<%BANNER%>
HIDE
 Title Page
 Front Matter
 Table of Contents
 Main














Ground water investigations in Florida ( FGS: Bulletin 11 )
CITATION SEARCH THUMBNAILS PDF VIEWER PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00000441/00001
 Material Information
Title: Ground water investigations in Florida ( FGS: Bulletin 11 )
Series Title: ( FGS: Bulletin 11 )
Physical Description: Book
Creator: Stringfield, V. T.
 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: ltqf - AAA1691
ltuf - AKM4749
alephbibnum - 002036989
System ID: UF00000441:00001

Downloads

This item has the following downloads:

PDF ( 10 MBs ) ( PDF )


Table of Contents
    Title Page
        Page 1
        Page 2
    Front Matter
        Page 3
    Table of Contents
        Page 4
    Main
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        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
Full Text







FLORIDA STATE GEOLOGICAL SURVEY

HERMAN GUNTER, State Geologist





BULLETIN No. 11






GROUND WATER INVESTIGATIONS IN
FLORIDA

By V. T. STRINGFIELD





Prepared in cooperation between the Florida State Geological Survey and
the United States Geological Survey





TALLAHASSEE, FLORIDA
1933































Published April 10, 19



















Published April 10, 1933


4,*
44 4
4. 4 4 4


44 4 4'
6 ~ 4 . 4 444444












LETTER OF TRANSMITTAL


To His Excellency, Hon. David Sholtz,
Governor of Florida.
Sir:
I have the honor to submit herewith for publication as
Bulletin No. 11 of the Florida Geological Survey a paper
entitled, "Ground Water Investigations in Florida" by
V. T. Stringfield of the United States Geological Survey,
which briefly describes the cooperative investigations car-
ried on in Manatee, Pinellas, Orange, Seminole and Duval
counties in 1930 and 1931. In the 23rd-24th Annual
Reports of the Florida Survey will be found detailed re-
ports covering the results of a survey of underground
waters in Sarasota County. These reports will give
needed information to the citizens of the State concern-
ing this important resource.
Respectfully,
HERMAN GUNTER,
State Geologist.
Tallahassee, Florida,
March 31, 1933.


4 y905







CONTENTS
Page
Introduction ................... .............. ............................ ........ 5
M anatee County ....................... .... .............................. 6
G geography ......................................................... 6
G eology ........................................................... 7
Ground water ............. ...................... ................. 7
Source ............. ....................... ................... 7
Public supplies ......................... .... ............8
Irrigation supplies ................ .... ....... .. ........ 8
Quality of water ........... ......... ........ ....... ......... 9
Artesian conditions ................... ........... ....... 9
Area of artesian flow ................................................... 9
Recharge .................................... .................. 10
Loss of head...... ............ ......... .................. 10
Contamination of wells by salt water.............................. 11
Conclusions and problems to be investigated........................ 11
Pinellas County and northwestern part of Hillsborough County.. 13
Geography ............ ............... ............. ..... 13
Geology ... ................................... ............ 13
Ground water .......... ................... ................. ........ 14
Source ............................................................ ..... ......... 14
Consum option .......................................... ....... 14
Q quality of w ater .............. ........ ....... .. ................... 14
Artesian conditions ..................................... ........... 15
R ech arg e ............................... ............. ............ 1 5
Conclusions and problems to be investigated......................... 16
Orange County .................... ....................................... 17
Geography ....... ... .................... ........... 17
Geology ..................................................... ...... ..... 18
Ground-water conditions of the Ocala limestone............... 19
Drainage w ells .................. ............. ... .... .... ................ 21
Sanitary problem of drainage wells.................................. 22
Conclusions and problems to be investigated.................. 23
Sem inole County ..... .. .......... ... .. .. .. .. .... ........ .. .............. 25
G geography .................... ....................................... 25
Geology ... .............................. ....... .......... 25
Duval County ... ............................. ...... .......... 26
Geography ................................................. 26
Geology ... ............................. ....... ........... 26
G round w ater ......................................................... 27
S ou rce ................................... ................... . ......... 2 7
Consum option ............... ...................................... ........ 28
Quality of water................. ........ .. .... .... ............ ........ 28
Artesian head ..................................... .............. .. 29
Fluctuations of artesian head.......................................... 31
R charge ......................................................... ... 31
Conclusions and problems to be investigated.................. 32









GROUND-WATER INVESTIGATIONS IN FLORIDA


(In cooperation between the Florida State Geological Survey and the United
States Geological Survey)

By V. T. STRINGFIELD



INTRODUCTION

In 1930, through a cooperative agreement between the
Florida State Geological Survey and the United States
Geological Survey, provisions were made for an intensive
investigation of the ground-water resources of Florida,
especially to determine the safe yield of the water-bear-
ing formations in localities where such suppliesare
especially valuable.
Field investigations were made during the summers of
1930, 1931, and 1932. Most of the work was carried on
in Sarasota, Manatee, Orange, Duval, and Pinellas coun-
ties, but some observations were also made in Seminole,
Hillsborough, and Charlotte counties. The plan adopted
for the field work was to make observations in a number
of counties and to carry on more detailed work in one or
more of these counties. Thus, as the detailed work
advances it can be extended while observations in all of
the areas are continued. This plan is especially desirable,
as observations in regard to such factors as the seasonal
changes in artesian head, consumption of water, and
quality of water must necessarily be extended over a
period of several years in order to arrive at definite
conclusions.
Information was obtained in regard to wells, the water-
bearing formations, the quality of water, and the general
geologic conditions that govern the occurrence of the
ground water. Measurements were made periodically on
numerous observation wells. Automatic water-stage re-







6 FLORIDA GEOLOGICAL SURVEY-BULLETIN ELEVEN

corders, which give continuous records of the fluctuations
of the water levels, were installed on two non-flowing
wells, and recording pressure gauges were installed on
three flowing wells that were shut down and not in use.
Altitudes of some of the observation wells were deter-
mined, so that the height of water in them with reference
to sea level may be accurately determined.
The preliminary work done during the summer of 1930
has been described briefly in previous publications,* and
reports on the work in Sarasota County have been pre-
pared.t The following account describes briefly the
investigation in Manatee, Pinellas, Orange, Seminole, and
Duval counties in 1930 and 1931.




