Technical Publication SJ93-7

VOLUME 1

OF THE

LOWER ST. JOHNS RIVER BASIN

RECONNAISSANCE

HYDROGEOLOGY

by

David J. Toth, Ph.D., P.G.

0

Professional Geologist

License No. 110

November 18, 1993

Soal

St. Johns River Water Management District

Palatka, Florida

1993
Northwest Florida

Water Management

District Suwannee

River Water

Management

District

St

River Water

Management

District

St. Johns River

Water

Management

District

Southwest

Florida

Water

Management

District

South

Florida Water

Management

District

The St. Johns River Water Management District (SJRWMD) was created by the Florida Legislature in 1972

to be one of five water management districts in Florida. It includes all or part of 19 counties in northeast

Florida. The mission of SJRWMD is to manage water resources to ensure their continued availability while

maximizing environmental and economic benefits. It accomplishes its mission through regulation; applied

research; assistance to federal, state, and local governments; operation and maintenance of water control

works; and land acquisition and management.

Technical reports are published to disseminate information collected by SJRWMD in pursuit of its mission.

Copies of this report can be obtained from:

Library

St. Johns River Water Management District

P.O. Box 1429

Palatka, FL 32178-1429

Phone: (904) 329-4132
Contents

CONTENTS

List of Figures vi

List of Tables viii

ABSTRACT 1

INTRODUCTION 3

HYDROGEOLOGY 9

Limestone 10

Hawthorn Group 10

Surficial Deposits 16

AQUIFER SYSTEMS 20

Floridan Aquifer System 21

Intermediate Aquifer System 36

Surficial Aquifer System 38

SUMMARY 44

RECOMMENDATIONS 48

References 49

St. Johns River Water Management District

V
HYDROGEOLOGY

FIGURES

1 Major surface water basins within the St. Johns River Water

Management District 4

2 Lower St. Johns River surface water basin 5

1.1 The lower St. Johns River ground water flow system and the

lower St. Johns River surface water basin 8

1.2 Typical hydrostratigraphic column in the lower St. Johns

River ground water flow system 12

1.3 Cross section showing geologic structure in the lower

St. Johns River ground water flow system 13

1.4 Location of cross-section A-A' 14

1.5 Depth to the top of the limestones of the Floridan aquifer

system in the lower St. Johns River ground water flow

system 15

1.6 Thickness of the Hawthorn Group in the lower St. Johns

River ground water flow system 17

1.7 Thickness of surficial deposits in the lower St. Johns River

ground water flow system 18

1.8 Direction of flow in the Floridan aquifer system of the lower

St. Johns River ground water flow system 23

1.9 Areas of natural recharge and discharge of the Floridan

aquifer system in the lower St. Johns River ground water

flow system and the lower St. Johns River surface water

basin 25

1.10 Major springs in the lower St. Johns River ground water flow

system 27

St. Johns River Water Management District

m
Figures

1.11 Chloride concentrations in the Upper Floridan aquifer of the

lower St. Johns River ground water flow system 30

1.12 Location of possible faults in the lower St. Johns River

ground water flow system 32

1.13 Sulfate concentrations in the Upper Floridan aquifer of the

lower St. Johns River ground water flow system 34

1.14 Total dissolved solids in the Upper Floridan aquifer of the

lower St. Johns River ground water flow system 35

1.15 Direction of flow in the surficial aquifer system of the lower

St. Johns River ground water flow system 41

1.16 Chloride concentrations in the upper 50 feet of the surficial

aquifer system in the lower St. Johns River ground water

flow system 43

St. Johns River Water Management District

vii
HYDROGEOLOGY

TABLES

1 Geologic time scale 9

2 Hydrogeologic framework of the lower St. Johns River

ground water flow system 11

3 Source of water used for public supply and domestic selfsupply in the lower St. Johns River surface water basin . . 21

St. Johns River Water Management District

Vlii
Abstract

ABSTRACT

This report is Volume 1 in a series of reconnaissance reports

about the Lower St. Johns River Basin (LSJRB). The lower

St. Johns River is the northern part of the St. Johns River from the

mouth of the Ocklawaha River in Putnam County to the inlet at

the Atlantic Ocean in Duval County. LSJRB includes parts of

nine counties in northeast Florida. The reconnaissance reports

compile information and make recommendations to help resource

managers identify priority needs for research into and

management of LSJRB. These reports are part of the research

funded under the Surface Water Improvement and Management

Act of 1987 (Sections 373.451-4595, Florida Statutes).

This volume examines the relationship and influence of the

interconnection between the lower St. Johns River and the ground

water flow system associated with the river. The mechanisms of

this interconnection are spring flow, diffuse upward leakage from

the Floridan aquifer system, and seepage from the surficial

aquifer system. Ground water within the lower St. Johns River

ground water flow system resides in the Floridan, intermediate,

and surficial aquifer systems.

Ground water movement within the portion of the Floridan

aquifer system that affects LSJRB generally flows eastward. Near

Green Cove Springs, the Floridan aquifer system is estimated to

lose 46 cubic feet per second (ft3/sec) to the surficial aquifer

system, the intermediate aquifer system, the St. Johns River, or a

combination of all three as a result of spring discharge and

diffuse upward leakage. In southern Putnam County, 80

discharges from the Floridan aquifer system to the St. Johns River

at Croaker Hole Spring.

In the Floridan aquifer system, moderately saline water

containing chloride concentrations between 250 and 1,000

milligrams per liter (mg/L) is present beneath part of the

St. Johns River in Putnam County and in southern St. Johns and

northern Flagler counties.

St. Johns River Water Management District

1
HYDROGEOLOGY

The intermediate aquifer system overlies the Floridan aquifer

system in portions of Duval, St. Johns, Clay, Putnam, and Flagler

counties. Water in the intermediate aquifer system is derived

locally either by upward leakage from the underlying Floridan

aquifer system or by downward leakage from the overlying

surficial aquifer system.

The water table in the surficial aquifer system generally is a

subdued reflection of the topography. Water flows away from

ridges toward streams, creeks, the St. Johns River, and the coast.

Chloride concentrations in the upper 50 feet of the surficial

aquifer system are above 1,000 mg/L within 1-4 miles of the coast

in Duval, Flagler, and Volusia counties.

St. Johns River Water Management District

2
Introduction

INTRODUCTION

This report is Volume 1 in a series of reconnaissance reports

about the Lower St. Johns River Basin (LSJRB). This compilation

of information and recommendations provides resource managers

with a basis for identifying priority needs for future research and

actions regarding LSJRB. The reconnaissance reports are part of

the research funded under the Surface Water Improvement and

Management (SWIM) Act of 1987 (Sections 373.451-4595, Florida

Statutes').

The SWIM Act declares that many natural surface water systems

in Florida have been or are in danger of becoming degraded from

point and nonpoint sources of pollution and from the destruction

of natural systems. The state's five water management districts,

in cooperation with state agencies and local governments, were

directed to set priorities for waterbodies of regional or statewide

significance and to design plans for surface water improvement

and management. Six waterbodies were named for immediate

action, including LSJRB.

LSJRB is one of ten surface water basins of the St. Johns River

Water Management District (SJRWMD) (Figure 1). LSJRB is

located in northeast Florida and represents about 22 percent of

the area within the boundaries of SJRWMD. LSJRB extends from

the City of De Land, in the south, to the inlet of the St. Johns

River at the Atlantic Ocean. LSJRB includes parts of nine

counties: Clay, Duval, Flagler, Putnam, St. Johns, Volusia,

Alachua, Baker, and Bradford (Figure 2).

The climate of LSJRB is classified as humid subtropical, with an

average summer maximum daily temperature of 32.2 degrees

Centigrade (°C) (90 degrees Fahrenheit). In the winter, LSJRB

experiences below-freezing temperatures an average of 10 to 15

times per year. Average annual rainfall in LSJRB is

approximately 132 centimeters (52 inches). A large portion of the

annual precipitation falls between June and September when

convective activity generates showers and thunderstorms.

St. Johns River Water Management District

3
8300W

30 00 N

BASINS

1. Nassau River

2. St. Marys River

3. Lower St. Johns River

4. Middle St. Johns River

5. Lake George

6. Upper St. Johns River

7. Ocklawaha River

8. Florida Ridge and

Orange Lake

9. Upper Coastal

10. Indian River Lagoon

2900N

Legend

County boundary

Surface water basin boundary

District boundary

Waterbody

aer k.

J INDIAN RIVER \ 1 0

8000W

ST. JOHNS RIVER

WATER MANAGEMENT

DISTRICT

16 32

J

Approximate scale in miles

Figure 1. Major surface water basins within the St. Johns

River Water Management District
Lower St. Johns River

surface water basin boundary

Approximate scale in miles

Figure 2. Lower St. Johns River surface water basin
HYDROGEOLOGY

Landscape features within LSJRB are relatively low and flat.

