HYDROLOGY OF THE FLORIDAN AQUIFER 

SYSTEM IN EAST-CENTRAL FLORIDA

\ SOUTH CAROLINA

U.S. GEOLOGICAL SURVEY PItOPESSIONAL PAPER 1403~E
AVAILABILITY OF BOOKS AND MAPS OF THE U.S. GEOLOGICAL SURVEY

Instructions on ordering publications of the U.S. Geological Survey, along with prices of the last offerings, are given in the current-year issues of the monthly catalog "New Publications of the U.S. Geological Survey." Prices of available U.S. Geological Survey publications released prior to the current year are listed in the most recent annual "Price and Availability List" Publications 

that are listed in various U.S. Geological Survey catalogs (see back inside cover) but not listed in the most recent annual "Price and 

Availability List" are no longer available.

Prices of reports released to the open files are given in the listing "U.S. Geological Survey Open-File Reports," updated monthly, which is for sale in microfiche from the U.S. Geological Survey, Books and Open-File Reports Section, Federal Center, Box 

25425, Denver, CO 80225. Reports released through the NTIS may be obtained by writing to the National Technical Information 

Service, U.S. Department of Commerce, Springfield, VA 22161; please include NTIS report number with inquiry.

Order U.S. Geological Survey publications by mail or over the counter from the offices given below.

BY MAIL

0 , OVER THE COUNTER 

Books

Books Professional Papers, Bulletins, Water-Supply Papers, Techniques

of Water-Resources Investigations, Circulars, publications of general in- Books of the U.S. Geological Survey are available over the 

icrest (such as leaflets, pamphlets, booklets), single copies of Earthquakes counter at the following Geological Survey Public Inquiries Offices, all 

&. Volcanoes, Preliminary Determination of Epicenters, and some mis- of which are authorized agents of the Superintendent of Documents: 

cellaneous reports, including some of the foregoing series that have gone 

out of print at the Superintendent of Documents, are obtainable by mail 

from WASHINGTON, D.C.--Main Interior Bldg., 2600 corridor,

18th and CSts.,NW.

U.S. Geological Survey, Books and Open-File Reports DENVER, Colorado-Federal Bldg., Rm. 169, 1961 Stout St. 

Federal Center, Box 25425 LOS ANGELES, California-Federal Bldg., Rm. 7638,300 N. 

Denver, CO 80225 Los Angeles St.

 MENLO PARK, Californla-Bldg. 3 (Stop 533), Rm. 3128,

Subscriptions to periodicals (Earthquakes & Volcanoes and 345 Middlefield Rd.

Preliminary Determination of Epicenters) can be obtained ONLY from RESTON, Virginia-503 National Center, Rm. 1C402,12201 

the Sunrise Valley Dr.

 SALT LAKE CITY, Utah-Federal Bldg., Rm. 8105,125 

Superintendent of Documents South State St.

Government Printing Office SAN FRANCISCO, California-Customhouse, Rm. 504,555 

Washington, D.C. 20402 Battery St.

 SPOKANE, Washington~U.S. Courthouse, Rm. 678, West

(Check or money order must be payable to Superintendent of Docu- 920 Riverside Ave.. 

ments.) ANCHORAGE, Alaska-Rm. 101,4230 University Dr.

 ANCHORAGE, Alaska-Federal Bldg, Rm. E-146, 701 C St.

Maps

For maps, address mail orders to

U.S. Geological Survey, Map Distribution Maps

Federal Center, Box 25286 Maps may ^ purchased over the counter at the U.S. GeologiDenver, CO 80225 caj Sm^gy 0fflces where books are sold (all addresses in above list) and

at the following Geological Survey offices: 

Residents of Alaska may order maps from

 ROLLA, Missouri-1400 Independence Rd. 

Alaska Distribution Section, U.S. Geological Survey, . DENVER, Colorado-Map Distribution, Bldg. 810, Federal

New Federal Building - Box 12 Center 

101 Twelfth Ave., Fairbanks, AK 99701 . FAIRBANKS, Alaska-New Federal Bldg., 101 Twelfth Ave.
Hydrology of the Floridan Aquifer System 

in East-Central Florida

By C.H. TIBBALS

REGIONAL AQUIFER SYSTEM ANALYSIS FLORIDAN AQUIFER SYSTEM

U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1403-E

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1990
DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, Jr., Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

Any use of trade, product, or firm names in this publication is for

descriptive purposes only and does not imply endorsement by the

U.S. Government

Library of Congress Cataloging in Publication Data

Tibbals, C.H.

Hydrology of the Floridan aquifer system in east-central Florida.

(Regional aquifer-system analysis) (Geological Survey professional paper ; 1403-E)

Bibliography: p.

Supt.ofDocs.no.: I 19.16:1403-E

1. Floridan Aquifer. 2. Aquifers Florida. I. Title. II. Series. III. Series: Geological Survey professional paper ; 1403-E.

GB1199.3.F6T53 1989 551.49'09759 86-600315

For sale by the Books and Open-File Reports Section, U.S. Geological Survey, 

Federal Center, Box 25425, Denver, CO 80225
FOREWORD

THE REGIONAL AQUIFER-SYSTEM ANALYSIS PROGRAM

The Regional Aquifer-System Analysis (RASA) Program was started in 

1978 following a congressional mandate to develop quantitative appraisals of 

the major ground-water systems of the United States. The RASA Program 

represents a systematic effort to study a number of the Nation's most 

important aquifer systems, which in aggregate underlie much of the country 

and which represent an important component of the Nation's total water 

supply. In general, the boundaries of these studies are identified by the 

hydrologic extent of each system and accordingly transcend the political 

subdivisions to which investigations have often arbitrarily been limited in the 

past. The broad objective for each study is to assemble geologic, hydrologic, 

and geochemical information, to analyze and develop an understanding of the 

system, and to develop predictive capabilities that will contribute to the 

effective management of the system. The use of computer simulation is an 

important element of the RASA studies, both to develop an understanding of 

the natural, undisturbed hydrologic system and the changes brought about in 

it by human activities, and to provide a means of predicting the regional 

effects of future pumping or other stresses.

The final interpretive results of the RASA Program are presented in a series 

of U.S. Geological Survey Professional Papers that describe the geology, 

hydrology, and geochemistry of each regional aquifer system. Each study 

within the RASA Program is assigned a single Professional Paper number, 

and where the volume of interpretive material warrants, separate topical 

chapters that consider the principal elements of the investigation may be 

published. The series of RASA interpretive reports begins with Professional 

Paper 1400 and thereafter will continue in numerical sequence as the interpretive products of subsequent studies become available.

Dallas L. Peck 

Director

CONTENTS

	Page

Foreword......................................................................... Ill

Abstract........................................................................... El

Introduction...................................................................... 2

Background................................................................ 2

Purpose and scope ....................................................... 2

Previous investigations................................................. 2

Acknowledgments........................................................ 4

Well-numbering system................................................ 4

Description of the area ....................................................... 4

Topography................................................................ 4

Drainage.................................................................... 4

Climate...................................................................... 4

Long-term variability of rainfall............................... 7

Evapotranspiration...................................................... 7

Hydrogeology................................................................... 10

Surficial aquifer........................................................... 10

Floridan aquifer system................................................ 11

Potentiometric surface............................................ 20

Recharge and discharge.......................................... 23

Hydraulic characteristics......................................... 32

Water quality........................................................ 35

Page

Digital computer model....................................................... E51

Steady-state predevelopment simulation.......................... 52

Transient simulation with modern-day (1978) pumping....... 55

Calibration........................................................... 55

Hydrologic effects of 1978 pumping........................... 56

Long-term effects of pumping Double-mass curve analyses .... 69

Simulated effects of selected hypothetical manmade changes on

the Floridan flow system ........................................... 73

Hydrologic effects of doubling 1978 municipal pumpage...... 73

Hydrologic effects of raising levels of selected spring pools. 77 

Hydrologic effects of lowering of water table.................... 77

Summary and conclusions.................................................... 78

Selected references............................................................ 79

Appendixes:

A Index to wells, other than drainage wells, used in this

study................................................................ 85

B Long-term hydrographs........................................... 87

C Investigations of Upper Floridan aquifer discharge to

springs, rivers, and lakes .................................... 93

ILLUSTRATIONS

Page

FIGURES 1-3. Maps showing:

1. Location of Floridan RASA subregional study areas ............................................................................... E3

2. Location of wells, other than drainage wells, used in this study............................................................... 5

3. Location of study area, generalized topography, and major surface drainage basins ..................................... 6

4. Graph showing mean monthly rainfall at Palatka, Orlando, and Avon Park............................................................. 7

5. Map showing average annual rainfall and maximum potential evaporation .............................................................. 8

6, 7. Graphs showing:

6. Cumulative departure from average rainfall at Jacksonville (1867-1981) and at Jacksonville, Palatka, Orlando,

and Avon Park (1903-81).............................................................................................................. 9

7. Estimated relation of evapotranspiration to water-table depth in east-central Florida................................... 10

8. Chart showing geologic units, hydrogeologic units, and equivalent layers used in computer model.............................. 12

9. Diagram of aquifers and confining units of the Floridan aquifer system .................................................................. 14

10-14. Maps showing:

10. Thickness of Floridan aquifer system ................................................................................................... 15

11. Altitude and depth to top of Floridan aquifer system.............................................................................. 16

12. Altitude of base of Floridan aquifer system ........................................................................................... 17

13. Altitude of top and thickness of middle semiconfming unit....................................................................... 18

14. Location of geologic and hydrogeologic sections ................................................................................... 19

15. Geologic section A-A' .................................................................................................................................... 20

16. Geologic section B-B'. .................................................................................................................................... 21

17. Geologic section C-C'.. ................................................................................................................................... 21

18. Geologic section D-D' .................................................................................................................................... 22

19. Hydrograph showing monthly average water levels in wells 43 (Upper Floridan aquifer) and 42 (Lower Floridan

aquifer), 1963-72 ................................................................................................................................... 23
VI CONTENTS

Page

FIGURE 20-23. Maps showing:

20. Potentiometric surface of the Upper Floridan aquifer prior to development, spring discharge, and model

boundary conditions for the Upper Floridan .................................................................................. E24

21. Upper Floridan aquifer recharge and discharge areas; potentiometric surface of the Upper Floridan,

May 1980; and selected ground-water basins................................................................................. 25

22. Model-derived rates of recharge and discharge to and from the Upper Floridan aquifer through the upper

confining unit.......................................................................................................................... 26

23. Location of drainage wells that recharge the Upper Floridan aquifer in the Orlando area ......................... 27

24-27. Sketches showing hydrogeologic units and ground-water flow:

24. Along model column 15 ................................................................................................................... 32

25. Along model column 25 ................................................................................................................... 33

26. Along model column 31 ................................................................................................................... 34

27. Along row 9, columns 50^12, and along model column 42, rows 9-20....................................................... 35

28-35. Maps showing:

28. Model-derived transmissivity of the Upper Floridan aquifer and locations of selected aquifer test sites........ 36

29. Model-derived transmissivity of the Lower Floridan aquifer and location of aquifer test site ...................... 37

30. Model-derived leakage coefficient of the upper confining unit of the Floridan aquifer system...................... 38

31. Average dissolved-solids concentration in water in the Upper Floridan aquifer ........................................ 40

32. Average hardness of water in the Upper Floridan aquifer .................................................................... 41

33. Average sulfate concentration in water in the Upper Floridan aquifer .................................................... 42

34. Average chloride concentration in water in the Upper Floridan aquifer................................................... 43

35. Chloride concentration in water in the upper 100 feet of the Upper Floridan aquifer................................. 44

36. Maps showing Pleistocene shorelines, much generalized................................................................................... 46

37. Hydrograph showing estimated changes in sea level........................................................................................ 47

38. Map showing estimated depth to water having chloride concentration greater than 10,000 milligrams per liter.......... 48

39, 40. Graph and sketch showing specific conductance, chloride concentration, water levels, and generalized lithology in:

39. Well 47, at Geneva, Seminole County, August 1981............................................................................. 49

40. Well 55, about 0.3 mile southwest of Blue Spring, Volusia County, August 1981 ...................................... 50

41. Graph and sketch showing specific conductance, hardness, dissolved solids, sulfate, water levels, and lithology in

core holes 1 and 2 (wells 14, 17) at Polk City, Polk County, 1979-80 ............................................................ 51

42. Map showing finite-difference grid superimposed on modeled area..................................................................... 53

43. Sketch showing conceptualized model input data............................................................................................. 54

44. Map showing results of transient model calibration.......................................................................................... 58

45. Sketch showing conceptualized pumping periods for transient model calibration ................................................... 59

46-48. Hydrographs showing computed versus observed water levels in:

46. Well 26 (southeast Orange County) for selected values of storage coefficient............................................ 59

47. Well 20 (north Osceola County) for selected values of storage coefficient................................................. 60

48. Well 40 (west-central Orange County) for selected values of storage coefficient........................................ 60

49-57. Maps showing:

49. Observed versus computed potentiometric surface of the Upper Floridan aquifer, May 1978 ...................... 61

50. Drawdown of potentiometric surface of Upper Floridan aquifer caused by average 1978 pumping, drainage

wells, and boundary flow to adjacent pumping centers ................................................................... 62

51. Effects of 1978 pumping on downward and upward leakage rates to and from the Upper Floridan aquifer,

flow of selected springs, and flow at boundaries............................................................................ 63

52. Drawdown of potentiometric surface of Upper Floridan and Lower Floridan aquifers caused by pumping for

municipal supplies, 1978............................................................................................................ 64

53. Drawdown of potentiometric surface of Upper Floridan aquifer caused by pumping for rural domestic and

privately owned public supplies, 1978.......................................................................................... 65

54. Drawdown of potentiometric surface of Upper Floridan aquifer caused by pumping by major industries, by

institutions, and for thermoelectric condenser cooling, 1978............................................................. 66

55. Drawdown of potentiometric surface of Upper Floridan aquifer caused by pumping for irrigation, 1978........ 67

56. Buildup of potentiometric surface of Upper Floridan aquifer caused by recharge through drainage wells,

1978....................................................................................................................................... 68

57. Drawdown of potentiometric surface of Upper Floridan aquifer caused by net boundary flows to or from

adjacent pumping centers, 1978.................................................................................................. 70

58. Hydrograph showing annual average discharge of Silver Springs near Ocala, Blue Spring near Orange City, Wekiva 

River near Sanford, Wekiva Springs near Apopka, Rock Springs near Apopka, Ponce De Leon Springs near 

De Land, and Sanlando, Palm, and Starbuck Springs near Longwood, 1929-82................................................. 71

59-61. Graphs showing double-mass curve of:

59. Discharge of Blue Spring near Orange City versus rainfall at De Land, 1932-82....................................... 71

60. Discharge of Wekiva River near Sanford versus rainfall at Orlando, 1935-82 ........................................... 72

61. Water level in well 40 (Orange 47 near Orlando) versus rainfall at Orlando, 1944-82, and pumping by cities

of Orlando and Winter Park, 1951-82 .......................................................................................... 72
CONTENTS VII

Page

FIGURES 62-64. Maps showing:

62. Drawdown of potentiometric surface of Upper Floridan and Lower Floridan aquifers caused by hypothetical doubling of pumping for municipal supplies; all other categories of pumping at average 1978 rates.... E74

63. Buildup of potentiometric surface of Upper Floridan aquifer caused by hypothetical raising of selected

spring pools by 10 feet and by actual construction of Rodman Reservoir ........................................... 75

64. Drawdown of potentiometric surface of Upper Floridan aquifer caused by hypothetical lowering of water

table in surficial aquifer by 5 feet ............................................................................................... 76

65-73. Hydrographs showing water levels in:

65. Well 2 near Brighton; well 7, about 30 miles northwest of Vero Beach; well 10, about 10 miles southwest

of Melbourne; and well 23 at Cocoa............................................................................................. 87

66. Well 6 near Frostproof; wells 21 and 22, about 25 miles southwest of Orlando; and wells 35 and 36

near Mascotte.......................................................................................................................... 87

67. Well 26, about 22 miles southeast of Orlando, and wells 29, 30, and 32 (three zones of salinity monitor well,

Cocoa well field), about 18 miles southeast of Orlando.................................................................... 88

68. Wells 37, 38, and 39 at Bithlo........................................................................................................... 88

69. Wells 40 and 41, about 6 miles west of Orlando, and in wells 42 and 43 at Orlando.................................... 89

70. Well 46 near Longwood; well 50 near Tavares; well 53 near Sanford; well 54 at Leesburg; and well 56,

about 13 miles southwest of New Smyrna Beach........................................................................... 89

71. Well 57 near Starkes Ferry; well 65 near Silver Springs; well 76 at Interlachen; and well 79 at Gainesville... 90

72. Wells 58, 59, and 60 (salinity monitor wells, central Volusia County), 7 miles northeast of De Land, and

wells 66 and 67, about 8 miles southwest of Daytona Beach ............................................................ 90

73. Well 63 at Astor Park; well 69 at Seville; well 71, about 10 miles northwest of Salt Springs; well 72 at

Bunnell; and well 77, about 10 miles southeast of Hastings ............................................................. 91

74, 75. Maps showing results of low-flow measurements:

74. Lake George area........................................................................................................................... 94

75. Wekiva River-Alexander Spring Creek area ...................................................................................... 95

76, 77. Sketches of:

76. Island Spring near Sanford ............................................................................................................. 96

77. Croaker Hole Spring near Welaka .................................................................................................... 96

78. Map showing results of low-flow measurements, Lake Jessup-Econlockhatchee River area.................................... 97

TABLES

TABLE 1. Ground-water discharge from the Upper Floridan aquifer: Spring flow; simulated discharge to rivers, lakes, lagoons, and

the Atlantic Ocean; and lateral flow at model boundaries..................................................................................... E30

2. Typical concentrations of dissolved solids, hardness, sulfate, and chloride in freshwater, brackish water, and seawater....... 39

3. Minimum time to flush brackish ground water from selected spring basins................................................................... 50

4. Simulated rates of recharge and discharge for steady-state and transient conditions ...................................................... 56

5. Average 1978 pumping rates and "dry period" pumping rates, by pumping category...................................................... 57

6. Change in Upper Floridan aquifer predevelopment ground-water flow rates caused by pumping...................................... 59

7. Average 1978 pumpage in Upper and Lower Floridan aquifer and average drawdown in the Upper Floridan attributable

to each category of pumping........................................................................................................................... 60

8. Changes in Floridan ground-water flow rates caused by selected manmade changes in the hydrologic regimen................... 73
VIII CONTENTS

METRIC CONVERSION FACTORS

For readers who wish to convert measurements from the inch-poound system of units to the metric system of units, the conversion factors are 

listed below:

Multiply inch-pound units By To obtain metric units

inch (in) 

foot (ft) 

mile (mi)

acre

square mile (mi2)

gallon (gal) 

cubic foot (ft3) 

million gallons (Mgal)

gallon per minute (gal/min)

inch per year (in/yr) 

cubic foot per second (ft3/s)

gallon per minute per foot [(gal/min)/ft]

foot squared per day (ft2/d) 

foot per day (ft/d)

foot per day per foot E(ft/d)/ft]

Length

25.4

0.3048

1.609

Area

0.4047

2.590

Volume

3.785

0.003785

28.32

0.02832

3,785

Flow

0.06309

0.00006309

25.4

0.02832

Specific capacity

0.2070

Transmissivity

0.09290

Hydraulic conductivity

0.3048

Leakance

1.000

millimeter (mm) 

meter (m) 

kilometer (km)

hectare (ha)

square kilometer (km2)

liter (L)

cubic meter (m3)

liter (L)

cubic meter (m3)

cubic meter (m3)

liter per second (L/s) 

cubic meter per second (m3/s) 

millimeter per year (mm/yr) 

cubic meter per second (m3/s)

liter per second per meter [(L/s)/m]

meter squared per day (m2/d) 

meter per day (m/d)

meter per day per meter [(m/d)/m]

Temperature in degrees Fahrenheit (°F) can be converted to degrees Celsius (°C) as follows: °C=(°F-32H1.8.

ALTITUDE DATUM

Sea Level: In this report "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929) a vertical datum derived from 

a general adjustment of the first-order level nets of both the United States and Canada, formerly called Sea Level Datum of 1929.
REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

HYDROLOGY OF THE FLORIDAN AQUIFER SYSTEM IN 

EAST-CENTRAL FLORIDA

By C.H. TIBBALS

ABSTRACT

The fresh-ground-water flow system of east-central Florida consists 

of a thin surficial sand aquifer underlain by the thick, highly productive 

carbonate rocks of the Floridan aquifer system. On the basis of 

permeability, this system is divided into the Upper and Lower Floridan 

aquifers, which are separated by a less permeable limestone sequence 

referred to as the "middle semiconfining unit." The transmissivity of 

the Upper Floridan ranges from about 10,000 to 400,000 feet squared 

per day based on field aquifer tests, but simulation suggests an average 

value of 120,000 feet squared per day. The transmissivity of the Lower 

Floridan is less well known, but simulation suggests values in the range 

of 30,000 to 130,000 feet squared per day. Storage coefficients of both 

the Upper and Lower Floridan aquifers are about 0.001. Leakage 

coefficients of the confining bed that overlies the Upper Floridan range 

from 0.000001 per day to about 0.0006 per day. The leakage coefficient 

of the middle semiconfining unit is about 0.00005 per day.

The chemical quality of the water in the Upper Floridan aquifer 

varies according to proximity to recharge and discharge areas. Low 

concentrations of dissolved solids (less than 250 milligrams per liter) 

generally occur in recharge areas. However, in the discharge areas 

along the Atlantic Coast and along the St. Johns River, the dissolvedsolids concentration is generally more than 1,000 milligrams per liter, 

and in places exceeds 25,000 milligrams per liter. The quality of water 

in the Lower Floridan is not well defined, but in east-central Florida, 

water in the Lower Floridan is probably more mineralized than water 

in the Upper Floridan.

The hydraulics of the Floridan aquifer system under predevelopment 

conditions involve mostly recharge to the Upper Floridan (by way of 

leakage from the surficial aquifer), lateral movement through the 

Upper Floridan for short distances, and discharge by way of springs 

and seepage to streams. Relatively small amounts of discharge occur 

along the coast, and small amounts move into and out of the underlying 

Lower Floridan. Thus, there is a vigorous flow system locally in the 

Upper Floridan and, except in west Orange County and southeast Lake 

County, a relatively sluggish flow system in the Lower Floridan.

The essential features of the predevelopment steady-state flow 

system are as follows:

 The highest rates of recharge to the Floridan are in four areas: the 

west flank of the Volusia County potentiometric surface "high"; 

the Putnam-Alachua County potentiometric surface "high"; the 

topographically high ridge areas of mid-Polk and Highlands Counties; and the northeast flank of the central Florida potentiometric 

surface "high" in Lake and Orange Counties and extending into 

east Marion County.

 Most discharge from Upper Floridan (about 68 percent of the total) 

occurs as point discharge to springs and streams located within 25 

miles of recharge areas.

 The highest rates of diffuse upward leakage from the Upper Floridan 

(about 27 percent of the total discharge) occur near areas where 

the downward leakage rates are also high. Thus, it is inferred that 

thin or very leaky confining beds are common to the areas of high 

upward leakage and to the nearby areas of high downward 

leakage.

 Lateral boundary outflow from the Upper Floridan aquifer (principally occurring along the Atlantic Coast) is about 4 percent of the 

total discharge. Lateral flow to the south is about 1 percent of the 

total discharge.

 Interchange between the Upper and Lower Floridan aquifer layers 

is relatively small (about 290 cubic feet per second) compared with 

the flow within the Upper Floridan (about 1,950 cubic feet per 

second).

 The model-derived transmissivities are considered to have more 

regional significance than transmissivity values derived from 

individual aquifer tests. 

The imposition of pumping has altered the flow system, but not to a

great degree. The simulated effects of 1978 pumpage (about 560 million

gallons per day) on the predevelopment Floridan aquifer system flow

regime are summarized as follows:

 An average areal drawdown of about 4 feet has occurred in the 

Upper Floridan aquifer.

 Downward leakage to the Floridan from the overlying surficial 

aquifer has increased by about 600 cubic feet per second (from 

about 1,900 to about 2,500 cubic feet per second).

 Upward leakage from the Floridan to the surficial aquifer has 

decreased about 150 cubic feet per second (from about 530 to about 

380 cubic feet per second).

 Spring flow has decreased about 90 cubic feet per second (from about 

1,330 to 1,240 cubic feet per second).

 Lateral outflow at boundaries has increased in some areas and 

decreased in other areas, resulting in a net increase of about 15 

cubic feet per second.

Simulation was used to investigate the effects of hypothetical development, as follows:

 Doubling the 1978 municipal pumpage would cause relatively small 

increases in drawdown, with 10 feet or more increase only near the 

centers of pumping and 20 feet or more only near Orlando.

 Raising elevations of spring pools would cause Upper Floridan head 

buildup near springs but little change in spring discharge when 

steady-state conditions are reached.

El
E2 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

 Floridan pumpage tends to induce leakage from the overlying 

surficial aquifer system and to reduce upward discharge to it, 

thereby lowering the water table.

 Hydrologic analysis of Floridan aquifer system discharge led to the 

discovery and measurement of two hitherto undocumented 

springs.

INTRODUCTION

BACKGROUND

The Floridan aquifer system is one of the most areally 

extensive and widely used sources of ground-water supplies in the Southeastern United States (Cederstrom and 

others, 1979). The Floridan underlies about 100,000 mi2 , 

including all of Florida, south Georgia, southwest Alabama, and extreme south South Carolina. More than 3 

billion gallons of water are pumped daily from the aquifer 

system, making it a major source of municipal, rural, 

industrial, and agricultural water supply in most of 

Florida and south Georgia, and in small parts of Alabama 

and South Carolina.

In October 1978, the U.S. Geological Survey began a 

study to provide a complete and detailed hydrogeologic 

description of the Floridan aquifer system, including its 

geology, geochemistry, and flow system. That investigation is herein referred to as the "Floridan aquifer 

system RASA" (Regional Aquifer-System Analysis), or 

"RASA." Early in the investigation and in some of the 

interim reports, the investigation was variously referred 

to as the "Southeastern Limestone RASA" or the "Tertiary Limestone RASA."

The Floridan aquifer system RASA was a 5-yr effort 

that included (1) synthesis of all existing data and 

presentation of a series of regional hydrogeologic and 

geochemical maps, (2) gathering of new hydrologic data 

to fill data voids, and (3) design and calibration of a 

large-scale, coarse-grid regional digital computer model 

of the aquifer system and four more detailed subregional 

models of selected areas of the Floridan aquifer system 

(fig. 1).

The results of the Floridan RASA study are presented 

in nine chapters in U.S. Geological Survey Professional 

Paper 1403. Professional Paper (PP) 1403-A summarizes 

the overall hydrology of the Floridan aquifer system. PP 

1403-B describes the regional hydrogeologic framework. 

PP 1403-C describes the regional ground-water flow 

system, hydraulics, and ground-water development. PP 

1403-D, -E, -F, and -H are detailed hydrologic descriptions that include computer simulation of the Floridan 

aquifer flow system in subregional areas: south Georgia, 

south South Carolina, and northeast Florida (PP 

1403-D), east-central Florida (PP 1403-E), west-central 

Florida (PP 1403-F), and southwest Georgia and northwest Florida (PP 1403-H). PP 1403-G describes the

hydrogeology and geochemistry of the saline groundwater flow system of south Florida. PP 1403-1 describes 

the regional Floridan aquifer system ground-water 

chemistry.

The development and calibration of the regional model 

and of three of the four subregional models took place in 

two phases. The first phase consisted of assembling and 

calibrating models that simulated flow in the aquifer 

system prior to its development. The models that 

resulted from phase 1 are reported in the U.S. Geological 

Survey Water-Resources Investigations Report series 

and cover (1) the regional aquifer system (Bush, 1982), 

(2) east-central Florida (Tibbals, 1981), (3) west-central 

Florida (Ryder, 1982), and (4) northeast Florida and 

coastal parts of Georgia and South Carolina (Krause, 

1982).

The second phase consisted of assembling and calibrating computer models that simulated flow in the aquifer 

system under pumping stresses. The models were also 

used to evaluate the effects of large future increases in 

ground-water pumpage in selected areas.

Prior to this RASA study, the U.S. Geological Survey 

had constructed two computer models to simulate Floridan aquifer ground-water flow in the east-central Florida 

area. Those models (Bush, 1978, and Grubb and Rutledge, 1979) simulated ground-water conditions in central Volusia County and in the Green Swamp area, 

respectively. General information and data from those 

models are incorporated in the RASA model described 

herein.

PURPOSE AND SCOPE

This report describes the hydrogeologic framework 

and ground-water flow in the Floridan aquifer system in 

east-central Florida, quantifies the amounts and determines the locations of recharge and discharge areas of 

the Floridan, and determines the effects that pumping 

stresses have had on hydraulic heads in the system.

Although Floridan aquifer system geology and 

ground-water chemistry are briefly described in this 

report, the reader is referred to PP 1403-B (Miller, 1986) 

and -I (Sprinkle, in press) for more complete discussions.

PREVIOUS INVESTIGATIONS

Many investigators have studied the Floridan aquifer 

system ground-water resource in east-central Florida. 

Among the more notable pioneer studies are those by 

Brown (1925, 1937), Cooke (1939, 1945), Fuller (1904, 

1905), Matson and Sanford (1913), Sellards (1908), 

Stringfield (1933, 1936a, 1936b, 1938), Stringfield and
INTRODUCTION E3

88° 87" 85° 84° 83° 82° 81° 80°

33°- ftorWfilxX % ^~

32° -

30°

29°

28°

27°

26°

25°

Gfy

EXPLANATION

| | Professional Paper 1403-E

50 100 MILES

50 100 KILOMETERS

FIGURE 1. Location of Floridan RASA subregional study areas.
E4 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

Westendick (1935), Thompson and Stringfield (1931), and 

Unklesbay (1944).

Later, important areal hydrogeologic studies were 

conducted by Back (1963), Bermes and others (1963), 

Brown and Reece (1979), Cederstrom and others (1979), 

Clark and others (1964), Cooper and others (1953), 

Cooper and Stringfield (1950), Grain and others (1975), 

Faulkner (1973), Ferguson and others (1947), Frazee 

(1980), Johnston and others (1980), Klein (1975), Klein 

and others (1964), Knochenmus (1971), Knochenmus and 

Beard (1971), Knochenmus and Hughes (1976), Kohout 

(1959), Kohout and others (1977), Lichtler (1960, 1972), 

Lichtler and others (1968), Manheim (1967), McGuinness 

(1963), Miller (1982a, b, c, d, e), Parker and others 

(1955), Pascale (1975), Pride and others (1966), Rosenau 

and others (1977), Shampine (1975a, b, c, d), Snell and 

Anderson (1970), E.G. Stewart, Jr. (1966), J.W. Stewart 

(1980), Stringfield (1966), Tibbals (1975b, 1977), White 

(1958, 1970), and Wyrick (1960).

Investigations that included computer simulations of 

ground-water flow were conducted by Bush (1978, 1982), 

Grubb and Rutledge (1979), Krause (1982), Ryder (1982), 

and Tibbals (1981).

ACKNOWLEDGMENTS

The author expresses his appreciation to Douglas 

Munch (St. Johns River Water Management District) 

and to Abe Kreitman (South Florida Water Management 

District) and their respective staffs for their contributions of data and helpful information. Special thanks are 

due Breck Johnson, Umatilla, Fla., for the loan of special 

diving equipment and for his active participation in the 

documentation and measurement of Croaker Hole 

Spring.

WELL-NUMBERING SYSTEM

Well data used in this study were taken from files and 

publications of various sources. Each source has a unique 

well-numbering system or site identifier. Therefore, to 

attain a consistent well-numbering system the wells used 

in this study were assigned reference numbers in sequential format. Well locations are shown in figure 2. Appendix A contains an index to wells used in this study.

DESCRIPTION OF THE AREA

The east-central Florida RASA study area (fig. 3) 

consists of about 13,700 mi2 and includes the counties of 

Brevard, Flagler, Indian River, Orange, Osceola, Putnam, Seminole, and Volusia and parts of the counties of

Alachua, Clay, Glades, Highlands, Lake, Marion, 

Okeechobee, Polk, St. Johns, and St. Lucie.

The principal industries are tourism, agriculture, 

space research, and light manufacturing. Agricultural 

products include citrus products, cattle, dairy products, 

vegetables, ornamental plants, poultry, timber, and 

pulp wood.

TOPOGRAPHY

The topography ranges from rolling highlands in the 

northwest, west-central, and southwest parts of the 

study area to flat, swampy lowlands along the east coast 

and along the St. Johns River flood plain (fig. 3). 

Land-surface altitudes in the rolling highlands generally 

range from 100 to 200 ft above sea level and rise to as 

much as 310 ft just west of Lake Apopka in southeast 

Lake County. In the north-central and south-central 

parts, the land surface is moderately rolling to flat and 

altitudes range from 35 to 100 ft. In the coastal areas and 

along the St. Johns River, altitudes are generally less 

than 35 ft and, except for the coastal dune ridges, the 

terrain is generally flat and swampy.

DRAINAGE

The north and southeast part of the study area is 

drained by the northward-flowing St. Johns River and its 

major tributary, the Oklawaha River (fig. 3). The southwest part is drained by the southward-flowing Kissimmee River and its tributaries. Parts of the extreme west 

part of the study area are drained by the Withlacoochee 

River and the Peace River. The extreme east part drains 

into the coastal basin. Runoff (unaugmented by sewage, 

spring flow, or irrigation return flow) to streams ranges 

from virtually nil in the rolling sandhills to as much as 18 

to 20 in/yr in the areas where the surface drainage 

system is well developed (Lichtler, 1972, p. 9).

CLIMATE

The climate of the study area is classified as subtropical humid and is characterized by warm, relatively wet 

summers and mild, relatively dry winters. The average 

air temperature ranges from about 69 °F in the north to 

about 73 °F in the south. Most years have a few days of 

freezing temperatures, but the minimum temperature 

rarely falls below 20 °F. The maximum temperature 

frequently rises to 90 °F but only occasionally exceeds 

100 °F.

Rainfall is unevenly distributed during the year. 

About 55 percent of the annual rainfall occurs during four 

summer months, June, July, August, and September
DESCRIPTION OF THE AREA E5

83° 82° 81°

j t nanc na beset 

\ NASSAU

I ' s 7 ;i s-"*\," V ,

i <'jaw <, \ '\ f 1 SCALE 1:2,000,000

--. ,.. " 10N \ I /I / ,UVAI 0 10 

ISCN/ ^ / ! BAKER \ /

t I "L 0 _* ' _y Ln.oj> ^ ^BIA 

80°

Madi 

MA!

