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Appraisal of the water resources of Charlotte County, Florida ( FGS: Report of investigations 78 )
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Title: Appraisal of the water resources of Charlotte County, Florida ( FGS: Report of investigations 78 )
Series Title: ( FGS: Report of investigations 78 )
Physical Description: Book
Creator: Sutcliffe, H. Jr.
Publisher: U. S. Geological Survey
Bureau of Geology, Florida Department of Natural Resources
Place of Publication: Washington, D. C.
Tallahassee
Fla.
Publication Date: 1975
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Statement of Responsibility: by H. Sutcliffe, Jr.
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Source Institution: University of Florida
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The author dedicated the work to the public domain by waiving all of his or her rights to the work worldwide under copyright law and all related or neighboring legal rights he or she had in the work, to the extent allowable by law.
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ltuf - ACL6397
System ID: UF00001265:00001

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STATE OF FLORIDA
DEPARTMENT OF NATURAL RESOURCES
Harmon Shields, Executive Director



DIVISION OF RESOURCE MANAGEMENT
Charles M. Sanders, Director



BUREAU OF GEOLOGY
Charles W. Hendry, Jr., Chief



REPORT OF INVESTIGATIONS NO. 78



APPRAISAL OF THE WATER RESOURCES OF
CHARLOTTE COUNTY, FLORIDA



By
H. Sutcliffe, Jr.



Prepared by the
UNITED STATES GEOLOGICAL SURVEY
in cooperation with the
SOUTHWEST FLORIDA WATER MANAGEMENT DISTRICT
and the
BUREAU OF GEOLOGY
FLORIDA DEPARTMENT OF NATURAL RESOURCES



Tallahassee, Florida
1975















DEPARTMENT
OF
NATURAL RESOURCES



REUBIN O'D. ASKEW
Governor


BRUCE A. SMATHERS
Secretary of State



PHILIP F. ASHLER
Acting Treasurer



RALPH D. TURLINGTON
Commissioner of Education


ROBERT L. SHEVIN
Attorney General



GERALD A. LEWIS
Comptroller



DOYLE CONNOR
Commissioner of Agriculture


HARMON W. SHIELDS
Executive Director







LETTER OF TRANSMITTAL


Bureau of Geology
Tallahassee
August 28, 1975


Governor Reubin O'D. Askew, Chairman
Florida Department of Natural Resources
Tallahassee, FL 32304

Dear Governor Askew:

The Bureau of Geology of the Division of Resource Management, Florida
Department of Natural Resources, is publishing as its Report of Investigations
No. 78, a study, "Appraisal of the Water Resources of Charlotte County,
Florida", by Mr. H. Sutcliffe, Jr. of the U. S. Geological Survey.

This study is to document the water resource potential in an area where
substantial growth is anticipated. This type of regional study is most impor-
tant to the planning of the development of the county, as it enables one to
realistically anticipate the quantity and quality of the water resource which
may be developed and where potential problems can be expected to occur. It
is hoped this type of study will be of substantial benefit to those persons and
agencies responsible for the conservation of the resource.



Respectfully yours,



Charles W. Hendry, Jr., Chief
Bureau of Geology















































Completed manuscript received
May 7, 1975
Printed for the
Florida Department of Natural Resources
Division of Resource Management
Bureau of Geology

Tallahassee
1975



iv







CONTENTS

Page
Abstract ...... ........... .................... ... ............... ... 1
Introduction ........... ............... ............ 2
Purpose and scope ......................... ..................................... ............................ 3
Methods of investigation ....... .............. ..... 3
Previous investigations ........ ............. ............ 3
Acknowledgments ..................... ............................ 4
Geography .................................... .......... ... 4
Drainage and topography ..... .. ..... 5
Climate ......................................... ...... 5
Urban and agricultural development ~~- 8
Geology .. ...................... .......... ...... ............................................................. 8
Hydrology .. .._ ._...... ... ..... ..10
Surface water .....-. ....4.. .... ... .....
Discharge _.._-14
Chemical quality .....-............................... .... 16
Public water supplies 20
Port Charlotte ..... ......... ........ .22
Punta Gorda ...... ..... .. .... ..... .. .- ....... .............. 22
Ground water ..... ............................ ----- 24
Ground-water conditions by area ............................... 30
Area A ..............................................3
Water-table aquifer ........... ..............- 30
Artesian aquifers -.......-35
Area B ........................... .......-................3..6
Water-table aquifer -38
Artesian aquifers ......--- --40
Area C ..............-..-.....--42
Water-table aquifer .4 ...42
Artesian aquifers .....-...- .....42
Area D -- .46
Water-table aquifer ....... 46
Artesian aquifers .------48
Well construction And use in relation to water quality 50
Saline water resources 50
Conclusions --- 51
Selected references 52







ILLUSTRATIONS

Figure Page

1. Map showing location of the study area 6
2. Map showing drainage basins in Charlotte County 7
3. Map showing areas of present and potential water supply
development and urban growth 9
4. Graphs showing monthly and annual rainfall at Punta Gorda,
North Port Charlotte, and Port Charlotte, from 1965 to 1969
and range in temperature at Punta Gorda, from 1931 to 1960 -........11
5. Graphic lithologic log and borehole geophysical logs from well 16 ___13
6. Generalized sections showing stratigraphic units underlying
central and eastern Charlotte County 15
7. Map of Charlotte County, showing location of wells referred
to in this report 17
8. Map showing location of the principal surface-water gaging
stations in Charlotte County and vicinity 119
9. Map showing location, depth, and chloride concentration of inven-
toried wells tapping the water-table aquifer in Charlotte County __27
10. Map showing location, depth, and chloride concentration of inven-
toried wells tapping Zone 1 in Charlotte County _-29
11. Map showing location, depth, and chloride concentration of inven-
toried wells tapping Zone 2 in Charlotte County .31
12. Map showing location, depth, and chloride concentration of inven-
toried wells tapping Zones 3 and 4 in Charlotte County -32
13- Map of Charlotte County showing hydrologic areas for which
ground-water conditions are described ...33
14. Hydrographs showing fluctuations of water level in observation
wells that penetrate the artesian aquifers in Area A __ 37
15. Hydrographs showing fluctuation of water levels in observation
wells that penetrate the artesian aquifers in Area B -...-. --A43
16. Hydrograph showing fluctuations of water level in a well
affected by nearby heavy pumping ............ ..........45
17. Hydrographs showing fluctuations of water level in wells tapping
Zone 2, Area C -.47
18. Generalized sections showing lithology of units underlying the
upper 80 feet of the Telegraph Swamp area, eastern
Charlotte County .49







TABLES
Table Page

1. Generalized stratigraphic section, Charlotte County 12

2. Geological Survey's laitude-longitude number assigned to well
in this report for computer storage and retrieval
of well data ...................... ... ...........18

3. Summary of discharge characteristics of principal streams in
the Charlotte County areas ..... ......... ..................... 21

4. Changes in quality of streamflow with changes in discharge
during medium and low flow 23

5. Chemical analyses of raw water from the public supply at
Port Charlotte --____24

6. Chemical analyses of water from Shell Creek and from wells
in Punta Gorda 2...... ..5...._

7. Hydrogeologic units underlying Charlotte County ... ........26

8. Chemical analyses of water from the water-table aquifer under-
lying the Cape Haze and Gasparilla Island well fields _...-34

9. Chemical analyses of water samples from well 25 ...._35

10. Chemical analyses of water from wells that tap the water-table
aquifer and Zone 2 underlying Port Charlotte 38

11. Chemical analyses of water from wells that tap Zone 2, Area B ....39

12. Chemical analyses of water from wells that tap Zones 2 and
3, Area B _.. ............___41

13. Chemical analyses of water from test wells that tap Zone
2, Area C .-.--.--. 46











APPRAISAL OF THEATER RESOURCES OF
CHARLOTTE COUNTY, FLORIDA


By
H. Sutcliffe, Jr.


ABSTRACT

The coastal area of Charlotte County, in west-central Florida, is undergoing
rapid urbanization and is experiencing major problems in obtaining sufficient
water of suitable quality to meet public-supply requirements. The relatively
flat county is drained by two major streams, the Myakka and Peace Rivers,
and many small streams and canals. Neither of the major streams is used for
water supply. Although the average rainfall is 54 inches per year, the low-flow
characteristics are such that little or no flow will occur in most streams for as
much as 30 consecutive days on the average once every 20 years. The chemical
quality of water in most of the streams and canals is suitable for use by public
water supplies. However, most favorable reservoir sites are already in use.
The rock units underlying the county range in age from Holocene to Eo-
cene and contain a water-table aquifer and five artesian aquifers. The water-
table aquifer contains permeable sand and shell beds, which extend 20 to 50
feet below land surface. In the western part of the county, the transmissivity
of the aquifer is about 1,880 ft2 per day (feet squared per day). In the eastern
part where the aquifer contains highly permeable shell beds, the transmissivity
may exceed 6,680 ft2 per day, and wells tapping the aquifer may yield as much
as 600 gpm (gallons per minute). The water-table aquifer is a source of
water supply for the Cape Haze and Gasparilla Island water systems.
The upper artesian aquifer, or Zone 1, lies 50 to 150 feet below land sur-
face. This zone is commonly used as a source for domestic and small irrigation
supplies and provides some water for public supplies. A few wells tapping
this zone yield as much as 400 gpm although most yield about 30 gpm. In
western Charlotte County, the dissolved-solids concentration of water in Zone
1 ranges from 500 to 5,000 milligrams per liter. In the eastern part, it is less
than 500 milligrams per liter.
Zone 2 lies 150 to 250 feet below land surface. Many wells that penetrate
this zone also are open to Zone 1. Zone 2 is used extensively by irrigators in
eastern Charlotte County, and 6-inch wells finished in this zone commonly
yield more than 400 gpm. In some areas the wells flow. Water from this zone
is usually more saline than water from Zone 1.






BUREAU OF GEOLOGY


Zone 3 lies 250 to 400 feet below land surface. Most wells finished in this
zone also are open to Zones 1 and 2. Irrigation wells that tap this zone flow
as much as 500 gpm, and the water level in many wells can rise about 30 feet
above land surface Many unused irrigation wells tapping this zone are being
plugged by land developers to prevent the movement of saline water (5000
milligrams per liter of dissolved solids) from Zone 3 into the upper zones.
Use of the water from Zone 3 is limited to flood irrigation.
Zone 4 lies 600 to 800 feet below land surface. Most wells drilled into
this zone are open to all zones above and flow as much as 500 to 600 gpm.
The water level in this zone may rise 30 feet or more above land surface. The
water from this zone is more saline than water from the upper zones.
In the western half of the county, the shallow aquifer has been intruded
by salt water from the Gulf and the estuaries and from deeper zones. The
intrusion from deeper zones results from a combination of well-construction
methods and naturally occurring differences in water levels--the water levels
in the deeper zones being higher than those in the shallow zones. The salt-
water intrusion from deeper zones can be lessened by changing well-construc-
tion methods and by plugging abandoned wells and holes.
Large water supplies for Charlotte County will be obtained in the future
chiefly from: (1) the water-table aquifer in the southeastern part where per-
meable shell beds can yield as much as 600 gpm of potable water; (2) Zones
1 and 2 where they have not been contaminated by saline water; (3) desalted
ground water; and (4) water imported from outside the county.

