Interim report on the ground-water resources of St. Johns County, Florida ( FGS: Information circular 14 )

STATE OF FLORIDA
STATE BOARD OF CONSERVATION
Ernest Mitts, Director

FLORIDA GEOLOGICAL SURVEY
Robert O. Vernon, Director

INFORMATION CIRCULAR NO. 14

INTERIM REPORT ON THE GROUND-WATER RESOURCES
OF ST. JOHNS COUNTY, FLORIDA

By
George R. Tarver

Prepared by
U. S. Geological Survey
in cooperation with the
Florida Geological Survey

Tallahassee, Florida
1958

Pages ii-iii Missing

Figure Page
8 Map of St. Johns County, showing the
piezometric surface in April 1956. . ... 18
9 Map of St. Johns County, showing the
piezometric surface in September and October
1956 . . . . . 19
10 Map of St. Johns County, showing the areas of
artesian flow in 1956. ............. 21
11 Map of St. Johns County, showing the chloride
content of water from the principal artesian
aquifer ........... ... ... ... 22
12 Map of the Hastings area, showing the
chloride content of artesian water, in parts
per million, in June 1956, from wells less
than 350 feet deep .................. 27
13 Map of the Hastings area, showing the
chloride content of artesian water, in parts
per million, in June 1956, from wells 350 to
700 feet deep .......... .... ... 28

Table
1 Chemical analyses of water samples from
wells in St. Johns County . . .. 30

INTERIM REPORT ON THE GROUND-WATER RESOURCES

OF ST. JOHNS COUNTY, FLORIDA

By
George R. Tarver

ABSTRACT

St. Johns Countyis onthe eastern seaboardin the north-
ern part of the Florida Peninsula. Beds of sand, clay, marl,
shell, and sandy limestone, of Pliocene, Pleistocene and
Recent age, are exposed at the surface over all the county.
They range from 25 to 140 feet in total thickness, and are
underlain by relatively impervious beds of clay, sand, and
limestone of Miocene or Pliocene age that range in thickness
from 50 to 220 feet. A series of limestone beds several thou-
sand feet thick underlies the Miocene or Pliocene clay. The
uppermost unit of this limestone series is the Ocala group
of the late Eocene age.

Measurements of artesian pressure head show that the
piezometric surface fluctuates through a range of about five
feet each year in most of the county, being high in the winter
and low in the summer. Withdrawal of large quantities of
water for irrigation in southwestern.St. Johns County, during
the potato-growing season of 1956, depressedthe piezometric
surface about 20 feet belowthe winter high. A study of old
water-level records indicates that there has been a decline
of about five feet in the piezometric surface in most of the
county in the past 16 years and a much greater decline in
the farming area.

1The stratigraphic nomenclati~re used in this report
conforms to the usage of the Florida Geological Survey. It
conforms also to the usage of the U. S. Geological Survey
with the exception of the Ocala group and its subdivisions.
The Florida Geological Survey has adopted the Ocala group
as described by Puri (1953). The U. S. Geological Survey
regards the Ocala as a formation, the Ocala limestone.

FLORIDA GEOLOGICAL SURVEY

The chloride content of water from the principal arte-
sian aquifer in St. Johns County ranges from less than 10
parts per million (ppm) in the northern section, where the
piezometric surface is relatively high, to more than 7,000
ppm near Crescent Beach, where the piezometric surface
is relatively low. Deep wells in the farming area produce
water having a chloride content as high as 2, 500 ppm, where-
as shallow wells in the same area produce less saline water,
indicating that the chloride content of the water increases
with depth.

INTRODUCTION

In St. Johns County, wells supply nearly all the water
for irrigation, municipal, and domestic uses. There has
been a gradual increase in population throughout the county
and a rapid increase in the tilled acreage in the' western
part of the county. The use of artesian water to prevent
drought and frost damage has increased, and the ground
water levels have shown a progressive decline during the
last three or four years. The decline in water levels could
result in the contamination of the fresh-water supply by an
intrusion of saline water from the deep zones of the princi-
pal artesian aquifer.

In recognition of this and other water-supply problems,
the State Legislature appropriated funds for an investiga-
tion of the water resources of the county. The ground-water
phase of the investigation was begun in November 1955 by
the U. S. Geological Survey as a part of the statewide
investigation in cooperation with the Florida Geological
Survey.

The purpose of this investigation is to make a study of
the geologyand ground-water resources of St. Johns County,
with emphasis upon salt-water contamination and declining
water levels in the artesian aquifer. This report reviews
the progress made in the county during the first year of the
investigation.

FLORIDA GEOLOGICAL SURVEY

The chloride content of water from the principal arte-
sian aquifer in St. Johns County ranges from less than 10
parts per million (ppm) in the northern section, where the
piezometric surface is relatively high, to more than 7,000
ppm near Crescent Beach, where the piezometric surface
is relatively low. Deep wells in the farming area produce
water having a chloride content as high as 2, 500 ppm, where-
as shallow wells in the same area produce less saline water,
indicating that the chloride content of the water increases
with depth.

INTRODUCTION

In St. Johns County, wells supply nearly all the water
for irrigation, municipal, and domestic uses. There has
been a gradual increase in population throughout the county
and a rapid increase in the tilled acreage in the' western
part of the county. The use of artesian water to prevent
drought and frost damage has increased, and the ground
water levels have shown a progressive decline during the
last three or four years. The decline in water levels could
result in the contamination of the fresh-water supply by an
intrusion of saline water from the deep zones of the princi-
pal artesian aquifer.

In recognition of this and other water-supply problems,
the State Legislature appropriated funds for an investiga-
tion of the water resources of the county. The ground-water
phase of the investigation was begun in November 1955 by
the U. S. Geological Survey as a part of the statewide
investigation in cooperation with the Florida Geological
Survey.

The purpose of this investigation is to make a study of
the geologyand ground-water resources of St. Johns County,
with emphasis upon salt-water contamination and declining
water levels in the artesian aquifer. This report reviews
the progress made in the county during the first year of the
investigation.

INFORMATION CIRCULAR NO. 14

Listed below are some of the most important data that
were collected.