1

|<.^pr, <

v / ih.-'itfn 1"1 "

^ n ' . -T_ *> 20

^ _UW/JNNEE Lt"' P o'

30 40 MILES

. , i i_____|

0 10 20 30 40 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY ' 

DIGITAL LINEGRAPHS FROM 1:2,000,000 SCALE MAPS

29

*DF~oW~t' ' '^5F^

o i ! .-'<'(^\

.tarKf , . ' ^*^~ \ 

\ , 1 - \^ 

;f \ Sai^SDnnssb-S " *- " "7,

V ^^\ < £%

i^ \ v

7K CITRUS ^ %

44 *, - j 07-00 \* C rt >n -'W'nief Of-oa J^itusv-iie +U,41fS;i --5 - v » ! S 

dANOb- * 43" ^,tn,o ,

f

^ui,oa^ ^ ^j Merritt Isi-and 

" ( -

j ' . ' I INDIAN 1 \U'

/! .J - ' RtVER I- -T^

t^ J . . __ i ju

^*\r kftur^ i iv/ii - k

on o J j____ i ?PV_ ^^

 13 WELL Selected well used in this report. , " ^

Number is well reference number. See v '

appendix A for well descriptions , ^

6<? WELL WITH HYDROGRAPH Number is 

well reference number. See appendix A 

for IUI well WCII descriptions UCOlfl I^JIIUI IO

BOUNDARY OF PRINCIPAL STUDY AREA

FIGURE 2. Location of wells, other than drainage wells, used in this study.
E6 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

83° 82° 8V

BASE FROM U.S. GEOLOGICAL SURVEY

DIGITAL LINE GRAPHS FROM 1:2,000.000 SCALE MAPS

S ,~ ~T

EXPLANATION

ALTITUDE OF LAND SURFACE, IN FEET 

ABOVE SEA LEVEL

BOUNDARY OF PRINCIPAL STUDY AREA

 " BOUNDARY OF MAJOR SURFACE-WATER 

DRAINAGE BASINS

H

FIGURE 3. Location of study area, generalized topography, and major surface drainage basins.
DESCRIPTION OF THE AREA E7

INCHES RAINFALL, IN MONTHLY MEAN

Oi -*J CD3-fcfOCO *kUl

RAINFALL STATION ___ .

Mean monthly rainfall 

computed for the 

period 1951-80

 Palatka 

- Orlando 

..... Avon Park

-

-

---

-

_

-

FIGURE 4. Mean monthly rainfall at Palatka, Orlando, and Avon Park 

(National Oceanic and Atmospheric Administration, 1951-80).

(fig. 4). The rainfall is usually unevenly distributed 

throughout the area, especially during the summer. This 

is because most of the summer rainfall is derived from 

local showers or thunderstorms that occur randomly. 

The normal summer rainfall can be substantially augmented by tropical storms and hurricanes that pass 

through or near the Florida peninsula from time to time. 

Winter rainfall generally results from large cold fronts 

that move from northwest to southeast and cause the 

warm, resident airmasses to lose their moisture. The 

precipitation is almost always in the form of rain, but it 

occasionally occurs as hail or, on extremely rare occasions, as snow. Winter rainfall generally occurs over 

wide areas and thus is not as spotty as is summer rainfall. 

The average annual rainfall is as high as 55 inches in the 

north and as high as 59 inches in the extreme southeast 

but generally is about 52 in over most of the study area 

(fig. 5).

LONG-TERM VARIABILITY OF RAINFALL

The short-term random nature of rainfall is obvious. 

Rainfall varies from place to place as well as from day to 

day and year to year. However, within these random 

occurrences and on an annual basis there are cycles of 

dry seasons and wet seasons.

Long-term, multiyear cycles, if they exist, are difficult 

to discern, primarily because of the relatively short 

length of rainfall record available. The longest rainfall 

record available in or near the study area is that of 

Jacksonville in northeast Florida. That record begins in 

1867 (fig. 6). The next longest period of record common 

to several rainfall stations in and near the study area

begins in 1903 and is that of Palatka, Orlando, and Avon 

Park. Figure 6 shows graphs of cumulative departure 

from average rainfall at Jacksonville from 1867 to 1981 

and at Jacksonville, Palatka, Orlando, and Avon Park 

from 1903 to 1981. The vertical positions of the graphs 

are not as diagnostic as are the slopes of the graphs or 

the changes in position of the graphs from one year to the 

next. A rising line slope indicates above-average rainfall 

whereas a declining line slope shows below-average 

rainfall. For example, the long-term record at Jacksonville shows that from 1867 to 1888 there was a total 

excess (that which is above average) of about 105 in, an 

average excess of about 4.75 in/yr. However, from 1888 

to about 1931 a drought of record proportions occurred. 

During that 43-yr period, the rainfall deficiency totaled 

about 192 in, an average deficiency of about 4.5 in/yr. 

From 1931 to 1943 there is no discernible trend; this 

indicates that, during that period, rainfall tended to be 

about average, with alternating short periods of wet and 

dry years.

The rainfall data for Palatka, Orlando, and Avon Park 

for the period 1903-81 can be analyzed similarly to that of 

Jacksonville for 1867-1981. For comparative purposes, 

the 1903-81 rainfall data for Jacksonville are included in 

figure 6. The records for Jacksonville and for two of the 

three east-central Florida stations show similarities. For 

example, the record for Jacksonville, Palatka, and Avon 

Park shows a dry period from about 1905 to about 

1917-18. The record for Orlando shows the dry period 

ending in about 1911, after which a sustained period of 

generally above-average rainfall began that ended in 

about 1961. All four rainfall stations show the drought 

that extended through 1981. That sustained dry period 

began earlier at some stations than at others. At 

Orlando, the drought began in about 1961, at Avon Park, 

in 1969, at Jacksonville, in 1973, and at Palatka, in 1976. 

During the period 1976-81 the rainfall deficiency for the 

four stations averaged about 5.5 in/yr. Though severe, 

that drought, at this writing (1982), has been going on a 

relatively short time and, aside from the effects of 

increased pumping, is probably not affecting the hydrologic regimen as did the drought of 1888 to 1931. The 

significance of the 1888-1931 drought on ground-water 

levels is discussed in a later section.

EVAPOTRANSPIRATION

It is difficult to quantify evapotranspiration, but the 

upper and lower limits of annual evapotranspiration 

rates can be estimated. The upper limit of evapotranspiration is approximately equal to the rate at which water 

can evaporate from a free-water surface (such as a lake) 

under natural conditions. The maximum potential evaporation ranges from about 46 in/yr in the northeast part
E8 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

30

SCALE 1:2,000,000 

0 10 20 30 40 MILES

BASE FROM U.S. GEOLOGICAL SURVEY

DIGITAL LINE GRAPHS FROM 1:2,000,000 SCALE MAPS

»m« .56 \VSUHTER

-> WHERNANDO 

58,, 

Brooksviiie

EXPLANATION

 48- - LINE OF EQUAL MAXIMUM ANNUAL

EVAPORATION FROM A FREE 

WATER SURFACE Interval 2 

inches (from Visher and 

Hughes, 1975)

56

h

RAINFALL STATION Number is 

average annual rainfall, 

1951-80, in inches (from 

National Oceanic and 

Atmospheric Administration)

BOUNDARY OF PRINCIPAL 

STUDY AREA

FIGURE 5. Average annual rainfall and maximum potential evaporation.
CO 

LUI

occ

LUCC 

LU

O 

ccLL

LU 

CCIDCC < CL 

LU 

Q

LU

ID O

130

120

110

100

908070605040

30

20

10

0

-10

-20

-30

-40-50-60-70-80

-90

-100-110-120

-130

iii|iiii|iiii[iiii|iiir-[Tiii[rn-r-f

.Jacksonville 1867-1981 1934-Period that 

is representative of predevelopment potentiometric surface

Average rainfall,

in inches Location

51.7250.6552.0751.1152.38

Jacksonville 1867-1981Jacksonville 1903-1981

Avon Park 1903-1981

Orlando 1903-1981

Palatka 1903-1981 1 / ^ '> / Jacksonville 1903-81

1870 75 80 85 90 95 1900 05 10 15 20 25 30 35 40 45 50 55 60 65 70

YEARS, 1867 TO 1981

FIGURE 6. Cumulative departure from average rainfall at Jacksonville (1S67-1981) and at Jacksonville, Palatka, Orlando, and Avon Park (1903-81).

75 80

G H

COo

I-H

3I-H

O

ffi H>to 

H
E10 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

of the study area (fig. 5) to about 50 in/yr in the 

southwest part (Visher and Hughes, 1975).

The lowest rates of evapotranspiration probably occur 

in those parts of the study area that have deep, welldrained soils and a deep water table. In those areas, the 

land surface tends to be pocked by sinkholes and there is 

little or no surface runoff. In several spring areas, almost 

all drainage is derived from vertical percolation to the 

water table in the surficial aquifer and, thence, to the 

Upper Floridan aquifer, from which, in turn, it is discharged by the springs. The water that is discharged by 

the springs is all that remains of the rain that fell on the 

springs' ground-water basins; the remainder of the water 

ran off, was returned to the atmosphere by evapotranspiration, or was pumped by wells. Evapotranspiration, 

then, is equal to rainfall minus spring flow, runoff, and 

pumpage. Various investigators have estimated the minimum rate of evapotranspiration to range from 25 to 35 

in/yr (Warren Anderson, oral commun., October 13, 

1975; Knochenmus and Hughes, 1976; Tibbals, 1978).

It is probable that, in east-central Florida, the best 

indicator of annual rates of evapotranspiration is depth to 

water table. If the water table is deep, say, more than 10 

to 15 ft below land surface, it is likely that the surface 

soils are well drained and that the water table is below 

the principal root zone of most plants. It follows, then, 

that evapotranspiration rates in areas where the water 

table is deep would be lower than they would be in areas 

where the water table is at or near land surface. Tibbals 

(1978) constructed a curve that describes an estimated 

relation of evapotranspiration rate to water-table depth 

in east-central Florida (fig. 7). The maximum evapotranspiration rate, 48 in/yr, occurs in areas where the 

water table is at or near land surface. The minimum rate, 

about 30 in/yr, occurs in areas where the water table is at 

depths of about 13 ft and greater. At those depths, little 

or no evapotranspiration occurs from the surface of the 

water table. Thus, evapotranspiration varies from about 

48 to about 30 in/yr and occurs in the depth interval 0 to 

13ft.

HYDROGEOLOGY

The geology of the study area has been described 

wholly or in part by many investigators, including Matson and Sanford (1913), Applin and Applin (1944), Cooke 

(1939, 1945), Puri and Vernon (1959), Stringfield (1966), 

and White (1958, 1970). The most recent comprehensive 

descriptions of the geology of the Floridan aquifer system are by Miller (1982a, b, c, d, e) and by Miller (1986) 

in chapter B of this Professional Paper series.

The occurrence, movement, availability, quality, and 

quantity of ground water are related to the geology. The 

study area is underlain mostly by sand, limestone, dolomite, gypsum, anhydrite, and shale which together

g 10

 ASSUMES NO CAPILLARY

FRINGE ABOVE WATER TABLE

- ASSUMES THAT CAPILLARY 

FRINGE EXTENDS ABOUT 

2 FEET ABOVE WATER TABLE

Surface- and

soil-moisture

evapotranspiration

30 40 

AVERAGE EVAPOTRANSPIRATION, IN INCHES PER YEAR

50

FIGURE 7. Estimated relation of evapotranspiration to water-table 

depth in east-central Florida (modified from Tibbals, 1978).

range in thickness from about 5,500 to 12,000 ft. Below 

those depths are the rocks that make up the basement 

complex (fig. 8).

In this report, discussion of geology and structure is 

limited to a brief description of the hydrogeologic framework of the Floridan aquifer system and related geologic 

units. This includes the permeable sequence of limestones that constitute the Floridan aquifer system and 

the hydraulically pertinent formations above and immediately below the Floridan to depths ranging from about 

1,800 to 3,500 ft. Figure 8 summarizes the hydrogeology 

by describing the geologic and hydrogeologic units and 

snowing their conceptual relations to the ground-water 

flow model described in a later section. The aquifers and 

confining units that make up the Floridan aquifer system 

have different nomenclature from place to place throughout the RASA study area. Figure 9 shows these differences in the various subregional study areas and how 

those differences are reconciled in the regional study 

area.

SURFICIAL AQUIFER

The uppermost water-bearing formation is the surficial aquifer. Throughout most of the study area, the 

surficial aquifer generally consists of fine to medium 

quartz sands that contain varying amounts of silt, clay, 

and loose shell. In some coastal areas the surficial aquifer
HYDROGEOLOGY Ell

also contains beds of cemented shell (coquina). Water in 

the surficial aquifer is unconfined. In the swampy lowlands and flatlands, the water table is generally at or 

near land surface throughout most of the year. In the 

rolling highlands, the water table is generally a subdued 

reflection of the topography (fig. 3) but can be several 

tens of feet below land surface. At depths usually less 

than 75 ft below the water table, the sands of the surficial 

aquifer generally grade into less permeable clayey or 

silty sands that act as the overlying confining unit for the 

limestones that constitute the Floridan aquifer system. 

The surficial aquifer is recharged by local rainfall, 

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

effluent, sewage or stormwater holding pond effluent, 

and, in areas where the potentiometric surface of the 

Upper Floridan aquifer is above the water table, upward 

leakage from the Upper Floridan. Water leaves the 

surficial aquifer by seepage to some lakes, ditches, and 

streams, by evapotranspiration where the water table is 

near land surface, by pumpage, and, where the potentiometric surface of the Upper Floridan aquifer is below 

the water table, by downward leakage to the Floridan. 

The surficial aquifer system is used for potable supplies 

only in coastal areas where the Floridan contains brackish water. In the remainder of the study area, the most 

important function of the surficial aquifer is to store 

water, some of which recharges the Upper Floridan 

aquifer. The surficial aquifer is little used as a source of 

water supply because, relative to the Floridan aquifer 

system, its permeability is low, resulting in relatively 

low yields to wells. Also, water from the surficial aquifer 

often contains high concentrations of dissolved iron and is 

sometimes highly colored.

FLORIDAN AQUIFER SYSTEM

The Floridan aquifer system is composed of a sequence 

of limestone and dolomitic limestone that ranges in 

thickness from about 1,500 ft in the northwest part of the 

study area to about 3,300 ft in the extreme southwest 

part (fig. 10). The top of the Floridan is defined as the 

first occurrence of vertically persistent, permeable, consolidated, carbonate rocks. The top of the Floridan 

aquifer system is highest in east Marion, Lake, central 

Volusia, west Orange, west Seminole, and north Polk 

Counties (fig. 11). In those areas the top is at or slightly 

above sea level. The top of the aquifer system dips to 

about 100 ft below sea level to the northwest, to about 

200 ft below sea level to the northeast, and to about 500 

ft below sea level at the south end of the study area. The 

aquifer system does not outcrop in the study area.

The faults shown on the top of the Floridan aquifer 

system in figure 11 have little vertical displacement and, 

except for the fault in the vicinity of Blue Spring,

probably extend only into the Upper Floridan (J.A. 

Miller, U.S. Geological Survey, written commun., January 1980). It should be noted that the faults shown are 

probably not all that exist. Small faults are not mappable 

on a regional basis. Significantly, the faults tend to be 

aligned with major surface-water features such as the St. 

Johns River, the Kissimmee River, and the Indian 

River. The effects of faulting on the Floridan aquifer 

system and its ground-water quality are discussed in a 

later section.

In addition to the relief on the top of the Floridan 

caused by faults, considerable relief is caused by subsurface subsidence. The surface expression of such subsidence is often in the form of closed or nearly closed 

topographic depressions that, in some instances, contain 

lakes. Subsurface subsidence is caused by the gradual 

dissolution of limestone and the collapse of the overlying 

sediments into the volume previously occupied by the 

limestone. The collapse of the overlying sediments can be 

subtle, affect large areas, and occur over a long period of 

time, or it can be quite pronounced, affect relatively 

small areas, and occur suddenly. A sudden subsidence is 

generally referred to as "sinkhole collapse." Almost all 

modern-day occurrences of sinkholes are in areas of the 

Floridan aquifer system where recharge rates are high 

and, generally, where the depth to the top of the 

Floridan is less than 200 ft.

The base of the Floridan aquifer system is defined as 

the first occurrence of vertically persistent beds of 

anhydrite or, in their absence, the top of the transition of 

the generally permeable carbonate sequence of rocks to 

the much less permeable gypsiferous and anhydritic 

carbonate beds. These beds have very low permeability 

and serve as the hydraulic base of the Floridan aquifer 

system. In the study area, the base of the Floridan 

ranges from about 1,700 ft below sea level in the northwest to about 3,800 ft below sea level in the extreme 

southwest (fig. 12).

The geologic formations (fig. 8) that make up the 

Floridan aquifer system in east-central Florida are, from 

top to bottom, Eocene rocks comprising the Suwannee 

Limestone (where present), the Ocala Limestone (where 

present), the Avon Park Formation, and, in some areas, 

all or part of the Oldsmar Formation. Paleocene rocks of 

the Cedar Keys Formation generally form the base of the 

Floridan aquifer system except in areas where the upper 

part of the Cedar Keys is permeable. In some areas the 

basal parts of the Oldsmar Formation are relatively 

impermeable.

The Ocala Limestone constitutes the top of the Floridan aquifer system over most of the study area (Miller, 

1982c). The Ocala Limestone is absent and the Avon 

Park Formation constitutes the top of the Floridan in 

southwest Volusia, north Seminole, and extreme north-
E12 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

GEOLOGIC UNITS

(ADAPTED FROM FAULKNER, 1973, FIG. 2)

Era

0

O

N 

O

z

LU 

0

o

o

N

O

UJ

O 2

u S ^|

2 E5

System

DC

Z

DC

LU

H

^

O

tr

H 

DC 

LU

H

tr

LU

Q_ 

Q. 3

tr

LU

O

 '

13

0

i

o

Series

<D

c

<D 

O

O

o

I

<D

C 

<D 

0

O

'Ej

Q.

<D

c 

0)

0

o

r£

<D

c

0)

o

o

5

-^_/-x_/-\_^

Oligocene

<D

c

<D

O 

O

LU

c

0

£

-^ x_x

0) 

O.

a.

ZJ

5 O

s

s

3

5

Stratigraphic 

unit

Unnamed

alluvial,

lake, and

w ndblown

deposits ^ \^^ ^*- ^ ** 

Pamlico

Formation

and marine

and estuadeposits s-^s^/-^/^/-

Jackson

Bluff

Formation

Alachua

Formation

Fort Preston1

Formation

Hawthorn

Formation

Suwannee 

Limestone

0)

c 

o

0)

re

re

0

O 

-/\^

^r^^ ^ / ^-^

Upper3 

member

Lower"

member

Avon Park

Fcjrmation

Oldsmar

Formation

Cedar Keys

Formation

'-^s^^\^~

Upper and Lower

Cretaceous

DEVONIAN

to

 *~s \^ ^~-

PRECAMBRIAN(?)

Thickness 

(feet)

0-75

^^^-^

0-75

V^\^N

0-75 ±

0-100±

0-100 ±

0-300 +

0-150

-\^\^\y

 0-325 

^^-^^-\

600-1600

300-1350

500-2200

^^^/^.^

1500-?

r~^S^-^- 

Basement

rocks

Lithology

Alluvium, freshwater marl, peats and muds in stream and lake

bottoms. Also, some dunes and other windblown sand.

~\. / -- ^^ ^ /^^^^\u co ormiiy \_/^^^ x s\^/ ^=s \^ X_/N>

Mostly marine quartz sand, unconsolidated and generally well

graded. Also, some fluviatile and lacustrine sand, clay, marl,

and peat deposits.

Marine sands, argillaceous, carbonaceous; and sandy shell marl.

Some phosphatic limestone.

Nonmarine interbedded deposits of clay, sand, and sandy clay; much

of unit is phosphatic, base characterized by rubble of phosphate

rock and silicified limestone residuum in a gray and green

phosphatic clay matrix.

Nonmarine fluviatile sand, white to gray, variegated orange,

purple and red in upper part, fine- to coarse-grained to

pebbly, clayey, crossbedded.

Marine interbedded sand, cream, white, and gray, phosphatic, often

clayey; clay, green to gray and white, phosphatic, often sandy;

dolomite, cream to white and gray, phosphatic, sandy, clayey; and

some limestone, hard, dense, in part sandy and phosphatic. Tends

to be sandy in upper part and dolomitic and limy in lower part.

Marine limestone, very pale orange, finely crystalline, small amounts of 

silt and clay.

Marine limestone, cream to white, soft, granular, highly porous, 

coquinal; often consists almost entirely of tests of foraminifers;

cherty in places.

Marine limestone, cream to tan and brown, granular, soft to firm,

porous, highly fossiliferous; lower part at places is dolomite,

gray and brown, crystalline, saccharoidal, porous.

Marine limestone, light brown to brown, finely fragmental, poor to

good porosity, highly fossiliferous (mostly foraminifers); and

dolomite, brown to dark brown, slightly porous to good porosity,

crystalline, saccharoidal; both limestone and dolomite are

carbonaceous or peaty; gypsum is present in small amounts.

Marine limestone, light brown to brown, fragmental, highly fossiliferous,

slightly carbonaceous or peaty and cherty; and dolomite, brown

to dark brown with very minor amounts of gypsum and anhydrite. Unit

is slightly porous to porous.

Aquifer

tr

LU

u_

^

o

^

o

LL

tr

co

LU

co

co

tr

LU 

LL

1Z

Q

tr

O

LL

Marine limestone, light brown to chalky, white, porous, fossiliferous,

with interbedded brown, porous, crystalline dolomite; minor amounts

of anhydrite and gypsum.

Marine dolomite, light gray, hard, slightly porous to porous,

crystalline, in part fossiliferous, with considerable anhydrite

and gypsum, some limestone.

_^^-^_s^-^^^^^-^s\s y xy \^x_^x/ \-/ ^^ \-/ ^-^

Mostly marine Upper Cretaceous carbonate and evaporite rocks, sands

and shales; thin Lower Cretaceous clastic section in some of area.

_/'\yVyX/Xy~\y'\- /Coastal Plain Bedrock v^--\^'X_/~\-/X/'~\_/'"V/~\y~V/~\_/~Vy 

Marine Devonian, Silurian, and Ordovician quartzose sandstone and dark

shale; lower Paleozoic (?) or Precambrian (?) rhyolite, tuff, and

agglomerate.

'Usage of Bureau of Geology, Florida Department of Natural Resources 

^cala Group of Bureau of Geology, Florida Department of Natural Resources. 

 Crystal River Formation of Ocala Group 

4lnglis Formation and Williston Formation (older to younger) of Ocala Group.

FIGURE 8. Geologic units, hydrogeologic units,
HYDROGEOLOGY E13

PRINCIPAL

HYDROGEOLOGIC UNITS 

(CONCEPTUAL MODEL)

EQUIVALENT LAYERS IN 

DIGITAL COMPUTER MODEL

UPPER FLORIDAN AQUIFER

MIDDLE SEMICONFINING UNIT

LOWER FLORIDAN AQUIFER

LOWER CONFINING UNIT 

(EXTREMELY LOW PERMEABILITY)

BASEMENT ROCKS

UPPER FLORIDAN AQUIFER 

(LAYER 2)

LOWER FLORIDAN AQUIFER 

(LAYER 1)

EXPLANATION

TYPICAL BOUNDARY CONDITIONS 

f ^1 Constant-head boundary

No-flow boundary 

Head-controlled flux boundary

Confining bed (simulated as a 

membrane by TK layer which is 

equal to vertical hydraulic 

conductivity divided by the 

thickness of the confining bed. 

It is also assumed that the 

horizontal flow in the confining 

bed is small and negligible)

\ 

\ 

\ 

\ 

\ 

\

\ 

\ 

\ 

\

and equivalent layers used in computer model.
E14 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

CO CO

CO A,B,C,I H

O COO Regional 

summaries

Florida 

panhandle

Southwest

Georgia

Northwest

Florida

South Carolina 

Southeast Georgia

Northeast 

Florida

East-central 

Florida

West-central 

Florida

Southwest 

Florida

Southeast 

Florida

UNIT

LU 

CO

CO 

DC 

LU 

LL

ID 

O

9

DC 

O

UPPER FLORIDAN AQUIFER

Middle

confining

unit,

Middle

serniepnfining 

unit

Middle

confining"

untt

LOWER FLORIDAN AQUIFER

Fernandina

permeable

zone

UNIT

FIGURE 9. Aquifers and confining units of the Floridan aquifer system.

east Lake Counties. The Suwannee Limestone constitutes the top of the Floridan aquifer system in the 

Highlands County area.

The Floridan aquifer system is divided on the basis of 

the vertical occurrence of two zones of relatively high 

permeability. Hereinafter, these zones are referred to as 

the "Upper Floridan" and "Lower Floridan" aquifers. 

The Upper and Lower Floridan are separated by a less 

permeable, soft, chalky limestone and dolomitic limestone sequence referred to as the "middle semiconfining 

unit." The unit is thin or absent in the west part of the 

study area, but is as much as 600 to 800 ft thick in east 

Orange County and in Okeechobee and west St. Lucie 

Counties (fig. 13). The depth to the middle semiconfining 

unit ranges from about 200 ft in Marion County to about 

1,100 ft in St. Lucie County. The middle semiconfining 

unit is leaky, and the hydraulic connection between the 

Upper and Lower Floridan aquifers varies from place to 

place.

Figures 14-18 show the locations and geologic sections 

that generally describe the geology in the east-central 

Florida area.

In the extreme west part of the study area there is a 

separate and distinct confining unit composed primarily 

of intergranular anhydritic and gypsiferous limestone 

(figs. 17, 18). This unit is considerably less permeable 

than the middle semiconfining unit that is found in most 

of the study area. Because of its small areal extent, the 

anhydritic and gypsiferous confining bed is of only minor 

importance to the Floridan aquifer system in east-central 

Florida. However, in west-central Florida, this unit 

functions hydraulically as the base of the Floridan flow 

system.

In the extreme south part of the study area and 

beneath the Lower Floridan aquifer, there exists the 

northernmost extremity of a highly permeable cavernous 

zone generally referred to as the "Boulder Zone" (fig. 

15). This zone, though important in south Florida from
HYDROGEOLOGY E15

83° 82°

0 10 20 30 40 MILES

BASE FROM U.S. GEOLOGICAL SURVEY

DIGITAL LINEGRAPHS FROM 1:2,000,000 SCALE MAPS

Bade J\° 

PASCOss LeoO

EXPLANATION

2000 LINE OF EQUAL THICKNESS OF 28 ° 

FLORIDAN AQUIFER SYSTEM 

Interval 100 feet

FIGURE 10. Thickness of Floridan aquifer system (adapted from Miller, 1982d).
E16 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

83° 82° 80'

G FernaPdina tieacr

Ojasper 

HAMILTON

,-s. >,

r v-~/

MADISON ,

l -V. f

J r-" COL Ln-O-f r-COLUMBIA

* c ..i.|.! mi,if-r ! Lake City , 1 SuW/jNNEE ' o

/ Lahe

BAKER 

MacclennyO L'

/ OUVAL 

/

, ^JACKSONVILLE o

SCALE 1:2,000,000

0 10 20 30 40 MILES i

I i L-1 r1- i ' ' '

0 10 20 30 40 KILOMETERS i

BASE FROM U.S. GEOLOGICAL SURVEY j 

DIGITAL LINE GRAPHS FROM 1:2,000,000 SCALE MAPS

DEPTH TO TOP OF FLORIDAN AQUIFER 

SYSTEM, IN FEET

 -200 STRUCTURE CONTOUR-Shows altitude of 

top of Floridan aquifer system. Hachures 

indicate depression. Contour interval 

100 feet. Datum is sea level

D

 NORMAL FAULT Vertical or nearly so.

U U, upthrown side. D, downthrown side

27 

BOUNDARY OF PRINCIPAL STUDY AREA

FIGURE 11. Altitude and depth to top of Floridan aquifer system (adapted from Miller, 1982c).
HYDROGEOLOGY E17

80°

i Ojaspet

! HAMILTON i.

1 -v -\

0 10 20 30 40 MILES

DISON/

i 

/ Live Oak

0 10 20 30 40 KILOMETERS ! "JACKSONVILLE^

BASE FROM U.S. GEOLOGICAL SURVEY

SUWV^NEE ' Lake gi(> DIGITAL LINE GRAPHS FROM 1:2,000,000 SCALE MAPS

mond Beach \ 

oria BeacIT \

EXPLANATION

 -2,000 STRUCTURE CONTOUR Shows altitude of 

base of Floridan aquifer system. Contour 

interval 100 feet. Datum is sea level

BOUNDARY OF PRINCIPAL STUDY AREA

FIGURE 12. Altitude of base of Floridan aquifer system (adapted from Miller, 1982b).
E18 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORID AN AQUIFER SYSTEM

83°

, , 0 10 20 30 40 MILES /

"'; >. ' 

~l '

, ~* ***. 3 0 10 20 30 40 KILOMETERS

'l |, ^JACKSONVILLE C 

Maccle-onyC \/.

BASE FROM U.S. GEOLOGICAL SURVEY

DIGITAL LINE GRAPHS FROM 1:2,000,000 SCALE MAPS

/ I

APPROXIMATE 

V i ^ ' LIMIT OF ZONE

/ ~~-_ J

\

-A

none! Beach -.

aytona Beaeff \

HEfiNANDO r

Broohsvule -

^_ _j

EXPLANATION

THICKNESS OF MIDDLE SEMICONFINING 28 

UNIT, IN FEET

 500-- STRUCTURE CONTOUR-Shows altitude of 

top of middle semiconfining unit. Dashed 

where approximately located. Hachures 

indicate depression. Contour interval 

50 and 100 feet. Datum is sea level

r1 BOUNDARY OF PRINCIPAL STUDY AREA

FIGURE 13. Altitude of top and thickness of middle semiconfining unit (modified from Miller, 1982a).
HYDROGEOLOGY E19

83° 82° 81°

29

0 10 20 30 40 MILES

0 10 20 30 40 KILOMETERS L'JACKSONVILLE 0 

1

BASE FROM U.S. GEOLOGICAL SURVEY

DIGITAL LINE GRAPHS FROM 1:2,000,000 SCALE MAPS

yiona BeacK\ 

See figure 26'

HERNANBO ^

O 

BrooKsville

EXPLANATION

LINE OF GEOLOGIC SECTION 

See figures 15 through 18

WELL Number is well reference number. 

See appendix A

LINE OF HYDROGEOLOGIC SECTION 

See figures 24 through 27

BOUNDARY OF PRINCIPAL STUDY AREA H

FIGURE 14. Location of geologic and hydrogeologic sections.
E20 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

FEET 

500-i

Well 

/BO

SEA LEVEL500-

1,000-

1,500-

2,000-

2,500-

3,000-

3,500-

QQ

o! Undifferentiated sand,

El HAWTHORN silt, and clay

<u! __..._._ Well / Well

O

6

w FORMATION /

45

Well 

33

Upper confining Well 

unit 8

Well 

4 \

AVON.. ^-"' 

" PARK

FORMATION

^v^-s-t'-cv;

STotal^epth 3,1x16 feet t r/-''o*/vVv'>'"'-;'-:

OCALA LIMESTONE Upper

Floridan 

-___ aquifer

Middle

semiconfining 

unit

Total depth 

8,730 feet

Total depth--^

10,796 feeVVERTICAL SCALE GREATLY EXAGGERATED 

0 10 20 30 40 MILES

0 10 20 30 40 KILOMETERS 

EXPLANATION

]_ WELL Number is well reference number. See appendix A

NORMAL FAULT Arrows show direction of vertical movement

FIGURE 15. Geologic section A-A' (adapted from Miller, 1986).

Well 

68

the standpoint of disposal of waste waters through injection wells, does not significantly affect the Floridan 

aquifer system in east-central Florida.

POTENTIOMETR1C SURFACE

The earliest known Upper Floridan aquifer potentiometric surface map for Florida was prepared by Gunter 

and Ponton (1929), who used water-level data collected in 

1928. That map represented only the north and north 

coastal parts of peninsular Florida from about Hillsborough County northward on the west coast and from

mid-Brevard County northward on the east coast. The 

general configuration of the contours on the map resemble contours on more recent maps.

The first map of the Upper Floridan aquifer potentiometric surface throughout peninsular Florida was prepared by Stringfield (1936a), who used water levels from 

wells measured during 1933-35. Many countywide or 

even multicounty potentiometric surface maps have 

since been constructed, but the next statewide potentiometric surface map was prepared by Healy (1962), who 

used data from more than 600 wells measured during a 

12-day period in July 1961.
HYDROGEOLOGY E21

FEET

500-1

SEA LEVEL -

II Well Well 

75 \ 77 \

1,000-

1.500J

2,000-

2,500-

Undifferentiated sand, 

silt, and clay

Well / 

774 /

Upper

confining

unit

Middle 

semiconfining

unit 

FORMATION

Lower

confining 

unit

-^ /'CRETACEOUS __

Total detrth ' * ' ^ //Total depTh

' 5,457,feet » ,*x * /, » 3,872 feet*

^aquifer

KEYS ---.-.. ^ ' 

 ._?

FORMATION

J- Total depth 

622 feet

Total depth 

4,601 feet

VERTICAL SCALE GREATLY EXAGGERATED

10 20 30

Well 

73

10 20 30 40 KILOMETERS

EXPLANATION

I WELL Number is well reference number. See appendix A 

^|[, NORMAL FAULT Arrows show direction of vertical movement

FIGURE 16. Geologic section B-B' (adapted from Miller, 

1986).

Currently, Upper Floridan potentiometric surface 

maps of central and north Florida are made on an annual 

or semiannual basis by the U.S. Geological Survey in 

cooperation with various State agencies and State watermanagement districts. However, these recent maps portray the potentiometric surface of only the Upper Floridan aquifer. Area-wide potentiometric surface maps of 

the Lower Floridan aquifer are not compiled because 

there are few wells that are deep enough to tap the 

Lower Floridan and that are hydraulically isolated from 

the Upper Floridan by well casing. Lichtler and others 

(1968) constructed a June 1962 potentiometric surface 

map of the Lower Floridan in the Orlando area using 11 

public supply wells that are drilled and cased to the 

Lower Floridan.

A hydrograph of water levels in a well that taps the 

Lower Floridan in the Orlando area (well 42, fig. 19) 

shows that its water level is generally only 1 to 2 ft below 

the level in nearby well 43, open only to the Upper

FEET ?

500- 

SEA LEVEL500-

1, 000-

1,500-

2.000-

2,500-

innnHAWTHORN 

FORMATION 

Well / 

/17 / Well

OCALA __J 

AVON 1 [ ]jt

PARK

^ FORMATION "

~^lntergranular 

K anhydritic and 

$ gypsiferous 

\ confining unit

TotaTdepth - . 

.1,996 feet

OLDSMAR 

FORMATION

~fff Lower 

^ confining 

ynlt

total depth 

6,040 feet

c Undifferentiated 

~ sand, silt, and clay

OJ /

1/3 / Well Well 

t^__ / 34 34A

t[MES7"ONE

Upper Floric 

aquifer

Middle 

semiconfini 

unit

~~- '-^

Lower

Floridan

aquifer

KEYSV>

FOBMATION

ning unn 

in

 _

^~~-^

"^^

__ -

Total depth Total depth 

6,524 feet 7,050 feet

VERTICAL SCALE GREATLY EXAGGERATED

10 40 MILES

10 20 30 40 KILOMETERS

Well 

17

EXPLANATION

J_ WELL Number is well reference number. See appendix A

1|[, NORMAL FAULT Arrows show direction of vertical movement

FIGURE 17. Geologic section C-C' (adapted from Miller, 

1986).