INTRODUCTION
Charlotte County has experienced a major increase in population during
the last decade, 1960-70, and growth probably will continue during the next
decade at a comparable or increased rate. Principal among the problems re-
sulting from growth is the need for water of acceptable quality in adequate
quantity.
Shallow surface-water reservoirs provide most of the public water supplies
in the populated coastal area of Charlotte County. However, they are generally
inadequate and unsatisfactory. Nearly 60 percent of the annual rainfall occurs
from June through September, providing more runoff than can be stored in
the reservoirs. In contrast, during extended periods of little or no rain, from
September through June, withdrawals may nearly exceed the combined inflow
and the storage capacity of the reservoirs. Also, the warm year-round climate
fosters lush growth of aquatic plants and weeds which rapidly clog drainage
ways and reservoirs and create taste and odor -problems in the supplies.
Ground water is used as a source of supply in the inland area and is used
locally for public supply along the coast. Salt-water intrusion is a problem in






REPORT OF INVESTIGATION NO. 78


developing ground water for public supply. Before the 1930's, water meeting
the State's standards for drinking water was probably available all along the
coast. Construction of tidewater canals and other waterways has resulted in
the lowering of groundwater levels in some areas and the intrusion of salt
water into the shallow aquifers in other areas. This intrusion has made parts
of these aquifers unsuitable as a source of drinking water. In the western
half of the county, saline water from deep zones has moved upward in well
bores and has intruded fresh-water zones in the shallow aquifers.

PURPOSE AND SCOPE
This 3-year cooperative investigation was begun in 1967 by the U. S.
Geological Survey at the request of the Southwest Florida Water Management
District as part of their continuing program of water-resources investigations
within the Management District. The purpose of the investigation was to pro-
vide a generalized description of the hydrology of Charlotte County and to
identify the major hydrologic problems of the county; particularly with re-
spect to use of ground and surface water for public supply. Because most of
the available surface-water resources in the County had already been devel-
oped, emphasis was placed on evaluating the ground-water resources. This
report summarizes the findings of the investigation.

METHODS OF INVESTIGATION
Information on the flow and water quality of major streams was obtained
from the existing basic records network in the area. Water samples were ob-
tained from most of the wells inventoried, and specific conductance, chloride,
and sulfate concentration of the samples were determined in the field. Water
samples were collected from the public supplies for more complete analyses by
the U. S. Geological Survey.
Geophysical logs including electric, gamma ray, and caliper, were obtained
from about 50 wells, and rock cuttings from about 60 wells were studied and
described. Seven observation wells were drilled, and information on the
changes in water level and chemical quality of distinct water-bearing zones
were obtained. Eighteen test holes were augured using hollow stem to deter-
mine the depth to water-bearing limestone and shell beds and to obtain infor-
mation on the quantity and q-iality of water available from the surficial plastic
sediments. Thirteen of these test holes were also used as observation wells.

PREVIOUS INVESTIGATIONS
Matson and Sanford (1913) and Sellards and Gunter (1913) were the first
to describe the ground-water resources of a part of Charlotte County. String-






BUREAU OF GEOLOGY


field (1936) included information on Charlotte County in his study of the
principal artesian aquifer in Florida. Parker and Cooke (1944) discussed the
relation of the geology and water resources of the County to those of southern
Florida. Additional references to the geology of Charlotte County were made
by Cooke (1945), MacNeil (1950) and Parker and others (1955). DuBar
(1958a, 1958b, 1962, 1968) reported on the Neogene stratigraphy and bio-
stratigraphy of the general area.
Specific information on the hydrology of the county was given by Toler
(1967) who provided information on the fluoride concentration of ground and
surface water; by Kaufman and Dion (1967, 1968) who summarized the
ground water resource data available in 1967 and the chemical quality of
water in the Floridan aquifer; by Flippo and Joyner (1968) who described
the low-flow conditions of some of the streams; and by Sutcliffe and Joyner
(1968) who presented the results of test drilling.

ACKNOWLEDGMENTS
Particular recognition is given C. R. Sproul, geologist, formerly with the
Florida Bureau of Geology, and H. J. Woodard, geologist, Florida Bureau of
Water Resources, for their assistance in geophysical logging and interpretation
of these logs. Jimmy Miller located many of the old wells in the area and
faithfully collected well cuttings from many of the wells he drilled. Bennet
and Bishop, Consulting Engineers, furnished data on tests made on production
wells in the Cape Haze and Gasparilla Island well fields. The Humble, Mobil,
and Chevron Oil Companies graciously permitted the collection, inspection,
and description of many sets of cuttings from test holes in the county. Appre-
ciation is expressed to Sidney Wells, Utilities Director, General Development
Corporation, the Babcock Florida Corporation, the Charlotte County Commis-
sion, and many county citizens for their interest and assistance.
Appreciation also is expressed to G. G. Parker, Chief Hydrologist, South-
west Florida Water Management District, for his comments and suggestions
concerning the report and to J. S. Rosenshein, U. S. Geological Survey, for
his extensive revision and technical and editorial review of the report. D. H.
Boggess, hydrologist, U. S. Geological Survey, provided information on the
correlation of geologic formations in Lee County and assisted in interpreting
many of the well cuttings.
The investigation was under the general direction of C. S. Conover, district
chief for Florida and the immediate supervision of J. S. Rosenshein, subdis-
trict chief.
GEOGRAPHY
Charlotte County borders the Gulf Coast of southwestern Florida (fig. 1)
and is the southernmost county in the Southwest Florida Water Management







REPORT OF INVESTIGATION NO. 78


District. The county has an area of 832 square miles, of which 703 are land.
The shoreline is about 120 miles long but only about 12 miles fronts directly
on the Gulf. The balance is frontage on the Charlotte Harbor estuary and
lagoons.

DRAINAGE AND TOPOGRAPHY
The State is divided into major and subdrainage basins (Kenner, Pride,
and Conover, 1967) to facilitate storage and retrieval of hydrologic informa-
tion on streamflow. The streams and canals in Charlotte County contribute
runoff to five of these drainage basins (fig. 2) four of which empty into
Charlotte Harbor, and the fifth into the Gulf via the Caloosahatchee River
which lies to the south of the investigation area. The position of the divides
is somewhat arbitrary inasmuch as most of the area drains by sheet flow.
In the interior part of the county, canals have been excavated to drain
agricultural land. Their excavation has not followed any general drainage
plan. On the other hand, the canal system in Port Charlotte (fig. 3), typical
of the urbanizing area, has been carefully planned and consists of about 26
miles of waterways. The longest of these canals is the 12-mile long Coco Plum
Waterway, which can transfer water through control gates from its western
end into the Big Slough Canal.
Much of Charlotte County forms a low-lying plain. The western part forms
a peninsula whose altitude is generally less than 10 feet above sea level. The
central part has a maximum altitude of about 40 feet, and much of the land
surface slopes gently toward the south. Except for the incised drainage of Shell
Creek, the eastern part forms a broad, gently-sloping, sandy, low-level plain.
The plain rises for several miles from the eastern edge of Charlotte Harbor to
an altitude of about 20 feet and is flat lying for the next 20 miles. The land
surface reaches its highest altitude-70 feet-in the northeast corner of the
county.

CLIMATE
The climate of Charlotte County is subtropical and is characterized by
warm, wet summers and mild, relatively dry winters. Frost occurs in the
eastern part in about three out of four winters. The dry period generally ex-
tends from November through May and the wet season from June through
September. Extreme tropical disturbances such as hurricanes may cause
torrential rainfall which may result in an unusually wet month.
Figure 4 shows the range in monthly temperature at Punta Gorda based
on records from 1931-60 and rainfall for 1965-67 at Punta Gorda, Port Char-
lotte, and North Port Charlotte. Although the annual rainfall on the county








6 BUREAU OF GEOLOGY






J__ ...... -




--












FLORIDA '
WATER ..iI "

II
MANAGEMENT
DISTRICT--












SARASOTA CO DE SOTO CO
CHARLOTTE CO








A I 0 10 MILES .


Figure 1.r-Area of investigation.











































Drainage divide 10B
0 5 MILES IOC
IOC Drainage basin number IOD
10E
IOF


Lake Okeechobee and Everglades
Coastal areas between Caloosahatchee and Peace Rivers


Peace River
Myakka River
Coastal area between


Myakka and Alafia Rivers


Figure 2.-Drainage basins in Charlotte County.







BUREAU OF GEOLOGY


averages 54 inches, the figure shows that rainfall varies noticeably from site to
site. In a specific year, a marked variation in areal distribution of rainfall
also occurs with about 60 percent of the total rainfall occurring in June-
September.

URBAN AND AGRICULTURAL DEVELOPMENT
The changing pattern of land use resulting from both urban and agricul-
tural development has markedly increased the water requirements in the
county. In addition, these changing patterns have had an impact on the hydrol-
ogy of the area through drainage of land and through increased urban and
agricultural irrigation water use from October-May. As the pattern of develop-
ment continues, competition for the available water resources between the
urban and agricultural user will become keener, and careful water manage-
ment. will be required to minimize conflicts between these two major water
users.
The areas of present and potential urban growth are concentrated along
the coastal part of Charlotte and adjacent counties (fig. 3). Charlotte County's
population increase of about 120 percent between 1960 and 1970 is one of
the highest in the State. This population was 27,559 in 1970. Four major
housing developments practically encircle Charlotte Harbor, and in the near
future the intervening open spaces will be filled with high-density housing,
which will be the impetus for continued population growth and an increased
need for water for public supplies.
Agricultural products have always been important to the economy of the
county. The long growing season and the lack of severe frosts permit growing
of two crops per year on truck farms. Before 1945, the coastal area south of
Punta Gorda was used'chiefly for cultivation of gladiolus. Since 1945, the land
cropped for this purpose has markedly decreased, owing in part to urban
growth. The county has about 7,000 acres in citrus concentrated in the
northern and eastern parts, about 75 percent of which has been planted since
1960.
Large acreages on some ranches are used to grow crops such as water-
melons, peppers, tomatoes, and eggplants. The growers clear and drain the
land and drill wells for irrigation. At the end of the growing year, this im-
proved land is converted to irrigated pasture for cattle. The amount of irri-
gated pasture increases from 1,000 to 3,000 acres annually and in part will be
the impetus for increased need for water for agricultural supplies.