1. Information concerning the depth, distribution,
use, and construction of wells.

2. Measurements of water levels throughout the
county to determine seasonal fluctuations,
long-term trends, and declines due to pumping.

3. Chemical analyses of ground-water to deter-
mine areal and vertical distribution of saline
water and possible changes in water quality
with time and pumping.

3. Drillers' logs and samples of formation pene-
trated by water wells, to determine the char-
acter of sediments and their relationship to
the water supply.

The investigation was made under the general super-
vision of A. N. Sayre, Chief, Ground Water Branch, U. S.
Geological Survey, and under the immediate supervision of
M. I. Rorabaugh, District Engineer for Florida.

Previous Investigation

The geology and ground-water resources of St. Johns
County are mentioned in several reports published by the
U. S. Geological Survey and the Florida Geological Survey.

A study of the geology and ground water of St. Augustine
well-field area was made by A. G. Unklesbay (1945). The
report included a geologic cross section of the well field and
a table of chemical analyses of water from all the city wells.
A structure andisopachous map of the Miocene sediments
in North Florida, and other geological information pertaining
to St. Johns County, were presented in a report by Vernon
(1951, fig. 11, 13, 33; pl. 2).

A report on the geology of Florida by Cooke (1945,

FLORIDA GEOLOGICAL SURVEY

p. 42, 48, 272. 296, 310; pl. 1), contains descriptions of the
surface and subsurface formations of the county and a geo-
logic map of the State.

St. Johns County was studied briefly by Stringfield
(1936) as part of an investigation of the ground-water re-
sources of the peninsula of Florida. Stringfield's report
included a general map of the areas of artesian flow, a map
of areas in which artesian water is highly mineralized, a
map of the piezometric surface of the principal artesian
aquifer in the peninsula, and a broad discussion of all aspects
of the artesian system.

A collection of 67 complete chemical analyses of water
from wells throughout the county was presented by Black
and Brown (1951, p. 97, 98).

GEOGRAPHY

St. Johns County is on the eastern seaboard of the
northern part of the Florida Peninsula and has an area of
608 square miles, or 389, 260 acres (fig. 1). In 1955 the
U. S. Bureau of the Census estimated the population to be
29, 378. Most of the population is concentrated within the
corporate limits of St. Augustine, the county seat and larg-
est city.

The mean temperature of the county is 70oF, and the
average annual rainfallis about 50 inches. Accordingto the
records of the St. Augustine and Racy Point stations of the
U. S. Weather Bureau, two-thirds of the rain falls during
the period June-October.

St. Johns County led the State in the production of Irish
potatoes in 1954, producing 3, 037, 887 bushels, according
to the 1954 Florida Agriculture Census (U. S. Dept. Com-
merce, Census Bureau, 1955).

Most of the county is covered by forests and pasture.
land, but an estimated 17, 500 acres or 41/2 percent of the
total acreage is tilled.

INFORMATION CIRCULAR NO. 14

Figure 1. Map of the peninsula of Florida showing the loca-
tion of St. Johns County.

FLORIDA GEOLOGICAL SURVEY

p. 42, 48, 272. 296, 310; pl. 1), contains descriptions of the
surface and subsurface formations of the county and a geo-
logic map of the State.

St. Johns County was studied briefly by Stringfield
(1936) as part of an investigation of the ground-water re-
sources of the peninsula of Florida. Stringfield's report
included a general map of the areas of artesian flow, a map
of areas in which artesian water is highly mineralized, a
map of the piezometric surface of the principal artesian
aquifer in the peninsula, and a broad discussion of all aspects
of the artesian system.

A collection of 67 complete chemical analyses of water
from wells throughout the county was presented by Black
and Brown (1951, p. 97, 98).

GEOGRAPHY

St. Johns County is on the eastern seaboard of the
northern part of the Florida Peninsula and has an area of
608 square miles, or 389, 260 acres (fig. 1). In 1955 the
U. S. Bureau of the Census estimated the population to be
29, 378. Most of the population is concentrated within the
corporate limits of St. Augustine, the county seat and larg-
est city.

The mean temperature of the county is 70oF, and the
average annual rainfallis about 50 inches. Accordingto the
records of the St. Augustine and Racy Point stations of the
U. S. Weather Bureau, two-thirds of the rain falls during
the period June-October.

St. Johns County led the State in the production of Irish
potatoes in 1954, producing 3, 037, 887 bushels, according
to the 1954 Florida Agriculture Census (U. S. Dept. Com-
merce, Census Bureau, 1955).

Most of the county is covered by forests and pasture.
land, but an estimated 17, 500 acres or 41/2 percent of the
total acreage is tilled.

FLORIDA GEOLOGICAL SURVEY

The Tolomato or North River, the Matanzas River, and
their tributaries drain the eastern third of the county. The St.
Johns River and its tributaries drain the western two-thirds.
The drainage divide is nearly a straight line that traverses
the county in a north-northwest-south- southeast direction.

The area may be divided into four general topographic
divisions, as follows: (1) An offshore bar that ranges in
width from a few yards to a mile, along the eastern coast,
(2) a lagoonal area about a mile wide immediately west of
and parallel to the bar, (3) a ridge and swamp belt about five
miles wide which parallels the coastline, and (4) a gently
sloping plain along the St. Johns River. The ridges and
swamps are relatively straight and narrow and form a dis-
tinct trellis drainage pattern. The plain that slopes gently
to the St. Johns River is the largest division. It occupies
nearly two-thirds of the county and has a dendritic drainage
pattern. The altitude of the land ranges from about 65 feet
in the ridge and swamp belt to sea level at the coast.

WELL-NUMBERING SYSTEM

Each well inventoried during this investigation was as-
signed an identifying well number. Therefore, wells referred
to by number in the text may be located on figure 2. The
well number was assigned by first locating each well ona
map which was divided into 1-minute quadrangles of lati-
tude and longitude, then numbering, consecutively, the wells
in each quadrangle. The well number is composed of the
last three digits of the line of latitude south of the well,
followed by the last three digits of the line of longitude east
of the well, followed by the number of the well in the quad-
rangle. For example, well 943-129-3 is the well numbered
3 in the quadrangle bounded by latitude 29043' on the south
and longitude 81029' on the east.