Floridan. Well 42 is 1,281 ft deep but is cased to a depth 

of only 601 ft. The casing extends into the middle 

semiconfining unit about 150 ft. In the Orlando area the 

middle semiconfining unit is about 600 ft thick. Therefore, the water levels measured in well 42 may not be the 

same as water levels in a well cased completely through 

the middle semiconfining unit and open only to the Lower 

Floridan. A well open only to the Lower Floridan would 

have a water level lower than that of well 42. Head 

measurements in a Lower Floridan aquifer monitor tube 

(open from 2,005 to 2,030 ft) in well 33 showed that, from 

February to April 1977, the head in the Lower Floridan 

was about 6 ft lower than that measured in the Upper 

Floridan (Geraghty and Miller, Inc., 1977, fig. 3).

At the beginning of this RASA study in October 1978, 

one of the first tasks was to construct a map of the
E22 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

FEET ^

500 -i Undifferentiated "* 

sand, silt, and clay o

SEA LEVEL -

500-

1,000 -

1,500 -

2,000 -

2,500 -

3,000 -

3,500 -

4,000 -

4,500 -

5,000

OLDSMAR ^, 

FORMATION

-^T^/Jotal depth' ' '

Confining

»-".»» > » » v

 > '/ » CRETACEOUS '% ' *

> * * TotafdeptV

> * 5. 1 47 feet*

Total depth 

12,665 feet

VERTICAL SCALE GREATLY EXAGGERATED

10 30 40 MILES

0 10 20 30 40 KILOMETERS

Well 

1

EXPLANATION

I WELL Number is well reference number. See appendix A

FIGURE 18. Geologic section D-D' (adapted from Miller, 

1986).

estimated potentiometric surface of the entire Upper 

Floridan aquifer system that portrayed the potentiometric surface prior to development (by pumping). That

predevelopment potentiometric map, by Johnston and 

others (1980), is a composite of many other maps: recent 

potentiometric surface maps in areas where pumping has 

been light, and older maps or modifications of them 

where ground-water development has been extensive. 

The predevelopment potentiometric map shows the best 

estimate of the configuration of the average predevelopment potentiometric surface of the Upper Floridan aquifer. The east-central Florida part of the predevelopment 

potentiometric map is shown in figure 20.

The "predevelopment" potentiometric surface was not 

static. Rather, it fluctuated seasonally in response to 

changes in rates of recharge during wet and dry seasons 

and to changes in rates of natural discharge. Also, the 

predevelopment potentiometric surface underwent 

longer term fluctuations in response to prolonged periods 

of above- or below-normal rainfall such as the wet period 

that ended in 1888 and the drought (as measured at 

Jacksonville) that lasted from 1888 to about 1931 (fig. 6). 

Most of the water-level data used in constructing the 

predevelopment potentiometric surface in Florida were 

collected in the late 1920's and early 1930's. It is probable 

that the potentiometric contours shown in figure 20 

represent "drought" rather than "average" predevelopment conditions in the north part of the study area.

The most recent potentiometric surface map of the 

entire Upper Floridan aquifer system was compiled by 

Johnston and others (1981) and represents the potentiometric surface in May 1980. The east-central Florida part 

of that map is shown in figure 21.

In general, the Upper Floridan potentiometric surface 

has declined from predevelopment levels measured in 

the 1930's. In a few areas, where little ground-water 

development has occurred, the potentiometric surface 

has remained virtually unchanged since predevelopment 

conditions. These areas are primarily in east Marion 

County and in east Polk County in the area immediately 

west of the Kissimmee River, in northeast Highlands 

County, and in south-central Volusia County. The areas 

of most decline in the potentiometric surface are in and 

near areas of heavy pumping from the Floridan aquifer 

system. These areas are in north-central Orange County 

(Orlando-Winter Park area), southeast Orange County 

(Cocoa well-field area), central Polk County, east Volusia 

County (Ormond Beach-Daytona Beach-New Smyrna 

Beach well fields), the potato-farming areas of south St. 

Johns County, and the citrus-growing areas of south 

Brevard, Indian River, and St. Lucie Counties.

Long-term hydrographs for wells in selected parts of 

the study area (fig. 2) are shown in appendix B.

The decline in the potentiometric surface from predevelopment conditions is due mostly to pumping. As 

mentioned in the section on long-term variability of 

rainfall, the predevelopment Upper Floridan aquifer
HYDROGEOLOGY E23

68

64

60

56

52

48

44

o

m

cc

HI

Well no. Location County Aquifer

Total depth 

(feet)

Cased depth 

(feet)

Upper Floridan 

Lower Floridan

1963 1964 1965 1966 1967 1968 1969 1970 1971 1972

YEAR

FIGURE 19. Monthly average water levels in wells 43 (Upper Floridan aquifer) and 42 (Lower Floridan aquifer), 1963-72.

potentiometric surface map was based on water-level 

measurements made during a relatively dry period in the 

north part of the study area and a relatively wet period 

in the central and south parts (fig. 6). However, longterm declines were at a fairly steady rate even during the 

relatively wet period from about 1945 to about 1960 

(appendix B). This indicates that increased ground-water 

development tended to offset the effects of greater than 

normal rainfall. Subsequent droughts, including that of 

1976-81, combined with the effects of pumping, generally caused steeper declines of the potentiometric surface. The drawdown effects of pumping, by category, are 

discussed in a later section.

RECHARGE AND DISCHARGE

The following discussion of recharge and discharge is 

based largely on computer-based model simulation. Only 

spring flow and Upper Floridan ground-water discharge 

to some streams have been measured. Rates of recharge 

and areal discharge as diffuse upward leakage are

derived from a digital computer model of the Floridan 

aquifer system. The computer model is described in a 

later section.

Water enters, or recharges, the Floridan aquifer system in east-central Florida by downward leakage from 

the surficial aquifer system to the Upper Floridan, by 

inflow from drainage wells, and by lateral inflow from 

areas adjacent to the study area.

In the aquifer recharge areas, water leaks downward 

from the surficial aquifer system, through the confining 

beds, and into the Upper Floridan (fig. 21). There, the 

watef table in the surficial aquifer system is above the 

potentiometric surface of the Upper Floridan. The rate 

of recharge depends on the difference between the 

surficial aquifer system and the Upper Floridan and on 

the thickness and permeability of the confining beds. 

Recharge rates are proportional to head difference and 

confining bed permeability and are inversely proportional to confining bed thickness. In east-central Florida, 

simulation indicates that, areally, Upper Floridan aquifer recharge rates are as high as 14 in/yr (fig. 22). It is 

probable that, locally, recharge rates are as high as
E24 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

83° 82° 8V 80"

Madison ' 

MADISON

j Ojasper ^ 

! HAMILTON ^

'KTX

- _ I Llve OakP

"' \ I

| ^ SUW/jUNEE

' i

~' " V

"V-

 COLUMBIA !

"" \

BAKER \^ 

MactlennyO

O Femar.cJina Beach

NASSAU ^-v 

r

/ DUVAL

/

'JACKSONVILLE o

A*V

\\

SCALE 1:2,000,000 

10 20 30 40 MILES

j Lake City

0 10 20 30 40 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY

DIGITAL LINE GRAPHS FROM 1:2,000,000 SCALE MAPS '

Mayc ^

30° ..1

Lake 

Butler _/ CLAY

-\ 

-A

LAFAYETTE! ^ f 

L I k/-' \

-T ~

i

I DIXIE 

o

Cross City

UNION y BRADFORD 

' O

K ,r-< A

A

:d--v'

29'

-.20.3

EXPLANATION

 50 POTENTIOMETRIC CONTOUR-Shows altitude 

at which water level would have stood in tightly 

cased wells that tapped the Upper Floridan 28 

aquifer prior to development. Hachures indicate 

depressions. Contour interval 10 feet. Datum 

is sea level. From Johnston and others, 1980

NO-FLOW BOUNDARY Shows limits of principal 

study area

4.7 HEAD-CONTROLLED FLUX BOUNDARY OTHER 

3 g THAN AT SPRING NODES Arrows show 

 ' direction of flow. Number is simulated flow, 

in cubic feet per second

,6 ? KNOWN UPPER FLORIDAN AQUIFER SPRING- 

 ^j Discharge, simulated by head-controlled flux 

node. Top number is simulated discharge, 

bottom number is observed discharge, in cubic 

feet per second

UPPER FLORIDAN AQUIFER POINT DISCHARGE 

PROBABLE Discharge simulated by headcontrolled flux node. Number is simulated 

discharge, in cubic feet per second 27

FIGURE 20. Potentiometric surface of the Upper Floridan aquifer prior to development, spring discharge, and model boundary conditions for

the Upper Floridan (revised from Tibbals, 1981).
HYDROGEOLOGY E25

82°

30°

SCALE 1:2,000,000 

0 10 20 30 40 MILES

0 10 20 30 40 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY

DIGITAL LIN E GRAPHS FROM 1 :2,000,000 SCALE MAPS

DacieC:tyu O ! i

GOOD RECHARGE AREA Recharge rates are 

3 to 20 inches per year 28

POOR RECHARGE AREA Recharge rates are 

0 to 3 inches per year

; i ; -J_|".. __ _ i_ - _ _ _JL - _A

DISCHARGE AREA (AREA OF ARTESIAN FLOW)- 

Discharge rates are 0 to 7 inches per year

\itjjjj^ NUMEROUS DRAINAGE (RECHARGE) WELLS

- -10 POTENTIOMETRIC CONTOUR-Shows altitude 

at which water level would have stood 

in tightly cased wells. Hachures 

indicate depressions. Contour interval 

10 feet. Supplementary dashed contours 

at selected 5-foot intervals. Datum is 

sea level. From Johnston and others, 1981

 - GROUND-WATER BASIN DIVIDE-For 

selected basins

 ^ SPRING Upper Floridan aquifer spring 

or springs

tf SELECTED AREA WHERE UPPER FLORIDAN

AQUIFER DISCHARGE IS ESTIMATED BY 27' 

MODEL SIMULATION OF SPRING 

DISCHARGE

FIGURE 21. Upper Floridan aquifer recharge and discharge areas; potentiometric surface of the Upper Floridan, May 1980; and selected

ground-water basins.
E26 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

83° 82

30°

/ OUVAL 

i.-flACKSONviLlEO

0 10 20 30 40 MILES

0 10 20 30 40 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY

DIGITAL LINE GRAPHS FROM 1:2,000,000 SCALE MAPS ! i SUW/iNNEE I e

lii BUS CSUMTEP

EXPLANATION

2 | AREA OF DOWNWARD LEAKAGE (RECHARGE) 

TO UPPER FLORIDAN AQUIFER 

Number is model-estimated recharge, 

in inches per year

2 | AREA OF UPWARD LEAKAGE (DISCHARGE) 

FROM UPPER FLORIDAN AQUIFER 

Number is model-estimated discharge, 

in inches per year

BOUNDARY OF MODELED AREA

FIGURE 22. Model-derived rates of recharge and discharge to and from the Upper Floridan aquifer through the upper confining unit.
HYDROGEOLOGY E27

82°30'

28°30' -

 *_____ _ _ _^_ ^__Jt _ °rl^ndij| ** ^____^-^' ^ TT^I&fe.

EXPLANATION

» DRAINAGE WELL

0 10 MILES

0 5 10 KILOMETERS 

FIGURE 23. Location of drainage wells that recharge the Upper Floridan aquifer in the Orlando area (modified from Kimrey, 1978).

20 in/yr. Recharge areas (fig. 21) are classified as good 

(3-20 in/yr) or poor (0-3 in/yr).

In addition to natural downward leakage, recharge 

also occurs through about 400 drainage wells in the 

Orlando area (fig. 23). These wells are constructed 

similarly to wells used for withdrawal; that is, they are 

cased to the top of the Upper Floridan aquifer and then 

drilled open-hole into the Upper Floridan. Drainage 

wells now (1982) are generally used to control lake levels 

and to dispose of street runoff from storm sewers, but in

the past they were used to drain wetlands, to dispose of 

surplus effluent from industrial sites7 and to receive 

effluent from septic tanks (Kimrey, 1978; Kimrey and 

Fayard, 1982). Additional construction of drainage wells 

is now prohibited by the Florida Department of Environmental Regulation.

The quantity of water that recharges the Upper Floridan by drainage wells in the Orlando area can only be 

approximated. Kimrey (1978, p. 15) states that recharge 

by drainage wells may be as much as 50 Mgal/d. How-
E28 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

ever, during this study, drainage-well recharge was 

estimated at about 33 Mgal/d. The reason for this lower 

estimate is discussed in a later section.

Lateral inflow from adjacent areas under predevelopment conditions is estimated at about 19 ft3/s (0.02 in/yr); 

it occurs primarily at the extreme east part of the north 

boundary of the study area (fig. 20). As is discussed in a 

later section, modern-day pumping stresses to the north 

of the study area have caused that lateral inflow to 

decrease.

Discharge from the Floridan aquifer system in the 

east-central Florida area occurs by diffuse upward leakage in discharge areas (fig. 21), areas where the potentiometric surface is above the water table, by pumping or 

flowing wells, by springs (fig. 20), and by lateral outflow 

to the Atlantic Ocean and at other places around the 

boundary of the study area. In areas where the Upper 

Floridan aquifer potentiometric surface is above land 

surface, wells that tap the Upper Floridan flow at the 

surface. Those areas are called areas of artesian flow. 

Simulation indicates that discharge by diffuse upward 

leakage from the Upper Floridan to the surficial aquifer 

ranges from 0 to about 7 in/yr (fig. 22).

Boundary flows are further discussed in a later section.

Twenty-nine named Upper Floridan springs in the 

study area (fig. 20, table 1) have discharges of 1 ft3/s or 

more. Other sites of naturally occurring Upper Floridan 

discharge are confirmed by estimates based on low-flow 

stream-gaging measurements and water-quality analyses. The stream-gaging measurements indicate the 

amount of increase in flow between measurement sites. 

The water-quality analyses are used to help determine if 

the origin of the increase in flow is upward leakage (or 

spring flow) from the Upper Floridan or is seepage from 

the surficial aquifer. If the hardness of the inflow water 

is greater than about 20 mg/L as CaC03 , or if the 

chloride concentration is more than about 10 mg/L, the 

inflow is attributed to the Upper Floridan aquifer. All 

the stream-gaging measurement sites and water-quality 

sampling sites are in areas of artesian flow where the 

potential for upward leakage exists.

Appendix C includes the results of the low-flow measurements and discussions of two newly documented 

springs Island Spring and Croaker Hole Spring.

In several areas, depressions in the potentiometric 

surface of the Upper Floridan (figs. 20, 21) indicate 

relatively large ground-water discharges by other than 

known springs. These areas include the vicinity of the 

lower reaches of the Oklawaha River (in and near what is 

now Rodman Reservoir); generally, the St. Johns River 

from about Palatka to Lake Harney and, specifically, the 

St. Johns River between the mouth of the Oklawaha 

River and south to Little Lake George, Lake George, 

Lake Jessup, and Lake Harney; the Kissimmee River

from the south part of Lake Tohopekaliga south to Lake 

Kissimmee; central Flagler County; and the coastline 

from Flagler Beach south to the north part of Merritt 

Island.

Stream-gaging records along the lower Oklawaha 

River during the spring low-flow seasons of 1945-50 

show an increase of about 150 ft3/s, all of which was 

discharge from the Upper Floridan aquifer. Of the 150 

ft3/s, about 8 ft3/s was from Orange Spring.

It is possible that channel dredging in the St. Johns 

River has, in places, breached or partially breached the 

confining unit overlying the Upper Floridan aquifer, and 

thus allowed the Upper Floridan to discharge into the 

river. Barraclough (1962, p. 35) described two instances 

in which relatively shallow excavations in Seminole 

County caused the development of Upper Floridan 

springs. One spring was near Lake Jessup, whose outlet 

is the St. Johns River, and the other was near the 

Wekiva River, a tributary to the St. Johns. The writer 

has observed "sand boils" discharging water from the 

Upper Floridan at a recently excavated boat ramp in 

Lake County on Alexander Spring Creek, a tributary to 

the St. Johns River. Other springs and "sand boils" are 

known to have occurred as a result of dredging or 

excavation.

The U.S. Army Corps of Engineers maintains a navigation channel in the St. Johns River that is 34 ft deep 

and 400 to 900 ft wide from the river mouth to Jacksonville, 13 ft deep and 200 ft wide between Jacksonville and 

Palatka, 12 ft deep and 100 ft wide between Palatka and 

Sanford, and 5 ft deep and 100 ft wide between Sanford 

and Lake Harney (Anderson and Goolsby, 1973, p. 20). 

From about Palatka to Lake Harney, the configuration of 

the Upper Floridan potentiometric surface indicates 

discharge from the Upper Floridan. There are several 

known Upper Floridan springs along this reach. All 

along the reach, Upper Floridan heads are above the 

river level; therefore, the potential exists for leakage 

from the Upper Floridan. The presence of the known 

springs implies that, in the vicinity of the springs, the 

Upper Floridan overlying confining bed is relatively 

thin. It is possible that the dredged channel does not 

actually incise the Upper Floridan aquifer but, rather, 

incises shell beds or other permeable layers in the 

overlying confining unit that are hydraulically connected 

to the Upper Floridan.

The depression in the Upper Floridan potentiometric 

surface between the mouth of the Oklawaha River and 

south to Little Lake George is attributed to the 80-ft3/s 

discharge of Croaker Hole Spring. Croaker Hole Spring 

was undocumented prior to this study and is discussed 

further in appendix C.

The configuration of the potentiometric surface in the 

vicinity of Lake George suggests that the Upper Floridan discharges near the east side of Lake George (figs.
HYDROGEOLOGY E29

20, 21). Tibbals (1981) simulated hypothetical spring 

discharge in Lake George as about 25 ft3/s (table 1, fig. 

20). Rutledge (1982, fig. 28, table 2) computed about 16 

ft3/s lateral Upper Floridan flow westward from Volusia 

County toward Lake George, presumably to be discharged there by either upward leakage or spring flow. 

The configuration of the potentiometric surface in the 

vicinity of Lake Jessup (figs. 20, 21) indicates that the 

Upper Floridan is discharging into Lake Jessup. Tibbals 

(1981, fig. 4) simulated a hypothetical spring discharge of 

about 6 ft3/s into Lake Jessup in addition to about 4 ft3/s 

from Clifton Spring and Lake Jessup Spring.

Along the St. Johns River, from State Highway 50 

downstream to State Highway 46, the increase in flow of 

the St. Johns River is attributed to inflow from the 

Econlockhatchee River (fig. 78). Thus, the Upper Floridan probably does not discharge large amounts into the 

St. Johns River along that reach. Stream-gaging measurements to detect Upper Floridan discharge along the 

St. Johns River downstream from State Highway 46 are 

virtually meaningless because wind action on Lake Monroe and Lake Harney combined with an extremely flat 

stream gradient can cause water to move upstream for 

several days at a time, especially during periods of low 

flow.

Figures 20 and 21 show a cone of depression on the 

potentiometric surface of the Upper Floridan aquifer in 

the Lake Harney area. Simulated hypothetical spring 

discharge (table 1) in the Lake Harney area and in the St. 

Johns River below Lake Harney and upstream from the 

mouth of Lake Jessup outlet is about 54 ft3/s.

Lichtler and others (1968, fig. 23) documented the 

occurrence of highly mineralized water in the St. Johns 

River above State Highway 50. Upstream from State 

Highway 50, flow in the St. Johns River during extended 

dry periods consists mostly of upward leakage from the 

Upper Floridan aquifer and return flow from irrigated 

farms. The total inflow is not known. Stream-gaging 

techniques are not adequate to quantify the increase in 

flow during dry periods because errors in estimating 

evaporation from the large water surfaces can mask 

measured increase in flow. For example, on April 30, 

1974, the measured flow at State Highway 50 was about 

86 ft3/s but the estimated evaporation from the approximately 11,000 acres of lakes upstream from State Highway 50 is estimated at about 90 ft3/s on that day.

The relatively closely spaced potentiometric contours 

west of Lake Tohopekaliga and Lake Kissimmee along 

the Kissimmee River (figs. 20, 21) imply a reduction in 

transmissivity of the Upper Floridan aquifer or discharge from the Upper Floridan or both. Fault displacement in that area (fig. 11) is minor and evidence of low 

transmissivity is lacking. Also, there is little pumping 

from the Upper Floridan in that area. A water-budget

calculation for Lake Kissimmee (Warren Anderson, U.S. 

Geological Survey, written commun., July 1980) suggested that, during the period July 15-28, 1956, the 

Upper Floridan was discharging about 35 ft3/s into Lake 

Kissimmee.

The depression in the potentiometric surface of the 

Upper Floridan aquifer in central and west Flagler 

County was first discussed by Bermes and others (1963, 

p. 61) and was attributed to diffuse upward leakage and 

springs in the Haw Creek basin. A subsequent investigation (Anthony Navoy, U.S. Geological Survey, written 

commun., July 1980) found no springs and no appreciable 

discharge by wells in the Haw Creek area, but the 

potentiometric depression was confirmed. Therefore, the 

depression is probably caused by diffuse upward leakage 

in the Haw Creek basin and, possibly, by discharge from 

unconfirmed submerged springs near the southeast side 

of nearby Crescent Lake. Simulation suggests that the 

rate of diffuse upward leakage in the area is about 16 ft3/s 

(Tibbals, 1981).

Along the coast from about Flagler Beach south to 

Merritt Island the potentiometric surface of the Upper 

Floridan aquifer was depressed under predevelopment 

conditions (fig. 20) owing to discharge by either diffuse 

upward leakage or by springs. The 1980 potentiometric 

surface (fig. 21) has further declined in response to 

pumping, especially in Volusia County. Tibbals (1981, 

fig. 4) indirectly simulated this discharge as about 50 ft3/s 

flowing laterally from the northeast model boundary 

between Flagler Beach and the Oak Hill area of south 

Volusia County (north part of east boundary) and as 

about 36 ft3/s of hypothetical spring flow in the area of 

north Merritt Island (Banana River, Mosquito Lagoon). 

The predevelopment figures are revised upward to 51 

ft3/s and 39 ft3/s, respectively, in this report (fig. 20, 

table 1).

Off the coast of Volusia County and in the north 

Merritt Island area, the top of the Floridan aquifer is 

about 80 to 100 ft below sea level and the sea bottom is at 

a depth of about 60 ft. Therefore, the materials that 

overlie the Floridan are as thin as 20 ft. There, conditions 

are favorable for spring formation or, if the overlying 

materials are sufficiently permeable, for high rates of 

diffuse upward leakage. Stringfield (1936a, p. 152) mentioned that a large spring was reported about 16 mi east 

of the south Volusia County-north Brevard County 

area. The existence of this spring is not confirmed.

Several investigators have confirmed a submarine 

spring about 2.5 mi east of Crescent Beach, Flagler 

County (Stringfield and Cooper, 1951; Brooks, 1961). 

Brooks described the spring and took water samples.

Upper Floridan lateral outflow occurs along the north 

and south parts of the east boundary and along the west 

part of the south boundary. Under predevelopment 

conditions, Tibbals (1981, fig. 4) simulated these flows at
E30 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

TABLE I. Ground-water discharge from the Upper Floridan aquifer: Spring flow; simulated discharge to rivers, lakes, lagoons, and the

Atlantic Ocean; and lateral flow at model boundaries 

[Negative numbers indicate flow into model area. ft3/s, cubic feet per second. Dashes indicate that no data are available]

Predevelopment, steady-state conditions

Model node

Row

2 

3 

4 

5 

5

6 

6 

8 

8 

8

9 

10

10 

10 

10

10 

10

10 

10 

11

11

11 

11 

12 

12

12 

12 

12 

12 

12

13 

13 

13 

14 

14

15 

15 

16 

16 

16

17 

18 

19 

20 

9n

Name of discharging water body

Column or location of discharge

2 

2

9

2 

31

2 

27 

42 

43 

44

44 

28

29 

31 

33

37 

38

40 

43 

28

35

38 

42 

30 

34

37 

38 

39 

42 

43

27 

30 

31 

27 

35

28 

49 

27 

28 

48

48 

48 

48

2 

^

West part of south boundary 

do. 

do. 

do. 

Blue Spring + Holiday Springs3

West part of south boundary 

Apopka Spring3 

Oklawaha River pickup 

do. 

Orange Spring3

Oklawaha River pickup 

Wekiva Springs +Witherington 

Spring ' 4 + Miami Spring 

Rock Springs3 ' 4 

Seminole Spring +Messant Springs3 

Camp La-No-Che Spring3

Juniper Springs + Fern Hammock 

Springs 

Juniper Creek pickup above State 

Highway 193 +Sweetwater Spring 

Salt Springs3 

Oklawaha River pickup 

Sanlando Springs + Palm Springs + 

Starbuck Spring3 '4

Alexander Springs + Alexander 

Spring Creek pickup above 

State Highway 4553 

Silver Glen Springs3 

Croaker Hole Spring3 

Island Spring3 

Alexander Spring Creek pickup 

below State Highway 455

Lake George 

do. 

do. 

Beecher Spring3 

Satsuma Spring3

Clifton Spring + Lake Jessup Spring3 

Gemini Spring3 

Blue Spring3 '4 

Lake Jessup 

Ponce De Leon Springs3 '4

St. Johns River below Lake Harney 

East end of north boundary 

Lake Harney 

do. 

East part of north boundary

do. 

do. 

do. 

South part of east boundary

r\n

Flow (ft3/s)'1 Observed2 Simulated 

(A) (B) \

30 

(10) 

(30) 

8

(50)

74+4+5 = 83 

65 

20+36-56

1

16+16-32

58 + 12-70

80 

(50)

19+10+17=46 

100+30-130

112

80 

6

(30)

(7) 

(7) 

(7) 

9 

2

._, i 1 '

8 

160

31

6.5 

4.7 

1.8 

0.7 

6.2

0.2 

31.3 

16.0 

33.6 

8.8

55.1

84.0 

65.4 

62.5 

0.8

27.6

75.9 

79.4 

43.1

46.7

136 

112 

64.9 

5.3

30.7

9.5 

7.3 

8.5 

10.8 

2.9

3.8 

7.2 

157 

5.6 

34.5

8.9 

6.0 

24.7 

20.3 

-1.2

-3.6 

-4.3 

-4.7 

2.0 

9 n

Percent error

(fflt^x.oo

4.3

10.0

1.2 

0.6 

11.6 

-20.0

too

8.4

O Q

1.5

4.6 

0.0

-11.7

20.0 

45.0

26.7 

-10.0

-1.9 

11.3

"Dry period," May 1978, 

transient conditions

Flow (ft3/s)

Observed2 Simulated 

) (C) (D)

1 7

A "-'

------ -1.7

-2.7

 2.6

...... -1.7

...... 11.7

 15.8

_, «-'«_,

o c

...... 41.8

64+(4) + 5 = 73 70.5 

57 44.8 

__ 45 5

...... o.7

 26.0

...... 75 i

TQ 1

...... 41.1

15+8+14=37 33.3 

__ 133

...... in

C 1 O

...... 4.4

/? /?

...... 7 5

...... 9.5 

...... 2.4

...... 2.2

5 (150) 144 

 3.5 

27 31.8

...... 6.8 

 ... -3.0 

 19.6 

 16.9 

...... -6.4

 -8.5 

-7.7 

...... -7.9 

...... 1.2

___ 1 9

Change in flow (ft3/s)

(C)-(D) (D)-(B) (C)-(A)

8

0

8

0

__ 3 5 __

__ 3 4 __

3

/?

...... -1.9 ......

-0.2

...... -4.4 ......

-0.2 -----

1 ^ ^

2.5 -13.5 -10 

12.2 -20.6 -8

i £ n

...... -o.l 

I

/?

O Q

...... -2.0

3.7 -13.4 -9 

__ 3 o __

i n

...... -0.9 

1 i

0 FI

 ... -o.7

...... -i.o 

1 3 ______

I

/?

6 -13.0 -10.0 

...... -2.1

-4.8 -2.7 -4.0

...... -2.1 

...... -9.0 

...... -5.1 ... 

... ... -3.4 ...... 

...... -5.2

...... -4.9 ...... 

...... -3.4 ...... 

-3.2 ------ 

... ... -0.8 

___ -OS ___

Footnotes at end of table.
HYDROGEOLOGY E31

TABLE 1. Ground-water discharge from the Upper Floridan aquifer: Spring flow; simulated discharge to rivers, lakes, lagoons, and the

Atlantic Ocean; and lateral flow at model boundaries Continued 

[Negative numbers indicate flow into model area. ft3/s, cubic feet per second. Dashes indicate that no data are available]

Model node

Row

20 

20 

20 

20 

20

20 

20 

20 

20 

20

20 

20 

20 

20 

20

20 

20 

20 

20 

20

20 

21 

22 

23

19 

19 

19

20 

20

20 

21 

21 

21

Column

4 

5 

6 

7 

8

9 

10 

11 

29 

30

31 

32 

33 

34 

35

36 

37 

38 

39 

40

48 

12 

13 

14

23 

24 

25 

23

24

25 

23 

24 

25

Name of discharging water body 

or location of discharge

South part of east boundary 

do. 

do. 

do. 

do.

do. 

do. 

do. 

North part of east boundary 

do.

do. 

do. 

do. 

do. 

do.

do. 

do. 

do. 

do. 

do.

East part of north boundary 

South part of east boundary 

do. 

do.

Banana River, Mosquito Lagoon 

do. 

do. 

do. 

do.

do. 

do. 

do. 

do.

Predevelopment, steady-state conditions

Flow (frVs) 1

 -2 - - - Percent error - 

Observed Simulated

(A) (B) ((B)(A)(A) X100)

...... 2.0

...... 2.0

...... 2.0 

9 n

9 n

9 n

9 n

...... 2.0 

4 4

4 F.

4. Ft

...... 4.6

...... 33

__ 3 5 __

__ 3 g ......

...... 4.7 ......

4 Q

0

0

0

0

Q a

K A

...... 5 7

...... 3.7 ......

9 8

...... 2.1 ----- -

i i

"Dry period," May 1978, 

transient conditions

Flow (ft3/s)

Observed2 Simulated 

(C) (D)

.2

...... .2

__ 2 

__ 3 

__ 3

 1.4

 1.5

I

/?

 3.1 

...... 2.6

2.7

...... 2.6

__ 1 9

...... 1.1

__ 1 5

1 8

----- - 2.4

2

0

- 31

3

0

*7 /?

31

25

31

_ g 5

 5.1

 4.5 

...... 4.7

__ 3 ]

...... 2.4

__ 9 8

1 Q

0 9

Change in flow

(C)-(D) (D)-(B)

0

0

n Q

0 8

-0.7 

0 7

... ... -0.6 

... ... -0.5 

...... -0.4

... ... -1.4

... ... -1.8

1 Q

__ 1 9

9 fi

___ S K

__ 3 1

____ 1 K

...... -1.1

n Q

n a

__ -09

...... -2.7

-1.7

9 9

i a

...... -1.4

... ... o 9

...... -i.o

A C.

 -0.4

0 5

0 3

 -0.2

(ft3/s)

(C)-(A)

 

......

......

 -

......

......

Total

Predevelopment steady-state conditions (ft3/s):

Total observed discharge of key springs: 1,019 

Total computed discharge of key springs: 1,023

May 1978 transient conditions (fts/s):

Total computed discharge of key springs: 904 

Total observed discharge of selected springs: 344 

Total computed discharge of selected springs: 323

1,394.5 1,145.2 -250.2

1 Revised from Tibbals (1981).

2 Numbers in parentheses are estimated discharges; others are observed discharges.

3 Key spring used in evaluation of predevelopment, steady-state model calibration.

4 Selected spring used in evaluation of May 1978 non-steady-state model calibration.

5 Average of discharges measured 1-10-78, 2-28-78, 4-20-78, and 5-30-78. Backwater from St. Johns River influences spring discharge by changing altitude of 

head at spring pool.
E32 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

FEET

200-,

SEA 

LEVEL

1,000-

1,500-

2,000 -

2,500 -

3,000 - - ;>

3,500

Surf icial aquifer system 

and upper confining unit 

for Upper Floridan aquifer

UppjirFloridan potentiometric surface

V V /

Upper Floridan aquifer

Lower Floridan aquifer

Water with chloride concentration less 

than 10,000 milligrams per liter

Water with chloride concentration more than 10,000 milligrams per titer ' ' '

*

Lower confining unit

i___i___j___i_

11 13 15 

ROW (see figure 14)

EXPLANATION

VERTICAL SCALE VARIES AND IS GREATLY EXAGGERATED

20 MILES

20 KILOMETERS

 > GENERAL DIRECTION OF GROUND-WATER FLOW Distribution 

of arrow shows the relative amounts of flow

11 \ NORMAL FAULT Arrows show direction of vertical movement 

2 SURFACE WATER LEVEL

 10,000 LINE OF EQUAL CHLORIDE CONCENTRATION, IN MILLIGRAMS 

PER LITER

FIGURE 24. Hydrogeologic units and ground-water flow along model column 15. Trace of section shown in figure 14.

about 52 ft3/s, 10 ft3/s, and about 14 ft3/s, respectively. 

Subsequent revision to the predevelopment steady-state 

model resulted in computed flows of about 51 ft3/s and 20 

ft3/s, respectively, for the north and south parts of the 

east boundary (fig. 20). Pumping stresses in 1978 tended 

to reduce boundary outflows in the southeast and southwest and to induce boundary outflow along the south part 

of the west boundary. The flow to the west is induced by 

heavy pumping in the phosphate mining and citrus 

growing areas primarily in Polk County. Boundary outflow to the west is estimated at about 78 ft3/s.

Hydrogeologic sections (figs. 24-27) show the generalized Floridan aquifer flow system along typical flow 

paths, that is, at right angles to potentiometric contours 

(figs. 20, 21) and in the direction of decreasing head.

These sections are aligned along rows and columns of the 

grid used for the digital flow model (see later discussion 

and fig. 42).

The flow arrows shown in the Upper and Lower 

Floridan indicate the general direction of flow, and the 

distribution of the arrows shows the relative amounts of 

flow. Typically, the Upper Floridan has the more vigorous flow system.

HYDRAULIC CHARACTERISTICS

The hydraulic characteristics of the Floridan aquifer 

system are described in terms of transmissivity and 

storage coefficient of the aquifer and leakage coefficients 

of both the upper confining unit and the middle semiconfining unit.
HYDROGEOLOGY E33

0>

= t

5 1

0 I » 1 CO f

Surfictal aquifer system 

and upper confining unit 

for Upper Floridan aquifer

Middle semiconf inmg unit

Lower Floridan aquifer

Water with chloride concentration less 

than 10,000 milligrams per liter

Water with chloride concentration more 

than 10,000 milligrams per liter

Lower confining unit

2,000 -

11 13 

ROW (see figure 14)

VERTICAL SCALE VARIES AND IS GREATLY EXAGGERATED

20 MILES

20 KILOMETERS

EXPLANATION

 > GENERAL DIRECTION OF GROUND-WATER FLOW 

Distribution of arrows shows the relative amounts of flow

^ NORMAL FAULT Arrows show direction of vertical movement 

SZ SURFACE WATER LEVEL

 10,000 - LINE OF EQUAL CHLORIDE CONCENTRATION, 

IN MILLIGRAMS PER LITER

FIGURE 25. Hydrogeologic units and ground-water flow along model column 25. Trace of section shown in figure 14.

