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Preliminary investigation of the ground-water resources of northeast Florida ( FGS: Information circular 27 )
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Permanent Link: http://ufdc.ufl.edu/UF00001087/00001
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Title: Preliminary investigation of the ground-water resources of northeast Florida ( FGS: Information circular 27 )
Series Title: ( FGS: Information circular 27 )
Physical Description: 28 p. : maps (1 fold.) diagrs., tables. ; 23 cm.
Language: English
Creator: Leve, Gilbert W ( Gilbert Warren ), 1928-
Geological Survey (U.S.)
Publisher: s.n.
Place of Publication: Tallahassee
Publication Date: 1961
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Subjects / Keywords: Groundwater -- Florida   ( lcsh )
Water-supply -- Florida   ( lcsh )
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General Note: "Prepared by the United States Geological Survey in cooperation with Florida Geological Survey."
General Note: "References": p. 28
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Source Institution: University of Florida
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The author dedicated the work to the public domain by waiving all of his or her rights to the work worldwide under copyright law and all related or neighboring legal rights he or she had in the work, to the extent allowable by law.
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Table of Contents
    Copyright
        Copyright
    Front Cover
        Front Cover
    Title Page
        Page i
        Page ii
    Table of Contents
        Page iii
        Page iv
    Abstract
        Page 1
        Page 2
    Introduction
        Page 3
        Page 6
        Page 7
    Geologic formations and their water-bearing properties
        Page 8
        Page 9
    Ground water
        Page 10
    Artesian aquifer
        Page 11
    Piezometric surface
        Page 12
        Page 13
        Page 14
    Water level data
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
    Quality of water
        Page 22 (MULTIPLE)
        Page 23
        Page 24
        Page 25
        Page 26
        Page 27
    Reference
        Page 28
Full Text
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Florida Agricultural Experiment Station Library
Gainesville, Florida


STATE OF FLORIDA STATE BOARD OF CONSERVATION
FLORIDA GEOLOGICAL SURVEY Robert O. Vernon, Director
INFORMATION CIRCULAR NO. 27
PRELIMINARY INVESTIGATION OF
THE GROUND-WATER RESOURCES OF
NORTHEAST FLORIDA
By
Gilbert W. Leve, Geologist U. S. Geological Survey
Prepared by the UNITED STATES GEOLOGICAL SURVEY in cooperation with the FLORIDA GEOLOGICAL SURVEY
Tallahassee, Florida 1961


tie. 21
AGRI-CU1TURAL WBRARY


TABLE OF CONTENTS
Page
Abstract....................................... 1
Introduction.................................... 3
Previous investigations....................... 4
Acknowledgments............................ 4
Well-numbering system...................... 4
Geography..................................... 5
Geologic formations and their water-bearing
properties.................................. 8
Ground water.................................. 10
Artesian aquifer............................. 11
Piezometric surface......................... 12
Water-level data............................. 15
Quality of water................................ 22
Salt-water contamination..................... 22
References.................................... 28
ILLUSTRATIONS
Figure
1 Map of the Florida Peninsula showing the location of the area covered by this report 6
2 Map of northeast Florida showing the location of wells.......................- 7
3 Correlation of formations penetrated by well 026-126-1 near Jacksonville and well 038-127-3 at Fernandina................ 9
4 Map of the Florida Peninsula showing the piezometric surface of the principal artesian aquifer................................ 13
5 Map of northeast Florida showing the piezometric surface of the principal artesian aquifer in January February I960....... 14
6 Maps of northeast Florida showing the piezometric surface of the principal artesian aquifer in 1880, 1943, 1955, and I960 ____ 16


7 Total municipal pumpage at Jacksonville and water levels in well 019-140-1 in Jacksonville.................................. 17
8 Hydrographs of wells 013-135-1, 018-140-1, 019-133-1, and 023-138-1 in Duval County 18
9 Hydrographs of wells 037-130-1, 037-142-1,
and 040-126-1 in Nassau County.......... 19
10 Annual discharge of artesian water in the Fernandina and Jacksonville areas and the average annual rainfall for three weather stations in the recharge area............ 21
11 Map of northeast Florida showing the approximate chloride content of water from
the artesian aquifer..................... 25
Table
1 Chemical analyses of water from artesian wells in Duval and Nassau counties....... 23
2 Chloride content of water from artesian wells in Duval and Nassua counties....... 26


