. Therefore the
potentiometric surface, or level to
which water will rise in a tightly
cased well, is above the top of its
upper confining layer. When this
occurs the well is called an artesian
well and the aquifer is said to exist
under artesian conditions. In some
cases the water level may rise above
the land surface, in which case the
well is known as a flowing artesian
Water in confined aquifers moves
from areas of high potentiometric
head (as measured by the level to
which water will rise in a tightly
cased well) to areas of low potentio-
metric head. Confined aquifers are
less susceptible to contamination
from local surface activities because
infiltrating water typically moves
very slowly through the confining
layer. However the confining layers
may be fractured and missing in
many places. Thus, contaminated
water may move horizontally on top


Figure 4. Principal aquifers in Florida

of the confining layer for some
distance before recharging the
confined aquifer through a brea
in the confining layer.

Major Florida

Figure 4 is a map of the prin(
aquifers that yield large quantil
of water to wells, streams, lakes
and springs in Florida. The pri
mary source of groundwater for
most of the state is the Floridar
aquifer. Figure 5 shows the are
extent of this formation, which:
one of the most prolific aquifers
the United States. It should be
noted however that the Floridai
aquifer is generally not usable i
regions of the state south of Lal
Okeechobee due to its high salt
In much of Florida the aquife
confined by low permeability
sediments of the Hawthorne for
tion. The Hawthorne formation
absent however in the north cer
part of the state along the Ocal
Uplift. In this area the aquifer
unconfined, and thus receives
recharge from water infiltrating
from the surface.


The potentiometric surface of the
Floridan aquifer is shown in Figure
6. This surface indicates that the
origin of subsurface flow for north-
ern Florida is in Alabama and
Georgia; however, the origin of
subsurface flow for peninsular
Florida is in the Central Uplands of
the state. In many areas the poten-
tiometric surface is above the land
surface, thus artesian flow occurs in
wells or along geologic openings
(springs). Figure 7 shows the areas
of potential artesian flow from the
Floridan aquifer. Not included in
this figure are small areas of local
artesian flow near springs that
derive their flow from the Floridan
The unconfined Biscayne aquifer
underlies an area of about 3000
square miles in Dade, Broward, and
Palm Beach Counties. This aquifer
is 100 to 400 feet thick near the
coast, but thins to a thickness of
only a few feet further inland.
Water in the Biscayne aquifer is
derived chiefly from local rainfall
and, during dry periods, from canals
ultimately linked to Lake
Okeechobee. The Biscayne is an
important source of water supply for
the lower east coast cities.

An unconfined, sand and gravel
aquifer is the major source of
groundwater in the extreme west-
ern part of the Florida panhandle.
This aquifer ranges in thickness
from 300 to 700 feet and consists
primarily of very coarse quartz
sand. Water in the sand and gravel
aquifer is derived chiefly from local
rainfall. Wells in this aquifer
furnish most of the groundwater
used in Escambia and Santa Rosa
Counties and part of Okaloosa
A shallow, unconfined aquifer is
present over much of the state, but
in most areas it is not an important
source of groundwater because a
better supply is available from
other aquifers. However where
water requirements are small, this
aquifer is tapped by small diameter
wells. In south Florida the shallow
aquifer is a major source of ground-
water in Martin, Palm Beach,
Hendry, Lee, Collier, Indian River,
St. Lucie, Galdes and Charlotte
Counties. The water in this shallow
aquifer is derived primarily from
local rainfall.

Sources of

Florida's unique hydrogeologic
features of a thin soil layer, high
water table, porous limestone, an<
large amounts of rainfall, coupled
with its rapid population growth,
result in a groundwater resource
extremely vulnerable to contain
tion. Numerous structures result
in~g from human activities through]
out Florida have the potential to
contribute to groundwater contain
nation. There are tens of thousand
of point sources such as surface
water impoundments, drainage
:wells, underground storage tanks
flowing saline artesian wells,
hazardous waste sites, power-
plants, landfills, and cattle and
dairy feedlots. Similarly, there ai
numerous septic tanks and urban
and industrial-commercial areas
that may recharge water of undes
able quality. Non-point sources,
which have vast potential for
contributing to groundwater con-
tamination, include coastal saltwC
ter bodies, urban storm water,
agricultural and silvicultural
practices, and mining.

Figure 5. Areal extent of the Floridan
aquifer [6].

Figure 6. Potentiometric surface of the
Floridan aquifer.[6]

Area of artesian flow
extent and distribution
of areas of artesian
flow vary fluctuations
of the potentiometric
surface. Areas of
artesian flow adjacent
springs, many rivers,
and coastal beach
ridge areas have not
been included.