MANATEE COUNTY
.~~s-.r-.
GEOGRAPHY

Manatee County is on the Gulf of Mexico, in the south-
western part of the Florida Peninsula. It has an area
of 823 square miles and a population in 1930 of 22,502.
The largest towns are Bradenton, Manatee, and Palmetto,
located on the Manatee River near the coast. In 1930
Bradenton, the county seat, had a population of 5,986,
Manatee 3,219, and Palmetto 3,043. The other towns
in the area had less than 1,000 each.
The western part of the county is comparatively level.
The altitudes range from sea level to about 40 feet, but
much of that part of the county is less than 30 feet above
sea level. Most of the eastern part of the county lies
more than 40 feet above sea level. In the northeastern
part the surface rises in some places to more than 100
feet.
Thompson, D. G., and Stringfield, V. T., Ground-water resources of Florida:
Florida State Geological Survey Press Bull. No. 13, April 4, 1931.
Thompson, D. G., Problems of Ground-water supply in Florida: American
Water Works Assoc. Jour., vol. 23, No. 12, pp. 2085-2100, Dec., 1931.
t Stringfield, V. T., Ground-water resources of Sarasota County, Florida, and
Exploration of Artesian Wells in Sarasota County, Florida: Florida Geol. Survey
Twenty-third-Twenty-fourth Ann. Repts., 1933.






GROUND WATER INVESTIGATIONS IN FLORIDA


The principal streams of Manatee County are the Man-
atee River, which rises in the eastern part of the county
and flows west into'Tampa Bay, and the Myakka River,.
which rises in the eastern part of the county and flows
southwest into Sarasota County. The Braden River,
which rises in the southwestern part of the county, is the
largest tributary of the Manatee River.

GEOLOGY

The formations underlying the surface of Manatee
County include the Ocala limestone (of Eocene age), the
Tampa limestone and Hawthorn formation (of Miocene
age), and surficial deposits of Pliocene, Pleistocene, and
Recent age.
The Ocala limestone consists chiefly of limestone and
yields water to some of the deeper wells. It lies at a
depth estimated to be about 500 to 600 feet below the
surface and crops out about 60 miles north of this c,,pty,
in Hernando and Sumter counties. The thickness of the
formation is estimated to be about 500 feet. It is under-
lain by older Eocene limestone.
The Tampa limestone, which overlies the Ocall lime-
stone, also yields water to wells. It is estimated to have
a thickness of about 150 feet. It is overlain by the
Hawthorn formation in the county and crops out in the
vicinity of Tampa. The Hawthorn formation consists of
about 400 to 500 feet of alternating beds of mall, clay,
limestone, and sand. It is exposed at or near the surface
and is overlain by younger surficial material. The largest
yields of water are obtained in the lower part of the
formation. It apparently is the most productivO water-
bearing formation of the area.

GROUND WATER-SOURCE
In Manatee County the water supplies are obtained
from wells. Most of the larger supplies are obtained
from wells 3 to 12 inches in diameter and about 50 to
1,000 feet in depth, which receive water from the Ocala






8 FLORIDA GEOLOGICAL SURVEY-BULLETIN ELEVEN

and Tampa limestones and the Hawthorn formation,
dependent upon their depths, and small domestic supplies
are obtained in the rural sections from shallow wells
ending in surficial material that overlies the Hawthorn
formation. In Bradenton water from the surficial mate-
rial is used for making ice. The casing of most of the
deeper wells does not extend more than 80 to 100 feet
below the surface. At Cortez and on Anna Maria Key
some wells require casing to a depth of about 100 feet
to keep out salt water.

PUBLIC SUPPLIES

The towns of Bradenton, Manatee, Palmetto, Ellenton,
and Anna Maria have public water supplies. All these
towns are on or near the coast. The public water supply
of Bradenton is obtained from two wells, 922 feet deep,
at the new city water plant. A well 650 feet deep fur-
nishes the public supply of Manatee. The supply of Pal-
metto comes from two wells 634 feet deep. The source
of the public supply of Ellenton is a well 800 feet deep.
Twq -nells, one 650 and the other 450 feet deep, furnish
the public supply of Anna Maria. Water of the public
supplypof Bradenton, Manatee, and Palmetto is aerated to
remove hydrogen sulphide.
The approximate average daily consumption of water
from the public supplies of the three largest towns in this
area is reported to be as follows: Bradenton, 385,000
gallons; Palmetto, 200,000 gallons; Manatee, 145,000
gallons.
IRRIGATION SUPPLIES

Manatee County is reported to have about 1,000 farms,
most of which are devoted to raising vegetables and citrus
fruits, which require irrigation. The water for irriga-
tion is obtained from wells. Many of the larger citrus
and truck growing districts are in the western part of the
county and within the area where flowing wells normally
may be obtained. It is estimated that approximately





GROUND WATER INVESTIGATIONS IN FLORIDA


1,000 wells are in use in the county for domestic and irri-
gation supplies. These wells range from about 3 to 8
inches in diameter and from approximately 250 to 700
feet in depth. Most of the wells flow by artesian pressure
and yield between 50 to 300 gallons a minute. Some of
the wells are equipped with pumps.

QUALITY OF WATER
Water from the Ocala and Tampa limestones is hard
and contains appreciable amounts of hydrogen sulphide.
The Hawthorn formation contains some water that is
hard and some that is relatively soft, with different
amounts of hydrogen sulphide. The surficial material
overlying the Hawthorn contains relatively soft water.

ARTESIAN CONDITIONS
In all the water-bearing formations in this area, except
the surficial material, the water is under artesian head.
The head of water in the Ocala or Tampa limestones and
the lower part of the Hawthorn formation is greater than
that in the upper part of the Hawthorn formation.
The artesian head ranges from a few feet to more than
40 feet above sea level. The lowest heads with reference
to sea level were observed near the coast, where large
amounts of water are being used; the highest heads are
recorded inland, where only a few wells are in use. In
most parts of the county flowing wells are not to be ex-
pected where the surface is more than 32 feet above sea
level, and near the coast the water may not rise more
than about 20 feet above sea level. Two flowing wells
near Fort Hamer have heads estimated to be about 33
feet above sea level. A flowing well at Myakka City has
a head of 40 feet or more above sea level.

AREA OF ARTESIAN FLOW
The area in which artesian flows are obtained from
wells penetrating the Ocala and Tampa limestones and
the lower part of the Hawthorn formation includes most




10 FLORIDA GEOLOGICAL SURVEY-BULLETIN ELEVEN

of the west half of the county and extends inland to the
east-central part of the county along the Manatee River
and into the southeastern part of the county along the
Myakka River.
Within the general area of artesian flow there are high
places where the water in wells will not rise quite to the
surface. One such area is a ridge on which Parrish is
located, extending north and south, about 5 miles long
and 1 mile wide, in the northern part of the county. Other
areas may be noted at Oneco and in the southeast part
of Bradenton.
In the lowest ground of the nonflowing area in the
eastern part of the county shallow wells penetrating the
Hawthorn formation may flow during wet seasons. A
few wells of this type are reported to have been developed
for use at portable sawmill sites. .In the highest localities
of the northeastern part of the county water in wells
penetrating the Ocala and Tampa limestones and the
lower part of the Hawthorn formation may stand as
much as 60 feet below the surface.