GEOLOGY
The land surface of Charlotte County consists chiefly of sand. This sand
forms a thin mantle, generally less than 25 feet thick, beneath which lie many








27 15'


Sv nrn Fort. W (a
P Nr Ch t r t |dn
W PDE SOTO CO
W diners r CHARLOT CO

27*00' PO

0" Englewood n or 1 ~
well fields P Gordo a
Capo e Isad untiot t 0 d
Carol Qay a L
Cape Haze HARBOR cc
EXPLANATION dct


45'- Presently developed water supplies E /a C aCO

Lacost r V1
Potential water supply areas Island o North
(3 oFort Mys

Areas of. present or potential @ Fort Myers 88
population growth
N o r th C a p t vp C
wall fields
0 5 MILES x

26030'



Figure 3.-Areas of present and potential water-supply development and
urban growth.







BUREAU OF GEOLOGY


more layers of sedimentary rock. The geologic units comprising the upper
1,500 feet of the sedimentary rock are the Caloosahatchee Marl; the Tamiami
and Hawthorn Formations; the Tampa and Suwanne Limestones; the Ocala
Group; and the Avon Park Limestone (table 1). The units below the Tamiami
Formation consist chiefly of limestone and dolomite and the sequence becomes
more dolomitic with depth. These rocks form the framework in which ground
water occurs, and the study of the areal and vertical extent and variation in
the properties of these rocks provides important information needed to evaluate
the county's water resources.
Because the terrain is so flat, the methods used to study the geology,
particularly the stratigraphic features, are limited to the interpretation of (1)
well cuttings, which are samples recovered during drilling, and (2) geophysi-
cal logs, which are graphic records of variations in electrical and radioactive
properties of the rocks in place.
The graphic lithologic log shown on figure 5 was prepared from samples
obtained from well 16. This well penetrated almost the entire stratigraphic
section listed in table 1, and the log is generally representative of rock ma-
terials encountered in Charlotte County. A suite of geophysical logs and an
interpretation of the stratigraphic units obtained through use of both the
samples and geophysical logs are shown with the lithologic log. Once the
geophysical characteristics have been correlated with actual geologic materials
found in wells, geophysical logs, particularly the gamma ray log, can be
used to interpret the formations in wells for which no rock samples are avail.
able for study. Both rock cuttings and geophysical logs were used to :( 1)
interpret the geologic framework in Charlotte County; (2) determine the
position of water-bearing rocks; and (3) determine changes in characteristics
of the rocks that would effect their water-bearing properties.
Geologic sections (fig. 6) were compiled for the eastern part of the county
by correlation of rock samples and geophysical logs. The location of the sec-
tions is shown in figure 7, and the latitude-longitude number of wells along
the sections are listed in table 2. These sections show the major stratigraphic
units in the upper 1,500 feet beneath the eastern part of the county and their
variation in thickness and depth. The thickness of each geologic unit such as
the upper and lower units of the Hawthorn Formation, varies markedly from
place to place as does the depth of each unit below land surface. Similarly,
these units vary in depth and thickness in the western part of the county.

HYDROLOGY
During wet weather, water in the streams that flow across Charlotte County
is derived from rain that either falls on the county or on the streams' head.









REPORT OF INVESTIGATION NO. 78










120

MAXIMUM AND MINIMUM 100
MONTHLY TEMPERATURE s so ------- MAXIMUM

PUNTA GORDA -
1931-60 .


q, 4O
2
wl 20
I-


-- MINIMUM


MONTHLY AND ANNUAL RAINFALL 1965-69
46s 4 5 48.29 57.3 57.52

I i .
10




PUNTA GORDA


NORTH PORT CHARLOTTE


PORT CHARLOTTE


Figure 4.-Rainfall at Punta Gorda, North Port Charlotte, and Port Charlotte,
1965-69, and range in temperature at Punta Gorda, 1931-60.










TABLE 1.-Generalied stratigraphic section, Charlotte County. (Stratigraphic nomenclature conforms in part to that of
the Florida Bureau of Geology, Puri and Vernon, 1964)

Thickness
System Series Stratigraphic unit (feet) Lithology

Holoe sd 00 Quartz sand, medium to fine-grained, some
Holocene Surface sand 020 localized yellow marl.

Quaternary Terrace sand 0-5 Quartz sand, same as above.
Pleistocene Caloaatchee 0-50 Shell, sand, marl, and limestone.

Green sandy clay; green and gray-green clay;
Late Miocee T m F n 7 0 tan limestone; gray sandstone. Phosphatic
Late Miocene Tamiami Formation 75-250 dark-gray sandy clay which may contain phos-
phorite pebbles at base; 5-40 feet thick.
Interbedded gray to gray-white sandy clay
M e M e Hawthorn U er 70-0 and gray-white sandy limestone; abundant
Tertiary Middle Miocene formation Uppe t 7-260 phosphorite throughout
Interbedded gray to gray-white limestone and
gray to green clay; occasional thin streaks of
Lower unit 50-130 dolomite; abundant phosphorite throughout;
_____ clay bed at the base.
Interbedded gray to tan sandy limestone and
Early Miocene Tampa Limestone 90.450 gray to white clay; less phosphorite than
above.
Tan to creamy-white limestone, sandy lime-
Oligocene Suwannee Limestone 140450 stone, and sand.

Late Eocene Ocala Group 400 Tan chalky limestone; darker and dolomitized
near the bottom.

Middle Eocene Avon Park Limestone 500 Tan to dark-brown dolomite and hard lime-
stone.









REPORT OF INVESTIGATION NO. 78
WCELtL I
ntjistlVity GAMMiA CAuPG
I775l.5t IhChlle


Figure 6.--Llthologle and borehole geophysleal logs, well 16.







BUREAU OF GEOLOGY


waters outside the county. Water in the'aquifer system is also derived from
rain that has either fallen on the county or on recharge areas outside the
county. During dry weather, most of the streamflow is derived from the shal-
low aquifers.
The demand for water from the streams and the aquifer system that meets
requirements for use as public supply has markedly increased with urbaniza-
tion of the county. Because of this demand, emphasis is placed in this section
on those aspects of the hydrology that govern the availability and current or
potential use of surface and ground water for this purpose. Many parts of the
county are prone to flooding from either streams or storm driven tides. Delin-
eation of flood prone areas and description of hydrologic problems associated
with flooding are beyond the scope of this investigation.

SURFACE WATER
DISCHARGE
Information on the flow of some of the streams draining the county has
been collected since the 1930's (fig. 8, table 3). The records for all the sites
measured since 1960 have been published in the annual series of reports on
water resources data for Florida. Records are also published every 5 years in
the U. S. Geological Survey Water Supply Papers entitled "Surface Water
Supply of the United States: South Atlantic Slope and Eastern Gulf of Mexico
Basins."
The average discharge of the major streams draining the county and ad-
jacent areas for which more than 5 years of record is available ranges from 67
mgd (million gallons per day) to 808 mgd (table 3).
Although the average discharge of even the smallest stream is sizeable, a
wide variation exists between maximum, average, and minimum discharge,
and little or zero flow has been recorded in all the streams except Peace River
at Arcadia. An unpublished evaluation of the low-flow characteristics of the
streams listed in table 3 (J. F. Turner, oral commun., 1972) indicates that
little or no flow will occur in all the streams except Prairie Creek and Peace
River for as much as 30 consecutive days on the average once every 20 years.
The average minimum 30-day low flow expected to occur on the average once
every 2 years is about equal to the discharge equaled or exceeded 90 percent
of the time. As a result of these low-flow characteristics, use of the major
streams for any sizeable water supply would require storage of water in a
reservoir-the storage capacity of which would depend in part upon the with-
drawal rate desired.
Flippo and Joyner (1968) described the discharge of a few small streams
and canals under low-flow conditions. Their report indicates that most have










REPORT OF INVESTIGATION NO. 78 15











EXPLANATION
FEET
A A Location of lines of section
100 I I 5 9 8 7 hnown on figure 7
SEA I UDIFF -
LEVEL
STAMIAMI Lithology of units shown
FORMATIO'
200 FOR N on figure 5 and table I
UPP I IUN AWTNOR
400 rSUNDIFF
Undit ferntiated deposits,
00 h1 Incldes the Coioosonatchee marl
@ eof tble 1.
0 5 MILES

/ s 0 Vertical exaggeration approximately XIO0

1000




1400




FEET
FEET FEET C
100 T 14 212 36
tSo -- EAI i 20 7 SEA
SEA -LEVEL ORMATION
LEVEL L FORMATIONRMA
00-V O O-R--C\ ~OR"-"FORMATION 200
00 00 ~ \ *y oN




4000





1000 16000 0
4000

100 1200-


00 OCALA


Figure 6.-Generalized sections across central and eastern Charlotte County,
Florida.







BUREAU OF GEOLOGY


negligible or no flow during normal dry weather periods and low annual
yields. Therefore, these small streams and canals have no potential for use as
a reliable source for water supply.

CHEMICAL QUALITY
The dissolved solids concentration of the surface water changes markedly
from wet to dry season, because the chemical quality in and around Charlotte
County varies with discharge (table 4).
During high discharge, the water in the streams generally is low in dis-
solved solids. Conversely, during low discharge, the water generally is high
in dissolved solids. During both high and low discharge, the dissolved solids
are made up chiefly of calcium, bicarbonate and sulfate. Included in the dis-
solved solids are some constituents whose concentrations at times limit the use
of water in the streams for public supply.
Florida has adopted the Public Health Service Drinking Water Standards
which set limits on the amount of dissolved solids and the concentrations of
specific constituents in water for public use on interstate carriers. Some con-
stituents in raw water in this part of Florida occur in concentrations that
exceed these limits. The principal problem constituents and Public Health
Service recommended limits are listed below.

Constituent Public Health Service
Recommended Limit
(milligrams per liter)
Dissolved solids 500
Sulfate (SO4) 250
Chloride (C) 250
Fluoride (F) 1.4
Iron (Fe) .3
Color (platinum and 15
cobalt units)

Water in all streams except Alligator Creek near Punta Gorda meet the
requirements for dissolved-solids concentration during high and low flow
(table 4). At this station, much of the low flow is ground water discharged
by irrigation wells and by uncontrolled flowing wells in the area. The ground-
water contribution during low flow increases the dissolved-solids concentration
in water from Alligator Creek to a point where this Public Health Service
limit is exceeded part of the time. Sulfate in water from the Peace River
usually does not occur naturally in concentrations as great as that listed in




































Figure 7.-Locations of wells referred to in this report.







