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


FGS



Interim report on the ground-water resources of Seminole County, Florida ( FGS: Information circular 5 )
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 Material Information
Title: Interim report on the ground-water resources of Seminole County, Florida ( FGS: Information circular 5 )
Series Title: ( FGS: Information circular 5 )
Physical Description: 43 l. : maps, diagrs. ; 28 cm.
Language: English
Creator: Heath, Ralph Cyrus, 1909-
Barraclough, Jack T
Publisher: s.n.
Place of Publication: Tallahassee
Publication Date: 1954
 Subjects
Subjects / Keywords: Groundwater -- Florida -- Seminole County   ( lcsh )
Water-supply -- Florida -- Seminole County   ( lcsh )
Genre: non-fiction   ( marcgt )
 Notes
Statement of Responsibility: by Ralph C. Heath and Jack T. Barraclough.
Bibliography: "References": leaves 42-43.
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 Seminole County, and the city of Sanford."
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 - 001692709
oclc - 01719593
notis - AJA4783
lccn - a 55009252
System ID: UF00001065:00001

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Table of Contents
    Title Page
        Page 1
    Table of Contents
        Page 2
        Page 3
    Abstract
        Page 4
        Page 5
    Introduction
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
    Geography
        Page 10
        Page 11
        Page 9
    Geology
        Page 12
        Page 11
        Page 13
        Page 14
        Page 15
        Page 16
    Ground water
        Page 17
        Page 18
        Page 19
        Page 20
        Page 16
        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
        Page 34
        Page 35
        Page 36
    Summary and conclusions
        Page 37
        Page 38
        Page 39
        Page 40
        Page 41
        Page 36
    References
        Page 42
        Page 43
        Copyright
            Main
Full Text




STATE OF FLORIDA

STATE BOARD OF CONSERVATION

Charlie Bevis, Supervisor


FLORIDA GEOLOGICAL SURVEY

Herman Gunter, Director








INFORMiATION CIRCULAR NO. 5








INTERIM REPORT ON THE GROUND-WATER

RESOURCES OF SEMINOLE COUNTY, FLORIDA

By

Ralph C. Heath
and
Jack T. Barraclough


Prepared by the
GEOLOGICAL SURVEY
UNITED STATES DEPARTi.ENT OF THE INTERIOR
in cooperation with the
FLORIDA GEOLOGICAL SURVEY
the
BOARD CF COUNTY COMMISSIONERS OF SEMINOLE COUNTY
and the
CITY OF SANFORD



August, 1954












CONTENTS




Page
Abstract . . . . . . 4

Introduction . . . . . . 5

Previous investigations . .. 7

Geography . . . . . .. 9

Geology . . . . . . 11

Ground water . . . .. . .. 16

Water-table aquifer . . . ...... 17

Artesian aquifer . . . . . 18

SPiezometric surface of the principal
artesian aquifer in Florida .. . 19

SPiezometric surface in Seminole County . 22

Area of artesian flow . . . 23

Wells . . . . . . 28

Salt-water contamination .. . . . . 31

Summary and conclusions . ..... . 36

References . . . . . . 42












ILLUSTRATIONS


Figure Page

1. Map of Florida showing location of Seminole County 10

2. Generalized geologic section showing the formations
penetrated by wells in Seminole County . 12

3. Map of Florida.showing the piezometric surface of
the principal artesian aquifer . .. 21

4. Map of the Sanford-Lake Mary area showing the
piezometric surface ........... 24

5. Map of Seminole County showing the approximate areas
of artesian flow . . . . .. 25

6. Map of the area between Lake Monroe and Lake Jessup
showing the height above the land surface to which
wells will flow. . . . . 27

7. Map of Seminole County showing the distribution of
wells that have been inventoried . . 29

8. Graph showing the relation between the static head
and the yield of flowing 3-inch artesian wells in
two areas in the northern part of Seminole County. 32

9. Map of Seminole County showing the chloride content
of water from the upper part of the limestone
aquifer . . . . .. 34

10. Graph showing the relation between the chloride
content and the artesian pressure head in well 31,
2 miles southwest of Sanford .. . 37

11. Graph showing the relation between the chloride
content and artesian pressure head in two wells
near Oviedo . . . . 38


-3-










INTERIM REPORT ON
THE GROUND-WATER RESOURCES OF
SEMINOLE COUNTY, FLORIDA

By

Ralph C. Heath and Jack T. Barraclough

ABSTRACT

Seminole County is in the east-central part of the Florida Peninsula.

The county is underlain, beginning at a depth of 75 to 150 feet, by a

series of limestone formations having a total thickness of several thousand

feet. The upper part of the limestone section is composed of the Lake City

limestone of early middle Eocene age, the Avon Park limestone of late

middle Eocene age, and the Ocala group I/ of late Eocene age. The limestone



lj The stratigraphic nomenclature used in this report conforms to the
usage of the Florida Geological Survey. It also conforms to the usage of the
U. S. Geological Survey with the exception of the Ocala group and its sub-
divisions.


formations are overlain by the Hawthorn formation of middle Miocene age, and,

where the Hawthorn is absent, by deposits of clay and sandy shell which are

referred to in this report as deposits of late Miocene or Pliocene age.

A blanket of Pleistocene and Recent sand underlies the surface of the county

to a depth of 25 to 50 feet.

The section of limestone that includes the Ocala group and the Avon

Park limestone is the most important source of ground water in the county.

Water in this section is under artesian pressure in most of the county and

will flow at the surface from wells penetrating the limestone in the lowland

areas. The artesian water is derived principally from recharge that enters

the limestones in Orange and Polk counties, although some may be derived

from small recharge areas in Seminole County.










Records of the seasonal fluctuations of artesian pressure show that the

pressure head is lowered during the periods of heaviest withdrawal as much

as 10 feet in the Oviedo area and 4 to 6 feet in the Sanford area. A com-

parison of measurements made in 1937 with ones made recently shows that, in

areas where withdrawals have increased, the artesian pressure head has

declined slightly, whereas, in areas where the withdrawals are unchanged or

have decreased, the pressure head has remained about the same.

The chloride content of water from artesian wells in Seminole County

ranges from less than 10 parts per million (ppm) in the recharge areas

around the towns of Lake Mary and Geneva to more than 5,000 ppm in the area

adjacent to Lake Harney. In the truck-farming areas, near Sanford and Oviedo,

the chloride content ranges from about 25 ppm to slightly more than 1,500 ppm.

A comparison of chloride analyses made in 1937 with those made recently shows

that there has been little or no change in the chloride content of the

artesian water in most of the county.