PRELIMINARY INVESTIGATION OF THE
GROUND-WATER RESOURCES OF NORTHEAST FLORIDA
By
Gilbert W. Leve
ABSTRACT
This report describes an area of about 2,000 square miles in northeast Florida and southeast Georgia. The principal source of water in the area is permeable limestones of Eocene age. The top of the limestone of Eocene age was found to be 570 feet below the land surface in well 026-126-1, 16 miles northeast of Jacksonville, and 550 feet below theland surface in well 038-127-3, 3miles southwest of Fernandina Beach. These limestones are overlain by the Hawthorn formation of middle Miocene age, which consists of beds of sandy clay and clayey sand containing limestone and dolomite lenses. The Hawthorn formation is overlain by undifferentiated deposits of sand, clay, marl, and shell of undetermined age. Impermeable beds in the Hawthorn formation and post-Hawthorn deposits serve as confining beds for the artesian water in the underlying limestones of Eocene age.
The principal recharge area to the artesian aquifer in northeast Florida is in the vicinity of a piezometric high that extends from northwestern Putnam County, through western Clay, Bradford, Union, and Baker counties into Georgia. From this recharge area, the piezometric surface slopes generally northeastward into northeast Florida toward discharge areas in Duval and Nassau counties.


Cones of depression have developed in the piezometric surface in Fernandina and in the vicinity of Jacksonville as a result of discharge of artesian water by municipal and industrial wells. Between 1880 and January I960, the decline of the piezometric surface in northeast Florida has ranged from about 10 feet to more than 60 feet, and there has been a great enlargement of the cones of depression since 1943.
Variations in discharge of industrial and municipal wells commonly cause the water levels in nearby wells to fluctuate more than 10 feet. Long-term trends in water levels can be attributed to a combination of cyclic trends of rainfall in recharge areas and an increase in both seasonal and perennial use of water in discharge areas. Water levels in wells throughout northeast Florida generally declined between 1940 and 1956 or 1957 because of a deficiency in rainfall and increased discharge of artesian water. Water levels rose from 4. 5 to 12 feet between 1956 or 1957 and January I960 in response to average to above average rainfall, but because of increased pumpage they remained well below previous recorded high water levels.
Presently, the rate of discharge at Fernandina and in the vicinity of Jacksonville does not exceed the perennial yield of the aquifer. However, with an expansion of industry and an increase in population in northeast Florida, the rate of discharge of artesian water can be expected to increase. At some future date, the rate of discharge may exceed the normal rate of recharge and water levels-may again continue to decline even during cycles of average rainfall.
The chloride content of the water is less.than 20 ppm (parts per million) in wells in the southwestern part of the area where the piezometric surface is highest and more than 30 ppm in wells in northern Duval and northern Nassau counties where the piezometric surface is lowest. The chloride content of the water was 860ppm inSeptember 1959 in a well located near the center of the cone of depression at Fernandina. The chloride content of water from most artesian wells increased from 1 to 13 ppm since 1940 and the chloride content of water from well 038-127-3 has increased more than 220 ppm from April 1956 to September 1959.


