Ground-water resources of Northwestern Collier County, Fla. ( FGS: Information circular 29 )

STATE OF FLORIDA
STATE BOARD OF CONSERVATION
DIVISION OF GEOLOGY

FLORIDA GEOLOGICAL SURVEY
Robert 0. Vernon, Director

INFORMATION CIRCULAR NO. 29

GROUND-WATER RESOURCES
OF
NORTHWESTERN COLLIER COUNTY, FLORIDA

By
C. B. Sherwood and Howard Klein
U. S. Geological Survey

Prepared by the
UNITED STATES GEOLOGICAL SURVEY
in cooperation with the
CITY OF NAPLES, COLLIER COUNTY
and the
FLORIDA GEOLOGICAL SURVEY

TALLAHASSEE
1961

AGRI.
CULTURAL
LIBRARY

Completed manuscript received
February 7, 1961
Printed by the Florida Geological Survey
Tallahassee

TABLE OF CONTENTS

Page
Abstract.......................... ............... 1
Introduction......... ............................ .
Purpose and scope........................... 2
Acknowledgments ........... .............. 3
Location of area ........................... 3
Clim ate ................................... 5
Topography and drainage .................... 5
Summary of well-field history and water demand 8
Geology and test drilling ......... ............... 10
Ground water .................................. 13
Water-level fluctuations ................... .. 15
Quality of water ................. .......... 28
Salt water contamination ................ 30
Quantitative studies.......................... 34
Aquifer tests ........................... 34
Analysis of aquifer-test data.............. 36
Summary and conclusions ....................... 42
References ................................... .. 44

ILLUSTRATIONS

Figure
1 Maps showing the locations of Collier County
and the area investigated................ 4
2 Map of northwestern Collier County showing
the locations of the Naples municipal well
fields and geologic cross sections......... 6
3 Map of northwestern Collier County showing
topography and drainage. ................ 7
4 Graph showing pumpage in the Naples well
fields ................................. 9
5 Geologic cross section and chloride content
along line A-A'......................... 12
6 Geologic cross section and chloride content
along line B-B'......................... 13

7 Geologic cross section and chloride content
along line C-C'.......................... 14
8 Water-level contour map of northwestern
Collier County, January 6, 1960 .......... 16
9 Water-level contour map of northwestern
Collier County, March 29, 1960.......... 17
10 Hydrograph of well 164, monthly pumpage
from the Naples well field and daily rain-
fall at Naples, June 1958-December 1959 19
11 Hydrographs of wells 151 and 164, daily
municipal pumpage, and daily rainfall at
Naples, September 6-20, 1958............ 20
12 Map of the Naples well field area showing
the location of municipal supply wells and
observation wells......................... 21
13 Map of northwestern Collier County showing
the chloride content of water from selected
wells and surface-water observation points 29
14 Hydrograph of well 163, in the Naples well
field'area, during the aquifer test of March 25,
1958 ................................... 35
15 Graph showing drawdowns in observation
wells at the end of the 30-hour aquifer test
January 9-10, 1959, and a sketch showing
locations of wells used in the test ........ 37
16 Idealized sketch showing flow in a leaky
artesian aquifer system ................. 38
17 Graph showing drawdowns observed in wells
158 and 188 during aquifer test January 9-10,
1959, and theoretical drawdowns for artesian
water-table, and leaky-aquifer conditions 40

Table
1 Analyses of water from selected wells .... 22
2 Chloride concentration in water samples
from selectedwells in northwestern Collier
County ................................. 23

GROUND-WATER RESOURCES
OF
NORTHWESTERN COLLIER COUNTY, FLORIDA

By
C. B. Sherwood and Howard Klein

ABSTRACT

This investigation was made to provide hydrologic
information for use in the development of safe water supplies
and water-control plans for northwestern Collier County.
Previous development in this area has been limited to a
narrow coastal ridge between the Big Cypress Swamp and
the Gulf of Mexico; however, the agricultural development
of large swampy inland areas is currently in progress.

The source of fresh ground water in northwestern
Collier County is an extensive shallow aquifer, which extends
from the land surface to a depth of about 130 feet. This
aquifer is composed chiefly of permeable limestone and
sand; however, its vertical permeability is restricted by
thin beds and lenses of shelly, sandy marl in coastal areas
and by a bed of very dense limestone which occurs near the
surface in inland areas.

Recharge is by local rainfall and to some extent by
surface water flowing seaward from the interior. Discharge
of ground water is chiefly by underflow to the gulf or tidal
streams, and by evapotranspiration. Water-level contour
maps indicate a high ground-water mound beneaththe center
of the coastal ridge and perennially high water levels in the
inland areas.

FLORIDA GEOLOGICAL SURVEY

Chemical analyses show that ground water in the report
area is relatively highly mineralized, except in areas on or
immediately east of the coastal ridge. The mineralization
along the coastal fringe areas results from recent salt-water
encroachment, whereas that in inland areas apparently is
dueto residual salt water from former invasions of the sea.

Tests on the coastal ridge indicate that the aquifer
will yield large quantities of water with moderate drawdown
of water level; however, increased decline of water level
caused by large additional ground-water withdrawals may
cause further salt-water encroachment into the aquifer. In
areas where surface water is available for recharge, draw-
downs due to pumping may be greatly reduced by induced
infiltration of water to the aquifer. The location of major
well fields along the eastern edge of the coastal ridge is
favored by higher transmissibility of the aquifer there and
by the presence of a large source of surface water that can
infiltrate into the aquifer.

INTRODUCTION

Purpose and Scope

During 1951-52 the U. S. Geological Survey investigated
the ground-water resources of the Naples area in cooperation
with the city of Naples. This investigation culminated in a
report entitled, "Ground-water resources of the Naples area,
Collier County, Florida, by Howard Klein, that was pub-
lished in 1954 by the Florida Geological Survey as Report of
Investigations No. 11. That study was requested by officials
of the city of Naples who were concerned regarding the
adequacy of the future water supply for the rapidly growing
population. The investigation was designed to meet the
immediate needs of the city as follows: (1) To determine
feasible means to protect the city's existing water supply
from contamination by sea water, (2) to locate additional
supplies to meet new water requirements, and (3) to deter-
mine the available ground-water supply from aquifers that
might be used in the future. The area covered by the early
report was chiefly within the city boundaries.

FLORIDA GEOLOGICAL SURVEY

Chemical analyses show that ground water in the report
area is relatively highly mineralized, except in areas on or
immediately east of the coastal ridge. The mineralization
along the coastal fringe areas results from recent salt-water
encroachment, whereas that in inland areas apparently is
dueto residual salt water from former invasions of the sea.

Tests on the coastal ridge indicate that the aquifer
will yield large quantities of water with moderate drawdown
of water level; however, increased decline of water level
caused by large additional ground-water withdrawals may
cause further salt-water encroachment into the aquifer. In
areas where surface water is available for recharge, draw-
downs due to pumping may be greatly reduced by induced
infiltration of water to the aquifer. The location of major
well fields along the eastern edge of the coastal ridge is
favored by higher transmissibility of the aquifer there and
by the presence of a large source of surface water that can
infiltrate into the aquifer.

INTRODUCTION

Purpose and Scope

During 1951-52 the U. S. Geological Survey investigated
the ground-water resources of the Naples area in cooperation
with the city of Naples. This investigation culminated in a
report entitled, "Ground-water resources of the Naples area,
Collier County, Florida, by Howard Klein, that was pub-
lished in 1954 by the Florida Geological Survey as Report of
Investigations No. 11. That study was requested by officials
of the city of Naples who were concerned regarding the
adequacy of the future water supply for the rapidly growing
population. The investigation was designed to meet the
immediate needs of the city as follows: (1) To determine
feasible means to protect the city's existing water supply
from contamination by sea water, (2) to locate additional
supplies to meet new water requirements, and (3) to deter-
mine the available ground-water supply from aquifers that
might be used in the future. The area covered by the early
report was chiefly within the city boundaries.