GEOLOGY

Rock cuttings from wells show that St. Johns County is
underlain by beds of linestone, clay, sand, and shells. The
lowermost rock penetrated by water wells is a series of

INFORMATION CIRCULAR NO. 14

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EXPLANATION
Inventored well
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Figure 2. Map of St. Johns County, showing the locations
of wells' that obtain water from the principal
artesian aquifer.

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t,.

-Ly-L--

^-P-Vi

FLORIDA GEOLOGICAL SURVEY

The Tolomato or North River, the Matanzas River, and
their tributaries drain the eastern third of the county. The St.
Johns River and its tributaries drain the western two-thirds.
The drainage divide is nearly a straight line that traverses
the county in a north-northwest-south- southeast direction.

The area may be divided into four general topographic
divisions, as follows: (1) An offshore bar that ranges in
width from a few yards to a mile, along the eastern coast,
(2) a lagoonal area about a mile wide immediately west of
and parallel to the bar, (3) a ridge and swamp belt about five
miles wide which parallels the coastline, and (4) a gently
sloping plain along the St. Johns River. The ridges and
swamps are relatively straight and narrow and form a dis-
tinct trellis drainage pattern. The plain that slopes gently
to the St. Johns River is the largest division. It occupies
nearly two-thirds of the county and has a dendritic drainage
pattern. The altitude of the land ranges from about 65 feet
in the ridge and swamp belt to sea level at the coast.

WELL-NUMBERING SYSTEM

Each well inventoried during this investigation was as-
signed an identifying well number. Therefore, wells referred
to by number in the text may be located on figure 2. The
well number was assigned by first locating each well ona
map which was divided into 1-minute quadrangles of lati-
tude and longitude, then numbering, consecutively, the wells
in each quadrangle. The well number is composed of the
last three digits of the line of latitude south of the well,
followed by the last three digits of the line of longitude east
of the well, followed by the number of the well in the quad-
rangle. For example, well 943-129-3 is the well numbered
3 in the quadrangle bounded by latitude 29043' on the south
and longitude 81029' on the east.

GEOLOGY

Rock cuttings from wells show that St. Johns County is
underlain by beds of linestone, clay, sand, and shells. The
lowermost rock penetrated by water wells is a series of

FLORIDA GEOLOGICAL SURVEY

massive limestone beds whose upper surface ranges in depth
from 90 feet below sea level in the southwestern section of
the countyto more than 290 feet below sealevel in the north-
ern section of the county. The limestones extend to a depth
of several thousand feet.

The upper part of this limestone section consists of the
Oldsmar, Lake City, and Avon Park limestones and the Ocala
group of Puri (1953), all of Eocene age. These limestones
are of marine origin and consist of alternating hard and soft
zones. The Ocala limestone described by. Cooke (1945,
p. 53-73) was established by Puri (1953, p. 130) as a group
composed of three similar formations. The first two were
named by Vernon (1951), who, however, did not retain the
name Ocala. The three formations, in ascending order, are
the Inglis arid Williston formations of Vernon (1951) and the
Crystal River formation of Puri (1953). All three are frag-
mental marine limestones which are differentiated on the
basis of fossil content and lithology.

The Crystal River formation of Puri is a white to cream
pure friable coquina composed of tests of large Foraminifera,
zoaria of Bryozoa, and other small marine fossils. The
upper two to 20 feet of this formation is composed of a hard,
dense, gray limestone containing many thin chert streaks.
This zone is commonly referred to as the bedrock.

Beds of clay of Miocene or Pliocene age overlie the
limestone and confine the water in it throughout the county.
These beds range in thickness from less than 50 feet at
Hastings and Marineland to more than 220 feet at Palm
Valley. The upper part is composed of gray to blue clay,
sandy clay, thin lenses of fine white quartz sand, and lenses
of large, well-preserved marine shells. The lower part is
composed of green and brown clay, thin lenses of black phos-
phatic pebbles and cobbles, and thin lenses of coarse, white
quartz sand. A limestone bed one foot to five feet thick
occurs about 40 feet above the base of the clay sequence.

Beds of sand, marl, shell, and sandy limestone of
Pliocene, Pleistocene, and Recent age overlie the beds of

INFORMATION CIRCULAR NO. 14

clay. They occur in no particular sequence except that sand
is exposedat the surface over the entire county. These beds
of Pliocene, Pleistocene, and Recent age have an aggregate
thickness of 140 feet in the ridge and swamp beltand a thick-
ness of less than 40 feet near the Atlantic Coast. Part of
this sequence has been named the Anastasia formation, a
formation occupying abelt about five miles wide that paral-
lels the Atlantic Coast from St. Augustine south to southern
Palm Beach County. The Anastasia formation is composed
of whole and broken mollusk shells and some quartz sand.
It occurs both as a loose aggregate and as well-indurated
coquina cemented with calcium carbonate. Beds of shells
in other sections of the county are composed principally of
mollusk shells and appear to be more widespread than the
Anastasia formation. The surficial sand in the county is
composed of fine to medium quartz grains that range in color
from white to black or buff, according to the amount of iron
and organic matter present. Underlying the land surface at
a depth of one foot to 10 feet is a thin hardpan composed of
buff to chocolate brown sand partially cemented with organic
material and iron.oxide. The lower surface of the hardpan
coincides approximately with the water table.

The geologic cross sections (fig. 3) show the approxi-
mate depth to the principal artesian aquifer in St. Johns
County, and figure 4 shows the configuration of the top of
the aquifer. The aquifer dips slightly to the north and its
upper surface is irregular. The irregularity was caused by
stream erosion, when thelimestone was exposedat the sur-
face, and by the solution and removal of the limestone by
circulating groundwater after the limestone was covered by
younger sediments (Stringfield, 1936, p. 124, 125).

GROUND WATER

Ground water is the subsurface water in that part of the
zone of saturation in which all pore spaces are filledwith
water under pressure greater than atmospheric. Water in
this zone moves more or less laterally under the influence
of gravity to places of discharge, such as rivers, springs,
wells, or the ocean.

Figure 3. Generalized geologic sections, showing the rocks
penetrated by wells in St. Johns County.