INTRODUCTION


Salt-water encroachment is undoubtedly the problem of most concern to

users of ground water in Florida. This is a problem in many coastal areas

where water levels are lowered excessively by heavy pumping. It is a

problem also in some inland areas where the water-bearing formations contain

salty water at relatively shallow depths. Among the coastal areas where wells

have become contaminated with salt water are Pinellas County and the Miami

area of Dade County. Inland areas where wells are likely to become con-

taminated with salt water include Seminole County and the southwestern part

of Volusia County.










Records of the seasonal fluctuations of artesian pressure show that the

pressure head is lowered during the periods of heaviest withdrawal as much

as 10 feet in the Oviedo area and 4 to 6 feet in the Sanford area. A com-

parison of measurements made in 1937 with ones made recently shows that, in

areas where withdrawals have increased, the artesian pressure head has

declined slightly, whereas, in areas where the withdrawals are unchanged or

have decreased, the pressure head has remained about the same.

The chloride content of water from artesian wells in Seminole County

ranges from less than 10 parts per million (ppm) in the recharge areas

around the towns of Lake Mary and Geneva to more than 5,000 ppm in the area

adjacent to Lake Harney. In the truck-farming areas, near Sanford and Oviedo,

the chloride content ranges from about 25 ppm to slightly more than 1,500 ppm.

A comparison of chloride analyses made in 1937 with those made recently shows

that there has been little or no change in the chloride content of the

artesian water in most of the county.


INTRODUCTION


Salt-water encroachment is undoubtedly the problem of most concern to

users of ground water in Florida. This is a problem in many coastal areas

where water levels are lowered excessively by heavy pumping. It is a

problem also in some inland areas where the water-bearing formations contain

salty water at relatively shallow depths. Among the coastal areas where wells

have become contaminated with salt water are Pinellas County and the Miami

area of Dade County. Inland areas where wells are likely to become con-

taminated with salt water include Seminole County and the southwestern part

of Volusia County.












Much of the economy of Seminole County is based on the growing of

winter vegetables. The most important farming areas are in the lowlands

adjacent to Lake Monroe and Lake Jessup, where adequate supplies of water

are available from the natural flow of artesian wells. In parts of the

farming areas, wells yield relatively salty water. Also, locally the

artesian pressure has declined as a result of the heavy withdrawal of

water for irrigation and vegetable packing. This decline has resulted in

a decrease in the area of artesian flow, and caused the use of pumps on

wells that had previously produced an adequate supply of water by natural

flow. It may lead also to contamination of the existing supplies with

salty water from the formations that underlie the producing aquifer.

Recognizing this possibility, the Board of County Commissioners of Seminole

County requested the United States Geological Survey and the Florida

Geological Survey to make an investigation of the ground-water resources

of the county. In response to this request, an investigation was begun in

October 1951 by the U. S. Geological Survey and the Florida Geological

Survey in cooperation with the Board of County Commissioners of Seminole

County and the City of Sanford.

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

geology and ground-water resources of the county with special emphasis on

the problems associated with declining water levels and salt-water

contamination. This report reviews briefly the progress of the investigation

through February 1954. The major phases of the investigation include the

following:











(1) An inventory of wells to determine their number and distribution,

their depths and diameters, their yields and artesian pressure, and other

pertinent information.

(2) A study of artesian pressure to determine the seasonal fluctuations

and progressive trends. This study will include mapping the height to which

water will rise in wells in the county.

(3) A study of water quality based on chemical analysis of samples

from selected wells.

(4) Collection of data on the use of water in order to arrive at an

estimate of the total quantity of ground water being withdrawn.

(5) Studies to locate the water-bearing zones and to determine the
water-transmitting and water-storing capacities of the artesian aquifer.

(6) Geologic studies to determine the thickness, character, and extent

of the different geologic formations.

(7) A study of the shallow, nonartesian aquifer to determine the

quantity and quality of water available from this source.

Previous Investigations

The geology and ground-water resources of Seminole County are

described in several reports published by the Florida Geological Survey,

the Florida Academy of Sciences, and the United States Geological Survey.

A report by Matson and Sanford (1913, p. 376-381) contains a brief

discussion of the geology and ground-water resources of Orange County which,

at that time, included the area that is now Seminole County. A report by

Sellards and Gunter (1913, p. 113) contains information on the wells in

Seminole County.











As part of a general investigation of the ground-water resources of

the State, Stringfield (1934) made a brief investigation of the ground-

water resources of Seminole County in the early thirties. The geology

and'ground water of Seminole County also is discussed by Stringfield

(1936, p. 135-136, 162, 174, and 188) in a report on the artesian water

in the Florida Peninsula. This report includes a map showing the area of

artesian flow, a map showing the areas in which the artesian water contains

more than 100 ppm of chloride, and the first published map of the piezometric

surface of the principal artesian aquifer. A study of the artesian water

supply and geology of Seminole County was made by Stubbs. His report (Stubbs,

1937, p. 24-36) includes two maps of the piezometric surface and a map

showing the areas of artesian flow. Stubbs' report also contains a discussion

of the different formations that underlie the county. As a part of his work

in the county, Stubbs periodically measured the water levels in selected

wells and analyzed the chloride content of water samples collected from

selected wells. 2/



2/ Unpublished records of Sidney A. Stubbs and Irving Feinberg in the
files of H. James Gut, Sanford, Fla.


A report by Unklesbay (1944), describing ground-water conditions in

Orlando and vicinity, includes records of three wells and one spring in

Seminole County. The geology of the State, including the formations in

Seminole County, is described in a report by Cooke (1945, p. 225).

A report by Ferguson and others (1947, p. 149-154) contains descriptions

of three of the largest springs in the county and chemical analyses of their










waters. Chemical analyses of water from wells in Seminole County are

contained in reports by Collins and Howard (1928, p. 228) and Black and

Brown (1951, p. 104).


GEOGRAPHY


Seminole County is in the east-central part of the Florida Peninsula

(see fig. 1). The area of the county is 321 square miles or 205,440 acres.

The mean temperature in the area is about 720F, according to the records of

the United States Weather Bureau. The average annual rainfall is about

50.5 inches.

The topography of Seminole County may be divided into two types: a

flat lowland, characteristic of the area adjacent to Lake Monroe in the

vicinty of Sanford; and hilly uplands, characteristic of the area in the

vicinity of Lake Mary.

The level lowland includes the area ranging from a few hundred feet

to more than 2 miles wide adjacent to the Wekiva and St. Johns rivers,

Lake Jessup, and Econlockhatchee Creek. Altitudes within this area range

from about 7 feet above sea level near the St. Johns River to about 25 feet

above sea level where the area merges into the hilly upland.