The transmissivity of the Upper and Lower Floridan 

varies throughout the model area. Figures 28 and 29 

show a comparison of field values of transmissivity 

derived from aquifer tests and transmissivity values 

obtained in the development and calibration of the predevelopment steady-state computer model (Tibbals, 

1981). The average of model-derived transmissivity values for the Upper Floridan is about 120,000 ft2/d; the 

range is from about 10,000 to about 400,000 ft2/d. The 

highest transmissivities are generally near springs. The 

transmissivity values obtained by aquifer test analyses 

do not always agree with the model-derived values. 

Generally, the model-derived transmissivities are higher 

than those obtained from aquifer tests. This is mainly 

because the wells used in the aquifer tests generally tap 

less than the full thickness of the Upper Floridan. Such 

partial penetration plus the highly heterogeneous and 

anisotropic nature of the cavernous limestone aquifer

system make the application of standard methods of 

aquifer test analysis uncertain and the results questionable. For example, in east Orange County, three aquifer 

test sites within an area of about 16 mi2 (fig. 28) has 

transmissivity values of 74,000, 210,000, and 510,000 

ft2/d, respectively. Furthermore, counter to what would 

be expected, the test that had the most penetration of 

the aquifer had the lowest transmissivity. The transmissivity range obtained from model calibration in the same 

16-mi2 area, about 100,000 to 200,000 ft2/d, is considered 

to have more regional significance than the individual 

test values. In general, however, the aquifer test values 

for transmissivity of the Upper Floridan are within the 

range of values determined by computer simulation of 

the Floridan aquifer system.

The transmissivity of the Lower Floridan (fig. 29) is 

less well known than that of the Upper Floridan. Only 

one aquifer test is known to have been conducted in the
E34 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

FEET 

200-1

100-

SEA 

LEVEL

1,000-

1,500-

2,000-

Surficial aquifer system 

and upper confining unit 

for Upper Floridan aquifer

Lower Floridan aquifer

Water with chloride concentration 

less than 10,000 milligrams per liter

Water with chloride concentration 

more than 10,000 rnitlfgrarns per liter

Lower confining unit 

l 1 1

9 11 

ROW (see figure 14)

13 19 20

VERTICAL SCALE VARIES AND IS GREATLY EXAGGERATED

20 MILES

10 20 KILOMETERS

EXPLANATION

 > GENERAL DIRECTION OF GROUND-WATER FLOW 

Distribution of arrows shows the relative amounts of flow

HI/ NORMAL FAULT Arrows show direction of vertical movement 

SURFACE WATER LEVEL

 -10,000- LINE OF EQUAL CHLORIDE CONCENTRATION, 

IN MILLIGRAMS PER LITER

FIGURE 26. Hydrogeologic units and ground-water flow along model column 31. Trace of section shown in figure 14.

Lower Floridan (Lichtler and others, 1968). Transmissivity values for the Lower Floridan obtained by model 

calibration (Tibbals, 1981) range from about 30,000 ft2/d 

to about 130,000 ft2/d; the highest values are in central 

and west Orange County. It is possible that transmissivities there are higher than 130,000 ft2/d. Lichtler and 

others (1968) reported an apparent transmissivity of 

about 570,000 ft2/d. Owing to the lack of model calibration for the Lower Floridan, the transmissivities derived 

from model simulation should be viewed as qualitative 

rather than quantitative.

The determination of values for storage coefficient 

from aquifer test analyses poses problems similar to 

those of obtaining values for transmissivity. Values for 

storage coefficient obtained during various investigations in the study area typically range from 5xlO~4 to 

lxlO~3 for the Upper Floridan. Estimates of storage 

coefficient for the Lower Floridan are not reliable, but it

is probable that the storage coefficient of the Lower 

Floridan is similar to that of the Upper Floridan.

The leakage coefficient of the confining unit that 

overlies the Upper Floridan (fig. 30) ranges from about 

IxlO"6 per day to about 6xlO~4 per day. The highest 

values occur where aquifer diffuse recharge and discharge rates are highest (fig. 22) areas where the 

confining beds are relatively thin or permeable. The 

lowest values occur where diffuse recharge and discharge rates are low areas where confining beds are 

relatively thick or have low permeability.

No data are available to determine the leakage coefficient of the middle semiconfining unit that separates the 

Upper and Lower Floridan aquifers. Calibration of the 

steady-state predevelopment model (Tibbals, 1981) was 

done using a leakage coefficient of about 5x 10~5 per day 

everywhere except the Blue Spring area. There, the 

leakage coefficient of the middle semiconfining unit is
HYDROGEOLOGY E35

Surficial aquifer system and 

upper confining unit for 

Upper Fiorldan aquifer

1,000-

1,500-

2,000-

Water with chloride concentration 

less than 10,000 milligrams per liter

Water with chloride concentrator* 

more than.1Q,OOQflUtfigrsms|>er liter

Lower confining unit

42 42 42 

COLUMN

9 11 13 

ROW (see figure 14)

42 42

EXPLANATION

VERTICAL SCALE VARIES AND IS GREATLY EXAGGERATED

20 MILES

20 KILOMETERS

 > GENERAL DIRECTION OF GROUND-WATER FLOW 

Distribution of arrows shows the relative amounts of flow

111/ NORMAL FAULT Arrows show direction of vertical movement 

^ SURFACE WATER LEVEL

 10,000 - - LINE OF EQUAL CHLORIDE CONCENTRATION, 

IN MILLIGRAMS PER LITER

FIGURE 27. Hydrogeologic units and ground-water flow along row 9, columns 5CM2, and along model column 42, rows

9-20. Trace of section shown in figure 14.

probably very high because of a geologic fault that 

provides good hydraulic connection between the Upper 

and Lower Floridan.

WATER QUALITY

The quality of water in the Floridan aquifer system in 

east-central Florida varies from place to place but, in 

most areas, remains fairly constant with time. Seasonal 

water-quality variations occur mostly in areas where 

there is a lateral or vertical transition from fresh to 

brackish water, near drainage wells, or where some 

sinkholes provide a direct or near-direct surface hydraulic connection to the Floridan.

Geology is a major factor affecting the natural quality 

of water in the Floridan. As water moves downgradient 

through the aquifer system it tends to become more 

highly mineralized because of the gradual dissolution of 

the rock materials it contacts.

A second major factor affecting the quality of water in 

the Floridan aquifer system is the mixing and chemical 

reaction of freshwater with highly mineralized water 

that is in the aquifer at depth, along the Atlantic Coast, 

and along the St. Johns River valley.

Few data are available on the quality of water in the 

Lower Floridan aquifer. However, in east-central Florida the water in the Lower Floridan is probably more 

highly mineralized than that in the Upper Floridan.
E36 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

83° 82° 81°

30°

29"

0 10 20 30 40 KILOMETERS 

BASE FROM U.S. GEOLOGICAL SURVEY

~, \. UNION j BRADFORD '

' ^ i \ ~»_^ '" C I

\ j ~

EXPLANATION

JJ>.- -=- - -J- <X-^

10,000-35,000

35,000-100,000

100,000-200,000

[___j 200,000-400,000

39,000

260

TRANSMISSIVITY DETERMINED FROM 

MULTIWELL AQUIFER TEST OR 

FLOW-NET ANALYSIS AT SPRINGTop number is transmissivity, in feet 

squared per day. Bottom number is depth 

of aquifer penetrated by pumped well, 

in feet

O TRANSMISSIVITY ESTIMATED FROM 

SPECIFIC CAPACITY TEST IN 

SINGLE WELL

BOUNDARY OF MODELED AREA

FIGURE 28. Model-derived transmissivity of the Upper Floridan aquifer and locations of selected aquifer test sites (from Tibbals, 1981).
HYDROGEOLOGY E37

83° 82° 81°

0 10 

III!

20 30 40 MILES

0 10 20 30 40 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY

DIGITAL LINE GRAPHS FROM 1:2,000,000 SCALE MAPS

UN'ON J BRADFORD

. . 

_ y ^.Hastings \

PASCOSSueoO ,

EXPLANATION

TRANSMISSIVITY BASED ON MODEL 

CALIBRATION, IN FEET SQUARED 

PER DAY

 570,000 TRANSMISSIVITY ESTIMATED FROM 

1,083 MULTIWELL AQUIFER TEST Top 

1,247 number is transmissivity, in feet squared 

per day. Middle number is cased depth, 

in feet. Bottom number is total depth 

of pumped well

H BOUNDARY OF MODELED AREA

FIGURE 29. Model-derived transmissivity of the Lower Floridan aquifer and location of aquifer test site (from Tibbals, 1981).
E38 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORID AN AQUIFER SYSTEM

83°

Madi»i,r < MADISON

°Jasper

HAMILTON

~T

u remam a eeacr

NASSAU

,^.-x

r "^

/ UveOakp

^ SUWA 

\

" V

Mayo°

30 N

LAFAYETTE

Cress Cit-/ I

MaeciennyO i.

But ^

_£!_ ../.__.

SCALE 1:2,000,000

0 10 20 30 40 MILES

i___ i ___i i_____|

0 10 20 30 40 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY , 

DIGITAL LINE GRAPHS FROM 1:2 000,000 SCALE MAPS

\

j GILCHRIS1 ,

y~ , _^_ j

29°

H BOUNDARY OF MODELED AREA

EXPLANATION

LEAKAGE COEFFICIENT OF UPPER 

CONFINING UNIT OF THE FLORIDAN 

AQUIFER SYSTEM, IN FEET PER DAY 

PER FOOT

1x10- 6 - 1x10~ 5 

1x10- 5 -5x10- 5 

5x10~ 5 - 1x10~ 4

CHARLOTTE

_ _ _ _ _ l '' 

PALM BEACH

FIGURE 30. Model-derived leakage coefficient of the upper confining unit of the Floridan aquifer system.
HYDROGEOLOGY E39

The concentration of dissolved solids, hardness, sulfate, and chloride shown in figures 31 through 34 are 

estimated as average concentrations that occur in the full 

thickness of the Upper Floridan. Concentrations of these 

constituents are generally less in water at the top of the 

Upper Floridan than in water at the bottom of the Upper 

Floridan; hence, the concentrations shown in figures 31 

through 34 are termed "average" for the Upper Floridan. 

Figure 35 shows the average chloride concentration in 

water in the upper 100 ft of the Upper Floridan.

The extent to which the water in the Upper Floridan is 

mineralized is best described by its concentration of 

dissolved solids. In east-central Florida, the highest 

concentrations of dissolved solids occur near the Atlantic 

Coast and in the vicinity of the St. Johns River. Most of 

the highly mineralized water in the Upper Floridan in 

the study area is probably a mixture of freshwater and 

relict seawater that entered the aquifer system during a 

higher stand of the sea in past geologic time. In places, 

flushing of the ancient seawater is incomplete and the 

Floridan contains water that is brackish. Table 2 shows 

typical concentrations of dissolved solids, hardness, sulfate, and chloride in freshwater, brackish water, and 

seawater. The term "saline" is often used to describe the 

mineralization of water. Hem (1973, p. 219) defined 

various levels of salinity in terms of dissolved-solids 

concentration. The slightly modified definitions used in 

this report are as follows:

Salinity

Fresh

Slightly saline 

Moderately saline 

Very saline 

Briny

Dissolved-solids

concentration

(mg/L)

<1,000 

1,000- 3,000 

3,000-10,000 

10,000-35,000 

>35,000

In Floridan aquifer system water, the dominant cations are calcium (Ca+2), magnesium (Mg+2), sodium 

(Na+ ), and potassium (K+). The dominant anions are 

bicarbonate (HC03~), chloride (CF), and sulfate 

(S04 ~2). Locally, smaller amounts of dissolved iron, 

manganese, nitrate, phosphate, fluoride, strontium, sulfide, and silica may contribute to the dissolved-solids 

concentration.

In about 40 percent of the area the dissolved-solids 

concentration in water in the Upper Floridan is less than 

250 mg/L (fig. 31). The areas of relatively low concentrations of dissolved solids generally correspond with the 

good recharge areas of the Upper Floridan aquifer (fig. 

21). In the discharge areas along the Atlantic Coast and 

along the St. Johns River, the dissolved-solids concentration is generally more than 1,000 mg/L and ranges to 

more than 25,000 mg/L. Insofar as is known, nowhere in

TABLE 2. Typical concentrations of dissolved solids, hardness, sulfate, and chloinde in freshwater, brackish water, and seawater 

[mg/L, milligram per liter]

Freshwater Brackish water Seawater 

Constituent (mg/L) (mg/L) (mg/L)

Dissolved solids ..........

Sulfate ..................

...... <1,000

...... <400

...... <250

...... <250

1,000-35,000 35,000

400-6,600 6,600

250-2,700 2,700

250-19,000 19,000

east-central Florida does the dissolved-solids concentration in water in the Upper Floridan equal that in 

seawater.

"Hardness" is a term that has long been used to 

describe the resistance of water to produce a lather from 

soap. The U.S. Geological Survey (Hem, 1973, p. 225) 

classifies water on the basis of hardness as follows:

Hardness range 

(mg/L of CaC03)

0-60 

61-120 

121-180 

>180

Description

Soft 

Moderately hard 

Hard 

Very hard

Though water that is very hard may be unsuitable for 

many industrial uses (because of boiler scaling problems, 

for example), it may be satisfactory for domestic purposes.

Recent studies (Schroeder, 1966; Sauer, 1974; Marier 

and others, 1979) have found a statistically significant 

correlation between increased levels of hardness in 

drinking water and decreased risk of cardiovascular 

disease.

In east-central Florida, hardness concentrations in 

water in the Upper Floridan aquifer range from 61 to 120 

mg/L in parts of the good Upper Floridan recharge areas 

(fig. 21) to several thousand milligrams per liter in and 

near the Upper Floridan discharge areas along the St. 

Johns River and near the Atlantic Coast (fig. 32).

Sulfate concentrations in water in the Upper Floridan 

aquifer (fig. 33) range from virtually zero in the good 

Upper Floridan recharge areas (fig. 21) to as much as 900 

mg/L in discharge areas near the St. Johns River and 

along the Atlantic Coast. A bacterial process in which 

sulfate is reduced to bisulfide causes hydrogen sulfide 

gas to form. It is this gas that causes the characteristic 

"rotten egg" odor of water from some wells and springs 

in the Upper Floridan.

Chloride is the predominant anion in seawater and is 

responsible for its salty taste. Chloride concentration is 

the single most important indicator of the presence of 

brackish water. Figure 34 shows the average chloride 

concentration of water estimated to occur in the full 

thickness of the Upper Floridan, whereas figure 35
E40 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

83° 82°

0 10 20 30 40 MILES

MADiSON /

' k 

Live OakP COLUMBIA !

BASE FROM U.S. GEOLOGICAL SURVEY

SUWNNEE i Lakeltv DIGITAL LINE GRAPHS FROM 1:2,000.000 SCALE MAPS

~, V UNION j BRADFORD

v ,' I ^-~-~-f Oil 

\

EXPLANATION

DISSOLVED SOLIDS CONCENTRATION, 28° 

IN MILLIGRAMS PER LITER

FIGURE 31. Average dissolved-solids concentration in water in the Upper Floridan aquifer (adapted from Sprinkle, 1982b).
HYDROGEOLOGY E41

SCALE 1:2,000,000

0 10 20 30 40 MILES

i i ii _____ |

0 10 20 30 40 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY

DIGITAL LINE GRAPHS FROM 1:2,000,000 SCALE MAPS

I ALACHUA''"*

HARDNESS, IN MILLIGRAMS 

PER LITER AS CaCO3

f1 60-120

[ | 120-180

[ I Morethanl80

I - BOUNDARY OF PRINCIPAL

I STUDY AREA

FIGURE 32. Average hardness of water in the Upper Floridan aquifer (adapted from Sprinkle, 1982d).
E42 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

83°

0 10 20 30 40 MILES

0 10 20 30 40 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY

DIGITAL LINE GRAPHS FROM 1:2,000,000 SCALE MAPS

EXPLANATION

SULFATE CONCENTRATION, IN 

MILLIGRAMS PER LITER

Less than 50 

| | 50-100 

100-250 

More than 250

BOUNDARY OF PRINCIPAL 

STUDY AREA

_ A ^K- GLAOES

h

FIGURE 33. Average sulfate concentration in water in the Upper Floridan aquifer (adapted from Sprinkle, 1982c).
HYDROGEOLOGY E43

83° 82°

sn.jndi.ia Ben

81° 80°

SCALE 1:2,000.000

10 20 30 40 MILES i i

1 0 10 20 30 40 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY

DIGITAL LINE GRAPHS FROM 1:2,000,000 SCALE MAPS

i

HLORIDE CONCENTRATI 

MILLIGRAMS PER LITER

I Less than 250

| | 250-500

[ | 500-1,000

[___I More than 1,000 

 I BOUNDARY OF PRINCIPAL STUDY AREA

i CHARLOTTE ' 1 ________

PALM BEACH

FIGURE 34. Average chloride concentration in water in the Upper Floridan aquifer (adapted from Sprinkle, 1982a).
E44 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

30

0 10 20 30 40 MILES

i i i i _____ |

0 10 20 30 40 KILOMETERS

MacclennyO L'

BASE FROM U.S. GEOLOGICAL SURVEY

DIGITAL LIN E G RAPHS FROM 1 :2,000,000 SCALE MAPS

DIX!E \ GILCHRIST '

EXPLANATION

CHLORIDE HLWniUC CONCENTRATION IsWINlsCIN I HM I IWIN UN IN WATER VVMId IN 28

THE UPPER 100 FEET OF THE UPPER 

FLORIDAN AQUIFER, IN MILLIGRAMS PER 

LITER

I I Less than 25 

| | 25-100

100-250

250-1,000 

 H 1,000-4,000 

HH| More than 4,000

H BOUNDARY OF PRINCIPAL 

STUDY AREA

FIGURE 35. Chloride concentration in water in the upper 100 feet of the Upper Floridan aquifer.
HYDROGEOLOGY E45

shows the chloride concentration of water in the upper 

100 ft of the Upper Floridan. Of the four chemical 

constituents discussed (dissolved solids, hardness, sulfate, and chloride), chloride is the constituent that, in its 

higher concentrations, is least tolerated by humans, 

animals, and plants. Because the upper 100 ft of the 

Upper Floridan aquifer is most likely to be tapped by 

most ground-water users, the chloride concentration 

there is mapped and shown in figure 35.

Though the upper limit of chloride concentration recommended for public water supplies in Florida is 250 

mg/L (Florida Department of Environmental Regulation, 1982), most people cannot detect a salty taste in 

water below concentrations of, say, 400 mg/L. In most of 

the area, the chloride concentration in the Upper Floridan is less than 250 mg/L (figs. 34, 35). Concentrations 

generally are more than 1,000 mg/L in the Upper Floridan along most of the course of the St. Johns River and 

along the Atlantic Coast from about Cocoa north to about 

St. Augustine. Measurements showed several occurrences of high-chloride water along the St. Johns River: 

(1) a well near the northeast shore of Lake Harney (south 

Volusia County) had water with a chloride concentration 

of about 9,000 mg/L, as did (2) a well near the southeast 

shore of Lake George (north Volusia County), and (3) a 

well near the north shore of Lake Poinsett (central 

Brevard County) had water with a chloride concentration 

of about 12,000 mg/L.

Along the Atlantic Coast, the highest chloride concentrations occurred in water from wells on the west shore 

of the Indian River near Titusville (13,000 mg/L) and on 

the southwest and northeast shores of Indian River near 

the north end of Merritt Island (12,000 mg/L).

In a few areas beneath the topographically high relict 

beach ridges of south Brevard and Indian River Counties, the uppermost part of the Upper Floridan aquifer 

contains water fresher than the water below or water 

immediately to the east or west. These freshwater areas 

are oriented parallel to the coast and are relatively long 

and narrow. The chloride concentration data there are 

very scattered and for that reason are not shown in 

figures 34 and 35. The source of the fresher water is not 

lateral flow because more brackish water is present 

upgradient from the fresher area. The fresher water 

cannot be the result of ongoing downward leakage or 

recharge from the surficial aquifer because the fresher 

water is in an Upper Floridan aquifer discharge area 

where heads in the Upper Floridan are above the water 

table and the land surface. The most probable explanation for the occurrence of the fresher waters is that 

sometime in the geologic past, the surficial aquifer 

system recharged the Upper Floridan and the fresher 

water in the Upper Floridan is the residual. Such an 

episode could have occurred when the sea stood at a

much lower level. At that time, the potentiometric 

surface of the Upper Floridan would also have stood at a 

lower level, especially near the coast. If the potentiometric surface was below the water table, then downward 

leakage or recharge could have occurred. Lower stands 

of the sea occurred during the Pleistocene Epoch. The 

following discussion is taken from Stringfield (1966):

The outstanding feature of Pleistocene time was the extensive 

continental glaciation in the northern hemisphere. Although this glaciation did not extend to the South Atlantic States, worldwide changes of 

sea level were caused by removal of water from the sea to form the 

continental glaciers. At times when the glaciers melted, as described 

by Cooke (1939), water returned to the sea, causing a rise in sea level.

Cooke (1939, figs. 12-16) and Stringfield (1966, figs. 

16-20) describe shorelines that result from sea-level 

altitudes that range between 270 ft above the present 

level to 300 ft below the present level (fig. 36). Zellmer 

(1979, fig. 17) estimated sea-level altitudes as low as 300 

ft below present level during at least eight periods in the 

last million years (fig. 37).

Thus, just as it is possible that the brackish water 

present in the Upper Floridan is water that entered the 

aquifer during a higher stand of the sea, it is possible that 

the isolated pockets of freshwater in what are now 

discharge areas could be the result of freshwater that 

was recharged during a lower stand of the sea. This 

freshwater is being flushed out at an extremely low rate 

and is, thus, essentially "trapped."

The lateral transition from freshwater to brackish 

water in the Upper Floridan in east-central Florida 

occurs over distances of one-half mile to several tens of 

miles (figs. 31-35).

The vertical transition from freshwater to brackish 

water occurs over intervals as small as a few tens of feet. 

The additional vertical transition of slightly brackish 

water to water that is, say, half as brackish as seawater 

(chloride concentration of about 10,000 mg/L) occurs 

over distances of a few tens of feet to several hundred 

feet.

Few wells, other than oil test wells, have penetrated 

the full thickness of freshwater in recharge areas. The 

drillers' logs of the oil test wells generally do not include 

information that defines the depth to which freshwater 

extends. Therefore, the few wells drilled specifically for 

hydrologic purposes provide the little information available. Figure 38 shows the estimated depth to water 

having a chloride concentration greater than 10,000 

mg/L. Some wells shown in figure 38 did not extend to 

depths at which the chloride concentration was as high as 

10,000 mg/L because drilling was generally terminated 

soon after brackish water was detected. Test wells 

drilled as part of this study, well 47 at Geneva (northeast 

Seminole County, fig. 39), well 55 near Blue Spring 

(southwest Volusia County, fig. 40), and wells 14 and 17 

at Polk City (north Polk County, fig. 41), are examples of
J____I____I____I j____I

BASE FROM U.S. GEOLOGICAL SURVEY NATIONAL ATLAS, 1971

EXPLANATION

-300 ft NUMBER IS ALTITUDE ABOVE OR BELOW 

PRESENT SEA LEVEL, IN FEET

ATLANTIC

CEAN

i____I

100 KILOMETERS

FIGURE 36. Pleistocene shorelines, much generalized (after Cooke, 1939, figs. 12-16).
HYDROGEOLOGY E47

SEA 

LEVEL

200

SEA 

LEVEL

300

400

300 600 700 800 900

TIME, IN THOUSANDS OF YEARS BEFORE PRESENT

FIGURE 37. Estimated changes in sea level (adapted from Zellmer, 1979, fig. 17).

wells drilled specifically to collect information on depth of 

freshwater.

The test well in the Geneva area (fig. 39) tapped 

brackish water at a depth of about 380 ft. The test well 

near Blue Spring yielded brackish water through its 

entire depth, but the sharpest change in chloride concentration occurred at a depth of about 425 ft. From 425 to 

442 ft the chloride concentration rose from about 4,000 to 

about 9,000 mg/L.

The Geneva test well was drilled to help define the 

vertical extent of an "island" of freshwater in the Upper 

Floridan in a good recharge area in Seminole County (fig. 

21). The Upper Floridan in northeast Seminole County 

contains brackish water except in the Geneva area (figs. 

31-35). This condition was first recognized by Stringfield 

(1936a), was verified by Barraclough (1962), and was 

further investigated by Tibbals (1977) and by G.G. 

Phelps (U.S. Geological Survey, written commun., 

1984).

The test well near Blue Spring (fig. 40) was drilled to 

help determine if an active zone of fresher water was 

circulating beneath a relatively sluggish zone in the 

uppermost part of the Upper Floridan near Blue Spring. 

The results were not conclusive because drilling was 

stopped when very brackish water was found at a 

relatively shallow depth. However, it is believed unlikely 

that a zone of fresher water exists at depth.

In Polk City, north Polk County, a corehole (well 17) 

was drilled to a depth of about 2,000 ft (Navoy, 1986). 

Though brackish water as defined by chloride concentration (table 2) was not found during drilling, the water 

became brackish with depth in terms of concentrations of 

dissolved solids, hardness, and sulfate (fig. 41). Though 

not shown in figure 41, the chloride concentration did not 

exceed 11 mg/L. The relatively low concentration of 

chloride and relatively high concentrations of dissolved 

solids, hardness, and sulfate indicate that any seawater 

that had been present in the aquifer has been flushed out, 

at least to a depth of about 2,000 ft. The increase in 

mineralization that starts at about 900 ft is caused by a

sluggish flow system that allows prolonged contact of the 

water with soluble rock minerals.

In 1976 and early 1977 a test well (well 32, fig. 38) was 

drilled at the Sand Lake Road wastewater treatment 

facility near Orlando, Orange County, to determine the 

feasibility of injecting treated wastewater into saline 

water zones that underlie the Lower Floridan aquifer 

(Geraghty and Miller, Inc., 1977). Test results determined that freshwater there extended to a depth of about 

2,400 ft. Below that depth the dissolved-solids concentration of the water sharply increased from about 200 to 

about 110,000 mg/L, approximately three times that of 

seawater. Water that is mineralized to that degree is 

referred to as "brine." As drilling progressed toward the 

final well depth of 6,193 ft, the dissolved-solids concentration rose to about 150,000 mg/L and the chloride 

concentration rose to about 85,000 mg/L. Aquifer testing 

showed that the brine zone had extremely low permeability (Geraghty and Miller, Inc., 1977). Extremely low 

permeability in rocks below the Lower Floridan aquifer 

was also reported in a deep test well in Alachua County, 

southwest of Gainesville, at the Kanapaha Lakes sewage 

treatment plant (CH2M Hill, Inc., Gainesville, Fla., 

written commun., 1977).

Brines probably exist at some depth throughout eastcentral Florida. Low permeability of the brine zones may 

be the single most important factor that tends to limit, or 

at least to minimize, upconing of salty water in response 

to pumping of freshwater from the Floridan aquifer 

system.

From Lake Harney northward along the St. Johns 

River, the brackish water in the Upper Floridan aquifer 

(figs. 31-35) is virtually stagnant. The relatively small 

amounts of brackish water discharged are believed to be 

continually replenished by upward movement of brackish 

water that occurs at depth. For example, if the 1980 

potentiometric surface map (fig. 21) is superimposed on 

the maps of chloride concentration (figs. 34, 35) it is 

apparent that the more highly mineralized waters in the 

Upper Floridan north of Lake Harney are present near
E48 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

83° 82

29°

I Ojasper

HAMILTON Madison ' 

MADISON/ !

0 10 20 30 40 MILES

i i i |

I 

COLUMBIA ,

0 10 20 30 40 KILOMETERS

__ _ _/ Live Oak!

SUWANNEE i LBhe Sily

BASE FROM U.S. GEOLOGICAL SURVEY

DIGITAL LINE GRAPHS FROM 1:2,000,000 SCALE MAPS

". V. UNION y BRADFORD 

v .,. ", ^-___' O

S«a.ke I s ^<^ J

fescent Beach \ 

I A 

! i

Cross City° j /

PASCO St. Leo O 9- Hp i'%

EXPLANATION

PALM BEACH \ k

--1,000 LINE OF EQUAL DEPTH TO WATER WITH 28 

CHLORIDE CONCENTRATION OF 10,000 

MILLIGRAMS PER LITER OR GREATER 

Interval 500 feet. Datum is sea level

55,

H

WELL IN OR NEAR UPPER FLORIDAN AQUIFER 

RECHARGE AREA USED TO ESTIMATE DEPTH 

TO VERY SALINE WATER Number is well 

reference number. See appendix A for well 

descriptions

BOUNDARY OF PRINCIPAL 

STUDY AREA

FIGURE 38. Estimated depth to water having chloride concentration greater than 10,000 milligrams per liter (adapted from C.L. Sprinkle,

written commun., 1982).
HYDROGEOLOGY E49

WATER LEVEL, IN FEET ABOVE SEA LEVEL

GENERALIZED LITHOLOGY AND 

WELL CONSTRUCTION 

Land surface

200

® WATER LEVEL

 SPECIFIC CONDUCTANCE

!~9~"! CHLORIDE CONCENTRATION, IN

L ' MILLIGRAMS PER LITER

B

Altitude of land surface is 

75.21 feet above sea level

I 63 |

/

I ~i

I 930 I

/

fS(

6-inch-dia. 

steel casing

Casing depth 

117 feet

200

300

1,000 2,000 3,000 4,000

SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER 

CENTIMETER AT 25 DEGREES CELSIUS

400

Total depth 

403 feet

Sand and clayey sand

Gray-blue clay and silt

Coarse shell, sand, gray clay

White to grayish-white soft limestone with 

occasional shell fragments

Tan to brown hard limestone and dolomite

Cream to gray, some tan soft limestone

Tan to brown hard limestone and dolomite

FIGURE 39. Specific conductance, chloride concentration, water levels, and generalized lithology in well 47, at Geneva, Seminole County,

August 1981.

areas where the Upper Floridan is discharging through 

springs. The springs discharge water that enters the 

aquifer in the upgradient direction within their groundwater basins (fig. 21). The larger springs and groups of 

smaller springs capture virtually all the water in their 

flow fields. In the direction opposite the predominant 

flow fields there is little hydraulic gradient and flow in 

the aquifer is extremely sluggish. Therefore, though the 

flushing of brackish water in the predominant flow fields 

is complete, the sluggish nature of the opposite flow 

fields has not allowed flushing to be complete.

The aquifer system along the St. Johns River from 

Lake Harney northward is, perhaps, as flushed as it will 

ever be. For example, the Blue Spring ground-water 

basin (fig. 21) is about 330 mi2 in area. If it is assumed 

that the average thickness of freshwater in the Floridan 

system in the Blue Spring ground-water basin is about 

700 ft (area around well 55, fig. 38) and the porosity of 

the aquifer materials is about 25 percent, then the 

volume (V) of freshwater in the aquifer is computed as

7=330 mi2 (5,280 ft/mi)2 (700 ft) (0.25) 

= 1.6xl012 ft3

The approximate period of time (0 that it would take 

for Blue Spring to discharge that total volume of water is 

calculated by dividing the spring's discharge rate into the 

total volume of water in the basin:

t= 1.6x10" ft

160 ftYs (3.1536x10's/yr) =320 yr.

These calculations are not meant to imply that it took 

only 320 yr to completely flush the brackish water from 

the basin. It may have taken many tens of such flushing 

cycles for the water in the Upper Floridan to have 

reached its present chemical composition.

It is estimated that if parts of the Floridan aquifer 

system were filled with brackish water or seawater 

during a previous high stand of the sea (fig. 36), then the 

most recent such event would have ended no sooner than 

120,000 yr ago (fig. 37). In the Blue Spring basin and in 

several other selected basins (table 3), enough time has 

passed for many flushing cycles to have occurred. Of the 

five spring basins analyzed, the two basins having the 

shortest flushing times tended to have springs that 

discharge water that is the most brackish. Therefore, 

only a small part of the brackish water being discharged 

from some of the springs is likely to be moving laterally
E50 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM 

WATER LEVEL, IN FEET ABOVE SEA LEVEL GENERALIZED LITHOLOGY 

AND WELL CONSTRUCTION

0

100

LU

O

Li.

