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 Abstract
 Introduction
 Geography
 Geology
 Ground water
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 References


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Interim report on the ground-water resources of Manatee County, Florida ( FGS: Information circular 6 )
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 Material Information
Title: Interim report on the ground-water resources of Manatee County, Florida ( FGS: Information circular 6 )
Series Title: ( FGS: Information circular 6 )
Physical Description: 38 l. : maps, diagrs. ; 28 cm.
Language: English
Creator: Peek, Harry M
Anders, Robert B
Publisher: s.n.
Place of Publication: Tallahassee
Publication Date: 1955
 Subjects
Subjects / Keywords: Groundwater -- Florida -- Manatee County   ( lcsh )
Water-supply -- Florida -- Manatee County   ( lcsh )
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: by Harry M. Peek and Robert B. Anders.
Bibliography: "References" : leaf 38.
General Note: "Prepared by the Geological Survey, United States Department of the Interior, in cooperation with the Florida Geological Survey, the Board of County Commissioners of Manatee County, and the Manatee River Soil Conservation District."
Funding: Digitized as a collaborative project with the Florida Geological Survey, Florida Department of Environmental Protection.
 Record Information
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management:
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.
Resource Identifier: aleph - 001692827
oclc - 09334172
notis - AJA4901
lccn - a 55009324
System ID: UF00001066:00001

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Table of Contents
    Title Page
        Page 1
        Page 2
        Page 3
    Abstract
        Page 4
        Page 5
    Introduction
        Page 5
        Page 6
        Page 7
        Page 8
    Geography
        Page 9
        Page 10
        Page 8
        Page 11
    Geology
        Page 12
        Page 13
        Page 11
        Page 14
    Ground water
        Page 15
        Page 16
        Page 14
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
    Summary and conclusions
        Page 34
        Page 35
        Page 36
        Page 37
        Page 33
    References
        Page 38
        Copyright
            Main
Full Text

STATE OF FLORIDA


STATE BOARD OF CONSERVATION
Ernest Mitts, Supervisor

FLORIDA GEOLOGICAL SURVEY
Herman Gunter, Director


INFORMATION CIRCULAR NO.


INTERIM REPORT ON THE

GROUND-WATER RESOURCES OF


MANATEE COUNTY,


FLORIDA


By

Harry M. Peek
and
Robert B. Anders


Prepared by the
GEOLOGICAL SURVEY
UNITED STATES DEPARTMENT OF THE INTERIOR
in cooperation with the
FLORIDA GEOLOGICAL SURVEY
the
BOARD OF COUNTY COMMISSIONERS OF MANATEE COUNTY
and the
MANATEE RIVER SOIL CONSERVATION DISTRICT


IMarch, 1955f


_ ___










CONTENTS


Page

Abstract ............................ .......... 4

Introduction. ................................... 5

Previous investigations .................... 7

Geography....................................... 8

G eology.... ...... ....... ........................ 11

Ground water .................................... 14

Artesian water........................ .. .. 14

Current-meter explorations .......... 15

Artesian head ..... ............... ... 20

Piezometric surface....... ............ 21

Area of artesian flow.................. 26

W ells ...................... ........ 26

Salt-water contamination............................... 28

Summary and conclusions......................... 33

References . ......... .................. 38




(V


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ILLUSTRATIONS



Page

Figure 1. Map of the peninsula of Florida showing location
of Manatee County .. ....... ...... ...... 9

2. Generalized cross section showing formations
penetrated by wells in the western part of
Manatee County................................ 12

3. Diagram showing the relative velocity and
chloride content of the water in well 400 .......... 17

4. Diagram showing the relative velocity and
chloride content of the water in well 189........... 19

5. Map of western Manatee County showing the
piezometric surface in September 1952........... 22

6. Map of western Manatee County showing the
piezometric surface in May 1953 ................. 24

7. Map of Manatee County showing area of
artesian flow................................... 25

8. Map of Manatee County showing distribution
of artesian wells that have been inventoried ........ 27

9. Map of western Manatee County showing the
chloride content of water from artesian wells..... 30

10. Relation between the chloride content of the
water and water level in well 29, 1 mile west
of Palma Sola. ............................... 34


-3-







GROUND-WATER RESOURCES OF
MANATEE COUNTY, FLORIDA
INTERIM REPORT

By

Harry M. Peek and Robert B. Anders


ABSTRACT


Manatee County comprises an area of about 800 square miles adjacent

to the Gulf of Mexico in the southwestern part of the Florida peninsula. The

county is underlain at depths ranging from about 200 to 350 feet by a series

of limestone formations of Tertiary age having a total thickness of several

thousand feet. The upper part of the limestone section consists of the Ocala

group of Eocene age, the Suwannee limestone of Oligocene age, and the Tampa

formation of early Miocene age. These limestone formations are overlain by

the Hawthorn formation of middle Miocene age which consists of interbedded

clay, limestone, and sand. The Hawthorn is overlain by undifferentiated

deposits of sand, limestone, and shell of Pliocene(?) and Pleistocene age

that range in thickness from a few feet to about 75 feet.

Ground water occurs in Manatee County under both unconfined (water-'

table) and confined (artesian) conditions. The unconfined water occurs in the

surficial deposits of sand, limestone, and shell and is the source of many

domestic water supplies. The Tampa formation and Suwannee limestone are

the principal source of artesian water in the county and most large industrial,

irrigation, and municipal supplies are obtained from these formations.

Permeable beds of the Hawthorn formation also yield relatively small quantities

of water to some domestic and irrigation wells.


-4-








Records of the fluctuation of artesian head show that withdrawals of

large quantities of artesian water create relatively large depressions in the

piezometric surface. During periods of heaviest withdrawals the piezometric

surface is lowered about 4 feet throughout the coastal area, and as much as

8 feet at some places.