Three ridge systems border the drainage area. Surface elevations

range from sea level at the inlet to greater than 61 meters (m)

(200 feet [ft]) in the western part of LSJRB.

The St. Johns River is an elongated, shallow estuary with an

extensive floodplain. The elevation of the St. Johns River at the

mouth of the Ocklawaha River is less than 3.0 m (10 ft) above sea

level, and the average gradient of the main river channel is only

0.022 meters per kilometer (0.1 ft per mile). Average annual tidal

amplitude is 1.5 m (4.9 ft) at the ocean inlet and varies unequally

upstream due to channel morphology. Due to the low gradient

of the river, however, tides affect the entire LSJRB along with the

lower reaches of its tributaries. The mixing of salt water and

fresh water has an influence on water quality as well as on the

quantity and characteristics of sediments deposited in LSJRB.

Water quality conditions for LSJRB range from good in the

sparsely populated southern end of the basin to poor in the urban

reaches of Jacksonville (Hand and Paulic 1992).

The Lower St. Johns River Basin reconnaissance report provides a

synthesis of what is known about the condition of the lower

St. Johns River and its tributaries from three perspectives:

hydrologic, environmental, and socioeconomic. Volume 1,

Hydrogeology, presents information on the ground water flow

system in the basin and its connection to surface waterbodies.

Volume 2, Surface water hydrology, discusses the surface water

system, including hydrologic and hydraulic data collection

networks. Volume 3, Hydrodynamics and salinity of surface water,

describes relationships between river water levels, velocity, flow,

storage, and salinity and reviews previous hydrodynamic

modeling studies. Volume 4, Surface water quality, and Volume 5,

Sediment characteristics and quality, present details on the levels

and trends of chemical contaminants present in the water column

and in the bottom sediments. Volume 6, Biological resources,

describes plant communities and fish, shellfish, and marine

animal communities. Volume 7, Population, land use, and water

use, ties population estimates and projections to land use and

residential, commercial, industrial, and agricultural water use.

St. Johns River Water Management District

6
Introduction

Volume 8, Economic values, discusses the commercial, recreational,

and aesthetic values of the river. Finally, Volume 9,

Intergovernmental management, discusses jurisdictional boundaries,

regulatory authorities, and management efforts of governmental

agencies, offices, and commissions involved in restoration or

protection of water quality and habitat.

This volume, Hydrogeology, examines the relationship and

influence of the interconnection between the lower St. Johns River

and the ground water flow system associated with the river.

Different boundaries delineate the ground water flow system and

the surface water basin of the lower St. Johns River (Figure 1.1).

Under steady-state conditions, ground water does not flow across

the ground water flow system boundary. The major differences

between the boundaries of the surface water basin and the

ground water flow system are in their eastern and southern

boundaries. Minor differences also occur in the northern and

western boundaries. The lower St. Johns River ground water

flow system underlies all of St. Johns County, most of Flagler,

Clay, Duval, and Putnam counties, and the northwestern corner

of Volusia County. The lower St. Johns River surface water

basin, for comparison, does not include eastern St. Johns and

Flagler counties or southwestern and southeastern Putnam

County but does include a portion of north-central Volusia

County. Discussions in this volume only pertain to the ground

water flow system. However, for completeness, most of the

graphics cover both the surface water basin and the ground water

flow system areas.

Information about the interconnection between the ground water

and the surface water systems will be used in the development of

a hydrodynamic model for the St. Johns River (volume 3 of this

reconnaissance series). The model will address such factors as

the effect of surface and ground water discharges on the salinity

of the river and the fate of nutrients and pollutants in the river.

St. Johns River Water Management District

7
30 DON

— 2930N

Legend

Lower St. Johns River surface

water basin boundary

am^^ Lower St. Johns River ground

water flow system boundary

>NNNNN\N\NNN\\NNN\NNNNNNN

Lower St. Johns River ground

water flow system inferred boundary

Peninsular divide

County boundary

Waterbody

Lake *?.'"'• *.

•% George

Lower St. Johns River

ground water flow system

V

i » :

-,

\ / ; : .*

V

la,

\J -\f ,BW.

\i

>

10 20

Approximate scale in miles

Figure 1.1 The lower St. Johns River ground water flow

system and the lower St. Johns River surface

water basin
Hydrogeology

HYDROGEOLOGY

Geology in LSJRB has been discussed in reports by Vernon (1951),

Wyrick (I960), Bermes et al. (1963), Clark et al. (1964), Leve

(1966), Navoy and Bradner (1987), Snell and Anderson (1970),

Spechler and Hampson (1984), and Toth (1990). In general,

several thousand feet of sediment overlie the basement complex

of granite and other crystalline rocks (Cederstrom et al. 1979,

p. 5).

The hydrogeologic framework of the lower St. Johns River

ground water flow system consists of three aquifer systems: the

Floridan, intermediate, and surficial. The Floridan aquifer system

consists of limestone formations from the Paleocene and Eocene

epochs (Table 1). The intermediate aquifer system consists of

Table 1. Geologic time scale

Period

Quarterly

Tertiary

Epoch

Holocene

Pleistocene

Pliocene

Miocene

Oligocene

Eocene

Paleocene

Time

(in rnltort y$a*8)

0.01

1.6

5.3

23.7

36.6

57.8

66.4

Miocene deposits of the Hawthorn Group and undifferentiated

post-Hawthorn Group sediments. The surficial aquifer system

consists of late and post-Miocene surficial deposits.

St. Johns River Water Management District

9
HYDROGEOLOGY

LIMESTONE

Limestone formations from the Paleocene and Eocene epochs

form part of the principal artesian aquifer—the Floridan aquifer

system, which is the major source of water in northern Florida.

The formations of the Floridan aquifer system include, in order of

increasing age, the Ocala, Avon Park, Oldsmar, and the upper

part of the Cedar Keys limestones (Table 2 and Figure 1.2).

The formations that comprise the Floridan aquifer system

typically vary in depth and thickness throughout the ground

water flow system (Figures 1.3 and 1.4). Miller (1986) mapped

the thickness and extent of the Floridan aquifer system in Florida

and in parts of Georgia, Alabama, and South Carolina. In

northern Florida, the limestone formations of the Floridan aquifer

system dip and thicken to the northeast (Figure 1.5). In eastern

Flagler County, the depth to the top of the Floridan aquifer

system is nearly 100 ft below the National Geodetic Vertical

Datum (NGVD). The depth to the top increases to 200 ft below

NGVD in central St. Johns County and reaches a maximum depth

of more than 600 ft below NGVD in Duval County near the

St. Johns River. Throughout most of Duval County, the depth to

the top of the Floridan aquifer system ranges from 300 ft below

NGVD in the western and southern part of the county to 600 ft in

the center of the county.

HAWTHORN GROUP

Eocene rocks are overlain by rocks of the Hawthorn Group. The

Hawthorn Group consists of early to middle Miocene clay,

limestone, and layers of interbedded sand and shell and serves as

a confining unit that separates the Floridan aquifer system from

the overlying surficial aquifer system (Table 2 and Figure 1.2).

The intermediate aquifer system consists of the Hawthorn Group

and undifferentiated post-Hawthorn Group sediments. The

Hawthorn Group is absent from much of Volusia County and

southeastern Flagler and Putnam counties but thickens to the

northeast, where it attains a localized maximum thickness of

St. Johns River Water Management District

10
Hydrogeology

Table 2. Hydrogeologic framework of the lower St. Johns River ground water flow

system (modified from Brown 1984 and Bermes et al. 1963)

Hytfrogeotogte Unit

Surficial aquifer

system

Upper confining unit

(Intermediate confining

unit)

Floridan

aquifer

system

Upper

waterbearing

zone

Semiconfining

unit

Middle

waterbearing

zone

Semiconfining

unit

Lower

waterbearing

zone

Lower confining unit

Stratigraphy

Surficial

deposits

Hawthorn

Group

Ocala

Limestone

Avon Park

Limestone

Oldsmar

Limestone

Cedar Keys

Limestone

Approximate

Thickness (fas*)