INFORMATION CIRCULAR NO. 14

-3000

-?9ree

EXPLANATION

--150-
Conlour line representing the opproximote
altitude, in feel referred to mean seo
level, of the top of the principal
artesian aquifer. /

Contour intervol 50 feet.
-2040'

I 0 2 3 4 5
Scale n MCIles

Figure 4. Map of St. Johns County, showing contours on

the top of the principal artesian aquifer.

1 I I

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b

1

O

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z

INFORMATION CIRCULAR NO. 14

clay. They occur in no particular sequence except that sand
is exposedat the surface over the entire county. These beds
of Pliocene, Pleistocene, and Recent age have an aggregate
thickness of 140 feet in the ridge and swamp beltand a thick-
ness of less than 40 feet near the Atlantic Coast. Part of
this sequence has been named the Anastasia formation, a
formation occupying abelt about five miles wide that paral-
lels the Atlantic Coast from St. Augustine south to southern
Palm Beach County. The Anastasia formation is composed
of whole and broken mollusk shells and some quartz sand.
It occurs both as a loose aggregate and as well-indurated
coquina cemented with calcium carbonate. Beds of shells
in other sections of the county are composed principally of
mollusk shells and appear to be more widespread than the
Anastasia formation. The surficial sand in the county is
composed of fine to medium quartz grains that range in color
from white to black or buff, according to the amount of iron
and organic matter present. Underlying the land surface at
a depth of one foot to 10 feet is a thin hardpan composed of
buff to chocolate brown sand partially cemented with organic
material and iron.oxide. The lower surface of the hardpan
coincides approximately with the water table.

The geologic cross sections (fig. 3) show the approxi-
mate depth to the principal artesian aquifer in St. Johns
County, and figure 4 shows the configuration of the top of
the aquifer. The aquifer dips slightly to the north and its
upper surface is irregular. The irregularity was caused by
stream erosion, when thelimestone was exposedat the sur-
face, and by the solution and removal of the limestone by
circulating groundwater after the limestone was covered by
younger sediments (Stringfield, 1936, p. 124, 125).

GROUND WATER

Ground water is the subsurface water in that part of the
zone of saturation in which all pore spaces are filledwith
water under pressure greater than atmospheric. Water in
this zone moves more or less laterally under the influence
of gravity to places of discharge, such as rivers, springs,
wells, or the ocean.

FLORIDA GEOLOGICAL SURVEY

Ground water may occur under either nonartesian
(water-table) or artesian conditions. Where it is unconfined,
its surface is free to rise and fall and it is said to.be under
nonartesian conditions. The upper surface of nonartesian
water is known as the water table. Where the water is con-
fined in a permeable bed that is overlain by a relatively im-
permeable bed, it is said to be under artesian conditions.
The term "artesian" is applied to water, which is under
sufficient pressure to rise above the top of the permeable
bed that contains it, although not necessarily above the land
surface.

An aquifer is a formation, group of formations, or part
of a formation, below the water table, that will yield water
in usable quantities to springs and wells. Areas of recharge
are those areas in whichan aquifer receives water, and areas
of discharge are those in which an aquifer loses water.

The Nonartesian Aquifer

The surficial sands of Pleistocene and Recent age in the
county contain water under nonartesian conditions (fig. 3),
though locally, artesian conditions may exist where the sand
contains interbedded clay.

Water from the nonartesian aquifer is used extensively
in the rural areas for domestic purposes and in the towns for
lawn irrigation. The city of St. Augustine obtains part of
its municipal supply from a shallow sand bed in this aquifer.
In most areas the water is very soft but contains objection-
able quantities of iron, which stains utensils and clothing.
Several wells along waterways and near the ocean yield
brackish water, but fresh water can generally be obtained
very close to bodies of salt water. Most of the wells are
less than 50 feet deep and are equipped with a sand-point
screen and a hand or electric suction pump.

The nonartesian aquifer receives most of its recharge
from rainfall in the immediate area, but in the farming area
it receives a considerable amount of recharge from irriga-
tion water flowing over the land. Many nonartesian wells in

INFORMATION CIRCULAR NO. 14

this area yield water very similar to the artesian water in
taste and chloride content.

The Thin Artesian Aquifers

Within the confining beds that overlie the principal arte-
sian aquifer (fig. 3) are many beds of shell, limestone, and
sand that contain water under artesian conditions. Water
fromthese beds is usedinthe rural areasfor domestic pur-
poses and small irrigation systems. The city of St. Augustine
obtains part of its supply from these beds. In 1956 the city
pumped approximately 1. 2 million gallons per day (gpd),
using an average of 12 wells, some screened in an artesian
sand and the others in the nonartesian sands.

Water from the thin artesian aquifers is relatively hard
and contains excessive amounts of iron. A rubble bed at
the base of the confining bed contains water very similar to
that obtained from the limestone immediatelybelow the bed-
rock surface. The wells are usually driven or drilled 20
to 280 feet deep and are cased to the bottom.

The Principal Artesian Aquifer

Limestone of Eocene age in the upper part of the prin-
cipal artesian aquifer of the Florida Peninsula and adjacent
areas (fig. 3), is the main source of water for irrigation in
the county. It is composed mostly of soft limestone contain-
ing streaks of hard limestone. Differences in artesian
pressure within the aquifer indicate that the hard streaks
are relatively impervious. Water from the aquifer is highly
mineralized, and in some areas of heavy pumping or natural
flow the mineralization of the water is extremely high,
rendering the water useless for irrigation and human con-
sumption. Most of the wells in this aquifer are less than
350 feetdeep and are cased either to the bedrock or to near
the bottom of the confining bed, the remainder of the well
being an open hole in the limestone. Centrifugal pumps
equipped with electric motors arethe type most widely used
in the areas where the natural flow of wells is insufficient
for irrigation use.

FLORIDA GEOLOGICAL SURVEY

The water that is obtained from artesian wells in St.
Johns County comes from rainfall which infiltrates through
sinkholes in areas to the north and west. Recharge may
take place also by a downward percolation of ground water
through the confining beds in areas where the water table is
higher than the piezometric surface. From these areas of
intake the water moves laterally through the limestone to
areas where discharge takes place throughwells and springs
and by upward leakage through the confining beds in areas
where the piezometric surface is higher than the water table.