Analyses of the chloride content of the artesian water indicate that

salt water is present in the aquifer in a zone about 5 miles wide along the

entire coast. Most of the wells that yield water of highest chloride content

penetrate the deeper formations and are in or near the areas where the

seasonal lowering of the artesian head is greatest. Periodic chloride

analyses indicate that the salinity of the water varies with changes in

artesian head. Thus, any decline in the artesian head is probably accom-

panied by an upward movement of salt water from the deeper formations.



INTRODUCTION

A large part of western Manatee County is devoted to the growing of

winter vegetables and citrus fruits. As in most of peninsular Florida,

rainfall in the county during the growing season is not sufficient for crop

production and large quantities of artesian water are used for irrigation.

The large withdrawals of artesian water for irrigation result in a considerable

decline of the artesian head in the western part of the county. This seasonal

decline of the artesian head has become larger as the withdrawal of artesian

water has increased.

The lowering of the fresh-water head in some coastal areas in the State

has resulted in an infiltration of sea water into the water-bearing formations.








Records of the fluctuation of artesian head show that withdrawals of

large quantities of artesian water create relatively large depressions in the

piezometric surface. During periods of heaviest withdrawals the piezometric

surface is lowered about 4 feet throughout the coastal area, and as much as

8 feet at some places.

Analyses of the chloride content of the artesian water indicate that

salt water is present in the aquifer in a zone about 5 miles wide along the

entire coast. Most of the wells that yield water of highest chloride content

penetrate the deeper formations and are in or near the areas where the

seasonal lowering of the artesian head is greatest. Periodic chloride

analyses indicate that the salinity of the water varies with changes in

artesian head. Thus, any decline in the artesian head is probably accom-

panied by an upward movement of salt water from the deeper formations.



INTRODUCTION

A large part of western Manatee County is devoted to the growing of

winter vegetables and citrus fruits. As in most of peninsular Florida,

rainfall in the county during the growing season is not sufficient for crop

production and large quantities of artesian water are used for irrigation.

The large withdrawals of artesian water for irrigation result in a considerable

decline of the artesian head in the western part of the county. This seasonal

decline of the artesian head has become larger as the withdrawal of artesian

water has increased.

The lowering of the fresh-water head in some coastal areas in the State

has resulted in an infiltration of sea water into the water-bearing formations.







The presence of salty water in the artesian aquifer in parts of the coastal area

of Manatee County indicates that sea water may also have entered the water-

bearing formations in this area as a result of the decline of artesian pressure

during the growing season.

Recognizing this possibility and in response to the concern of the farmers

of the county, the Board of County Commissioners and tb.e Supervisors of the

Manatee River Soil Conservation District requested the United States Geological

Survey and the Florida Geological Survey to make an investigation of the ground-

water resources of the county. As a result of this request, an investigation was

begun in December 1950 by the U. S. Geological Survey in cooperation with

the above agencies.

The purpose of the investigation is to make a detailed study of the geology

and ground-water resources of the county, primarily to determine whether

salt-water encroachment has occurred or is likely to occur in the coastal area.

The investigation consists of the following phases:

1. An inventory of selected wells to obtain the location, diameter, depth,

and other pertinent information related to the occurrence and use of ground

water in the county.

2. Collection of data on water levels and artesian pressures to determine

progressive trends, to determine the magnitude of seasonal fluctuations, and for

use in constructing maps showing the altitude to which water will rise in artesian

wells.

3. Analyses of the chloride content of water from a sufficient number

of wells to determine the location and extent of areas in which the ground water

is salty.


-6-







4. Periodic analyses to determine the chloride content of water from

selected wells and the relation between salinity and artesian pressure.

5. A study of the geologic conditions governing the occurrence and

movement of ground water.

6. Exploration of selected wells with a deep-well current meter to

determine the depth and thickness of the water-bearing zones in the Tampa

formation and Suwannee limestone.

7. Collection of water samples from selected wells with a deep-well

sampler for the determination of the chloride content, total hardness, and

temperature of the water from the various permeable zones of the Tampa and

Suwannee limestones.

8. Studies to determine the water-transmitting and water-storing

properties of the water-bearing formations.

9. Collection of data on the present use of ground water for use in

predicting the quantity that may be safely withdrawn.



Previous Investigations

No detailed investigations of the geology and ground-water resources of

Manatee County have been made prior to the present study. However, several

short studies have been made and the results published in the reports of the

Florida Geological Survey and the U. S. Geological Survey. Some of the more

informative reports are briefly described below.

A report by Matson and Sanford (1913, pp. 237, 254, 362, 363, 364, and

pl. 5) (see references at end of report) includes a section on the geology and

water supply of Manatee County and a table of selected well records. A "


-7-







report by Sellards and Gunter (1913, pp. 266-269 and fig. 16) also includes a

brief summary of the geology and ground-water resources of the county and

contains a map showing the area of artesian flow. A report by Collins and

Howard (1928, pp. 220 and 221) contains a table of analyses of water from

several wells and springs in Manatee County.

A report of a reconnaissance investigation of several counties in the

State by Stringfield (1933, pp. 3-5) contains a brief discussion of the geography,

geology, and ground water of Manatee County. Another report by Stringfield

(1936, pp. 145, 164, 169, 170, 180, 182, 191, 192, and pls. 10, 12, and 16),

which gives the results of a study of the artesian water of the Florida peninsula,

contains water-level measurements and other data on about 90 wells in the

county. Also, the report includes maps of the Florida peninsula showing

the area of artesian flow, the height above sea level to which water in the

principal artesian aquifer will rise, and the areas in which water with a

chloride content of more than 100 parts per million (ppm) is present at

moderate depths.

The formations that crop out are briefly described in a report on the

geology of Florida by Cooke (1945, pp. 138, 153, 157, 208, 223, and 307).

A report by MacNeil (1950, pl. 19), describing the Pleistocene shorelines in

Florida and Georgia, contains a map showing the general configuration of

these shorelines in Manatee County.