INFORMATION CIRCULAR NO. 29

Upon completion of Report of Investigations No. 11,
a cooperative study was begun that was directed mainly at
obtaining data to determine changes in the amount of ground
water in storage and to monitor the movement of salt water
in the area. Additional information was obtained on the
physical character of the aquifer and the chemical quality
of the water during construction of a new well field in the
northeastern part of Naples. The construction of new high-
ways into the Big Cypress Swamp in 1959, made exploratory
work possible inthe area east of Naples. This supplementary
report was prepared chiefly from data obtained through the
city's efforts to establish a permanent well field. The area
investigated is shown in figure 1.

The investigation was made under the general super-
vision of P. E. LaMoreaux, chief, Ground Water Branch,
U. S. Geological Survey, and Robert O. Vernon, director,
Florida Geological Survey; and under the immediate super-
vision of M. I. Rorabaugh, district engineer, U. S. Geological
Survey.
W. F. Lichtler, of the U. S. Geological Survey, con-
ducted a 30-hour pumping test in the Naples well field and
analyzed the test data. In 1959, as part of the field work for
the investigation of the ground-water resources of Collier
County, H. J. McCoy, of the U. S. Geological Survey,
furnished data obtained from several test wells in the
western part of the county.

Acknowledgments

The investigation was greatly aided by the cooperation
and assistance of officials of the city of Naples and Collier
County. The wholehearted cooperation of W. F. Savidge,
superintendent, and other personnel of the Naples Water
Department was especially helpful. W. H. Turner, county
engineer, made possible the collection of geologic and water
samples during the drilling of several privately owned wells.

Location of Area

The city of Naples is onthe lower west coast of Florida
(fig. 1). The area reported on extends from the mouth of
the Gordon River northward to the Cocohatchee River and

FLORIDA GEOLOGICAL SURVEY

LES COLLIER oADE

SCALE 1I KIE I

1' 0 4E, 55*

Figure 1. Maps showing the locations of Collier County
and the area investigated.

INFORMATION CIRCULAR NO. Z9 5

from the gulf coast eastward for about 9 miles (fig. 2).

Climate

The climate of the Naples area is subtropical. Rainfall
averages approximately 53 inches per year. Approximately
75 percent of the total falls during June through October
which includes both the normal rainy season and the hurricane
season. The average annual temperature is 76 F.

Topography and Drainage

The city of Naples is on a low coastal ridge about 2
miles wide, which rises from the marshes of the Ten
Thousand Islands in southwestern Collier County and extends
northward along the Gulf of Mexico. Figure 3, a compilation
of U. S. Geological Survey topographic quadrangle maps,
shows the topographic and drainage features of the area
investigated. The coastal ridge is bordered on the east by
Naples Bay and the Gcrdon River to a point near the northern
city boundary, and north of there by a natural shallow
depression that forms the upper reaches of the Gordon
River drainageway. A poorly defined divide between the
southward drainage to the Gordon River and the northward
drainage to the Cocohatchee River is about 1 mile south of
Vanderbilt Beach (fig. 3). The Gordon River drainageway
is flooded or remains swampy during long periods of each
year. The areas to the east of the river are occupied by
cypress swamps, except fora small area east of Naples Bay
that is well drained.

The land surface throughout most of the coastal ridge
is 10 to 20 feet above msl (mean sea level) except in the
southern part where the average altitude is about 5 feet. A
large part of the coast is mangrove swamp less than 5 feet
above msl. The Gordon River drainageway rises from near
sea level at Naples Bay to about 10 feet above msl near the
drainage divide. Farther eastward in the cypress swamps
the land-surface altitude ranges from about 10 to 15 feet
above msl.

FLORIDA GEOLOGICAL SURVEY

EXPLANATION
LINE OF CROSS SECTION
A-----A'
WELL FIELDS
UNUSED IN USE PROPOSED

TEST AND OBSERVATION
WELL
*

SCLE IN MILES
I 0 I

Map of northwestern Collier County showing
the locations of the Naples municipal well
fields and geologic cross sections.

Figure 2.

INFORMATION CIRCULAR NO. 29

Figure 3. Map of northwestern Collier County showing
topography and drainage.

Drainage of the coastal ridge is chiefly downward
through the permeable sandy mantle. Ground water moves
laterally to points of discharge in the gulf, Naples Bay,
and the Gordon River. During the rainy season the depres-
sions scattered along the ridge are filled with water and
remain swampy for several months. Overland runoff appears
tobe restricted tothe area east of the ridge where drainage
is southward and southwestward as slow sheet flow. The
extreme northern part of the area is drained by the Coco-
hatchee River. During each rainy season the eastern part of
the area is inundated and remains swampy for long periods.

FLORIDA GEOLOGICAL SURVEY

A recently constructed canal that extends several miles
eastward from the Cocohatchee River has speeded the re-
moval of flood water from adjacent lands. As a result of
the improved drainage, new agricultural areas have been
opened on both sides of this canal.

Summary of Well-Field History and Water Demand

Prior to 1945, the municipal supply for Naples was
obtained from one 6-inch well and two 4-inch diameter wells
located in the southern part of the city between Naples Bay
and the Gulf of Mexico (fig. 2). These wells were closely
spaced and were pumped heavily for short periods, which
caused salt water to move inland and upward and, thus, to
contaminate the aquifer.

During 1945-46, a new well field was established
north of the original well field (fig. 2). This well field
comprised 22 small-diameter wells (3-inch and 4-inch),
spaced 400 feet apart. In order to diminish the effect of
large local drawdowns of the water level each well was
pumped at a rate not to exceed 30 gpm (gallons per minute).
This method distributed the effect of pumping over a large
area and reduced the hazard of salt-water encroachment.
The annual pumpage from this well field increased from
about 33 million gallons in 1947 to 122 million gallons in
1954.

The city officials proposed the establishment of a new
permanent well field because of the constantly increasing
demand for water (fig. 4), the high cost of pumping 22 wells,
and the constant threat of salt-water encroachment fromthe
Gulf of Mexico and the Gordon River to the old well field.
Their ultimate objective was a well field in the cypress-
swamp area, east and north of the city; but no data were
available as to the continuity of the aquifer and the quality
of the ground water in that area. The city officials believed
that a productive field in this area could furnish sufficient
water for all of the coastal ridge area of Collier County.
With these goals in mind they established a well field at the
present location (fig. 2) in the northeastern part of the city,

INFORMATION CIRCULAR NO. 29

assuming that further expansion of facilities would be inland.
Total pumpage from this field in 1959 was 295 million gallons.

Graph showing pumpage
fields.

in the Naples well

In 1957 a system of coastal canals was constructed for
a waterfront housing development directly west of the new
well field. This canal network was a definite threat to the
city water supply because it introduced a source of sea-
water contamination about 2,000 feet closer to the well
field. As a precautionary measure observation wells were
drilled between the well field and the canal system in order
to detect movement of the salt-water front in the aquifer by
periodic water sampling. Similar wells were drilled east of
the wellfieldto monitor the extent of salt-water encroachment
from tidal parts of the Gordon River.