The hilly upland includes the remainder of the county. The surface

features of this area include numerous sand hills, a few relatively level

areas, and numerous lakes. Many of the lakes were probably formed by

the collapse of the surface deposits into caverns formed by solution of the

underlying limestone. Altitudes in this area range from about 25 feet,

where the area adjoins the level lowlands, to about 100 feet in the

vicinity of Altamonte Springs.


























































Figure 1. Map of Florida showing location of Seminole County.











10










The level lowlands and some small areas of the hilly uplands are drained

by the St. Johns River and its tributaries, which include Lake Jessup, the

Wekiva River, and Econlockhatchee Creek. The remainder of the hilly uplands

are drained through lakes and sinkholes into the limestone aquifer.

According to the Florida State Marketing Bureau's annual fruit and

vegetable report for the 1952-53 season (Scruggs and Scarborough, 1953)

Seminole County, with a total of 8,575 acres under cultivation, ranked

seventh among the counties of the State in the growing of vegetables. Thus,

although Seminole is the fourth smallest county in the State, it ranks high

in agricultural production. The county ranks second in the growing of

celery, is tied with St. Johns County for second place in the production of

cabbage, and ranks seventeenth in the production of citrus fruits, having

7,829 acres planted in groves. The county's large production of vegetables

is due principally to the availability of adequate supplies of water from

the natural flow of relatively shallow wells.


GEOLOGY


Only a few sets of the cuttings collected from wells drilled in the

county during the current investigation have yet been studied. Therefore,

only a generalized description of the subsurface geology will be included

in this interim report.

A generalized cross section showing the formations penetrated by water

wells is shown in figure 2. As may be seen from the figure the lowermost

formation penetrated by water wells in Seminole County is the Lake City

limestone of early middle Eocene age. However, only a few wells have been

drilled into this formation because adequate supplies of water can generally


-11-










waters. Chemical analyses of water from wells in Seminole County are

contained in reports by Collins and Howard (1928, p. 228) and Black and

Brown (1951, p. 104).


GEOGRAPHY


Seminole County is in the east-central part of the Florida Peninsula

(see fig. 1). The area of the county is 321 square miles or 205,440 acres.

The mean temperature in the area is about 720F, according to the records of

the United States Weather Bureau. The average annual rainfall is about

50.5 inches.

The topography of Seminole County may be divided into two types: a

flat lowland, characteristic of the area adjacent to Lake Monroe in the

vicinty of Sanford; and hilly uplands, characteristic of the area in the

vicinity of Lake Mary.

The level lowland includes the area ranging from a few hundred feet

to more than 2 miles wide adjacent to the Wekiva and St. Johns rivers,

Lake Jessup, and Econlockhatchee Creek. Altitudes within this area range

from about 7 feet above sea level near the St. Johns River to about 25 feet

above sea level where the area merges into the hilly upland.

The hilly upland includes the remainder of the county. The surface

features of this area include numerous sand hills, a few relatively level

areas, and numerous lakes. Many of the lakes were probably formed by

the collapse of the surface deposits into caverns formed by solution of the

underlying limestone. Altitudes in this area range from about 25 feet,

where the area adjoins the level lowlands, to about 100 feet in the

vicinity of Altamonte Springs.




























S


0 -

III


-50. OCALA GROUP LIU nt hU uKret MLu tH u -l

-I00I


-150


J AVON PARK LIMESTONE

SAVON PARK LIMESTONE
0 "50

- 400

W 4560

-500-
I-
-550

-600





-750.

-BOO LAKE CITY LIMESTONE T-- S KrC MAP SHM ,IT OF
EODW SECTOnH
"050

-900

-950
1000-
SSCALE i1 MILES A SEMI.E COU.nTY
-1050-






Figure 2. Generalized geologic section showing the formations penetrated by
wells in Seminole County.


_ ~___ ___ ~~__~_










The level lowlands and some small areas of the hilly uplands are drained

by the St. Johns River and its tributaries, which include Lake Jessup, the

Wekiva River, and Econlockhatchee Creek. The remainder of the hilly uplands

are drained through lakes and sinkholes into the limestone aquifer.

According to the Florida State Marketing Bureau's annual fruit and

vegetable report for the 1952-53 season (Scruggs and Scarborough, 1953)

Seminole County, with a total of 8,575 acres under cultivation, ranked

seventh among the counties of the State in the growing of vegetables. Thus,

although Seminole is the fourth smallest county in the State, it ranks high

in agricultural production. The county ranks second in the growing of

celery, is tied with St. Johns County for second place in the production of

cabbage, and ranks seventeenth in the production of citrus fruits, having

7,829 acres planted in groves. The county's large production of vegetables

is due principally to the availability of adequate supplies of water from

the natural flow of relatively shallow wells.


GEOLOGY


Only a few sets of the cuttings collected from wells drilled in the

county during the current investigation have yet been studied. Therefore,

only a generalized description of the subsurface geology will be included

in this interim report.

A generalized cross section showing the formations penetrated by water

wells is shown in figure 2. As may be seen from the figure the lowermost

formation penetrated by water wells in Seminole County is the Lake City

limestone of early middle Eocene age. However, only a few wells have been

drilled into this formation because adequate supplies of water can generally


-11-







be obtained from the overlying formations. The Lake City limestone consists

generally of alternating layers of dark-brown and chalky limestone. In

some areas, it has been altered to dolomitic limestone and dolomite. The

water from the Lake City is somewhat less mineralized than the water from

the overlying formations in areas where these formations do not contain

salty water. This may be due to the fact that the formation contains an

appreciable percentage of dolomite or dolomitic limestone which is less

soluble in water than pure limestone.

The principal source of ground water in the vicinity of Sanford is the

Avon Park limestone of late middle Eocene age. It consists of chalky lime-

stone ranging in color from white to buff. The formation has been irregularly

dolomitized since deposition, although the original structures of the rock are

commonly preserved. The Avon Park is the first limestone penetrated by wells

in the north-central part of the county, and as it is a highly productive

source of water, many of the wells in the north-central part of the county

draw from it exclusively.

Prior to work in Levy and Citrus Counties by Vernon (1951, p. 156-171)

all the deposits of late Eocene age in Florida were referred to the Ocala

limestone (Cooke, 1945, p. 53-62). On the basis of differences in the

fossil content and lithology of these deposits Vernon restricted the name

Ocala limestone to the upper part and placed the lower part in the Moodys

Branch formation. He further subdivided the Moodys Branch formation into

the Williston member at the top and the Inglis member at the bottom. Recently,

Puri (1953, p. 130) changed the name of the Ocala limestone (restricted) to

Crystal River formation and raised the Williston and Inglis members of the


-13-







Moodys Branch to the rank of formations. These three formations, the

Crystal River, Williston, and Inglis, are now collectively referred to as

the Ocala group by the Florida Geological Survey.