GEOGRAPHY

Manatee County comprises an area of about 800 square miles adjacent to

the Gulf of Mexico in the southwestern part of the Florida peninsula (fig. 1). It


-8-

















0


0


N


0


25 0 25 50 75 10
6. = E aJ


0 Miles


APPROXIMATE SCALE AIN o

FIGURE I. MAP OF THE PENINSULA OF FLORIDA
SHOWING THE LOCATION OP MANATEE COUNTY


7-
C>


G,
< &< ,,


. ..








is bounded on the north by Hillsborough County, on the east by Hardee and

Desoto Counties, and on the south by Sarasota County.

The climate of the county is subtropical and the mean temperature is

about 72*F. According to the records of the United States Weather Bureau the

mean January temperature is about 58*F, and the mean July temperature is

about 81 F. The average annual rainfall at Bradenton since 1880 is 54. 6

inches, of which an average of 33. 85 inches falls between June 1 and

September 30.

The land surface of the county consists of a series of relatively flat

Pleistocene terraces. These terraces generally slope gently toward the

Gulf of Mexico and are modified by many shallow ponds and depressions and

by a few low hills and ridges. The hills and ridges are generally less than 20

feet high and probably represent beach ridges or/bars associated with the

different Pleistocene shorelines. The higher terraces have been modified to

some extent by stream dissection.

Most of the western part of the county consists of a coastal lowland

that represents the youngest of the Pleistocene terraces. This terrace was

formed when the sea stood about 25 feet above the present level. Most of the

coastal lowland is less than 20 feet above sea level, but a few low sand hills

and ridges have elevations of more than 25 feet. From the coastal lowland,

the land surface rises gradually to elevations of more than 100 feet at places

in the eastern part of the county.

The surface drainage of the county is principally through the Manatee,

Little Manatee, Braden, and Myakka Rivers and their tributaries. Parts of

the coastal lowland are drained by small streams that empty directly into the

-10-







report by Sellards and Gunter (1913, pp. 266-269 and fig. 16) also includes a

brief summary of the geology and ground-water resources of the county and

contains a map showing the area of artesian flow. A report by Collins and

Howard (1928, pp. 220 and 221) contains a table of analyses of water from

several wells and springs in Manatee County.

A report of a reconnaissance investigation of several counties in the

State by Stringfield (1933, pp. 3-5) contains a brief discussion of the geography,

geology, and ground water of Manatee County. Another report by Stringfield

(1936, pp. 145, 164, 169, 170, 180, 182, 191, 192, and pls. 10, 12, and 16),

which gives the results of a study of the artesian water of the Florida peninsula,

contains water-level measurements and other data on about 90 wells in the

county. Also, the report includes maps of the Florida peninsula showing

the area of artesian flow, the height above sea level to which water in the

principal artesian aquifer will rise, and the areas in which water with a

chloride content of more than 100 parts per million (ppm) is present at

moderate depths.

The formations that crop out are briefly described in a report on the

geology of Florida by Cooke (1945, pp. 138, 153, 157, 208, 223, and 307).

A report by MacNeil (1950, pl. 19), describing the Pleistocene shorelines in

Florida and Georgia, contains a map showing the general configuration of

these shorelines in Manatee County.


GEOGRAPHY

Manatee County comprises an area of about 800 square miles adjacent to

the Gulf of Mexico in the southwestern part of the Florida peninsula (fig. 1). It


-8-








Gulf of Mexico. Canals have been dug throughout most of the county to supplement

the natural drainage.



GEOLOGY

Most of the surface of the county is underlain by undifferentiated deposits

of Pliocene(?) and Pleistocene age and no rocks older than middle Miocene

are exposed at the surface. The formations penetrated by water wells in

the western part of the county range in age from Pleistocene to Eocene, as

shown in the generalized cross section in figure 2. The formations are separated

by unconformities and generally dip toward the southwest. The Ocala group _/



/ The stratigraphic nomenclature in this report conforms to the
usage ofthe U. S. Geological Survey with the following exceptions: The
Ocala limestone is herein referred to as the Ocala group, and the Tampa
limestone is referred to as the Tampa formation. These exceptions are
made in order to conform to the nomenclature currently used by the Florida
Geological Survey.


and older Eocene limestones are penetrated by relatively few wells in the

county as the overlying formations generally yield sufficient quantities of

water. The Ocala is composed predominantly of light-cream to tan soft, chalky

fossiliferous limestone and a few layers of hard, dense limestone. The Ocala

is probably more than 200 feet thick in the western part of the county and the

top of the formation is generally more than 600 feet below sea level.

The Suwannee limestone of the Oligocene age, which overlies the Ocala,

is about 200 feet thick in the western part of the county. The top of the

Suwannee is about 400 feet below sea level in the northwestern part of the

county and about 500 feet below sea level-in the southwestern part. The

-.11-
11-







ALTITUDE IN FEET WITH REFERENCE
41A a


Cn
C

I7

fT


rC


0
2
M


SEA LEVEL
5
0 0


BRAOEN RIVER


MANATEE RIVER


Figure 2. Generalized cross section showing formations penetrated
by wells in the western part of Manatee County


-12.


TO MEAN

9








Suwannee is generally a creamy-white to brown, soft, granular limestone/con-

taining many foraminifers, mollusks, and echinoids, although in places it

contains thin layers of hard, dense limestone or dolomite. It is probably

the most productive water-bearing formation penetrated by wells in the county.

Overlying the Suwannee is the Tampa formation of early Miocene age

which is about 150 to 200 feet thick in the western part of the county. The depth

to the top of the Tampa ranges from about 200 to more than 350 feet below sea

level. The formation consists predominantly of a gray-white to tan, fairly

hard, dense, sandy limestone, containing a few thin layers of chert, silicified

limestone, and a few thin beds of clay. Because of the numerous interconnecting

cavities, formed by solution of the limestone, that occur throughout the formation,

the Tampa is a very productive source of artesian water in most parts of the

county.