18 BUREAU OF GEOLOGY

TABLE 2.-Geological Survey's latitude-longitude number assigned to wells
referred to in this report for computer storage and retrieval of
well data.

Well referred to
in this report Latitude-longitude number


1 264611N0815554.1.
2 264644N0820009.1.
8 264808N0820208.1
4 264811N0815188.1.
5 264811N0815158.1.
6 264842N0813405.1.
7 264848N0813940.1.
8 264848N0814242.1.
9 264844N0814535.1
10 264859N0818684.1.
11 264912N0815856.1
12 264938N0815522.1
13 265017N0821587.1
14 265128N0813947.1
15 265124N0814587.1
16 265124N0820124.1
17 26.127N0815825.1
18 265188N0820022.1
19 265222N0815082.1
20 265408N0814822.1
21 265410N0813939.1
22 265534N0820251.1
23 265557N0821522.1
24 265606N0820806.1
25 265612N0821104.1
26 265640N0818940.1
27 265642N0814585.1
28 265646N0815545.1
29 265745N0820619.1
30 265759N0820401.1
31 265902N0820328.1
32 265916N0820449.1
33 265922N0820456.1
34 265941N0815614.1
35 270080N0820718.2
36 270118N0818988.1
37 270188N0820346.1
38 270188N0820846.2
39 270159N0820881.1

















0


0

-4


cJ)



-4
0


9
'.4
CO







'0


Figure 8.-Location of principal surface-water gaging sites in Charlotte
County and vicinity.


27 15'


2700'









45'









26go0'


i


I -






BUREAU OF GEOLOGY


table 4. Most of this sulfate is derived from leakage and discharge from ponds
in the mining areas upstream. The concentration of chloride in Alligator Creek
exceeds the Public Health Service limit during low flow as a result of well
discharge. The flouride limit of 1.4 mg/1 (milligrams per liter) is exceeded in
water from the Peace River during low flows as a result of mining activities
upstream.
Although no Public Health Service limit is placed on the phosphate con-
centration of water, high concentrations can create taste and odor problems
in supplies derived from surface-water bodies in the county. Phosphorus from
phosphate in combination with other plant nutrients stimulates growth of
algae and plants such as hyacinths in streams, canals, and reservoirs. The
undesirable taste and odor is produced during extensive growth and die-off of
these plants.
The iron concentration in water from the streams exceeds the Public
Health Service limit generally during high flow. Both color and iron in the
water from streams is caused chiefly by organic compounds derived from the
decay of vegetation. Color is more apparent during high flow when the streams
receive runoff from marshes, swamps, and ponded areas. During low flow, the
color of water and the concentration are generally low. With proper treatment,
the iron concentration can be lowered to an acceptable level. The State re-
quires that the color of finished water for public supply not exceed 15 units.

PUBLIC WATER SUPPLIES
Most surface-water bodies containing water of acceptable quality in the
county have been developed for public supplies. However, an undetermined
amount of additional water could be made available by impounding Myrtle
Slough (fig. 3). Several potential surface-water sources lie outside the county.
The Peace River north of Ft. Ogden is a potential source although its flow is
subject to contamination from several sources. For short periods during ex-
tremely high tides, salt water from the Gulf can move upstream beyond Ft.
Ogden, and some type of barrier would be required to prevent salt water from
entering a public-supply diversion from the Peace River at Ft. Ogden or
farther downstream. In addition, failure of dams in the mining areas upstream
have allowed turbid water containing a high concentration of phosphate to
enter the stream for as long as several weeks at a time. Therefore, if water
were diverted from the Peace River for public supply, an alternate source
would be required when the water in the Peace River is not usable.
Horse Creek near Ft. Ogden in DeSoto County and the Myakka River
in Sarasota County have potential impoundment sites (fig. 3). Deer Prairie
Creek in Sarasota County might also be able to provide a small amount of






TABLE 3.-Summary of discharge characteristics of principal streams in the Charlotte County area.
8 for location of station. Discharge: cfs, cubic feet per second; mgd, million gallons a day.)


(Station: See figure


Discharge
Drainage Period Minimum equalled
area of Minimum daily Average or exceeded 90
(square record flood discharge discharge percent of time
Station miles) (years) (cfs) fs mgd efs mgd cfs mgd


1. Peace River
at Arcadia 1,367 38 36,200 37 24 1,250 808 -


2. Horse Creek
near Arcadia 218 19 11,700 0 0 228 147 2.8 .1.8


3. Myakka River
near Sarasota 235 33 8,670 0 0 265 171 .04 .03


4. Big Slough
near Murdock 87.5 6 2,560 .02 .01 104 67 1.2 .8


5. Prairie Creek
near Fort Ogden 233 5 2,860 0 0 166 107 4.4 2.8


6. Shell Creek
near Punta Gorda 373 3 3,680 0 0 -







BUREAU OF GEOLOGY


water. All three, together, could supply quantities of water ranging fromn4.5
to 24.5 mgd depending on reservoir storage as shown in the following table.

Storage required to
Withdrawal sustain withdrawal
Station Drainage area (million gallons through a drought
(square miles) a day) period of 20-year
recurrence (acre-feet)

Horse Creek near 1.5 190
Arcadia 218 7.0 1,960
14.0 5,000
Myakka River 1.5 520
near Sarasota 235 7.5 2,600
Deer Prairie Creek 1.5 400
near Woodmere 56 3.0 950

PORT CHARLOTTE
The principal water source for Port Charlotte is an impoundment on Yale
and Fordham waterways. This source is supplemented by water from wells.
The estimated storage capacity of the impoundment and its tributary canals
(1965) is 101 million gallons, and inflow to the impoundment averages
about 1.5 mgd. Water is routed to a treatment plant which has a design capac-
ity of about 2 mgd and treats about 1 mgd. In 1969, the system supplied 163
commercial and 5, 646 domestic connections in the Port Charlotte area.
Growth of aquatic plants in the tributary canals of Port Charlotte's supply
is a continuing problem. Frequent chemical treatment of the water in the
canals is-required to retard growth of the aquatic plants, and the plants must
be removed. Although the water from the canals is acceptable for use on the
basis of the chemical constituents listed in table 5, it often must be specially
treated at the water plant to control taste, odor, and color. Also, because the
canals receive runoff and seepage from the urbanized areas in Port Charlotte,
the city is considering either importing ground water or surface water, or
desalting locally available ground water.

PUNTA GORDA
Before 1936, individual or community wells, such as Punta Gorda's water-
fountain well (well 24), furnished water to the town's residents. In 1936, a
supply was obtained primarily from a small, shallow reservoir on Alligator






TABLE 4.-Changes in quality of streamflow with changes in discharge during medium and low flow. (Station location
shown on figure 8. Discharge: cfs, cubic feet per second. Color: Pt-Co, Platinum-Cobalt. Results in milligrams
per liter except where indicated.)

Specific con-
Station Bicar. ductance (mi- Color
Location Discharge Iron bonate Sulfate Chloride Fluoride Nitrate Phosphate Dissolved solids cromhosat (Pt-Co
Date (cd) (Fe) (HC0a) (S04) (Cl) (F) .(NOa) (P04) (Calculated) 25"C) pH units)

6/1/65 76 0.08 109 120 18 1.5 0.9 6.8 800 460 7.6 10
7/31/65 3,850 .33 21 14 8.0 .7 0 2.9 64 105 6.6 240
Peace River 2/23.28/66 5,563 .16 16 15 12 1.0 .2 10 71 120 6.8 120
1. at 5/1-10/66 160 .01 84 92 18 2.0 .3 18 270 435 7.7 15
Arcadia 5/11-20/67 94 0 104 140 16 2.4 0 11 840 540 7.2 5
8/18-1/67 2,010 .33 29 29 11 1.0 1.5 4.4 99 157 6.9 240
5/11/65 .5 .01 139 25 20 .7 .2 1.6 180 326 8.0 40
2/28/66 808 .09 15 5.1 13 .4 .1 42 91 6.1 120
Horse Creek 5/28/66 3.4 .05 105 99 19 .7 .7 260 450 7.8 50
2. near 6/8/07 1.7 .02 136 F9 24 .8 .2 2.1 250 450 7.3 30
Arcadia 9/1-7,9,12- 569 .17 15 8.8 7.2 .3 0 40 64 6.1 120
15,29/67
6/1-7/65 0 .1 28 19 29 .4 0 .3 92 170 7.1 80
Myakka River 8/2-5/65 1,930 .21 16 6.4 6.8 .4 .3 .92 38 62 6.8 200
3. near 5/21-31/66 .01 .32 27 25 20 .4 .5 .73 92 175 6.8 120
Sarasota 6/22-28/66 765 .21 20 1.6 8.0 .4 .2 .81 39 72 6.4 280
5/1/67 0 .16 71 28 29 .4 .2 .37 140 270 7.4 100
1/7/65 .7 .02 215 72 68 .7 0 .58 380 651 7.4 30
Big Slough 5/3/65 1.1 .05 203 62 66 .8 .2 .92 360 630 7.7 20
4. near 4/27/66 1.8 0 211 78 71 .9 .8 .65 400 700 7.7 45
Murdock 6/6/66 10.8 .13 63 48 32 .5 0 .95 170 280 7.2 120
5/4/67 0 .03 198 18 47 .6 .9 1.6 270 490 7.3 35

5 Creenear 4/21/66 9.2 .09 220 36 57 .2 .4 0 330 590 7.4 100
Fort Ogden 5/9/67 3.8 .03 208 90 78 1.0 0 .02 430 748 7.6 20
Shell Creek 4/28/66 70 .06 118 10 44 .2 .7 0 180 349 7.4 35
6. neqr Punta 5/4/67 0 08 200 12 77 1.0 .6 .06 310 575 7.5 60
Gorda ,
Alligator 4/27/66 1.0 0 232 98 450 .6 1.7 0 1,000 2,000 7.6 15
7. Creek near 5/5/67 1.7 .04 272 11 130 .5 1.2 0 460 850 8.1 20
Punta Gorda







BUREAU OF GEOLOGY


Creek just south of Punta Gorda and a supplemental supply from a well. In
1938, a treatment plant was added. This system sufficed until 1965 when
water was diverted from a reservoir built on Shell Creek. This reservoir has a
capacity of about 9 billion gallons and supplies Punta Gorda and several near-
by housing developments. During high water in the spring of 1970, tha center
of the reservoir dam was undermined threatening a dam failure and the loss of
the reservoir. However, the dam was reinforced, and the immediate need for
developing supplemental source of supply was alleviated.
The water from this reservoir is high in color and is low in dissolved solids,
chloride and sulfate (table 6). The water is treated in a plant which hasa
capacity of 2.4 mgd, and activated carbon is used to remove color, taste and
odor. The water from this reservoir is of better chemical quality than that
obtained from the older wells and the reservoir on Alligator Creek.