The Ocala group unconformably overlies the Avon Park limestone in all

except the north-central part of the county, where it is absent. The Ocala

group is about 75 feet thick in the southern part of the county and thins

toward the north. It consists of white to cream chalky limestone in the

upper part and cream to buff fragmental limestone and dolomitic limestone

in the lower part. It is highly fossiliferous and locally is composed

almost entirely of foraminiferal shells. The Ocala group constitutes one

of the most productive zones of the limestone aquifer, and hundreds of

irrigation and domestic wells draw from it exclusively.

The Hawthorn formation of middle Miocene age consists of beds of blue

to gray calcareous clay, alternating with beds of white to gray sandy

limestone containing numerous grains of black to cream phosphate rock

and fragments of chert. The beds of sandy limestone of the Hawthorn yield

small quantities of water to a few wells. However, because the Hawthorn

includes beds of clay, having low permeability, it serves as an effective

confining bed for the artesian water in the underlying limestones.

The Hawthorn has been removed by erosion in the northern part of the

county. Here, a deposit consisting of sticky blue clay in the upper part

and sandy shell at the base overlies the Hawthorn formation where it is

present and overlies the limestones of Eocene age where the Hawthorn is

absent. Stubbs (1937, p. 30-31) and Cooke (1945, P. 225) thought that

these deposits were of Pliocene age and placed them in the Caloosahatchee

marl. Vernon (1951) in figures 13 and 33 placed these beds in the upper


-14-









Miocene in geologic sections and contoured beds. Recent studies in other

parts of the State appear to confirm the age assigned to these deposits

by Vernon. As no attempt has been made during the current investigation

to determine the correct age of these deposits, they are referred to in

this report as deposits of Pliocene or late Miocene age.

The bed of sandy shell in the lower part of these deposits yields small

to moderate quantities of water to wells, and many wells draw only from this

bed. Most wells, however, are open to this bed and the limestone beneath it

and draw water from both sources. Pressure measurements and chemical analyses

indicate that the pressure head and chemical character of the water in this

bed are essentially the same as that of the water in the underlying limestones.

In view of this, it appears probable that there is circulation of water be-

tween the bed of sandy shell and the limestones of Eocene age.

The county is underlain from the surface to as much as 25 to 50 feet by

deposits of Pleistocene and Recent age. These deposits consist predominantly

of sand except in the vicinity of lake basins and swamps, where they consist

of sandy peat. In the area adjacent to the St. Johns River, in the eastern

part of the county, these deposits contain some shelly sand and thin beds of

clay. One notable feature of the Pleistocene and Recent deposits is the

presence of a layer of sand, generally less than 2 feet thick, whose grains

have been cemented together with iron oxide and other cementing agents. This

layer, referred to locally as hardpan, underlies most of the level lowlands

at a depth of 3 to 5 feet. Because this layer of hardpan retards the downward

percolation of water and thereby bends to retain water in the soil, it makes

possible the local practice of irrigating through drain tile buried about 3


-15-








feet beneath the surface. The Pleistocene and Recent deposits serve as the

source of supply for a few driven wells equipped with screens. The water

from these deposits is generally low in mineral content.


GROUND WATER


Ground water is the subsurface water that is in the zone of saturation,

which is the zone In which all the pore spaces are completely filled with

water under positive hydrostatic head. The water in the zone of saturation

is derived from rain that falls on the earth's surface. Not all the rain

falling on the surface reaches the zone of saturation, however. Part of it

returns to the atmosphere by evaporation and by the transpiration of plants

and part of it enters lakes, streams, and other open bodies of water and

becomes surface water. Only the water in the zone of saturation--ground

water--is available to supply wells and springs.

Water in the zone of saturation moves laterally under the influence

of gravity toward places of discharge, such as wells, springs, surface

streams, or the ocean. Ground water may occur under either water-table

(nonartesian) conditions or artesian conditions. Where the ground water is

unconfined and its surface is free to rise and fall, it is said to be under

water-table conditions. The upper surface of unconfined ground water is called

the water table. Where the water is confined, as where it completely fills a

permeable bed that is overlain by a relatively impermeable bed, its surface is

not free to rise and fall, and it is said to be under artesian conditions.

Technically, the term "artesian" is applied to ground water that is confined

under sufficient pressure to rise above the top of the permeable bed that con-

tains it, but not necessarily to or above the land surface.








A formation in the zone of saturation that is permeable enough to

yield water in a usable quantity to wells and springs is called an aquifer

or water-bearing formation. Areas in which aquifers receive replenishment

from infiltration are called recharge areas. Water-table aquifers are

usually exposed at the land surface and receive recharge over most of their

expanse, whereas artesian aquifers generally receive most of their recharge

in areas where the confining beds are discontinuous or absent.

Water-Table Aquifer

Ground water in Seminole County occurs under both water-table and

artesian conditions. The water in the blanket of surficial sands of

Pleistocene and Recent age is under water-table conditions in all parts of the

county except in a few small areas in which the sands are overlain by thin beds

of peat or clay. Water from wells drawing from these sands is used mainly for

domestic supplies, although a few such wells in the vicinity of Sanford are used

to irrigate lawns and gardens. Wells that draw from the water-table aquifer

generally are equipped with hand pumps, although a few, used for irrigating lawns

and gardens, are equipped with electric pumps. The number of wells in the

county drawing from sands of Pleistocene and Recent age probably does not

exceed 400.

The water-table aquifer is replenished by rain falling on the county.

In addition to this natural recharge, the aquifer probably receives recharge

also in the truck-farming areas as a result of the slow percolation of irrigation

water downward through the hardpan. Water is lost from the aquifer by natural

discharge through springs and seeps into the lakes and streams, by downward

percolation into the artesian aquifer in the nonflowing areas, and by with-

drawal from wells. Water from the water-table aquifer generally contains about


-17-







50 ppm of dissolved solids in those areas in which the water in the aquifer

has not been contaminated by relatively highly mineralized artesian water.

In a few areas the water contains an excessive amount of iron, which stains

clothes, porcelain fixtures, and kitchen utensils.

Artesian Aquifer

The principal source of water in Seminole County is an artesian

aquifer, that forms a part of the principal artesian aquifer of the Florida

Peninsula and adjacent area. The aquifer in Seminole County is composed of

the beds of sand and shell in the lower part of the deposits of Pliocene or

late Miocene age, and the limestone formations of middle and late Eocene age.

It appears probable, also, that permeable beds near the bottom of the Hawthorn

formation, at least in the southwestern part of the county, may be a part of

the artesian aquifer. All these deposits will be referred to collectively in

this report as the artesian aquifer. It should be pointed out, however, that

the differences in static head, chloride content, and temperature of water

at different depths in some partsof the county suggest that impermeable beds

may be continuous over large areas, and that the Eocene limestones consist of

several relatively thin aquifers rather than one thick aquifer.