20 to 175

0 to 500

0 to 350

6010210

500 to 750

700

Unknown

Li»iOiaSy

Discontinuous

sand, clay,

and shell beds

Interbedded

phosphatic

sand, clay,

marl, and

limestone

Massive

fossiliferous

chalky to

granular

marine

limestone

sequence

Alternating

beds of

massive

granular and

chalky

limestone and

dense

dolomites

Uppermost

appearance of

evaporites;

dense

limestone

Hydragacfogfc Properties

Sand and shell deposits provide local limited

water supplies. Yields moderate to large

quantities of water in Duval County and

central and eastern Flagler and St. Johns

counties and small quantities of water

throughout the remainder of the area

Sand, shell, and limestone deposits provide

local, limited water supplies, both artesian

and nonartesian. Low-permeability days

serve as the principal confining bed for the

Floridan aquifer system below. Important

source of water in Clay, Duval, and parts of

eastern Flagler and St. Johns counties

Principal source of ground water. High

permeability overall. Primary waterproducing zone in Flagler, Putnam, and

St. Johns counties in the top 50-200 ft of the

aquifer

Low-permeability limestone and dolomite

Principal source of ground water

Low-permeability limestone and dolomite

Highly permeable; increases in salinity noted

Highly mineralized water, very low

permeability

St. Johns River Water Management District

11
Land surface

;Hawthorn Group;

Intermediate aquifer system

"T" 1.', '.',' , U l_~T'j'JI . 1 ,-J . i .I'M . I... 1 71

i i i i i i i i i i i i i i i i i i i

t ' i ' ,--L,--l-1 ' , ',',', ' H--I --I-I--I-, ' ,

WAvon Park Li !!Rrida aquifer system

* ' ' i ' i ' i ' i ' i ' . ' i ' i ' i

!

i ' i ' i ' i ' t ' i ' i ' i ' r i i i i i i i i i i i i i i

smar Limestone^^

,',', ' .'.', ' ,',', ' ,',', ' ,',' , i ' i ' i ' i ' i '

Legend

Sand

Jiiia Sand, shell, and limestone

Limestone

Figure 1.2 Typical hydrostratigraphic column in the lower

St. Johns River ground water flow system

12
Ul

CQ

L I -t^" I I I I I I

r^AVON PARK LIMESTONE_J

10

Approximate horizontal scale in miles

0 260 500

Approximate vertical scale in feet

Figure 1.3 Cross section showing geologic structure in the lower St. Johns

River ground water flow system
\\N\\\\\\\\\\\\\\XW\X\\X\NNN\\NXNN\\\\\\\\V

lragend

Well location

Cross-section location

Lower St. Johns River ground

water flow system boundary

Lower St. Johns River ground

water flow system inferred boundary

Peninsular divide

County boundary

County seat

Waterbody

Lower St. Johns River

ground water flow system

Approximate scale in miles

Figure 1.4 Location of cross-section A-A'

14
Legend

Waterbody

—200— Top of Floridan aquifer contour line

Contour interval = 100 feet

Datum is feet below mean sea level (NGVD - 1929)

Lower St. Johns River ground

water flow system boundary

.v\x\\w\ Lower St. Johns River ground

water flow system inferred boundary

Peninsular divide

County boundary

Lower St. Johns River

ground water flow system

Approximate scale in miles

Figure 1.5 Depth to the top of the limestones of the

Floridan aquifer system in the lower St. Johns

River ground water flow system

15
HYDROGEOLOGY

more than 500 ft in central Duval County near the St. Johns River

(Figure 1.6).

SURFICIAL DEPOSITS

The surficial aquifer system consists of deposits of extremely

variable lithology (clay, sand, coquina, limestone) that overlie the

Hawthorn Group (Table 2 and Figure 1.2). Where the Hawthorn

Group is absent, the surficial materials rest directly on the Eocene

limestone. The thickness of surficial deposits in the lower

St. Johns River ground water flow system ranges from less than

50 ft to more than 150 ft (Figure 1.7).

In Duval County, a younger limestone unit occurs at the base of

Pliocene or upper Miocene deposits and overlies the Hawthorn

Group. This limestone unit generally consists of a soft, friable,

cavernous, sandy limestone and ranges from 5 to 40 ft in

thickness (Spechler 1982). Along the coast and in the southern

part of the county, the limestone becomes discontinuous and

grades into medium to coarse sand and shell deposits.

In western Putnam County, the sediments that overlie the

Hawthorn Group are non-marine deposits that consist of

undifferentiated beds of coarse, poorly sorted sand, kaolin, and

variegated sandy clay (the Citronella Formation). These nonmarine beds are discontinuous and cannot be differentiated

lithologically for any great distance (Bermes et al. 1963).

The sediments that blanket the surface in the lower St. Johns

River ground water flow system are from the Pleistocene and

Holocene epochs (see Table 1). The Pleistocene deposits consist

of fine to medium quartz sand and thin lenses of clay and shell in

the eastern part of the area and fine to coarse poorly sorted sand

and sandy clay in the western part. Along the coastal islands and

inland for approximately 3-10 miles, the Anastasia Formation of

the Pleistocene Epoch occurs. The Anastasia Formation primarily

consists of shell beds that contain varying amounts of quartz

sand, silt, and organic material. The formation extends more than

150 miles south of St. Augustine but rarely extends inland

St. Johns River Water Management District

16
•\NVVV\N\NVVSVSV\\\X\V\V\NV\\V\NNNSS\SSNXXV

Legend

County boundary

sS\\\\\\\\\\\\\\\\x\\\\ws

Lower St. Johns River ground

water flow system boundary

Lower St. Johns River ground

water flow system inferred boundary

Peninsular divide

Waterbody

ioo— Equal thickness contour line

Contour interval = 100 feet

Lower St. Johns River

ground water flow system

Approximate scale in miles

Figure 1.6 Thickness of the Hawthorn Group in the lower

St. Johns River ground water flow system

17
82 SOW 82 00 W,.1 NASSAU 8100W

3030N

>XNNXNNX\\X\\\\\\\X\X\\\N\XXX\\XX\\\XXXXX\\\\

30 DON

— 29 SON

Legend

TMTM «»»»»» County boundary

•amiinii Lower St. Johns River ground

water flow system boundary

\xxxxxxx- Lower St. Johns River ground

water flow system inferred boundary

— ^ Peninsular divide

"^•'^iil! Waterbody

Equal thickness contour line

Contour interval = 50 feet

Lower St. Johns River

ground water flow system

j

 VS VOLUSIA

' V ^ VHftttff f , fV»

\ *

S

10 20

I i I

Approximate scale in miles

Figure 1.7 Thickness of surficial deposits in the lower

St. Johns River ground water flow system

18
Hydrogeology

beyond the Intracoastal Waterway. Highly variable and

undifferentiated Holocene sediments cover the Pleistocene

deposits.

St. Johns River Water Management District

19
HYDROGEOLOGY

AQUIFER SYSTEMS

Aquifers within the lower St. Johns River ground water flow

system belong to the Floridan aquifer system, the intermediate

aquifer system, or the surficial aquifer system. Each aquifer

system has a different influence on river flow. The Floridan

aquifer system contributes to river flow directly through spring

discharge and indirectly through diffuse upward leakage. The

intermediate aquifer system indirectly contributes to river flow

through diffuse upward leakage. The surficial aquifer system can

discharge directly into the river. Unlike the Floridan and

intermediate aquifer systems, the surficial aquifer system is

areally in direct contact with the river.

The Floridan aquifer system is the principal artesian aquifer in

north Florida and is the one most frequently tapped for water

supply. It is tapped for both public supply and domestic selfsupply in Duval, St. Johns, Clay, Putnam, Flagler, and Volusia

counties (Table 3). Besides public and domestic self-supply, the

Floridan aquifer also is used for commercial/industrial selfsupply, agricultural irrigation, self-supplied power generation,

uncontrolled free-flowing (abandoned artesian) wells, and heating

and cooling heat pump units.

Intermediate aquifers occur within the Hawthorn Group or

undifferentiated post-Hawthorn sediments and contain limited

quantities of potable water. Many domestic water supply wells

in Duval, Clay, Flagler, and St. Johns counties tap this source. In

Flagler County, the intermediate aquifer system is also tapped for

public supply.

The surficial aquifer system is less extensive than the Floridan

aquifer system and is tapped when the Floridan aquifer system

contains nonpotable water or when the Floridan aquifer system is

generally deeper than 200 ft. The surficial aquifer system is

tapped as a domestic source of water in Duval, St. Johns, Putnam,

Flagler, and Volusia counties and as a public supply source in

St. Johns County.