Further geologic testing and exploratory work was
begun as part of a plan to extend the well field northward

Figure 4.

o /
50C

4 /

2 40 4 -

Lu

-4 0
*-. -- ---- -- -- -- ---
C -- -
4 -

I p~~1 T6~

FLORIDA GEOLOGICAL SURVEY

along the western edge of the Gordon River drainageway.
Also, an exploratory program was undertaken east-of the
Gordon River drainageway and northward toward the Coco-
hatchee River. These tests showed that, although the water-
bearing materials were similar to those penetrated near the
coast, the quality of the ground water was not as good as
the existing supply. Additional exploration in 1959 and early
1960 indicated that most of the ground water in the large
swampy area east of the ridge was not of acceptable quality
for municipal use. The city still has the problem of obtain-
ing water to satisfy increased demands from a small area
close to the sea.

GEOLOGY AND TEST DRILLING

A shallow aquifer extending from land surface to a depth
of about 130 feet is the only source of fresh ground water in
northwestern Collier County. Limestones of the Floridan
aquifer, at depths of 600 to 800 feet, yield large quantities
of water under artesian pressure, but the water is highly
mineralized and unsuitable for general use. The Floridan
aquifer is not discussed in this report.

Information obtained from test wells and an inventory
of existing wells indicates that the shallow aquifer ranges
in thickness from about 110 to 130 feet and is underlain by
relatively impermeable fine sand, silt, and marl. In gen-
eral the aquifer is composed of permeable beds of soft shelly
limestone, separated by thin layers or lenses of shelly marl
of low permeability. The unconsolidated materials retard
but do not prevent the vertical movement of ground water
within the aquifer. The uppermost unit of the aquifer is
well-sorted, medium-grained sand, about 20 feet thick.
Infiltration in this material is rapid and surface runoff ac-
cordingly is negligible. The upper part of the aquifer is
tapped by many small domestic or irrigation wells but most
wells for large municipal or irrigation supplies are developed
at depths ranging from 50 to 80 feet below land surface.
Klein (1954, p. 8-22) described the geology of the southern
part of the coastal strip and the water-bearing character-
istics of the shallow sediments; therefore, no further

INFORMATION CIRCULAR NO. 29

discussion of these features is given in this report.

During 1957-59, approximately 15 test wells were
drilled northeast and east of Naples in connection with the
expansion of well-field facilities and the exploration of inland
areas. The initial test wells were drilled in accessible
areas to the east and northeast of the present well field, in
the vicinity of the upper reaches of the Gordon River (wells
160, 161, 178, and 179, fig. 2). After the completion in
1959 of the highway system extending eastward from Rock
Creek and the Cocohatchee River, the drilling program was
extended to include these heretofore unexplored areas. The
objectives of the test drilling were to furnish information
relating to: (1) The extent of salt-water encroachment in
the aquifer in the vicinity of the Gordon River, (2) the
continuity, thickness, and general water-bearing charac-
teristics of the shallow aquifer in the area east of the
coastal ridge, and (3) the quality of the ground water in the
area east of the coastal ridge.

Outpost-observation wells also were drilled west of
the existing well field to detect salt-water movement from
the Gulf of Mexico caused by large withdrawal of water at
the well field and by the construction of the coastal canal
system. The locations of test wells and the lines of geologic
cross sections are shown in figure 2.

The lithology and chloride content of the water at
selected depths along the geologic sections are shown in
figures 5-7. The test drilling indicated that the aquifer is
continuous east of the ridge and north to the Cocohatchee
River. A significant difference in the lithology is indicated
by an increase in the proportion of limestone in the aquifer
east of Naples and the thinning or disappearance of the
uppermost sand component of the aquifer toward the eastern
part of the area. Throughout much of the area east of the
coastal ridge a layer of very hard, dense, tan to gray
limestone occurs at or immediately below the land surface.
Examination of this limestone, excavated during the con-
struction of the canal east of the Cocohatchee River, indi-
cated that its permeability is low. The low permeability of
the rock retards downward infiltration of rainwater to the
water table. If the dense layers are uniform in occurrence

EXPLANATION

LIMEITONE

SAND

MARL

SHELLS
--28O--
LINE OF EOLAL CHLORIOD
CONTENT IN PPM

- -

SCALE IN MILK$

Figure 5. Geologic cross section and chloride content along line A-A'.

INFORMATION CIRCULAR NO. 29

throughout the eastern area, and presumablythey are, much
of the potential recharge to the aquifer will be rejected and
the overland runoff will be proportionally greater.

Figure 6. Geologic cross section and chloride content
along line B-B'.

GROUND WATER

Local rainfall is the source of all the water that
replenishes the shallow aquifer in the vicinity of Naples.
Part of the rainfall is returned to the atmosphere by evapo-
transpiration, part infiltrates to the shallow aquifer, and
the remainder runs off into streams and to the gulf. After
reaching the saturatedzone of the aquifer water flows under
gravitational forces from points of recharge, where water
levels are high, to points of discharge where water levels
are low. In general, the limestone beds in the aquifer are

FLORIDA GEOLOGICAL SURVEY

along the western edge of the Gordon River drainageway.
Also, an exploratory program was undertaken east-of the
Gordon River drainageway and northward toward the Coco-
hatchee River. These tests showed that, although the water-
bearing materials were similar to those penetrated near the
coast, the quality of the ground water was not as good as
the existing supply. Additional exploration in 1959 and early
1960 indicated that most of the ground water in the large
swampy area east of the ridge was not of acceptable quality
for municipal use. The city still has the problem of obtain-
ing water to satisfy increased demands from a small area
close to the sea.

GEOLOGY AND TEST DRILLING

A shallow aquifer extending from land surface to a depth
of about 130 feet is the only source of fresh ground water in
northwestern Collier County. Limestones of the Floridan
aquifer, at depths of 600 to 800 feet, yield large quantities
of water under artesian pressure, but the water is highly
mineralized and unsuitable for general use. The Floridan
aquifer is not discussed in this report.

Information obtained from test wells and an inventory
of existing wells indicates that the shallow aquifer ranges
in thickness from about 110 to 130 feet and is underlain by
relatively impermeable fine sand, silt, and marl. In gen-
eral the aquifer is composed of permeable beds of soft shelly
limestone, separated by thin layers or lenses of shelly marl
of low permeability. The unconsolidated materials retard
but do not prevent the vertical movement of ground water
within the aquifer. The uppermost unit of the aquifer is
well-sorted, medium-grained sand, about 20 feet thick.
Infiltration in this material is rapid and surface runoff ac-
cordingly is negligible. The upper part of the aquifer is
tapped by many small domestic or irrigation wells but most
wells for large municipal or irrigation supplies are developed
at depths ranging from 50 to 80 feet below land surface.
Klein (1954, p. 8-22) described the geology of the southern
part of the coastal strip and the water-bearing character-
istics of the shallow sediments; therefore, no further

'"to
rlo~~~~ ~ I ------- r

M +20
mT1 +10

-30o -30

-40 -90 / -40

-50 -176 -50
-73 EXPLANATION M
-60 |0 -%o O
LIMESTONE /
, -70 666 -70
*-55 SAND
/ / C)
so80 -80 1

SHELLS / / -90
,o-90 | / '-eo / / | -o >
-100 9 --N o-- t -100
4-O0 LINE OF EDUAL CHLORIDE 2O
CONTENT IN PPM
110 CHLORIDE CONTENT IN PPM / -110
SJ AT DEPTH INDICATED -151
-120 / / *f -
-130 2100- -130

-140 -140

-150 -150.
-10 CALE IN MILES

Figure 7. Geologic cross section and chloride content along line C-C
Figure 7. Geologic cross section and chloride content along line C-C'.

INFORMATION CIRCULAR NO. 29

permeable and yield water freely to wells. Klein (1954,
p. 15-22) described the hydrologic properties of the water-
bearing materials and discussed the effects of recharge to
and dischargefromthe aquifer in the Naples area; therefore
they are not described in this report.