The height to which water will rise in an artesian well is called the

artesian pressure head. The head at any place in the artesian aquifer is

controlled in part by the head in the recharge area, which is in turn determined

by the amount of replenishment that reaches the aquifer from rainfall. Periodic

measurements of the pressure head and the water levels in wells are an impor-

tant part of a ground-water investigation.

In his investigation in the early thirties, Stringfield (1936, p. 195)

made a series of water-level measurements in selected wells in the county.









In 1937, Stubbs resumed measurements in several of the wells measured by

Stringfield and also began measurements in other selected wells. 3/ During



/ Unpublished records of Sidney A. Stubbs and Irving Feinberg in the
files of H. James Gut, Sanford, Fla.


the current investigation, measurements were resumed in many of the wells

measured by Stringfield and Stubbs, in an attempt to determine whether there

has been any progressive decline of artesian head. In addition, measurements

are being made periodically in approximately 40 other wells in order to

determine the seasonal fluctuation of the water level in different parts of

the county.

The measurements made in 1937 were referred by Stubbs to mean sea level

in order to determine the direction of movement of the artesian water and the

location of recharge and discharge areas. Therefore, before the measurements

being made currently can be compared to those made in 1937, the height of

the wells above mean sea level must be determined. As the altitudes of only

a few wells have been determined so far, it is not yet possible to arrive

at any final conclusions regarding progressive changes in water levels. It

can be stated, however, that the studies appear to show that in those areas

in which the use of water has increased,water levels have declined, but probably

no more than 5 feet. Where the use of water has remained about the same,

there appears to have been little or no change.

Piezometric Surface of the Principal
Artesian Aquifer in Florida

One of the most important parts of an investigation of ground water is

the construction of maps representing the altitude of the water levels in


-19-









wells. In the case of a water-table aquifer, such a map shows the altitude

and configuration of the water table. A map showing the altitude to which

the water levels in artesian wells will rise depicts an imaginary surface

because the water in the aquifer is confined under pressure and will rise in

wells to some height above the top of the aquifer. This imaginary surface

is referred to as a "piezometric surface."

The piezometric surface of water in the principal artesian aquifer in

Florida is shown by the contour lines in figure 3. This aquifer consists of

several limestone formations of Eocene, Oligocene, and Miocene age that act

more or less as a single hydrologic unit. Stringfield (1936, pi. 12) first

mapped the piezometric surface and described the aquifer. The shape of the

piezometric surface indicates the direction of movement of the artesian water

and the areas in which the aquifer is replenished. Water enters the aquifer

in those areas i( which the piezometric surface is high and moves in a

direction approximately perpendicular to the contour lines toward the areas

in which the piezometric surface is low. One of the most notable features

of the piezometric surface in Florida is the dome centered in Polk County,

which indicates that considerable recharge enters the artesian aquifer in

Polk County and the surrounding area.

In Polk County and also in the western part of Orange County water

enters the artesian aquifer through numerous sinkholes, filled with permeable

material, that penetrate the Hawthorn and younger formations. As shown by

the contours on the map in figure 3, the artesian water flows northeastward

from the recharge area in Polk and Orange counties into Seminole County and

the adjacent area.


-20-








feet beneath the surface. The Pleistocene and Recent deposits serve as the

source of supply for a few driven wells equipped with screens. The water

from these deposits is generally low in mineral content.


GROUND WATER


Ground water is the subsurface water that is in the zone of saturation,

which is the zone In which all the pore spaces are completely filled with

water under positive hydrostatic head. The water in the zone of saturation

is derived from rain that falls on the earth's surface. Not all the rain

falling on the surface reaches the zone of saturation, however. Part of it

returns to the atmosphere by evaporation and by the transpiration of plants

and part of it enters lakes, streams, and other open bodies of water and

becomes surface water. Only the water in the zone of saturation--ground

water--is available to supply wells and springs.

Water in the zone of saturation moves laterally under the influence

of gravity toward places of discharge, such as wells, springs, surface

streams, or the ocean. Ground water may occur under either water-table

(nonartesian) conditions or artesian conditions. Where the ground water is

unconfined and its surface is free to rise and fall, it is said to be under

water-table conditions. The upper surface of unconfined ground water is called

the water table. Where the water is confined, as where it completely fills a

permeable bed that is overlain by a relatively impermeable bed, its surface is

not free to rise and fall, and it is said to be under artesian conditions.

Technically, the term "artesian" is applied to ground water that is confined

under sufficient pressure to rise above the top of the permeable bed that con-

tains it, but not necessarily to or above the land surface.
































































EXPLANATION --
Contour lines represent opproximolely the height, in DADl
feet, to which water will rise with reference to mean seea "30
level in lightly cased wells that penetrole the principal
ortesion aquifer, 1949






... ........ ...'



Figure 3. Map of Florida showing the piezometric surface of the principal artesian
aquifer.









Although the location of the principal recharge areas for the artesian

aquifer can be determined from the map, the map is not detailed enough to

show the many small recharge areas that are known to exist. It does not

reveal, for example, that the artesian aquifer receives recharge in at least

two areas in Seminole County, which will be discussed in the following section.

Piezometric Surface in Seminole County

Although the altitudes of measuring points have not yet been determined

on a sufficient number of wells to map the piezometric surface in Seminole

County, previous work indicates that in general the flow of water in the

artesian aquifer is to the northeast (Stubbs, 1937, p. 25-26, 34). Informa-

tion obtained by Stringfield and Stubbs during their investigations indicates

that in addition to the water entering the county from the recharge area

centered in Polk County the artesian aquifer receives replenishment in the

areas around the towns of Lake Mary and Geneva. The aquifer probably receives

a small amount of replenishment in the Longwood-Altamonte Springs area also.

Although the geologic conditions under which replenishment occurs have not yet

been investigated, it appears probable that most of the replenishment is

through sinkholes filled with permeable material.

The St. Johns River and associated lakes, Palm Springs, Sanlando Spring,

Sheppard Springs, and parts of the Wekiva River are places of natural discharge

of the artesian water in Seminole County. In fact, natural discharge from the

artesian aquifer forms most of the base flow in the St. Johns River. The

magnitude of the ground-water discharge into the St. Johns River and its

tributaries is indicated by the fact that the combined discharge of the three

springs referred to above is approximately 31 million gallons a day (Ferguson

and others, 1947, p. 149-153). Wells are places of artificial discharge of the


-22-








artesian water.