-60- Potentiometric contour
shows altitude at which
water level would have
stood in tightly cased
wells that penetrate the
floridan aquifer, May
1974. Contour interval
20 feet. Datum is mean
sea level.


Figure 7. Areas of potential artesian flow
the Floridan aquifer.[6]


Salt water intrusion
Florida's situation as a penin-
sula between two bodies of salt
water creates the potential for salt
Water intrusion into the fresh
groundwater supply. Salt water is
-more dense than fresh water and
thus exerts a constant pressure to
flow into the fresh water aquifers.
As long as fresh water levels in the
aquifer are above sea level, the
fresh water pressure limits the
inland movement of the salt water.
-Over-pumping of coastal wells,
however, can increase the salt
water intrusion. If water is
pumped out faster than the aquifer
is replenished, the pressure of the
fresh water is decreased. This
causes the level at which the salt
water and fresh water meet to rise
in the aquifer, degrading the fresh
water quality. The problem of salt
water intrusion is aggravated by
periods of drought during which
there is not enough rainfall to
replenish the fresh water aquifers.
All of the aquifers shown in
Figure 4 experience problems with
salt water intrusion in coastal
areas. In south Florida, fresh
water levels in coastal canals are


managed carefully to control the
fresh water level in the Biscayne
aquifer and thus minimize salt
water intrusion. Figure 8 shows
areas of the Floridan aquifer which
contain chloride concentrations
greater than 250 milligrams per
liter, due to salt water intrusion.
In south Florida, where the
Floridan aquifer is artesian and
underlies the Biscayne and shallow
aquifers, its saline water may
recharge the overlying fresh water
aquifers increasing their salt
content. This type of recharge may
occur naturally by upward seepage
through the confining layer or it
may be increased by flowing
artesian wells.

Hazardous waste
SThe Florida Department of
Environmental Regulation has
identified 413 potential hazardous
waste sites in Florida. The distri-
bution of these sites over the state
is shown in Figure 9. One hundred
and eighty-five of these sites have
some type of water or soil contami-
nation, and 84 additional sites are
suspected of contamination.

Groundwater contamination h
been confirmed at 156 sites.
Enforcement action requiring
contamination assessment anc
remedial action has been initie
at 118 sites. Because of the
absence of a significant amoun
impermeable material to retar
downward movement of contain
nants, leakage from many of tI
sites poses a direct threat to tf
principal aquifers.

Gasoline storage
The Florida Department of
-Environmental Regulation has
documented more than 400 in-
stances of groundwater contain
tion from leaking gasoline pipe
_storage tanks. The greatest fre
quency of gasoline contaminat:
has occurred in Dade, Browarc
and Palm Beach Counties, affe
ing the quality of water in som
locations of the Biscayne aquif
The most environmentally and
financially significant incident
the leaking of 10,000 gallons o:
gasoline between October 197c
March 1980, which contaminai
the public water supply for 2,0
residents in Belleview Florida.
Other smaller gasoline leaks h
caused local contamination of
aquifers in several Florida cou

Municipal landfills
Florida has about 300 activ(
500 inactive landfill sites. Mo4
the landfills are unlined, incre
ing the chance that rainwater
which percolates through then
may dissolve harmful chemical
and ultimately reach the groui
water. Six of Florida's 39
Superfund sites are landfills, E
all have contaminated ground&
ter. Three in southeastern Flc
have directly contaminated the
Biscayne aquifer.

Figure 8. Areas of the upper Floridan
aquifer containing non-potable water [6].

Figure 9. Potential hazardous waste sites
in Florida [8].

~ -7---

D Explanation
Areas where upper part
of the Floridan Aquifer
contains water with
chloride concentration
greater than 250
milligrams per liter.

r~cTEl" 1.1i, FY R.)
1J r i
A P eO-

Organic compounds
Contamination of groundwater
by volatile organic compounds
(VOC) from industrial discharges
have become a concern, particularly
in southern Florida. A recent study
of public supplies from the Biscayne
aquifer in Broward, Dade and Palm
Beach Counties reported that four
supplies serving 290,000 people
contained VOC (primarily trichloro-
ethylene and vinyl chloride) concen-
trations that slightly exceeded
Florida drinking water standards.
Recent incidents of VOC contamina-
tion in groundwater supplies have
also occurred in other parts of the
state. Several city wells for
Pensacola, Gainesville and Talla-
hassee have been closed tempo-
rarily because of VOC contamina-