TABLE 5.-Chemical analysis of raw water from the public supply at Port
Charlotte. (Results in milligrams per liter except as indicated.)
Date of Collection 11/18/69
Silica (SiO) 6.7
Calcium (Ca) 71
Magnesium (Mg) 3.8
Sodium (Na) 27
Potassium (K) 0
Bicarbonate (HCO3) 218
Sulfate (SO4) 15
Chloride (Cl) 47
Fluoride (F) .4
Nitrate (NOs) 0
Nitrite (NO2) .2
Dissolved solids:
Calculated 280
Residue on evaporation 311
Hardness, as CaCOs 190
Noncarbonate hardness 14
Specific conductance
(micromhos at 25C) 480
pH 7.9
Color (Pt-Co units) 60



GROUND WATER
Charlotte County is underlain by a sequence of hydrogeologic units that,
to a depth of about 1,500 feet, comprise a water-table and five artesian aqui-
fers (table 7). The water-table aquifer is the uppermost hydrogeologic unit
and occurs in the surficial sand and the Caloosahatchee Marl. Most of the re-







REPORT OF INVESTIGATION NO. 78


charge to this aquifer is from local rainfall. Some recharge is derived from
the slow upward movement of water from the deeper artesian aquifers in the
southern and western part of the county. Additional recharge comes from
flowing wells. The water-table aquifer discharges chiefly by evapotranspira-
tion, and from springs, lakes, rivers, canals, drainage ditches and wells. Some
water also moves downward into the underlying artesian aquifers in the
northern and eastern part of the county where the elevation of the potentio-
metric surface of the artesian system is lower than the elevation of the water


TABLE 6.-Chemical analyses of water from Shell Creek and from wells in
Punta Gorda. (Results in milligrams per liter except as indicated.)


4.))









F fluoride (F ) ................ ................. ........2 1.3 1.







Dissolved solids:
Calculate M ............. ............................ .............. 1 30

Hardness, as(CaCO ...................................... 78 -
Noncartbonate h( ar dness ............................. 18 -
Specific conductance
02 )i









(microm hosat 25C) ...........-................ 240 5,
Calcium (C5a)... .. .. 25 -

Strontium (Sr)... -. .66 5
Sodium (Na):.Colle ....... 18 1 1


Pot si.. ( )...................................................... 6.8 -
Color nate (HCOs) .................................... 9 -
S le ate u r (S ).... ......................................... 9 5 51.
ble. ide (wate ta.. ma at o .......... .d s e fr m s in
Fluoride (F)............ ............. .2 1.3 1.0


draineho ate (0a ) ha4 1 ............ ..below.. l s i a t
Dissolved solids:
Calculated........................-..... 130
Residue on evaporation..................... 163
Hardness, as CaCO3................................... 78 -
Noncarbonate hardness............................. 18 -
Specific conductance
(micromhos at 25"C)......................... 248 1,490 5,100
pH ....................._ ................................. 6.8 -
Color (Pt-Co units)................................ 90 -
Temperature C.............................................. 25 26.5 29


table. The water table may be at or above land surface for months in poorly
drained areas and more than 10 feet below land surface in areas that are
extensively drained or where wells are heavily pumped. The water level in









TABLE 7.-Hydrogeologic units underlying Charlotte County.

Hydrogeologic Equivalent
unit stratigraphic unit Remarks

Source of water for domestic and public supply wells along
Surface and terrace sand the coast. Also used for lawn irrigation and watering stock.
Water-table Wells tapping shell beds in Caloosahatchee Marl yield as
aquifer Caloosahatchee Marl much as 600 gpm (gallons per minute) in eastern part of the
county.
Confining bed Green clay
Domestic and irrigation wells tapping limestone beds in this
Zone 1 Tamiami Formation aquifer yield as much as 200 gpm. Used chiefly for irrigation
in the eastern part of the county.
Confining bed Sandy clay, phosphorite pebbles
Source of water for domestic and irrigation wells. Aquifer
Zone 2 used extensively in the populated areas. Wells tapping aqul- 0
Hawthorn Formation, upper unit fer yield as much as 200 gpm. Water in aquifer is saline west
of Charlotte Harbor.

Confining bed White clay
Hawthorn Formation, lower unit Source of water for irrigation wells only. Yield of wells tap-
ping aquifer usually increases with depth of penetration.
Zone 3 Most of the water obtained near the contact between the
Hawthorn Formation and Tampa Limestone. Contains saline
water in western part of the county.
Confining beds Tampa Limestone White to gray impermeable limestones and clays.
Source of water for irrigation wells only. Most permeable
part of the aquifer occurs near the contact between the
Zone 4 Tampa and Suwannee Limestones and near the contact
Suwannee Limestone between the Suwannee Limestone and Ocala Group. Gen-
erally, the upper part of the aquifer yields as much as 1,000
gpm and the lower part more than 1,000.
Ocala Group
Confining bed Tan, chalky, impermeable limestone
Zone 5 Avon Park Limestone Not used as a source of water in Charlotte County.

































Figure 9.-Location, depth, and chloride concentration of inventoried wells
tapping the water-table aquifer in Charlotte County.






BUREAU OF GEOLOGY


the aquifer generally fluctuates less than 5 feet seasonally. The aquifer is as
thick as 85 feet in some places but is generally less than 50 feet thick.
The chloride concentration of water in the water table aquifer ranges from
20 to 1,100 mg/l (fig. 9). The water is generally acceptable for domestic use
except locally where mixed with water from the Gulf or with saline water from
nearby deep wells.
Underlying the water-table aquifer is a thick sequence of rock units con-
sisting chiefly of soft limestones which grade downward into harder, dense,
crystalline limestone and dolomite. These rock units form a complex hydro-
geologic system that contains five artesian aquifers (table 7) and- their in-
terbedded leaky confining layers. These confining layers are composed chiefly
of beds of clayey limestone and clay like those that occur in the upper unit of
the Hawthorn Formation (fig. 5). The water levels in wells that tap the aqui-
fers rise above the top of the aquifers and, in the southern and western part of
the county, frequently rise above land surface. These aquifers are referred to
in this report as Zone 1, 2, 3, 4, and 5 and, the rock units in which they occur
are listed in table 7. These hydrogeologic units underlie the Myakka River
basin to the northwest and may, in part, underlie the northern edge of Lee
County. Somewhere north and east of Charlotte .County, Zones 3, 4, and 5
lose their hydrogeologic identity and form a single hydrogeologic unit, the
Floridan Aquifer.
The permeability of the deeper artesian aquifers is generally greater than
that of the shallower artesian aquifers. For example, Zone 4 is more permeable
than Zones 1-3. The permeability of the rock within each zone also changes
vertically, particularly in Zones 3 and 4. These aquifers are most permeable
near the contact of contiguous stratigraphic units (table 7).
Zones 1 and 2 are recharged chiefly by leakage from the water-table aqui-
fer where differences in water levels between the aquifers permit downward
movement of water. Zones 3.5 are recharged by leakage from the overlying
zones in the eastern part of the county and by lateral inflow from areas north-
east and east of the county. All the zones discharge by: (1) diffused upward
leakage into the water-table aquifer in the western part of the county; (2)
flow from springs to the south of the county; (3) flowing wells; and (4)
pumping from wells.
Water levels in the artesian aquifers range from about 30 feet above land
surface along the coast to about 20 feet below land surface in the highest areas
of the county. However, the depth to the water level at any given well is de-
pendent on: (1) which zone or zones are open to the well bore, (2) altitude
of land surface, and (3) the amount of water being withdrawn from other
wells in the area. In general, the deeper aquifers have higher heads so that the


















27600'






4S'






60'





2646'1


Figure 10.-Location, depth, and chloride concentration of inventoried wells
tapping Zone 1 in Charlotte County.






BUREAU OF GEOLOGY


deeper wells have higher water levels. Wells producing from the artesian aqui-
fers are generally open to more than one producing zone, and the water level
in the well is a composite of the levels of all the zones tapped by the well.
Withdrawals of water from wells can lower water levels several feet at small
pumping rates to several tens of feet at large pumping rates.
Chloride can be used in Charlotte County as a general indicator of the
salinity of water-although chloride is not the only ion present in the water
from the artesian zones. Where the chloride concentration exceeds 1,000 mg/l,
the chloride generally constitutes 40 to 50 percent of the dissolved solids con-
tributing to the salinity of the water. At most places in the county, the chlo-
ride concentration and the salinity of the water from the artesian aquifers
increases with depth (figs 10, 11, and 12). Therefore water from Zone 1 is
less saline than that from Zone 2, and water from Zone 2 is less saline than
that from the deeper zones.

GROUND-WATER CONDITIONS BY AREA
Ground-water conditions vary widely within the county. To facilitate a
description of these conditions, the county has been divided into four hydro-
logic areas (fig. 13).

AREA A
Area A lies in the western, peninsular part of the county. The only source
of fresh water in this area is the shallow water-table aquifer, which is used by
all the public water supplies and most of the private supplies. The water in the
artesian aquifers is too saline to be used without demineralization.

Water-Table Aquifer
The water-table aquifer consists of 25 to 50 feet of permeable shell and
sand and is underlain by clay. The aquifer is subject to intrusion by salt
water from the Gulf during exceptionally high storm tides, and in places
water from the aquifer may contain as much as 12,000 mg/1 chloride. Intru-
sion by salt water also takes place where the low lying land of the peninsula
has been drained by sea level canals. Where the aquifer has not been subjected
to intrusion as at Cape Haze and Gasparilla Island (fig. 3), fresh water with a
chloride concentration less than 75 mg/1 (table 8) can be obtained from wells
less than 30 feet deep.
Isolated lenses of fresh water occur in the water-table aquifer on the
offshore barrier islands. These lenses are underlain by saline water at shallow
depths, and only small quantities of fresh water can be pumped without caus-
ing upward movement of saline water into the wells. Water is generally con-
sidered saline if its dissolved-solids concentration is 1,000 mg/1 or more.












lO36I'


Figure 11.-Location, depth, and chloride concentration of inventoried wells
tapping Zone 2 in Charlotte County.




















wasu \kers Gra | e
CHAnRR rr'r Oo -"- --d


"-... *.. .T ', "
S( 41 HARLOTTE c
Sl *LEE i C o




Figure 12.-Location, depth, and chloride concentration of Inventoried well
tapping Zones 3 and 4 in Charlotte County.