As a part of recent studies in the Sanford area by the Florida

Geological Survey and by Robert M. Angas and Associates, altitudes were

determined for 35 wells. As most of these wells are between Sanford and

Lake Mary they provided adequate control for the construction of a map of

the piezometric surface of the area (see figure 4). Owing to changing rates

of replenishment and withdrawal, the piezometric surface is continuously

rising and falling and changing in configuration. Therefore, figure 4,

which was drawn from water-level measurements made in May, 1952, will only

approximately represent the piezometric surface at other times. As may be

seen from the figure, the flow of the artesian water is generally to the

northeast. The curvature of the 40-foot contour line east of the town of

Lake Mary shows the effect of the recharge in that area. The small cone of

depression south of Lake Ada is a result of the pumping of approximately

1 million gallons of water a day from the municipal well field of the city of

Sanford. The tendency of the contours to parallel the shore of Lake Monroe

is probably a result of the discharge of artesian water into the lake.

Area of Artesian Flow

Wherever the piezometric surface stands higher than the land surface,

artesian wells will flow. The areas of artesian flow in Seminole County

are shown approximately in figure 5. As may be seen from the figure, the

principal area of flow extends in an unbroken band along the Wekiva River to

the St. Johns River and along the St. Johns to a point about 2 miles east of

the outlet of Lake Jessup. From the St. Johns, the band extends down both

sides of Lake Jessup into the farming area southwest of Oviedo. East of


-23-












































































LEGEND
- Principol roods

* Observation well on which otiItude of meauring polnd
has been determined.

35.6 Elevallon of water surface In well In feet above
maon an l8vl .

SContour lInes represent Oh opproximrte height. In
fI It) above mean eno level to whloh other would
S 111ie in cooed well that penetrate he flt Imetone
q ulfer. Mey 1962 .

1/2 0 1/2

Baolt in miles


Figure 4. Map of the Sanford-Lake Mary area showing the piezometric surface.



























.5




=




a
n

















a




a

*o


-LTAMONTtFfS *^ FIRN IE


M cULUOar




S_ SEMINOLE COUNTY
-- - ORANGE COUNTY








Oviedo the area of flow extends down the valley of the Econlockhatchee Creek

into the level lowlands along the west side of the St. Johns River. The

area of artesian flow is generally 1 to 2 miles wide. However, along the

Wekiva River, in the area northwest of Paola, the area is only a few hundred

feet wide. The area is narrow also in downtown Sanford and in a small area

along the southwest shore of Lake Jessup. In addition to the principal area

of artesian flow, there is a small area of flow in a dry lake basin near

the Forest Lake Academy in the southwestern corner of the county.

The area of artesian flow was doubtless appreciably wider prior to the

agricultural development in the county. In fact, in parts of the farming

areas in the vicinity of Sanford, it was probably more than half a mile wider

than it is at present. In most of the farming areas the boundary of the area

of flow has receded out onto the level lowlands, where a decline in artesian

pressure of 1 foot results in a decrease of several hundred feet in width.

A more detailed view of the area of artesian flow between Lake Monroe

and Lake Jessup is shown in figure 6. The contours on the figure represent

the height in feet above the land surface to which water would rise in

artesian wells penetrating the top of the limestone aquifer in May, 1952.

As may be seen from the figure, wells will flow at a height of more than 15

feet above the land surface in small areas both east and west of Sanford. In

an area along the north shore of Lake Jessup wells will flow at a height of

more than 20 feet. The water-.level measurements used to draw figure 6 were

made at a time when the use of water was relatively slight. Therefore, during

times of heavy withdrawals, as during the peak of the winter growing season,

the position of the lines will shift toward Lake Monroe and Lake Jessup. In

fact, owing to continual changes in the rates of replenishment and withdrawals,


-26-



























































Figure 6. Map of the area between Lake Monroe and Lake Jessup showing the
height above the land surface to which wells will flow.








27










the contours represent only the approximate conditions at any particular

time.

Wells

One of the most important phases of any ground-water investigation is

the collection of data on the location, distribution, and construction of

wells, commonly referred to as the well inventory. Figure 7 shows the

distribution of 732 wells that have been inventoried during the investigation.

Of this total 34 draw water from the water-table aquifer and 698, of which

371 are flowing wells, draw from the artesian aquifer. The following table

shows a breakdown of the wells according to the purpose for which the water

is used.

Breakdown of the Inventoried Wells According to Use



Use of Well Number


Irrigation 313
Domestic 259
Unused 75
Industrial 28
Stock 26
Other uses 31



A breakdown of the inventoried wells according to diameter is shown in

the following table.


-28-








































































Figure 7. Map of Seminole County showing the distribution of wells that have
ben. Inventoried. 29









Diameter of Inventoried Wells


Well Diameter Number of Wells Percentage of Total
(inches)


1 1/4 36 5.2
2 337 6,.0
2 1/2 27 3.7
3 147 20.1
4 105 14 .4
5 8 1.1
6 47 6.4
8 15 2.0
Over 8 8 1.1


The relative percentage of the well of each dClameter in the tabl. would

probably remain essentially unchanged if: all the well in the county were

inventoried. As may be seen from the table, h6 percent of the inventoried

wells are 2 inches in diameter. The final report on the inveLstigation in

the county will include all the data collected on the inventori:ed wells.

Artesian wells in the county range in depth from bout 50 to 1,122 feet.

However, more than 95 percent of the artesiai well are between 7'5 tnd 250

feet in depth. The botal number of we]llu in thu county that draw water from

the artesian aquifer is estimated to be more than 411000.

The more or less uniform tIranumisi:b:ili.ty of the upper part of the

artesian aquifer in large areas of the county hau resulted in mout small-

diameter wells in the same area being finished with approximately the same

length of open hole. As a result, the yield of flowing well in any particular

area depends primarily on the (1) diameter, (2) height of the static head

above the well outlet, and (3) age and hence the extent of corrosion in the

well.

The relation between the height of the static head above the well outlet


-30-









and the yield in gallons per minute for 3-inch wells in two areas near

Sanford is shown in figure 8. The points used in constructing the two

graphs in figure 8 are shown as solid dots. Each graph was drawn as a wedge

in order to indicate the range in yield that can be expected as a result

of differences in the construction of individual wells and small differences

in the water-transmitting capacity of the aquifer in each area.

The yield of a flowing well depends primarily upon the water-transmitting

capacity of the formations penetrated by the well and the height of the

static head. One of the best methods of comparing the yield of different

wells is to compare the specific capacity--that is, the yield in gallons per

minute for each foot of drawdown. In the case of flowing wells, such as

those used to construct figure 8, the drawdown is equal to the height of the

static head above the well outlet. Therefore, the specific capacity of wells

in the northern part of Seminole County may be determined from figure 8 by

dividing the yield of the wells in gallons per minute by the static head in

feet. For wells in the area west of Sanford (see upper graph) this is found

to be about 14 gpm. The specific capacity of wells in the area south and

east of Sanford (see lower graph) is about 10 gpm, or only about two-thirds as

much as in the area west of Sanford.