Florida ranks second in
agrichemical application in the
nation, primarily due to the warm
humid climate, sandy soil condi-
tions, and large planted acreage.
As a result, pesticide and nitrate
contamination of groundwater has
become a major environmental
issue in Florida. Since 1983, water
from more than 1,000 public and
private supply wells, primarily in
the Floridan aquifer system, have
been found to contain levels of the
soil fumigant ethylene dibromide
(EDB) above the state regulation of
0.02 micrograms per liter. The
distribution of EDB contamination
was extensive, with detections in 22
of the 66 counties tested. Most
were in Jackson, Lake, Highlands
and Polk Counties.
Aldicarb has also been detected
in groundwater at seven agricul-
tural study sites in Hillsborough,
Martin, Polk, St. Johns, Seminole
and Volusia Counties. Contamina-
tion by nitrate from fertilizers and/
or wastewater effluent has occurred
in some localized portions of the

Floridan aquifer, however it has not
yet been detected as a widespread

Solutions to the
quality problem

Historically, people have re-
garded groundwater as pristine,
believing that soil cleanses the
water as it seeps down into the
aquifer. While it is true that the
organic matter in soil has some
ability to retain or absorb organic
compounds such as VOCs, petro-
leum products and pesticides, it is
by no means an infinite sink for
these compounds. In addition, the
soil has no ability to absorb inor-
ganic anions such as nitrate or
chloride. Whether or not the soil
filters out viruses and other mi-
crobes remains an open question.
Therefore, man must actively
reclaim and restore soils and
aquifers with existing contamina-
tion problems, and prevent future
groundwater contamination
through effective land-use planning
and thoughtful management of
potential groundwater contamina-
tion sources.
Future land-use plans must
prevent potential contamination
sources from locating over critical
'recharge areas. Industries, farmers
and citizens located above ground-
water supplies should minimize
their use of hazardous chemicals,
and exercise good chemical disposal
practices. Site-specific best manage-
ment practices for both industry
and agriculture must be developed
which take local soils, geology,
aquifer characteristics, and climatic
conditions into account. Groundwa-
ter monitoring networks should be
installed at all potential contamina-
tion sources to provide data to fine
tune management practices, and to
provide early detection of ground-
water contamination problems.

References and
further reading

1. Baldwin, L.B., and R.R.
Carricker, Water Resource
Management in Florida, 1985,
Institute of Food and Agricul-
tural Sciences Bulletin 206,
University of Florida, Gainesvi]
FL, 16p.
2. Carriker, R.R., and A.L. Starr,
Florida's Water Resources, 198'
Food and Resource Economics
Bulletin FRE 40, Institute of
Food and Agricultural Sciences
University of Florida, Gainesvil
FL, 6p.
3. Freeze, R.A., and J.A. Cherry,
1979, Ground Water, Prentice-
Hall, Inc., Engelwood Cliffs, N(
Jersey, 604p.
4. Haman, D.Z. and A.B. Bottcher
Home Water Quality and Safet:
1986, Institute of Food and
Agricultural Sciences Circular
703, University of Florida,
Gainesville FL, 12p.
5. Hornsby, A.G., Ground Water:
The Hidden Resource, 1986, Soi
Science Fact Sheet SL 48, Insti-
tute of Food and Agricultural
Sciences, University of Florida,
Gainesville FL, 4p.
6. Spangler, D.P., Florida's Water
Resources, with Particular
Emphasis on Ground Water,
Proceedings of the First Annual
Symposium on Florida
Hydrogeology, 36 p.
7. U.S. Geological Survey, 1986,
Water for Florida Cities, U.S.
Geological Survey Water Re-
sources Investigations Report 81
4122, 30 p.
8. U.S. Geological Survey, 1986,
National Water Summary 1986.
Ground Water Quality: Florida,

r !7 1 B RIP, r TIC

This material is based upon work supported by the USDA, Extension Service, under special project
# 90-EWQI-1-9214.
in cooperation with the United States Department of Agriculture, publishes this information to further the purpose of the May 8 and June 30, 1914 Acts of
Congress; and is authorized to provide research, educational information and other services only to individuals and institutions that function without regard
to race, color, sex, handicap or national origin. Single copies of extension publications (excluding 4-H and youth publications) are available free to Florida
residents from county extension offices. Information on bulk rates or copies for out-of-state purchasers is available from C.M. Hinton, Publications Distribution --..
Center, IFAS Building 664, University of Florida, Gainesville, Florida 32611. Before publicizing this publication, editors should contact this address to
determine availability. Printed 6/91.

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