The Tampa formation is overlain by the Hawthorn formation of middle

Miocene age. In western Manatee County the top of the Hawthorn is an

irregular erosion surface that is generally not more than 20 feet above or below

sea level. The thickness of the formation ranges from about 200 feet in the

northwestern part of the county to about 350 feet at the southern end of the

county. Studies of well cuttings and surface exposures indicate that the

Hawthorn consists predominantly of interbedded calcareous clay and clayey

limestone, with some thin beds of sand. The clay and limestone layers contain

varying amounts of chert, dolomite, sand, and phosphate-bearing grains and

pebbles. The beds of sand and permeable zones in the limestone yield artesian

water to many domestic and irrigation wells. However, becauseof the low


-13-








Gulf of Mexico. Canals have been dug throughout most of the county to supplement

the natural drainage.



GEOLOGY

Most of the surface of the county is underlain by undifferentiated deposits

of Pliocene(?) and Pleistocene age and no rocks older than middle Miocene

are exposed at the surface. The formations penetrated by water wells in

the western part of the county range in age from Pleistocene to Eocene, as

shown in the generalized cross section in figure 2. The formations are separated

by unconformities and generally dip toward the southwest. The Ocala group _/



/ The stratigraphic nomenclature in this report conforms to the
usage ofthe U. S. Geological Survey with the following exceptions: The
Ocala limestone is herein referred to as the Ocala group, and the Tampa
limestone is referred to as the Tampa formation. These exceptions are
made in order to conform to the nomenclature currently used by the Florida
Geological Survey.


and older Eocene limestones are penetrated by relatively few wells in the

county as the overlying formations generally yield sufficient quantities of

water. The Ocala is composed predominantly of light-cream to tan soft, chalky

fossiliferous limestone and a few layers of hard, dense limestone. The Ocala

is probably more than 200 feet thick in the western part of the county and the

top of the formation is generally more than 600 feet below sea level.

The Suwannee limestone of the Oligocene age, which overlies the Ocala,

is about 200 feet thick in the western part of the county. The top of the

Suwannee is about 400 feet below sea level in the northwestern part of the

county and about 500 feet below sea level-in the southwestern part. The

-.11-
11-






permeability-of-the bedsolay and clayeyimestone, the formation serves

as a confining layer for the water in the underlying limestone formations.

The Hawthorn formation is overlain by undifferentiated deposits of

Pliocene(?) and Pleistocene age consisting of thin layers of limestone, sand,

shell, and clay. These deposits range in thickness from a few feet to about

75 feet, and where sufficiently thick are the source of many domestic water

supplies. The water in these deposits in most areas is generally unconfined

and replenished by local rainfall. In a few areas, however, the water is confined

under a low artesian head by thin beds of clay and limestone.



GROUND WATER

/ Ground water in usable quantities generally occurs in all formations

/penetrated by wells in the western part of Manatee County. Many small

domestic supplies are obtained from the shell beds and unconsolidated sands

of Pliocene(?) and Pleistocene age. The water in these deposits is replenished

by local rainfall and occurs under water-table conditions in all except a few small

areas where it is confined by thin beds of clay or limestone. The water in the

Hawthorn and older formations occurs under artesian conditions.


Artesian Water

As in most of Florida, the principal artesian aquifer in Manatee County

consists of the limestone formations of Eocene, Oligocene, and Miocene age.

As revealed by Stringfield (1936, pl. 12, p. 148), most of the artesian water

in the limestone formations in central and southern Florida is derived from

rainfall in the lake region of Polk County and adjacent counties where numerous

sinkholes, filled with permeable material, penetrate the confining beds and

-14-








constitute avenues through which water from the surface may reach the limestone

formations. From the recharge area, where the head is relatively high, the

water moves laterally through the pores and cavities in the limestone toward

areas of lower head where discharge is occurring. Water that enters

the limestone formations in northen Polk County must move underground for

a distance of about 50 miles to reach the coastal area of Manatee County.

Although a few of the deeper wells yield some water from the Ocala

group and older Eocene limestone, most of the artesian water used in Manatee

County is derived from the permeable zones in the Tampa formation and Suwannee

limestone. These permeable zones are generally separated by relatively

impermeable layers which retard the vertical movement of the water. However,

in many areas these impermeable layers are probably not continuous or are

breached by openings which provide hydraulic connections between the permeable

zones.

The artesian water in the Hawthorn formation occurs in thin beds of sand

and sandy limestone which are generally separated by relatively thick beds of

clay or clayey limestone. In western Manatee County the permeable zones of

the Hawthorn formation are generally separated from the Tampa formation by

beds of clay or limestone which are relatively impermeable. Thus, the hydraulic

connection between the Hawthorn and older formations is generally poor except

where the beds of low permeability are absent or have been breached.


Current-Meter Explorations

In order to determine the depth, thickness, and relative productivity

of the permeable zones in the different formations that yield water to wells in


-15-







Manatee County, explorations were made in selected wells with a deep-well

current meter, a device for measuring the velocity of flow of water through

a well bore,

The results of a current-meter traverse in well 400, a nonflowing well

about 3a miles south of Palma Sola, are shown graphically in figure 3. A

diagram showing the cased and uncased portions of the well also appears on

figure 3. The well was pumped at the rate of 230 gallons per minute (gpm) while

the traverse was being made. Velocities are expressed as revolutions per

minute (rpm) of the current meter. Inasmuch as the well bore is not uniform

in the uncased part of the well, flow rates, which are a function of velocity

and cross-sectional area, cannot be computed accurately. As shown on the

graph, the observed velocities indicate that little or no water enters the well

below 510 feet. The increase in velocity up the well from 0 rpm at 510 feet to

more than 110 rpm at 440 feet indicates that most of the total yield of the well

is derived from this interval which probably represents the upper part of the

Suwannee limestone. The observed velocities indicate that the Tampa formation

yields little or no water to the well in the interval between 440 and 400 feet.