SALT-WATER CONTAMINATION


Salt water is present naturally in the artesian aquifer in many areas

in Florida. Although the salty water may be derived from several sources,

in Seminole County the relatively highly mineralized water present in both the

water-table and artesian aquifers appears to be due principally to the flooding

of salty water into the aquifer during Pleistocene time when the sea stood

higher than at present. Since the last decline of sea level, fresh water


..LL-.W












6








SEMINOLE COUNTY

3-







2W 0
ISEMINOLE COUNTY




















YIELD GALLONS PER MINUTE











Figure 8. Graph showing the relation between the static head and the yield of
flowing 3-inch artesian wells in two areas in the northern part of
Se pl eCounty. --
I- / -
w I


















6 .-___5 -- O--- V---- __B_"-"--iB" "-

YIELD IN GALLONS PER MINUTE


32










entering the aquifer has been slowly diluting and flushing out the salty

water. Water samples collected from wells of different depths in the

northern and central parts of the county show that flushing has progressed

further in the upper part of the artesian aquifer than in the lower part.

Thus, the deeper wells in that area yield water with the highest salt con-

tent. One of the most important water problems facing the county is the

danger that, as withdrawals from the upper part of the aquifer are increased,

water from the lower zones will move upward and contaminate the producing

zones.

The chloride content of ground water is generally a reliable index of

contamination by salt water because about 91 percent of the dissolved-solids

content of sea water consists of chloride salts. Thus, one of the most

important phases of the investigation consists of analyzing the chloride

content of water from wells. To date water samples from 637 wells have been

analyzed and the results show that the chloride content of the water from

the upper part of the artesian aquifer ranges from about 5 ppm to more than

5,000 ppm. The lowest chloride content, 4 ppm, was determined for samples

from wells near Paola, near the southwest shore of Lake Jessup, and southeast

of Lake Mary. The highest chloride content so far determined was one of

5,440 ppm for a sample of water from a well located along the south shore of

Lake Harney. The generalized results of these analyses are shown by the

shaded areas in figure 9. As may be seen from the figure, water from the

artesian aquifer beneath most of the hilly upland areas has a chloride content

of less than 25 ppm. The relatively low chloride content of the artesian

water in this area is believed to be due to the fact that there is little


-33-




















LAKE MONROE


Sod


LEGEND



I I M M

",ae m tst


-n



3"
co
C
-I




-B











o


.
a






Co a




o




"0
aI





.a


*4


*' 1B.


VARNEY
I
(









surface runoff and the rainfall that is not returned to the atmosphere by

evaporation and transpiration must percolate downward to recharge the

artesian aquifer. The effect of this local recharge in flushing out the

salty water can be seen by the difference in chloride content of the artesian

water in the Geneva area, where it is fresh, and in the surrounding areas

where it is salty.

The lowness of the chloride content of artesian water in local recharge

areas was first noted by Stringfield (1936, pl. 16) in his investigation of

the artesian water in the Florida peninsula. After making subsequent

investigations in Seminole County and mapping 4/ the chloride content of the



V/ Unpublished map in the files of the U. S. Geological Survey.


artesian water in the county,he concluded that the lowness of the chloride

content in the Geneva area was a result of flushing by local recharge. 5/



V/ Personal Communication.


The areas in which the artesian water contains more than 26 ppm of

chloride include the northeastern half of the county, with the exception of

the hilly area around Geneva, and a narrow belt along the valleys of the

Wekiva and Little Wekiva Rivers. Within the heavily shaded parts of this

area (see figure 9) the water would have a distinctly salty taste. In

relatively large parts of this area the chloride content of the water exceeds

1,000 ppm and is unsuitable for many uses, including the irrigation of certain

crops (Westgate, 1950, p. 116-123).


-35-








Analyses of water samples collected periodically at the times when the

measurements of artesian pressure were made indicate that the chloride con-

tent of the artesian water varies with changes in artesian pressure.

Decreases in artesian pressure are accompanied by increases in the chloride

content, and vice versa, as shown in figures 10 and 11. Figure 10 includes

data collected by Stubbs in 1937 and Feinberg in 1939, as well as data

collected during the present investigation. This figure shows a change in

chloride content of 25 to 50 ppm with each change in head of 1 foot in well

31, which is about 2 miles southwest of Sanford. The graph for this well

also shows an increase in chloride content of about 100 ppm since 1937. This

increase is probably a result of the increased withdrawal of water in the area

in which the well is located.

Figure 11 shows the changes in chloride content of water from two wells

near Oviedo. A comparison of the graph for well 167 with that for well 31,

in figure 10, indicates that the chloride content of the water in the Oviedo

area changes less in response to changes in pressure than that in the Sanford

area. This may be due to the fact that the upper part of the aquifer in the

Oviedo area is underlain by a relatively impermeable zone which retards the

upward movement of salty water from the lower zones of the aquifer.


SUMMARY AND CONCLUSIONS


The following progress has been made on each of the phases of the

investigation outlined in the introduction:

1. Information has been obtained on more than 700 wells in the well

inventory. In addition, the location of approximately 1,000 other wells have

been plotted on aerial photographs.

2. Periodic water-level measurements are being made in more than


-36-















1939


O0
/


-'0C C-____


Figure 10. Graph showing the relation between the chloride content and the
artesian pressure head in well 31, 2 miles southwest of Sanford.


-I
w
w
J36

4
U)

z

234


o0
/ \










1952 1953


z WELL 159, 2 1/2 miles north of Oviedo
-i











2 WATER LEVEL 0 1


1000 WELL 167, 2 1/2 miles northeast of Oviedc
10
S250 -- 0- T N:-" --oo-o--









s0








0
i 20 CHLORIDE CONTENT OF WATER










II
1000 WELL 167, 2 1/2 miles northeost of Oviedc











0
pressure head in two wells near Oviedo.
i 90 CHLORIDE CONTENT OF WATER




jW 6 -- --%/-


-0-*wo


W WATER LEVEL


Figure 11. Graph showing the relation between the chloride content and artesian
pressure head in two wells near Oviedo.


1954











70 wells.

3. The chloride content of water samples from 637 wells has been

determined during the investigation. Periodic chloride analyses have been

made on samples from about 20 wells for a period of more than 2 years in

order to determine the relation between changes in chloride content and

changes in water levels.

4. Chemical analyses of water samples from about 100 wells have been

made in order to determine the chemical content of the water in different

parts of the county.

5. Rock cuttings from about 15 wells have been collected for use in

preparing geologic structure maps.

6. Recording gages have been installed on two wells to determine

progressive trends of water levels and rapid fluctuations that cannot be

detected by means of periodic measurements.