Ie0' I0 I0' I' ABe00' IS' o' 40' 040' Ol '"
er go$SAR O"A oS lei ~ l "OTO 0 e4. moss












MARALOOTE I&lV ILr






EXPLANATION "
MI i_0 'LOA










SMILES Boun ry of hydrologic area
Hydrologic area






CHARLOTTE....Jll C C

EXPLANATION


Figure 13.-Hydrologic areas for which ground-water conditions are described.






34 BUREAU OF GEOLOGY

Interpretation of data obtained from tests on production wells at the
Gasparilla Island well field indicates that the aquifer has a transmissivity that
ranges from 1,340 to 1,870 ft2 per day and a hydraulic conductivity that
ranges from 47 to 60 ft. per day. The specific capacity of production wells in
this well field is 5 gallons per minute per foot of drawdown, and the wells yield
as much as 60 gpm. The yield of each well is restricted to about 20 gpm to
prevent excessive drawdawn which might produce upcoming of the underlying
salty water.


TABLE 8.--Chemical analyses of water from the water-table aquifer under-
lying the Cape Haze and Gasparilla Island well fields. (Results in
milligrams per liter except as indicated.)

Cape Haze Gasparilla Island
Well Field Well Field
Date of Collection 11-19-69 11-18-69
Silica (SiO2) 11 9.4
Calcium (Ca) 100 120
Magnesium (Mg) 2.1 5.6
Strontium (Sr) .45 .35
Sodium (Na) 26 42
Potassium (K) .3 0
Bicarbonate (HC03) 262 354
Sulfate (SO4) 8.8 0
Chloride (Cl) 48 74
Fluoride (F) .3 .2
Nitrate (NO3) .8 .8
Dissolved solids:
Calculated 370 470
Residue on evaporation 327 421
Hardness, as CaCO3 260 310
Noncarbonate hardness 47 21
Specific conductance
(micromhos at 25"C) 600 750
pH 7.6 8
Color (Pt-Co units) 40 50



The water-table aquifer is used as a source of water for public-supply
water for Cape Haze and Gasparilla Island (fig. 3). Cape Haze, a large hous-
ing development, installed a water-treatment plant in 1953 with a capacity
of 0.288 mgd. The plant treats water from 18 shallow wells and serves about
350 people (1969) through 1 commercial and 113 domestic connections. In






REPORT OF INVESTIGATION NO. 78


addition, a supplemental supply of 350 gpm is available from a reservoir on
the west branch of Coral Creek (fig. 3).
The Gasparilla Island Water System started operation September 1968 and
has a plant capacity of 0.57 mgd. Water is obtained from 16 shallow wells. An
expansion area has been reserved for an additional 16 wells. In 1969, the
system served about 400 persons through 250 connections on Gasparilla Island.
The well field is bounded on three sides by salt water. Part of the recharge to
the well field comes from seepage from the reservoir on the west branch of
Coral Creek northwest of the field. Without this recharge, the well field might
be subject to salt-water intrusion.



TABLE 9.-Chemical analyses of water samples from well 25. (Results in
milligrams per liter except as indicated.)
Interval sampled
(feet) 65 85 85 -189 85 410 85 743 85-1,031 85 -1,406
Zone penetrated 1 1,2 1,2 1,2,3 1-5 1-5
Silica (SiO2) 17 26 18 22 17 7.9
Iron (Fe) .19 0 .07 .02 0 0
Calcium (Ca) 300 130 240 240 300 460
Magnesium (Mg) 470 90 180 170 270 670
Strontium (Sr) 18 27 41 38 39 32
Sodium (Na) 3,400 230 1,200 1,000 1,900 5,200
Potassium (K) 120 15 32 28 60 190
Bicarbonate (HCOs) 196 194 148 154 148 134
Sulfate (SO4) 500 17 520 510 720 1,500
Chloride (C1) 7,000 760 2,300 2,100 3,600 9,900
Fluoride (F) .7 1.3 1.0 1.0 1.3 1.5
Nitrate (NO3) 5.8 2.4 1.7 6.3 13 7.5
Phosphate (P04) .14 0 0 .04 0 .03
Dissolved solids
Residue on
evaporation 24,500 2,130 5,320 4,900 8,040 18,000
Hardness (as CaCOa) 2,700 730 1,400 1,400 1,900 3,900
Noncarbonate
hardness 2,600 570 1,200 1,200 1,800 3,800
Specific conduct-
ance (micromhos
at 25 C) 21,600 2,730 7,880 7,350 11,800 28,600
pH 7.5 7.2 7.4 7.5 7.1 7.0
Color (Pt-Co Units) 10 0 0 0 0 5
Temperature C 33 28


Artesian Aquifers
Much of Zones 1 and 2 in Area A contain saline water. Specific informa-
tion on salinity of water in the aquifers has been obtained from test drilling.
Test well 23, (fig. 7) yielded water with dissolved-solids concentration of
about 5,000 mg/l from depths less than 225 feet (Zones 1 and 2). Test well 13






BUREAU OF GEOLOGY


yielded water with a dissolved-solids concentration less than 9,000 mg/l from
depths less than 340 feet (Zones 1 and 2). The differences in quality of water
from the same zones penetrated by these test wells suggests that the dissolved-
solids concentration of water in Zones 1 and 2 decreases to the north.
Well 25 (fig. 7) penetrated Zones 1-5, and during its drilling the dissolved-
solids concentration of the water in the aquifer generally increased with depth
(table 9) except within the interval 85-189 feet. In this interval, the well
penetrated Zone 2, and the dissolved-solids concentration of the water de-
creased as a result of a decrease in chloride concentration. This decrease
indicates that Zone 2 at this site contains water with lower salinity than water
contained in the other areas.
The altitude of the water level in Zones 1-5 is above land surface, and all
wells penetrating these zones flow. Seasonal fluctuation of water levels in these
zones probably does not exceed 4 feet (fig. 14). The artesian pressure is
higher in the deeper zones than in shallow zones as is shown by comparison of
the altitudes in well 23 which taps Zone 2 and well 25 which taps Zones 1-5.
As a result of this increase with depth, an upward gradient exists which per-
mits water to move from the deeper to the shallower zones in wells open to
more than one zone. Because the water in deeper zones is more saline than
water in shallower zones (table 9), this upward movement results in local
deterioration in the quality of the water in the shallower zones. In addition,
where water from these wells discharges at the surface, this water has caused
the quality of water in the water-table aquifer to deteriorate. This condition
exists in the eastern part of the area where many unused irrigation wells that
penetrate Zones 2 and 3 flow freely.
Although none of the artesian aquifers contains fresh water, some of
the water contained in Zones 1 and 2, at depths less than 280 feet below land
surface, may be usuable for irrigation of salt-tolerant crops. A properly con-
structed well, cased to about 130 feet and drilled to less than 280 feet, may
yield 10 to 30 gpm of water whose chloride concentration probably would not
exceed 2,000 mg/1.
AREA B
Area B lies between the Myakka and Peace Rivers (fig. 13) and is the
most urbanized part of Charlotte County. The area has undergone a marked
population growth since the mid-1950s. The original plan of development for
Port Charlotte included a public water-supply system for the central part and
an individual well for each home in the rest of the development. However, of
311 test wells drilled in the area to be served by individual home wells, only
9 produced water usuable without-treatment; 39 produced water that could
readily be treated by household water conditioners; 76 produced water suit-








REPORT OF INVESTIGATION NO. 78


32



WelH 25
Open Zon: 68-1407 feet
30 L- Aquifer Zones 1-5
Land Surface : 38 feet
above mean sa level


28




26



Z Well 23
24 Open Zone : 258 298 feet
Aquifer : Zone 2
Land Surface : 14 feet above
mean sea level


22 -Well 13
Open Zone : 342-413 feet
SAquifer: Zone 3
Land Surface : 5 feet above
mean sea level
20




18




16

1966 1967 1968 1969


Figure 14.-Hydrographs of observation
aquifer in Area A.


wells that penetrate the artesian







38 BUREAU OF GEOLOGY

able for treatment commonly used in public-supply systems; and 187 pro-
duced water unsuitable for use without demineralization. As a result, plans
were altered to supply water to the entire development from an undetermined
source or sources.

Water-Table Aquifer
The thickness of the water-table aquifer averages about 40 feet and ranges
from 20 to 60 feet. The aquifer consists chiefly of fine to medium sand with
locally interbedded gravel and shell. As a result, its hydraulic conductivity



TABLE 10.-Chemical analyses of water from wells that tap the water-table
aquifer in Zone 2 underlying Port Clarlotte. (Results in milli-
grams per liter except as indicated.)


Aquifer Water Table Water table Zone 2
Date Collected 9/25/56' 5/10/61b 11/18/69e
Silica (Si02) 17
Iron (Fe) 3.0 0.5 -
Calcium (Ca) 96 110 100
Magnesium (Mg) 10 9.0 18
Strontium (Sr) 1.1
Sodium (Na) 42
Potassium (K) 5.8
Bicarbonate (HCO3) 329 288 322
Sulfate (SOs) 22 0 13
Chloride (Cl) 48 100
Fluoride (F) .40 .6
Nitrate (NO3) 0
Nitrite (NO.) .07
Dissolved solids:
Calculated 430 460
Residue on evaporation 509
Hardness as CaCOa 310 330
Noncarbonate hardness 24 64
Specific conductance 800
(micromhos at 25"C)
pH 7.3 7.6
Color (Pt-Co Units) 150 35 10
Temperature C 24 24 _
SSample from one of Port Charlotte's original water-supply wells. Analysis
by General Development Utilities.
SComposite sample from 19 6-inch diameter wells, about 45 feet deep. Analy-
sis by General Development Utilities.
SComposite sample from seven wells at Port Charlotte's golf course. Analysis
by U. S. Geological Survey.



may be higher in places than in area A. Based on the hydraulic properties
determined for the aquifer in Area A, its hydraulic conductivity is estimated







REPORT OF INVESTIGATION NO. 78


to average about 53 ft per day and its transmissivity 2,140 ft2 per day. In
places where the aquifer is thicker or contains shell beds of higher hydraulic
conductivity, transmissivity may be more than 3,340 ft2 per day.
The altitude of the water table ranges from near sea level adjacent to the
Charlotte Harbor estuary to more than 25 feet above mean sea level in the
northeastern part of the area. Seasonal fluctuations of the water table in this
area are generally less than 5 feet.