Water-Level Fluctuations

Fluctuations of the water table indicate changes in
the amount of ground water stored in the shallow aquifer.
Variations in ground-water storage are caused by recharge
by rainfall, and by discharge to the gulf and to streams and
canals, by pumping, and by evapotranspiration. The water
table is highest during June-October, the wettest season,
but is low during December-May, the drier season.

Figure 8 shows the approximate altitude and configura-
tion of the water table in the Naples area onJanuary 6, 1960.
These contours are based on water-level measurements
made in shallow wells that tap the uppermost section of the
aquifer. A ground-water mound occurs about 2 miles north
of the city boundary indicating that recharge occurs along
the coastal ridge. A steep water-table gradient on the west
side of the ridge suggests that the sandy surface material is
only moderately permeable and can, therefore, retain large
amounts of ground water in storage. In general, the water
table conforms tothe topography of the area; and the contours
suggest that underflow is westward tothe Gulf of Mexico and
eastward to the Gordon River drainageway.

Figure 9 shows the configuration of the water table at
the end of March 1960, after a period of deficient rainfall.
The pattern of the contours is the same as that of January 6,
1960, but the altitude of the water surface is somewhat
lower. The greatest decline occurred in the center of the
ridge area and east of the ridge.

Figures 7 and 8 both show the effect of pumping in the
municipal well field, which is indicated by a shallow water-
table depression in the northeastern part of Naples.

INFORMATION CIRCULAR NO. 29

throughout the eastern area, and presumablythey are, much
of the potential recharge to the aquifer will be rejected and
the overland runoff will be proportionally greater.

Figure 6. Geologic cross section and chloride content
along line B-B'.

GROUND WATER

Local rainfall is the source of all the water that
replenishes the shallow aquifer in the vicinity of Naples.
Part of the rainfall is returned to the atmosphere by evapo-
transpiration, part infiltrates to the shallow aquifer, and
the remainder runs off into streams and to the gulf. After
reaching the saturatedzone of the aquifer water flows under
gravitational forces from points of recharge, where water
levels are high, to points of discharge where water levels
are low. In general, the limestone beds in the aquifer are

FLORIDA GEOLOGICAL SURVEY

EXPLANATION
Observation well
and woter level

Contour showing altitude of water level
Infeet above mean seo level
JANUARY 6, 1960

I SC.LM IW MLES

Water-level contour map of northwestern
Collier County, January 6, 1960.

Figure 8.

INFORMATION CIRCULAR NO. 29

EXPLANATION
.5.23
Observation well
and water level
,-8.0--'
Contour showing altitude olwater level
in feet above mean sea level
MARCH 29,1960

Water-level contour map of northwestern
Collier County, March 29, 1960.

Figure 9.

FLORIDA GEOLOGICAL SURVEY

Water-level measurements made during the drilling
of test wells and supply wells along the ridge area showed
differences in head between the upper and lower parts of
the aquifer. Along the central part of the ridge, the water
levels in shallow wells (25-30 feet deep) ranged from 1 to 3
feet higher than the water levels in wells penetrating the
deeper part of the aquifer (60 to 100 feet deep). This head
differential would cause downward leakage of ground water.
It is typical in the recharge areas and the magnitude of the
differential is related to the degree of confinement. In the
peripheral areas where ground-water discharge takes place,
the head relationship is reversed. The water levels in deep
wells range from 1 to 2 feet higher than those in shallow
wells and upward leakage occurs. In the municipal well-
field area, where wells 60 to 80 feet deep are pumped
heavily, the head differential is substantial, and a large part
of the water pumped is supplied by downward leakage in the
area of the cone of depression.

The graphs in figure 10 show the relationship between
pumpage, rainfall, and the water-level fluctuations at well
164, in the Naples well field, for the period June 1958-
December 1959. Although well 164 taps the lower permeable
zone of the aquifer, the response of the water level to rain-
fall in the well is rapid. Pumping is the chief factor that
causes large declines in the vicinity of the well field; other
fluctuations such as those caused by ocean tides and varia-
tions in barometric pressure are minor.

The effect of heavy municipal pumping is shown better
inthehydrographs of figure 11 for the period September 6-20,
1958, when supply wells near the water plant were the only
wells pumping in the area. Water levels in wells 151 and
164 are compared with pumping in the well field and rainfall.
The locations of wells 151 and 164, with respect to the
municipalwells near the plant, are shown in figure 12. Well
151 is about 2, 500 feet west of the center of the well field
and well 164 is about 4,000 feet northeast of the center of
pumping. The drawdown due to pumping reaches well 151
considerably before it reaches well 164, and the fluctuation
is greater in well 151 than in well 164. Also, the effect of
starting and stopping pumps in the field is indicated by the

1958 1959
U SEPT, A FEU V AG. SPT OC. NO 0 .
I-

wz I
LL;C:i |

30

U-

SI
CD

Zs 1 J O RFCO

I.
>W

-U,. 0,_j
.0L

_ SUIWi I .1. IM

Figure 10. Hydrograph of well 164, monthly pumpage from the Naples well %o
field and daily rainfall at Naples, June 1958-December 1959.

- FLORIDA GEOLOGICAL SURVEY

irregularity of the water-level fluctuations in well 151, but
this effect is less pronounced in the hydrograph of well 164
because of its greater distance from the well field. .An
interesting feature of the hydrograph is the rapid rise of the
water levels caused by heavy rainfall on September 13. The
hydrograph of well 164 shows a fairly rapid flattening of the
drawdown curve caused by daily well-field pumping during
September 17-19. The rate of flattening suggests that ad-
ditional sources of replenishment are being intercepted and
that the quantity of downward leakage to the lower permeable
zone is approaching the quantity of water that is being with-
drawn from the well field.

SEPTEMBER 1958
6 7 a 9 10 II I 13 14 15 I 17 is 19 20

i-c-
1 1

rI"

i iT
0 II I I I I

'IV
i --

Figure 11. Hydrographs of wells 151 and 164, daily
municipal pumpage, and daily rainfall at
Naples, September 6-20, 1958.

EXPLANATION
0
OBSERVATION WELL
SUPPLY WELL
A
RECORDING GAGE

.M^S '" iSS81 lie

A164 190

Figure 12. Map of the Naples well field area showing the location
of municipal supply wells and observation wells.

, pi3 i +

161 8-22.57 135

163 3.19-58 24 11

163 3-19-58 63 11

174 7-16.58 41 17

175 .7-17-58 44 12

177 7-20-58 58 24

178 7-28-58 -28

178 7-28-58 52 --

178 7-28-58 96

179 7-30-58 48 .

179 7-30.58 85 ---

;03 7.28.59 46 10

303 8. 3-59 240 20

Table I. Analyses of Water from Selected Wells in Northwestern Collier County

(All result are in parts per million except those for color, pH and specific conductance)

I io0

0 -

Ui I i
0 L l 11 1 to
a S 1 i a l a r-

0.041 76

.27 72

.09 166

.01, 166

1.0 134

119

-- 146

214

.06 105

.03 103

2.3 170

.76 196

... ... ... --- ---. 304

2.6 7.0 2.4 0 243 2.2 19 0,1 1.1 243

.1 9,0 .9 0 220 1.0 18 .1 .7 225

32 16Z 5.6 0 438 77 325 .2 1.5 1,000

15 97 2,6 0 464 7.5 205 ,3 .9 735

29 162 7.2 0 418 122 275 ,3 .1 960

6.6 35 .7 .--.. ... 10 68 --...

13 102 2,7 --- --- 43 202 ... ..

36 315 4.4 --- -- 178 655 -... .

6.3 41 2.0 --- --- 12 90 --- ...