Most water samples analyzed during this investigation did not indicate sufficient chloride content to endanger the industrial or municipal supplies. However, if the artesian pressure declines below the record lows of 1956 and 1957, contamination of fresh-water supplies might increase until eventually these supplies might become unsuitable for industrial and municipal use.
INTRODUCTION
Fresh water for industrial, municipal, and agricultural use in northeast Florida is supplied almost entirely by artesian wells. In recent years, the use of artesian water in the area has increased to meet the needs of industrial expansion and population growth. To meet the increased demand for fresh water, many additional artesian wells have been drilled, many existing wells have been deepened, and pumps have been installed on wells that had previously produced an adequate supply of water by natural flow. The increase in water use can be correlated with the decline of artesian pressures in the artesian aquifer. Records of pressure, in artesian wells in northeast Florida showthat in some parts of the area pressures have declined more than 60 feet since 1880. In many parts of Florida such a decline in artesian pressures has resulted in salt-water encroachment into the fresh-water supply. Salt-water encroachment into the artesian-water supply in northeast Florida would probably inhibit the area's economic growth and result in hardship for the population.
The U. S. Geological Survey in cooperation with the Florida Geological Survey made a reconnaissance to determine the extent and cause of the decline in artesian pressures, and to determine if this decline has resulted in salt-water intrusion in northeast Florida. This report presents and interprets the information collected during the reconnaissance made in January to March I960.
The investigation was made under the general supervision of Philip E. LaMoreaux, chief, Ground Water Branch, U. S. Geological Survey, and of Robert O. Vernon, director, Florida Geological Survey; and under the immediate supervision of M. I. Rorabaugh, district engineer for Florida.


Figure 1. Map of the Florida Peninsula showing the location of the area covered by this report.


Figure 2. Map of northeast Florida showing the location of wells.


into the ocean. Drainage throughout northeast Florida is generally sluggish and poorly developed and this results in numerous marshes onboth the higher terraces and lowplain.
GEOLOGIC FORMATIONS AND THEIR WATER-BEARING PROPERTIES1
The formations generally penetrated by water wells in northeast Florida are shown in figure 3. The permeable limestones of Eocene age are the principal source of fresh water in the area. As shown on figure 3, the top of the limestone is 570 feet below the surface in well 026-126-1 near Jacksonville, and 550 feet below the surface in well 038-127-3 in Fernandina. In well 038-127-3 more than 1,500 feet of Eocene limestone was penetrated without reaching older rocks.
Limestones of early and middle Eocene agethe Oldsmar, Lake City, and Avon Park limestones consist predominantly of alternating beds of soft, porous limestone and hard, dense, crystalline limestone and dolomite. The Ocala group, thelnglis, Williston, and Crystal River formations of late Eocene age consist of a relatively homogeneous sequence of hard to soft, granular, porous limestone containing a few thin dolomite beds near the base.
Greenish, calcareous, phosphatic, sandy clay and clayey sand beds containing lenses of limestone and dolomite overlie the limestones of Eocene age. These relatively impermeable beds comprise the Hawthorn formation of early and middle Miocene age. The Hawthorn formation is more than 450 feet thick in both wells shown on figure 3.
The classification and nomenclature of the rock units conform to the usage of the Florida Geological Survey and also, except for the Ocala group and its subdivisions, with those of the U. S. Geological Survey, which regards the Ocala as two formations, the Ocala limestone and the Inglis limestone.


200 -
400 -
w 600 -
1000 -
1200
5 1400
LU
a 1600 h
1800
L I THOLOGY
Cliar to brawn stained, vary fine to medium grained (and', gray cloy i morh, and shell
^ Greenish-gray, sandy, caleoreous, phosphorltle day with beds of sandy, phosphorltle limestone
Cream la tan, soft to hard, granular, parous limestone. Soma beds composed of foramlnlferal eoqulna, Contains thin dolomite beds,
Cream, granular to pasty limestone containing beds of to brown, hard, dense crystalline dolomite, Some beds have flecks of peat,
Tan to brown, soft, pasty to hard, dense, finely > crystalline limestone, Contains beds of cream to tan, hard dense dolomite becoming thicker with depth.
Cream soft porous, granular limestone with tan to brown hard crystalline dolomite.______
Figure 3. Correlation of formations penetrated by well 026-126-1 near Jacksonville and well 038-127-3 at Fernandina.
199?1587
75