The large changes in velocity between 400 and 300 feet are probably due to

differences in the size of the well bore, although a small quantity of water

may enter the well in this interval. The construction of the well, shown

diagrammatically on the left side of the figure, indicates that the changes in

velocity above 300 feet represent differences in the size of the well bore

rather than changes in the volume of flow. Thus, the greater velocities

between 300 feet and 205 feet probably represent the flow of water through the

6-inch casing which is somewhat smaller than the open hole below 300 feet


-16-






permeability-of-the bedsolay and clayeyimestone, the formation serves

as a confining layer for the water in the underlying limestone formations.

The Hawthorn formation is overlain by undifferentiated deposits of

Pliocene(?) and Pleistocene age consisting of thin layers of limestone, sand,

shell, and clay. These deposits range in thickness from a few feet to about

75 feet, and where sufficiently thick are the source of many domestic water

supplies. The water in these deposits in most areas is generally unconfined

and replenished by local rainfall. In a few areas, however, the water is confined

under a low artesian head by thin beds of clay and limestone.



GROUND WATER

/ Ground water in usable quantities generally occurs in all formations

/penetrated by wells in the western part of Manatee County. Many small

domestic supplies are obtained from the shell beds and unconsolidated sands

of Pliocene(?) and Pleistocene age. The water in these deposits is replenished

by local rainfall and occurs under water-table conditions in all except a few small

areas where it is confined by thin beds of clay or limestone. The water in the

Hawthorn and older formations occurs under artesian conditions.


Artesian Water

As in most of Florida, the principal artesian aquifer in Manatee County

consists of the limestone formations of Eocene, Oligocene, and Miocene age.

As revealed by Stringfield (1936, pl. 12, p. 148), most of the artesian water

in the limestone formations in central and southern Florida is derived from

rainfall in the lake region of Polk County and adjacent counties where numerous

sinkholes, filled with permeable material, penetrate the confining beds and

-14-









DEPTH IN FEET WITH


REFERENCE TO MEAN

o 0
O O
O O
! J


SEA LEVEL

0


. .6"c' casingco








which was drilled with a 6-inch bit. The sharp decrease in velocity above

205 feet corresponds to the bottom of the hole that was drilled with an 8-inch

bit and does not represent a loss of water to the Hawthorn formation. This is

substantiated by the fact that velocity measurements made when no water was

being pumped from the well showed no movement of water between the different

water-bearing zones.

The dashed line in figure 3 shows the observed velocities in the part of

the well that was drilled with an 8-inch bit converted to represent the velocities

in a well with a diameter of 6 inches. The conversion was made by multiplying

the observed velocity by the ratio of the cross-sectional area of a 6-inch hole

to the cross-sectional area of an 8-inch hole, which is the assumed diameter

of the larger hole. The velocity observed at 30 feet below sea level probably

represents the velocity inside the 8-inch casing and when converted to represent

the velocity in a 6-inch well, it closely corresponds to the velocities that were

measured inside the 6-inch casing between 205 and 290 feet. Thus, the well

bore between 30 and 205 feet is probably much larger than 8 inches. In fact,

calculations indicate that the average diameter of the well bore in this interval

is about 10 inches.

The results of a current-meter traverse in well 189, about 2 miles

north of Gillette, are shown graphically in figure 4. The well was flowing at

the rate of about 400 gpm when the velocity measurements were made. The

observed velocities indicate that very little if any water is derived from the

formations below 445 feet and about half of the total yield enters the well in the

interval between 445 and 415 feet. The top of this producing zone corresponds

roughly to the top of the Suwannee limestone which is between 400 and 415 feet


-18-











0
O 1



.z




OQ
3
e-*







qg
0




I-
0 i o




So e
02
I. o
0-


DEPTH IN FEET WITH REFERENCE TO MEAN SEA LEVEL
* a a o .
o 8 0 8 8 8
o0l 0 0 0 6 0
L I I I I
1 .. ..._ _____ n *",.,;-. i .__ I---" ------'--I -









below sea level as determined from an electric log of the formations

penetrated by the well. The observed velocities indicate that the

interval between 415 and 375 feet is nonproductive. The increase in

velocity between 375 and 300 feet indicate that this part of the Tampa

formation contributes about half the total yield of the well. The changes

in velocity above 300 feet correspond to differences in the size of the

well bore, as shown in the diagram of the construction of the well. Thus,

this section, which is in the Hawthorn formation, probably yields little

or no water to the well. Conversion of the observed velocities in the

8-inch casing and in the open hole that was drilled with an 8-inch bit to

represent the velocities in a 6-inch well, as shown by the dashed line in

figure 4, indicates that no water was being lost to the Hawthorn formation.


Artesian Head

The water in the Tampa formation and Suwannee limestone is

generally under approximately the same artesian head, although small

differences may occur locally during periods of heavy withdrawals. The

artesian head of the water in the Hawthorn formation in the western part

of the county is generally about 5 to 8 feet lower than the head in the

underlying limestones. However, water-level measurements indicate

that the difference in head decreases toward the east.

As a result of the difference in head between the Hawthorn formation

and the Tampa formation and Suwannee limestone in the western part of

the county, conditions are favorable for subsurface leakage through wells

that are cased to only shallow depths. Thus, during times when there is no


-20-








discharge at the surface, water from the Tampa formation and Suwannee

limestone may move up through the wells and flow out into the permeable

beds of the Hawthorn formation.

Fluctuations of artesian head, ranging from a fraction of a foot to

several feet, occur almost continuously and may be caused by one or more

factors. The most significant fluctuations in Manatee County are caused

by the daily and seasonal variations in withdrawals from wells; however,

observable fluctuations are also caused by earthquakes, ocean tides, and

barometric pressure changes. In order to obtain continuous records of

the fluctuations of artesian head in different parts of the county, automatic

water-stage recorders have been installed on four wells. In addition to

the continuous records, water-level or pressure measurements are made

at intervals of about 6 weeks in more than 30 selected wells in different

parts of the county in order to determine the magnitude of seasonal

fluctuations. Measurements are also made about once a year in a large

number of wells for use in constructing maps showing, by means of

contour lines, the height in feet above sea level to which water will rise

in wells that penetrate the principal artesian aquifer.