8.0 46 2.3 --- --- 10 92 -... -

6.3 26 .2 0 520 4.4 46 .0 .3 599

89 631 21 0 236 440 1,150 .1 1.0 2,660

204 -

204 25

180 28

731 20

572 z2

565 17

324 ---

418 ---

682 -

288 .

290 -

474 68

1,517 5

SIron in solution at time of analysis

aj
u o

-.. 493

7.6 435

7.6 394

7.3 1,720

7.3 1,Z70

7.3 1,640

... 753

--- 1,280

2,790

743

766

7.1 911

4,530

INFORMATION CIRCULAR NO. 29

Table 2. Chloride Concentration in Water Samples from
Selected Wells in Northwestern Collier County

Well No.

Chloride,
Date in ppm

May 6, 1954

Depth of.sample
in feet, below
land surface

78

64
84
120
130
140
157

72

75

117

123

130

148

Mar. 14, 1956
Mar. 14, 1956

16

11
8
18
17
16
28
25
21
17
21
14

168
181
168
169
165
182
190

20
15
17
20
26
16
15
24

15
13

Mar. 7,
Mar. 7,
Mar. 14,
Mar. 14,
Mar. 14,
Mar. 14,
Mar. 20,
Feb. 13,
Mar. 4,
Dec. 3,
Mar. 29,

Dec. 31,
May 15,
May 6,
Feb. 28,
Mar. 7,
Feb. 27,
Mar. 20,

Feb. 28,
Mar. 7,
Aug. 5,
May 4,
June 8,
Dec. 3,
Jan. 6,
Mar. 29,

1952
1952
1956
1956
1956
1956
1958
1959
1959
1959
1960

1952
1953
1954
1955
1956
1957
1958

1955
1956
1958
1959
1959
1959
1960
1960

FLORIDA GEOLOGICAL SURVEY

Table 2. (Continued)

Depth of sample
in feet, below Chloride,
Well No. land surface Date in ppm

150 33 Aug. 16, 1956 22
59 Aug. 16, 1956 25
151 60 Aug. 16, 1956 18
123 Mar. 20, 1958 16
145 Mar. 20, 1958 32
166 Mar. 20, 1958 85
May 4, 1959 79
June 8, 1959 60
Mar. 20, 1960 44
152 35 Aug. 17, 1956 14
58 Aug. 17, 1956 13

156 50 July 29, 1956 18

158 51 Mar. 25, 1958 59
Jan. 19, 1959 59
160 20 Aug. 20, 1957 1,430
44 Aug. 20, 1957 22
60 Aug. 20, 1957 43
90 Aug. 20, 1957 24
110 Aug. 20, 1957 18
141 Aug. 20, 1957 385
156 Aug. 21, 1957 965
May 4, 1959 352
June 8, 1959 340
Dec. 3, 1959 615
Jan. 6, 1960 470
Mar. 29, 1960 1,020

161 17 Aug. 21, 1957 29
40 Aug. 21, 1957 23
61 Aug. 21, 1957 73
80 Aug. 22, 1957 55

INFORMATION CIRCULAR NO. 29

Table 2. (Continued)

Depth of sample
in feet, below Chloride,
Well No. land surface Date in ppm

100
135

163

Aug. 22, 1957
Aug. 22, 1957
Mar. 26, 1958

Mar.
Mar.
Mar.

July
July
July

July
July
July
July

19, 1958
19, 1958
19, 1958

14, 1958
14, 1958
16, 1958

17, 1958
17, 1958
17, 1958
17, 1958

July 18, 1958

July 20, 1958

July
July
July
July
July

July
July
July
July
July

28, 1958
28, 1958
28, 1958
28, 1958
29, 1958

29, 1958
29, 1958
30, 1958
30, 1958
30, 1958

60 Nov. 13, 1958

174

44
70
123

177

69
67
72

18
19
18

325
445
885

205
580
1,750
1,250

87

275

68
202
242
655
875

67
90
78
97
151

179

28
48
72
100
123

FLORIDA GEOLOGICAL SURVEY

Table 2. (Continued)

Depth of sample,
in feet, below Chloride,
Well No. land surface Date in ppm -

Nov. 13, 1958

Nov. 13, 1958

Nov.
Nov.
Nov.
Nov.
Nov.

Nov.
Nov.
Nov.
Nov.

Nov.
Nov.
Dec.
Dec.
Dec.
Dec.

206

207

120

303

1958
1958
1958
1958
1958

1958
1958
1958
1958

1958
1958
1958
1958
1958
1958

Jan. 2, 1959

Jan. 2, 1959

Jan. 2, 1959

Jan. 2, 1959

Jan. 16, 1959

Jan. 16, 1959

July
July

29, 1959
29, 1959

187

34

28

83
92
153
304
472

70
176
260
260

45
51
644
666
2,400
2,100

130

172

174

134

119

127

28
46

INFORMATION CIRCULAR NO. 29

Table 2. (Continued)

Well No.

319

320

321

322

326

327

343

344

345

346

349

353

355

356

Depth of sample,
in feet, below
land surface

99
140
240

14

14

14

14

14

14

100

61

67

72

70

50

142

45

Date

July 29,
July 29,
Aug. 3,

Nov. 11,

Nov. 11,

Nov. 11,

Nov. 11,

Nov. 12,

Nov. 12,

Mar. 28,

Mar. 28,

Mar. 28,

Mar. 29,

Mar. 29,

Mar. 23,

Mar. 29,

Mar. 29,

1959
1959
1959

1959

1959

1959

1959

1959

1959

1960

1960

1960

1960

1960

1960

1960

1960

Chloride,
in ppm

72
140
1,150

51

18

19

24

30

34

314

200

530

19

190

290

20

290

- -

FLORIDA GEOLOGICAL SURVEY

Quality of Water

Ground-water samples were collected at different
depths during the drilling of the test wells and periodically
from existing observation wells. The chemical character
of the water in the aquifer was determined from 13 analyses
of ground-water samples shown in table 1 and the chloride
content of ground-water samples shown in table 2. The
chloride content of water samples collected at different
depths in the test wells are shown in figures 5, 6, and 7.
Figure 13 shows the approximate chloride content of water
samples from wells and surface water sampling points in
the report area.

These data and the analyses reported by Klein (1954,
p. 38-40) show that ground water in the area is relatively
high in mineral content except along the coastal ridge. The
chemical analyses of water samples from wells along the
coastal ridge indicate a hard limestone water that is suitable
for most uses. As ground water must seep through a con-
siderable thickness of sand and rock to reach the producing
zones in the aquifer, it is generallyfree of harmful bacteria
and suspended material. However, it does exert a solvent
action upon the rocks through which it moves. This action
is aided bythe presence of carbon dioxide absorbed by rain-
fall from the atmosphere and from organic material in the
soil. Calcium and bicarbonate, fromthe solution of calcium
carbonate in the lime stone by water containing carbon dioxide,
are the principal ions in solution in ground water in most of
the coastal ridge area.

The high mineral content of the ground water in the
area east of the coastal strip is due primarily to constituents
derived from sea water, inadditiontothecalciumand bicar-
bonate derived from the limestone in the aquifer. The chloride
content of the water ranged fromless than 10 ppm (parts per
million) to more than 2,000 ppm which may comefromthree
possible sources: (1) Direct movement inland from the sea
and along tidal reaches of streams; (2) residual sea water left
in the sediments at the time of deposition or during former
invasions of the sea; and (3) upward movement of salty water
from deeper artesian aquifers.

INFORMATION CIRCULAR NO. 29

EXPLANATION
0JM Chloride content
123 partss per million)
Well;upper number O
s number of well, 0-50
lower number s 0
depth of well 1 100

Surface water 101-250
observation point 0
and station number 251-500
Mor 500
More than 500

SCALE IN MILE
0

Figure 13. Map of northwestern Collier County showing

the chloride content of water from selected

wells and surface-water observation points.