Undifferentiated deposits of sand, clay, marl, and shell overlie the Hawthorn formation and are exposed at the surface. The age of these deposits was not determined during the investigation and they are referred to in this report as post-Hawthorn deposits. They are about 90 feet thick in wells 026-126-1 and 038-127-3.
Generally, only small quantities of water are obtained from thin sandy limestone and sand lenses in the Hawthorn formation and post-Hawthorn deposits. However, a few large diameter wells that tap these shallow permeable beds yield moderate to large quantities of fresh water. The impermeable clay, marl, and dolomite beds in these deposits serve as confining beds for the artesian water in the underlying limestones of Eocene age.
GROUND WATER
Ground water is that part of the subsurface water that is in the zone of saturation and in which all pore spaces in the rock are filled with water. It is derived almost entirely from precipitation but not all precipitation becomes ground water. Part of it is returned to the atmosphere by evapo-transpiration and part of it drains overland into lakes, streams, and the ocean.
Ground water is under artesian conditions when the water is confined in a permeable bed that is overlain by an impermeable bed, so that the water surface is not free to rise and fall. The term "artesian" is applied to ground water that is confined under sufficient pressure to rise above the top of the permeable bed that contains it. The height to which artesian water will rise in a tightly cased well is called the artesian pressure head, and the imaginary surface coinciding with the water levels of the artesian wells is called the piezometric surface.
An aquifer is a formation, group of formations, or part of a formation in the zone of saturation that is permeable enough to transmit usable quantities of water. Areas in which the aquifers are replenished are called recharge areas'


and areas in which water leaves the aquifer are called discharge areas.
Artesian Aquifer
The principal artesian aquifer in northeastern Florida consists of beds of limestone of Eocene age. Water is confined under pressure in the limestone by beds of clay, marl, and dolomite in the overlying Hawthorn formation and post-Hawthorn deposits.
The principal artesian aquifer is the principal source of ground water in northeast Florida; accordingly, the information collected and studied during this investigation concerns only that aquifer.
The artesian aquifer is recharged to the north and west of the area in southeastern Georgia and north-central Florida. In the recharge area the limestones of Eocene age either crop out at the surface and are recharged directly by rainfall, or the formations are hydrologically connected to lakes, streams, sinkholes, and the nonartesian aquifer.
Groundwater moves laterally away from the recharge area through the permeable limestone toward areas where discharge is occurring. In northeastern Florida, water is discharged by numerous wells that penetrate the artesian aquifer.
Figure 3 shows that below the Inglis formation, the principal artesian aquifer contains beds of hard, dense crystalline dolomite and limestone. These beds are less permeable than the soft porous limestone and tend to restrict the vertical movement of water in the aquifer. Water from the formations below the Inglis formation comes from several relatively permeable beds that are separated by less permeable beds. Differences in head and in the chloride content of water from some of these permeable beds indicates that some may be partly or entirely isolated from the rest of the aquifer by impermeable beds.


In the past the Inglis, Williston, and Crystal River formations have supplied sufficient quantities of water to industrial and municipal wells, and the underlying formations were not used as a source of water. Recently, however, a number of industrial and municipal wells have been deepened and new wells have been drilled into the underlying formations because of the increasing demand for water.
Piezometric Surface
The direction of ground-water movement and the general areas of recharge and discharge can be determined by constructing a contour map on the piezometric surface. In areas where water enters the aquifer the piezometric surface is high. The direction of ground-water movement is approximately perpendicular to the contour lines toward areas where the piezoemtric surface is low.
Figure 4 shows the piezometric surface of the principal artesian aquifer in Florida in 1949. The principal recharge area for the artesian aquifer in northeast Florida is the area marked by a piezometric high that extends from northwestern Putnam County, through western Clay, Bradford, Union, and Baker counties into Georgia. From this recharge area, the piezometric surface slopes toward discharge areas in northeast Florida. The configuration of the 50-foot contour lines in Duval and Nassau counties indicates in a general way the effect of discharge in these areas.
Measurements of the water levels in 94 wells in northeast Florida and southeast Georgia in January and February I960 were used to construct the piezometric map shown in figure 5. As artesian pressures are constantly changing, the altitude and configuration of the piezometric surface shown in this figure is only an approximate representation of the piezometric surface at other times. The closed contour lines at Fernandina and in the vicinity of Jacksonville indicate depressions in the piezometric surface. Within these depressions, discharge of artesian water by industrial and municipal wells has lowered the artesian head in the aquifer. These withdrawals have formed a cone of depression',


Figure 4. Map of the Florida Peninsula showing the piezometric surface of the principal artesian aquifer.