Piezometric Surface

The contour lines on the map in figure 5, which were constructed

from water-level measurements made in September 1952, represent the

height to which the water level in artesian wells will rise in feet above

sea level. The imaginary surface represented by these contour lines is

Referred to as the"piezometric surface. The configuration of the contour


-21-



























ANAA MARIA U




O e* ... .w u I.

inSepltemibn 192im
6.9~ PON" o am.





CO K SCALE Il MILES

Y 0





.. -.. ..- I 'A r S--" O' A -C-F o W -. . ..

0

Figure 5. Map of western Manatee County showing the piezometric surface
in September 1952.








lines on a map of the piezometric surface indicates the direction of

movement of the artesian water. The water moves from the higher

toward the lower head in the direction of steepest gradient, which is at

right angles to the contours. Thus, the configuration of the contours in

figure 5 indicates that the movement of the artesian water in Manatee

\ County is generally from east to west.

As shown in figure 5, the piezometric surface in September 1952

was more than 20 feet above sea level throughout the coastal area except

in the shallow depression centered in the vicinity of Palma Sola. This

depression in the piezometric surface indicates that an appreciable quantity

of water was being discharged from the aquifer at the time the water-level

measurements were made. As very little water was being withdrawn

through wells in the area the depression may be due in part to subsurface

leakage through unused irrigation wells and also to natural leakage through

the confining bed.

The contour lines on the map in figure 6 show the piezometric

surface in the coastal area in May 1953, during a dry period when large

quantities of water were being withdrawn through irrigation wells. A

comparison of figures 5 and 6 indicates that the large withdrawals in

May had lowered the piezometric surface about 4 feet throughout the

coastal area, and more than 8 feet at some places. The depression in the

vicinity of Palma Sola, shown in figure 5, had been enlarged and had

coalesced with depressions that had formed near Palmetto and Bradenton.

These depressions probably represent the combined drawdown of industrial,

irrigation, public-supply, and domestic wells. The depression centered

-23-

























AMA mm D a 1





G) u- /} /
00 0 EXPLANATION

III L I

NO**bm ago a .
*3 SD *M OU a"
O"








^3, ^^.B ^ ^-T^
0 M
LOW11 PEACH IL 17= .1, _- .,UNT
S*L 10 MILES







S A R r K -f Tf N


Figure 6. Map of western Manatee County showing the piezometric surface
in May 1953.











ArA1


9 u 2 3 *l


CITY





& CO
. l_. UTt. COUTY j
UIKUOTA COUrT r


Map of Manatee County showing area of artesian flow.


TO
o
1 \ '

N
(*

y


A*ATEOT COUITT
tIUOt OUIT


i


Figure 7.







north of Gillette represents the drawdown of a large number of irrigation

wells.

Area of Artesian Flow

The shaded areas on the map in figure 7 represent the approximate

areas in which artesian wells will flow, perennially or intermittently.

the area of artesian flow in the western part of the county includes a

zone along the coast about 10 to 15 miles wide, with extensions along the

larger stream valleys. Within this zone there are several isolated areas

where the land surface is relatively high and wells will not flow. The area

of artesian flow also includes a zone about 2 to 3 miles wide along the

Myakka River in the southeastern part of the county.


Wells

Ground water is the source of practically all the water that is used

in Manatee County except the Bradenton municipal supply, which is obtained

from the Braden River. Most large irrigation, industrial, and municipal

supplies are obtained from wells that penetrate the Tampa formation and

Suwannee limestone. The remaining ground-water supplies are obtained

from the Hawthorn and younger formations.

Figure 8 shows the distribution of more than 500 artesian wells that

have been inventoried. As may be seen from the figure, most of these

are in the western part of the county and in or near the area of artesian

flow. The deeper wells in the county are generally between 350 and 600

feet deep and have diameters ranging from 3 to 12 inches, although most

are between 6 and 10 inches in diameter. Shallow wells range in depth


-26-






























1 .ea. -0 l:




0-AR A S O T A... .. .. . c'-



SItermittenly flowing weil l
O Nonflowing well 0se~ .. t t 0
SFlowig well on which recording i
gage is installed l
+ Nonnflowing well on which recording
goge is installed o 0









Figure 8. Map of Manatee County showing distribution of artesian wells
that have been inventoried.






from about 25 to more than 200 feet and range in diameter from 1j to 6

inches. During the construction of wells, a surface casing is generally

seated in clay or limestone at depths ranging from about 30 to 100 feet.

In addition, some wells are equipped with an inner casing to prevent

sands in the Hawthorn and Tampa formations from caving into the well.



SALT WATER CONTAMINATION

Saline water is present in the principal a:tesian aquifer a.t relatively

Shallow depths throughout much of the coastal area of Florida. The

presence of this salty water appears to be due principally to the infil-

tration of sea water into the aquifer, either thousands of years ago as

a result of natural processes or in recent years as a result of the excessive

lowering of artesian head caused by withdrawal of large o--mntities of fresh

water through wells. The artesian aquifer was partly filled with sea

water several times during the interglacial stages of the Pleistocene

epoch when the sea stood above the present level. Since the last recession

of the sea, the circulation of fresh water through the aquifsr has been

gradually diluting and flushing out the salty water. However, in much of

the coastal area, the flushing is incomplete and a part o.: all of the water-

bearing formations still contain water which, although generally less

salty than sea water, is too salty for most ures. .(n such areas, the

flushing of the aquifer will continue as long as the artesian head remains

relatively high. However, excessive lowering of the head will result

in a vertical migration of the salty water from the lower zones of the

aquifer, where flushing is less complete, into the upper part of the aquifer,

-28-







except where such migration is prevented by impermeable beds.