St. Johns River Water Management District

20
Aquifer Systems

Table 3. Source of water used for public supply and domestic

self-supply in the lower St. Johns River surface water

basin

County

Duval

St. Johns

Clay

Putnam

Flagler

Volusia

Public Supply

Floridan aquifer system

Floridan aquifer and surficial

aquifer systems

Floridan aquifer system

Floridan aquifer system

Floridan aquifer and

intermediate aquifer systems

Floridan aquifer system

Domeslic SeS-suppty

Floridan aquifer, intermediate

aquifer, and surficial aquifer

systems

Floridan aquifer, intermediate

aquifer, and surficial aquifer

systems

Floridan aquifer and intermediate

aquifer systems

Floridan aquifer and surficial

aquifer systems

Floridan aquifer, intermediate

aquifer, and surficial aquifer

systems

Floridan aquifer and surficial

aquifer systems

FLORIDAN AQUIFER SYSTEM

In LSJRB, the Floridan aquifer system is composed of an Upper

Floridan aquifer and a Lower Floridan aquifer separated by the

middle semiconfining unit (Miller 1986). Older and deeper rocks

of the Lower Floridan aquifer are not generally tapped by wells

in the study area because sufficient water can be obtained from

the overlying formations and because the water from deeper

rocks is generally more saline.

The primary water-bearing zones in the Floridan aquifer system

consist of porous limestone and dolomite. Massive dolomitic

limestone and dolomite beds generally yield little or no water

and act as confining units (Brown 1984). In northeastern Florida,

these relatively impermeable beds restrict the vertical movement

St. Johns River Water Management District

21
HYDROGEOLOGY

of water through the aquifer and separate it into three relatively

isolated water-bearing zones (see Table 2). The upper waterbearing zone consists of the Ocala Limestone and the upper part

of the Avon Park Limestone. The thickness of the upper waterbearing zone averages 250 ft at Fort George Island, which is

located north of the river near the inlet (Motz 1987). The middle

water-bearing zone occurs in the lower part of the Avon Park

Limestone and is 575 ft thick at Fort George Island. The lower

water-bearing zone occurs in the lower part of the Oldsmar

Limestone and is approximately 100 ft thick at Fort George Island

(Motz 1987). These zones have been identified at Fernandina

Beach, 20 miles north of the lower St. Johns River ground water

flow system boundary (Brown 1984). No additional information,

however, is available about the thickness of the upper, middle,

and lower water-bearing zones beneath the LSJRB boundary.

Miller (1986) considered the upper water-bearing zone to be part

of the Upper Floridan aquifer. The discussions on the middle

and lower water-bearing zones are contained in Miller's (1986)

discussion of the Lower Floridan aquifer.

Water within the lower St. Johns River ground water flow system

flows from areas of higher hydraulic head to areas of lower

hydraulic head in a direction that is generally at right angles to

the potentiometric surface contour lines (Figure 1.8). The

elevation of the potentiometric surface of the Floridan aquifer

system defines the level to which ground water will rise in tightly

cased wells that penetrate the aquifer system. The elevation of

the potentiometric surface fluctuates both seasonally and yearly.

Water within the Floridan aquifer system that affects the lower

St. Johns River surface water basin generally flows eastward.

Recharge

Recharge to the Floridan aquifer system is the addition of water

to the Upper Floridan aquifer from the overlying surficial aquifer

or, more directly, from rainfall in areas where the surficial aquifer

is thin or absent and the limestones of the Floridan aquifer are at

or near land surface. Recharge to the Upper Floridan aquifer also

can occur from the underlying Lower Floridan aquifer. Principal

St. Johns River Water Management District

22
8230W

30 SON

30 DON

Wi'^W*^*.*

J w.

^ TM 4, BRADFORD

29 SON

L

Legend

Potentiometric surl

Jontour interval =

Saturn is feet abov

NN\\\\\\

•

Direction of ground water flow

County boundary

Lower St. Johns River around

water flow system boundary

Lower St. Johns River ground

water flow system inferred ooundary

Spring location

Peninsular divide

Waterbody

Lower St. Johns River

ground water flow system

ice contour (May 1990) ,,

i mean sea level (NGVD -1929) *

Approximate scale in miles

Figure 1.8 Direction of flow in the Floridan aquifer

system of the lower St. Johns River ground

water flow system (based on potentiometric

surface contours)

23
HYDROGEOLOGY

recharge areas for the Floridan aquifer system in the lower

St. Johns River ground water flow system and surface water basin

occur in southwestern Clay County, northwestern and

southeastern Putnam County, and northwestern and west-central

Volusia County (Figure 1.9) (Boniol et al. 1993). Areas of

recharge of 0-4 or 4-8 inches per year occur in western Duval and

Clay counties, western and southeastern Putnam County,

northwestern Volusia County, and central St. Johns and Flagler

counties.

The lake region of southwestern Clay and northwestern Putnam

counties is recognized as an area with a relatively high potential

for lake-level decline in response to lowered Floridan aquifer

potentiometric levels (Motz and Heaney 1991,1992). This

interconnection is important because these lakes are part of the

Etonia Creek chain of lakes that discharges to a tributary of the

St. Johns River.

Discharge

Discharge from the Floridan aquifer system can be direct (e.g.,

wells or springs) or discharge can be indirect or diffuse (e.g.,

diffuse upward leakage to overlying aquifer systems). Generally,

discharge occurs in the eastern portion of LSJRB (see Figure 1.9).

Outside LSJRB but within the lower St. Johns River ground water

flow system, discharge occurs off-shore in the Atlantic Ocean.

Paleosinkholes occur in the St. Johns River near Blount Island

(about 8 miles upstream from the mouth of the St. Johns River)

(Spechler 1993).

When the elevation of the potentiometric surface of the Floridan

aquifer system is higher than the elevation of the water table of

the surficial aquifer system, water from the Floridan aquifer

system will leak upward to the intermediate aquifer and surficial

aquifer systems. When the potentiometric surface of the Floridan

aquifer system is higher than land surface, wells drilled into the

Floridan aquifer system, unless capped or valved, will flow freely

at land surface. In the lower St. Johns River ground water flow

system, free-flowing wells can occur in eastern Duval and

St. Johns River Water Management District

24
8230W 8100W

3030N

Areas of recharge

0-4 inches per year

4-8 Inches per year

8-12 inches per year

12 or more inches per year

30 DON

2930N

Lower St. Johns River ground

Peninsular divide

County boundary

Lower St. Johns River

ground water flow system

1 1 1 1 1 1 1 Lower St. Johns River surface

water basin boundary

SS\\XXSN Lower St. Johns Rive. .

water flow system inferred boundary

Approximate scale in miles

Figure 1.9 Areas of natural recharge and discharge of the

Floridan aquifer system in the lower St. Johns

River ground water flow system and the lower

St. Johns River surface water basin

25
HYDROGEOLOGY

Putnam counties, northeastern Clay County, and in both eastern

and western St. Johns and Flagler counties.

Along the coast south of St. Augustine, the elevation of the

potentiometric surface slopes toward the southeast as a result of

submarine discharges. Crescent Beach Spring, a submarine

spring about 2.5 miles east of Crescent Beach (Figure 1.10), has

been described by Stringfield and Cooper (1951, p. 63) and

Brooks (1961). Red Snapper Sink is located about 22.5 miles east

of Crescent Beach Spring; it is situated in water about 88 ft deep

(Rosenau et al. 1977).

Depressions in the elevation of the potentiometric surface

generally indicate discharge areas for the Floridan aquifer system

(see Figure 1.8). The depression at Green Cove Springs in Clay

County is due to a combination of ground water withdrawals

from domestic and public supply wells at Green Cove Springs,

pumping from irrigation wells just south of the area, and the

natural discharge from the spring at Green Cove Springs (Toth

1990). In this area, the Floridan aquifer system loses

approximately 46 cubic feet per second (ft3/sec) to the surficial

aquifer system, the intermediate aquifer system, the river, or a

combination of all three as a result of spring discharge and

diffuse upward leakage (Durden 1991). An unknown part of this

discharge of 46 ft3/sec could be attributed to additional

unconfirmed springs discharging in the vicinity of Green Cove

Springs.

A depression in the elevation of the potentiometric surface in

southern Putnam County is probably due to Floridan aquifer

system discharge at Croaker Hole Spring (see Figure 1.8).

Croaker Hole Spring is a relatively deep, small-diameter hole in

the bottom of the St. Johns River at Little Lake George. Little

Lake George is about 5-9 ft deep except in the immediate vicinity

of Croaker Hole, where it plunges to a depth of about 48 ft. The

discharge of Croaker Hole Spring was about 80 ft3/sec on

September 17,1981 (Tibbals 1990).