Piezometric Surface

The piezometric surface is the imaginary surface that
everywhere coincides with the static water level in the aqui-
fer. It is the surface to which the water from a given aqui-
fer will rise under its full head.

The piezometric surface for the principal artesian
aquifer in Florida is shown by the contour lines in figure 5.
The contour lines on this map indicate thatwater enters the
aquifer in the north-central part of Florida andmoves south-
ward and eastward through the county to areas of discharge
in St. Johns County and south and east of the county. Water
levels in severalwells in St. Johns County have been meas-
ured periodically since 1940 by the U. S. Geological Survey.
The measurements show that there has been a loss of five
to 10 feet in artesian pressure head over the area in the past
16 years, the greatest loss having occurred in the south-
western section where irrigation has increased rapidly. In
figure 6, the water level in well 953-118-1 shows a decline
of about eightfeet between 1946 and 1956. Figure 7 is a map
showing the piezometric surface in Flagler, Putnam, and
St. Johns counties. It gives a broader picture of the move-
ment of water in the principal artesian aquifer than is given
in figures 8 and 9, which show the piezometric surface in
St. Johns County. During the potato-growing season, when
withdrawal is heavy and the piezometric surface is relatively
low, the artesian water in the southern part of the county
reverses its direction of flow, which is normally south-
eastward, and moves northwestward from Flagler County
intothe Hastings area (fig. 8, 9). Figure 7 shows that some

INFORMATION CIRCULAR NO. 14

EXPLANATION

Contour lines represent approximately the
height, in feet, to which water will rise with
reference to mean sea level in tightly cased
wells that penetrate the principal artesian
aquifer, 1949.

25 0 :25 50 75 100
Approximate Scale
Miles

Figure 5. Map of the peninsula of Florida, showing the
piezometric surface of the principal artesian
aquifer.

I

L)

I

w
0

I.
w
LL

-J
w
_J
w.
-i

23 23

21 21

1946 1947

1956 1

Figure 6. Hydrograph of well 953-118-1, in east-central

1948 1949 1950 1951 i 1952 1953 1954 1955

I a-~l~-s~-a----- --ib-rillb ~a ------ I.~--~-~r-aa~

L

^3 ---------------------------------- 3

33r------ -- --- -- ---------------- -- ----1----33

33- 33

317 31

29 ----f\ 7-- 29

27 -- ----------- --- --V -- \-*- --- -- 27
25 --- -- -- ----------- ----- --IV~l L

INFORMATION CIRCULAR NO. 14

Figure 7. Map of Flagler, Putnam, and St. Johns counties,
showing the piezometric surface in 1956.

FLORIDA GEOLOGICAL SURVEY

EXPLANATION o

Ccealr line representing the approximate height, 1
in feet above mean sea level, to which water 1 N
would rise in tightly cased wells that penetrated |
the principal ortesion aquifer in April, 1956 4 -

Contour interval 5 feet \ l

1 0 I 2 3 4 5
Sct m MilI

Map of St. Johns County,

surface in April 1956.

showing the piezometric

I
0M

Figure 8.

-xrw

~;no

rra~

ra

I W

INFORMATION CIRCULAR NO. 14 19

w "o EXPLANATION 5'4 s.
-35- 50
Contour line representing the approximate height, ,
in leet above mean sea level, to which water W ,
would rise in tightly cased wells that penetrate N
the principal artesian aquifer i September and
October 1956. ;i
Contour interval 5 feet a,

1 0I i 3 4 5i
s..n n MI.es

___m w\ t ___- JZ C \

40

sr c = Sb

30
t

25

*0FLAGLER COU ITY

Figure 9. Map of St. Johns County,. showing the piezometric

surface in September and October 1956.

FLORIDA GEOLOGICAL SURVEY

of the water pumped in the Hastings area has entered the
aquifer a few miles to the west in the hilly recharge area of
northwestern Putnam County.

Measurements were made in 90 wells in 1956 to deter-
mine the seasonal fluctuations of water level and the effect
of pumping on the water level. From these measurements,
the two maps of the piezometric surface in St. Johns County
were made. Elevations of the measuring points -were esti-
mated from topographic maps. Figure 8, which is based on
measurements made during the last week of the potato-
growing season, shows four discharge areas. Figure 9 is
based on measurements made in September and October,
when very little water was being used for irrigation, and
the piezometric surface was rising.

The two depressions in the Hastings and Elkton areas
(fig. 8) are caused by the withdrawal of large quantities of
water for irrigation during the potato-growing season.
Water levels in some wells in the Elkton area dropped 20
feet below observed highs during times of maximum with-
drawal. A third depression, centered in the Crescent Beach
area, is caused at least in part by the continuous dis-
charge of a large submarine spring about two miles east of
Crescent Beach. The curving of the contour lines to the
north in the St. Augustine area indicates another area of
artesian discharge. Hundreds of wells in the St. Augustine
area are used for lawn irrigation, swimming pools, and
domestic purposes, and a few overflowing wells discharge
water freely to waste. Their combined discharge is prob-
ably large enough to cause a sizable depression in the pie-
zometric surface.

Some recharge probably occurs over much of the area
of no artesian flow in St. Johns County, but the thick, rela-
tively impermeable confining beds probably prevent any
large volume of water from reaching the aquifer (fig. 10).
Recharge may be indicated by the southward bulge in the
contour lines northwest of St. Augustine. A slight decrease
in the salinity of the water immediately west of Moultrie
(fig. 11) may be due to recharge in the high ridge and swamp
belt in that area. A comparison of figures 8 and 9 shows

INFORMATION CIRCULAR NO. 14

lwd ers' ar Br2r eris'

Figure 10. Map of St. Johns County,. showing the areas oj
artesian flow in '1956.

_ I

]

f

FLORIDA GEOLOGICAL SURVEY

9-16-

- sooO

Figure 11. Map of St. Johns
content of water
aquifer.