DC 

CO

O 

< 200

 '

^

3HI

m

iHl 

HI

H. 300

Z

I

t 

HI

O

400

Rnn

31234

I I I I

® WATER LEVEL

®^ SPECIFIC CONDUCTANCE

~~~ ^ -^ !~2,500~JCHLORIDE CONCENTRATION, 

 - ^ ~ IN MILLIGRAMS PER LITER

T ^"~"~ ~~ - ~

I ^~"(ft *ot

\

\

J \

^

^\

V

r , \

 Ll?2?J Altitude of land surface is approximately 8 ®\

\ feet above sea level ®

- \ I -

\, -, I

J 2,500 ' ®

~ 3--^»\ T 3' 300 !

- L --^ 'x^: __ L&2_\ m ~

1 9,000 ~[

I 1 1 1

5 o6-inch-diameter

steel casing 

\

Casing depth

84 feel

55 Land surface

!

Sand and clayey sand

Light tan soft limestone 

with green clay

100 \ ^

cavity - 

200 -

> Limestone, shell, sand, clay

ll

r

\

300-5

cavity

400

!

Tan to light tan, soft to

medium hard limestone

with some fossils and

occasional chert pieces

I

Tan dolomite with some 

gray limestone

^ Total depth 442 feet

5,000 10,000 15,000 20,000 25,000 30,000

SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER CENTIMETER 

AT 25 DEGREES CELSIUS

FIGURE 40. Specific conductance, chloride concentration, water levels, and generalized lithology in well 55, about 0.3 mile southwest of Blue

Spring, Volusia County, August 1981.

from areas of relatively stagnant flow. Hence, it is likely 

that most of the brackish water being discharged is 

moving upward from depth in the vicinity of the springs. 

The sharp increase in mineralization of water from well

55 (near Blue Spring) as it was being drilled tends to 

support this conclusion.

The reader should be aware that the preceding calculations and hypothetical conclusions are based on the

TABLE 3. Minimum time to flush brackish ground water from selected spring basins 

[mi2 , square miles; ft, feet; ft3 , cubic feet; fts/s, cubic feet per second; mg/L, milligrams per liter]

Approximate

Average 

thickness Volume of Total known

Number 

of years

Chloride concentration in:

Spring basin or basins

basin area of freshwater Aquifer freshwater spring discharge to flush Recharge area Discharged water 

(mi2) (ft) porosity (ft3) (ft3/s) basin (mg/L) (mg/L)

Blue .................................... 330

Rock; Wekiva and Miami; Sanlando, Palm, 

and Starbuck; Seminole and Messant; 

Apopka; Island. ........................ 890

Alexander and Alexander Spring Creek .... 450 

Ponce De Leon. .......................... 150

Juniper and Fern Hammock; Juniper Creek 

and Sweetwater; Silver Glen; Salt. ....... 470

700 0.25 1.6x 101 160 320 75 500

2,000

1,600

1,000

1,000

.25

.25

.25

.25

1.2xl013

5.0X1012

l.OxlO12

3.3xl012

286

130

31

294

1,300

1,200

1,000

360

20

40

100

50

35

220

150

812
DIGITAL COMPUTER MODEL E51

105 Oi 110

WATER LEVEL, IN FEET ABOVE SEA LEVEL

115 120 125 130

400

UJ 

O

800

O

Ltl 

CO

UJ

UJ 1,200

1,600

2,000

135 lO

 SPECIFIC CONDUCTANCE

DISSOLVED SOLIDS 

® SULFATE

A HARDNESS AS CaCO3 

+ WATER LEVEL

Altitude of land surface is approximately 

137 feet above sea level

Core hole 1 (Well 14) 

Core hole 2~(WellT7)

400

1,200

1,600

2,000

400 800 1,200 1,600 2,000 2,400

CONCENTRATION, IN MILLIGRAMS PER LITER, OR SPECIFIC CONDUCTANCE, IN 

MICROSIEMENS PER CENTIMETER AT 25 DEGREES CELSIUS

GENERALIZED LITHOLOGY 

Land surface

Sand and silt

Inter bedded phosphatic clay, 

limestone, and sand______

Limestone, soft, porous

Limestone, medium hard, porous

Dolomite, hard, low porosity

Limestone, soft, porous

Dolomite with some chalk and 

pelletal limestone; hard, low 

porosity, overall permeability high, 

800 as in limestone layers above

Dolomite, hard with inclusions of 

anhydrite and some selenitic 

gypsum pore fillings; low to fair 

porosity, overall permeability low

Limestone with some dolomitrc 

limestone, low porosity, overall 

permeability higher than in 

dolomitic interval above

FIGURE 41. Specific conductance, hardness, dissolved solids, sulfate, water levels, and lithology in core holes 1 and 2 (wells 14, 17) at Polk City,

Polk County, 1979-80.

assumptions that (1) the ground-water basins of the 

springs have remained essentially the same size over the 

past 120,000 yr as they are now, and (2) the springs' 

discharges have remained about the same during the 

flushing period.

The faults that are believed to be present along the St. 

Johns River (fig. 11) could provide an avenue for substantial upward movement of brackish water to replace 

that which is discharged either by springs or by diffuse 

upward leakage. However, even if faults are absent, 

brackish water can be discharged and still be continually 

replenished by brackish water from depth. The natural 

upward hydraulic gradient that is present near springs 

provides the hydraulic potential to move brackish water 

upward. For example, as well 55 near Blue Spring was 

drilled the water level in the well rose about 4 ft (fig. 40). 

This indicates that as the well was drilled, it tapped 

zones of increasingly higher head.

DIGITAL COMPUTER MODEL

A digital computer model was used to simulate both 

predevelopment and present-day (1978) flow conditions 

in the Floridan aquifer system in east-central Florida. 

Features and assumptions of the model are described in 

a previous RASA report by Tibbals (1981). The reader is 

referred to that report for discussions of the steady-state 

model calibration, boundary conditions, methods used to 

simulate spring flow, and derivation of confining-unit 

leakage coefficients. Model simulations described in this 

report use the same basic model framework except as 

follows:

 Some very minor revisions to boundary flow coefficients on the Atlantic Coast were made.

 Croaker Hole Spring and Island Spring were added.

 The fixed boundary head matrix in the vicinity of the 

lower reaches of the Oklawaha River was changed to
E52 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

reflect the rise in head caused by the impoundment 

that created Lake Oklawaha, or Rodman Reservoir.

 Storage coefficients for the Upper and Lower Floridan 

aquifer were input to simulate transient flow rather 

than steady-state flow.

 Matrices for 1978 pumping from the Upper and Lower 

Floridan were added. These matrices also include 

the effects of recharge by drainage wells in the 

Orlando area (fig. 23) and of cross-boundary flow to 

the west to simulate model outflow to adjacent 

pumping centers.

Except for those changes or additions, the model is 

identical to that described by Tibbals (1981). Further 

discussion of the model is limited to the following:

 Discussion of figure 8, which shows reconciliation of 

the more complex geologic units with a simplified 

conceptualization of the hydrogeologic units and 

their equivalent layers as simulated by the model,

 Description of the model grid (fig. 42),

 Portrayal of the conceptualization model input data 

(fig. 43),

 Brief discussion of the results of the predevelopment 

steady-state simulation (Tibbals, 1981), and

 Discussion of the method of calibration of the transient 

model used for simulations described in this chapter.

The computer source code is adapted from the threedimensional ground-water flow model developed by 

Trescott (1975) and Trescott and Larson (1976). Steven 

Larson and James Tracy, U.S. Geological Survey (written commun., September 1979), modified the model to 

include the head-controlled flux boundary condition that 

also is used to simulate spring flow. The model was 

further modified by the writer to facilitate data handling, 

error analysis, and output manipulation, and by Anthony 

Navoy, U.S. Geological Survey, to plot hydraulic cross 

sections.

The model is structured to simulate a three-layered 

system with the layers separated by confining units (fig. 

8). Vertical resistance to flow between layers is simulated by areally variable leakage coefficients that characterize the vertical hydraulic conductivity and thickness 

of the confining units.

The model area is subdivided into a finite-difference 

grid of 24 rows and 50 columns (fig. 42). Each of the 1,200 

grid blocks, or nodes, is 4 mi on a side and 16 mi2 in area. 

Because of the configuration of the model boundaries, 

only 857 model nodes are active. These 857 nodes represent a surface area of about 13,700 mi2.

At each of the active nodes, values of starting head, 

transmissivity, and storage coefficient are input for each 

aquifer layer. Pumping values are also input at each node 

for the Upper and Lower Floridan. The Upper Floridan 

also has input data for boundary heads and boundary 

flow coefficients at selected nodes. Confining units have

leakage coefficients input at each node. The model input 

data can be conceptualized as a "sandwich" of data, as 

shown in figure 43.

The Lower Floridan aquifer is modeled as having 

no-flow boundaries around its sides and an impermeable 

base (fig. 8). This means that all flow into or out of the 

Lower Floridan (except for pumping) must ultimately 

flow through the Upper Floridan.

Though three aquifer layers are simulated (surficial 

aquifer and Upper and Lower Floridan aquifers), only 

the Upper Floridan is considered calibrated. The overlying surficial aquifer is treated as a constant-head 

(though areally variable) source-sink layer for leakage to 

and from the Upper Floridan. The Lower Floridan 

aquifer flow system is simulated but is not considered 

calibrated because of the lack of head data for the Lower 

Floridan. In essence, then, the Lower Floridan aquifer 

and the middle semiconfining unit act as a leaky basal 

boundary condition for the Upper Floridan.

STEADY-STATE PREDEVELOPMENT SIMULATION

Model results indicate that under predevelopment 

conditions, about 1,930 ft3/s (1.91 in/yr) is recharged by 

downward leakage to the Upper Floridan (table 4) aquifer. Areally, the highest rate of recharge from the 

surficial aquifer to the Upper Floridan in the approximately 6,550 mi2 in which recharge occurs (figs. 21, 22) is 

about 14 in/yr, in southeast Marion County. The 

recharge areas that have the lowest rates are in southeast Orange County, southeast Volusia County, most of 

northeast Okeechobee County, and the north-south 

length of the central parts of Osceola, St. Johns, and 

Flagler Counties. In those areas, recharge rates are 

typically 1 in/yr or less.

Lateral inflow to the Upper Floridan is about 21 ft3/s 

(0.02 in/yr) and occurs chiefly along the east part of the 

north boundary (fig. 20).

As simulated, net flow between the Upper and Lower 

Floridan aquifers is zero. That is because water that 

leaks downward from the Upper Floridan and recharges 

the Lower Floridan in some areas ultimately leaks 

upward and returns to the Upper Floridan in other 

areas. The amount of water that circulates between the 

two aquifers is about 290 ft3/s (0.25 in/yr). In the model 

nodes that discharge to the Upper Floridan from the 

Lower Floridan, the flow rate averages about 0.6 in/yr. 

The maximum rate for all nodes except that of the Blue 

Spring area (row 13, column 31) is about 3 in/yr.

In the node that contains Blue Spring, the Upper 

Floridan is recharged by the Lower Floridan at a rate of 

about 41 ft3/s. The leakage coefficient at that node was 

set very high to hydraulically simulate a geologic fault
DIGITAL COMPUTER MODEL E53

83°

10 20 30 40 MILES

i_____i_____i_____i

BAKER \

V i

MacclennyP L

0 10 20 30 40 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY

DIGITAL LINE GRAPHS FROM 1:2,000,000 SCALE MAPS

i , > ' .

\ i J / Lake

 f=v "L 1________£_______O I / BuJ!.e

Vr~UN!ON" "/BRADFORD"*

EXPLANATION

BOUNDARY OF MODELED AREA

FIGURE 42. Finite-difference grid superimposed on modeled area.
E54 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

MATRIX

S3

Starting head 

Transmissivity 

Storage coefficient

TK2 Leakage coefficient

MODELED

AQUIFER

UNIT

Surficial 

aquifer

(Layer3)

Upper

confining

unit

S2

HSS2

CSS2

Q2

Starling head 

Transmissivity 

Storage coefficient

Fixed boundary head 

Boundary flow coefficient 

Pumpage

Upper 

Floridan 

aquifer

(Layer 2)

TK1 Leakage coefficient

Middle

semiconfining 

unit

S1

Lower 

Floridan 

aquifer

(Layer 1)

Starting head 

Transmissivity 

Storage coefficient 

Pumpage

FIGURE 43. Conceptualized model input data.

(figs. 11, 26) that is believed to provide a very good 

hydraulic connection between the Upper and Lower 

Floridan.

The Upper Floridan aquifer, as simulated under predevelopment conditions, discharges water by springs, by 

diffuse downward leakage to the Lower Floridan in some 

areas, by diffuse upward leakage to the surficial aquifer 

in discharge areas (fig. 21), and by lateral outflow along 

parts of the model boundaries.

Total simulated spring flow is about 1,330 ft3/s (table 4) 

and includes about 1,020 ft3/s of discharge from known 

springs ("key springs" used in steady-state calibration) 

for which discharge data are available. About 190 ft3/s 

discharge into rivers where Upper Floridan spring flow 

has been indirectly determined by streamflow and waterquality measurements. About 120 ft3/s is estimated to 

discharge in areas where depressions in the Upper

Floridan potentiometric surface strongly suggest spring 

discharge.

Total discharge from the Upper Floridan as diffuse 

upward leakage to the surficial aquifer is simulated as 

about 530 ft3/s (0.53 in/yr) (table 4). The average discharge rate in the approximately 7,150 mi2 that are 

discharge areas (figs. 21, 22) is about 1 in/yr. The 

maximum rates are about 7 in/yr in west-central Flagler 

County and 6 in/yr in the Lake Kissimmee area. The 

lowest rates of diffuse upward leakage occur in south 

Brevard County, Indian River County, and north St. 

Lucie County. In those areas, leakage rates are generally 0.5 in/yr or less.

Discharge from the Upper Floridan by lateral boundary flow is about 90 ft3/s (table 4) and occurs chiefly along 

the east and southwest model boundaries (fig. 20).

Based on the predevelopment steady-state model, the 

essential features of the predevelopment flow system are 

described as follows:

 The highest rates of recharge to the Upper Floridan 

are in four areas: the west flank of the Volusia 

County potentiometric surface "high" (figs. 20, 21); 

the Putnam-Alachua County potentiometric surface 

"high"; the topographically high ridge areas of midPolk and Highlands Counties (fig. 3); and the northeast flank of the central Florida potentiometric 

surface "high" in Lake and Orange Counties and 

extending into east Marion County.

 About 68 percent of the discharge from the Upper 

Floridan is in the form of point discharge to springs 

and streams located within 25 mi of recharge areas.

 The highest rates of diffuse upward leakage from the 

Upper Floridan (about 27 percent of the total discharge) occur near areas where downward leakage 

rates are also high. Thus, it is inferred that thin or 

permeable confining units are common to the areas 

of high upward leakage and to the nearby areas of 

high downward leakage.

 Lateral boundary outflow from the Upper Floridan 

aquifer (mostly along the Atlantic Coast) is relatively small and consists of about 4 percent of the 

total discharge. Lateral flow to the south is about 1 

percent of the total discharge.

 Interchange between the Upper and Lower Floridan 

aquifers is relatively small (290 ft3/s) compared with 

the flow within the Upper Floridan (about 1,950 

ft3/s).

 The model-derived transmissivities of the Upper 

Floridan are considered to have more regional significance than transmissivity values derived from 

individual aquifer tests.

In summary, the hydraulics of the Floridan aquifer 

system under predevelopment conditions are characterized by recharge to the Upper Floridan (by way of
DIGITAL COMPUTER MODEL E55

leakage from the surficial aquifer), lateral movement 

through the Upper Floridan for short distances, and 

discharge by way of springs and diffuse upward leakage. 

Relatively small amounts of discharge occur along the 

coast, and small amounts move into and out of the 

underlying Lower Floridan. The ground-water flow system is relatively vigorous in the Upper Floridan and, 

except in west Orange County and southeast Lake 

County, is relatively sluggish in the Lower Floridan.

TRANSIENT SIMULATION WITH 

MODERN-DAY (1978) PUMPING

The purpose of the transient simulation is to determine 

how pumping affects the Floridan aquifer flow system. 

The transient simulation requires input of data on the 

storage characteristics of the Floridan and on the amount 

and areal distribution of pumping.

CALIBRATION

To calibrate the transient model, computed drawdown 

due to pumping is matched to observed drawdown. The 

ideal method of matching computed and observed drawdown would be to run the model through a series of 

year-long (or shorter) simulation periods that, together, 

constitute the length of the observed long-term record of 

water levels (appendix B). The appropriate values for 

pumping would be input at each simulation period. Then, 

after adjusting the storage coefficients areally, the best 

match between computed and observed long-term water 

levels would be achieved. At least four problems are 

associated with this method of calibration:

1. The model does not compensate for climatic changes 

that affect recharge from simulation period to simulation period (and would not even if those data 

could be obtained). Climatic considerations make it 

difficult to compare computed and observed water 

levels except where the amount of water being 

recharged is small compared with that being 

pumped.

2. Long-term pumping data, except for large municipal 

supply systems, are sparse.

3. Short-term and long-term pumping data are poor for 

the categories of rural domestic supplies, privately 

owned public supplies, irrigation, industrial and 

institutional supplies, and thermoelectric cooling.

4. Data on the areal distribution of pumping are poor.

The pumping data used in this study are best estimates 

of the amounts and areal distribution of ground-water 

withdrawals in the study area.

In east-central Florida, the only time of year in which 

changes in recharge rates are small with respect to 

discharge by pumping is during the last 2 weeks in 

March, all of April, and, usually, the first 1 or 2 weeks in

May about 60 days altogether. The timing of the "dry 

period" varies from place to place. During the dry period, 

pumping is at a maximum rate for the year. It is this 

60-day period that was chosen for comparison of 

observed and computed changes in ground-water levels 

in response to pumping and thus for calibration of the 

transient model. Table 5 gives estimated rates of pumping for selected categories of ground-water use in the 

study area, and of outflow to pumping centers west of the 

model area.

Transient-model calibration is accomplished by comparing observed and computed declines in water levels 

for the 60-day-long dry period in 1978 at 39 sites in the 

model area (fig. 44). The computed water-level declines 

are simulated by running the model for two pumping 

periods (fig. 45). The first period, 210 days, simulates a 

run to the almost steady-state conditions that might have 

occurred near the end of March 1978; the pumping rate 

input at each node is the average annual rate for 1978. 

The second pumping period has "dry period" pumping 

rates and does not run to steady state but is terminated 

at the end of 60 days. "Dry period" pumping rates were 

also run for a period of only 45 days in order to compute 

heads for comparison with water levels measured during 

mid-May for an area-wide potentiometric surface map.

The degree to which transient calibration is accomplished and the effects of using different storage coefficients are shown by example in figures 46-48. Figure 46 

is an example of a "good" match of slope and magnitude 

of drawdown using aquifer storage coefficients of 1 x 10 ~3 

for both the Upper and Lower Floridan aquifers. Figures 

47 and 48 are examples of "fair" and "poor" matches of 

slope and magnitude of drawdown, respectively, also 

using storage coefficients of 1 x 10~3 for both the Upper 

and Lower Floridan aquifer. Better matches could have 

been obtained at the latter two sites (figs. 47, 48) by 

changing the storage coefficients, but this writer 

believes that most of the error is caused by errors in 

estimating the rates and areal distribution of pumping. 

With all other aquifer parameters being equal, the water 

level in an aquifer is more sensitive to a change in 

pumping rate than to the same percentage change in 

storage coefficient. On a model-wide basis, storage coefficients of lxlO~3 gave the best calibration at most sites 

(fig. 44).

The average absolute error in estimating the magnitude of the "dry period" drawdown at sites shown in 

figure 44 is about 27 percent. Average absolute error is 

the average of the errors without regard to mathematical 

sign. The algebraic average of the errors is about -1 

percent. This means that about as much error occurs on 

the plus side as on the minus side. Therefore, on a 

model-wide basis, there is a slight tendency toward 

underestimating computed drawdown.
E56 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

TABLE 4. Simulated rates of recharge and 

[ft3/s, cubic feet per second; in/yr,

Recharge

Vertical

Pumping 

period 

no. Simulation

0 

1 

2

Predevelopment, steady-state 

(revised from Tibbals, 1981)

At end of 210 days pumping at average 1978 pumping rates

At end of additional 45 days pumping 

at estimated dry period pumping 

rates

Lower Floridan ..................

2A At end of additional 15 days pumping at 

estimated dry period pumping rates 

tinner Floridan ..................

i

2

Lower Floridan. .................

From aquifer above. 

To aquifer above.

Downward leakage 1

(ft3/s)

1,927 

290

2,445 

367

3,043 

310

3,080 

325

(in/yr)

(1.91) 

(0.29)

(2.42) 

(0.36)

(3.01) 

(0.31)

(3.05) 

(0.32)

Drainage wells

(ft3/s)

51

0

0 

0

0 

0

(in/yr)

(0.05) 

(0)

(0) 

(0)

(0) 

(0)

Lateral

Head-controlled flux

(ft3/s)

21 

0

38 

0

59 

0

63

0

(in/yr)

0.02 

0

(0.04) 

(0)

(0.06) 

(0)

(0.06) 

(0)

Constant flux

(ft3/s)

4 

0

9 

0

9 

0

(in/yr)

(0.00) 

(0)

(0.01) 

(0)

(0.01) 

(0)

A second check on the calibration of the model is to 

compare an Upper Floridan aquifer potentiometric surface map based on model-derived heads with a map based 

on measured heads (fig. 49). In general, the potentiometric contours drawn from model-derived heads are within 

10 ft of those drawn from measured heads and the 

configuration of the computed map is very similar to the 

map constructed from observed data. Overall, the 

transient-model calibration (and the estimates of pumping) are considered to be fair to good. Therefore, the 

calibrated transient model probably simulates the effects 

of pumping well enough to allow further analysis of the 

flow system.

HYDROLOGIC EFFECTS OF 1978 PUMPING

The areal distribution of pumping at average annual 

1978 rates and the corresponding drawdown of heads in 

the Upper Floridan aquifer are shown in figure 50. The 

largest drawdowns are in areas where pumping rates are 

highest: in the Palatka area of Putnam County (10 ft); in 

the Ormond Beach-Daytona Beach-New Smyrna Beach 

area of east Volusia County (6 ft); in northwest Seminole 

County (6 ft); in the Cocoa well-field area of southeast 

Orange County (8 ft); in the Orlando-Winter Park area of 

Orange County (6 ft); and in central Polk and Highlands 

Counties (8 ft).

Drawdown in the Upper Floridan aquifer in the 

Orlando-Winter Park area is not as great as might be 

expected considering that about 68 to 70 Mgal/d is

pumped from the Floridan aquifer system there. Drawdown in the Upper Floridan is minimized because

 Of the 68 to 70 Mgal/d pumped, all but about 3 to 4 

Mgal/d is pumped from the Lower Floridan,

 The Upper Floridan aquifer is recharged by drainage 

wells at an estimated average rate of about 33 

Mgal/d, and

 Both the Upper and Lower Floridan aquifers are 

highly transmissive and, thus, can be pumped at 

relatively high rates and cause relatively small 

drawdown.

Table 4 shows computed rates of upward and downward leakage, lateral inflow and outflow, spring flow, 

pumpage, recharge through drainage wells, water 

released from aquifer storage, and changes in average 

model-wide drawdown. Table 6 summarizes the changes 

in computed rates of upward and downward leakage, 

spring flow, net lateral boundary outflow, and water 

released from aquifer storage caused by pumping for 210 

days at the average 1978 pumping rates and an additional 

45 days at "dry period" rates.

In 1978, the average rate of pumping was 555 Mgal/d, 

boundary outflow toward adjacent pumping centers was 

about 41 Mgal/d, and recharge through drainage wells 

was about 33 Mgal/d. Therefore, the total net withdrawal 

from the aquifer system was 563 Mgal/d. The effects of 

this withdrawal on the predevelopment Floridan aquifer 

system are shown in figure 51 and tables 4 and 6 and are 

summarized as follows:
DIGITAL COMPUTER MODEL E57

discharge for steady-state and transient conditions 

inches per year; ft, feet]

Discharge

Vertical Lateral Area drawdown since

Pumping wells Upward leakage2 Springs Head-contro . _ _, , _ Plus or minus change previous pumping period

in storage Average Maximum

(ft3/s) (in/yr) (ft3/s) (in/yr) (ft%) (in/yr) (ft3/s) (in/yr) (ft3/s) (in/yr) (ft3/s) (in/yr) (ft) (ft)

... ... ...... 532 (0.53) 1,326 (1.30) 90 (0.09) 0 (0) 

...... ... 290 (0.29) 0 (0) 0 (0) 0 (0) 

753 (0.75) 377 (0.37) 1,236 (1.22) 58 (0.06) 68 (0.07) -59 (-0.06) 3.7 150.0 

105 i0.10) 292 (0.29) 0 (0) 0 (0) 0 (0) 4.0 20.0

1,705 (1.69) 278 (0.28) 1,164 (1.15) 42 (0.04) 137 (0.14) -354 (-0.35) 2.9 6.1 

139 (0.14) 375 (0.37) 0 (0) 0 (0) 0 (0) 2.3 9.2

1,705 (1.69) 265 (0.26) 1,159 (1.15) 41 (0.04) 137 (0.14) -293 (-0.29) 0.4 0.5 

139 (0.14) 358 (0.35) 0 (0) 0 (0) 0 (0) 0.6 0.8

 Average areal drawdown in the Upper Floridan is 

about 4 ft. 

 Downward leakage to the Upper Floridan from the 

overlying surficial aquifer increased 518 ft3/s, from 

1,927 to 2,445 ft3/s, an increase of about 27 percent. 

 Upward leakage from the Upper Floridan to the 

surficial aquifer decreased 155 ft3/s, from 532 to 377 

ft3/s, a decrease of about 29 percent. 

 Spring flow decreased 90 ft3/s, from 1,326 to 1,236 ft3/s 

(selected springs shown in fig. 51), a decrease of 

about 7 percent. 

 Net lateral flow at boundaries increased 14 ft3/s, from 

69 ft3/s outflow to 83 ft3/s, an increase of about 20 

percent. 

The drawdown due to pumping at average 1978 rates 

had not reached equilibrium at the end of the 210-day 

simulation. At the end of the period, heads were still 

declining and loss from aquifer storage was still occurring at a rate of 58 ft3/s. Therefore, steady-state conditions had not been reached. A 210-day pumping period 

rather than a simple steady-state pumping simulation 

was chosen for this simulation because (1) variations in 

pumping and recharge and natural discharge rates make 

it impossible for the aquifer system to reach a truly 

steady-state condition, and (2) 210 days is about the 

longest period of time during the year in which pumping, 

recharge, and natural discharge rates are reasonably 

constant at about-average rates. A steady-state simulation with the same pumping rates showed drawdowns 

that were about 10 percent greater than that of the 210-

day simulation. Therefore, steady-state conditions are 

nearly reached with a 210-day simulation. 

Table 7 lists the selected categories and 1978 average 

rates of pumping from the Floridan aquifer system. Also 

listed are the average drawdowns in the Upper Floridan 

aquifer attributed to each category of pumping. 

Pumping for municipal supplies in 1978 was about 156 

Mgal/d (table 7), about 28 percent of the total pumpage. 

Municipal pumpage is the most accurately documented 

pumping category in terms of both rates and areal 

distribution (fig. 52). The average areal drawdown in the 

Upper Floridan caused by municipal pumpage was about 

0.8 ft (table 7), with the greatest drawdowns occurring in 

the Orlando-Winter Park area (4 ft), the Cocoa well field

TABLE 5. Average 1978 pumping rates and "dry period" pumping 

rates, by pumping category

[Qavg, average annual pumping rate in 1978; Qdry, "Dry period" 

pumping rate in 1978; X, ratio of dry period pumping rate to average 

annual pumping rate in 1978; Mgal/d, million gallons per day. 

Negative number indicates recharge]

Qavg Qdry 

Pumping category (Mgal/d) X (Mgal/d)

Municipal supplies. ..................... 156 1.34 209

Domestic and private public supplies ..... 47 1.34 63 

Industrial and institutional supplies and for

Irrigation ............................. 258 2.0-1.0 825

Outflow to adjacent pumping centers. .... 41 2.0 82

Total ............................. 563 1,274
E58 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

83° 82 8V

30

BASE FROM U.S. GEOLOGICAL SURVEY

DIGITAL LINE GRAPHS FROM 1:2.000.000 SCALE MAPS

O 

O

H

WELL IN THE UPPER FLORIDAN AQUIFER USED FOR 

TRANSIENT CALIBRATION OF 1978 FLOW 

CONDITIONS Top number is well reference 

number. Bottom number is percent error for 

observed versus computed drawdown during dry 

period pumping simulation in 1978. Positive number 

means computed drawdown is less than that 

observed. Negative number means computed 

drawdown is more than that observed

ADEQUACY OF CALIBRATION AND RANGE OF 

ERROR,IN PERCENT

GOOD, ±20 

FAIR, ±50

POOR, more than ± 50 

BOUNDARY OF PRINCIPAL STUDY AREA

FIGURE 44. Results of transient model calibration.
DIGITAL COMPUTER MODEL E59

2.5

2.0 -

CO 1.5 -

_ 

Z> CO

</) uj 

u. > 

O <

op

1.0

"Dry period" 

pumping 

condition

Average pumping condition

i i i i

45 days 15 

day

i

s

-

50 100 150 200 

TIME, IN DAYS

300

FIGURE 45. Conceptualized pumping periods for transient model 

calibration.

in southeast Orange County (6 ft), and the Daytona 

Beach well field in east Volusia County (6 ft). Drawdown 

in the Lower Floridan aquifer was computed only for the 

Orange County area, where about 65 Mgal/d were 

pumped from the Lower Floridan for municipal supply 

by the cities of Orlando and Winter Park. The computed 

drawdown in the Lower Floridan in the Orlando-Winter 

Park area was about 14 ft.

Pumpage for rural domestic and privately owned public supplies in 1978 was about 47 Mgal/d (table 7), about 

8 percent of the total pumpage. Data for this category of 

pumping are not as reliable as those for municipal 

supples in terms of either rates or areal distribution (fig. 

53). Average areal drawdown in the Upper Floridan

Well no.

Model node (row, col.) 

U.S. Geol. Survey no. 

Altitude of land surface 

(feet above sea level) 

Well depth (feet) 

Casing length (feet) 

Aquifer

26

(14,21)

282341081040101

75

516 

301 

Upper Floridan

51 (storage coefficient, Lower Floridan)

52 (storage coefficient, Upper Floridan)

39

38

36

35

34

33

32

31

\ i i i r

OBSERVED LEVEL 

COMPUTED LEVELS

,

O S1,S2 = 1 x10~ 3 

 S1,S2 = 5x10~ 4

FEBRUARY MARCH APRIL 

1978

JUNE

FIGURE 46. Computed versus observed water levels in well 26 

(southeast Orange County) for selected values of storage coefficient.

aquifer caused by pumping for rural domestic and private 

public supplies is about 0.3 ft.

Pumping for major self-supplied industries and institutions and for thermoelectric condenser cooling in 1978 

was about 94 Mgal/d (table 7), about 17 percent of the

Pumping

period

no.

TABLE 6. Change in Upper Floridan aquifer predevelopment ground-water flow rates caused by pumping

[Cubic feet per second]

Simulation

Net1 Downward

pumping rate leakage

(change)2 (change)

Net

Upward boundary Change 

leakage Springflow outflow in 

(change) (change) (change) storage

0 Predevelopment steady-state (revised from Tibbals, 

1981)........................................

At end of 210 days pumping at average 1978 pumping

1,927 532 1,326 69

2 At end of additional 45 days pumping at estimated

807

(807) 

1,844

(1,844)

2,445

(518) 

3,043

(1,116)

377

(-155) 

278

(-254)

1,236

(-90) 

1,164

(-162)

84

(14) 

111

(42)

-59

(-59) 

-354

(-354)

1 Net pumping is equal to amount pumped from Upper and Lower Floridan aquifer minus the amount recharged through drainage wells.

2 Change from predevelopment conditions.
EGO REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

Well no.

Model node (row, col.) 

U.S. Geol. Survey no. 

Altitude of land surface 

(feet above sea level) 

Well depth (feet) 

Casing length (feet) 

Aquifer

20

(12, 20)

281714081093001 

65

750 

394 

Upper Floridan

47

_i

LU

> 46

UJ

<

UJ 

CO

£ 45 

O

CO

43

42

41

51 (storage coefficient, Lower Floridan)

52 (storage coefficient, Upper Floridan)

\ I I I T

-OBSERVED LEVEL 

COMPUTED LEVELS

© S1,S2 = 5x10~ 3 

O S1,S2 = 1x10- 3 

 S1,S2 = 5x10~ 4

l I i i i I

FEBRUARY MARCH APRIL 

1978

MAY JUNE

FIGURE 47. Computed versus observed water levels in well 20 

(north Osceola County) for selected values of storage coefficient.

TABLE 7. Average 1978 pumpage in Upper and Lower Floridan 

aquifer and average drawdown in the Upper Floridan attributable 

to each category of pumping

[Mgal/d, million gallons per day; ft, feet]

Average 1978 pumping rate (Mgal/d) 

Upper

Pumping category Floridan

Lower 

Floridan Total

Average areal

drawdown in

the Upper Floridan

aquifer (ft)

Municipal supply... 92

Rural domestic and 

private public 

supplies........ 47

Industrial, institutional, and recreational sup64 156

47

0.78

0.28

plies

Recharge (drainage) wells ......

Boundary outflow 

(net). ..........

Total ........

QO

258

-33

41

495

4

0

0

0

68

94

258

-33

41

563

0.37

1.97

-0.22

0.27

J3.58

1 The drawdowns for the individual pumping categories do not sum to the 

drawdown resulting from the total of all pumping stresses because of random 

errors inherent in the model's computational process.

Well no.

Model node (row, col.) 

U.S. Geol. Survey no. 

Altitude of land surface 

(feet above sea level) 

Well depth (feet) 

Casing length (feet) 

Aquifer

40

(9, 26)

283253081283401 

72

350 

328 

Upper Floridan

51 (storage coefficient, Lower Floridan)

52 (storage coefficient. Upper Floridan)

61

60

59

57

< 55

54

TT

I I

OBSERVED LEVEL

COMPUTED LEVEL

S1,S2 = 5x10- 3

S1,S2 = 1 x10~ 3

S1. 52 = 5x10-"

I I I I I I I

FEBRUARY MARCH APRIL

1978

MAY JUNE

FIGURE 48. Computed versus observed water levels in well 40 

(west-central Orange County) for selected values of storage 

coefficient.

total pumpage. About 4 Mgal/d were pumped from the 