Ca
<^1-

FLORIDA GEOLOGICAL SURVEY

Salt- Water Contamination

The encroachment of sea water into a coastal aquifer
is governed bythe relationship of ground-water levels to sea
level. The lighter fresh water floats on top of the heavier
salt water, and the depth to the salt water is related to the
height of fresh water above sea level. If specific gravities
of 1.0 and 1.025 are assumed forfresh water and sea water,
respectively, then under static conditions, each foot of head
of fresh water above sea level indicates 40 feet of fresh
water below sea level. This relationship is modified by the
mixing of fresh and salt water and the seaward flow of fresh
water (Kohout, 1960), and by the presence of beds of low
permeability in the aquifer, but it holds sufficiently well to
be considered valid.

Contamination by the encroachment of sea waterhas
occurred chiefly in areas adjacent to major streams and
drainage canals that flow to the ocean. These waterways
enhance the possibility of sea-water encroachment in two
ways: (1) They lower ground-water levels, thereby reduc-
ing the fresh-water head opposing the inland movement of
sea water; and (2) they provide access for sea water to move
inland during dry periods.

Examples of both types of encroachment are shown by
data collected during the drilling of well 160, located east
of the well-field extension and near the upper tidal reach of
the Gordon River (fig. 6, 7). Chloride analyses of water
samples taken from test well 160, as shown in figure 6,
indicate that salt water from the Gordon River had infil-
trated downward to a depth of about 25 feet below msl in the
uppermost limestone bed of the aquifer. The salt-water
contamination from the river was reported to be the cause
of the loss of severalrows of litchi nut trees near the river
in the Caribbean Botanical Gardens (fig. 12).

Lithologic (fig. 6, section B-B')and chloride datafrom
well 160 show that the uppermost layer of limestone is
underlain by 10 feet of marl which separates shallow water
of high chloride content from deeper water of low chloride
content. The difference in the quality of the water may be

INFORMATION CIRCULAR NO. 29

caused by either or a combination of the following factors:
(1) The marl layer is sufficiently impermeable to form an
effective seal between the upper and lower limestones;
(2) well 160 is located near the Gordon River, a discharge
area (see p. 15), and the pressure head in thelower part of
the aquifer is greater than it is in the shallow part; there-
fore, the downward movement of salty water is prevented.

The high chloride content below 130 feet in well 160
indicates that salt water has moved inland beneath the Gordon
River, presumably as a result of local lowering of the
ground-water levels in the adjacent drainage area. The
fluctuation of chloride content of water samples collected
periodically from a depth of 156 feet below the land surface
reflects the movement of the salt front deep in the aquifer
in response to changes in ground-water levels (table 2).
The low chloride content of the water at a depth of 135 feet
in well 161 (table 2) indicates that in 1958 the deep salt
wedge had not reached that well.

The extent of salt-water encroachment at depth in the
GCocohatchee River basinhas not been determined because of
ithe lack of deep observation wells nearthe lower reaches of
the river. However, the presence of water containing 664
ppm of chloride at a depth of 60 feet, and 2,400 ppm of
chloride ata depth of 103feet belowland surface in well 187,
suggests the possibility of recent encroachment beneath
canals that extend inland from the river. A determination
of the origin of this high chloride content water canbe made
by periodic sampling of the well and complete chemical
analyses of the water.

Extensive encroachment fromthe sea has not occurred
in the area west of the well field although water levels in the
area are lowered by pumping in the well field and by the
numerous canals extending inland from the gulf. However,
inland movement of salt water is indicated by fluctuations of
'chloride content of periodic samples at a depth of 166feet in
well 151 which ranged between 44 and 85 ppm during the
period March 1958 to March 1960.

FLORIDA GEOLOGICAL SURVEY

Major encroachment probably is being retarded by
high ground-water levels (fig. 8, 9, 11). There is close
correlation between the hydrographs of wells 151 and 164
(fig. 11); accordingly, the long-term hydrograph of well 164
(fig. 10) suggests that the water levels in well 151 have
probably averaged between 4 and 5 feet above sea level during
the period 1958 through September 1959, a period of heavy
rainfall and above normal ground-water levels. The head
of fresh ground water above sea level would indicate that
fresh water extends to the base of the aquifer at this point.
Encroachment maybe retarded also bythe presence of beds
of marlin the aquifer, which probably extend seaward under
the gulf.

Although the encroachment of salt water toward the
well field has been slight, the presence of the salt-water
front near well 151 indicates that long-term lowering of
ground-water levels caused by an extension of the canal sys-
tem or increased pumping during an extended dry period'
could cause encroachment that would endanger the well field.

Since the chloride content of the water is an indicator
of changes in mineral content, the data in figure 13 show
that highly mineralized water occurs north of Naples near
the Cocohatchee River and east of the coastal ridge as much
as 10 miles inland fromthe coast. Comparison of the water-
level contour maps of figures 8 and 9 and the topographic
map of figure 3 indicates that ground-water levels in the area
east of the ridge range from 5 to 15 feet above sea level.
The lines of equal chloride content in figures 5, 6, and 7
showthat the chloride content of the groundwater increases
gradually with depth in the eastern part of the area, but rises
sharply in material of low permeability at depth in the aquifer.
The high water levels and the inland location of the Big
Cypress area indicate that the high mineral content of the
ground water in that area is not caused by the recent en-
croachment of sea water. The high mineral content of ground
water in materials of low permeability in the lower part of
the aquifer suggests that the source of contamination is
connate salt water or upward leakage from the deeper artesian
aquifer.

INFORMATION CIRCULAR NO. 29

Data pertaining to the possibility of upward movement
of saltwater from deep water-bearing strata were collected
during the drilling of well 303 inthe northeastern part of the
area. Well 303 was drilled to a depth of 300 feet in January
1959. The analyses of samples collected at 46 feet and 240
feet below land surface are given in table 1. Materials of
very low permeability were penetrated between the base of
the shallow aquifer (about 130 feet below land surface) and a
permeable bed at 230 to 240 feet below land surface from
which the lower sample was taken. Water levels measured
as drilling progressed in the section of low permeability
ranged from 5. 4 to 14. 8 feet below the land surface. Water
levels in both the shallow aquifer and the lower permeable
zone were less than 1 foot below the land surface. The
extremely high mineral content of the lower sample from
well 303 indicates the possibility of contamination from below
the shallow aquifer, but the head differential betweenthe two
levels suggests that no upward flow was occurring.

The chloride content of a sample collected July 18,
1958, at 26 feet below land surface in well 176 was 87 ppm,
and the chloride content of a sample collected July 29, 1959,
from approximately the same depth in well 303 at the same
location was 38 ppm. This decrease in chloride content of
the water indicates flushing of ground water by continuous
ground-water discharge into the adjacent drainage canal
during the 1-year interval. Further evidence of flushing is
shown by the analyses of samples collected from the bottom
of canals (fig. 13) during June of 1960, when the canals were
receiving ground water from the aquifer. The chloride
content of the canalwater samples that were collected along
the eastern periphery of the area (fig. 13, stations 1-9)
ranged from 35 to 239 ppm, whereas the chloride content of
water from a shallow pond east of the Naples Airport (station
12) was 14 ppm.