St. Johns River Water Management District

26
8230W 8100W

30 SON

• 30 DON

• 2930N

K>XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

Rod Snapper

Sink

Legend

County boundary

County seat

Lower St. Johns River ground

water flow system boundary

Lower St. Johns River ground

water flow system inferred boundary

Peninsular divide

Waterbody

Spring

i,XXXXXXXXVX\XXVX\NXXXXXXNV

-r

Lake

, ^ George

DeUnd

Lower St. Johns River

ground water flow system

0

I

10 20

Approximate scale in miles

Figure 1.10 Major springs in the lower St. Johns River

ground water flow system

27
HYDROGEOLOGY

Beecher Springs, Welaka Spring, Satsuma Spring, and Mud

Spring also occur in southern Putnam County near the St. Johns

River (Figure 1.10). The discharge of Beecher Springs was

9 ftVsec on April 20, 1972 (Tibbals 1990). The discharge from

Welaka Spring was so small that is could not be measured on

June 8,1972. The discharge from Satsuma Spring was 1 ftVsec

on November 13 and 14,1980, and the discharge from Mud

Spring was 2 ftYsec on June 8,1972 (Tibbals 1990). All of the

previous spring discharges are low-flow measurements made

during periods of deficient rainfall; therefore, the discharges

probably represent a minimum flow for the period 1972-81.

A daily total of approximately 59.5 million gallons per day

(mgd)—92 ftVsec—of Floridan aquifer system water is

discharged into the St. Johns River through these springs (not

including Green Cove Spring and the other possible springs in

the vicinity of Green Cove Springs). This is a substantial amount

of ground water discharged in a day. For comparison, the City of

Jacksonville withdrew an average 70.49 mgd from the Floridan

aquifer system in 1990 for public supply (Florence 1992). The

combined discharge of Floridan aquifer system water to the

St. Johns River, however, is a minor amount of the total surface

water flow. For comparison, the mean total discharge of the

St. Johns River at Palatka and Jacksonville is approximately 5,900

and 7,300 ft3/sec, respectively (Morris 1993).

The depression in the elevation of the potentiometric surface of

the Floridan aquifer system in central and western Flagler County

(see Figure 1.8) is probably caused by diffuse upward leakage

and possibly by discharge from unconfirmed submerged springs

near the southeast side of nearby Crescent Lake. Computer

modeling suggests that the rate of diffuse upward leakage in the

area is about 16 ft*/sec (Tibbals 1981).

Several Floridan aquifer system wells discharge water to Etonia

Creek near its confluence with Rice Creek, a tributary to the

St. Johns River. This ground water, about 17 mgd, is used to

support operations of a pulp and paper mill that withdraws

water from Rice Creek downstream of the confluence.

St. Johns River Water Management District

28
Aquifer Systems

The U.S. Geological Survey is conducting a study to estimate the

natural discharge and chemical-constituent loading from the

Upper Floridan aquifer to the lower St. Johns River in the lower

St. Johns River surface water basin. In addition, SJRWMD is

developing ground water flow and water quality models to be

used as tools for predicting changes in potentiometric levels and

water quality in response to changes in rates of ground water

withdrawals. These models can be used to predict changes in

spring discharge in response to changes in ground water

withdrawals.

Quality of Ground Water

Chloride, sulfate, and total dissolved solids (TDS) are common

indicators of the presence of saline water in the Floridan aquifer

system. These three constituents vary widely in concentrations in

the lower St. Johns River ground water flow system, and, in some

instances, concentrations of these constituents exceed the public

drinking water standards (i.e., chloride—250 milligrams per liter

[mg/L], sulfate—250 mg/L, and TDS—500 mg/L). Moderately

saline water (chloride and sulfate concentrations between 250 and

1,000 mg/L and TDS concentrations between 500 and

3,000 mg/L) in the Floridan aquifer system enters the overlying

surface water system through direct discharge from springs or

through diffuse upward leakage.

Chloride. Chloride concentration is a primary indicator of the

presence of seawater in ground water. In the lower St. Johns

River ground water flow system, chloride concentrations are

generally below 50 mg/L in the northern and western part of

LSJRB but increase to over 1,000 mg/L in southern Flagler

County (Figure 1.11). This information is based on data collected

from wells less than 1,400 ft deep. The deepest wells sampled

(depths near 1,400 ft) are located in Duval County where chloride

concentrations are generally below 50 mg/L. In Volusia County,

chloride concentrations are below 250 mg/L in the middle of the

county but increase to over 1,000 mg/L in both the eastern and

St. Johns River Water Management District

29
1 Green Cove Springs ^

;„,»•.<"" starke

"^BRADFORD

Legend

County boundary

County seat

Lower St. Johns River ground

water flow system boundary

..\\N\\\XN Lower St. Johns River ground

water flow system inferred boundary

Waterbody

«_250— Chloride concentration contour line (in mg/L)

Lower St. Johns River

ground water flow system

Approximate scale in miles

Figure 1.11 Chloride concentrations in the Upper

Floridan aquifer of the lower St. Johns River

ground water flow system. Data are from

1965 to 1987 for wells less than 1,400 feet

deep.

30
Aquifer Systems

western portions of the county (along the Atlantic coast and

along the St. Johns River).

In the Floridan aquifer system, moderately saline water

containing chloride concentrations between 250 and 1,000 mg/L

is present beneath part of the St. Johns River in Putnam County

and in southern St. Johns and northern Flagler counties.

Discharge from hundreds of irrigation wells in southern St. Johns

and central Flagler counties seasonally lowers the elevation of the

potentiometric surface in the area and causes highly mineralized

water to move upward into the production zones of those wells

(Bermes et al. 1963). As a result, some wells that yield fresh

water during nonpeak irrigation demand months yield

moderately saline water during the crop-growing season. Area

agricultural drainage districts control irrigation and stormwater

runoff that connects with the St. Johns River. SJRWMD currently

is analyzing data that will give scientists an idea of the influence

of the quality of the ground water pumped for agricultural

purposes on the surface water system.

Localized areas where chloride concentrations are above 50 mg/L

occur along the coast and near the St. Johns River in Duval and

northern St. Johns counties. These areas of higher chlorides are

probably due to upward movement of higher chloride waters that

exist at depth (Toth 1990). Chloride concentrations above

7,000 mg/L occur in the Lower Floridan aquifer at depths greater

than 2,000 ft below mean sea level in the coastal portions of

northeast Florida (Leve 1983). Some areas with chloride

concentrations above 50 mg/L occur near the north-south faults

mapped by Miller in 1982 (Figure 1.12), suggesting that the faults

may be the avenue for some of this upward movement.

According to Miller (1982), displacements of between 50 and

100 ft may occur along these faults. None of the faults appear to

have an effect on ground water flow within the Floridan aquifer

system, probably because permeabilities are similar on both sides

of the faults. Spechler (1993) speculated that paleokarst features

in this area may provide avenues for this upward movement.

St. Johns River Water Management District

31
\\S\\\\\\\\\\\\NS\\\\\\\\\\\\\\\\\\\\\\N\\N

~**»^ Vy%^*v>->**'

!

^'-"'^^

Legend

Fault location

Fault's upward side

Fault's downward side

County boundary

Lower St. Johns River grour

water flow system boundary

Lower St. Johns River ground

water flow system interred Boundary

Peninsular divide

Waterbody

Lower St. Johns River

ground water flow system

Approximate scale in miles

Figure 1.12 Location of possible faults in the lower

St. Johns River ground water flow system

Source: Miller 1982

32
Aquifer Systems

In areas of the aquifer where chloride concentrations are greater

than 250 mg/L, water also has the relative chemical composition

of seawater, connate water, or relict (fossil) seawater. Connate

water refers to water of a marine or non-marine origin that has

been out of contact with the atmosphere for an appreciable part

of geologic time. It is water that was entrapped in the rocks

when the rocks were deposited as sediment. Compared to

seawater, connate water is enriched in calcium, magnesium, and

sulfate. Relict seawater is water that was entrapped in the rocks

during a past geologic age when seawater inundated the Florida

peninsula, such as occurred during the Pleistocene Epoch. Relict

seawater is similar in composition to seawater and can be

distinguished from it only by isotopic analysis.

Sulfate. The Upper Floridan aquifer contains sulfate

concentrations which vary throughout the lower St. Johns River

ground water flow system (Figure 1.13). The source of sulfate in

the Floridan aquifer system is dissolution of gypsum and

anhydrite, the oxidation of iron sulfides, or the mixing of either

relict seawater or connate water with fresher water. The

dissolution of sulfur minerals is a slow process and can increase

the concentrations of sulfate by a rate of 1-8 mg/L per 100 years

(Toth 1990). Sulfate concentrations are generally below 50 mg/L

in the western part of the ground water flow system but increase

to above 500 mg/L in southern and eastern St. Johns County and

northeastern Flagler County. This information is based on data

collected from wells less than 1,400 ft deep. The deepest wells

sampled (depths near 1,400 ft) are located in Duval County where

sulfate concentrations are generally below 250 mg/L. Moderately

saline water in the Floridan aquifer system (sulfate concentrations

between 250 and 1,000 mg/L) is present in much of St. Johns,

northern and southwestern Flagler, northeastern Putnam, and

western Volusia counties.