RECHARGE

The nearest intake area of the Ocala limestone is pre-
sumably about 60 miles north of Manatee County, where
the limestone is at or near the surface. Probably the
nearest intake area of the Tampa limestone is about 25
miles north of Manatee County, where it is at or near the
surface. It is believed that little or no recharge of the
Ocala and Tampa limestones takes place locally because
the formations are overlain by the Hawthorn formation,
which contains impervious members. Recharge of the
Hawthorn formation doubtless takes place locally and
in areas to the north and east where the formation is
at or near the surface.

LOSS OF HEAD
During dry seasons, when much water is required for
irrigation, the artesian head is lower than during other






GROUND WATER INVESTIGATIONS IN FLORIDA


seasons, when little water is being used. This temporary
loss of head is reported to be as much as 10 feet in some
of the areas of heavy draft. The records indicate that
there has also been permanent loss of head. During the
last few years the head in a number of wells has de-
creased as much as 10 feet.

CONTAMINATION OF WELLS BY SALT WATER
On Longboat and Anna Maria Keys and in localities
north and south of Palma Sola Bay salty water is en-
countered in wells penetrating the Hawthorn formation
at depths of about 90 to 100 feet. In the northwest part
of Palmetto two wells drilled for oil encountered saline
water at a depth of about 1,000 feet. Moreover, most
of the analyses of water from wells in the area lying
between the coast and a line extending north and south
through the east part of Manatee show higher chloride
contents than the analyses of water from wells farther
inland. This area includes most of the important farming
and trucking centers, where large amounts of ground
water are used, and also includes the wells of the public
supplies of the county. Many wells on Anna Maria Key,
the district north and south of Palma Sola Bay, Sneads
Island, Terra Ceia Island, Palmetto and vicinity, and the
district south of Oneco yield water that contains from 100
to 500 parts per million of chloride. In contrast, the
water from the wells in the eastern part of the county
contains less than 50 parts per million of chloride.

CONCLUSIONS AND PROBLEMS TO BE INVESTIGATED

In most of the area in which much water is used the
wells flow by artesian pressure. In the localities of heavy
draft the artesian head and flow of the wells are diminish-
ing as the draft increases.
Many' of the flowing wells are equipped with valves or
pipe connections that leak and thus permit waste of
water. Also some of the flowing wells in the area are en-
tirely neglected and permitted to flow at full capacity all





12 FLORIDA GEOLOGICAL SURVEY-BULLETIN ELEVEN

the time. In the northwestern part of Palmetto two wells
that were drilled in search of oil are producing water by
artesian flow. The flow of these wells lowers the head
of the artesian water in that vicinity. Moreover, the wells
are flowing salt water from a depth of 1,000 feet or more,
and analyses of water from a shallow well near them
indicate that the salt water is spreading in the higher
fresh-water bearing beds. To prevent this contamina-
tion the wells that flow salt water should be effectively
plugged.
Realizing the need of protecting the water supplies, the
Legislature of the State of Florida enacted a law in 1929
regulating the drilling and operation of wells and the
conservation of ground water in this county. Strict en-
forcement of this law will be especially valuable in the
conservation and protection of ground-water supplies in
this area. In order to reach definite conclusions relative
to the safe yield of the water-bearing formations, obser-
vations on representative wells should be continued over
a period of several years. Consumption of water during
the different seasons of the year and seasonal changes
and permanent loss of head caused by the draft of the
wells should be accurately determined. Additional
analyses of water made from time to time will be of
value in order to determine any changes in the salinity of
the water and the relation of such changes to the artesian
head. Moreover, it will be desirable to establish the
altitude of all observation wells and to collect data con-
cerning the recharge of the formations.






GROUND WATER INVESTIGATIONS IN FLORIDA


PINELLAS COUNTY AND NORTHWESTERN' PART
OF HILLSBOROUGH COUNTY

GEOGRAPHY
Pinellas County forms the peninsula between Tampa
Bay and the Gulf of Mexico and extends northward to
Pasco County. Hillsborough County lies east of Pinellas
County and borders Tampa Bay. St. Petersburg, in
Pinellas County on Tampa Bay, had a .population in 1930
of 40,425. Surface altitudes in the area covered by this
investigation (Pinellas County and the northwestern part
of Hillsborough County) range from sea level to approx-
imately 70 feet above sea level in the northeastern part
of the area. Surface streams are poorly developed, but
lakes are numerous in the northern part of the area.

GEOLOGY
The geologic formations that underlie this area include
the Ocala limestone, of Eocene age, and the Tampa lime-
stone, of Miocene age, and surficial deposits of Pleistocene
and Recent age. The Ocala limestone-a porous, almost
pure limestone-crops out north of this area in Sumter
and Citrus counties. Its thickness is not definitely known
but it is estimated to be about 500 feet.
The Ocala limestone is overlain by the Tampa lime-
stone, which is approximately 100 to 200 feet thick. The
Tampa limestone, varying somewhat in composition,
is a notable water-bearing formation of this area. The
Tampa limestone appears at or near the surface in
part of the area, but in the northern part, near Cosme,
it is covered with about 60 feet of undifferentiated mate-
rials. Outcrops occur at different places along the coast
as far south as Indian Rocks* and to the east and north
of this area, in Hillsborough, Pasco, and Hernando coun-
ties. According to Stuart Mossomt this area is on the
Cooke, C. W., and Mossom, Stuart, Geology of Florida: Florida Geol. Survey
Twentieth Ann. Rept., p. 84, 1929.
t Mossom, Stuart, A review of the structure and stratigraphy of Florida:
Florida Geol. Survey Seventeenth Rept., pp. 171-268, 1926.





14 FLORIDA GEOLOGICAL SURVEY-BULLETIN ELEVEN

southwest flank of a large anticlinal fold or arch. Data
concerning the local structure are not sufficient to out-
line definitely the attitude of the formations, but pre-
sumably they dip with a low angle to the southwest.

GROUND WATER-SOURCE
The Tampa limestone is the chief source of water sup-
plies in this area. Large quantities of water can also be
obtained from the Ocala limestone, but the water is gen-
erally harder than that from the younger overlying forma-
tions. The material overlying the Tampa limestone yields
small amounts of relatively soft water to shallow wells.