Lower Floridan aquifer. The distribution of pumping and 

its drawdown effects are shown in figure 54. Average 

areal drawdown in the Upper Floridan caused by this 

category of pumping is about 0.4 ft.

Water pumped for irrigation is the largest single 

ground-water use in the study area; however, the rate 

and areal distribution of this pumpage is poorly defined. 

Water pumped for irrigation in 1978 is estimated at 258 

Mgal/d (table 7), about 46 percent of the total pumpage. 

The areal distribution of irrigation and the estimated 

drawdowns (fig. 55) are qualitative rather than quantitative. Average areal drawdown caused by irrigation 

pumpage is about 2 ft.

Rates of recharge through drainage wells in the 

Orlando area are not accurately known, but estimates 

are as high as 50 Mgal/d (Kimrey, 1978, p. 15). A lower 

rate of 33 Mgal/d (table 7) was used in the simulation in 

this study. The rationale for using the lower rate is given 

in a later section. Recharge through drainage wells and 

the resultant buildup of the potentiometric surface of the 

Upper Floridan is mainly in the Orlando area (fig. 56).
DIGITAL COMPUTER MODEL E61

83° 82° 81' 80°

Madison i 

MADISON/

Ojasper 

HAMILTON

f

L.ve Oakf 

SUWANNEE

-V 

r~~ COLUMBIA i

Lake City

30'

AFAYE~TE

SCALE 1:2,000,000

10 20 30 40 MILES

0 10 20 30 40 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY

DIGITAL LINE GRAPHS FROM 1:2,000,000 SCALE MAPS

LaKe 

Butler J

^BRADFORD

DIXIE 

O

Cross C *v

^ ~ ^ UNION y BRADFORD ,

\ r ' i ^~-^-' O i

^v/^ \ . T Starke , i

--^V 

( 

?

^

GILCHRIST

;\

29

EXPLANATION

POTENTIOMETRIC CONTOURS OF UPPER 

FLORIDAN AQUIFER Shows altitude of 

potentiometric surface. Hachures indicate 

depressions. Contour interval 10 feet. 

Datum is sea level

- Based on water-level measurements in wells 

May 1978 (revised from Watkins and others, 

1979)

 50 Derived from computer model simulation of 

potentiometric heads for May 1978

 50-

H BOUNDARY OF PRINCIPAL STUDY AREA

FIGURE 49. Observed versus computed potentiometric surface of the Upper Floridan aquifer, May 1978.
E6S REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

82°

29° 

SCALE 1:2,000,000 

10 20 30

10 20 30 40 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY

DIGITAL LINE GRAPHS FROM 1:2,000,000 SCALE MAPS ,

HERNANDO 

O

B'OOkSviiit;

EXPLANATION

AREA WHERE PUMPING OCCURS IN THE 

UPPER FLORIDAN AQUIFER-Number is 

total average pumping rate for all categories 

of ground-water use within area including 

constant flux boundary flow (see fig. 57),in 

millions of gallons per day

[8.7 AREA WHERE PUMPING OCCURS IN THE 

LOWER FLORIDAN AQUIFER-Number is 

total average pumping rate for all categories 

of ground-water use within area including 

constant flux boundary flow (see fig. 57), in 

millions of gallons per day

 - LINE OF EQUAL DRAWDOWN-lnterval 2 feet 

 I BOUNDARY OF PRINCIPAL STUDY AREA

FIGURE 50. Drawdown of potentiometric surface of Upper Floridan aquifer caused by average 1978 pumping, drainage wells, and boundary

flow to adjacent pumping centers.
DIGITAL COMPUTER MODEL E63

83° 82

30°

SCALE 1:2.000,000 

10 20 30

BASE FROM U.S. GEOLOGICAL SURVEY

DIGITAL LINE GRAPHS FROM 1:2,000,000 SCALE MAPS

HERNANDO ^

O 

Brooksvii'e

EXPLANATION

INCREASE IN DOWNWARD LEAKAGE TO OR

DECREASE IN UPWARD LEAKAGE FROM UPPER 

FLORIDAN AQUIFER FROM PREDEVELOPMENT 28° 

CONDITIONS TO 1978. IN INCHES PER YEAR

« SELECTED SPRING Upper number is simulated

 6 6 change in discharge from simulated predevelopment

 pr- conditions to 1978; Middle number is observed

 ^ change in discharge; Bottom number is simulated

 ~" predevelopment discharge (revised from Tibbals, 

1981), in cubic feet per second

k 1 _ BOUNDARY FLOW Arrows show direction of

boundary flow, 1978. Number is change in flow from

1> 1.6 predevelopment conditions (revised from Tibbals, 

L Q - 1981). in cubic feet per second. Negative number

H

means flow is reduced 

BOUNDARY OF PRINCIPAL STUDY AREA

FIGURE 51. Effects of 1978 pumping on downward and upward leakage rates to and from the Upper Floridan aquifer, flow of selected

springs, and flow at boundaries.
E64 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

30°

29° -

SCALE 1:2,000,000 

10 20 30

BASE FROM U.S. GEOLOGICAL SURVEY

DIGITAL LINE GRAPHS FROM 1:2,000,000SCALE MAPS

DadeCity~ O 

PASCOSt LeoO

EXPLANATION

ji.2' AREA WHERE MAJOR PUBLIC SUPPLY

PUMPING OCCURS IN THE UPPER FLORIDAN 

AQUIFER Number is average pumping rate 

within the area, in millions of gallons per day

\4~5, AREA WHERE MAJOR PUBLIC SUPPLY

PUMPING OCCURS IN THE LOWER FLORIDAN 

AQUIFER Number is average pumping rate 

within the area, in millions of gallons per day

 4 LINE OF EQUAL DRAWDOWN IN THE UPPER 

FLORIDAN AQUIFER-lnterval 1 and 2 feet

__4__ |_| NEOF EQUAL DRAWDOWN IN THE LOWER 

FLORIDAN AQUIFER-lnterval 2 and 4 feet

BOUNDARY OF PRINCIPAL STUDY AREA

FIGURE 52. Drawdown of potentiometric surface of Upper Floridan and Lower Floridan aquifers caused by pumping for municipal

supplies, 1978.
DIGITAL COMPUTER MODEL E65

83° 82°

0 10 20 30 40 MILES

0 10 20 30 40 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY 

! DIGITAL LINE GRAPHS FROM 1:2.000,000 SCALE MAPS

UNION } BRADFORD

EXPLANATION

|03i AREA WHERE PUMPING OCCURS-Rural 28°( -> j 

domestic pumping includes water pumped 

for air conditioning and heating. Number is 

average pumping rate within the area, in 

millions of gallons per day

 1 LINE OF EQUAL DRAWDOWN IN THE UPPER 

FLORIDAN AQUIFER Interval 1 foot

| I BOUNDARY OF PRINCIPAL STUDY AREA

FIGURE 53. Drawdown of potentiometric surface of Upper Floridan aquifer caused by pumping for rural domestic and privately owned

public supplies, 1978.
E66 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

SCALE 1:2,000,000 

10 20 30 40 MILES

0 10 20 30 40 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY

DIGITAL LINE GRAPHS FROM 1:2,000,000 SCALE MAPS

EXPLANATION

jO.7 AREA WHERE MAJOR INDUSTRIAL PUMPING 

OCCURS IN THE UPPER FLORIDAN 

AQUIFER Number is average pumping rate 

within the area, in millions of gallons per day

J3.7 AREA WHERE MAJOR INDUSTRIAL PUMPING 

' ' OCCURS IN THE LOWER FLORIDAN

AQUIFER Number is average pumping rate 

within the area, in millions of gallons per day

 T LINE OF EQUAL DRAWDOWN IN THE UPPER 

FLORIDAN AQUIFER- Interval 1 and 2 feet

BOUNDARY OF PRINCIPAL STUDY AREA

FIGURE 54. Drawdown of potentiometric surface of Upper Floridan aquifer caused by pumping by major industries, by institutions, and for

thermoelectric condenser cooling, 1978.
DIGITAL COMPUTER MODEL E67

83° 82° 81°

r 

/ DUVAL

BAKEP * __ ' '

-CuuiKD.* ' * I - JACKSONVILLE °

COLUMBIA s MacclennyO L

0 10 20 30 40 MILES 

I i ___ i 

0 10 20 30 40 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY

DIGITAL LINE GRAPHS FROM 1:2,000.000 SCALE MAPS

 OR

p.8 AREA WHERE IRRIGATION PUMPING 

OCCURS IN THE UPPER FLORIDAN 

AQUIFER Number is average pumping 

rate within the area, in millions of gallons 

per day

H

LINE OF EQUAL DRAWDOWN IN THE UPPER 

FLORIDAN AQUIFER-lnterval 1 and 2 feet

BOUNDARY OF PRINCIPAL STUDY AREA

FIGURE 55. Drawdown of potentiometric surface of Upper Floridan aquifer caused by pumping for irrigation, 1978.
E68 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORID AN AQUIFER SYSTEM

83°

SCALE 1:2,000,000 

0 10 20 30 40 MILES

! '-"JACKSONVILLE O

BASE FROM U.S. GEOLOGICAL SURVEY

DIGITAL LINE GRAPHS FROM 1:2,000,000 SCALE MAPS

PASCOSt.LaoO 9

EXPLANATION

4-Oj AREA WHERE MAJOR RECHARGE OCCURS

THROUGH DRAINAGE WELLS-Number is 28 ° 

average recharge rate within the area, in 

millions of gallons per day

1 LINE OF EQUAL POTENTIOMETRIC BUILDUP IN 

THE UPPER FLORIDAN AQUIFER-lnterval 

1 foot

BOUNDARY OF PRINCIPAL STUDY AREA

FIGURE 56. Buildup of potentiometric surface of Upper Floridan aquifer caused by recharge through drainage wells, 1978.
LONG-TERM EFFECTS OF PUMPING-DOUBLE-MASS CURVE ANALYSES E69

The 0.2-ft average areal buildup is insignificant (table 7). 

Maximum buildup is about 4 ft and occurs in the immediate Orlando area.

In the transient simulation, cross-boundary flow is 

simulated in two ways:

1. As flow through head-controlled flux boundaries (as 

described by Tibbals, 1981) (flow that varies in 

response to pumping stresses inside the model 

area), and

2. As outflow through constant-flux boundaries (table 7) 

(outflow that is the result of pumping stresses in 

areas adjacent to the model, primarily to the west 

and north).

The boundary flows shown in figure 57 were obtained 

by determining internodal flows from a coarser grid 

regional model (see Professional Paper 1403-C; Bush and 

Johnson, in press) under pumping conditions along rows 

or columns that correspond to the boundaries of this 

subregional model. Where a constant-flux boundary node 

corresponds with a head-controlled flux boundary node, 

the internodal constant flows were adjusted so that only 

one flow was considered.

Most of the constant-flux cross-boundary outflow 

occurs along the south end of the west boundary and is 

the result of heavy pumping by phosphate mines, citrus 

processing plants, and irrigation west of the model area 

(see Professional Paper 1403-F). Net constant-flux 

cross-boundary flow is simulated as 41 ft3/s. Maximum 

drawdown is about 8 ft and occurs in Polk County. The 

areal distribution of cross-boundary flow and its drawdown effects in the model area are shown in figure 57.

LONG-TERM EFFECTS OF PUMPINGDOUBLE-MASS CURVE ANALYSES

The model described in this report cannot adequately 

simulate the year-to-year hydraulic effects of pumping 

from predevelopment conditions to 1978. However, an 

attempt is made to show some general trends in spring 

flow and water levels at selected sites. Several individual 

springs, a group of springs, a stream whose base flow is 

almost entirely spring flow, and well 40 are selected for 

long-term-trend analyses. Hydrographs of average 

annual discharge at the springs and river sites (fig. 58) 

and average annual water levels in well 40 (fig. 69 in 

appendix B) show trends, but the fluctuations in the 

records are caused by at least two factors: variations in 

rainfall and nearby pumping. To separate the effects of 

pumping and rainfall, double-mass analyses were done 

for Blue Spring near Orange City versus rainfall at De 

Land (fig. 59), for the Wekiva River near Sanford versus 

rainfall at Orlando (fig. 60), and for water levels in well

40 near Orlando (see fig. 2) versus rainfall at Orlando 

(fig. 61).

A double-mass curve analysis consists of plotting the 

cumulative data of one variable versus the cumulative 

data of a related variable. The resulting graph plots as a 

straight line if the relation between the variables 

remains unchanged as the data accumulate. For example, a double-mass graph of cumulative annual rainfall on 

a drainage basin versus cumulative annual runoff from 

the basin would plot as a straight line if other hydrologic 

conditions remained unchanged. If part of the runoff 

were diverted to another drainage basin and thus were 

not measured as discharge from the parent basin, the 

double-mass curve would show a change in slope (change 

in the rainfall-runoff relation) beginning at the time of 

the diversion. However, an apparent change in relation 

suggested by a change in slope can also reflect changes in 

the way data were collected at either of the two sites, 

such as changes in location of the rain gage or in the way 

stream records are computed. The data upon which the 

following analyses are based are considered representative of the hydrologic conditions.

About 10 Mgal/d (15 ft3/s) are pumped from the 

Floridan aquifer system in the Blue Spring ground-water 

basin (figs. 21, 50). That amount is relatively small 

compared with the approximately 97 Mgal/d (150 ft3/s) 

modern-day average discharge of Blue Spring. A doublemass analysis of discharge of Blue Spring versus rainfall 

at De Land (fig. 59) shows that for the 50-year period 

1932-82 the graph is essentially a straight line. Thus, the 

relation between rainfall and the discharge of Blue 

Spring has remained virtually unchanged. This is as 

expected because of the relatively small pumpage in the 

Blue Spring ground-water basin. Also, some of the 

ground water pumped eventually recharges the aquifer 

system by percolation from septic tanks and lawn and 

crop irrigation.

The base flow of the Wekiva River during dry periods 

is about 190 to 210 ft3/s and is derived almost entirely 

from spring flow. The base flow is derived from Wekiva 

Springs (73 ft3/s), Rock Springs (57 ft3/s), Miami Spring 

(5 ft3/s), Witherington Spring (4 ft3/s), Sanlando, Palm, 

and Starbuck Springs (37 ft3/s), and a few smaller 

springs, plus discharge from flowing wells 51 and 52 (see 

fig. 2; only since 1974 and probably less than 25 ft3/s) and 

about 10 ft3/s inflow from the Little Wekiva River.

The double-mass curve of flow of the Wekiva River 

versus rainfall at Orlando shows that the average annual 

flow of the Wekiva River has increased about 64 ft3/s 

since about 1960 (fig. 60). Of the 189-mi2 topographic 

drainage basin of the Wekiva River, about 40 mi2 contributes surface runoff to the river. Of that 40 mi2, most 

is drained by the Little Wekiva River, a tributary of the 

Wekiva. In the remaining 149 mi2 the surface drainage
E70 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

83°

29°

Madison ! .-,

MADISON/

i 

/ Live Da*

0 10 20 30 40 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY

DIGITAL LINE GRAPHS FROM 1:2,000,000 SCALE MAPS

z \. UNION y BRADFORD; i 

\ * _/ - ' o i

EXPLANATION

0.4! AREA WHERE CROSS-BOUNDARY FLUX IS 28 

SIMULATED BY PUMPING WELLS-Flow is 

out of model. Number Is average rate of flow, 

in millions of gallons per day

|0.2j FLOW IS INTO MODEL-Number is average 

rate of flow, in millions of gallons per day

i

(_*.__ _ __ _ __L_ _

 1_. LINE OF EQUAL DRAWDOWN IN THE UPPER 

FLORIDAN AQUIFER-Interval 1 and 2 feet

H BOUNDARY OF PRINCIPAL STUDY AREA

FIGURE 57. Drawdown of potentiometric surface of Upper Floridan aquifer caused by net boundary flows to or from adjacent pumping

centers, 1978.
P S- co

hO 5. *<

g » ri

^3 a

"-i S» B

£<? - 

f^ co

O CL ,

53 HJ <

»Q B. ^ 

^ s M e-s-*

^crg

JB^5- 

o. <t> 9 §- £- <^ nj <r> 

1 B <

3 ffq SL

§ * «

a?!

S' c^-

jo tr g

?r n> s

SB c^

Orq (^ 

^S ? 

P^ »

?5" ^ rtrt*jS

?§ §.

!-! l-(

SO C^ p 

& S co"

85 .2 S

Pit sr ha & s R C T 3 OfQ O- p «, co

C o 2 -<

e. P*T

ANNUAL AVERAGE DISCHARGE, IN CUBIC FEET PER SECOND

_i _i _i -i -i ro £> 

§

ro ^ o> oo o

_______o_____o______o o o

~1 I I I CD

3.3

85

l-ij

oo pr

£

 13

s'

rt)

S3

CUMULATIVE AVERAGE ANNUAL 

NEAR ORANGE CITY IN EX

PER SECOND, IN CUBIC F

9 s o c+ rt) C

^3 -

^ -n
E72 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

7,000

1,400 cubic feet 

per second-years

22 yearsIncrease in _ 1,400_ 64 cubic feet 

annual flow 22 per second

200 400 600 600 1,000

CUMULATIVE RAINFALL AT ORLANDO IN EXCESS OF 

30 INCHES PER YEAR, IN INCHES

FIGURE 60. Double-mass curve of discharge of Wekiva River near 

Sanford versus rainfall at Orlando, 1935-82.

a result, there would be increased head difference 

between the surficial aquifer and the Floridan, and thus 

more downward leakage, or recharge, would be induced. 

Unfortunately, there are no long-term ground-water 

records in the ground-water basins of the springs that 

discharge to the Wekiva River. Therefore, the effects of 

increased spring flow on ground-water levels cannot be 

verified. The phenomenon of an apparent increase in 

spring flow was also observed at Weekiwachee Springs 

in Hernando County (Tibbals and others, 1980). A 

double-mass analysis of flow of Weekiwachee Springs 

versus rainfall at St. Leo, Pasco County, showed an 

increase in spring flow beginning in about 1950-53 following a period of record high spring flows in west 

peninsular Florida.

Double-mass curve analysis of water levels in well 40 

versus rainfall at Orlando (fig. 61) shows that, beginning 

in about 1961, there has been a decline in water levels 

that cannot be attributed solely to deficient rainfall. The 

break in slope of the double-mass curve is not sharp and 

the graph of the line after 1961 is not straight. This 

indicates that the change in relation between water 

levels and rainfall is gradual and suggests a gradual 

lowering of water levels caused by year-to-year 

increases in ground-water pumping. The Orlando-Winter 

Park area began a period of sustained growth in the early 

1960's. Ground-water use increased during the 1960's

100

50

Pumping by Orlando and Winter Park

1951 1960 1970 1980

z w

 OT c/3 _i uj a:

600

500

* 400 --j_r

< OC UJ

z 5 -1

< < < 300

200

100

100 200 300 400 500 600

CUMULATIVE RAINFALL AT ORLANDO IN EXCESS 

OF 30 INCHES PER YEAR, IN INCH-YEARS

700 800

FIGURE 61. Double-mass curve of water level in well 40 (Orange 47 

near Orlando) versus rainfall at Orlando, 1944-82, and pumping by 

cities of Orlando and Winter Park, 1951-82.

and 1970's and is continuing to increase into the early 

1980's (fig. 61). If the break in slope of the double-mass 

curve of figure 61 is due entirely to pumping in the 

Orlando-Winter Park area, it is possible that the break 

occurred as late as 1961 because, prior to that time, 

pumping was mostly offset by recharge through drainage 

wells in that area (fig. 23). If so, then recharge through 

the drainage wells must be about equal to the pre-1960 

pumpage by the cities of Orlando and Winter Park plus 

nearby industrial, rural domestic, and irrigation pumpage. During the period 1956-61, average pumpage by 

Orlando and Winter Park was about 20 Mgal/d. Pumpage 

by all other users in the area is estimated at about 10 to 

15 Mgal/d. Therefore, if drainage-well recharge equals 

area pumpage in 1956-61, the amount of recharge that 

occurs through drainage wells is, on the average, about 

30 to 35 Mgal/d.
SIMULATED EFFECTS OF SELECTED HYPOTHETICAL MANMADE CHANGES E73

TABLE 8. Changes in Floridan ground-water flow rates caused by selected manmade changes in the hydrologic regimen

[Cubic feet per second]

Simulation features

Predevelopment steady state (revised from 

Tibbals, 1981)

Doubled the 1978 municipal pumpage (all 

other categories of pumping remain at 

1978 level)

Seven spring pools 

raised 10 feet, no pumping4

Water table in surficial aquifer 

lowered 5 feet; no pumping

Net 

pumping 

rate

0

'1,054 

2(1,054) 

3[247]

0

0

Downward 

leakage

1,927

2,618 

(691) 

[173]

1,877 

(-50)

1,704 

(-223)

Upward 

leakage

532

352 

(-180) 

[-25]

540 

(8)

623 

(91)

Springflow

1,326

1,202 

(-124) 

[-34]

1,266 

(-60)

1,087 

(-239)

Net 

boundary 

outflow

69

78 

(9) 

[-6]

70 

(1)

32 

(-33)

Rate of change 

in storage at end 

of simulation period

0

-68 

(-68) 

[-9]

1

(1)

-38 

(-38)

1 Net pumping is equal to amount pumped from Upper and Lower Floridan aquifer minus the amount recharged through drainage wells.

2 Change from predevelopment conditions.

3 Change from transient 1978 pumping conditions after 210 days pumping (table 6).

4 Wekiva Springs, Rock Springs, Miami Spring, Sanlando Springs, Palm Springs, Starbuck Spring, and Witherington Spring.

It is possible that some of the break in slope of the 

double-mass curve after 1961 is attributable to the 

distant effects of the previously discussed increased 

spring discharge in the Wekiva, Rock, Sanlando, Palm, 

and Starbuck Springs ground-water-basin. A groundwater-basin divide can shift in response to hydrologic 

stresses in an adjacent basin and thus cause changes in 

the potentiometric surface in both basins.

SIMULATED EFFECTS OF SELECTED

HYPOTHETICAL MANMADE CHANGES ON THE

FLORIDAN FLOW SYSTEM

The computer model described in this report cannot be 

used to evaluate small-scale or localized stresses on the 

Floridan aquifer system because

1. The grid size is coarse (4x4 mi) and, therefore, 

provides poor resolution of drawdown effects;

2. The model cannot compensate for the effects of variations in rainfall and recharge;

3. Data on pumping and its geographic distribution are 

poorly defined except for municipal pumpage; and

4. Data on the Lower Floridan aquifer are sparse and 

results of simulations involving the Lower Floridan 

are debatable.

The model can, however, be used to simulate the 

effects of large-scale or widespread hypothetical stresses 

placed on the aquifer system. Three hypothetical conditions were evaluated:

1. Doubling municipal pumpage and holding all other 

categories of water use at 1978 levels (fig. 62, table 

8);

2. Raising the levels of selected spring pools in the 

Orlando area (fig. 63, table 8);

3. Lowering the water table in the surficial aquifer 

throughout the model area (fig. 64, table 8).

HYDROLOGIC EFFECTS OF 

DOUBLING 1978 MUNICIPAL PUMPAGE

Municipalities in east-central Florida can be expected 

to grow and, consequently, to increase their pumpage. 

To simulate the effects of increased municipal pumpage, 

the model was run with municipal pumpage arbitrarily 

doubled and with all other categories of water use at 

average 1978 rates. For the municipalities of Orlando, 

Winter Park, Daytona Beach, Ormond Beach, New 

Smyrna Beach, and Cocoa, the hypothetical increase in 

pumpage was areally distributed in nodes adjacent to 

nodes that contain the existing well fields.

Increased pumpage in the Orlando-Winter Park area 

was distributed in the Lower Floridan aquifer around the 

periphery of the present centers of pumping. The 

increases for Daytona Beach, Ormond Beach, and New 

Smyrna Beach were distributed in the Upper Floridan 

mostly westward of their existing well fields. Increased 

pumpage by the Cocoa well field in east Orange County 

was distributed in the Upper Floridan west and south of 

the existing well field.

The coastal areas in the vicinity of St. Augustine (St. 

Johns County), Bunnell (Flagler County), Titusville 

(Brevard County), Vero Beach (Indian River County), 

and Fort Pierce (St. Lucie County) tap the surficial 

aquifer for municipal supplies, so increased Floridan 

pumpage is not simulated. Melbourne (Brevard County) 

uses surface water for supply (Lake Washington in the 

St. Johns River).

Figure 62 shows the drawdown from predevelopment 

conditions that results from the simulation of hypotheti-
E74 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

0 10 20 30 40 MILES

0 10 20 30 40 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY

DIGITAL LINE GRAPHS FROM 1:2,000,000 SCALE MAPS

EXPLANATION

2 LINE OF EQUAL WATER-LEVEL DRAWDOWN

IN THE UPPER FLORIDAN AQUIFER 

Interval 2 feet

 4 LINE OF EQUAL WATER-LEVEL DRAWDOWN 

IN THE LOWER FLORIDAN AQUIFER 

Interval 4 feet

BOUNDARY OF PRINCIPAL STUDY AREA

FIGURE 62. Drawdown of potentiometric surface of Upper Floridan and Lower Floridan aquifers caused by hypothetical doubling of pumping for municipal supplies; all other categories of pumping at average 1978 rates.
SIMULATED EFFECTS OF SELECTED HYPOTHETICAL MANMADE CHANGES E75

83° 82" 81°

0 10 20 30 40 MILES

i i i i i y !ADi c Orv /

BASE FROM U.S. GEOLOGICAL SURVEY

DIGITAL LINE GRAPHS FROM 1:2,000,000 SCALE MAPS

' PUTNAM Increase in stage of Oklawaha River

, ^ -.mi-j..! cal} secj by construction of Rodman Reservoir

K "- h"" in ciorth Marion and south Putnaro.Counties.

EXPLANATION

 2 LINE OF EQUAL WATER-LEVEL BUILDUP IN 

THE UPPER FLORIDAN AQUIFER Interval 

2 feet

r1

FIGURE 63. Buildup of potentiometric surface of Upper Floridan aquifer caused by hypothetical raising of selected spring pools by 10 feet

and by actual construction of Rodman Reservoir.
E76 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

A>; Ferns..c,;ia Beach

Ojssper t 

HAMiLTON «

0 10 20 30 40 MILES

i i i i

0 10 20 30 40 KILOMETERS

BASE FROM U.S. GEOLOGICAL SURVEY

DIGITAL LINE GRAPHS FROM 1:2.000.000 SCALE MAPS

1TLAKTH

ond Beach 

..yiona BeacffA

EXPLANATION

 LINE OF EQUAL DRAWDOWN OF

POTENTIOMETRIC SURFACE OF UPPER 

FLORIDAN AQUIFER Interval 2 feel

BOUNDARY OF PRINCIPAL STUDY AREA

FIGURE 64. Drawdown of potentiometric surface of Upper Floridan aquifer caused by hypothetical lowering of water table in surficial aquifer by 5 feet.
SIMULATED EFFECTS OF SELECTED HYPOTHETICAL MANMADE CHANGES E77

cal doubling of 1978 municipal pumpage. Table 8 

describes the attendant changes in downward leakage, 

upward leakage, spring flows, and boundary flows. In 

general, the drawdown effects of doubling the 1978 

municipal pumpage are greatest near the larger municipalities, and the effects extend to outlying areas. Of the 

approximately 247 ft3/s (160 Mgal/d) simulated increase 

in municipal pumping from 1978 rates, about 70 percent 

is derived from increased downward leakage (from 1978 

rates) from the surficial aquifer, about 10 percent is from 

decreased upward leakage, about 14 percent is from 

decreased spring flow, about 2 percent is from decreased 

boundary outflow, and, because steady-state conditions 

had not been reached at the end of the 210-day simulation 

period, about 4 percent is from storage (table 8).

HYDROLOGIC EFFECTS OF RAISING LEVELS OF 

SELECTED SPRING POOLS

Occasionally it is suggested that, in order to conserve 

the ground-water resource, the Floridan aquifer system 

springs be plugged or dammed to halt their flow. The 

feasibility of plugging a spring is problematical because 

the spring might develop new vents or orifices. If the 

plugging were successful, undesirable side effects would 

include loss of recreational value and diminished base 

flow in the receiving stream. A compromise solution 

would be to build a low-head (say, 10-ft-high) cofferdam 

around the spring to raise the spring pool. The increase 

in head or back pressure would temporarily reduce 

spring flow until the back pressure effects were distributed throughout the spring basin (assuming new vents or 

orifices did not break open as a result of the increase in 

pressure) and the hydraulic gradient reestablished 

toward the spring. At that time, the discharge of the 

spring would be almost as great as before the cofferdams 

were built and the potentiometric surface would be 

higher throughout the spring basin. An analogous condition was imposed by the construction of Rodman Dam on 

the lower reaches of the Oklawaha River. The lake that 

resulted from the impoundment by the dam is called 

Rodman Reservoir, or Lake Oklawaha. The Upper Floridan aquifer, under predevelopment conditions, discharged approximately 150 ft3/s into the lower reaches of 

the Oklawaha River. About 89 ft3/s of discharge by 

springs (nodes (8,43) and (9,44)) in the area of Rodman 

Reservoir are simulated. The predevelopment simulated 

spring pool heads in these nodes were 15 and 13 ft above 

sea level, respectively.

The model was run without pumping but with the 

spring pools of seven springs in the Orlando area elevated 10 ft and the pool level of Rodman Reservior set at 

18 ft above sea level. The springs involved are Wekiva 

Springs, Rock Springs, Miami Spring, Sanlando Springs,

Palm Springs, Starbuck Spring, and Witherington 

Spring. The average combined (simulated) discharge of 

these springs under predevelopment conditions is about 

196 ft3/s (table 1). Their simulated total discharge after 

their spring pools were raised 10 ft is about 141 ft3/s a 

decrease of 55 ft3/s from predevelopment conditions. The 

accompanying buildup in Upper Floridan head caused 

the discharge of some neighboring springs to increase by 

about 6 ft3/s. The head buildup in the area of the seven 

springs reached a maximum of about 6 ft and extended 

about 15 to 20 mi (fig. 63).

Along with the simulated raising of the spring pools, 

the effects of Rodman Reservior (Lake Oklawaha) were 

also simulated. The increase in pool elevation caused by 

Rodman Dam reduced Upper Floridan aquifer discharge 

from 89 ft3/s to about 75 ft3/s-a decline of about 14 ft3/s. 

The accompanying buildup of Upper Floridan potentiometric head caused some neighboring springs to increase 

their discharge by about 4 ft3/s. The Upper Floridan 

head buildup in the area of Rodman Reservoir reached a 

maximum of about 2 ft and extended about 10 to 15 mi 

(fig. 63).

HYDROLOGIC EFFECTS OF 

LOWERING OF WATER TABLE

Water managers are concerned about the effect that 

pumping from the Floridan aquifer system has had on 

water levels in the surficial aquifer system. Though the 

surficial aquifer system is not a major source of water 

supply except in some coastal communities, the water 

level (or water table) in the surficial aquifer system has 

important implications with regard to water levels in 

lakes and streams throughout the area. The described 

computer model has a model layer that represents the 

surficial aquifer system; however, the surficial is not an 

active layer. Rather, it is simulated as a constant-head 

(constant in time though variable in head from place to 

place) source-sink bed. In Floridan aquifer system 

recharge areas (fig. 21), the surficial aquifer system leaks 

water into the Floridan and, in Floridan aquifer system 

discharge areas, accepts upward leakage from the Floridan. The model cannot directly evaluate the effect of 

Floridan pumping on the water table. It can, however, 

give some insight into the degree of interaction between 

the surficial aquifer system and the Upper Floridan 

aquifer. To simulate this interaction the model was run 

with the water-table simulated as being 5 ft lower than 

originally simulated. Starting heads for the Upper and 

Lower Floridan aquifers were left unchanged. Though 

arbitrary, this hypothetically imposed stress is hydrologically reasonable because during an extended drought, 

the water table and some lake and stream levels com-
E78 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORID AN AQUIFER SYSTEM

monly decline by as much as 5 ft. The results of the model 

simulation are shown in figure 64 and table 8.

Lowering the water table 5 ft caused the potentiometric surface of the Upper Floridan aquifer to decline as 

much as 4 ft in good recharge areas (figs. 21, 64) and also 

in discharge areas where the higher rates of diffuse 

upward leakage occur (fig. 22). In good recharge areas 

and high-rate discharge areas, the confining beds that 

overlie the Floridan tend to be thin or permeable and 

there is an intimate hydraulic connection between the 

Upper Floridan aquifer and the surficial aquifer system. 

Therefore it can be assumed that, in good recharge areas 

and high-rate discharge areas, the water table will be 

most affected by pumping from the Upper Floridan 

aquifer. The drawdown of the Upper Floridan potentiometric surface caused by pumping in good recharge areas 

will induce more water to leak downward from the 

surficial aquifer system and thereby lower the water 

table in the surficial. Similarly, the lowering of the 

Upper Floridian potentiometric surface in the high-rate 

discharge areas will tend to capture some of the water 

that would have leaked upward to recharge the surficial 

aquifer system.

SUMMARY AND CONCLUSIONS

The fresh-ground-water flow system of east-central 

Florida consists of a thin surficial sand aquifer underlain 

by the thick, highly productive carbonate rocks of the 

Floridan aquifer system. On the basis of permeability, 

this system is divided into the Upper and Lower Floridan aquifers which are separated by a less permeable 

limestone sequence referred to as the "middle semiconfining unit." The transmissivity of the Upper Floridan 

ranges from about 10,000 to about 400,000 ft2/d based on 

aquifer tests, but simulation suggests an average value 

of 120,000 ft2/d. In general, however, the aquifer test 

values for transmissivity of the Upper Floridan are 

within the range of values determined by computer 

simulation. The transmissivity of the Lower Floridan is 

less well known, but the range of transmissivities determined by simulation was from about 30,000 to about 

130,000 ft2/d. Storage coefficients of both the Upper and 

Lower aquifer are about 1 x 10~3 . Leakage coefficients of 

the confining bed that overlies the Upper Floridan range 

from about 1 x 10~6 to about 6x 10~4 per day. The leakage 

coefficient of the middle semiconfining unit is about 

5xlO~5 per day.

The chemical quality of the water in the Upper Floridan aquifer varies according to proximity to recharge 

and discharge areas. Low concentrations of dissolved 

solids (less than 250 mg/L) generally occur in recharge 

areas. However, in the discharge areas along the Atlantic Coast and along the St. Johns River, the dissolvedsolids concentration is generally more than 1,000 mg/L, 

and in places exceeds 25,000 mg/L. The quality of water 

in the Lower Floridan is not well defined, but in eastcentral Florida, water in the Lower Floridan is probably 

more mineralized than water in the Upper Floridan.

Most discharge from the Upper Floridan occurs at 

springs and along streams. Many discharge rates are 

known from field measurements. Rates of recharge and 

areal discharge (diffuse upward leakage) are estimated 

using digital computer simulation.

The essential features of the predevelopment steadystate flow system are as follows:

 The highest rates of recharge to the Floridan are in 

four areas: the west flank of the Volusia County 

potentiometric surface "high"; the Putnam CountyAlachua County potentiometric surface "high"; the 

topographically high ridge areas of mid-Polk and 

Highlands Counties; and the northeast flank of the 

central Florida potentiometric surface "high" in 

Lake and Orange Counties and extending into east 

Marion County.

 Most discharge from the Upper Floridan (about 68 

percent of the total) is in the form of point discharge 

to springs and streams located within 25 mi of 

recharge areas.

 The highest rates of diffuse upward leakage from the 

Upper Floridan (about 27 percent of the total discharge) occur near areas where the downward leakage rates are also high. Thus, it is inferred that thin 

or very leaky confining beds are common to the 

areas of high upward leakage and to the nearby 

areas of high downward leakage.

 Lateral boundary outflow from the Upper Floridan 

aquifer (principally occurring along the Atlantic 

Coast) is about 4 percent of the total discharge. 

Lateral flow to the south is about 1 percent of the 

total discharge.

 Interchange between the Upper and Lower Floridan 

aquifers is relatively small (about 290 ft3/s) compared with the flow within the Upper Floridan 

(about 1,950 ft3/s).

 The model-derived transmissivities are considered to 