County, showing the chloride
from the principal artesian

~"" """'""' '""' ...,

~

':O i

a*2 rrn~ ` ku` ~d

30.o-

INFORMATION CIRCULAR NO. 14

that between April and September or October the water level
rose about five feet throughout the county and that the de-
pressions created by pumping in the Hastings and Elkton
areas disappeared completely. The water levels and artesian
pressures in approximately 20 wells in the county were
measured periodically to determine the seasonal fluctua-
tions.

Area of Artesian Flow

Water will flowfrom artesian wells when the piezometric
surface stands higher than the land surface. Figure 10
shows approximately the areas where water flowed perenni-
ally or intermittently from wells in St. Johns County during
1956. The measurements of artesian pressure head from
which figure 10 was constructed were made in April and
September, the times of maximum andminimum use of arte-
sian water.

The area of perennial artesian flow extends in a wide
belt up the St. Johns River valley, across the northern part
of the county, down the east coast, andinlandin narrow belts
along the valleys of Pellicer Creek, Moultrie Creek, Deep
Creek, and others. It becomes considerably narrower to
the south because the artesian pressure head is less.

In the Hastings-Elkton area there is a broad area of
intermittent artesian flow where the piezometric surface is
lowered below the land surface as the result of heavy pump-
ing during the potato-growing season. Immediately after
the season, the area of artesianflowbegins to expand rapid-
ly to the east until it occupies the area of intermittent flow
shown in figure 10. The area of artesian flow does not
change perceptibly in the northern part of the county, where
water is withdrawn at a relatively constant rate throughout
the year.

The area of no artesian flow is principally in the south-
central part of the county, where the land surface is rela-
tively high and the artesian pressure head is low. In a few
isolated areas in the northern part of the county wells do not
flow (fig. 10), and there is no flow from artesian wells at

FLORIDA GEOLOGICAL SURVEY

the top of many sand dunes along the Atlantic Coast. Many
wells in the area of no artesian flow once overflowed through-
out the year and supplied water to second-story bathrooms
and elevated, spray-tank refill lines. A map similar to
figure 10 was made by Stringfield (1936). It indicated that
the area of artesian flow encompassed all the county except
for a small wedge- shaped area that extended southward from
a point in the center of the county, about 15 miles north of
the Flagler-St. Johns county line, to the county line where
the wedge was about eight miles wide. All available evidence
indicates that 40 years ago the area of flow probably would
have covered the entire county with the exception of a small
areaat Durbin, a very small area at the southwestern corner
of the county and a narrow strip about two miles wide that
extended northward about 12 miles from the Flagler-St.
Johns county line, in the ridge and swamp belt. The area
of artesian flow will continue to diminish if the withdrawal
of artesian water continues to increase.

Artesian Pressure Heads and Their Fluctuations

Artesian pressure heads in several wells in St. Johns
County are reported to increase with depth. A driller's log
for well 953-118-1, at the Ponce de Leon Hotel, indicated
an increase in artesian pressure head of 10 feet between
depths of 170 feet and 520 feet. Also, the artesian pressures
in well 950-119-1, at Moultrie, and well 957-120-2, north
of St. Augustine, were reported to have increased with depth.
Wells 943-128-3 and 943-128-1, at Spuds, were completed
at 180 feet with 180 feet of casing and at 350 feet with 300
feet of casing, respectively. They are less than 10 feet
apart and have a difference in artesian pressure of 0. 35
foot, which indicates that water will leak from the lower
zones to the upper zones in the uncased parts of wells. A
slow leakage from lower zones to higher zones, throughbeds
of low permeability, probably occurs over the entire area.

Fluctuations in atmospheric pressure affect water levels
in all artesian wells. A drop of an inch of mercury on a
barometer will be accompanied by a rise of as much as 0. 7
foot in water level. This explains why some wells com-
mence to flow just before storms, which are character-
ized by low atmospheric pressure. Water levels in wells

INFORMATION CIRCULAR NO. 14

near the ocean are affected by the tides. The water level
in well 945-115-1, a few yards from the ocean at Crescent
Beach, was observed to fluctuate about two feet with each
tidal cycle.

Wells

It is estimated that 450 irrigation wells penetrate the
principal artesian aquifer in the county. Information ob-
tained for 170 of these wells shows that they range in depth
from 150 to 900 feet but that most are less than 350 feet
deep. Almost all are four or six inches in diameter. It is
estimated that an additional 1, 000 artesian wells completed
in this aquifer are used for other purposes. These range
in depth from 156 to 1, 440 feet. Information obtained for
192 of these wells shows that they range in diameter from
itwo to 12 inches, most being four inches in diameter and
less than 300 feet deep.'

About 40 known artesian wells have uncontrolled dis-
charges totaling about 3, 000, 000 gallons per day.

QUALITY OF WATER

The water that falls as rain is almost devoid of mineral
matter other than carbon dioxide and other gases dissolved
from the air, but upon entering the ground it immediately
begins to acquire organic acids, more carbon dioxide, and
other substances which help it to dissolve rocks andminerals
through which it moves. There are three possible sources
of chloride contamination of the water inthe principal arte-
sian aquifer: (1) Connate sea water, which is water that was
in the materials when they were deposited, (2) sea water
that entered the formation during Pleistocene time when the
sea covered the present land surface, and (3) present-day
'intrusion of water from the ocean. The first two sources
are probably the cause of most of the salinity of the water
in the principal artesian aquifer in St. Johns County.

The concentration of chloride in ground water is of
great concern to water users in the county. Chloride salts
constitute about 90 percent of the dissolved solids in sea

FLORIDA GEOLOGICAL SURVEY

water; thus, the chloride content of ground water is generally
a reliable index of the amount of contamination from the sea.

Analyses were made of 500 water samples collected
from wells of different depths throughout the county. Many
wells were sampled several times to observe variations of
chloride concentration. The chloride content ranged from a
low of three ppm in well 004-137-1 at Switzerland, in the
northwestern part of the county where the piezometric sur-
face is relatively high, to 7, 200 ppm in well 946-116-1, two
miles west of Crescent Beach, where the piezometric sur-
face is relatively low.