CONSUMPTION
St. Petersburg, the largest consumer of ground water in
this area, has an average consumption from its public
supply of approximately 3,000,000 gallons daily. For-
merly the supply was obtained from wells at St. Peters-
burg, but in the summer of 1930, because of the poor
quality of the water, a new supply was developed from
12 wells near Cosme, in the northwestern part of Hills-
borough County, about 30 miles north of St. Petersburg.
Ten of the new wells end in the Tampa limestone and
two of them in the Ocala limestone. Several smaller
cities and towns in the area obtain water from wells pene-
trating the Tampa limestone. Clearwater is the largest
of these. In addition to the wells used to supply the
public waterworks there are numerous wells used for
private supplies.
QUALITY OF WATER
Water from the Tampa and Ocala limestones in this
area is hard and contains varying amounts of hydrogen
sulphide. The water from the Tampa limestone gener-
ally has a hardness of about 150 parts per million and
that from the Ocala about 300 parts per million. Along
the Gulf coast and Tampa Bay in the peninsula area of
Pinellas County many of the wells produce water that is
very hard and high in chloride, the chloride content of





GROUND WATER INVESTIGATIONS IN F'ORIDA


water from some of these wells being more than 1,000
parts per million. In St. Petersburg the wells that
formerly furnished the public water supply and many of
the private wells produce water that is unsuitable, for
domestic use because of its hardness and salinity. This
condition also exists in many of the private wells on the
east shores of Tampa Bay and the wells that formerly
furnished the public water supply of the city of Tampa.
Among the wells of high salinity are included the wells
on the coast at Clearwater and Pass a Grille Beach. The
water from many of these wells was at first usable, but
as' the draft increased and the head was lowered the
salinity increased. In a number of the wells in St. Peters-
burg the salinity has increased more than 1,000 parts
per million during the last few years. There is, however,
great variation in the salinity in different wells. Thus
the water from a well penetrating the Tampa limestone
in the north part of St. Petersburg contains only about
55 parts per million of chloride. In the northeastern part
of the area covered by this report the chloride content
of much of the well water is less than 10 parts per million.

ARTESIAN CONDITIONS

The ground water of the Ocala and Tampa limestones
is under artesian head in this area. In the lower areas
along the coast and on Tampa Bay flowing wells may be
obtained, and farther inland the water will rise within a
few feet of the surface. Ocean tides affect the artesian
head of wells on the Gulf coast at Clearwater and in
Tampa near Tampa Bay. Thus two wells in Tampa were
reported to overflow only during high tide.

RECHARGE

Recharge of the ground water of the Ocala limestone
occurs chiefly where it crops out north of this area, in
Sumter, Citrus, and Marion counties. Recharge of the
Tampa limestone occurs chiefly east and north of this
area, where the formation crops out in Hillsborough,





16 FLORIDA GEOLOGICAL SURVEY-BULLETIN ELEVEN

Pasco, and Hernando counties. Presumably local re-
charge takes place in the northern part of the area,
where the Tampa limestone appears at or near the
surface.

CONCLUSIONS AND PROBLEMS TO BE INVESTIGATED

The high salinity of the water from a number of wells
in this region indicates that the limestones are contami-
nated with salt water in a part of the Pinellas Peninsula.
Apparently this contamination is confined to areas near
the coast, where the draft from the wells has lowered the
artesian head and has permitted saline water to reach
the fresh-water bearing beds. The Tampa limestone
crops out at points along the shore and may be exposed
to salt water in Tampa Bay and the Gulf of Mexico. It
is therefore possible that saline water can move inland
through limestone where the pressure from artesian head
is not sufficient to counterbalance the pressure caused by
the ocean water, which has a higher specific gravity than
the fresh Water. Although some of the wells of the
Peninsula area continue to produce water of normal hard-
ness and salinity from the Tampa limestone, any well
or group of wells producing large quantities of water is
in danger of eventual contamination by salt water.
The city of St. Petersburg now receives water from
wells northeast of the Pinellas Peninsula. However, in-
formation concerning ground-water conditions in the
Pinellas Peninsula and in Tampa and vicinity would be of
value in connection with water supplies from private wells
in this area and the wells for public supply of towns such
as Clearwater along the coast. Observations on represen-
tative wells should be continued in the area in order to
note the variation in artesian head and quality of water.
Altitudes of wells should be determined, and additional
water samples should be analyzed to determine any
changes in the quality of the water.
The old wells of the St. Petersburg waterworks afford
an exceptional opportunity for the study of changes that





GROUND WATER INVESTIGATIONS IN FLORIDA


may take place in a salt-contaminated formation when
there is a decrease in the draft and of the possibilities
of applying remedial measures that will restore the fresh-
ness of the water. A study of these conditions will also
assist in determining the danger of salt-water contamina-
tion in other areas along the coast of Florida and the
steps that should be taken to prevent contamination.



ORANGE COUNTY
GEOGRAPHY
Orange County is in the east-central part of Florida.
The investigation in this county is concerned largely with
the problems of wells used for drainage. The popula-
tion of the county was 19,890 in 1920 and 49,737 in 1930.
Orlando, the county seat, had a population of 9,282 in
1920 and 27,330 in 1930. These figures show'a marked
increase in population in 10 years, a large part of which
has been in areas where the problems of drainage wells
are most acute.
The county consists of a lowland area in the eastern
part extending to the St. Johns River and an upland area
in the central and western parts, which belongs to the
physiographic division known as the lake region. Surface
altitudes range from less than 25 feet above sea level
in the lowland to more than 100 feet in the upland.
The upland area is rolling, with numerous completely
closed depressions that are occupied by lakes. Lake
Apopka, in the northwestern part of Orange County and
the eastern part of Lake County, has an extent of about
8 miles in a northerly direction and about 8 miles in an
easterly direction. The other lakes of the area are much
smaller. Many of them are elongated, some having a
length of about 3 miles and a minimum width of only a
fraction of a mile.
Few surface streams are present in the upland area.
In the northern part of the county, north of Apopka, a





18 FLORIDA GEOLOGICAL SURVEY-BULLETIN ELEVEN

small drainage area is tributary to the Wekiva River,
which flows northeast into the St. Johns River, in Semi-
nole County. Lawne Lake, about 2 miles west of
Orlando, drains into Lake Wekiva, about 3 miles north-
west of Orlando, and Lake Wekiva drains into the Little
Wekiva River, in Seminole County, and finally into the
Wekiva River. In the southern part of the upland area
a few creeks, as Shingle Creek and Reedy Creek, flow
southward into Osceola County. The surface drainage of
the lowland area in the eastern part of the county is con-
trolled by streams flowing north, northeast, and east into
the St. Johns River. The largest of these is the Econ-
lockhatchee River, which rises in Osceola County and
flows in a northerly course approximately parallel to the
St. Johns River across Orange County and thence into the
St. Johns River. The Little Econlockhatchee River and
some of its tributaries rise a few miles east of Orlando
and afford drainage for that general area. The Little
Econlockhatchee flows into the Econlockhatchee River in
Seminole County.
In the western part of the county most of the surface
drainage accumulates in the lakes.
Rock Springs and Wekiva Springs, north and northeast
of Apopka, in Secs. 15 and 36, T. 20 S., R. 28 E., respec-
tively, are the only two large springs of the area. Rock
I Springs flow into the Rock Spring Run, a tributary of the
Wekiva River. Wekiva Springs flow into the Wekiva
River. The water i;' ich nofter than that from the Ocala
S limestone and is probably a mixture of waters from the
. Hawthorn formation and the Ocala.