have more regional significance than transmissivity 

values derived from individual aquifer tests. In 

general, however, the aquifer test values for transmissivity of the Upper Floridan are within the range 

of values determined by computer simulation. 

The hydraulics of the Floridan aquifer system under 

predevelopment conditions involve mostly recharge to 

the Upper Floridan (by way of leakage from the surficial 

aquifer), lateral movement through the Upper Floridan 

for short distances, and discharge by way of springs and 

seepage to streams. Relatively small amounts of dis-
SELECTED REFERENCES E79

charge occur along the coast, and small amounts move 

into and out of the underlying Lower Floridan. Thus, 

there is a vigorous flow system locally in the Upper 

Floridan and, except in west Orange County and southeast Lake County, a relatively sluggish flow system in 

the Lower Floridan.

The imposition of pumping has altered the flow system, but not to a great degree. The simulated effects of 

1978 pumpage (about 560 Mgal/d) on the predevelopment 

Floridan aquifer system flow regime are summarized as 

follows:

 An average areal drawdown of about 4 ft has occurred 

in the Upper Floridan aquifer.

 Downward leakage to the Floridan from the overlying 

surficial aquifer has increased by about 600 ft3/s 

(from about 1,900 to about 2,500 ft3/s).

 Upward leakage from the Floridan to the surficial 

aquifer has decreased about 150 ft3/s (from about 530 

to about 380 ft3/s).

 Spring flow has decreased about 90 ft3/s (from about 

1,330 to about 1,240 ft3/s).

 A slight net increase in lateral flow at boundaries has

occurred (about 15 ft3/s).

Simulation was used to investigate the effects of 

hypothetical development; the effects are summarized 

below:

 Doubling the 1978 municipal pumpage would cause 

relatively small increases in drawdown, with 10 ft or 

more increase only near the centers of pumping and 

20 ft or more only near Orlando.

 Raising elevations of spring pools would cause Upper 

Floridan head buildup near springs and some decline 

in spring discharge when steady-state conditions are 

reached.

 Floridan pumpage tends to induce leakage from the 

overlying surficial aquifer and to reduce upward 

discharge to it, thereby lowering the water table.

 Hydrologic analysis of Floridan aquifer system discharge led to the discovery and measurement of two 

hitherto undocumented springs.

SELECTED REFERENCES

Anderson, Warren, 1967, Flow and characteristics of the St. Johns

River at Palatka, Florida: U.S. Geological Survey Open-File

Report FL-67001, 19 p. 

Anderson, Warren, and Goolsby, D.A., 1973, Flow and chemical

characteristics of the St. Johns River at Jacksonville, Florida: U.S.

Geological Survey Open-File Report 73008, 105 p. 

Anderson, Warren, and Hughes, G.H., 1975, Hydrology of three

sinkhole basins in southwestern Seminole County, Florida: Florida

Bureau of Geology Report of Investigations 81, 35 p. 

Anderson, Warren, Lichtler, W.F., and Joyner, B.F., 1965, Control of

lake levels in Orange County, Florida: Florida Geological Survey

Information Circular 47, 15 p.

Applin, P.L., and Applin, E.R., 1944, Regional subsurface stratigraphy and structure of Florida and southern Georgia: American 

Association of Petroleum Geologists Bulletin, v. 28, no. 12, 

p. 1673-1753.

Back, William, 1963, Preliminary results of a study of calcium carbonate saturation of ground water in central Florida: International 

Association of Scientific Hydrology, v. 8, no. 3, p. 43-51.

Barraclough, J.T., 1962, Ground-water resources of Seminole County, 

Florida: Florida Geological Survey Report of Investigations 27, 

91 p.

Bentley, C.B., 1977, Aquifer test analyses for the Floridan aquifer in 

Flagler, Putnam, and St. Johns Counties, Florida: U.S. Geological 

Survey Water-Resources Investigations 77-36, 50 p.

 1979, Aquifer coefficients determined from multiple well 

effects, Fernandina Beach, Florida: Ground Water, v. 17, no. 6, 

p. 525-531.

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

ground-water resources of Flagler, Putnam, and St. Johns Counties, Florida: Florida Geological Survey Report of Investigations 

32, 97 p.

Bishop, E.W., 1956, Geology and ground-water resources of Highlands 

County, Florida: Florida Geological Survey Report of Investigations 15, 115 p.

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

Quarterly Journal of the Florida Academy of Sciences, v. 24, no. 2, 

p. 122-134.

Brown, D.W., Kenner, W.E., Crooks, J.W., and Foster, J.B., 1962, 

Water resources of Brevard County, Florida: Florida Geological 

Survey Report of Investigations 28, 104 p.

Brown, J.S., 1925, A study of coastal ground water: U.S. Geological 

Survey Water-Supply Paper 537, 101 p.

 1937, The Florida ship canal: Economic Geology, v. 32.

Brown, M.P., and Reece, D.E., 1979, Hydrologic reconnaissance of the 

Floridan aquifer system, Upper East Coast Planning Area: South 

Florida Water Management District Technical Map Series 79-1.

Bush, P.W., 1978, Hydrologic evaluation of part of central Volusia 

County, Florida: U.S. Geological Survey Water-Resources Investigations 78-89, 50 p.

 1979, Connector well experiment to recharge the Floridan 

aquifer, east Orange County, Florida: U.S. Geological Survey 

Water-Resources Investigations 78-73, 40 p.

-1982, Predevelopment flow in the Tertiary limestone aquifer,

Southeastern United States: A regional analysis from digital 

modeling: U.S. Geological Survey Water-Resources Investigations 

82-905, 41 p., 8 sheets.

Bush, P.W., and Johnston, R.H., in press, Ground-water hydraulics, 

regional flow, and ground-water development of the Floridan 

aquifer system in Florida and in parts of Georgia, South Carolina, 

and Alabama: U.S. Geological Survey Professional Paper 1403-C.

Causey, L.V., and Leve, G.W., 1976, Thickness of the potable-water 

zone in the Floridan aquifer: Florida Bureau of Geology Map 

Series 74.

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

appraisals of the Nation's ground-water resources South 

Atlantic-Gulf Region: U.S. Geological Survey Professional Paper 

813-0, 35 p.

Claiborne, Maude, Nierstheimer, L.O., and Hoy, N.D., 1983, Bibliography of U.S. Geological Survey reports on the water resources of 

Florida, 1886-1982: U.S. Geological Survey Open-File Report 

83-540, 311 p.

Clark, W.E., 1965, Relation of ground-water inflow and of bank and 

channel storage to streamflow pickup in the Santa Fe River, 

Florida: U.S. Geological Survey Professional Paper 525-D, 

p. D211-D213.
E80 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

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

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

Counties, Florida: Florida Geological Survey Report of Investigations 35, 170 p.

Cooke, C.W., 1939, Scenery of Florida interpreted by a geologist: 

Florida Bureau of Geology Bulletin 17, 118 p.

 1945, Geology of Florida: Florida Bureau of Geology Bulletin

29, 342 p. 

Cooper, H.H., Jr., 1959, A hypothesis concerning the dynamic balance

of freshwater and saltwater in a coastal aquifer: Journal of

Geophysical Research, v. 64, no. 4. 

Cooper, H.H., Jr., Kenner, W.E., and Brown, Eugene, 1953, Ground

water in central and northern Florida: Florida Geological Survey

Report of Investigations 10, 37 p. 

Cooper, H.H., Jr., and Stringfield, V.T., 1950, Ground water in

Florida: Florida Geological Survey Information Circular 3, 7 p. 

Grain, L.J., Hughes, G.H., and Snell, L.J., 1975, Water resources of

Indian River County, Florida: Florida Bureau of Geology Report

of Investigations 80, 75 p. 

Dohrenwend, R.E., 1977, Evapotranspiration patterns in Florida:

Florida Scientist, v. 40, no. 2, p. 184-192.

Duerr, A.D., and Trommer, J.T., 1982, The Benchmark Farm Program A method for estimating irrigation water use in southwest

Florida: U.S. Geological Survey Water-Resources Investigations

82-17, 49 p. 

Fairchild, R.W., andBentley, C.B., 1977, Saline-water intrusion in the

Floridan aquifer in the Fernandina Beach area, Nassau County,

Florida: U.S. Geological Survey Water-Resources Investigations

77-32, 27 p. 

Faulkner, G.L., 1973, Geohydrology of the Cross-Florida Barge Canal

area with special reference to the Ocala vicinity: U.S. Geological

Survey Water-Resources Investigations 1-73, 117 p.

 1976, Flow analysis of karst systems with well developed 

underground circulation: Yugoslavian Symposium on Karst 

Hydrology, June 1975, Proceedings, v. 1, p. 137-164.

Ferguson, G.E., Lingham, C.W., Love, S.K., and Vernon, R.O., 1947, 

Springs of Florida: Florida Bureau of Geology Bulletin 31, 198 p.

Florida Department of Environmental Regulation, 1982, Public drinking water systems: chap. 17-22 in Florida Administrative Code.

Foster, J.B., 1962, Well design as a factor contributing to loss of water 

from the Floridan aquifer, eastern Clay County, Florida: Florida 

Geological Survey Information Circular 35, 10 p.

Frazee, J.M., Jr., 1980, Ground water in Osceola County, Florida: U.S. 

Geological Survey Water-Resources Investigations Open-File 

Report 79-1595, 1 sheet.

Fuller, M.L., 1904, Contributions to the hydrology of Eastern United 

States, 1903-Florida: U.S. Geological Survey Water-Supply 

Paper 102, p. 238-275.

 1905, Underground waters of Eastern United States: U.S. 

Geological Survey Water-Supply Paper 114, p. 159-163. 

-1911, Drainage by wells: U.S. Geological Survey Water-Supply

Paper 114, p. 6-22.

Geraghty and Miller, Inc., 1977, Feasibility of deep-well wastewater 

disposal at the Sand Lake Road treatment facility, Orange County, 

Florida: Tampa, Fla. (13902 North Dale Mabry Highway), Geraghty and Miller, Inc. (consulting ground-water hydrologists and 

geologists), 77 p. (EPA project C120314.010)

Goolsby, D.A., 1971, Hydrogeochemical effects of injecting wastes into 

a limestone aquifer near Pensacola, Florida: National Water Well 

Association, Ground Water Journal, v. 9, no. 1, 7 p.

Grubb, H.F., 1978, Potential for downward leakage to the Floridan 

aquifer, Green Swamp area, central Florida: U.S. Geological 

Survey Water-Resources Investigations 77-71, 1 sheet.

Grubb, H.F., Chappelear, J.W., and Miller, J.A., 1978, Lithologic and

borehole geophysical data, Green Swamp area, Florida: U.S.

Geological Survey Open-File Report 78-574, 270 p. 

Grubb, H.F., and Rutledge, A.T., 1979, Long-term water supply

potential, Green Swamp area, Florida: U.S. Geological Survey

Water-Resources Investigations 78-99, 76 p. 

Gunter, Herman, and Ponton, G.M., 1929, Need for conservation and

protection of our water supply with special reference to waters

from the Ocala Limestone: The Florida Engineer and Contractor,

May 1929, p. 74-80. 

Hall, B., 1904, Measurement of springs of Florida: U.S. Geological

Survey Water-Supply Paper 102. 

Hanshaw, B.B., and Back, William, 1972, On the origin of dolomites in

the Tertiary aquifer of Florida: Florida Bureau of Geology Special

Publication 17, 228 p. 

Healy, H.G., 1962, Piezometric surface of the Floridan aquifer in

Florida, July 6-17,1961: Florida Division of Geology Map Series 1.

 1978, Appraisal of uncontrolled flowing artesian wells in Florida: U.S. Geological Survey Water-Resources Investigations 

78-95, 26 p.

Heath, R.C., and Conover, C.S., 1981, Hydrologic almanac of Florida: 

U.S. Geological Survey Open-File Report 81-1107, 239 p.

Hem, J.D., 1973, Study and interpretation of the chemical characteristics of natural water (2d ed.): U.S. Geological Survey WaterSupply Paper 1473, 363 p.

Hickey, J.J., 1981, Hydrogeology, estimated impact, and regional well 

monitoring of effects of subsurface wastewater injection, Tampa 

Bay area, Florida: U.S. Geological Survey Water-Resources 

Investigations 80-118, 40 p.

 1982, Hydrogeology and results of injection tests at wasteinjection test sites in Pinellas County, Florida: U.S. Geological 

Survey Water-Supply Paper 2183, 42 p.

Hickey, J.J., and Wilson, W.E., 1982, Results of deep-well injection 

testing at Mulberry, Florida: U.S. Geological Survey WaterResources Investigations 81-75, 15 p.

Hughes, G.H., 1974, Water balance of Lake Kerr A deductive study 

of a landlocked lake in north-central Florida: Florida Bureau of 

Geology Report of Investigations 73, 49 p.

 1975, Perspective on use of fresh water for cooling systems of 

thermoelectric power plants in Florida: U.S. Geological Survey 

Water-Resources Investigations 75-43, 35 p.

 1978, Runoff from hydrologic units in Florida: Florida Bureau 

of Geology Map Series 81.

-1979, Analysis of water-level fluctuations of Lakes w'inona and

Winnemissett Two landlocked lakes in a karst terrane in Volusia 

County, Florida: U.S. Geological Survey Water-Resources Investigations 79-55, 24 p.

Hughes, G.H., Hampton, E.R., and Tucker, D.F., 1971, Annual and 

seasonal rainfall in Florida: Florida Bureau of Geology Map Series 

40.

Hughes, J.L., 1979, Saltwater-barrier line in Florida: Concepts, considerations, and site examples: U.S. Geological Survey WaterResources Investigations 79-75, 29 p.

Hull, R.W., and Yurewicz, M.C., 1979, Quality of storm runoff to 

drainage wells in Live Oak, Florida: U.S. Geological Survey 

Open-File Report 79-1073, 40 p.

Hunn, J.D., and Cherry, R.N., 1969, Remote sensing of offshore 

springs and spring discharge along the gulf of central Florida: 

National Aeronautics and Space Administration, Hydrology and 

Oceanography, v. 3.

Hutchinson, C.B., and Wilson, W.E., 1974, Evaluation of a proposed 

connector well, northeastern DeSoto County, Florida: U.S. Geological Survey Water-Resources Investigations 5-74, 41 p.

Hyde, L.W., 1975, Principal aquifers in Florida (2d ed.): Florida 

Bureau of Geology Map Series 16.
SELECTED REFERENCES E81

Johnson, L.C., 1905, History of artesian wells in Florida: U.S. Geological Survey Open-File Report FL-05001, 10 p.

Johnston, R.H., 1978, Planning report for the southeastern limestone 

regional aquifer system analysis: U.S. Geological Survey OpenFile Report 78-516, 26 p.

 1983, The saltwater-freshwater interface in the Tertiary limestone aquifer, southeast Atlantic outer-continental shelf: Journal 

of Hydrology, v. 61, p. 239-249.

Johnston, R.H., and Bush, P.W., in press, Summary of the hydrology 

of the Floridan aquifer system in Florida and in parts of Georgia, 

South Carolina, and Alabama: U.S. Geological Survey Professional 

Paper 1403-A.

Johnston, R.H., Bush, P.W., Krause, R.E., Miller, J.A., and Sprinkle, 

C.L., 1982, Summary of hydrologic testing in Tertiary limestone 

aquifer, Tenneco offshore exploratory well Atlantic OCS, Leaseblock 427 (Jacksonville NH 17-5): U.S. Geological Survey WaterSupply Paper 2180, 15 p.

Johnston, R.H., Healy, H.G., and Hayes, L.R., 1981, Potentiometric 

surface of the Tertiary limestone aquifer system, Southeastern 

United States, May 1980: U.S. Geological Survey Open-File 

Report 81-486, 1 sheet.

Johnston, R.H., Krause, R.E., Meyer, F.W., Ryder, P.D., Tibbals, 

C.H., and Hunn, J.D., 1980, Estimated potentiometric surface for 

the Tertiary limestone aquifer system, Southeastern United 

States, prior to development: U.S. Geological Survey Open-File 

Report 80-406, 1 sheet.

Kaufman, M.I., and McKenzie, D.J., 1975, Upward migration of 

deep-well waste injection fluids in Floridan aquifer, south Florida: 

U.S. Geological Survey Journal of Research, v. 3, no. 3, 

p. 261-271.

Kenner, W.E., 1964, Maps showing depths of selected lakes in Florida: 

Florida Geological Survey Information Circular 40, 82 p.

 1966, Runoff in Florida: Florida Division of Geology Map

Series 22. 

Kenner, W.E., Pride, R.W., and Conover, C.S., 1967, Drainage basins

in Florida: Florida Division of Geology Map Series 28. 

Kimrey, J.O., 1978, Preliminary appraisal of the geohydrologic aspects

of drainage wells, Orlando area, central Florida: U.S. Geological

Survey Water-Resources Investigations 78-37, 24 p. 

Kimrey, J.O., and Fayard, L.D., 1982, Geohydrologic reconnaissance

of drainage wells in Florida An interim report: U.S. Geological

Survey Open-File Report 82-860, 59 p. 

Klein, Howard, 1975, Depth to base of potable water in the Floridan

aquifer (2d ed.): Florida Bureau of Geology Map Series 42. 

Klein, Howard, and Hull, J.E., 1978, Biscayne aquifer, southeast

Florida: U.S. Geological Survey Water-Resources Investigations

78-107, 52 p. 

Klein, Howard, Schroeder, M.C., and Lichtler, W.F., 1964, Geology

and ground-water resources of Glades and Hendry Counties,

Florida: Florida Geological Survey Report of Investigations 37,

134 p. 

Knochenmus, D.D., 1967a, Shoreline features as indicators of high

lake levels: U.S. Geological Survey Professional Paper 575-C,

p. C236-C241.

 1967b, Tracer studies and background fluorescence of ground 

water in the Ocala, Florida, area: U.S. Geological Survey OpenFile Report FL-67004, 35 p.

 1971, Ground water in Lake County, Florida: Florida Bureau of 

Geology Map Series 44.

 1975, Hydrologic concepts of artificially recharging the Floridan aquifer in eastern Orange County, Florida A feasibility 

study: Florida Bureau of Geology Report of Investigations 72, 

36 p.

Knochenmus, D.D., and Beard, M.E., 1971, Evaluation of the quantity 

and quality of the water resources of Volusia County, Florida: 

Florida Bureau of Geology Report of Investigations 57, 59 p.

Knochenmus, D.D., and Hughes, G.H., 1976, Hydrology of Lake 

County, Florida: U.S. Geological Survey Water-Resources Investigations 76-72, 100 p.

Kohout, F.A., 1959, Hydrologic features of the Lake Istokpoga area, 

Highlands County, Florida: Florida Geological Survey Report of 

Investigations 19, pt. 1, 33 p.

 1965, A hypothesis concerning cyclic flow of salt water related 

to geothermal heating in the Floridan aquifer: New York Academy 

of Sciences, v. 28, no. 2, p. 249-271.

 1974, Hydrologic significance of a geothermal submarine spring

off Florida west coast: Florida Science, v. 37, supp. 1.

Kohout, F.A., and Hartwell, J.H., 1965, The Area B flood-control 

plan Its influence on the future water resources of the Miami 

area, Florida: U.S. Geological Survey Open-File Report 

FL-65003, 95 p.

Kohout, F.A., Henry, H.R., and Banks, J.E., 1977, Hydrogeology 

related to geothermal conditions of the Floridan plateau: Florida 

Bureau of Geology Special Publication 21, p. IX-41.

Kohout, F.A., and Hoy, N.D., 1963, Some aspects of sampling salty 

ground water in coastal aquifers: National Water Well Association, 

Ground Water Journal, v. 1, no. 1.

Kohout, F.A., and Munson, R.C., 1974, Geothermal spring off Florida 

west coast: Geological Society of America, v. 6, no. 7.

Krause, R.E., 1982, Digital model evaluation of the predevelopment 

flow system of the Tertiary limestone aquifer system, southeast 

Georgia, northeast Florida, and south South Carolina: U.S. Geological Survey Open-File Report 82-173, 27 p.

Krause, R.E., and Randolph, R.B., in press, Hydrology of the Floridan 

aquifer system in southeast Georgia and adjacent parts of Florida 

and South Carolina: U.S. Geological Survey Professional Paper 

1403-D.

Laughlin, C.P., 1973, Potentiometric surface of the Floridan aquifer in 

east-central Florida, May 1973: U.S. Geological Survey Open-File 

Report FL-73030, 1 sheet.

Leach, S.D., 1977, Water use inventory in Florida, 1975: U.S. Geological Survey Open-File Report 77-577, 57 p.

 1978a, Freshwater use in Florida, 1975: Florida Bureau of 

Geology Map Series 87.

 1978b, Source, use, and disposition of water in Florida, 1975: 

U.S. Geological Survey Water-Resources Investigations 78-17, 

90 p.

 1982, Estimated water use in Florida, 1980: Florida Bureau of 

Geology Map Series 103.

 1983a, Consumptive use of freshwater in Florida, 1980: Florida 

Bureau of Geology Map Series 105.

-1983b, Source, use, and disposition of water in Florida, 1980:

U.S. Geological Survey Water-Resources Investigations 82-4090,

337 p. 

Leach, S.D., and Healy, H.G., 1980, Estimated water use in Florida,

1977: U.S. Geological Survey Water-Resources Investigations

79-112, 76 p. 

Lichtler, W.F., 1960, Geology and ground-water resources of Martin

County, Florida: Florida Geological Survey Report of Investigations 23, 149 p. 

 1972, Appraisal of water resources in the east-central Florida

region: Florida Bureau of Geology Report of Investigations 61,

52 p. 

Lichtler, W.F., Anderson, Warren, and Joyner, B.F., 1968, Water

resources of Orange County, Florida: Florida Division of Geology

Report of Investigations 50, 150 p.
E82 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

Lichtler, W.F., Hughes, G.H., and Pfischner, F.L., 1976, Hydrologic 

relations between lakes and aquifers in a recharge area near 

Orlando, Florida: U.S. Geological Survey Water-Resources Investigations 76-65, 61 p.

Lichtler, W.F., and Joyner, B.F., 1966, Availability of ground water in 

Orange County, Florida: Florida Geological Survey Map Series 21.

Lohman, S.W., 1972, Ground-water hydraulics: U.S. Geological Survey Professional Paper 708, 70 p.

Manheim, F.T., 1967, Evidence for submarine discharge of water on 

the Atlantic continental slope of the southern United States and 

suggestions for further research: New York Academy of Sciences 

Transactions, v. 29, no. 7.

Marier, J.R., Neri, L.C., and Anderson, T.W., 1979, Water hardness, 

human health, and the importance of magnesium: National 

Research Council of Canada Publication 17581, 119 p.

Maslia, M.L., and Hayes, L.R., in press, Hydrogeology and simulated 

effects of ground-water development of the Floridan aquifer 

system, southwest Georgia, northwest Florida, and southernmost 

Alabama: U.S. Geological Survey Professional Paper 1403-H.

Matson, G.C., and Sanford, Samuel, 1913, Geology and ground waters 

of Florida: U.S. Geological Survey Water-Supply Paper 319, 445 p.

McGuinness, C.L., 1963, The role of ground water in the national water 

situation: U.S. Geological Survey Water-Supply Paper 1800, 

1,121 p.

 1964, Generalized map showing annual runoff and productive 

aquifers in the conterminous United States: U.S. Geological Survey Hydrologic Investigations Atlas HA-194.

Meinzer, O.E., 1927, Large springs in the United States: U.S. Geological Survey Water-Supply Paper 557, 94 p.

Merritt, M.L., 1982, Subsurface storage of freshwater, south Florida: 

ASCE National Specialty Conference on Environmentally Sound 

Water and Soil Management, Orlando, Fla., 1982, Proceedings, 

p. 242-250.

 1983, Subsurface storage of freshwater in south Florida: A 

digital model analysis of recoverability: U.S. Geological Survey 

Open-File Report 83-536, 73 p.

Merritt, M.L., Meyer, F.W., Sonntag, W.H., and Fitzpatrick, D.J., 

1983, Subsurface storage of freshwater in south Florida: A prospectus: U.S. Geological Survey Water-Resources Investigations 

Report 83^214, 69 p.

Meyer, F.W., 1974, Evaluation of hydraulic characteristics of a deep 

artesian aquifer from natural water-level fluctuations, Miami, 

Florida: Florida Bureau of Geology Report of Investigations 75, 

32 p.

Meyer, F.W., in press, Ground-water movement in the Floridan 

aquifer system, south Florida: U.S. Geological Survey Professional Paper 1403-G.

Miller, J.A., 1979, Potential subsurface zones for liquid-waste storage 

in Florida: Florida Bureau of Geology Map Series 94.

 1982a, Configuration of the base of the upper permeable zone of 

the Tertiary limestone aquifer system, Southeastern United 

States: U.S. Geological Survey Water-Resources Investigations 

Open-File Report 81-1177, 1 sheet.

 1982b, Geology and configuration of the base of the Tertiarylimestone aquifer system, Southeastern United States: U.S. Geological Survey Water-Resources Investigations Open-File Report 

81-1176, 1 sheet.

 1982c, Geology and configuration of the top of the Tertiarylimestone aquifer system, Southeastern United States: U.S. Geological Survey Water-Resources Investigations Open-File Report 

81-1178, 1 sheet.

 1982d, Thickness of the Tertiary limestone aquifer system, 

Southeastern United States: U.S. Geological Survey WaterResources Investigations Open-File Report 81-1124, 1 map sheet.

 1982e, Thickness of the upper permeable zone of the Tertiary 

limestone aquifer system, Southeastern United States: U.S. Geological Survey Water-Resources Investigations Open-File Report 

81-1179, 1 sheet.

-1986, Hydrogeologic framework of the Floridan aquifer system

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

U.S. Geological Survey Professional Paper 1403-B, 91 p.

Miller, J.A., Hughes, G.H., Hull, R.W., Vecchioli, John, and Seaber, 

P.R., 1978, Impact of potential phosphate mining on the hydrology 

of Osceola National Forest, Florida: U.S. Geological Survey 

Water-Resources Investigations 78-6, 159 p.

National Oceanic and Atmospheric Administration, 1867-1981, Climatological data, Florida.

Navoy, A.N., 1986, Hydrogeologic data from a 2,000-foot deep core 

hole at Polk City, Green Swamp area, central Florida: U.S. 

Geological Survey Water-Resources Investigations Report 

84^257, 89 p.

Parker, G.G., Ferguson, G.E., Love, S.K., and others, 1955, Water 

resources of southeastern Florida, with special reference to geology and ground water of the Miami area: U.S. Geological Survey 

Water-Supply Paper 1255, 965 p.

Pascale, C.A., 1975, Estimated yield of freshwater wells in Florida: 

Florida Bureau of Geology Map Series 70.

Peale, C.A., 1886, Lists and analyses of the mineral springs of the 

United States: U.S. Geological Survey Bulletin 32, 235 p.

 1894, Natural mineral waters of the United States, 1892-93: 

U.S. Geological Survey 14th annual report, p. 49-88.

Peek, H.M., 1951, Cessation of flow of Kissengen Spring in Polk 

County, Florida: Florida Geological Survey Report of Investigations 7, pt. 3, p. 73-82.

Phelps, G.G., 1984, Recharge and discharge areas of the Floridan 

aquifer in the St. Johns River Water Management District and 

vicinity, Florida: U.S. Geological Survey Water-Resources Investigations 82^058, 1 sheet.

Pitt, W.A.J., Jr., Mattraw, H.C., Jr., and Klein, Howard, 1975, 

Ground-water quality in selected areas serviced by septic tanks, 

Dade County, Florida: U.S. Geological Survey Open-File Report 

75-607, 82 p.

Planert, Michael, and Aucott, W.R., 1985, Water supply potential and 

digital model analysis of the Floridan aquifer in Osceola, eastern 

Orange and southwestern Brevard Counties, Florida: U.S. Geological Survey Water-Resources Investigations Report 84-4135, 

69 p.

Pride, R.W., Meyer, F.W., and Cherry, R.N., 1966, Hydrology of 

Green Swamp area in central Florida: Florida Geological Survey 

Report of Investigations 42, 137 p.

Puri, H.S., Faulkner, G.L., andWinston, G.O., 1973, Hydrogeology of 

subsurface liquid-waste storage in Florida: International Association of Hydrological Sciences Publication 111, p. 825-849.

Puri, H.S., and Vernon, R.O., 1959, Summary of the geology of Florida 

and a guide to the classic exposures: Florida Geological Survey 

Special Publication 5, 255 p.

Putnam, A.L., 1975, Summary of hydrologic conditions and effects of 

Walt Disney World development in the Reedy Creek Improvement District, 1966-1973: Florida Bureau of Geology Report of 

Investigations 79, 115 p.

Rhoades, Roger, and Sinacori, M.N., 1941, Pattern of ground-water 

flow and solution: Journal of Geology, v. 49, no. 8, p. 785-794.

Robertson, A.F., 1971, A preliminary evaluation of hydrologic conditions of the Lakeland Ridge area of Polk County, Florida: U.S. 

Geological Survey Open-File Report FL-71007, 37 p.

Rosenau, J.C., and Faulkner, G.L., 1975, An index to springs of 

Florida (2d ed.): Florida Bureau of Geology Map Series 63.
SELECTED REFERENCES E83

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

1977, Springs of Florida (2d ed.): Florida Bureau of Geology 

Bulletin 31, 461 p.

Rosenshein, J.S., and Hickey, J.J., 1977, Storage of treated sewage 

effluent and storm water in a saline aquifer, Pinellas peninsula, 

Florida: Ground Water, v. 15, no. 4, p. 284-293.

Rutledge, A.T., 1982, Hydrology of the Floridan aquifer in northwest 

Volusia County, Florida: U.S. Geological Survey Water-Resources 

Investigations Open-File Report 82-108, 116 p, 1 sheet.

Rutledge, A.T., and Grubb, H.F., 1978, Hydrogeologic maps of a flood 

detention area proposed by Southwest Florida Water Management 

District, Green Swamp area, Florida: U.S. Geological Survey 

Open-File Report 78-460, 17 p., 7 sheets.

Ryder, P.D., 1982, Digital model of predevelopment flow in the 

Tertiary limestone (Floridan) aquifer system in west-central Florida: U.S. Geological Survey Water-Resources Investigations 

81-54, 61 p.

 1985, Hydrology of the Floridan aquifer system in west-central

Florida: U.S. Geological Survey Professional Paper 1403-F, 63 p. 

Sauer, H.I., 1974, Relationship between trace element content of

drinking water and chronic diseases: Water-Quality Conference,

16th, University of Illinois, Urbana, 1974, Proceedings, p. 39^8. 

Schroeder, H.A., 1966, Municipal drinking water and cardiovascular

death rate: Journal of the American Medical Association, v. 185,

no. 2, p. 81-85. 

Sellards, E.H., 1908, A preliminary report on the underground water

supply of central Florida: Florida Bureau of Geology Bulletin 1,

103 p. 

Sellards, E.H., and Gunter, Herman, 1913, The artesian water supply

of eastern and southern Florida: Florida Geological Survey 5th

annual report, p. 103-290. 

Shampine, W.J., 1975a, Chloride concentration in water from the

upper part of the Floridan aquifer in Florida: Florida Bureau of

Geology Map Series 12.

 1975b, Dissolved solids in water from the upper part of the 

Floridan aquifer in Florida (2d ed.): Florida Bureau of Geology 

Map Series 14.

 1975c. Hardness of water from the upper part of the Floridan 

aquifer in Florida (2d ed.): Florida Bureau of Geology Map 

Series 13. 

-1975d, Sulfate concentration in water from the upper part of the

Floridan aquifer in Florida (2d ed.): Florida Bureau of Geology 

Map Series 15.

Simonds, E.P., Jr., McPherson, B.F., and Bush, P.W., 1980, Shallow 

ground-water conditions and vegetation classification, central 

Volusia County, Florida: U.S. Geological Survey Water-Resources 

Investigations Open-File Report 80-752, 1 sheet.

Slack, L.J., and Rosenau, J.C., 1979, Water quality of Florida springs: 

Florida Bureau of Geology Map Series 96.

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

Florida: Florida Bureau of Geology Report of Investigations 54, 

77 p.

Sprinkle, C.L., 1982a, Chloride concentration in water from the upper 

permeable zone of the Tertiary limestone aquifer system, Southeastern United States: U.S. Geological Survey Water-Resources 

Investigations Open-File Report 81-1103, 1 map sheet.

 1982b, Dissolved-solids concentration in water from the upper 

permeable zone of the Tertiary limestone aquifer system, Southeastern United States: U.S. Geological Survey Water-Resources 

Investigations Open-File Report 82-94, 1 map sheet.

 1982c, Sulfate concentration in water from the upper permeable 

zone of the Tertiary limestone aquifer system, Southeastern 

United States: U.S. Geological Survey Water-Resources Investigations Open-File Report 81-1101, 1 map sheet.

 1982d, Total hardness of water from the upper permeable zone 

of the Tertiary limestone aquifer system, Southeastern United 

States: U.S. Geological Survey Water-Resources Investigations 

Open-File Report 81-1102, 1 map sheet. 

-in press, Geochemistry of the Floridan aquifer system in

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

U.S. Geological Survey Professional Paper 1403-1. 

Stewart, H.G., Jr., 1966, Ground-water resources of Polk County,

Florida: Florida Geological Survey Report of Investigations 44,

170 p. 

Stewart, J.W., 1980, Areas of natural recharge to the Floridan aquifer

in Florida: Florida Bureau of Geology Map Series 98. 

Stringfield, V.T., 1933, Ground water investigations in Florida: Florida

Geological Survey Bulletin 11, 33 p.

 1936a, Artesian water in the Florida peninsula: U.S. Geological 

Survey Water-Supply Paper 773-C, p. 115-195.

 1936b, Florida's water supply and canal: Engineering NewsRecord, v. 116, no. 2.

 1938, Ground-water supplies in Florida: Civil Engineering, v. 8,

no. 7.

 1966, Artesian water in Tertiary limestone in the Southeasten 

States: U.S. Geological Survey Professional Paper 517, 226 p.

Stringfield, V.T., and Cooper, H.H., Jr., 1951, Geologic and hydrologic 

features of an artesian submarine spring east of Florida: Florida 

Geological Survey Report of Investigations 7, pt. 2, p. 57-72.

Stringfield, V.T., and LeGrand, H.E., 1969, Relation of sea water to 

fresh water in carbonate rocks in coastal areas, with special 

reference to Florida, U.S.A., and Cephalonia (Kephallinia), 

Greece: Journal of Hydrology, v. 9. no. 4, p. 387-404.

Stringfield, V.T., and Westendick, F.C., 1935, Artesian water in the 

Florida peninsula: American Water Works Association, Florida 

Section, Annual Convention, 9th, Proceedings.

Stubbs, S.A., 1937, A study of the artesian water supply of Seminole 

County, Florida: Florida Academy of Sciences, Proceedings, v. 2, 

1937, p. 24-36.

Theis, C.V., 1935, Relation between the lowering of the piezometric 

surface and the rate and duration of discharge of a well using 

ground-water storage: American Geophysical Union Transactions, 

pt. 2, p. 519-524; Dupl. as U.S. Geological Survey Ground-Water 

Note 5, 1952.

Thompson, D.G., and Stringfield, V.T., 1931, Ground-water resources 

of Florida: Florida Geological Survey Press Bulletin 13, 18 p.

Tibbals, C.H., 1972, Temporary storage of freshwater in a saline 

aquifer by use of wells A field experiment: American Water 

Resources Association annual conference, 8th, St. Louis, Mo., 

Oct. 30-Nov. 2, 1972, Short papers, p. 69-70.

 1975a, Aquifer tests in the Summit reach of the proposed 

Cross-Florida Barge Canal near Ocala, Florida: U.S. Geological 

Survey Water-Resources Investigations 28-75, 42 p.

 1975b, Recharge areas of the Floridan aquifer in Seminole 

County and vicinity, Florida: Florida Bureau of Geology Map 

Series 68, 1 map sheet.

 1977, Availability of ground water in Seminole County and 

vicinity, Florida: U.S. Geological Survey Water-Resources Investigations 76-97, 4 sheets.

 1978, Effects of paved surfaces on recharge to the Floridan 

aquifer in east-central Florida A conceptual model: U.S. Geological Survey Water-Resources Investigations 78-76, 42 p.

-1981, Computer simulation of the steady-state flow system of

the Tertiary limestone (Floridan) aquifer system in east-central 

Florida: U.S. Geological Survey Water-Resources Investigations 

Open-File Report 81-681, 31 p., 9 sheets.

Tibbals, C.H., Anderson, Warren, and Laughlin, C.P., 1980, Groundwater hydrology of the Dade City area, Pasco County, Florida,