Total dissolved solids. TDS concentrations in the Upper

Floridan aquifer also vary dramatically throughout the lower

St. Johns River ground water flow system (Figure 1.14). TDS

concentration is the sum of all dissolved constituents in ground

water. It includes sodium, potassium, calcium, magnesium,

St. Johns River Water Management District

33
<«* ^\^-^f,.^>"

r ^*i, BRADFORD

* <..> ^ft-.--.-.r.1

ALACHUA

Legend

County boundary

Lower St. Johns River ground

water flow system boundary

• Lower st. jonns myer grquna

water flow system inferred boundary

Peninsular divide

Waterbody

§

qual thickness contour line

ontour interval = 50 feet

Lower St. Johns River

ground water flow system

Approximate scale in miles

Figure 1.13 Sulfate concentrations in the Upper Floridan

aquifer of the lower St. Johns River ground

water flow system

34
Qreen Cove Springs , <

|i SI Augustine

iqoo;

L3T JOHNS

yv>w « .

FLAOLER

Newnans

Gainesville • Lake

Legend

County boundary

County seat

Lower St. Johns River ground

water flow system boundary

\wvsv<.v Lower St. Johns River ground

water flow system inferred boundary

Peninsular divide

Waterbody

Total dissolved solids contour line (in mg/L)

Lower St. Johns River

ground water flow system

Approximate scale in miles

Figure 1.14 Total dissolved solids in the Upper Floridan

aquifer of the lower St. Johns River ground

water flow system

35
HYDROGEOLOGY

chloride, sulfate, bicarbonate, iron, silica, and other minor

components dissolved in water. TDS concentrations are generally

below 500 mg/L in the western and northern part of the ground

water flow system but increase to above 5,000 mg/L in

southeastern St. Johns County and northwestern and eastern

Volusia County. This information is based on data collected from

wells less than 1,400 ft deep. The deepest wells (depths near

1,400 ft) are located in Duval County, where TDS concentrations

are generally below 500 mg/L. Moderately saline water

containing TDS concentrations between 500 and 3,000 mg/L in

the Floridan aquifer system is present in southern St. Johns,

eastern Putnam, most of Flagler, eastern and western Volusia,

and northeastern Duval counties.

In addition to measuring TDS from well water, TDS and other

water quality parameters can be measured from spring discharge.

For example, the quality of ground water discharging from

Croaker Hole Spring was measured in 1981. 'The temperature

and dissolved solids concentration of the spring water were 23°C

and 1,430 mg/L, respectively. The temperature and dissolved

solids concentration of the river water immediately upstream

from the spring were 25°C and 680 mg/L, respectively. The

spring water in September was colder, more mineralized, and

thus denser than the river water. The denser spring water

probably flowed up the spring bore and moved downstream

along the bottom of the river" (Tibbals 1990). Chloride and

sulfate concentrations of the spring water were 680 and

160 mg/L, respectively; the chloride and sulfate concentrations of

the upstream river water were 280 and 84 mg/L, respectively

(Tibbals 1990).

INTERMEDIATE AQUIFER SYSTEM

The intermediate aquifer system is not areally extensive, but

occurs in portions of Duval, St. Johns, Clay, Putnam, and Flagler

counties. It ranges from less than 10 to about 300 ft below mean

sea level and varies in thickness from less than 1 to about 15 ft

(Bermes et al. 1963).

St. Johns River Water Management District

36
Aquifer Systems

Intermediate aquifers within the Hawthorn Group or

undifferentiated post-Hawthorn sediments are an important

source of water in Duval, Clay, and parts of eastern Flagler and

St. Johns counties.

More precise information is needed about the geographic

location, depth, and thickness of the intermediate aquifer system.

More information also is needed about the relationship of the

intermediate aquifer system with the overlying surfitial aquifer

system and the underlying Floridan aquifer system.

Recharge

Discharge

Intermediate aquifers are recharged from at least two different

sources, depending on potentiometric pressures. When

potentiometric levels in the surficial aquifer system are greater

than those in the intermediate aquifer system, the intermediate

aquifer system is recharged by downward leakage from the

surficial aquifer system. Similarly, when potentiometric levels in

the Floridan aquifer system are greater than those in the

overlying intermediate aquifer system, the intermediate aquifer

system is recharged by upward leakage from the Floridan aquifer

system.

Intermediate aquifers discharge to two different sources,

depending on potentiometric pressures. When potentiometric

levels in the intermediate aquifer system are greater than those in

the surficial aquifer system, the intermediate aquifer system loses

water by upward leakage to the surficial aquifer system. When

potentiometric levels in the intermediate aquifer system are

greater than the elevation of the potentiometric surface of the

Floridan aquifer system, the intermediate aquifer system loses

water by downward leakage to the underlying Floridan aquifer

system.

St. Johns River Water Management District

37
HYDROGEOLOGY

Quality of Ground Water

Chloride, sulfate, and TDS are common indicators of the presence

of saline water in the intermediate aquifer system. Where the

intermediate aquifer system contains moderately saline water

(chloride and sulfate concentrations between 250 and 1,000 mg/L

and TDS concentrations between 500 and 3,000 mg/L), the water

could enter the overlying surface water system through diffuse

upward leakage.

Water in the intermediate aquifer system is derived locally either

by upward leakage from the underlying Floridan aquifer system

or by downward leakage from the overlying surfitial aquifer

system. Water quality in the intermediate aquifer system is

similar to the water quality in one of the other aquifer systems

within the same general area. In the deep intermediate aquifers,

the quality of water usually is similar to water in the underlying

Floridan aquifer system, and in the shallow intermediate aquifers

the quality of water usually is similar to water in the overlying

surficial aquifer system (Bermes et al. 1963). Navoy and Bradner

(1987) specify chloride and TDS concentrations for the

intermediate aquifer in Flagler County. Chloride concentrations

ranged from 21 to 1,230 mg/L; TDS concentrations ranged from

356 to 2,016 mg/L. The higher values occurred beneath the

barrier island. West of the Intracoastal Waterway, chloride and

TDS concentrations were less than 200 mg/L and 704 mg/L,

respectively. Little additional information has been published on

the chloride, sulfate, or TDS concentrations of the intermediate

aquifer in LSJRB. More precise information about the water

quality of the intermediate aquifer system needs to be collected.

SURFICIAL AQUIFER SYSTEM

The surficial aquifer system is the principal source of potable

water in St. Johns County and an important source of domestic

self-supply water in Duval and Flagler counties. In most of

Duval County, a limestone unit is the principal water-producing

unit in the surficial aquifer system. Water in the surficial aquifer

system generally is unconfined. In swampy lowland and flatland

St. Johns River Water Management District

38
Aquifer Systems

areas, the water table is generally at or near land surface

throughout most of the year.

The general direction of surficial ground water flow is away from

ridges (Bergman 1992). Ridges occur along the coast in Duval,

St. Johns, and Flagler counties and in southeastern Putnam

County (Bergman 1992). Uplands, or areas of higher land, occur

in western Clay and Putnam counties. In these areas, the water

table is generally a subdued reflection of the topography, but it

can be 10-30 ft below land surface.

More precise information has not been documented or mapped

regarding the distribution and thickness of the surficial aquifer

system and about the water levels in the surficial aquifer system

of the lower St. Johns River ground water flow system.

Information regarding water levels in the water table of the

surficial aquifer system is particularly lacking. All of this

information would be useful to support the development of

ground water flow models. Model simulations can estimate the

amount of surficial aquifer system water discharging to the lower

St. Johns River surface water basin.

Recharge

Discharge

The surficial aquifer system is recharged by local rainfall,

irrigation, some lakes, ditches, streams, septic tank effluent,

sewage or stormwater holding pond effluent, and, in areas where

the elevation of the potentiometric surface of the Floridan aquifer

system is above the water table, upward leakage from the Upper

Floridan aquifer. The surficial aquifer system is generally

recharged at the ridges and water moves away from the ridges

toward the St. Johns River and the coast.

Water leaves the surficial aquifer system by seepage to some

lakes, ditches, and streams; by evapotranspiration where the

water table is at or near land surface; by well withdrawals; and,

where the elevation of the potentiometric surface of the Floridan

St. Johns River Water Management District

39
HYDROGEOLOGY

aquifer system is below the elevation of the water table, by

downward leakage to the Floridan aquifer system. No

quantitative information is available on the flow of water from

the surficial aquifer system to the St. Johns River; however, water

generally flows toward streams and creeks, the St. Johns River,

and the coast (Figure 1.15).