As the investigation is incomplete at this time, available data are not

adequate for final conclusions to be reached concerning the ground-water

problems confronting the county. However, the results obtained so far may be

summarized as follows:

1. The principal source of ground-water supply in Seminole County is a

thick section of limestone that underlies the county at depths ranging from

75 to 150 feet. This limestone is overlain by a deposit consisting of 50 to

75 feet of relatively impermeable clay which confines the water in the lime-

stone under pressure. Overlying the clay deposit is from 25 to 75 feet of

sand and sandy peat. Small supplies of water are obtained in some parts of the

county from screened wells penetrating these sand deposits.


-39-











2. Most of the ground water in Seminole County probably is derived

from rain falling on the recharge areas in Polk and Orange counties, although

there are important recharge areas in Seminole County also. The local areas

of recharge are in the vicinity of the towns of Lake Mary and Geneva, and in

the southern part of the county. Natural discharge of ground water in

Seminole County is through large artesian spring such as Sanlando, and through

springs and seeps in the bottom of Lake Jessup, and the St. Johns and Wekiva

rivers.

3. Records of the seasonal fluctuations of artesian pressures show that

they are lowered as much as 10 feet in parts of the Oviedo area during the

periods of heaviest withdrawal. In the Sanford area the seasonal fluctuations

are between 4 and 6 feet. A comparison of water-level measurements made in

1937 with measurements made during the present investigation shows that, where

withdrawals have been increased, water levels have declined only slightly. In

those areas in which there has been no increase in withdrawals, as for example

in the western part of Sanford, the water levels appear to have remained

relatively unchanged or to have risen slightly.

4. The chloride content of water from artesian wells in Seminole County

ranges from less than 10 ppm near the recharge areas to more than 5,000 ppm

in the area adjacent to Lake Harney. In the Sanford-Oviedo farming area,

the chloride content ranges from about 25 ppm to slightly more than 1,500 ppm.

A comparison of chloride analyses made in 1937 with those made during the

current investigation shows that, in general, the chloride content of the

artesian water has remained about the same. An exception to this is a small

area .southwest of Sanford where the chloride content appearsto have increased


-40-










as much as 100 ppm. The seasonal variation in chloride content in response

to fluctuations in artesian pressure in the farming areas near Sanford is

from 50 to 150 ppm. In the farming areas near Oviedo the seasonal change is

generally less than 50 ppm. Chloride analyses of water samples from wells

of different depths also show that the chloride content increases with depth.

Future studies in Seminole County will include:

1. An inventory of additional wells in the more sparsely settled areas.

2. Determinations of the altitudes of measuring points on water-level

observation wells for use in mapping the piezometric surface.

3. Pumping tests to determine the water-transmitting and water-storing

capacity of the artesian aquifer.

4. The exploration of selected wells with a current meter to determine

the position and thickness of the producing strata. Deep-well sampling

equipment will be used also to determine ;he quality of water in each zone.

5. A study of well cuttings and electric logs to determine the position

and thickness of the different geologic formations.

6. Collection of data on the use of ground water in order to arrive at

an estimate of the annual withdrawal. This information will be used in

conjunction with data on water levels and the water-transmitting and storing

capacity of the aquifer to predict the effect on water levels of increased

withdrawals.


-41-








Analyses of water samples collected periodically at the times when the

measurements of artesian pressure were made indicate that the chloride con-

tent of the artesian water varies with changes in artesian pressure.

Decreases in artesian pressure are accompanied by increases in the chloride

content, and vice versa, as shown in figures 10 and 11. Figure 10 includes

data collected by Stubbs in 1937 and Feinberg in 1939, as well as data

collected during the present investigation. This figure shows a change in

chloride content of 25 to 50 ppm with each change in head of 1 foot in well

31, which is about 2 miles southwest of Sanford. The graph for this well

also shows an increase in chloride content of about 100 ppm since 1937. This

increase is probably a result of the increased withdrawal of water in the area

in which the well is located.

Figure 11 shows the changes in chloride content of water from two wells

near Oviedo. A comparison of the graph for well 167 with that for well 31,

in figure 10, indicates that the chloride content of the water in the Oviedo

area changes less in response to changes in pressure than that in the Sanford

area. This may be due to the fact that the upper part of the aquifer in the

Oviedo area is underlain by a relatively impermeable zone which retards the

upward movement of salty water from the lower zones of the aquifer.


SUMMARY AND CONCLUSIONS


The following progress has been made on each of the phases of the

investigation outlined in the introduction:

1. Information has been obtained on more than 700 wells in the well

inventory. In addition, the location of approximately 1,000 other wells have

been plotted on aerial photographs.

2. Periodic water-level measurements are being made in more than


-36-









REFERENCES

Black, A. P.
1951 (and Brown, Eugene) Chemical character of Florida's waters,
l L: Florida State Bd. of Cons., Water Survey and Res.
Paper 6.

Brown, Eugene (see Black, A. P.)

Collins, W. P.
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.

Ferguson, G. E.
1947 (and Lingham, C. W., Love, S. K., and Vernon, R. O.) Springs
of Florida: Florida Geol. Survey Bull. 31.

Gunter, Herman (see Sellards, E. H.)

Howard, C. S. (see Collins, W. P.)

Lingham, C. E. (see Ferguson, G. E.)

Love, S. K. (see Ferguson, G. E.)

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

Puri, Harbans S.
1953 Zonation of the Ocala group in Peninsula Florida (abstract):
Jour. Sed. Petrology, vol. 23.

Sanford, Samuel (see Matson, G. C.)

Scarborough, E. F. (see Scruggs, F. H.)

Scruggs, F. H.
1953 (and Scarborough, E. F.) Annual fruit and vegetable report;
production, transportation, and marketing analysis: Florida
State Marketing Bureau, Jacksonville, Fla.

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

Stringfield, V. T.
1934 Ground water in Seminole County, Florida: Florida Geol. Survey
Rept. Invest. 1.










1936 Artesian water in the Florida Peninsula: U. S. Geol. Survey
Water Supply Paper 773-C.

Stubbs, Sidney A.
1937 A study of the artesian water supply of Seminole County,
Florida: Proc. Florida Acad. Sci., vol. 2.


Unklesbay,
1944


Vernon, R.
1951


A. G.
Ground-water conditions in Orlando and vicinity, Florida:
Florida Geol. Survey Rept. Invest. 5.


0. (see also Ferguson, G. E.)
Geology of Citrus and Levy counties, Florida:
Survey Bull. 33.


Florida Geol.


Westgate,
1950


P. J.
Effects of soluble soil salts on vegetable production at
Sanford: Proc. Florida State Hort. Soc., Oct.-Nov. 1950.


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