E84 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

with emphasis on the hydrologic effects of pumping from the 

Floridan aquifer: U.S. Geological Survey Water-Resources Investigations 80-33, 64 p.

Tibbals, C.H., and Frazee, J.M., Jr., 1976, Ground-water hydrology of 

the Cocoa well-field area, Orange County, Florida: U.S. Geological 

Survey Open-File Report 75-676, 67 p.

Tibbals, C.H., and Grubb, H.F., 1982, Aquifer test results, Green 

Swamp area, Florida: U.S. Geological Survey Water-Resources 

Investigations 82-35, 29 p.

Trescott, P.C., 1975, Documentation of finite-difference model for 

simulation of three-dimensional ground-water flow: U.S. Geological Survey Open-File Report 75-438, 99 p.

Trescott, P.C., and Larson, S.P., 1976, Supplement to Open-File 

Report 75-438, Documentation of finite-difference model for simulation of three-dimensional ground-water flow: U.S. Geological 

Survey Open-File Report 76-591, 21 p.

Unklesbay, A.G., 1944, Ground water conditions in Orlando and 

vicinity, Florida: Florida Geological Survey Report of Investigations 5, 75 p.

Unklesbay, A.G., and Cooper, H.H., Jr., 1946, Artificial recharge of 

artesian limestone at Orlando, Florida: Economic Geology, v. 41, 

no. 4, p. 293-307.

Vanlier, K.E., and others, 1975a, Water resources information needs 

for the Northwest Florida Water Management District: U.S. 

Geological Survey Open-File Report 75-160, 68 p.

 1975b, Water resources information needs for the St. Johns 

River Water Management District: U.S. Geological Survey OpenFile Report 75-44, 82 p.

Vecchioli, John, 1979, Monitoring of subsurface injection of wastes, 

Florida: National Water Well Association, Ground Water Journal, 

v. 17, no. 3, p. 244-249.

Vecchioli, John, Ehrlich, G.G., Godsy, E.M., and Pascale, C.A., 1980, 

Alterations in the chemistry of an industrial waste liquid injected 

into limestone near Pensacola, Florida: International Association 

of Hydrogeologists book on Karst Hydrology.

Vecchioli, John, McKenzie, D.J., Pascale, C.A., and Wilson, W.E., 

1979, Active waste-injection systems in Florida, 1976: U.S. Geological Survey Open-File Report 79-1296, 33 p.

Visher, F.N., and Hughes, G.H., 1975, The difference between rainfall 

and potential evaporation in Florida (2d ed.): Florida Bureau of 

Geology Map Series 32.

Visher, F.N., and Wetterhall, W.S., 1965, Desalination of aquifers in 

Florida: American Geophysical Union Transactions, v. 46, no. 1.

 1967, The effect of filled cavities on the hydrology of the 

limestone terrain in Florida: U.S. Geological Survey Open-File 

Report FL-67014.

Watkins, F.A., Jr., 1977, Effectiveness of pilot connector well in 

artificial recharge of the Floridan aquifer, western Orange 

County, Florida: U.S. Geological Survey Water-Resources Investigations 77-112, 28 p.

Watkins, F.A., Jr., Laughlin, C.P., and Hayes, E.G., 1979, Potentiometric surface map of the Floridan aquifer in the St. Johns River 

Water Management District and vicinity, Florida, September 

1978: U.S. Geological Survey Open-File Report 79-986, 1 sheet.

White, W.A., 1958, Some geomorphic features of central peninsular 

Florida: Florida Bureau of Geology Bulletin 41, 92 p.

 1970, The geomorphology of the Florida peninsula: Florida

Bureau of Geology Bulletin 51, 164 p., 5 sheets. 

Wyant, Timothy, and Shoemyen, John, 1980, Estimating irrigation

water use through selective monitoring: A north Florida case

study: American Water Resources Association Bulletin, v. 16, no.

6, p. 1074-1079. 

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

Florida: Florida Geological Survey Report of Investigations 22,

65 p. 

Zellmer, L.R., 1979, Development and application of a Pleistocene sea

level curve to the coastal plain of southeastern Virginia: Master's

thesis, School of Marine Science, College of William and Mary,

Williamsburg, Va., 85 p.
APPENDIX A: INDEX TO WELLS, OTHER THAN DRAINAGE WELLS, USED IN THIS STUDY

[Aquifer codes: s, surficial aquifer; c, secondary artesian aquifer in confining bed overlying Floridan aquifer system; u, Upper Floridan aquifer; 

m, middle semiconfining unit; 1, Lower Floridan aquifer; um, Upper Floridan aquifer and middle semiconfining unit; uml, Upper Floridan 

aquifer, middle semiconfining unit, and Lower Floridan aquifer. Well depths and cased depths are referenced to land surface except where 

noted]

Map 

location no. 

(See fig. 2)

1

2

q

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

34A

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

Identification 

no.

270730081240001 ....

271150081054401 ....

272010080221501 ....

272225080573001 ....

274206080225501 ....

274440081314801 ....

274607080493001 ....

274800080593001 ....

275840081391101 ....

275955080434601 ....

281008081441801 ....

281008081441802 ....

281058081364201 ....

281058081495001 ....

281058081495002 ....

281058081495003 ....

281058081495004 ....

281532081345001 ....

281532081345002 ....

281714081093001 ....

282202081384601 ....

282202081384602 ....

282245080471601 ....

282245081492601 ....

282245081492602 ....

282341081040101 ....

282528081340901 ....

282528081340902 ....

282533081082202 ....

282533081082204 ....

282533081082205....

282533081082206 ....

282650081262501 ....

282800081131501 ....

282730081023001 ....

283204081544901 ....

283204081544902 ....

283249081053201 ....

283249081053202 ....

283249081053203 ....

283253081283401 ....

283253081283402 ....

283333081233501 ....

283333081233502 ....

283816081225501 ....

284122081330501 ....

284147081220201 ....

284428081072601 ....

284428081072602 ....

284428081072603 ....

County

.....Glades

. . . . . Indian River

.....Polk

.....Polk

. . . . .Polk

. . . . . do.

. . . . . do.

. . . . . do.

. . . . . do.

. . . . . do.

. . . . . do.

. . . . . do.

. . . . . do.

. . . . .Osceola

. . . . . do.

. .. . .Lake

. . . . . do.

. . . . . do.

. . . . . do.

..... do.

..... do.

..... do.

..... do.

..... do.

..... do.

..... do.

..... do.

..... do.

..... do.

..... do.

..... do.

..... do.

..... do.

..... do.

..... do.

..... do.

..... do.

..... do.

Local name or number

Gl 155 near Brighton

Coley Well at Frostproof

P44 P.E. Williams well near Davenport

USGS core hole 1 at Polk City

USGS annular monitor at Polk City

USGS core hole 2 at Polk City

Bithlo 1 deep well at Bithlo

Bithlo 3 shallow well at Bithlo

Orange 47 near Orlando

USGS Avenue C 6" annular monitor

Model 

row

1

6

9

19

3

13

10

3

16

3

3

5

1

1

1

1

5

5

12

5

5

18

3

3

14

7

7

13

13

13

13

8

13

22

3

3

14

14

14

9

9

10

10

11

9

11

15

15

15

Model 

column

3

2

4

6

13

10

12

17

13

21

21

21

22

22

99

22

22

22

20

24

24

20

25

25

21

25

25

22

22

22

22

24

22

15

28

28

24

24

24

26

26

26

26

27

29

28

27

27

27

Total 

depth 

(ft)

12,685

600

Ir i \rt

40,796

2,020

319

630

'8,730

612

447

425

9

195

908

908

1,996

250

32

750

318

30

129

192

23

516

223

18

1,357

1,224

1,050

1,004

16,040

'6,524

'7,050

160

30

492

75

15

350

20

1,281

400

374

'995

158

403

393

353

Cased 

depth 

(ft)

2,430

4,045

424

208

3,882

91

125

102

6

85

350

840

OfTA

900

85

29

394

103

13

114

100

18

301

104

13

1,351

1,218

1 044

248

2,442

3,256

63

17

151

65

12

328

17

601

105

325

218

63

117

388

117

Aquifer

u

uml

u

s

u

1

u

u

u

1

u

1

u

Date 

record 

begins

Jan. 1946

Dec. 1971

July 1957

Sep. 1955

June 1977

Nov. 1949

Nov. 1951

Dec. 1946

Nov. 1958

Aug. 1934

July 1959

Oct. 1959

Dec. 1946

Dec. 1979

Sep. 1980

Aug. 1960

Jan. 1964

Nov. 1969

Feb. 1959

Jan. 1961

Aug. 1955

Jan. 1959

Jan. 1959

Mar. 1960

Mar. 1966

Mar. 1966

Dec. 1965

Feb. 1966

Feb. 1966

Feb. 1966

Mar. 1977

Sep. 1955

Oct. 1970

Jan. 1959

Jan. 1959

Oct. 1960

Oct. 1960

Oct. 1960

July 1930

Sep. 1948

Jan. 1961

Nov. 1962

May 1961

Dec. 1956

Oct. 1951

July 1981

July 1982

Sec. 1981

Footnote at end of table.

E85
E86 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

APPENDIX A.-CONTINUED

[Aquifer codes: s, surficial aquifer; c, secondary artesian aquifer in confining bed overlying Floridan aquifer system; u, Upper Floridan aquifer; 

m, middle semiconfining unit; 1, Lower Floridan aquifer; um, Upper Floridan aquifer and middle semiconfining unit; uml, Upper Floridan 

aquifer, middle semiconfining unit, and Lower Floridan aquifer. Well depths and cased depths are referenced to land surface except where 

noted]

, ,. Identification location no.

(See fig. 2) n0"

50 

51 

52 

53 

54

55 

56

57 

58 

59

60 

61 

62 

63 

64

65 

66 

67 

68 

69

70 

71 

72 

73 

74

75 

76 

77 

78 

79

80

284445081462101 ....

284740081251701 ....

284740081251702 ....

284750081132301 ....

284842081533001 ....

285638081203101 ....

285745081054001 ....

285920081490501 ....

290541081132902....

290541081132903....

290541081132904....

290920081063001 ....

290920081063002 ....

290950081315501 ....

291025081050201 ....

291115081592501....

291133081040601 ....

291133081040602....

291254081450001 ....

291715081281801 ....

291905081251001 ....

292546081513301 ....

292750081152001 ....

293045081431501 ....

293115082251501 ....

293310081284001 ....

293720081534501 ....

293729081221201 ....

293933081342801 ....

294207082163201 ....

294210082094501 ....

County

. . . . . do.

. . . . . do.

. . . . . do.

. . . . . do.

. . . . . do.

. . . . . do.

. . . . . do.

. . . . . do.

. . . . . do.

. . . . . Flagler

. .. . .Putnam

. ....Flagler

. . . . . do.

T , U M°del Local name or number 

row

Lake Yale Groves well near Tavares 

Wekiva Falls, Inc. 14"-diameter well 

Wekiva Falls, Inc. 24"-diameter well 

Seminole 257 near Sanford 

College Street well at Leesburg

USGS well 0.3 mi SW. of Blue Spring 

USGS well at Alamana 

Marion 48, Starkes Ferry near Oklawaha 

USGS 04 deep test near De Land 6" Csg 

USGS 05 deep test near De Land 4" Csg

USGS 06 deep test near De Land 1" Csg 

USGS 6" observation well near Daytona Beach 

USGS 2" observation well near Daytona Beach 

Astor Park well at Astor Park 

1-95 well at Daytona Beach

Marion 5, Sharpes Ferry at Silver Springs 

GE plant 6" well near Daytona Beach 

GE plant 2" well near Daytona Beach 

Amoco, USA unit 6-4 (oil test) 

J.C. Mew well at Seville

R. Noland well near Seville 

USGS well CE 67 near Salt Springs 

Flagler 14 at Bunnell 

Sun, H.E. Westbury (oil test) 

Texaco, A.M. Creighton (oil test)

Humble, J.W. Campbell (oil test) 

Interlachen city well 

Florida dot well near Hastings 93712201 

SJRWMD well p-172 at East Palatka 

Sperry Rand well at Gainesville

Tidewater, J.A. Phifer (oil test)

6 

11 

11 

14 

5

13 

17 

7 

16 

16

16 

18 

18 

12 

19

6 

19 

19 

9

14

14 

9

18 

12

7

15 

10 

17 

14 

5

2

,, , , Total Model , ,, 

. depth column f[ (ft)

31 

30 

30 

29 

33

31 

31 

35 

34 

34

34 

34 

34 

36

34

39 

34 

34

38 

38

38 

43 

40 

43

48

43 

46 

43 

45 

49

47

200 

107 

120 

206 

245

442 

121 

152 

575 

1,200

1,290 

235 

496 

254

498

135 

235 

500 

X020 

180

138 

340 

417 

13,872 

^,457

^.eoi

303 

622 

547 

447

^ne

Cased 

depth 

(ft)

112 

58 

80

90

84 

113

94 

639

1,275 

102 

480

152

135 

115 

483 

2,699

307

1,758 

1,062

2,962 

300 

142 

113

175

1,377

Date 

Aquifer record 

begins

u Oct. 1963 

u Feb. 1973 

u Feb. 1973 

u Dec. 1951 

u Sep. 1973

u Aug. 1981 

u May 1936 

u Mar. 1936 

u May 1955 

m Sep. 1969

1 Sep. 1969 

u Feb. 1955 

m June 1955 

u Feb. 1936 

um May 1955

u Jan. 1933 

u May 1955 

m May 1955 

...... Aug. 1975 

u Mar. 1936

u Feb. 1936 

u Sep. 1964 

u Mar. 1936 

...... jan. 1949 

...... Aug. 1955

...... Feb. 1947 

u Apr. 1934 

u Nov. 1958 

u Nov. 1977 

u June 1957

 Apr. 1947

1 Depth referenced to sea level.
APPENDIX B: LONG-TERM HYDROGRAPHS

Figures 65-73 are long-term hydrographs of water 

levels in selected wells in the east-central Florida area. 

The hydrographs were selected on the basis of the longest term record available in each part of the study area. 

In the central and north-central parts, several well 

records begin in the early 1930's, when Stringfield (1933) 

began collecting ground-water data. The longest record, 

for well 40 near Orlando (fig. 69), begins in 1930. Longterm record is scarce in the Kissimmee River basin and 

in the area north and west of Lake Okeechobee.

County Aquifer

Glades 

Indian River 

Brevard 

Brevard

Upper Floridan 

Upper Floridan 

Upper Floridan 

Upper Floridan

60

SJ 40

Well 10

I i I i

County

Polk

Orange

Orange

Lake

Lake

Aquifer

Upper Floridan 

Upper Floridan 

Surficial 

Upper Floridan 

Surficial

1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1983

FIGURE 65. Water levels in well 2 near Brighton; well 7, about 30 

miles northwest of Vero Beach; well 10, about 10 miles southwest of 

Melbourne; and well 23 at Cocoa.

Well35

1950 1965 1970 1975

FIGURE 66. Water levels in well 6 near Frostproof; wells 21 and 22, 

about 25 miles southwest of Orlando; and wells 35 and 36 near 

Mascotte.

E87
E88 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

County

Orange 

Orange 

Orange 

Orange

Aquifer or unit

Upper Flondan

Lower Floridan

Middle semiconfimng unit

Upper Floridan

i I I I T I I I I I F

(Water level corrected for density)

i i i i I i i i i i i I i i i i I

1970

FIGURE 67. Water levels in well 26, about 22 miles southeast of 

Orlando, and in wells 29, 30, and 32 (three zones of salinity monitor 

well, Cocoa well field), about 18 miles southeast of Orlando.

County

Orange 

Orange 

Orange

Aquifer or unit

Upper Floridan 

Upper confining unit 

Surficial

l I I r I I I I I I I I I

30

1960

I I I I I I I I i I I 

1965 1970

I I I I I I I I I I

1975 1980 1983

FIGURE 68.-Water levels in wells 37, 38, and 39 at Bithlo.
APPENDIX B E89

County

Orange 

Orange 

Orange 

Orange

Aquifer

Upper Flondan 

Surficial 

Lower Floridan 

Upper Flondan

40

I iTi I I I I I I | I ]

I I I I I i I i I I I I M I I i i i I I I I

Well 42

i i I i i i I I I I I I I I i I i I i I i i

1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 19801983

FIGURE 69. Water levels in wells 40 and 41, about 6 miles west of 

Orlando, and in wells 42 and 43 at Orlando.

County Aquifer

Seminole

Lake

Seminole

Lake

Volusia

Upper Floridan 

Upper Floridan 

Upper Floridan 

Upper Floridan 

Upper Floridan

60

10

I l i | i i i i | i i l i | l l l l I I I l l | l i I i | i i l i | l i l l | i l I l

Well 50

-'V

I I I I I I I I I I I I I I I I I I I I I I I I I I

1936 1940 1945 1950 1955 1960 1965 1970 1975 1980 1983

FIGURE 70. Water levels in well 46 near Longwood; well 50 near 

Tavares; well 53 near Sanford; well 54 at Leesburg; and well 56, 

about 13 miles southwest of New Smyrna Beach.
E90 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

57

65

76

79

County

Marion 

Marion 

Putnam 

Alachua

Aquifer

Upper Floridan 

Upper Floridan 

Upper Floridan 

Upper Floridan

80 Well 76

Well 79

19331935 1940 1945 1950 1955 1960 1965 1970 1975 19801983

FIGURE 71. Water levels in well 57 near Starkes Ferry; well 65 near 

Silver Springs; well 76 at Interlachen; and well 79 at Gainesville.

County

Volusia 

Volusia 

Volusia 

Volusia 

Volusia

Aquifer or unit

Upper Floridan

Middle semiconfining unit

Lower Floridan

Upper Floridan

Middle semiconfining unit

40

30

q 20

10

i i i i I i i i I I I I I I I I I I

Well 67

_ 10 l i i i i I i i l i I i i i I I I I I I I I I I I I I I 

1955 1960 1965 1970 1975 1980 1983

FIGURE 72. Water levels in wells 58, 59, and 60 (salinity monitor 

wells, central Volusia County), 7 miles northeast of De Land, and 

in wells 66 and 67, about 8 miles southwest of Daytona Beach.
APPENDIX B E91

30

Well

63

69

71

72

77

County Aquifer

Lake 

Volusia 

Marion 

Flagler 

St. Johns

Upper Floridan 

Upper Floridan 

Upper Floridan 

Upper Floridan 

Upper Floridan

20

Well 69

Well 63

10

1936 1940 1945 1950 1955 1960 1965 1970 1975 1980 1963

FIGURE 73. Water levels in well 63 at Astor Park; well 69 at Seville; well 71, about 10 miles northwest of Salt Springs; well 

72 at Bunnell; and well 77, about 10 miles southeast of Hastings.

APPENDIX C: INVESTIGATIONS OF UPPER FLORIDAN AQUIFER DISCHARGE TO SPRINGS,

RIVERS, AND LAKES

The low-flow measurements shown in figures 74, 75, 

and 78 were made during periods of deficient rainfall and 

were preceded by several months of deficient rainfall. 

There was no surface inflow; therefore, any increase in 

flow between sites on a stream represents only groundwater inflow. Some of the measurement sites were at 

known springs that had not been previously or recently 

measured. Island Spring (fig. 76) and Croaker Hole 

Spring (fig. 77) were not known to exist prior to this 

study. These springs are discussed in greater detail 

later in this section.

Apparently there is about 15 ft3/s of increase in flow 

between Salt Springs and the mouth of Salt Springs Run 

(fig. 74). Some Upper Floridan aquifer discharge definitely occurs in this reach because a spring was observed 

flowing about 50 ft downstream from the measurement 

site at Salt Springs. This spring was in an area where 

the spring run was so wide that a measurement could 

not be made that included the spring's measured flow 

with that of Salt Springs. The water-quality data 

obtained at Salt Springs are representative of the 

spring, but the water samples taken at the mouth of Salt 

Springs Run may include fresher water blown upstream 

from Lake George by a very strong breeze that persisted prior to and during the sampling. Overall flow was 

definitely downstream, but it was very sluggish at the 

water surface.

Along Juniper Creek from Juniper and Fern Hammock Springs to Cypress Landing (fig. 74) there is an 

increase in flow of about 33 ft3/s and a slight increase in 

mineralization of the water. From Cypress Landing 

downstream to State Highway 19 there is an additional 

37 ft3/s increase, of which 12 ft3/s is due to inflow from 

Sweetwater Spring. Streamflow measurements were 

not made on Juniper Creek downstream from State 

Highway 19, but there is inflow of at least 13 ft3/s of 

Upper Floridan aquifer water into Juniper Creek that 

had been previously discharged by springs into Mormon 

Branch and into an unnamed stream that empties into 

Juniper Creek downstream from the confluence of Juniper Creek with Mormon Branch.

Low-flow measurements along Alexander Spring 

Creek (fig. 75) showed an increase in flow of about 33 

ft3/s from Alexander Springs downstream to State Highway S-445. There was no surface inflow along that reach 

of the spring run. The chloride concentration and hardness of water in the spring run did not appreciably 

change along the reach; thus, the 33 ft3/s of ground 

water that discharged into the reach was of the same 

quality as that discharged by Alexander Springs. From 

State Highway 8^445 downstream to the last measurement site on Alexander Spring Creek, there is little, if 

any, increase in inflow due to discharge from the Upper 

Floridan aquifer.

Along Blackwater Creek (fig. 75) from Lake Tracy to 

just above the Wekiva River, there is about 10 to 20 ft3/s 

of Upper Floridan aquifer inflow that cannot be attributed to known springs. Most of the inflow occurs 

between Lake Norris and State Highway 44A.

Along Rock Springs Run, the Little Wekiva River, 

and the Wekiva River downstream to State Highway 46, 

most Upper Floridan aquifer inflow can be attributed to 

known springs and to two large free-flowing wells. The 

free-flowing wells (wells 51, 52) are near the west bank 

of the Wekiva River just upstream from State Highway 

46 and are 14 and 24 inches in diameter, respectively. 

The discharge from these wells was not measured at the 

time of the low-flow measurements, but measurements 

of the discharge of the 24-in-diameter well were made 

July 8, 9, and 11, 1975, and averaged about 20 ft3/s 

(about 13 Mgal/d). The combined discharge of the two 

wells is probably greater than 20 ft3/s but probably does 

not exceed 25 ft3/s. Both wells are equipped with valves 

that can regulate the wells' discharge. The valves are set 

to allow continuous flow, but it is not known if the wells 

are flowing at full capacity.

Based on stream-gaging measurements from State 

Highway 46 downstream to the St. Johns River made 

April 6 and 7, 1981, the Wekiva River picked up about 

66 ft3/s of inflow from Blackwater Creek, almost all of 

which is Upper Floridan aquifer discharge (fig. 75). No 

increase in flow was measured between State Highway 

46 and a site just upstream from Blackwater Creek. 

However, the specific conductance of the water greatly 

increased about 0.5 mi downstream from State Highway 

46. An underwater investigation was made on May 7, 

1982. A small, completely submerged spring, hereinafter referred to as "Island Spring," was found near the 

middle of the Wekiva River (fig. 76). No boil was visible 

at the surface. About 6 ft3/s was measured at the 

spring's orifice. It is possible that Island Spring discharged more than 6 ft3/s prior to the installation of 

free-flowing wells 51 and 52 in 1972, approximately 2 mi 

to the south. Discharge of water from wells 51 and 52 

may have caused a reduction in flow of Island Spring. A 

water sample shows that the spring is discharging water 

that is more highly mineralized than any of the known 

springs in the vicinity (fig. 76). Parts of the vertical 

sidewalls of the spring vent are grooved. The grooves 

are vertical, fairly smooth, about 0.25 in deep, and 

spaced fairly uniformly at about 0.5 in. The origin of the 

grooves is unknown.

E93
E94 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

81°45' 81°30'

29" 

30

i____ _.__ 

Little C\ 

Lake > \ 

Kerr I \ Salt Springs

29° 

15'

Sweef water 

Springs

Cypress 

Land in

VOLUSiA COUNTY

EXPLANATION

 STREAM MEASUREMENT OR SAMPLING SITE

 - SPRING MEASUREMENT SITE

MEASUREMENT SITE NUMBERS Dates of measurements 

except as noted are April 6-8. 1981, and November 

13-14, 1980, and are color keyed to measurements

^Discharge, in cubic feet per second

102

13C Chloride concentration, in milligrams per liter

620^.

\Total hardness as CaCO3 , in milligrams per liter 

0 5 MILES

5 KILOMETERS

FIGURE 74. Results of low-flow measurements, Lake George area.
APPENDIX C E95

81°30'

Ponce De Leon 

Springs

,90 70-7-80

29° 

00'

EXPLANATION

STREAM MEASUREMENT OR SAMPLING SITE 

SPRING MEASUREMENTSITE 

WELLS 51 AND 52

MEASUREMENT SITE NUMBERS Dates of measurements 

except as noted are April 6-7, 1981, October 30, 1980, 

and May 10 1973 , and are color keyed to measurement

Discharge, in cubic feet per second 

Chloride concentration, in milligrams per liter 

Total hardness as CaCO3, in milligrams per liter

5 MILES

5 KILOMETERS

COUNTY

28° 

45'

Semmole Springs

32

Rock Springs

FIGURE 75. Results of low-flow measurements, Wekiva River-Alexander Spring Creek area.
E96 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

10

12

_ Water surface elevation approximately 7.2 feet above sea level 5-7-82

WEKIVA RIVER

Flow: approximately 300 cubic feet per second (5-7-82)

n= Limestone 

: (Upper Floridan 

aquifer)

Flow: 6 cubic feet per 

second (5-7-82)

Measuring section

ISLAND SPRING

View from west

Island Spring

Station number

Date

Discharge (cubic feet per second)

Temperature (degrees Celsius)

Color (platinum-cobalt units)

284922-081250300 

5-7-82

24.0

10

Dissolved solids (milligrams per liter) 2,680

Chloride (milligrams per liter) 

Sulfate (milligrams per liter)

1,200

350

Hardness as CaCO3 (milligrams per liter) 790

Specific conductance (microsiemens 4,500 

at 25 degrees Celsius)

pH 7.5

Wekiva River

0223500

4-7-81

193

21.0

7

187 

22 

24 

120 

296

7.8

1 2 FEET

0.5 METERS

FIGURE 76. Sketch of Island Spring near Sanford.

Water surface elevation approximately 0.9 foot above sea level 9-17-81

Croaker Hole Spring

St. Johns River 

50 feet above Croaker Hole

Station number 292618-081412100 292617-081412100 

Date 9-17-81 9-19-81 

Discharge (cubic feet per second) 80

Temperature (degrees Celsius) 23.0 25.0 

Color (platinum-cobalt units) 1 38 

Dissolved solids (milligrams per liter) 1,430 680 

Chloride (milligrams per liter) 680 280 

Sulfate (milligrams per liter) 160 84 

Hardness as CaCO, (milligrams per liter) 400 310

Specific conductance (microsiemens 1,200

at 25 degrees Celsius)

3,000

Note: River is tidal and had reverse flow daily during 

September 17-19, 1981. River water may have mixed 

with water from Croaker Hole Spring.

FIGURE 77. Sketch of Croaker Hole Spring near Welaka.
APPENDIX C E97

81° 81°00'

VOLUSIA

COUNTY

Sweetwater Cr. (1)

IT

707 \

 \ State Highway 46 

W~S< _^ 

3< __JV^ 370"- ~J 

200

BREVARD 

COUNTY

, " &/

EXPLANATION

STREAM MEASUREMENT OR SAMPLING SITE 

SPRING MEASUREVENTSITE

MEASUREMENT SITE NUMBERS Dates of measurements 

areApnld T96\ April 30, 1974, and ,. ^e*i i» , 

and are color keyed to measurements

ORANGE

COUNTY

Discharge, in cubic feet per second

(580) 97_ Chloride concentration, in milligrams per liter

720

Total hardness as CaCO3, in milligrams per liter

Specific conductance, in microsiemens per centimeter at 25°C

28°30' 

FIGURE 78. Results of low-flow measurements, Lake Jessup-Econlockhatchee River area.
E98 REGIONAL AQUIFER-SYSTEM ANALYSIS-FLORIDAN AQUIFER SYSTEM

The depression in the Upper Floridan aquifer potentiometric surface north of Lake George and south of the 

mouth of the Oklawaha River (figs. 20, 21) is due in part 

to Upper Floridan discharge upstream from the mouth of 

the Oklawaha. However, the cone of depression is centered near the southwest quadrant of Little Lake George 

(St. Johns River) in an area shown as Croaker Hole Cove 

on U.S. Geological Survey 7V2-minute topographic quadrangle maps. Croaker Hole Cove was named by fishermen after Croaker Hole, a relatively deep, smalldiameter hole in the bottom of the river and lake. Little 

Lake George is about 5 to 9 ft deep except in the 

immediate vicinity of Croaker Hole, where it plunges to 

a depth of about 48 ft.

On September 17, 1981, U.S. Geological Survey divers 

and Breck Johnson, Umatilla, Fla., descended into 

Croaker Hole, took water samples, and measured the 

discharge at the bottom near the mouth of Croaker Hole 

Spring (fig. 77). The divers reported that, to a depth of 

about 7 to 10 ft, the water was turbid and dark brown, 

the same as that of the river. Below about 10 ft the water 

became very clear. Strong artificial lights were needed 

because the dark and turbid water near the surface 

allowed little natural light to penetrate to the depth at 

which the divers were working. No spring boil was 

visible at the surface.

The discharge of Croaker Hole Spring was measured 

at about 80 fts/s. The temperature and dissolved-solids 

concentration of the spring water were 23 °C and 1,430 

mg/L, respectively. The temperature and dissolvedsolids 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. This is probably why no boil was observed at the 

surface. During the late winter months, when the river 

water is colder than the spring water, the warmer spring 

water would tend to rise to the surface and perhaps 

would cause a noticeable boil.

Though underwater lighting equipment was used, 

visibility at the bottom of Croaker Hole was limited to 

only a few feet. Therefore, the sketch of Croaker Hole 

Spring (fig. 77) should be considered only a crude representation of the configuration of Croaker Hole.

Low-flow stream-gaging measurements made May 

16-23, 1973, on streams and springs tributary to Lake 

Jessup (fig. 78) total about 44 fts/s. About 21 fts/s is from 

sewage treatment plants that discharge into Howell 

Creek above Bear Gully Creek (16 fts/s) and into Gee 

Creek (5.1 fts/s). Approximately 21 fts/s is from irrigation return flow into Bear Gully Creek above Lightwood 

Knox Canal (1.2 fts/s), Lightwood Knox Canal (8.1 fts/s), 

Sweetwater Creek (3.3 fts/s), Shortcut Canal (6.5 fts/s), 

Salt Creek (1.6 fts/s), and Clifton Spring (1.3 fts/s). All 

the streams and canals have a seepage component of flow 

derived from the surficial aquifer, but the total of these 

seepage components to the Lake Jessup tributaries was 

probably less than 3 fts/s.

An increase of about 5 fts/s of Upper Floridan aquifer 

water was found along the lower reaches of the Econlockhatchee River from Snow Hill Road to the river 

mouth, April 30, 1974 (fig. 78). However, some increase 

may be due to irrigation return flow.
SELECTED SERIES OF U.S. GEOLOGICAL SURVEY PUBLICATIONS

Periodicals

Earthquakes & Volcanoes (issued bimonthly). 

Preliminary Determination of Epicenters (issued monthly).

Technical Books and Reports

Professional Papers are mainly comprehensive scientific reports of 

wide and lasting interest and importance to professional scientists and engineers. Included are report*; on the results of resource studies and of 

topographic, hydrologic, and geologic investigations. They also include 

collections of related papers addressing different aspects of a single scientific topic.

Bulletins contain significant data and interpretations that are of lasting scientific interest bui are generally more limited in scope or 

geographic coverage than Professional Papers. They include the result* 

of resource studies and of geologic and topographic investigations; as well 

as collections of short r-apers related to a specific topic

Water-Supply Papers are comprehensive reports that present significant interpretive results of hydrologic investigations of wide interes: 

to nrofessaona! geologists, hydrologists, and engineers, The series covers 

investigation!: IT all phases of hydrology, including hydrogeology, 

availability of water, quality of water, and use of water.

Circulars present administrative information or important scientific 

information of wide popular interest in a format designed for distribution 

at no cost to the public Information Is usually of short-term interest.

Water-Resources Investigations Reports are papers of an interpretive nature made available to the public outside the formal USGS publications series. Copies are reprouuced on request unlike formal USGS 

publications, and they are also available for public inspection at 

depositories indicated in USGS catalogs.

Open-File Reports include unpublished manuscript reports, maps, 

and other material that are made available for public consultation at 

depositories. They are a nonpermanent form of publication that may be 

cited in other publications as sources of information.

Maps

Geologic Quadrangle Maps are multicolor geologic maps on 

topographic bases in 71/2- or 15-minute quadrangle formats (scales mainly 1:24,000 or 1:62,500) showing bedrock, surficial, or engineering geology. Maps generally include brief texts; some maps include structure 

and columnar sections only.

Geophysical Investigations Maps are on topographic or planimetric 

bases at various scales; they show results of surveys using geophysical 

techniques, such as gravity, magnetic, seismic, or radioactivity, which 

reflect subsurface structures that are of economic or geologic significance. 

Many maps include correlations with the geology.

Miscellaneous Investigations Series Maps are on planimetric or 

topographic bases of regular and irregular areas at various scales; they 

present a wide variety of format and subject matter. The series also includes 7 1/2-minute quadrangle photogeologic maps on planimetric bases 

which show geology as interpreted from aerial photographs. Series also 

includes maps of Mars and the Moon.

Coal Investigations Maps are geologic maps on topographic or 

planimetric bases at various scales showing bedrock or surficial geology, stratigraphy, and structural relations in certain coal-resource areas.

Oil and Gas Investigations Charts show stratigraphic information 

for certain oil and gas fields and other areas having petroleum potential.

Miscellaneous Field Studies Maps are multicolor or black-andwhite maps on topographic or planimetric bases on quadrangle or irregular areas at various scales. Pre-1971 maps show bedrock geology 

in relation to specific mining or mineral-deposit problems; post-1971 

maps are primarily black-and-white maps on various subjects such as 

environmental studies or wilderness mineral investigations.

Hydrologic Investigations Atlases are multicolored or black-andwhite maps on topographic or planimetric bases presenting a wide range 

of geohy drologic data of both regular and irregular areas; principal scale 

is 1:24,000 and regional studies are at 1:250,000 scale or smaller.

Catalogs

Permanent catalogs, as well as some others, giving comprehensive listings of U.S. Geological Survey publications are available under 

the conditions indicated below from the U.S. Geological Survey, Books 

and Open-File Reports Section, Federal Center, Box 25425, Denver, 

CO 80225. (See latest Price and Availability List)

"Publications of the Geological Survey, 1879-1961" may be purchased by mail and over the counter in paperback book form and as a 

set of microfiche.

"Publications of the Geological Survey, 1962-1970" may be purchased by mail and over the counter in paperback book form and as a 

set of microfiche.

"Publications of the U.S. Geological Survey, 1971-1981" may be 

purchased by mail and over the counter in paperback book form (two 

volumes, publications listing and index) and as a set of microfiche.

Supplements for 1982,1983,1984,1985,1986, and for subsequent 

years since the last permanent catalog may be purchased by mail and 

over the counter in paperback book form.

State catalogs, "List of U.S. Geological Survey Geologic and 

Water-Supply Reports and Maps For (State)," may be purchased by mail 

and over the counter in paperback booklet form only.

"Price and Availability List of ILS. Geological Survey Publications," issued annually, is available free of charge in paperback booklet form only.

Selected copies of a monthly catalog "New Publications of the U.S. 

Geological Survey" available free of charge by mail or may be obtained 

over the counter in paperback booklet form only. Those wishing a free 

subscription to the monthly catalog "New Publications of the U.S. 

Geological Survey" should write to the U.S. Geological Survey, 582 

National Center, Reston, VA 22092.

Note. Prices of Government publications listed in older catalogs, 

announcements, and publications may be incorrect. Therefore, the 

prices charged may differ from the prices in catalogs, announcements, 

and publications.