GEOLOGY
The formations underlying Orange County include the
Ocala limestone (of Eocene age), the Hawthorn and
Choctawhatchee formations (of Miocene age), and undif-
ferentiated Pleistocene and Recent material. The Ocala
limestone is the oldest formation penetrated by most
wells in this county and is underlain by undifferentiated
Eocene and Cretaceous sediments. Well records indi-







GROUND WATER INVESTIGATIONS IN FLORIDA


cate that the toL pofthe-Ocala is from 100 to 150 feet
tbrremrt--the surface. The total thickness of the formation
is not known, but it is estimated to be about 500 feet.
The Ocala consists of almost pure limesttone. Parts of it
are porous and contain solution channels -that permit free
circulation of ground water. This is the chief water-
bearing formation of the area. In a-ddtitr to fluinishing
'-iirt of the public anid private water il-ipplie' of Orange
County, the formation is used as an outlet for drainage
wells. The Ocala limestone is overlain unconformtiab1 by
<5u7 the Hawthorn formation, which consist' of clay. iand. and :
marl. The Hat\tholrn is overlain by unconsolidated (ye"
wr .-youngerT~laterFal, consisting principally of sand and clay,
,-.. .'-' which lie at or near the surface.

GROUND-WATER CONDITIONS OF THE OCALA LIMESTONE

Throu-hi.lhout LIe .'rea. in wells drilled to the Ocala
limestone, the water rises above the beds to which it was
confined before the wells were drilled. This condition in-
dicTates that the water is under artesian pressure. The
pressure is sufficient to cause the water to rise above the
land surface in the lowland area along the St. Johns River
and along the south margin of Lake Apopka but not in
the higher areas. In the vicinity of Orlando the static
water levels in the Ocala li-ti :tone \\t i1 ran ge from only
a, few feet toi .iprx.iniately 30 feet below the surface.
Wherever the water levels are below the surface it is
possible o drain the u-rfacec water into the wells.
The altitudes of representative drainage wells were
determined, and observations on the water levels in the
wells were made during 1930, 1931, and 1932. The data
thus obtained indicate that the hydraulic gradient of the
artesian water in the Ocala limestone is about 2 feet to
tihemile toward the northeast and that therefore the
water is moving in that-direction. In general, the gradient
is fairly uniform, excepting in Orlando and vicinity,
where the influence of drainage wells is apparent. In
August, 1930, the water in the wells in Orlando rose to






20 FLORIDA GEOLOGICAL SURVEY-BULLETIN ELEVEN

levels 6 to 7 feet higher than in August, 1931, and there
was a hydraulic gradient in all directions from a central
point in the city. The high water levels in 1930 were due
to the heavy rainfalfTiofthe summer of that year. During
th-ewet season the water levels rose to such heights that
some of the wells flowed under artesian head instead of
taking in water from the surface. Examples of this con-
dition were noted in the southeastern part of Orlando and
also in county drainage well 13, northwest of Orlo Vista.
County drainage well 13 was drilled to a depth of 328
feet in a depression that appears to be a sink hole. White
sand was encountered from the surface to a depth of
265 feet, where the Ocala limestone was encountered. As
the Ocala limestone would normally be encountered at a
depth of about 100 feet in that locality, it is inferred that
part of the Ocala limestone has been removed by a col-
lapse of a roof of a cavern or by solution by water or a
combination of both, and that the depression thus formed
has been filled with sand. Although the water in the
sink stood several feet above the open top of the well, the
well did not take in any water. This condition seems to
show that the water of the Ocala was under sufficient
head to rise above the surface of the bottom of the
depression.
Measurements of the water levels in wells show wide
fluctuations over short periods of time. Several factors,
such as changes in barometric pressure, pumping from
wells, discharge of surface water into wells, and natural
recharge of the formation are believed to contribute to
these fluctuations. During periods of rainfall doubtless
the natural recharge and the recharge through drainage
into wells are the principal causes of the rise in the water
levels.
A continuous water-level recorder on a well near Ocoee
shows the marked influence of this recharge. No water
entered the mouth of the well at any time during the
record, but the record shows the influence of recharge by
drainage into other wells in that vicinity. The maximum
rise in water level during a three-day period, March 30





GROUND WATER INVESTIGATIONS IN FLORIDA


to April 1, 1931, was about 6 feet. There was a rise in
water level following each rain.
Natural recharge of the Ocala limestone occurs where
the formation crops out northwest of Orlando, in Sumter
and Marion counties, and also locally through the sink
holes that have open underground outlets and the drain-
age wells. It seems likely that only a comparatively small
amount of surface water reaches the Ocala limestone
locally except through the sink holes and drainage wells,
because the Hawthorn formation, which overlies the
Ocala limestone, contains impervious members that prob-
ably prevent the water from passing downward. Pre-
sumably most of the lakes of the area occupy sink holes,
the underground outlets of which have become clogged
to a greater or less extent.
DRAINAGE WELLS
The use of wells for drainage in Orange County began
about 1904. At that time a sink hole in the southeastern
part of Orlando became flooded after heavy rains.
Normally, water entering the depression was discharged
through an open underground outlet that afforded drain-
age for the sink and the surrounding area. However, the
underground passage apparently became clogged, and
water accumulated in the depression and low ground sur-
rounding the sink, causing a considerable area in that
vicinity to become flooded. Several unsuccessful attempts
were made to open the outlet of the sink. When this
failed a plan was tried whereby wells were drilled to the
Ocala limestone to permit water to pass underground as
it formerly did through the natural outlet of the sink.
This drilling revealed the value of wells for drainage,
and now more than 120 wells penetrating the Ocala lime-
stone are used for drainage in Orlando and vicinity.
Approximately 90 of the wells are owned by the city of
Orlando, and practically all of the sewage and run-off
from rainfall in the city is disposed of through drainage
wells. About 30 wells are owned and operated by the
highway department of Orange County for drainage of