The difference in the mineral content of the ground
water underlying the coastal ridge and the inland areas
probably is related to the amount of flushing that has occurred
in each area. The permeable quartz sand and limestone that
form the shallow subsurface materials on the coastal ridge
allow rain to infiltrate rapidly into the aquifer. Also, the

FLORIDA GEOLOGICAL SURVEY

water-table contour maps in figures 8 and 9 show that the
distances to points of ground-water outflow are short and
the water-table gradients are fairly steep. In contrast, the
presence of dense beds of relatively impermeable limestone
at shallow depths in the inland areas probably greatly retards
the infiltration of rainfallintothe aquifer. This is suggested
by the fact that the ground water at very shallow depths
contains considerable chloride, whereas the surface water
contains very little chloride. Moreover, the ground-water
gradient toward points of outflow is flat, except in areas
immediately adjacent to tidal streams or Naples Bay. Such
evidence indicates that some improvement in the quality of
ground water may occur with increased drainage in inland
areas.

Quantitative Studies

Late in 1953 the city of Naples began preliminary work
for a new well field and water plant in the northern part of
the city (fig. 2). During the period 1953-59, four aquifer
tests were made at wells in the vicinity of the water plant
and in the area proposed for the well-field extension. These
tests furnished information on the ability of the aquifer to
store and to transmit water. Such data are useful in making
predictions of drawdown due to pumping, and in determining
the proper spacing of wells in a well field.

Aquifer Tests

The first aquifer test was made at the site of the water
plant (fig. 12), in September 1953. Well 142, a 6-inch-
diameter supply well, 96 feet deep, was pumped for 7 hours
at the rate of 298 gpm (gallons per minute) and the water was
dischargedinto a roadside ditch. Water -level measurements
were made in well 123, 695 feet west of the pumping well,
and well 143, 845 feet east of the pumping well. At the end
of the 7-hour test the drawdown due to pumping well 142 was
1.68feet in well 123 and 1.18 feet in well 143. In June 1955,
a test was made on the same wells except that well 142 was
pumped for 8 hours at the rate of 345 gpm and the water was

INFORMATION CIRCULAR NO. 29

discharged into the city's storage reservoir. Drawdowns
measured in observation wells at the end of this test were
1.71 feet in well 123 and 1. 18 feet in well 143.

In March 1958, the first aquifer test was made in the
area of the well-field extension northeast of the water plant.
Well 164 (fig. 12) was pumped at the rate of 360 gpm for 12-
hours and the water was discharged into a shallow ditch which
drained eastward toward the Gordon River. After the pump
had been in operation for 41 hours a heavy rain started and
continued for the duration of the test. A hydrograph of well
163, 545 feet east of the pumped well, for the period of the
test, is shown in figure 14. The hydrograph shows the

Figure 14. Hydrograph of well 163, in the
Naples well field area, during
the aquifer test of March 25,
1958.

FLORIDA GEOLOGICAL SURVEY

drawdown caused by pumping and the effect of recharge to
the aquifer by the rain.

A final aquifer test of long duration was made in the
area northeast of the water plant on January 9-10, 1959.
Well 189 was pumped for 30 hours at the rate of 360 gpm
and the water was discharged into the adjacent shallow drain-
age ditch. The ditch became clogged during the test causing
flooding of a large part of the areabetweenthe pumping well
and Gordon River. Figure 15 shows the drawdowns in different
observation wells at the end of the 30-hour period of pumping,
a sketch of the locations of observation wells, and an outline
of the area which was flooded by discharge water. The draw-
downs in the observation wells between the pumping well and
the Gordon River were appreciably less than the drawdowns
in wells west of the pumping well.

Analysis of Aquifer-Test Data

The drawdown data collected during the aquifer tests
were adjusted to correct for fluctuations caused by factors
other than pumping, such as variations in barometric
pressure and evapotranspiration. The corrected drawdowns
then were analyzed to determine the hydraulic properties
of the aquifer. Because there was evidence of considerable
downward leakage to the main producing limestone in the
lower part of the aquifer, the test data were analyzed by
use of a family of leaky-aquifer type curves developed by
H. H. Cooper, Jr. U. S. Geological Survey, Tallahassee,
Florida, from a method outlined by Hantush (1956). This
method provides a means to compute the values of the co-
efficients of transmissibility and storage of the producing
zone, and the coefficient of leakage of the semiconfining
beds that overlie the producing zone. Figure 16 is an ideal-
ized sketch showing flow in a leaky aquifer (Jacob, 1946).
Although the characteristics of the shallow aquifer in Naples
do not match the theoretical conditions assumed in this method
of analysis, the determined coefficients provide valuable
indications of the capacities of the aquifer.

INFORMATION CIRCULAR NO. 29

DISTANCE IN FEET,FROM PUMPING WELL

Figure 15.

Graph showing drawdowns in observation
wells at the end of the 30-hour aquifer test
January 9-10, 1959, and a sketch showing
locations of wells used in the test.

EXPLANATION
el89
PUMPING WELL
0163
OBSERVATION WELL

APPROXIMATE AREA
FLOODED DURING TEST

158
O 100 E0O 300 400 500
SCALE IN FEET

- GORDON RIVER 1700 FEET EAST-----

FLORIDA GEOLOGICAL SURVEY

Figure 16. Idealized sketch showing flow in a leaky
artesian aquifer system.

The coefficient of transmissibilityis a measure of the
ability of an aquifer to transmit water. It is defined as the
quantity of water in gpd (gallons per day) that will flow through
a vertical section 1 foot wide and extending the full saturated
height of the aquifer, under a unit hydraulic gradient, at the
prevailing temperature of the water (Theis, 1938, p. 892).
The coefficient of storage is a measure of the capacity of an
aquifer to store water and is definedas the volume of water
released from ortaken into storage per unit surface area of
the aquifer per unit change in the component of head normal
to that surface. The leakage coefficient (Hantush, 1956,
p. 702) characterizes the ability of semiconfining beds above
or below an aquifer to transmit water into the bed being
tested. It maybe definedas the quantity of water that crosses
a unit area at the interface between the main aquifer and its
confining bed if the difference between the head in the main
aquifer and the beds supplying the leakage is unity.

IMPERVIOUS BED

INFORMATION CIRCULAR NO. 29

Computed coefficients of transmissibility and storage
for the water-plant area were approximately 80,000 gpd per
foot and 0.0004, and for the area of the well-field extension
185,000 gpd per foot and 0. 0004. Because of the short dura-
tion of the first three tests and major interference by other
influences than the test pumping, the coefficient of leakage
was computed only from the data obtained in the January
1959 test. Computations based on data from the latter part
of that test indicated that the coefficient of leakage ranged
from 0. 001 to 0. 008 gpd per square foot per foot of head
differential. The largest coefficient was computed from the
data from well 190 which is adjacent to the shallow ditch
into which water was discharged. In general, the leakage
coefficient increased eastward. This may be a reason for
the variation in drawdowns shown in figure 15.

In an ideal leaky aquifer system (fig. 16) in which water
levels in overlying beds are maintained constant by some
source of recharge, pumping causes a cone of depression,
which expands until downward leakage equals the amount of
water takenfrom storage by pumping. However, inthe ridge
area of Naples the supply of water in the upper sand beds is
limited; when the water table declines the amount of leakage
throughthe confining bed declines andthe cone of depression
continues to expand.

Figure 17 shows the drawdown curves for wells 158
and 188 during the January 1959 test. The curves have been
extended to show the water-level changes that might occur if
pumping had been continued. The rapid rate of flattening of
the water-level plots near the end of the test indicates that
leakage through the confining material was supplying most
3f the water pumped. If water levels were maintained at a
constant position in the beds supplying the leakage, the draw-
down would have remained the same during continued pumping
at the constant rate, and any increase inthe rate of pumping
would have caused a proportional increase in drawdown. If
unwatering of the upper part of the aquifer had occurred the
Extended drawdown curve would have declined and the cone
pf depres sion in both parts of the aquifer would have expanded.
After an extended period, if no recharge had occurred, the
water level in the sand supplying the leakage would have

40 FLORIDA GEOLOGICAL SURVEY

approached the head in the permeable zone that was being
pumped, and the entire aquifer would act as a unit under
water-table conditions.