Figure 5. Map of northeast Florida showing the piezometric surface of the principal artesian aquifer in January February I960.


and have created a hydraulic gradient toward the discharging wells. As shown in figure 5, the altitude of the piezometric surface within the cones of depression in the vicinity of Jacksonville is between 30 and 40 feet above sea level and in the center of the cone of depression in the Fernandina area the piezometric surface is below sea level.
Figure 6 shows the altitude and configuration of the piezometric surface in northeast Florida in 1880, 1943, 1945, and I960. A comparison of the piezometric surface at different times show that since 1880 the decline of the piezometric surface has ranged from about 10 feet in the southwestern part of the area to more than 60 feet in the Fernandina area. The maps also show a considerable enlargement in the cones of depression in Fernandina and in the vicinity of Jacksonville since 1943.
Water-Level Data
Water levels in wells are constantly changing in the artesian aquifer. The most conspicious changes in water levels in northeast Florida are those that are caused by the discharge of artesian wells. When water is discharged from an artesian well, the water level in the well and the artesian head in the aquifer near the well is lowered. The greatest decline of the artesian head is at the well and the decline decreases as the distance from the well increases.
The effect of municipal pumpage on the water levels in a nearby well can be seen in figure 7. A comparison of the total monthly municipal pumpage at Jacksonville with the water level in well 019-140-1, located in Jacksonville, shows that as the pumpage increases, the water level in well 019-140-1 declines and vice versa. Seasonal fluctuations of more than 10 feet are common, particularly during the late spring and summer months when municipal pumpage is generally greatest.
Hydrographs of wells in Duval and Nassau counties (fig. 8, 9) show the seasonal fluctuations and long-term trends of water levels from 1940 to January I960. All of


1955 1960
(Prepared by E. Doragon.) (Prepared by W. Leve I960)
0 10 20 30 miles
Figure 6. Maps of northeast Florida showing the piezometric surface of the principal artesian aquifer in 1880, 1943, 1955, and I960.


g25
*
20
||l5
"8 io
\ /I / A i
V u N / V V
Well 019 -140-1 V V
I/) -C
I 11400
E 1200 ,E a.
of w 1000 o J
pa 8oo
Q- o 600
Figure 7. Total municipal pumpage at Jacksonville and water levels in well 019-140-1 in Jacksonville.


A A
\ *** ./ V
r L \
V V w!
V V V I, A
Well 013- 35-1 V v / n
V l J N
V I
0
*
- -8
Wtll 019- 133-1
1
/\ h A
\ A / / V V
/ / 1 i
V V |\A
Wtll 023- 138- | v V
1 M A
V V
IMS sar TS5F 1ST TOT flBT V tifer 1
Figure 8. Hydrographs of wells 013-135-1, 018-140-1, 019-133-1, and 023-138-1 in Duval County.


Figure 9. Hydrographs of wells 037-130-1, 037-142-1, and 040-126-1 in Nassau County.


the hydrographs show a consistent decline in water levels between 1940 and 1956 or 1957 and rise in water levels between 1956 or 1957 and January I960.
Wells near areas of pumpage generally showed the greatest changes in water level. As shown on figure 9 water levels in well 040-126-1 between June 1949 and May 1956, located near the center of the cone of depression at Fernandina, declined 41.5 feet. During about the same period water levels in well 037-142-1, located about 14 miles west of Fernandina, declined approximately 15 feet.
The cause of the long-term decline trends in water levels in northeast Florida is attributed to a combination of the effects of cyclic decline of rainfall on recharge areas and an increase in use of artesian water.
The average of annual rainfall for three stations in the recharge area and estimates of annual discharge of artesian water in Fernandina and in the Jacksonville area since 1940 are shown by graphs in figure 10. The estimates of discharge were made from records of the municipal pumpage and from a survey of water used by private utilities, individual well owners, and by major industries.
A comparison of the bar graphs in figure 10 with hydrographs of wells in figures 8 and 9 indicates that between 1940 and 1956 or 1957, water levels declined even during years of above average rainfall. This decline was probably due to a progressive increase in ground-water use. A combination of below average rainfall and increased groundwater use resulted in a rapid decline in water levels during 1954 and 1955 and the lowest recorded water levels were in 1956 and 1957. From 1956 or 1957 to January I960, average to above average rainfall re suited in a 4.5- to 12-foot rise in water levels. However, increased ground-water use during this period caused the water levels to remain below the record high water levels of 1940-53.
The rise in water levels between 1956 or 1957 and 1959 in response to average and above average rainfall in the recharge area indicates that the perennial yield of the.