22 FLORIDA GEOLOGICAL SURVEY-BULLETIN ELEVEN

roads in the vicinity of Orlando. A number of the smaller
towns in the upland area also have drainage wells, and
there are also privately owned wells used for drainage.
The drainage wells are located in sink holes or other
depressions, along the margins of lakes, or in ditches, in
order that the mouths of the wells will be lower than the
areas drained. The wells range from about 6 to 16
inches in diameter and from about 160 to more than 800
feet in depth. A number of the wells are cased to the
Ocala limestone. The estimated drainage capacity of the
wells ranges from less than 100 gallons to several thou-
sand gallons a minute. The maximum capacity reported
was 9,500 gallons a minute for county well 16, 4 miles
northeast of Orlo Vista.
The drainage wells are apparently adequate to dis-
pose of the surface water until in the summer of 1930,
when heavy rains caused a recurrence of the flooding of
the sink-hole district similar to that reported in 1904,
Lake Davis overflowed and backed into the street and
lawns of one of the attractive residential districts, and a
section of highway northwest of Orlo Vista that is nor-
mally drained by county drainage well 13 was flooded.
The effectiveness of a drainage well depends upon the
permeability of the formation into which it discharges the
water, the size and construction of the well, and the depth
of the static water level below the intake at or near the
surface.

SANITARY PROBLEMS OF DRAINAGE WELLS

As surface water and sewage are discharged in large
quantities through drainage wells into the Ocala lime-
stone, the water in the limestone is subject to contamina-
tion. The public water supply of Orlando is obtained
from surface lakes, but there are many public and private
wells in Orange County that obtain water from the Ocala
limestone. The public supplies that are obtained from
this formation include those of Winter Garden, Ocoee,
Apopka (part of the supply), Winter Park, and Maitland.





GROUND WATER INVESTIGATIONS IN FLORIDA


The data available indicate that in most parts of the
county the hydraulic gradient of the water in the Ocala
limestone is toward the northeast, and hence in most
localities drainage wells form the greatest menace to-the
supplies obtained from wells northeast of them. How-
ever, as the discharge into a well tends to raise the head
in its locality, the polluted water is likely to move in all
directions from the well and to pollute the supplies from
all wells in the same locality. Thus, wells in the vicinity
of Orlando may be polluted by drainage wells in the same
area.
In the summer of 1930 a deep well furnishing the
public supply of Ocoee apparently became contaminated
with surface water. It was reported that the contamina-
tion possibly was caused by county drainage well 13,
several miles southeast of Ocoee. However, the direction
of flow of the water in the Ocala limestone indicates that
the contamination possibly came from a sink or drainage
well in the immediate vicinity of Ocoee or west of Ocoee.
The danger of contamination is increased by the fact
that the water in the Ocala limestone generally moves
through rather large channels, which are not effective as
filters. Obviously, therefore, the water from wells cannot
be regarded as safe and should be chlorinated or other-
wise treated before it is used for drinking or domestic
purposes.

CONCLUSIONS AND PROBLEMS

In some of the lower areas the static levels of water in
drainage wells penetrating the Ocala limestone are only
a few feet below the surface. During rainy seasons the
artesian head of the water in the Ocala limestone may be
several feet higher than that during normal conditions,
and water in the wells may rise to levels at or above the
surface. Under such conditions the wells are of no value
for drainage and may even aggravate conditions by
flowing.




24 FLORIDA GEOLOGICAL SURVEY-BULLETIN ELEVEN

Locally the artesian head of water in the Ocala may
be increased several feet within a few days after heavy
rains. This increase of head apparently is caused, to a
large extent, by the recharge of the formation by drain-
age wells. Consideration should be given the problem
of contamination of the waters of the Ocala limestone
caused by surface waters entering the formation through
drainage wells in view of the fact that some of the public
and domestic water supplies are drawn from the Ocala.
Water from the Ocala in this area subject to pollution
should be considered unsafe for public or domestic.con-
sumption until it is chlorinated or otherwise treated.
Measurements of the depth to water in drainage wells
in Orlando and the county were made, and a continuous
water-level recorder was installed on a well in order to
determine the fluctuation of the artesian head of water
in the Ocala limestone. The altitudes of a number of
these observation wells were determined and the water
levels referred to a common datum. Staff gauges were
installed on a number of lakes in Orlando, and observa-
tions of the changes in water level of the lakes are being
made in order to determine the recharge that takes place
through the lake bottoms. However, in order to interpret
the records from these gauges properly it would also be
necessary to make observations on the evaporation from
the lake surface. Observations on representative drain-
age wells should be continued, so as to record the fluc-
tuations of the water levels through a period of several
years. This record should be compared with the data
on the rainfall to help in determining the amount of local
recharge of the Ocala limestone. The intake area of the
Ocala and the natural recharge in that area should be
determined.






GROUND WATER INVESTIGATIONS IN FLORIDA


SEMINOLE COUNTY

GEOGRAPHY
Seminole County is in the east-central part of Florida.
It is bounded on the north and east by the St. Johns River
and a number of lakes in the course of the river, on the
south by Orange County, and on the west in part by
Orange County and the Wekiva River. Sanford is the
largest town and the county seat. The county leads in
the production of celery in Florida and is one of the chief
truck-growing centers of the State. During 1929 the
value of the celery crop from 280 farms, with a total
acreage of 3,736 in Seminole County was reported by the
United States Department of Commerce to be $2,549,619.
The total acreage of the truck crops in Seminole County
in 1929 was 4,931. The reported value of the crops was
$2,889,673. Irrigation of the truck crops is necessary,
and the water for irrigation is obtained from wells.

GEOLOGY
The geology of the county is similar to that of Orange
County. A few drainage wells penetrating the Ocala
limestone are in use in the southwest part of the area.
Wells penetrating the Ocala limestone flow.in an area
in the northern and eastern parts of the county along the
St. Johns River. It is estimated that more than 1,000
flowing wells are used for irrigation of truck crops in the
county, most of this water being used for the celery crops.
Analyses of water collected from wells penetrating the
Ocala limestone show that some of the wells are contami-
nated with salt water. Data concerning the geologic con-
ditions in the county indicate that the ground water may
be contaminated with sea water and that the salinity of
the water may increase as the withdrawal of water from
wells lowers the artesian head.
A detailed study of the area should be made to deter-
mine the extent of ~s..tit-\at- coijtimination, the changes






26 FLORIDA GEOLOGICAL SURVEY-BULLETIN ELEVEN

that are taking place in the salinity of the water, the
quantity of water that can safely be withdrawn each
year, and the best methods of conserving and protecting
the water supply.