0o I

TIME ,N MINUTES,SINCE PUMPING BEGAN
00 1000 IO0o 100.000

i li l l I I 1 1 in nl r- -. -p - :: - -
i I I ntl ea

WERL IEI kw

-ii
-- -- l-- -- 1![- -- -- t'l v t----l ----
F V I CU I
[r rEr 9

"- ..U. _, -, ..... _"'--. __1.1 I'I',LII---

o 1 t I d I month I oar

EXPLANATION
CURVE A s Cu h c i
I Q (no recharge)
CURVE
Theorecal drowdo-n lwater-tobl conditions
(no recharge) UR
CURVE C1

Obtlrved dra*down
I 5TheoreICol dra-down(unlimsted recharge)
CURVE 0
Theorahcol drowdownqohya quifer condilons
(no recharger I

Figure 17. Graph showing drawdowns observed in wells
158 and 188 during aquifer test January 9-10,
1959, and theoretical drawdowns for artesian
water-table, and leaky-aquifer conditions.

Curve A was constructed by using the coefficients
of transmissibility and storage determined from the test
and assuming that artesian conditions exist in the aquifer.
Curve B was plotted by using a coefficient of storage of
0. 15 (characteristic of water-table conditions) and a coef-
ficient of transmissibility somewhat (10 percent) higher

INFORMATION CIRCULAR NO. 29

than that computed for the test (to take into account the
transmissibility of the upper beds); it shows the theoretical
drawdown under water-table conditions after extended time.
Curve C extends the test data assuming an unlimited water
supply on the surface. Curve D indicates the theoretical
drawdown under conditions of no replenishment to the upper
zone. The drawdown caused bylong-term pumping from the
deep zone is reflected at the water table, and it is controlled
bythe coefficients of storage and transmissibility of both the
pumped zone and the overlying beds and by the availability of
recharge from surface sources. The possibility of large
drawdowns in the shallow beds in this area is decreased by
the diversion of water from the Gordon River and its drain-
ageway for recharge.

Cities in southeastern Florida have developed large
supplies near the sea by locating well fields near canals
which drain large areas of the Everglades. Water levels in
the wellfields near these canals are maintained by infiltration
of water from the canals into the aquifer. Detailed studies
of the development of water supplies by induced infiltration
in these areas were presented by Parker (1955, p. 277-290,
482-484). The development of a theory on induced infiltration
was described by Rorabaugh (1956). Supplies developed by
this method would generally carry more mineral matter than
the surface water but less thanthe ground water. Salt-water
encroachment through surface channels in these areas has
been effectively controlled by salinity-control dams located
downstream from the well fields.

The topography and drainage pattern of northwestern
Collier County and the hydraulic characteristics of the aquifer
indicate that supplies equal to present water needs can be
developed along the eastern edge of the coastal ridge and the
adjacent drainageway. Additional supplies to meet very
large future needs may be developed from the same area by
the use of induced infiltration in conjunction with the drainage
of inland areas. Present and future well fields may be safe-
guarded from salt-water encroachment from the sea by the
construction of salinity-control dams near the gulf in major
streams.

FLORIDA GEOLOGICAL SURVEY

SUMMARY AND CONCLUSIONS

Fresh-water supplies in northwestern Collier County
are obtained from an extensive shallow aquifer which extends
from the land surface to a depth of about 130 feet below the
land surface. It is composed chiefly of permeable sand and
shelly limestone; however, its vertical permeability is re-
stricted by thin beds and lenses of shelly, sandy marl in
coastal areas, and by a bed of very dense limestone that
occurs near land surface in areas east of the coastal ridge.

The aquifer is recharged by local rainfall and to some
extent by surface water that flows overland fromthe interior
toward the coast. Water-level contour maps show a ground-
water mound underlying the coastal ridge and steep gradients
westward toward the Gulf of Mexico and eastward toward the
narrow Gordon River drainageway east of the ridge. The
contour maps and topographic maps suggest that water levels
in inland areas are perennially near or above land surface
(10 to 15 feet above msl) and that discharge is westward into
the Gordon River drainageway, southward into tidal streams,
and northward into the Cocohatchee River and its tributary
canals.

Chemical analyses of water from selected wells show
that the chief factor limiting the use of ground water is
mineralization due to contamination by sea water. Ground
water inthe area is relatively high in mineral content except
in areas on or immediately east of the coastal ridge. The
chief source of the mineralization in the fringe areas along
the gulf, Naples Bay, and tidal streams is recent salt-water
intrusion, whereas the source of mineralization inthe inland
areas is apparently residual sea water left in the sediments
during former invasions of the sea. Because of the poor
quality of ground water in the inland areas, local ground-
water supplies for Naples and other coastal communities are
available only in a relatively small area close to the sea.

The results of aquifer tests inthe municipal well fields
indicate that the aquifer will produce large quantities of water

INFORMATION CIRCULAR NO. 29

with moderate drawdowns in water level, especially in areas
where surface water can rechargethe aquifer readily. Data
from test drilling and aquifer tests suggest that the perme-
ability of the aquifer increases near the eastern edge of the
coastal ridge where relatively large sources of surface water
can be diverted into the aquifer.

The topography and drainage pattern of northwestern
Collier County and the hydraulic characteristics of the aquifer
indicate that supplies equal to present water needs can be
developed along the eastern edge of the coastal ridge and the
adjacent drainageway. Additional supplies to meet future
needs may be developed from the same area by the use of
induced infiltration in conjunction with the drainage of inland
areas. Present and future well fields may be safeguarded
from salt-water encroachment fromthe seabythe construc-
tion of salinity-control dams near the gulf in major streams.

A continuing appraisal of the quantity and quality of
water in storage will be needed for the maximum development
of the area. The immediate need is for water-level and
streamflow data for use in the design of a comprehensive
water-control system.

Studies of flood-control and drainage systems in south-
eastern Florida have shown that, with proper location and
operation of salinity controls and carefully planned overall
drainage systems, large inland areas can be developed for
urban or agricultural use without depletion of essential
ground-water resources.

FLORIDA GEOLOGICAL SURVEY

REFERENCES

Hantush, M. C.
1956 Analysis of data from pumping tests in leaky
aquifers: Am. Geophys. Union Trans. v. 37,
no. 6, p. 702-714.

Jacob, C.E.
1946 Radial flow in a leaky artesian aquifer: Am.
Geophys. Union Trans. v. 27, no. 2, p. 199.

Klein, Howard
1954 Ground-water resources of the Naples area,
Collier County, Florida: Florida Geol. Sur-
vey Rept. Inv. 11, 64 p. 15 figs.

Kohout, F.A.
1960 Cyclic flow of salt water in the Biscayne
aquifer of southeastern Florida: Geophys.
Research Jour., v.65, no.7, p.2133-2141.

Parker, G.G.
1955 (and others) Water resources of south-
eastern Florida, with special reference to
the geology and ground water of the Miami
area: U. S. Geol. Survey Water-Supply
Paper 1255, p. 277-290, 482-484.

Rorabaugh, M.I.
1956 Ground water in northeastern Louisville,
Kentucky, with reference to induced infil-
tration: U. S. Geol. Survey Water-Supply
Paper 1360-B, 168 p., 17 pis., 25 figs.

Theis, C.V.
1938 The significance and nature of the cone of
depression in ground-water bodies: Econ.
Geology, v. 33, no. 8, p. 892.

FLRD GEOLOSk ( IC SUfRiW

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	Title Page
	Table of Contents
	Abstract
	Introduction
	Geology and test drilling
	Ground water
	Summary and conclusions
	References