Figure 10. Annual discharge of artesian water in the Fernandina and Jacksonville area and the average annual rainfall for three weather stations in the recharge area.


aquifer has not been exceeded by discharge at Fernandina and Jacksonville. However, with future expansion of industry and increasing population in the area the rate of discharge of artesian water can be expected to increase. It is possible that the rate of discharge will eventually exceed the normal rate of recharge and water levels will decline even during cycles of average rainfall.
QUALITY OF WATER
The chemical character of ground water is largely dependent upon the type of material with which the water comes in contact, or contamination with sea water. When the water first enters the ground it is only slightly mineralized, but as it moves through the ground it becomes more mineralized by dissolving mineral matter from the rocks and mixing with mineralized water already in the rocks.
Chemical analyses of water from five artesian wells sampled periodically are shown in table 1. The degree of mineralization, expressed by the dissolved-solids content) has generally increased in each well in the past few years. The greatest increase was in well 038-127-3, which is located near the center of the cone of depression at Fernandina. The dis solved-8 olids content of water from this well increased from 1,960 ppm in April 1956 to 3,050 in September 1959.
Salt-Water Contamination
In many parts of Florida, where there has been a decline in artesian pressure, the existing fresh-water supply has been contaminated by intrusion of salt water. These intrusions have occurred in various ways, depending upon the location and geologic characteristics of the different areas. In some areas, particularly near the coast, salt water from the ocean has moved laterally or vertically into zones of reduced pressure. In other areas, salt water has moved upward from deep, highly mineralized zones, or laterally from separate, relatively thin mineralized zones within the aquifer into fresh-water zones. 1


. Chemical Analyses of Water from Artesian Wells in Duval and Nassau Counties
Veil nunber Depth of veil (feet) Total casing (feet) Date sampled Dissolved solids s CO a 4* ft to a o u H Calcium (Ca) Magnesium (Mg) Sodium and Potassium (Na-K) Bicarbonate (HC03) Sulfate (SO4) Chloride (CI) pll St? <5 "E ^ ts m SB sd
018-138-1 1,348 504 5-20-50 438 21 ---- 75 31 12 167 184 8 7.6 313
3-31-60 462 ---- ---- ---- ---- 12 164 ---- 11 7.8 320
020-139-1 1,250 9-27-41 325 26 0.12 61 23 14 178 96 16 ---- 246
5-20-50 348 27 ---- 60 22 10 190 83 14 7.6 240
3-31-60 349 ---- ---- ---- ---- 13 188 ---- 18 7.6 244
025-138-1 942 660 1- 9-43 308 26 .10 76 24 0 197 72 4 7.2 289
5-20-50 317 27 .08 55 24 6.4 204 98 22 7.4 236
6-10-58 392 ---- .07 55 22 ---- 163 63 26 7.8 232
038-127-3 1,826 ---- 4-17-56 1, 960 ---- ---- 178 86 ---- ---- 360 644 ---- 790
9- 3-59 3,050 ---- ---- 170 101 ---- ---- 403 864 841
040-127-2 731 9-28-37 ---- 22 .31 60 44 19 195 159 33 7.3 330
4- 2-50 480 33 .01 71 39 21 200 166 33 7.4 334
4- 1-59 509 ---- .06 72 28 ---- 202 144 29 7.4 300