As the chloride content of ground water is generally a reliable

index of salt-water contamination, water samples from several hundred

wells were analyzed in order to determine the relative salinity of the

artesian water in Manatee County. These analyses indicate that the

chloride content of the artesian water, which is about 15 to 20 parts per

million in the eastern part of the county, gradually increases towards

the coast. The results of analyses of water samples from more than

400 wells in the western part of the county are shown by symbols on the

map in figure 9. These symbols do not represent the exact chloride

content of water from each well, but show the limits within which each

chloride content is included.

The open circles represent wells that yield water having a chloride

content of 30 ppm or less. This is about the chloride content that one would

expect to find in water that has not been contaminated by salt water. The

circles that are partly or completely filled represent wells that yield

water having a chloride content of more than 30'ppm, and indicate the

areas in which salty water is present in the aquifer. In the area north

of the Manatee River, as shown in figure 9, most of the wells that yield

water having a relatively high chloride content are restricted to a narrow

zone along the coast. In the area south of the Manatee River wells that

yield water having a chloride content in excess of 30 ppm occur as far

east as the Braden River.

The wells represented by symbols in figure 9 range in depth from

less than 100 feet to more than 600 feet, but most are between 350 and 600

-29-























ANNA MAP" 9WIPW Q a P-maw-, -Sqma

PL PALMETTO%






SR DNT ON.
n 0 0















Figure 9. Map of western Manatee County showing the chloride content
of water from artesian wells.
MANAT






feet deep. Many wells are cased to only shallow depths and are thus open

to all the formations they penetrate below the surficial sands. Thus, the

data on the chloride content of water from these wells generally do not

represent the chloride content of water from a single formation or

producing zone, but represent the chloride content of a composite of the

water from all the producing zones penetrated by each well. The wells

that penetrate the deeper formations generally yield water of highest

chloride content. In any given area, therefore, most differences in

chloride content are a result of differences in the depths of the wells.

Most of the completely filled circles in figure 9 represent wells that

yield water from the Suwannee limestone or older formations. The

chloride content of water from these deeper wells ranges from 500 to

more than 1,000 ppm. However, the actual chloride content of the

water in the Suwannee limestone in this area is probably much higher than

indicated by the analyses of the composite samples, as most of these wells

also yield relatively large quantities of water from the Tampa formation

which generally contains less than 400 ppm of chloride. Analyses for

chloride in water samples collected with a deep-well sampler at different

depths in selected wells were made in order to determine the relative

salinity of the water from the different formations. The results of

analyses of water samples from two wells are shown graphically in

figures 3 and 4. As indicated on these graphs, the saltier water enters

the wells from the deeper producing zones, which are in the upper part

of the Suwannee limestone. The fact that the chloride content is less in

the upper part of the well indicates that water with a lower chloride content

-31-







enters the wells from the producing zones in the Tampa formation.

Analyses of water samples collected in a flowing well about 3 miles

southwest of Palma Sola showed that the chloride content of the water at

a depth of 500 feet was more than 2, 000 ppm, whereas, at a depth of

445 feet, the chloride content was only 1, 330 ppm. This difference in

chloride content indicates that water having a chloride content considerably

lower than 1,330 ppm entered the well in the interval between 445 and 500

feet.

The wells that yield water of highest chloride content are generally

in or near areas in which the seasonal lowering of the artesian head is

greatest. As the maps of the piezometric surface (figs. 5 and 6) indicate

that the mean artesian head along the coast is sufficiently high to prevent

the infiltration of sea water at the present time, the higher chloride

content in these areas appears to be due to a vertical movement of salty

water from the lower water-bearing formations during periods of heavy

withdrawal. The analyses indicate that the movement of fresh water

through the aquifer has flushed most of the salt water from the upper

water-bearing zones. The water in the deeper formations also doubtless

has been considerably diluted by fresh water moving through the aquifer.

However, the water in these formations is still too salty for most uses.

Vertical movement of water from the deeper water-bearing

formations during times of heavy withdrawal is indicated by the analyses

of water samples collected periodically from the deeper wells. These

analyses show that the salinity of the water varies with changes in artesian

head. Generally, a decrease in head is accompanied by an increase in

-32-






chloride content, and vice versa, as shown in figure 10.

Salty water is present at relatively shallow depths in the Hawthorn

and younger formations at some places along the coast. Beneath Anna

Maria Island, the water in the Hawthorn formation is saltier than sea

water. Water samples obtained from the Hawthorn during the drilling

of wells on the island had chloride concentrations ranging from 25, 000

to 44, 500 ppm, whereas normal sea water contains about 19, 500 ppm of

chloride. The extremely high salt content of the water in the Hawthorn in

this area is probably due to deposits of mineral salts within the formation.



SUMMARY AND CONCLUSIONS


The principal results of the investigation of the ground-water

resources of Manatee County to date are summarized below.

1. The county is underlain at depths ranging from about 200 to

350 feet by a thick section of limestone consisting of formations of Eocene,

Oligocene, and Miocene age. The limestone formations penetrated by

water wells include the Ocala group of late Eocene age, the Suwannee

limestone of Oligocene age, and the Tampa formation of early Miocene

age. The limes tone section is overlain by the Hawthorn formation of

middle Miocene age which consists of interbedded clay, clayey limestone,

and sand. The Hawthorn is overlain by deposits of sand, shell, and limestone

of Pliocene(?) and Pleistocene age that range in thickness from a few feet

to about 75 feet.

2. Ground water in usable quantities generally occurs in all


-33-






1951
June


Jul


j t_______. ._ WATER LEVEL




SIs -
II



U n










gCHLORIDE CONTENT OF WA ER


0. -
'k-lu_____ _____ HLORIE COTENT OF0111__












.j ___ ______ ___ __________


1- 0- ---_--
,_n __ n i ,, I.
____ ___ ___ ___ _______ ___ ___ ___ ___


-II- -


Figure 10. Relation between the chloride content of the water and the
water level in well 29, 1 mile west of Palma Sola.