Saline water has been partially flushed from the aquifer
by fresh water that entered the aquifer from rainfall, and
generally the flushing has been more complete in the upper
partof the aquifer. An isochloride map (fig. 11) represent-
ing the approximate chloride content of the water was made
from analyses of samples collected in June 1956. A com-
parison of this map with a piezometric map of the same
area indicates a general correlation between low artesian
pressure heads and high chloride content. The correlation
suggests either that the aquifer has been flushed less in
low-pressure areas or that higher artesian pressures in
deep zones of the principal artesian aquifer are causing
saline waters topercolate upward into the zones that supply
water to wells. Another possibility is that the Pleistocene
seas encroached farther into the aquifer in areas where the
piezometric surface was low. Figures 12 and 13 indicate
that water from wells deeper than 350 feet has much higher
chloride content than that from wells of shallower depth.
Analyses of water collected at 50-foot intervals in well
940-128-6, which draws water from the aquifer to a depth of
457 feet in the Hastings area, showed that the salinity in-
creased from 1,470 ppm at 300 feet to 1,735 ppm at 350
feet. The samples were collected from the open hole after
the well was drilled.

Well 942-130-1, in the town of Hastings, where little
water is used, is 700 feet deep and yields water having a
chloride content of 200 ppm. Wells 500 to 600 feet deep,
half a mile to the southwest, in the irrigated area, yield

INFORMATION CIRCULAR NO. 14

EXPLANATION

-100--
Line of equal chloride conter

I le i 0mi
S Scale in miles

Figure 12. Map of the Hastings area, showing the chloride
content of artesian water, in parts per million,
in June 1956, from wells less than 350 feet
deep.

INFORMATION CIRCULAR NO. 14

water having chloride contents as high as Z, 500 ppm. Such
high chloride concentrations indicate that saline waters are
being drawn up from deeper zones in the areas of greatest
water use.

Chemical analyses of water samples collected periodi-
cally from wells in the Hastings area showed a general in-
crease in salinity during the pumping seasons, when the
piezometric surface was lowest, and a general decline in
salinity when heavy pumping terminated.

Water from the principal artesian aquifer is relatively
hard, which is to be expected of water obtained from beds
of limestone and dolomite. Excessive hardness causes dif-
ficulty in the use of soap. Iron, which is present in objec-
tionable quantities in the water of the shallow aquifers, is
absent or occurs in minute quanitites in water from the prin-
cipal artesian aquifer. The most objectionable constituent
in the artesian water, with reference to domestic use, is
hydrogen sulfide, which gives the water a distinct odor of
rotten eggs and turns silverware and metal plumbing fixtures
black. Chloride and sulfate ions are present in the artesian
water throughout the county, but occur in different propor-
tions in the north and south sections. The general ratio in
sea water off Florida is seven parts of chloride to one part
of sulfate. This ratio is completely reversed in northern
St. Johns County, indicating the absence of sea water and
suggesting deposits of anhydrite or gypsum. The seven to
one ratio ispresentin southern St. Johns County, suggesting
the presence of sea water. The analyses for selected wells
are given in table 1.

SUMMARY AND CONCLUSIONS

The following things have been accomplished to date in
this investigation:

1. Information was collected on 362 artesian
wells that obtain water from the principal
artesian aquifer.

Table 1. Chemical Analyses of Water from Wells In St. Johns County
(Analyses in parts per million by Geological Survey)

Well number 941.129-3 954-135.1 946-116.1 007.137-1 957-120-1 011-121-1
Date of collection 1956 Aug. 9 Aug. 8 Aug. 9 Aug. 8 Aug. 8 Aug. 8

Silica (SiO2)
Iron (Fe), dissolved 1
Iron (Fe), total
Manganese (Mn), dissolved
Manganese (Mn), total
Calcium (Ca)
Magnesium (Mg)
Sodium (Na)
Potassium (K)
Bicarbonate (HCO3)
Carbonate (C003)
SSulfate (604)
Chloride (Cl)
Fluoride (F)
Nitrate (NO3)
Dissolved solids
Sum
Residue on evaporation at
180C
Hardness as CaCO3
Noncarbonate
Specific conductance
(micromhos at 250C)
pH
Color
Density at gms/ml at 20C

16 16 22 18 25 26

354
250
1,070
20
120
0
850
2,250

.00 .00
.61 .28

228
107
11
2.6
98
0
830
16
.5
.1

389
459
3,890
119
159
0
1,080
7,090
.6
.0

38
23
8.9
2.0
132
0
79
10

4,870 1,260 13,100

1,910
1,810

8,070
7.7
4

--. --- 247
1,010 2,860 189
928 2,730 81

1,550
7,7
2

21,200
7.6
3
1. 008

451
7.8
2

.00
.26

94
60
51
3.9
164
0
288
82
1.0
.2

64
39
19
2.4
166
0
175
23

790
481
346

1,010
7.8
2

452
320
184

641
7.8
4

INFORMATION CIRCULAR NO. 14

2. Continuous water-level recording gages were
installed on two wells, to determine rapid
fluctuations of the piezometric surface which
are not detected by periodic measurements.

3. Water-level measurements weremade every
six weeks on 30 wells in the county, to deter-
mine progressive trends of the water levels.

4. Water-level measurements were made twice
a year on 90 wells, for use in making piezo-
metric maps.

5. Analyses of chloride content were made of
500.water samples from 300 wells. Periodic
analyses of the chloride content of water
samples from 15 wells were made to deter-
mine changes in salinity in relation to fluct-
uations in the piezometric surface.

6. Comprehensive chemical analyses of six
water samples were made, to determine the
chemical quality of artesian water in differ-
ent parts of the. county.

7. Logs, of 40 wells were made by the author or
collected from drillers, and borehole cut-
tings were collected from six wells, for use
in making.geologic structure maps and geo-
logic cross sections.

The principal conclusions, which follow, .cannot be con-
sidered final, owing to lack of data in many areas. Many
more data will have to be collected before firm conclusions
can be reached.

Large quantities of ground water. are available in all
parts of the county from the principal artesian aquifer, a
limestone aquifer whose upper surface. ranges from less
than 125 feet below the land surface in the, southern section
of the county to more than 290, fe.et.in the northern section..

FLORIDA GEOLOGICAL SURVEY

The aquifer is overlain by a relatively impervious clay
sequence, 50 to 220 feet thick, that confines the water in the
limestone under pressure. Many thin lenses of sand, shell,
ai limestone within the confining clay sequence supply
water to small domestic wells.