The chloride content of ground water is generally a reliable indication of the extent to which normally fresh ground water has become contaminated with sea water because about 91 percent of the dissolved-solids content of sea water consists of chloride compounds.
Water samples from 66 artesian wells in northeast Florida and southeast Georgia were analyzed for chloride content; the results of these analyses are shown infigure 11.
In the southwest part of the area, closetothe recharge area where the piezometric surface is highest (fig. 5), the chloride content of water from wells :1s less than 20 ppm. The chloride content generally increases northeastward in the direction of ground-water movement to more than 30 ppm in northern Duval County and northern Nassau County. In well 038-127-3, located near the center of the cone of depression at Fernandina, where the piezometric surface is below sea level, the chloride content of the water exceeded 860 ppm in 1959 (table 1).
The chloride content of water of several wells that were sampled periodically from 1940 to I960 in Duval and Nassau counties is shown in table 2. A comparison of the chloride content of water sampled in I960 with water sampled previously shows that there has been an increase in the chloride content of water from most of the wells since 1940.
This increase in chloride content can generally be correlated with the decline in artesian pressures. In areas of northeast Florida where the piezometric surface has declined 10 to 20 feet since 1880 (fig. 6) the increase in chloride content of the artesian water has been small, ranging from 1 to 13 ppm since 1940 (table 2). However, in the cone of depression at Fernandina, where the piezometric surface has declined over 60 feet since 1880, the increase appears to be much greater particularly in the deeper wells. In well 038-127-3, 1,826 feet deep and located near the center of the cone of depression at Fernandina, the chloride content of the water increased 220 ppm between April 1956 and September 1959 (table 1). The relatively rapid increase in chloride content in well 038-127-3 gives evidence that


Figure 11. Map of northeast Florida showing the approximate chloride content of water from the artesian aquifer.


Table 2. Chloride Content of Water from Artesian Wells in Duval and Nassau Counties
Well number Depth n f Total Chloride content, In parts per million
County O L well (feet) casing (feet) o 5 ft 3 i ft 1/1 ft 1-4 < ft 19481 r-t -1 1950 ft ui 0> ft N iri Cn ft rn *l 0* ft ft 1955 1956 n. m o> CO m 9\ ft 1959 1960
011-141-1 Duval 403 252 12 12

013-135-1 Duval 625 461 14 15 20

015-141-1 Duval 600 470 10 10 11

018-123-1 Duval 585 357 14-20
20 24
019-132-1 Duval 762 509 15 17-18
18 16

019-140-1 Duval 755 14 14

020-144-1 Duval 630 500 11 16 18

021-123-1 Duval 575 15 18 22
021-138-1 Duval 1,060 543 13 23

025-141-1 Duval 725 500 11 19 24

026-126-1 Duval 455 19 19 20 24

026-145-1 Duval 658 21 16 29

027-143-1 Duval 610 446 23 26 30

032-126-1 Nassau 680 23 23 26

033-150-1 Nassau 580 26 28-29
30
035-127-2 Nassau 580* 350 25 31 30 26

037-129-1 Nassau 578 27 27 28 30

037-130-1 Nassau 540 504 27 28 33 32

03 7-136-1 Nassau 1,000 450 30 28 30

038-126-1 Nassau 550 28 28 29 36 39



contamination is proceeding at a faster rate in the deeper wells. It is possible that the deeper wells, particularly in areas of heavy pumpage may become contaminated with salt water before the relatively shallow artesian wells in the same area.
The increase in chloride content of the artesian water during the past few years and the decline in artesian pressures indicates that salt water is gradually moving into the zones of reduced pressure and contaminating the existing fresh-water supply. The relatively low chloride content of the water sampled from most wells during the investigation indicates that at present serious contamination is restricted to a small area at Fernandina and there is little immediate danger to the industrial and municipal supplies elsewhere. However, if the artesian pressures decline below the level of 1956 and 1957, it can be expected that increased amounts of salt water will contaminate the fresh-water supplies. Then the present fresh water in the aquifer will become progressively saltier until at some future date it is conceivable that the water will become unsuitable for industrial and municipal use.


REFERENCES
Black, A. P.
1951 (and Brown, Eugene) Chemical character of
Florida's waters 1951: Florida State Board Cons- Div. Water Survey and Research, Paper 6.
Brown, Eugene (see Black, A. P.)
Cooper, H. H. Jr.
1944 Ground-water investigations in Florida (with
special reference to Duval and Nassau counties): Am. Water Works Assoc. Jour. v. 36, no. 2.
Leve, Gilbert W.
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