TABLE 11.-Chemical analyses of water from wells that tap Zone 2, Area B.
(Results in milligrams per liter except as indicated.)
Well 37' Well 32b Well 29b
Interval sampled 183-235 121-230 185-205
(feet)
Date collected 11/11/65 3/13/61 2/6/68
Silica (SiO2) 22 -
Iron (Fe) .01 0.1 0
Calcium (Ca) 62 50 170
Magnesium (Mg) 36 29 97
Sodium (Na) 78 -
Potassium (K) 8 -
Bicarbonate (HCOs) 218 151 156
Sulfate (SO4) 8 15 320
Chloride (Cl) 210 150 1,000
Fluoride (F) 1.5 1.1 1.3
Nitrate (NOs) 0 -
Phosphate (P04) .04 -
Dissolved solids:
Calculated 530 430 2,600
Residue on evaporation 560 -
Hardness as CaCO3 300 240 820
Noncarbonate hardness 120 120 690
Specific conductance 1,100 -
(micromhos at 25*C)
pH 7.9 7.9 7.4
Color (Pt-Co Units) 5 5 5
Temperature C 24 25
SAnalysis by U. S. Geological Survey.
SAnalysis by General Development Utilities.


Although the quality of the water in the aquifer is generally good (table
10), the aquifer is not commonly used as a source of supply for drinking
water. The dissolved-solids concentration meets the State's standards for pub-
lic supply. The iron and color are high, and the water would require treatment
if used for public supply. The chloride concentration of the water in the aqui-
fer is highest near the Charlotte Harbor estuary and in areas adjacent to the
salt-water-canals that have been dredged inland as part of urban development.
These canals have allowed salt water to intrude south of U. S. Highway 41,
which has been established as a salt-water barrier line. Controls have been






BUREAU OF GEOLOGY


installed in the canals at the barrier line to prevent salt water from moving
farther inland.
Port Charlotte's original water supply was obtained from six 4-inch wells
20 feet deep. These wells tapped a shell bed in the aquifer. Later 19 wells
about 45 feet deep were drilled. In 1959, the original 23 wells were replaced
by wells tapping Zone 2.
Although the water-table aquifer is not extensively used in Area B, it is a
potential source of a large quantity of water. Use of infiltration galleries may
be effective in providing large quantities where the aquifer is thin. Well
screens are needed to obtain maximum yields from the aquifer where it is
thick although screens arc not commonly used in the area. A properly screened
well requires a screen length equal to 25 to 50 percent of the saturated thick-
ness. Where the aquifer is fine-grained, a coarse sand pack can help decrease
the drawdown in the well due to entrance loss by permitting use of a screen
with a larger slot opening than normally would be used. Estimates of the
hydraulic properties of the aquifer indicate that screened wells 6 inches in
diameter should produce 7 to 10 gpm per foot of drawdown and where the
water level is 10 to 25 feet above sea level and the aquifer more than 30 feet
thick, 70 to 200 gpm without causing salt-water intrusion.

Artesian Aquifers
Zone 1.-Zone 1 lies about 70 feet below land surface, and the water
levels in the few wells that penetrate the zone rise nearly to land surface. At
many places in Area B, the zone contains layers of loose sand, and the sand is
generally cased out to prevent caving into the well bore. To complete a well
in the sandy part of the aquifer, a screen with proper-sized openings would
be required to prevent the hole from caving and to keep sand out of the well.
In the north central part of Area B, several wells which yield 20 to 30
gpm have been completed in the limestone and clay sections of Zone 1. The
chloride concentration of the water from the wells exceeds State limits for
public-water supply and is marginal for irrigation use.
Zone 2.-Zone 2 is the most heavily pumped aquifer underlying area B.
The top of the zone lies 115 to 120 feet below land surface and the zone's
thickness ranges from 110 to 135 feet. Wells tapping this zone yield more
than 30 gpm. The quality of the water is usually suitable for irrigation use
but generally does not meet State standards for drinking water except locally
as at Port Charlotte (table 10). Here, water from seven 6-inch wells is used to
supplement Port Charlotte's surface-water supply. Wells tapping Zone 2 that
are tightly cased to about 150 feet and are less than 230 feet deep can gen-
erally produce water with a dissolved-solids concentration less than 1,000







REPORT OF INVESTIGATION NO. 78


mg/1 (table 11). The water levels in wells that tap the upper part of the zone
usually rise to about land surface. The water level in wells tightly cased into
the lower part of the zone generally rises above land surface, and the wells
flow.







TABLE 12.-Chemical analyses of water from wells that tap Zones 2 and 3,
Area B. (Results in milligrams per liter except as indicated.)

Well 31 Well 39 Well 30 Well 35
Interval sampled (feet) 146-586 69-427 162-270 144-450
Date Collected 10/28/69 11/11/65 4/5/65 10/28/69
Silica (SiO2) 17 -
Calcium (Ca) 93 220 -
Magnesium (Mg) 62 150 -
Sodium (Na) 800 -
Potassium (K) 23 -
Bicarbonate (HCOs) 134 -
Sulfate (S04) 280 210 530 430
Chloride (Cl) 650 420 1,600 1,200
Fluoride (F) 1.1 1.2 1.2 1.1
Phosphate (P04) .03 .03 .20 .02
Dissolved solids:
Calculated 3,400 -
Residue on evaporation 4,040 -
Hardness as CaCO3 1,200 -
SNoncarbonate hardness 1,000 -
Specific conductance
(micromhos at 25C) 2,750 2,050 5,800 4,700
pH 7.9 7.6 -
Temperature *C 26.5 '25 29 27


Zone 3.-Zone 3 is the deepest aquifer underlying area B for which hy-
drologic information was obtained. The top of Zone 3 generally lies about
250 feet below land surface, and the zone is about 150 feet thick. The upper
part of the zone is less permeable'than the lower part, and wells that tap both
the upper and lower part yield as much as 300 gpm. The dissolved solids
concentration of water increases with depth and exceeds 2,000 mg/I in the
lower part. The water from this part of the aquifer also has a high concentra-
tion of chloride and sulfate. Most wells in the area that tap Zone 3 also tap
Zone 2, and the quality of water from some wells that produce from these
zones is shown in table 12.






BUREAU OF GEOLOGY


The water levels of wells that penetrate Zone 3 generally rise above land
surface so that the wells flow. The water level in this zone is higher than that
in Zones 1 and 2 (fig. 15). As a result, a strong upward vertical gradient
exists between Zone 3 and the shallower Zones 1 and 2 and water moves up-
ward in wells that are open to any of the shallower zones. In older wells where
the casing is broken or corroded, water from Zone 3 will move upward in the
well bore into the water-table aquifer. Because the water in Zone 3 is of poorer
quality than that in the overlying aquifers, this upward movement is a cause
of widespread salt-water intrusion into the overlying aquifer.

AREA C
Area C lies in the central part of the county and is bordered on its western
edge by Charlotte Harbor. The coastal part of the area is partly urbanized,
and obtaining water of good quality for public supply from the water-table and
artesian aquifers is a major problem.

Water-Table Aquifer
The water-table aquifer is used extensively as a source of water for domes-
tic and some irrigation supplies. Most wells tap the sand and discontinuous
shell beds and are generally less than 30 feet deep. Small diameter wells that
tap the shell beds yield as much as 20 gpm. Wells constructed with screens may
yield considerably larger quantities.
During the investigation, 10 test wells were drilled in the aquifer. One
2-inch screened well yielded as much as 40 gpm, and all but one yielded water
that met the State's standards for drinking water. However, many wells that
tap the aquifer produce water with more than 2 mg/1 of iron. Wells drilled
near Charlotte Harbor or on fill overlying former salt-water marshes produce
water whose chloride concentration exceeds 250 mg/1.
Locally inland, some salt water has migrated into the aquifer. The salt
water comes from free-flowing wells that tap artesian aquifers containing
saline water. A test well drilled immediately north of South Loop Road (fig.
9) yielded water from a depth of 26 feet with a chloride concentration of 490
mg/L

Artesian Aquifers
Most of the flowing wells that tap the artesian aquifers underlying area C
were drilled before 1935 for irrigating gladioli and truck crops. As the area
became urbanized, use of these wells was discontinued. Many were improperly
plugged and then buried beneath the land surface after the casings were either









REPORT OF INVESTIGATION NO. 78 43


Well 37 I |
52 Open Zone: 312-350 ft --
Aqulfer : Zone 3
Land Surfaoo: 26 feet above
movn sea level

50




48 V




-j 26
> Well l 8i
Oe Open Zone:83-88 feet
AquIfer : Zone I
Land Surface : 2 feet
<, above mean soa level














% 2 --- ------^- --- -- --
24




0 22




< 20




16
Well1 33
Open Zone :129-156 feet
.i Aquifer : Zone 2
W Land Surface: 12 feet
> _bove mean sea level







4 -








O4 ---- --- --- --- -- -- ---
i, ,











-4


1964 1965 1966 1967 1968 1969

Figure 15.-Hydrographs of observation wells that penetrate the artesian
aquifers in Area B.






BUREAU OF GEOLOGY


cut or broken off when the land was prepared for home building. The buried,
improperly plugged wells act as conduits that allow saline water from deeper
zones to contaminate the shallow artesian and water-table aquifers.
Zone 1.-Zone 1 is the most heavily pumped artesian aquifer underlying
Area C. The zone is a source of supply for domestic use and irrigation. Wells
for domestic use are commonly 2 inches in diameter and generally yield 15 to
30 gpm. Wells for irrigation are of larger diameter and commonly yield less
than 200 gpm.
In the western half of the area water from Zone 1 generally does not meet
the State's drinking water standards. These standards are exceeded by chloride
(concentration more than 250 mg/1) and dissolved solids (concentration more
than 500 mg/1). In a few isolated places as at well 1 (fig. 7), water from this
zone meets these standards. Water from this well had a specific conductance of
840 mircromhos, a dissolved-solids concentration less than 500 mg/1 (based
on specific conductance), a chloride concentration of 220 mg/l and a sulfate
concentration of 10 mg/l. Although this well is open to Zones 1 and 2 from
140 to 190 feet below land surface, most of the water comes from the phos-
phatic gravel, sandstone, and limestone of Zone 1.
In the eastern half, water from Zone 1 meets the State's drinking water
standards. The chloride generally is less than 100 mg/l..and the dissolved
solids less than 500 mg/l. Water levels in Zone 1 are nearly everywhere less
than 15 feet below land surface and fluctuate naturally less than 1 foot an-
nually. During the irrigation season, water levels in wells affected by pumping
may be lowered as much as 25 feet (fig. 16).
Zone 2.-Zone 2 is used chiefly as a source of irrigation water because the
water it contains does not meet the State's standards for drinking water. Wells
that tap this zone generally are less than 400 feet deep; are 4 inches or more
in diameter; and are open also to Zone 1. In the eastern part of the area, wells
yield as much as 400 gpm.
The chloride concentration of the water in the aquifer increases from
north to south, and the sulfate concentration seems to increase with depth of
penetration (table 13).
Water levels in the aquifer rise above land surface in parts of the area
(fig. 17), and many wells that penetrate Zone 2 flow. Seasonal fluctuations of
water levels in the aquifer probably do not exceed several feet (well 17, fig.
17). Locally, where large quantities of water are withdrawn for irrigation, this
fluctuation may range from 2 to 4 feet (wells 28 and 34).
Zone 3 and deeper zones.-Many of the irrigation wells drilled before 1935
along the coast between Punta Gorda and Fort Myers obtained water from
Zone 3 and other zones at depths greater than 900 feet. Nearly all of these







REPORT OF INVESTIGATION NO. 78 45






16

W
w




46 ---(----i-------








-4
/J 8



-O
,4



0
U-

|o ~-------





I- -4





- Open Zone:84-125feet
-4






< Land Surface 2feetet above
mean sea leveT


Figure 16.-Hydrograph of a well affected by nearby heavy pumping.