In Duval County, there are interconnections between the St. Johns

River and the basal limestone unit of the surficial aquifer system

(Spechler and Stone 1983). "Water in the limestone is moving

toward and discharging into the St. Johns River. Most of the

discharge is occurring along the south side of the river where the

potentiometric gradient is steepest" (Spechler and Stone 1983).

Quality of Ground Water

Chloride, sulfate, and TDS are common indicators of the presence

of saline water in the surficial aquifer system. Moderately saline

water (chloride and sulfate concentrations between 250 and 1,000

mg/L and TDS concentrations between 500 and 3,000 mg/L) in

the surficial aquifer system enters the overlying surface water

system directly through discharge and indirectly through diffuse

upward leakage. Where the surficial aquifer system underlies

surface waterbodies containing moderately saline water, this

water can enter the surficial aquifer system through downward

leakage. During times of excessive rain, the elevation of the

water table in the surficial aquifer system can rise, causing septic

tanks to malfunction, which can result in the discharge of

leachate to the St. Johns River. A situation such as this is known

to occur near Palatka on the east side of the St. Johns River.

Where water in the limestone is unconfined in Duval County,

saline river water can move naturally through the overlying

sediments and into the limestone until a hydraulic equilibrium is

reached. Where the limestone adjacent to the river is

semiconfined but the limestone in the river channel is breached

and when the stage of the river is greater than the potentiometric

pressure of water in the limestone unit, saline river water can

move through the breached section of the limestone. The location

St. Johns River Water Management District

40
/ ''

./ I,-

Leggnd

County boundary

Lower St. Johns River ground

water flow system boundary

\\vovxxv Lower St. Johns River ground

water flow system inferred boundary

Peninsular divide

Waterbody

Direction of ground water flow

Lower St. Johns River

ground water flow system

Approximate scale in miles

Figure 1.15 Direction of flow in the surficial aquifer

system of the lower St. Johns River ground

water flow system

41
HYDROGEOLOGY

of the 250-mg/L isochlor is estimated to be less than 1,000 ft from

the river (Spechler and Stone 1983); chloride concentrations

increase as the river is approached.

Most of the surficial deposits in the lower St. Johns River ground

water flow system are greater than 50 ft thick (see Figure 1.7).

Chloride concentrations in the upper 50 ft of the surficial aquifer

system are generally below 50 mg/L (Figure 1.16). Chloride

concentrations in the surficial aquifer system generally increase

with depth. Chloride concentrations are above 1,000 mg/L

within 1-4 miles of the coast in Duval, Flagler, and Volusia

counties. There is not adequate areal coverage to prepare maps

of the sulfate or IDS concentrations of the upper 50 ft of the

surficial aquifer in LSJRB.

More precise information about the water quality of the surficial

aquifer system needs to be collected and documented. There is a

paucity of data regarding changes (permanent or seasonal) in

water quality at depths. This information would be useful in

model simulations, which can estimate the constituent loadings of

surficial aquifer system discharge to the lower St. Johns River

surface water basin.

St. Johns River Water Management District

42
,1000

\\N>.\\\\\\\\N\\\\\\X\\\\\\\\\\\\\\\\\\\\\\V

Legend

County boundary

County seat

Lower St. Johns River ground

water flow system boundary

,\\\\\w.> Lower St. Johns River ground

water flow system inferred boundary

Peninsular divide

•\ ~*s». yVaterbody

Chloride concentration contour line (in mg/L)

Lower St. Johns River

ground water flow system

Approximate scale in miles

Figure 1.16 Chloride concentrations in the upper 50 feet

of the surficial aquifer system in the lower

St. Johns River ground water flow system

43
HYDROGEOLOGY

SUMMARY

This volume examines the relationship and influence of the

interconnection between the lower St. Johns River and the ground

water flow system associated with the river. The mechanisms of

this interconnection are spring flow, diffuse upward leakage from

the Floridan aquifer and intermediate aquifer systems, and

seepage from the surficial aquifer system.

The geology of the lower St. Johns River ground water flow

system consists of several thousand feet of Paleocene Epoch and

younger aged rocks overlying a basement complex of granite and

other crystalline rocks. Limestone formations dip and thicken

toward the northeast in northern Florida and form part of the

principal artesian aquifer, the Floridan aquifer. The Floridan

aquifer system is separated from the overlying surficial aquifer

system by the intermediate aquifer system. The intermediate

aquifer system consists of Miocene deposits of the Hawthorn

Group and undifferentiated post-Hawthorn Group sediments.

The Hawthorn Group is absent over the southern portion of the

lower St. Johns River ground water flow system, but thickens to

the northeast. Deposits of extremely variable lithology overlie the

Hawthorn Group and form part of the surficial aquifer system.

The primary water-bearing zones in the Floridan aquifer system

consist of porous limestone and dolomite. Massive dolomitic

limestone and dolomite beds generally yield little or no water

and act as confining units. In northeastern Florida, these

relatively impermeable beds restrict the vertical movement of

water through the aquifer and separate it into three relatively

isolated water-bearing zones.

Principal recharge areas for the Floridan aquifer system in the

lower St. Johns River ground water flow system occur in

southwestern Clay County, northwestern and southeastern

Putnam County, and northwestern and west-central Volusia

County.

St. Johns River Water Management District

44
Summary

Water within the Floridan aquifer system that affects LSJRB

generally flows eastward. Discharge from the Floridan aquifer

system can be direct (e.g., wells or springs) or discharge can be

indirect or diffuse (e.g., diffuse upward leakage to overlying

aquifer systems). Discharge areas occur along the eastern portion

of LSJRB. Outside LSJRB but within the lower St. Johns River

ground water flow system, discharge occurs off-shore in the

Atlantic Ocean.

Several depressions occur in the elevation of the potentiometric

surface of the Floridan aquifer system in the lower St. Johns River

ground water flow system. The depressions signify areas where

water is being removed from the Floridan aquifer system by well

withdrawals, diffuse upward leakage, or spring discharge. Near

Green Cove Springs, the Floridan aquifer system is estimated to

lose approximately 46 ft3/sec to the surficial aquifer system, the

intermediate aquifer system, the St. Johns River, or a combination

of all three as a result of spring discharge and diffuse upward

leakage. In southern Putnam County, 80 ft3/sec discharges from

the Floridan aquifer system to the St. Johns River at Croaker Hole

Spring.

In the Floridan aquifer system, chloride concentrations are

generally below 50 mg/L in the northern and western part of the

lower St. Johns River ground water flow system but increase to

over 1,000 mg/L in southern Flagler County. In the Floridan

aquifer system, moderately saline water containing chloride

concentrations between 250 and 1,000 mg/L is present beneath

part of the St. Johns River in Putnam County and in southern

St. Johns and northern Flagler counties. In Volusia County,

chloride concentrations are below 250 mg/L in the middle of the

county but increase to over 1,000 mg/L in both the eastern and

western portions of the county (along the Atlantic coast and the

St. Johns River).

Sulfate concentrations in the Floridan aquifer are generally below

50 mg/L in the western part of the lower St. Johns River ground

water flow system but increase to more than 500 mg/L in

southern and eastern St. Johns County and northeastern Flagler

St. Johns River Water Management District

45
HYDROGEOLOGY

County. Moderately saline water (sulfate concentrations between

250 and 1,000 mg/L) is present in much of St. Johns, northern

and southwestern Flagler, northeastern Putnam, and western

Volusia counties.

TDS concentrations in the Floridan aquifer are generally below

500 mg/L in the western and northern part of the lower St. Johns

River ground water flow system but increase to above

5,000 mg/L in southeastern St. Johns County and northwestern

and eastern Volusia County. Moderately saline water (TDS

concentrations between 500 and 3,000 mg/L) is present in

southern St. Johns, eastern Putnam, most of Flagler, eastern and

western Volusia, and northeastern Duval counties.

The intermediate aquifer system is not areally extensive, but

occurs in portions of Duval, St. Johns, Clay, Putnam, and Flagler

counties. It ranges from less than 10 to about 300 ft below mean

sea level and varies in thickness from less than 1 to 15 ft. Water

in the intermediate aquifer system is derived locally either by

upward leakage from the underlying Floridan aquifer system or

by downward leakage from the overlying surficial aquifer system.

Water quality in the intermediate aquifer system is similar to the

water quality of one of the other aquifer systems within the same

general area.

The surficial aquifer system is the principal source of potable

water in St. Johns County and an important source of domestic

self-supply water in Duval and Flagler counties. Water in the

surficial aquifer is unconfined, and the water table is generally a

subdued reflection of the topography. The surficial aquifer

system is generally recharged at the ridges and water moves

away from the ridges toward the St. Johns River and the coast.