DUVAL COUNTY

GEOGRAPHY
Duval County is on the Atlantic coast in the north-
eastern part of Florida. Jacksonville, the largest city in
Florida, is on the St. Johns River, in the central part of
the county.
The surface ranges in altitude from sea level along the
Atlantic coast to more than 150 feet above sea level in
the western part of the, county. A large part of the area
along the St. Johns River and the eastern part of the
county is not more than about 30 feet above sea level.
Swamps and marshes characterize part of the low, flat
area. The surface drainage is controlled by the St. Johns
River, which flows northward across the central part of
the county and thence eastward to the Atlantic Ocean.

GEOLOGY

The rocks underlying the county include the Ocala
limestone of Eocene age, the Hawthorn formation of
Miocene age, and surficial material of Pleistocene and
Recent age.
The Ocala limestone is the most productive water-
bearing formation in the county. According to6 the'de-
sc.riptioil of C'oo:ke and lMosor, the Ocala is comi :oed
essentially of pure limestone that ranges in color from
pure white through cream color to yellow. It commonly
has a granular texture, but parts of it have been changed
to hard, compact rock. In some places it consists of mate-
rial so porous that water can percolate freely through it.
Cooke, C. W., and Mossom o'ft-rt Geology of F1.. ;.1 : Florida Geol. Survey
Twentieth Ann. Rept., p. 48, 1'.-" '






GROUND WATER INVESTIGATIONS IN FLORIDA


The porosity is, in part, original with the formation, but
the free circulation of the water has resulted in the for-
mation of numerous channels by solution of the limestone.
The thickness of the Ocala limestone is variable, "and
although the total thickness in this area is unknown, it is
estimated to be about 500 feet.
S-Te-Hawthorn formation consists of about 500 feet of
alternating beds of clay, marl, sand, and limestone in this
area. It rests unconformably on the Ocala limestone and
is overlain by a thin overburden of younger material,
which is present at or near the surface. This formation
yields some water but is not of great value as a source of
water for large supplies.
According to Mossom,* this county lies on a local struc-
tural depression on the northeast flank of a broad anti-
cline or elongated dome that trends northwestward
through central and northern Florida. The outline of the
local structure has not been definitely determined, but in
general the Ocala limestone dips at a low angle from the
northwest, west, and south toward Jacksonville. The
direction of dip east of the Jacksonville area is unknown,
but probably it is eastward, toward the ocean, beneath
which the Ocala presumably crops out some miles off
shore. According to the interpretation of well data by
Mossom, the Ocala is about 500 feet below sea level at
Jacksonville and approximately 200 feet below sea level
in the vicinity of St. Augustine. The formation crops out
at the surface about 40 miles southwest of Duval County,
on the crest of the anticlinal fold.

GROUND WATER-SOURCE

The largest water supplies of Duval County are ob-
tained from the Ocala limestone, including the public
supplies of Jacksonville, South Jacksonville, and Jackson-
ville Beach. Several hundred wells in the county pene-
trate this formation, most of which are in the vicinity of
Mossom, Stuart, A review of the structure and stratigraphy of Florida:
Florida Geol. Survey Seventeenth Ann. Rept., pp. 29-228, 1926.






28 FLORIDA GEOLOGICAL STJRVEY-BULLETIN ELEVEN

Jacksonville. The wells range in depth from about 500
to 1,000 feet. Under normal conditions they flow under
artesian head except in the west part of the county and
in other localities that are more than about 65 feet above
sea level.
Some water is obtained from the Hawthorn formation.
In the vicinity of Baldwin, the artesian head is sufficient
to raise the water from this formation to within a few feet
of the surface, and a large part of the water supply is
pumped from wells 75 to 100 feet deep that penetrate
the formation.
Wells 15 to 25 feet in depth that penetrate the uncon-
solidated material overlying the Hawthorn formation
furnish water for domestic and farm use in some of the
rural districts.
CONSUMPTION

The largest consumption of ground water in this county
is in Jacksonville. The public water supply of Jackson-
ville is obtained from wells about 700 to 1,000 feet deep
that penetrate the Ocala limestone. The average daily
consumption of the city in 1929 was more than 11,000,000
gallons. During the period from 1920 to 1929 the max-
imum monthly demand increased more than 200,000,000
gallons.
Many private wells in Jacksonville and vicinity produce
water from the Ocala limestone, and it is estimated that
the total consumption from these wells is approximately
equal to that of the public supply.

QUALITY OF WATER

Water from the Ocala limestone is hard and has vary-
ing but in some places considerable amounts of hydrogen
sulphide. However, in some of the public supplies the
hydrogen sulphide is removed simply by aeration. The
hardness probably averages about 300 parts per million.
The Hawthorn formation contains both hard and rela-
tively soft water. At Baldwin water from a depth of





GROUND WATER INVESTIGATIONS IN FLORIDA


about 110 feet has a hardness of 270 parts per million.
The unconsolidated material overlying the Hawthorn
formation yields relatively soft water. The chloride con-
tent of samples collected from wells that are being used
at the present time in Jacksonville and vicinity is gener-
ally less than 20 parts per million. The highest deter-
mined chloride content (63 parts per million) has been
reported from a well in the northeast part of the county
on Fort George Island. Sanford* reported "saline" water
in some of the deep wells of Duval County, which in-
cluded one well 1,025 feet deep in Jacksonville. How-
ever, as wells in the city have since been drilled to a
greater depth without encountering salt water, the occur-
rence of salt water in the well mentioned is to be
questioned.
ARTESIAN HEAD
o The area in which wells that penetrate the Ocala lime-
stone will normally flow includes most of the county
except the southwestern part. Flowing wells may be
obtained as far west as Marietta, but beyond that locality
the surface rises above 65 feet and flows are not generally
obtained. Within the general area of artesian flow there
are relatively higher areas in which the wells will not
flow. For example, a few miles east of Jacksonville there
is a ridge trending north on which some of the higher
points are about 65 feet above sea level.
The artesian head in the county ranges from about 30
to 65 feet above sea level. The maximum pressure was
observed in wells on Fort George Island, on the coast
northeast of Jacksonville, and at Dinsmore, in the north-
western part of the county. The lowest artesian head
was noted in the vicinity of the public supply wells of
Jacksonville. This area of low head apparently forms
somewhat of an inverted cone in the piezometric surface,
or imaginary surface that indicates the head, the apex of
the cone being in the vicinity of the Water Works Park
wells. This area of low head has been described by
Matson, G. C., and Sanford, Samuel, Geology and ground waters of Florida:
U. S. Geol. Survey Water-Supply Paper 319, p. 300, 1913.