Jan.


Feb.


Mar.


Apr.


Mov


-


L _


Au0.


Sep.


Oct.







formations penetrated by wells in the western part of the county. The

surficial deposits of sand, limestone, and shell are the source of many

domestic water supplies. The water in these deposits is generally

unconfined and replenished by local rainfall. The water in the Hawthorn

formation and the underlying limestone formations is confined under

artesian pressure by the layers of clay and clayey limestone in the

Hawthorn. The permeable beds in the Hawthorn yield water to many

domestic, irrigation, and small public-supply wells. The Tampa formation

and Suwannee limestone are the source of most large irrigation, industrial,

and public supplies.

3. Observations during the drilling of wells and current-meter

explorations in two wells indicate that the artesian water in the limestone

formations occurs in permeable zones which are separated, at least

locally, by relatively thick beds of low permeability that yield little or

no water.

4. The artesian head of the water in the Hawthorn formation in

the western part of the county is generally several feet lower than the

head in the Tampa formation and Suwannee limestone. Because of this

difference in head, some water probably moves through well bores from

the Tampa formation and Suwannee limestone into the Hawthorn formation

during times when the wells are not being used. The depression in the

piezometric surface in the vicinity of Palma Sola (see fig. 5) may be due

in part to subsurface leakage.

5. Records of fluctuations of artesian head show that withdrawals

of large quantities of artesian water create relatively large depressions in

-35-







the piezometric surface (see figs. 5 and 6). During periods of heaviest

withdrawal the piezometric surface is lowered about 4 feet throughout the

coastal area, and as much as 8 feet in some small areas.

6. Analyses for the chloride content of the artesian water from

wells in the western part of the county indicate that salt water is present

in the aquifer in a zone about 5 miles wide that extends along the entire

coast. The wells that yield water of highest chloride content generally

penetrate the Suwannee limestone or older formations and several of these

wells yield water containing more than 1,000 ppm of chloride. The

actual chloride content of the water in the Suwannee limestone is probably

much higher than indicated by the analyses of water samples collected at

the surface, as these samples represent a mixture of the water from all

the producing zones penetrated by the well. Most of the wells yield

appreciable quantities of water from the Tampa formation which generally

contains less than 400 ppm of chloride.

7. Salty water occurs at relatively shallow depths in the permeable

beds of the Hawthorn formation at many places along the coast. Beneath

part of Anna Maria Island, the water in the Hawthorn has a higher salt

content than sea water.

8. Most of the wells that yield water of highest chloride content are

in or near the areas in which the seasonal lowering of the artesian head is

greatest. As the piezometric surface (figs. 5 and 6) indicates that the

mean artesian head along the coast is sufficiently high to prevent infil-

tration of salt water directly from the sea, the higher chloride content of

the artesian water in these areas is probably due to a vertical movement of


-36-








salty water from the deeper water-bearing formations during periods

of heavy withdrawals. Periodic analyses for chloride indicate that the

salinity of the water varies with changes in artesian head. Thus, decline

of the artesian head in the coastal area is probably accompanied by a

vertical movement of salty water and expansion of the contaminated

area.

As indicated by the results of the investigation outlined above,

only generalized conclusions can be derived from the data presently

available. Completion of the investigation will require additional work

on all the several phases listed at the beginning of this report. However,

it seems safe to say that the maximum yield of water of acceptable

quality can be obtained only by spreading the pumping so as to prevent

excessive local drawdowns insofar as possible.


-37-






chloride content, and vice versa, as shown in figure 10.

Salty water is present at relatively shallow depths in the Hawthorn

and younger formations at some places along the coast. Beneath Anna

Maria Island, the water in the Hawthorn formation is saltier than sea

water. Water samples obtained from the Hawthorn during the drilling

of wells on the island had chloride concentrations ranging from 25, 000

to 44, 500 ppm, whereas normal sea water contains about 19, 500 ppm of

chloride. The extremely high salt content of the water in the Hawthorn in

this area is probably due to deposits of mineral salts within the formation.



SUMMARY AND CONCLUSIONS


The principal results of the investigation of the ground-water

resources of Manatee County to date are summarized below.

1. The county is underlain at depths ranging from about 200 to

350 feet by a thick section of limestone consisting of formations of Eocene,

Oligocene, and Miocene age. The limestone formations penetrated by

water wells include the Ocala group of late Eocene age, the Suwannee

limestone of Oligocene age, and the Tampa formation of early Miocene

age. The limes tone section is overlain by the Hawthorn formation of

middle Miocene age which consists of interbedded clay, clayey limestone,

and sand. The Hawthorn is overlain by deposits of sand, shell, and limestone

of Pliocene(?) and Pleistocene age that range in thickness from a few feet

to about 75 feet.

2. Ground water in usable quantities generally occurs in all


-33-








REFERENCES


Collins, W. D.
1928 (and Howard, C. S.) Chemical character of waters
of Florida: U. S. Geol. Survey Water-Supply Paper 596-G.

Cooke, C. W.
1945 Geology of Florida: Florida Geol. Survey Bull. 29.

MacNeil, F. S.
1949 Pleistocene shorelines in Florida and Georgia: U. S. Geol.
Survey Prof. Paper ZZ5-F.

Matson, G. C.
1913 (and Sanford, Samuel) Geology and ground water of Florida:
U. S. Geol. Survey Water-Supply Paper 319.

Sellards, E. H.
1913 (and Gunter, Herman) The artesian water supply of eastern
and southern Florida: Florida Geol. Survey 5th Annual
Report.

Stringfield, V. T.
1933 Ground-water investigations in Florida: Florida Geol.
Survey Bull. 11.
1936 Artesian water in the Florida peninsula: U. S. Geol. Survey
Water-Supply Paper 773-C.


-38-










FLRD GEOLOSk ( IC SUfRiW


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