Water leaves the surficial aquifer system by seepage to some

lakes, ditches, and streams; by evapotranspiration where the

water table is at or near land surface; by well withdrawals; and,

where the elevation of the potentiometric surface of the Floridan

aquifer system is below the water table, by downward leakage to

the Floridan aquifer system.

St. Johns River Water Management District

46
Summary

In the upper 50 ft of the surficial aquifer system, chloride

concentrations are above 1,000 mg/L within 1-4 miles of the coast

in Duval, Hagler, and Volusia counties. In Duval County, there

is an interconnection between the surficial aquifer system and the

St. Johns River.

St. Johns River Water Management District

47
HYDROGEOLOGY

RECOMMENDATIONS

A review of the available literature indicates a need for additional

information about the relationship and influence of the

interconnection of the lower St. Johns River ground water flow

system with the surface water basin. The following activities,

therefore, are recommended.

• Collect more information on the surficial aquifer system.

This information should be used to map the distribution,

thickness, water levels, and water quality of the surficial

aquifer system.

• Quantify discharge to the St. Johns River from the surficial

aquifer system. No quantitative information is available on

the flow of water from the surficial aquifer system to the

St. Johns River.

• Collect more information on the intermediate aquifer system

in order to identify geographic locations where surface water

may be influenced by the intermediate aquifer system.

• Continue to document the location, flow, and water quality

of submerged springs and areas of diffuse upward leakage

from the Horidan aquifer system to LSJRB.

• Coordinate with local public health units to identify areas in

close proximity to the St. Johns River where there are high

concentrations of septic tanks. A determination should be

made concerning the potential for these septic tanks to

malfunction and discharge undesirable quantities and

concentrations of leachate to the surficial aquifer system and

the St. Johns River during periods of excessive rain.

St. Johns River Water Management District

48
References

REFERENCES

Bergman, M.J. 1992. Volume 2 of the Lower St. Johns River Basin

reconnaissance: Surface water hydrology. Technical Publication

SJ92-1. Palatka, Ha.: St. Johns River Water Management

District.

Bermes, B.J., G.W. Leve, and G.R. Tarver. 1963. Geology and

ground water resources ofFlagler, Putnam, and St. Johns counties,

Florida. Report of Investigations No. 32. Tallahassee, Ha.:

Horida Geological Survey.

Boniol, D., M. Williams, and D. Munch. 1993. Mapping recharge

to the Floridan aquifer using a geographic information system.

Technical Publication SJ93-5. Palatka, Ha.: St. Johns River

Water Management District.

Brooks, H.K. 1961. The submarine spring off Crescent Beach,

Horida. Quart. Jour. Fla. Acad. Sci. 24(2):122-134.

Brown, D.P. 1984. Impact of development on availability and quality

of ground water in eastern Nassau County, Florida, and

southeastern Camden County, Georgia. Water Resources

Investigations Report 83-4190. Tallahassee, Ha.: U.S.

Geological Survey.

Cederstrom, D.J., E.H. Boswell, and G.R. Tarver. 1979. Summary

appraisals of the nation's ground water resource - South Atlantic

Gulf Region. Professional Paper 813-0. Washington, D.C.:

U.S. Geological Survey.

Clark, W.E., R.H. Musgrove, C.G. Menke, and J.W. Cagle, Jr.

1964. Water resources of Alachua, Bradford, Clay, and Union

counties, Florida. Report of Investigations No. 35.

Tallahassee, Ha.: Horida Geological Survey.

Durden, D.W. 1991. Computer simulation of the predevelopment and

current Floridan aquifer system in northeast Florida. Technical

St. Johns River Water Management District

49
HYDROGEOLOGY

Publication SJ91-4. Palatka, Fla.: St. Johns River Water

Management District.

Florence, B.L. 1992. Annual water use survey: 1990. Technical

Publication SJ92-4. Palatka, Fla.: St. Johns River Water

Management District.

Hand, J., and M. Paulic. 1992. 1992 Florida water quality

assessment 305(b) technical appendix. Bureau of Surface Water

Management. Tallahassee, Fla.: Florida Department of

Environmental Regulation.

Leve, G.W. 1966. Ground water in Duval and Nassau counties,

Florida. Florida Geological Survey Report of Investigations

No. 43. De Land, Fla.: E.O. Painter Printing.

. 1983. Relation of concealed faults to water quality and

the formation of solution features in the Floridan aquifer,

northeastern Florida, U.S.A. Journal of Hydrology 61:251-264.

Miller, J.A. 1982. Geology and configuration of the top of the Tertiary

limestone aquifer system, southeastern United States. Open File

Report 81-1178. Atlanta, Ga.: U.S. Geological Survey.

. 1986. Hydrologic frameworks of the Floridan aquifer system

in Florida and in parts of Georgia, Alabama, and South Carolina.

Professional Paper 1403-B. Washington, D.C.: U.S.

Geological Survey.

Morris, F.W. 1993, draft. Volume 3 of the Lower St. Johns River

Basin reconnaissance: Hydrodynamics and salinity of surface

water. Palatka, Fla.: St. Johns River Water Management

District.

Motz, L.H. 1987. Source term equations and solute transport

model for consumptive use permit application. In

Proceedings of the NWWA conference and exposition on solving

St. Johns River Water Management District

50
References

ground water problems with models, Vol. 1. Dublin, Ohio:

National Water Well Association.

Motz, L.H., and J.P. Heaney. 1991. Upper Etonia Creek hydrologic

study: Phase I: Final report. Special Publication SJ91-SP5.

Palatka, Fla.: St. Johns River Water Management District.

. 1992. Upper Etonia Creek hydrologic study: Phase II: Final

report. Special Publication SJ92-SP18. Palatka, Fla.: St. Johns

River Water Management District.

Navoy, A.S., and L.A. Bradner. 1987. Ground water resources of

Flagler County, Florida. Water Resources Investigations

Report 87-4021. Tallahassee, Fla.: U.S. Geological Survey.

Rosenau, J.C., G.L. Faulkner, C.W. Hendry, Jr., and R.W. Hull.

1977. Springs of Florida. Bulletin No. 31 (revised).

Tallahassee, Fla.: Florida Department of Natural Resources.

Snell, L.J., and W. Anderson. 1970. Water resources of northeast

Florida. Report of Investigations No. 54. Tallahassee, Fla.:

Florida Department of Natural Resources.

Spechler, R.M. 1982. Generalized configuration of the top of the

limestone unit of the lower part of the surftcial aquifer, Duval

County, Florida. Open File Report 82-336. Tallahassee, Fla.:

U.S. Geological Survey.

. 1993, in press. Saltwater intrusion and quality of water in

the Floridan aquifer system, northeast Florida. Water Resources

Investigations Report 92-4174. Tallahassee, Fla.: U.S.

Geological Survey.

Spechler, R.M., and P.S. Hampson. 1984. Ground water resources

of St. Johns County, Florida. Water Resources Investigations

Report 83-4187. Tallahassee, Fla.: U.S. Geological Survey.

St. Johns River Water Management District

51
HYDROGEOLOGY

Spechler, R.M., and R.B. Stone, Jr. 1983. Appraisal of the

interconnection between the St. Johns River and the surficial

aquifer, east-central Duval County, Florida. Water Resources

Investigations Report 82-4109. Tallahassee, Fla.: U.S.

Geological Survey.

Stringfield, U.T., and H.H. Cooper, Jr. 1951. Geologic and

hydrologic features of an artesian spring east of Florida. Report

of Investigations No. 7, pt. 2. Tallahassee, Fla.: Florida

Geological Survey.

Tibbals, C.H. 1981. Computer simulation of the steady-state flow

system of the Tertiary limestone (Floridan) aquifer system in eastcentral Florida. Water Resources Investigations Open File

Report 81-681. Tallahassee, Fla.: U.S. Geological Survey.

. 1990. Hydrology of the Floridan aquifer system in eastcentral Florida. Professional Paper 1403-E. Washington, D.C.:

U.S. Geological Survey.

Toth, D.J. 1990. Geohydrologic summary of the Floridan aquifer in

coastal areas of Nassau, Duval, and northeast St. Johns counties.

Technical Report SJ90-5. Palatka, Fla.: St. Johns River Water

Management District.

Vernon, R.O. 1951. Geology of Citrus and Levy counties, Florida.

Geological Bulletin No. 33. Tallahassee, Fla.: Florida

Geological Survey.

Wyrick, G.G. 1960. The ground-water resources of Volusia County,

Florida. Report of Investigations No. 22. Tallahassee, Fla.:

U.S. Geological Survey.

St. Johns River Water Management District

52