30 FLORIDA GEOLOGICAL SURVEY-BULLETIN ELEVEN

Malcom Pirnie, consulting engineer, who has made a
careful study of the artesian conditions in the Jackson-
ville area, as a depression cone with a diameter of about
6 miles and a depth of about 30 feet. Depressions also
exist in the piezometric surface at Ortega, where the head
ranges from 34 to 48 feet above sea level and at the
United States Rifle Range, south of Jacksonville, where
the head is about 48 feet above sea level. These are,
however, only small depression areas as compared with
that of Jacksonville. Apparently the Ortega cone of
depression is located within the large Jacksonville cone.
Measurements of head made during the summer of
1930 at Jacksonville Beach, on the Atlantic coast about
7 miles .east of Jacksonville, show that the artesian head
here and at Woodstock Park was approximately the
same. The head in a 1,075-foot well in Woodstock Park,
in the western part of Jacksonville, was 58 feet above sea
level, whereas the head in the 875-foot well on the Reisz
dairy farm, several miles farther west, was only 53 feet
above sea level. This suggests that the deeper artesian
horizons may have higher artesian head. The logs of,
several wells in Jacksonville and St. Augustine show a
definite increase in head and flow with an increase of
depth.
Details of the history pf artesian head are not com-
plete, but the available data reveal a loss of head in the
vicinity of Jacksonville. The initial head in a 10-inch
well, 980 feet deep, drilled in Jacksonville in 1903 by
R. N. Ellis, was 58 feet above the surface, or about 68
feet above sea level.* Well data compiled in 1905 by
N. H. Dartont show that several of the representative
wells of Jacksonville had heads of about 62 feet above
the surface. At the present time the 'minimum head
noted in this immediate vicinity is about 30 feet above
sea level, and the maximum is approximately 54 feet
above sea level.
Fuller, M. L., and Sanford, Samuel, Record of deep well drilling for 1905:
U. S. Geol. Survey Bull. 298, p. 47, 1906.
t Darton, N. H., Preliminary list of deep borings in the United States: U. S.
Geol. Survey Water-Supply Paper 149, p. 25, 1905.






GROUND WATER INVESTIGATIONS IN FLORIDA


FLUCTUATIONS OF ARTESIAN HEAD

Automatic pressure recorders were installed on two
wells in Jacksonville and on one well in Jacksonville
Beach to obtain information in regard to the fluctuation
of head. The records from the well in Jacksonville
Beach show an average increase of about 2 feet in arte-
sian head during the later part of November and Decem-
ber, 1930. Probably this increase is local, in view of the
fact that records from a well in the northern part of
Jacksonville do not show a similar change during that
time. A fluctuation of about 18 feet has been recorded
on the well in Water Works Park, but this is undoubtedly
due to changes in the rate of draft from the wells that
furnish the public supply and possibly from industrial
wells near by.
The continuous records, indicate that there is a semi-
daily variation of 1 to 2 feet in the artesian head on the
coast at Jacksonville Beach, which is undoubtedly caused
by the tide in the ocean. The maximum pressure cor-
responds with the high tide and the low pressure with
the low tide at the coast. Tidal influence on artesian head
is reported in the well at the United States Rifle Range
on the St. Johns River south of Jacksonville.

RECHARGE

Local recharge of the artesian water in the Ocala lime-
stone of this area is not probable in view of the fact that
it is overlain by about 500 feet of the Hawthorn forma-
tion, part of which consists of impervious clay and marl
and is therefore only slightly permeable. This opinion is
also supported by the fact that sink holes are absent in
the area. Most of the recharge of this formation pre-
sumably occurs where it crops out at the surface. The
nearest area where conditions appear to be favorable for
such recharge is in Alachua County and the western part
of Marion County, more than 50 miles southwest of Jack-
sonville.






32 FLORIDA GEOLOGICAL SURVEY-BULLETIN ELEVEN

The loss of head that has occurred in the Ocala forma-
tion is a normal process that invariably accompanies the
withdrawal of artesian water in large amounts. Be-
cause of its greater distance from the ocean the danger
of contamination of the ground water in Jacksonville may
not be as great as at Jacksonville Beach and other places
along the coast. However, heavy withdrawals of water
at Jacksonville may conceivably result in the salt water
contaminating the wells nearer the ocean.

CONCLUSIONS AND PROBLEMS TO BE INVESTIGATED

The available records show that there has been a loss
of artesian head accompanied by decline in rate of
artesian flow from wells penetrating the Ocala limestone
in the localities of heaviest withdrawals of water. The
loss of flow and head is due in large part to the increased
draft on the artesian reservoir as additional wells have
been drilled and the demand for water has increased.
The greatest decrease of artesian head is in Jacksonville
and is caused by the draft from wells of the Jacksonville
public supply and many other wells of the city.
There are some indications of an area of equal pressure
of artesian flow between Jacksonville and the Atlantic
coast. If this condition exists it may be caused by back
pressure from salt water of the ocean, which has a higher
specific gravity than the artesian water, and may indi-
cate danger of salt water being drawn into the area from
below or from the oceanic outcrop if the draft in the
formation is increased too much. The possibility of such
contamination by salt water is yet to be determined.
The factors involved in the solution of this problem
require the collection of information in regard to the
depth, yield, materials penetrated, and head in many
wells in the county. Accurate levels must be run in order
to determine the head in wells in different parts of the
area. Observations must be made to determine the rela-
tion of fluctuations of the head to fluctuations in the rate
of withdrawal of water. In this connection it is important




GROUND WATER INVESTIGATIONS IN FLORIDA


to determine the nature and extent of fluctuations of head
that may be due to other influences, such as the effects
of the tide and changes in atmospheric pressure, in order
that proper allowance may be made in considering
changes that are due solely to draft. Analyses of the
water from selected wells should be made from time to
time to determine whether there is any change in the
chloride content. It is also necessary to study conditions
affecting the recharge of the water-bearing formation in
the area in which it crops out at the surface. If the con-
clusions are to have a reasonable degree of reliability the
basic data in regard to fluctuations of head, pumpage,
and chloride content of the water must extend over a
period of years. It is therefore desirable that studies be
started some years in advance of the time when an answer
to the problem will be needed. In fact, experience in
other localities shows that certain types of data should
be obtained as early as possible, for as time passes and
conditions change the opportunity is lost to obtain the full
history of hydrologic conditions that is necessary to give
the complete solution.