Relatively large quantities of ground water may be ob-
tained from beds of sand, clay, marl, shell, and sandy lime
that overlie the confining clay and range in thickness from
25 to 140 feet. The city of St. Augustine and most farm
homes obtain part or all of their water supplies from these
beds.

Analyses of water samples from artesian wells in south-
ern St. Johns County indicate that salt water is present in
the deep zones of the aquifer. Analyses of water from
wells completed at depths greater than 350 feet, in the
Hastings area, show a maximum chloride content of 2, 500
ppm. The chloride content at the bottoms of the wells is
probably much higher because most samples were collected
at the well head and were mixtures of highly saline water
from the lower zone and less saline water from the upper
zone. Water from wells completed at depths less than 350
feet have a maximum chloride content of approximately 500
ppm. Water in the upper part of the artesianaquiferis con-
taminated by saline water that is drawn upward from deeper
zones when the wells are pumped.

The chloride content of water from artesian wells in
northern St. Johns County ranges from less than three ppm
near Switzerland to slightly more than 100 ppm north of St.
Augustine. There is no noticeable increase in salinity with
increased depth in these wells.

The principal artesian aquifer in St. Johns County is
replenished almost entirelyby rainfall that enters the aqui-
fer in the recharge area to the north and west. Local re-
charge occurs to a minor degree in part of the ridge and
swamp belt of the county. Natural discharge occurs by flow
from small springs in the northwest section and probably
by leakage through the confining beds in the area of artesian
flow. A large depressionhas beenformed inthepiezometric

INFORMATION CIRCULAR NO. 14

surface near Crescent Beach owing to the discharge of a
submarine spring two miles to the east.

A combination of drawdown from pumping and a seasonal
decline lowered the piezometric surface more than 20 feet
in some wells in the farming section at the height of the
potato-growing season in 1956. There has been a net de-
cline of about five feet in the piezometric surface over the
entire county since 1940, and an even greater decline in the
farming section. Most of this decline has occurred between
1950 and 1956, a period of subnormal rainfall.

Future work will consist of the following:

1. An inventory of all wells that obtain water
from the principal artesian aquifer in the
farming area.

2. An inventory of many wells that obtain water
from the nonartesian and thin artesian aqui-
fers.

3. A study of nonartesian conditions and the
mapping of the water table.

4. Determinations of more accurate elevations
of the measuring points on wells used to map
the piezometric surface and the water table.

5. Additional pumping tests to determine the
water-transmitting and water- storing capac-
ities of the aquifers.

6. Exploration of selected wells with a deep-
well current meter and a water-sampling
device, to determine the quantity and quality
of water from each producing zone.

7. A study of drillers' logs, electric logs, and
borehole cuttings, to determine the thick-
ness and extent of geologic formations.

34 FLORIDA GEOLOGICAL SURVEY

8. A collection of data on ground-water use, to
permit an estimate of the total annual with-
drawal.

9. An interpretation of information collected on
withdrawals, water levels, and water-
transmitting and storing capacities of the
producing zones, to predict changes in water
levels that would result from increased pump-
ing.

INFORMATION CIRCULAR NO. 14

near the ocean are affected by the tides. The water level
in well 945-115-1, a few yards from the ocean at Crescent
Beach, was observed to fluctuate about two feet with each
tidal cycle.

Wells

It is estimated that 450 irrigation wells penetrate the
principal artesian aquifer in the county. Information ob-
tained for 170 of these wells shows that they range in depth
from 150 to 900 feet but that most are less than 350 feet
deep. Almost all are four or six inches in diameter. It is
estimated that an additional 1, 000 artesian wells completed
in this aquifer are used for other purposes. These range
in depth from 156 to 1, 440 feet. Information obtained for
192 of these wells shows that they range in diameter from
itwo to 12 inches, most being four inches in diameter and
less than 300 feet deep.'

About 40 known artesian wells have uncontrolled dis-
charges totaling about 3, 000, 000 gallons per day.

QUALITY OF WATER

The water that falls as rain is almost devoid of mineral
matter other than carbon dioxide and other gases dissolved
from the air, but upon entering the ground it immediately
begins to acquire organic acids, more carbon dioxide, and
other substances which help it to dissolve rocks andminerals
through which it moves. There are three possible sources
of chloride contamination of the water inthe principal arte-
sian aquifer: (1) Connate sea water, which is water that was
in the materials when they were deposited, (2) sea water
that entered the formation during Pleistocene time when the
sea covered the present land surface, and (3) present-day
'intrusion of water from the ocean. The first two sources
are probably the cause of most of the salinity of the water
in the principal artesian aquifer in St. Johns County.

The concentration of chloride in ground water is of
great concern to water users in the county. Chloride salts
constitute about 90 percent of the dissolved solids in sea

INFORMATION CIRCULAR NO. 14

REFERENCES

Black, A.
1951

P.
(and Brown, Eugene) Chemical character of
Florida's waters 1951: Florida State Bd.Cons.,
Div. Water Survey and Research, Paper 6.

Brown, Eugene (see Black)

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

Gunter, Herman (see Sellards)

Meinzer, O. E.
1923 Outline of ground-water hydrology, with defini-
tions: U. S. Geol. Survey Water-Supply Paper 494.

Puri, H. S.
1953 Zonation of the Ocala group in peninsular Florida
(abstract): Jour. Sedimentary Petrology, vol. 23.

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

U. S. Department of Commerce, Bureau of The Census
1955 Florida Agriculture Census of 1954: Department
of Agriculture Bull. 176.

Unklesbay, A. G.
1945 Ground-water investigation at St. Augustine,
Florida: (Typewritten manuscript in files of
U.S. Geol. Survey, Tallahassee, Florida.)

36 FLORIDA GEOLOGICAL SURVEY

Vernon, R. O.
1951 Geology of Citrus and Levy counties, Florida;
Florida Geol. Survey Bull. 33.

FLRD GEOLOSk ( IC SUfRiW

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	Title Page
	Table of Contents
	Abstract
	Introduction
	Geography
	Geology
	Ground water
	Quality of water
	References

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