BUREAU OF GEOLOGY


wells were also open to the overlying zones. The shut-in pressure was as much
as 30 feet above land surface, and 6-to 8-inch wells would flow at least 500
gpm. The water was saline but suitable for flood irrigation. When irrigation
was not needed, rainfall ordinarily .flushed the salts from the soil, preventing
an accumulation that could not be tolerated by crops. As the coastal area ur-
banized, many of these wells were capped, and water of poor quality has con-
tinued to move up the bore into the shallower zones. Within recent years,
some effort has been made to plug these wells using methods that follow State
requirements.
AREA D
Area D is sparsely populated. The land is used chiefly for.raising live-
stock, citrus, and truck-farm crops. Several thousand acres are under cultiva-
tion for watermelons, cucumbers, tomatoes, peppers, and citrus.
This area is underlain by several shallow aquifers that have a large public
water-supply potential. These aquifers, tapped only by a few irrigation wells,
represent the only major undeveloped source of fresh water in the county.

TABLE 13.--Chemical analyses of water from test wells that tap Zone 2, Area
C. (Results in milligrams per liter except as indicated.)

Well 17 Well 28 Well 34
Interval sampled (feet) 187-195 214-264 194-215 124-160 172-225
Date of collection 7/1/68 8/1/68 7/22/68

Sulfate (S04) 24 280 62 36
Chloride (C1) 1,200 1,200 330 180 260
Fluoride (F) .9 1.1
Phosphate (P04) .01 .01 -
Specific conductance
(micromhos at 250C) 3,900 4,050 1,460 860 1,140


Water-Table Aquifer
The eastern two-thirds of Area-D is underlain by a water-table aquifer
which has a potential for development of large quantities of water for public
supply in Charlotte County. The upper part of the aquifer consists of sand
and the lower part interbedded shell and limestone (fig. 18). These beds are
underlain by a clay layer. The aquifer ranges in thickness from less than 25
to more than 100 feet, is thickest beneath Telegraph Swamp, and thins toward
the east and west.






REPORT OF INVESTIGATION NO. 78


52


50



48

44


1\J1 V4G


SI I I I lF I-
0 Well 17b
m 42 Open Zone :215-264 feet
< Aquifer: Zone 2
-Land Surface: 30,feet
w above mean sea. level
w 40 1
-_
W
0> 30
w
.J

w 28
I-

26 _Well 280
S Open Zone:194-280feet
Aquifer Zone: 2
Land Surface :19 feet
above mean sea level
24 I I
1968 1969
a Water level in well affected by
nearby pumping
b Water level in well unaffected by
pumping


Figure 17.-Hydrographs of wells tapping Zone 2, Area C.


Well 34a
Open Zone:329-360 feet
Aquifer: Zone 2
Land Surface: 18 feet
above mean sea level
I. I i I I I _






BUREAU OF GEOLOGY


Irrigation wells that tap the shell and limestone beds generally are 6 inches
in diameter and less than 40 feet deep. The wells, equipped with centrifugal
pumps, yield as much as 600 gpm. Water from these wells is low in chloride
and sulfate.
The hydraulic conductivity of the shell and limestone beds is not known;
it probably varies from less than 53 to more than 135 ft per day. Where the
aquifer is thickest and hydraulic conductivity is high, its transmissivity may
exceed 6,680 ft2 per day. Because of this relatively high transmissivity, the
hydraulic connection with Telegraph Swamp, and the ease with which the
aquifer can be recharged by precipitation, the aquifer has a potential for
yielding large quantities of water to properly constructed wells. In addition,
where the aquifer is thin, moderately large quantities of water might be
obtained through use of horizontal infiltration galleries.

Artesian Aquifer
Zone 1.-Zone 1 lies about 100 feet below land surface, beneath a blue-
green clay. Although this aquifer is less than 50 feet thick it yields as much
as 200 gpm to wells that tap a 10-foot section in the area south of Highway 74
and east of Highway 31. Elsewhere, the aquifer is not tapped. Based on spe-
cific conductance measurements, water from Zone 1 may have as much as
400 mg/1 dissolved solids.
Zone 2.-Zone 2 lies about 175 feet below land surface. In area D, this
aquifer contains water that meets the State's standards for drinking water, on
the basis of analysis of water from well 15. The water from this well had less
than 200 mg/1 dissolved solids (based on specific conductance); 30 mg/l
chloride; less than 1 mg/l sulfate; and 0.1 mg/l fluoride. This well was open
to the aquifer from 212 to 235 feet below land surface.
Zone 3 and deeper zones.-Zone 3 is the deepest aquifer tapped in Area
D and lies 250 to 300 feet below land surface. Water from Zone 3 meets the
State's standards for drinking water in some places. Water from wells that
tap the aquifer ranges in specific conductance from 500 to 1,200 micromhos,
in dissolved solids (based on specific conductance)' from 300 to 700 mg/l,
in chloride from 80 to 180 mg/l, and in sulfate from 30 to 40 mg/l. Water
from aquifers deeper thanZone 3 does not meet the State's standards for drink-
ing water as indicated by samples obtained from a 1,310-foot well. This well,
drilled in the north-central part of the area, penetrated Zone 4 at a depth of
about 900 feet and is cased to 715 feet. This water had a specific conductance
of 3, 980 micromhos, a dissolved-solids concentration of 2,500 mg/1 (based on
specific conductance), and chloride and sulfate concentrations of 970 and 370
mg/1, respectively. The water was not suitable for irrigation of citrus, and the






170SS'


A


I I I


I I I I


---3 #% )'k


EXPLANATION



SAND CLAY



SHELL LIMESTONE


SANDY CLAY


JL
LOCATION
OF IEST
HOLE


50'

SEA
LEVELS

50'-





1

SEA .




LEVEL

50'-

SEA I
LEVEL

SOU-


II a I I


IM- -- --


0 1000 FEET
VrtgI * Vertical eaggerotlon XI1


Figure 18.-Generalized sections across the Telegraph Swamp area, eastern
Charlotte County.


40' 8a15'


er -








045' -
*r'4a5


0h


0f

0d
-I



w





pr



co


= =--=-~---a =25-


.. .. --r -M T- WK(K 0-IM M


, r






BUREAU OF GEOLOGY


well was plugged to prevent intrusion of this water into the upper producing
zones.

WELL CONSTRUCTION AND USE IN RELATION TO WATER QUALITY
In Areas A, B, and C, saline water occurs in the artesian aquifers at a
shallow depth. The potentiometric surface of each aquifer increases with
depth, and in many places the water level rises above land surface. As a result,
saline water moves upward in wells that tap both shallow and deep aquifers
to invade shallow artesian aquifers formerly containing only fresh water.
Locally, saline water has intruded the water-table aquifer by way of uncon-
trolled flowing wells and corroded well casings that formerly sealed off the
water-table aquifer from multiaquifer wells.
Modifying the construction of wells in Charlotte County would prevent
upward movement of water in them. Installing casing opposite aquifers where
dissolved-solids concentration markedly exceeds 500 mg/l and whose water-
level will rise to or above that in the overlying aquifer, will prevent the up-
ward movement of water into'the overlying aquifers. The well casing could
be extended through the zone or zones containing potable water and be firmly
seated in the rock zone that forms the confining layer of the underlying aqui-
fer. The annular space between the casing and the well bore could be filled
with neat cement grout. This type of well construction will minimize the effects
of saline water intruding the overlying aquifers.
The problems associated with intrusion of saline ground water could be
lessened by following conservation practices. Flowing wells could be fitted
with shutoff valves at the well heads to be closed when the water is not being
used. Unused wells that yield saline water should be carefully plugged from
bottom to top with grout. Burying such wells by breaking off the casing
below land surface and back filling the well site will not keep them from con-
taminating shallow aquifers. It is nearly impossible to relocate and properly
plug these buried wells. The construction of many wells currently in use in
the county could be improved by installing and grouting several hundred feet
of casing. This modification is needed in all areas, but particularly where
irrigation wells are near urbanized areas.

SALINE WATER RESOURCES
The artesian aquifers underlying Charlotte County contain a large quan-
tity of saline water whose dissolved-solids concentration is less than 5,000
mg/l. Water with this dissolved-solids concentration is generally suitable for
demineralization and represents a potential future source of raw water for
public supply for coastal Charlotte County. The depth to the zones containing






REPORT OF INVESTIGATION NO. 78


this water increases inland from the coast in Areas A to D. As a result, the
shallow Zones 1 and 2 in Area A contain water whose dissolved-solids concen-
tration is about 5,000 mg/l and only the deeper zones 4 and 5 in Area D
contain water of this salinity.
Some ground water with a dissolved-solids concentration of 3,000 mg/1
is already being desalted by several small water utility companies near Char-
lotte County. The water is desalted using the reverse osmosis and electrodialy.
sis process. The finished water delivered to the customers has a dissolved-
solids concentration that is reported to be 450 mg/l. In general, no use is now
being made of saline water resources of the county.

CONCLUSIONS
Most of the fresh surface water of usuable quality in Charlotte County
has already been developed for public supply. A reservoir on Myrtle Slough
could yield an additional small supply. Fresh surface water might be imported
into the county from Horse Creek in DeSoto County or from Myakka River
in Sarasota County, where reservoir sites exist.
The largest potential source of fresh ground water is the water-table aqui-
fer underlying the Telegraph Swamp area. This aquifer also has a potential
for use as a source for small supplies in other parts of the county. The artesian
aquifers underlying the county contain large quantities of saline water which
is suitable for demineralization. Moderately saline water can be obtained from
shallow zones in the artesian aquifers near the Gulf coast and around Charlotte
Harbor and from the deeper zones in the eastern part of the county.
Bringing fresh water some distance to the coastal urban area or demineral-
izing saline ground water for use as a water supply will sustain the urbanizing
coastal area so that the county can continue to grow.






52 BUREAU OF GEOLOGY


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REPORT OF INVESTIGATION NO. 78 53


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